| At present, China’s economy is still in a period of rapid development, and the energy consumption, at the same time, remains rising, which have brought serious environmental problems coupled with the energy crisis. Facing the unfavorable situation, the national "Thirteen Five" plan made a further exposition that it is significant to develop clean energy and improve the primary energy ratio. Distributed combined cooling, heating and power (DCCHP) system is a kind of multi-generation total energy system based on energy cascaded utilization, with the characteristics of high energy efficiency, low energy costs, high environmental performance and high safety performance, which is coincident with the trend of the second-generation energy systems development. Combined with cooling, heating and generating units, the system can meet customer’s requirements at all aspects and becomes one of the most active systems. Supported by National Nature Science Fund, this paper studied the cooling system of DCCHP system with following majorities:Firstly, the classical DCCHP systems were analyzed in this paper, and the microturbine-steam DCCHP system was selected as the integral project, and LiBr-H2O steam-driven double-effect absorption chillers as its cooling sub-system.Secondly, lumped-parameter mathematical models of all parts were established based on the analysis of physical process of the chiller, and taking the chiller’s working conditions parameters and empirical formulas for thermophysical properties of LiBr solution and water into consideration, the dynamic simulation model of the chiller system was built using Simulink. Using this simulation system, startup and running performances were tested.Thirdly, based on the simulation model of the LiBr-H2O absorption chiller, changes of cooling capacity and COP were observed by altering parameters of heat source, cooling water and refrigerant water. Then the relationships between external conditions and refrigeration effect were found.Fourthly, energy regulation strategies of LiBr chillers were designed. Above all, in order to follow variation of users’ load, a scheme of multi-chillers paralleling was proposed, which aims at energy saving and assigns the real load to each refrigeration unit according to the cooling load and the requirements of chillers’ 50%～100% load ratio. The next, given the relationships between external conditions and refrigeration effect, heat source flow regulation was chosen as the energy regulation method of the refrigeration unit by comparing merits and drawbacks of all energy regulation methods. Finally, according to the nonlinear, large delay, time-varying characteristics of chiller system, fuzzy PID control algorithm and Smith predictor apply were combined and applied to the design of controllers. Then the relevant tests were completed by the aid of MATLAB/Simulink software. Simulation results show that the fuzzy PID controller based on improved Smith predictor in this thesis has a better dynamic characteristics and control quality for automatic controls of chillers.In summary, this paper analyzed the performance of LiBr-H2O steam-driven double-effect absorption chillers by simulating, and proposed the control strategies for the chillers, which has instructional significance to the promotion of DCCHP system and the application of LiBr chillers. |
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