Research On Grid-forming Control Strategy Of Microgrid Inverter

The development and utilization of new energy,energy conservation and emission reduction,and the construction of a new generation of power grids have become an important strategic deployment in the world.In order to adapt to the strategy of energy development and improve the utilization of new energy,it is a trend to build a new generation of power system by using high power electronic devices.In this paper,we researched on the grid-forming control method of inverters with energy storage devices.In one hand,we focused on the method of multi-mode control in grid-on or grid-off modes.In another hand,we researched the current sharing control of the parallel inverters.The main research contents and innovations were listed as follows:(1)We summarized the research background,definition and operation mode of microgrid,as well as the control structure of microgrid.The current research status and current sharing methods of parallel inverters are analyzed.(2)Firstly,we analyzed the topology of three-phase full bridge inverter,and then,we deduced the inverter's physical model in abc coordination,?? coordination and dq coordination,respectively.Also,we analyzed their characteristics when considering the complexity of the realization of the controller.Lastly,we analyzed the commonly used control strategy of inverter and its characteristics.(3)The multi-mode control method of microgrid inverter was studied.A method of frequent deviation-free control method,based on virtual synchronous machine control(VSGC)was presented in this paper.This method used a proportion integration(PI)block to replace damping block in rotor motion equation of the VSGC.This method can realize the multi-mode control of the inverter and eliminate the frequency deviation of output voltage of the inverter.The reduced order small signal model is established,and the influence of controller parameters on system stability is analyzed.(4)The power sharing control method of microgrid inverter parallel system was studied.Firstly,this paper analyzed the mechanism of circulating current in the inverter parallel system based on droop control and its suppression method.The controller adopted two level control structure.Firstly,an adaptively virtual impedance method was used to realize the accurate power sharing between the parallel invertermodules of the inverter.Secondly,the voltage and frequency of the parallel system are repaired by the distributed secondly layer control.(5)We research the grid-forming control of microgrid inverter by experiment.Firstly,we introduced the topology structure and hardware design of the experimental platform.The proposed methods of frequent deviation-free control based on VSGC and the parallel power sharing control based on consensus control were validated by experiment.Finally,experience results proved the effectiveness and feasibility of the proposed method.