Control of permanent-magnet synchronous machines in automotive applications

University dissertation from Chalmers University of Technology

Abstract: This thesis deals with the design and analysis of control system structures for electric drives equipped with permanent-magnet synchronous machines (PMSMs) in automotive applications. Sensorless control, meaning vector control without a mechanical rotor position sensor, is considered and a speed and position estimator of phase-locked loop type is analyzed thoroughly. Modifications are proposed to allow for operation in the whole speed range and to improve the estimator's capacity to handle large speed estimation errors. It is shown that rotor saliency affects the estimator dynamics which may become unstable for certain parameter selections and operating conditions. Simple parameter selection rules are therefore derived in order to guarantee stability and to simplify an implementation. Of particular interest for PMSMs with small or negligible rotor saliency, an estimator, extracting position information solely from the back-electromotive force is also considered. The estimator is based on the well known "voltage model" and modifications are proposed in order to improve the estimator's performance in the low-speed range by guaranteeing synchronization at startup and allowing stable rotation reversals. The theory of loss minimization by means of control is applied to a PMSM drive intended for propulsion in a hybrid electric vehicle. Through stronger field weakening, the fundamental core losses can be reduced at the expense of increased resistive losses. The study shows, however, that the additional inverter losses, due to the addition of extra field weakening, reduce the potential to minimize the total losses considerably. A review of fault-tolerant PMSM drives is presented and control algorithms are proposed for achieving sensorless control, closed-loop field-weakening control, and maximum utilization of the available inverter voltage for a drive that, for redundancy, adopts an additional inverter leg connected to the neutral point of the machine. The impact of various electrical faults in a vehicle equipped with in-wheel motors and individual steering actuators is also investigated. Here, it is shown that vehicle stability can be maintained with only minor displacements using a closed-loop path controller and an optimal approach, recently reported in the literature, to allocate tire forces.