The increasing integration of wind power generation brings more uncertainty into the power system. Since the correlation may have a notable influence on the power system,the output powers of wind farms are generally c...The increasing integration of wind power generation brings more uncertainty into the power system. Since the correlation may have a notable influence on the power system,the output powers of wind farms are generally considered as correlated random variables in uncertainty analysis. In this paper, the C-vine pair copula theory is introduced to describe the complicated dependence of multidimensional wind power injection, and samples obeying this dependence structure are generated. Monte Carlo simulation is performed to analyze the small signal stability of a test system. The probabilistic stability under different correlation models and different operating conditions scenarios is investigated. The results indicate that the probabilistic small signal stability analysis adopting pair copula model is more accurate and stable than other dependence models under different conditions.展开更多
With good adaptability to weak power grids,the grid-forming inverter becomes the foundation of future power grids with high-proportion renewable energy.Moreover,the virtual synchronous generator(VSG)control is recogni...With good adaptability to weak power grids,the grid-forming inverter becomes the foundation of future power grids with high-proportion renewable energy.Moreover,the virtual synchronous generator(VSG)control is recognized as the mainstream control strategy for grid-forming inverters.For permanent magnet synchronous generator(PMSG)based wind generation systems connected to power grid via VSG-controlled grid-forming inverters,some novel impacts on the low-frequency oscillations(LFOs)emerge in power grids.The first impact involves the negative/positive damping effect on LFOs.In this paper,the small-signal torque model of VSG-controlled PMSGbased wind generation systems is established based on the damping torque analysis method,revealing the influence mechanism of machine-side dynamics on LFOs and proving the necessity of the double-mass model for accurate stability analysis.The second impact is the resonance effect between torsional oscillation and LFOs.Subsequently,this paper uses the open-loop resonance analysis method to study the resonance mechanism and to predict the root trajectory.Then,a damping enhancement strategy is proposed to weaken and eliminate the negative damping effect of machine-side dynamics on LFOs and the resonance effect between torsional oscillation and LFOs.Finally,the analysis result is validated through a case study involving the connection of the VSG-controlled PMSG-based wind generation system to the IEEE 39-bus AC grid,supporting the industrial application and stable operation of VSG-controlled PMSGbased wind generation systems.展开更多
Most permanent magnet synchronous generator(PMSG)based wind generation systems currently employ grid-following control,relying on a phase-locked loop(PLL)for grid connection.However,it leads to a lack of inertia suppo...Most permanent magnet synchronous generator(PMSG)based wind generation systems currently employ grid-following control,relying on a phase-locked loop(PLL)for grid connection.However,it leads to a lack of inertia support in the system.To address this,the virtual inertia control(VIC)is crucial for improvement,yet it introduces potential instability due to torsional oscillation interaction with PLL and low-frequency oscillations,which is an underexplored area.This paper presents a comprehensive analysis of the grid-connected PMSG-based wind generation system.It confirms the necessity of employing a full-order model for studying stability on the quasi-electromechanical timescale(QET)by a comparison with the reduced-order model.Then,a comprehensive modal analysis is conducted to analyze the effect of VIC parameters,shaft inertia time constant,PLL parameters,and torsional oscillation damping(TOD)controller gain on the interaction of QET oscillations under two typical control strategies.The occurrence of interaction and mode conversion is observed when the oscillation frequency and root loci of the torsional,PLL,and low-frequency oscillations are close.Finally,a theoretical analysis is validated via simulation verification in Simulink.These findings offer a valuable guidance for industrial PMSG applications considering VIC.展开更多
External disturbances can induce torsional oscillation with weak damping in the shaft system of permanent magnet synchronous generators(PMSGs)based wind generation system,thereby inducing low-frequency oscillations.Ho...External disturbances can induce torsional oscillation with weak damping in the shaft system of permanent magnet synchronous generators(PMSGs)based wind generation system,thereby inducing low-frequency oscillations.However,the influence of electromagnetic torque on the shaft system damping and corresponding parameter laws have been scarcely explored.We define the electrical damping coefficient as a quantitative measure for the influence of electromagnetic torque on the shaft system damping.The torsional oscillation damping characteristics of the shaft system under vector control are analyzed,and the transfer function for electromagnetic torque and speed is derived.Additionally,we elucidate the mechanism by which the electromagnetic torque influences the shaft system damping.Simultaneously,laws describing the influence of wind speed,system parameters,and control parameters on the torsional oscillation damping are analyzed.Accordingly,the optimal damping angle of the shaft system a torsional oscillation suppression strategy is proposed to compensate for with uncertainty in the parameters affecting damping.The studied system is modeled using MATLAB/Simulink,and the simulation results validate the effectiveness of the theoretical analysis and proposed torsional oscillation suppression strategy.展开更多
Parallel operation of inverter modules is the solution to increase the reliability,efficiency,and redundancy of inverters in microgrids.Load sharing among inverters in distributed generators(DGs)is a key issue.This st...Parallel operation of inverter modules is the solution to increase the reliability,efficiency,and redundancy of inverters in microgrids.Load sharing among inverters in distributed generators(DGs)is a key issue.This study investigates the feasibility of power-sharing among parallel DGs using a dual control strategy in islanded mode of a microgrid.PQ control and droop control techniques are established to control the microgrid operation.P-f and Q-E droop control is used to attain real and reactive power sharing.The frequency variation caused by load change is an issue in droop control strategy whereas the tracking error of inverter power in PQ control is also a challenge.To address these issues,two DGs are interfaced with two parallel inverters in an islanded AC microgrid.PQ control is investigated for controlling the output real and reactive power of the DGs by assigning their references.The inverter under enhanced droop control implements power reallocation to restore the frequency among the distributed generators with predefined droop characteristics.A dual control strategy is proposed for the AC microgrid under islanded operation without communication link.Simulation studies are carried out using MATLAB/SIMULINK and the results show the validity and effective power-sharing performance of the system while maintaining a stable operation when the microgrid is in islanding mode.展开更多
Transient angle stability of inverters equipped with the robust droop controller is investigated in this work.At first,the conditions on the control references to guarantee the existence of a feasible post-disturbance...Transient angle stability of inverters equipped with the robust droop controller is investigated in this work.At first,the conditions on the control references to guarantee the existence of a feasible post-disturbance operating point are derived.Then,the post-disturbance equilibrium points are found and their stability properties are characterized.Furthermore,the attraction regions of the stable equilibrium points are accurately depicted by calculating the stable and unstable manifolds of the surrounding unstable equilibrium points,which presents an explanation to system transient stability.Finally,the transient control considerations are provided to help the inverter ridethrough the disturbance and maintain its stability characteristics.It is shown that the transient angle stability is not a serious problem for droop controlled inverters with proper control settings.展开更多
The electric vehicle(EV)charging station is a critical part of the infrastructure for the wide adoption of EVs.Realtime simulation of an EV station plays an essential role in testing its operation under different oper...The electric vehicle(EV)charging station is a critical part of the infrastructure for the wide adoption of EVs.Realtime simulation of an EV station plays an essential role in testing its operation under different operating modes.However,the large numbers of high-frequency power electronic switches contained in EV chargers pose great challenges for real-time simulation.This paper proposes a compact electromagnetic transient program(C-EMTP)algorithm for FPGA-based real-time simulation of an EV station with multiple high-frequency chargers.The C-EMTP algorithm transforms the traditional EMTP algorithm into two parallel sub-tasks only consisting of simple matrix operations,to fully utilize the high parallelism of FPGA.The simulation time step can be greatly reduced compared with that of the traditional EMTP algorithm,and so the simulation accuracy for high-frequency power electronics is improved.The EV chargers can be decoupled with each other and simulated in parallel.A CPU-FPGA-based realtime simulation platform is developed and the proposed simulation of the EV station is implemented.The control strategy is simulated in a CPU with 100μs time-step,while the EV station circuit topology is simulated in a single FPGA with a 250 ns time-step.In the case studies,the EV station consists of a two-level rectifier and five dual-active bridge(DAB)EV chargers.It is tested under different scenarios,and the real-time simulation results are validated using PSCAD/EMTDC.展开更多
Globally abundant wave energy for power generation attracts ever increasing attention. Because of non-linear dynamics and potential uncertainties in ocean energy conversion systems, generation productivity needs to be...Globally abundant wave energy for power generation attracts ever increasing attention. Because of non-linear dynamics and potential uncertainties in ocean energy conversion systems, generation productivity needs to be increased by applying robust control algorithms. This paper focuses on control strategies for a small ocean energy conversion system based on a direct driven permanent magnet synchronous generator (PMSG). It evaluates the performance of two kinds of control strategies, i.e., traditional field-oriented control (FOC) and robust adaptive control. The proposed adaptive control successfully achieves maximum velocity and stable power production, with reduced speed tracking error and system response time. The adaptive control also guarantees global system stability and its superiority over FOC by using a non-linear back-stepping control technique offering a better optimization solution. The robustness of the ocean energy conversion system is further enhanced by investigating the Lyapunov method and the use of a DC-DC boost converter. To overcome system complexity, turbine-generator based power take-off (PTO) is considered. A Matlab/Simulink study verifies the advantages of a non-linear control strategy for an Oscillating Water Column (OWC) based power generation system.展开更多
Fully harnessing the ocean wave’s renewable energy resources could benefit coastal countries.However,ocean wave energy harvesting systems encounter several challenges,i.e.,marine uncertainties,long-distance mainte-na...Fully harnessing the ocean wave’s renewable energy resources could benefit coastal countries.However,ocean wave energy harvesting systems encounter several challenges,i.e.,marine uncertainties,long-distance mainte-nance,power fluctuations,irregular wave currents,non-linear generator dynamics,turbine limitations,cost optimization,and power smoothing issues.To overcome these challenges,this paper proposes a new multi-stage con-trol design approach for performance evaluation of the os-cillating water column(OWC)-based ocean wave energy conversion(OWEC)system.The first stage optimizes the Wells turbine by implementing an efficient airflow control strategy.It achieves maximum power-harvesting ability by eliminating stalling phenomena.In the second stage,we investigate the robustness of the permanent magnet syn-chronous generator-based OWEC system by designing adaptive back-stepping controllers,taking into account the Lyapunov stability theory.It accomplishes precise speed regulation for optimal power extraction while delivering reduced delay response and percentage errors.To ensure the OWEC system’s availability,the third stage incorporates fault-ride-through capabilities.It executes a fault reconfig-urable control for a parallel converter configuration,elimi-nating only the faulty leg instead of the entire power con-verter.In the fourth stage,a supercapacitors-based energy management system achieves power smoothing,even when the OWC plant output power fluctuates.We accomplish this by implementing a model predictive control strategy.Finally,the Matlab/Simulink results verify that the presented mul-ti-stage control for the OWC OWEC system is an effective design approach,offering an optimal,robust,reliable,and power-smoothing solution.展开更多
基金supported by the National Natural Science Foundation of China(51307107,51477098,51877133)SRFDP(20130073120034)State Grid Corporation of China Science and Technology Project(Hybrid AC/DC Power Grid Planning and Optimization Study Under the Framework of GEI)。
文摘The increasing integration of wind power generation brings more uncertainty into the power system. Since the correlation may have a notable influence on the power system,the output powers of wind farms are generally considered as correlated random variables in uncertainty analysis. In this paper, the C-vine pair copula theory is introduced to describe the complicated dependence of multidimensional wind power injection, and samples obeying this dependence structure are generated. Monte Carlo simulation is performed to analyze the small signal stability of a test system. The probabilistic stability under different correlation models and different operating conditions scenarios is investigated. The results indicate that the probabilistic small signal stability analysis adopting pair copula model is more accurate and stable than other dependence models under different conditions.
基金supported in part by the National Key R&D Program of China(No.2022YFE0105200)in part by the State Grid Zhejiang Electric Power Company Science and Technology Program(No.5211JX230004)。
文摘With good adaptability to weak power grids,the grid-forming inverter becomes the foundation of future power grids with high-proportion renewable energy.Moreover,the virtual synchronous generator(VSG)control is recognized as the mainstream control strategy for grid-forming inverters.For permanent magnet synchronous generator(PMSG)based wind generation systems connected to power grid via VSG-controlled grid-forming inverters,some novel impacts on the low-frequency oscillations(LFOs)emerge in power grids.The first impact involves the negative/positive damping effect on LFOs.In this paper,the small-signal torque model of VSG-controlled PMSGbased wind generation systems is established based on the damping torque analysis method,revealing the influence mechanism of machine-side dynamics on LFOs and proving the necessity of the double-mass model for accurate stability analysis.The second impact is the resonance effect between torsional oscillation and LFOs.Subsequently,this paper uses the open-loop resonance analysis method to study the resonance mechanism and to predict the root trajectory.Then,a damping enhancement strategy is proposed to weaken and eliminate the negative damping effect of machine-side dynamics on LFOs and the resonance effect between torsional oscillation and LFOs.Finally,the analysis result is validated through a case study involving the connection of the VSG-controlled PMSG-based wind generation system to the IEEE 39-bus AC grid,supporting the industrial application and stable operation of VSG-controlled PMSGbased wind generation systems.
基金supported by the National Key R&D Program of China(No.2022YFB2402800).
文摘Most permanent magnet synchronous generator(PMSG)based wind generation systems currently employ grid-following control,relying on a phase-locked loop(PLL)for grid connection.However,it leads to a lack of inertia support in the system.To address this,the virtual inertia control(VIC)is crucial for improvement,yet it introduces potential instability due to torsional oscillation interaction with PLL and low-frequency oscillations,which is an underexplored area.This paper presents a comprehensive analysis of the grid-connected PMSG-based wind generation system.It confirms the necessity of employing a full-order model for studying stability on the quasi-electromechanical timescale(QET)by a comparison with the reduced-order model.Then,a comprehensive modal analysis is conducted to analyze the effect of VIC parameters,shaft inertia time constant,PLL parameters,and torsional oscillation damping(TOD)controller gain on the interaction of QET oscillations under two typical control strategies.The occurrence of interaction and mode conversion is observed when the oscillation frequency and root loci of the torsional,PLL,and low-frequency oscillations are close.Finally,a theoretical analysis is validated via simulation verification in Simulink.These findings offer a valuable guidance for industrial PMSG applications considering VIC.
基金supported in part by the National Key R&D Program of China(No.2022YFE0105200)in part by State Grid Zhejiang Electric Power Company Science and Technology Program(No.5211JX230004).
文摘External disturbances can induce torsional oscillation with weak damping in the shaft system of permanent magnet synchronous generators(PMSGs)based wind generation system,thereby inducing low-frequency oscillations.However,the influence of electromagnetic torque on the shaft system damping and corresponding parameter laws have been scarcely explored.We define the electrical damping coefficient as a quantitative measure for the influence of electromagnetic torque on the shaft system damping.The torsional oscillation damping characteristics of the shaft system under vector control are analyzed,and the transfer function for electromagnetic torque and speed is derived.Additionally,we elucidate the mechanism by which the electromagnetic torque influences the shaft system damping.Simultaneously,laws describing the influence of wind speed,system parameters,and control parameters on the torsional oscillation damping are analyzed.Accordingly,the optimal damping angle of the shaft system a torsional oscillation suppression strategy is proposed to compensate for with uncertainty in the parameters affecting damping.The studied system is modeled using MATLAB/Simulink,and the simulation results validate the effectiveness of the theoretical analysis and proposed torsional oscillation suppression strategy.
基金This work was supported in part by the National Natural Science Foundation of China under Grant 51477098National Key R&D Program of China(2016YFB0900504).
文摘Parallel operation of inverter modules is the solution to increase the reliability,efficiency,and redundancy of inverters in microgrids.Load sharing among inverters in distributed generators(DGs)is a key issue.This study investigates the feasibility of power-sharing among parallel DGs using a dual control strategy in islanded mode of a microgrid.PQ control and droop control techniques are established to control the microgrid operation.P-f and Q-E droop control is used to attain real and reactive power sharing.The frequency variation caused by load change is an issue in droop control strategy whereas the tracking error of inverter power in PQ control is also a challenge.To address these issues,two DGs are interfaced with two parallel inverters in an islanded AC microgrid.PQ control is investigated for controlling the output real and reactive power of the DGs by assigning their references.The inverter under enhanced droop control implements power reallocation to restore the frequency among the distributed generators with predefined droop characteristics.A dual control strategy is proposed for the AC microgrid under islanded operation without communication link.Simulation studies are carried out using MATLAB/SIMULINK and the results show the validity and effective power-sharing performance of the system while maintaining a stable operation when the microgrid is in islanding mode.
基金supported in part by National Natural Science Foundation of China (No.51877133)China Scholarship Council,and National Science Foundation (Award No.1810105)。
文摘Transient angle stability of inverters equipped with the robust droop controller is investigated in this work.At first,the conditions on the control references to guarantee the existence of a feasible post-disturbance operating point are derived.Then,the post-disturbance equilibrium points are found and their stability properties are characterized.Furthermore,the attraction regions of the stable equilibrium points are accurately depicted by calculating the stable and unstable manifolds of the surrounding unstable equilibrium points,which presents an explanation to system transient stability.Finally,the transient control considerations are provided to help the inverter ridethrough the disturbance and maintain its stability characteristics.It is shown that the transient angle stability is not a serious problem for droop controlled inverters with proper control settings.
基金supported by China Postdoctoral Science Foundation(BX20200221,2020 M671122)National Key Research and Development Program of China(2019YFE012784)National Natural Science Foundation of China(51877133).
文摘The electric vehicle(EV)charging station is a critical part of the infrastructure for the wide adoption of EVs.Realtime simulation of an EV station plays an essential role in testing its operation under different operating modes.However,the large numbers of high-frequency power electronic switches contained in EV chargers pose great challenges for real-time simulation.This paper proposes a compact electromagnetic transient program(C-EMTP)algorithm for FPGA-based real-time simulation of an EV station with multiple high-frequency chargers.The C-EMTP algorithm transforms the traditional EMTP algorithm into two parallel sub-tasks only consisting of simple matrix operations,to fully utilize the high parallelism of FPGA.The simulation time step can be greatly reduced compared with that of the traditional EMTP algorithm,and so the simulation accuracy for high-frequency power electronics is improved.The EV chargers can be decoupled with each other and simulated in parallel.A CPU-FPGA-based realtime simulation platform is developed and the proposed simulation of the EV station is implemented.The control strategy is simulated in a CPU with 100μs time-step,while the EV station circuit topology is simulated in a single FPGA with a 250 ns time-step.In the case studies,the EV station consists of a two-level rectifier and five dual-active bridge(DAB)EV chargers.It is tested under different scenarios,and the real-time simulation results are validated using PSCAD/EMTDC.
基金supported by National Natural Science Foundation of China(51477098).
文摘Globally abundant wave energy for power generation attracts ever increasing attention. Because of non-linear dynamics and potential uncertainties in ocean energy conversion systems, generation productivity needs to be increased by applying robust control algorithms. This paper focuses on control strategies for a small ocean energy conversion system based on a direct driven permanent magnet synchronous generator (PMSG). It evaluates the performance of two kinds of control strategies, i.e., traditional field-oriented control (FOC) and robust adaptive control. The proposed adaptive control successfully achieves maximum velocity and stable power production, with reduced speed tracking error and system response time. The adaptive control also guarantees global system stability and its superiority over FOC by using a non-linear back-stepping control technique offering a better optimization solution. The robustness of the ocean energy conversion system is further enhanced by investigating the Lyapunov method and the use of a DC-DC boost converter. To overcome system complexity, turbine-generator based power take-off (PTO) is considered. A Matlab/Simulink study verifies the advantages of a non-linear control strategy for an Oscillating Water Column (OWC) based power generation system.
基金supported by the National Natural Science Foundation of China(No.52107113 and No.51877133).
文摘Fully harnessing the ocean wave’s renewable energy resources could benefit coastal countries.However,ocean wave energy harvesting systems encounter several challenges,i.e.,marine uncertainties,long-distance mainte-nance,power fluctuations,irregular wave currents,non-linear generator dynamics,turbine limitations,cost optimization,and power smoothing issues.To overcome these challenges,this paper proposes a new multi-stage con-trol design approach for performance evaluation of the os-cillating water column(OWC)-based ocean wave energy conversion(OWEC)system.The first stage optimizes the Wells turbine by implementing an efficient airflow control strategy.It achieves maximum power-harvesting ability by eliminating stalling phenomena.In the second stage,we investigate the robustness of the permanent magnet syn-chronous generator-based OWEC system by designing adaptive back-stepping controllers,taking into account the Lyapunov stability theory.It accomplishes precise speed regulation for optimal power extraction while delivering reduced delay response and percentage errors.To ensure the OWEC system’s availability,the third stage incorporates fault-ride-through capabilities.It executes a fault reconfig-urable control for a parallel converter configuration,elimi-nating only the faulty leg instead of the entire power con-verter.In the fourth stage,a supercapacitors-based energy management system achieves power smoothing,even when the OWC plant output power fluctuates.We accomplish this by implementing a model predictive control strategy.Finally,the Matlab/Simulink results verify that the presented mul-ti-stage control for the OWC OWEC system is an effective design approach,offering an optimal,robust,reliable,and power-smoothing solution.
