Multivariable Control of Vapor Compression Systems

He, Xiangdong; Liu, Sheng; Asada, H. Harry; Itoh, Hiroyuki

doi:10.1080/10789669.1998.10391401

Cited by 147 publications

(65 citation statements)

References 11 publications

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“…Equation (4) is consistent with the result in e.g. [11] for a fully open expansion valve and C v is also called the orifice coefficient. A valve with variable opening degree OD is added to (4).…”

Section: Pressure Estimator Design and Adaptionsupporting

confidence: 76%

Evaporator superheat control With one temperature sensor using qualitative system knowledge

Vinther

Lyhne

Sørensen

et al. 2012

2012 American Control Conference (ACC)

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Abstract-This paper proposes a novel method for superheat control using only a single temperature sensor at the outlet of the evaporator, while eliminating the need for a pressure sensor. An inner loop controls the outlet temperature and an outer control loop provides a reference set point, which is based on estimation of the evaporation pressure and suitable reference logic. The pressure is approximated as being linear and proportional to the opening degree of the expansion valve. This gain and the reference logic is based on calculation of the variance in the outlet temperature, which have shown to increase at low superheat. The parameters in the proposed controller structure can automatically be chosen based on two open loop tests. Results from tests on two different refrigeration systems indicate that the proposed controller can control the evaporator superheat to a low level giving close to optimal filling of the evaporator, with only one temperature sensor. No a priori model knowledge was used and it is anticipated that the method is applicable on a wide variety of refrigeration systems.

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Section: Pressure Estimator Design and Adaptionsupporting

confidence: 76%

Evaporator superheat control With one temperature sensor using qualitative system knowledge

Vinther

Lyhne

Sørensen

et al. 2012

2012 American Control Conference (ACC)

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show abstract

“…The numerical solution may describe the system quite well and results are shown in [12] and [13]. The moving boundary model is very general and may be fitted to most evaporator types.…”

Section: Model Overviewmentioning

confidence: 99%

Non-linear and adaptive control of a refrigeration system

Rasmussen

Larsen

2011

IET Control Theory &Amp; Applications

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In a refrigeration process heat is absorbed in an evaporator by evaporating a flow of liquid refrigerant at low pressure and temperature. Controlling the evaporator inlet valve and the compressor in such a way that a high degree of liquid filling in the evaporator is obtained at all compressor capacities ensures a high energy efficiency. The level of liquid filling is indirectly measured by the superheat. Introduction of variable speed compressors and electronic expansion valves enables the use of more sophisticated control algorithms, giving a higher degree of performance and just as important are capable of adapting to variety of systems. This paper proposes a novel method for superheat and capacity control of refrigeration systems; namely by controlling the superheat by the compressor speed and capacity by the refrigerant flow. A new low order nonlinear model of the evaporator is developed and used in a backstepping design of a nonlinear adaptive controller. The stability of the proposed method is validated theoretically by Lyapunov analysis and experimental results show the performance of the system for a wide range of operating points. The method is compared to a conventional method based on a thermostatic superheat controller.

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“…During steady-state operations, the length of the two-phase zone in evaporator and condenser is much larger than that of the single-phase zone [5] . Therefore, for the sake of simplicity,…”

Section: Modelmentioning

confidence: 99%

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

Zheng¹,

Li²,

Wang³

2017

Proceedings of the 2017 2nd Joint International Information Technology, Mechanical and Electronic Engineering Conference (JIMEC

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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...

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Multivariable Control of Vapor Compression Systems

Cited by 147 publications

References 11 publications

Evaporator superheat control With one temperature sensor using qualitative system knowledge

Evaporator superheat control With one temperature sensor using qualitative system knowledge

Non-linear and adaptive control of a refrigeration system

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

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