how to find time interval of peak value in a timeseries ?

i have a load profile data set.. Time vs Load Demand as a timeseries object. If I have a threshold for peak as 800KW How do I find at what time my value goes above 800 kW ? The time series object is for every 30 mins interval over 24 hrs.

I need to find the highlighted time interval in the picture. Any idea?

Answer 1

[Star Strider]

If you want to interpolate to find the ‘exact’ time, this works:

t = 0 : 30 : 1440;
LD = 500 + 400*sin(2*pi*t/2880);

zci = @(v) find(v(:).*circshift(v(:), [-1 0]) <= 0);                    % Returns Approximate Zero-Crossing Indices Of Argument Vector
X800_idx = zci(LD - 800);                                               % Subtract 800, Find Approximate Zero-Crossing

LD800_Rng = LD(X800_idx-1 : X800_idx+1)';                               % Define Range For Interpolation
t800_Rng = t(X800_idx-1 : X800_idx+1)';                                 % Define Range For Interpolation

t800 = interp1(LD800_Rng, t800_Rng, 800, 'linear', 'extrap');           % Find ‘Exact’ Time (Minutes)

figure(1)
plot(t, LD)
hold on
plot(t800, 800, '*r')
hold off
grid

[Star Strider]

A slightly more robust version that finds the points where ‘LD’ crosses 800:

t = 0 : 30 : 1440;                                                      % Create Data
LD = 500 + 400*sin(2*pi*t/2880);                                        % Create Data

zci = @(v) find(v(:).*circshift(v(:), [-1 0]) <= 0);                    % Returns Approximate Zero-Crossing Indices Of Argument Vector
X800_idx = zci(LD - 800);                                               % Subtract 800, Find Approximate Zero-Crossing

for k1 = 1:numel(X800_idx)
    LD800_Rng = LD(X800_idx(k1)-1 : X800_idx(k1)+1)';                   % Define Range For Interpolation
    t800_Rng = t(X800_idx(k1)-1 : X800_idx(k1)+1)';                     % Define Range For Interpolation
    t800(k1) = interp1(LD800_Rng, t800_Rng, 800, 'linear', 'extrap');   % Find ‘Exact’ Time (Minutes)
end

figure(1)
plot(t, LD)                                                             % Plot Load Curve
hold on
plot(t800, [1 1]*800, '*r')                                             % Plot ‘Load = 800’ Points
hold off
grid

Answer 2

[fbaillon]

You can use the find function:

T= ... % Time
LD= .... % Load Demand

timeYouWant=T(find(LD>800e3,1,'first))

Something like that...