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, noload, and load conditions. In order to perform a careful evaluation in the experiments, the motor is tested at various rotational speeds, namely 750 min −1 , 1500 min −1 , and 2250 min −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 750 min −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.Keywords: finite element analysis, interior permanent magnet synchronous motor, iron loss, PWM inverter, effect of load torque

Conceptual Diagrams of Extended Building Factor for Analysis and Evaluation of Factors on Core Loss Density Increase in IPMSM

“…From that, we can specify the appropriate boundary between the teeth and yoke parts on the stator core. Moreover, the boundary should be suitably determined so that we can accurately calculate the individual mass of the experimental teeth and yoke parts, i.e., MT and MY presented in Table 4 and (12). The issue of determining the boundary between the teeth and yoke parts may also have an effect on the obtained results of BFEX; however, with the five search coils wound on the stator core as tentatively suggested and shown in Fig.…”

“…Step 3: The stator core consists of the teeth and yoke parts. From (11), the stator core loss density WIPM-STρ can be estimated by (12), where the masses of the teeth and yoke are MT and MY, respectively.…”

“…As examined in the past works (4) (6) (7) , the harmonics in the IPMSM current and voltage may cause the increase of the motor core loss. Besides, the detailed results of the FFT and harmonics analysis of the IPMSM current, voltage and magnetic flux density under the PWM inverter excitation as well as their impacts on the iron loss can be referred to our previous studies (2) (5) (12) .…”

“…Harmonics components were also evaluated to increase the iron loss of the IPMSM (6)- (8) . In addition, the finite element analysis (FEA) has been widely applied to analyze and assess the iron loss of the IPMSM (9)- (12) . Furthermore, loss models and analysis in high-speed synchronous motors were discussed (13) (14) .…”

Iron loss analysis and calculation of high energy density permanent magnet machine

“…The DC bus voltage and harmonic components in the output voltage of the inverter can generate current ripples increasing the losses in the electric machine [14][15]. With a PWM DC-AC inverter, the effect of load torque on iron losses was studied by considering three different driving conditions, including no-current, no-load and load conditions [16]. Katsumi Yamazaki proposed a loss calculation method considering minor hysteresis loops for permanent magnet machines driven by pulse-width modulated inverters [17].…”