Abstract

With the limits of power source taken into consideration, the efficiency of the traction drive is of particular importance in the engineering of electric vehicle and plug-in hybrid electric vehicle (EV/PHEV). Thanks to its high power density, high efficiency and high torque to weight ratio, Permanent Magnet Synchronous Machine (PMSM) distinguishes itself from other traction system candidates in the EV/PHEV application market. This research sets out to explore how the control strategy of PMSM can be optimized so as to achieve a better efficiency performance of EV/PHEV.
Prior research has put forth Loss Minimization Control Strategy (LMC) and developed its algorithm by considering a certain operating point. The focus has been placed on how to approximately solve the optimal current reference from a high order expression. So far, very limited effort has been made toward a generalized form of LMC algorithm over the full machine operation region, i.e. constant torque and constant power region. In this thesis, a generalized relationship between d-q current for the LMC of PMSM is presented, and maximum torque per ampere (MTPA) and maximum torque per voltage (MTPV) can be derived as special cases of LMC. The proposed control strategy shows better response and enhancement of the machine efficiency over full speed range when compared to conventional control strategies.
In order to develop the control method, the machine operation principle is discussed first, and the machine model is built for the control purpose. Then based on the analysis of PMSM operation performance with voltage and current constrains, the boundary of the machine operating is defined. In the light of literature review, the LMC is derived from the equivalent model of PMSM by considering the core loss. And the performance of the LMC is analyzed in detail for both constant torque and constant power region. In addition, the effects of parameters variation are investigated. Thus the control strategy is improved by considering full speed range. A Simulink model of PMSM with core loss taken into consider is developed to test the proposed control method. The experiment is performed on a lab surface-mounted PMSM. The experiment results are found to be consistent with simulation results.