Two-Degree-of-Freedom Self-Tuning Control for Motor Drives Using Pole-Zero Cancellation Method

Abstract

In this paper, we present an excellent method named pole-zero cancellation (PZC) for designing motor control systems. PZC is performed in the z plane. A control system consists of three controllers, i.e., a speed controller, a position controller, and an adaptive identifier. The speed controller has two degrees of freedom: disturbance suppression and tracking speed, both of which can be regulated. The pulse transfer function used for regulating the tracking speed has two poles and one zero. When one pole and one zero coincide and cancel each other, the pulse transfer function is of the first-order lag type, and overshoots do not appear. The adaptive controller determines the coefficients of the pulse transfer function and adjusts the speed controller automatically so that the poles and zeros coincide. The transfer function of the position controller also has one pole and one zero, which cancel another pole and zero; pole 1 in the closed loop is not cancelled, and hence, position overshoots do not appear.A 2.2-kW induction motor is tested. The motor torque is controlled using a rapid torque control method. In this paper, first, the tracking-speed characteristics and the tracking-position characteristics are presented. Next, the identified transient coefficients are given, and finally, the disturbance-suppression characteristics are discussed. The experimental results prove the usefulness of the proposed method.