Adaptive Super Twisting Sliding Mode Control of a HVAC System

In this paper an adaptive super twisting sliding mode cascaded control strategy to control superheat temperature of an evaporator of Heating Ventilation Air Conditioning Systems(HVAC) is presented. Two internal loop and external loop of the cascaded controller are designed using sliding mode by utilizing feedback linearization method. By controlling superheat temperature, T-sh, in the external loop, and evaporating temperature of refrigerant, T-e, in the internal loop, a better performance with robustness against parameter uncertainty is achieved. The value of superheat temperature is determined by using the estimated value of length of two phase flow of the refrigerant inside the evaporator. The performance of the proposed control strategy against disturbance and parameter uncertainties is illustrated through simulation in MATLAB/Simulink environment. It is shown that in comparison with super-twisting method, the proposed adaptive super twisting method improves the performance of system by reduction of undesirable chattering in the response of system.