More and more car manufactures are combining a normal combustion engine and an electric motor to satisfy the standards for CO2 emissions. In order to take advantage of this technology in the most efficient way, for example in companies car fleets, realistic simulation models are required. In this paper, we present an accurate yet computationally inexpensive energy demand model for the microscopic simulation of plug-in hybrid vehicles. Our model mostly consists of a combustion engine, an electric motor and, most importantly, a realistic engine management model. Furthermore, a pragmatic kinematic model as well as a model for recuperation of energy while breaking are provided. Modularly designed, our simulation model allows for simple replacement and adjustment of each module. As input values, our model only requires the vehicle's speed and a set of constant predefined parameters. Consequently, this also enables the model to be easily connected with current sophisticated traffic simulators. We show the correctness of our model regarding the consumption of fuel and electric energy using comprehensive real-world experiments.