New earth-fault protection of AC-drives with DC-choke & DC-link current sensing

DC-link current sensing enables adjustable speed drives to be designed compactly. Except for the low-impedance earth-fault protection the whole drive is protected by a single current-sensing element as well as drives with three current sensors on the output phases. A new indirect detection method for improving the low-impedance earth-fault protection of adjustable speed drives with a low-side DC-link shunt and a high-side DC-choke is proposed. The method is analyzed theoretically and practically. Test results at 2.2kW and 22kW power levels are presented.