Microgrid Control Based On Virtual Synchronous Generator Research On Strategy And Island Detection

In recent years,the increasingly serious energy problems have led to the rapid development of new energy power generation technologies such as wind power and photovoltaic,and the microgrid system based on new energy power generation and gridconnected inverters is also growing.However,due to the lack of moment of inertia and damping,a large number of microgrid systems incorporated into the power grid will reduce the stability of the power system.The virtual synchronous generator technology controls the microgrid inverter by simulating the working characteristics of the synchronous generator,which can make the microgrid system have rotating inertia and damping,and then maintain the stable operation of the power system.This paper mainly studies the control technology,off-grid switching strategy and island detection method of virtual synchronous generator.Firstly,the virtual synchronous generator is modeled according to its working characteristics.The working process and mechanism of synchronous generator are analyzed,including governor,exciter,stator and rotor motion equations,etc.The corresponding virtual control model is established,and the output characteristics of inverter under the control of virtual synchronous generator are derived The working characteristics of the model are simulated and analyzed when it is off-grid and connected to grid,and compared with traditional P/Q control and droop control,which further highlights the obvious advantages of virtual synchronous generator control.Secondly,aiming at the key scientific problem that constant damping inertia is insufficient to suppress wave dynamics when the given power value of the system changes,the physical meaning of damping inertia is analyzed in detail,and its influence on system performance and its action rule are deeply explored,and a virtual synchronous generator control strategy that can adjust damping inertia in real time according to the specific changes of the system is designed,thus achieving the effects of reducing system power overshoot and speeding up system stability time.Compared with the control modes of constant damping inertia,constant damping variable inertia and constant inertia variable damping,the superiority of the algorithm is verified.Then,aiming at the current shock problem in the process of switching virtual synchronous generator from off-grid mode to grid-connected mode,the switching mechanism of virtual synchronous generator from off-grid to grid-connected mode is analyzed in detail,and the conditions for seamless switching from off-grid are given.According to the principle that SOGI phase-locked loop can accurately extract the voltage phase,an off-grid switching strategy is designed,so that the amplitude,frequency and phase of the inverter output voltage can be quickly adjusted to be consistent with the amplitude and frequency of the grid voltage before switching the grid-connected switch,thus realizing seamless switching of the virtual synchronous generator from off-grid to grid-connected.Finally,aiming at the problem that the system failed to detect or even failed to detect when the virtual synchronous generator running in the grid passively entered the island state due to the sudden power failure and other faults,the research on the island detection scheme of the virtual synchronous generator was carried out.Firstly,the islanding detection principle of virtual synchronous generator is analyzed.Then,by studying the phase change principle of virtual synchronous generator suddenly switching from gridconnected to off-grid,an island detection method based on phase offset is proposed,and the detection situation of this method when the circuit parameters change is simulated and analyzed,and the method is summarized Then,on this basis,frequency criterion is added to ensure the reliability of the system detection and improve the detection sensitivity,and a simulation model is built to verify it.