A Study of Reduced Torque Compensation Method Under Temperature Variation Based on Single Torque-Current Lookup Table

In permanent magnet motors, the stator resistance and magnetic flux of the magnet change as the temperature increases. These changes result in a change in the maximum torque point per unit ampere (MTPA) of the motor. Without adequate compensation, this leads to a decrease in output torque. For this reason, look-up table (LUTs) are prepared over the temperature range and used for interpolation. This paper proposes a method to compensate for the output torque reduction due to a temperature increase using only a single LUT prepared at a base temperature. First, an estimation of the magnetic flux linkage and the output torque using a single LUT is performed. Second, the problem is modeled as a limited optimization problem to minimize the loss due to the torque reduction. The magnetic flux linkage and output torque are calculated in real time through the fundamental active power. The compensation value is calculated using the Lagrange multiplier method, an optimization technique, using the estimated magnetic flux linkage and output torque. The proposed method is verified by comparing it with other algorithms through simulation and experiment.