Position Offset Injection Based Fast and Accurate Maximum Torque Per Ampere (MTPA) Control of Interior PMSMs

For the permanent magnet synchronous machine (PMSM), the maximum torque per ampere (MTPA) control is crucial to improve the torque capability and reduce the copper loss. However, the nonlinearities, such as magnetic saturation and temperature rise, make it challenging to identify the optimal current angle accurately during the online operation. This paper proposes a fast and accurate MTPA angle detection method using the small dc position offset injection. Through the positive and negative position offset injection, the objective function of MTPA control is derived based on the voltage equations, which is not affected by the parameter change and temperature rise. The objective function simplification is conducted to improve the computation efficiency. With the objective function, online polynomial curve fitting is utilized to find the MTPA angle rapidly. Through the comparison with existing methods and experiments on a laboratory PMSM drive, the effectiveness of the proposed method is validated.