Research On Parallel Control Strategy Of T-type Three-level Inverters Based On Virtual Synchronous

The auxiliary power inverter is an important component of EMU and other vehicles.In order to realize the power supply system of redundant auxiliary power supply for train with high power,high reliability and easy expansion,most of the advanced auxiliary power inverters of EMU adopt the technology of parallel connection without interconnection.Virtual synchronous generator(VSG)technology originates from microgrid control,Its main idea is to introduce the operation characteristics of synchronous generator into the control of inverters,so that the inverters not only have steady-state droop characteristics and no interconnected lines,but also simulate the inertia of synchronous generator,which can dynamically compensate for the power difference and reduce the frequency fluctuation.Therefore,VSG technology to auxiliary power inverter control is applied in this paper.At the same time,because of the simple structure and high reliability of T-type three-level inverters,which meet the urgent need of auxiliary power inverters for high-voltage and large-capacity converters.Therefore,the parallel control of T-type three-level inverters based on VSG in the background of auxiliary power supply system for trains is mainly studied in this paper.Firstly,taking the independent operation of a single T-level three-level inverter as the research object,the control strategy of a single system based on VSG is designed,which includes VSG power outer loop,voltage and current inner loop and T-type three-level neutral-point potential balance control.The influence of core parameters moment of inertia and damping coefficient on the output frequency response of the system is further analyzed.Secondly,taking the parallel operation of T-type three-level inverters based on VSG as the research object,the characteristic equation of VSG parallel system is established.According to the eigenvalue,the influence of core parameters on the output active response of parallel system is analyzed,and the range of core parameters is limited.Then,aiming at the problem that the dynamic regulation performance of active power and frequency cannot be taken into account when the core parameters of VSG parallel system are fixed,an optimization control strategy of self-adjusting core parameters is proposed.Finally,an integrated control scheme of VSG parallel system with parallel pre-synchronization control is presented.In order to verify the validity of the control strategy designed in this paper,two T-type three-level inverters parallel simulation models are established by PSIM simulation software,and parallel experimental platform based on two T-type three-level inverters with STM32F407ZG as the main control chip is built,which can not only suppress the active oscillation in the process of VSG merging into AC bus,but also improve the stability of the system.The support capability of frequency reduces the influence of damping coefficient on active power-frequency sag characteristics,and ensures the power sharing of the two inverters after parallel stabilization.