Research On Parallel Strategy Based On The Droop Control Of Three-Phase Inverter

Microgrid is of great significance to promote energy conservation and emission reduction and the sustainable development of energy.As the interface of the distributed generation and the microgrid,the control performance of the inverter will be directly related to the performance of the microgrid.In this paper,the closed loop control strategy of three-phase inverter and the circulation current suppression strategy of the parallel inverter system are researched.The stable operation of the inverter is the basis of the parallel operation of the inverter.In order to have favorable control performance,the resonance problem of the LC filter of the inverter is studied.The mathematical model of three-phase inverter in static three-phase coordinate and static two-phase coordinate is established,and the influence of resonance on the performance of inverter open-loop control system and closed-loop control system is analyzed.Then,the inductor current active damping control is used to suppress the resonance of LC filter,so as to improve the stability of the closed-loop control system of inverter with quasi proportional resonant control,and improve the steady-state and dynamic performance of the system.The droop control of the three-phase inverter is studied.A small signal model of inverter parallel system is established,and the droop control parameters are optimized.Calculating the instantaneous power output of the three-phase inverter by using inductor current instead of output current,reducing the number of sensors required by the parallel system of inverter with droop control and improving system reliability.The circulation of the inverters is analyzed when the droop control strategy is adopted.The circulating current is calculated by the equivalent impedance of the inverter,and the influence of the equivalent impedance difference on the circulation is analyzed.Based on the analysis results,a circulation suppression method based on the equivalent impedance difference is proposed,and the realization of this method is given.Through Matlab/Simulink simulation and platform experiment of three-phase inverter parallel system,the correctness of the analysis conclusion and the feasibility and effectiveness of the proposed control strategy are verified.