Perform Fourier analysis of signal
Control and Measurements/Measurements
The Fourier block performs a Fourier analysis of the input signal over a running window of one cycle of the fundamental frequency of the signal. The Fourier block can be programmed to calculate the magnitude and phase of the DC component, the fundamental, or any harmonic component of the input signal.
Recall that a signal f(t) can be expressed by a Fourier series of the form
where n represents the rank of the harmonics. (n = 1 corresponds to the fundamental component.) The magnitude and phase of the selected harmonic component are calculated by these equations:
As this block uses a running average window, one cycle of simulation must complete before the outputs give the correct magnitude and angle. For the first cycle of simulation, the outputs are held to the values specified by the initial input parameter.
Specify the fundamental frequency, in hertz, of the input signal.
Specify the harmonic component for the Fourier analysis. Enter 0 to analyze the DC component. Enter 1 to analyze the fundamental frequency, or enter a number corresponding to the desired harmonic.
Specify the initial magnitude and phase in degrees of the output signal.
Specify the sample time of the block, in seconds. Set to 0 to implement a continuous block.
Connect to the signal to be analyzed. Typical input signals are voltages or currents measured by Current Measurement or Voltage Measurement blocks.
The first output returns the magnitude of the harmonic component specified, in the same units as the input signal.
The second output returns the phase, in degrees, of the harmonic component specified.
|Sample Time||Specified in the Sample Time parameter|
Continuous if Sample Time = 0
|Scalar Expansion||Yes, of the parameters|
shows two applications of the Fourier measurement block. The upper
part of the model shows how to use the Fourier block to compute the
DC component, fundamental value, and second and third harmonic content
of the same input signal. In the lower part of the model, the block
computes the fundamental value (magnitude and phase) of three different
inputs. For this application, specify initial values for the three
output signals in the dialog box of the mask.
The model sample time is parameterized by the Ts variable set to a default value of 50e-6 s. Set Ts to 0 in the command window to simulate the model in continuous mode.