Bachelor's thesis Julian Matthes


Development of modular simulation models for Combined Heat and Power systems (CHP)

Internal circuit diagram Copyright: EBC Internal circuit diagram of the modular and scalable CHP model in Modelica

The renewable energy sector will be expanded in order to achieve the climate protection targets adopted by the EU and the german government. The resulting growing share of fluctuating feedin burdens the electricity grids and increases the need for flexible systems in order to guarantee energy supply and grid stability even in the event of weather-related fluctuations. Combined heat d power plants represent a key technology as a stabilising supplement to the energy system and, in contrast to central power plants, enable a more efficient use of primary energy. Computer-aided analysis is required for the development and integration of these plants into the increasingly complex ergy systems. For this purpose, dynamic and component-based simulation models can be used which map the thermal and electrical behaviour of combined heat and power plants. The development of such a model for a combined heat and power unit, consisting of a combustion engine, haust gas heat exchanger and electrical machine, is presented in the context of this thesis. In addition to the high level of detail, modularity, scalability and parameterizability of the developed model architecture are being focused. the most comprehensive submodel, the combustion engine is the centre of the modelling. The engine combustion and the resulting mechanical power are calculated using a mean value model. Furthermore, empirical approaches and estimations are used to map the exhaust enthalpy and the at flow to the cooling medium. The material composition of the exhaust gas is also determined by the assumption of overstoichiometric and complete combustion. The exhaust gas heat exchanger calculates a usable heat flow from the remaining thermal energy the exhaust gas. For this purpose, the exhaust gas mass flow and the material composition are taken into account when determining the convective heat transfer. As a function of the lowest temperature in the flue gas system, use of condensing technology is an option. r the model of the electric machine, which functions both as starter motor and generator, an analytical approach is implemented for the calculation of the torque and current characteristics as a function of the speed. In addition, a loss calculation to determine the released heat, when oling heat is used, is implemented. Finally, a model evaluation of the aggregated overall model is performed on the basis of experimental data. A manual calibration for static and dynamic operating processes is performed. The vestigation indicates a simulation time of the model suitable for long-term simulations. By adjusting the parameters, the errors can be reduced by up to 75% and dynamic operating processes can be reproduced with high agreement at a constant flow rate and return temperature.