Research Of Auxiliary Inverter Parallel Technology Based On Virtualsynchronous Generator

Auxiliary inverter is an important protection for the operation of vehicles such as CRH.At present,parallel power supply technology has been commonly used in advanced CRH auxiliary inverter to realize N+1 redundance,improve reliability and maintainability,ensure uninterrupted power supply.Circumfluence reduction of the parallel inverter system has become the key technical problem to solve.Originated from micro-grid control,virtual synchronous generator technology is adopted to control the inverter to perform as synchronous generator.Thus the parallel inverter can adjust the output voltage amplitude and frequency based on real-time output of active and reactive power automatically.Therefore,the load balancing between inverters is realized without communication,achieving the purpose of reducing circumfluence.In this paper,the virtual synchronous generator technology is applied in vehicle-assisted inverter control to verify its feasibility.This paper is organized as follows.Firstly,the dynamic model of virtual synchronous generator is established,including electrical part and mechanical part.And using the Rotor Motion Equation,Flux Equation and Electromagnetic Transient Equation to build up the mathematical model of synchronous motor.Based on this,the frequency-active power and voltage-reactive power controller is designed to enable the synchronous inverter has the droop characteristic of synchronous generator.Then,considering the actual situation,the inverter topology and modulation mode are designed.According to the load characteristics of the auxiliary inverter,the main circuit part adopts three-phase four-leg structure.Deducing the mathematical model of the inverter bridge topology,and Considering its characteristics,3D SVPWM technique is adopted in the modulation method.The reason of the circulation generation between multiple inverters is analyzed theoretically.It's due to the inverter output voltage amplitude,frequency and phase can not be exactly the same.The factors influencing the size and direction of the circulation are deduced from the formula.It is judged that the virtual synchronous generator algorithm can make the parallel inverter system evenly distribute the active and reactive loads to achieve the current sharing.According to the technical requirements of the system,the various parts of the circuit and device selection,including inverter,LCL filter,drive circuit,sampling circuit,and the controller parameters are designed respectively.Guided by the analysis result,a single inverter simulation and a parallel inverter system are simulated.Then,comparison on control effect between traditional sagging algorithm and virtual synchronous motor algorithm is achieved to verify the feasibility of the scheme proposed.Finally,a 2000W parallel inverter system physical platform is established.The experiment results show that the single inverter controlled by the virtual synchronous motor can supply power to the load successfully.The load can also be divided averagely between the identical inverters in parallel with constrained circumfluence,reaching the same effect as the traditional algorithm.Also,it has a simpler structure without coordinate transformation and phase-locked loop(PLL)than the double-loop controller based on Park transformation,which proves the effectiveness further.