Pole-placement self-tuning control of nonlinear Hammerstein system and its application to pH process control

By taking advantage of the separation characteristics of nonlinear gain and dynamic sector inside a Hammerstein model, a novel pole placement self tuning control scheme for nonlinear Hammerstein system was put forward based on the linear system pole placement self tuning control algorithm. And the nonlinear Hammerstein system pole placement self tuning control (NL-PP-STC) algorithm was presented in detail. The identification ability of its parameter estimation algorithm of NL-PP-STC was analyzed, which was always identifiable in closed loop. Two particular problems including the selection of poles and the on-line estimation of model parameters, which may be met in applications of NL-PP-STC to real process control, were discussed. The control simulation of a strong nonlinear pH neutralization process was carried out and good control performance was achieved.

Graphical abstractA Hammerstein model composed of a static nonlinear sector followed in series by a linear dynamic element was selected to represent nonlinear processes with static nonlinearity commonly encountered in industry. The linear pole placement control algorithm was extended to nonlinear Hammerstein system through effectively remove the static nonlinearity of Hammerstein model from the control problem. When the nonlinear process was time varying at some degree, the parameters of its Hammerstein model were estimated on line using system identification method. Thus a nonlinear pole placement self tuning controller (NL-PP-STC) was put forward by combining the iterative least square estimation method with forgetting factor and the nonlinear Hammerstein system pole placement control algorithm.Figure optionsDownload full-size imageDownload as PowerPoint slideA pilot plant pH neutralization process with soda (NaCO3) and acid (HCl) was chosen to carry out control simulation test to demonstrate the effectiveness of NL-PP-STC algorithm which was implemented on an industrial PC. The control simulation results show that NL-PP-STC has good control performance.Figure optionsDownload full-size imageDownload as PowerPoint slide