Research On Field Modulated Permanent Magnet Machine And Its Control System For Direct Drive Wind Power Generation

With increasing concerns on energy crisis and environmental deterioration, the development and utilization of renewable energy is attracting more and more attention. It is known that wind power as a clean and renewable energy is widespread on earth and has been widely utilized by the way of wind power generation. Compared with the gearbox-driven wind turbine system, direct-drive wind power generation has rapidly developed due to the advantages of high efficiency, fast dynamic response, low maintenance cost, etc.. Due to operating at a low speed, traditional direct-drive wind power generators generally encounter such problems:bulk size, heavy weight, low power density, high cost, technical difficulties of transportation and assembly. In this thesis, a new type of coaxial magnetic gear is presented, and its operation principle and torque transmission characteristics are investigated. Also, based on the "magnetic gearing effect", a novel flux-concentrating field-modulated permanent-magnet (FCFMPM) machine is proposed for direct-drive wind power generation. Based on the equivalent magnetic circuit method and the finite element analysis (FEA), the operating principle of the proposed FCFMPM machine is analyzed to reveal the evidence for high torque capability. Moreover, the performance characteristics analysis and optimal design of the proposed machine are conducted, and a prototype machine is also fabricated in order to build a wind power generation testing platform for experimental research.The main research content of this thesis can be summarized as follows:1. According to the operation principle, the existing magnetic gears can be classified as two types: converted magnetic gear and field-modulated magnetic gear. The key features, merits, demerits and performances of these two types of magnetic gear are comparatively analyzed in this thesis. Also, an improved coaxial magnetic gear (CMG) using flux focusing is proposed as well as compared with existing CMGs and mechanical gears, aiming at demonstrating the attractive features of CMG2. By using the 2-D FEA, the three viable magnetic-geared PM (MGPM) machines are discussed and quantitatively compared, thus demonstrating the intrinsic relationship among the CMG, MGPM machine and vemier machine. Based on the "magnetic gearing effect", a novel FCFMPM machine is proposed. The operating principle with detailed theoretical derivation based on the equivalent magnetic circuit method is analyzed to reveal the evidence for high torque capability of the FCFMPM machine.3. Based on the 2-D FEA, the electromagnetic performances of the FCFMPM machine including field distribution, aix-gap flux density, no-load PM flux linkage, no-load electromotive force (EMF), phase inductance, cogging torque and electromagnetic torque are analyzed and compared with the split-slot surface permanent-magnet vernier (S3PMV) machine. Moreover, the armature reaction reactance voltage drop expression is theoretically derived for finding methods to improve the output characteristics of the field-modulated PM (FMPM) machine.4. The power-size equation of the FCFMPM machine is also derived, which offers a foundation for the initial design of the machine. And based on the 2-D FEA, the influence of pole-slot combination on the torque density and the relationship between the length-diameter ratio and the output characteristics of the FCFMPM machine are investigated. Consequently, the optimal design process of the machine is conducted for achieving a high torque density, and a prototype machine is also fabricated for experimental testing.5. According to the basic electromagnetic laws and operation principle of the FMPM machine, the math modeling of the FCFMPM machine in stator reference frame and d-q frame are built. Then, in terms of this model as well as electromagnetic parameters obtained from FEA, the MATLAB/SIMULINK simulation model of the wind power generation system based on the FCFMPM generator and a DC motor set as the wind turbine is established. The performances of this system and the maximum wind power tracking method are investigated by the numerical simulation.6. The test platform of the proposed generation system is also built. Both the hardware circuit and software program based on DSP controller core for system experiments have been designed. Then, the performance testing focusing on achieving the maximum wind power tracking is performed to verify the effectiveness of the proposed control strategy.