30-03-2012, 01:59 PM
Power Quality Improvement Using DVR
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INTRODUCTION
Dynamic voltage restores (DVRs) are now
becoming more established in industry to reduce the
impact of voltage dips on sensitive loads[1-3]. A voltage
dip is commonly defined as any low voltage drop event
between 10% and 90% of the nominal RMS voltage,
lasting between 0.5 cycles and 1 min[4]. In comparison
with interruptions, voltage dips affect a large number of
customers and for some cases may cause extremely
serious problems. Voltage dips are one of the most
occurring power quality problems.
DYNAMIC VOLTAGE RESTORER
A Dynamic Voltage Restorer (DVR) is a recently
proposed series connected solid state device that injects
voltage into the system in order to regulate the load side
voltage. The DVR was first installed in 1996[6]. It is
normally installed in a distribution system between the
supply and the critical load feeder[7]. Its primary
function is to rapidly boost up the load-side voltage in
the event of a disturbance in order to avoid any power
disruption to that load[8,9].
In-Phase Advance Compensation (IPAC):
Pre-Dip and in-phase compensation method must inject active
power to loads to correct voltage disturbance. However,
the amount of possible injection active power is
confined to the stored energy in DC link, which is one
of the most expensive components in DVR. Due to the
limit of energy storage capacity of DC link, the DVR
restoration time and performance are confined in these
methods.
SIMULATION
In order to show the performance of the DVR in
voltage sags and swells mitigation, a simple distribution
network was simulated using MATLAB (Fig. 1). A
DVR was connected to the system through a series
transformer with a capability to insert a maximum
voltage of 50% of the phase to ground system nominal
voltage. In this simulation the In-Phase Compensation
(IPC) method was used. The load considered in the
study is a 5.5 MVA capacity with 0.92 p.f, lagging.
CONCLUSION
The simulation results showed clearly the
performance of the DVR in mitigating voltage sags and
swells. The DVR handled both balanced and
unbalanced situations without any difficulties and
injected the appropriate voltage component to correct
rapidly any anomaly in the supply voltage to keep the
load voltage balanced and constant at the nominal
value. The efficiency and the effectiveness in voltage
sags/swells compensation showed by the DVR makes
him an interesting power quality device compared to
other custom power devices.