PCC voltage feed-forward robust control strategy of grid-connected converter under complex conditions

The grid-connected operation of the converter is easily affected by the background harmonics of the power grid voltage and the complex operating conditions of the power grid impedance, which will not only cause the output current to distort, but even cause the converter to oscillate and cannot operate stably. Through the analysis of the equivalent impedance model of the converter, it can be seen that the main reason for the system instability is the low phase margin at the intersection frequency point of the grid impedance and the converter impedance amplitude, that is, the impedance ratio of the two cannot meet the Nyquist stability criterion. In this paper, a new impedance model is established by introducing the impedance stability criterion when the converter is connected to the power grid. The use of grid-connected point voltage feed-forward compensation control can greatly expands the passive frequency domain range of the impedance, and ensures that the converter can stably output the grid-connected current with high waveform quality under the influence of wide-range time-varying grid impedance. The simulation model is built in MATLAB. The active power of the load is 6 kW and the reactive power is 8 kVar. By setting different parameters, it is verified that the strategy has good operating characteristics in both high frequency band and low frequency band.