Research on the Stability of Black Start for Voltage Source Controlled Inverters

The black start process is very important for smart microgrids. In order to ensure that the output current of the grid-connected inverter is synchronized with the grid voltage, the phase-locked loop is used to lock the detected grid voltage and it is used as a reference voltage. The bandwidth of the phase-locked loop affects the instantaneous phase difference between the grid-connected inverter and the grid, which in turn affects the stability of the grid-connected system. In order to ensure the stability of the system under weak grid, the impedance model of the droop control inverter is first derived. An impedance model of the inverter waiting to be connected in parallel with the system is then established, which includes a voltage-current closed loop and a phase locked loop. Based on the impedance stability criterion, the inherent causes of the instability of the parallel process are discussed, and the dynamic parallel process and the final operating state are linked. The experimental results verify the effectiveness of the method.