Research On Control And Test Technology Of Virtual Synchronous Generator For Microgrid Inverters

Energy is the basis of economic development,the demand for energy and the pressure of the environment make the microgrid be the focus of research for a period of time,the development of micro-grid put forward higher requirements for the control strategy of microgrid inverters.The virtual synchronous generator(VSG)control strategy can operate in two modes of parallel grid and off grid,which is conducive to smooth switching of the micro-grid system;VSG control can enhance the stability of the micro-grid system by adding virtual inertia,damping and synchronous impedance in the control algorithm,therefore,VSG control has become a research hot spots at the present stage.In this paper,based on the control strategy of micro-grid,the control of virtual synchronous generator was analyzed and studied,the main contents of this paper were as follows:(1)Several typical VSG control structures were compared,Closed loop transfer function expressions of active power and frequency were derived,and the characteristic differences of several control structures were compared by zero pole distribution.For the first typical phase-lockless loop control structure,the effects of inertia,damping and impedance parameters under different damping systems were analyzed.For the problem of dynamic over-limit risk and steady-state error that occurs when the grid frequency deviates from the rated value of the VSG control,an integral control of the active power deviation was proposed to reduce the influence of the grid frequency change.(2)The differences between VSG and the real synchronous generator in terms of parameter flexibility,stability and overload capacity and energy transfer process were compared and analyzed.It provided a theoretical basis for the grid connected inverter testing to adopt VSG control.The differences and connections between droop control and VSG control were analyzed.By improving the droop control structure,it was equivalent to VSG.Based on differences of droop and VSG characteristics,the test plan of microgrid inverter under two modes of distinguishing and leaving the network was raised.The main points of future VSG test standards were proposed,which can provide reference for the development of microgrid inverter test standards.(3)Matlab/Simulink simulation models in different frequencies situation was established to verify the traditional VSG and the improved VSG control strategy,and the simulation models of droop control and VSG control were established to verify the proposed VSG test schemes.