29-05-2012, 03:54 PM
Dynamic Voltage Restorer against Voltage Sag
Dynamic Voltage Restorer against Voltage Sag.pdf (Size: 493.7 KB / Downloads: 205)
INTRODUCTION
One of the major concerns in electricity industry today is
power quality problems to sensitive loads. Presently, the
majority of power quality problems are due to different fault
conditions. These conditions cause voltage sag [1]. Voltage
sag may cause the apparatus tripping, shutdown commercial,
domestic and industrial equipment, and miss process of drive
system. Dynamic voltage restorer (DVR) can provide the
cost effective solution to mitigate voltage sag by establishing
the appropriate voltage quality level, required by the
customer [2, 3]. It is recently being used as the active solution
for voltage sag mitigation.
CONTROL PHILOSOPHY
Voltage sag is created at load terminals by a three-phase
fault as shown in Fig.3. Load voltage is sensed and passed
through a sequence analyzer. The magnitude is compared
with reference voltage (Vref). Pulse width modulated (PWM)
control technique is applied for inverter switching so as to
produce a three phase 50 Hz sinusoidal voltage at the load
terminals. Chopping frequency is in the range of a few KHz.
SIMULATION RESULTS
Detailed simulations are performed on the DVR test
system using MATLAB SIMULINK. System performance is
analyzed for compensating voltage sag with different DC
storage capacity so as to achieve rated voltage at a given load.
Various cases of different load condition are considered to
study the impact DC storage on sag compensation. These
various cases are discussed below: