Temperature issues in saliency-tracking based sensorless methods for PM synchronous machines

High frequency carrier signal excitation has been widely investigated for the position sensorless control of permanent magnet synchronous machines (PMSM´s) near and at zero speed. Selection of the injected signal characteristics (shape, frequency, magnitude, etc.) is a trade-off between performance criteria of the sensorless control (stability, accuracy, robustness, bandwidth, etc.) and minimization of its adverse effects (additional losses, noise, vibration, etc.). The increased losses due to the injected signal can be of importance in PMSM´s, since they can produce a significant increase of the temperature in the rotor magnets. This can adversely impact the normally operation of the machine and can eventually result in the irreversible demagnetization of the magnets. This paper analyzes the impact that excitation using a high frequency signals for sensorless control of PMSM´s has on the machine´s temperature. The machine design, as well as the type of injected high frequency signal, will be shown to strongly influence the machine´s thermal behavior. Analytical models will be developed to explain this behavior, with experimental results being used to verify the analysis.