Design and Application of Flywheel-Lithium Battery Composite Energy System for Electric Vehicles

For different types of electric vehicles, improving the efficiency of on-board energy utilization to extend the range of vehicle is essential. Aiming at the efficiency reduction of lithium battery system caused by large current fluctuations due to sudden load change of vehicle, this paper investigates a composite energy system of flywheel-lithium battery. First, according to the design requirements of vehicle performance, the essential parameters of the hybrid energy storage system are designed using CPE function. Then, based on the vehicle dynamics and operating principle of the hybrid energy system, a mathematical model for performance analysis of the hybrid energy electric vehicle is established. Finally, energy management strategy for the hybrid energy system is designed with the use of wavelet algorithm. Research results show significant improvement of the storage system efficiency. Specially, compared with the original scheme, owing to the flywheel battery, the maximum current and discharge rate of the lithium battery are reduced by 6.55% and 4.76% under WLTC working condition. Meanwhile, the average current is decreased by 14.93%. Furthermore, the average efficiency of lithium battery is improved by 3.07%. The overall efficiency of energy storage system is increased by 2.01%.