The optical storage microgrid system composed of power electronic converters is a small inertia system.Load switching and power supply intermittent will affect the stability of the direct current(DC)bus voltage.Aiming...The optical storage microgrid system composed of power electronic converters is a small inertia system.Load switching and power supply intermittent will affect the stability of the direct current(DC)bus voltage.Aiming at this problem,a virtual inertia optimal control strategy applied to optical storage microgrid is proposed.Firstly,a small signal model of the system is established to theoretically analyze the influence of virtual inertia and damping coefficient on DC bus voltage and to obtain the constraint range of virtual inertia and damping coefficient;Secondly,aiming at the defect that the Sailfish optimization algorithm is easy to premature maturity,a Sailfish optimization algorithm based on the leak-proof net and the cross-mutation propagation mechanism is proposed;Finally,the virtual inertia and damping coefficient of the system are optimized by the improved Sailfish algorithm to obtain the best control parameters.The simulation results in Matlab/Simulink show that the virtual inertia control optimized by the improved Sailfish algorithm improves the system inertia as well as the dynamic response and robustness of the DC bus voltage.展开更多
Renewable energy sources, such as photovoltaic wind turbines, and wave power converters, use power converters to connect to the grid which causes a loss in rotational inertia. The attempt to meet the increasing energy...Renewable energy sources, such as photovoltaic wind turbines, and wave power converters, use power converters to connect to the grid which causes a loss in rotational inertia. The attempt to meet the increasing energy demand means that the interest for the integration of renewable energy sources in the existing power system is growing, but such integration poses challenges to the operating stability. Power converters play a major role in the evolution of power system towards SmartGrids, by regulating as virtual synchronous generators. The concept of virtual synchronous generators requires an energy storage system with power converters to emulate virtual inertia similar to the dynamics of traditional synchronous generators. In this paper, a dynamic droop control for the estimation of fundamental reference sources is implemented in the control loop of the converter, including active and reactive power components acting as a mechanical input to the virtual synchronous generator and the virtual excitation controller. An inertia coefficient and a droop coefficient are implemented in the control loop. The proposed controller uses a current synchronous detection scheme to emulate a virtual inertia from the virtual synchronous generators. In this study, a wave energy converter as the power source is used and a power management of virtual synchronous generators to control the frequency deviation and the terminal voltage is implemented. The dynamic control scheme based on a current synchronous detection scheme is presented in detail with a power management control. Finally, we carried out numerical simulations and verified the scheme through the experimental results in a microgrid structure.展开更多
Implementation of large virtual inertia with high stability margin is a significant challenge for DC microgrid systems.In this paper,a filter time constant,a new degree of freedom,is utilized to enhance voltage loop s...Implementation of large virtual inertia with high stability margin is a significant challenge for DC microgrid systems.In this paper,a filter time constant,a new degree of freedom,is utilized to enhance voltage loop stability and its relationship with virtual inertia and stability margin is further explored.Then,the virtual resistance concept is introduced as an intuitive design parameter to decouple stability margin from virtual inertia.In this way,large virtual inertia can be realized in a simple and practical way,making it easy to be emulated quantitatively and applied in engineering practice.Moreover,performance analysis of virtual resistance is conducted,which suggests virtual resistance with proper value brings little effect on its dynamic response while greatly enhances stability margin.Finally,the proposed decoupling method is validated in both simulation and experiment.展开更多
Most permanent magnet synchronous generator(PMSG)based wind generation systems currently employ grid-following control,relying on a phase-locked loop(PLL)for grid connection.However,it leads to a lack of inertia suppo...Most permanent magnet synchronous generator(PMSG)based wind generation systems currently employ grid-following control,relying on a phase-locked loop(PLL)for grid connection.However,it leads to a lack of inertia support in the system.To address this,the virtual inertia control(VIC)is crucial for improvement,yet it introduces potential instability due to torsional oscillation interaction with PLL and low-frequency oscillations,which is an underexplored area.This paper presents a comprehensive analysis of the grid-connected PMSG-based wind generation system.It confirms the necessity of employing a full-order model for studying stability on the quasi-electromechanical timescale(QET)by a comparison with the reduced-order model.Then,a comprehensive modal analysis is conducted to analyze the effect of VIC parameters,shaft inertia time constant,PLL parameters,and torsional oscillation damping(TOD)controller gain on the interaction of QET oscillations under two typical control strategies.The occurrence of interaction and mode conversion is observed when the oscillation frequency and root loci of the torsional,PLL,and low-frequency oscillations are close.Finally,a theoretical analysis is validated via simulation verification in Simulink.These findings offer a valuable guidance for industrial PMSG applications considering VIC.展开更多
Virtual synchronous generator(VSG)simulates the first-order motion equation of a synchronous generator(SG)with the algorithm.VSG can improve the system voltage and frequency support capabilities of a microgrid or a we...Virtual synchronous generator(VSG)simulates the first-order motion equation of a synchronous generator(SG)with the algorithm.VSG can improve the system voltage and frequency support capabilities of a microgrid or a weak grid.It is now widely applied at a high penetration level of distributed generation(DG)systems.However,because there is a contradiction between active power steady-state deviation of VSG and dynamic impact regulation,the VSG running in grid-connected mode with existing strategies cannot meet the steady and dynamic control requirements.Thus,an improved virtual inertial control strategy of VSG is proposed in this paper.The active power impact is reduced effectively under the circumstance of damping coefficient Dωequal to 0 and a large inertia,thus the dynamic characteristic of active power is improved and its steady-state characteristic is maintained.Firstly,based on the analysis of the damping coefficient effect on the system dynamic process,two forms of improved virtual inertia algorithms are put forward by cascading a differential link into different positions of the first-order virtual inertia forward channel.Then,by comparing the characteristics of the system with the two improved algorithms,the improved virtual inertial strategy based on differential compensation is proven to be better,and the design of its parameters is analyzed.Finally,simulation and experimental results verify the effectiveness of the proposed algorithm.展开更多
With the rapid development of inverter-based generators(IGs),power grid is faced with critical frequency stability challenges because the existing IGs have no inertia.To equip IGs with inertial response,researchers ha...With the rapid development of inverter-based generators(IGs),power grid is faced with critical frequency stability challenges because the existing IGs have no inertia.To equip IGs with inertial response,researchers have proposed several virtual inertia control methods,which can be classified into two categories:virtual synchronous generator(VSG)control and droop control based on rate of change of frequency(ROCOFdroop control).In this paper,the comparison between both virtual inertia control methods is conducted from three perspectives:mathematical model,output characteristic and small-signal stability.State-space models are firstly built to analyze the control mechanism of VSG control and ROCOF-droop control methods.Simulation and eigenvalue analysis are conducted to study the transient responses and oscillation characteristics of both methods,which is helpful to understand the advantages and limitations of existing virtual inertia control methods.Finally,the obtained theoretical results are validated through realtime laboratory(RT-LAB)hardware-in-loop simulation platform.展开更多
As conventional synchronous generators are replaced by large-scale converter-interfaced renewa-ble-energy sources(RESs),the electric power grid en-counters the challenge of low rotational inertia.Conse-quently,system ...As conventional synchronous generators are replaced by large-scale converter-interfaced renewa-ble-energy sources(RESs),the electric power grid en-counters the challenge of low rotational inertia.Conse-quently,system frequency deviation is exacerbated and system instability may occur when the frequency deviates beyond the acceptable range.To mitigate this effect,this study proposes a virtual inertia control(VIC)strategy based on a fractional-order derivative and controller parameter-tuning method.The tuning method uses the stability boundary locus and provides a stability criterion for identifying the stability region in the parameter space.The controller parameters are then optimized within the identified stability region to suppress frequency deviation and enhance system robustness.The proposed controller and tuning method is applied to a battery energy-storage system(BESS)in a low-inertia power system with the integration of RESs.Time-domain simulations are carried out to verify the stability region and compare the per-formance of the optimized proposed controller to that of the traditional integral-order controller.The simulation results show that the stability-analysis method is effective and that the fractional-order VIC,tuned with the pro-posed method,outperforms the traditional method in both frequency-regulation performance and parametric robustness.展开更多
Doubly-fed induction generator(DFIG)-based wind farms(WFs)are interfaced with power electronic converters.Such interfaces are attributed to the low inertia generated in the WFs under high penetration and that becomes ...Doubly-fed induction generator(DFIG)-based wind farms(WFs)are interfaced with power electronic converters.Such interfaces are attributed to the low inertia generated in the WFs under high penetration and that becomes prevalent in a fault scenario.Therefore,transient stability enhancement along with frequency stability in DFIG-based WFs is a major concern in the present scenario.In this paper,a cooperative approach consisting of virtual inertia control(VIC)and a modified grid-side converter(GSC)approach for low voltage ride-through(LVRT)is proposed to achieve fault ride-through(FRT)capabilities as per the grid code requirements(GCRs)while providing frequency support to the grid through a synthetic inertia.The proposed approach provides LVRT and reactive power compensation in the system.The participation of the VIC in a rotor-side converter(RSC)provides frequency support to the DFIG-based WFs.The combined approach supports active power compensation and provides sufficient kinetic energy support to the system in a contingency scenario.Simulation studies are carried out in MATLAB/Simulink environment for symmetrical and unsymmetrical faults.The superiority of the proposed scheme is demonstrated through analysis of the performance of the scheme and that of a series resonance bridge-type fault current limiter(SR-BFCL).展开更多
Wind energy systems (WESs) based on doubly-fed induction generators (DFIGs) have enormous potential for meeting the future demands related to clean energy. Due to the low inertia and intermittency of power injection, ...Wind energy systems (WESs) based on doubly-fed induction generators (DFIGs) have enormous potential for meeting the future demands related to clean energy. Due to the low inertia and intermittency of power injection, a WES is equipped with a virtual inertial controller (VIC) to support the system during a frequency deviation event. The frequency deviation measured by a phase locked loop (PLL) installed on a point of common coupling (PCC) bus is the input signal to the VIC. However, a VIC with an improper inertial gain could deteriorate the damping of the power system, which may lead to instability. To address this issue, a mathematical formulation for calculating the synchronizing and damping torque coefficients of a WES-integrated single-machine infinite bus (SMIB) system while considering PLL and VIC dynamics is proposed in this paper. In addition, a power system stabilizer (PSS) is designed for wind energy integrated power systems to enhance electromechanical oscillation damping. A small-signal stability assessment is performed using the infinite bus connected to a synchronous generator of higher-order dynamics integrated with a VIC-equipped WES. Finally, the performance and robustness of the proposed PSS is demonstrated through time-domain simulation in SMIB and nine-bus test systems integrated with WES under several case studies.展开更多
In this paper,inspired by the concept of virtual inertia in alternating current(AC)systems,a virtual impedance controller is proposed for the dynamic improvement of direct current microgrids(DCMGs).A simple and inexpe...In this paper,inspired by the concept of virtual inertia in alternating current(AC)systems,a virtual impedance controller is proposed for the dynamic improvement of direct current microgrids(DCMGs).A simple and inexpensive method for injecting inertia into the system is used to adjust the output power of each distributed generation unit without using additional equipment.The proposed controller consists of two components:a virtual capacitor and a virtual inductor.These virtual components can change the rate of change of the DC bus voltage and also improve the transient response.A small-signal analysis is carried out to verify the impact of the proposed control strategy.Numerical simulation studies validate the effectiveness of the proposed solution for increasing the inertia of DCMGs.展开更多
A modern power system is expected to consist primarily of renewables,which either lack or have less rotating masses(i.e.,source of inertia)compared to the traditional generation sources.However,the growth of renewable...A modern power system is expected to consist primarily of renewables,which either lack or have less rotating masses(i.e.,source of inertia)compared to the traditional generation sources.However,the growth of renewables generation,based on power electronics,can substantially decrease the inertia levels of renewable power grids,which can create several frequency stability issues,resulting in power system degradation.To address this issue,this paper presents a recent virtual inertia scheme predicated on electric vehicles(EVs)to mimic the necessary inertia power in low-inertia smart hybrid power systems(SHPSs),thus regulating the system frequency and avoiding system instability.Moreover,to guarantee robust performance and more stability for SHPSs against multiple perturbations,system uncertainties,and physical constraints,this paper also proposes a robust control strategy relying on a coefficient diagram method(CDM)for the load frequency control(LFC)of SHPSs considering high renewables penetration and EVs.The efficacy of the proposed system(i.e.,robust LFC with the proposed VIC strategy)is validated by comparison with a conventional LFC with/without the proposed VIC system.In addition,the simulation outcomes show that the proposed system can considerably support smart low-inertia hybrid power systems for many different contingencies.展开更多
The power-electronics-based DC microgrid system composed of new energy sources in railway field has low inertia,weak damping characteristics,and the voltage fluctuation microgrid systems caused by the power disturbanc...The power-electronics-based DC microgrid system composed of new energy sources in railway field has low inertia,weak damping characteristics,and the voltage fluctuation microgrid systems caused by the power disturbance of solar.In order to improve the inertia of the DC microgrid system,a virtual DC generator technology is adopted in the interface converter of photovoltaic(PV)power generation unit,so that it has the external characteristics of DC generator.However,the influence of PV maximum power point tracking(MPPT)is not considered in the traditional virtual DC generator control.Therefore,an improved control strategy for virtual DC generator is proposed,and its small signal model is established to analyze the influence of inertia and damping coefficient on stability.The results show that the proposed method effectively weakens the impact on DC bus voltage when the output of PV power unit changes suddenly,which improves the stability of the microgrid.Meanwhile,the correctness and feasibility of the method are verified.展开更多
With the increasing penetration of wind power,using wind turbines to participate in the frequency regulation to support power system has become a clear consensus.To accurately quantify the inertia provided by the doub...With the increasing penetration of wind power,using wind turbines to participate in the frequency regulation to support power system has become a clear consensus.To accurately quantify the inertia provided by the doubly-fed induction generator(DFIG)based wind farm,the frequency response model of DFIG with additional frequency control is established,and then by using Routh approximation,the explicit expression of the virtual moment of inertia is derived for the DFIG gridconnected system.To further enhance the availability of the expression,an estimation method is proposed based on the matrix pencil method and the least squares algorithm for estimating the virtual moment of inertia provided by the wind farm.Finally,numerical results tested by a DFIG grid-connected system and a modified IEEE 30-bus system verify the derived expression of the virtual moment of inertia and the proposed estimation method.展开更多
In recent years, the penetration of renewable energy sources (RES) is increasing due to energy and environmental issues, causing several problems in the power system. These problems are usually more apparent in microg...In recent years, the penetration of renewable energy sources (RES) is increasing due to energy and environmental issues, causing several problems in the power system. These problems are usually more apparent in microgrids. One of the problems that could arise is frequency stability issue due to lack of inertia in microgrids. Lack of inertia in such system can lead to system instability when a large disturbance occurs in the system. To solve this issue, providing inertia support to the microgrids by a virtual synchronous generator (VSG) utilizing energy storage system is a promising method. In applying VSG, one important aspect is regarding the set value of the active power output from the VSG. The amount of allocated active power during normal operation should be determined carefully so that the frequency of microgrids could be restored to the allowable limits, as close as possible to the nominal value. In this paper, active power allocation of VSG using particle swarm optimization (PSO) is presented. The results show that by using VSG supported by active power allocation determined by the method, frequency stability and dynamic stability of the system could be improved.展开更多
随着柔性直流(direct current,DC)异步互联工程相继推进,高水电占比高带来的超低频振荡问题威胁着电力系统频率的稳定。针对超低频振荡现象的发生,提出基于柔性直流输电即电压源换流器的高压直流输电(voltage source converter based hi...随着柔性直流(direct current,DC)异步互联工程相继推进,高水电占比高带来的超低频振荡问题威胁着电力系统频率的稳定。针对超低频振荡现象的发生,提出基于柔性直流输电即电压源换流器的高压直流输电(voltage source converter based high voltage direct current transmission,VSC-HVDC)系统的附加频率控制策略。首先,构建含水电、火电机组的频率响应模型,通过阻尼转矩分析揭示超低频振荡产生机理,明确各类调速器参数以及不同水电占比对系统超低频振荡发生的影响;随后,根据直流电容电压与交流系统频率耦合特性,对换流站参与抑制超低频振荡机理进行研究,提出换流站虚拟惯性与V_(DC)-f下垂的控制方式,并通过约束条件对虚拟惯性与下垂参数进行设计;最后,基于MATLAB/SIMULINK平台搭建含水电、火电机组的负荷频率控制模型,通过对比水轮机参数优化方法验证所提方法的有效性。展开更多
基金the National Natural Science Foundation of China(52177184)。
文摘The optical storage microgrid system composed of power electronic converters is a small inertia system.Load switching and power supply intermittent will affect the stability of the direct current(DC)bus voltage.Aiming at this problem,a virtual inertia optimal control strategy applied to optical storage microgrid is proposed.Firstly,a small signal model of the system is established to theoretically analyze the influence of virtual inertia and damping coefficient on DC bus voltage and to obtain the constraint range of virtual inertia and damping coefficient;Secondly,aiming at the defect that the Sailfish optimization algorithm is easy to premature maturity,a Sailfish optimization algorithm based on the leak-proof net and the cross-mutation propagation mechanism is proposed;Finally,the virtual inertia and damping coefficient of the system are optimized by the improved Sailfish algorithm to obtain the best control parameters.The simulation results in Matlab/Simulink show that the virtual inertia control optimized by the improved Sailfish algorithm improves the system inertia as well as the dynamic response and robustness of the DC bus voltage.
基金Swedish Research Council(VR)STandUP for Energy,MaRINET2 and Erasmus Mundus(EMINTE)Ph.D.Scholarship for the support of the work
文摘Renewable energy sources, such as photovoltaic wind turbines, and wave power converters, use power converters to connect to the grid which causes a loss in rotational inertia. The attempt to meet the increasing energy demand means that the interest for the integration of renewable energy sources in the existing power system is growing, but such integration poses challenges to the operating stability. Power converters play a major role in the evolution of power system towards SmartGrids, by regulating as virtual synchronous generators. The concept of virtual synchronous generators requires an energy storage system with power converters to emulate virtual inertia similar to the dynamics of traditional synchronous generators. In this paper, a dynamic droop control for the estimation of fundamental reference sources is implemented in the control loop of the converter, including active and reactive power components acting as a mechanical input to the virtual synchronous generator and the virtual excitation controller. An inertia coefficient and a droop coefficient are implemented in the control loop. The proposed controller uses a current synchronous detection scheme to emulate a virtual inertia from the virtual synchronous generators. In this study, a wave energy converter as the power source is used and a power management of virtual synchronous generators to control the frequency deviation and the terminal voltage is implemented. The dynamic control scheme based on a current synchronous detection scheme is presented in detail with a power management control. Finally, we carried out numerical simulations and verified the scheme through the experimental results in a microgrid structure.
基金supported in part by the National Key Research and Development Program of China under Grant 2022YFE0101900in part by the National Natural Science Foundation of China under Grant 52107214in part by the Provincial Key Research and Development Program of Inner Mongolia under Grant 2021D0026.
文摘Implementation of large virtual inertia with high stability margin is a significant challenge for DC microgrid systems.In this paper,a filter time constant,a new degree of freedom,is utilized to enhance voltage loop stability and its relationship with virtual inertia and stability margin is further explored.Then,the virtual resistance concept is introduced as an intuitive design parameter to decouple stability margin from virtual inertia.In this way,large virtual inertia can be realized in a simple and practical way,making it easy to be emulated quantitatively and applied in engineering practice.Moreover,performance analysis of virtual resistance is conducted,which suggests virtual resistance with proper value brings little effect on its dynamic response while greatly enhances stability margin.Finally,the proposed decoupling method is validated in both simulation and experiment.
基金supported by the National Key R&D Program of China(No.2022YFB2402800).
文摘Most permanent magnet synchronous generator(PMSG)based wind generation systems currently employ grid-following control,relying on a phase-locked loop(PLL)for grid connection.However,it leads to a lack of inertia support in the system.To address this,the virtual inertia control(VIC)is crucial for improvement,yet it introduces potential instability due to torsional oscillation interaction with PLL and low-frequency oscillations,which is an underexplored area.This paper presents a comprehensive analysis of the grid-connected PMSG-based wind generation system.It confirms the necessity of employing a full-order model for studying stability on the quasi-electromechanical timescale(QET)by a comparison with the reduced-order model.Then,a comprehensive modal analysis is conducted to analyze the effect of VIC parameters,shaft inertia time constant,PLL parameters,and torsional oscillation damping(TOD)controller gain on the interaction of QET oscillations under two typical control strategies.The occurrence of interaction and mode conversion is observed when the oscillation frequency and root loci of the torsional,PLL,and low-frequency oscillations are close.Finally,a theoretical analysis is validated via simulation verification in Simulink.These findings offer a valuable guidance for industrial PMSG applications considering VIC.
基金supported by the Natural Science Foundation of Anhui Province of China(No.1908085QE208,No.1808085QE156)the 2018 Academic Foundation Program for the Major’s Talents of Anhui Colleges and Universities(No.GXBJZD40)。
文摘Virtual synchronous generator(VSG)simulates the first-order motion equation of a synchronous generator(SG)with the algorithm.VSG can improve the system voltage and frequency support capabilities of a microgrid or a weak grid.It is now widely applied at a high penetration level of distributed generation(DG)systems.However,because there is a contradiction between active power steady-state deviation of VSG and dynamic impact regulation,the VSG running in grid-connected mode with existing strategies cannot meet the steady and dynamic control requirements.Thus,an improved virtual inertial control strategy of VSG is proposed in this paper.The active power impact is reduced effectively under the circumstance of damping coefficient Dωequal to 0 and a large inertia,thus the dynamic characteristic of active power is improved and its steady-state characteristic is maintained.Firstly,based on the analysis of the damping coefficient effect on the system dynamic process,two forms of improved virtual inertia algorithms are put forward by cascading a differential link into different positions of the first-order virtual inertia forward channel.Then,by comparing the characteristics of the system with the two improved algorithms,the improved virtual inertial strategy based on differential compensation is proven to be better,and the design of its parameters is analyzed.Finally,simulation and experimental results verify the effectiveness of the proposed algorithm.
基金supported by the technology project of State Grid Corporation of China and the technology project of State Grid Jibei Electric Power Corporation
文摘With the rapid development of inverter-based generators(IGs),power grid is faced with critical frequency stability challenges because the existing IGs have no inertia.To equip IGs with inertial response,researchers have proposed several virtual inertia control methods,which can be classified into two categories:virtual synchronous generator(VSG)control and droop control based on rate of change of frequency(ROCOFdroop control).In this paper,the comparison between both virtual inertia control methods is conducted from three perspectives:mathematical model,output characteristic and small-signal stability.State-space models are firstly built to analyze the control mechanism of VSG control and ROCOF-droop control methods.Simulation and eigenvalue analysis are conducted to study the transient responses and oscillation characteristics of both methods,which is helpful to understand the advantages and limitations of existing virtual inertia control methods.Finally,the obtained theoretical results are validated through realtime laboratory(RT-LAB)hardware-in-loop simulation platform.
基金supported by the Science and Technology Project of State Grid Corporation of China(No.5419-202199551A-0-5-ZN)the Joint Funds of the National Natural Science Foundation of China(No.U22A6007)the National Excellent Youth Science Fund Project of National Natural Science Foundation of China(No.52222703).
文摘As conventional synchronous generators are replaced by large-scale converter-interfaced renewa-ble-energy sources(RESs),the electric power grid en-counters the challenge of low rotational inertia.Conse-quently,system frequency deviation is exacerbated and system instability may occur when the frequency deviates beyond the acceptable range.To mitigate this effect,this study proposes a virtual inertia control(VIC)strategy based on a fractional-order derivative and controller parameter-tuning method.The tuning method uses the stability boundary locus and provides a stability criterion for identifying the stability region in the parameter space.The controller parameters are then optimized within the identified stability region to suppress frequency deviation and enhance system robustness.The proposed controller and tuning method is applied to a battery energy-storage system(BESS)in a low-inertia power system with the integration of RESs.Time-domain simulations are carried out to verify the stability region and compare the per-formance of the optimized proposed controller to that of the traditional integral-order controller.The simulation results show that the stability-analysis method is effective and that the fractional-order VIC,tuned with the pro-posed method,outperforms the traditional method in both frequency-regulation performance and parametric robustness.
文摘Doubly-fed induction generator(DFIG)-based wind farms(WFs)are interfaced with power electronic converters.Such interfaces are attributed to the low inertia generated in the WFs under high penetration and that becomes prevalent in a fault scenario.Therefore,transient stability enhancement along with frequency stability in DFIG-based WFs is a major concern in the present scenario.In this paper,a cooperative approach consisting of virtual inertia control(VIC)and a modified grid-side converter(GSC)approach for low voltage ride-through(LVRT)is proposed to achieve fault ride-through(FRT)capabilities as per the grid code requirements(GCRs)while providing frequency support to the grid through a synthetic inertia.The proposed approach provides LVRT and reactive power compensation in the system.The participation of the VIC in a rotor-side converter(RSC)provides frequency support to the DFIG-based WFs.The combined approach supports active power compensation and provides sufficient kinetic energy support to the system in a contingency scenario.Simulation studies are carried out in MATLAB/Simulink environment for symmetrical and unsymmetrical faults.The superiority of the proposed scheme is demonstrated through analysis of the performance of the scheme and that of a series resonance bridge-type fault current limiter(SR-BFCL).
文摘Wind energy systems (WESs) based on doubly-fed induction generators (DFIGs) have enormous potential for meeting the future demands related to clean energy. Due to the low inertia and intermittency of power injection, a WES is equipped with a virtual inertial controller (VIC) to support the system during a frequency deviation event. The frequency deviation measured by a phase locked loop (PLL) installed on a point of common coupling (PCC) bus is the input signal to the VIC. However, a VIC with an improper inertial gain could deteriorate the damping of the power system, which may lead to instability. To address this issue, a mathematical formulation for calculating the synchronizing and damping torque coefficients of a WES-integrated single-machine infinite bus (SMIB) system while considering PLL and VIC dynamics is proposed in this paper. In addition, a power system stabilizer (PSS) is designed for wind energy integrated power systems to enhance electromechanical oscillation damping. A small-signal stability assessment is performed using the infinite bus connected to a synchronous generator of higher-order dynamics integrated with a VIC-equipped WES. Finally, the performance and robustness of the proposed PSS is demonstrated through time-domain simulation in SMIB and nine-bus test systems integrated with WES under several case studies.
文摘In this paper,inspired by the concept of virtual inertia in alternating current(AC)systems,a virtual impedance controller is proposed for the dynamic improvement of direct current microgrids(DCMGs).A simple and inexpensive method for injecting inertia into the system is used to adjust the output power of each distributed generation unit without using additional equipment.The proposed controller consists of two components:a virtual capacitor and a virtual inductor.These virtual components can change the rate of change of the DC bus voltage and also improve the transient response.A small-signal analysis is carried out to verify the impact of the proposed control strategy.Numerical simulation studies validate the effectiveness of the proposed solution for increasing the inertia of DCMGs.
文摘A modern power system is expected to consist primarily of renewables,which either lack or have less rotating masses(i.e.,source of inertia)compared to the traditional generation sources.However,the growth of renewables generation,based on power electronics,can substantially decrease the inertia levels of renewable power grids,which can create several frequency stability issues,resulting in power system degradation.To address this issue,this paper presents a recent virtual inertia scheme predicated on electric vehicles(EVs)to mimic the necessary inertia power in low-inertia smart hybrid power systems(SHPSs),thus regulating the system frequency and avoiding system instability.Moreover,to guarantee robust performance and more stability for SHPSs against multiple perturbations,system uncertainties,and physical constraints,this paper also proposes a robust control strategy relying on a coefficient diagram method(CDM)for the load frequency control(LFC)of SHPSs considering high renewables penetration and EVs.The efficacy of the proposed system(i.e.,robust LFC with the proposed VIC strategy)is validated by comparison with a conventional LFC with/without the proposed VIC system.In addition,the simulation outcomes show that the proposed system can considerably support smart low-inertia hybrid power systems for many different contingencies.
基金supported by National Natural Science Foundation of China(No.52067013)Natural Science Foundation of Gansu Province(No.20JR5RA395)Tianyou Innovation Team of Lanzhou Jiaotong University(No.TY202010).
文摘The power-electronics-based DC microgrid system composed of new energy sources in railway field has low inertia,weak damping characteristics,and the voltage fluctuation microgrid systems caused by the power disturbance of solar.In order to improve the inertia of the DC microgrid system,a virtual DC generator technology is adopted in the interface converter of photovoltaic(PV)power generation unit,so that it has the external characteristics of DC generator.However,the influence of PV maximum power point tracking(MPPT)is not considered in the traditional virtual DC generator control.Therefore,an improved control strategy for virtual DC generator is proposed,and its small signal model is established to analyze the influence of inertia and damping coefficient on stability.The results show that the proposed method effectively weakens the impact on DC bus voltage when the output of PV power unit changes suddenly,which improves the stability of the microgrid.Meanwhile,the correctness and feasibility of the method are verified.
基金This work was supported in part by the National Science Foundation of China(No.51877015)the Science and Technology Foundation of State Grid Corporation of China(No.SGTYHT/19-JS-215).
文摘With the increasing penetration of wind power,using wind turbines to participate in the frequency regulation to support power system has become a clear consensus.To accurately quantify the inertia provided by the doubly-fed induction generator(DFIG)based wind farm,the frequency response model of DFIG with additional frequency control is established,and then by using Routh approximation,the explicit expression of the virtual moment of inertia is derived for the DFIG gridconnected system.To further enhance the availability of the expression,an estimation method is proposed based on the matrix pencil method and the least squares algorithm for estimating the virtual moment of inertia provided by the wind farm.Finally,numerical results tested by a DFIG grid-connected system and a modified IEEE 30-bus system verify the derived expression of the virtual moment of inertia and the proposed estimation method.
文摘In recent years, the penetration of renewable energy sources (RES) is increasing due to energy and environmental issues, causing several problems in the power system. These problems are usually more apparent in microgrids. One of the problems that could arise is frequency stability issue due to lack of inertia in microgrids. Lack of inertia in such system can lead to system instability when a large disturbance occurs in the system. To solve this issue, providing inertia support to the microgrids by a virtual synchronous generator (VSG) utilizing energy storage system is a promising method. In applying VSG, one important aspect is regarding the set value of the active power output from the VSG. The amount of allocated active power during normal operation should be determined carefully so that the frequency of microgrids could be restored to the allowable limits, as close as possible to the nominal value. In this paper, active power allocation of VSG using particle swarm optimization (PSO) is presented. The results show that by using VSG supported by active power allocation determined by the method, frequency stability and dynamic stability of the system could be improved.
文摘随着柔性直流(direct current,DC)异步互联工程相继推进,高水电占比高带来的超低频振荡问题威胁着电力系统频率的稳定。针对超低频振荡现象的发生,提出基于柔性直流输电即电压源换流器的高压直流输电(voltage source converter based high voltage direct current transmission,VSC-HVDC)系统的附加频率控制策略。首先,构建含水电、火电机组的频率响应模型,通过阻尼转矩分析揭示超低频振荡产生机理,明确各类调速器参数以及不同水电占比对系统超低频振荡发生的影响;随后,根据直流电容电压与交流系统频率耦合特性,对换流站参与抑制超低频振荡机理进行研究,提出换流站虚拟惯性与V_(DC)-f下垂的控制方式,并通过约束条件对虚拟惯性与下垂参数进行设计;最后,基于MATLAB/SIMULINK平台搭建含水电、火电机组的负荷频率控制模型,通过对比水轮机参数优化方法验证所提方法的有效性。
