Overload Considerations for Design and Operation of IPMSMs

Although interior permanent magnet synchronous machines and their cooling are designed to match the rated power, power demands other than rated may arise. One may keep the same machine dimensions and basic electromagnetic design, but increase the cooling for different operating conditions. Modifications of the cooling system can compensate for the increase in machine losses in the windings, magnets, or iron. Increasing the allowed stator current affects the machine performance in other ways as well. These include demagnetization of the magnets, and hence, shrinking of the speed range to avoid this. In this paper, these effects are studied for a baseline machine, as well as for machines with the same stator but modified rotor design. A cross-saturated model is developed and shown to be more accurate than the classic one. To account for higher stator current with higher temperatures, the effects on efficiency, torque, and speed range by changing the magnet material from the more commonly used NdFeB to SmCo are also studied and discussed.