5 Theory and internal operation
80
n-th current harmonic:
∑
−
=
+
⋅
=
1
1
2
)
10
(
,
k
k
n
C
n
p
I
h
I
p: 1,2,3
(19)
Total harmonic distortion is calculated as ratio of the RMS value of the harmonic
subgroups
to the RMS value of the subgroup associated with the fundamental:
Total voltage harmonic distortion:
2
40
2
1
∑
=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=
n
p
n
p
p
U
h
U
h
U
THD
,
p: 1,2,3
(20)
Total current harmonic distortion:
2
50
2
1
∑
=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=
n
p
n
p
Ip
h
I
h
I
THD
,
p: 1,2,3
(21)
50
100
150
200
Uc,k
Uh
1
{
Uh
2
{
Uh
3
{
Uh
4
{
Freqency
Figure 5.5: Illustration of harmonic subgroup for 50 Hz supply
5.1.9 Flicker
Standard compliance:
IEC 61000-4-30 Class S (Section 5.3)
IEC
61000-4-15
Flicker is a visual sensation caused by unsteadiness of a light. The level of the
sensation depends on the frequency and magnitude of the lighting change and on the
observer.
Change of a lighting flux can be correlated to a voltage envelope on figure bellow.
