Integrated signal processing and nonlinear control for valve positioners systems in precision chemical manufacturing

In precision chemical manufacturing, valve positioner systems serve as critical hubs between distributed control systems and control valves, processing multi-source signals and driving control valves to precisely regulate flow, pressure, and temperature. However, noise-contaminated valve displacement signals, process-fluctuation interference, time-varying nonlinearities, parameter uncertainties, and dead zones degraded its performance. This paper proposes an integrated signal processing and nonlinear control scheme. First, a Fal-function filter suppresses high-frequency noise in valve displacement signals, while a composite observer, combining a state observer and a disturbance observer, accurately estimates unmeasurable states and rapidly compensates disturbances. Then, a nonlinear controller employs radial basis function neural networks to approximate unmodeled dynamics arising from time-varying nonlinearities and parameter uncertainties, thereby improving model accuracy. In parallel, dynamic surface control prevents the “explosion of complexity” caused by higher-order derivatives, yielding a smooth and bounded control law. Utilize a BLF-based constraint mechanism to handle valve position, valve-stem velocity, and input saturation within a unified framework. This reduces dead-zone induced start-up delay, prevents end-stroke impacts, and suppresses overshoot and oscillations caused by excessive stem speed and overly large control amplitudes. In addition, an auxiliary system based on an approximate coordinate transformation compensates the saturation nonlinearity, enhancing robustness under large control amplitudes. Finally, experiments confirm that the controller achieves efficient signal processing and precise control, ensuring semi-globally uniformly ultimately bounded closed-loop signals and strict compliance with state constraints. It attains a 0.94 % steady-state error, 3.7 s settling time, and 0.14 mm overshoot, significantly improving the accuracy and operational stability of precision chemical manufacturing.