MI 2792 PowerQ4 Plus
Theory and internal operation
106
Phase voltage and current harmonics are calculated as RMS value of harmonic
subgroup
(sg)
: square root of the sum of the squares of the RMS value of a harmonic
and the two spectral components immediately adjacent to it.
n-th voltage harmonic:
1
1
2
)
10
(
,
k
k
n
C
n
p
U
h
U
p: 1,2,3
(18)
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
40
2
1
n
p
n
p
Ip
h
I
h
I
THD
,
p: 1,2,3
(21)
Spectral component between two harmonic subgroups are used for interharmonics
assessment. Voltage and current interharmonic subgroup of n-th order is calculated
using RSS (root sum square) principle:
n-th voltage interharmonic:
8
2
2
)
10
,(
k
k
n
C
n
p
U
ih
U
p: 1,2,3
(22)
n-th current interharmonic:
8
2
2
)
10
,(
k
k
n
C
n
p
I
ih
I
p: 1,2,3
(23)
Figure 5.5: Illustration of harmonics / interharmonics subgroup for 50 Hz supply
5.1.9 Signallling
Standard compliance: IEC 61000-4-30 Class A (Section 5.10)
