20-11-2012, 06:28 PM
Low Cost Dynamic Voltage Restorer
low cost dvr.pdf (Size: 399.19 KB / Downloads: 88)
Abstract.
In this paper a low cost topology for compensation
of voltage sags and swells is proposed. The dynamic voltage
restorer neither uses rectifier stage nor dc capacitor and thyristors
can be used as switching devices, resulting in a significant cost
reduction. The control system is simple, eliminating the use of
powerful computational platforms, causing also a cost reduction
and reliability increase. To validate the simulation models, an
experimental control platform is used to evaluate the proposed
dynamic voltage restorer.
Introduction
Sensitive equipment and non-linear loads have become
common for all consumers in sectors commercial,
industrial and residential. In the past, most electrical
equipment were insensitive to small supply voltage
variations. Nowadays, since many industrial, commercial
and even residential electrical loads have electronic logic
circuits or microprocessors, they became very sensitive to
voltage supply disturbances [1].
Considering this scenario, some problems about power
quality can be cited mentioned: voltage sags usually
caused by faults; harmonic distortions caused by nonlinear
loads; voltage unbalance; flickers; frequency
variations.
In a general way, any disturbance in the voltage, current or
frequency that results in fail or abnormal operation of an
equipment can be classified as a power quality problem
[1]. Studies in this subject indicate that the European
Union spends around 150 billions of Euros annually due to
the power quality problems.
The Proposed Low Cost DVR
The single-phase version of the proposed scheme is seen in
Fig. 2. The three-phase proposed configuration uses three
single-phase sets.
Low Cost DVR
Observing Fig. 2, it can be seen four transformers, Tseries1,
Tseries2, Tseries3 and Tparallel. The transformers Tseries1, Tseries2
and Tseries3 have their secondary windings connected in
series with the load, with the objective of providing a
voltage increment or decrement. The primary windings are
connected to the switches St1, St2 and St3 and to the central
tap of the transformer Tparallel. The switch Sab selects if the
voltage applied to the transformers Tseries1, Tseries2 and
Tseries3 is additive or subtractive in relation to supply
voltage since Tparallel is the feeding transformer. Note that
the transformers turns ratio Tseries1, Tseries2 and Tseries3 are
2:1, 4:1 and 8:1.
Simulation Results
The DVR proposed in Fig. 4 was simulated in
MATLAB/simulink in a 220 V grid. Situations with
three-phase (type A) and single-phase (type B) faults
were tested in the system [1]. The faults occur between
100 and 200 ms. Figs. 6 and 7 show the performance of
the proposed DVR for three-phase and single-phase
faults, respectively. The proposed low cost DVR is
capable of compensating both balanced and unbalanced
voltage sags.
Experimental Results
An experimental control platform was used to evaluate
and validate the proposed DVR. The control uses a
reference voltage of 100 V, compensation step of 5%,
seven steps of compensation and tolerance of 5%. In the
experimental results, channel 1 shows the the grid
voltage and channels 2, 3 and 4 show the switches states
of the lowest, medium and highest power transformers,
respectively.
Conclusion
In this paper, a low cost dynamic voltage restorer is
proposed for application in three-phase systems. The
proposed topology is very attractive because the
traditional dynamic voltage restorer has not been used in
power systems applications due to high cost of its
components. A comparative analysis between the
proposed and classical dynamic voltage restorers is done
and simulation results show that the low cost topology
presents a better cost-benefit solution in relation to the
traditional topology. Experimental results of the control
system of the proposed topology are also presented.