Abstract
A new cooperative braking control strategy (CBCS) is proposed for a parallel hybrid electric vehicle (HEV) with both a regenerative braking system and an antilock braking system (ABS) to achieve improved braking performance and energy regeneration. The braking system of the vehicle is based on a new method of HEV braking torque distribution that makes the antilock braking system work together with the regenerative braking system harmoniously. In the cooperative braking control strategy, a sliding mode controller (SMC) for ABS is designed to maintain the wheel slip within an optimal range by adjusting the hydraulic braking torque continuously; to reduce the chattering in SMC, a boundary-layer method with moderate tuning of a saturation function is also investigated; based on the wheel slip ratio, battery state of charge (SOC), and the motor speed, a fuzzy logic control strategy (FLC) is applied to adjust the regenerative braking torque dynamically. In order to evaluate the performance of the cooperative braking control strategy, the braking system model of a hybrid electric vehicle is built in MATLAB/SIMULINK. It is found from the simulation that the cooperative braking control strategy suggested in this paper provides satisfactory braking performance, passenger comfort, and high regenerative efficiency.
Highlights
It is found from the simulation that the cooperative braking control strategy suggested in this paper provides satisfactory braking performance, passenger comfort, and high regenerative efficiency
In the hybrid electric vehicle, regenerative braking takes place by transforming the mechanical energy into electric energy via a generator, the electric energy is stored in the energy storing device such as battery or supercapacitor, and the stored energy is recycled to propel the vehicle via a motor
The cooperative braking control strategy is divided into two parts: the first part is used to adjust the antilock braking torque in the conventional hydraulic braking system using a sliding mode controller that is based on the target slip ratio to control the braking pressure increase, holding, and decrease; the second part is used to adjust the regenerative braking torque from the electric motor using a fuzzy logic control strategy that is based on the target slip ratio, battery state of charge (SOC), and the motor speed to adjust the regenerative braking torque dynamically
Summary
In the hybrid electric vehicle, regenerative braking takes place by transforming the mechanical energy into electric energy via a generator, the electric energy is stored in the energy storing device such as battery or supercapacitor, and the stored energy is recycled to propel the vehicle via a motor. Taking advantage of the quick response and accurate control of the motor torque, researchers worldwide have explored a way to introduce the motor torque into an antilock brake system (ABS) control, expecting a better control effect [9,10,11] These strategies neglected the cooperative control between the conventional hydraulic braking system and the regenerative braking system, and it is difficult to achieve good braking stability and high regenerative braking efficiency simultaneously. The magnitude of the regenerative torque varies depending on the vehicle velocity, and the problem of fluctuating vehicle velocity (variable motor input speeds) has not been addressed in the paper Because of problems such as nonlinearity in the vehicle-braking dynamics and variations in model parameters over a wide range due to variations in road surface and vehicle conditions, conventional ABS controller cannot achieve satisfactory performance. Based on the wheel slip ratio, battery state of charge (SOC), and the motor speed, a fuzzy logic control strategy (FLC) is proposed in this paper
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