Research On Autonomous Parallel Technology Of Virtual Synchronous VSC

With the increasing depletion of traditional fossil fuels and the increasingly serious environmental pollution,the application of renewable energy such as solar energy and wind power has become more and more extensive.Inverter can convert the DC that solar panels generate and the variable frequency AC that wind turbines generate to constant frequency AC,therefore it is an essential equipment for new energy generation.When the inverter works in the controlled voltage source mode,it can operate in parallel to the grid or can operate in island,and seamless switch between the two modes can enhance the flexibility of system operation.When the voltage source inverter is controlled by the virtual synchronous machine,the voltage source inverter can be more friendly to the grid because of the rotor inertia similar to the traditional synchronous generator,which is favorable to the stability of the system.When multiple voltage source inverters with the characteristics of virtual synchronous machines operate in parallel,the utilization efficiency of new energy sources is increased correspondingly by effectively concentrating distributed distributed power sources.In this paper,the structure and operation characteristics of a traditional synchronous generator are analyzed in detail.Based on this,a virtual synchronous generator control strategy for a single voltage source inverter is proposed.According to the topological structure of the virtual synchronous generator and the overall control model,the system's segment transfer function is obtained,and the control parameters of the virtual synchronous machine control strategy are set accordingly.The mechanism of virtual synchronous VSC parallel circulation is analyzed,and the difference of concentrated parallel connection and autonomous parallel connection is compared,and an autonomous parallel circulation suppression strategy is obtained.By improving the virtual synchronous machine power control,combined with a virtual negative resistance,suppression of circulation is achieved.Finally,a simulation example of single virtual synchronous VSC grid-connected and islanded operation and two virtual synchronous VSCs parallel operation is built in PSCAD software,which proves the external characteristics of the vir tual synchronous VSC and the feasibility of the proposed circulation suppression method in autonomous parallel circulation suppression.