A rule-based energy management strategy for a series hybrid vehicle

A rule-based control and energy management strategy for a series hybrid vehicle is presented. The strategy is based on splitting the power demand between the engine and the battery such that these power sources are operated at high efficiency. The power demand is estimated as the output of a high gain PI controller that controls the longitudinal acceleration of the vehicle. The focus was to improve the fuel economy of the vehicle by suitable power assignment to the power sources. This power split (assignment) is implemented under a rule-base frame. The rules depend on the values of selected variables: the power demand itself, the driver's acceleration command and the status of the SOC (state of charge) of the battery. The rules ensure that the engine and the battery operate at high efficiency whenever possible. At high power demand the engine will operate at its maximum rated power. Simulation results of the proposed strategy showed improvement in fuel economy over the "thermostat" strategy. An improvement of 11% in the urban cycle and of 6% in the highway cycle have been achieved for a series hybrid vehicle driven by a 40 KW diesel engine and a 60 kW lead acid battery.