Cogeneration system and method for controlling the same

A cogeneration system including a pre-heater (50) to pre-heat outdoor air blown toward the outdoor heat exchanger (45) during a heating operation of a heat pump type air conditioner (40), an auxiliary evaporator (60) to evaporate a refrigerant emerging from the outdoor heat exchanger during the heating operation of the heat pump type air conditioner, and waste heat recovering means (20,30) to transfer waste heat of the engine to at least one of the pre-heater and the auxiliary evaporator. The cogeneration system exhibits a high energy efficiency.