This dissertation defines and examines the techno-economic models of trigeneration systems based on the power units internal combustion engine or gas turbine of the electric power between 0,2 and 0,5 MW with absorption or compressor refrigeration units. Thermodynamic, ecological and economic features of trigeneration systems are analyzed with different load in relation to the basic model of producing energy with a boiler and a compressor refrigeration unit. Different models, actions of optimization are described together with the analysis of the sensitivity of trigeneration systems, based on which the advantages for using such systems as rational and ecologically acceptable ways of energy transformation in stationary and changeable conditions of power can be expressed. Based on the data gained from the manufacturer of equipment, curves of functional dependency of separate components are made depending on the extent of the load, and they enable the construction of the model of the system composed of a power units (internal combustion engine/gas turbine), a one-degree absorption refrigeration unit, a two-degree absorption refrigeration unit, a compressor refrigeration unit and a boiler i.e. peak boiler. The program solution is made by applying the object-oriented modelling and the programming language Modelica which enables the insight into the behavior and the techno-economic justification for the usage of the analyzed systems in stationary and changeable work conditions. It is shown that using the programming language Modelica for modelling complex physical systems, such as trigeneration systems, solutions are gained that can be applied in the process of modelling, simulation and optimization for scientific and expert analysis. This dissertation considers various energy models and defines the optimal value of the total degree of efficiency, time of equity payback and reducing the impact on the environment for the influential parameters (the price of electric energy, of fuel, costs of the investment and the degree of heat recovery). The results of optimization show that the system powered by a gas engine and a one-degree absorption refrigeration unit is optimal for the considered work conditions, and the range of the power as such is the most convenient for the systems of small and middle trigenerations. The strategy of conducting the process following the thermal load has shown to be a justified and acceptable solution in relation to the strategy of the maximum electricity load.