Dynamic Optimization of Energy Supply Systems with Modelica Models

The paper describes a design tool for decentralised energy supply by preferable use of renewable energy. The powerful modelling language Modelica has been used to develop a model library for input data generation and/or predicting and modelling the main parts of the energy supply system for the simulation tool Dymola. An optimal control design using the well suited Dymola model in connection with Matlab [21] is performed with the solver HQP [15]. Application to a solar heating supply system with two storages demonstrates the effect of minimizing the use of additional heating and the realization by a model predictive control strategy. Introduction To build a moor it needs about 50 000 years, the youngest brown coal dates from 65 million years ago, about 1850 the first coal (also oil and a bit later gas) was excavated and newest estimations predict that coal, oil and gas from soil may be spent in about 2250, completely. That means human activity has consumed all the natural resources developed in millions of years within a delta impulse on time scale i.e. within about 400 years! Realizing these facts it is high time that renewable energy sources become more and more important, mainly due to the shortage of fossil fuels, which is well known. Fortunately, we still can dispose over mixed energy supply, with great challenges arising for planning and control of heat supply systems, if these systems also work with different renewable energy sources (earth heat, solar radiation, exhaust air heat from building), which lead to control problems with a higher rank of complexity. The main goal of these control strategies (taking into account the weather of the past and predictions of energy requirement in the future) is the reduction of operational cost as well as an increase in the rate of return for the investment. The paper describes the simulation of a heat supply system by means of object-oriented modelling with Dymola/Modelica. The final aim of such a simulation is to develop a model predictive control strategy on the basis of the proposed object-oriented model in Dymola/Modelica. To develop such a control strategy it is necessary to gain knowledge about the heat demand of buildings and the power usage of its different components. The use of Computer Aided Engineering (CAE) can lead to a further reduction of development costs. A Dymola library named RECOMB has been created with the purpose of modelling and simulation of such heat supply systems. The name RECOMB [16] stands for Renewable Energy Components mOdelling and optiMisation of Buildings. The library itself consists of multi sub-libraries and following sub-libraries of crucial importance: • Weather • Predict • HESys • Buildings The components and the resulting models for the thermodynamic models of the sub-library HESys were validated by comparing them with existing simulation software [11], [12], while the building models were validated with help of German guidelines [9] as well as with other simulation software [8],[10]. Fig. 1 show the structures of the library RECOMB. 599 Dynamic Optimization of Energy Supply Systems with Modelica Models