This document discusses three issues related to reactive power control at wind farms:
1. The ability of individual wind turbines to provide reactive power is often limited by voltage saturation in the collector system, meaning the total reactive power available at the collector bus is much less than the specified capability of individual turbines.
2. Under some conditions, independent control laws for different reactive power equipment (e.g. a tap-changing transformer and reactive current source) can interact in unexpected ways and even cause instability, such as a tap-changing transformer not behaving as expected.
3. It is desirable to treat all reactive power equipment at the substation or wind farm as an integrated system rather than independent devices, in order to meet
International Refereed Journal of Engineering and Science (IRJES) is a peer reviewed online journal for professionals and researchers in the field of computer science. The main aim is to resolve emerging and outstanding problems revealed by recent social and technological change. IJRES provides the platform for the researchers to present and evaluate their work from both theoretical and technical aspects and to share their views.
www.irjes.com
Steady State Operation And Enhancement Of Transient Stability In Hydel Power...IJMER
In this paper, the effect of STATCOM for improving the stability and steady state operation of
the hydel power system is investigated. The STATCOM is used to control power flow of power system by
injecting appropriate reactive power during dynamic state. Simulation results show that STATCOM not
only considerably improves transient stability but also compensates the reactive power in steady state.
Therefore STATCOM can increase reliability and capability of AC transmission system. To illustrate the
performance of the FACTS controller (STATCOM), a three machine nine bus, Multi-Machine Power
System has been considered.
ELECTRICAL POWER QUALITY ENHANCEMENT OF GRID INTERFACED WITH WIND POWER SYSTE...MamtaRathod4
The document presents a presentation on power quality improvement in a grid connected wind energy system using STATCOM. The objectives of the proposed scheme are reactive power compensation, unity power factor, sinusoidal source current, reduced total harmonic distortion, maintained voltage profile, and effective response from the STATCOM controller. The system is modeled in MATLAB/Simulink and includes a wind turbine, nonlinear load, STATCOM connected to a battery energy storage system. Simulation results show the STATCOM is able to mitigate power quality issues and reduce harmonic distortion from 24.62% to 3.5%.
STATCOM for Improved Dynamic Performance of Wind Farms in Power Grid IJMER
Application of FACTS controller called Static Synchronous Compensator STATCOM to
improve the performance of power grid with Wind Farms is investigated .The essential feature of the
STATCOM is that it has the ability to absorb or inject the reactive power with power grid. Therefore,
the voltage regulation of the power grid with STATCOM FACTS device is achieved. Moreover restoring
the stability of the power system having wind farm after occurring severe disturbance such as faults or
wind farm mechanical power variation is obtained with STATCOM controller. The dynamic model of
the power system having wind farm controlled by proposed STATCOM is developed. To validate the
powerful of the STATCOM FACTS controller, the studied power system is simulated and subjected to
different severe disturbances. The results prove the effectiveness of the proposed STATCOM controller
in terms of fast damping the power system oscillations and restoring the power system stability.
1) The document discusses using an SVC (Static Var Compensator) to improve the voltage stability of a grid-connected wind-driven induction generator.
2) An SVC can generate or absorb reactive power to regulate voltage and improve stability. It contains thyristor-controlled reactors and thyristor-switched capacitors to dynamically control reactive power.
3) Simulation results show that an SVC is able to maintain terminal voltage and allow continuous operation when the grid voltage varies, improving stability compared to without an SVC.
APPLICATION OF STATCOM to IMPROVED DYNAMIC PERFORMANCE OF POWER SYSTEMijsrd.com
Application of FACTS controller called Static Synchronous Compensator STATCOM to improve the performance of power grid with Wind Farms is investigated .The essential feature of the STATCOM is that it has the ability to absorb or inject fastly the reactive power with power grid . Therefore the voltage regulation of the power grid with STATCOM FACTS device is achieved. Moreover restoring the stability of the power system having wind farm after occurring severe disturbance such as faults or wind farm mechanical power variation is obtained with STATCOM controller . The dynamic model of the power system having wind farm controlled by proposed STATCOM is developed . To validate the powerful of the STATCOM FACTS controller, the studied power system is simulated and subjected to different severe disturbances. The results prove the effectiveness of the proposed STATCOM controller in terms of fast damping the power system oscillations and restoring the power system stability.
FACTS DEVICES AND POWER SYSTEM STABILITY pptMamta Bagoria
This presentation provides an overview of Flexible AC Transmission Systems (FACTS) and power system stability. It defines FACTS as using power electronics to control power flow and enhance transmission system capacity and stability. The document outlines different types of FACTS controllers including series compensation and shunt compensation. It also classifies power system stability into rotor angle stability, voltage stability, and frequency stability and discusses factors that can lead to losses of each type of stability.
Enhancement of Voltage Stability on IEEE 14 Bus Systems Using Static Var Comp...paperpublications3
Abstract: This paper investigates the effects of Static Var Compensator (SVC) on voltage stability of a power system. One of the major causes of voltage instability is the reactive power limit of the system. Improving the system’s reactive power handling capacity via Flexible AC transmission system (FACTS) devices is a remedy for prevention of voltage instability and hence voltage collapse. The effects of Static Var Compensator (SVC) in static voltage stability margin enhancement will be studies. Prediction of the stability margin or distance to voltage collapse is based on the reactive power load demand. The load is connected to several selected buses. The analysis is performed for IEEE 14 Bus system. Then, the most critical mode is identified for each system. IEEE standard test system has been considered and Load flows were computed by using Newton Raphson method with the help of MATLAB and a weak bus is identified.
International Refereed Journal of Engineering and Science (IRJES) is a peer reviewed online journal for professionals and researchers in the field of computer science. The main aim is to resolve emerging and outstanding problems revealed by recent social and technological change. IJRES provides the platform for the researchers to present and evaluate their work from both theoretical and technical aspects and to share their views.
www.irjes.com
Steady State Operation And Enhancement Of Transient Stability In Hydel Power...IJMER
In this paper, the effect of STATCOM for improving the stability and steady state operation of
the hydel power system is investigated. The STATCOM is used to control power flow of power system by
injecting appropriate reactive power during dynamic state. Simulation results show that STATCOM not
only considerably improves transient stability but also compensates the reactive power in steady state.
Therefore STATCOM can increase reliability and capability of AC transmission system. To illustrate the
performance of the FACTS controller (STATCOM), a three machine nine bus, Multi-Machine Power
System has been considered.
ELECTRICAL POWER QUALITY ENHANCEMENT OF GRID INTERFACED WITH WIND POWER SYSTE...MamtaRathod4
The document presents a presentation on power quality improvement in a grid connected wind energy system using STATCOM. The objectives of the proposed scheme are reactive power compensation, unity power factor, sinusoidal source current, reduced total harmonic distortion, maintained voltage profile, and effective response from the STATCOM controller. The system is modeled in MATLAB/Simulink and includes a wind turbine, nonlinear load, STATCOM connected to a battery energy storage system. Simulation results show the STATCOM is able to mitigate power quality issues and reduce harmonic distortion from 24.62% to 3.5%.
STATCOM for Improved Dynamic Performance of Wind Farms in Power Grid IJMER
Application of FACTS controller called Static Synchronous Compensator STATCOM to
improve the performance of power grid with Wind Farms is investigated .The essential feature of the
STATCOM is that it has the ability to absorb or inject the reactive power with power grid. Therefore,
the voltage regulation of the power grid with STATCOM FACTS device is achieved. Moreover restoring
the stability of the power system having wind farm after occurring severe disturbance such as faults or
wind farm mechanical power variation is obtained with STATCOM controller. The dynamic model of
the power system having wind farm controlled by proposed STATCOM is developed. To validate the
powerful of the STATCOM FACTS controller, the studied power system is simulated and subjected to
different severe disturbances. The results prove the effectiveness of the proposed STATCOM controller
in terms of fast damping the power system oscillations and restoring the power system stability.
1) The document discusses using an SVC (Static Var Compensator) to improve the voltage stability of a grid-connected wind-driven induction generator.
2) An SVC can generate or absorb reactive power to regulate voltage and improve stability. It contains thyristor-controlled reactors and thyristor-switched capacitors to dynamically control reactive power.
3) Simulation results show that an SVC is able to maintain terminal voltage and allow continuous operation when the grid voltage varies, improving stability compared to without an SVC.
APPLICATION OF STATCOM to IMPROVED DYNAMIC PERFORMANCE OF POWER SYSTEMijsrd.com
Application of FACTS controller called Static Synchronous Compensator STATCOM to improve the performance of power grid with Wind Farms is investigated .The essential feature of the STATCOM is that it has the ability to absorb or inject fastly the reactive power with power grid . Therefore the voltage regulation of the power grid with STATCOM FACTS device is achieved. Moreover restoring the stability of the power system having wind farm after occurring severe disturbance such as faults or wind farm mechanical power variation is obtained with STATCOM controller . The dynamic model of the power system having wind farm controlled by proposed STATCOM is developed . To validate the powerful of the STATCOM FACTS controller, the studied power system is simulated and subjected to different severe disturbances. The results prove the effectiveness of the proposed STATCOM controller in terms of fast damping the power system oscillations and restoring the power system stability.
FACTS DEVICES AND POWER SYSTEM STABILITY pptMamta Bagoria
This presentation provides an overview of Flexible AC Transmission Systems (FACTS) and power system stability. It defines FACTS as using power electronics to control power flow and enhance transmission system capacity and stability. The document outlines different types of FACTS controllers including series compensation and shunt compensation. It also classifies power system stability into rotor angle stability, voltage stability, and frequency stability and discusses factors that can lead to losses of each type of stability.
Enhancement of Voltage Stability on IEEE 14 Bus Systems Using Static Var Comp...paperpublications3
Abstract: This paper investigates the effects of Static Var Compensator (SVC) on voltage stability of a power system. One of the major causes of voltage instability is the reactive power limit of the system. Improving the system’s reactive power handling capacity via Flexible AC transmission system (FACTS) devices is a remedy for prevention of voltage instability and hence voltage collapse. The effects of Static Var Compensator (SVC) in static voltage stability margin enhancement will be studies. Prediction of the stability margin or distance to voltage collapse is based on the reactive power load demand. The load is connected to several selected buses. The analysis is performed for IEEE 14 Bus system. Then, the most critical mode is identified for each system. IEEE standard test system has been considered and Load flows were computed by using Newton Raphson method with the help of MATLAB and a weak bus is identified.
Stability Modeling Of Storage Devices In FACTS Applicationspreeti naga
The document discusses modeling of storage devices like SMES and BESS for stability applications in FACTS. It describes the need for storage devices to improve controllability in FACTS. It explains SMES, with the superconducting coil producing large fringe fields and power conversion through a VSC and DC-DC chopper. Steady state models are used in power flow studies to maintain real and reactive power injections. State of operation models storage devices as quasi-steady interfaces with dynamic controls. Static VAR compensators are also discussed with thyristor controlled reactors and capacitors to regulate voltage. Dynamic models of the superconducting inductor and battery are also presented.
This document provides a review of the Unified Power Flow Controller (UPFC), a type of Flexible AC Transmission System (FACTS) device. It discusses the basic components and operating principles of the UPFC, which combines the functions of a STATCOM and SSSC to control active and reactive power flow. The UPFC consists of two voltage source converters connected back-to-back via a DC link. One converter injects a voltage in series with the transmission line to control power flow while the other exchanges reactive power with the line to regulate the DC link voltage. Control schemes for both converters are described. The document also presents Simulink models of the UPFC and concludes it is effective for improving power system stability
Simulation of 3 Phase, 24 Pulse GTO Converter for Flow Control of Transmissio...ijtsrd
Gate Turn off GTO thyristor based power control controller for flow control of transmission system is used to regulate voltage and reactive power improment. GTO thyristor switching devices with high power handling capability and the advancement of the other type of power semiconductor devices such as IGBTs, MOSFETs, Ideal switch and so on have led to the development of fast controllable reactive power source utilizing new electronic switching and converter technology. Nowadays, the development of a large capacity Gate Turn off thyristor has made it possible to manufacture self commutated converter employing GTO thyristor for power applications. At present, most of the research on GTO thyristor has focused on their use in power electronic systems at high switching frequencies. GTO thyristor enable the design of the solid state shunt equipment based upon switching technology. The improved rating of GTOs made possible the use of voltage sourced converter VSC in power system applications. In this paper, GTO based voltage source converter VSC is used in high power Flexible AC Transmission Systems FACTS which are used to control power flow on transmission grids. It can be used to build a model of shunt or series static compensator STATCOM or SSSC or, using two such converters, a combination of shunt and series devices known as Unified Power Flow Controller UPFC . This paper has shown a basic application of MATLAB SimPowerSystems programming for 24 pulse GTO converter STATCOM. Zin Wah Aung | Aye Myo Thant | Hnin Yu Lwin "Simulation of 3-Phase, 24 Pulse GTO Converter for Flow Control of Transmission System" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-5 , August 2019, URL: https://www.ijtsrd.com/papers/ijtsrd27887.pdfPaper URL: https://www.ijtsrd.com/engineering/electrical-engineering/27887/simulation-of-3-phase-24-pulse-gto-converter-for-flow-control-of-transmission-system/zin-wah-aung
LOW VOLTAGE RIDE - THROUGH CAPABILITY OF WIND FARMSEditor IJMTER
Nowadays wind turbines are generally required to offer ancillary services similar to those
provided by conventional generators. One of the most important services wind turbines must offer is
to stay connected to the grid in fault situations delivering the reactive current specified in the recent
grid codes. In this paper, FACTS solutions for fixed speed wind farms such as DVR (Dynamic
Voltage Restorer) are presented as well as classic control and crowbar solutions for variable speed
wind turbines.
A Matlab/Simulink Model for the control scheme utilized to improve power qual...AM Publications
the wind energy generation, utilization and its grid penetration in electrical grid are increasing worldwide. The
integration of wind energy into the power system is to minimize the environmental impact on conventional plant but the injection
of the wind power into an electric grid affects the power quality. The wind generated power is always fluctuating due to its time
varying nature and causing stability problem. The power quality is determined on the basis of measurements and the norms
followed according to the guideline specified in International Electro-technical Commission standard, IEC-61400. The influence
of the wind turbine in the grid system concerning the power quality measurements are-the active power, reactive power, variation
of voltage, flicker, harmonics, and electrical behavior of switching operation and these are measured according to
national/international guidelines. The project demonstrates the power quality problem due to installation of wind turbine with
the grid. In this proposed scheme Static Compensator (STATCOM) is connected at a point of common coupling with a battery
energy storage system (BESS) to mitigate the harmonics. The battery energy storage is integrated to sustain the real power
source under fluctuating wind power. The STATCOM control scheme for the grid connected wind energy generation system for
power quality improvement is simulated using MATLAB/SIMULINK in power system block set. The effectiveness of the
proposed scheme relives the main supply source from the reactive power demand of the load and the induction generator. The
development of the grid co-ordination rule and the scheme for improvement in power quality norms as per IEC-standard on the grid has been presented.
Design of self tuning pi controller for statcom using bats echolocation algor...g.kumaravel
The document describes a study that designed a self-tuning PI controller for a Static Synchronous Compensator (STATCOM) using a Bats Echolocation Algorithm (BEA). A STATCOM is a Flexible AC Transmission Systems device that helps maintain power system stability. The proposed BEA was used to optimize the PI controller gains to regulate the load bus voltage for a power system configuration that included a STATCOM. Digital simulations showed the self-tuning PI controller using the BEA had a faster dynamic response in maintaining the load bus voltage compared to a fixed gain PI controller, especially for a non-linear load.
USING SSSC & STATCOM --IMPROVE TRANSIENT STABILITY--P & Q OSICALLATIONSIJSRD
In a deregulated power system, the electric power demand is extending ordinary which may lead to overloads and loss of generation. Transient stability studies put a fundamental part in power systems, which give information related to the capacity of a power structure to stay in synchronism during major disturbances resulting from either the loss of generation or transmission facilities, sudden or sustained changes. The examination of transient quality is discriminating to work the power structure more secure and this paper focuses on growing the transient relentlessness using FACTS devices like Static Synchronous Series Compensator (SSSC) and static synchronous compensator (STATCOM). These FACTS contraptions are in a perfect world set on transmission structure using Sensitivity approach framework.
This document discusses reactive power compensation techniques using FACTS (Flexible AC Transmission System) devices. It provides an overview of reactive power and why compensation is needed to regulate voltages and improve stability. Several FACTS devices for reactive power compensation are described, including STATCOM, SVC, TCSC, and UPFC. The document compares these devices based on their ability to control load flow, voltage, and stability. UPFC is found to be most effective for higher load flow control and voltage regulation, while STATCOM is suitable for smaller distribution systems. Reactive power compensation using FACTS devices can enhance power transfer capability and stability.
This document presents a new control scheme for a STATCOM (Static Synchronous Compensator) to improve power quality in a grid-connected wind energy system. A STATCOM equipped with a battery energy storage system is connected at the point of common coupling between the wind farm and the grid. The STATCOM control scheme uses a hysteresis current control technique to inject compensating current and regulate the grid voltage. Simulation results show the STATCOM can mitigate reactive power demand and harmonics, as well as respond quickly to changes in load to help regulate voltage and current waveforms at the point of connection to the grid.
Transient Stability of Power System using Facts Device-UPFCijsrd.com
This paper is based on Occurrence of a fault in a power system causes transients. To stabilize the system, The Flexible Alternating Current Transmission (FACTS) devices such as UPFC are becoming important in suppressing power system oscillations and improving system damping. The UPFC is a solid-state device, which can be used to control the active and reactive power.. By using a UPFC the oscillation introduced by the faults, the rotor angle and speed deviations can be damped out quickly than a system without a UPFC. The effectiveness of UPFC in suppressing power system oscillation is investigated by analyzing their oscillation in rotor angle and change in speed occurred in the two machine system considered in this work. A proportional integral (PI) controller has been employed for the UPFC. It is also shown that a UPFC can control independently the real and reactive power flow in a transmission line. A MATLAB simulation has been carried out to demonstrate the performance of the UPFC in achieving transient stability of the two-machine five-bus system.
This document describes a study on implementing Vernier mode operation of a STATCOM to regulate the terminal voltage of a 3-phase self-excited induction generator (SEIG) supplying power to resistive and inductive loads. A thyristor switched reactor and STATCOM are used to control the voltage. Mathematical modeling of the system is presented and simulations in MATLAB/Simulink are performed. Experimental results on a laboratory model show that the STATCOM is able to mitigate terminal voltage drops of the SEIG during different load conditions and provide voltage regulation.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
This document provides a literature survey of Flexible AC Transmission Systems (FACTS) controllers and their applications in power systems. It discusses various FACTS controllers such as thyristor-controlled and voltage source converter-based devices. FACTS controllers can be categorized as series-connected, shunt-connected, series-series connected, or series-shunt connected based on how they are connected to transmission lines. They are used to enhance power system performance in areas such as reactive power support, loss reduction, voltage profile improvement, and damping of power oscillations. The survey concludes that FACTS controllers are effective alternatives to new transmission line construction for improving power system controllability and capacity.
Comparison of facts devices for two area power system stability enhancement u...IAEME Publication
This document summarizes a research paper that compares the performance of SVC and STATCOM FACTS devices for enhancing transient stability in a two area power system modelled in MATLAB. The paper reviews previous research on using FACTS controllers like SVC, STATCOM, SSSC, TCSC and UPFC to improve power system stability. Simulation results from the paper indicate that a two machine system installed with STATCOM provided better damping of rotor angle oscillations compared to an SVC installation, demonstrating improved transient stability when using a STATCOM.
This document discusses FACTS (Flexible AC Transmission System) devices. It defines FACTS as using static power electronics controllers to control reactive power and enhance AC transmission system controllability. The document outlines the necessity of FACTS devices to compensate for reactive power and improve power transmission efficiency. It describes different types of FACTS controllers including shunt controllers like STATCOM, TCR, TSR, and TSC. The benefits of FACTS in providing fast, flexible control of transmission parameters and improving power flow capability are also summarized.
This document discusses methods for controlling voltages and reactive power in power system networks using automatic voltage regulators (AVRs) and static var compensators. It provides an overview of these control methods, including AVRs on generators for voltage regulation and static var compensators for reactive power support. The document evaluates the performance of these methods for enhancing voltage control, improving system stability, and minimizing reactive power flows and losses. Key methods discussed are synchronous generator excitation control using AVRs, transmission system voltage control using shunt capacitors and static var compensators.
This presentation provides an overview of Flexible AC Transmission Systems (FACTS) devices. It defines FACTS as power electronics-based static equipment used to improve power transfer capability and enhance controllability of AC transmission systems. The presentation categorizes FACTS devices based on their connection type to the transmission network and technology. It describes common first and second generation FACTS devices such as SVC, STATCOM, SSSC, TCSC, and UPFC; and their technical benefits regarding load flow control, voltage control, and stability. Potential applications and future enhancements of FACTS are also discussed, along with benefits, operation, and maintenance.
This document presents a multi-objective fuzzy-genetic algorithm approach for optimal placement and sizing of shunt Flexible AC Transmission System (FACTS) controllers. The objectives are to maximize the distance to voltage instability, minimize voltage deviations, and minimize the size of the FACTS controller. Membership functions are developed for each objective and a fitness function is defined based on the membership functions. The approach is tested on the IEEE 14-bus system and results show that placing a STATCOM at bus 9 provides the best improvement in voltage stability and profile.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Performance Improvement of a Grid Connected Wind Farm SystemIOSRJEEE
Renewable energy sources are becoming more promising means of green energy production. But the increasingly penetration level of wind energy into existing power system presents many technical challenges. Power quality is a measure of the system performance. It requires consideration of problems like voltage regulation, stability, harmonics etc. This paper presents an overview of grid connected system and analysis of its stability. The system is assumed with fixed speed Induction generator integrated to a weak grid. Change and improvement in performance is observed with various FACT devices. The simulation model has been developed in MATLAB/SIMULINK R2016a.
Power system operation Question and answersAdhithyaS5
The document contains questions and answers related to power system operation and control. It discusses topics like the objectives of power system operation and control, definitions of terms like average demand and spinning reserve, types of load forecasting and frequency regulation needs in a power system, economic dispatch control and functions of an excitation system. It also covers concepts like area frequency response characteristic, coherent group of generators, static and dynamic response of ALFC loops, and unit commitment constraints.
Stability Modeling Of Storage Devices In FACTS Applicationspreeti naga
The document discusses modeling of storage devices like SMES and BESS for stability applications in FACTS. It describes the need for storage devices to improve controllability in FACTS. It explains SMES, with the superconducting coil producing large fringe fields and power conversion through a VSC and DC-DC chopper. Steady state models are used in power flow studies to maintain real and reactive power injections. State of operation models storage devices as quasi-steady interfaces with dynamic controls. Static VAR compensators are also discussed with thyristor controlled reactors and capacitors to regulate voltage. Dynamic models of the superconducting inductor and battery are also presented.
This document provides a review of the Unified Power Flow Controller (UPFC), a type of Flexible AC Transmission System (FACTS) device. It discusses the basic components and operating principles of the UPFC, which combines the functions of a STATCOM and SSSC to control active and reactive power flow. The UPFC consists of two voltage source converters connected back-to-back via a DC link. One converter injects a voltage in series with the transmission line to control power flow while the other exchanges reactive power with the line to regulate the DC link voltage. Control schemes for both converters are described. The document also presents Simulink models of the UPFC and concludes it is effective for improving power system stability
Simulation of 3 Phase, 24 Pulse GTO Converter for Flow Control of Transmissio...ijtsrd
Gate Turn off GTO thyristor based power control controller for flow control of transmission system is used to regulate voltage and reactive power improment. GTO thyristor switching devices with high power handling capability and the advancement of the other type of power semiconductor devices such as IGBTs, MOSFETs, Ideal switch and so on have led to the development of fast controllable reactive power source utilizing new electronic switching and converter technology. Nowadays, the development of a large capacity Gate Turn off thyristor has made it possible to manufacture self commutated converter employing GTO thyristor for power applications. At present, most of the research on GTO thyristor has focused on their use in power electronic systems at high switching frequencies. GTO thyristor enable the design of the solid state shunt equipment based upon switching technology. The improved rating of GTOs made possible the use of voltage sourced converter VSC in power system applications. In this paper, GTO based voltage source converter VSC is used in high power Flexible AC Transmission Systems FACTS which are used to control power flow on transmission grids. It can be used to build a model of shunt or series static compensator STATCOM or SSSC or, using two such converters, a combination of shunt and series devices known as Unified Power Flow Controller UPFC . This paper has shown a basic application of MATLAB SimPowerSystems programming for 24 pulse GTO converter STATCOM. Zin Wah Aung | Aye Myo Thant | Hnin Yu Lwin "Simulation of 3-Phase, 24 Pulse GTO Converter for Flow Control of Transmission System" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-5 , August 2019, URL: https://www.ijtsrd.com/papers/ijtsrd27887.pdfPaper URL: https://www.ijtsrd.com/engineering/electrical-engineering/27887/simulation-of-3-phase-24-pulse-gto-converter-for-flow-control-of-transmission-system/zin-wah-aung
LOW VOLTAGE RIDE - THROUGH CAPABILITY OF WIND FARMSEditor IJMTER
Nowadays wind turbines are generally required to offer ancillary services similar to those
provided by conventional generators. One of the most important services wind turbines must offer is
to stay connected to the grid in fault situations delivering the reactive current specified in the recent
grid codes. In this paper, FACTS solutions for fixed speed wind farms such as DVR (Dynamic
Voltage Restorer) are presented as well as classic control and crowbar solutions for variable speed
wind turbines.
A Matlab/Simulink Model for the control scheme utilized to improve power qual...AM Publications
the wind energy generation, utilization and its grid penetration in electrical grid are increasing worldwide. The
integration of wind energy into the power system is to minimize the environmental impact on conventional plant but the injection
of the wind power into an electric grid affects the power quality. The wind generated power is always fluctuating due to its time
varying nature and causing stability problem. The power quality is determined on the basis of measurements and the norms
followed according to the guideline specified in International Electro-technical Commission standard, IEC-61400. The influence
of the wind turbine in the grid system concerning the power quality measurements are-the active power, reactive power, variation
of voltage, flicker, harmonics, and electrical behavior of switching operation and these are measured according to
national/international guidelines. The project demonstrates the power quality problem due to installation of wind turbine with
the grid. In this proposed scheme Static Compensator (STATCOM) is connected at a point of common coupling with a battery
energy storage system (BESS) to mitigate the harmonics. The battery energy storage is integrated to sustain the real power
source under fluctuating wind power. The STATCOM control scheme for the grid connected wind energy generation system for
power quality improvement is simulated using MATLAB/SIMULINK in power system block set. The effectiveness of the
proposed scheme relives the main supply source from the reactive power demand of the load and the induction generator. The
development of the grid co-ordination rule and the scheme for improvement in power quality norms as per IEC-standard on the grid has been presented.
Design of self tuning pi controller for statcom using bats echolocation algor...g.kumaravel
The document describes a study that designed a self-tuning PI controller for a Static Synchronous Compensator (STATCOM) using a Bats Echolocation Algorithm (BEA). A STATCOM is a Flexible AC Transmission Systems device that helps maintain power system stability. The proposed BEA was used to optimize the PI controller gains to regulate the load bus voltage for a power system configuration that included a STATCOM. Digital simulations showed the self-tuning PI controller using the BEA had a faster dynamic response in maintaining the load bus voltage compared to a fixed gain PI controller, especially for a non-linear load.
USING SSSC & STATCOM --IMPROVE TRANSIENT STABILITY--P & Q OSICALLATIONSIJSRD
In a deregulated power system, the electric power demand is extending ordinary which may lead to overloads and loss of generation. Transient stability studies put a fundamental part in power systems, which give information related to the capacity of a power structure to stay in synchronism during major disturbances resulting from either the loss of generation or transmission facilities, sudden or sustained changes. The examination of transient quality is discriminating to work the power structure more secure and this paper focuses on growing the transient relentlessness using FACTS devices like Static Synchronous Series Compensator (SSSC) and static synchronous compensator (STATCOM). These FACTS contraptions are in a perfect world set on transmission structure using Sensitivity approach framework.
This document discusses reactive power compensation techniques using FACTS (Flexible AC Transmission System) devices. It provides an overview of reactive power and why compensation is needed to regulate voltages and improve stability. Several FACTS devices for reactive power compensation are described, including STATCOM, SVC, TCSC, and UPFC. The document compares these devices based on their ability to control load flow, voltage, and stability. UPFC is found to be most effective for higher load flow control and voltage regulation, while STATCOM is suitable for smaller distribution systems. Reactive power compensation using FACTS devices can enhance power transfer capability and stability.
This document presents a new control scheme for a STATCOM (Static Synchronous Compensator) to improve power quality in a grid-connected wind energy system. A STATCOM equipped with a battery energy storage system is connected at the point of common coupling between the wind farm and the grid. The STATCOM control scheme uses a hysteresis current control technique to inject compensating current and regulate the grid voltage. Simulation results show the STATCOM can mitigate reactive power demand and harmonics, as well as respond quickly to changes in load to help regulate voltage and current waveforms at the point of connection to the grid.
Transient Stability of Power System using Facts Device-UPFCijsrd.com
This paper is based on Occurrence of a fault in a power system causes transients. To stabilize the system, The Flexible Alternating Current Transmission (FACTS) devices such as UPFC are becoming important in suppressing power system oscillations and improving system damping. The UPFC is a solid-state device, which can be used to control the active and reactive power.. By using a UPFC the oscillation introduced by the faults, the rotor angle and speed deviations can be damped out quickly than a system without a UPFC. The effectiveness of UPFC in suppressing power system oscillation is investigated by analyzing their oscillation in rotor angle and change in speed occurred in the two machine system considered in this work. A proportional integral (PI) controller has been employed for the UPFC. It is also shown that a UPFC can control independently the real and reactive power flow in a transmission line. A MATLAB simulation has been carried out to demonstrate the performance of the UPFC in achieving transient stability of the two-machine five-bus system.
This document describes a study on implementing Vernier mode operation of a STATCOM to regulate the terminal voltage of a 3-phase self-excited induction generator (SEIG) supplying power to resistive and inductive loads. A thyristor switched reactor and STATCOM are used to control the voltage. Mathematical modeling of the system is presented and simulations in MATLAB/Simulink are performed. Experimental results on a laboratory model show that the STATCOM is able to mitigate terminal voltage drops of the SEIG during different load conditions and provide voltage regulation.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
This document provides a literature survey of Flexible AC Transmission Systems (FACTS) controllers and their applications in power systems. It discusses various FACTS controllers such as thyristor-controlled and voltage source converter-based devices. FACTS controllers can be categorized as series-connected, shunt-connected, series-series connected, or series-shunt connected based on how they are connected to transmission lines. They are used to enhance power system performance in areas such as reactive power support, loss reduction, voltage profile improvement, and damping of power oscillations. The survey concludes that FACTS controllers are effective alternatives to new transmission line construction for improving power system controllability and capacity.
Comparison of facts devices for two area power system stability enhancement u...IAEME Publication
This document summarizes a research paper that compares the performance of SVC and STATCOM FACTS devices for enhancing transient stability in a two area power system modelled in MATLAB. The paper reviews previous research on using FACTS controllers like SVC, STATCOM, SSSC, TCSC and UPFC to improve power system stability. Simulation results from the paper indicate that a two machine system installed with STATCOM provided better damping of rotor angle oscillations compared to an SVC installation, demonstrating improved transient stability when using a STATCOM.
This document discusses FACTS (Flexible AC Transmission System) devices. It defines FACTS as using static power electronics controllers to control reactive power and enhance AC transmission system controllability. The document outlines the necessity of FACTS devices to compensate for reactive power and improve power transmission efficiency. It describes different types of FACTS controllers including shunt controllers like STATCOM, TCR, TSR, and TSC. The benefits of FACTS in providing fast, flexible control of transmission parameters and improving power flow capability are also summarized.
This document discusses methods for controlling voltages and reactive power in power system networks using automatic voltage regulators (AVRs) and static var compensators. It provides an overview of these control methods, including AVRs on generators for voltage regulation and static var compensators for reactive power support. The document evaluates the performance of these methods for enhancing voltage control, improving system stability, and minimizing reactive power flows and losses. Key methods discussed are synchronous generator excitation control using AVRs, transmission system voltage control using shunt capacitors and static var compensators.
This presentation provides an overview of Flexible AC Transmission Systems (FACTS) devices. It defines FACTS as power electronics-based static equipment used to improve power transfer capability and enhance controllability of AC transmission systems. The presentation categorizes FACTS devices based on their connection type to the transmission network and technology. It describes common first and second generation FACTS devices such as SVC, STATCOM, SSSC, TCSC, and UPFC; and their technical benefits regarding load flow control, voltage control, and stability. Potential applications and future enhancements of FACTS are also discussed, along with benefits, operation, and maintenance.
This document presents a multi-objective fuzzy-genetic algorithm approach for optimal placement and sizing of shunt Flexible AC Transmission System (FACTS) controllers. The objectives are to maximize the distance to voltage instability, minimize voltage deviations, and minimize the size of the FACTS controller. Membership functions are developed for each objective and a fitness function is defined based on the membership functions. The approach is tested on the IEEE 14-bus system and results show that placing a STATCOM at bus 9 provides the best improvement in voltage stability and profile.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Performance Improvement of a Grid Connected Wind Farm SystemIOSRJEEE
Renewable energy sources are becoming more promising means of green energy production. But the increasingly penetration level of wind energy into existing power system presents many technical challenges. Power quality is a measure of the system performance. It requires consideration of problems like voltage regulation, stability, harmonics etc. This paper presents an overview of grid connected system and analysis of its stability. The system is assumed with fixed speed Induction generator integrated to a weak grid. Change and improvement in performance is observed with various FACT devices. The simulation model has been developed in MATLAB/SIMULINK R2016a.
Power system operation Question and answersAdhithyaS5
The document contains questions and answers related to power system operation and control. It discusses topics like the objectives of power system operation and control, definitions of terms like average demand and spinning reserve, types of load forecasting and frequency regulation needs in a power system, economic dispatch control and functions of an excitation system. It also covers concepts like area frequency response characteristic, coherent group of generators, static and dynamic response of ALFC loops, and unit commitment constraints.
Review Grid Connected Wind Photovoltaic Cogeneration Using Back to Back Volta...IJSRED
This document reviews a proposed system for grid-connected wind and photovoltaic cogeneration using back-to-back voltage source converters. The system uses a permanent magnet synchronous generator for wind power generation and a boost converter for maximum solar power generation through maximum power point tracking. Simulation results are provided to validate the proposed system, which is designed to maximize energy capture from the wind turbine and solar array and deliver it to the utility grid. Control systems are designed for maximum power point tracking of the solar array and synchronization of the inverters with the grid voltage.
This document provides a review of low-voltage ride-through (LVRT) control methods for grid-connected photovoltaic systems. It discusses several control techniques that allow photovoltaic inverters to maintain grid functionality during faults. The techniques aim to regulate the unregulated output power of photovoltaic power stations during abnormal grid conditions. The review covers control approaches in different reference frames and for controlling positive, negative, and zero sequences. It identifies areas for further research and concludes with a brief summary and critique of existing LVRT control methods.
This paper studies the suitability of a vector based current control which is mostly employed for its faster response in the reactive current applications of static compnesators (STATCOMs). The current control is mostly achieved using proportional-integral (PI) controllers because of the advantage of their good tracking and small variations. However, due to the dependency of PI controllers on the modular multilevel converter (MMC) system dynamics, performance variations arise during steady-state STATCOM non-ideal operations. This paper presents an improved MMC based STATCOM control with a d-q compensation algorithm added to the vector based current control. The algorithm is derived to tackle the effects of the dynamics of the MMC and the STATCOM ideal variations without the use of any additional controller. The control is achieved by providing a power compensation in the d,q-axis which injects currents at the input of the PI controllers in order to improve the steady-state performance of the STATCOM control.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
07 22 sep15 8711 18507-2-sm -edit_FACT Device for Reactive Power Compensation...IJPEDS-IAES
In the deregulating electricity market, many private sector power producers
are participating actively. With growing number of the wind mills and solar
power generation, the reactive power production will be more because of
induction generator and inductive type load. Many blackouts have happened
in the past decades due to more reactive power which lead to a decrease in
the magnitude of real power. It is very essential to compensate the reactive
power, increase the real power flow in the transmission line, increase the
transmission efficiency, improve the system stability and be in a safer place
to save the fossil fuels for the future. In this paper the importance of reactive
power and its various compensation techniques are applied to a five bus
deregulated test case modeled and analyzed. The simulations were done
using Matlab Simulink, for various FACT controllers such as STATCOM,
SVC, SSSC and UPFC compensation and the results were tabulated and
compared.
This document discusses a proposed hybrid energy system configuration for grid connection that includes photovoltaic generation, battery energy storage, and wind energy conversion. It describes the control strategies used for various components of the system, including maximum power point tracking for photovoltaic arrays, bidirectional converter control for the battery storage system, and control of the wind turbine generator and grid-side converter. The full hybrid system is modeled and simulated in MATLAB/Simulink to validate the performance and feasibility of the proposed configuration and control approaches.
Voltage Stabilization of a Wind Turbine with STATCOM Using Intelligent Contro...ijeei-iaes
Application of FACTS controller called Static Synchronous Compensator STATCOM to improve the performance of power grid with Wind System is investigated. The essential feature of the STATCOM is that it has the ability to absorb or inject fastly reactive power with power grid. Therefore the voltage regulation of the power grid with STATCOM FACTS device is achieved. Moreover restoring the stability of the wind system at suddenly step up or down in wind speed is obtained with STATCOM. This paper describes a complete simulation of voltage regulation of a wind system using STATCOM. Conventional control technique as proportional plus integral controller , and intelligent techniques as FLC and ANFIS are used in this work. The control technique is performed using MATLAB package software. The dynamic response of uncontrolled system is also investigated under wide range of disturbances. The voltage regulation by using STATCOM whose output is varied so as to maintain or control output voltage in the system. The dynamic response of controlled system is shown and comparison between the uncontrolled system and the controlled system is described to assure the validity of the proposed controller. Also comparison between the proposed control methods scheme is presented. To validate the powerful of the STATCOM FACTS controllers, the studied power system is simulated and subjected to different severe disturbances. The results prove the effectiveness of the proposed STATCOM controller in terms of fast damping the power system oscillations and restoring the power system stability and voltage.
IRJET- Improved IUPQC Controller to Provide Grid Voltage as a STATCOMIRJET Journal
This document discusses an improved controller for the integrated Unified Power Quality Conditioner (iUPQC) that expands its capabilities. The iUPQC can now provide reactive power support to regulate both the load bus voltage and grid side bus voltage, allowing it to function as a Static Synchronous Compensator (STATCOM) on the grid side while still providing conventional UPQC compensation on the load side. Experimental results confirm the new functionality of the device. The iUPQC with the enhanced controller provides power quality compensation like a UPQC as well as reactive power and voltage regulation like a STATCOM.
This document discusses power quality enhancement using Flexible AC Transmission System (FACTS) devices. It provides an overview of various FACTS devices including Static Var Compensator (SVC), Static Synchronous Compensator (STATCOM), and Static Synchronous Series Compensator (SSSC). MATLAB simulations of systems using SVC, STATCOM and SSSC are presented to demonstrate how each FACTS device can improve power quality by mitigating issues like voltage fluctuations and power oscillations. The document concludes that FACTS devices provide better power quality under varying source voltages and sudden loading conditions.
International Journal of Engineering Research and DevelopmentIJERD Editor
This document discusses power quality enhancement using Flexible AC Transmission System (FACTS) devices. It provides an overview of various FACTS devices including Static Var Compensator (SVC), Static Synchronous Compensator (STATCOM), and Static Synchronous Series Compensator (SSSC). MATLAB simulations of systems using SVC, STATCOM and SSSC are presented to demonstrate how each FACTS device can improve power quality by mitigating issues like voltage fluctuations and power oscillations. The document concludes that FACTS devices provide better power quality under varying source voltages and sudden loading conditions.
Comparison of upqc and dvr in wind turbine fed fsig under asymmetric faultselelijjournal
This paper presents the mitigation of faults in wind turbine connected fixed speed induction generator using unified power quality conditioner and static compensator. The UPQC consists of shunt and series converters connected back-to-back through a dc-to-dc step up converter. The presence of the dc-to-dc step converter permits the UPQC to compensate faults for long duration. The series converter is connected to the supply side whereas the shunt converter is connected to the load side. The control system of the proposed UPQC is based on Id-Iq theory. The DVR consists of shunt and series converters connected back-to-back through a dc-to-dc step up converter. The presence of the dc-to-dc step converter permits the DVR to compensate faults for long duration. The series converter is connected to the supply side whereas the shunt converter is connected to the load side. The control system of the proposed DVR is based on
hysteresis voltage controlThe proposed wind turbine fed fixed speed induction generator is evaluated and simulated using MATLAB/SIMULINK environment with UPQC and DVR under asymmetric faults
This document summarizes a study on implementing load frequency control (LFC) in a microgrid system using battery storage and diesel generation units. The microgrid consists of two diesel generators, two solar panels, and a battery storage system. LFC was implemented to minimize frequency deviations from the scheduled frequency of 60Hz under different scenarios like random load changes and loss of a diesel unit. The control aims to balance generation and demand in real-time to maintain a stable frequency during both normal and emergency conditions in the isolated microgrid system.
STATCOM Based Wind Energy System by using Hybrid Fuzzy Logic ControllerIJMTST Journal
The influence of the hybrid system in the grid system concerning the power quality measurements are the active power, reactive power, voltage deviation, flicker, harmonics, and electrical behavior of switching operation and these are measured according to International Electro-Technical Commission (IEC). The STATCOM provides reactive power support to hybrid system and load. These voltage fluctuations can be eliminated with the help of advanced reactive power compensator device such as SVC and STATCOM. This work focus on design, modeling and analysis of FACTS device in wind farm interconnected with grid during fault. These devices can be controlled by Synchronous Reference Frame theory. The performance is analyzed with the help of PI controller and Fuzzy logic technique. by using Matlab/Simulink Model.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
An intelligent based fault-tolerant system 2018Premkumar K
This document presents an intelligent fault-tolerant system for solar photovoltaic (PV) inverters using cascaded multilevel inverters. It uses an artificial neural network controller to monitor, detect, and diagnose faults in solar PV panels, batteries, semiconductor switches, and inverters. The system was able to continue delivering power to loads even under faulty conditions through the use of an auxiliary inverter controlled by the neural network controller. Simulations and experiments on a 3 kW PV system demonstrated the effectiveness of the proposed fault-tolerant system.
Stability Improvement in Grid Connected Multi Area System using ANFIS Based S...IJMTST Journal
Generally, the non-conventional energy sources are being extensively used in case of power electronic
converter based distribution systems. This paper mainly focuses on the wind energy system integrating with
grid connected system and also improvement of power quality features. The wind energy power plant is
modelled based on associated equations. For improving this power quality problems, this paper proposes the
concepts of shunt converter controllers. This paper also proposes the concepts of ANFIS based Static
Compensator. And also the results are compared for this cases. Thus with such a control, a balanced load
currents are obtained even in the presence of non-linear load. The experimental setup is done in Matlab and
verified the simulation results
LOAD FREQUENCY CONTROL IN TWO AREA NETWORK INCLUDING DGIAEME Publication
Automatic Generation Control (AGC) is associate integral a part of Energy Management
System. This paper deals with the automatic generation control of interconnected multi area grid
network. The first purpose of the AGC is to balance the full system generation against system load
and losses so the specified frequency and power interchange with neighboring systems are
maintained. Any pair between generation and demand causes the system frequency to deviate from
regular worth. So high frequency deviation could result in system collapse. This necessitates
associate correct and quick acting controller to take care of constant nominal frequency. The
limitations of the conventional controls are slow and lack of efficiency in handling system nonlinearity.
This leads to develop a control technique for AGC. In this paper both conventional and
PI viz. Proportional Integral controller approach of automatic generation control has been
examined. PI based AGC has been used for all optimization purposes. System performance has
been evaluated at various disturbances such as, load disturbances, grid disturbances and both load
and grid disturbances. Various responses due to conventional and proposed PI based AGC
controllers have been compared at load disturbances, grid disturbances and both load and grid
disturbances.
End-to-end pipeline agility - Berlin Buzzwords 2024Lars Albertsson
We describe how we achieve high change agility in data engineering by eliminating the fear of breaking downstream data pipelines through end-to-end pipeline testing, and by using schema metaprogramming to safely eliminate boilerplate involved in changes that affect whole pipelines.
A quick poll on agility in changing pipelines from end to end indicated a huge span in capabilities. For the question "How long time does it take for all downstream pipelines to be adapted to an upstream change," the median response was 6 months, but some respondents could do it in less than a day. When quantitative data engineering differences between the best and worst are measured, the span is often 100x-1000x, sometimes even more.
A long time ago, we suffered at Spotify from fear of changing pipelines due to not knowing what the impact might be downstream. We made plans for a technical solution to test pipelines end-to-end to mitigate that fear, but the effort failed for cultural reasons. We eventually solved this challenge, but in a different context. In this presentation we will describe how we test full pipelines effectively by manipulating workflow orchestration, which enables us to make changes in pipelines without fear of breaking downstream.
Making schema changes that affect many jobs also involves a lot of toil and boilerplate. Using schema-on-read mitigates some of it, but has drawbacks since it makes it more difficult to detect errors early. We will describe how we have rejected this tradeoff by applying schema metaprogramming, eliminating boilerplate but keeping the protection of static typing, thereby further improving agility to quickly modify data pipelines without fear.
Global Situational Awareness of A.I. and where its headedvikram sood
You can see the future first in San Francisco.
Over the past year, the talk of the town has shifted from $10 billion compute clusters to $100 billion clusters to trillion-dollar clusters. Every six months another zero is added to the boardroom plans. Behind the scenes, there’s a fierce scramble to secure every power contract still available for the rest of the decade, every voltage transformer that can possibly be procured. American big business is gearing up to pour trillions of dollars into a long-unseen mobilization of American industrial might. By the end of the decade, American electricity production will have grown tens of percent; from the shale fields of Pennsylvania to the solar farms of Nevada, hundreds of millions of GPUs will hum.
The AGI race has begun. We are building machines that can think and reason. By 2025/26, these machines will outpace college graduates. By the end of the decade, they will be smarter than you or I; we will have superintelligence, in the true sense of the word. Along the way, national security forces not seen in half a century will be un-leashed, and before long, The Project will be on. If we’re lucky, we’ll be in an all-out race with the CCP; if we’re unlucky, an all-out war.
Everyone is now talking about AI, but few have the faintest glimmer of what is about to hit them. Nvidia analysts still think 2024 might be close to the peak. Mainstream pundits are stuck on the wilful blindness of “it’s just predicting the next word”. They see only hype and business-as-usual; at most they entertain another internet-scale technological change.
Before long, the world will wake up. But right now, there are perhaps a few hundred people, most of them in San Francisco and the AI labs, that have situational awareness. Through whatever peculiar forces of fate, I have found myself amongst them. A few years ago, these people were derided as crazy—but they trusted the trendlines, which allowed them to correctly predict the AI advances of the past few years. Whether these people are also right about the next few years remains to be seen. But these are very smart people—the smartest people I have ever met—and they are the ones building this technology. Perhaps they will be an odd footnote in history, or perhaps they will go down in history like Szilard and Oppenheimer and Teller. If they are seeing the future even close to correctly, we are in for a wild ride.
Let me tell you what we see.
4th Modern Marketing Reckoner by MMA Global India & Group M: 60+ experts on W...Social Samosa
The Modern Marketing Reckoner (MMR) is a comprehensive resource packed with POVs from 60+ industry leaders on how AI is transforming the 4 key pillars of marketing – product, place, price and promotions.
The Building Blocks of QuestDB, a Time Series Databasejavier ramirez
Talk Delivered at Valencia Codes Meetup 2024-06.
Traditionally, databases have treated timestamps just as another data type. However, when performing real-time analytics, timestamps should be first class citizens and we need rich time semantics to get the most out of our data. We also need to deal with ever growing datasets while keeping performant, which is as fun as it sounds.
It is no wonder time-series databases are now more popular than ever before. Join me in this session to learn about the internal architecture and building blocks of QuestDB, an open source time-series database designed for speed. We will also review a history of some of the changes we have gone over the past two years to deal with late and unordered data, non-blocking writes, read-replicas, or faster batch ingestion.
STATATHON: Unleashing the Power of Statistics in a 48-Hour Knowledge Extravag...sameer shah
"Join us for STATATHON, a dynamic 2-day event dedicated to exploring statistical knowledge and its real-world applications. From theory to practice, participants engage in intensive learning sessions, workshops, and challenges, fostering a deeper understanding of statistical methodologies and their significance in various fields."
Codeless Generative AI Pipelines
(GenAI with Milvus)
https://ml.dssconf.pl/user.html#!/lecture/DSSML24-041a/rate
Discover the potential of real-time streaming in the context of GenAI as we delve into the intricacies of Apache NiFi and its capabilities. Learn how this tool can significantly simplify the data engineering workflow for GenAI applications, allowing you to focus on the creative aspects rather than the technical complexities. I will guide you through practical examples and use cases, showing the impact of automation on prompt building. From data ingestion to transformation and delivery, witness how Apache NiFi streamlines the entire pipeline, ensuring a smooth and hassle-free experience.
Timothy Spann
https://www.youtube.com/@FLaNK-Stack
https://medium.com/@tspann
https://www.datainmotion.dev/
milvus, unstructured data, vector database, zilliz, cloud, vectors, python, deep learning, generative ai, genai, nifi, kafka, flink, streaming, iot, edge
2. connecting to a collector system (L3) that transmits power
to a substation (buses 2 and 3). Many turbines are connected
through a single substation, which typically contains switched
capacitors for passive reactive power support, as well as active
reactive support in the form of SVCs or STATCOMs. A step-
up tap-changing transformer T2 connects the substation to the
power grid and the infinite bus 1.
Fig. 1: A generic wind farm layout.
The equipment on buses 2 and 3 are physically located in
the same substation to provide overall reactive power support
for the wind farm.
While the overall layout of the wind farm is shown in Figure
1, the following sections will focus on particular aspects of
the problem and will make simplifying assumptions. Section
III analyzes the collector grid, and Sections IV-VI focus on
the substation. Each section will specify the particular model
under consideration.
III. COLLECTOR SYSTEM IMPACT ON REACTIVE POWER
AVAILABILITY
Type 3 and 4 WTGs employ power electronic converters
that allow production or absorption of reactive power. Many
WTGs, for example, are capable of operating over a power
factor range of 0.95 lagging (generating reactive power) to
0.95 leading (absorbing reacting power) at full active power
output. Manufacturers specify active/reactive capability curves
for their WTGs to describe their exact operational character-
istics. Often wind farm developers use those capability curves
directly to determine the total reactive power available at
the point of interconnection. Whilst such calculations take
into account losses on the collector system, they tend not to
consider voltage rises/falls across the collector feeders and
WTG step-up transformers. The following discussion shows
that as a result, the total reactive power (both lagging and
leading) that’s available at the collector bus tends to be
overstated.
In discussing the restrictions on reactive power that arise
due to collector bus voltages, it is convenient to refer to the
example system shown in Figure 2. For clarity, the figure does
not show the step-up transformers associated with each WTG,
though those transformers have been included in the analysis.
Also, the discussion focuses on reactive power production
(WTGs operating in lagging power factor), though a similar
argument holds for reactive power absorption (leading power
factor).
slack
HVLV
A
MVA
A
MVA
WTG#5WTG#6WTG#11WTG#4JBXA
WTG#3
WTG#2
WTG#10 WTG#7WTG#12WTG#12A
WTG#13WTG#14WTG#15WTG#18WTG#21
WTG#17WTG#16WTG#19WTG#20
1.65 MW
0.00 Mvar
1.65 MW
0.00 Mvar
1.65 MW
0.00 Mvar
1.65 MW
0.00 Mvar
1.65 MW
0.00 Mvar
-30.77 MW
-0.17 Mvar
1.65 MW
0.00 Mvar
1.65 MW
0.00 Mvar
1.65 MW
0.00 Mvar
1.65 MW
0.00 Mvar
1.65 MW
0.00 Mvar
1.65 MW
0.00 Mvar
1.65 MW
0.00 Mvar
1.65 MW
0.00 Mvar
1.65 MW
0.00 Mvar
1.65 MW
0.00 Mvar
1.65 MW
0.00 Mvar
1.65 MW
0.00 Mvar
1.65 MW
0.00 Mvar
1.65 MW
0.00 Mvar
1.05 pu
1.07 pu 1.07 pu 1.07 pu 1.07 pu 1.07 pu
1.07 pu 1.07 pu 1.07 pu
1.07 pu
1.06 pu 1.06 pu
1.07 pu 1.07 pu
1.07 pu
1.07 pu 1.07 pu
1.08 pu 1.08 pu 1.08 pu
1.08 pu
1.06 pu
Fig. 2: Example wind farm topology.
0 0.5 1 1.5
−1
0
1
2
3
4
5
6
7
Reactive power setpoint, Q
set
(MVAr)
Totalreactivepoweroutput(MVAr)
Fig. 3: Variation of total reactive power with setpoint Qset.
Consider a process where the reactive power output from
all WTGs is increased simultaneously. This could be achieved
by a central controller sending every WTG a reactive power
setpoint Qset. With Qset = 0, none of the WTGs would be
at their voltage limits, so all could respond to a change in the
setpoint ∆Qset. The example system consists of 19 WTGs, so
the total change in reactive power supplied to the collector bus
would be approximately 19×∆Qset. (Losses would change by
a small amount.) As Qset increases, voltages across the col-
lector system will increase, with the most dramatic increases
occurring at the remote ends of radial feeders. Eventually
those WTGs at the ends of feeders will encounter their upper
voltage limits. To ensure the voltage limit is not exceeded,
protection overrides the Qset setpoint. Reactive power output
can no longer increase with increasing Qset, and in fact may
fall to ensure the voltage does not rise above the limit. As
Qset continues to increase, more and more WTGs will reach
their upper voltage limits, preventing further increase in their
reactive power output.
The process described above was simulated using a contin-
uation power flow. Results of this process, for the example
system of Figure 2, are shown in Figure 3. Each curve in
the figure corresponds to a different, randomly chosen, set
of active power generation values for the WTGs. It can be
3. seen that the reactive power output saturates in every case.
For small Qset, the slope of each curve is close to 19, the
number of WTGs. However, as Qset increases, and WTGs
progressively encounter their voltage limits, the slope steadily
decreases. Eventually all WTGs are on voltage limits, and
further increases in Qset have no effect.
For this example, all WTGs are rated to produce 1.65 MW
at 0.95 power factor (lagging and leading), which corresponds
to maximum reactive power of 0.54 MVAr. This suggests the
WTGs should be capable of supplying total reactive power of
around 19 × 0.54 = 10.3 MVAr. In fact, based on Figure 3,
the maximum available reactive power is actually less than
6.5 MVAr, and may be as low as 3.7 MVAr. The restriction
is due to each WTG’s upper voltage limit of Vmax = 1.1 pu.
Wind farms that include long radial feeders are most prone
to saturation in total reactive power output. The effect is
less significant for short feeders. Clearly, the collector system
topology must be taken into account when assessing the total
reactive power available from WTGs.
IV. TRANSFORMER TAP-CHANGING GAINS
A. Background
It is not uncommon for step-up transformers associated with
traditional generators to be used to regulate their high-side
bus voltage. In a similar way, numerous wind farms have
sought to use the tap-changing capability of their collector
transformers to regulate the voltage at the (high voltage) point
of interconnection. In many cases, tap changing frequently
exhibits unstable behavior, with the transformer tapping to
an upper or lower limit and remaining there. Consequently,
tapping-based voltage regulation is often disabled.
Fig. 4: Power system for analyzing tap-changing dynamics.
In the following analysis, the simple power system of
Figure 4 will be used to explore the nature of tap-changing
instability, and to suggest sufficient conditions for ensuring
stable behavior. Given the tapping arrangement shown in
Figure 4, the voltage regulator requires dV2
dn > 0 for correct
operation, i.e., it is assumed that an increase in tap raises the
voltage on the high-voltage (tapped) side of the transformer.
The following analysis shows that such a condition is not
always satisfied.
0.6 0.7 0.8 0.9 1 1.1 1.2
0.8
0.85
0.9
0.95
1
1.05
1.1
1.15
1.2
1.25
1.3
Tap position
Voltage,V2
(pu)
Increasing capacitive susceptance
Increasing inductive susceptance
Fig. 5: Curves of V2 versus n for various values of capacitive
and inductive susceptance.
B. Passive voltage support
Initially consider the case where the wind farm has zero
output, and the only device connected to the collector bus is
a capacitor C. The injected current is given by
I3 = −jBV3
where B = ωC is the capacitive susceptance. Simple circuit
analysis yields
V2 =
1
1 − X1B
n2(1−BX2)
× V1. (1)
In per unit, it is normal for BX2 1. This allows (1) to be
simplified, giving
V2 =
1
1 − X1B
n2
× V1. (2)
Assuming constant susceptance B, differentiating gives
dV2
dn
= −
2nX1BV1
(n2 − X1B)2
. (3)
With capacitance connected to the collector bus, susceptance
B is positive. It follows that dV2
dn < 0, implying that tap chang-
ing is unstable. Capacitance is commonly connected to the
collector bus to provide power factor correction and reactive
support. Furthermore, when a Static VAR Compensator (SVC)
is at its capacitive limit, it is effectively just a capacitor.
Notice that if shunt reactors (inductors) are connected to
the collector bus, then the susceptance becomes B = − 1
ωL .
According to (3), dV2
dn > 0 in this case. It follows that the tap
changer would operate correctly to achieve voltage regulation.
Figure 5 shows plots of V2 versus tap position n for the
system shown in Figure 4, with various levels of capacitive
and inductive susceptance. The slopes of the curves are in
agreement with (3).
The simplified analysis above assumed zero active power
production from the WTGs. To explore this effect, active
power of 1.0 pu, at unity power factor, was injected by the
4. 0.6 0.7 0.8 0.9 1 1.1 1.2
0.8
0.85
0.9
0.95
1
1.05
1.1
1.15
1.2
1.25
1.3
Tap position
Voltage,V
2
(pu)
Increasing capacitive susceptance
Increasing inductive susceptance
Fig. 6: Curves of V2 versus n taking into account WTG active
power production.
WTGs into the collector bus. The continuation power flow
cases of Figure 5 were repeated with this power injection, and
are shown in Figure 6. Notice that the conclusions drawn in
the prior analysis remain true:
capacitive susceptance ⇒
dV2
dn
< 0
inductive susceptance ⇒
dV2
dn
> 0.
When STATCOMs encounter a limit, they act as a current
source. It is therefore useful to consider the case of a reactive
current source
I3 = j ˆI3 (4)
injecting current into the collector bus. Note that ˆI3 > 0
for an inductive source (reactive power delivered from the
grid to the STATCOM), with ˆI3 < 0 for a capacitive source
(reactive power delivered from the STATCOM to the grid.)
Again, simple circuit analysis yields
V2 = V1 − X1
ˆI3
n
(5)
and so
dV2
dn
= X1
ˆI3
n2
.
If the current source is inductive, dV2
dn > 0 and hence tapping-
based voltage regulation will operate correctly. However, if the
current source is capacitive, dV2
dn < 0, so tap-changer control
will go unstable. The continuation power flows of Figure 5
were repeated for these current injection cases, with the results
shown in Figure 7.
C. Active voltage support
Consider a reactive support device that injects voltage
dependent current
I3(V3) = j ˆI3(V3)
0.6 0.7 0.8 0.9 1 1.1 1.2
0.8
0.85
0.9
0.95
1
1.05
1.1
1.15
1.2
1.25
1.3
Tap position
Voltage,V2
(pu)
Increasing capacitive current
Increasing inductive current
Fig. 7: Curves of V2 versus n for various values of capacitive
and inductive current injection.
into the collector bus. It can be shown that in this general case,
dV2
dn takes the form
dV2
dn
=
ˆI3(V3) + V3
dˆI3(V3)
dV3
n2
X1
+ dˆI3(V3)
dV3
. (6)
In the special case where reactive support is provided by a
capacitor, we have
ˆI3(V3) = −BV3. (7)
Substituting this into (6) and simplifying gives (3), as ex-
pected. The advantage of (6), though, is that more general
forms of support may be considered.
1) STATCOMs: Assume a STATCOM has current limits
of ±¯Istat. (Recall the current convention of Figure 4, which
implies capacitive current is negative.) It is common for
voltage control to employ a droop characteristic, such that the
current injected into the collector bus is given by,
Istat =
¯Istat
Dstat
V − ¯V (8)
where Dstat is the droop value (typically around 0.03-0.05), ¯V
is the target voltage at zero output, and V is the collector bus
voltage. This yields full output when the voltage difference
exceeds the droop value. All quantities are in per unit.
With a fixed capacitor and a STATCOM at the collector bus,
the total injected current is,
ˆI3(V3) = −BV3 +
¯Istat
Dstat
V3 − ¯V , (9)
and hence
dˆI3(V3)
dV3
= −B +
¯Istat
Dstat
. (10)
From (6), positive (stable) dV2
dn requires that
ˆI3(V3) + V3
dˆI3(V3)
dV3
> 0. (11)
5. Substituting (9) and (10) into (11) and simplifying gives
−2BV3 +
¯Istat
Dstat
2V3 − ¯V > 0.
Exploiting the fact that V3 ≈ ¯V allows further simplification,
¯Istat
Dstat
> 2B. (12)
For a capacitor, B > 0, implying Dstat > 0. Therefore, dV2
dn
will be positive if
0 < Dstat <
¯Istat
2B
. (13)
It is interesting that the STATCOM droop characteristic
must over-compensate the capacitor to ensure dV2
dn > 0. To
explore this result further, consider the situation if the droop
characteristic only just compensated the fixed capacitor, i.e.,
¯Istat
Dstat
= B. According to (9), the net current injection would
be
ˆI3(V3) = −B ¯V , (14)
which is effectively a constant capacitive current. It was shown
in Figure 7, though, that dV2
dn < 0 for such a current injection.
By requiring the condition (12), the inductive effect of the
droop characteristic overcomes the combined effects of the
actual capacitor and the “apparent” capacitive current source
(14).
2) SVCs: SVCs introduce a variable susceptance B into the
current injection equation (7). With B functionally dependent
upon V3, the derivative dˆI3
dV3
becomes,
dˆI3
dV3
= −B − V3
dB
dV3
. (15)
Substituting (7) and (15) into (11) gives,
−BV3 − V3 B + V3
dB
dV3
> 0
⇒ 2B + V3
dB
dV3
< 0
⇒
dB
dV3
< −
2B
V3
. (16)
Assume an SVC has symmetric susceptance limits ± ¯Bsvc,
where capacitive susceptance is positive. A typical droop
characteristic has the form
Bsvc =
¯Bsvc
Dsvc
¯V − V (17)
where parameters are defined similarly to (8), and are again
in per unit. If a fixed capacitor with susceptance −Bfix is
connected to the collector bus together with the SVC, then
the total susceptance is
B(V3) = Bfix + Bsvc(V3),
and
dB(V3)
dV3
= −
¯Bsvc
Dsvc
.
It follows from (16) that dV2
dn is positive (stable) when
¯Bsvc
Dsvc
>
2B
V3
.
To ensure this condition is satisfied over the full range of
B(V3) requires that
¯Bsvc
Dsvc
>
2(Bfix + ¯Bsvc)
V3
,
or rewriting,
0 < Dsvc <
V3
¯Bsvc
2(Bfix + ¯Bsvc)
.
V. TRANSFORMER TAP-CHANGING DYNAMICS
This section addresses a similar issue to Section IV, but
now considers the system dynamics rather than the steady-
state condition. The results derived in Section IV are “static”
in that they do not depend on time or the previous states of
the system. There are no functions of time or time derivatives.
Now, we consider the case where the tap-changing and volt-
age support controllers have their own dynamics. Specifically,
the controllers for tap-changing and reactive support are single
input single output (SISO) integral controllers that operate
independently, as is typically the case when control is isolated
on each particular piece of hardware.
The main consideration is the relative speed between the
two control loops. We will show that if the tap-changing
controller is sufficiently fast (aggressive) compared to the
reactive support, it can cause instability.
Using the same system considered in Section IV and shown
in Figure 4, we assume a reactive current injection into the
collector bus as in (4). V2 is given by (5) and V3 is
V3 =
V1
n
− X
ˆI3(V3)
n2
. (18)
Let target voltages (set by the operator) at bus 2 and 3 be
¯V2 and ¯V3. For simplicity, assume that continuous tap ratios
are available. Then the independent SISO integral controllers
for the tap ratio n and the reactive power injection ˆI3 are
˙n = −kn(V2 − ¯V2) (19)
˙ˆI3 = (V3 − ¯V3). (20)
Normally, the speed of each control loop would be scaled by
some gain. In this case, we are primarily interested in stability
and the important factor is the relative speed between the two
loops. Therefore, the gains are normalized by the gain of the
reactive support loop (20), leaving it with a gain of one. The
gain kn (positive) in (19) represents the relative speed of the
two loops; increasing kn means the tap changing is becoming
faster and more aggressive relative to the reactive support.
To check the stability of the system, we linearize the
dynamics about an equilibrium point. For simplicity, let us
assume that the desired set points are ¯V3 = 1, and ¯V2 is a
function of the equilibrium tap ratio ¯n. This leaves ¯V2 = ¯nV3
(i.e. ¯n = 1.05). At this equilibrium point, all derivatives will be
zero and the system will remain there unless perturbed. Setting
the derivatives (19) and (20) equal to zero and substituting (5)
and (18),
6. ˙n = 0 = −kn(V1 − X
ˆI3(V3)
n
− ¯V2) (21)
˙ˆI3 = 0 = (
V1
n
− X
ˆI3(V3)
n2
− ¯V3). (22)
An important distinction is the difference between a state (n or
V2) and the linearization point (¯n or ¯V2). A fixed equilibrium
point, denoted by a bar, is selected to conduct the linearization,
but the system dynamics still evolve about that point.
Equations (21) and (22) are identical given our definition of
¯V2 and may be solved for the equilibrium current injection,
ˆI3(V3) = −
n(¯n − 1)V1
X
(23)
completing our specification of the equilibrium point.
Taking the partial derivatives of (21) and (22), substituting
(23) and assuming that V1 = 1 we are left with the linearized
system dynamics
˙n
˙ˆI3
=
1
¯n2
kn¯n(¯n − 1) kn¯nX
1 − 2¯n −X
δn
δ ˆI3
, (24)
which has a characteristic polynomial
s2
+ s(−kn¯n(¯n − 1) + X) + ¯n2
knX. (25)
Given that the final term is positive by the definition of kn,
the s term must contain a positive coefficient to yield two
stable eigenvalues. This condition holds when 0 < ¯n < 1 for
positive X. However, when ¯n > 1, there is a maximum tap
changing gain kn to ensure stability,
kn <
X
¯n(¯n − 1)
. (26)
In short, if the bus 2 voltage setpoint ¯V2 is less than 1 p.u.
(¯n < 1) there is no stability issue, but if not, a sufficiently
aggressive tap changer can make the system go unstable.
VI. SUPERVISORY CONTROL OF REACTIVE POWER
SUPPORT
As previously discussed, reactive power may be controlled
by a combination of capacitors, tap-changing transformers, and
FACTS devices. The system operator desires to use this equip-
ment in the most efficient way possible to meet requirements
and often has multiple conflicting goals. For example, these
goals may include minimizing capacitor switching, tap chang-
ing, and power losses while maximizing reactive reserve. More
sophisticated objectives are possible, like prioritizing different
kinds of reactive reserve (i.e. capacitors vs. STATCOMS)
or maximizing the possibility of successfully dealing with a
system fault. There is significant potential for better control
performance by incorporating future knowledge, including
wind and load forecasts.
This level of complexity suggests the need for a system-
level control approach. Here we focus on the control of
reactive power support, where all the reactive power sources
are controlled by a single controller. This approach may yield
better performance than controllers simply based on individual
devices. This section focuses on the long-term supervisory
control which makes decisions at a relatively slower rate,
roughly once per minute or slower. Fault conditions or fast
transients are assumed to be handled by standard control
methods.
A. Problem Formulation
This system level control problem is treated as a dynamic
optimization problem. An important aspect of this type of
problem is the type of future information available, its quality,
and the forecasting horizon. The goal here is to generate the
best possible controller given the available information.
Consider an optimization problem with a finite horizon,
even if very long, perhaps a year. We group the various types
of future information into five broad classes:
1) Exact Future Knowledge - Exact knowledge of the
future for the full time horizon. This yields the maxi-
mum attainable performance, although it is unrealistic in
practice. A less restrictive case assumes that exact future
knowledge is available, but only for a short duration, i.e.
a 24-hour exact forecast.
2) Uncertain Future Knowledge - Time-dependent future
information with uncertainty of some type, including un-
certain forecasts and time-dependent markov transition
probabilities. This information may be available for the
full time horizon or a shorter duration.
3) Cyclical Stochastic Knowledge - General stochastic
predictions about the future that are repetitive and cycli-
cal. An example are markov transition probabilities that
change based on the time of day, but are repeated each
day. This category is well-suited to model daily demand
fluctuations as well as day/night wind patterns.
4) Stationary Stochastic Knowledge- Stationary stochas-
tic predictions about the future, including markov-chain
based wind models. No explicit forecasting or time-
dependent knowledge is required.
5) No Explicit Future Knowledge- Both optimization- and
rule-based methods that do not explicitly account for the
future.
Each of these five classes will generate controllers with
different characteristics. Several controller subtypes are avail-
able for each class; the information class is identified for each
controller type proposed in the following Section VI-B. The
list is ordered roughly in decreasing order of complexity and
performance. In general, having more information available
is not guaranteed to improve performance, but it should do
no worse than the baseline case. The two extreme cases
(1 & 5) listed above may be undesirable, which forces the
determination of the best tradeoff between performance and
complexity. Specifically, the designer should determine the
performance improvement available with increasing controller
complexity in order to make an informed decision
1) Overall Optimization Strategy: The most general formu-
lation describes the system dynamics using a function of the
system state x, control input u, and disturbance w,
7. xk+1 = fk(xk, uk, wk). (27)
The function f may or may not change with time, as repre-
sented by fk.
For a given time series of states (x1...xT ), controls
(u1...uT ), and disturbances (w1...wT ) a performance metric J
is assigned to represent the total cost. A general optimization
formulation represents this cost as a function Φ that is of the
states, controls, and disturbances over a time window T,
J = Φ(x1...xT , u1...uT , w1...wT ). (28)
Other formulations are available that generate a finite cost even
with infinite stopping time, for example by discounting future
costs.
Many different techniques are available to solve these types
of problems, but optimal solutions can be difficult to obtain
because the number of possible control sequences grows
exponentially with time. If the total cost is restricted to be
an additive cost function ck(xk, uk) that can be evaluated at
each individual time step,
T
0
ck(xk, uk), (29)
techniques are available to drastically reduce computation
requirements. The subscript k denotes that the cost may be a
function of time. We focus on problems of this type. Thus, the
optimization problem may be stated formally as minimizing
(29) subject to possibly time-dependent constraints gk(xk, uk),
min
T
0 ck(x, u)
such that (30)
gk(xk, uk) ≤ 0 ∀ k.
In this work we generate test optimization-based controllers
for three cases including the two extremes extreme cases: exact
future knowledge, stationary stochastic knowledge, and no
explicit future knowledge. In addition, these three controllers
are compared to a “baseline” algorithm that uses hysteresis-
based switching of the capacitors based on current reactive
power demand.
2) Example System: To illustrate the control techniques
presented here, a simple test system is studied. This system
consists of a wind farm collector system connected to an
infinite bus through a substation. The substation has four
capacitor banks and a STATCOM for reactive power compen-
sation, just as shown in Figure 1. The optimization goal is to
minimize both STATCOM usage and capacitor switching. The
STATCOM is assumed to perfectly regulate the bus voltage V3
and supply any reactive power not supplied by the capacitors.
For now, the STATCOM is also assumed to have unlimited
capability, but realistic limits may be easily implemented. This
yields a relatively simple power flow problem, while clearly
illustrating the control problem. The power flow equations are
solved to determine the reactive power required to hold the
bus at 1 V p.u., and the optimization is simply the distribution
of this reactive power between the STATCOM and capacitors.
To model this system in terms of (30), the system has four
states x representing the current state of each capacitor bank,
either on or off. Four controls u represent the command to
turn each capacitor bank on or off. Thus the system dynamics
(27) reflect the simple result that at the next time step, the
capacitor state xk+1 will match the current command uk.
For the cost function, the number of capacitor switches NCS
is weighted by a penalty α to reflect maintenance and wear
costs. The STATCOM usage ¯S is calculated based on the
current reactive power demand and the capacitance supplied by
the control uk. ¯S is defined as the time integral of STATCOM
usage over the time step. We are interested in the relative
tradeoff between capacitor switches and STATCOM usage and
need only one tuning parameter, so ¯S has penalty one,
ck(xk, uk) = αNCS + abs( ¯S). (31)
These two definitions of ck(x, u) and fk(x, u) form the
basic optimization problem and are used in the various al-
gorithms.
B. Control Design Methods for Various Information Classes
The control design methods proposed here are standard
techniques. The main ideas are presented here, but full details
are available in standard texts [4], [5].
1) Deterministic Dynamic Programming: In the case of
exact future knowledge, Deterministic Dynamic Programming
(DDP) is used to solve (30). For each time step, the optimal
“cost to go” function J∗
k (x) is calculated. It represents the
minimum cost required to go from time k and state x to the
final time T. Starting at the final time T, the terminal cost
(if any) is assigned for the final state, yielding J∗
T (x). The
algorithm proceeds by backward recursion,
J∗
k (x) = min
u∈U
[ck(x, u) + J∗
k+1(fk(xk, u))], (32)
where c(x, u) is the instantaneous cost as a function of state
and control. Recall that the function fk(xk, uk) determines
the next state xk+1. This equation represents a compromise
between minimizing the current cost ck(x, u) and the future
cost J(xk+1). This formulation is entirely deterministic with
no stochastic disturbances because the exact future is known.
Anything that changes with time, e.g. reactive power demand,
is included in the time-varying cost ck(x, u) or dynamics
fk(xk, uk). In this case, the cost is given by (31) and changes
based on the required reactive power.
The optimal control u∗
is any control that achieves the
minimum cost J∗
k (x) in (32),
u∗
k(x) = argmin
u∈U
c(xk, u) + J∗
k (fk(xk, u))]. (33)
This method requires two steps: an off-line step to calculate
the controller using the future knowledge, and an on-line step
where the control is causally implemented, possibly in real-
time. The off-line step solves (32), and the end result is a
control policy u∗
k(x) and a cost-to-go Jk(x), both for all times
k. In the on-line implementation, one may either use the policy
u∗
k(x) or calculate the control on-line using (33) and the cost-
to-go Jk(x). Intuitively, Jk(x) represents the minimum cost
8. required to operate from time k until time T when starting in
state x. It essentially contains the future information about the
system.
2) Stochastic Dynamic Programming: Stochastic Dynamic
Programming (SDP) is used to incorporate uncertain future
knowledge, stationary stochastic knowledge in this case. This
algorithm is a variant of the deterministic version described
previously, but the main ideas are the same. The key difference
is that the future is uncertain, so everything is based on an
expectation of the future Ew over the disturbance w. While
the designer still wished to solve (30), the algorithm can no
longer solve it exactly due to the uncertain future. Instead, the
algorithm uses a slightly different optimization formulation,
min Ew
∞
0 γk
c(x, u)
such that (34)
g(x, u) ≤ 0 ∀ k.
(35)
This formulation differs from (30) in several ways. The future
cost is discounted by the factor γ < 1, which keeps the sum
finite. This technique is called “infinite horizon discounted
future cost.” Although the time horizon is no longer finite,
a value of γ close to one forces the algorithm to consider
a “reasonable” time horizon, while discounting the infinite
future.
To use the algorithm,
V ∗
(x) = min
u∈U
Ew[c(x, u) + V ∗
(f(x, u, w))] (36)
is solved for the “Value Function” V (x). The value function
is very similar to the cost-to-go Jk(x) in (32). The primary
difference is that V (x) is not a function of time, only the state.
It represents the expected future cost of being in state x. The
time horizon is infinite, and hence V (x) does not change with
k. The optimal control u∗
is again any control that achieves
the minimum cost V ∗
(x) in (36),
u∗
(x) = argmin
u∈U
Ew[c(x, u) + V ∗
(f(x, u, w))]. (37)
The control policy is also independent of time and hence is a
stationary policy.
The future disturbances, wind power in this case, are speci-
fied via a finite-state Markov chain rather than exact future
knowledge. This wind model adds additional states to the
model. In general, the designer must determine the probability
distribution of the disturbance w based on the current state and
control,
P(wk|xk, uk). (38)
In this paper we use a one state Markov chain. The current
wind power Pk is the state, and the probability of the next
wind power depends on the current wind power. This means
estimating the function
P(Pk+1|Pk). (39)
The designer may choose how this disturbance is specified.
For example, the disturbance may be the next wind power, or
it may be the change in wind power. More complex models
can be used by adding additional model states, perhaps the
last three recorded wind powers.
The transition probabilities (39) are estimated from known
wind patterns. The powers P are discretized to form a grid. For
each discrete state Pk there are a variety of outcomes Pk+1.
The probability of each outcome Pk+1 is estimated based on
its frequency of occurrence, and is a function of the current
wind power.
3) Instantaneous Optimization: The simplest optimization-
based algorithm seeks to minimize cost with no future knowl-
edge. This technique is termed Instantaneous Optimization
(IO) because it has no estimate or prediction of the future
and the control is generated by minimizing the current cost at
each instant,
u∗
(x) = argmin
u∈U
c(x, u). (40)
The control decision clearly lacks the future estimates of (33)
and (37).
4) Baseline Controller: The baseline controller is not based
on optimization at all, but a simple rule-based hysteresis.
Recall that the STATCOM usage ¯S is the difference between
the required reactive power and that supplied by the capacitors.
A switching threshold β is assigned, and when the STATCOM
usage exceeds this threshold, an additional capacitor bank is
switched in or out. Define NC as the number of capacitor
banks currently switched in. This leaves the update rule as
NCk+1 =
NCk + 1 if ¯S > β
NCk − 1 if ¯S < −β
NCk otherwise.
(41)
C. Simulation Results
The various types of controllers discussed in Section VI-B
are designed and tested the example system to evaluate their
effectiveness. Wind data from the National Renewable Energy
Lab’s EWITS study are used. The simulation covers a 30-
day period, and the controller commands update every 5
minutes. Each controller is designed with the appropriate level
of information: controllers that use exact future knowledge are
given the entire wind power trace ahead of time, stochastic
controllers are given the probability distribution (39) for the
test period, and the other two controllers are given no future
information.
For each controller type, a number of different controllers
are designed with varying values of the penalty α (31) or
the hysteresis threshold β in (41). This yields a range of
controllers of the same type with varying attributes. The
results are shown in Figure 8. The horizontal axis shows the
number of capacitor switches. The vertical axis represents
total STATCOM usage, measured as cumulative absolute value
abs( ¯S). As our optimization goal is to minimize both ca-
pacitor switching and STATCOM usage, the best performance
is found in the lower left of the plot.
9. 100 150 200 250 300 350 400 450
1500
2000
2500
3000
3500
Capacitor Switches
TotalSTATCOMUsage(MVAR−hr)
Hysteresis
Local Min
DDP
SDP
Fig. 8: Performance of various types of optimal controllers
based on different types of information. Best performance
is attained with low STATCOM usage and low capacitor
switching, in the bottom left of the figure. These data are for
one month periods. Detailed time traces are shown in Figure
9.
D. Discussion
The DDP controllers designed with perfect information
demonstrate the best performance, which is to be expected.
Perhaps more surprising is that the other three controller
types all generate similar performance. This motivates an
open research question: What level of future information is
appropriate? For the five information classes enumerated in
Section VI-A, the two simplest cases (classes 4 & 5) yield
similar performance, but the most complex case (class 1)
yields vast improvements. This points to a “middle ground” of
controller complexity, where significant improvements may be
found with reasonably complex controllers of classes 2-4. If
exact future knowledge provided no benefit, simple controllers
could be used while attaining optimal performance.
The IO controllers generate identical performance to the
baseline hysteresis method because they essentially do the
same task. With no future knowledge, the instantaneous
optimization is based solely on the cost function (31). A
capacitor switch will not occur until the STATCOM usage
exceeds the cost of the capacitor switch, which acts as a
threshold policy. Arguably, the simple hysteresis method is
a rudimentary optimization.
The behavior of the instantaneous optimization has a discon-
tinuity, as shown by the unpopulated gap in capacitor switches.
At each time step, the STATCOM usage is evaluated for only
that time step. The maximum savings of switching in one
capacitor bank is finite, specifically the value of the capacitor
bank times the time step. If the cost of a capacitor switch
exceeds this maximum, no capacitors will ever be switched
on because the decrease in STATCOM usage is always less
than the cost of a capacitor switch.
The performance of the SDP stochastic controllers is iden-
tical to that of the simpler controllers without any future
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
−5
0
5
10
15
20
25
30
time (Days)
MVAR
MVAR Required
Capacitance
(a) Minimum STATCOM/max switching case for Dynamic Program-
ming with exact future knowledge.
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
−5
0
5
10
15
20
25
30
time (Days)
MVAR
MVAR Required
Capacitance
(b) Moderate switching (98 Switches) with Deterministic Dynamic
Programming and exact future knowledge.
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
−5
0
5
10
15
20
25
30
time (Days)
MVAR
MVAR Required
Capacitance
(c) Moderate switching (98 Switches) with Stochastic Dynamic Pro-
gramming and future statistics. knowledge.
Fig. 9: Time traces of wind farm reactive power control. The
solid black line is the required reactive power, the solid blue
line is the capacitance and changes in discrete steps with the
switches. The green and red regions represent the positive
and negative STATCOM usage required to exactly meet the
reactive power demand.
10. knowledge. This implies that the Markov chain wind model
used does not provide any additional future information. This
is clear from the calculated statistics (39) as the distribution of
change in wind power is approximately constant regardless of
the current wind power. The SDP controllers studied here use
a very simple Markov chain wind model. More sophisticated
controllers can be designed that use additional states and
generate better performance, for example by storing the last
few wind power values rather than just the current value.
They will still be classified as having stationary stochastic
knowledge (class 4). Markov chains are not particularly good
at wind forecasting [6].
Although the example system used here is very simple, the
optimization framework of Section VI-A1 can handle very
complex systems. Additional attributes [7] may be considered
including reserve requirements, failure probabilities, capaci-
tor discharge times, short and long term STATCOM limits,
etc. The downside of this framework is computation, which
typically grows exponentially with the number of system
states. Including all the equipment in a substation is feasible,
including all the equipment in a region is probably not.
These techniques can provide the most benefit for systems
with complex dynamics, constraints, non-intuitive behavior,
and a relatively small number of actuators (< 15). Large
problems can often be partitioned [8], [9] with some loss of
optimality, i.e. solving for the reactive power output of each
substation, then solving for the reactive power supply within
each substation to meet that requirement.
VII. CONCLUSIONS
The control of reactive power support for wind generation
is a challenging problem on several levels. WTGs themselves
may be used to provide reactive power support, but the design
of the collector system may limit their reactive power output
as demonstrated on an example system.
Two cases of low-level system stability were analyzed,
highlighting the difficulty of incorporating multiple types of
equipment with independent SISO controllers together to form
a cohesive unit. In one case, capacitive susceptance causes a
tap-changing transformer to change voltage gain - the high
side voltage decreases with increasing tap ratio. In a second
case, the active controllers for a tap changing transformer and
a reactive current source interact to create an instability. Even
for devices that may be stable on their own, under certain
conditions they can interact and yield unexpected behavior.
System-level considerations also play a role and optimiza-
tion methods can be important. Various types of controllers
were used to control the reactive power support in a substation.
These controllers all had varying levels of future information:
some had perfect prediction, some had stochastic predictions,
and some had no information. The results demonstrate that
future knowledge plays an important role in determining
optimal solutions, but rudimentary future knowledge in the
form of simple wind forecasts based on Markov chains provide
no additional benefit. This leaves an open research question
about the role of forecasting in these systems, and the relative
tradeoff between controller complexity and performance as
more and more information becomes available.
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