A Multi-Channel Temperature Monitoring System for Inverter-Fed Electrical Machines

The demand for ever increasing efficiency keeps challenging the design and control of electrical machines. Thermal monitoring is in that perspective an important addition to the electromagnetic aspect. Temperature measurements in electrical machines can be challenging, especially in high-frequency inverter-fed motors. High dv/dt ratios in the stator windings give rise to noise exhibiting high amplitude and frequency. In this paper a multi-channel temperature monitoring system is proposed, implemented and experimentally tested for Resistance Temperature Detectors embedded at various locations in a 5.5 kW inverter-fed induction motor. The system ensures a galvanic isolation between the sensors in the motor and the data-acquisition system. After calibration, the linearity error, common-mode rejection ratio and signal-to-noise ratio are measured to be 0.12 % of full scale, -79.2 dB and 0.125 mV/V respectively. Fiber-Bragg Gratings thermal measurements are performed to confirm the accuracy of the proposed temperature monitoring system. For various operating conditions the temperature measurements have noise amplitudes that remain limited to 0.1 ° C-0.2 °C. The presented temperature monitoring system has the potential to further enhance motor performance when integrated into real-time motor controllers.