Steady-state error analysis and improvement for signal injection based MTPA control of interior permanent magnet synchronous motor

This paper analyzes the steady-state performance of the high-frequency current injection based maximum torque per ampere (MTPA) control for interior permanent magnet synchronous motor (IPMSM). The expression of MTPA angle error is derived under the condition that the calculated input power of the motor is utilized to extract the MTPA criterion and the phase delay of the injected high-frequency current is taken into account. It is shown that this MTPA error can be attributed to the residual reactive power when separating the high-frequency mechanical power from the input power. Because the mechanical power is proportional to the rotor speed, but the reactive power is independent of the speed, the MTPA angle error may be unacceptably large at low speed. In order to improve the performance, two modified schemes are proposed. The theoretical results are verified by simulations.