IEEE Transactions on Industrial Electronics, 2013
ABSTRACT
Dynamic Voltage Restorer (DVR) is a definitive solution
towards compensation of voltage sag with phase jump. Conventional DVR
topologies however have dc-link and two stage power conversion. This increases
its size, cost and associated losses. Therefore topologies without the dc-link,
mitigating sag by utilizing direct ac-ac converters, are preferable over the
conventional ones. As no storage device is employed, compensation by these
topologies is limited only by the voltages at the point of common coupling that
is feeding the converters. In this paper, a direct ac-ac converter based
topology fed with line voltages is proposed. The arrangement provides increased
range of compensation in terms of magnitude and phase angle correction.
Detailed simulations have been carried out in MATLAB to compare the capability
of the proposed topology with other similar topologies.
KEYWORDS:
1. Dynamic voltage restorer (DVR)
2. Voltage source inverter (VSI)
3. Voltage sag compensation
4. Voltage phase jump compensation.
5. AC-AC
converter
SOFTWARE:
MATLAB/SIMULINK
BLOCK
DIAGRAM:
Fig. 1. Interphase ac-ac converter topology
Fig. 2. Proposed
converter topology.
EXPECTED SIMULATION RESULTS:
Fig.
3. Compensation of a sag type Ba. (a) Three phase voltage at the PCC with sag
of 0.3 p.u. magnitude and 100 phase jump.
(b) Three phase load voltage(c) Injected voltage. (d) The duty cycle of
choppers in phase a sag supporter.
Fig.
4. Compensation of a sag type Ca. (a) Three phase voltage at the PCC with sag
of 0.4 p.u. characteristic voltage magnitude and 200 phase jump. (b)
Three phase load voltage at the PCC. (c) Injected voltages. (d) The duty cycle
of voltages in phase b sag supporter. (e) The duty cycle of choppers in phase c
sag supporter.
Fig.
5. Compensation of symmetrical sag. (a) Three phase voltage at the PCC with
sag of 0.5 p.u. magnitude and 600 phase jump.
(b) Three phase load voltage at the PCC. (c) Injected voltages. (d) The duty
cycle of voltages
in all sag supporters.
CONCLUSION
In
this paper, an ac-ac converter based voltage sag supporter fed with line
voltage has been proposed to compensate voltage sag with phase jump. The
operation and switching logic of this topology are explained in detail. The
capability of the topology is tested for different types of voltage sags are compared
with other topologies. This topology has the advantage of eliminating storage
device and providing increased range of compensation. The efficacy of the
proposed topology is validated through simulation and experimental studies. An
intuitive method of classification of voltage sags [2], assorts sag into four
basic types as shown in Fig. In the figure, the dashed lines represent the
pre-sag voltage, and the solid lines represent the voltages during sag. The
pre-sag voltages are given by V j , and during sag voltages by V0 j ,where j = a,
b, and c. A single phase fault causes voltage sag in one phase (type B) at the
terminals of a star connected load and in two phases (type C) at the terminals
of a delta connected load. A phase-to-phase fault causes type C sag at the
terminals of a star connected load and type D sag at the terminals of a delta
connected load. A three phase symmetrical sag (type A) is caused by three phase
fault. Further, voltage sag gets transformed into other sag types as it
propagates in power system to lower voltage levels through transformers.
Transformation of a voltage sag due to single phase fault i.e. type B sag, is
illustrated in Fig. The type B sag when propagates through a star-delta
transformer it transforms to a type C sag. When type C sag in-turn propagates
through a star-delta transformer, it transforms to a type D sag. Each sag type
is further classified into three subtypes based on the phase(s) that is/are
affected. The subtypes are represented by a, b or c subscript, for easy
reference. For instance, sag type Ba and Da have voltage sag in phase-a; while
for sag type Ca, the line voltage bc is faulty and phase- a is healthy. Characterization
of each type of sag is done in terms of the type and the complex characteristic
voltage (V0 ch). The characteristic voltage defines three phase voltage sag.
The phase voltages as a function of the characteristic voltage and the
pre-fault voltage (which is usually 1 p.u.) is given in Table IV for the basic
four types [2].
REFERENCES
[1]
R. S. Vedam and M. S. Sarma, Power
Quality: VAR Compensation in Power Systems. CRC press, 2009.
[2]
M. H. J. Bollen, Understanding Power
Quality Problems. New York: IEEE press, 2000.
[3]
M. Mohseni, S. M. Islam, and M. A.
Masoum, “Impacts of symmetrical and asymmetrical voltage sags on dfig-based
wind turbines considering phase-angle jump, voltage recovery, and sag
parameters,” IEEE Trans. Power Electron., vol. 26, no. 5, pp. 1587–1598, May
2011.
[4]
A. Massoud, S. Ahmed, P. Enjeti, and B.
Williams, “Evaluation of a multilevel cascaded-type dynamic voltage restorer
employing discontinuous space vector modulation,” IEEE Trans. Ind. Electron.,
vol. 57, no. 7, pp. 2398–2410, Jul. 2010.
[5]
Y. W. Li, D. Vilathgamuwa, F. Blaabjerg,
and P. C. Loh, “A robust control scheme for medium-voltage-level dvr
implementation,” IEEE Trans. Ind. Electron., vol. 54, no. 4, pp. 2249–2261,
Aug. 2007.
