259 – Maximum Torque Current Phase Search and Torque Characteristics Evaluation

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Model Data

Overview

In the low speed side of an N-T curve, there is a region where the maximum torque is constant regardless of the rotation speed because of current limitation. In this region, the current phase that maximizes the torque is selected. When designing motor components, many designs are compared using dimensions as design variables. In such a situation, the current phase at which the torque is maximum differs depending on the motor geometry.
When comparing a large number of designs using simulation, torque characteristics can be evaluated by automatically searching for the current phase that provides the maximum torque.
In this example, the current phase that maximizes the torque is searched for each of three rotor geometries. The motor average currents and torque ripples are evaluated using the obtained current phases.

Evaluation Details

There are three rotor geometry cases.
Inductance values are calculated at 10-deg increments in the current phase range of 0 to 60 deg.
Torque is calculated from the obtained results using a torque equation.
The current phase that provides the maximum torque is searched for.
Motor torque analysis is performed with the obtained current phase, from which the average torque and torque ripple ratio are obtained.
Fig. 1 shows the flow of evaluation.

Torque Equation

Torque can be calculated from inductance as in Fig. 2.

Current Phase – Torque Graph

Fig. 3 shows the current phase – torque graph. From this, the current phase where the torque is maximum is found for each rotor geometry. The current phases for the maximum torque for cases 1 to 3 are shown in red.

Average Torque and Ripple Ratio

Fig. 4 shows the average torque and torque ripple ratio at the current phase for the maximum torque.
Case 1 has a rotor geometry with high average torque and a low ripple ratio.

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