RDFT – Running discrete Fourier transform

Block SymbolLicensing group: ADVANCED

Function Description
The RDFT function block analyzes the analog input signal using the discrete Fourier transform with the fundamental frequency freq and optional higher harmonic frequencies. The computations are performed over the last m samples of the input signal u, where $m = nper ∕ freq ∕ T_{S}$ , i.e. from the time-window of the length equivalent to nper periods of the fundamental frequency.

If $nharm > 0$ the number of monitored higher harmonic frequencies is given solely by this parameter. On the contrary, for $nharm = 0$ the monitored frequencies are given by the user-defined vector parameter freq2.

For each frequency the amplitude (vAmp output), phase-shift (vPhi output), real/cosine part (vRe output) and imaginary/sine part (vIm output). The output signals have the vector form, therefore the computed values for all the frequencies are contained within. Use the VTOR function block to disassemble the vector signals. The output thd indicates the total harmonic distortion, i.e. the part of fundamental and higher harmonic frequencies (only if $nharm \geq 1$ ).

This block propagates the signal quality. More information can be found in the 1.4 section.

Input

u	Analog input of the block	Double (F64)
HLD	Hold	Bool

Parameter

freq	Fundamental frequency $↓$ 1e-09 $↑$ 1e+09 $⊙$ 1.0	Double (F64)
nper	Number of periods to calculate upon $↓$ 1 $↑$ 10000 $⊙$ 10	Long (I32)
nharm	Number of monitored harmonic frequencies $↓$ 0 $↑$ 16 $⊙$ 3	Long (I32)
ifrunit	Frequency units $⊙$ 1	Long (I32)
	1 .... Hz 2 .... rad/s
iphunit	Phase shift units $⊙$ 1	Long (I32)
	1 .... degrees 2 .... radians
nmax	Allocated size of array $↓$ 10 $↑$ 10000000 $⊙$ 8192	Long (I32)
freq2	Vector of user-defined monitored frequencies $⊙$ [2.0 3.0 4.0]	Double (F64)

Output

amp	Amplitude of the fundamental frequency	Double (F64)
thd	Total harmonic distortion	Double (F64)
vAmp	Vector of amplitudes at given frequencies	Reference
vPhi	Vector of phase-shifts at given frequencies	Reference
vRe	Vector of real parts at given frequencies	Reference
vIm	Vector of imaginary parts at given frequencies	Reference
E	Error indicator	Bool
iE	Error code	Error

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