Owing to their high power density, good efficiency and high dynamics, permanentmagnet synchronous machines (PMSMs) find increasing acceptance in the industry, energy generation and in electric and hybrid-electric vehicles applications. The most widely-used rare-earth magnet in PMSMs is neodymium-iron-boron (NdFeB) since it is characterized with high energy density. However, neodymium magnets reveal very low thermal stability which is predominantly expressed is lower remanence flux density and reduced intrinsic coercivity upon temperature increased. Since the magnets in a PMSM are exposed to high temperature differences, an online monitoring of the magnet temperature becomes very meaningful in order to increase the quality of control and the reliability of the machine. Due to rotation, direct measurement of the magnet temperature is an inherently cumbersome task associated with high additional costs. In the current thesis, a method for estimating the magnet temperature in (PMSM´s) without using any temperature sensors is proposed. The method presents a robust and inexpensive solution to monitor the magnet temperature in the motor under normal operation. The main idea is based on exploitation of saturation effects in the d-axis of the steel stator core that are produced by the d-current, the q-current and the rotor flux excitation. Procedures are proposed where by meaningful application of the voltage pulses in the d-axis of the motor, the resulting d-current response is made function of the magnetization level of the magnets. Thus, a temperature dependent variation in the magnetization level of the permanent magnets is reflected in a variation of the d-current slope. The analytical discussions and the corresponding experimental validation are successively introduced. First, a magnet temperature monitoring based on a single positive voltage pulse in the d-axis of the motor and zero load current is investigated. This approach is generally valid and applicable in control setups where the motor speed varies in a narrow range. For applications characterized by wider speed range, a speed compensation approach is developed that implies a combination of a voltage pulse in the positive and negative d-axis of the motor, whereby a symmetry of speed dependent induced voltages can be achieved in a manner that the difference of the d-current responses from the positive and negative pulse is not affected by the motor speed. Finally, under consideration of cross-saturation effects and the influence of the q-current on the d-current response, a q-current compensation approach is introduced and temperature monitoring under various load conditions is demonstrated.
|Betreuer/-in / Berater/-in
|Datum der Bewilligung
|31 Okt. 2013
|Veröffentlicht - 2013
- Ehemaliges Research Field - Low Emission Transport