5. A survey conducted by the Georgia Power Company in which both the utility personnel and
customers were polled out about what causes power quality problems. Both have their own vantage
points !
5
7. Effects of
Current on
Power Quality 7
Power = Voltage X Current
Hence it would be difficult
to define the quality of this
quantity in any meaningful
manner
• Utility has only control the
voltage, and Current is
regulated through load
• Therefore the standards of
power quality is maintained
by regulating the voltage
parameters only
8. The increasing application
of electronic equipment
and distributed generation
has heightened the interest
in power quality in recent
years
This has caused a
considerable amount of
confusion as both vendors
and end users have
struggled to understand
why electrical equipment
is not working as expected
For example, surge is
used to describe a wide
variety of disturbances
that cause equipment
failures or mis
operation. A surge
suppressor can suppress
some of these but will
have absolutely no effect
on others.
Unscrupulous
marketers take
advantage of the
ignorance of the
general public, selling
overpriced gadgets with
near miraculous claims
for improving the
power quality
8
If They won’t tell you
what is in the box and
how it works, don’t
buy it !
9. 9
Power quality standards must provide guidelines,
recommendations, and limits to help assure
compatibility between end use equipment and
the system where it is applied
10. 10
The international standards development organization is the IEC. The IEC has
defined a category of standards called Electromagnetic Compatibility (EMC)
Standards that deal with power quality issues. They fall into the following six
categories:
12. 1212
• Another word in common usage that
is often considered synonymous with
transient is surge.
• A utility engineer may think of a surge
as the transient resulting from a
lightning stroke for which a surge
arrester is used for protection.
• End users frequently use the word in
discriminately to describe anything
unusual that might be observed on
the power supply ranging from sags to
swells to interruptions.
39. 1. This is the most popular
UPQC system configuration
to compensate the power
quality problems in single-
phase two wire (1P2W)
supply system consisting of
two H-bridge inverters (total
eight semiconductor
switches).
2. A CSI-based topology can
also be realized for 1P2W
UPQC.
1. Nasiri and Emadi
introduced two additional
reduced part configurations for
single phase UPQC [40],
namely, three-leg single-phase
UPQC (total six semiconductor
switches) shown in Fig. (b) and
half-bridge single-phase UPQC
(total four semiconductor
switches shown in Fig. (c).
2. These topologies can be
considered for low-cost low-
power applications.
3. In a three-leg topology,
the series inverter consists
of switches S1 and S2 (leg
one), whereas, switches S3
and S4 are for shunt
inverter (leg two). The third
leg, switches S5 and S6, is
common for both the series
and shunt inverters.
4.The half-bridge topology
consists of one leg each for
shunt and series inverters.
39
(b)(a) (c)
(a) (c)(b) (b) (c)
40. 40
1. Several nonlinear loads,
such as, adjustable speed
drives fed
from3P3W,currentregulat
or,frequencyconverters,arc
welding machines, and arc
furnace, impose
combinations of previously
listed power quality
problems.
2. A 3P3W VSI-based
UPQC is depicted in Fig.
d.
1. Apart from the three-
phase loads, many industrial
plants often consist of
combined loads, such as, a
variety of single-phase loads
and three-phase loads,
supplied by 3P4W source.
The presence of fourth wire,
the neutral conductor,
causes an excessive neutral
current flow and, thus,
demands additional
compensation
2. To mitigate the neutral
current in 3P4W system,
various shunt inverter
configurations have been
attempted, namely, two
split capacitor (2C), four-
leg and three H-bridge
(3HB).
3. The related figures are
presented in Fig. (e) and
Fig. (f).
40
(d) (e) (f)
(d) (e) (f) (e) (f)
41. 41
1. Right and Left Shunt
UPQC (UPQC-R ( as
indicated in UPQC
architecture section ) and
UPQC-L (as indicated in
Fig.(g)))
2. The shunt inverter can be
located either on the right
(thus the name right shunt
UPQC (UPQC-R)) or left
(hence the name left shunt
UPQC(UPQC-L)) side of the
series inverter.
3. In UPQC-R, the
current(s) that flow through
series transformer is(are)
mostly sinusoidal
irrespective to the nature of
load current on the system
(provided that the shunt
inverter compensate current
harmonics, reactive current,
unbalance, etc., effectively).
Thus, UPQC-R gives a better
overall UPQC performance
compare to UPQC-L.
1. Fig. (h) depicts an
interesting UPQC system
configuration, suggested by
in daletal., where the two
inverters of the UPQC are
connected between two
distribution feeders named
as interline UPQC (UPQC-
I).
2. Another converter is used
to fed the dc-bus through an
extra converter as indicated
in Fig. (i) . The name of the
strategy is UPQC-MC 41
(g) (h) (i)
(g) (h) (i)(g)
42. Names Explanation
UPQC-D 3P3W and 3P4W distributed UPQC
UPQC-DG Distributed Generator integrated with UPQC
UPQC-I Interline UPQC
UPQC-L Left Shunt UPQC
UPQC-MC Multi converter UPQC
UPQC-MD Modular UPQC
UPQC-ML Multi-level UPQC
UPQC-P UPQC mitigates sags by regulating active power
UPQC-Q UPQC mitigates sags by regulating reactive power
UPQC-R Right shunt UPQC
UPQC-S UPQC mitigates sags by regulating both active and reactive power 42
