18-05-2012, 01:44 PM
Power Electronic Hybrid System
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Abstract
The proposed power electronic hybrid system which
consists of a thyristor-controlled reactor (TCR) and a resonantimpedance-
type hybrid active power filter (RITHAPF) is used for
compensating reactive power and harmonic current. From the
point of the nature of load balancing compensation, the calculation
of balancing controlled susceptance based on voltage vector
transformation is proposed for the TCR to exactly compensate
negative-sequence current caused by asymmetrical loads in industrial
field.
INTRODUCTION
WITH THE development of power electronic devices
and these related control technologies, more and more
power electronic equipment has been installed in grids [1]–
[3]. However, many power electronic consumers, such as arc
furnaces and rectifiers, because of these special operation characteristics,
would cause serious voltage fluctuation, negativesequence
current, high-order harmonic current pollution, low
power factor (PF), etc. Therefore, a lot of specialists have given
attention to improving such power quality problems [4]–[7].
II. SYSTEM CONFIGURATION
The PEHS configuration shown in Fig. 1 which is composed
of a TCR and an RITHAPF is connected at the point of
common connection. The TCR uses the delta connection and
is connected nearby asymmetrical and nonlinear loads. The
RITHAPF consists of an APF and PPFs. The APF is a voltagesource
converter (VSC) whose dc link is a capacitor and whose
ac link is connected to a filter inductor. The APF crossing over
a matching transformer is connected in parallel with an FSRC,
which is in series with the PPFs. The PPFs can compensate a
fixed capacity of capacitive reactive power, corresponding to
FCs of SVCs. Because the FSRC is resonant at fundamental
frequency and, thus, the PPFs mainly sustain fundamental
voltage at the point of common connection, whereas the APF
only supports harmonic voltage, which greatly minimizes the
voltage level of power electronic devices of the APF, the
RITHAPF can be equipped in medium–high-voltage grids, and
its initial investment would be cut down.
Depending on its excellent configuration characteristics, the
PEHS could be effective to dynamically compensate reactive
power and negative-sequence current caused by asymmetrical
loads and to suppress the harmonic current generated by both
the TCR and nonlinear loads.
SIMULATION AND APPLICATION
A. Simulation Results
The simulation for verifying the performance of the proposed
PEHS is finished in MATLAB/Simulink, and its parameters
are listed in Table I. The asymmetrical linear and nonlinear
loads are represented by a three-phase asymmetrical linear
impedance and six harmonic current sources, respectively. The
asymmetrical linear impedance uses delta connection. These
loads are used to simulate the conditions in a chemical plant
in central China. The amplitude of the triangular carrier is 10,
V. CONCLUSION
This paper has proposed a PEHS that is composed of a TCR
and an RITHAPF to improve power quality in industrial field
where there are asymmetrical and nonlinear loads. The PEHS
configuration and control principle have been analyzed in detail.
The proposed load balancing compensation strategy for
the PEHS based on the voltage vector transformation can completely
compensate the negative-sequence current caused by
the asymmetrical loads without phase-locked loops. The phase
shift varies with the harmonic current frequency. It is difficult
to achieve the special phase shift compensation with only one
predictor.