A supercharger assembly includes a supercharger in series with an engine that has a crankshaft and has an air intake manifold defining a plenum through which air flow is provided to the engine. A supercharger is upstream of the plenum in air flow to the engine and has a first rotor rotatable with a first shaft and a second rotor rotatable with a second shaft. The supercharger assembly also includes an electric motor-generator that is selectively alternately operable as a motor and as a generator, and a planetary gearing arrangement having a first member operatively connected to the electric motor-generator, a second member connectable to be rotated by the engine crankshaft, and a third member operatively connected for rotation with the first shaft. The supercharger assembly has only two selectively engageable torque-transmitting mechanisms and a control system configured to control the electric motor-generator and the torque-transmitting mechanisms.