Optimization of Control Strategy for Engine Start-stop in a Plug-in Series Hybrid Electric Vehicle 2010-01-2214

Plug-in hybrid electric vehicles (PHEVs) provide significantly improvement in fuel economy over conventional vehicles as well as reductions in greenhouse gas and petroleum. Numerous recent reports regarding control strategy, power train configuration, driving pattern, all electric range (AER) and their effects on fuel consumption and electric energy consumption of PHEVs are reported. Meanwhile, the control strategy for engine start-stop and mileage between recharging events from the electricity grid also has an important influence on the petroleum displacement potential of PHEVs, but few reports are published.

In this paper, a detailed simulation model is set up for a plug-in series hybrid electric vehicle (PSHEV) employing the AVL CRUISE. The model was employed to predict the AER of the baseline PSHEV using rule-based logical threshold switching control strategy. A possible adjustment method to optimize the control strategy for engine start-stop was then discussed and evaluation was performed by the simulation model with different driving distances under various driving cycles. The number of engine ON/OFF events, engine operating time and fuel consumption were analyzed.

The results showed that an optimal state of charge (SOC) value can be found to decide when to start or stop the engine according to the driving distance under a certain driving cycle and it's an effective way to reduce fuel consumption. With the optimized control strategy, the engine can either turn on at a proper SOC value during charge depleting mode or turn off at a proper SOC value during on-board charging mode. Both can achieve sharp reductions in engine operating time and gasoline consumption. For the former case, it can get a reduction in engine operating time by 46% and 53% under New European Driving Cycle (NEDC) cycle and the Environmental Protection Agency's (EPA) Urban Dynamometer Driving Schedule (UDDS) cycle respectively and thus a sharp reduction in fuel consumption. The similar results can be found in the latter case. It can also be found that the engine demonstrated less frequent and intense operation which contributes to the high fuel consumption. The modified control strategy is also expected to be a reference control strategy for the engine start-stop control of mileage-extending electric vehicles.