Permanent magnet temperature distribution estimation in PMSMs using BEMF harmonics

PM temperature measurement/estimation in permanent magnet synchronous machines (PMSMs) is convenient both for torque control and monitoring purposes. Most of existing methods provide and averaged/punctual temperature. However, PM temperature distribution is not uniform, which can have unexpected adverse effects like reduced accuracy estimating the torque produced by the machine or local demagnetization e.g. due to hot spots. PM temperature distribution can be measured or estimated. Since the PMs are not visible, measuring the PM temperature distribution would require an array of temperature sensors attached to the PM. While this is technically feasible, it is unaffordable in commercial products due to cost and robustness issues. Alternatively, the PM temperature distribution can be estimated. The paper analyzes the use of BEMF harmonics to estimate the differential temperature in the PM, i.e. the temperature difference between the hottest and coldest parts of the magnets. Combined with average PM temperature estimation methods, this information can be used to estimate the PM temperature spatial distribution.