Abstract
This paper provides convex modeling steps for the problem of optimal battery sizing and energy management of a plug-in hybrid electric vehicle with an electric variable transmission. Optimal energy management is achieved by a switched model control, with driving modes identified by the engine on/off state. In pure electric mode, convex optimization is used to find the optimal torque split between two electric machines, in order to maximize powertrain efficiency. In hybrid mode, optimization is performed in a bilevel program. One level optimizes speed of a compound unit that includes the engine and electric machines. Another level optimizes the power split between the compound unit and the battery. The proposed method is used to minimize the total cost of ownership of a passenger vehicle for a daily commuter, including costs for battery, fossil fuel and electricity.
Highlights
Hybrid Electric Vehicles (HEVs) are being considered a convenient intermediate product in the conversion process from conventional to pure electric vehicles, due to their compromise on cost, fuel consumption and driving range
This paper extends previous studies by providing convex modeling steps for the problem of optimal battery sizing and control of a series-parallel Plug-in HEV (PHEV) powertrain equipped with an Electric Variable Transmission (EVT)
To the optimal Energy Management Strategy (EMS) of a planetary gear powertrain [30], we show that the EVT powertrain can be optimally controlled by a bilevel optimization, where one level optimizes the speed of a compound unit including the Internal Combustion Engine (ICE) and Electric Machines (EMs), and another layer optimizes power split between the compound unit and the battery
Summary
Hybrid Electric Vehicles (HEVs) are being considered a convenient intermediate product in the conversion process from conventional to pure electric vehicles, due to their compromise on cost, fuel consumption and driving range. When designing PHEV powertrains, typical optimization problems involve battery sizing and design of Energy Management Strategy (EMS). Which in the HEV context typically includes engine on/off and gearshift control [16] Another EMS optimization approach that has been shown to require less computational power, relies on Pontryagin’s Minimum Principle (PMP) [12, 17,18,19]. When applying PMP in the HEV problems, it is assumed that the battery size is large enough to guarantee a constant Lagrange multiplier, while searching for the optimal control that does not activate battery energy limits [12] Another limitation of PMP is the inability of handling integer state variables. This paper extends previous studies by providing convex modeling steps for the problem of optimal battery sizing and control of a series-parallel PHEV powertrain equipped with an EVT.
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