Siti Marhainis Othman
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Preferred name
Siti Marhainis Othman
Official Name
Siti Marhainis, Othman
Alternative Name
Marhainis, Siti
Othman, S. M.
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Scopus Author ID
55210362500
Researcher ID
ABF-6513-2020

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Design and implementation of closed-loop PI control strategies in real-time for Linear ARMAX Models of Vapour Compression Refrigeration System using R600a Refrigerant

2022-01-01 , Rajaie M.N. , Mohd Saifizi Saidon , Siti Marhainis Othman , Wan Azani Wan Mustafa

The objective of the research undertaken in this paper is to design a control strategy using a Linear Auto-Regressive Moving-Average Exogenous (ARMAX), which is a mathematical modelling method in real time, which to be implemented into the closed-loop Proportional-Integral controller. The ARMAX model is developed using SIMULINK tool from the MATLAB R2020a software. The Vapour Compression Refrigeration System consists of an evaporator, an expansion valve, a condenser and a compressor which was modified to a variable speed compressor. This modification is required due to the usage of R600a refrigerant that has thermophysical properties that can be described as with a slight change in its pressure will cause a considerable change in its temperature [1]. R600a refrigerant was chosen for this paper, despite the difficulty is due to it is more environmental-friendlier refrigerant compared to other types of refrigerant [2]. Two types of ARMAX model were designed, the first type of ARMAX model will have a polynomial order of na= 2, nb= 2, nc= 1 while the second type of ARMAX model will have a polynomial order of na= 2, nb= 2, nc= 2. Both types of controller were tested and compared the performance in terms of settling time, steady-state error, overshoot and peak-time. From the test conducted, it was found that the controller with the ARMAX model will have a polynomial order of na= 2, nb= 2, nc= 1 has a better overall performance.

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Optimization of PD Controller based on ARMAX Model for Vapor Compression Refrigeration System using R600a Refrigerant

2022-01-01 , Rajaie M.N. , Mohd Saifizi Saidon , Siti Marhainis Othman , Wan Azani Wan Mustafa

The research undertaken in this paper is to investigates the difference in approaches to the modelling, design and implementation of an adaptive controller tuned using Auto-Regressive Moving-Average Exogenous (ARMAX) 2,1,1 model in an environment simulated in SIMULINK, applied to a variable speed compressor vapor compression refrigeration system running R600a refrigerant. A vapor compression refrigeration system is chosen for this paper research as it’s the most commonly used type of refrigeration system in all over the world, either for domestic, commercial or industrial application. The refrigeration system consists of a condenser, an expansion valve, an evaporator and a compressor which are modified from a fixed speed compressor to a variable speed compressor. The compressor was modified to be able to accommodate the usage of R600a refrigerant. R600a refrigerant has a thermophysical properties which can roughly be define as a slight change in pressure will result in a drastic change in temperature [1]. To be able to control the pressure for R600a with precision, an optimized adaptive controller is required. For the purpose of the simulation, the refrigeration system mathematical model is simplified to a linear polynomials ARMAX model. This is to reduce the complexity of the control design strategies, which in term improve the implementation of the new controller design. The optimization of the adaptive controller design, its simplicity of implementation, speed of convergence and robustness are concluded at the end part of the paper.

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Comparative study of controller performance for variable speed compressor using R600a refrigerant

2022-01-01 , Rajaie M.N. , Mohd Saifizi Saidon , Siti Marhainis Othman , Wan Azani Wan Mustafa

R600a is a refrigerant that is more environmental-friendlier compared to other types of refrigerant (Borokinni et al. in NAŠE MORE 65:11–17, 2018). However, it required the use of a Variable Speed Compressor (VSC) in order to be able to regulate its thermophysical properties, which vary the temperature drastically with the slight change in pressure (ASHRAE: 2009 ASHRAE Handbook—Fundamentals (SI). SI edn. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., United States (2009).). In order to efficiently control the speed of VSC, three types of controllers, namely, Adaptive Proportional Controller (P-ARMAX), Fuzzy-Logic (FL) controller and Sliding Mode Controller (SMC) are studied and compared the performance of each controller. The performance of each type of controller was evaluated based on the criteria of its settling time, steady state error, control effort and response temperature. From the studied conducted, it was found that the fuzzy logic controller has the most efficient control effort between the three with an acceptable settling time and steady state error.

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