Modeling and Comparison of Machine and Converter Losses for PWM and PAM in High-Speed Drives

For variable-speed drives, the interaction of the machine and the converter is becoming increasingly important, especially for high-speed applications, mainly due to the effect of the converter modulation on the machine losses. The allocation of the losses to different components of the drive system needs to be known in order to choose the ideal machine and modulation combination. In this paper, individual models are introduced for calculating the rotor, copper, and core losses of the machine as well as the inverter losses, taking the modulation type into account. These models are developed by considering two typical high-speed permanent-magnet synchronous motor topologies (slotted and slotless machines) driven by pulse-amplitude modulation (PAM) and pulsewidth modulation (PWM) converters. The models are applied to two off-the-shelf machines and a converter operating with either PAM or PWM. The test bench used to experimentally verify the models is also described, and the model results are compared to the measurements. The results show that PAM produces a higher overall efficiency for the high-speed machines considered in this paper. However, PWM can be used to move the losses from the rotor to the converter at the expense of decreasing the overall drive efficiency. The possible benefits of these results are discussed.