Description of pid_structure

AutotunerPID Toolkit

pid_structure

PURPOSE

Structure selection for a ISA-PID regulator.

SYNOPSIS

function regStruct = pid_structure(model,reqStruct)

DESCRIPTION

PID_STRUCTURE Structure selection for a ISA PID regulator.

   REGSTRUCT = PID_STRUCTURE(MODEL,REQSTRUCT) returns the ``best''
   structure for the regulator, assuming that the controlled plant can be
   described with a FOPDT model.
   MODEL is a structure with the description of the process model with the
   fields {m L T} (parameters of a FOPDT model M(s) = m*exp(-sL)/(1+s*T)).
   The structure may be computed through the function setting the flag
   REQSTRUCT to 'AUTO', or may be constrained to a particular one by
   setting the flag REQSTRUCT to 'PI' or 'PID' respectively.

   The structure selection is performed only if a FOPDT model of the
   process is given, otherwise the PID structure is selected.  If the
   control problem is intrinsically difficult the PID structure is
   selected, and a warning message is prompted.

   Author:    William Spinelli ([e-mail])
   Copyright  2004 W.Spinelli
   $Revision: 1.0 $  $Date: 2004/02/27 12:00:00 $

CROSS-REFERENCE INFORMATION

This function calls:

This function is called by:

• pid_autotuner PID_SUPERV Supervisor of a PID autotuner (implmented as an S-function)

SOURCE CODE

0001 function regStruct = pid_structure(model,reqStruct)
0002 %PID_STRUCTURE Structure selection for a ISA-PID regulator.
0003 %
0004 %   REGSTRUCT = PID_STRUCTURE(MODEL,REQSTRUCT) returns the ``best''
0005 %   structure for the regulator, assuming that the controlled plant can be
0006 %   described with a FOPDT model.
0007 %   MODEL is a structure with the description of the process model with the
0008 %   fields {m L T} (parameters of a FOPDT model M(s) = m*exp(-sL)/(1+s*T)).
0009 %   The structure may be computed through the function setting the flag
0010 %   REQSTRUCT to 'AUTO', or may be constrained to a particular one by
0011 %   setting the flag REQSTRUCT to 'PI' or 'PID' respectively.
0012 %
0013 %   The structure selection is performed only if a FOPDT model of the
0014 %   process is given, otherwise the PID structure is selected.  If the
0015 %   control problem is intrinsically difficult the PID structure is
0016 %   selected, and a warning message is prompted.
0017 %
0018 %   Author:    William Spinelli ([e-mail])
0019 %   Copyright  2004 W.Spinelli
0020 %   $Revision: 1.0 $  $Date: 2004/02/27 12:00:00 $
0021 
0022 if nargin < 2
0023    reqStruct = 'AUTO';
0024 end
0025 
0026 switch reqStruct
0027    case 'PI'
0028       % override selection
0029       regStruct  = 'PI';
0030       
0031    case 'PID'
0032       % override selection
0033       regStruct  = 'PID';
0034       
0035    case 'AUTO'
0036       if isfield(model,'m')
0037          % selection performed only if a FOPDT model is provided
0038          m = model.m; L = model.L; T = model.T;
0039          
0040          % compute the ultimate frequency
0041          wmin = (-pi/2)/L;    % lower bound
0042          wmax = (-pi)/L;      % upper bound
0043          w    = real(logspace(log10(wmin),log10(wmax),1024));
0044          phaseM = angle(m*exp(-j*L*w)./(1+j*w*T));
0045          wu = w(find(phaseM==min(phaseM)));
0046          
0047          k1  = 1/abs(m*exp(-j*L*wu)/(1+j*wu*T));
0048          th1 = L/T;
0049          
0050          if th1>1 & k1<1.5
0051             regStruct = 'PI';
0052             msgbox('Bad results expected','AutotunerPID','warn');
0053          elseif (th1>0.6 & th1<1) & (k1>1.5 & k1<2.25)
0054             regStruct = 'PI';
0055          elseif th1<0.6 & k1>2.25
0056             regStruct = 'PID';
0057          else
0058             regStruct = 'PID';
0059             msgbox('Bad results expected','AutotunerPID','warn');
0060          end
0061       else
0062          regStruct = 'PID';
0063       end
0064       
0065    otherwise
0066       msgbox('Unknown structure','AutotunerPID','warn');
0067       regStruct  = 'PID';
0068 end

pid_isatd

pid_tuning

Generated on Wed 17-Mar-2004 09:29:44 by m2html © 2003