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
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
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
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
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
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
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
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
电力电子化的直流配电网存在低惯性问题,不利于系统稳定运行。混合储能设备可向电网提供虚拟惯性,但不同类型的储能之间存在功率协调问题,并且储能的荷电状态(state of charge, SOC)对虚拟惯性的调节也有约束作用。针对上述问题,提出了...电力电子化的直流配电网存在低惯性问题,不利于系统稳定运行。混合储能设备可向电网提供虚拟惯性,但不同类型的储能之间存在功率协调问题,并且储能的荷电状态(state of charge, SOC)对虚拟惯性的调节也有约束作用。针对上述问题,提出了一种自适应时间常数的分频控制策略,时间常数根据混合储能系统(hybridenergy storage system, HESS)的SOC而动态调整以改变功率分配。首先,通过分析储能SOC与虚拟惯性的关系,并考虑储能充放电极限问题,研究兼顾SOC、电压变化率以及电压幅值的自适应虚拟惯性控制策略,提高系统惯性。然后,建立控制系统的小信号模型,分析虚拟惯性系数对系统的影响。最后,基于Matlab/Simulink搭建直流配电网仿真模型,验证了所提控制策略能合理分配HESS功率,提高超级电容器利用率,改善直流电压与功率稳定性。展开更多
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.
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.
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 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.
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).
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.
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.
