Research On Hybrid Regenerative Braking Energy Recovery Control Strategy

The development of automobile industry is facing two aspects of pressures,environmental pollution and energy shortage. It is an important task to vigorouslydevelop pollution-free, zero-emission new energy vehicles in the world. Regenerativebraking plays a key role to improve the fuel economy of HEV and increase themileage. In the process of braking, the motor is in condition of generator, and storesthe braking energy in the form of electrical energy in the battery. At the same time, itgenerates braking force on driving wheel. When the car is started again, the energystored in the battery can be used by the driving energy again. At present, theutilization efficiency of regenerative braking energy recovery is the main problemduring hybrid electric vehicle braking.This paper firstly introduces the basic structure and working principle ofregenerative braking system for hybrid electric vehicles, and analyzes the distributionrelationship between the mechanical braking and electric braking. And I compare thecomposite braking with the conventional friction braking. Then I analyze the brakingprocess of hybrid electric vehicle from the force and efficacy, and draw the constraintsand impact factors in the braking energy recovery process.Considering the two factors that the regenerative braking and mechanical brakingmust be coordinated to control, as well as the traditional fuel vehicle driver operatesthe brake pedal driving habits. So this paper adopts the constant braking currentcontrol strategy. That is the motor armature current as control object when braking.Conventional PID controller and fuzzy PID controller are used to control DC/DCconverter’s duty ratio D, and makes the armature current of motor to have goodfollowing on the brake pedal in the state of braking. Based on the dynamics analysisof the regenerative braking system and the working principle of two quadrant DC/DCconverter, I establish the mathematical model of the regenerative braking operationstate. Then the model is integrated into the Matlab/Simulink environment simulation.The experimental results show that:(1) when demand braking force is less than themaximum electric braking force, hybrid electric vehicle’s braking force is providedwhole by the electric braking system. Under the premise of meeting the braking safetyand the braking constrained conditions, the motor armature current is greater that thebraking force is greater, the braking distance is shorter, and the recovering braking energy is more.(2) When demand braking force is greater than the maximum electricbraking force, hybrid electric vehicle’s braking force is provided by the compositebraking system. During the composite braking, the braking force is greater, thebraking distance is shorter, and the braking energy recovery is less.(3) Fuzzy PIDcontroller greatly improves the robustness of system to adapt to external interference.Compared with the conventional PID controller, it reduces the dynamic deviation, andimproves the stability of the equilibrium point.