Overview

The efficiency of EV/HEV drive motors is evaluated through driving cycles. When a motor is in driving cycles, the losses from magnetic field analysis are affected by temperature, and the temperature in thermal analysis is affected by the losses. Therefore, it is necessary to perform calculations that take their mutual influence into account.
By using a simulation with an efficiency map that has temperature dependency, it is possible to evaluate the increase in losses due to the temperature rise of coils and magnets during driving cycles. In JMAG, thermal circuits can be configured using cooling models such as cooling jackets that consider variations in coolant temperature and shaft cooling combined with sprays.
In this example, we evaluate the time variation of losses and temperature during WLTC driving cycles when using an efficiency map with temperature dependency in an IPM motor.

Analysis Flow

In driving cycle calculations that consider temperature variations, magnetic field analysis and thermal analysis are performed sequentially.
In the magnetic field analysis, multiple efficiency maps containing loss information are generated according to the combination of coil and magnet temperatures.
In the thermal analysis, based on the operating points of the driving cycle and the temperature from the previous step, the heat generation of each component is extracted from the efficiency map, and the temperature of the current step is determined.

Maps Before and After Temperature Rise

The motor operating points during WLTC driving on the efficiency map are shown in Fig. 2, the efficiency map before and after temperature rise is shown in Fig. 3, and the loss difference map is shown in Fig. 4.
From Fig. 2, it can be seen that the motor operating points during WLTC driving are spread over a wide range.
From Fig. 3, it can be seen that the maximum efficiency decreases by about 0.8 points due to the rise in component temperature.
From Fig. 4, it can be seen that the copper loss of the coil increases on the high load side due to increased resistance from the rise in coil temperature, and the iron loss of the stator decreases on the high rotation side due to reduced magnetic flux from the rise in magnet temperature. As such, losses change complexly with the rise in component temperature, making it necessary to perform driving cycle calculations that consider these factors.

Driving Cycle Calculation Considering Temperature Variation

An analysis of WLTC driving considering the temperature variations of coils and magnets was conducted. The time variation of losses for each component is shown in Fig. 5, and the time variation of temperature is shown in Fig. 6.
From Fig. 5, it can be seen that the losses of the stator core and coil are significant.
From Fig. 6, it can be seen that the temperature of the stator core and coil, which have high losses, is high and changes rapidly.