Because of its significant impact on the cooperative regenerative braking performance of electrified vehicles, the modulation effect of a hydraulic brake is of great importance. To improve the hydraulic brake control performance further, a novel pressure-difference-limiting control method for hydraulic pressure modulation based on on-off solenoid valves is proposed. The linear relationship between the coil current and the pressure difference across the valve is obtained. The characteristics of pressure-difference-limiting modulation are simulated and analysed. Then, a cooperative regenerative braking control algorithm based on the pressure-difference-limiting modulation of the hydraulic brake is designed. Hardware-in-the-loop tests of the algorithm under typical braking procedures are carried out. The test results demonstrate the validity and feasibility of the developed regenerative braking control algorithm and indicate that the proposed pressure-difference-limiting modulation method, which has an advantage over the conventional control based on a pulse-width-modulated signal with respect to the control accuracy of the hydraulic brake pressure, has great potential to improve the braking performance of a vehicle.

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The traditional regenerative braking control strategy usually uses the torque control mode and does not perform closed-loop control on the charging current, when the vehicle needs to be charged with a small current, the regenerative braking system cannot work effectively. The dual-mode regenerative braking control strategy proposed in this paper unifies the closed-loop control of regenerative current and the closed-loop control of regenerative torque. Especially when the battery is in a state of high charge or the temperature of the battery is too high or too low, this strategy can ensure charging safety, regeneration efficiency, and ride comfort. In the current closed-loop control mode, this proposal uses the ADRC controller to dynamically adjust the motor torque to achieve the purpose of accurately controlling the regenerative current. This method does not need to change the original vector control frame of the motor, which is convenient for engineering applications. The designed regenerative control strategy is verified through typical braking simulation. Bench tests are carried out and the results validate the feasibility and effectiveness of the designed strategy. Based on the realization of the safety of charging and the vehicle ride comfort, the proposed regenerative braking control strategy can achieve higher regeneration efficiency under the dynamical limitation of battery charging current, which further expands the operating range of the regenerative braking system.