Sensorless rotor temperature estimation of permanent magnet synchronous motor under load conditions

The work proposes a method for estimating the magnet temperature in permanent magnet synchronous machines (PMSM´s) under load conditions. The method implies an intermittent injection of a voltage pulse in the positive and negative d-axis of the motor. Thus, the difference of the resulting d-current responses depends on the machine operating point which is defined by the d-current, the q-current and the actual magnetization level of the permanent magnets. Since the magnetization of the magnets depends on the temperature, different d-current slopes reflect different temperature levels of the magnets. By applying a voltage pulse in the positive and negative d-axis of the motor, symmetry of the induced voltages can be achieved in a manner that the difference of the current responses from the positive and negative pulse is to a great extent speed independent.