Study On Control Strategy Of Bidirectional DC/AC Converter

Flexible substation is a new generation substation characterized by wide application of power electronic technology,whitch has important application prospects in flexible access of centralized and distributed new energy,diversified power supply for users,and AC/DC hybrid interconnection,etc.The bidirectional DC/AC converter is an important part of the flexible substation.To ensure its safe and reliable operation,it is necessary to study the control strategy of bidirectional DC/AC converter applied in flexible substation.Therefore,the research on control strategy of bidirectional DC/AC converter has practical significance.Based on power electronics technology and automatic control theory,the operation mode of the bidirectional DC/AC converter and the problems to be solved in different modes for the application environment of flexible substations are deeply analyzed in this paper.Its single-alone control mainly includes rectification mode and on-grid and off-grid inverter and its switching mode.The on-grid and off-grid inverter mode can be operated in parallel to realize system expansion.In the rectifier operation mode,the voltage and current double closed-loop control strategy is used to control the DC bus voltage;in the on-grid and off-grid inverter and its switching mode,the virtual synchronous generator control strategy is used to control the fundamental wave.On the basis of synchronous generator control,the respective harmonic compensation strategy based on VPI control strategy to solve the low-order harmonic problem.And a voltage imbalance control strategy based on VPI control strategy is used to address voltage imbalance during off-grid operation;In parallel operation mode,a virtual synchronous generator control strategy is adopted for power distribution to achieve load power sharing.Aiming at zero-sequence circulating current problem caused by parallel operation of a common AC and DC bus,a zero sequence circulating current suppression strategy based on proportional differential(PD)is proposed.In order to verify the correctness of the control strategy adopted and the effectiveness of the proposed control strategy,the Matlab/Simulink simulation software and the experimental platform are used to study the control strategies of the bidirectional DC/AC converter under different operating modes.The correctness of the control strategy adopted in the thesis and the effectiveness of the proposed control strategy are verified by simulation and experimental results,Provide reference for practical application.