PD controller (Time domain)
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I would like to design a PD controller, to control a moving mass (=1Kg) along the x-axis so it moves from rest (point A) to another point B, like this:
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/546387/image.gif)
I would appreciate any help!
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Accepted Answer
Mathieu NOE
on 12 Mar 2021
hello again
so this is a modified code :
- the integration process computes the velocity first (from acceleration) , then the position (from the velocity)
- force can be limited , so you can have large gains from the controller (faster response) but you can then saturate the controller output to any given Fmax value. Results will look pretty much like a bang bang controller
- plot update by using handles (faster than re plotting the entire plot at each step)
- still need to figure out how to add the moving rectangle at the top of the figure
hope it helps
clf
clc
%Time:
t_ges = 2.5;
dt = 0.025;
t_vect = 0 : dt : t_ges;
%Initial position, Initial velocity, Initial acceleration:
q_0=0;
dq_0=0;
ddq_0=0;
%The position, velocity, acceleration:
q = q_0;
dq = dq_0;
ddq = dq_0;
%PD constants
Kp=10;
Kd=Kp/2;
% force limitation to Fmax (limitation of output of PD controller)
Fmax = 1;
%Matrices to store the calculate values:
n_times = length(t_vect);
q_Matrix = zeros(1, n_times);
dq_Matrix = zeros(1, n_times);
ddq_Matrix = zeros(1, n_times);
F_Matrix = zeros(1, n_times);
%// initiallize plot. Get a handle to graphic object
f = figure(1);
s1 = subplot(3,1,1);
p1 = plot(NaN,NaN,'b');
title('Position')
ylabel('m');
axis([0 t_ges -0.25 1.25]);%// freeze axes to their final size, to prevent Matlab from rescaling them dynamically
s2 = subplot(3,1,2);
p2 = plot(NaN,NaN,'b');
title('Velocity');
ylabel('m/s');
axis([0 t_ges -1 2]);%// freeze axes to their final size, to prevent Matlab from rescaling them dynamically
s3 = subplot(3,1,3);
p3 = plot(NaN,NaN,'b');
title('Force');
ylabel('N');
axis([0 t_ges -Fmax*1.25 Fmax*1.25]);%// freeze axes to their final size, to prevent Matlab from rescaling them dynamically
for ci = 1:n_times
%Velocity calculation:
dq = dq + dt * ddq;
dq_Matrix(1,ci) = dq;
%position calculation:
q = q + dt * dq;
q_Matrix(1,ci) = q;
%PD controller calculation: (closed-loop, with the reference is 1 meter (Point B))
F = Kp*(1-q) + Kd*(0-dq);
% force limitation (optionnal)
if abs(F)> Fmax
F = Fmax*sign(F);
end
F_Matrix(1,ci) = F;
%acceleration calculation:
ddq = F;
ddq_Matrix(1,ci) = ddq;
% update the plot
ind = (1:ci);
t_plot = t_vect(ind);
pause(0.01)
set(p1, 'XData', t_plot, 'YData', q_Matrix(ind));
set(p2, 'XData', t_plot, 'YData', dq_Matrix(ind));
set(p3, 'XData', t_plot, 'YData', F_Matrix(ind));
end
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More Answers (1)
Mathieu NOE
on 11 Mar 2021
a very simple and straigthforward simulation without much science behind :
NB : controller and plant in series in the main path, unitary feedback
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/546512/image.png)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% original plant
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
s = tf('s');
% Gs = 1.44e09/(s^2+5333*s+9.6e07);
Gs = 1/(s^2+0*s+0);
%PID
P= 10;
I= 0.0;
D= 1*P;
Ct = P+I/s+D*s/(1e-6*s+1);
figure()
Gscl = feedback(series(Ct,Gs),1);
step(Gscl);
legend('closed loop');
grid on;
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