Abstract
A single-stage magnetic suspended positioning stage directly driven by an inverter-fed linear ac motor with precision positioning capability is developed in this dissertation. The magnetic suspension positioning system is established with all constituted parts being properly matched and constructed. In the propulsion system, the double-sided linear permanent magnet synchronous motor (LPMSM) is adopted. The LPMSM is powered by a hysteresis current-controlled PWM inverter with commutation according to the moving member position information. The dynamic model is indispensable for controller design, but it is not easy to obtain accurately from physical derivation. Hence, the estimation approach is employed as an alternative to obtain the estimated one from measurements. As generally recognized, the driving performance of an inverter-fed electromechanical system is significantly affected by the current switching control performance of its current-controlled PWM scheme, which forms the innermost loop of the multi-loop control system. Owing to its simplicity and robustness, the hysteresis PWM scheme has been widely employed in motor speed driving control. However, it is rarely used for position servo drive, since it possesses varying output harmonic spectrum, and the fixed current error bound becomes comparatively larger as the motor current becomes smaller. In this dissertation, the studies about the promotion of hysteresis PWM inverter for servo application are made. In the proposed control approaches, the error band of hysteresis PWM inverter is tuned to yield the desired constant and random harmonic spectrum distribution characteristics. Effectiveness of the developed control approaches is first tested in a single-phase electrodynamic shaker system. Then the designed three-phase inverter is used to power the magnetic suspension positioning system. Simulated and measured results show that better performances in current tracking control, harmonic spectrum distribution characteristics and position control can be achieved by the proposed varying-band hysteresis current-controlled PWM schemes. As to the positioning control, in order to obtain the desired robust command tracking and load regulation control requirements simultaneously, a two-degrees-of-freedom (2DOF) control scheme combining the H_inf feedback control, the command feedforward control and the model following control is developed. The loop shaping H_inf design procedure is employed to find the feedback controller, which is emphasized in obtaining the desired disturbance and uncertainty rejection control requirements and the guarantee of closed-loop stability. Then, the H_inf feedback controller is augmented with a command feedforward controller to form the 2DOF control structure. Through properly shaping the command by the feedforward controller, the prescribed command tracking control performance can then be independently satisfied. As the operating condition and parameter changes occurred, a model following tracking error driven control is further employed to improve the control performance degradation. It follows that the prescribed control requirements at nominal case still can be preserved for the disturbed cases.