Strategy for the instantaneous torque control of permanent-magnet brushless DC drives

The paper describes an instantaneous torque control for a permanent magnet motor driven in a brushless direct current drive configuration. The motor has high torque capabilities, which makes it suitable for direct drive applications, but unfortunately it suffers from torque pulsations when controlled by a conventional sinusoidal current controller. Instantaneous torque control is aimed at eliminating such torque pulsation, thereby improving speed and position control. The approach adopted is to design an instantaneous torque control algorithm based on a variable structure strategy in the dq rotating reference frame. The switching commands for the inverter are generated by the digital controller directly. The required instantaneous torque feedback information is estimated from knowledge of the motor parameters and measurements of instantaneous currents and rotor position. The performance of the proposed controller design and torque feedback technique are investigated in computer simulation studies and experimental implementations. Experimental results for drive applications using instantaneous torque control and conventional sinusoidal current control are evaluated and compared.