Design Of Vehicle Controller Software For Parallel Hybrid Electric Buses

The vehicle control strategy is one of the core technologies for parallel hybridelectric vehicles. In this paper the vehicle control strategy of single-axis parallel hybridelectric buses is researched and the software for the vehicle controller is developed.In this paper, the parallel hybrid electric bus model is built. Dynamic programmingis used to optimize the multi-energy torque-split strategy of parallel hybrid electricbuses in the China Typical City Bus Cycle globally. A rule-based parallel hybrid electricbus control strategy is designed based on the analysis and extraction of the optimizedtorque-split strategy.The vehicle controller software on the Freescale16-bit microprocessorMC9S12XEP100is written in C language based on the research of the control strategyof hybrid electric vehicles. The vehicle operation states are divided into five modes,which are the start mode, the engine mode, the motor mode, the motor-assisting modeand the regenerate mode. The modules for CAN communication, torque-split, shiftingcontrol, clutch control, coordination for vehicle modes and transient processes,diagnosis and working mode after failure are developed. The online calibration moduleis designed and the host computer software for online calibration is developed based onthe virtual instrument software LabVIEW. The functions of the vehicle controllersoftware are tested on the hybrid electric system test bench and the fuel economy of thevehicle is tested under the China Typical City Bus Cycle on the hybrid electric bus. Thereliability of the controller is also tested for5000kilometers on the bus. The experimentshows that the hybrid electric bus equipped with this controller has good fuel efficiencyand reliability, without any fault.The software for the32-bit MotoTron research and development platform isdeveloped in the Matlab/Simulink environment for the convenience of control strategyand software development. The low level drivers and initialization module is compiled.The programs on the16-bit microcontroller are ported to the new platform. The processof the core of the control strategy is redesigned for modularization, and the energymanagement strategy is separated so that other energy management strategies can betest in this controller. The functions of this vehicle controller software are tested on thehybrid electric system test bench. Test result shows that the controller software meets the design requirements.In order to improve the fuel economy of the hybrid electric bus, this paper presentsa model predictive control (MPC) torque-split control strategy for parallel hybridelectric vehicles. The first-order model is used to describe the engine torque and fuelconsumption based on the linearized engine steady-state map and a transient enginemodel is built. A torque request prediction method based on the driver’s acceleratorpedal is presented. In considering the motor’s compensation to the engine’s dynamictorque response delay, the constraints of the torque-split problem are designed. TheMPC algorithm can be converted to a linear programming by discretizing the model andobjective. This algorithm is real-time capable. The simulation result shows that thestrategy can improve the fuel economy of the hybrid electric bus to some extent.