Cascaded control of an average value of a process parameter to a desired value

摘要

A multi-tier controller directs operation of a system performing a process. The process has multiple process parameters (MPPs), at least one of the MPPs being a controllable process parameter (CTPP) and one of the MPPs being a targeted process parameter (TPP). The process also has a defined target limit (DTV) representing a first limit on an actual average value (MV) of the TPP over a defined time period of length TPL_AAV2. The AAV is computed based on actual values (AVs) of the TPP over the defined period. A first logical controller predicts future average values (FAVs) of the TPP over a first future time period (FFTP) having a length of at least TPL_AAV2 and extending from a current time T₀ to an future time T_AAV2, prior to which the TPP will move to steady state. The FAVs are predicted based on (i) the AAVs of the TPP at various times over a first prior time period (FPTP) having a length of at least TPL_AAV2 and extending from a prior time of T_-AAV2 to the current time T₀, (ii) the current values of the MPPs, and (iii) the DTV. A second logical controller establishes a further target limit (FTV) representing a second limit on the MV of the TPP for a second future time period (SFTP) having a length equal to TPL_AAV2, which is less than the length TPL_AAV2, and extending from the current time T₀ to a future time T_AAV1. The FTV is established based on one or more of the predicted FAVs of the TPP over the FFTP. The second logical controller also determines a target set point for each CTPP based on (i) the AAVs of the TPP at various times over a second prior time period (SPTP) having the length TPL_AAV1 and extending from a prior time T_-AAV1 to the current time T₀, (ii) the current values of the MPPs, and (iii) the FTV. The second logical controller additionally has logic to direct control of each CTPP in accordance with the determined target set point for that CTPP.