Virtual synchronous generators(VSGs)are widely introduced to the renewable power generation,the variablespeed pumped storage units,and so on,as a promising gridforming solution.It is noted that VSGs can provide virtua...Virtual synchronous generators(VSGs)are widely introduced to the renewable power generation,the variablespeed pumped storage units,and so on,as a promising gridforming solution.It is noted that VSGs can provide virtual inertia for frequency support,but the larger inertia would worsen the synchronization stability,referring to keeping synchronization with the grid during voltage dips.Thus,this paper presents a transient damping method of VSGs for enhancing the synchronization stability during voltage dips.It is revealed that the loss of synchronization(LOS)of VSGs always accompanies with the positive frequency deviation and the damping is the key factor to remove LOS when the equilibrium point exists.In order to enhance synchronization stability during voltage dips,the transient damping is proposed,which is generated by the frequency deviation in active power loop.Additionally,the proposed method can realize seamless switching between normal state and grid fault.Moreover,detailed control design for transient damping gain is given to ensure the synchronization stability under different inertia requirements during voltage dips.Finally,the experimental results are presented to validate the analysis and the effectiveness of the improved transient damping method.展开更多
In the DC microgrid,the lack of inertia and damping in power electronic converters results in poor stability of DC bus voltage and low inertia of the DC microgrid during fluctuations in load and photovoltaic power.To ...In the DC microgrid,the lack of inertia and damping in power electronic converters results in poor stability of DC bus voltage and low inertia of the DC microgrid during fluctuations in load and photovoltaic power.To address this issue,the application of a virtual synchronous generator(VSG)in grid-connected inverters control is referenced and proposes a control strategy called the analogous virtual synchronous generator(AVSG)control strategy for the interface DC/DC converter of the battery in the microgrid.Besides,a flexible parameter adaptive control method is introduced to further enhance the inertial behavior of the AVSG control.Firstly,a theoretical analysis is conducted on the various components of the DC microgrid,the structure of analogous virtual synchronous generator,and the control structure’s main parameters related to the DC microgrid’s inertial behavior.Secondly,the voltage change rate tracking coefficient is introduced to adjust the change of the virtual capacitance and damping coefficient flexibility,which further strengthens the inertia trend of the DC microgrid.Additionally,a small-signal modeling approach is used to analyze the approximate range of the AVSG’s main parameters ensuring system stability.Finally,conduct a simulation analysis by building the model of the DC microgrid system with photovoltaic(PV)and battery energy storage(BES)in MATLAB/Simulink.Simulation results from different scenarios have verified that the AVSG control introduces fixed inertia and damping into the droop control of the battery,resulting in a certain level of inertia enhancement.Furthermore,the additional adaptive control strategy built upon the AVSG control provides better and flexible inertial support for the DC microgrid,further enhances the stability of the DC bus voltage,and has a more positive impact on the battery performance.展开更多
The synchronous virtual machine uses inverter power to imitate the performance of the conventional synchronous machine.It also has the same inertia,damping,frequency,voltage regulation,and other external performance a...The synchronous virtual machine uses inverter power to imitate the performance of the conventional synchronous machine.It also has the same inertia,damping,frequency,voltage regulation,and other external performance as the generator.It is the key technology to realize new energy grid connections’stable and reliable operation.This project studies a dynamic simulation model of an extensive new energy power system based on the virtual synchronous motor.A new energy storage method is proposed.The mathematical energy storage model is established by combining the fixed rotor model of a synchronous virtual machine with the charge-discharge power,state of charge,operation efficiency,dead zone,and inverter constraint.The rapid conversion of energy storage devices absorbs the excess instantaneous kinetic energy caused by interference.The branch transient of the critical cut set in the system can be confined to a limited area.Thus,the virtual synchronizer’s kinetic and potential energy can be efficiently converted into an instantaneous state.The simulation of power system analysis software package(PSASP)verifies the correctness of the theory and algorithm in this paper.This paper provides a theoretical basis for improving the transient stability of new energy-connected power grids.展开更多
The brushless doubly-fed wind power system based on conventional power control strategies lacks ‘inertia’ and the ability to support grid,which leads to the decline of grid stability.Therefore,a control strategy of ...The brushless doubly-fed wind power system based on conventional power control strategies lacks ‘inertia’ and the ability to support grid,which leads to the decline of grid stability.Therefore,a control strategy of brushless doubly-fed reluctance generator(BDFRG) based on virtual synchronous generator(VSG) control is proposed to solve the problem in this paper.The output characteristics of BDFRG based on VSG are similar to a synchronous generator(SG),which can support the grid frequency and increase the system ‘inertia’.According to the mathematical model of BDFRG,the inner loop voltage source control of BDFRG is derived.In addition,the specific structure and parameter selection principle of outer loop VSG control are expounded.The voltage source control inner loop of BDFRG is combined with the VSG control outer loop to establish the overall architecture of BDFRG-VSG control strategy.Finally,the effectiveness and feasibility of the proposed strategy are verified in the simulation.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
With the increasing integration of new energy generation into the power system and the massive withdrawal of traditional fossil fuel generation,the power system is faced with a large number of stability problems.The p...With the increasing integration of new energy generation into the power system and the massive withdrawal of traditional fossil fuel generation,the power system is faced with a large number of stability problems.The phenomenon of low-frequency oscillation caused by lack of damping and moment of inertia is worth studying.In recent years,virtual synchronous generator(VSG)technique has been developed rapidly because it can provide considerable damping and moment of inertia.While improving the stability of the system,it also inevitably causes the problem of active power oscillation,especially the low mutual damping between the VSG and the power grid will make the oscillation more severe.The traditional time-domain state-space method cannot reflect the interaction among state variables and study the interaction between different nodes and branches of the power grid.In this paper,a frequency-domain method for analyzing low-frequency oscillations considering VSG parameter coupling is proposed.First,based on the rotor motion equation of the synchronous generator(SG),a secondorder VSG model and linearized power-frequency control loop model are established.Then,the differences and connections between the coupling of key VSG parameters and low-frequency oscillation characteristics are studied through frequency domain analysis.The path and influencemechanism of a VSG during low-frequency power grid oscillations are illustrated.Finally,the correctness of the theoretical analysis model is verified by simulation.展开更多
Power inverter adopting virtual synchronous generator(VSG)control can provide inertia support for distributed generation systems.However,it cannot take into account the dynamic regulation characteristics of frequency....Power inverter adopting virtual synchronous generator(VSG)control can provide inertia support for distributed generation systems.However,it cannot take into account the dynamic regulation characteristics of frequency.Thus,when the system encounters a sudden change in load or disturbance,the dynamic process of frequency regulation will be greatly influenced.In view of this issue,an improved VSG control strategy based on a coordinated self-adaptive(CSA)method is proposed.The time domain analysis method is used to study the influences of virtual inertia and damping parameter perturbation on the system steady and dynamic performances.Furthermore,in order to make the control strategy suitable for large load changes and suppress frequency variations beyond the limit,the secondary frequency modulation is introduced into the control loop.Through the coordinated adaptive control of virtual inertia,virtual damping and frequency modulation,the dynamic performance of vSG frequency regulation can be obviously improved.Simulation and experiment results have verified the effectiveness of the proposed CSA control strategy.展开更多
Grid-forming(GFM)converters can provide inertia support for power grids through control technology,stabilize voltage and frequency,and improve system stability,unlike traditional grid-following(GFL)converters.Therefor...Grid-forming(GFM)converters can provide inertia support for power grids through control technology,stabilize voltage and frequency,and improve system stability,unlike traditional grid-following(GFL)converters.Therefore,in future“double high”power systems,research on the control technology of GFM converters will become an urgent demand.In this paper,we first introduce the basic principle of GFM control and then present five currently used control strategies for GFM converters:droop control,power synchronization control(PSC),virtual synchronous machine control(VSM),direct power control(DPC),and virtual oscillator control(VOC).These five strategies can independently establish voltage phasors to provide inertia to the system.Among these,droop control is the most widely used strategy.PSC and VSM are strategies that simulate the mechanical characteristics of synchronous generators;thus,they are more accurate than droop control.DPC regulates the active power and reactive power directly,with no inner current controller,and VOC is a novel method under study using an oscillator circuit to realize synchronization.Finally,we highlight key technologies and research directions to be addressed in the future.展开更多
As synchronous generators(SGs)are gradually displaced by renewable energy sources(RESs),the frequency stability of power systems deteriorates because RESs,represented by utility-scale solar and wind power sources,do n...As synchronous generators(SGs)are gradually displaced by renewable energy sources(RESs),the frequency stability of power systems deteriorates because RESs,represented by utility-scale solar and wind power sources,do not provide the inertial response,primary frequency response,secondary frequency response,and tertiary frequency regulation.As a result,the remaining SGs may not be sufficient to maintain the power balance and frequency stability.The concept and control strategies of virtual synchronous generators(VSGs)enable the inverter-based wind and solar power sources to emulate the outer characteristics of traditional SGs and participate in the active power and frequency control of power systems.This paper focuses on the automatic generation control(AGC)with virtual synchronous renewables(VSRs).First,the VSR strategy that enables the RESs to participate in AGC is introduced.Second,based on the interval representation of uncertainty,the output of RES is transformed into two portions,i.e.,the dispatchable portion and the stochastic portion.In the dispatchable portion,the RESs can participate in AGC jointly with SGs.Accordingly,a security-constrained economic dispatch(SCED)model is built considering the RESs operating in VSR mode.Third,the solution strategy that employs the slack variables to acquire deterministic constraints is introduced.Finally,the proposed SCED model is solved based on the 6-bus and 39-bus systems.The results show that,compared with the maximum power point tracking(MPPT)mode,VSRs can participate in the active power and frequency control jointly with SGs,increase the maximum penetration level of RESs,and decrease the operating cost.展开更多
Renewable energy is connected to the grid through the inverter,which in turn reduces the inertia and stability of the power grid itself.The traditional grid-connected inverter does not have the function of voltage reg...Renewable energy is connected to the grid through the inverter,which in turn reduces the inertia and stability of the power grid itself.The traditional grid-connected inverter does not have the function of voltage regulation and frequency regulation and can therefore no longer adapt to the new development.The virtual synchronous generator(VSG)has the function of voltage regulation and frequency regulation,which has more prominent advantages than traditional inverters.Based on the principle of VSG,the relationship between the frequency characteristics and the energy storage capacity of the feedforward branch-based virtual synchronous machine(FVSG)is derived when the input power and grid frequency change.Reveal the relationship between the virtual inertia coefficient,damping coefficient,and frequency characteristics of VSG and energy storage capacity.An energy storage configuration method that meets the requirements of frequency variation characteristics is proposed.A mathematical model is established,and the Matlab/Simulink simulation software is used for modeling.The simulation results verify the relationship between the inertia coefficient,damping coefficient,and energy storage demand of the FVSG.展开更多
This paper proposes a novel virtual inertia controller for converters in power systems,whichcan solve the system’s nonlinearity for frequency support.First,the system dynamics are formulatedas a nonlinear state-space...This paper proposes a novel virtual inertia controller for converters in power systems,whichcan solve the system’s nonlinearity for frequency support.First,the system dynamics are formulatedas a nonlinear state-space,in which the reciprocal of inertia is modeled as controlinput.Correspondingly,a cost function is defined by considering frequency deviation andrate of change of the frequency,which can preserve a tradeoff between critical frequencylimits and respective control energy.Following,the optimal frequency regulation problemis solved by using an online adaptive dynamic programming method,where the actor andcritic neural networks are constructed to approximate the optimal control input and optimalcost function,respectively.After that,the small-signal analysis is provided to identify the stabilityof the converter under the proposed controller.Finally,simulation results verify thatthe frequency response of the system is significantly improved,while retaining more DC sideenergy.展开更多
Virtual synchronous control has been widely studied for the advantages of emulating inertia for voltage source converters (VSCs). A constant dc-link voltage is usually assumed in existing literature to estimate transi...Virtual synchronous control has been widely studied for the advantages of emulating inertia for voltage source converters (VSCs). A constant dc-link voltage is usually assumed in existing literature to estimate transient stability of virtual synchronous generators (VSGs). However, actual power supply in the dc-side of VSGs is limited and different dc-link voltage controllers are needed to achieve power balance between DC side and AC side. Addition of dc-link voltage controller has great influence on transient behavior of VSGs, which has not been investigated by previous research. To fill this gap, this paper gives insights into the effect of dc-link voltage dynamics on transient stability of VSGs. First, two typical kinds of VSGs with dc-link voltage controllers are introduced. Then, mathematical models considering dc-link dynamics are established and the effect of dc-link voltage controllers on transient synchronization stability of VSGs is revealed through equal area criterion (EAC). It is found that dc-link voltage controller would reduce stability margin of VSGs and design-oriented transient stability analysis is carried out quantitively using critical clearing time (CCT). Finally, simulation results are given to validate correctness of theoretical analysis.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
As more and more power electronic based generation units are integrated into power systems, the stable operation of power systems has been challenged due to the lack of system inertia. In order to solve this issue, th...As more and more power electronic based generation units are integrated into power systems, the stable operation of power systems has been challenged due to the lack of system inertia. In order to solve this issue, the virtual synchronous generator(VSG), in which the power electronic inverter is controlled to mimic the characteristics of traditional synchronous generators, is a promising strategy. In this paper, the representation of the synchronous generator in power systems is firstly presented as the basis for the VSG. Then the modelling methods of VSG are comprehensively reviewed and compared.Applications of the VSG in power systems are summarized as well. Finally, the challenges and future trends of the VSG implementation are discussed.展开更多
This paper aims at developing a data-driven optimal control strategy for virtual synchronous generator (VSG) in the scenario where no expert knowledge or requirement for system model is available. Firstly, the optimal...This paper aims at developing a data-driven optimal control strategy for virtual synchronous generator (VSG) in the scenario where no expert knowledge or requirement for system model is available. Firstly, the optimal and adaptive control problem for VSG is transformed into a reinforcement learning task. Specifically, the control variables, i.e., virtual inertia and damping factor, are defined as the actions. Meanwhile, the active power output, angular frequency and its derivative are considered as the observations. Moreover, the reward mechanism is designed based on three preset characteristic functions to quantify the control targets: ① maintaining the deviation of angular frequency within special limits;② preserving well-damped oscillations for both the angular frequency and active power output;③ obtaining slow frequency drop in the transient process. Next, to maximize the cumulative rewards, a decentralized deep policy gradient algorithm, which features model-free and faster convergence, is developed and employed to find the optimal control policy. With this effort, a data-driven adaptive VSG controller can be obtained. By using the proposed controller, the inverter-based distributed generator can adaptively adjust its control variables based on current observations to fulfill the expected targets in model-free fashion. Finally, simulation results validate the feasibility and effectiveness of the proposed approach.展开更多
The virtual inertia and virtual damping affect both the dynamic stability of the virtual synchronous generator(VSG)and the configuration of energy storage,but there is a conflict between them while selecting the virtu...The virtual inertia and virtual damping affect both the dynamic stability of the virtual synchronous generator(VSG)and the configuration of energy storage,but there is a conflict between them while selecting the virtual inertia and virtual damping.An optimal coordination control strategy of micro-grid inverter and energy storage based on variable virtual inertia and damping is proposed to mitigate this conflict.With the integrated optimal constraint of the VSG frequency variation and the energy storage capacity,the virtual inertia and damping of VSG are configured dynamically,adopting linear quadratic optimal control.It can suppress the oscillations of the active power and frequency to improve the stability of VSG and optimally configure the energy storage capacity of VSG simultaneously.The proposed strategy aims to improve the control performance of micro-grid inverter and the system economy.The simulation and experimental results verify the effectiveness of the strategy.展开更多
In order to enhance the stability of single-phase microgrid,virtual synchronous generator(VSG)control method is investigated in this paper.Its electromagnetic model and electromechanical model are established to illus...In order to enhance the stability of single-phase microgrid,virtual synchronous generator(VSG)control method is investigated in this paper.Its electromagnetic model and electromechanical model are established to illustrate the performance of VSG.Considering the 2 nd fluctuation of fundamental-frequency in the output power,an instantaneous power calculation strategy is proposed based on the intrinsic frequency of single-phase VSG.Besides,a virtual power calculation method is presented to achieve islanded/grid-connected seamless transition.Stability analysis and comparison simulation results demonstrate the correctness of the presented power calculation method.At last,the effectiveness of the proposed approach is verified by comparison experiments of islanded/gridconnected operations in a 500 VA single-phase inverter.展开更多
A virtual synchronous generator(VSG)control has been proposed as a means to control a voltage source converter interfaced generation and storage to retain the dynamics of a conventional synchronous generator.The stora...A virtual synchronous generator(VSG)control has been proposed as a means to control a voltage source converter interfaced generation and storage to retain the dynamics of a conventional synchronous generator.The storage is used to provide the inertia power and droop power in the VSG control to improve the frequency stability.Since the parameters in the VSG control can be varied,it is necessary for it to be tuned to be adaptive,in order to achieve an optimal response to grid frequency changes.However,the storage cannot provide infinite power and the converter has a strict power limitation which must be observed.The adaptive VSG control should consider these limitations,which have not been considered previously.This paper proposes an adaptive VSG control aimed at obtaining the optimal grid supporting services during frequency transients,accounting for converter and storage capacity limitations.The proposed control has been validated via hardware-in-the-loop testing.It is then implemented in storage co-located with wind farms in a modified IEEE 39-bus system.The results show that the proposed control stabilizes the system faster and has better cooperation with other VSGs,considering storage and converter limits.展开更多
文摘Virtual synchronous generators(VSGs)are widely introduced to the renewable power generation,the variablespeed pumped storage units,and so on,as a promising gridforming solution.It is noted that VSGs can provide virtual inertia for frequency support,but the larger inertia would worsen the synchronization stability,referring to keeping synchronization with the grid during voltage dips.Thus,this paper presents a transient damping method of VSGs for enhancing the synchronization stability during voltage dips.It is revealed that the loss of synchronization(LOS)of VSGs always accompanies with the positive frequency deviation and the damping is the key factor to remove LOS when the equilibrium point exists.In order to enhance synchronization stability during voltage dips,the transient damping is proposed,which is generated by the frequency deviation in active power loop.Additionally,the proposed method can realize seamless switching between normal state and grid fault.Moreover,detailed control design for transient damping gain is given to ensure the synchronization stability under different inertia requirements during voltage dips.Finally,the experimental results are presented to validate the analysis and the effectiveness of the improved transient damping method.
基金funded by the National Natural Science Foundation of China(52067013),and the Provincial Natural Science Foundation of Gansu(20JR5RA395).
文摘In the DC microgrid,the lack of inertia and damping in power electronic converters results in poor stability of DC bus voltage and low inertia of the DC microgrid during fluctuations in load and photovoltaic power.To address this issue,the application of a virtual synchronous generator(VSG)in grid-connected inverters control is referenced and proposes a control strategy called the analogous virtual synchronous generator(AVSG)control strategy for the interface DC/DC converter of the battery in the microgrid.Besides,a flexible parameter adaptive control method is introduced to further enhance the inertial behavior of the AVSG control.Firstly,a theoretical analysis is conducted on the various components of the DC microgrid,the structure of analogous virtual synchronous generator,and the control structure’s main parameters related to the DC microgrid’s inertial behavior.Secondly,the voltage change rate tracking coefficient is introduced to adjust the change of the virtual capacitance and damping coefficient flexibility,which further strengthens the inertia trend of the DC microgrid.Additionally,a small-signal modeling approach is used to analyze the approximate range of the AVSG’s main parameters ensuring system stability.Finally,conduct a simulation analysis by building the model of the DC microgrid system with photovoltaic(PV)and battery energy storage(BES)in MATLAB/Simulink.Simulation results from different scenarios have verified that the AVSG control introduces fixed inertia and damping into the droop control of the battery,resulting in a certain level of inertia enhancement.Furthermore,the additional adaptive control strategy built upon the AVSG control provides better and flexible inertial support for the DC microgrid,further enhances the stability of the DC bus voltage,and has a more positive impact on the battery performance.
文摘The synchronous virtual machine uses inverter power to imitate the performance of the conventional synchronous machine.It also has the same inertia,damping,frequency,voltage regulation,and other external performance as the generator.It is the key technology to realize new energy grid connections’stable and reliable operation.This project studies a dynamic simulation model of an extensive new energy power system based on the virtual synchronous motor.A new energy storage method is proposed.The mathematical energy storage model is established by combining the fixed rotor model of a synchronous virtual machine with the charge-discharge power,state of charge,operation efficiency,dead zone,and inverter constraint.The rapid conversion of energy storage devices absorbs the excess instantaneous kinetic energy caused by interference.The branch transient of the critical cut set in the system can be confined to a limited area.Thus,the virtual synchronizer’s kinetic and potential energy can be efficiently converted into an instantaneous state.The simulation of power system analysis software package(PSASP)verifies the correctness of the theory and algorithm in this paper.This paper provides a theoretical basis for improving the transient stability of new energy-connected power grids.
基金supported in part by the National Natural Science Foundation of China under Grant 51537007。
文摘The brushless doubly-fed wind power system based on conventional power control strategies lacks ‘inertia’ and the ability to support grid,which leads to the decline of grid stability.Therefore,a control strategy of brushless doubly-fed reluctance generator(BDFRG) based on virtual synchronous generator(VSG) control is proposed to solve the problem in this paper.The output characteristics of BDFRG based on VSG are similar to a synchronous generator(SG),which can support the grid frequency and increase the system ‘inertia’.According to the mathematical model of BDFRG,the inner loop voltage source control of BDFRG is derived.In addition,the specific structure and parameter selection principle of outer loop VSG control are expounded.The voltage source control inner loop of BDFRG is combined with the VSG control outer loop to establish the overall architecture of BDFRG-VSG control strategy.Finally,the effectiveness and feasibility of the proposed strategy are verified in the simulation.
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 by Science and Technology Project of State Grid Liaoning Electric Power Supply Co.,Ltd.(2021YF-82).
文摘With the increasing integration of new energy generation into the power system and the massive withdrawal of traditional fossil fuel generation,the power system is faced with a large number of stability problems.The phenomenon of low-frequency oscillation caused by lack of damping and moment of inertia is worth studying.In recent years,virtual synchronous generator(VSG)technique has been developed rapidly because it can provide considerable damping and moment of inertia.While improving the stability of the system,it also inevitably causes the problem of active power oscillation,especially the low mutual damping between the VSG and the power grid will make the oscillation more severe.The traditional time-domain state-space method cannot reflect the interaction among state variables and study the interaction between different nodes and branches of the power grid.In this paper,a frequency-domain method for analyzing low-frequency oscillations considering VSG parameter coupling is proposed.First,based on the rotor motion equation of the synchronous generator(SG),a secondorder VSG model and linearized power-frequency control loop model are established.Then,the differences and connections between the coupling of key VSG parameters and low-frequency oscillation characteristics are studied through frequency domain analysis.The path and influencemechanism of a VSG during low-frequency power grid oscillations are illustrated.Finally,the correctness of the theoretical analysis model is verified by simulation.
基金supported by National Natural Science Foundation of China(No.51577124,No.51877148)National Key Research and Development Program of China(SQ2023YFE0198100)。
文摘Power inverter adopting virtual synchronous generator(VSG)control can provide inertia support for distributed generation systems.However,it cannot take into account the dynamic regulation characteristics of frequency.Thus,when the system encounters a sudden change in load or disturbance,the dynamic process of frequency regulation will be greatly influenced.In view of this issue,an improved VSG control strategy based on a coordinated self-adaptive(CSA)method is proposed.The time domain analysis method is used to study the influences of virtual inertia and damping parameter perturbation on the system steady and dynamic performances.Furthermore,in order to make the control strategy suitable for large load changes and suppress frequency variations beyond the limit,the secondary frequency modulation is introduced into the control loop.Through the coordinated adaptive control of virtual inertia,virtual damping and frequency modulation,the dynamic performance of vSG frequency regulation can be obviously improved.Simulation and experiment results have verified the effectiveness of the proposed CSA control strategy.
基金supported by the National Natural Science Foundation of China(No.52177122)the“Transformational Technologies for Clean Energy and Demonstration”,Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA 21050100)the Youth Innovation Promotion Association CAS(No.2018170)。
文摘Grid-forming(GFM)converters can provide inertia support for power grids through control technology,stabilize voltage and frequency,and improve system stability,unlike traditional grid-following(GFL)converters.Therefore,in future“double high”power systems,research on the control technology of GFM converters will become an urgent demand.In this paper,we first introduce the basic principle of GFM control and then present five currently used control strategies for GFM converters:droop control,power synchronization control(PSC),virtual synchronous machine control(VSM),direct power control(DPC),and virtual oscillator control(VOC).These five strategies can independently establish voltage phasors to provide inertia to the system.Among these,droop control is the most widely used strategy.PSC and VSM are strategies that simulate the mechanical characteristics of synchronous generators;thus,they are more accurate than droop control.DPC regulates the active power and reactive power directly,with no inner current controller,and VOC is a novel method under study using an oscillator circuit to realize synchronization.Finally,we highlight key technologies and research directions to be addressed in the future.
基金supported by the Research and Application of Key Technologies of Flexible Power Supply System Under Various Emergency Scenarios(No.5442PD210001)。
文摘As synchronous generators(SGs)are gradually displaced by renewable energy sources(RESs),the frequency stability of power systems deteriorates because RESs,represented by utility-scale solar and wind power sources,do not provide the inertial response,primary frequency response,secondary frequency response,and tertiary frequency regulation.As a result,the remaining SGs may not be sufficient to maintain the power balance and frequency stability.The concept and control strategies of virtual synchronous generators(VSGs)enable the inverter-based wind and solar power sources to emulate the outer characteristics of traditional SGs and participate in the active power and frequency control of power systems.This paper focuses on the automatic generation control(AGC)with virtual synchronous renewables(VSRs).First,the VSR strategy that enables the RESs to participate in AGC is introduced.Second,based on the interval representation of uncertainty,the output of RES is transformed into two portions,i.e.,the dispatchable portion and the stochastic portion.In the dispatchable portion,the RESs can participate in AGC jointly with SGs.Accordingly,a security-constrained economic dispatch(SCED)model is built considering the RESs operating in VSR mode.Third,the solution strategy that employs the slack variables to acquire deterministic constraints is introduced.Finally,the proposed SCED model is solved based on the 6-bus and 39-bus systems.The results show that,compared with the maximum power point tracking(MPPT)mode,VSRs can participate in the active power and frequency control jointly with SGs,increase the maximum penetration level of RESs,and decrease the operating cost.
基金National Key Research and Development Plan Project(2017YFB1201003-20)Quality Inspection,Monitoring and Operation and Maintenance Guarantee Technology of New Power Supply SystemVehicles for UrbanRail Transit and Their on-Board Energy Storage Technology.
文摘Renewable energy is connected to the grid through the inverter,which in turn reduces the inertia and stability of the power grid itself.The traditional grid-connected inverter does not have the function of voltage regulation and frequency regulation and can therefore no longer adapt to the new development.The virtual synchronous generator(VSG)has the function of voltage regulation and frequency regulation,which has more prominent advantages than traditional inverters.Based on the principle of VSG,the relationship between the frequency characteristics and the energy storage capacity of the feedforward branch-based virtual synchronous machine(FVSG)is derived when the input power and grid frequency change.Reveal the relationship between the virtual inertia coefficient,damping coefficient,and frequency characteristics of VSG and energy storage capacity.An energy storage configuration method that meets the requirements of frequency variation characteristics is proposed.A mathematical model is established,and the Matlab/Simulink simulation software is used for modeling.The simulation results verify the relationship between the inertia coefficient,damping coefficient,and energy storage demand of the FVSG.
基金the National Key Research and Development Program of China[2018YFA0702200]National transformative subject:Intelligent evolution mechanism and design of distributed information energy system,National Natural Science Foundation of China[62073065,51907098]China Postdoctoral Science Foundation[2020T130337].
文摘This paper proposes a novel virtual inertia controller for converters in power systems,whichcan solve the system’s nonlinearity for frequency support.First,the system dynamics are formulatedas a nonlinear state-space,in which the reciprocal of inertia is modeled as controlinput.Correspondingly,a cost function is defined by considering frequency deviation andrate of change of the frequency,which can preserve a tradeoff between critical frequencylimits and respective control energy.Following,the optimal frequency regulation problemis solved by using an online adaptive dynamic programming method,where the actor andcritic neural networks are constructed to approximate the optimal control input and optimalcost function,respectively.After that,the small-signal analysis is provided to identify the stabilityof the converter under the proposed controller.Finally,simulation results verify thatthe frequency response of the system is significantly improved,while retaining more DC sideenergy.
基金supported in part by National Natural Science Foundation of China(grant No.52207190)Funds for International Cooperation and Exchange of the National Natural Science Foundation of China(No.52061635104)。
文摘Virtual synchronous control has been widely studied for the advantages of emulating inertia for voltage source converters (VSCs). A constant dc-link voltage is usually assumed in existing literature to estimate transient stability of virtual synchronous generators (VSGs). However, actual power supply in the dc-side of VSGs is limited and different dc-link voltage controllers are needed to achieve power balance between DC side and AC side. Addition of dc-link voltage controller has great influence on transient behavior of VSGs, which has not been investigated by previous research. To fill this gap, this paper gives insights into the effect of dc-link voltage dynamics on transient stability of VSGs. First, two typical kinds of VSGs with dc-link voltage controllers are introduced. Then, mathematical models considering dc-link dynamics are established and the effect of dc-link voltage controllers on transient synchronization stability of VSGs is revealed through equal area criterion (EAC). It is found that dc-link voltage controller would reduce stability margin of VSGs and design-oriented transient stability analysis is carried out quantitively using critical clearing time (CCT). Finally, simulation results are given to validate correctness of theoretical analysis.
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As more and more power electronic based generation units are integrated into power systems, the stable operation of power systems has been challenged due to the lack of system inertia. In order to solve this issue, the virtual synchronous generator(VSG), in which the power electronic inverter is controlled to mimic the characteristics of traditional synchronous generators, is a promising strategy. In this paper, the representation of the synchronous generator in power systems is firstly presented as the basis for the VSG. Then the modelling methods of VSG are comprehensively reviewed and compared.Applications of the VSG in power systems are summarized as well. Finally, the challenges and future trends of the VSG implementation are discussed.
基金This work was supported by the U.S.National Science Foundation(No.1711951).
文摘This paper aims at developing a data-driven optimal control strategy for virtual synchronous generator (VSG) in the scenario where no expert knowledge or requirement for system model is available. Firstly, the optimal and adaptive control problem for VSG is transformed into a reinforcement learning task. Specifically, the control variables, i.e., virtual inertia and damping factor, are defined as the actions. Meanwhile, the active power output, angular frequency and its derivative are considered as the observations. Moreover, the reward mechanism is designed based on three preset characteristic functions to quantify the control targets: ① maintaining the deviation of angular frequency within special limits;② preserving well-damped oscillations for both the angular frequency and active power output;③ obtaining slow frequency drop in the transient process. Next, to maximize the cumulative rewards, a decentralized deep policy gradient algorithm, which features model-free and faster convergence, is developed and employed to find the optimal control policy. With this effort, a data-driven adaptive VSG controller can be obtained. By using the proposed controller, the inverter-based distributed generator can adaptively adjust its control variables based on current observations to fulfill the expected targets in model-free fashion. Finally, simulation results validate the feasibility and effectiveness of the proposed approach.
基金Supported by National Key R&D Program of China(2016YFB0900300)National Natural Science Foundation of China(51677049).
文摘The virtual inertia and virtual damping affect both the dynamic stability of the virtual synchronous generator(VSG)and the configuration of energy storage,but there is a conflict between them while selecting the virtual inertia and virtual damping.An optimal coordination control strategy of micro-grid inverter and energy storage based on variable virtual inertia and damping is proposed to mitigate this conflict.With the integrated optimal constraint of the VSG frequency variation and the energy storage capacity,the virtual inertia and damping of VSG are configured dynamically,adopting linear quadratic optimal control.It can suppress the oscillations of the active power and frequency to improve the stability of VSG and optimally configure the energy storage capacity of VSG simultaneously.The proposed strategy aims to improve the control performance of micro-grid inverter and the system economy.The simulation and experimental results verify the effectiveness of the strategy.
基金supported by the National Basic Research Program of China(973 Program)(No.2013CB02708201)
文摘In order to enhance the stability of single-phase microgrid,virtual synchronous generator(VSG)control method is investigated in this paper.Its electromagnetic model and electromechanical model are established to illustrate the performance of VSG.Considering the 2 nd fluctuation of fundamental-frequency in the output power,an instantaneous power calculation strategy is proposed based on the intrinsic frequency of single-phase VSG.Besides,a virtual power calculation method is presented to achieve islanded/grid-connected seamless transition.Stability analysis and comparison simulation results demonstrate the correctness of the presented power calculation method.At last,the effectiveness of the proposed approach is verified by comparison experiments of islanded/gridconnected operations in a 500 VA single-phase inverter.
基金This work was supported by the Science Foundation Ireland(SFI)under the projects ESIPP,Grant No.SFI/15/SPP/E3125,AMPSAS,Grant No.SFI/15/IA/3074under the project EdgreFLEx,Grant No.883710。
文摘A virtual synchronous generator(VSG)control has been proposed as a means to control a voltage source converter interfaced generation and storage to retain the dynamics of a conventional synchronous generator.The storage is used to provide the inertia power and droop power in the VSG control to improve the frequency stability.Since the parameters in the VSG control can be varied,it is necessary for it to be tuned to be adaptive,in order to achieve an optimal response to grid frequency changes.However,the storage cannot provide infinite power and the converter has a strict power limitation which must be observed.The adaptive VSG control should consider these limitations,which have not been considered previously.This paper proposes an adaptive VSG control aimed at obtaining the optimal grid supporting services during frequency transients,accounting for converter and storage capacity limitations.The proposed control has been validated via hardware-in-the-loop testing.It is then implemented in storage co-located with wind farms in a modified IEEE 39-bus system.The results show that the proposed control stabilizes the system faster and has better cooperation with other VSGs,considering storage and converter limits.