Effect of cooling conditions on the design and operation of IPMSM

High power Interior Permanent Magnet Synchronous Machines (IPMSM) are used extensively in hybrid vehicle applications due to their high power density, wide speed range and better efficiency. In general, a high power IPMSM and its cooling is designed according to its rated power. Depending upon the application, specific power demand (other than rated) may arise to run the same machine at less or more than rated current. One may like to keep the same machine but change its cooling. Modification in machine cooling can compensate for the increase in machine losses due to its current change. The design of such a machine needs special attention because every machine designed for rated current may not be used continuously at current greater than that. In this paper, the operational range of a baseline machine design is presented and analyzed at less as well as more than rated current, using a cross saturated dq model. It is imperative to consider the demagnetization limit of permanent magnets in the analysis of machine operation. Different machine designs are presented and compared for torque-speed profile and efficiency at different current conditions with increased machine cooling. Machine design with increased width of permanent magnets provides more wider operating region at the cost of reduction in its efficiency for higher speeds.