Determination of Resistive Parameters and Iron Losses in Vector Controlled PM Synchronous Motors with Rotor Saliency

This paper presents a new approach to estimate the resistive parameters of the equivalent circuit in inverter-fed vector-controlled salient rotor permanent magnet synchronous motors. The method is based on the particular two-values shape of the loss power-vs.-current characteristic, when the motor is operated at constant output torque, constant speed and variable direct (d) current component. Such a profile allows to process the standard current/power/voltage measurements with a differential criteria, in order to minimize and theoretically cancel out the effects of non easily quantifiable phenomena, such as temperature, fundamental frequency, inverter feeding and additional losses. The presented method allows the contemporary estimation of the stator resistance and the iron losses equivalent resistor. A particular feature is that the resistive parameters are achieved in the practical operating conditions in the constant torque region. In fact they are identified near the minimum of the loss power vs.-current characteristics, which is close to the maximum torque-to-current trajectory in the d-q currents plane. The paper covers the illustration of the basic elements of the method, some issues on the implementation problems, and the experimental results achieved on a motor-drive system for city-scooter application, which confirm the goodness of the proposal.