Optimal starting control strategy of compound power-split system based on dynamic programing algorithm

Hybrid electric vehicle has the advantages of internal combustion engine vehicle and pure electric vehicle. The mode transition from EV (electric vehicle) mode to HEV (hybrid electric vehicle) mode requires frequent engine starting. The engine ripple torque (ERT) at low speed will affect the stable operation of the output shaft and has a significant impact on ride comfort. In order to improve the effect of mode transition process, the distribution of motor torque is optimized. The engine ripple torque model is established by combining theoretical formula with experimental data. The dynamic torque of the compound power-split model is decoupled. The mode transition process from EV mode to HEV mode is analyzed. Aiming at power, ride comfort and economy, the optimal starting control strategy of engine is designed based on dynamic programing algorithm. The influence factors of starting process are studied. When the optimization grid of motor torque is 5, the best trade-off between optimization accuracy and calculation cost is obtained. The results show that, the best ride comfort is obtained by using the dynamic programing algorithm when the speed is 30 km center dot h(-1) and the load torque is -178 N center dot m. The starting effect is the best when the initial crank angle is 0 degrees while the transient response time is 0.84 s, compared with the initial crank angle of 90 degrees, the economy is improved by 21%.