Research On Optimizing Control Of Energy Efficiency In A Distributed Refrigeration System

At the present time, the economy of china has maintained rapid growth and people had paid more and more attention to the energy problem. At the same time new energy was developed and utilized, the effective utilization rate of energy had gotten the important problem. While energy was expended in the refrigeration industry, the supermarket refrigeration chain was the most important part, as most of the terminal sales was achieved by supermarkets. The reduction in the power consumption was achieved; meanwhile, the quality of foodstuff must be guaranteed. Therefore the way to optimize the design of supermarket's refrigeration system had become an important task. This thesis researched on supermarket's refrigeration system energy savings by advanced control method.Firstly the components of refrigeration systems and the influence of the parameters were discussed. In the control system of refrigeration, it was researched that how the condensing pressure and the evaporating pressure etc influenced the optimal set-points. For each of the components, the compressor, the condenser, and the evaporator, a static model was derived. These models were all tied together by the flow of refrigerant between them. By applying this, a static model, a dynamic model as well as a control system model of the entire system was constructed by combining the individual component models.After the circulating characteristic of the refrigeration system was analyzed, the optimizing control scheme of supermarket refrigeration system's power consumption was designed. In supermarket refrigeration system, the loop's parameter, such as condensing pressure and evaporating pressure, directly effected the power consumption. Therefore the adaptation model prediction control strategy was designed in order to adjust the set-points of operation and optimize the parameter of control loop according to the variation of operation condition. The adaptation of a set-points optimization structured the out-loop control system. The in-loop control system was the dynamic optimization layer oriented subsystem of refrigeration system. In order to reduce the power consumption because of the fluctuation of suction pressure, the desynchronizing control of supermarket refrigeration was introduced utilizing MPC control strategy. By desynchronizing control the compressors efficiency was improved, the consumption energy was saved.In the dynamic optimization layer the control problem was significantly complicated by the fact that many of the control inputs was restricted to discrete values, such as the opening /closing of the valves and the stepwise control of the compressor. So the supermarket refrigeration system was a hybrid system. In order to achieve the better control performance the attempt was made to represent the hybrid system by the MLD (mixed logical dynamical) model. And the MPC control strategy of supermarket refrigeration system based on the MLD model was discussed.In order to give an idea of the potential energy savings using an energy optimal control scheme, the simulation platform of supermarket refrigeration system based on matlab was established. The energy consumption using the conventional constant set-point control was compared to the optimal set-point control. And the suction pressure MPC control scheme was furthermore compared with a traditional control scheme.Experimental simulation results illustrated that the optimal set-point control was able to drive the condensing set-point very close to the true optimum. It proved that the optimizing scheme was able to follow even quite abrupt changes in the ambient temperature. The simulation indicated that a substantial reduction in the power consumption could be achieved by introducing a set-point optimizing control scheme. Moreover the simulation of a supermarket refrigeration system illustrated the suction pressure MPC control scheme was able to minimine the variation in the suction pressure. This led to a lower wear in the compressor and a higher energy efficiency of the supermarket refrigeration system.