A Protection Scheme Against Voltage Sags for Electrolytic Capacitorless AC Drives

This paper presents a protection strategy for the semiconductor switches in an electrolytic capacitorless converter. The proposed protection strategy is capable of protecting the semiconductor switches from overvoltage breakdown caused by the regenerative energy flowing from the load to the grid after the source lines are disconnected by the grid interruption. The energy stored in the machine inductance also may result in excessive dc-bus overvoltage due to the small dc capacitance in the electrolytic capacitorless converter. According to the proposed algorithm, the energy in the q-axis inductance is transferred to the d-axis inductance in the rotor reference frame while the dc-bus voltage is maintained within an allowable range by the proposed dc-bus voltage regulation during the grid (or source) interruption. The proposed protection strategy was verified by the experiments with an elevator system with a 10.8-kW 380-V interior permanent-magnet (IPM) hoist machine.