| With a larger scale of distributed generation in micro-grid integrated into the grid,it is a challenge for the stable operation of the grid that the power electronic device-based distributed power systems have a lack of inertia,damping and can’t participate in the frequency and voltage regulation of the electric system.The virtual synchronous generator(VSG)control mimics the mechanical properties and the droop characteristic of synchronous generators,it provides the micro-grid or the distribution network with voltage and frequency support.This paper illustrates the realization of virtual synchronous generator control on a battery energy storage system(BESS).Firstly,this paper introduces the application and key techniques of BESS in micro-grid,and several traditional control methods of BESS as well as VSG structures are summarized.The global VSG control structure for BESS is then illustrated,including the rotor swing function and stator voltage equation,the droop characteristic,and voltage-current dual closed-loop with improved output impedance characteristic by designing virtual impedance as the bottom control of converter.A micro-grid system,with the VSG-controlled BESS as the main power supply,is established to analyze its operation mechanism under islanded and grid connected mode as well as the switch process between them.By studying the small-signal stability and active power transient response of the system under grid connected mode,this paper presents a design scheme for key control parameters.Finally,a simulation model and low-power experimental platform is built,the simulation and experimental results verify that the VSG-controlled BESS can support the micro-grid bus with a stable voltage and frequency under islanded mode,respond to the grid frequency fluctuation and provide power output with a good transient performance under grid-connected mode,and realize a seamless transition between the two modes. |
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