中央空调蒸发器建模及过热度控制

发布时间：2018-07-03 18:18

本文选题：蒸发器 + 过热度　；参考：《沈阳工业大学》2017年硕士论文

【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。
[Abstract]:In recent years, central air conditioning has become one of the necessary household appliances in people's work and life, providing people with comfortable environment to meet the requirements of people's quality of life, but at the same time, it also found that air conditioning consumes a lot of electric energy. Therefore, stability and energy-saving performance gradually become the focus of central air-conditioning design and research. The evaporator in the central air-conditioning refrigeration cycle system is the key component of the cooling capacity, which has an important impact on the energy saving and stability of the central air conditioning system for the research on the control of the outlet superheat degree of the central air-conditioning evaporator. In this paper, the modeling of central air conditioner evaporator and the control of refrigerant superheat at evaporator outlet are studied. Firstly, after analyzing the working principle of central air conditioning evaporator, the mechanism model of evaporator is established. The evaporator is divided into two regions according to the physical state of the refrigerant in the tube (two-phase region and superheated region). The one-dimensional simplified hydrodynamic conservation differential equation is applied to each region, and the Leibniz formula is used to integrate the evaporator. The equations are arranged into a fifth order nonlinear system model. Then the model is linearized at the stable working point and transformed into a standard five-order linear state space model. Considering that in the process of analyzing and linearizing the controlled object, the parameters of the model have some errors and the parameters of the model are uncertain, the mathematical model describing the evaporator is changed to the length of the evaporator two-phase zone. A five-order linear uncertain state space model with evaporation pressure, refrigerant enthalpy at the outlet of evaporator, wall temperature in two-phase region and tube wall temperature in superheated region is a five-order linear state space model. Secondly, a robust output tracking control strategy based on the improved linear quadratic optimal algorithm is designed. In view of the control strategy of superheat at the outlet of central air-conditioning evaporator, the actual superheat of evaporator outlet can be tracked to the set value of target superheat, and the output tracking error converges to zero gradually. The control strategy is based on the fifth order mathematical model of evaporator established in Chapter 3 to construct the augmented state equation. Then the optimal control rate is obtained by using the traditional linear quadratic optimal algorithm. Finally, the adjustment factor is introduced. The improved optimal control rate is obtained. Finally, the robust output tracking control strategy based on the improved linear quadratic optimal algorithm is verified for the control effect of refrigerant superheat control for the outlet refrigerant of central air-conditioning evaporator, and the simulation analysis is carried out in MATLAB environment. The simulation results show that the proposed robust output tracking control strategy is effective and fast, and can track the target superheat quickly.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB657.2

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