Estimation of parameters and performance of rare-earth permanent-magnet motors avoiding measurement of load angle

Abstract

The paper describes a static test which, in conjunction with a no-load test, can be used to determine the parameters needed to apply the two-axis machine analysis to modern rare-earth permanent magnet synchronous motors. An iterative solution of the two-axis theory is presented which, together with the static test, avoids the use of the load angle. The solution includes the effect of core (iron) loss and allows for the estimation of current, power factor and efficiency for a motor running normally from inputs of terminal voltage and torque alone. The parameter values and machine performance predicted by the new methods are confirmed against test data obtained from a samarium-cobalt synchronous motor which has an asymmetrical buried magnet rotor. For this configuration, it is observed that saturation can cause significant variation in the permanent magnet excitation and the direct-axis synchronous reactance as well as the quadratureaxis synchronous reactance. When the variation of each of these parameters is included in the analysis, it is found that the two-axis theory gives a good representation of the motor performance in both the preferred and nonpreferred directions of rotation at a variety of voltages, frequencies and loads.