Comparison of electromagnetic performance and power losses of a high-speed machine fed by PWM and PAM inverter strategies

This paper presents a comparative study of electromagnetic performance and power losses of a high-speed surface-mounted permanent magnet (SPM) machine supplied by a pulse-width modulation (PWM) and pulse-amplitude modulation (PAM), also known as quasi-square wave modulation (QSM). In the simulation the inverter is operated at different DC-bus voltage levels and different modulation indices, i.e. amplitude and frequency, for the PWM. The analysis is achieved using circuit simulation of the inverter linked with a 2D-finite element analysis (FEA) of the machine. The comparison focuses on the phase current and voltage, and distortion of the torque waveforms and the core, rotor and inverter losses. It is found that, at higher DC-bus voltage, higher phase current distortion is found and consequently higher torque ripple and induced harmonics in the rotor loss. Moreover, similar effect is found when higher amplitude modulation index is applied. Furthermore, higher frequency modulation index results in lower phase current harmonics and hence lower torque ripple and rotor loss however, this comes at the expense of the inverter loss.