A Newly Designed Instantaneous-Torque Control of Direct-Drive PMSM Servo Actuator With Improved Torque Estimation and Control Characteristics

In this paper, a newly designed instantaneous-torque-control scheme with improved instantaneous-torque estimation and control characteristics in a direct-drive permanent-magnet synchronous motor (DD-PMSM) is presented. A hybrid control structure that combines the internal-model principle and the variable-structure control approach is proposed. The appropriate control voltage vector is determined using the control effort of the variable-structure torque and d-axis current controllers combined with the estimated dynamic back-EMF vector in a feedforward control manner. Subsequently, the dynamic back-EMF vector, which contains the flux-harmonics information, is included in the reference voltage generation as an internal model. As a result, better disturbance rejection can be obtained with the proposed cascaded control structure. To robustly obtain the instantaneous-torque information, an adaptive motor model is proposed. The adaptive model is realized by adopting recursive estimators to estimate unknown machine electrical quantities and parameters. In addition to its robust estimation performance, the proposed adaptive model includes the dynamic model of the estimated disturbance to enhance the estimation characteristics. Experimental results are presented to demonstrate the validity and effectiveness of the proposed instantaneous-torque-control scheme.