How to measure the rotor temperature of a permanent magnet synchronous motor (PMSM)?

There are two types of motors used in modern electric vehicles: Asynchronous and synchronous motors. Synchronous motors either require a DC voltage to be applied to the rotor for a magnetizing coil through which current flows, and are then referred to as externally or current-excited. Or they have a permanent magnet in the rotor (permanently excited). However, for permanent magnet synchronous motors (PMSM), it is important to know that their load capacity is limited by the rotor temperature. If the Curie temperature of the magnets is exceeded, the electrical polarization is lost and the motor will fail. If the rotor temperature is too high, this can lead to potential thermal safety issues in the system.

When using PMSMs as electric vehicle motors, it is critical to be able to predict the evolution of the rotor temperature in order to achieve stable motor performance and to ensure and improve the operational reliability of the system. For this purpose, it is necessary to determine the energy flow and the resulting temperature evolution of the motor in order to create a thermal model of the stator and rotor.

One data acquisition solution to improve the performance of a PMSM and to develop it in a thermally safe manner is to use telemetric data acquisition, as measurements are made on the test bench during the endurance test on the running rotor. imc offers the universal D^x telemetry for data acquisition on rotating parts. This is a very compact and lightweight multi-channel telemetry system. Thanks to the universal transmitter module, it can be used flexibly and allows wireless measurements with different numbers of channels and sensor assignments. Up to four transmitters can be operated synchronously with one receiver, allowing simultaneous acquisition of spatially distributed measurement points.

In this solution, the thermocouples are located in the rotor and the leads are routed through the hollow shaft to the transmitter. The transmitter is powered by an inductive ring stator which allows continuous operation. Data is transmitted by radio. Overall, this test system is very robust and suitable for harsh conditions; it is designed for up to 20,000 rpm and an ambient temperature of up to 110°C [230°F].

Author: Rolf Spellmeyer, Business Development E-Mobility

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