ABSTRACT:
Unintentional series and/or parallel resonances, due
to the tuned passive filter and the line inductance, may result in severe
harmonic distortion in the industrial power system. This paper presents a
hybrid active filter to suppress harmonic resonance and reduce harmonic
distortion as well. The proposed hybrid filter is operated as variable harmonic
conductance according to the voltage total harmonic distortion, so harmonic distortion
can be reduced to an acceptable level in response to load change or parameter
variation of power system. Since the hybrid filter is composed of a
seventh-tuned passive filter and an active filter in series connection, both dc
voltage and Kva rating of the active filter are dramatically decreased compared
with the pure shunt active filter. In real application, this feature is very
attractive since the active power filter with fully power electronics is very
expensive. A reasonable trade-off between filtering performances and cost is to
use the hybrid active filter. Design consideration are presented and
experimental results are provided to validate effectiveness of the proposed
method. Furthermore, this paper discusses filtering performances on line impedance,
line resistance, voltage unbalance and capacitive filters.
KEYWORDS:
1.
Hybrid active
filter
2.
Harmonic resonance
3.
Industrial power system
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig.
1. The proposed hybrid active filter unit (HAFU) in the industrial power
system
and its associated control.
EXPECTED SIMULATION RESULTS:
Fig. 2. Line voltage e, source current is, load current iL, and filter current
i in case of NL1 initiated. X axis: 5ms/div.
Fig. 3. Line voltage e, source current is, load current iL, and filter current i in case of NL2 initiated. X axis: 5ms/div.
(a)
Terminal
voltage
(b)
Source current.
(c) Filter current.
(d) Load current.
Fig. 4 The HAFU is off for single-phase nonlinear load.
(a)
Terminal voltage.
(b)
Source current
(c) Filter current.
(d) Load current.
Fig. 5. The HAFU is on for single-phase
nonlinear load.
CONCLUSION:
This
paper presents a hybrid active filter to suppress harmonic resonances in
industrial power systems. The proposed hybrid filter is composed of a seventh
harmonic-tuned passive filter and an active filter in series connection at the
secondary side of the distribution transformer. With the active filter part
operating as variable harmonic conductance, the filtering performances of the passive filter can be
significantly improved. Accordingly, the harmonic resonances can be avoided and the harmonic distortion can be maintained
inside an acceptable level in case of load changes and variations of line
impedance of the power system. Experimental results verify the effectiveness of
the proposed method. Extended discussions are summarized as follows:
•
Large line inductance and large nonlinear load may result in severe voltage
distortion. The conductance is increased to maintain distortion to an
acceptable level.
•
Line resistance may help reduce voltage distortion. The conductance is
decreased accordingly.
•
For low line impedance, THD_ should be reduced to enhance filtering
performances. In this situation, measuring voltage distortion becomes a
challenging issue.
•
High-frequency resonances resulting from capacitive filters is possible to be
suppressed by the proposed method.
•
In case of unbalanced voltage, a band-rejected filter is needed to filter out
second-order harmonics if the SRF is realized to extract voltage harmonics.
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[3] E. J. Currence, J. E. Plizga, and H. N. Nelson,
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[4] C.-J. Wu, J.-C. Chiang, S.-S. Yen, C.-J. Liao,
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