Simulation and optimization applied to power flow in hybrid vehicles

Abstract

This chapter describes the application of optimization to power flow in hybrid electric vehicles, first using a strategy based on bang-bang optimal control and then comparing it with Pontryagin's alternative. The first strategy, known as the planetary gears system (PGS), focuses on satisfying the kinematic and dynamic constraints of the gears system, starting from the allocation of the electric machine power. The second uses Pontryagins minimum principle (PMP) to solve the energy management problem and decide the amount of power that the electric machine and combustion engine should provide. The approach of the PMP strategy entails three basic elements, namely: first of all, getting the demanded power to be supplemented by the drive machines; secondly, maintaining the state of charge at a level in and around a reference so as to avoid discharging and overloading the batteries and thirdly, saving on fuel. By using the above considerations, a cost function is set out that considers the power from both machines to be inputs. The simulations were performed in Matlab's Simulink using detailed models of the elements of a hybrid diesel-electric city bus in parallel configuration. The demands are represented by driving cycles while the combustion engine and electric machine are coupled using a planetary gears system.