Research On Control Strategy Of Grid-connected Inverter Based On Virtual Synchronous Generator In Unbalanced Grid

The grid-connected inverter controlled by the virtual synchronous generator algorithm can provide inertia for the power grid,and can participate in the regulation of voltage and frequency of the power grid,which is more friendly to the power grid.However,when it is applied to unbalanced power grid,the grid-connected active and reactive power will fluctuate at 2 times the frequency,and the grid-connected current will be unbalanced.Therefore,this paper takes new energy power generation as the application background,aiming at how to improve the grid-connected power quality,proposes a grid-connected inverter power fluctuation compensation control strategy based on virtual synchronous generator under the condition of unbalanced grid.Firstly,the relation between the 1/4 period delay vector of the grid voltage and its positive and negative sequence components is derived in the αβ coordinate system,and the instantaneous active power and reactive power expressed by the delay vector are obtained.On this basis,the reference power expressions under three control objectives of constant active power,constant reactive power and balance current are derived,and the power fluctuation compensation channels are designed to achieve the three control objectives respectively.Compared with the strategy based on negative sequence current control,there is no need to extract the positive sequence and negative sequence of grid voltage and grid-connected current,and there is no need to extract the positive sequence component of the reference voltage output from the virtual synchronous generator algorithm,which relatively simplifies the control algorithm.Finally,the simulation and experiment under the condition of island mode,balanced grid and unbalanced grid are completed.The simulation and experimental results show that,compared with the traditional virtual synchronous generator,the proposed scheme can reduce the fluctuation of active power and reactive power while improving the unbalance degree of grid-connection current,which indicates that the unbalance control algorithm is more superior.Compared with the scheme based on negative sequence current control,the proposed scheme has similar effect,but the proposed scheme has better effect in suppressing the power fluctuation,and the running time is shorter,the control algorithm is more concise.