High Speed PM Brushless DC Motor Design In The Flywheel Energy Storage System And The Simulation Study Of Charging And Discharging Control Strategy

Flywheel energy storage system (FESS) has wide range of application prospects in uninterruptible power supply (UPS), peak-adjustment of small isolated power grid, pusled power supply, security and stability control in power grid, power quality improvement, vehicle regenerative braking and so on, and has always been one of hot issuses during recent years.Flywheel energy storage system is a typical mechatronics equipment, including these challenging techniques:high speed motor/generator, bearing support system, high power electric equipment, energy-storage rotor made by composite material etc. In this paper, the main tasks are the80kw/30000rpm high speed surface mounted permanent magnet (SPM) brushless DC motor (BLDC) design and simulation study of the charging and discharging control strategy of the system.With the characteristics of high speed and high flux frequency, first of all, we introduce the choice feature of the parameters such as the motor material, main dimension, electromagnetic load,winding design and so on in the progress of the high speed motor design.The design of the high speed motor involves multiple subjects such as mechanical, eletronmagnetic and thermal, the design process of the high speed motor was concluded, which emphasized the importance of the loss of the electrical machine and the analysis of the rotor strength.A2D-simplified model was used to analyze the motor rotor strength.According to the analytical theory, a rotor strength analysis programme was written based on Matlab/GUI. The above mentioned analytical method was adopted to study the influence of the protective sleeve thickness and interference fit on the rotor mechanical properties. Furthermore, the result of FEM analysis for the rotor strength indicated the analytical theory reliable and correct. Then, main loss of the high speed motor was studied and rotor eddy current losses was highlighted. The influence of slot width, air gap length and sleeve thickness on the rotor eddy current losses was carried out, which indicated that reducing the stator slot width or sleeve thickness and increasing air gap length could reduce rotor eddy current loss. The orthogonal analysis of the above three factors indicated increasing the valid air gap length was the most effective way but reducing the sleeve thickness the least to decrease the rotor eddy current loss.In the end, the simulation study of charging and discharging control strategy for the flywheel energy storage system was carried out. For the charge process, the traditional speed and current double back-feed closed-loop control strategy was adopted, and the current hysteresis band control method was used in the inner current loop. For the discharge process, the boost topology was choosen and voltage back-feed closed-loop control strategy was adopted. The charging and discharging simulation model of the flywheel enegy storage system were setted up in Matlab/simulink enviroment, the simulation results indicated the design plan reasonable and reliable.