A new low-cost, fully fault-protected PWM-VSI inverter with true phase-current information

This paper proposes a new topology for a low-cost three-phase pulse width modulation (PWM) VSI inverter where a true phase current information exists with the use of only one current sensor in the DC link. The topology also has the benefits of full protection of the inverter such as short circuits in the DC link, output phase faults, and output earth faults. Previously suggested methods have problems at low speed in detecting the phase current, but by the use of space vector modulation in a double-sided implementation, the PWM-pulses are adjusted so true information about the phase current exists even at very low speed. The DC link current is sampled twice during one switching period, and it is proposed to sample in the center of the PWM-pulses to obtain a real average phase current. The effects of blanking-time and overmodulation are also discussed. The strategy is implemented in a 16-b microcontroller, and the test results show the technique is useful in the whole speed range. It is concluded by the use of the proposed topology that only one current sensor will be necessary in the future for PWM-VSI inverters.