High Precision Online MTPA Algorithm Considering Magnet Flux Parameter Mismatch for a PMa-SynRM

To improve the controlled current angle accuracy and reduce the copper loss for a Permanent Magnet assisted Synchronous Reluctance Machine (PMa-SynRM), this paper proposes an online Maximum Torque per Ampere (MTPA) control strategy based on Virtual High-Frequency Signal Injection (VHSI) to find its control current angle. The proposed method considers the nonlinear characteristics of the d- and q-axis inductance, d- and q-axis flux linkage, and permanent magnet flux. An error was identified in the mathematical determination of the MTPA control angle, stemming from the omission of the inductance's dependency on the current angle in the analysis. To solve the problem, an improved error supplementary control strategy considering permanent magnet flux mismatch was proposed, which features a lower calculation burden, less motor parameters information required, and higher precision. In this process, only permanent magnet flux information needs to be identified. The proposed MTPA detection and its supplementary control scheme was analyzed from mathematical derivation and verified by experiments.