Switching Optimal Controller For Evaporation Temperature And Superheat Of Air-Conditioning Cooling System

Abstract

In this paper, a 2 input-2 output dynamic lumped parameter model of the refrigeration cycle is established for residential air-conditioning equipment. Based on the nonlinear characteristics of the refrigeration system and the idea of switching control, the system model is linearized at some selected stable operating points, and respectively a set of linear system models are obtained. By using the linear quadratic optimal control, the optimal state feedback controller is designed for each sub-model, and then the switching controller is designed. The simulation results show the effectiveness of the designed controller. IntroductionIn the air-conditioning control system, the control of both evaporation temperature and superheat degree is an important part. The rapid and stable control of the evaporating temperature and superheat degree is also the key to realize the high efficiency and energy saving operation.Theoretically, the vapor compression cycle can be described by the amount of evaporation temperature, condensation temperature, superheat degree at the outlet of the evaporator, and subcooling degree at the outlet of the condenser. Through the dynamic adjustment of these state variables can not only achieve the purpose of energy conservation, but also extend the service life of equipment [1] . Among them, in the air-conditioning and refrigeration control system, the compressor speed control and evaporator superheat degree control are the most basic and most important link. In the control of variable speed compressor and electronic expansion valve, the traditional single-input single-output control system can not describe this control system well because the refrigeration system has many control components and strong coupling between parameters. Therefore, in order to achieve better control effect, multi-input multi-output control system must be referenced [2] .In this paper, firstly, the mechanism model of air conditioning refrigeration system is deduced according to the law of conservation of mass, energy and momentum in physics. Then, the non-linear model obtained after modeling the mechanism is linearized at multiple stable operating points, and a set of linearized models are obtained. Finally, the corresponding optimal state feedback controller is designed for each sub-model, and then the switching rules are designed to realize the switching control [3] . ModelThe schematic diagram of the vapor compression cycle system for residential air-conditioning with six state variables is shown in Figure 1. Based on the laws of conservation of mass, energy and momentum, under the assumption conditions: 1) The heat exchanger is a long, thin, horizontal tube.2) The refrigerant flowing through the heat exchanger tube is in one dimension.3) The axial heat transfer of the heat exchanger is neglected. The one-dimensional partial differential equations of the refrigerant flowing through the heat exchanger is as follows [1][4] .Where  :density, u : velocity,  : friction coefficient, P : pressure, i D : inner di...