A Protection of the Electrolytic Capacitor-less Drive System against the Input Grid Interruption

This paper presents a protection strategy for the semiconductor switches in an electrolytic capacitor-less converter. The proposed protection strategy can prevent them from breaking down of the semiconductors due to the over-voltage stress caused by the regenerative energy flowing from the load to the grid at the moment when the source lines are disconnected by the grid interruption. The energy stored in the inductor may result in excessive over-voltage in DC bus due to the very small DC capacitance in the electrolytic capacitor-less converter. The energy at q-axis can be dumped to d-axis while the DC bus voltage is maintained within an allowable range by the proposed active current regulation during the interruption. The proposed protection strategy is verified by the experiments with an elevator system which has a 10.8kW, 380V permanent magnet AC motor as a hoist machine