Frequency analysis and experimental validation for stiction phenomenon in multi-loop processes

The existence of static friction, also known as stiction nonlinearity, in a control valve may lead the entire system to limit cycles. Despite numerous studies on modeling, detection and compensation of this phenomenon, lack of a reliable methodology to predict occurrence and properties of such oscillations, particularly in multi-loop settings, is quite sensible. This work focuses on frequency analysis of multi-loop processes oscillating due to stiction. Before using any of the existing stiction models for the analysis, a comparison between existing stiction models and actual lab data is carried out. Derivation of a mathematical representation of the condition, under which stiction-induced oscillations occur in a multi-loop system, is the main achievement of the proposed analysis. This condition enables users to predict and compare the severity of the oscillations, i.e. values of frequencies and magnitudes, in different situations. Results of the theoretical discussion are validated by both simulation and experimental studies.