Online copper-loss minimization of interior permanent magnet synchronous machines for automotive applications: A geometrical approach

For the torque control of interior permanent magnet synchronous machines (IPMSMs), it is necessary to set a pair of reference currents based on the reference torque. At base speed the reference currents should be chosen in a way on which total current is minimized. This strategy provides copper-loss minimization and is known as Maximum Torque per Ampere (MTPA). Current methods present various disadvantages, e.g. torque ripple, high measurement effort, heavy assumptions and convergence issues. This paper presents an algorithm to calculate MTPA point online using known machine parameters. It is based on a geometric interpretation of the MTPA condition, which allows the reduction of the space of possible solutions. The convergence of the proposed solution is proven and its feasibility and performance are demonstrated through simulation and experiments.