Study On Electro-mechanical Braking Control Strategy For A Distributed Driving Electric Vehicle

The increasing prominence of environment problems and resource issues has providegreat propulsion for the development of new energy vehicles. Electric vehicle(EV)is animportant branch of new energy vehicles, among which the distributed driving EVrepresents the developing direction of the power system because of its out-standingdynamic control performance. As an important working mode of electric vehicle, theregenerative braking enables an improvement of braking performance and recovery of thebraking energy. It reduces vehicle fuel consumption and the wear of the friction brakegreatly. Hence, different from the traditional braking, in EV there are two kinds ofbraking force: the regenerative braking and thehydraulic braking. It’s been a researchhotspot to coordinate the two different breakings to get the maximum energy recovery onthe premise of keeping the braking stability. Based on the national “863” project-“study onkey technology for high-performance EV compatible with V2G technology”, the controlstrategy for the electro-mechanical braking in distributed driving EV is studied.Firstly, parameter matching is completed for further strategy design and simulation.Hierarchical control strategy is then proposed for distributed driving EV. Hierarchicalcontrol strategy can be divided into the top-level control strategy and the low-level controlstrategy. Top-level control strategy takes braking stability as the control objective. It can bedivided into normal braking condition control strategy and anti-lock condition controlstrategy. In the top-level control, the slip rate of each wheel is calculated during braking todetermine which control strategy is to be applied. The objective of the top-level control isto equalize the slip rate of each wheel. As for the low-level control strategy, the controlobjective is to regenerate as much energy as possible. Thirdly, to verify the effect ofhierarchical control strategy, a joint dynamics simulation platform is established withMATLAB/Simulink and AMESim. At last, simulation analysis of the hierarchical controlstrategy is conducted with different road adhesion conditions, different vehicle load statesand different brake intensity.The simulation results indicate that the top-level control strategy can well control theslip rate of each wheel according to different braking conditions: in normal braking conditions, it can keep the front slip rate and the rear slip rate at the same value; while inanti-lock braking conditions, it can keep the slip rate of each wheel around the optimumslip rate. The low-level control strategy can make the maximum energy recovery whilekeeping the braking stability at required braking intensity.The results prove that theproposed control strategy is reasonable and feasible.