Research On Key Control Schemes For Consequent Pole Permanent Magnet Machines In Electric Vehicle

Electric vehicle (EV) has been considered as a important solution to energy and environmental issues. The electric propulsion system is the core unit in the EV. The Consequent Pole Permanent Magnet (CPPM) machine is a special type of Hybrid Excitation Synchronous Machine (HESM). It has good potential for EV due to high efficiency, high power density and adjustable flux over a wide range. In this dissertation, the electric propulsion system based on the CPPM machine is selected as the research object. In order to obtain good performance with wide speed range, high efficiency and high reliability, the three key control issues of the CPPM machine are investigated as flux-weakening control scheme, efficiency optimization control scheme and speed sensor fault tolerant control scheme.The structure of stator and rotor, operating principal and characteristics in the CPPM are different from the traditional Permanent Magnet Synchronous Machine (PMSM). Therefore, the flux adjustment principal and characteristics are introduced. Furthermore, the mathematical model of the CPPM machine is derived and verified by experiment results. The characteristics of mutual inductance, d-and q-axis inductance in the mathematical model are discussed. It can be concluded that the CPPM is with relatively small saliency. These analyses and discussions on modeling provide a theoretical basis for designing the CPPM machine control schemes.For the EV’s propulsion system based on the CPPM machine, a proper flux-weakening control scheme should be designed to extend the torque capability over the whole speed range. Through analyzing the CPPM machine operating constraints, it is demonstrated that, the maximum torque output can be approximately achieved by id=0control scheme according to the small saliency characteristics of the CPPM machine in the constant torque region. Then, the necessary conditions of the maximum torque output for the CPPM machine over the whole speed range are derived. Considering the parameters characteristics of the CPPM machine at the same time, a compound flux-weakening control scheme is proposed to improve the dynamic performance of the CPPM machine in the constant power region.In order to improve the efficiency of the propulsion system based on the CPPM machine effectively, the efficiency optimization control scheme should take the characteristics of the CPPM machine into account. The loss model of the CPPM is described briefly and the variation of the total controllable loss is derived to demonstrate that one-dimensional search algorithm is suitable for optimizing the CPPM machine’s efficiency. Then, by discussing the drawbacks of the existing efficiency optimization search algorithms comparatively, an efficiency optimization search algorithm with adaptive flux step is designed and realized according to the loss characteristics of the CPPM machine. The proposed search algorithm can accelerate the convergence speed without precise machine’s parameters, and maintain the system high efficiency operation by minimizing the total loss of the CPPM machine propulsion system.A short time continuous safely operating capability of the CPPM machine should be obtained when the speed sensor is failure in practical application. Therefore a proper speed sensor fault tolerant control scheme for the CPPM machine is required. The magnetic saliency characteristics of a CPPM machine in high-frequency excitation is analyzed by the finite-element analysis (FEA), and the HF impedances are measured by experiment to confirm the saliency. Consequently, a high-frequency (HF) voltage injection method in low speed range is proposed to detect the rotor position from the magnetic saliency of the CPPM machine. Simultaneously, the extended-electromotive force (EMF) method at high speed range is derived to reconfigure the rotor position. According to the characteristics of the reconfiguration methods presented above, a speed sensor reconfiguration scheme based on a single PI controller is proposed to combine the two methods which could ensure a smooth transition of different estimating procedure.At last, the propulsion system based on the CPPM machine is developed, and the control schemes are fully implemented to verify the effectiveness of proposed control schemes. The detail experimental results confirm that system characteristics with wide constant power operation range, high efficiency and high reliability can be showed due to the proposed control schemes. Therefore, the overall performance of the propulsion system based on the CPPM machine is improved significantly.