This work presents a detailed and generic dynamic modelling and simulation method of scroll expander for small scale power generation system. The geometric models of the scroll were built step by step, including the scroll involute, scroll dimensions, chamber areas and volumes, the scroll profile modifications and so on. The valve model, internal leakage model, motion equation, heat transfer equation and energy balance equation were combined with the geometric models to complete the scroll expander modelling. A mathematic model of a direct current generator or an experimentally determined correlation of generated power against rotational speed of the used generator was integrated to the expander model as the power output unit. To enhance the adaptability of the current model, an overall dynamic friction coefficient of the scroll expander and the generator was innovatively proposed and introduced as one of the key parameters in the present study. The accurate value of this coefficient should be experimentally determined for a specific expander - generator system; with the knowledge of such a parameter, the mechanical friction loss can be accurately and easily calculated in the simulation study. The present modelling and simulation method have been validated by several sets of experimental results based on different scroll expanders studied by different researchers, and the corresponding overall dynamic friction coefficient was found in the order of magnitude of 10(-3) N m s. (C) 2016 The Authors. Published by Elsevier Ltd.