An optimum modulation strategy for a novel "notch" commutated 3-Φ PWM inverter

The introduction of soft switching features in medium power static converters promises improved semiconductor utilization and higher switching frequencies. In this paper a DC-side commutated zero voltage switching (ZVS) PWM 3-Φ VSI topology is discussed. This topology consists of a typical six-switch bridge with the addition of a simple DC bus commutating subcircuit which can provide, on demand, the necessary soft switching zero-volts interval across the inverter DC bus. The objective of this paper is to identify a specific PWM technique which, in combination with the proposed ZVS scheme, can provide optimum overall converter switching performance. Moreover, the combination of the inverter topology and the modulation strategy proposed here yields a soft switching environment at the lowest possible switching frequency. Reduction in switching losses is further enhanced by increasing the effective and reducing the actual switching frequency. Finally, this paper includes a detailed analysis and design procedure for the proposed notch commutated inverter topology. Simulation and experimental results are also presented to verify key predicted results.