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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)
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