Abstract
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.
Original language | English |
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Awarding Institution |
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Supervisors/Advisors |
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Award date | 31 Oct 2013 |
Publication status | Published - 2013 |
Research Field
- Former Research Field - Low Emission Transport