Torque control in constant power region for IPMSM under six-step voltage operation

To increase output torque in the constant power region of interior permanent magnet synchronous motor (IPMSM) for electric vehicle/hybrid electric vehicle applications, a novel torque control based on voltage phase angle control is proposed to provide more accurate torque for the IPMSM. First, the mathematic model of the IPMSM under six-step voltage operation is derived. Then, the phasor diagram based on the fundamental frequency and ideal condition is used to explain the relation between the torque, power, and voltage phase angle. Moreover, Maxwell 2D simulation for the IPMSM shows the detailed phenomena including generated torque, phase current, and magnetic flux distribution for developing controllers. Hence, the proposed method uses phase voltage advancing angle to yield torque, which consists of a command feed-forward controller to give a fast dynamic response, a proportional-integral regulator, a high-resolution voltage angle injection to reduce torque ripple and an efficiency-based torque estimator to enhance torque accuracy under six-step voltage operation. Finally, a digital signal processor(DSP)-based motor drive is built to verify the proposed method using a 6kW/47Nm/1200rpm IPMSM. The experimental results measured by a torque transducer are derived to show that the torque ripple is significantly reduced, torque accuracy is improved, and constant power control achieved is from 1800 to 3600rpm. These results, therefore, confirm the superior performance of the proposed control method.