Title: Performance Comparison of State Variable Based Controllers for Single-Stage Refrigeration System
Authors: Chukwudi Christian Chigozie Osinachi Bright Abika Martin Ngwaldi Dillum Okhueleigbe Vincent Onos Chisom Victory Onyenagubo Iwu Phinehas Ikechukwu Jeremiah Henry Chijioke
Volume: 9
Issue: 1
Pages: 34-45
Publication Date: 2025/01/28
Abstract:
Refrigeration systems need control mechanisms to maintain efficient operation so that the cycle can go ON and OFF to keep a fixed (setpoint) temperature.In this paper, the performance of different state variable based controllers for control of temperature in a vapour-compression single-stage refrigeration system has been examined. The mathematical expressions representing the thermal dynamic characteristics of a vapour-compression system were determined and represented as multivariable state space model. Simulink state space model was developed to represent the system. Different state variable based controllers such as full state feedback controller, Linear Quadratic Regulator (LQR), and hybrid PID-LQR were implemented. Each of the controllers was separately incorporated into the closed loop control system for temperature in a sing-stage refrigeration system. The control system was subjected to unit step forcing function in MATLAB/Simulink simulation environment considering different scenarios so as to evaluate and obtain the time domain parameters that characterized the transient and steady state response performances. The simulation results obtained showed that the addition of the various controllers provided improved temperature response performance such that the desired temperatures for evaporator, compressor, condenser, and expansion valve were achieved when unit step temperature input was applied. The time domain performance characteristics obtained with full state feedback controller, LQR, and PID-LQR controller with respect to evaporator, compressor, condenser, and expansion valve temperatures in terms of rise time,settling time, overshoot, and steady-state error revealed that the full state feedback controller offered the most efficient and smooth response with zero overshoot for all the temperatures in various unit.