International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 5, May 2014)
Hybrid Active Power Filter for Power Quality Improvement
Kavya Mittal1, Ankita Kosti2
1
Kavya Mittal, M.Tech Student, S.R.I.T., Jabalpur (M.P.)
Ankita Kosti, Assistant Professor, Department of Electrical Engineering, Jabalpur (M.P.)
2
Active power filters (APF) generate either harmonic
currents or voltages in a manner such that the grid current
or voltage waves conserve the sinusoidal form. The APFs
can be connected to the grid in series (Series APF), shunt
(SAPF) to compensate voltage harmonics or current
harmonics respectively. Or can be associated with passive
filters to construct the hybrid filters (HAPF).
Abstract— This paper deals with the power quality (PQ)
improvement by using Hybrid Active Power Filter (HAPF)
which increases the reliability of power supply by reducing
the Total Harmonic Distortion (THD) as per IEEE-519
standard limits. In this paper two compensation strategies (pq
and dq) are used for the harmonic compensation and their
performances are compared by the simulation.
Keywords— hybrid active power filter (HAPF), pq method,
dq method, IEEE-519 harmonic standard, total harmonic
distortion (THD).
I. INTRODUCTION
With the increasing use of non-linear devices either for
residential or industrial applications, the power distribution
system is polluted with harmonics. These harmonics not
only lead to current and voltage stress but also responsible
for other effects such as electromagnetic interference, more
losses and capacitor failure. For a particular type of load,
IEEE-519 Standard limits the maximum amount of
harmonics that a supply system can tolerate. Thus filters
are very much essential for the harmonic compensation and
improving the power quality and hence increases the
reliability of the distribution system.
The harmonic compensation can be obtained by Passive
Filters (PF), Active Power Filters (APF) and hybrid filters
(HPF) [1]. PF and APF have some advantage and
disadvantages, but hybrid active power filters contain their
advantages but not their disadvantages.
Passive filter have been traditionally used for the
mitigation of distortion due to harmonic current in
industrial power systems but due to some drawbacks such
as resonance problem, dependency of their performance on
the system impedance, absorption of harmonic current of
nonlinear load, which could lead to further harmonic
propagation through the power system.
Fig.2. Shunt Active Filter Topology
There are different models of hybrid filters [2]. The
common HAPF is obtained by connecting PF and APF as
shown in fig.1.
Fig.3. Hybrid Filter Topology
APF generally consists of two distinct main blocks: the
Current-Controlled Voltage-Source Inverter (CCVSI) and
active filter controller [3].APF sense the load current iL
continuously with control algorithm, and calculate the
instantaneous values of the compensating current reference
for the VSI.
The passive filter consists of simple LC filters per phase
tuned near the lowest harmonics (5th or 7th or…). It
performs main functions: reactive compensation,
absorption of harmonic currents produced by the loads.
This paper presents the configuration of HAPF. Then
different control strategies including pq method [4], dq
method [5] are presented.
Fig.1 Passive Filter Topology
402
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 5, May 2014)
Final section present simulation results that are
conducted in MATLAB/Simulink environment and under
various non-ideal mains test scenarios. Then a comparison
of the methods is made for various conditions.
III. MODELLING OF CURRENT EXTRACTION METHODS
A. Instantaneous Reactive Power Theory (pq Method)
The Clarke transformation for the voltage variables is
given by [7]:
II. HARMONIC CURRENT EXTRACTION METHODS
(1)
A. Instantaneous Reactive Power Theory (pq Method)
This method is also known as pq method. Most APFs
have been designed on the basis of instantaneous reactive
power theory or pq method to calculate the desired
compensation current. This theory was first proposed by
Akagi and co-workers in 1984 [4].
The p-q theory is based on a set of instantaneous powers
defined in the time domain. The three-phase supply
voltages (ua, ub, uc) and currents (ia, ib, ic) are
transformed using the Clarke (or α-β) transformation into a
different coordinate system yielding instantaneous active
and reactive power components. This transformation may
be viewed as a projection of the three-phase quantities onto
a stationary two-axis reference frame.
Similarly, this transform can be applied on the distorted
load currents to give:
(2)
The instantaneous active power p(t) is given by:
(3)
This expression can be given in the stationary frame by:
(4)
(5)
Where, p(t) is the instantaneous active power, p0(t) is the
instantaneous homo-polar sequence power. Similarly the
instantaneous reactive power can be given by following (6)
Fig.4. Principle of instantaneous active and reactive power theory
B. Synchronous Reference Theory (d-q Method)
In this method, called also the method of instantaneous
currents id, iq, the load currents are transformed from three
phase frame reference abc into synchronous reference in
order to separate the harmonic contents from the
fundamentals [6]. It gives better performance even in the
case where the three phase voltage is not ideal.
(7)
In matrix form, the instantaneous active and reactive
power can be given by:
(8)
After separating the direct and alternating terms of
instantaneous power, the harmonic components of the load
currents can be given by using the inverse of equation (8)
which gives:
(9)
Fig.5. Principle of the synchronous reference method
403
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 5, May 2014)
The APF reference current can be then given by:
Following figure shows the THD analysis before filter
which is found to be many more times as per IEEE-519
standard limits.
(10)
A. Synchronous Reference Theory (d-q Method)
Transformation from three phase frame reference abc
into synchronous reference is given by [8]:
(11)
Fig.9. THD of Source Current After Filter
The next figure shows the voltage waveform.
The currents in the synchronous reference can be
decomposed into two parts as:
(12)
The APF reference currents are given by:
(13)
Fig.9. Load Voltage
By DQ harmonic current extraction technique:
This figure shows the source current waveform after
using hybrid filter which clearly shows the transient period
and steady state period of the current waveform.
It can be seen that the transient period by using dq
technique is less than using pq technique.
In three phase system, APF currents can be calculated by
the inverse Park transform which is defined as:
(14)
IV. SIMULATION RESULTS
On applying PQ harmonic current extraction technique,
the following simulation results are obtained which clearly
explains the power quality improvement from THD
analysis by using Hybrid Filter.
Fig.6. shows the source current waveform before filter
using PQ method. Figure shows the effect of load variation.
Fig.10. Source Current After Filter
Following figure shows the THD analysis after filter
which is found to be approximate as per IEEE-519 standard
limits.
This clearly explains the power quality improvement by
reducing the THD.
Fig.6. Source Current before Filter
404
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 5, May 2014)
VI. CONCLUSION
In this paper, different control methodologies are
implemented and simulated to understand the performance
of HAPF under different load conditions. On the basis of
simulation results performed in MATLAB/Simulink
environment, it is concluded that dq method is more stable
than pq method and hence improved the power quality by
reducing the THD.
Fig.11. THD of Source Current After Filter
REFERENCES
V. SIMULATION PARAMETERS
[1]
TABLE I
Supply System
Active Filter
Line Voltage (r.m.s.
value)
220V
Line Frequency
50 Hz
Source inductance, Ls
0.1mH
[3]
AC inductor to the
rectifier
.002mH
[4]
Vdc(V)
650
Cdc(µF)
0.1
Lc(mH)
0.2
Cf(µF)
1
Lf(mH)
1
[2]
[5]
[6]
[7]
Passive Filter
[8]
30
Nonlinear load
1
Nonlinear load
2
RL(Ω)
LL(mH)
0.3
RL(Ω)
50
LL(mH)
0.1
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