Study On H-bridge Multi-level Grid Simulator Based On Improved Repetitive Control

In the process of researching wind power generation systems,testing is indispensable to study the operating characteristics of wind power generation system in the event of grid failure.Due to the randomness and uncontrollability of grid faults,it is of great significance to study grid simulators that can simulate various fault conditions in the grid.In this paper,the topology of the grid simulator is analyzed,and the control strategy of the inverter side is studied and improved.The specific research contents contains:Firstly,the main circuit form of the grid simulator is studied.The whole system is divided into three single-phase subsystems,each of which simulates one phase of the grid.All three subsystems are in the form of AC-DC-AC.In the AC-DC link,the three-phase PWM rectifier is used to make the energy return to the grid to realize the four-quadrant operation of the system;the DC-AC link uses the cascaded H-bridge inverter to generate the AC voltage to simulate the grid.Secondly,starting from the working principle and modulation strategy of single-phase H-bridge,the principle of cascaded H-bridge and carrier-phase-shifted PWM control strategy is analyzed and studied.The H-bridge cascaded multilevel inverter based on carrier phase-shifted PWM modulation strategy is designed and implemented.The simulation model of single-phase H-bridge circuit and H-bridge cascaded five-level inverter and H-bridge cascaded seven-level inverter is built on Matlab/simulink experimental platform,and the simulation results are compared.Thirdly,n the control of H-bridge cascade inverter,aiming at the problem of error and slow dynamic response in repeated control,an improved repeating control strategy is proposed.The filter is designed by linear interpolation method to make it close to the ideal model.To achieve fast tracking of rapid changes in the frequency of the reference signal.The state-space equation of the three-phase cascade h-bridge inverter was established,and the simulation model was built through Matlab/simulink in combination with the improved repetitive control.Fourthly,based on the previous research,the simulation model of the grid simulator is built.The steady state performance and dynamic performance of the design model are analyzed through simulation.The grid simulator simulates the normal grid voltage,three-phase voltage imbalance,waveform distortion and voltage amplitude.Mutation,voltage frequency mutation and other functions are verified.