Nonlinear Proportional Gain Based Robust Control: Its Application to Surface-mounted Permanent Magnet Synchronous Motors

Abstract

This dissertation has been written to deliver comprehensive information on a nonlinear proportional gain based robust control method and its application to a Surface-mounted Permanent Magnet Synchronous Motor (SPMSM) system for those who need to realize the precise motion control of SPMSM.

First, this dissertation describes the operating principle of a permanent magnet synchronous motor system and coordinate transformation, which is utilized in the 3-phase AC motor controller. Furthermore, the mathematical dynamics of the mechatronics system, in which the input torque is attained from the SPMSM, is described. Based on the mathematical dynamics, this dissertation discusses the concerns of a conventional control framework for the SPMSM current control (current signal issue such that the transformed current signals are subordinate to the rotor position), and this dissertation presents the torque modulation-based nonlinear current control, which is not using the direct-quadrature transformation.

Second, this dissertation describes the possible disturbances components that can hinder the robust motion-tracking performance of SPMSM. And conventional disturbance observers, which are developed to reduce the performance degradation of SPMSM, are described. The conventional DOBs have constant estimation gains, so it has a fixed damping ratio and natural frequency of the step input response. From the insight that the adaptive change of the damping ratio according to the estimation circumstance can enhance the DOB performance, the author developed a different structure of the DOB, and this dissertation presents a novel nonlinear-proportional integral (N-PI) structure of the DOB. A comparative study between the proposed N-PI-DOB and the conventional DOB shows that the N-PI-DOB can reduce the overshoot of the step response without the performance degradation of the rise time. By presenting the application of the N-PI-DOBs to SPMSM, this dissertation shows that the electromechanical system, including the motion controller, disturbance observer, and inverter controller, are presented in a three-cascaded form, and the inverter control performance impacts the performance of disturbance estimation and motion controller. It is proved that the disturbance estimation errors of the inverter system and the current tracking errors converge to the bounded balls. Furthermore, it is shown that the motion tracking system of an SPMSM has an Input-State Stability property.

During the design process of the precision motion control of SPMSM, there existed the assumption that the angular position, velocity, and currents were measurable. However, in some industrial applications of SPMSM, the measurement of position/velocity might be hard to apply due to the installation and manufacturing cost. So the position/speed observers of the SPMSM are needed to perform a position-sensorless control of SPMSM. Once the position observer is used to perform the sensorless control, there must exist a difference between the actual rotor position and the estimated position. This difference impacts the performance of the position-sensorless control. For that reason, this dissertation presents Variable-Gain Proportional Integral (VG-PI) back electromagnetic force (back-EMF) estimator and Phase Locked Loop (PLL) based angular position estimator, and stability of the proposed methods. The validation results of the proposed back-EMF estimator, the sensorless control in the steady-state speed operating region, and the sensorless control in the transient speed operating region shows that the proposed observers and controller performance outperform the conventional method.