How to add a horizontal line in a plot that corresponds to a maximum?

movRMS = dsp.MovingRMS
% The Signal Codes (assume no noise)
t   =   (0:0.0001:1);           % signal duration : 1s
a   =   0.60;                   % the decrease of rms voltage range from 0.1 pu to 0.9 pu (10% to 90% decreased)            
w   =   100;                    % the phase angle jump ( ex. 50, 100, 170)
t   =   (0:0.0001:1);           % signal duration : 1s
a   =   0.60;                   % the decrease of rms voltage range from 0.1 pu to 0.9 pu (10% to 90% decreased)         
f   =   50;                     % frequency
ti  =   0.10;                   % initiation
tr  =   0.50;                   % recovery (duration: 0.4s) 
y   =   (1  - a*(heaviside(t-ti) - heaviside (t-tr))).*(sin(2*pi*f*t+w));  % heaviside is the unit step
rmsval = 2*movRMS(y)            % RMS detection code

% Plot Disturbance waveform
figure (1)
subplot(2,1,1)
plot (t,y)
xlabel('Time (s)')
ylabel('Amplitude (pu)')
title('Voltage Sag')

% Plot RMS waveform
subplot(2,1,2)
plot (t,rmsval)
xlabel('Time (s)')
ylabel('Magnitude (pu)')
title('RMS Detection')

Edit: I would like to add a horizontal line (blue horizontal line in figure 2) corresponding to the maximum value of the waveform which only change when the peak amplitude also changes as you can see in figure 2. I also attached my simulation result in figure 1. Thank you for your attention.

Figure 1 : My simulation

Figure 2 : Sag voltage with RMS Detection

[Sam Chak]

@Irfanudin Nor Anwar

Can you provide the 14 peak coordinates (x, y)?

[Irfanudin Nor Anwar]

@Sam Chak you mean from the example picture? Sorry I cant because I dont have access to the codes (got the example from other's thesis and he didnt mention it).

[Jeffrey Clark]

@Irfanudin Nor Anwar, use Find local maxima - MATLAB islocalmax (mathworks.com) and create the blue line plot from spline of the local maxima and ppval the spline to get the y values of the blue line.

[Irfanudin Nor Anwar]

@Jeffrey Clark Thanks, I will read them and try it.

Answer 1

[Sam Chak]

Hi @Irfanudin Nor Anwar

No worries, I take your samples. Generally, you need to guess the function of a curve that might fit into the peaks:

% find peaks
[pks, locs] = findpeaks(y, t);
pks  = [pks(1:25) pks(27:31)];
locs = [locs(1:25) locs(27:31)];

% curve fitting
fo = fitoptions('Method', 'NonlinearLeastSquares', ...
               'Lower', [1e44, 0.2], ...
               'Upper', [1e46, 0.4], ...
               'StartPoint', [1.5e44 0.3]);
ft = fittype('1 - 0.6*exp(-b*(x - c)^64)', 'options', fo);
[curve, gof] = fit(locs', pks', ft)

% plotting
plot(t, y)
axis([0 0.6 -1.5 1.5])
hold on
plot(curve)
hold off

[Irfanudin Nor Anwar]

@Sam Chak Thank you for the help, I will study your code and make some adjustment later.

Answer 2

[Star Strider]

Another option is the envelope function —

movRMS = dsp.MovingRMS;
% The Signal Codes (assume no noise)
t   =   (0:0.0001:1);           % signal duration : 1s
a   =   0.60;                   % the decrease of rms voltage range from 0.1 pu to 0.9 pu (10% to 90% decreased)            
w   =   100;                    % the phase angle jump ( ex. 50, 100, 170)
t   =   (0:0.0001:1);           % signal duration : 1s
a   =   0.60;                   % the decrease of rms voltage range from 0.1 pu to 0.9 pu (10% to 90% decreased)         
f   =   50;                     % frequency
ti  =   0.10;                   % initiation
tr  =   0.50;                   % recovery (duration: 0.4s) 
y   =   (1  - a*(heaviside(t-ti) - heaviside (t-tr))).*(sin(2*pi*f*t+w));  % heaviside is the unit step
rmsval = 2*movRMS(y);           % RMS detection code

yenv = envelope(y, 500, 'analytic');
rmsenv = envelope(rmsval, 85, 'peak');

% Plot Disturbance waveform
figure (1)
subplot(2,1,1)
plot (t,y)
hold on
plot(t, yenv, '-r', 'LineWidth',2)
hold off
xlabel('Time (s)')
ylabel('Amplitude (pu)')
title('Voltage Sag')

% Plot RMS waveform
subplot(2,1,2)
plot (t,rmsval)
hold on
plot(t, rmsenv, '-r', 'LineWidth',2)
hold off
xlabel('Time (s)')
ylabel('Magnitude (pu)')
title('RMS Detection')

.