Real-Time Powertrain Control Strategy for Series-Parallel Hybrid Electric Vehicles

The series-parallel hybrid electric vehicle(HEV), which employs a planetary gear set to combine one internal combustion engine(ICE) and two electric motors(EMs), can take advantages of both series and parallel hybrid system. The efficient powertrain operating point of the system can be obtained by the instantaneous optimization of equivalent fuel consumption. However, heavy computational requirements and variable constraints of the optimization process make it difficult to build real-time control strategy. To overcome the difficulty, this study suggests the control strategy which divides the optimization process into 2 stages. In the first stage, a target of charge/discharge power is determined based on equivalent fuel consumption, then in the second stage, an engine operating point is determined taking power transfer efficiency into account. Since all variable constraints are related to battery power limit, the variable constraints can be applied effectively in the determination process of charge/discharge power. In the engine operating point determination process, the calculation load can be reduced by employing the control map which offers the optimal engine operating point for given driving conditions and battery power. The developed control strategy has been implemented in a vehicle simulation to verify its effectiveness.