Online optimized stator flux reference approximation for maximum torque per ampere operation of interior permanent magnet machine drive under direct torque control

This paper presents an online optimized stator flux reference approximation scheme for application of direct torque control (DTC) technique to interior permanent magnet (IPM) brushless AC (BLAC) drives with maximum torque per ampere (MTPA) operation. It is found that by considering dq-axis stator flux components instead of stator flux magnitude, straightforward mathematical functions for computing stator flux reference from the relevant torque reference to achieve MTPA operation can be derived. It is also demonstrated that by properly selecting initial value for approximating the proposed stator flux equation utilizing the Newton-Raphson method, a high degree of accuracy can be obtained utilizing only one computing step. It is shown that MTPA operation can be achieved for a DTC-based IPM BLAC drive using the proposed stator flux reference approximation scheme. Simulation results confirm validity of the proposed method.