Maximum Torque Per Ampere (MTPA) Control for Interior PMSM Using Position-Offset Injection Considering Inverter Distortion and Saturation

For the interior permanent magnet synchronous machine (IPMSM), online maximum torque per ampere (MTPA) control can be affected by the nonlinearities, such as magnetic saturation, inverter distortion and temperature rise. This article proposes a fast and accurate MTPA angle tracking method using the small dc position offset injection. Through position offset injection, the objective function model of MTPA control, the ratio of torque to stator current, is derived from machine model, which is not affected by the parameter variation. Online curve fitting is adopted to track the MTPA angle using the computed objective values based on position offset injection. The saturation is compensated with nonlinear modeling and the inverter distortion can be cancelled in the proposed model, both of which can effectively improve the performance of MTPA angle tracking. Moreover, the position offset injection will not affect the motor output torque and speed, and the MTPA angle detection is fast, which can effectively reduce the influence from the temperature rise. The effectiveness of the proposed method is validated through tests and comparison on a laboratory IPMSM drive.