Computationally efficient gear shift strategy for hybrid electric vehicles

A collaborative control strategy for gear optimization and energy management of hybrid electric vehicles based on Pontryagin’s minimum principle (PMP) and numerical iteration is proposed in this paper. First, based on PMP, an analytical solution of the power distribution is obtained by introducing a second-order polynomial approximation model of the power-train. The gear control at each moment is obtained by comparing the Hamiltonian function. Then, to solve the problem that the fixed costate brought by the discrete gear cannot satisfy the state of charge (SOC) constraint, the weighted average method is proposed to obtain the reference trajectory to adjust the costate in real time. The simulation results show that the proposed method can satisfy the SOC boundary and terminal constraints, and the fuel economy is close to that of dynamic programming (DP), but the computing speed has increased by more than 24 times.