Discrete Fourier transformation analysis (DFT)
4.3.1
DFT overview
(i)
Figure 4.3-1 shows the phase-to-natural voltage waveforms, which are distorted by high-order
harmonic component (). Using the equation (2.26-1), the DFT computation results can be
given in complex number, which consists of real part () and imaginary part ():
where,
High order harmonic number
:
:
Sampling time location
Total sampling number in an analysis cycle
:
():
Amplitude value of waveform at x sampling location
:
Frequency of high-order harmonic component
RMS value, approximate 1.0, can be computed with equation (4.3-2).
where,
Gain factor of Low-Pass Filter at high order () component
:
The DFT analysis will be performed in currents (except I 2 , I
for three-phase, V3, V4 for represented one)†.
†Note: For the information about entering signals, see Chapter
Transformer module for AC analog input.
currents (I 2 , I
Figure 4.3-1 High-order () harmonic wave
−1
1
−2
∑ ( )
=
=0
2
(
= √
|
|
).
N
- 554 -
(
)
= +
2
)
+
/
2
N
The DFT cannot operate for residual
6F2T0207 (0.01)
Time
(4.3-1)
(4.3-2)
for SEF,) and voltages (V1, V2
Technical description:
GRE200 (5,6)