A variable speed hybrid electric supercharger assembly is controlled to regulate an adaptive state of charge of an energy storage device and/or to boost an engine based on a performance mode selected by a driver. In one example, a reference state of charge is determined based upon driving characteristics of a vehicle and compared to an actual state of charge of the energy storage device. If the difference indicates a deficit, an operation mode is selected to regenerate the energy storage device. In another example, a planetary gearing arrangement between an engine and an electric motor is configured to increase or decrease power transferred to the supercharger by the engine based upon the performance mode selected by the driver.