The optimal power flow problem involves minimizing the total cost of operating a power grid system while meeting power demand and equipment constraints. It is a difficult nonlinear optimization problem to solve, as it requires balancing generation and load across hundreds of generators and thousands of buses in real-time. While iterative numerical methods can provide approximations, finding exact solutions for large systems remains challenging. Improving solution speed could significantly reduce costs by allowing more optimal grid operation.
Optimum Reactive Power Calculation for Reducing Power System Operation CostPower System Operation
Reactive power plays a key role in reducing power system operation costs. This paper develops an optimal power flow model to determine the optimal reactive power at each node to minimize total system operation costs. The model is tested on the IEEE 57-bus system, and results show that adjusting reactive power at certain critical nodes can significantly reduce costs. Optimal reactive power adjustments are assumed to be provided by distributed energy resources and microgrids connected to those nodes.
Load Flow Analysis of Jamshoro Thermal Power Station (JTPS) Pakistan Using MA...sunny katyara
This article summarizes a study analyzing the load flow of Jamshoro Thermal Power Station (JTPS) in Pakistan using MATLAB programming. The study models the power plant and transmission network in MATLAB to calculate active and reactive power flows, line losses, voltage profiles and angles at different buses. This provides information for efficient scheduling and future planning of the power system. MATLAB code was developed using the Gauss-Siedel iterative method to solve the load flow equations. The results provide voltage magnitudes and angles at each bus and active/reactive power flows on each transmission line. This analysis can help optimize the economic operation and future expansion of the JTPS power system.
International Journal of Engineering Research and DevelopmentIJERD Editor
The document discusses optimizing the location and size of distributed generations (DGs) in a power distribution system to reduce power losses and improve voltage profiles. It proposes using the Kalman filter algorithm to determine optimal DG sizes after their locations have been selected. The locations are chosen by considering total power loss in the system. Power losses are calculated using distribution factor equations that model power flows from generators to loads and vice versa. The approach will be tested on the IEEE 30-bus system model.
International Journal of Engineering Research and DevelopmentIJERD Editor
Electrical, Electronics and Computer Engineering,
Information Engineering and Technology,
Mechanical, Industrial and Manufacturing Engineering,
Automation and Mechatronics Engineering,
Material and Chemical Engineering,
Civil and Architecture Engineering,
Biotechnology and Bio Engineering,
Environmental Engineering,
Petroleum and Mining Engineering,
Marine and Agriculture engineering,
Aerospace Engineering.
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.
Optimum Reactive Power Calculation for Reducing Power System Operation CostPower System Operation
Reactive power plays a key role in reducing power system operation costs. This paper develops an optimal power flow model to determine the optimal reactive power at each node to minimize total system operation costs. The model is tested on the IEEE 57-bus system, and results show that adjusting reactive power at certain critical nodes can significantly reduce costs. Optimal reactive power adjustments are assumed to be provided by distributed energy resources and microgrids connected to those nodes.
Load Flow Analysis of Jamshoro Thermal Power Station (JTPS) Pakistan Using MA...sunny katyara
This article summarizes a study analyzing the load flow of Jamshoro Thermal Power Station (JTPS) in Pakistan using MATLAB programming. The study models the power plant and transmission network in MATLAB to calculate active and reactive power flows, line losses, voltage profiles and angles at different buses. This provides information for efficient scheduling and future planning of the power system. MATLAB code was developed using the Gauss-Siedel iterative method to solve the load flow equations. The results provide voltage magnitudes and angles at each bus and active/reactive power flows on each transmission line. This analysis can help optimize the economic operation and future expansion of the JTPS power system.
International Journal of Engineering Research and DevelopmentIJERD Editor
The document discusses optimizing the location and size of distributed generations (DGs) in a power distribution system to reduce power losses and improve voltage profiles. It proposes using the Kalman filter algorithm to determine optimal DG sizes after their locations have been selected. The locations are chosen by considering total power loss in the system. Power losses are calculated using distribution factor equations that model power flows from generators to loads and vice versa. The approach will be tested on the IEEE 30-bus system model.
International Journal of Engineering Research and DevelopmentIJERD Editor
Electrical, Electronics and Computer Engineering,
Information Engineering and Technology,
Mechanical, Industrial and Manufacturing Engineering,
Automation and Mechatronics Engineering,
Material and Chemical Engineering,
Civil and Architecture Engineering,
Biotechnology and Bio Engineering,
Environmental Engineering,
Petroleum and Mining Engineering,
Marine and Agriculture engineering,
Aerospace Engineering.
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.
In power engineering the power flow analysis (also known as load flow study) is an important tool involving numerical analysis applied to a powe r system. This project deals with a model of existing power system using the actual data taking care of all parameters required for the simulation and analysis. With the help of Maharasht ra State Electricity Transmission co. Ltd.,a model of 220KV lines,of Solapur District grid usin g MATLAB software will be modeled. In this project,an algorithm will be used for power f low study and data collection and coding required for modeling. Load flow studies will be ca rried out using Newton Raphson method and voltage profile of buses will be analyzed. New meth od for the improvement of voltage profile will be suggested and analyze using the developed m odel. The optimization techniques include power factor compensation,tap changing,up gradati on of substation,up gradation of line and load shifting will be analyzed. Importance of power flow or Load flow studies is in planning future expansion of power system as well as determi ning the best operation of existing systems. From results of simulation buses with low voltage p rofile will be identified and possible solutions can be suggested.
The document discusses assessing spinning reserve requirements in a deregulated power system. It defines key terms like spinning reserve, spot market, and day-ahead market. It describes a test power system with 3 generating zones and a 49-step load forecast uncertainty model. It outlines assumptions and develops a cost model to minimize hourly costs based on spinning reserve levels and constraints. The results show that spinning reserve requirements are affected by the load forecast uncertainty percentage, spot market price, spinning reserve price, and generator reloading limits. Future work could incorporate generator failure rates and do a cost-benefit analysis of requirements based on load forecast uncertainty.
Design of Full Order Optimal Controller for Interconnected Deregulated Power ...ijceronline
International Journal of Computational Engineering Research (IJCER) is dedicated to protecting personal information and will make every reasonable effort to handle collected information appropriately. All information collected, as well as related requests, will be handled as carefully and efficiently as possible in accordance with IJCER standards for integrity and objectivity.
On the optimal transmission policy in hybrid energy supply wireless communica...MNIT Jaipur
This document discusses energy efficient transmission scheduling in wireless communication systems with hybrid energy supplies. It presents a system model where the transmitter is powered by both a primary battery and an energy harvester. It formulates two optimization problems: 1) minimizing the outage probability by deriving the optimal saving factor and 2) minimizing the battery energy consumption through optimal packet scheduling and saving factor selection. The document concludes that for high throughput requirements, it is best to transmit using only battery energy rather than harvested energy.
The document discusses power flow analysis, which determines bus voltages and power flows in a power system under normal steady-state operating conditions. It provides the mathematical formulation of the power flow problem as a set of nonlinear algebraic equations that must be solved iteratively. Buses are classified as slack, generator, or load buses depending on which two of four associated quantities - real power, reactive power, voltage magnitude, and voltage angle - are specified versus solved for. Solution methods like the Gauss-Seidel method are commonly used to iteratively solve the power flow equations until bus voltages converge.
This document summarizes key concepts regarding economic dispatch of power systems. It discusses how different generation technologies have varying capital and operating costs. Thermal generator costs are typically represented by input/output, fuel cost, heat rate, and incremental cost curves. The incremental cost curve, which plots the incremental cost per MWh as a function of output, is used to determine the optimal dispatch of generators to minimize total operating costs while meeting demand. Formulas for approximating generator cost curves with quadratic functions are also presented.
This document provides an overview and summary of different load flow analysis methods. It begins with an introduction to load flow studies and the power flow equations. It then summarizes three classical iterative methods: Gauss-Seidel, Newton-Raphson, and Fast Decoupled. The document also briefly discusses other optimization methods like fuzzy logic, genetic algorithms, and particle swarm optimization that can be applied to load flow problems. Case studies are presented at the end to demonstrate the different techniques.
1. The document describes the process of load flow analysis using the Newton-Raphson power flow method.
2. The Newton-Raphson power flow method uses Newton's method to solve the nonlinear power balance equations to determine the voltage magnitude and angle at each bus in the power system.
3. It derives the real and reactive power balance equations, defines the power flow variables, describes calculating the Jacobian matrix and its elements, and provides an example of applying the method to a two bus system to solve for the unknown voltage magnitude and angle at the second bus.
INTRODUCTION BASIC TECHNIQUES TYPE OF BUSES
Y BUS MATRIX POWER SYSTEM COMPONENTS BUS ADMITTANCE MATRIX
Power (Load) flow study is the analysis of a power system in normal steady-state operation
This study will determine:
DISTRIBUTION LOAD FLOW ANALYSIS FOR RDIAL & MESH DISTRIBUTION SYSTEMIAEME Publication
This document presents a new and efficient method for solving load flow problems in radial and weakly meshed distribution systems. The proposed method is based on network topology, circuit laws, and power summation techniques. It uses loop analysis to account for the impact of tie lines in meshed networks. The algorithm calculates effective power injections, voltage drops, and loop currents to solve for bus voltages and power losses. It was coded in MATLAB and tested on IEEE 33-bus test systems. Results show the voltage profile, power losses, computation time, and number of iterations for different systems and operating conditions. The proposed method provides an efficient way to analyze load flow in distribution networks with radial and weakly meshed topologies.
This document summarizes a lecture on economic dispatch in power systems. It begins with announcements about homework assignments and readings. It then discusses the formulation of economic dispatch as minimizing generation costs subject to meeting demand. The document uses an example two generator system to illustrate solving the optimization using Lagrange multipliers. It describes the lambda iteration method for solving economic dispatch with multiple generators. Finally, it discusses including transmission losses in the economic dispatch formulation.
The document discusses load flow studies and the Gauss-Siedel method for solving power flow equations. Load flow studies calculate voltage drops, bus voltages, and power flows under various conditions to determine if voltages remain within limits and equipment is not overloaded. The Gauss-Siedel method iteratively solves power flow equations represented by a non-linear algebraic equation using the bus admittance matrix and known real and reactive power values at buses to calculate unknown bus voltages until converging on a solution. An example applies the Gauss-Siedel method with an acceleration factor to a three bus system to calculate voltages after the first iteration.
The document discusses power flow analysis, which determines voltages, currents, real power, and reactive power in a power system under steady-state load conditions. It describes the different types of buses in a power system and how they are modeled. The key component of power flow is the bus admittance matrix, which relates nodal voltages to branch currents based on Kirchhoff's current law. Solving the matrix equations provides the voltage magnitude and angle at each bus.
Basics of Power systems
Network topology
Transmission and Distribution
Load and Resource Balance
Economic Dispatch
Steady State System Analysis
Power flow analysis
Dynamic System Analysis
Transient stability
International Refereed Journal of Engineering and Science (IRJES)irjes
The core of the vision IRJES is to disseminate new knowledge and technology for the benefit of all, ranging from academic research and professional communities to industry professionals in a range of topics in computer science and engineering. It also provides a place for high-caliber researchers, practitioners and PhD students to present ongoing research and development in these areas.
Power losses reduction of power transmission network using optimal location o...IJECEIAES
Due to the growth of demand for electric power, electric power loss reduction takes great attention for the power utility. In this paper, a low-level generation or distributed generation (DG) has been used for transmission power losses reduction. Karbala city transmission network (which is the case study) has been represented by using MATLAB m-file to study the load flow and the power loss for it. The paper proposed the particle swarm optimization (PSO) technique in order to find the optimal number and allocation of DG with the objective to decrease power losses as possible. The results show the effect of the optimal allocation of DG on power loss reduction.
Comparative power flow analysis of 28 and 52 buses for 330 kv power grid netw...Onyebuchi nosiri
Newton-Raphson technique was formulated and used to evaluate the electrical performances of the existing 28-bus and improved 52-bus Nigerian 330kV power networks. The Jacobian matrix for both the existing 28-bus and the improved 52-bus Nigerian power system was derived using Newton-Raphson power flow solution method. The steady-state critical bus voltages, voltage and angle profiles at each bus, active and reactive power flows, transformer tap settings, component or circuit loading, generator exciter regulator voltage set points and system losses of these networks were determined to ascertain their effectiveness and proper network reconfiguration. The results obtained showed a better performance of the 52-Bus system in power quality, voltage and angle profiles over the conventional 28-bus system
The document describes an experiment using MATLAB to implement the Newton-Raphson load flow method to analyze a 3-bus power system network. The Newton-Raphson method approximates non-linear power flow equations using Taylor series expansion, allowing faster convergence compared to other methods. The experiment specifies bus voltages, real/reactive power demands and generations, and solves for reactive power output using a tolerance of 0.01 power mismatch. The MATLAB code is run and the load flow solution is obtained.
Malformações do sistema nervoso central; Os autores estudaram 32 recém-nascidos com malformação do sistema nervoso central. Destacam a importância do estudo das malformações desde que consistem na segunda causa de morbidade e mortalidade neonatal.
In power engineering the power flow analysis (also known as load flow study) is an important tool involving numerical analysis applied to a powe r system. This project deals with a model of existing power system using the actual data taking care of all parameters required for the simulation and analysis. With the help of Maharasht ra State Electricity Transmission co. Ltd.,a model of 220KV lines,of Solapur District grid usin g MATLAB software will be modeled. In this project,an algorithm will be used for power f low study and data collection and coding required for modeling. Load flow studies will be ca rried out using Newton Raphson method and voltage profile of buses will be analyzed. New meth od for the improvement of voltage profile will be suggested and analyze using the developed m odel. The optimization techniques include power factor compensation,tap changing,up gradati on of substation,up gradation of line and load shifting will be analyzed. Importance of power flow or Load flow studies is in planning future expansion of power system as well as determi ning the best operation of existing systems. From results of simulation buses with low voltage p rofile will be identified and possible solutions can be suggested.
The document discusses assessing spinning reserve requirements in a deregulated power system. It defines key terms like spinning reserve, spot market, and day-ahead market. It describes a test power system with 3 generating zones and a 49-step load forecast uncertainty model. It outlines assumptions and develops a cost model to minimize hourly costs based on spinning reserve levels and constraints. The results show that spinning reserve requirements are affected by the load forecast uncertainty percentage, spot market price, spinning reserve price, and generator reloading limits. Future work could incorporate generator failure rates and do a cost-benefit analysis of requirements based on load forecast uncertainty.
Design of Full Order Optimal Controller for Interconnected Deregulated Power ...ijceronline
International Journal of Computational Engineering Research (IJCER) is dedicated to protecting personal information and will make every reasonable effort to handle collected information appropriately. All information collected, as well as related requests, will be handled as carefully and efficiently as possible in accordance with IJCER standards for integrity and objectivity.
On the optimal transmission policy in hybrid energy supply wireless communica...MNIT Jaipur
This document discusses energy efficient transmission scheduling in wireless communication systems with hybrid energy supplies. It presents a system model where the transmitter is powered by both a primary battery and an energy harvester. It formulates two optimization problems: 1) minimizing the outage probability by deriving the optimal saving factor and 2) minimizing the battery energy consumption through optimal packet scheduling and saving factor selection. The document concludes that for high throughput requirements, it is best to transmit using only battery energy rather than harvested energy.
The document discusses power flow analysis, which determines bus voltages and power flows in a power system under normal steady-state operating conditions. It provides the mathematical formulation of the power flow problem as a set of nonlinear algebraic equations that must be solved iteratively. Buses are classified as slack, generator, or load buses depending on which two of four associated quantities - real power, reactive power, voltage magnitude, and voltage angle - are specified versus solved for. Solution methods like the Gauss-Seidel method are commonly used to iteratively solve the power flow equations until bus voltages converge.
This document summarizes key concepts regarding economic dispatch of power systems. It discusses how different generation technologies have varying capital and operating costs. Thermal generator costs are typically represented by input/output, fuel cost, heat rate, and incremental cost curves. The incremental cost curve, which plots the incremental cost per MWh as a function of output, is used to determine the optimal dispatch of generators to minimize total operating costs while meeting demand. Formulas for approximating generator cost curves with quadratic functions are also presented.
This document provides an overview and summary of different load flow analysis methods. It begins with an introduction to load flow studies and the power flow equations. It then summarizes three classical iterative methods: Gauss-Seidel, Newton-Raphson, and Fast Decoupled. The document also briefly discusses other optimization methods like fuzzy logic, genetic algorithms, and particle swarm optimization that can be applied to load flow problems. Case studies are presented at the end to demonstrate the different techniques.
1. The document describes the process of load flow analysis using the Newton-Raphson power flow method.
2. The Newton-Raphson power flow method uses Newton's method to solve the nonlinear power balance equations to determine the voltage magnitude and angle at each bus in the power system.
3. It derives the real and reactive power balance equations, defines the power flow variables, describes calculating the Jacobian matrix and its elements, and provides an example of applying the method to a two bus system to solve for the unknown voltage magnitude and angle at the second bus.
INTRODUCTION BASIC TECHNIQUES TYPE OF BUSES
Y BUS MATRIX POWER SYSTEM COMPONENTS BUS ADMITTANCE MATRIX
Power (Load) flow study is the analysis of a power system in normal steady-state operation
This study will determine:
DISTRIBUTION LOAD FLOW ANALYSIS FOR RDIAL & MESH DISTRIBUTION SYSTEMIAEME Publication
This document presents a new and efficient method for solving load flow problems in radial and weakly meshed distribution systems. The proposed method is based on network topology, circuit laws, and power summation techniques. It uses loop analysis to account for the impact of tie lines in meshed networks. The algorithm calculates effective power injections, voltage drops, and loop currents to solve for bus voltages and power losses. It was coded in MATLAB and tested on IEEE 33-bus test systems. Results show the voltage profile, power losses, computation time, and number of iterations for different systems and operating conditions. The proposed method provides an efficient way to analyze load flow in distribution networks with radial and weakly meshed topologies.
This document summarizes a lecture on economic dispatch in power systems. It begins with announcements about homework assignments and readings. It then discusses the formulation of economic dispatch as minimizing generation costs subject to meeting demand. The document uses an example two generator system to illustrate solving the optimization using Lagrange multipliers. It describes the lambda iteration method for solving economic dispatch with multiple generators. Finally, it discusses including transmission losses in the economic dispatch formulation.
The document discusses load flow studies and the Gauss-Siedel method for solving power flow equations. Load flow studies calculate voltage drops, bus voltages, and power flows under various conditions to determine if voltages remain within limits and equipment is not overloaded. The Gauss-Siedel method iteratively solves power flow equations represented by a non-linear algebraic equation using the bus admittance matrix and known real and reactive power values at buses to calculate unknown bus voltages until converging on a solution. An example applies the Gauss-Siedel method with an acceleration factor to a three bus system to calculate voltages after the first iteration.
The document discusses power flow analysis, which determines voltages, currents, real power, and reactive power in a power system under steady-state load conditions. It describes the different types of buses in a power system and how they are modeled. The key component of power flow is the bus admittance matrix, which relates nodal voltages to branch currents based on Kirchhoff's current law. Solving the matrix equations provides the voltage magnitude and angle at each bus.
Basics of Power systems
Network topology
Transmission and Distribution
Load and Resource Balance
Economic Dispatch
Steady State System Analysis
Power flow analysis
Dynamic System Analysis
Transient stability
International Refereed Journal of Engineering and Science (IRJES)irjes
The core of the vision IRJES is to disseminate new knowledge and technology for the benefit of all, ranging from academic research and professional communities to industry professionals in a range of topics in computer science and engineering. It also provides a place for high-caliber researchers, practitioners and PhD students to present ongoing research and development in these areas.
Power losses reduction of power transmission network using optimal location o...IJECEIAES
Due to the growth of demand for electric power, electric power loss reduction takes great attention for the power utility. In this paper, a low-level generation or distributed generation (DG) has been used for transmission power losses reduction. Karbala city transmission network (which is the case study) has been represented by using MATLAB m-file to study the load flow and the power loss for it. The paper proposed the particle swarm optimization (PSO) technique in order to find the optimal number and allocation of DG with the objective to decrease power losses as possible. The results show the effect of the optimal allocation of DG on power loss reduction.
Comparative power flow analysis of 28 and 52 buses for 330 kv power grid netw...Onyebuchi nosiri
Newton-Raphson technique was formulated and used to evaluate the electrical performances of the existing 28-bus and improved 52-bus Nigerian 330kV power networks. The Jacobian matrix for both the existing 28-bus and the improved 52-bus Nigerian power system was derived using Newton-Raphson power flow solution method. The steady-state critical bus voltages, voltage and angle profiles at each bus, active and reactive power flows, transformer tap settings, component or circuit loading, generator exciter regulator voltage set points and system losses of these networks were determined to ascertain their effectiveness and proper network reconfiguration. The results obtained showed a better performance of the 52-Bus system in power quality, voltage and angle profiles over the conventional 28-bus system
The document describes an experiment using MATLAB to implement the Newton-Raphson load flow method to analyze a 3-bus power system network. The Newton-Raphson method approximates non-linear power flow equations using Taylor series expansion, allowing faster convergence compared to other methods. The experiment specifies bus voltages, real/reactive power demands and generations, and solves for reactive power output using a tolerance of 0.01 power mismatch. The MATLAB code is run and the load flow solution is obtained.
Malformações do sistema nervoso central; Os autores estudaram 32 recém-nascidos com malformação do sistema nervoso central. Destacam a importância do estudo das malformações desde que consistem na segunda causa de morbidade e mortalidade neonatal.
This document is a resume for Muhammad Hassan, a senior audit assistant at M. Yousuf Adil Saleem & Co. Chartered Accountants in Pakistan. The summary highlights his objective to pursue professional development, over 3.5 years of audit experience at Deloitte including leading audit teams, and qualifications including being a CA finalist and Bachelor's degree from Karachi University.
This document provides information about Goodmans, a British consumer electronics brand established in 1925. It discusses Goodmans' focus on innovative, attractive and affordable products, and their vision of developing technology essential for modern living through careful consideration, passion and integrity. The document presents information on Goodmans' heritage and various product lines that combine latest features with uncomplicated functionality and intuitive designs for everyone. It also shares interviews about a film and book collaboration between Goodmans and other creative partners.
This document provides an abstract and literature review for a research paper on applying cargo bicycles for last kilometer deliveries in Melbourne, Australia. The abstract outlines that increasing population is generating more goods deliveries, causing pollution and congestion issues from fuel-powered vans. Cargo bicycles are proposed as an environmentally friendly alternative, but are limited by delivery range and capacity. The research aims to develop and evaluate models of an urban consolidation terminal network to optimize bicycle deliveries. The literature review covers topics like current traffic issues, last mile deliveries, cargo bicycles, urban consolidation terminals, and evaluation criteria like total distance, emissions, time, and cost. Methodologies will include literature review, data acquisition from local bicycle companies
Optimal Power Flow with Reactive Power Compensation for Cost And Loss Minimiz...ijeei-iaes
One of the concerns of power system planners is the problem of optimum cost of generation as well as loss minimization on the grid system. This issue can be addressed in a number of ways; one of such ways is the use of reactive power support (shunt capacitor compensation). This paper used the method of shunt capacitor placement for cost and transmission loss minimization on Nigerian power grid system which is a 24-bus, 330kV network interconnecting four thermal generating stations (Sapele, Delta, Afam and Egbin) and three hydro stations to various load points. Simulation in MATLAB was performed on the Nigerian 330kV transmission grid system. The technique employed was based on the optimal power flow formulations using Newton-Raphson iterative method for the load flow analysis of the grid system. The results show that when shunt capacitor was employed as the inequality constraints on the power system, there is a reduction in the total cost of generation accompanied with reduction in the total system losses with a significant improvement in the system voltage profile
A fault-tolerant photovoltaic integrated shunt active power filter with a 27-...IJECEIAES
This paper introduces a fault-tolerant shunt active power filter (SAPF). The novility in of this work is that it poposes a solutions to increase the reliability of shunt active power filter to maintain its operation under a single-phase open-circuit fault in the SAPF. This will increase the reliability of the whole power system. The SAPF is composed of a 4-leg 27-level inverter based on asymmetric cascaded H-bridge topology. If an open-circuit fault is introduced to the operation of the SAPF, a special control technique will be implemented and the redundant leg of the SAPF will be activated. The faulttolerant SAPF can do many tasks under healthy operating conditions and post and open circuit fault depending on the state of charge (SOC) of the batteries. It can mitigate harmonics in the power system, improve power factor in the system by injecting reactive power, and inject real power to the system. The proposed SAPF is tested and simulated in MATLAB/Simulink and the results have shown a significant improvement in total harmonics distortion (THD) of the source current from 13.9% to 3.9% under the normal operating condition and from 42% to 8.4% post and open circuit fault.
The high penetration of power electronic based distributed energy resources (DERs) has increased the importance and attention given to voltage security of distribution systems. Voltage control in the electrical power system is critical for a proper operating condition. Therefore, distribution systems must have the ability to maintain a secure voltage profile. Using inverters for Volt/VAR control (VVC) can provide a faster response for voltage regulation than traditional voltage regulation devices, such as transformer load tap changers and voltage regulators. The primary objective of this paper is to demonstrate how smart inverters can be used to eliminate the voltage deviation by solving a mixed-integer quadratic program to determine the amount of reactive power that should be injected or absorbed at the appropriate nodes. The proposed method incorporates capacitor banks connected to the network and determines whether to turn on or off the capacitor bank for voltage regulation. These processes will be demonstrated in several cases that are focused on mitigating voltage-dips and swells.
The high penetration of power electronic based distributed energy resources (DERs) has increased the importance and attention given to voltage security of distribution systems. Voltage control in the electrical power system is critical for a proper operating condition. Therefore, distribution systems must have the ability to maintain a secure voltage profile. Using inverters for Volt/VAR control (VVC) can provide a faster response for voltage regulation than traditional voltage regulation devices, such as transformer load tap changers and voltage regulators. The primary objective of this paper is to demonstrate how smart inverters can be used to eliminate the voltage deviation by solving a mixed-integer quadratic program to determine the amount of reactive power that should be injected or absorbed at the appropriate nodes. The proposed method incorporates capacitor banks connected to the network and determines whether to turn on or off the capacitor bank for voltage regulation. These processes will be demonstrated in several cases that are focused on mitigating voltage-dips and swells.
NOVEL PSO STRATEGY FOR TRANSMISSION CONGESTION MANAGEMENTelelijjournal
In post deregulated era of power system load characteristics become more erratic. Unplanned transactions
of electrical power through transmission lines of particular path may occur due to low cost offered by
generating companies. As a consequence those lines driven close to their operating limits and becomes
congested as the lines are originally designed for traditional vertically integrated structure of power
system. This congestion in transmission lines is unpredictable with deterministic load flow strategy.
Rescheduling active and reactive power output of generators is the promising way to manage congestion.
In this paper Particle Swarm Optimization (PSO) with varying inertia weight strategy, with two variants
e1-PSO and e-2 PSO is applied for optimal solution of active and reactive power rescheduling for
managing congestion. The generators sensitivity technique is opted for identifying participating generators
for managing congestion. Proposed algorithm is tested on IEEE 30 bus system. Comparison is made
between results obtained from proposed techniques to that of results reported in previous literature.
Performance Improvement of the Radial Distribution System by using Switched C...idescitation
Distribution system is the major link which provides supply to the consumers
from the high voltage transmission system. The load on the distribution system is not
constant and it changes with respect to time throughout the working period. The voltage
drop and power losses occur in the distribution system mainly depends on the nature of the
load which is applied on the system. The voltage drop and power losses frequently occurs
mainly on those systems which are supplying load to the industrial areas, this is mainly
because of the existence of more reactive power. To overcome these problems shunt
compensation is employed to reduce or suppress those effects to an extent. The main aim of
this paper is to determine the specific value of the shunt capacitance required to achieve the
permissible voltage tolerance limits and maximum percentage of power loss reduction in a
sample two feeder radial distribution system.
A Novel Technique for Enhancing Active and Reactive Power Quality for Renewab...IJMER
Renewable energy resources (RES) are being increasingly connected in distribution systems utilizing power electronic converters. This paper presents a novel control strategy for achieving maximum benefits from these grid-interfacing inverters when installed in 3-phase 4-wire distribution systems. The inverter is controlled to perform as a multi-function device by incorporating active power filter functionality. The inverter can thus be utilized as: 1) power converter to inject power generated from RES to the grid, and 2) shunt APF to compensate current unbalance, load current harmonics, load reactive power demand and load neutral current. All of these functions may be accomplished either individually or simultaneously. With such a control, the combination of grid-interfacing inverter and the 3-phase 4-wire linear/non-linear unbalanced load at point of common coupling appears as balanced linear load to the grid. This new control concept is demonstrated with extensive MATLAB/Simulink simulation studies and results.
A Particle Swarm Optimization for Reactive Power Optimizationijceronline
This paper presents implementation of new algorithm Particle Swarm Optimization (PSO) for Energy Saving through minimizing power losses. The PSO Algorithm Solution is tested in standard IEEE 30 Bus system. The objective is to optimize the reactive power dispatch with optimal setting of control variables without violating inequality constraints and satisfying equality constraint. Control Variables are of both types: Continuous and Discrete. The continuous control variables are generator bus voltage magnitudes;whereas the discrete variables are transformer tap settings and reactive power of shunt compensators (Capacitor banks) .
A Study of Load Flow Analysis Using Particle Swarm OptimizationIJERA Editor
Load flow study is done to determine the power system static states (voltage magnitudes and voltage angles) at each bus to find the steady state working condition of a power system. It is important and most frequently car-ried out study performed by power utilities for power system planning, optimization, operation and control. In this project a Particle Swarm Optimization (PSO) is proposed to solve load flow problem under different load-ing/ contingency conditions for computing bus voltage magnitudes and angles of the power system. With the increasing size of power system, this is very necessary to finding the solution to maximize the utilization of ex-isting system and to provide adequate voltage support. For this the good voltage profile is must. STATCOM, if placed optimally can be effective in providing good voltage profile and in turn resulting into stable power sys-tem. The study presents a hybrid particle swarm based methodology for solving load flow in electrical power systems. Load flow is an electrical engineering well-known problem which provides the system status in the steady-state and is required by several functions performed in power system control centers.
Analysis of Design, and Control of Sustainable Energy Based Hybrid Power SystemIJSRED
This document presents a new control strategy for grid synchronization of a sustainable energy-based hybrid power system consisting of a wind turbine with a permanent magnet synchronous generator and a photovoltaic solar generator. The wind turbine and solar generator harvest sustainable energy which is converted to electrical power and interfaced to the grid via back-to-back voltage source converters. The control strategy aims to maximize power extraction from both generators while providing smooth sinusoidal voltages to the grid with fixed frequency and minimizing total harmonic distortion. The system and control algorithms are modeled and validated through MATLAB simulations.
Artificial Intelligence Technique based Reactive Power Planning Incorporating...IDES Editor
This document summarizes a research paper that proposes using artificial intelligence techniques and FACTS controllers for reactive power planning in real-time power transmission systems. The paper formulates the reactive power planning problem and incorporates flexible AC transmission system (FACTS) devices like static VAR compensators (SVC), thyristor controlled series capacitors (TCSC), and unified power flow controllers (UPFC). Evolutionary algorithms like evolutionary programming (EP) and differential evolution (DE) are applied to find the optimal locations and settings of the FACTS controllers to minimize losses and costs. Simulation results on IEEE 30-bus and 72-bus Indian test systems show that UPFC performs best in reducing losses compared to SVC and TCSC.
Comparative power flow analysis of 28 and 52 buses for 330 kv power grid netw...Onyebuchi nosiri
Newton-Raphson technique was formulated and used to evaluate the electrical performances of the existing 28-bus and improved 52-bus Nigerian 330kV power networks. The Jacobian matrix for both the existing 28-bus and the improved 52-bus Nigerian power system was derived using Newton-Raphson power flow solution method. The steady-state critical bus voltages, voltage and angle profiles at each bus, active and reactive power flows, transformer tap settings, component or circuit loading, generator exciter regulator voltage set points and system losses of these networks were determined to ascertain their effectiveness and proper network reconfiguration. The results obtained showed a better performance of the 52-Bus system in power quality, voltage and angle profiles over the conventional 28-bus system
Differential Evolution Based Optimization Approach for Power Factor CorrectionIDES Editor
In radial distribution systems, the voltages at buses
reduces when moved away from the substation, also the losses
are high. The reason for decrease in voltage and high losses is
the insufficient amount of reactive power, which can be
provided by the shunt capacitors. For this purpose, in this
paper, two stage methodologies are used. In first stage, the
load flow of pre-compensated distribution system is carried
out using ‘Dimension reducing distribution load flow
algorithm’. In the second stage, Differential Evolution (DE)
technique is used to determine the optimal location and size
of the capacitors. The above method is tested on IEEE 69 bus
system. In this paper a new method is proposed to improve the
power factor of those buses having low power factor (less than
0.8lag) to unity power factor simultaneously by placing the
capacitors.
International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
Nowadays, the electricity demand is increasing daily and hence it is important not only to extract electrical energy from all possible new power resources but also to reduce power losses to an acceptable minimum level in the existing distribution networks where a huge amount of power dissipation occurred. A lot of power is remarkably dissipated in Yangon distribution system. Network reconfiguration method is employed for loss reduction and exhaustive search technique is also applied to achieve the minimal loss switching scheme. Network reconfiguration is performed by opening sectionalizing switches and closing tie switches of the network for loss reduction. The distribution network for existing and reconfiguration conditions are modelled and simulated by Electrical Transient Analyzer Program (ETAP) 7.5 version software. The proposed method is tested on 83-Bus and 74-Bus radial distribution system in Yangon city since it is long-length, overloaded lines and high level of power dissipation is occurred in this system. According to simulation results of load flow analysis, voltage profile enhancement, power loss reduction and cost saving for proposed system are revealed in this paper.
Keywords — exhaustive search technique, loss reduction, load flow analysis, cost saving
.
A photovoltaic integrated unified power quality conditioner with a 27-level i...TELKOMNIKA JOURNAL
This paper presents a Unified Power Quality Conditioner (UPQC) with a 27-level inverter based on
an asymmetric H-bridge topology. Each phase of the inverter is composed of three H-bridges, supplied by
three DC sources scaled in the power of three. The output of the multilevel inverter is connected directly to
the point of common coupling (PCC) without the need to a transformer or a filter. The calculation of the Shunt
Active Power Filter (SAPF) compensation current is based on the generalized theory of synchronous frame
(d-q theory) while the calculation of a series active filter voltage is based on Instantaneous Reactive Power
(p-q theory). The control of the SAPF is achieved by using a closed-loop vector control followed by a new
multilevel modulation technique. In addition to the capability of harmonic elimination of both current and
voltage drawn from the source, the UPQC can produce real and reactive power to feed the loads during
prolonged voltage outages or source shortage. Batteries pack are used as a dc link, which is charged from
photovoltaic array connected to the battery through a maximum power point tracker and charge controller.
The injection of real and reactive power depends on the state of charge (SOC) of batteries, the frequency of
the system, real and reactive power of the load, and power factor at the point of PCC. The proposed UPQC
strategy is simulated in MATLAB SIMULINK and the results have shown a significant improved in Total
Harmonics Distortion (THD) of both the voltage and currents.
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.
Energy Storage Systems – Grid Connection Using SynchronvertersGal Barzilai
This document summarizes a research project investigating energy storage systems connected to the electric grid using synchronverters. It discusses using lithium-ion batteries for storage, dual active bridges for DC-DC conversion, and a synchronverter to transfer energy between the DC bus and utility grid. Simulation results are presented for the synchronverter control algorithm and dual active bridge converter control to regulate voltage and respond to load changes. The goal of the research is to develop an experimental small-scale energy storage system demonstrating the key components and control approaches for integrating storage to provide grid services while maximizing economic benefits.
A Power quality problem is an occurrence of nonstandard voltage, current or frequency that results in a
failure or a misoperation of end user equipments. Utility distribution networks, sensitive industrial loads and
critical commercial operations suffer from various types of outages and service interruptions which can cost
significant financial losses. With the increase in load demand, the Renewable Energy Sources (RES) are
increasingly connected in the distribution systems which utilizes power electronic Converters/Inverters. This
paper presents a single-stage, three-phase grid connected solar photovoltaic (SPV) system. The proposed system
is dual purpose, as it not only feeds extracted solar energy into the grid but it also helps in improving power
quality in the distribution system. The presented system serves the purpose of maximum power point tracking
(MPPT), feeding SPV energy to the grid, harmonics mitigation of loads connected at point of common coupling
(PCC) and balancing the grid currents. The SPV system uses a three-phase voltage source converter (VSC) for
performing all these functions. An improved linear sinusoidal tracer (ILST)-based control algorithm is proposed
for control of VSC. In the proposed system, a variable dc link voltage is used for MPPT. An instantaneous
compensation technique is used incorporating changes in PV power for fast dynamic response. The SPV system
is first simulated in MATLAB along with Simulink and simpower system toolboxes.
Similar to DFisher ETLS 747 Paper - Optimal Power Flow (20)
1. 1
The Optimal Power Flow Problem:
Definitions, Solutions, and Challenges
Daniel R. Fisher, MSEE Student, University of St. Thomas
in partial fulfillment of
ETLS 747 Electric Machines
Dr. Cal Hardie
Spring 2016
Abstract
Grid level power systems are designed to deliver power from generators to customer
loads as economically as possible while operating within the various equipment constraints (e.g.
transmission line and transformer thermal limits, generator real and reactive power limits,
scheduled tie-line power flows, etc.). This must be managed while simultaneously maintaining
system stability, such as controlling for area frequency, bus voltage magnitudes and phases, and
real and reactive power flows. The problem, called Optimal Power Flow (OPF), has been well
defined since the 1960s but has proven difficult to solve [1]. It is comprised of a coupled system
of non-linear equations for which no exact solution can be found. Instead, iterative algorithms
are employed to solve the problem numerically. For a moderately sized grid, there are typically
hundreds of generators providing power to thousands of buses. Advances in CPU speeds have
enabled faster and more precise numerical solutions, but are still unable to solve the entire
problem quickly enough for certain applications. This project gives an overview of the OPF
problem, defines the important variables and constraints, demonstrates the time required for
solving IEEE test networks using a MATLAB package called MATPOWER, and discusses
methodologies for improving solution times.
2. 2
Introduction
Since the advent of large electrical grids in the first half of the 20th century, system
operators have concerned themselves with providing reliable service to their customers at a
minimum of cost. This involves meeting a varying demand for electricity over the course of each
24-hour period. Multiple generators inject real and reactive power at certain locations (generator
or PV buses) which is sent over transmission lines of varying lengths for customers to receive at
the other ends (load or PQ buses).
Peter Fox-Penner describes the electric power grid in his 2014 book, Smart Power [2],
with a “pond system analogue.” Imagine a network of ponds connected by free flowing channels,
as in Figure 1. The ponds are fed by water towers adding water to the ponds. Simultaneously,
homes draw water out of the ponds for their own use via pipes. At all times, the water added
from the towers must balance the water drawn out by the homes. Otherwise the ponds could
either flood or dry up. Note that the water drawn by one home is not necessarily from one tower,
but instead drawn from the collective contribution of all towers to the pond system.
Figure 1. “Pond system analogue” for the power grid (Fig. 3-1 from Smart Power [2])
3. 3
In the grid, generators act as the water towers, transmission lines are similar to the
interconnecting channels, and customers draw real and reactive power for loads similar to the
homes drawing water from the ponds. However, this balance between generation and load must
be maintained over much smaller time scales than the pond system analogy suggests. At all
moments the power produced by generators must be equal to the power consumed at loads (there
is not often large scale energy storage on the grid like the ponds in the analogy above).
Original operators of early 20th century power grids dealt with this balancing act in a
variety of ad hoc ways. These could involve modeling a power system with a smaller analog
analyzer. Calculations were done on special slide rules. In the end, system adjustments were
often made with a good deal of experienced engineering judgment and intuition.
The problem of optimal power flow was well defined in 1962 [3], but finding a solution
that is fast enough for large power grids remains elusive even today. As we will see, the problem
involves minimizing a non-linear objective function (system cost in $/hr) subject to a large
number of non-linear equality constraints (power flow equations) along with other inequality
constraints (power limitations of generators, transformers and transmission lines). It is a problem
that requires a solution as often as every 5 minutes, accomplished for large systems only through
varying degrees of approximation. More accurate solutions to the optimal power flow problem
could provide an increase in efficiency of 5% for energy markets worldwide, leading to savings
of $19 billion annually in the United States alone [1, p. 5].
This paper will provide an overview of power flow and economic dispatch, then discuss
how they are combined into the optimal power flow (OPF) problem. Finally, various solvers will
be used in MATLAB to illustrate the challenges encountered when trying to solve OPF
problems.
Power Flow
Consider the simple 2-bus system in Figure 2 where the transmission line is modeled as
inductive only.
Figure 2. A simple 2-bus system.
The real and reactive power transmitted to the receiving bus is:
(1)
(2).
We see that the variables related to power flow at each bus are P, Q, voltage magnitude V, and
voltage angle . In order to maintain frequency synchronicity, is kept small. It is important to
note that for small voltage angles, sin ≈ and cos ≈ 1. This fact means that P is closely
𝑃𝑅 =
𝑉𝑆 𝑉𝑅
𝑋
sin 𝛿
𝑄 𝑅 =
𝑉𝑆 𝑉𝑅
𝑋
cos 𝛿 −
𝑉𝑅
2
𝑋
4. 4
coupled to , and Q is closely coupled to V. This will later lead to the decoupling of the P- and
Q-V power flow equations to allow for faster approximate solutions.
For more than two buses, the power flow at each bus is affected by each of the other
interconnected buses. Consider N-buses connected by transmission lines expresses by the
standard bus admittance matrix Ybus. If ymn is the total complex admittance between bus-m and
bus-n, and ymm is the shunt admittance from bus-m to earth ground, then
(3)
(4).
For computation convenience, each element of the Ybus matrix can be expressed in polar form.
(5)
The power flow at the kth bus is then
(6)
(7).
Each bus is specified by 4 variables (P, Q, V, and , but 2 variables are assumed as given
and 2 are unknown. Generators are considered PV-buses where known real power P is injected at
voltage magnitude V, but Q and need to be solved. Loads are expressed as PQ-buses where
known real and reactive power is consumed and and V need to be solved. Finally, one bus is
left as a reference or slack bus where V = 1.0 pu and = 0o
(typically), but P and Q need to be
solved to “pick up the slack” of the system. The slack bus is left until the end and simply back-
solved once the other buses are found. We are left with 2(N – 1) non-linear equations to solve for
an equal number of unknown variables. This can be done through various numerical solvers,
among which the Newton-Raphson method is the most common [4].
At this point it is worth noting that the real power set points for each generator in the
network is specified before running the power flow solution (with the exception of the slack
bus). The question remains, which generators should be most utilized to provide power for the
required loads? The answer lies in considering the economics of running each generator.
Economic Dispatch
A system operator must decide what power each generator in the system should provide
in order to meet the ever changing customer demand. However, the power flow equations do not
provide this information. For example, consider the system of Figures 3a and 3b. Both
configurations provide the necessary real and reactive power to the load bus, but which is
Y𝑘𝑘 = ∑ 𝑦 𝑘𝑛
𝑁
𝑛=1
Y𝑘𝑖 = −𝑦 𝑘𝑖
Y𝑘𝑛 = 𝑌𝑘𝑛 𝑒 𝑗𝜃 𝑘𝑛
5. 5
favored? The costs associated with running each generator must be included in the decision such
that the system runs at the lowest possible overall cost. This process of finding the lowest cost
configuration is called Economic Dispatch.
Figure 3a. A possible dispatch where each generator carries half the required load.
Figure 3b. Another dispatch where the slack generator provides significantly less than half the real power to the
system.
Each generator has associated with it a cost rate function F(P) expressing the $/hr
required to run the generator as a function of output real power, P. The function can be modeled
in different ways, but is typically either quadratic (as in Figure 4) or piecewise-linear. Generators
have both a maximum and minimum power output Pmin and Pmax ind which they can operate
efficiently.
6. 6
Figure 4. Input-output cost function for a typical thermal (steam) generating unit.
The economic dispatch problem is one of optimization: minimize the total system cost of
generation subject to the constraints that all power generated is equal to all power consumed by
the loads, and that all generators are operating within (or at) their operational limits. Stated
mathematically:
Minimize total cost per hour (cost rate) to run Ngen generators:
(8)
Subject to the constraints:
(9)
(10)
The general method for solving an economic dispatch problem involves forming a Lagrange
function with multiplier , then solving using a lambda iteration method through the application
of linear or dynamic programming.
(11)
(12)
𝐹𝑇 = 𝐹1 + 𝐹2 + ⋯ + 𝐹 𝑁 𝑔𝑒𝑛
= ∑ 𝐹𝑖(𝑃𝑖)
𝑁 𝑔𝑒𝑛
𝑖=1
𝑃𝑙𝑜𝑎𝑑 = ∑ 𝑃𝑖
𝑁 𝑔𝑒𝑛
𝑖=1
𝑃𝑖,𝑚𝑖𝑛 ≤ 𝑃𝑖 ≤ 𝑃𝑖,𝑚𝑎𝑥
ℒ = 𝐹𝑇 + 𝜆𝜙
where
𝜙 = 𝑃𝑙𝑜𝑎𝑑 − ∑ 𝑃𝑖
𝑁 𝑔𝑒𝑛
𝑖=1
= 0
7. 7
The Lagrange multiplier is interpreted as the incremental (marginal) cost, dF/dP. It can be
shown that the total system cost is minimized (assuming all generators are operating within
power limits) when all generators run at the same incremental cost [5]:
(13)
When the boundaries of the inequality constraints are included, the additional formal conditions
of the Karush-Kuhn-Tucker (KKT) method are required:
(14)
(15)
The lambda iteration method searches for the system , iterating until the desired
tolerance is reached (Figure 5).
Figure 5. Lambda iteration method for determining economic dispatch
START
Set
Calculate Pi
for i = 1 ... Ngen
Calculate
e = Pload - S Pi
First
iteration?
|e| <
Tolerance?
Project
𝑑𝐹 𝑖
𝑑𝑃𝑖
= 𝜆 for 𝑃𝑖,𝑚𝑖𝑛 < 𝑃𝑖 < 𝑃𝑖,𝑚𝑎𝑥
𝑑𝐹 𝑖
𝑑𝑃𝑖
≤ 𝜆 for 𝑃𝑖 = 𝑃𝑖,𝑚𝑎𝑥
𝑑𝐹 𝑖
𝑑𝑃𝑖
≥ 𝜆 for 𝑃𝑖 = 𝑃𝑖,𝑚𝑖𝑛
Print schedule
END
YES
NO
NO
YES
8. 8
Optimal Power Flow
Optimal power flow seeks to minimize the total system cost function FT, while at the
same time solving the system power flow. Since the transmission line admittances are built into
the power flow solution there is no need to separately consider losses when solving for economic
dispatch. Summarizing the OPF problem:
Minimize the total system generation cost FT (Eqn. 8)
Include generator limit inequality constraints for real and reactive power (Eqn. 10 and
similar for reactive power, Qi,min ≤ Qi ≤ Qi,min)
Include transmission system thermal inequality constraints, expressed as either apparent
power or effective current limits for lines and transformers
Include bus voltage magnitude inequality constraints, Vi,min ≤ Vi ≤ Vi,min
Include equality constraints for real and reactive power flow (Eqns. 6 and 7)
This problem is LARGE, requiring the repeated solving of 2(N – 1) nonlinear equations
while trying to optimize (minimize) an objective function subject to a large number of
constraints. A moderately sized power system can have thousands of voltage buses with
hundreds of generating units. For large grids the buses number in the tens of thousands. Couple
this with the need to solve for OPF repeatedly to economically schedule generators for a
constantly changing demanded load. The more often OPF needs to be solved, the less time there
is to solve it. It must be solved [1]:
Weekly in 8 hrs
Daily in 2 hrs
Hourly in 15 min
Every 5 min in 1 min
Perhaps every 30s as we move toward “self-healing” smart grids
Despite the fact that computation speeds have increased by a factor of 107
over the 20
years leading up to 2012 [1], modern computers are still not fast enough to solve the full OPF
problem as often as it is needed. As such, approximate models are employed. Most common is
the so-call “DC” OPF.
Simplifications required for DCOPF solutions:
Decouple P and V, and Q and . As was noted following Eqns. 1 and 2, for small voltage
angles real power is primarily affected by voltage angles, and reactive power is primarily
affected by voltage magnitudes. By neglecting the all the partial derivatives in the
Jacobian matrix (required in the Newton-Raphson method) of the form 𝜕𝑃𝑘/𝜕𝑉𝑖 and
𝜕𝑄 𝑘/𝜕𝛿𝑖, the power flow equations are formulated as two decoupled equations, namely
the P – and Q – V equations.
Use small angle approximations for sine and cosine functions.
Assume all voltage magnitudes are constant, Vi = 1.0 pu.
To clarify, we are still dealing with a balanced 3-phase AC system. But because the
voltage magnitudes are assumed constant, the system has fixed, or “DC”, voltage. The DCOPF
approximation results in a single linear matrix equation with a straightforward non-iterative
9. 9
solution. While this approximate solution is significantly faster than the full ACOPF, it is limited
to real (MW) power information, since the reactive power is completely neglected.
The full ACOPF has about twice as many variables as the DCOPF formulation.
Furthermore, the ACOPF network equations are non-linear, making it much more difficult to
reliably solve. It can be approached by solving an initial power flow and using it as an operating
point Pgen
0
, Qgen
0
, V0
and 0
about which the objective function and constraints are linearized.
Then the techniques of linear programming (the details of which are not covered in this paper)
can be used to iterate towards a solution.
Steps for the incremental linear programming (LP) solution to the ACOPF [5, p. 372]:
1) Solve a base power flow
2) Linearize the objective function
3) Linearize the constraints (including power flow equations with full Jacobian matrix)
4) Set variable limits
5) Solve the LP
6) Check P, Q, V tolerances and go to step 1 at a new operating point as necessary
Comparison of OPF Solutions
MATPOWER is a package of MATLAB M-files for solving power flow and optimal
power flow problems. It is intended as a simulation tool for researchers and educators that is easy
to use and to modify [6, 7]. Included in the package are a set of sample cases which allow for the
comparison of DCOPF and ACOPF solutions. Figures 6, 7, and 8 show a summary of
convergence times for a series of test cases performed on the author’s laptop, followed by the
MATPOWER summary of the largest included case (case9241pegase.m) for both the DCOPF
and ACOPF solvers.
Figure 6. Comparison of MATPOWER convergence times for DCOPF and ACOPF of test case networks.
Case Nbuses Ngenerators Nloads DCOPF (s) ACOPF (s) % Increase
case118 118 54 99 0.07 0.14 200
case300 300 69 201 0.20 0.24 120
case1354pegase 1354 260 673 0.70 2.15 307
case2869pegase 2869 510 1485 1.63 4.99 306
case3120sp 3120 505 2277 4.51 5.63 125
case9241pegase 9241 1445 4895 1.68 22.13 1317
10. 10
Figure 7. MATPOWER output for DCOPF for case9241pegase.m
>> rundcopf('case9241pegase')
MATPOWER Version 5.1, 20-Mar-2015 -- DC Optimal Power Flow
The interior-point algorithm uses a built-in starting point;
ignoring user-supplied X0.
Optimization terminated.
Converged in 1.68 seconds
Objective Function Value = 312410.98 $/hr
=============================================================================
| System Summary |
=============================================================================
How many? How much? P (MW) Q (MVAr)
--------------------- ------------------- ------------- ----------------
Buses 9241 Total Gen Capacity 530107.3 0.0 to 0.0
Generators 1445 On-line Capacity 530107.3 0.0 to 0.0
Committed Gens 1445 Generation (actual) 312411.0 0.0
Loads 4862 Load 312354.1 0.0
Fixed 4862 Fixed 312354.1 0.0
Dispatchable 0 Dispatchable -0.0 of -0.0 -0.0
Shunts 292 Shunt (inj) -56.9 0.0
Branches 16049 Losses (I^2 * Z) 0.00 0.00
Transformers 1319 Branch Charging (inj) - 0.0
Inter-ties 0 Total Inter-tie Flow 0.0 0.0
Areas 1
Minimum Maximum
------------------------- --------------------------------
Voltage Magnitude 1.000 p.u. @ bus 1 1.000 p.u. @ bus 1
Voltage Angle -44.03 deg @ bus 1265 28.88 deg @ bus 4286
Lambda P 1.00 $/MWh @ bus 2131 1.00 $/MWh @ bus 4835
Lambda Q 0.00 $/MWh @ bus 1 0.00 $/MWh @ bus 1
11. 11
Figure 8. MATPOWER output for ACOPF for case9241pegase.m
>> runopf('case9241pegase')
MATPOWER Version 5.1, 20-Mar-2015 -- AC Optimal Power Flow
MATLAB Interior Point Solver -- MIPS, Version 1.2, 20-Mar-2015
(using built-in linear solver)
Converged!
Converged in 22.13 seconds
Objective Function Value = 315912.43 $/hr
=============================================================================
| System Summary |
=============================================================================
How many? How much? P (MW) Q (MVAr)
--------------------- ------------------- ------------- ----------------
Buses 9241 Total Gen Capacity 530107.3 -799009.7 to
931271.2
Generators 1445 On-line Capacity 530107.3 -799009.7 to
931271.2
Committed Gens 1445 Generation (actual) 315912.4 13550.3
Loads 4895 Load 312354.1 73581.6
Fixed 4895 Fixed 312354.1 73581.6
Dispatchable 0 Dispatchable -0.0 of -0.0 -0.0
Shunts 7327 Shunt (inj) -63.8 101110.9
Branches 16049 Losses (I^2 * Z) 3494.56 41079.54
Transformers 1319 Branch Charging (inj) - 0.0
Inter-ties 0 Total Inter-tie Flow 0.0 0.0
Areas 1
Minimum Maximum
------------------------- --------------------------------
Voltage Magnitude 0.815 p.u. @ bus 2159 1.162 p.u. @ bus 8640
Voltage Angle -32.18 deg @ bus 1265 6.58 deg @ bus 5226
P Losses (I^2*R) - 16.42 MW @ line 4426-5616
Q Losses (I^2*X) - 205.46 MVAr @ line 6-3068
Lambda P 0.97 $/MWh @ bus 8289 1.19 $/MWh @ bus 2159
Lambda Q -0.19 $/MWh @ bus 8524 0.17 $/MWh @ bus 7822
Figure 6 shows how the ACOPF solution always requires more time than the DCOPF
solution, and takes a significantly longer amount of time as N increases. Figures 7 and 8
highlight the fact that the DCOPF completely neglects the Q – V power flow equations. As such,
the voltage magnitudes are all 1.0 pu and Q values are simply zeroed out.
Future implications
Despite the advances in computer CPU clock speeds, the full ACOPF is still not able to
be solved quickly or reliably enough for large power grids. Figure 9 shows the flattening of the
well-known Moore’s Law, which predicted that computer CPU power should double every 2
years but remain at the same price [8]. This means that the huge decrease in solution times over
the past 20 years is unlikely to continue. A calculation that took 10 years on 1990 computers
would take less than 1 minute today [1]. But other computational advances are needed as the
brute force hardware advances slow down.
12. 12
Figure 9. Moore’s Law has failed to predict CPU advances over the past 10 years as new chips have proven more
expensive and more difficult to cool. [8]
The problem is highlighted when looking at DCOPF and ACOPF solution times from
larger grids. Figure 10 shows convergence times for various test networks over a range
algorithm-based solvers implemented in MATLAB [7]. Note that for the largest 42k-bus
networks, the fastest full ACOPF solution took over an hour. In security-constrained studies,
where engineers are studying the effects of losing various system elements, repeated ACOPF
solutions are required. Clearly, waiting an hour for each one becomes unwieldy. Furthermore, as
more grids implement “smart switching” equipment, OPF solutions will be needed more quickly
as the system automatically adapts to changes.
Figure 10. Comparison of solution times for various test networks, implemented in MATLAB. Note that case42k
required at least 3,700 s = 61.7 min to find a single full ACOPF solution [7].
13. 13
With individual CPU clock speeds remaining more or less constant, ACOPF solutions
that leverage parallel computing are being developed. In a 2013 industry white paper [9], FERC
states that there is “a clear advantage to employing a multistart strategy, which leverages parallel
processing in order to solve the ACOPF on large-scale networks for time-sensitive applications.”
A multistart strategy is “a global optimization procedure that applies a solution technique for
numerous starting points on parallel threads/processes and then terminates with increasing
confidence in a unique optimal solution.” These types of parallel computing strategies are easily
scalable ad hoc with available cloud computing resources.
Other research efforts are underway to find more robust solving algorithms which more
reliably converge to an optimal solution. One such paper [10] reformulates the ACOPF problem
based on a current injection approach that linearly couples the quadratic constraints at each bus.
This results in a set of linear equations rather than a set of coupled non-linear equations (Eqns. 6
and 7). These are then solved with a successive linear programming (SLP) algorithm. It was
shown that these performed favorably when compared to the best non-linear programming (NLP)
approaches.
Conclusion
The Optimal Power Flow problem remains a challenge for power systems operators. The
OPF problem seeks to find a generator dispatch schedule that both minimizes the total system
cost while simultaneously satisfying the constraints imposed by transmission power flows and
component limits. A faster, more robust solution to this problem will mean savings of billions of
dollars annually. Currently, many time-sensitive applications rely on the faster approximate
DCOPF solutions which can be unsuitable for tightly coupled power systems. However,
researchers in optimization algorithms hope to achieve faster solutions to the full ACOPF
problem. This will enable the development of “smart grid” implementations with their self-
healing switching schemes. Perhaps growing resources available through scalable cloud
computing will be the key. Only time will tell.
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