An iron loss calculation method for motor driven by PWM inverter power supply

Abstract

An application of Finite Element Method for iron loss calculation is proposed. The motor iron loss is predicted by taking into account current ripple caused by PWM inverter power supply. This paper describes simulation method about iron loss under inverter drive system. In this method, drive system simulation is used to obtain the motor current waveform. The skin effect in the laminated core is considered by using results of two-dimensional magnetic field analysis. The method is applied to an interior permanent motor and shows the result of iron loss distribution in the motor. The characteristics of motor losses such as copper loss, mechanical loss and iron loss are necessary for the prediction of the efficiency of the motor and the rise in temperature. Iron loss can account for a significant component of the total loss. Iron loss in a motor that is driven by inverter power supply is especially increased in comparison to one using a sinusoidal power supply. The increased iron loss, which is called carrier loss or residual loss, is caused by current ripple which is affected by switching of power devices controlled by PWM and control system. Therefore, there is a need to take into account drive system for precise iron loss calculation. The current ripple has high frequency components that are comparable to carrier frequency of PWM. The skin effect has appeared at such higher frequency. The influence of the skin effect is different in laminated core parts and magnet parts. In the laminated core it is possible to calculate eddy current precisely by using three dimensional magnetic field analysis. However, it requires long calculation time because the number of elements becomes enormous in the analysis. In this paper, an iron loss calculation method based on two-dimensional magnetic field analysis and a result of iron loss distribution under inverter drive are presented.