Super-twisting algorithm-based sliding mode controller for a refrigeration system

This study presents a second-order sliding mode controller (2-SMC) for PI-controlled refrigeration system whose relative degree is one. 2-SMC is an effective tool for control of uncertain nonlinear system since it overcomes chattering phenomenon of the classical first-order sliding mode controller (1-SMC) and guarantees higher accuracy in presence of system imperfections. Super-twisting algorithm is used to design 2-SMC. This algorithm has been developed for the case of systems with relative degree one to avoid chattering phenomenon. By using this super-twisting algorithm-based 2-SMC, we control superheat ratio of refrigeration system. We compare 2-SMC with 1-SMC and backstepping controller which are designed for the same target system. The proposed controller eliminates chattering phenomenon, main drawback of 1-SMC, and reduces steady state error of 1-SMC. Compared with backstepping controller, presented controller is much more robust at external noise.