Dynamic modeling, validation, and control for vapor compression systems

Pangborn, Herschel C.

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https://hdl.handle.net/2142/88074 Copy

Description

Title

Dynamic modeling, validation, and control for vapor compression systems

Author(s)

Pangborn, Herschel C.

Issue Date

2015-07-20

Director of Research (if dissertation) or Advisor (if thesis)

Alleyne, Andrew G.

Department of Study

Mechanical Science & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Vapor compression system
• Heat exchanger model
• Humidity model
• Model-based control
• Switched linear control

Abstract

This thesis traces the complete process of model-based control design for vapor compression systems (VCSs), from nonlinear model development to linearization and control formulation. Addressing gaps in the previous literature, the equations behind each model and control approach are clearly stated and emphasis is placed on conducting experimental validation at every stage. Both finite volume and switched moving boundary approaches for nonlinear control-oriented heat exchanger modeling are presented, illustrating the key differences in the method of discretization between these approaches. Practical considerations for the numerical implementation of these approaches in simulation are also provided. A detailed linearization of the switched moving boundary approach leads to the creation of a family of four-component linear models for different modes of operation of a VCS. The nonlinear and linear models are then validated with experimental data to reveal the tradeoffs of each. Furthermore, an augmentation to the switched moving boundary method is derived which captures the effects of air humidity. Experimental validation demonstrates that this augmented model more accurately predicts both air-side and refrigerant-side outputs at high humidity in addition to providing accurate predictions of liquid condensate formation and air outlet humidity. Finally, the value of the linear VCS models is demonstrated by their application in model-based control. A switched LQR approach is shown in both simulation and experimental application to be capable of driving the system between operational modes in order to regulate about a desired nominal operating condition. In particular, the experiments demonstrate improved robustness at low evaporator superheat of the switched LQR approach as compared to a decentralized PI approach.

Graduation Semester

2015-8

Type of Resource

text

Permalink

http://hdl.handle.net/2142/88074

Copyright and License Information

Copyright 2015 Herschel Pangborn

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