Investigation of PM Eddy Current Losses in Surface-Mounted PM Motors Caused by PWM

It is well known that spatial field harmonics will cause high eddy current losses in surface-mounted permanent magnets (PMs) especially for the fractional-slot PM motors. However, the influence of temporal current harmonics, especially of the high-order temporal harmonics caused by pulsewidth modulation voltages from an inverter, lacks attentions. This paper studies the eddy current losses of the PMs caused by high-order current harmonics. In order to simplify the calculation and save computation time, analytical methods are used to predict the current harmonics caused by the PWM inverter, and the armature reaction field, the eddy current density, and losses in the PMs generated by the current harmonics. Finite element analysis, coupling simulation, and experimental studies are used to verify the analytical results. The study results show that the high-order current harmonics cause much higher eddy current losses than those caused by slotting and fundamental current even though the amplitudes of the high-order current harmonics are much lower.