In this paper the harmonic stability is investigated for multi paralleled three-phase photovoltaic inverters connected to grid. The causes to harmonically stabilize/destabilize the multi-paralleled PV inverters when tied to the grid isanalysed by the impedance-based stability criterion (IBSC). In this paper stability of the system is investigated by varying the grid inductance with constant grid resistance and also by varying load impedance while maintaining grid inductance constant. Stability of the multiple three phase inverters tied to the grid with different grid impedance, inductance value inparticular are analyzed. Overall system is stable up to grid inductance of5mH even though there is change in load admittance. It is concluded that system stability depends only on grid impedance. It is verified with Matlab Simulations.
This work includes the establishment of a Photovoltaic system connected to the grid by means of an inverter. The fundamental goal of the work is to incorporate an advanced active power flow management scheme in order to adopt load at any weather condition along with the advantage of maximum active power flow and zero harmonics from PV inverter to the grid. The outcome of analysis and control design of grid connected PV inverter using a Proportional-Integral (PI) control technique is based on synchronous dq rotating reference frame so as to achieve maximum output voltage and record the active power. It has been observed that the model provides a better rate of stability as compared to the existing topology.
Adaptive Fuzzy PI Current Control of Grid Interact PV Inverter IJECEIAES
This document summarizes an article from the International Journal of Electrical and Computer Engineering that presents an adaptive fuzzy PI current controller for a grid-interactive photovoltaic inverter. The controller uses fuzzy logic to update the gains of the proportional-integral controller based on the error current and change in error current. This allows the controller to maintain good dynamic response and low steady-state error under varying operating conditions. Simulation results show the controller enables the inverter to track a step change in the reference current with less transient behavior and zero steady-state error while keeping the total harmonic distortion of the grid current below 5%.
Two fuzzy logic controllers are proposed in this paper to control a three phase inverter for grid connected photovoltaic system. The first controller was used to predict the DC voltage that allows the three phase inverter to track the maximum power point of photovoltaic array under different environmental conditions such as irradiances and temperature. The second was used to control the active power and reactive power injected into the grid in order to inject the maximum active power produced by photovoltaic systems into grid with high efficiency and low total harmonic distortion using the same three phase inverter. The system components are photovoltaic array, DC link voltage, three-phase inverter, inverter control, LC filter, transformer and grid. To verify the effectivnesse of the introdueced system, modeling and simulation are verified in Matlab/Simulink due to its frequent use and its effectiveness.
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.
This paper presents a grid-connected photovoltaic (PV) interface for delivering both active and reactive powers. The PV interface employs H-bridge topology DC-DC converter and inverter with analog control technology. The power flow is controlled solely by the adjustable DC output voltage of the DC to DC converter. In order to evaluate the PV interface system’s performances, it is tested by delivering power to the grid with low pawer factor. The experimental results show that at 300W active load, the inverter could deliver the reactive power of 400VAR. The PV interface could also produce very low harmonic voltage and current distorsions. The laboratory measurements show that the total harmonic distortions of inverter output voltage and current are 0.46% and 0.05%, respectively.
This document describes a design for a five-level photovoltaic (PV) inverter that uses a unipolar phase disposition pulse width modulation (PWM) technique. A fuzzy logic controller is applied to enhance the performance of the inverter. Simulation results using MATLAB/Simulink show that the total harmonic distortion (THD) of the output current is reduced when using the fuzzy controller compared to other modulation techniques. The fuzzy controller helps produce a sinusoidal output current at near unity power factor for different modulation indices to improve power transfer from the PV system to the grid.
The growing demand for electricity and the increasing integration of clean energies into the electrical grids requires the multiplication and reinforcement of high-voltage direct current (HVDC) projects throughout the world and demonstrates the interest in this electricity transmission technology. The transmitting system of the voltage source converter-high-voltage direct current (VSC-HVDC) consists primarily of two converter stations that are connected by a dc cable. In this paper, a nonlinear control based on the backstepping approach is proposed to improve the dynamic performance of a VSC-HVDC transmission system, these transport systems are characterized by different complexities such as parametric uncertainties, coupled state variables, neglected dynamics, presents a very interesting research topic. Our contribution through adaptive control based on the backstepping approach allows regulating the direct current (DC) bus voltage and the active and reactive powers of the converter stations. Finally, the validity of the proposed control has been verified under various operating conditions by simulation in the MATLAB/Simulink environment.
Modeling and simulation of three phases cascaded H-bridge grid-tied PV inverterjournalBEEI
In this paper a control scheme for three phase seven level cascaded H-bridge inverter for grid tied PV system is presented. As power generation from PV depends on varing environmental conditions, for extractraction of maximum power from PV array, fuzzy MPPT controller is incorporated with each PV array. It gives fast and accurate response. To maintain the grid current
sinusoidal under varying conditions, a digital PI controller scheme is adopted. A MATLAB/Simulink model is developed for this purpose and results are presented. At last THD analysis is carried out in order to validate the performance of the overall system. As discussed, with this control strategy the balanced grid current is obtained keeping THD values with in the specified range of IEEE-519 standard.
This work includes the establishment of a Photovoltaic system connected to the grid by means of an inverter. The fundamental goal of the work is to incorporate an advanced active power flow management scheme in order to adopt load at any weather condition along with the advantage of maximum active power flow and zero harmonics from PV inverter to the grid. The outcome of analysis and control design of grid connected PV inverter using a Proportional-Integral (PI) control technique is based on synchronous dq rotating reference frame so as to achieve maximum output voltage and record the active power. It has been observed that the model provides a better rate of stability as compared to the existing topology.
Adaptive Fuzzy PI Current Control of Grid Interact PV Inverter IJECEIAES
This document summarizes an article from the International Journal of Electrical and Computer Engineering that presents an adaptive fuzzy PI current controller for a grid-interactive photovoltaic inverter. The controller uses fuzzy logic to update the gains of the proportional-integral controller based on the error current and change in error current. This allows the controller to maintain good dynamic response and low steady-state error under varying operating conditions. Simulation results show the controller enables the inverter to track a step change in the reference current with less transient behavior and zero steady-state error while keeping the total harmonic distortion of the grid current below 5%.
Two fuzzy logic controllers are proposed in this paper to control a three phase inverter for grid connected photovoltaic system. The first controller was used to predict the DC voltage that allows the three phase inverter to track the maximum power point of photovoltaic array under different environmental conditions such as irradiances and temperature. The second was used to control the active power and reactive power injected into the grid in order to inject the maximum active power produced by photovoltaic systems into grid with high efficiency and low total harmonic distortion using the same three phase inverter. The system components are photovoltaic array, DC link voltage, three-phase inverter, inverter control, LC filter, transformer and grid. To verify the effectivnesse of the introdueced system, modeling and simulation are verified in Matlab/Simulink due to its frequent use and its effectiveness.
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.
This paper presents a grid-connected photovoltaic (PV) interface for delivering both active and reactive powers. The PV interface employs H-bridge topology DC-DC converter and inverter with analog control technology. The power flow is controlled solely by the adjustable DC output voltage of the DC to DC converter. In order to evaluate the PV interface system’s performances, it is tested by delivering power to the grid with low pawer factor. The experimental results show that at 300W active load, the inverter could deliver the reactive power of 400VAR. The PV interface could also produce very low harmonic voltage and current distorsions. The laboratory measurements show that the total harmonic distortions of inverter output voltage and current are 0.46% and 0.05%, respectively.
This document describes a design for a five-level photovoltaic (PV) inverter that uses a unipolar phase disposition pulse width modulation (PWM) technique. A fuzzy logic controller is applied to enhance the performance of the inverter. Simulation results using MATLAB/Simulink show that the total harmonic distortion (THD) of the output current is reduced when using the fuzzy controller compared to other modulation techniques. The fuzzy controller helps produce a sinusoidal output current at near unity power factor for different modulation indices to improve power transfer from the PV system to the grid.
The growing demand for electricity and the increasing integration of clean energies into the electrical grids requires the multiplication and reinforcement of high-voltage direct current (HVDC) projects throughout the world and demonstrates the interest in this electricity transmission technology. The transmitting system of the voltage source converter-high-voltage direct current (VSC-HVDC) consists primarily of two converter stations that are connected by a dc cable. In this paper, a nonlinear control based on the backstepping approach is proposed to improve the dynamic performance of a VSC-HVDC transmission system, these transport systems are characterized by different complexities such as parametric uncertainties, coupled state variables, neglected dynamics, presents a very interesting research topic. Our contribution through adaptive control based on the backstepping approach allows regulating the direct current (DC) bus voltage and the active and reactive powers of the converter stations. Finally, the validity of the proposed control has been verified under various operating conditions by simulation in the MATLAB/Simulink environment.
Modeling and simulation of three phases cascaded H-bridge grid-tied PV inverterjournalBEEI
In this paper a control scheme for three phase seven level cascaded H-bridge inverter for grid tied PV system is presented. As power generation from PV depends on varing environmental conditions, for extractraction of maximum power from PV array, fuzzy MPPT controller is incorporated with each PV array. It gives fast and accurate response. To maintain the grid current
sinusoidal under varying conditions, a digital PI controller scheme is adopted. A MATLAB/Simulink model is developed for this purpose and results are presented. At last THD analysis is carried out in order to validate the performance of the overall system. As discussed, with this control strategy the balanced grid current is obtained keeping THD values with in the specified range of IEEE-519 standard.
IRJET- Optimal Control of Multilevel Inverter to Minimize Harmonic Distortion...IRJET Journal
This document summarizes research on using multilevel inverters to minimize harmonic distortion from photovoltaic power generation arrays. It discusses 2-level, 3-level, 5-level and 7-level inverters and compares their performance. Selective harmonic elimination is also covered as a control strategy to reduce harmonic content by pre-determining switching angles. The document aims to show that multilevel inverters can help integrate renewable energy sources onto the grid more efficiently with lower voltage and current stresses on semiconductor switches.
Next Generation Researchers in Power Systems_Tao Yang_UCD EITao Yang
This document discusses solid state transformers (SSTs) and their potential applications in future distribution systems. It provides background on SSTs, explaining how they use power electronics to convert AC power to high frequency AC or DC before converting it back to the desired output. The document outlines research objectives to modularly design and optimize an SST for a distribution system. Simulation results show the modular SST has higher efficiency and lower weight than a traditional low frequency transformer under daily loading profiles. The document also explores how SSTs can address issues like imbalanced loads by independently controlling positive, negative, and zero sequence components.
Research Inventy : International Journal of Engineering and Scienceresearchinventy
Research Inventy : International Journal of Engineering and Science is published by the group of young academic and industrial researchers with 12 Issues per year. It is an online as well as print version open access journal that provides rapid publication (monthly) of articles in all areas of the subject such as: civil, mechanical, chemical, electronic and computer engineering as well as production and information technology. The Journal welcomes the submission of manuscripts that meet the general criteria of significance and scientific excellence. Papers will be published by rapid process within 20 days after acceptance and peer review process takes only 7 days. All articles published in Research Inventy will be peer-reviewed.
This document describes a fifteen-level inverter developed to transmit photovoltaic power from a solar array to the electric grid. The fifteen-level inverter uses a cascaded H-bridge configuration with low voltage MOSFET switches to reduce switching losses and harmonic distortion. It consists of a dual-buck converter to generate two DC voltages as inputs, and a full-bridge inverter to convert the output to a fifteen-level AC voltage synchronized to the grid. Simulation results show the fifteen-level output waveform is close to sinusoidal, reducing harmonic distortion below 0.5% compared to conventional two-level inverters. A controller regulates the current injected into the grid to be in phase. The system aims to provide
Power Quality Improvement Using Custom Power Devices in Squirrel Cage Inducti...IJPEDS-IAES
1) The document describes a system using a UPQC (Unified Power Quality Conditioner) to improve power quality when connecting a squirrel cage induction generator wind farm to a weak grid. The UPQC regulates the wind farm terminal voltage and mitigates harmonics at the point of common coupling.
2) It uses a neuro-fuzzy control strategy to manage the active and reactive power exchange between the series and shunt converters of the UPQC via the DC link.
3) Simulation results show the UPQC is able to compensate for voltage fluctuations at the point of common coupling due to variations in wind power generation and regulate the voltage during load connection/disconnection events.
This paper presents a droop control technique for equal power sharing in islanded microgrid. In this study, the proposed controller is based on the frequency droop method, is applied to a robust droop controller in parallel connected inverters. The previous robust droop controller deals with voltage droop method. A modification has been formed against this controller by adding a fuzzy logic controller with the frequency droop method. The only sharing error which is concentrated in this paper is the error in sharing the rated frequency among the inverters. By adapting fuzzy in the robust droop, it tries to eliminate the frequency error, hence that the frequency reference of the inverters keeps maintain at 50Hz. A derivation of generalized models of a single-phase parallel-connected inverter system is shown. The simulation results show that the proposed controller with FLC is able to improve the stability of frequency reference and the performance of power sharing between the inverters under the inductive line impedance.
Autonomous microgrid based parallel inverters using droop controller for impr...journalBEEI
The existing microgrid has become a challenge to the sustainable energy source to provide a better quality of power to the consumer. To build a reliable and efficient microgrid, designing a droop controller for the microgrid is of utmost importance. In this paper, multiple voltage source inverters connected in parallel using an active power-frequency/reactive power-voltage droop scheme. The proposed method connected to two distributed generators local controllers, where each unit consists of a droop controller with an inner voltage-current controller and a virtual droop controller. By adding this controller to the microgrid reliability and load adaptability of an islanded system can be improved. This concept applied without any real-time communication to the microgrid. Thus, simulated using MATLAB/Simulink, the obtained results prove the effectiveness of the autonomous operation's microgrid model.
This document presents a new PQ controller for regulating the output of a DC source connected to a microgrid or electrical grid. The controller independently controls active and reactive power output. It compares measured active and reactive power to reference values and uses PI controllers and phase calculations to generate PWM signals for the inverter. Simulation results in MATLAB/Simulink show the controller effectively regulates active and reactive power injection according to reference values. The proposed PQ controller could be used to control distributed energy resources in interconnected microgrid systems.
Improvement of Power Quality using Fuzzy Logic Controller in Grid Connected P...IAES-IJPEDS
In this paper, the design of combined operation of UPQC and PV-ARRAY is designed. The proposed system is composed of series and shunt inverters connected back to back by a dc-link to which pv-array is connected. This system is able to compensate voltage and current related problems both in inter-connected mode and islanding mode by injecting active power to grid. The fundamental aspect is that the power electronic devices (PE) and sensitive equipments (SE) are normally designed to work in non-polluted power system, so they would suffer from malfunctions when supply voltage is not pure sinusoidal. Thus this proposed operating strategy with flexible operation mode improves the power quality of the grid system combining photovoltaic array with a control of unified power quality conditioner. Pulse Width Modulation (PWM) is used in both three phase four leg inverters. A Proportional Integral (PI) and Fuzzy Logic Controllers are used for power quality improvement by reducing the distortions in the output power. The simulated results were compared among the two controller’s strategies With pi controller and fuzzy logic controller
Improving Stability of Utility-Tied Wind Generators using Dynamic Voltage Res...IJMTST Journal
The generation of electricity using wind power is significantly increasing and has received considerable attention in recent years. One important problem with the induction generator based wind farms is that they are vulnerable to voltage disturbances and short circuit faults. Any such disturbance may cause wind farm outages. Since wind power contribution is in considerable percentage, such outages may lead to power system stability issues and also violate the grid code requirements. Thus, improving the reliability of wind farms is essential to maintain the stability of the system. The proposed strategy is to use Dynamic Voltage Restorer (DVR), which is one of the promising devices to compensate the voltage disturbance and to improve the stability of the system. It provides the wind generator with the fault ride through capability and improves the reliability of the system. Fuzzy Logic controller is used as a controller in order to control the dc link voltages and to reduce the harmonics. Simulation results for a 2 MW wind turbine are presented, especially for asymmetrical grid faults. They show the effectiveness of the DVR in comparison to the low voltage ride-through of the DFIG using a crowbar that does not allow continuous reactive power production. Extensive simulation results are included to illustrate the operation of DVR and fault compensation.
A New Control Method for Grid-Connected PV System Based on Quasi-Z-Source Cas...IAES-IJPEDS
In this paper, a new control method for quasi-Z-source cascaded multilevel inverter based grid-connected photovoltaic (PV) system is proposed. The proposed method is capable of boosting the PV array voltage to a higher level and solves the imbalance problem of DC-link voltage in traditional cascaded H-bridge inverters. The proposed control system adjusts the grid injected current in phase with the grid voltage and achieves independent maximum power point tracking (MPPT) for the separate PV arrays. To achieve these goals, the proportional-integral (PI) controllers are employed for each module. For achieving the best performance, this paper presents an optimum approach to design the controller parameters using particle swarm optimization (PSO). The primary design goal is to obtain good response by minimizing the integral absolute error. Also, the transient response is guaranteed by minimizing the overshoot, settling time and rise time of the system response. The effectiveness of the new proposed control method has been verified through simulation studies based on a seven level quasi-Z- Source cascaded multilevel inverter.
This document discusses various control strategies for power sharing in AC microgrids, including droop control approaches. It provides details on several types of droop control methods and their advantages and drawbacks. Specifically, it describes conventional droop control based on frequency-power (P/f) and voltage-reactive power (Q/V) drooping characteristics. It also discusses voltage-power droop and frequency-reactive power boosting control for microgrids with resistive lines, as well as complex line impedance-based droop control methods.
This paper presents a novel shunt active power filter (SAPF). The power converter that is used in this SAPF is constructed from a four-leg asymmetric multi-level cascaded H-bridge (CHB) inverter that is fed from a photovoltaic source. A three-dimensional space vector modulation (3D-SVPWM) technique is adopted in this work. The multi-level inverter can generate 27-level output with harmonic content is almost zero. In addition to the capability to inject reactive power and mitigating the harmonics, the proposed SAPF has also, the ability to inject real power as it is fed from a PV source. Moreover, it has a fault-tolerant capability that makes the SAPF maintaining its operation under a loss of one leg of the multi-level inverter due to an open-circuit fault without any degradation in the performance. The proposed SAPF is designed and simulated in MATLAB SIMULINK using a single nonlinear load and the results have shown a significant reduction in total harmonics distortion (THD) of the source current under the normal operating condition and post a failure in one phase of the SAPF. Also, similar results are obtained when IEEE 15 bus network is used.
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
Control of Two Stage PV Power System under the Unbalanced Three Phase Grid Vo...ijtsrd
This paper proposes a dynamic power decoupling DPD strategy for the three phase grid tied PV power system without increasing the dc link capacitance. Under normal condition, the interleaved boost converter will extract the maximum power point MPP from the PV array and the three phase inverter will inject the power to the grid. During the unbalanced grid fault scenario, the input power and current of the interleaved boost converter will be controlled by the proposed DPD to achieve the power decoupling capability as well as to eliminate the dc link voltage oscillation. The proposed work has been carried out in MATLAB, and the results are presented. Manasa | Nirmaladevi ""Control of Two Stage PV Power System under the Unbalanced Three-Phase Grid Voltages"" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-4 | Issue-2 , February 2020,
URL: https://www.ijtsrd.com/papers/ijtsrd30091.pdf
Paper Url : https://www.ijtsrd.com/engineering/electrical-engineering/30091/control-of-two-stage-pv-power-system-under-the-unbalanced-three-phase-grid-voltages/manasa
Analysis of power quality improvement in grid connected wind driven induction...eSAT Journals
Abstract As a promising renewable alternative, the wind power is one of the significant sources of generation. Reactive power compensation and harmonic reduction in a low voltage distribution networks for integration of wind power to the grid are the main issues addressed in this paper. This paper proposes a control scheme based on instaneous Pq theory for compensating the reactive power requirement of a three phase grid connected wind driven induction generator as well as the harmonics produced by the non linear load connected to the PCC using STATCOM. The proposed control scheme is simulated using MATLAB/SIMULINK. The Simulation results are presented in this paper. Keywords- wind power, distribution network, induction generator, STATCOM, reactive power.
This document summarizes a research paper that proposes a FACTS-based Static Switched Filter Compensator (SSFC) scheme for improving power quality when integrating wind energy into smart grids. The SSFC scheme uses controlled switching between two capacitor banks to provide series and shunt compensation. It is controlled using a tri-loop dynamic error controller and VSC controller to mitigate harmonics, stabilize voltages, improve power factor, and reduce losses. Simulation results using Matlab/Simulink show the SSFC scheme improves voltage regulation, reduces current and voltage harmonics to within IEEE limits, and enhances the power factor at generator, load and grid buses compared to without SSFC.
Comparative Analysis of Linear Controllers used for Grid Connected PV System IJECEIAES
Requirement for electrical energy is increasing in a ramp function manner. To meet the steady increasing in energy demand it is required to find some alternate source of energy. Except the conventional source of energy one type of renewable energy i.e PV may be regarded as a clean source of energy to meet the energy demand. PV modules generating DC power cannot be directly connected to the electrical infrastructure as most of the grid infrastructure uses either 230volt or 120 volt. Therefore power electronic device most be connected (inverter) between PV and grid. In order to make a competitive market between the renewable generated power and conventional way of generating the power it is required to design a cost effective inverter, qualitative output which is pure sinusoidal and harmonics free. In this paper a comparative analysis among the various linear controllers are presented. Proposed Optimised PID Controller is Presented through MATLAB Simulink based environment.
This document discusses optimizing the energy production of an autonomous photovoltaic (PV) system with a simple charge regulator. The study determines the optimal open circuit voltage range of the PV field for 12V and 24V storage systems. Mathematical models are developed for PV modules, storage batteries, and charge regulators. Simulation results show that a PV field's open circuit voltage between 16-23V optimizes energy production for a 12V system, and between 34-43V for a 24V system, under standard test conditions. The optimal voltage ensures the intersection point between the PV and battery voltage-current characteristics is near the PV module's maximum power point.
Reliability analysis of pmu using hidden markov modelamaresh1234
As modern electric power systems are transforming into smart grids, real time wide area monitoring system (WAMS) has become an essential tool for operation and control. With the increasing applications of WAMS for on-line stability analysis and control in smart grids, phasor measurement unit (PMU) is becoming a key element in wide area measurement system and the consequence of the failure of PMU is very severe and may cause a black out. Therefore reliable operation of PMU is very much essential for smooth functioning of the power system. This thesis is focused mainly on evaluating the reliability of PMU using hidden Markov model. Firstly, the probability of given observation sequence is obtained for the individual modules and PMU as a whole using forward and backward algorithm. Secondly, the optimal state sequence each module passes through is found. Thirdly, the parameters of the hidden Markov model are re-estimated using Baum-Welch algorithm.
IRJET- Power Quality Improvement in Solar by using Fuzzy Logic ControllerIRJET Journal
This document describes a proposed system for improving power quality in solar photovoltaic systems using a fuzzy logic controller. The system uses a single-phase inverter controlled by a predictive control algorithm to perform maximum power point tracking from the PV array and deliver power to the grid, while also compensating for current harmonics and reactive power from nonlinear loads. A fuzzy logic control method is applied for maximum power point tracking to handle model uncertainties and nonlinearity. The performance of the proposed system is evaluated using MATLAB simulation.
In a distributed generation system, divers renewable agents are connected to the low voltage 3 phase utility grid by an inverter which is used as power condition and must assurance the higher efficiency of the renewable agent. To achieve this level of efficiency, a unitary power factor between the utility grid voltages and the inverter currents is necessary, and a synchronization algorithm is required for the perfect synchronization between the 3-phase utility grid and the renewable agent. The aim of this paper is to present the optimization of the performance of a Synchronization controller for a 3-phase photovoltaic grid-connected system, assessing its accuracy under different conditions and studying their drawbacks and advantages. A grid connected photovoltaic system with a nominal power of 5 kW is used so as to assess the behavior of the synchronization algorithm when the 3 phase utility grid is affected by some disturbances such as voltage unbalances.
IRJET- Optimal Control of Multilevel Inverter to Minimize Harmonic Distortion...IRJET Journal
This document summarizes research on using multilevel inverters to minimize harmonic distortion from photovoltaic power generation arrays. It discusses 2-level, 3-level, 5-level and 7-level inverters and compares their performance. Selective harmonic elimination is also covered as a control strategy to reduce harmonic content by pre-determining switching angles. The document aims to show that multilevel inverters can help integrate renewable energy sources onto the grid more efficiently with lower voltage and current stresses on semiconductor switches.
Next Generation Researchers in Power Systems_Tao Yang_UCD EITao Yang
This document discusses solid state transformers (SSTs) and their potential applications in future distribution systems. It provides background on SSTs, explaining how they use power electronics to convert AC power to high frequency AC or DC before converting it back to the desired output. The document outlines research objectives to modularly design and optimize an SST for a distribution system. Simulation results show the modular SST has higher efficiency and lower weight than a traditional low frequency transformer under daily loading profiles. The document also explores how SSTs can address issues like imbalanced loads by independently controlling positive, negative, and zero sequence components.
Research Inventy : International Journal of Engineering and Scienceresearchinventy
Research Inventy : International Journal of Engineering and Science is published by the group of young academic and industrial researchers with 12 Issues per year. It is an online as well as print version open access journal that provides rapid publication (monthly) of articles in all areas of the subject such as: civil, mechanical, chemical, electronic and computer engineering as well as production and information technology. The Journal welcomes the submission of manuscripts that meet the general criteria of significance and scientific excellence. Papers will be published by rapid process within 20 days after acceptance and peer review process takes only 7 days. All articles published in Research Inventy will be peer-reviewed.
This document describes a fifteen-level inverter developed to transmit photovoltaic power from a solar array to the electric grid. The fifteen-level inverter uses a cascaded H-bridge configuration with low voltage MOSFET switches to reduce switching losses and harmonic distortion. It consists of a dual-buck converter to generate two DC voltages as inputs, and a full-bridge inverter to convert the output to a fifteen-level AC voltage synchronized to the grid. Simulation results show the fifteen-level output waveform is close to sinusoidal, reducing harmonic distortion below 0.5% compared to conventional two-level inverters. A controller regulates the current injected into the grid to be in phase. The system aims to provide
Power Quality Improvement Using Custom Power Devices in Squirrel Cage Inducti...IJPEDS-IAES
1) The document describes a system using a UPQC (Unified Power Quality Conditioner) to improve power quality when connecting a squirrel cage induction generator wind farm to a weak grid. The UPQC regulates the wind farm terminal voltage and mitigates harmonics at the point of common coupling.
2) It uses a neuro-fuzzy control strategy to manage the active and reactive power exchange between the series and shunt converters of the UPQC via the DC link.
3) Simulation results show the UPQC is able to compensate for voltage fluctuations at the point of common coupling due to variations in wind power generation and regulate the voltage during load connection/disconnection events.
This paper presents a droop control technique for equal power sharing in islanded microgrid. In this study, the proposed controller is based on the frequency droop method, is applied to a robust droop controller in parallel connected inverters. The previous robust droop controller deals with voltage droop method. A modification has been formed against this controller by adding a fuzzy logic controller with the frequency droop method. The only sharing error which is concentrated in this paper is the error in sharing the rated frequency among the inverters. By adapting fuzzy in the robust droop, it tries to eliminate the frequency error, hence that the frequency reference of the inverters keeps maintain at 50Hz. A derivation of generalized models of a single-phase parallel-connected inverter system is shown. The simulation results show that the proposed controller with FLC is able to improve the stability of frequency reference and the performance of power sharing between the inverters under the inductive line impedance.
Autonomous microgrid based parallel inverters using droop controller for impr...journalBEEI
The existing microgrid has become a challenge to the sustainable energy source to provide a better quality of power to the consumer. To build a reliable and efficient microgrid, designing a droop controller for the microgrid is of utmost importance. In this paper, multiple voltage source inverters connected in parallel using an active power-frequency/reactive power-voltage droop scheme. The proposed method connected to two distributed generators local controllers, where each unit consists of a droop controller with an inner voltage-current controller and a virtual droop controller. By adding this controller to the microgrid reliability and load adaptability of an islanded system can be improved. This concept applied without any real-time communication to the microgrid. Thus, simulated using MATLAB/Simulink, the obtained results prove the effectiveness of the autonomous operation's microgrid model.
This document presents a new PQ controller for regulating the output of a DC source connected to a microgrid or electrical grid. The controller independently controls active and reactive power output. It compares measured active and reactive power to reference values and uses PI controllers and phase calculations to generate PWM signals for the inverter. Simulation results in MATLAB/Simulink show the controller effectively regulates active and reactive power injection according to reference values. The proposed PQ controller could be used to control distributed energy resources in interconnected microgrid systems.
Improvement of Power Quality using Fuzzy Logic Controller in Grid Connected P...IAES-IJPEDS
In this paper, the design of combined operation of UPQC and PV-ARRAY is designed. The proposed system is composed of series and shunt inverters connected back to back by a dc-link to which pv-array is connected. This system is able to compensate voltage and current related problems both in inter-connected mode and islanding mode by injecting active power to grid. The fundamental aspect is that the power electronic devices (PE) and sensitive equipments (SE) are normally designed to work in non-polluted power system, so they would suffer from malfunctions when supply voltage is not pure sinusoidal. Thus this proposed operating strategy with flexible operation mode improves the power quality of the grid system combining photovoltaic array with a control of unified power quality conditioner. Pulse Width Modulation (PWM) is used in both three phase four leg inverters. A Proportional Integral (PI) and Fuzzy Logic Controllers are used for power quality improvement by reducing the distortions in the output power. The simulated results were compared among the two controller’s strategies With pi controller and fuzzy logic controller
Improving Stability of Utility-Tied Wind Generators using Dynamic Voltage Res...IJMTST Journal
The generation of electricity using wind power is significantly increasing and has received considerable attention in recent years. One important problem with the induction generator based wind farms is that they are vulnerable to voltage disturbances and short circuit faults. Any such disturbance may cause wind farm outages. Since wind power contribution is in considerable percentage, such outages may lead to power system stability issues and also violate the grid code requirements. Thus, improving the reliability of wind farms is essential to maintain the stability of the system. The proposed strategy is to use Dynamic Voltage Restorer (DVR), which is one of the promising devices to compensate the voltage disturbance and to improve the stability of the system. It provides the wind generator with the fault ride through capability and improves the reliability of the system. Fuzzy Logic controller is used as a controller in order to control the dc link voltages and to reduce the harmonics. Simulation results for a 2 MW wind turbine are presented, especially for asymmetrical grid faults. They show the effectiveness of the DVR in comparison to the low voltage ride-through of the DFIG using a crowbar that does not allow continuous reactive power production. Extensive simulation results are included to illustrate the operation of DVR and fault compensation.
A New Control Method for Grid-Connected PV System Based on Quasi-Z-Source Cas...IAES-IJPEDS
In this paper, a new control method for quasi-Z-source cascaded multilevel inverter based grid-connected photovoltaic (PV) system is proposed. The proposed method is capable of boosting the PV array voltage to a higher level and solves the imbalance problem of DC-link voltage in traditional cascaded H-bridge inverters. The proposed control system adjusts the grid injected current in phase with the grid voltage and achieves independent maximum power point tracking (MPPT) for the separate PV arrays. To achieve these goals, the proportional-integral (PI) controllers are employed for each module. For achieving the best performance, this paper presents an optimum approach to design the controller parameters using particle swarm optimization (PSO). The primary design goal is to obtain good response by minimizing the integral absolute error. Also, the transient response is guaranteed by minimizing the overshoot, settling time and rise time of the system response. The effectiveness of the new proposed control method has been verified through simulation studies based on a seven level quasi-Z- Source cascaded multilevel inverter.
This document discusses various control strategies for power sharing in AC microgrids, including droop control approaches. It provides details on several types of droop control methods and their advantages and drawbacks. Specifically, it describes conventional droop control based on frequency-power (P/f) and voltage-reactive power (Q/V) drooping characteristics. It also discusses voltage-power droop and frequency-reactive power boosting control for microgrids with resistive lines, as well as complex line impedance-based droop control methods.
This paper presents a novel shunt active power filter (SAPF). The power converter that is used in this SAPF is constructed from a four-leg asymmetric multi-level cascaded H-bridge (CHB) inverter that is fed from a photovoltaic source. A three-dimensional space vector modulation (3D-SVPWM) technique is adopted in this work. The multi-level inverter can generate 27-level output with harmonic content is almost zero. In addition to the capability to inject reactive power and mitigating the harmonics, the proposed SAPF has also, the ability to inject real power as it is fed from a PV source. Moreover, it has a fault-tolerant capability that makes the SAPF maintaining its operation under a loss of one leg of the multi-level inverter due to an open-circuit fault without any degradation in the performance. The proposed SAPF is designed and simulated in MATLAB SIMULINK using a single nonlinear load and the results have shown a significant reduction in total harmonics distortion (THD) of the source current under the normal operating condition and post a failure in one phase of the SAPF. Also, similar results are obtained when IEEE 15 bus network is used.
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
Control of Two Stage PV Power System under the Unbalanced Three Phase Grid Vo...ijtsrd
This paper proposes a dynamic power decoupling DPD strategy for the three phase grid tied PV power system without increasing the dc link capacitance. Under normal condition, the interleaved boost converter will extract the maximum power point MPP from the PV array and the three phase inverter will inject the power to the grid. During the unbalanced grid fault scenario, the input power and current of the interleaved boost converter will be controlled by the proposed DPD to achieve the power decoupling capability as well as to eliminate the dc link voltage oscillation. The proposed work has been carried out in MATLAB, and the results are presented. Manasa | Nirmaladevi ""Control of Two Stage PV Power System under the Unbalanced Three-Phase Grid Voltages"" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-4 | Issue-2 , February 2020,
URL: https://www.ijtsrd.com/papers/ijtsrd30091.pdf
Paper Url : https://www.ijtsrd.com/engineering/electrical-engineering/30091/control-of-two-stage-pv-power-system-under-the-unbalanced-three-phase-grid-voltages/manasa
Analysis of power quality improvement in grid connected wind driven induction...eSAT Journals
Abstract As a promising renewable alternative, the wind power is one of the significant sources of generation. Reactive power compensation and harmonic reduction in a low voltage distribution networks for integration of wind power to the grid are the main issues addressed in this paper. This paper proposes a control scheme based on instaneous Pq theory for compensating the reactive power requirement of a three phase grid connected wind driven induction generator as well as the harmonics produced by the non linear load connected to the PCC using STATCOM. The proposed control scheme is simulated using MATLAB/SIMULINK. The Simulation results are presented in this paper. Keywords- wind power, distribution network, induction generator, STATCOM, reactive power.
This document summarizes a research paper that proposes a FACTS-based Static Switched Filter Compensator (SSFC) scheme for improving power quality when integrating wind energy into smart grids. The SSFC scheme uses controlled switching between two capacitor banks to provide series and shunt compensation. It is controlled using a tri-loop dynamic error controller and VSC controller to mitigate harmonics, stabilize voltages, improve power factor, and reduce losses. Simulation results using Matlab/Simulink show the SSFC scheme improves voltage regulation, reduces current and voltage harmonics to within IEEE limits, and enhances the power factor at generator, load and grid buses compared to without SSFC.
Comparative Analysis of Linear Controllers used for Grid Connected PV System IJECEIAES
Requirement for electrical energy is increasing in a ramp function manner. To meet the steady increasing in energy demand it is required to find some alternate source of energy. Except the conventional source of energy one type of renewable energy i.e PV may be regarded as a clean source of energy to meet the energy demand. PV modules generating DC power cannot be directly connected to the electrical infrastructure as most of the grid infrastructure uses either 230volt or 120 volt. Therefore power electronic device most be connected (inverter) between PV and grid. In order to make a competitive market between the renewable generated power and conventional way of generating the power it is required to design a cost effective inverter, qualitative output which is pure sinusoidal and harmonics free. In this paper a comparative analysis among the various linear controllers are presented. Proposed Optimised PID Controller is Presented through MATLAB Simulink based environment.
This document discusses optimizing the energy production of an autonomous photovoltaic (PV) system with a simple charge regulator. The study determines the optimal open circuit voltage range of the PV field for 12V and 24V storage systems. Mathematical models are developed for PV modules, storage batteries, and charge regulators. Simulation results show that a PV field's open circuit voltage between 16-23V optimizes energy production for a 12V system, and between 34-43V for a 24V system, under standard test conditions. The optimal voltage ensures the intersection point between the PV and battery voltage-current characteristics is near the PV module's maximum power point.
Reliability analysis of pmu using hidden markov modelamaresh1234
As modern electric power systems are transforming into smart grids, real time wide area monitoring system (WAMS) has become an essential tool for operation and control. With the increasing applications of WAMS for on-line stability analysis and control in smart grids, phasor measurement unit (PMU) is becoming a key element in wide area measurement system and the consequence of the failure of PMU is very severe and may cause a black out. Therefore reliable operation of PMU is very much essential for smooth functioning of the power system. This thesis is focused mainly on evaluating the reliability of PMU using hidden Markov model. Firstly, the probability of given observation sequence is obtained for the individual modules and PMU as a whole using forward and backward algorithm. Secondly, the optimal state sequence each module passes through is found. Thirdly, the parameters of the hidden Markov model are re-estimated using Baum-Welch algorithm.
IRJET- Power Quality Improvement in Solar by using Fuzzy Logic ControllerIRJET Journal
This document describes a proposed system for improving power quality in solar photovoltaic systems using a fuzzy logic controller. The system uses a single-phase inverter controlled by a predictive control algorithm to perform maximum power point tracking from the PV array and deliver power to the grid, while also compensating for current harmonics and reactive power from nonlinear loads. A fuzzy logic control method is applied for maximum power point tracking to handle model uncertainties and nonlinearity. The performance of the proposed system is evaluated using MATLAB simulation.
In a distributed generation system, divers renewable agents are connected to the low voltage 3 phase utility grid by an inverter which is used as power condition and must assurance the higher efficiency of the renewable agent. To achieve this level of efficiency, a unitary power factor between the utility grid voltages and the inverter currents is necessary, and a synchronization algorithm is required for the perfect synchronization between the 3-phase utility grid and the renewable agent. The aim of this paper is to present the optimization of the performance of a Synchronization controller for a 3-phase photovoltaic grid-connected system, assessing its accuracy under different conditions and studying their drawbacks and advantages. A grid connected photovoltaic system with a nominal power of 5 kW is used so as to assess the behavior of the synchronization algorithm when the 3 phase utility grid is affected by some disturbances such as voltage unbalances.
Power quality optimization using a novel backstepping control of a three-phas...IJECEIAES
A novel nonlinear backstepping controller based on direct current (DC) link voltage control is proposed in three-phase grid-connected solar photovoltaic (PV) systems to control the active and reactive power flow between the PV system and the grid with improved power quality in terms of pure sinusoidal current injection with lower total harmonic distortion (THD), as well as to ensure unity power factor, or to compensate for reactive power required by the load, i.e., the electrical grid. The output power of the PV array is supplied to the grid through a boost converter with maximum power point tracking (MPPT) control and an inverter. Simulation results of the proposed controller show good robustness under nominal conditions, parameter variations, and load disturbances, which presents the main advantage of this controller as compared to an existing controller. The performance of this work was evaluated using a MATLAB/Simulink environment.
The work presented in this paper is devoted to the control of a photovoltaic system connected to grid by a three level diode clamed inverter. A control structure based on three parts: dc link voltage control, power injected control and current control is proposed. In this work, the random PWM strategy is used to generate control signals for the multilevel inverter used us an interface to connect photovoltaic generators to the grid. Numerical simulations are performed using MATLAB / Simulink software, the simulation results for the proposed system indicate the performances of the proposed control structure, minimization of harmonics by the random PWM strategy applied and injection to the grid more active power by the multilevel inverter structure.
In this paper a grid interconnected system with wind energy source linked with a FACTs based SSFC device ( Static switched filter compensator ) at load for enhancing power quality is considered .Analysis is done for the proposed system by varying Carrier frequency over a wide range and observed system performance at all 3 busses wise Grid bus, Generator Bus and Load Bus. Two regulators are used to organize the FACTS SSFC-device, these are based on a tri-loop dynamic error obsessed inter-coupled input to VSC controller. Investigation is made in MATLAB/SIMULINK Environment for the proposed system ,it is observed that system performance in terms of percentage Total harmonic Distortion is satisfactory along with the Enhanced Power Quality.
Performance of Maximum Power Point Tracking Algorithm based Photovoltaic Arra...IRJET Journal
This document summarizes a research paper that models and simulates a hybrid microgrid system interconnected with a photovoltaic array and utility grid. It uses a DC-DC boost converter controlled by an incremental conductance maximum power point tracking algorithm connected to the photovoltaic panels. A three-phase three-level inverter with IGBT switches is used to convert the DC power to AC power that is synchronized to the utility grid using a phase locked loop control algorithm. The system is simulated under varying sunlight conditions and the desired results are obtained, demonstrating effective maximum power point tracking and grid integration of solar power.
1.compensation of reactive power using d statcom in grid interfaced pv systemEditorJST
This document summarizes a research paper on using a D-STATCOM (Distribution Static Compensator) with an LCL passive filter to compensate for reactive power and improve power quality in a grid-interfaced photovoltaic (PV) system. The D-STATCOM injects current to mitigate voltage fluctuations. Simulation results show improvements in three-phase output voltage at the transmission and distribution levels as well as increased power generation from both the transmission system and PV system. In conclusion, the integration of FACTS devices like the D-STATCOM can help maintain desired power quality standards while reducing distortions and improving the power factor.
Modeling and simulation of three phases cascaded H-bridge grid-tied PV inverterjournalBEEI
In this paper a control scheme for three phase seven level cascaded H-bridge inverter for grid tied PV system is presented. As power generation from PV depends on varing environmental conditions, for extractraction of maximum power from PV array, fuzzy MPPT controller is incorporated with each PV array. It gives fast and accurate response. To maintain the grid current sinusoidal under varying conditions, a digital PI controller scheme is adopted. A MATLAB/Simulink model is developed for this purpose and results are presented. At last THD analysis is carried out in order to validate the performance of the overall system. As discussed, with this control strategy the balanced grid current is obtained keeping THD values with in the specified range of IEEE-519 standard.
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This document summarizes a research paper that presents an output feedback nonlinear control strategy for a three-phase grid-connected photovoltaic (PV) power generation system. The control objectives are to ensure global stability of the system, achieve maximum power point tracking for the PV array, and ensure a unity power factor grid connection. A nonlinear controller is developed using Lyapunov stability analysis. Simulation results confirm the controller meets the objectives despite changing climatic conditions such as temperature and radiation. The paper models the three-phase grid-connected PV system and develops the output feedback controller and analysis to prove the control objectives are achieved.
The document describes a study investigating the design and performance of a photovoltaic system acting as a static synchronous compensator (PV-STATCOM) to enhance power quality in a microgrid application. Key components of the PV-STATCOM design are described, including the voltage source converter, DC bus capacitor, interfacing inductor, and control strategy using proportional-integral and hysteresis current controllers. Simulation results in MATLAB show the PV-STATCOM effectively mitigating current harmonics from nonlinear loads and injecting compensating current to improve power quality from 0.1 to 0.2 seconds as demonstrated in the current and voltage waveforms.
Hysteresis-based Voltage and Current Control Techniques for Grid Connected So...IJECEIAES
Solar PV system development and integration with existing grid is very fast in recent years all over the world, as they require limited maintenance, pollution free and simple structure. When observing the factors affecting the performance of the grid connected solar photovoltaic system, the inverter output voltage with harmonics add with the harmonics generated due to the non-linear loads, retain a bigger challenge to maintain power quality in the grid. To maintain grid power quality, better inverter control technique should be developed. This paper presents the two control techniques for grid-tied inverters. This study developed the hysteresis controller for the inverter. Hysteresis controller used in this work two way (i) Voltage control mode (ii) Current control mode. Matlab/Simulink model is developed for the proposed system. Further the study presents the comparative evaluation of the performance of both control techniques based on the percentage of total harmonic distortion (THD) with the limits specified by the standards such as IEEE 1547 and IEC 61727 and IEEE Std 519-2014.
Solar energy based impedance-source inverter for grid systemIJECEIAES
In this work, the fickleness of solar energy can be overcome by using Maximum Power Point Tracking algorithm (MPPT). Perturb and Observation (P&O) MPPT algorithm accomplish fast the maximum power point for rapid change of environmental conditions such as irradiance intensity and temperature. The MPPT algorithm applied to solar PV system keep the boost converter output constant. Output from boost converter is taken to three phase impedance-source inverter with RL load and grid system. Impedance-source inverter performs the transformation of variable DC output of the solar PV system in to near sinusoidal AC output. This near sinusoidal AC output consecutively is served to the RL load first and then to grid system. The simulation is carried out in matlab/simulink platform both for RL load and grid system and the simulation results are experimentally validated for RL load arrangement only.
This paper describes the Grid connected solar photovoltaique system using DC-DC boost converter and the DC/AC inverter (VSC) to supplies electric power to the utility grid. The model contains a representation of the main components of the system that are two solar arrays of 100 kW, boost converter and the grid side inverter. The paper starts with a system description, in this part we have given a definition and a short overview of every component used in this system and they are taken separately. The PV cell model is easy, accurate, and takes external temperature and solar radiation into consideration. It also proposes a maximum power point tracking (MPPT) algorithm. The algorithm incorporated in a DC/DC converter is used to track the maximum power of PV cell. Finally, the DC/AC inverter (VSC) of three- level is used to regulate the ouput voltage of DC/DC converter and connects the PV cell to the grid. Simulation results show how a solar radiation’s change can affect the power output of any PV system, also they show the control performance and dynamic behavior of the grid connected photovoltaic system.
This paper presents a grid-connected photovoltaic system (PV) used as a shunt active power filter (SAPF) to provide the power factor correction, harmonic elimination, reactive power compensation and to simultaneously supply power from a PV system to the utility. A direct power control (DPC) method is used for controlling the system to feed the photovoltaic energy in synchronization with grid and provide power quality improvement. The PI parameters of DC-link voltage controller are tuned using the Particle Swarm Optimization (PSO) algorithm without the need for an exact mathematical model of system. This PI-PSO controller gives better results for robustness, harmonic minimization and reduces the overshoot and undershoots of PI controller. The overall control of system is tested in Matlab/Simulink environment. Then, the simulations results demonstrate the robustness and feasibility of proposed method.
Design, modeling and performance investigation of gcAlexander Decker
This document summarizes a research paper that proposes a new topology for a photovoltaic power injection system using two voltage source inverters connected in parallel. One inverter operates with a quasi-square voltage waveform at the grid frequency, while the other uses pulse width modulation at a higher switching frequency. The quasi-square inverter injects power from the PV system, while the PWM inverter controls current quality. The proposed system was modeled and simulated in MATLAB/Simulink to analyze power flow characteristics under varying solar intensity and modulation index. Simulation results showed that the system optimizes design, reduces losses, and increases energy injected into the grid compared to a conventional single inverter system.
11.design, modeling and performance investigation of gcAlexander Decker
This document summarizes a research paper that proposes a new topology for a photovoltaic power injection system. The system uses two voltage source inverters in parallel - a quasi-square wave inverter and a PWM inverter. The quasi-square inverter injects power from the PV system into the grid, while the PWM inverter controls current quality. The design is modeled and simulated in MATLAB/Simulink. Simulation results show the power flow characteristics for varying solar intensity and modulation indices. The proposed topology optimizes the system design by reducing losses and increasing the energy injected into the grid compared to traditional boost converter and PWM inverter designs.
Performance Analysis of CSI Based PV system During LL and TPG faultsIOSR Journals
This document analyzes the performance of a current source inverter (CSI)-based photovoltaic (PV) system during line-to-line (LL) and three-phase-to-ground (TPG) faults. It presents simulation results showing the CSI system is able to limit DC-side current oscillations during faults, unlike voltage source inverter systems. The controller regulates DC and AC currents to maximize PV power extraction and provide sinusoidal current to the grid. Simulation results show DC-side current oscillations dampen quickly after faults clear, while AC current undergoes overmodulation during faults. The CSI provides overcurrent protection and restricts currents on both sides during faults.
An Overview of MPPT for Photovoltaic Panels Using Various Artificial Intellig...IRJET Journal
This document provides an overview of various maximum power point tracking (MPPT) techniques for photovoltaic panels using artificial intelligence methods. It discusses photovoltaic systems and components like PV panels and DC-DC converters. It then summarizes several common MPPT techniques including fractional open-circuit voltage, perturb and observe, and incremental conductance. Finally, it outlines different artificial intelligence approaches that can be combined with PV systems and MPPT, such as artificial neural networks, genetic algorithms, fuzzy logic, and particle swarm optimization. The document aims to compare various MPPT and AI techniques to effectively maximize power output from PV systems.
Hysteresis SVM for Coupled Inductor Z Source Diode Clamped 3-Level Inverter B...IAES-IJPEDS
Due to its advantages such as it can defeat problems such as leakage current
and insertion of DC in the grid and provides low stress on power devices,
Diode-clamped three-level inverter (DCTLI) is habitually used in
transformerless photovoltaic (PV) connected to grid network. But it still has
a problem of shoot-through which dwells in its legs, so its operation not
reliable. Z source network is employed to permit operation without shoot
through risk and improve its reliability. Coupled inductors are replaced the
line transformers in to attain lower cost, reduced size, and improved its
reliability and efficiency. Coupled inductor which avoids leakage current
problem and losses. It employs coupled inductor z source diode clamped
three level inverter (CI-Z-DC-TLI) to boost the voltage and further progress
the consistency of the proposed system by avoiding the shoot through the
problem. The proposed system assures that common-mode voltage
and shoot-through risk is avoided. Moreover, controlling DC-TLI with
Hysteresis SVM algorithm which improves output voltage and current
control. Simulation and experimental results of this proposed system were
analyzed using MATLAB environment and FPGA hardware.
Similar to Harmonic stability analysis of multi-paralleled 3-phase PV inverters tied to grid (20)
The aim of this research is the speed tracking of the permanent magnet synchronous motor (PMSM) using an intelligent Neural-Network based adapative backstepping control. First, the model of PMSM in the Park synchronous frame is derived. Then, the PMSM speed regulation is investigated using the classical method utilizing the field oriented control theory. Thereafter, a robust nonlinear controller employing an adaptive backstepping strategy is investigated in order to achieve a good performance tracking objective under motor parameters changing and external load torque application. In the final step, a neural network estimator is integrated with the adaptive controller to estimate the motor parameters values and the load disturbance value for enhancing the effectiveness of the adaptive backstepping controller. The robsutness of the presented control algorithm is demonstrated using simulation tests. The obtained results clearly demonstrate that the presented NN-adaptive control algorithm can provide good trackingperformances for the speed trackingin the presence of motor parameter variation and load application.
The document presents a new method for fault classification and direction discrimination in transmission lines using 1D convolutional neural networks (1D-CNNs). A 132kV transmission line model is simulated to generate training and testing data for the 1D-CNN algorithm. The proposed 1D-CNN approach directly uses the voltage and current signals from one end as input, merging feature extraction and classification into a single learning process. Testing shows the 1D-CNN method accurately classifies and discriminates fault direction with higher accuracy than conventional neural network and fuzzy neural network methods under different fault conditions.
Among the most widespread renewable energy sources is solar energy; Solar panels offer a green, clean, and environmentally friendly source of energy. In the presence of several advantages of the use of photovoltaic systems, the random operation of the photovoltaic generator presents a great challenge, in the presence of a critical load. Among the most used solutions to overcome this problem is the combination of solar panels with generators or with the public grid or both. In this paper, an energy management strategy is proposed with a safety aspect by using artificial neural networks (ANNs), in order to ensure a continuous supply of electricity to consumers with a maximum solicitation of renewable energy.
In this paper, the artificial neural network (ANN) has been utilized for rotating machinery faults detection and classification. First, experiments were performed to measure the lateral vibration signals of laboratory test rigs for rotor-disk-blade when the blades are defective. A rotor-disk-blade system with 6 regular blades and 5 blades with various defects was constructed. Second, the ANN was applied to classify the different x- and y-axis lateral vibrations due to different blade faults. The results based on training and testing with different data samples of the fault types indicate that the ANN is robust and can effectively identify and distinguish different blade faults caused by lateral vibrations in a rotor. As compared to the literature, the present paper presents a novel work of identifying and classifying various rotating blade faults commonly encountered in rotating machines using ANN. Experimental data of lateral vibrations of the rotor-disk-blade system in both x- and y-directions are used for the training and testing of the network.
This paper focuses on the artificial bee colony (ABC) algorithm, which is a nonlinear optimization problem. is proposed to find the optimal power flow (OPF). To solve this problem, we will apply the ABC algorithm to a power system incorporating wind power. The proposed approach is applied on a standard IEEE-30 system with wind farms located on different buses and with different penetration levels to show the impact of wind farms on the system in order to obtain the optimal settings of control variables of the OPF problem. Based on technical results obtained, the ABC algorithm is shown to achieve a lower cost and losses than the other methods applied, while incorporating wind power into the system, high performance would be gained.
The significance of the solar energy is to intensify the effectiveness of the Solar Panel with the use of a primordial solar tracking system. Here we propounded a solar positioning system with the use of the global positioning system (GPS) , artificial neural network (ANN) and image processing (IP) . The azimuth angle of the sun is evaluated using GPS which provide latitude, date, longitude and time. The image processing used to find sun image through which centroid of sun is calculated and finally by comparing the centroid of sun with GPS quadrate to achieve optimum tracking point. Weather conditions and situation observed through AI decision making with the help of IP algorithms. The presented advance adaptation is analyzed and established via experimental effects which might be made available on the memory of the cloud carrier for systematization. The proposed system improve power gain by 59.21% and 10.32% compare to stable system (SS) and two-axis solar following system (TASF) respectively. The reduced tracking error of IoT based Two-axis solar following system (IoT-TASF) reduces their azimuth angle error by 0.20 degree.
Kosovo has limited renewable energy resources and its power generation sector is based on fossil fuels. Such a situation emphasizes the importance of active research and efficient use of renewable energy potential. According to the analysis of meteorological data for Kosovo, it can be concluded that among the most attractive potential wind power sites are the locations known as Kitka (42° 29' 41" N and 21° 36' 45" E) and Koznica (42° 39′ 32″ N, 21° 22′30″E). The two terrains in which the analysis was carried out are mountain areas, with altitudes of 1142 m (Kitka) and 1230 m (Koznica). the same measuring height, about 84 m above the ground, is obtained for these average wind speeds: Kitka 6,667 m/s and Koznica 6,16 m/s. Since the difference in wind speed is quite large versus a difference in altitude that is not being very large, analyses are made regarding the terrain characteristics including the terrain relief features. In this paper it will be studied how much the roughness of the terrain influences the output energy. Also, that the assumption to be taken the same as to how much they will affect the annual energy produced.
The document summarizes a research paper that proposes using a battery energy storage system (BESS) with droop control to reduce frequency fluctuations in a multi-machine power system connected to a large-scale photovoltaic (PV) plant. The paper develops a droop control strategy for the BESS that incorporates a frequency error signal and dead-band. Simulation results using PSCAD/EMTDC software show that the proposed droop control-based BESS can efficiently curtail frequency oscillations caused by fluctuations in PV power injection due to changing solar irradiance.
This study investigates experimentally the performance of two-dimensional solar tracking systems with reflector using commercial silicon based photovoltaic module, with open and closed loop control systems. Different reflector materials were also investigated. The experiments were performed at the Hashemite University campus in Zarqa at a latitude of 32⁰, in February and March. Photovoltaic output power and performance were analyzed. It was found that the modified photovoltaic module with mirror reflector generated the highest value of power, while the temperature reached a maximum value of 53 ̊ C. The modified module suggested in this study produced 5% more PV power than the two-dimensional solar tracking systems without reflector and produced 12.5% more PV power than the fixed PV module with 26⁰ tilt angle.
This paper focuses on the modeling and control of a wind energy conversion chain using a permanent magnet synchronous machine. This system behaves a turbine, a generator, DC/DC and DC/AC power converters. These are connected on both sides to the DC bus, where the inverter is followed by a filter which is connected to the grid. In this paper, we have been used two types of controllers. For the stator side converter, we consider the Takagi-Sugeno approach where the parameters of controller have been computed by the theory of linear matrix inequalities. The stability synthesis has been checked using the Lyapunov theory. According to the grid side converter, the proportional integral controller is exploited to keep a constant voltage on the DC bus and control both types of powers. The simulation results demonstrate the robustness of the approach used.
The development of modeling wind speed plays a very important in helping to obtain the actual wind speed data for the benefit of the power plant planning in the future. The wind speed in this paper is obtained from a PCE-FWS 20 type measuring instrument with a duration of 30 minutes which is accumulated into monthly data for one year (2019). Despite the many wind speed modeling that has been done by researchers. Modeling wind speeds proposed in this study were obtained from the modified Rayleigh distribution. In this study, the Rayleigh scale factor (Cr) and modified Rayleigh scale factor (Cm) were calculated. The observed wind speed is compared with the predicted wind characteristics. The data fit test used correlation coefficient (R2), root means square error (RMSE), and mean absolute percentage error (MAPE). The results of the proposed modified Rayleigh model provide very good results for users.
This paper deals with an advanced design for a pump powered by solar energyto supply agricultural lands with water and also the maximum power point is used to extract the maximum value of the energy available inside the solar panels and comparing between techniques MPPT such as Incremental conductance, perturb & observe, fractional short current circuit, and fractional open voltage circuit to find the best technique among these. The solar system is designed with main parts: photovoltaic (PV) panel, direct current/direct current (DC/DC) converter, inverter, filter, and in addition, the battery is used to save energy in the event that there is an increased demand for energy and not to provide solar radiation, as well as saving energy in the case of generation more than demand. This work was done using the matrix laboratory (MATLAB) simulink program.
The objective of this paper is to provide an overview of the current state of renewable energy resources in Bangladesh, as well as to examine various forms of renewable energies in order to gain a comprehensive understanding of how to address Bangladesh's power crisis issues in a sustainable manner. Electricity is currently the most useful kind of energy in Bangladesh. It has a substantial influence on a country's socioeconomic standing and living standards. Maintaining a stable source of energy at a cost that is affordable to everyone has been a constant battle for decades. Bangladesh is blessed with a wealth of natural resources. Bangladesh has a huge opportunity to accelerate its economic development while increasing energy access, livelihoods, and health for millions of people in a sustainable way due to the renewable energy system.
When the irradiance distribution over the photovoltaic panels is uniform, the pursuit of the maximum power point is not reached, which has allowed several researchers to use traditional MPPT techniques to solve this problem Among these techniques a PSO algorithm is used to have the maximum global power point (GMPPT) under partial shading. On the other hand, this one is not reliable vis-à-vis the pursuit of the MPPT. Therefore, in this paper we have treated another technique based on a new modified PSO algorithm so that the power can reach its maximum point. The PSO algorithm is based on the heuristic method which guarantees not only the obtaining of MPPT but also the simplicity of control and less expensive of the system. The results are obtained using MATLAB show that the proposed modified PSO algorithm performs better than conventional PSO and is robust to different partial shading models.
A stable operation of wind turbines connected to the grid is an essential requirement to ensure the reliability and stability of the power system. To achieve such operational objective, installing static synchronous compensator static synchronous compensator (STATCOM) as a main compensation device guarantees the voltage stability enhancement of the wind farm connected to distribution network at different operating scenarios. STATCOM either supplies or absorbs reactive power in order to ensure the voltage profile within the standard-margins and to avoid turbine tripping, accordingly. This paper present new study that investigates the most suitable-location to install STATCOM in a distribution system connected wind farm to maintain the voltage-levels within the stability margins. For a large-scale squirrel cage induction generator squirrel-cage induction generator (SCIG-based) wind turbine system, the impact of STATCOM installation was tested in different places and voltage-levels in the distribution system. The proposed method effectiveness in enhancing the voltage profile and balancing the reactive power is validated, the results were repeated for different scenarios of expected contingencies. The voltage profile, power flow, and reactive power balance of the distribution system are observed using MATLAB/Simulink software.
The electrical and environmental parameters of polymer solar cells (PSC) provide important information on their performance. In the present article we study the influence of temperature on the voltage-current (I-V) characteristic at different temperatures from 10 °C to 90 °C, and important parameters like bandgap energy Eg, and the energy conversion efficiency η. The one-diode electrical model, normally used for semiconductor cells, has been tested and validated for the polemeral junction. The PSC used in our study are formed by the poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM). Our technique is based on the combination of two steps; the first use the Least Mean Squares (LMS) method while the second use the Newton-Raphson algorithm. The found results are compared to other recently published works, they show that the developed approach is very accurate. This precision is proved by the minimal values of statistical errors (RMSE) and the good agreement between both the experimental data and the I-V simulated curves. The obtained results show a clear and a monotonic dependence of the cell efficiency on the studied parameters.
The inverter is the principal part of the photovoltaic (PV) systems that assures the direct current/alternating current (DC/AC) conversion (PV array is connected directly to an inverter that converts the DC energy produced by the PV array into AC energy that is directly connected to the electric utility). In this paper, we present a simple method for detecting faults that occurred during the operation of the inverter. These types of faults or faults affect the efficiency and cost-effectiveness of the photovoltaic system, especially the inverter, which is the main component responsible for the conversion. Hence, we have shown first the faults obtained in the case of the short circuit. Second, the open circuit failure is studied. The results demonstrate the efficacy of the proposed method. Good monitoring and detection of faults in the inverter can increase the system's reliability and decrease the undesirable faults that appeared in the PV system. The system behavior is tested under variable parameters and conditions using MATLAB/Simulink.
The document describes a proposed modified bridge-type nonsuperconducting fault current limiter (NSFCL) for distribution networks. The NSFCL consists of a bridge rectifier, two DC reactors (one small in series and one large in parallel), and an IGBT semiconductor switch controlled by a command circuit. During normal operation, the IGBT is on and the parallel reactor is bypassed, making the NSFCL invisible. During a fault, the IGBT turns off, inserting the parallel reactor to limit fault current. Simulation results showed the design effectively limits fault current while minimally affecting normal operation.
This paper provides a new approach to reducing high-order harmonics in 400 Hz inverter using a three-level neutral-point clamped (NPC) converter. A voltage control loop using the harmonic compensation combined with NPC clamping diode control technology. The capacitor voltage imbalance also causes harmonics in the output voltage. For 400 Hz inverter, maintain a balanced voltage between the two input (direct current) (DC) capacitors is difficult because the pulse width modulation (PWM) modulation frequency ratio is low compared to the frequency of the output voltage. A method of determining the current flowing into the capacitor to control the voltage on the two balanced capacitors to ensure fast response reversal is also given in this paper. The combination of a high-harmonic resonator controller and a neutral-point voltage controller working together on the 400 Hz NPC inverter structure is given in this paper.
Direct current (DC) electronic load is a useful equipment for testing the electrical system. It can emulate various load at a high rating. The electronic load requires a power converter to operate and a linear regulator is a common option. Nonetheless, it is hard to control due to the temperature variation. This paper proposed a DC electronic load using the boost converter. The proposed electronic load operates in the continuous current mode and control using the integral controller. The electronic load using the boost converter is compared with the electronic load using the linear regulator. The results show that the boost converter able to operate as an electronic load with an error lower than 0.5% and response time lower than 13 ms.
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Harmonic stability analysis of multi-paralleled 3-phase PV inverters tied to grid
1. International Journal of Power Electronics and Drive System (IJPEDS)
Vol. 12, No. 2, Jun 2021, pp. 783~792
ISSN: 2088-8694, DOI: 10.11591/ijpeds.v12.i2.pp783-792 783
Journal homepage: http://ijpeds.iaescore.com
Harmonic stability analysis of multi-paralleled 3-phase PV
inverters tied to grid
R.S. Ravi Sankar, K. K. Deepika, A.V. Satyanarayana
Department of Electrical and Electronics Engineering, Vignan’s Institute of Information Technology, Visakhapatnam,
Andhra Pradesh, India
Article Info ABSTRACT
Article history:
Received Jun 12, 2020
Revised Mar 27, 2021
Accepted Apr 5, 2021
In this paper the harmonic stability is investigated for multi paralleled three-
phase photovoltaic inverters connected to grid. The causes to harmonically
stabilize/destabilize the multi-paralleled PV inverters when tied to the grid is
analysed by the impedance-based stability criterion (IBSC). In this paper
stability of the system is investigated by varying the grid inductance with
constant grid resistance and also by varying load impedance while
maintaining grid inductance constant. Stability of the multiple three phase
inverters tied to the grid with different grid impedance, inductance value in
particular are analyzed. Overall system is stable up to grid inductance of
5mH even though there is change in load admittance. It is concluded that
system stability depends only on grid impedance. It is verified with
MATLAB Simulations.
Keywords:
Distribution generation
Grid impedance
Impedance based stability
criterion
Inverter output impedance
Maximum power point tracking
Minor loop gain
Proportional-resonant current
controller
PV array
This is an open access article under the CC BY-SA license.
Corresponding Author:
R.S. Ravi Sankar
Department of Electrical and Electronics Engineering
Vignan’s Institute of Information Technology
Visakhapatnam, Andhra Pradesh, India
Email: satya_ravi2001@yahoo.com
1. INTRODUCTION
Proliferation of renewable energy sources is the current scenario to the meet the increasing load
demand. When these sources are connected to the grid there is interaction between the LCL filter, grid
impedance, and inner current loop of the inverters. Thereby, it causes the harmonic instability [1], [2]. Which
further leads to amplification of resonance over the range of frequencies. This sometimes leads to unwanted
withdrawal of the PV inverters from the grid [3], [4]. The interaction of the admittances of multiple inverters
causes two issues one is amplification of Resonance and seconed one harmonic instability. These two issues
are analyzed and answered by means of IBSC analysis. IBSC was applied to design the output filter in
chopper circuits [5], [6]. The conversion method for harmonic transfer function-based model for a Voltage
source converter into a simple and efficient Single Input Single Output model [7]. Stability characteristics
were obtained with the frequency coupling effect. In [8], Impedance model in dq-frame was developed for
offshore wind power plant to study the effect of inverters and transmission cables. The analyzed the
harmonic stability in modular multilevel based DC systems. It was verified with hardware experimentation as
well as simulation. DC impedance model of the system was developed by considering the capacitor voltage
fluctuation, harmonic responses [9].
2. ISSN: 2088-8694
Int J Pow Elec & Dri Syst, Vol. 12, No. 2, June 2021 : 783 – 792
784
In this work, IBSC tool is used in the multi-inverters tied to grid to examine the harmonic stability.
The system stability is evaluated by graphical analysis using minor loop gain of the overall system. If the
system obeys the nyquiest stability criteria than the system is stable otherwise it is unstable. The concept of
passivity-based stability analysis has recently gained attention in control system [10] and from this stability
analysis each subsystem has a phase margin lies between -90 to 90. Then the system is stable otherwise
system is unstable.
In this paper, Section 2 deals with the Mathematicall modeling of the PV system, in Section 3, the
calculation of the Output Impedance of inverter and the modeling of the PR current controller. In Section.4.
simulation results of the two case studies are discussed.
2. MATHEMATICALL MODELING OF PV SYSTEM
2.1. Modeling of PV array
In this study PV array provides the DC voltage to boost converter. Single diode model of a PV Cell
is depicated in Figure 1. It represents simple modeling where resistances are neglected [11]-[16]. The
parameters of the PV module are shown in Table.1. These are used to simulate the PV array in matlab
simulation. two modules are connected in series to give the voltage of 700 V and the PV current supplied is
40A. The PV power supplied by the inverter is 2KW even though it is designed for the 14KW. The PV array
voltage, current and power wave forms are depicted in Figure 2 to Figure 4.
2.2. Maximum power point tracking (MPPT)
PV panel output is highly depending on climatic conditions, extracted maximum power from PV
panels. Different MPPT techniques are proposed in literature. For simple implementation, P&O technique is
implemented in this paper [17], [18].
Table 1. Specifications of the PV module
Parameter Variable Value
Current at PMax Im 8.30A
Voltage at PMax Vm 30.2V
O.C Voltage Voc 37.3V
S.C Current Isc 8.71A
Series Resistance Rs 0.217ohm
Ref. Solar Radiation Sref 1000W/m2
Ref. Temperature Tref 300k
PV
I 1
D
I I
V
Figure 1. PV cell equivalent circuit Figure 2. PV voltage (in volts)
Figure 3. PV current (in amps)
Figure 4. PV power (in watts)
3. Int J Pow Elec & Dri Syst ISSN: 2088-8694
Harmonic stability analysis of multi-paralleled 3-phase PV inverters tied to grid (R.S. Ravi Sankar)
785
3. MODELING OF INVERTER OUTPUT ADMITTANCE
3.1. Calculation of inverter output admittance
The small signal modeling of grid connected inverter is shown in Figure 5. in that PV inverter is tied
to the grid, for filtering purpose LCL filter is used. The overall system is represented in block diagrame in
Figure 6. In this work PR current controller is taken as current controller [19], [20].
-
+
Figure 5. 1-Ph. depication of system
+
-
+
-
Figure 6. Block diagrame of the system
Where ( c
G ) Current controller, ( d
G ) delay gain and ( PWM
K ) PWM gain are defined as [21], [22]:
1
)
( K
s
GC = ,
s
T
d
S
e
s
G 5
.
1
)
( −
= , 1
=
PWM
K (1)
The converter output admittance is defined as ( )
M
d
C
C
Y
G
G
Y
s
Y
+
=
1
0 (2)
The output admittance of LCL filter is given by
)
(
1
)
( 2
2
0 g
f
g
f
f
f
f
v
PCC
g
o
L
L
L
L
C
s
s
L
C
s
v
i
s
Y
M
+
+
+
=
−
=
=
(3)
The trans admittance of the LCL filter is given by
)
(
1
)
( 2
0 g
f
g
f
f
v
M
g
M
L
L
L
L
C
s
s
v
i
s
Y
PCC
+
+
=
=
=
(4)
Finally, the converter admittance is given by
4. ISSN: 2088-8694
Int J Pow Elec & Dri Syst, Vol. 12, No. 2, June 2021 : 783 – 792
786
s
T
g
f
g
f
f
f
f
M
d
c
O
i
PCC
g
C S
g
Ke
L
L
s
L
L
C
s
L
C
s
Y
G
G
Y
v
i
s
Y 5
.
1
3
2
0 )
(
1
1
)
( −
= +
+
+
+
=
+
=
=
(5)
Here K1 -Gain of controller, s
T - sampling time, g
i -Grid current, VM, VPCC -converter output voltage, PCC
voltages, Lf, Lg - filter inductance value inverter side and grid side.
3.2. Proportional resonant current controller:
A proportional resonant (PR) controller exhibits a better steady state and dynamic performance.
Input- output relation of an ideal PR controller is expressed by (6) [22], [23]. In the same way, for a non-ideal
PR Controller it is given by (7) [24]:
Ideal proportional resonant controller:
2
2
2
)
(
+
+
=
s
s
K
K
s
G r
P
PR
(6)
Non- ideal PR controller: 2
c
2
c
r
P
PR
s
2
s
s
K
2
K
)
s
(
G
+
+
+
= (7)
3.3. Harmonic stability analysis of multilevel inverters tied to the grid
The block diagram of overall system is shown in Figure 8 and its corresponding Matlab-Simulink
diagram is presented in Figure 9. A capacitor bank of 12μF is connected parallel at PCC. Grid specifications
are taken as 400V, 50Hz and impedance 𝑍𝑔 = (0.1 + 𝑗400) 𝛺. A PR controller is used to drive the inverter
and an LCL filter is used to improve the quality of grid current [25]-[28]. PWM technique is implemented to
produce switching pulses to converter. Specifications and parameters of the five inverters are stated in
Table 2.
PV Array
With
MPPT
3-Ø
Inverter-I
Grid
PR Current
Controller
LCL-Filter
PV Array
With
MPPT
3-Ø
Inverter-III
LCL-Filter
PR Current
Controller
PV Array
With
MPPT
3-Ø
Inverter-IV LCL-Filter
PR Current
Controller
PV Array
With
MPPT
3-Ø
Inverter-V LCL-Filter
PR Current
Controller
PV Array
With
MPPT
3-Ø
Inverter-II
LCL-Filter
PR Current
Controller
*
1
R
i
*
2
R
i
*
3
R
i
*
4
R
i
*
5
R
i
400 V,
50HZ
3-Ø AC SUPPLY
Figure 8. Five PV arrays tied to grid
5. Int J Pow Elec & Dri Syst ISSN: 2088-8694
Harmonic stability analysis of multi-paralleled 3-phase PV inverters tied to grid (R.S. Ravi Sankar)
787
Figure 9. Single line diagram of a PV inverter tied to grid
Table 2. System specifications
Inverters Parameters INV.1 INV.2 INV.3 INV.4 INV.5
Rating KVA 5.6 3.5 10.5 4.2 7
Switching frequency KHz 10 10 15 10
DC Voltage 600V
Filter Values
Lf [mH] 20 22 24 25 15
Cf[μf]/rd 22/0.2 15/0.4 2/7 3/42 15/0.9
Lg[mH] 0.22 0.3 1.7 1.3 0.2
Parasitic Values
rLf[mH] 11.4 15.7 66.8 49.7 10
rCf[mf] 7.5 11 21.5 14.5 11
rLg[mΩ] 2.9 3.9 22.3 17 2.5
Control Gain
Kp 5.6 8.05 28.8 16.6 5.6
KI 1000 1500 1500 1000 1000
The expression for source admittance is given in the (8).
S
S
SG
sL
R
Y
+
=
1
(8)
where 𝑅𝑆-Grid resistance, 𝐿𝑆-Grid inductance
The expression for source admittance is depicated in (9)
5
4
3
2
1 CL
CL
CL
CL
CL
CPFC
LG Y
Y
Y
Y
Y
SY
Y +
+
+
+
+
= (9)
where 𝑌𝐶𝑃𝐹𝐶 denotes the admittance of capacitor CPFC, minor loop gain 𝑇𝑀𝐺 is obtained as:
𝑌𝐿𝐺 = 𝑌𝐶𝐹𝑃𝐶 + ∑ 𝑌𝐶𝐿𝑋
5
1 , 𝑇𝑀𝐺 =
𝑌𝑀𝐺
𝑌𝐿𝐺
(10)
The minor loop gain (TMG) is highly depending on the load admittance given by (10). In this study,
load impedance is assumed to be constant. It means that all 5 inverters are tied to the grid and grid inductance
is varied from 1mH to 1000mH, with the grid resistance constant. If the MLG of the overall system obeys the
Nyquist stability criteria for different values of grid impedance, then the system is harmonically stable,
otherwise overall system is said to be unstable.
PV
V
a
b
c
PLL
+
-
M
v f
L g
L
Lf
r Lg
r
Cf
r
f
C
d
R
g
i
i
CB PCC
v
0
abc
*
g
i
+
-
i
+ 2
0
2
+
s
s
KI
P
K
0
2
1
dc
v
num
den
abc
Limiter
s
TS
e 5
.
1
−
PWM
*
i
6. ISSN: 2088-8694
Int J Pow Elec & Dri Syst, Vol. 12, No. 2, June 2021 : 783 – 792
788
4. SIMULATION RESULTS AND DISCUSSION
Two different case studies are considered to examine the harmonic stability analysis with the above
defined system parameters given in Table 2, where five PV inverters are tied to the grid. In first case study,
grid impedance is variable and load impedance is constant. In the second case study, load impedance are
variable and grid impedance is constant at 𝑍𝑔 = (0.1 + 𝑗400) 𝛺.
4.1. Case study 1: Constant grid resistance and varying grid inductance
4.1.1. Grid inductance up to 5mH
Here grid resistance is kept constant and grid inductance is varied. The system becomes stable upto
LS = 5mH. In this case all the 5 inverters are tied to grid. The grid iducatance 𝐿𝑆 = 5𝑚𝐻, total grid current
is 44A. Nyquist Plot of the minor loop gain and the simulation results of THD of grid current, grid curent
wave form, individual individual inverter currents, %THD of the grid currents for the overal system are
shown in Figure 10 to Figure 13. respectively.
Figure 10. Nyquist plot of minor loop gain Figure 11. THD analysis of the grid current with grid
inducatane upto 5mH
Figure 12. Grid current (in Amp) Figure 13. Individual inverter currents (in Amp)
4.1.2. Grid inductance more than 5mH
This case is used to illustrate when the grid inductance (LS) is more than 5mH. The overall system
becomes unstable. Nyquist Plot of minor loop gain with gird inductance value 𝐿𝑆 = 6𝑚𝐻 is shown in
Figure 14. %THD of the grid current, Grid current and inverter currents are shown in Figure 15, 16, 17
respectively.
7. Int J Pow Elec & Dri Syst ISSN: 2088-8694
Harmonic stability analysis of multi-paralleled 3-phase PV inverters tied to grid (R.S. Ravi Sankar)
789
Figure 14. Nyquist plot of minor loop gain with
mH
Ls 6
=
Figure 15. THD response of the grid current
Figure 16. Grid current (Amp) Figure 17. Individual inverter currents (Amp)
4.2. Case study 2: Constant grid impedance with varying load admittance
In in practical suitutions there is is possibility of change in load admittance will changes de to te
disconnection inverter from grid. Thereby affects the overall system stability. To analyze this situation when
INVs are removed from the grid, two cases are considered. In first case, INV 1 is removed and in case B
INVs 1, 5 are removed. The constant grid impedance is 𝑍𝑔 = (0.1 + 𝑗400) and the reference is INV 1 given
in (11).
1
CL
SA Y
Y = (11)
Calculation for MLG in this case is given in (13).
5
CL
4
CL
3
CL
2
CL
CPFC
G
LA Y
Y
Y
Y
Y
Y
Y +
+
+
+
+
= (12)
Minor loop gain of the system
LA
SA
MA
Y
Y
T = (13)
In First case, the INV 2, INV 3, INV4, and INV 5 are injecting the currents of 8A, 5A, 15A, and 6A
respectively into grid. So total grid current 34A. Nyquist plot of MLG of the system is depicated in Figure
18. From IBSC, it is concluded that the system is stable. The quality of the grid current is 2.37% as illustrated
in Figure 19. Total grid current and individual inverter currents are shown in Figure 20 and Figure 21
respectively.
8. ISSN: 2088-8694
Int J Pow Elec & Dri Syst, Vol. 12, No. 2, June 2021 : 783 – 792
790
Figure 18. Nyquist plot of system INV -1 OFF Figure 19. THD response of the grid current
Figure 20. Grid current (Amp) Figure 21. Individual inverter currents (Amp)
In this case INV 1 & INV5 are disconnected from grid. Nyquist plot of MLG of the system is given
in Figure 22. From IBSC, the system is stable. The Quality of the grid current is given in Figure 23. Grid
current and individual inverter currents are shown in Figure 24 and Figure 25 respectively.
.
Figure 22. Nyquist plot of INV 1 & 5 are
disconnected
Figure 23. THD response of the grid current
Figure 24. Grid current (Amp) Figure 25. Individual grid current (Amp)
9. Int J Pow Elec & Dri Syst ISSN: 2088-8694
Harmonic stability analysis of multi-paralleled 3-phase PV inverters tied to grid (R.S. Ravi Sankar)
791
5. CONCLUSION
In this work, investigation of harmonic Stability of multiple PV fed 3-Ø INV is tied to grid is
confirmed by new impedance based stability criterion (IBSC). Stability of the system is investigated by
varying the grid inductance with constant grid resistance and also by varying load impedance and
maintaining grid inductance constant. It was observed that overall system is stable up to grid inductance of
5mH and above this value, the system becomes unstable. It is also demonstrated that stability of the system
depends on grid impedance only and does not depend on load impedance. It is substantiated by means of
graphical analysis and Matlab Simulations.
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BIOGRAPHIES OF AUTHORS
Dr. R.S. Ravi Sankar Currently working as Associate Professor in the department of EEE in
Vignan’s Institute of InformationTechnology, Visakhapatnam, Andhra Pradesh, India. Received
his Bachelors, Masters and Doctoral degree from Institution of Engineers, JNTU Hyderabad,
JNTUA Ananthapuram. His research interests include power quality in distribution systems,
Renewable energy Sources, electric drives.
K.K. Deepika is currently pursuing her Ph. D. degree in Electrical Engineering at KLEF,
Vijayawada, Andhra Pradesh, India. She is working as Assistant Professor in the Department of
EEE in Vignan’s Institute of InformationTechnology, Visakhapatnam, Andhra Pradesh, India.
Her research interests include power quality in distribution systems, Renewable energy Sources
and Demand Side Management.
AV Satyanarayana is currently working as Assistant Professor in the Department of EEE in
Vignan’s Institute of InformationTechnology, Visakhapatnam, Andhra Pradesh, India. Received
his Bachelors, Masters and Doctoral degree from Institution JNTU Kainaa. His research interests
include Renewable energy Sources, electric vehicles, optimization techniques.