Model-based loss minimization in high-speed motors

High-speed drives are becoming increasingly important as the need of higher power densities has been driving the trend towards higher speeds in electrical drives. This trend, however, possesses several challenges, one of which is the thermal constraints due to the higher loss densities in the machines. For example, rotor losses are critical in applications where the rotor runs in vacuum, whereas the total drive efficiency including the converter and the motor is critical in applications such as blowers. In order to find a loss-optimal design, it is important not only to limit the amount of losses but also to predict and influence where they occur. In this paper, loss models developed in a previous work are used to evaluate different converter modulation schemes as well as changes in the machine construction, in order to find a loss-optimal drive system. Typical modulation schemes such as Pulse-Amplitude-Modulation (PAM) and Pulse-Width-Modulation (PWM) as well as Pulse-Width-Amplitude-Modulation (PWAM) are compared for two off-theshelf high-speed machines. On the machine side, different options such as using different retaining sleeve or permanent magnet materials as well as the segmentation of the permanent magnets are analyzed to evaluate their effects on different loss components of the drive system.