Restarting strategy for an induction machine driven with medium-voltage inverter

Electric machine drive systems have a protection mechanism for momentary power interruption. Generally, when the momentary power interruption is occurred, outputs of a drive system are stopped for the protection. For stable continuous operation, it is sometimes required the restarting strategy which is called as a flying start when the input power is recovered and the rotor is still rotating freely due to the large inertia of high power electric machine. The paper suggests the flying start strategy at momentary power loss. The proposed strategy is composed of the phase-locked loop(PLL) and Double Second-Order Generalized Integrator(DSOGI), based on the measured input voltages at electric machine side and the voltage compensation. The magnitude, frequency and phase angle of the residual voltages are estimated with PLL and DSOGI and the induced initial voltage is compensated considering the operating conditions. With the proposed strategy, the target drive system can be restored to the operation point of a prior failure. The proposed method is validated by the experiment with a miniature of MV drives.