Stability analysis of model-free control under constrained inputs for control of building HVAC systems

Recently introduced model-free control method has witnessed successful applications in various domains. While the framework of model-free control renders it simple and efficient, it imposes difficulties in implementing the method for complex applications under external constraints. Moreover, there is a lack of literature on the study and application of model-free control under constrained environments. This paper attempts to further the study of model-free control by employing it for monitoring indoor temperature of buildings through the control of heating, ventilation and air-conditioning (HVAC) systems, and studying the control design stability conditions under constrained inputs. Two kinds of constraints on the control input are considered and their stability conditions are investigated. The developed framework aims to highlight a potential path to analyze the stability under a given set of constraints. Accordingly, the developed framework is applied to a previously developed methodology that aimed to control the indoor temperatures of buildings with locally generated solar photovoltaic (PV) energy, by structuring the constraints therein. The results of employing model-free control on building HVAC systems under unconstrained and constrained inputs are presented. The role of the model estimation error on the stability is also discussed.