1. A powertrain system for a vehicle and selectively configured as a series hybrid powertrain, comprising: an engine; an electrical energy storage system including an electrical energy storage device selectively electrically coupled to a remote electric power source; a transmission comprising: a transmission input member operatively connected to the engine, a first electric machine operatively connected to a transmission output member and electrically-operatively coupled to the electrical energy storage system, a second electric machine operatively connected to the transmission input member and electrically-operatively coupled to the electrical energy storage system, a planetary gear set including first, second and third gear members, a transmission case, said first gear member connected to said second electric machine, said second gear member connected to said transmission output member, a first selectively engageable torque transfer device between said third gear member and said transmission case, a second selectively engageable torque transfer device between said third gear member and said first electric motor, and a third selectively engageable torque transfer device operable when engaged to connect said first electric motor and said transmission input member; and a control system signally connected to a plurality of inputs and operatively connected to a plurality of actuators, said control system operative to execute program code to control the actuators to operate the engine and the transmission, the program code comprising: a) determining operator demands, a powertrain operating state, and operating conditions based upon the inputs, b) selecting as an operating strategy a charge depletion strategy based upon the operator demands, the powertrain operating state, and the operating conditions, c) determining as a preferred powertrain operating state an electric vehicle operating state, d) controlling the powertrain to the preferred powertrain operating state based upon the selected operating strategy, the operator demands and the operating conditions, wherein controlling the powertrain to the preferred powertrain operating state comprises one of i) controlling said first selectively engageable torque transfer device engaged, said second and third selectively engageable torque transfer devices disengaged, and said second electric machine to provide torque, and ii) controlling said second selectively engageable torque transfer device engaged, said first and third selectively engageable torque transfer devices disengaged, and said first and second electric machines to provide torque, and e) compelling engine operation when an operating temperature of at least one of the first and second electric machines exceeds a predetermined temperature.