The UC Davis team developed a comprehensive vehicle model based on PSAT (Partnership for a New Generation of Vehicles Systems Analysis Toolkit), a Simulink based modeling program developed by Argonne National Laboratory. They simulated their Suburban’s four-wheel-drive powertrain to determine a control strategy, settling on a combination of charge-depletion and charge-sustaining strategies. In charge-sustaining vehicles, the onboard battery is recharged by the combustion engine while the vehicle is being driven. During charge-depletion, electric energy from the battery powers the vehicle. The vehicle is recharged when the driver returns home that night.