An optimal multivariable controller for transcritical CO2 refrigeration cycle with an adjustable ejector

Abstract The fixed ejector has to work under a restricted operating condition to keep its positive effectiveness on the transcritical CO 2 refrigeration cycle, and a controllable ejector will be helpful. In this paper, an optimal multivariable controller based on the dynamic model is proposed to improve transcritical CO 2 refrigeration cycle with an adjustable ejector (TCRAE). A nonlinear dynamic model is first developed to model the dynamic characteristic of TCRAE. The corresponding model linearization is carried out and the simulation results reproduce transient behavior of the nonlinear model very well. Based on the developed model, an optimal multivariable controller with a tracker based linear quadratic state feedback algorithm and a predictor using steepest descent method is designed. The controller is finally applied on the experimental apparatus and the performance is verified. Using the tracker only, the gas cooler pressure and chilled water outlet temperature (cooling capacity) are well tracked rejecting the disturbances from each other. Furthermore, by the predictor, the optimal gas cooler pressure for a constant cooling capacity is actually approached on the experimental apparatus with a settling time about 700 s.

[1]  Fabio Inzoli,et al.  Ejector refrigeration: A comprehensive review , 2016 .

[2]  H. Kursad Ersoy,et al.  Experimental investigation on motive nozzle throat diameter for an ejector expansion refrigeration system , 2016 .

[3]  Marco Corradi,et al.  A real-time algorithm for the determination of R744 systems optimal high pressure. , 2012 .

[4]  Juergen Koehler,et al.  Experimental investigation of the COP improvement of a refrigeration cycle by use of an ejector , 2012 .

[5]  Masafumi Nakagawa,et al.  Experimental investigation on the effect of mixing length on the performance of two-phase ejector for CO2 refrigeration cycle with and without heat exchanger , 2011 .

[6]  Hua Li,et al.  Feedforward control of capacity and superheat for a variable speed refrigeration system , 2009 .

[7]  Shengming Liao,et al.  A correlation of optimal heat rejection pressures in transcritical carbon dioxide cycles , 2000 .

[8]  Shiming Deng,et al.  Multivariable control-oriented modeling of a direct expansion (DX) air conditioning (A/C) system , 2008 .

[9]  Pei-Xue Jiang,et al.  Particular characteristics of transcritical CO2 refrigeration cycle with an ejector , 2007 .

[10]  P. Naidoo,et al.  A review of the control of schistosomiasis in South Africa , 2015 .

[11]  Min-Soo Kim,et al.  A study on the real time optimal control method for heat rejection pressure of a CO2 refrigeration system with an internal heat exchanger , 2014 .

[12]  Zhongjie Huan,et al.  A review of carbon dioxide as a refrigerant in refrigeration technology , 2015 .

[13]  Jianqiang Deng,et al.  Performance optimization of a transcritical CO2 refrigeration system using a controlled ejector , 2017 .

[14]  Christian J.L. Hermes,et al.  A model-driven multivariable controller for vapor compression refrigeration systems , 2009 .

[15]  Jianqiang Deng,et al.  Thermodynamic study on a new transcritical CO2 ejector expansion refrigeration system with two-stage evaporation and vapor feedback , 2014 .

[16]  Sergio Colle,et al.  A general model for evaluation of vapor ejectors performance for application in refrigeration , 2012 .

[17]  Ma Yitai,et al.  Thermodynamic analysis of transcritical CO2 refrigeration cycle with an ejector , 2011 .

[18]  Pei-Xue Jiang,et al.  Dynamic model of a transcritical CO2 ejector expansion refrigeration system. , 2015 .

[19]  Min-Soo Kim,et al.  Experimental study on the improvement of CO2 air conditioning system performance using an ejector , 2011 .

[20]  Zaoxiao Zhang,et al.  Dynamic simulation of an improved transcritical CO2 ejector expansion refrigeration cycle , 2016 .

[21]  Predrag Stojan Hrnjak,et al.  Experimental validation of a prototype ejector designed to reduce throttling losses encountered in transcritical R744 system operation , 2008 .

[22]  Clark W. Bullard,et al.  Development of a microchannel evaporator model for a CO2 air-conditioning system , 2001 .

[23]  Hua Tian,et al.  A review of transcritical carbon dioxide heat pump and refrigeration cycles , 2013 .

[24]  Savvas A. Tassou,et al.  Performance evaluation and optimal design of supermarket refrigeration systems with supermarket model "SuperSim", Part II: Model applications , 2011 .

[25]  Neal Lawrence,et al.  Review of recent developments in advanced ejector technology , 2016 .

[26]  Junjie Gu,et al.  The optimum high pressure for CO2 transcritical refrigeration systems with internal heat exchangers , 2005 .

[27]  Yong Chan Kim,et al.  Heat transfer and pressure drop characteristics during the in-tube cooling process of carbon dioxide in the supercritical region , 2003 .

[28]  M. Grimble,et al.  Recent trends in linear optimal quadratic multivariable control system design , 1987 .

[29]  Andrew G. Alleyne,et al.  Control-Oriented Modeling of Transcritical Vapor Compression Systems , 2004 .

[30]  F. Liu,et al.  Performance enhancement of CO2 air conditioner with a controllable ejector , 2012 .

[31]  V. Gnielinski.  New equations for heat and mass transfer in turbulent pipe and channel flow , 1976 .

[32]  Jianlin Yu,et al.  Thermodynamic analysis on a two-stage transcritical CO2 heat pump cycle with double ejectors , 2014 .