Study On Combined Control Of Regenerative Braking And Anti-Lock Braking System For Hybrid Electric Vehicle

Energy regeneration during braking is an important technique for hybrid electric vehicle (HEV: Hybrid Electric Vehicle) to improve their fuel economy and extend their driving range. During braking course, the electric motor acts as generator, the regenerative energy stores in battery as electrical energy. Energy regeneration is a wide used technique for electric vehicle manufacture; using assistant braking which adds by electric motor, some kinetic energy during braking can be regenerated into battery, the utilization of energy can be improved greatly. Considering the braking performance and stability, most HEV employs both ABS (ABS: Anti-Lock Braking System) hydraulic braking system and regenerative braking system at the same time, so how to make the hydraulic braking system assorts with the regenerative braking system, to get more regenerative energy under assurance of braking safety is a key technique for HEV research. With the hybrid electric vehicle project and its affiliated vehicle control system sub-project of the national"863 program"as background, the main topic of this study is designed a hydraulic/ electric braking combination control strategy for HEV and its implementation in the real vehicle.Braking control strategy is an important part in the design of HEV braking system, braking control strategy is a complicated problem which involves decision making of complex problems and time varying nonlinear system control. Because the braking system of HEV involves the cooperation of hydraulic/electric braking system, it is very difficult to construct an accurate simulation model to reflect the real state of braking system, and the influence of road adhesion coefficients, the unpredictability braking intention of driver also increases the difficulty of the design braking control strategy. This dissertation addresses the braking safety and regenerative efficiency, toward this end, four issues are explored. They are: builds simulation model for HEV braking system; designs the combined braking control strategy (CBCS) for HEV braking system; designs the optimal slip ratio fuzzy logic control strategy(FCS) and braking torque distribution fuzzy logic control strategy; and test investigation and validation of the braking control strategy. A dynamic model for HEV braking system has been built up as one important part of design of braking system control strategy, it has strong influence on the efficiency and effectiveness of developed controller. The modeling course using theoretical modeling approach combined with empirical modeling. The vehicle system dynamic model main consists of vehicle model; non-steady semi-empirical tire model; ABS hydraulic system model; electric motor and its controller model; battery and its controller model. This dissertation make a deep insight into the non-steady semi-empirical tire model and ABS hydraulic system model, in order to get the needed simulation parameters, design the experiments schedule and make the related experiments. Using chassis dynamometer to obtain the input and output characteristics of battery and electric motor. Simulation results and experiment tests prove the braking system model is correct and steady which can fit for the real time control accuracy requirements and the need of future investigation.A simulation platform is constructed based on the braking system model, on this simulation platform, firstly, the regeneration energy management strategy, braking modes and regenerative braking restrained conditions can be researched and analyzed, in the following, a combined braking control strategy (CBCS) for hybrid electric vehicle and its design procedure are presented, and then, the practical and detailed algorithms of ABS hydraulic system control variables is presented, such as how to collection and calculation of wheel speed, calculation of acceleration/deceleration and wheel slip ratio, etc. After a deep analysis of braking system, braking control strategy and program have been designed; the different control functions between hydraulic braking system and regenerative braking system has been defined. Aimed at the different braking requirement, braking simulation for NEDC driving cycle, slightly braking, mean braking and emergency braking have been researched respectively, the simulation results shows the CBCS can regenerate energy effectively during the braking course of NEDC cycle and under slightly/mean braking requirement, for emergency braking requirement, braking control strategy can assure the braking safety on different adhesion coefficient road.Based on the CBCS, a fuzzy logic braking control strategy (FCS) for hybrid electric vehicle is designed by employing fuzzy logic control theory. A slip ratio fuzzy logic controller and a braking torque distribution fuzzy logic controller have been designed respectively. The slip ratio fuzzy logic controller can assure wheels work with optimal wheel slip ratio and the braking torque distribution fuzzy logic controller can dynamic adjust the braking torque based on the braking system requirement. A rule library on different adhesion coefficient road is constructed for slip ratio fuzzy logic controller and braking torque distribution fuzzy logic controller; and comparison between CBCS and FCS have been made, Simulation results reveals that FCS is better than the CBCS on braking torque distribution, braking performance and regenerative efficiency improvement. The above work has laid the foundation for the application of fuzzy logic control in the real HEV.The last part of this dissertation presents the results of the real vehicle field test on chassis dynamometer and performance road. The experiment on chassis dynamometer validates the combined braking control strategy (CBCS) for NEDC driving cycle, the experiment results shows the CBCS control strategy can control the braking torque effectively, the well agreement of the regenerative efficiency between the simulation and real test demonstrates the HEV model developed in this dissertation is exact enough for analysis braking control system. The experiment on performance road is executed on three kind adhesion coefficients road, the experiment results shows the CBCS control strategy can achieve a good braking performance with emergency braking command, the effectiveness and stability of braking control strategy is proved to reach that of original braking control system.As one of the major key techniques of HEV, the research of braking control technique plays an important role in HEV study and design, the significance of the work in this dissertation lies in improving the domestic research and development of the HEV braking control system.