[W-MO-114] Efficiency Map Measurement Comparisons

Contents
Overview
1. Problem
2. Verification motor
 2.1 Motor
 2.2 Control / inverter
3. Measurement system
4. Simulation model
 4.1 Loss modeling high-accuracy model
 4.2 Verifying high-accuracy model time intervals and mesh divisions
5. Efficiency map comparison results
 5.1 Efficiency map
 5.2 The level of contribution of loss factors for efficiency maps
  5.2.1 Harmonic iron loss due to PWM carrier
  5.2.2 AC copper loss
  5.2.3 Stress
  5.2.4 Residual strain
  5.2.5 Surface eddy current loss
  5.2.6 Minor loop
6. Summary
7. References

Overview

Traction motors are required to be of a high efficiency in a wide range of operating regions, ranging from low-speed and low-load operation to high-speed rotation. It is because PM motors possess a high maximum efficiency that there is a need to improve efficiency by an order of 1%, and it is for this reason that high-accuracy simulations are required within a wide range of operating regions.
This document compares an efficiency map obtained with simulations with an efficiency map consisting of actual measurements, achieving an error of 1% or less for entire regions. The contribution of loss factors to these efficiency maps is also evaluated, and for the model featured in this document, there exists a large amount of influence from both the harmonic iron loss that occurs as a result of the PWM carrier, as well as AC copper loss.

1. Problem

In developing and designing high-efficiency motors for automobiles, simulation efficiency is required to of 1% error or less to eliminate prototypes and enable verifications and performance evaluation via simulations. The efficiency of a motor is its output, with efficiency in other words being derived from torque and loss. For motors with 90% efficiency, for example, loss error must be kept at 11% or less in order to maintain efficiency error at 1% or less.
Simulations are typically performed with 2D models under ideal conditions with no stress or residual strain. Differences from efficiency maps consisting of actual measurements will occur as a result of this because the loss factors that determine motor efficiency are not taken into full consideration. Examples of these factors include the influence of time harmonics (hereafter referred to as carrier harmonics) due to the PWM inverter that drives the motor, and eddy current loss in hairpin coils due to the rectangular wires often used in automobile traction motors in recent years (hereafter referred to as AC copper loss). The stress and residual strain applied when manufacturing the motor core from electromagnetic steel sheets additionally increases the loss of electromagnetic steel sheets as the material used within actual machines (otherwise known as the building factor). These factors must be considered in order to achieve an error of 1% efficiency. 


Mesh division diagram


Efficiency map comparison

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