Application Catalog

200 - Iron Loss Analysis of IPM Motor using Hysteresis Model

2014-12-15

Module: DP, LS

Overview

Overview

Recently, PM motors are being applied in home appliances and electric automobiles, and the demand for compactness and high power is increasing. On the other hand, small and high-power motors tend to be affected by high-frequency components due to magnetic saturation and high rotations, which results in increased loss in the motor, therefore, they are also expected to have increased efficiency. In the realization of highly-efficient motors, it will become increasingly important to accurately estimate loss.
In the drive circuit of a PM motor, there are times when current vector control using PWM control (pulse width modulation) is run. Current waveform that is being supplied by PWM control have carrier harmonic current superimposed on the basic wave control, and with this carrier harmonic current, high-frequency of the magnetic field is applied to the motor core and iron loss occurs. With harmonic components and magnetic saturation of the iron core due to permanent magnets, it will be necessary to evaluate iron loss with magnetic flux density waveform that is different from the conventional sinusoidal alternating current. Also, in a high rotation PM motor, the variable frequency of magnetic flux density becomes increasingly high and the eddy current distribution of the depth direction of the laminated steel due to skin effect becomes difficult to ignore. With these conditions, evaluation using the highly-accurate iron loss calculation function becomes required.
Therefore, in this case study, a hysteresis model accounting for minor loops of the direct current bias magnetism and the lamination analysis function accounting for eddy current distribution in the lamination direction are run simultaneously to evaluate iron loss due to high carrier harmonic components in the IPM motor.

Iron Loss

Fig.1 Iron loss

Iron loss is indicated in Fig.1. The result of the hysteresis model and lamination analysis is compared with the loss analysis result of the conventional iron loss properties.
It can be confirmed that joule loss obtained based on the conventional iron loss properties is overestimated. This may be because the reference frequency exceeds the reference frequency of iron loss properties and extrapolated data was used. On the other hand, hysteresis loss in rotor cores is underestimated. It is thought that the rotor core was affected by the minor loop, and these effects in the hysteresis model were even more accurately captured.

Joule Loss / Hysteresis Loss Density Distribution

Fig. 2 Hysteresis loss density and joule loss density distribution

The distribution of joule loss density and hysteresis loss density is displayed in Fig.2.
It can be confirmed that hysteresis loss is higher in the rotor core surface. This is thought to be the effects of the minor loop. Also, joule loss density using iron loss properties has obtained higher density than in the lamination analysis. This may be because extrapolated iron loss properties were used in the calculation of loss density of high frequencies.

Magnetic Flux Density Waveform

Fig. 3 Magnetic flux density waveform of the rotor core and stator core

The waveform of magnetic flux density in the rotor core and stator core are displayed in Fig. 3.
Super imposed direct current components that affect the minor loop appear in the magnetic flux density waveform of the rotor core.