High-Efficiency Converter for Vari-able Speed Drives

The V-BBC enables bidirectional power flow at a high conversion efficiency with a rather simple topology of only 12 semiconductor switches. Thereby, the Voltage-Source Rectifier (VSR) facing the grid, and the Voltage-Source Inverter (VSI) driving the load are usually both run with a 2/3 discontinuous pulse-width modulation (DPWM), where the switches in two out of three legs of both the VSR and VSI are active at any given time and the DC-link voltage is fixed at a constant (high) value.

The invention introduces a new form of swit-ching pattern of the semiconductor switches of the V-BBC. As in the regular case, either the VSR or VSI runs with a 2/3 DPWM, with two legs switching and one leg clamped to one of the DC-link rails. However, on the other side of the V-BBC, only one leg is switching, while the remaining legs are clamped to the negative and positive rail of the DC link respectively. The voltage of the DC link follows the highest line voltage. This still allows for synthesizing AC currents in all phases while reducing the number of switching transitions, maintaining the minimum possible DC-link voltage, and thus minimizing the switching losses.