Optimization and Comparison of Heuristic Control Strategies for Parallel Hybrid-Electric Vehicles

Due to the structure of a parallel hybrid, different operating states and degrees of freedom for the torque of the combustion engine arise. To manage the transition between the different operating states as well as to provide the setpoint for the torque of the combustion engine, a control strategy is required. The transition between the different operating states can be initiated depending on various vehicular variables like vehicle speed or required drive torque. For the torque setpoint of the combustion engine different approaches are known [1]. The vehicular variables which initiate the transition between the operating states and the approaches for the setting of the torque of the combustion engine can be combined to different heuristic control strategies by basic IF-THEN-rules. The determination of the design parameters of the different control strategies can be regarded as an optimization problem with the objective to “minimize fuel consumption”. As a constraint for the optimization, the state of charge (SOC) of the electrical energy storage has to be sustained. From the optimization results it becomes apparent that for nearly all developed control strategies in all driving cycles and for all vehicle masses a charge sustainability and a reduction of fuel consumption are possible compared to a conventional reference vehicle. The optimal parameters of the strategies depend more or less on the driving cycle and the vehicle mass, but some parameters and approaches for setting the torque of the combustion engine turn out to be comparatively independent. Thus, these control strategies are predestinated for the use in a real vehicle