Comparison of Different PWM Methods Assuming Equal Harmonic Loss Conditions

Inhalt:
Pulse-width modulation (PWM) methods used in variable-speed drives (VSD) do not only differ in the way of using the zero vectors, but also in the quantity of producing inverter and motor losses. Often, the normalized weighted total harmonic distortion (WTHDn) or similar criteria are used as benchmarks of PWM-induced motor losses when comparing different PWM schemes. To provide a better basis for comparison, in this paper the real losses in a 7.5-kW motor are calculated and set in relation to the WTHDn. The carrier frequencies of the investigated PWM methods are adjusted such that all PWM methods generate equal harmonic motor losses. Different known PWM methods (e.g. DPWM2) are then benchmarked under these conditions. Furthermore, a hybrid PWM consisting of a mix of continuous and discontinuous PWM schemes is investigated in terms of reducing the inverter and motor losses simultaneously. The simulation results are validated against measured losses.