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
The grid-forming virtual synchronous generator(GFVSG)not only employs a first-order low-pass filter for virtual inertia control but also introduces grid-connected active power(GCAP)dynamic oscillation issues,akin to t...The grid-forming virtual synchronous generator(GFVSG)not only employs a first-order low-pass filter for virtual inertia control but also introduces grid-connected active power(GCAP)dynamic oscillation issues,akin to those observed in traditional synchronous generators.In response to this,an improved strategy for lead-lag filter based GFVSG(LLF-GFVSG)is presented in this article.Firstly,the grid-connected circuit structure and control principle of typical GFVSG are described,and a closed-loop small-signal model for GCAP in GFVSG is established.The causes of GCAP dynamic oscillation of GFVSG under the disturbances of active power command as well as grid frequency are analyzed.On this basis,the LLF-GFVSG improvement strategy and its parameter design method are given.Finally,the efficiency of the proposed control strategy in damping GCAP dynamic oscillations under various disturbances is verified using MATLAB simulations and experimental comparison results.展开更多
To improve the living standards,economical efficiency and environmental protection of isolated islands,remote areas and other areas with weak electric power facilities construction,a multi-source independent microgrid...To improve the living standards,economical efficiency and environmental protection of isolated islands,remote areas and other areas with weak electric power facilities construction,a multi-source independent microgrid system is studied,including diesel generators,photovoltaic power generation system,wind power generation system and energy storage unit.Meanwhile,in order to realize the voltage and frequency stability control of AC bus of multisource microgrid,the virtual synchronous generator technology is introduced into the energy storage unit,and the charge and discharge control of the energy storage battery are simulated as the control behavior characteristics of synchronous motors,so as to provide damping and inertia support for the microgrid.The operation mode and control principle of each energy subsystem are expounded and analyzed.The algorithm principle of virtual synchronous generator and the control method of energy storage unit are given.Then,the working modes of the microgrid system under different environmental conditions are analyzed,and the multi-source microgrid system simulation model is built based on MATLAB/Simulink.The simulation results show that the microgrid system can run stably under different working modes and the energy storage unit using the virtual synchronous generator technology can provide good voltage and frequency support for the microgrid system.Finally,experiments verify the supporting function of energy storage unit on the voltage and frequency of the microgrid system.展开更多
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
With the application of distributed power sources,the stability of the power system has been dramatically affected.Therefore,scholars have proposed the concept of a virtual synchronous generator(VSG).However,after the...With the application of distributed power sources,the stability of the power system has been dramatically affected.Therefore,scholars have proposed the concept of a virtual synchronous generator(VSG).However,after the system is disturbed,how to make it respond quickly and effectively to maintain the stability of the system becomes a complex problem.To address this problem,a frequency prediction component is incorporated into the control module of the VSG to enhance its performance.The Convolutional Neural NetworkLong Short-Term Memory(CNN-LSTM)model is used for frequency prediction,ensuring that the maximum energy capacity released by the storage system is maintained.Additionally,it guarantees that the inverter's output power does not exceed its rated capacity,based on the predicted frequency limit after the system experiences a disturbance.The advantage of real-time adjustment of inverter parameters is that the setting intervals for inertia and damping can be increased.The selection criteria for inertia and damping can be derived from the power angle oscillation curve of the synchronous generator.Consequently,an adaptive control strategy for VSG parameters is implemented to enhance the system's frequency restoration following disturbances.The validity and effectiveness of the model are verified through simulations in Matlab/Simulink.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 renewable energy,microgrids are increasingly facing stability challenges,primarily due to the lack of inherent inertia in inverter-dominated systems,which is traditionally provided b...With the increasing integration of renewable energy,microgrids are increasingly facing stability challenges,primarily due to the lack of inherent inertia in inverter-dominated systems,which is traditionally provided by synchronous generators.To address this critical issue,Virtual Synchronous Generator(VSG)technology has emerged as a highly promising solution by emulating the inertia and damping characteristics of conventional synchronous generators.To enhance the operational efficiency of virtual synchronous generators(VSGs),this study employs smallsignal modeling analysis,root locus methods,and synchronous generator power-angle characteristic analysis to comprehensively evaluate how virtual inertia and damping coefficients affect frequency stability and power output during transient processes.Based on these analyses,an adaptive control strategy is proposed:increasing the virtual inertia when the rotor angular velocity undergoes rapid changes,while strengthening the damping coefficient when the speed deviation exceeds a certain threshold to suppress angular velocity oscillations.To validate the effectiveness of the proposed method,a grid-connected VSG simulation platform was developed inMATLAB/Simulink.Comparative simulations demonstrate that the proposed adaptive control strategy outperforms conventional VSGmethods by significantly reducing grid frequency deviations and shortening active power response time during active power command changes and load disturbances.This approach enhances microgrid stability and dynamic performance,confirming its viability for renewable-dominant power systems.Future work should focus on experimental validation and real-world parameter optimization,while further exploring the strategy’s effectiveness in improvingVSG low-voltage ride-through(LVRT)capability and power-sharing applications in multi-parallel configurations.展开更多
The damage of extreme disasters to a power grid is becoming increasingly severe,and energy storage control technology is emerging as a measure to enhance grid resilience.In this study,a novel adaptive inertia control ...The damage of extreme disasters to a power grid is becoming increasingly severe,and energy storage control technology is emerging as a measure to enhance grid resilience.In this study,a novel adaptive inertia control for virtual synchronous generators is proposed for the control of wind-solar-storage combined power generation systems to form the ability for long-term power supply for load.This technology can not only provide inertia for the system but also dynamically adjust inertia according to frequency variation caused by power disturbance,avoiding rapid rise and drop of frequency in the transient process and increasing damping of a wind-solar-storage combined power generation system when the main network fails.Through low pass filtering of the sampled signal and design of the inertia control law,frequent inertia adjustment caused by measurement noise and random small fluctuation of wind speed can be avoided,and the inertia adjustment amount would not exceed the limit under any large power disturbance.The inertial boundary of the system is discussed according to the primary energy storage capacity and the tolerant power of the inverter.Convergence of a novel adaptive control algorithm is proved.Finally,a simulation model is built on PSCAD/EMTDC platform,and the effectiveness of the proposed control strategy is verified.展开更多
The virtual synchronous generator(VSG),utilized as a control strategy for grid-forming inverters,is an effective method of providing inertia and voltage support to the grid.However,the VSG exhibits limited capabilitie...The virtual synchronous generator(VSG),utilized as a control strategy for grid-forming inverters,is an effective method of providing inertia and voltage support to the grid.However,the VSG exhibits limited capabilities in low-voltage ride-through(LVRT)mode.Specifically,the slow response of the power loop poses challenges for VSG in grid voltage support and increases the risk of overcurrent,potentially violating present grid codes.This paper reveals the mechanism behind the delayed response speed of VSG control during the grid faults.On this basis,a compound compensation control strategy is proposed for improving the LVRT capability of the VSG,which incorporates adaptive frequency feedforward compensation(AFFC),direct power angle compensation(DPAC),internal potential compensation(IPC),and transient virtual impedance(TVI),effectively expediting the response speed and reducing transient current.Furthermore,the proposed control strategy ensures that the VSG operates smoothly back to its normal control state following the restoration from the grid faults.Subsequently,a large-signal model is developed to facilitate parameter design and stability analysis,which incorporates grid codes and TVI.Finally,the small-signal stability analysis and simulation and experimental results prove the correctness of the theoretical analysis and the effectiveness of the proposed control strategy.展开更多
The integration of converter-interfaced generators(CIGs)into power systems is rapidly replacing traditional synchronous machines.To ensure the security of power supply,modern power systems require the application of g...The integration of converter-interfaced generators(CIGs)into power systems is rapidly replacing traditional synchronous machines.To ensure the security of power supply,modern power systems require the application of grid-forming technologies.This study presents a systematic small-signal analysis procedure to assess the synchronization stability of gridforming virtual synchronous generators(VSGs)considering the power system characteristics.Specifically,this procedure offers guidance in tuning controller gains to enhance stability.It is applied to six different grid-forming VSGs and experimentally tested to validate the theoretical analysis.This study concludes with key findings and a discussion on the suitability of the analyzed grid-forming VSGs based on the power system characteristics.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
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
By simulating the operating dynamics of synchronous generators(SGs),the use of virtual synchronous gen-rators(VSGs)can help overcome inverter-based generators'shortcomings of low inertia and minimal damping for gr...By simulating the operating dynamics of synchronous generators(SGs),the use of virtual synchronous gen-rators(VSGs)can help overcome inverter-based generators'shortcomings of low inertia and minimal damping for gridforming applications.VSGs'stability are very important for their solar and wind electricity applications.Currently,the related research primarily focuses on VSGs and their applications for microgrids.There has been little research to explore how VSGs effect low frequency oscillations in power transmission systems.This paper describes a small-signal model of a VSGSG interconnected system,which is suitable for studying low frequency oscillation damping in a power transmission grid.Based on this model,the effects of VSGs on low frequency oscillations are compared with the effects of SGs to reveal the mechanism of how VSGs infuence damping characteristics.The influence of each VSG control loop on oscillations is also analyzed in this paper.Then,the low frequency oscillation risks with different types of VSGs are described.Finally,experiments on a real-time laboratory(RT-LAB)platform are conducted to verify the small-signal analysis results.展开更多
In this paper,the dynamic coupling between the wind turbine rotor speed recovery(WTRSR)and inertial response of the conventional virtual synchronous generator(VSG)controlled wind farms(WFs)is analyzed.Three distinguis...In this paper,the dynamic coupling between the wind turbine rotor speed recovery(WTRSR)and inertial response of the conventional virtual synchronous generator(VSG)controlled wind farms(WFs)is analyzed.Three distinguishing features are revealed.Firstly,the inertial response characteristics of VSG controlled WFs(VSG-WFs)are impaired by the dynamic coupling.Secondly,when the influence of WTRSR is dominant,the inertial response characteristics of VSG-WFs are even worse than the condition under which WFs do not participate in the response of grid frequency.Thirdly,this phenomenon cannot be eliminated by only enlarging the inertia parameter of VSG-WFs,because the influence of WTRSR would also increase with the enhancement of inertial response.A decoupling scheme to eliminate the negative influence is then proposed in this paper.By starting the WTRSR process after inertial response period,the dynamic coupling is eliminated and the inertial response characteristics of WFs are improved.Finally,the effectiveness of the analysis and the proposed scheme are verified by simulation results.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
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
The Photovoltaic(PV)plants are significantly different from the conventional synchronous generators in terms of physical and electrical characteristics,as it connects to the power grid through the voltage-source conve...The Photovoltaic(PV)plants are significantly different from the conventional synchronous generators in terms of physical and electrical characteristics,as it connects to the power grid through the voltage-source converters.High penetration PV in power system will bring several critical challenges to the safe operation of power grid including transient stability.To address this problem,the paper proposes a control strategy to help the PVs work like a synchronous generator with variable inertia by energy storage system(ESS).First,the overall control strategy of the PV-based virtual synchronous generator(PV-VSG)is illustrated.Then the control strategies for the variable inertia of the PV-VSG are designed to attenuate the transient energy of the power system after the fault.Simulation results of a simple power system show that the PV-VSG could utilize the energy preserved in the ESS to balance the transient energy variation of power grid after fault and improve the transient stability of the power system.展开更多
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supported by the Key Laboratory of Modern Power System Simulation and Control&Renewable Energy Technology(Northeast Electric Power University)Open Fund of China under Grant MPSS2024-08.
文摘The grid-forming virtual synchronous generator(GFVSG)not only employs a first-order low-pass filter for virtual inertia control but also introduces grid-connected active power(GCAP)dynamic oscillation issues,akin to those observed in traditional synchronous generators.In response to this,an improved strategy for lead-lag filter based GFVSG(LLF-GFVSG)is presented in this article.Firstly,the grid-connected circuit structure and control principle of typical GFVSG are described,and a closed-loop small-signal model for GCAP in GFVSG is established.The causes of GCAP dynamic oscillation of GFVSG under the disturbances of active power command as well as grid frequency are analyzed.On this basis,the LLF-GFVSG improvement strategy and its parameter design method are given.Finally,the efficiency of the proposed control strategy in damping GCAP dynamic oscillations under various disturbances is verified using MATLAB simulations and experimental comparison results.
基金supported by the Science and Technology Research&Development Project of China Construction Second Engineering Bureau Ltd.(No.91110000100024296D180009)。
文摘To improve the living standards,economical efficiency and environmental protection of isolated islands,remote areas and other areas with weak electric power facilities construction,a multi-source independent microgrid system is studied,including diesel generators,photovoltaic power generation system,wind power generation system and energy storage unit.Meanwhile,in order to realize the voltage and frequency stability control of AC bus of multisource microgrid,the virtual synchronous generator technology is introduced into the energy storage unit,and the charge and discharge control of the energy storage battery are simulated as the control behavior characteristics of synchronous motors,so as to provide damping and inertia support for the microgrid.The operation mode and control principle of each energy subsystem are expounded and analyzed.The algorithm principle of virtual synchronous generator and the control method of energy storage unit are given.Then,the working modes of the microgrid system under different environmental conditions are analyzed,and the multi-source microgrid system simulation model is built based on MATLAB/Simulink.The simulation results show that the microgrid system can run stably under different working modes and the energy storage unit using the virtual synchronous generator technology can provide good voltage and frequency support for the microgrid system.Finally,experiments verify the supporting function of energy storage unit on the voltage and frequency of the microgrid system.
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With the application of distributed power sources,the stability of the power system has been dramatically affected.Therefore,scholars have proposed the concept of a virtual synchronous generator(VSG).However,after the system is disturbed,how to make it respond quickly and effectively to maintain the stability of the system becomes a complex problem.To address this problem,a frequency prediction component is incorporated into the control module of the VSG to enhance its performance.The Convolutional Neural NetworkLong Short-Term Memory(CNN-LSTM)model is used for frequency prediction,ensuring that the maximum energy capacity released by the storage system is maintained.Additionally,it guarantees that the inverter's output power does not exceed its rated capacity,based on the predicted frequency limit after the system experiences a disturbance.The advantage of real-time adjustment of inverter parameters is that the setting intervals for inertia and damping can be increased.The selection criteria for inertia and damping can be derived from the power angle oscillation curve of the synchronous generator.Consequently,an adaptive control strategy for VSG parameters is implemented to enhance the system's frequency restoration following disturbances.The validity and effectiveness of the model are verified through simulations in Matlab/Simulink.
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financially supported by the Talent Initiation Fund of Wuxi University(550220008).
文摘With the increasing integration of renewable energy,microgrids are increasingly facing stability challenges,primarily due to the lack of inherent inertia in inverter-dominated systems,which is traditionally provided by synchronous generators.To address this critical issue,Virtual Synchronous Generator(VSG)technology has emerged as a highly promising solution by emulating the inertia and damping characteristics of conventional synchronous generators.To enhance the operational efficiency of virtual synchronous generators(VSGs),this study employs smallsignal modeling analysis,root locus methods,and synchronous generator power-angle characteristic analysis to comprehensively evaluate how virtual inertia and damping coefficients affect frequency stability and power output during transient processes.Based on these analyses,an adaptive control strategy is proposed:increasing the virtual inertia when the rotor angular velocity undergoes rapid changes,while strengthening the damping coefficient when the speed deviation exceeds a certain threshold to suppress angular velocity oscillations.To validate the effectiveness of the proposed method,a grid-connected VSG simulation platform was developed inMATLAB/Simulink.Comparative simulations demonstrate that the proposed adaptive control strategy outperforms conventional VSGmethods by significantly reducing grid frequency deviations and shortening active power response time during active power command changes and load disturbances.This approach enhances microgrid stability and dynamic performance,confirming its viability for renewable-dominant power systems.Future work should focus on experimental validation and real-world parameter optimization,while further exploring the strategy’s effectiveness in improvingVSG low-voltage ride-through(LVRT)capability and power-sharing applications in multi-parallel configurations.
基金supported by National Natural Science Foundation of China(51777069)Science and Technology Program of China Southern Power Grid Company(037700KK52190010(GDKJXM20198272)).
文摘The damage of extreme disasters to a power grid is becoming increasingly severe,and energy storage control technology is emerging as a measure to enhance grid resilience.In this study,a novel adaptive inertia control for virtual synchronous generators is proposed for the control of wind-solar-storage combined power generation systems to form the ability for long-term power supply for load.This technology can not only provide inertia for the system but also dynamically adjust inertia according to frequency variation caused by power disturbance,avoiding rapid rise and drop of frequency in the transient process and increasing damping of a wind-solar-storage combined power generation system when the main network fails.Through low pass filtering of the sampled signal and design of the inertia control law,frequent inertia adjustment caused by measurement noise and random small fluctuation of wind speed can be avoided,and the inertia adjustment amount would not exceed the limit under any large power disturbance.The inertial boundary of the system is discussed according to the primary energy storage capacity and the tolerant power of the inverter.Convergence of a novel adaptive control algorithm is proved.Finally,a simulation model is built on PSCAD/EMTDC platform,and the effectiveness of the proposed control strategy is verified.
基金supported by the National Natural Science Foundation of China(No.62222309)the Natural Science Foundation of Shandong Province(No.ZR2022JQ29).
文摘The virtual synchronous generator(VSG),utilized as a control strategy for grid-forming inverters,is an effective method of providing inertia and voltage support to the grid.However,the VSG exhibits limited capabilities in low-voltage ride-through(LVRT)mode.Specifically,the slow response of the power loop poses challenges for VSG in grid voltage support and increases the risk of overcurrent,potentially violating present grid codes.This paper reveals the mechanism behind the delayed response speed of VSG control during the grid faults.On this basis,a compound compensation control strategy is proposed for improving the LVRT capability of the VSG,which incorporates adaptive frequency feedforward compensation(AFFC),direct power angle compensation(DPAC),internal potential compensation(IPC),and transient virtual impedance(TVI),effectively expediting the response speed and reducing transient current.Furthermore,the proposed control strategy ensures that the VSG operates smoothly back to its normal control state following the restoration from the grid faults.Subsequently,a large-signal model is developed to facilitate parameter design and stability analysis,which incorporates grid codes and TVI.Finally,the small-signal stability analysis and simulation and experimental results prove the correctness of the theoretical analysis and the effectiveness of the proposed control strategy.
基金supported by Grant PID2021-124571OB-I00 funded by MICIU/AEI/10.13039/501100011033FEDER,EU。
文摘The integration of converter-interfaced generators(CIGs)into power systems is rapidly replacing traditional synchronous machines.To ensure the security of power supply,modern power systems require the application of grid-forming technologies.This study presents a systematic small-signal analysis procedure to assess the synchronization stability of gridforming virtual synchronous generators(VSGs)considering the power system characteristics.Specifically,this procedure offers guidance in tuning controller gains to enhance stability.It is applied to six different grid-forming VSGs and experimentally tested to validate the theoretical analysis.This study concludes with key findings and a discussion on the suitability of the analyzed grid-forming VSGs based on the power system characteristics.
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.
文摘By simulating the operating dynamics of synchronous generators(SGs),the use of virtual synchronous gen-rators(VSGs)can help overcome inverter-based generators'shortcomings of low inertia and minimal damping for gridforming applications.VSGs'stability are very important for their solar and wind electricity applications.Currently,the related research primarily focuses on VSGs and their applications for microgrids.There has been little research to explore how VSGs effect low frequency oscillations in power transmission systems.This paper describes a small-signal model of a VSGSG interconnected system,which is suitable for studying low frequency oscillation damping in a power transmission grid.Based on this model,the effects of VSGs on low frequency oscillations are compared with the effects of SGs to reveal the mechanism of how VSGs infuence damping characteristics.The influence of each VSG control loop on oscillations is also analyzed in this paper.Then,the low frequency oscillation risks with different types of VSGs are described.Finally,experiments on a real-time laboratory(RT-LAB)platform are conducted to verify the small-signal analysis results.
基金supported by Science and Technology Project of State Grid Corporation of China(No.5102-201956300A-0-0-00)。
文摘In this paper,the dynamic coupling between the wind turbine rotor speed recovery(WTRSR)and inertial response of the conventional virtual synchronous generator(VSG)controlled wind farms(WFs)is analyzed.Three distinguishing features are revealed.Firstly,the inertial response characteristics of VSG controlled WFs(VSG-WFs)are impaired by the dynamic coupling.Secondly,when the influence of WTRSR is dominant,the inertial response characteristics of VSG-WFs are even worse than the condition under which WFs do not participate in the response of grid frequency.Thirdly,this phenomenon cannot be eliminated by only enlarging the inertia parameter of VSG-WFs,because the influence of WTRSR would also increase with the enhancement of inertial response.A decoupling scheme to eliminate the negative influence is then proposed in this paper.By starting the WTRSR process after inertial response period,the dynamic coupling is eliminated and the inertial response characteristics of WFs are improved.Finally,the effectiveness of the analysis and the proposed scheme are verified by simulation results.
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.
文摘The Photovoltaic(PV)plants are significantly different from the conventional synchronous generators in terms of physical and electrical characteristics,as it connects to the power grid through the voltage-source converters.High penetration PV in power system will bring several critical challenges to the safe operation of power grid including transient stability.To address this problem,the paper proposes a control strategy to help the PVs work like a synchronous generator with variable inertia by energy storage system(ESS).First,the overall control strategy of the PV-based virtual synchronous generator(PV-VSG)is illustrated.Then the control strategies for the variable inertia of the PV-VSG are designed to attenuate the transient energy of the power system after the fault.Simulation results of a simple power system show that the PV-VSG could utilize the energy preserved in the ESS to balance the transient energy variation of power grid after fault and improve the transient stability of the power system.
