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Improvement of the Electric Power Quality Using
Series Active and Shunt Passive Filters
P. Salmerón and S. P. Litrán
Abstract—A control algorithm for a three-phase hybrid power
filter is proposed. It is constituted by a series active filter and a passive filter connected in parallel with the load. The control strategy
is based on the vectorial theory dual formulation of instantaneous
reactive power, so that the voltage waveform injected by the active
filter is able to compensate the reactive power and the load current harmonics and to balance asymmetrical loads. The proposed
algorithm also improves the behavior of the passive filter. Simulations have been carried out on the MATLAB-Simulink platform
with different loads and with variation in the source impedance.
This analysis allowed an experimental prototype to be developed.
Experimental and simulation results are presented.
Index Terms—Active power filters, harmonics, hybrid filters, instantaneous reactive power, power quality.
I. INTRODUCTION
T
HE increase of nonlinear loads due to the proliferation of
electronic equipment causes power quality in the power
system to deteriorate. Harmonic current drawn from a supply by
the nonlinear load results in the distortion of the supply voltage
waveform at the point of common coupling (PCC) due to the
source impedance. Both distorted current and voltage may cause
end-user equipment to malfunction, conductors to overheat and
may reduce the efficiency and life expectancy of the equipment
connected at the PCC.
Traditionally, a passive LC power filter is used to eliminate
current harmonics when it is connected in parallel with the load
[1]. This compensation equipment has some drawbacks [2]–[4],
due to which the passive filter cannot provide a complete solution. These disadvantages are mainly the following.
— The compensation characteristics heavily depend on the
system impedance because the filter impedance has to be
smaller than the source impedance in order to eliminate
source current harmonics.
— Overloads can happen in the passive filter due to the circulation of harmonics coming from nonlinear loads connected near the connection point of the passive filter.
— They are not suitable for variable loads, since, on one hand,
they are designed for a specific reactive power, and on the
other hand, the variation of the load impedance can detune
the filter.
Manuscript received October 24, 2008; revised May 07, 2009. Paper no.
TPWRD-00781-2008.
The authors are with the Electrical Engineering Department, Huelva University, Huelva, Spain (e-mail: patricio@uhu.es; salvador@uhu.es).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TPWRD.2009.2034902
Fig. 1. Series active filter and parallel passive filter.
— Series and/or parallel resonances with the rest of the
system can appear.
An active power filter, APF, typically consists of a threephase pulsewidth modulation (PWM) voltage source inverter
[5]. When this equipment is connected in series to the ac source
impedance it is possible to improve the compensation characteristics of the passive filters in parallel connection [6], [7]. This
topology is shown in Fig. 1, where the active filter is represented
by a controlled source, where is the voltage that the inverter
should generate to achieve the objective of the proposed control
algorithm.
Different techniques have been applied to obtain a control
signal for the active filter [8]–[10]. One such is the generation of a voltage proportional to the source current harmonics
[11], [12]. With this control algorithm, the elimination of series
and/or parallel resonances with the rest of the system is possible. The active filter can prevent the passive filter becoming a
harmonics drain on the close loads. Additionally, it can prevent
the compensation features depending on the system impedance.
From the theoretical point of view, the ideal situation would
be that the proportionality constant, k, between the active filter
output voltage and source current harmonics, had a high value.
However, at the limit this would be an infinite value and would
mean that the control objective was impossible to achieve. The
chosen k value is usually small so as to avoid high power active
filters and instabilities in the system. However, the choice of the
appropriate k value is an unsolved question since it is related to
the passive filter and the source impedance values. Besides, this
strategy is not suitable for use in systems with variable loads because the passive filter reactive power is constant, and therefore,
the set compensation equipment and load has a variable power
factor.
In another proposed control technique, the APF generates a
voltage waveform similar to the voltage harmonics at the load
side but in opposition [13]. This strategy only prevents the parallel passive filter depending on the source impedance; the other
limitations of the passive filter nevertheless remain.
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IEEE TRANSACTIONS ON POWER DELIVERY
Other control strategies combining both the above have been
proposed to improve the parallel passive filter compensation
characteristics [14], [15], but they continue to suffer from the
difficulty of finding an appropriate value for the APF gain k.
Finally, another approach has recently been proposed [16]. It
suggests that the active filter generates a voltage which compensates the passive filter and load reactive power, so it allows the
current harmonics to be eliminated. The calculation algorithm
is based on the instantaneous reactive power theory [17]. There,
the control target is to achieve constant power in the source side.
In this paper a new control strategy based on the dual formulation of the electric power vectorial theory [18], [19] is proposed.
For this, a balanced and resistive load is considered as reference
load. The strategy obtains the voltage that the active filter has
to generate to attain the objective of achieving ideal behavior
for the set hybrid filter-load. When the source voltages are sinusoidal and balanced the power factor is unity, in other words,
the load reactive power is compensated and the source current
harmonics are eliminated. By this means, it is possible to improve the passive filter compensation characteristics without depending on the system impedance, since the set load-filter would
present resistive behavior. It also avoids the danger that the passive filter behaves as a harmonic drain of close loads and likewise the risk of possible series and/or parallel resonances with
the rest of the system. In addition, the compensation is also possible with variable loads, not affecting the possible the passive
filter detuning.
Although the APF series control based on the instantaneous
reactive power theory is not new, in this paper the authors propose a new formulation that has consequences in the control
loop design. In fact, the instantaneous reactive power here is
defined from a dot product whereas in [16], [17] it is defined as
a cross product; this results in a remarkable simplification in the
implementation of the reference generation method. The final
development allows any compensation strategy to be obtained,
among them, unit power factor.
The compensated electric system was simulated in
MATLAB-Simulink, and the strategy was applied to a
three-phase system with balanced and unbalanced loads.
The simulation results used to verify the theoretical behavior
are presented. Finally, an experimental prototype was manufactured and its behavior checked. Experimental results are also
presented.
Fig. 2. Transformation from the phase reference system (abc) to the 0
system.
Fig. 3. Three-phase system.
The vector transformations from the phase reference system
coordinates can be obtained, thus
a-b-c to
(2)
(3)
The instantaneous real power in the
culated as follows:
frame is cal-
(4)
This power can be written as
(5)
where is the instantaneous real power without zero sequence
component and given by
(6)
II. THE DUAL INSTANTANEOUS REACTIVE POWER THEORY
The instantaneous reactive power theory is the most widely
used as a control strategy for the APF. It is mainly applied to
compensation equipment in parallel connection. This theory is
based on a Clarke coordinate transformation from the phase coordinates (see Fig. 2).
In a three-phase system such as that presented in Fig. 3,
voltage and current vectors can be defined by
It can be written in vectorial form by means of dot product
(7)
where
is the transposed current vector in
coordinates
(8)
In the same way,
dinates
is the voltage vector in the same coor-
(1)
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3
collinear to the supply voltages and the system will have unity
power factor. If, in Fig. 3, voltages are considered as balanced
and sinusoidal, ideal currents will be proportional to the supply
voltages
(16)
is the equivalent resistance, the load voltage vector and
the load current vector.
The average power supplied by the source will be
Fig. 4. Decomposition of the voltage vector.
In (5), is the zero sequence instantaneous power, calculated
as follows:
(10)
In a three-wire system there are no zero-sequence current
components, that is,
. In this case, only the instantaneous
axes exists, because the product
power defined on the
is always zero.
The imaginary instantaneous power is defined by the equation
(17)
In this equation, is the square rms value of the fundamental
harmonics of the source current vector. It must be supposed that
when voltage is sinusoidal and balanced, only the current fundamental component transports the power consumed by the load.
Compensator instantaneous power is the difference between
the total real instantaneous power required by the load and the
instantaneous power supplied by the source
(18)
(11)
In accordance with (7), this can be expressed by means of the
dot product
In this equation, the average power exchanged by the compensator has to be null, that is
(19)
(12)
where
is the transposed current vector perpendicular to
and it can be defined as follows:
When average values are calculated in (18), and (17) and (19)
are taken into account
(13)
Both power variables previously defined can be expressed as
(20)
Therefore, the equivalent resistance can be calculated as
(14)
In the
plane,
and
vectors establish two coordican be decomposed in its ornates axes. The voltage vector
thogonal projection on the axis defined by the currents vectors,
Fig. 4. By means of the current vectors and the real and imaginary instantaneous power, the voltage vector can be calculated
(15)
In a four-wire system, the zero sequence instantaneous power,
, is not null. In this case, (15) would have to include an ad, where is the zero seditional term with the form
quence current vector.
III. COMPENSATION STRATEGY
Electric companies try to generate electrical power as sinusoidal and balanced voltages so it has been obtained as a reference condition in the supply. Due to this fact, the compensation
target is based on an ideal reference load which must be resistive, balanced and linear. It means that the source currents are
(21)
where
is the load average power, defined as
(22)
Fig. 5 shows the system with series active filter, parallel passive filter and unbalanced and nonsinusoidal load. The aim is
that the set compensation equipment and load has an ideal behavior from the PCC. The voltage at the active filter connection
coordinates can be calculated as follows:
point in
(23)
is the source current in
coordinates. In this equation,
the restriction of null average power exchanged by the active
filter is imposed.
The load voltage is given according to (15) by
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IEEE TRANSACTIONS ON POWER DELIVERY
Fig. 5. System with compensation equipment.
Fig. 6. Series active power and passive filter topology.
where
is the real instantaneous power and
is the load
imaginary instantaneous power.
The reference signal for the output voltage of the active filter
is
TABLE I
PASSIVE ELEMENT VALUES
(25)
Considering (23) and (24), the compensation voltage is
(26)
When the active filter supplies this compensation voltage, the
set load and compensation equipment behaves as a resistor .
Finally, if currents are unbalanced and nonsinusoidal, a balanced resistive load is considered as ideal reference load. Therefore, the equivalent resistance must be defined by the equation
(27)
Here,
is the square rms value of the positive sequence
fundamental component. In this case, (26) is modified, where
is replaced by , that is
(28)
Reference signals are obtained by means of the reference calculator shown in Fig. 9 and Fig. 10. In the case of unbalanced
loads, the block “fundamental component calculation” in Fig. 9
is replaced by the scheme shown in Fig. 17, which calculates
the current positive sequence fundamental component.
The compensation target imposed on a four-wire system is
the one presented in (16). However, a modification in the control scheme of Fig. 9 is necessary. This consists in including a
in the conthird input signal from the zero sequence power
is generated.
trol block where
The proposed control strategy may be suitable in a stiff feeder,
where voltage could be considered undistorted.
IV. SIMULATION RESULTS
The system shown in Fig. 6 has been simulated in the MatlabSimulink platform to verify the proposed control. Each power
device has been modeled using the SimPowerSystem toolbox
library. The power circuit is a three-phase system supplied by
a sinusoidal balanced three-phase 100-V source with a source
inductance of 5.8 mH and a source resistance of 3.6 . The
inverter consists of an Insulated Gate Bipolar Transistor (IGBT)
bridge. On the dc side, two 100-V dc sources are connected.
An LC filter has been included to eliminate the high frequency
components at the output of the inverter. This set is connected to
the power system by means of three single-phase transformers
with a turn ratio of 1:1.
The passive filter is constituted by two LC branches tuned to
the fifth and seventh harmonics. Each element value is included
in Table I.
The selection criteria to fix the ripple filter were, in the case
of low frequency components, that the inverter output voltage
. However, in the case of
be almost equal to voltage across
high-frequency components, the reduced voltage in
must be
. Furthermore,
and
values
higher than in the capacitor
must be selected so as not to exceed the transformer burden.
Therefore, the following design criteria must be satisfied.
, to ensure that inverter output voltage drops
—
at the switching frequency;
across
, to ensure that voltage divider is between
—
and
, where
is the source impedance,
the
shunt passive filter, reflected by the secondary winding.
,
,
At 20-kHz switching frequency,
,
.
Two load types were simulated:
— nonlinear balanced load;
— nonlinear unbalanced load.
A. Case 1: Nonlinear Balanced Load
In this case, the nonlinear load consists of an uncontrolled
three-phase rectifier with an inductance of 55 mH and a 25
resistor connected in series on the dc side.
Fig. 7 shows the phase “a” load current. The load current
total harmonics distortion (THD) is 18.6% and the power factor
0.947, when the system is not compensated.
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Fig. 7. Load current of the phase “a”.
Fig. 9. Control scheme.
Fig. 8. Source current when the passive filter is connected.
The 5th and 7th harmonics are the most important in the current waveform. They are 16.3% and 8.4% of the fundamental
harmonic, respectively.
Two LC branches were connected to mitigate the fifth and
seventh harmonics. The source current waveform with the passive filter connected is shown in Fig. 8. The THD falls to 4.7%.
The 5th and 7th harmonics decrease to 3.6% and 0.9%, respectively. The passive filter was designed only to compensate the
source current harmonics; the reactive power was not considered. The power factor of the set load and passive filter is 0.97.
To simulate the active filter series connection with a passive
filter, Fig. 6, it is necessary to determine the APF reference
signal. The control scheme used to calculate the active filter
compensation voltage is shown in Fig. 9. The voltage vector on
the load side and the source current vectors are the input sige
vectors in
nals. By means of a calculation block,
coordinates can be determined. The product of these vectors allows the instantaneous real power to be calculated, obtaining its
average value with a low-pass filter (LPF). This is the power required by the set passive filter and load. The average power is
divided by the average value of the sum of the square of the instantaneous values of the current fundamental component.
The fundamental component is obtained by means of a block
with the scheme shown in Fig. 10. Each component of the source
and
where is the
current vector is multiplied by
fundamental frequency in rad/s. The average values of the results are obtained using two low-pass filters. They are multiplied
and
again and then by 2. This allows the current
by
vector fundamental component to be obtained; conversely, the
. The result is mulreal instantaneous power is divided by
, which allows the first term in
tiplied by the current vector
the compensation voltage in (26) to be determined.
Fig. 10. Calculation fundamental component.
Fig. 11. Source current when the active filter is connected.
On the other hand, the imaginary instantaneous power is oband finally multiplied by the current
tained and divided by
. This determines the second term in the compensavector
tion voltage (26).
When the active filter is connected, the source current THD
falls to 1.30%. The waveform is shown in Fig. 11. Now, the
power factor rises to 0.99. This allows the proposed control to
be verified, the passive filter compensation characteristic to be
improved and unity power factor is practically achieved.
The passive filter impedance has to be lower than the system
impedance in order to be effective. When the branch LC or
impedance source quality factor is low, the harmonics filtering
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Fig. 12. Source current when passive filter is only connected. Source
impedance, 1.3 and 2.34 mH.
Fig. 14. Source current when only the passive filter is connected and the resistor
on the dc side is 50 .
Fig. 15. Source current when the active filter is connected and the resistor on
the dc side is 50 .
Fig. 13. Source current when the active filter is connected. Source impedance,
1.3 and 2.34 mH.
deteriorates. To verify the behavior of the compensation equipment in this situation, the source impedance is modified. It is
changed from 3.6 and 5.8 mH to 1.3 and 2.34 mH. The
source current has a THD of 10.1%, when the active filter is not
connected and the compensation equipment is only the passive
filter. The source current waveform is shown in Fig. 12. The 5th
and 7th harmonics are 8.2% and 2.5% of the fundamental harmonic and the power factor is 0.97.
When the active filter is working with the proposed control
algorithm, the THD of the source current improves to 1.6% and
the power factor is 0.99. This current waveform is shown in
Fig. 13.
In a distribution system, variations may appear in the load
power. To verify the behavior of the proposed control algorithm,
the resistor value connected at the dc side of the uncontrolled
three-phase rectifier was changed from 25 to 50 . The source
impedance is 3.6 and 5.8 mH. When the passive filter is connected, the source current waveform is shown in the Fig. 14,
which has a THD of 4.9%. In this case, the power factor is 0.91.
With the active filter connected the source current has the
waveform shown in Fig. 15. The THD falls from 4.9 to 1.8%
and the power factor rises to 0.99
Therefore, with the proposed control algorithm, the set active
filter and passive filter allow the compensation of variable loads.
This control algorithm can compensate reactive power and can
improve the behavior of the passive filter.
TABLE II
PASSIVE ELEMENT VALUES OF THE LOAD
Fig. 16. Source current without filters. Unbalanced load.
B. Case 2: Non-Linear Unbalanced Load
In this case, the three-phase load is built with three singlephase uncontrolled rectifiers with capacitors and resistors connected in parallel at the dc side with the values shown in Table II.
Fig. 16 shows the source currents in the uncompensated
system. Current THDs of “a”, “b”, and “c” phase are 18.8%,
35.0%, and 37.6%, respectively.
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Fig. 17. Modification in the control scheme for unbalanced load.
Fig. 19. Experimental prototype.
Fig. 18. Source current with active filters and unbalanced load.
The control scheme for the active filter shown in Fig. 9, is
modified for unbalanced loads. The block “fundamental component calculation” in Fig. 9 is replaced by the scheme shown
in Fig. 17. Now the average power P is divided by the square
rms value of positive sequence fundamental component. In this
case, the positive sequence component is calculated by means
of the block “positive sequence component”, where the opernecessary to implement the Fortescue transator
formation is obtained with an all pass filter. Subsequently, its
fundamental value is calculated and the Fortescue inverse transformation applied.
Fig. 18 shows the three source currents when this control is
applied to the active filter. The system presents a behavior similar to a resistive and balanced load. The source currents THD
are 1.4%, 0.85%, and 1.3% in phases “a”, “b”, and “c”.
In (16), the compensation aim is to obtain unity power factor.
When the voltage is sinusoidal and balanced, a sinusoidal and
balanced source current is obtained. When the voltage is distorted, unity power factor is achieved, although the source current is distorted.
V. EXPERIMENTAL RESULTS
The experimental prototype which has been developed is
shown in Fig. 19. It is a three-phase system supplied by a sinusoidal balanced three-phase 100-V rms source. Fig. 5 shows
the power circuit scheme.
The converter is a Semikron SKM50GB123-type IGBT
bridge at the dc side, two 100-V capacitors are connected. At
the ac side, an LC filter has been included to eliminate high
switching frequency. This set is matched to the power system
by means of three single-phase transformers with a turn ratio
of 1:1 to ensure galvanic isolation.
Two dc sources in the APF simulation model were considered. It simplifies the control scheme and makes the simulation
easier. The prototype also includes two capacitors. The control
scheme includes a loop with PI controller to ensure the capacitor voltages remain constant [11].
The passive power filter compensation is formed by two LC
branches tuned to the fifth and seventh harmonics. Each passive
element values are included in Table I.
The control strategy was implemented in a control and general application data acquisition cards compatible with MatlabSimulink and developed by dSPACE were used.
dSPACE Real-Time Interface (RTI) together with Mathworks
Real Time Workshop (RTW) automatically generate real time
code in dSPACE. This allows the processor board to be programmed and I/O boards to be selected. It is based on the DS
1005 PPC placed in a dSPACE expansion box. The input board
was the dSPACE DS 2004 A/D and the output board the DS
51001 DWO.
The control board has a PowerPC 750GX processor running
at 1 GHz. For the experimental prototype the sampling rate was
in order to avoid overrun errors.
limited to 50
A hysteresis band control was developed. The IGBT gating
signals were generated comparing the reference signal with
the inverter output voltage considering a hysteresis band.
This method switches the transistor when the error exceeds a
fixed magnitude: the hysteresis band. Therefore, the switching
frequency is variable, although in our design this frequency
is limited to 20 kHz so as not to reach the IGBTs maximum
switching frequency.
The prototype was verified using two different loads: a nonlinear balanced load and a nonlinear unbalanced load.
A. Case 1. Nonlinear Balanced Load
In the first experiment the source impedance has a inductance of 5.8 mH and resistance of 3.6 . The nonlinear load
consists of an uncontrolled three-phase rectifier with an inductance of 55 mH and a 25 resistor connected on the dc side.
Fig. 20 shows the phase “a” load current and voltage, measured without compensation. This waveform is obtained using a
LECROY Wavesurfer 424- type oscilloscope. The current THD
measured using the Fluke 43 power quality analyzer is 21.5%
and the voltage THD 11.2%. The measured power factor is 0.96.
Fig. 21 shows source current and voltage at the connection
point when the shunt passive filter is connected. This current
and voltage have a THD of 5.1% and 4.3% respectively. The
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Fig. 20. Source voltage and current, phase “a”, uncompensated system. Voltage
48 V/div and current 4 A/div.
Fig. 23. Source voltage and current, phase “a”, system with passive filter and
source impedance modified. Voltage 48 V/div and current 10 A/div.
Fig. 21. Source voltage and current, phase “a”, in the system with passive filter.
Voltage 48 V/div and current 4 A/div.
Fig. 24. Source voltage and current, phase “a”. System with active and passive
filter and variation in source impedance. Voltage 48 V/div and current 4 A/div.
Fig. 22. Source voltage and current, phase “a”, system with active filter.
Voltage 48 V/div and current 4 A/div.
passive power filter was designed to eliminate source current
harmonics; the reactive power was not taken into account. The
power factor corresponding to the set load and passive filter is
0.86.
When the series active filter is connected, the source current
THD falls to 1.0%. This current waveform is shown in Fig. 22.
Now, the power factor rises to 0.99, practically achieving unity
power factor. The voltage THD in the PCC is 1.3%. Its waveform is shown in Fig. 22 with the phase “a” current. These results verify the resistive behavior of the system; voltage and current are sinusoidal and they are in phase.
Another experiment to verify the behavior of the system was
to modify the source impedance. This was changed from 3.6
and 5.8 mH to 1.3 and 2.34 mH. Fig. 23 shows the voltage
and source current waveforms at the point of common coupling
when the load is compensated with only a passive filter. The
waveforms are worse than the previous experiment. The voltage
and current THD are 5.5% and 10.8% , respectively. The power
factor is 0.95.
When the active filter is connected, the voltage THD at the
point of common coupling is 0.8% and the source current THD
is 0.9%. The power factor rises to 0.99. This waveform is shown
in Fig. 24.
Another typical situation in a power system is that corresponding to variable load. To verify hybrid filter behavior, the
resistance at the dc side is changed from 25 to 50 . Fig. 25
shows the voltage and current waveforms with the passive filter
connected. When the active filter is connected, the voltage THD
falls from 7% to 1.5% and the current THD changes from 5.7%
to 0.5%. Fig. 26 shows the waveforms.
Finally, to verify the system dynamic response experimentally, load impedance was changed and current waveform was
recorded. The APF transient performance was mainly determined by the dynamic response of the low-pass filters in the
control scheme. The control circuit was automatically implemented with MATLAB-Simulink and the toolbox Real Time
Workshop (RTW) together with the Real Time Interface (RTI)
from dSpace, which generated the code to program the control
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Fig. 25. Source voltage and current, phase “a”, system with passive filter and
variation in load. Voltage 48 V/div and current 10 A/div.
9
Fig. 28. Source currents, system without compensating, unbalanced load. 4
A/div.
Fig. 26. Source voltage and current, phase “a”. System with active filter and
variation in load. Voltage 48 V/div and current 10 A/div.
Fig. 29. Source currents, system with active filter, unbalanced load. 4 A/div.
Fig. 27. Dynamic response of the compensated system. Current 4 A/div.
board. Therefore, the low-pass filters were implemented within
a Simulink block. This block was modeled as a second order
filter with a cut-off frequency fixed to 100 Hz and the damping
factor to 0.707. It allowed a settling time of 8 ms to be achieved.
Fig. 27 shows the dynamic response of the source current
when a sudden change of load happens. The resistance at the
dc side of the three-phase rectifier changes from 50 to 25 .
The response time is about 4 cycles.
B. Case 2. Nonlinear Unbalanced Load
The nonlinear unbalanced load consisted of three
single-phase uncontrolled rectifiers with a capacitor and a
resistor connected in parallel at the dc side. The capacitor was
, however, the resistor
the same in the three phases, 2200
was different for each one. It was 16.7 for phase “a”, 25
for phase “b” and 50 for phase “c”. Fig. 28 shows the three
source currents. The THD measured was 15.6%, 38.7%, and
42.2% in each phase.
When the active filter was connected using the proposed control strategy for unbalanced loads, the source currents waveforms were almost sinusoidal and balanced, which is the aim
of the control strategy. Fig. 29 shows these currents. The THD
values are 1.8%, 1.0%, and 1.7% in each phase.
Fig. 30 shows the common connection point voltage and
source current in phase “a”. Both signals are almost sinusoidal
and in phase. When only phase “a” is considered the power
factor measured is 0.99.
VI. CONCLUSIONS
A control algorithm for a hybrid power filter constituted by a
series active filter and a passive filter connected in parallel with
the load is proposed. The control strategy is based on the dual
vectorial theory of electric power. The new control approach
achieves the following targets.
— The compensation characteristics of the hybrid compensator do not depend on the system impedance.
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10
IEEE TRANSACTIONS ON POWER DELIVERY
Fig. 30. Common coupling connection voltage and source current in phase
“a”. system with active filter. Unbalanced load. Voltage 48 V/div and current
10 A/div.
— The set hybrid filter and load presents a resistive behavior.
This fact eliminates the risk of overload due to the current harmonics of nonlinear loads close to the compensated
system.
— This compensator can be applied to loads with random
power variation as it is not affected by changes in the
tuning frequency of the passive filter. Furthermore, the reactive power variation is compensated by the active filter.
— Series and/or parallel resonances with the rest of the
system are avoided because compensation equipment and
load presents resistive behavior.
Therefore, with the proposed control algorithm, the active
filter improves the harmonic compensation features of the passive filter and the power factor of the load.
Simulations with the MATLAB-Simulink platform were performed with different loads and with variation in the source
impedance. This fact allowed an experimental prototype to be
developed. Experimental and simulation results are presented.
They allow the verification of the developed theoretical analysis.
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P. Salmerón was born in Huelva, Spain. He received
the Ph.D. degree from the Electrical Engineering
Department, University of Seville, Seville, Spain, in
1993.
In 1983, he joined the University of Seville as an
Assistant and then Associate Professor in the Department of Electrical Engineering. Since 1993, he has
been a Professor, and is currently Dean, at Escuela
Politécnica Superior, University of Huelva, Huelva,
Spain. He has joined various projects in connection
with research in power theory of nonsinusoidal systems and power control in electrical systems. His research interests include electrical power theory, electrical power systems, active power filters, and power
conversion systems.
S. P. Litrán was born in Sanlúcar de Barrameda,
Spain. He received the B.Sc. degree in automation
and industrial electronics engineering from the
University of Seville, Seville, Spain, in 2002.
Since 1989, he has been teaching circuit theory
and power electric systems with the Escuela Politécnica Superior, Department of Electrical Engineering,
University of Huelva, Huelva, Spain. His current
research includes power quality, electrical power
theory, and active power filters.
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