Research On Axial Flux Permanent Magnet Flywheel Machine For Regenerative Braking In Electric Vehicles

Electric vehicle which utilized the electric power and driven by the traction motor is considered to be one of the environment friendly traffic tools, plays an important role in the city public transportation system. Its operation identifying operation characteristic include frequent starting and braking. Therefore, it’s of great importance to recover and recycle the energy through the regenerative braking system. Flywheel energy storage system has gain rapid development in recent years with its outstanding performance. In this paper, the flywheel energy storage system with a novel axial flux flywheel motor/generator utilized for absorbing the braking energy is researched. The main contents are as following:Firstly, the current research status of electric vehicle regenerative braking and flywheel energy storage technology are summarized, and the city subway train regenerative braking energy characteristics is quantitative analyzed with Matlab/Simulink simulation models which established from the perspective of kinematics and train traction as well as braking characteristic curves of Nanjing subway line one. Accordingly, the basic performance requirements of flywheel motor in flywheel energy storage applications are derived. Moreover, performance comparison of motors with different structures are completed, and the structure selection and design requirements of the flywheel energy storage motor/generator are finally determined by taking many aspects into account.Secondly, a relatively fast and accurate reluctance network model which based on magnetic equivalent circuit method is established for field and performance calculation of the proposed axial flux permanent magnet machine magnetic. The model is able to account for the magnetic saturation, ferromagnetic nonlinearity, and the interaction between the permanent and armature reaction magnetic field. The established reluctance network can be analogy to an electrical network to simplify the calculation. The static and dynamic electromagnetic performance characteristic parameters are attained by accessing magnetic potential of the network of each node obtained by MATLAB simulation. Based on the model, a genetic algorithm optimization model with goals of motor torque density and efficiency is established by taking into account the motor electromagnetic and mechanical performance constraints. The single-objective and multi-objective optimization results are obtained by Matlab genetic algorithm optimization toolbox, and the feasibility of the magnetic equivalent circuit model and the genetic algorithm optimization are verified by three dimensional finite element analysis.Finally, an axial flux permanent magnet machine with yokeless and segment armature prototype is built, and the basic performance is tested, which further verified the correctness of the magnetic equivalent circuit method.