Study On Evaluation Methods Of Braking Energy Recovery For Battery Electric Vehicles

Braking energy recovery is an important technology to highlight the advantages and characteristics, and determine the energy economy and vehicle safety for electric vehicles of different forms. Currently, the design and control of regenerative braking systems have become hotspots for world-renowned automobile and components companies. Relevant researches on the control strategy have been conducted in many well-known universities. Yet a set of unified evaluation index and test method is not formed. This study is targeted at the performance of braking energy recovery of small and medium battery electric vehicles for passengers based on generator-battery regenerative braking technology(BEV-RB) and evaluation methods are put forward to provide a reference for the draft of relevant standard.A set of evaluation index of the performance of braking energy recovery for BEV-RB is proposed as braking energy recovery efficiency and energy contribution rate on the basis of the summary of a unified route of braking energy recovery. The former is the ratio of recovered braking energy and theoretical maximum braking energy. The latter is the ratio of recovered braking energy and energy consumption. Test method is obtained on the basis of revising the existing energy consumption test method for battery electric vehicles, that is, instruments are installed between the inverter and battery to obtain the current and voltage data required in the index calculation. The dynamometer system for braking energy recovery is built according to the test method, and 3 kinds of typical BEV-RB models are tested to get the current and voltage data in the first NEDC condition. Complementary to vehicle test, computing models of evaluation index are built and integrated into the GM_EV1 model on the platform of Matlab/ Simulink. And the new vehicle model is simulated in 6 kinds of driving cycles and 4 kinds of control strategies on the platform of Advisor 2002.According to the test and simulation results, the impacts of model parameters, driving cycles(including micro conditions) and control strategies are discussed. It is indicated that a power system of a large battery pack and a big motor is not necessarily resulting in good performance of braking energy recovery. Thus matching dynamic parameters for a BEV-RB, one reasonable recovery strategy should be taken into consideration. It is also found that the recovery technology is likely to improve the energy economy most significantly during the smoothly braking process from high speed to medium speed in the outskirts. It is also indicated that the energy economy is improved significantly in FTP75 driving cycle in which both the regenerative potential and recovery efficiency are considerable. It is also found that the mileage is significantly affected by the control strategy. The initial speed and the proportion of motor braking can be increased to extend the mileage, on the basis of vehicle safety.Both the capability of braking energy recovery and the effect of recovered energy on vehicle economy improvement are reflected in the proposed index. Both the interaction among different systems and external factors such as road, are investigated in the proposed test method. It is also simple, time-saving and cost-saving. Several advices are provided to obtain a better recovery performance in the discussion on the factors of the proposed index.