【作者】 李娜；

【导师】 王向东；

【作者基本信息】 沈阳工业大学 ， 控制理论与控制工程， 2017， 硕士

【摘要】 近年来,中央空调成为人们工作生活中的必备家用电器之一,为人们提供舒适的环境以满足人们对生活品质的要求,但同时也发现空调对于电能的大量消耗的问题。因此稳定性与节能性能的好坏逐渐成为中央空调的设计研发者们研究的重点。而中央空调制冷循环系统中的蒸发器是制取冷量的关键部件,对于中央空调蒸发器出口过热度的控制研究于空调系统的节能与稳定性有重要的影响。本文主要以中央空调蒸发器的建模与蒸发器出口制冷剂过热度的控制问题进行研究。首先,在分析中央空调蒸发器的工作原理后以蒸发器为研究对象,对蒸发器建立机理模型。将蒸发器按照制冷剂在管内的物理状态分为两个区域(两相区与过热区),对每个区域先应用一维简化的流体力学守恒微分方程,用莱布尼兹公式进行积分,将方程联立整理为五阶的非线性系统模型。然后对模型在稳定工作点进行线性化处理,并转化为标准的五阶线性状态空间模型。考虑到在对被控对象进行分析、以及线性化处理的过程中,使模型的参数产生一定的误差,模型参数具有不确定性,则描述蒸发器的数学模型变为以蒸发器两相区长度、蒸发压力、蒸发器出口制冷剂焓值、两相区管壁温度与过热区管壁温度为状态变量的五阶线性不确定状态空间模型。其次,设计了基于改进的线性二次最优算法的鲁棒输出跟踪控制策略。针对中央空调蒸发器出口过热度控制的控制策略应满足蒸发器出口的实际过热度能跟踪到目标过热度的设定值,并且输出跟踪误差逐渐收敛为零。此控制策略首先基于第三章建立的蒸发器五阶数学模型构建增广状态方程,然后应用传统的线性二次最优算法,求出最优控制率,最后在此基础上引入调整因子,得到改进后的最优控制率。最后,验证基于改进的线性二次最优算法的鲁棒输出跟踪控制策略针对中央空调蒸发器出口制冷剂过热度控制的控制效果,并在MATLAB环境下进行仿真分析。仿真结果表明,所设计的鲁棒输出跟踪控制策略的有效性,且反应速度快,能快速跟踪目标过热度的设定值。更多还原

【Abstract】 In recent years,the central air-conditioning becomes one of essential household appliances in people’s life.It provides a comfortable environment to meet the requirement of the quality of life for people,but also it is found that air conditioning will consume a lot of power.Therefore,whether its stability and energy efficiency are good or not is becoming the main point of the developers of central air conditioning gradually.The evaporator in refrigeration cycle system is a key part to get cooling capacity,and the research on controlling the superheat at the evaporator outlet of the central air conditioning system has an important influence on the energy saving and stability of the air conditioning system.This thesis mainly carries out researches on the problems of modelling of evaporator and the controlling of refrigerant superheat at evaporator outlet of the central air conditioning.Firstly,based on the analysis of the working principle of evaporator of the central air-conditioning and taking the evaporator as the research object,the mechanism model of evaporator is established.The evaporator is divided into two zones according to the physical state of the refrigerant in the tube(two-phase region and overheated region),a simplified one-dimensional fluid conservation differential equation is first applied for each region,and using Leibniz formula for integration,the equations are sorted into a fifth-order nonlinear system model.Then,the model is linearized at the stable operating point and transformed into a standard fifth-order linear state space model.Because the process of modelling and linearization will make parameters of model produce certain errors and uncertainty,then the mathematical model describing the evaporator has been changed into the five order linear uncertain state space model,in which the state variables are chosen as the length of two-phase zone of evaporator,evaporation pressure,enthalpy of refrigerant at the outlet of the evaporator,the tube wall temperature of the two-phase region and the tube wall temperature of the overheated zone.Secondly,a robust output tracking control strategy based on improving linear quadratic optimal algorithm is designed.It is proved that the control strategy satisfy that the practical superheat at the outlet of the central air-conditioning evaporator can trace the target set value and make output tracking error converge to zero gradually.The design process of controlstrategy is presented as follow.Firstly,an augmented state equation based on fifth-order mathematical model of evaporator in the third chapter is constructed.And secondly,the traditional linear quadratic optimal algorithm is adopted to obtain the optimal control rate,and at last an adjustment factors is chosen to obtain the improved optimal control rate.At last,the control effect is tested and verified based on the improved linear quadratic optimal algorithm of robust output tracking control strategy against superheat at the outlet of the central air-conditioning evaporator and the control system is simulated under the MATLAB.The result of simulation shows the feasibility of robust output tracking control strategy.It also shows that the closed-system responds fast and can track the set value of the superheat quickly.更多还原