1 Abstract-- The paper discusses aspects of dynamic modelling and simulation of fuel cell and micro-turbine units as a part of a multi-machine electrical network. The focus is on the consideration of a large number of units connected to different low voltage nodes. In the study, the total power generated in decentralized units reaches up to 30% of the 110-kV-network demands. Therefore, it is expected that decentralized sources impact the dynamic behaviour of the high voltage network and vice versa. Hence, the investigated power system comprises also the high voltage grid and the corresponding conventional power plants supplying into this network. To evaluate the performance of the network, various disturbances are applied and the results are discussed. Index Terms- Dynamic modelling, Fuel cells, Gas turbines, Power system analysis, Stability problem I. INTRODUCTION HE use of the Distributed Energy Resources –DER- represents an important support to the main centralized electrical power plants. The extension of this type of power generation with a large variety of types and capacities became a real fact [1]. It is expected in the near future to utilize more energy from small distributed units [2]. With the increasing rate of DER in the electricity production and their integration into the existing network several problems arise. One of the issues concerns the dynamic interaction of DER with the overlaying network. Until now, such interactions were neglected or solved in such a way that DER, in emergency situations, were disconnected from the network. However, disconnections may lead to more aggravation and thus it is not acceptable in general. Furthermore, controllers located on the network side and DER controller may interact with each other and thus cause unacceptable dynamic behaviour. The problems will assume a new dimension in the near future, when the contributions of DER further increases according to the political and social expectations and technological progress. Micro-turbine and the fuel cell units are two types of DER, whose performance within a network still needs more investigation. The micro-turbines are known for a long time now as reliable main or back-up sources in a wide field of applications [3]-[6]. Fuel cells are also promising units, which Ahmed M. Azmy is with the Institute of Electrical Power Systems, University of Duisburg-Essen, Germany (e-mail: azmy@uni-duisburg.de) István Erlich, is the head of the Institute of Electrical Power Systems, University of Duisburg-Essen, Germany (e-mail: erlich@uni-duisburg.de) have many advantages. High efficiency, low emission and the possibility of cogeneration are some of them [7]. The dynamic modelling and simulation of the micro- turbine as well as the construction and operation of the fuel cell have been discussed in detail in many literatures [1]-[12]. This mostly included the stand-alone mode or the case where a limited number of units is connected to a small network. The dynamic operation of several units within a multi-machine network, however, is a different task, which remains to be studied. This paper presents a dynamic-simulation study for the case where many fuel cells and micro-turbines operate within a multi-machine network. The selected DER units are candidate to be used in large scale in the power system especially when the technical solutions for hybrid units consisting of fuel cell and micro-turbine are well developed [12]. Because of the expected interaction with the conventional power plants the high voltage network is modelled in detail. Furthermore, the connection of DER requires modelling of the network down to the low voltage level. Therefore, one 110-kV-network and the underlying voltage levels are modelled too with representative equivalents. The DER units are assumed to cover up to 30% of the total demand at the end-user terminals. This situation differs from the case where a limited number is used, which will have a small effect on the network. The dynamic models for both fuel cells and micro-turbine units, which are accomplished using the simulation tool “Power System Dynamics (PSD)” [13], are introduced in this paper. The topology of the multi-machine network is also described and the simulation process is presented. Finally, the performance of the plants will be evaluated on the basis of some simulation results. II. MODELLING THE PROPOSED SYSTEM The test system consists of several fuel cells and micro- turbines with various capacities as a part of a multi-machine network. The ratings of these units vary from 150-400 kW for the micro-turbines and from 250 to 500 kW for the fuel cells. Typical configurations and parameters are used to model and simulate the network, which is called “PST16” network denoting the 16 generating units. [14] A. Network description Fig. 1 illustrates the layout of the PST16 network. Dynamic Simulation of Fuel Cells and Micro-turbines Integrated with a Multi-Machine Network Ahmed M. Azmy, and István Erlich, Member, IEEE T Paper accepted for presentation at 2003 IEEE Bologna Power Tech Conference, June 23th-26th, Bologna, Italy