Reconstruction of output currents and fault detection in a B4-inverter with only one current sensor

A three-phase inverter with four switches and four free-wheeling diodes (B4) is an alternative to the classical B6-inverter in order to reduce cost and complexity. This paper proposes a method to reduce the number of current sensors in a B4-inverter to one but still keep the knowledge of the three output currents. Different current sensing topologies are proposed and one is selected for implementation which protects the inverter. The current is only sensed in the DC-link fault protection. Practical problems are discussed and solved. An implementation is done in a hardware setup and experimental work validate that the proposed method can identify the output phase currents by only measuring the DC-link current.