The Novel Control Strategies For AC Drives

In view of the development trends of electric drives, the novel control strategies, which are aimed at the unsolved control problems in the conventional AC drives and SRD, are applied to drives, and the theory and industrial applications are studied.In the conventional AC drives, since the control performance of the systems with general PID controller is significantly influenced by various uncertainties of the plant, which usually comprise unpredictable plant parameter variations, external load disturbance, unmodelled dynamics, or neglected nonlinearities, etc.. To overcome these, a MAC control scheme is proposed. The PMSM speed control system and AC position servo drive are set up based on the model algorithmic control, their robustness for both stability and performance are analyzed, and their performances are verified by simulations and experiments. The results show that the performances of the MAC control systems for AC drive are greatly improved, the system is robust with regard to plant parameter variations and external load disturbance.The decoupling controller of current loop is designed based on the internal model control. The controller only has an adjustable parameter and the design procedure is simple. According to the maximum torque/ampere control, the reluctance torque for PMSM with p>l is made full use of. Compared with i_d=0 control, the stator current amplitude is reduced by a large percentage and the power factor is improved a lot.The conventional PID vector control rests on accurate motor models and parameters and its system is very complex. So, in the synchronous motor drives, using the L~∞DMC control and the stepping motion control instead of the PID vector control, the synchronous motor L~∞DMC speed and position control systems are designed creatively. The predictive model based on unit response is used, as breaks free from the conventional drive control methods, such that the complexity of modeling of synchronous motors is avoided. The implementation of the system is simple, the better dynamic and static performances and stronger robustness are obtained. In order to surmount a difficulty caused by the application of the general DMC to synchronous motor speed control system, an improvement on the predictive control algorithm is proposed.In the SRD, by analysis of the cause for feeding-voltage saturation with the conventional single-phase conduction strategy and its effect on the control performance, a novel commutation strategy whose primary purpose is the cancellation of the torque-ripple of...