Study of the Effect of Load Torque on the Iron Losses of Permanent Magnet Motors by using Finite Element Analysis

Abstract

The output torque of a three-phase interior permanent magnet synchronous motor (IPMSM) can be controlled within its allowable range using a pulse-width modulation (PWM) DC-AC inverter. In this paper, the effect of load torque on the iron losses of an IPMSM is studied by considering three different driving conditions, namely no-current, no-load, and load conditions. In order to perform a careful evaluation in the experiments, the motor is tested at various rotational speeds, namely 750min^-1, 1500min^-1, and 2250min^-1; the voltage modulation index of the PWM inverter and the load torque are also varied. The experimental results in all the test cases show that the iron losses of the motor vary when the excitation condition is varied among the no-current, no-load, and load cases. Furthermore, a three-dimensional (3D) finite element analysis (FEA) is performed for the main test case when the motor is operated at the rated speed of 750min^-1 for reference purpose. The harmonic components caused by the excitation inverter in the stator voltage, current, and magnetic flux density are found to be the main reasons for the increase in iron losses of the motor in the no-load and load conditions compared to the no-current condition; an increase in torque also causes a relatively significant increase in the iron losses.