Iron Loss Calculation Method of Interior Permanent Magnet Motor Taking Carrier Harmonics into Account Based on Reluctance Network Analysis Representing Dynamic Hysteresis Characteristics

Abstract

It is necessary to accurately estimate iron loss including magnetic hysteresis behavior to develop high-efficiency electric machines. In a previous paper, a novel magnetic circuit model incorporating the play model [1] and Cauer circuit theory [2] was proposed. The play model is one of phenomenological models of the dc hysteresis characteristic. The Cauer circuit theory can simply express the skin effect by formulating the frequency characteristic of the complex permeability. Its calculation accuracy was proved by comparing the measured and calculated results of hysteresis loops and iron loss under PWM excitation by using simple-shaped ring cores. This paper presents that the above model is extended a reluctance network analysis (RNA) model to analyze devices with more complicated shapes such as motors. The proposed method is experimentally validated by using an IPM motor, which is generally driven by a PWM converter, as an object of discussion.Fig. 1(a) and (b) show the proposed RNA model of the IPM motor. In the stator core, each reluctance expresses the dc hysteresis characteristic and classical and anomalous eddy current losses. The dc hysteresis characteristic is represented by the play model, the classical eddy current loss is represented by the Cauer circuit theory, and the anomalous eddy current loss is represented by a simple controlled source element, respectively. On the other hand, each reluctance in an air gap and a rotor is determined by dimensions of each element and permeability of the materials, and each MMF generated from winding currents and permanent magnets is concentrated as a form of controlled source.Fig. 2(a) - (c) show the measured and calculated characteristics of torque, iron loss, and efficiency, respectively. Here, the theoretically infinite number of stages of the ladder circuit part which denotes classical eddy current loss is truncated at 3rd stage for practical use. From these figures, it is understood that both results are in good agreement. Besides, as shown in Fig. 2(d), the proposed method can draw the local hysteresis loop in a certain divided element, which is generally difficult to measure and calculate, though its calculation accuracy should be experimentally verified.