How to set a constraint to limit rate of change of output in s function
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I have a simulink model where I have used an s-function block and based on the value of Preq and SOC the s-function provides an output based the algorithm shown below. I want the rate of change of output y(1) to be limited to 50. Please let me know how to do it. I am using fmincon optimization to obtain the output. I think a non linear constraint must be used to do this where the difference between the current output value and the previous output value must be 50. but I do not know how to call the current output value and previous output value while using an s function
function [sys,x0,str,ts,simStateCompliance] = trail1(t,x,u,flag)
switch flag
% Initialization %
case 0
[sys,x0,str,ts,simStateCompliance]=mdlInitializeSizes;
% Derivatives %
case 1
sys=mdlDerivatives(t,x,u);
% Update %
case 2
sys=mdlUpdate(t,x,u);
% Outputs %
case 3
sys=mdlOutputs(t,x,u);
% GetTimeOfNextVarHit %
case 4
sys=mdlGetTimeOfNextVarHit(t,x,u);
% Terminate %
case 9
sys=mdlTerminate(t,x,u);
% Unexpected flags %
otherwise
DAStudio.error('Simulink:blocks:unhandledFlag', num2str(flag));
end
% end sfuntmpl
%
%=============================================================================
% mdlInitializeSizes
% Return the sizes, initial conditions, and sample times for the S-function.
%=============================================================================
%
function [sys,x0,str,ts,simStateCompliance]=mdlInitializeSizes
sizes = simsizes;
sizes.NumContStates = 0;
sizes.NumDiscStates = 0;
sizes.NumOutputs = 3; %% the three outputs are the power delivered by fuel cell, battery and the equivalent factor
sizes.NumInputs = 2; %% Inputs are Power required and SOC
sizes.DirFeedthrough = 1; %% because output is a function of SOC
sizes.NumSampleTimes = 1; %% at least one sample time is needed
sys = simsizes(sizes);
%
% initialize the initial conditions
%
x0 = [];
%
% str is always an empty matrix
%
str = [];
%
% initialize the array of sample times
%
ts = [-1 0];
% Specify the block simStateCompliance. The allowed values are:
% 'UnknownSimState', < The default setting; warn and assume DefaultSimState
% 'DefaultSimState', < Same sim state as a built-in block
% 'HasNoSimState', < No sim state
% 'DisallowSimState' < Error out when saving or restoring the model sim state
simStateCompliance = 'UnknownSimState';
% end mdlInitializeSizes
%
%=============================================================================
% mdlDerivatives
% Return the derivatives for the continuous states.
%=============================================================================
%
function sys=mdlDerivatives(t,x,u) %#ok<*INUSD>
sys = [];
% end mdlDerivatives
%
%=============================================================================
% mdlUpdate
% Handle discrete state updates, sample time hits, and major time step
% requirements.
%=============================================================================
%
function sys=mdlUpdate(t,x,u)
sys = [];
% end mdlUpdate
%
%=============================================================================
% mdlOutputs
% Return the block outputs.
%=============================================================================
%
function sys=mdlOutputs(t,x,u)
%constants initialization
Pbatt_char= 7000;
SOC_min=0.4;
SOC_max=0.90;
Pfc_min=5000;
Pfc_max=7000;
Pbatt_max=15000;
%define Matrix Aeq
Aeq=[0 1 0;1 0 1];
%define Matrix beq
mu = 0.6;
beq=[(1-2*mu*((u(2)-0.5*(SOC_max-SOC_min))/(SOC_max-SOC_min))); u(1)];
%define boundary conditions
lb=[Pfc_min, 0, -Pbatt_char];
ub=[Pfc_max, 100, Pbatt_max];
%defining initial conditions
x0 = [7000 0 6000];
options = optimoptions('fmincon','Algorithm','active-set','Display','off','MaxFunctionEvaluations',1000,'MaxIterations',100);
[y,fval] = fmincon('OF_ECMS',x0,[],[],Aeq,beq,lb,ub,[],options); %#ok<*ASGLU>
Pfc=y(1); Pbatt=y(3); alpha=y(2);
sys = [Pfc Pbatt alpha];
% end mdlOutputs
%
%=============================================================================
% mdlGetTimeOfNextVarHit
% Return the time of the next hit for this block. Note that the result is
% absolute time. Note that this function is only used when you specify a
% variable discrete-time sample time [-2 0] in the sample time array in
% mdlInitializeSizes.
%=============================================================================
%
function sys=mdlGetTimeOfNextVarHit(t,x,u)
sampleTime = 1; % Example, set the next hit to be one second later.
sys = t + sampleTime;
% end mdlGetTimeOfNextVarHit
%
%=============================================================================
mdlTerminate
Perform any end of simulation tasks.
% =============================================================================
function sys=mdlTerminate(t,x,u)
sys = [];
% end mdlTerminate
Objective function code is
function f = OF_ECMS(x)
f = (x(1)+x(2)*x(3));
2 commentaires
Réponses (1)
Stephen Eltinge
le 7 Déc 2022
Hi aditya,
To write an S-Function block that recalls its previous output, please look into adding a discrete state to the S-Function. See the "unit delay" Level-2 MATLAB S-Function example for a simple starting point. You should then be able to use the state's data to provide an additional constraint for your optimization function.
6 commentaires
Stephen Eltinge
le 10 Jan 2023
Hi aditya,
Please try replacing "OutPort" with "OutputPort" in its four occurrences near the end of your code.
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