Research On The Control Strategy Of Power Sharing For Multi Parallel VSG Inverters

In order to effectively avoid the various disadvantages of distributed generation and achieve distributed power friendly access to the power grid,scholars at home and abroad have proposed inverter control strategy based on virtual synchronous generator(VSG).Simulating the external characteristics of the synchronous generator to improve the operating performance of the inverter is conducive to the stable operation of the system.In actual operation,in order to realize the requirement of high power supply of the system,the parallel operation of the VSG inverter is imperative.This paper mainly focuses on the research of power sharing control technology of VSG inverter in parallel operation.The main contents are as follows:1)The mathematical model of the VSG inverter is set up,and the parameter selection method of the LCL filter is given.And the parameter selection method of LCL filter is analyzed.Based on the frequency modulation,voltage regulation and rotor motion equation of synchronous generator,a virtual synchronous generator model is designed,including virtual active power governor,virtual excitation controller and VSG control algorithm.The overall optimization of the traditional inverter improves the compatibility of the inverter.2)In the parallel VSG inverter system,the influence of circulating current on the power distribution is analyzed.The conditions that the physical circuit and control strategy need to meet when the shunt VSG inverter distributes power accurately according to the rated capacity ratio are described.Aiming at the limitations of P-f,Q-U droop control in medium and low voltage networks,the virtual impedance is introduced to realize the power decoupling control.On this basis,a power sharing scheme for adaptive virtual impedance is proposed.The control strategies of P-f,Q-U droop control,traditional virtual impedance control and virtual impedance adaptive control are compared and analyzed.The superiority of the proposed strategy in the realization of power allocation is proved.3)In the distributed control parallel VSG inverter system with a small amount of information interaction,the consensus algorithm introduced is proposed to apply the consistent coordinated control strategy of active power and frequency of VSG inverters based on the principle of consistent coordinated control.The PSCAD/EMTDC model simulation verification:in the parallel system,the inverter only interacts with adjacent inverters to obtain the physical quantity information,which not only achieves the frequency stability control,but also realizes the power distribution under different requirements.