02-09-2013, 04:32 PM
MODELING AND SIMULATION FOR VOLTAGE SAGS/SWELLS MITIGATION USING DYNAMIC VOLTAGE RESTORER (DVR)
MODELING AND SIMULATION .pdf (Size: 97.21 KB / Downloads: 65)
ABSTRACT
This paper describes the problem of voltage sags and swells and its severe impact on non linear loads or
sensitive loads. The dynamic voltage restorer (DVR) has become popular as a cost effective solution for the
protection of sensitive loads from voltage sags and swells. The control of the compensation voltages in
DVR based on dqo algorithm is discussed. It first analyzes the power circuit of a DVR system in order to
come up with appropriate control limitations and control targets for the compensation voltage control. The
proposed control scheme is simple to design. Simulation results carried out by Matlab/Simulink verify the
performance of the proposed method.
INTRODUCTION
Power Quality problems encompass a wide range
of disturbances such as voltage sags/swells,
flicker, harmonics distortion, impulse transient,
and interruptions [1].
Voltage sags can occur at any instant of time,
with amplitudes ranging from 10 – 90% and a
duration lasting for half a cycle to one minute [3].
Voltage swell, on the other hand, is defined as a
swell is defined as an increase in rms voltage or
current at the power frequency for durations from
0.5 cycles to 1 min. typical magnitudes are
between 1.1 and 1.8 up. Swell magnitude is also
is also described by its remaining voltage, in this
case, always greater than 1.0. [2,3,4].
PROPOSED METHOD
Main Circuit
Figure 3 shows the configuration of the proposed
DVR design using MATLAB/SIMULINK, where
the outputs of a three-phase half-bridge inverter
are connected to the utility supply via wye-open
connected series transformer.
Once a voltage disturbance occurs, with the aid of
dqo transformation based control scheme, the
inverter output can be steered in phase with the
incoming ac source while the load is maintained
constant. As for the filtering scheme of the
proposed method, output of inverter is installed
with capacitors and inductors.
Control Algorithm
The basic functions of a controller in a DVR are
the detection of voltage sag/swell events in the
system; computation of the correcting voltage,
generation of trigger pulses to the sinusoidal
PWM based DC-AC inverter, correction of any
anomalies in the series voltage injection and
termination of the trigger pulses when the event
has passed. The controller may also be used to
shift the DC-AC inverter into rectifier mode to
charge the capacitors in the DC energy link in the
absence of voltage sags/swells.
Voltage Sags
The first simulation shows of three phase voltage
sag is simulated. The simulation started with the
supply voltage 50% sagging as shown in Figure
5 (a).In Figure 5 (a) also shows a 50% voltage sag
initiated at 0.15s and it is kept until 0.35s, with
total voltage sag duration of 0.2s.
compensation. As a result of DVR, the load
voltage is kept at 1 pu.
The effectiveness of the DVR under unbalanced
conditions is shown in figure 6, in figure 6 also
shows the occurrence of 50% single phase voltage
sag on a utility grid. Through simulation the
supply voltage with one phase voltage dropped
down to 50% as shown in Figure 6 (a). The DVR
injected voltage and the load voltage are shown in
Figures 6 (b) and © respectively. Its
corresponding load voltages are shown in Figure
6© where it is possible to see that the
compensation method is keeping the load voltages
constant at 1 p.u.
CONCLUSION
The modeling and simulation of a DVR using
MATLAB/SIMULINK has been presented. A
control system based on dqo technique which is a
scaled error of the between source side of the
DVR and its reference for sags/swell correction
has been presented. The simulation shows that the
DVR performance is satisfactory in mitigating
voltage sags/swells.