Optimal power distribution control for parallel hybrid electric vehicles

Optimal power distribution control algorithm is investigated for parallel HEVs. In order to find the optimal control algorithm, optimization problem is defined, which finds the optimal control variables to minimize the fuel consumption while satisfying the constraint equations. Scale factors in weighting the motor usage are selected as the control variables on how to distribute the demanded vehicle power into the electric motor and the internal combustion engine. Dynamic models of the HEV powertrain are represented with state space equations. The optimization problem is solved for the single shaft parallel HEV and double shaft parallel HEV using the HEV performance simulator developed in MATLAB Simulink and the mathematical optimization algorithm, SQP which is based on FORTRAN for multi-variables design optimization. It is found that the optimal control algorithm of the double shaft HEV provides better fuel economy than the single shaft HEV since the recuperation energy due to the regenerative braking can be increased by the engine off and clutch operation.