Download Cascaded Nine-Level Inverter for Hybrid

IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 57, NO. 8, AUGUST 2010
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Cascaded Nine-Level Inverter for Hybrid-Series
Active Power Filter, Using Industrial Controller
Alexander Varschavsky, Juan Dixon, Senior Member, IEEE, Mauricio Rotella, and Luis Morán, Fellow, IEEE
Abstract—An industrial controller, specifically designed for
two- and three-level converters, was adapted to work on an
asymmetrical nine-level active power filter (APF). The controller
is now able to make all required tasks for the correct operation
of the APF, such as current-harmonic elimination and removal of
high-frequency noise. The low switching-frequency operation of
the nine-level converter was an important advantage in the application of the industrial controller. In addition, with the nine-level
filter, switching losses were significantly reduced. The filter was
designed to work as voltage source and operates as harmonic
isolator, improving the filtering characteristics of the passive filter.
The control strategy for detecting current harmonics is based on
the “p−q theory” and the phase-tracking system in a synchronous
reference frame phase-locked loop. The dc-link voltage control
is analyzed together with the effect of controller gain and delay
time in the system’s stability. Simulations for this application
are displayed and experiments in a 1-kVA prototype, using the
aforementioned industrial controller, were tested, validating the
effectiveness of this new application.
Index Terms—Active filters, harmonic distortion, multilevel
systems, power quality.
I. I NTRODUCTION
T
HE constant increase in power electronic devices, used
by industrial and commercial consumers, has deteriorated
seriously electric power systems. More transmission losses,
power-transformer and neutral-conductor overheating, powerfactor correction-capacitor overloading, and induced noise in
control systems are only a few of the problems that harmonic
distortion may bring into home and industrial installations
[1], generating considerable economic losses to distribution
companies and end users [2].
During many years, the solution used to minimize harmonic
pollution has been tuned passive filters. However, they have
quite a few disadvantages, like fixed compensating characteristic (given only by the tuned frequencies), parallel and
series resonance with source-voltage harmonics, and filtering
characteristics strongly affected by source impedance. They are
also bulky, and they lost their effectiveness with the passage of
time [3], [4].
Several topologies of active power filters (APFs) have been
proposed [5]–[7] as a solution to passive-filter problems. Most
of the APFs that have been implemented until now are of shunt
type [8]–[11], but they are comparatively more expensive due
to its large rating of about 30%–60% of the load [12]. Even
more, they cannot compensate correctly for harmonic voltage
produced by power rectifiers with large dc-link capacitor [13].
Numerous series APF have been proposed [3], [4], [12], [14],
[15], most of them operating as hybrid, in conjunction with
shunt passive filters. The advantages of hybrid topologies are
quite significant since the series active filter can be very low
rated, between 3% and 10% [12], and the disadvantages of the
passive filters are mitigated. Another advantage of this hybrid
topology is that harmonic voltage and current-producing loads
can be effectively compensated. However, series active filters
proposed until now had been implemented in two-level PWM
based inverters, with the known disadvantages that they present,
such as high-order harmonic noise and additional switching
losses due to high-frequency commutation [16].
Multilevel inverters have become very popular in the last
few years, due to their capability to generate cleaner voltage
waves and lower switching losses [17], [18]. If the cascaded
H-bridge topology scaled in powers of three is utilized, the
number of sources and semiconductors is minimized [19]–[24].
With this topology, each H bridge operates at a lower frequency,
decreasing switching losses and permitting the use of slower
semiconductors. This paper shows that lower frequency operation of the asymmetrical converter has permitted the adaptation
of industrial controllers for filtering purposes.
II. S YSTEM D ESCRIPTION
A. System Configuration
Manuscript received October 22, 2008; revised August 19, 2009; accepted
September 26, 2009. Date of publication October 20, 2009; date of current
version July 14, 2010. This work was supported by the Comisión Nacional de
Investigación Científica y Tecnológica (CONICYT) through Project Fondecyt
1070751, ABB Chile, and Millenium Project P-04-048-F.
A. Varschavsky is with the CGE Distribución S.A., Santiago 8340434, Chile
(e-mail: [email protected]).
J. Dixon is with the Department of Electrical Engineering, Pontificia Universidad Catolica de Chile, Santiago 7820436, Chile (e-mail: [email protected]).
M. Rotella is with the ABB S.A., Santiago 7780006, Chile (e-mail: mauricio.
[email protected]).
L. Morán is with the Department of Electrical Engineering, Universidad de
Concepción, Concepción 53-C, Chile (e-mail: [email protected]).
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/TIE.2009.2034185
The circuit of Fig. 1 shows the basic topology of the system,
which is composed by three 9-level inverters connected in series
between the source and the load and a shunt passive filter tuned
at fifth and seventh harmonics. The passive filter presents a
low-impedance path to load-current harmonics and also helps
to partially correct the power factor.
B. Multilevel Inverter
Each phase of the nine-level series APF comprises two
H bridges connected at the same dc-link capacitor. The
two bridges are connected to the ac line using independent
0278-0046/$26.00 © 2010 IEEE
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IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 57, NO. 8, AUGUST 2010
Fig. 3.
Single-phase equivalent circuit for harmonics.
equal to the harmonic voltage appearing across the resistor. The
load is represented as a harmonic voltage source.
Equation (2) can be directly derived from Fig. 3 and (1)
Fig. 1. Main components of the hybrid-series APF.
is,h =
vs,h − vL,h
.
Zs + K
(2)
If K is large enough (several times Zs ), the harmonic current
is,h becomes zero, and an almost purely sinusoidal current is
drawn from the utility. The voltage at the point of common
coupling vPCC is also improved with the action of the filter,
depending only on the utility-voltage distortion instead of the
harmonic voltage of the load.
D. Harmonic-Current Detection
Fig. 2. Multilevel inverter topology (one phase).
transformers scaled in power of three, as shown in Fig. 2. More
than nine levels increases hardware complexity and does not
improve noticeably the filtering characteristics.
The H-bridge converter is able to produce three levels of
voltage at the ac side: +vdc , −vdc , and zero. The outputs of
the modules are connected through transformers whose voltage
ratios are scaled in power of three, allowing 3n levels of voltage
[23]. Then, with only two converters per phase (n = 2), nine
different levels of voltage are obtained: four levels of positive
values, four levels of negative values, and zero.
The transformer located at the bottom of the figure has the
highest voltage ratio and, with its corresponding H bridge,
is called main converter. The other transformer defines the
auxiliary converter (Aux). The main converter manages most of
the power but works at the lowest switching frequency, which
is an additional advantage of this topology.
Amplitude modulation is used to determine the output level
of the inverter, rounding the reference signal to the nearest
integer between the nine possible levels.
To detect the harmonic content of the line current, the socalled p−q theory [25] was used. According to this theory,
when three symmetrical and sinusoidal source voltages and
three asymmetrical or distorted line currents are present in a
three-phase power system, the dc components ip_dc and iq_dc
of the instantaneous active and reactive currents ip and iq
correspond to the fundamental active and reactive components
of the line current, whereas the corresponding ac components
of ip and iq , ip_ac and iq_ac , are related to the asymmetric and
harmonic components.
The complete control scheme of the APF is shown in Fig. 4.
In the diagram, it can be seen that the instantaneous active and
reactive currents ip and iq are obtained by transforming the
instantaneous source currents ia , ib , and ic (which is obtained
by subtracting both ia and ib ) by means of Clark and Park
transformations as shown in
⎡ ⎤
ia
1 − 21 − 12
2 sin ωt − cos ωt
ip
√
√
=
· ⎣ ib ⎦ .
·
3
iq
sin ωt
3 cos ωt
0
− 23
2
i
c
(3)
C. Operation Principle
In order to eliminate line-current harmonics, the APF is
controlled to present very high impedance to these currents.
This is achieved by generating a voltage proportional to the
harmonic current is,h . To keep the dc-link voltage constant, it is
necessary to add to the reference signal a compensating signal
of fundamental frequency, being the reference voltage to each
phase as shown in
∗
∗
= K · is,h + vAF,f
.
vAF
(1)
Fig. 3 shows an equivalent circuit for the harmonics, where
the APF is represented as a resistor of value K since vAF,h is
A low-pass filter (LFP) then extracts the dc components of
ip and iq , resulting in ip_dc and iq_dc . A compensating dc-link
voltage is subtracted from the fundamental active current ip ,
and the resulting signal, together with iq_dc are transformed
back to a three-phase system by the inverse Park and Clark
transformations as shown in (4). The cutoff frequency of the
LPF used in this paper was 10 Hz
⎤
⎡ ⎤ ⎡
1
ia
√0
sin ωt
cos ωt
i
3 ⎦
⎣ ib ⎦ = 2 · ⎣ − 21
·
· p .
2√
−
cos
ωt
sin
ωt
iq
3
ic
− 21 − 23
(4)
VARSCHAVSKY et al.: CASCADED NINE-LEVEL INVERTER FOR HYBRID-SERIES ACTIVE POWER FILTER
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Fig. 4. p−q-based control-system scheme of the APF.
Fig. 5.
DC-link voltage-control block diagram.
Then, this three-phase reference signals, which correspond to
the fundamental active and reactive components, are subtracted
from the line currents; In this way, the harmonic-current component plus the dc-link compensating voltage are obtained. A
K factor is then multiplied to the output signal of the system so
that the APF acts as a high-harmonic impedance.
To get the reference signals “sin” and “cos” shown in Fig. 4,
a synchronous reference frame phase-locked loop (PLL) was
used [26]. A low-bandwidth proportional–integral (PI) controller was used in the PLL control loop so that the reference
signals stay clear and in phase with the source, even under the
presence of source harmonics.
where Is is the effective value of line current. Doing a linearization of (5) at the operation point vdc (t) = vdc_o and ie (t) =
ie_o , where vdc_o is the reference voltage from the capacitor,
the transfer function G(s) can be obtained as follows:
√
3 · K · Is · cos(φ)
Δvdc
=
.
(6)
G(s) =
Δie
s · C · vdc_0
Since the controller is a proportional plus integral one, its
transfer function is
1
C(s) = KP · 1 +
.
(7)
TI · s
Then, the closed-loop transfer function of the dc-link control
system is as shown in
√
3KP KIs cos φ
·s+
Cvdc_0
√
3KP KIs cos φ
·s
Cvdc_0
Δvdc
=
Δvref
s2 +
√
3KP KIs cos φ
TI Cvdc_0
√
P KIs cos φ
+ 3K
TI Cvdc_0
.
(8)
E. DC-Link Voltage Control
The capacitor voltage at the dc-link must remain constant
so that the APF can work properly. This voltage should not
fluctuate because the APF should neither supply nor absorb
active power from the utility. However, due to commutation,
conductance, and own-capacitor losses plus control system
delays, dc-link voltage fluctuations occur. To compensate the
voltage variations, the filter operates as a controlled rectifier,
transferring a little amount of active power from the ac to the dc
side of the inverter. This is achieved by generating a sinusoidal
voltage signal in phase with the line current, whose product is
the transferred active power.
Owing to the fact that the three inverters share the dc capacitor, only one control system is needed, which output signal is
added to the fundamental active component of the line current
ip_dc obtained as was shown in Fig. 4.
Fig. 5 shows the block diagram of a dc-link control loop,
where C(s) is the transfer function of the PI controller and G(s)
the transfer function between the capacitor voltage vdc and the
compensation current generated by the PI controller ie .
The transfer function G(s) can be derived directly doing a
power balance between the ac and dc side of the three inverters.
This yields to
√
3 · K · ie (t) · Is · cos φ = C · vdc (t) ·
d
vdc (t)
dt
(5)
Equation (8) corresponds to a second-order system, where
the damping factor ζ and natural angular velocity ωn can be
calculated from (9) and (10). Since the poles of the system are
always at the left side of the s-plane, the system is always stable
√
3 · KP · TI · K · Is · cos(φ)
1
(9)
ζ=
2
C · vdc_0
√
3 · KP · K · Is · cos(φ)
.
ωn =
TI · C · vdc_0
(10)
For simulations and experiments, ζ = 1 and ωn = 2π ·
100 rad/s were used. In this way, a critically damped response,
where minimal voltage oscillation happens, is obtained.
F. Stability Analysis for Harmonic Currents
The delay times introduced by the controller, large gain
K, and high system stiffness seriously affect the active-filter
stability [27].
Assuming purely inductive source impedance, (11) can be
directly derived from Fig. 3
is,h =
vs,h − vL,h − vAF,h
.
s · Ls
(11)
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IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 57, NO. 8, AUGUST 2010
TABLE I
PASSIVE F ILTERS U SED
Fig. 6. Harmonic-current-control diagram.
Fig. 7. Series APF prototype used in the experiments.
If a delay time τ is introduced by the controller, the harmonic
voltage generated by the filter in Laplace domain is
vAF,h = K · is,h · e−sτ .
(12)
Hence, the closed-loop block diagram of the harmonic control system can be represented as shown in Fig. 6.
From the Nyquist stability criterion, the selected gain K of
the filter must satisfy (13) so that the system will be stable
K<
π
· τ · Ls .
2
(13)
For a typical line inductance Ls = 0.02 per unit (p.u.) in a
50-Hz system and a gain K = 2, the delay time should be less
than 50 μs, which will ensure system stability.
III. S IMULATIONS AND E XPERIMENTAL R ESULTS
The proposed hybrid-series APF was simulated in
MATLAB/Simulink, using a source impedance of 2% p.u.
For the experiments, a 1-kVA/110-V 50-Hz system using an
IGBT-based multilevel inverter was implemented. All the
control tasks in the experiments were performed by the aforementioned industrial controller, which combines a 600-MHz
CPU and a large field-programmable gate array (FPGA). The
controller and the complete experimental system are shown in
Fig. 7.
The high-speed control tasks are programmed into the industrial controller using the MATLAB/Simulink. This allows implementing the same model used in simulations for real-world
operation, ensuring an error-free and fast implementation. The
complete control loop is executed by the controller every 50 μs.
Fig. 8. Simulated transient response under APF connection. (a) Source voltage vs . (b) Line current is . (c) Load current iL . (d) Active-filter voltage vAF .
(e) Capacitor voltage vdc .
A gain K = 24, equivalent to 2 p.u. was used in both
simulation and experiments. The turn ratios of the output transformers were 220 : 18 and 220 : 54 for the auxiliary and main
transformers, respectively. The dc-link capacitor was selected
to be C = 4700 μF. The load connected to the six-pulse diode
rectifier was RL = 22 Ω, and CL = 4700 μF.
The values of the shunt passive filters can be seen in Table I.
The quality factor Q of the passive filters is very low in
comparison with industrial passive filters that operate without
an active section. This can be an advantage considering that the
cost of passive filters with a lower Q factor is lower. The passive
filters were also slightly off tuned, decreasing its performance
even more.
In the simulations shown in Fig. 8, the active filter starts to
operate at t = 0.08 s. It can be seen that the source voltage
and line current are improved with a negligible delay, changing
to an almost purely sine wave. As the load current iL does
not change with APF operation, the rectifier operation is not
being affected. It is quite important to mention that the maximum switching frequency of the main converter (which manages 70% of the kilovolt-ampere) is only 500 Hz. This small
switching frequency allows using the APF in the high-power
range, using the relatively slow gate-turn-off thyristor. On the
other hand, the Aux, which only manages 30% of the power,
VARSCHAVSKY et al.: CASCADED NINE-LEVEL INVERTER FOR HYBRID-SERIES ACTIVE POWER FILTER
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Fig. 9. Line-current and source-voltage harmonic contents (a) without filters,
(b) with passive filters, and (c) with active and passive filters.
switches at a maximum frequency of only 2 kHz. For a very
high power application using two-level converters and PWM to
compensate, the switching frequency must be at least 10 kHz
to get a similar result. Following the analysis given in Fig. 8,
a considerable fundamental voltage appears at the terminals of
the active filter, which is due to resistive losses at the ac side
of the filter transformers. This problem can be improved using
better quality transformers. The capacitor voltage vdc follows
its reference, and minimal fluctuations appear when the filters
start their operation.
The harmonic content and total harmonic distortion (THD)
of line current and source voltage without filters, only with
passive filters and with both passive and active sections, are
shown in Fig. 9. It can be seen that the line-current THD
dramatically improves with the APF, passing from 20% to
2.4%, and hence, all harmonics goes to almost zero. The THD
of the line current without passive filters was 34%. The sourcevoltage THD improves from 2.3% to 0.65% when the APF
starts its operation. The improvement in this case depends on
utility stiffness; if the system is very strong, the source voltage
is not too affected by harmonic currents flowing to the load, and
the action of the APF cannot be seen clearly. In the other case,
if the system is weak, line current affects the source voltage
noticeably, and the effect of the APF is more evident.
In Fig. 10, the response of the active filter under a load
change can be seen. The load of the rectifier changes from
RL = 22 Ω to RL = 44 Ω, without affecting neither the sourcecurrent clearness nor dc voltage stability.
Experimental results corroborate the successful operation of
the active filter shown in the simulations. Fig. 11 shows the
transient response when APF starts to operate. The line current immediately becomes sinusoidal and the capacitor-voltage
behavior is as expected.
The reduction in harmonic content, as seen on Fig. 12, is also
similar to the simulated one, but in the experiments, the effect
of passive filters is greater, the line-current THD, with only the
passive filters connected, being 15%. This is due to bigger line
inductance introduced by the autotransformer used to connect
the system to the grid.
Fig. 10. Simulated transient response after load change. (a) Source voltage vs . (b) Line current is . (c) Load current iL . (d) Active-filter voltage vAF .
(e) Capacitor voltage. vdc .
Fig. 11. Experimental transient response under APF connection. From top to
bottom: Active-filter voltage vAF , line current is , and capacitor voltage vdc .
Fig. 12. Left: line-current-harmonic content without APF. Right: line-currentharmonic content with APF operating.
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IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 57, NO. 8, AUGUST 2010
capacitor voltage returns to its reference in two cycles, with
minimum variation when the load changes. In the experimental
results, the load was increased from RL = 44 Ω to RL = 22 Ω.
IV. C ONCLUSION
A hybrid-series AFP based on a low-rated multilevel inverter,
acting as a high-harmonic impedance, and a shunt passive filter
acting as a harmonic-current path, were developed and tested.
All the control tasks were programmed in an industrial controller, which was adapted for this particular application. With
the proposed control algorithm and taking advantage of the
multilevel topology of the active filter, almost purely sinusoidal
currents and voltages were achieved, without the usual highfrequency content present in PWM inverters
The proposed filter, which compensate harmonic-voltage
source generated by contaminating loads, was simulated and
tested using MATLAB/Simulink. It has been demonstrated that
the filter responds very fast under connections and sudden
changes in the load conditions, reaching its steady state in about
two cycles of the fundamental.
R EFERENCES
Fig. 13. Line current and active-filter voltage close-up. Up: Only with passive
filter. Bottom: With both active and passive filters operating.
Fig. 14. Experimental transient response under load change. From top to
bottom: Active filter voltage vAF , line current is , and capacitor voltage vdc .
A detailed waveform of the line current and active-filter
voltage, without and with the APF, can be seen in Fig. 13, where
it becomes evident the effect of the APF. In addition, no highfrequency commutation content, like the ones introduced by
PWM-based converters, is present. The importance of this feature is that this kind of filter behaves almost like an ideal APF.
In Fig. 14, the response of the series active filter under load
change is shown. The line current remains sinusoidal and the
[1] W. Mack Grady and S. Santoso, “Understanding power system harmonics,” IEEE Power Eng. Rev., vol. 21, no. 11, pp. 8–11, Nov. 2001.
[2] H. Rudnick, J. Dixon, and L. Moran, “Delivering clean and pure power,”
IEEE Power Energy Mag., vol. 1, no. 5, pp. 32–40, Sep./Oct. 2003.
[3] F. Z. Peng, H. Akagi, and A. Nabae, “A new approach to harmonic
compensation in power systems—A combined system of shunt passive
and series active filters,” IEEE Trans. Ind. Appl., vol. 26, no. 6, pp. 983–
990, Nov./Dec. 1990.
[4] Z. Wang, Q. Wang, W. Yao, and J. Liu, “A series active power filter
adopting hybrid control approach,” IEEE Trans. Power Electron., vol. 16,
no. 3, pp. 301–310, May 2001.
[5] B. Singh, K. Al-Haddad, and A. Chandra, “A review of active filters for
power quality improvement,” IEEE Trans. Ind. Electron., vol. 46, no. 5,
pp. 960–971, Oct. 1999.
[6] F. Z. Peng, “Harmonic sources and filtering approaches,” IEEE Ind. Appl.
Mag., vol. 7, no. 4, pp. 18–25, Jul./Aug. 2001.
[7] H. Akagi, “Modern active filters and traditional passive filters,” Bull. Pol.
Acad. Sci. Tech. Sci., vol. 54, no. 3, pp. 255–269, Sep. 2006.
[8] B. Singh and J. Solanki, “Implementation of an adaptive control algorithm
for a three-phase shunt active filter,” IEEE Trans. Ind. Electron., vol. 56,
no. 8, pp. 2811–2820, Aug. 2009.
[9] B. Kedjar and K. Al-Haddad, “DSP-based implementation of an LQR
with integral action for a three-phase three-wire shunt active power
filter,” IEEE Trans. Ind. Electron., vol. 56, no. 8, pp. 2821–2828,
Aug. 2009.
[10] F. D. Freijedo, J. Doval-Gandoy, O. Lopez, P. Fernandez-Comesana, and
C. A. Martinez-Penalver, “Signal-processing adaptive algorithm for selective current harmonic cancellation in active power filters,” IEEE Trans.
Ind. Electron., vol. 56, no. 8, pp. 2829–2840, Aug. 2009.
[11] E. Lavopa, P. Zanchetta, M. Sumner, and F. Cupertino, “Real-time estimation of fundamental frequency and harmonics for active shunt power
filters in aircraft electrical systems,” IEEE Trans. Ind. Electron., vol. 56,
no. 8, pp. 2875–2884, Aug. 2009.
[12] J. W. Dixon, G. Venegas, and L. A. Moran, “A series active power filter
based on a sinusoidal current-controlled voltage-source inverter,” IEEE
Trans. Ind. Electron., vol. 44, no. 5, pp. 612–620, Oct. 1997.
[13] F. Z. Peng, “Application issues of active power filters,” IEEE Ind. Appl.
Mag., vol. 4, no. 5, pp. 21–30, Sep./Oct. 1998.
[14] S. Bhattacharya and D. Divan, “Design and implementation of a hybrid
series active filter system,” in Proc. Power Electron. Spec. Conf., 1995,
vol. 1, pp. 189–195.
[15] A. Hamadi, S. Rahmani, and K. Al-Haddad, “A novel hybrid series
active filter for power quality compensation,” in Proc. Power Electron.
Spec. Conf., 2007, pp. 1099–1104.
[16] J. Dixon and L. Moran, “Multilevel inverter, based on multi-stage connection of three-level converters scaled in power of three,” in Proc. IEEE
IECON, 2002, vol. 2, pp. 886–891.
VARSCHAVSKY et al.: CASCADED NINE-LEVEL INVERTER FOR HYBRID-SERIES ACTIVE POWER FILTER
[17] J. Rodriguez, J.-S. Lai, and F. Z. Peng, “Multilevel inverters: A survey
of topologies, controls, and applications,” IEEE Trans. Ind. Electron.,
vol. 49, no. 4, pp. 724–738, Aug. 2002.
[18] S. Daher, J. Schmid, and F. L. M. Antunes, “Multilevel inverter topologies
for stand-alone PV systems,” IEEE Trans. Ind. Electron., vol. 55, no. 7,
pp. 2703–2712, Jul. 2008.
[19] S. Kouro, J. Rebolledo, and J. Rodriguez, “Reduced switching-frequencymodulation algorithm for high-power multilevel inverters,” IEEE Trans.
Ind. Electron., vol. 54, no. 5, pp. 2894–2901, Oct. 2007.
[20] Y. Liu and F. L. Luo, “Trinary hybrid 81-level multilevel inverter for
motor drive with zero common-mode voltage,” IEEE Trans. Ind.
Electron., vol. 55, no. 3, pp. 1014–1021, Mar. 2008.
[21] J. Dixon and L. Moran, “A clean four-quadrant sinusoidal power rectifier
using multistage converters for subway applications,” IEEE Trans. Ind.
Electron., vol. 52, no. 3, pp. 653–661, Jun. 2005.
[22] F.-S. Kang, S.-J. Park, M. H. Lee, and C.-U. Kim, “An efficient multilevelsynthesis approach and its application to a 27-level inverter,” IEEE Trans.
Ind. Electron., vol. 52, no. 6, pp. 1600–1606, Dec. 2005.
[23] M. E. Ortuzar, R. E. Carmi, J. W. Dixon, and L. Moran, “Voltage-source
active power filter based on multilevel converter and ultracapacitor dc
link,” IEEE Trans. Ind. Electron., vol. 53, no. 2, pp. 477–485, Apr. 2006.
[24] A. Chen and X. He, “Research on hybrid-clamped multilevel-inverter
topologies,” IEEE Trans. Ind. Electron., vol. 53, no. 6, pp. 1898–1907,
Dec. 2006.
[25] H. Akagi, Y. Kanazawa, and A. Nabae, “Instantaneous reactive power
compensators comprising switching devices without energy storage components,” IEEE Trans. Ind. Appl., vol. IA-20, no. 3, pp. 625–630,
May 1984.
[26] S.-K. Chung, “A phase tracking system for three phase utility interface
inverters,” IEEE Trans. Power Electron., vol. 15, no. 3, pp. 431–438,
May 2000.
[27] S. Srianthumrong, H. Fujita, and H. Akagi, “Stability analysis of a series
active filter integrated with a double-series diode rectifier,” IEEE Trans.
Power Electron., vol. 17, no. 1, pp. 117–124, Jan. 2002.
Alexander Varschavsky was born in Santiago,
Chile. He received the B.S. degree in electrical engineering and the M.Sc. degree from the Pontificia
Universidad Católica de Chile, Santiago, in 2008.
From 2007 to 2008, he was a Student Researcher
with the “Núcleo de Electrónica Industrial y Mecatrónica,” Santiago, where he was involved with the
design and application of power electronics devices.
Currently, he is an Engineer with CGE Distribución,
Santiago, a Chilean utility company. His research
interests are active power filters, electrical machines,
power electronics, and power systems.
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Juan Dixon (M’90–SM’95) was born in Santiago,
Chile. He received the B.S. degree in electrical engineering from the Universidad de Chile, Santiago,
Chile, in 1977 and the M.S.Eng. and Ph.D. degrees
from McGill University, Montreal, QC, Canada, in
1986 and 1988, respectively.
In 1976, he was with the State Transportation
Company in charge of trolleybuses operation. In
1977 and 1978, he was with the Chilean Railways
Company. Since 1979, he has been with the Electrical Engineering Department, Pontificia Universidad Catolica de Chile, Santiago, where he is currently a Professor. He has
presented more than 70 works in international conferences and has published
more than 30 papers related with power electronics in IEEE Transactions and
IEE proceedings. His main areas of interests are in electric traction, power
converters, PWM rectifiers, active power filters, power-factor compensators,
multilevel, and multistage converters. He has consulting work related with
trolleybuses, traction substations, machine drives, hybrid electric vehicles, and
electric railways. He has created an electric vehicle laboratory where he has
built state-of-the-art vehicles using brushless dc machines with ultracapacitors
and high specific-energy batteries.
Mauricio Rotella received the Electrical Engineer
Professional and Master of Science degrees from
Pontificia Universidad Católica de Chile, Santiago,
Chile, in 1999 and 2006, respectively.
Since 1998, he has been working with ABB in various positions, including product manager for large
drives in ABB Chile and Regional Sales Manager
for Latin America MV Drives in ABB Switzerland.
Currently, he is with Automation Products Local
Division in ABB Chile.
Luis Morán (F’05) was born in Concepción, Chile.
He received the Ph.D. degree from Concordia University, Montreal, QC, Canada, in 1990.
Since 1990, he has been with the Electrical Engineering Department, University of Concepción,
Concepción, where he is a Professor. He has written and published more than 30 papers in active
power filters and static Var compensators in IEEE
Transactions. His main areas of interests are in ac
drives, power quality, active power filters, FACTS,
and power protection systems.
Dr. Morán is the principal author of the paper that got the IEEE Outstanding
Paper Award from the Industrial Electronics Society for the best paper published in the IEEE T RANSACTION ON I NDUSTRIAL E LECTRONICS during
1995, and the coauthor of the paper that was awarded in 2002 by the IAS Static
Power Converter Committee.