A reference flux calculation method with stator flux linkage synchronous frame for MTPA control in direct torque controlled PMSM drives

When direct torque control (DTC) is applied to permanent magnet synchronous motor (PMSM) drives, the relationship between the torque and stator flux linkage is important for high-efficiency drives because DTC requires them as references. In the stator flux linkage synchronous frame (M-T frame), the torque equation is described as a simple equation using the T-axis current. However, the M-axis current is neglected in the equation. This paper derives the relationship between the M-axis current and the stator flux linkage and proposes a maximum torque per ampere control strategy for direct torque controlled PMSM drives using the derived relationship. In addition, the q-axis inductance can be compensated using that relationship because the error in the q-axis inductance causes the estimation error in M-axis current. The simulation results validate the proposed method.