System of Temperature Stabilization in a Heating Furnace Based on Sliding Mode Control and Fuzzy Logic

Abstract

The paper addresses issues of temperature control in heating furnaces using the example of a strand-type furnace for steel strip annealing of a continuous hot-dip galvanizing unit. The authors demonstrate that one of the main problems is variability of dynamic properties in the controlled object upon flexible production management with changes in the furnace capacity. Using a model of thermal state of the furnace cavity and metal, considering the impact of furnace temperature conditions on heat losses, variation limits of the parameters in a simplified model of object dynamics are determined. Issues of controlling a temperature object with variable dynamic parameters are reviewed. Advantages and disadvantages of systems used to control such objects, based on fuzzy logic and sliding mode control, are studied. It is shown that, in controlling a temperature object, a sliding mode control system can lead to fluctuating transient responses due to the absence of amplitude modulation in the control action when approaching the set-point. The authors suggest a system for automatic stabilization of the controlled parameter of a temperature object where sliding mode control and fuzzy logic are combined. In the stabilization system suggested, the direction of changes in the control action is determined using sliding mode control, while the control action level is determined using fuzzy logic. The paper provides results of simulation experiments comparing the efficiency of control using the system suggested and efficiency of control using the system based only on fuzzy logic. During those experiments, optimal system setting parameters were determined using complete enumeration and computer simulation of control for an object with the set variation of dynamic properties. Computer simulation was performed in the VisSim environment. The paper also shows that, with constant values of signal scaling parameters used in fuzzy logic, the requirement for qualitative transient responses with various set-point change levels results in the significantly reduced response speed in comparison with the system that combines fuzzy logic and sliding mode control. The authors demonstrate that it is possible to adjust quality of transient responses in the system that combines fuzzy logic and sliding mode control, changing dynamic properties of the object.