(A) study on auto-tuning PI/PI-PD controllers applied to servomotor drives

Abstract

This thesis shows auto-tuning of simple regulators that are used for servomotor speed and position control, respectively. Servomotors can be divided into two categories such as DC servomotors and AC servomotors. Among them, DC servomotors are traditionally used for the variable speed and position drives. Though AC motors provided increased power density and ruggedness, their native coupling and nonlinearity have been tackled accurate motion control. Recently, vector current control scheme and advanced microprocessor technologies drastically refined torque control performance of AC motors such as the separately excited DC motors. As a result, AC servomotors such as PM synchronous motors are gradually replacing DC servomotors in motion control applications. Torque is the basic control variable of a motor because it is directly depends on driving current. With an inertial load, electromagnetic torque of a motor is related to the angular acceleration. Since the angular speed and the angle is also related to the angular acceleration through integral and double integral respectively, current control dynamics for the electromagnetic torque regulation is the primary dynamics of motor control. In general, the dynamics of current control could be handled much faster than the mechanical dynamics. Therefore a speed or position controller could be designed for the mechanical dynamics where the electrical dynamics is assumed to be ideal. Minimum requirements of speed and position control structures could be explained as follows. For a constant inertial load, a servomotor under speed control is modeled as a first order plus dead time (FOPDT) process with small dead time. As many theoretical researchers agree, a PI controller is enough for this case. For the position control applications, motor is modeled as a second order integrating process because the angular position is represented as the time integration of angular acceleration. Obviously, a simple PID controller does no...