Energy Management Method Optimizing Engine Ignition on/off Timing and Operating Points of Powertrain Components for Series Hybrid Electric Vehicle

This paper proposes a novel optimal control method for operating each powertrain component of a series hybrid electric vehicle (SHEV) while reducing the total energy loss during a trip with a given speed profile. The proposed method formulates the SHEV energy management problem (EMS) as a novel optimization problem. This study has novel aspects: 1) The proposed method simultaneously optimizes the ignition on/off timing and operating points of powertrain components without involving any binary variable. 2) Function 1) is realized by defining the reference values and actual values of ignition on/off timing, engine output torque, and inverter conversion rate as continuous variables separately, setting the reference values as optimization variables and including a designed function in the performance function to avoid engine ignition when the engine speed is lower than the idling speed. 3) The entire brake-specific fuel consumption (BSFC) map is modeled for optimization instead of restricting the engine operating point to the optimal line of BSFC. 4) A rule-based control method is established according to the control method used on commercial SHEVs to validate the effectiveness of the proposed method. 5) The control results under four initial conditions are compared to validate the rationality and effectiveness of the rule-based and proposed methods in reducing the total energy loss. Both methods can efficiently control the powertrain components. However, in all four case studies with different initial state of charge values, the proposed method and the rule-based method generate different ignition timing and operating points for the components in the powertrain. The proposed method reduces the total energy loss and fuel consumption by over 19.41% and 13.75%, respectively. Moreover, the proposed method eliminates the chattering of the engine ignition on/off switch.