On Control of Permanent-Magnet Synchronous Motors in Hybrid-Electric Vehicle Applications

Licentiate thesis, 2004

This thesis deals with design and analysis of the control system structure for electric drives equipped with permanent-magnet synchronous motors with a salient rotor. The intended application is propulsion in electric- and hybrid-electric vehicles. Particulary, sensorless control, meaning vector control without a mechanical rotor position sensor, is considered. A speed and position estimator of phase-locked loop type, previously reported in the literature, is analyzed with respect to the salient rotor and impact of parameter errors. Modifications are proposed to allow for operation in the whole speed range and the estimator's capacity to handle large speed estimation errors is improved. As a result of the analysis, simple parameter selection rules are derived, reducing the amount of trial-and-error work required in the design and tuning of the drive. A transient model taking harmonics into account is reviewed and its impact on current harmonics, when utilizing synchronous-frame PI current controllers, is investigated, both through simulations and experiments. Field-weakening operation is also considered. The closed-loop dynamics of a field-weakening controller, previously reported in the literature, is analyzed and verified experimentally, considering salient permanent-magnet synchronous motors. The theory considering loss minimization, by means of control, is reviewed and some analytical results are presented which can function as a useful tool when designing the control system of any electrical drive consisting of a permanent-magnet synchronous motor and corresponding inverter.