Magnet Temperature Estimation in Permanent Magnet Synchronous Machines Using the High Frequency Inductance

Permanent magnet synchronous machines (PMSMs) torque production capability depends on the permanent magnets (PMs) magnetization state, which can be affected by PMs' temperature and by the current flowing throughout the stator windings; knowledge of the PMs' temperature can be therefore of great importance both for control and monitoring purposes. PMs' temperature can be measured or estimated; PM temperature measurement is not easy and is not normally implemented in commercial drives. PM temperature estimation methods can be divided into thermal models based, back electromotive force (BEMF)-based, and signal injection based methods. Existing high frequency (HF) signal injection methods estimate the PM temperature from the measured stator HF resistance. Unfortunately, the resistance is also affected by magnetoresistive effect, which can limit the accuracy of the estimates. This paper proposes the use of the stator d-axis HF inductance for PM temperature estimation. This makes temperature estimation insensitive to magnetoresistive effect. In addition, it allows the use of higher frequencies, reducing the adverse impact of the injected signal on machine performance.