Decoupling controller for use with a process having two input variables and two output variables
AssigneeImpact Systems, Inc.
InventorCharles H. Wells
Life of this patent
Estimating the term…
Abstract
A decoupling controller for use with a process such as paper-making having two input variables such as stock flow and steam pressure and two output variables such as moisture and basis weight. Decoupling is accomplished by the use of linked internal model controllers where for each individual unit of the linked pairs, a P.I.D. (proportional, integral, derivative) unit includes all of the feedback loop gains and then the process itself is modeled by a first order transfer function and deadtime units with two cross-linked error signals fed back. A specific technique of cross-linking the internal model controllers eliminates cross-coupling between the input and output variables.
Claims9
A decoupling controller for use with a paper making machine process having two input variables (U1 and U2) which are dry stock flow and steam pressure and two output variables (X1 and X2) which are basis weight and moisture where in the process each input variable affects both output variables, such process having desired setpoints (S1, S2) for said output variables such decoupling controller comprising:
- linked internal model controller means including two pairs of proportional, integral, derivative P.I.D. velocity units (C11, C21;
- and C12, C22) each pair respectively receiving from a first pair of difference junctions total process error, (et1, et2) in a feedback loop for the process and producing said inputs (U1, U2), which are control inputs to the process itself, such P.I.D. units taking into account loop, proportional, integral, and derivative gains of the feedback loop for both direct and cross-coupling;
- four first order transfer function units (K11, K12, K21, and K22) for receiving as inputs U1, U2, said K11, K22 units providing predicted values of X1, X2, said K21, K12 units providing predicted outputs of X1, X2 due to cross-coupling;
- means for feeding back to a pair of second summing junctions the outputs of K11, K12 and K22, K21 respectively;
- means for coupling the outputs of said second summing junctions, which are total predicted values of X1 and X2 taking into account cross-coupling, to a pair of third summing junctions;
- means for feeding the summed output of said third pair of summing junctions to said first pair of difference junctions, which have as the other difference input the setpoints S1, S2 to provide said total process error inputs et1 and et2 to C11, C21 and C12, C22, respectively;
- means for taking the deadtime of said process into account which is the lag time between the change of input variables and output variables, including four deadtime units, (D11, D21, and D12, D22), having their inputs respectively connected to the outputs of K11, K21, K12, and K22, including a pair of fourth summing junctions having as outputs current estimated values (Y1, Y2) of the X1, X2 output variables where one of the pair of fourth summing junctions, sums the outputs of D11, D12 and the other of the pair of summing junctions, sums the outputs of D22, D21;
- means for coupling the outputs of said fourth pair of summing junctions, to a fifth pair of difference junctions to take the difference between the actual outputs X1, X2 and the estimated values Y1, Y2, such differences being modeling error output signals;
- means for feeding back said modeling error output signals to said third pair of summing junctions;
- and where said K11 the process gain for stock, is increased for an increase in the paper machine speed and said feed back loop gain of the correspondin a P.I.D. unit, C11, is decreased.
Dependencies are inferred from the claim text.