Study On Brake Coordinated Control Strategy For HEV Bus Based On The System Characteristics

Hybrid electric vehicles reduce fuel consumption and improve emission quality. For somecities where traffic is heavy, the status of HEV is becoming increasingly important.Regenerative braking is one of the main reasons why HEVs save energy, Regenerativebraking uses motor to recuperate braking energy and stores it in batteries for future use. Thestatus of vehicle and relative parts determine whether vehicle can recuperate braking energy.When some certain conditions are met, vehicle conducts regenerative braking, otherwisevehicles exits regenerative braking. Hybrid electric vehicle has three braking modes. Totalbraking force will fluctuate in the switching process of braking mode because of thedifference between pneumatic braking force and regenerative braking force. The purpose ofthis paper is to coordinate motor and mechanical braking system in the switching process ofbraking mode so that the total braking force can meet driver’s demands and also enable thebraking force fluctuations as small as possible. Thereby the fluctuation of brakingdeceleration is reduced and the braking comfort is improved. The couple of regenerativebraking force and mechanical braking force is non-linear, and some parameters are uncertain.Experimental curves show that the dynamic response of pneumatic braking force is fasterthan regenerative braking force. This paper proposed a new compensation control algorithmbased on the dynamic response characteristics of pneumatic braking force and regenerativebraking force. This algorithm organically combines fuzzy control, sliding mode control andadaptive control, it can effectively solve uncertain or time-varying parameter controlproblem, it can also reduce or avoid the chattering in conventional sliding mode control.This paper is to study dynamic coordinated control strategy for hybrid electric bus. Tostudy this issue, the following works are done in this paper:1. An improved scheme of braking system is proposed. Parameter matching andcharacteristic study for new hardware is made. Characteristic analysis and experimentalresearch on pneumatic braking system and motor braking system are conducted. Dynamicsimulation model of pneumatic braking system is established. Transfer functions of motorbraking system is fitted for braking force coordinated control. 2. Analysis on theory of braking force coordinated control is conducted and hierarchicalcontrol method is proposed. Allocation method of braking force between front axle and rearaxle and between pneumatic braking force and regenerative force of rear axle is introduced.Aimed at keeping the total braking force of friction and regenerative braking force undersmall fluctuation when braking mode switches, based on the characteristics of pneumaticbraking system and motor braking system, we design an adaptive fuzzy sliding modecontroller to control the pneumatic braking system to compensate for error of the motorbraking force.3. Vehicle dynamic model is established using Cruise and the model of braking forcedistribution algorithm and braking force coordinated control algorithm are established usingMatlab/Simulink. Simulation of model with braking force coordinated control and withoutbraking force coordinated control is conducted through interface in MATLAB, and thenanalysis on simulation results is carried out.4. After the building of off-line simulation platform, braking force coordinated controlhardware in the loop test platform is built based on Matlab/xPC, on which the dynamiccoordination control algorithm is further validated. The braking force coordinated controlalgorithm can effectively control the braking force fluctuations during mode-switchingprocess according to the tests.