Optimal control of a parallel hybrid vehicle equipped with a dual electrical storage system

This work studies the minimization of the fuel consumption of a parallel hybrid vehicle over a driving cycle. The considered vehicle is a conventional vehicle equipped with a low cost hybridization system. A single electric machine replaces both the starter and the alternator. Fuel savings result mainly from two functionalities, namely the regenerative braking and the engine stop&start. A dual electrical power source is also used. An ultra-capacitor is combined to a lead-acid battery by means of a DC/DC converter. Under an assumption commonly made in the literature, it is shown that the optimal control problem with the two electrical storage systems can be reformulated as a new problem where a single equivalent electrical buffer is involved. The optimal power split between the electrical and mechanical paths is determined offline using the Pontryagin's Maximum Principle. The converter control is optimized in a second step in such way that some recommendations on the battery usage are met.