Accurate Modeling of Switching Losses in H-bridges with Unipolar or Bipolar PWM

Voltage spikes during the switching transients play an important role in determining the power losses in hard-switching converters. These spikes are functions of several factors at the instant of switching such as DC-link voltage, load current, transistor and diode switching delay times, reverse recovery current of the diode, parasitic capacitance and inductance of the circuit. This paper introduces a numerical approach to accurately model the switching power losses of a single-phase H-bridge (SPHB) inverter. The data required to obtain the equivalent resistance is extracted from the experimental double-pulse tests (DPTs). Then, the concept of local and global rms currents is considered to incorporate the effect of pulse width modulation (PWM) in the estimation of the switching losses. The results are computed for unipolar and bipolar PWM schemes. Finally, the reflection rule is utilized to obtain an equivalent output resistance for the inverter switching losses.