04-07-2012, 03:40 PM
CASCADED 5-LEVEL INVERTER TYPE DSTATCOM FOR POWER QUALITY
IMPROVEMENT
CASCADED 5-LEVEL INVERTER.pdf (Size: 378.49 KB / Downloads: 67)
Abstract:
In energy transmission systems, effective equipments on
power control are generally known as Flexible AC Transmission
System (FACTS). In addition, the power electronics-based
equipment, which are called power conditioners are use to solve
power quality problems. Since the topologies of these equipments
are similar to those used in FACTS equipment, power
conditioners are also called Distribution FACTS (DFACTS).
DSTATCOM is one such power conditioner used for improving
power quality. This study proposes a cascaded multilevel inverter
type DSTATCOM to compensate voltage sags in utility voltages in
power distribution network.
INTRODUCTION
Voltage sags are one of the most dominating power quality
assets, which dragged the attention of many researchers as
the sensitivity of loads are increasing due extensive usage of
power electronic devices. Fault at distribution level, sudden
increase of loads, motor starting are some of the causes of the
voltage sags. Such sudden variations of voltage are
undesirable for sensitive loads. These undesirable voltage
sags can be mitigated by connecting controlled devices either
in series or shunt to the load.
CONTROLLER
The aim of the control scheme is to maintain constant voltage
magnitude at the point where a sensitive load is connected,
under system disturbances. The control system only measures
the r.m.s voltage at the load point, i.e., no reactive power
measurements are required. The VSC switching strategy is
based on a sinusoidal PWM technique which offers
simplicity and good response. Since custom power is a
relatively low-power application, PWM methods offer a
more flexible option than the Fundamental Frequency
Switching (FFS) methods favored in FACTS applications.
Besides, high switching frequencies can be used to improve
on the efficiency of the converter, without incurring
significant switching losses.
TEST SYSTEM
Single line diagram of the test system for DVR is shown in
Figure-4 and the test system employed to carry out the
simulations for DSTATCOM is shown in Fig.5. Such system
is composed by a 13 kV, 50 Hz generation system, feeding
two transmission lines through a 3-winding transformer
connected in Y/Δ/Δ, 13/115/15 kV. Such transmission lines
feed two distribution networks through two transformers
connected in Δ/Y, 15/11 kV
CONCLUSIONS
The cascaded 5 level inverter topology has been presented
for shunt active power filter (DSTATCOM). The advanced
pulse width modulation technique (PSPWM) is used for 5
level inverter. The advantages of cascaded inverter in
modeling of DSTATCOM are presented clearly.
The following observations are made based on simulation
results.