Reducing the dv/dt of Motor Inverters by a Two Leg Resonant Switching Cell

Abstract:
The switching speed of modern inverter semiconductor devices (esp. wide-bandgap devices) increasingly rise resulting in low switching losses but high output voltage dv/dt rates causing stress on the insulation system of the load (i.e. traction motor). This paper presents and analyzes a novel concept for reducing the output voltage dv/dt of motor inverters avoiding any reduction of the semiconductor’s basic switching speed (which would be an alternative for dv/dt reduction in principle, however, paid by increased switching losses). The proposed concept is achieved by splitting up the half-bridge of a single phase into two legs which are gated slightly delayed against each other and combining their output voltages by a small interphase transformer. The transformer’s stray inductance in connection with an additional capacitor forms a resonant circuit which shows a cosine edge shaped output (motor) voltage at low dv/dt rates for a properly tuned design.