09-11-2012, 04:41 PM
Voltage Flicker Compensation using STATCOM
29.Voltage Flicker Compensation using STATCOM.pdf (Size: 1.31 MB / Downloads: 141)
INTRODUCTION
The relationship between power quality and distribution
system has been a subject of interest for several years. The
concept of power quality describes the quality of the supplier
voltage in relation to the transient breaks, falling voltage,
harmonics and voltage flicker [1]. Voltage Flicker is the
disturbance of lightning induced by voltage fluctuations. Very
small variations are enough to induce lightning disturbance for
human eye for a standard 230V, 60W coiled-coil filament
lamp. The disturbance becomes perceptible for voltage
variation frequency of 10 Hz and relative magnitude of 0.26%
[1-2]. Huge non-linear industrial loads such as the electrical
arc furnaces [3-4], pumps, welding machines, rolling mills and
others are known as flicker generators. In this respect, the
quality of supplied voltage is significantly reduced in an
electrical power system and the oscillation of supplied voltage
appears to be a major problem.
CONTROLLING SYSTEM
The concept of instantaneous reactive power is used for the
controlling system. Following this, the 3-phase voltage upon
the use of the park presented by Akagi [24] has been
transformed to the synchronous reference frame (Park or dq0
transformation). This transformation leads to the appearances
of three instantaneous space vectors: Vd on the d-axis (real or
direct axis), Vq on the q-axis (imaginary or quadrature axis)
and V0, from the 3-phase voltage of Va, Vb and Vc. The related
equations of this transformation, expressed in the MATLAB
software, are as follows:
COMPENSATION SYSTEM
A typical two-bus power system shown in figure 3 is
simulated in MATLAB for this study. It can be seen that the
voltage oscillation was produced by a 3-phase flicker source
connected to the main bus-bar.
The complete STATCOM control system scheme
implemented on MATLAB is shown in figure 4. First, using a
3-phase converter to dq0, the instantaneous vectors Vd, Vq and
V0, are evaluated from the output 3-phase voltages whose
equations were explained in the previous section. Then, from
the obtained instantaneous components, sampling is taken
place. Since the controlling system uses just Vq to control the
STATCOM, a de-multiplexer is used to extract Vq voltage from
Vd and V0. The obtained Vq is then entered as an input to the
controlling function upon the MATLAB software. The
controlling function generates the amount of conducting angle,
needed for the GTOs of the STATCOM. A phase shifting block
is designed to control the appropriate phase angle of the
exerting pulses upon the GTOs of the STATCOM. The outputs
of this unit are entered into the STATCOM as inputs.
CONCLUSION
The design and application of STATCOM technology
based on voltage-source converters for voltage flicker
mitigation is discussed in this paper. Mitigation is done in
three stages and the results are compared and contrasted. First,
FCTCR is used to compensate for the voltage flicker, then a 6-
pulse voltage-source converter STATCOM and finally a 12-
pulse STATCOM based on voltage-source converter equipped
with an RLC filter are designed for complete voltage flicker
compensation without harmonics.
All the simulated results which have been performed in
MATLAB show that a 6-pulse STATCOM is efficiently
effective in decreasing the voltage flicker of the generating
loads. However, there is injection of the harmonic from
STATCOM into the system which can be improved with the
increase of the voltage source converters of STATCOM using
a 12-pulse STATCOM equipped with an RLC filter. The
obtained results clearly demonstrate that 12-pulse STATCOM
equipped with an RLC filter can reduce the voltage flicker
caused by nonlinear loads such as electric arc furnaces.