Signal Compensation Based Adaptive Cascade Control for Regrinding Processes

Abstract

The hematite regrinding process is a multivariable nonlinear industrial process with variant dynamic characteristic. When there are high-frequency disturbances on the pulp density and flowrate caused by the one-stage grinding and separation system, the dynamic characteristics of the hematite regrinding process becomes time variant. In this article, considering the fact that the regrinding system mostly works near its operating point, the dynamic characteristics of the regrinding system can be described as a combination of a deterministic linear model and an unknown high-order nonlinearity. Based on this description, a hydrocyclone feeding pressure (HFP) inner-loop proportional integral (PI) control system is proposed, and a dynamic model of the sump level (SL) outer-loop is established. The unknown change of the high-order nonlinearity is described by the previous sampled high-order nonlinearity and its change rate. A PI feedforward controller is then designed to compensate the previous sampled high-order nonlinearity based on a one-step optimal feedforward control law design approach. A one-step optimal regulate law based adaptive compensator is designed by using the tracking error and the exactly calculated value of the previous sampled high-order nonlinearity and its change rate. With the proposed PI feedforward controller and the adaptive compensator, a signal compensation based adaptive level outer-loop PI controller and an adaptive cascade control structure are proposed. Finally, the performance analysis and the industrial application demonstrate that, when the unknown high-frequency disturbances and the unknown change on the model parameters are in presence, the proposed algorithm can maintain the HFP, the hydrocyclone feeding density, and the SL in the desired ranges during the entire operation.