DSP-based high precision torque control of permanent magnet DD motor.

Abstract

Direct drive motor drives the mechanical load without a reduction gear and, therefore, the required precision of torque control is higher than that of the ordinary AC servo motors. The current control is the key technology to realize the high precision torque control.A new software-implemented current control is proposed. Since the proposed method is the extension of the conventional current hysteresis controlled PWM, the algorithm is quite simple and can be implemented within 20 μs using TMS 32010. The processing time is so short that 3-axis control by 1 DSP can be realized.Further, the analysis of the torque ripple due to the non-sinusoidal flux distribution is given and it is shown that the ripple can be compensated by the proposed current control. The additional processing time is 12 μs.Torque ripple is also caused by the offset involved in the current pick up loop. Based on the analysis of torque ripple due to the offset, the compensation algorithm with processing time of 26 μs is proposed and proved to be excellent by experiments. This means the realization of tuning-less drive system.