335 A three-level quasi-two-stage three

335 A three-level quasi-two-stage three
International Journal of Multidisciplinary Research and Development
International Journal of Multidisciplinary Research and Development
Online ISSN: 2349-4182, Print ISSN: 2349-5979, Impact Factor: RJIF 5.72
Volume 4; Issue 7; July 2017; Page No. 335-344
A three-level quasi-two-stage three-phase PFC converter
Bhagyashri C Chavan, 2 Netra M Lokhande
Me Student at Tssm’s Bscoer, Electrical Engineering, Savitribai Phule Pune University, Pune, Maharashtra, India
Professor at Tssm’s Bscoer, Electrical Engineering, Savitribai Phule Pune University, Pune, Maharashtra, India
This paper presents a three-level two-stage Three-phase power factor correction (PFC) converter that has flexible output voltage
and improved conversion efficiency. The proposed PFC converter features sinusoidal input current, three-level output
characteristic, and a wide range of output DC voltages, and it will be very suitable for high power applications where the output
voltage can be either lower or higher than the peak AC input voltage, e.g. plug-in hybrid electric vehicle (PHEV) charging
Moreover, the involved DC/DC buck conversion stage may only need to process partial input power rather than full scale of the
input power, and therefore the system overall efficiency can be much improved. Through proper control of the buck converter, it is
also possible to mitigate the double-line frequency ripple power that is inherent in a three-phase AC/DC system, and the resulting
load end voltage will be fairly constant. The dynamic response of this regulation loop is also very fast and the system is therefore
insensitive to external disturbances. In this paper, the operation of the new converter is explained, its features and design are
discussed in simulation & experimental results, and its operation is confirmed with experimental results obtained from a prototype.
Keywords: PFC converter, three level characteristics, active power decoupling, conduction losses, current regulation, power factor
correction, harmonic distortion, discontinuous conduction mode
1. Introduction
Three phase rectifiers have a wide range of application many
industrial as well as residential applications like
electrochemical processes, arc furnaces, adjustable speed
drives, variable speed drive, electric vehicle (EV) chargers,
and power supplies for consumer electronics. With the ever
increasing use of power electronic equipment, employing
rectifiers is unavoidable in many applications. The major
problem with the conventional rectifiers is harmonic pollution
. Today’s standards like International Electro-technical
Commission (IEC) 61000-3-2 limit the harmonics produced
by these devices as long as their power ratings exceed 75W [2].
Therefore, to satisfy the standards, power-factor-correction
(PFC) converters are used for ac–dc conversion. The
conventional PFC converter is a boost converter, and thus, the
output voltage must be greater than the input voltage [3]. In
spite of this problem, this converter is widely used because of
its simplicity.
The most common approach to PFC is to use two-stage power
conversion schemes. These two-stage schemes use a front-end
ac–dc converter stage to perform ac–dc conversion with PFC
with the output of the front-end converter fed to a back-end
dc–dc converter stage that produces the desired isolated dc
output voltage [4]. The front-end converter for various
applications must achieve high power factor, low harmonic
distortion, high efficiency, high power density, high reliability
and low electromagnetic interference (EMI) noise. To reduce
the cost of the front-end converter, the PFC stage must be
inexpensive, while still complying with standards for
harmonic distortion.
That the first stage of each module is used to perform the PFC
function to meet harmonic current standards such as the IEC
61000-3-2, while the second-stage DC/DC converter regulates
the DC output voltage of the system and guarantees system
current sharing.
In large number of applications, like offline low-voltage
power supplies, where it is preferred to have the PFC output
voltage lower than the input ac voltage, a buck-type converter
is required. However, the input current of buck converter is
discontinuous, and to filter this current, another passive filter
must be used at the buck converter input. Presently, Threephase power factor correction (PFC) converters are a very
popular solution to ensure the compliance of such regulations
because of their simplicity, cost effectiveness and good current
shaping capability. However, most of the existing Three-phase
PFC converters are of boost type and can only provide an
output voltage that is higher than the peak voltage of the AC
input [5-6]. Wide range of output voltage is indeed desired in
some applications like in plug-in hybrid electric vehicle
(PHEV) charging systems where the terminal voltage of
battery packs may vary between 100V to 600V, In this case, a
second stage DC/DC buck converter has to be implemented to
further step down the PFC output voltage, which undoubtedly
decreases the system overall efficiency.
2. Literature Review
In order to provide flexible DC output voltages, PFC
converters with buck-boost capabilities have been studied in
the literatures and they are usually based on buck-boost, fly
back, Cuk, and Single-ended primary inductance converter
(SEPIC) topologies, and can be derived in both non-isolated
and isolated versions [7-9]. A common problem for these
topologies is that there is no direct energy transfer path during
power conversion and all input power must be processed by
active switches and stored by intermediate passive
components (either inductors or capacitors) before being
International Journal of Multidisciplinary Research and Development
supplied to the end loads [10]. This indicates that the
components will be working under increased voltage/current
stresses, which may consequently lead to decreased power
density and conversion efficiency.
In order to improve the performance of Cuk and SEPIC based
PFC topologies, their bridgeless variants have recently been
proposed in [11-13] with most of them being operated in
discontinuous conduction mode (DCM). In this case, the PFC
converter can be constructed with less semiconductor switches
and the on-state conduction losses can be reduced. The
switching losses are reduced as well due to their DCM
operation. However, the main power switches in these
bridgeless topologies are still under high voltage stress and the
DCM operation also implies that they are only suitable for
relatively low power applications because of the high peak
current in the boost inductor.
In view of this, AC/DC converters with direct buck capability
are highly desired in high power PHEV battery charger
applications and a buck type PFC topology, named as Swiss
Rectifier has already been proposed in [14, 15] for three-phase
AC/DC systems.
The bridgeless derivative of the buck PFC was also proposed
in [18] to further improve its conversion efficiency.
Unfortunately, such buck PFC converters may inherently
subject to a so-called “dead angle” limitation when the input
voltage is lower than the output voltage. The AC side input
current cannot be regulated to be purely sinusoidal and unity
power factor is not achievable. An improved buck PFC
converter with high power factor is proposed in [19], where an
auxiliary switch and two diodes are added in the circuit to
provide current regulation during the “dead angle” period.
Although the power factor can be improved, the input current
waveform is still not sinusoidal and therefore, they may only
be suited for low power applications (less than 1kW), e.g.
laptop adapter, TV sets power supplies. Another buck PFC
converter with power decoupling capability has recently been
proposed in [20], and it features high quality input current as
well as ripple free output voltage. However, the limitation of
this topology is that, its output voltage must be lower than half
of the peak AC input voltage
Previously proposed three-phase single-stage ac–dc
converters, however, have at least one of the following
drawbacks that have limited their widespread use.
1. They are implemented with three separate ac–dc singlestage modules [13, 14].
2. The converter components are exposed to very high dc bus
voltages so that switches and bulk capacitors with very
high voltage ratings are required [16-17].
3. The input currents are distorted and contain a significant
amount of low-frequency harmonics because the converter
has difficulty performing PFC and dc–dc conversion
simultaneously [16].
4. The output inductance must be very low, which makes the
output current to be discontinuous. This results in a very
high output ripple so that secondary diodes with high peak
current ratings and large output capacitors to filter the
ripple are needed [13, 17].
5. Most of them are in discontinuous conduction mode at the
input and need to have a large input filter to filter out large
high-frequency harmonics [13, 15, 17, 22]
This paper presents a new interleaved three-phase two-stage
rectifier that does not have any of these drawbacks. This
topology has a high efficiency single-phase PFC converter that
features sinusoidal input current, three-level output
characteristic and flexible output DC voltage. Its attractiveness
is that, in case of buck operation mode, the embedded
bidirectional DC/DC converter may only need to process
partial input power rather than full scale of the input power,
and therefore its conversion efficiency can be much improved
as compared with the conventional two-stage solution. Also,
the PFC stage exhibits three-level output voltage, and the
dV/dt across the switches are reduced, so as the switching
losses. An added benefit of this converter is that, the
fluctuating 100/120Hz harmonic power in the single-phase
system can be almost diverted into the dc-link capacitor
through proper control design, and the load voltage will be
fairly constant.
In this paper, the operation of the new converter is explained,
its features and design are discussed and its operation is
confirmed with simulation & experimental results obtained
from a prototype.
3. System Description
The circuit diagram of the proposed three-phase AC/DC
converter is shown in Fig. 1, which consists of a standard
diode rectifier bridge, a three-level PFC, and a bidirectional
DC/DC converter. The PFC stages are connected with two DC
buses, i.e. a low voltage DC bus that directly supplies power
to the load, and a high voltage DC bus that supports threelevel operation and absorbs system harmonic power. Power
Factor increases in two stages, First stage consist of two
switching device Q1 & Q2 (MOSFET’s).Q1 & Q2 for charging
& discharging purpose. Diode D1 for reverse protection
purpose & one inductor Lin which is inrush current limiting
inductor. Diode D2 also for reverse current protection. CL & RL
loads of stage first stages. Second stage consists of another
one inductor Ldc through which center out-put is given to
second stage. It consist of another switching device Q3 & Q4,
for providing smooth out put voltage, Q 3 & Q4 provide ripple
power consumption during both operating period. CH is the
high output load. In order to control the PFC & intermittent
operation of Q1 & Q2 impose the disturbance to the system, PI
controller i.e. AVR microcontroller is used. For isolation
purpose opt coupler is used. The IRF630 is high voltage, high
speed power MOSFET drivers with independent high and low
side referenced output channels. The floating channel can be
used to drive an N-channel power MOSFET in the high side
configuration which operates up to 500 or 600 volts.
International Journal of Multidisciplinary Research and Development
Fig 1: Circuit diagram of the proposed three-level PFC converter
4. System Operation
4.1 Operating stage first
The proposed three-level PFC has a wide range of output
voltages and it can function as either a buck or a boost
converter. During buck operation, there are two operation
modes for Q1 and Q2. When the low DC bus voltage or
simply the load voltage VL is higher than the instantaneous
input voltage Vin|sinωt|, where Vin is the peak value of input
voltage and ω is the fundamental angular frequency, Q2 will
be always on. Q1 and D1 then form up a standard boost PFC
that directly converts input power for DC load consumption,
and the converter pole voltage VAB will be changed between 0
and VL. In order to realize PFC function, the duty cycle of Q1
should comply with,
It is the basic equation for a boost PFC. It should be noted
that, in this operation period, Q3 and Q4 of the buck converter
theoretically do not need to switch because all input power can
be directly supplied into the load through D1 and Q2.
However, in order to obtain a smooth output voltage, Q3 and
Q4 still need to work and provide ripple power compensation
during this operation period.
4.2 Operating stage second
In the second operation interval when VL is less than
Vin|sinωt|, Q1 remains off. Q2 and D2 will modulate and form
up another boost PFC. In this case, the converter pole voltage
VAB is changing between VL and the high DC bus voltage VH.
Again, to ensure sinusoidal input current and unity power
factor, the duty cycle of Q2 must comply with,
Intuitively, when D2 is conducting, excessive input power
will be flowing into the dc-link capacitor CH and this high bus
voltage will be subsequently stepped down by the
bidirectional DC/DC converter to cater for load consumption,
and this is the root reason that why the DC/DC converter may
only process partial input power and higher conversion
efficiency can be obtained through the proposed topology. The
idealized operating waveforms during these two modes
presented in Fig. 2. In order to ensure smooth transition
between the low and high voltage level commutations, an
offset is injected into the carrier of the pulse-width modulation
(PWM) for Q2 as shown in Fig. 2. As a result, a unified
reference signal Vm can be derived to simultaneously
modulate Q1 and Q2, which is written as,
Compared with the conventional boost PFC, the proposed
converter will have slightly higher conduction losses because
of the series connection of Q2 and D1. However, its switching
losses can be greatly reduced due to its three-level output that
splits the high DC bus voltage into two low voltage portions.
Moreover, efficiency gain from the DC/DC converter is also
significant because it only converts the input power that flow
through D2.
International Journal of Multidisciplinary Research and Development
Fig 2: Idealized operating waveforms for the proposed three-level PFC converter.
To estimate the percentage of input power that is converted by
this buck stage, it is assumed that the power converter is
lossless and harmonic free. In this case, the instantaneous
input power from AC side will be,
Iin is the peak value of boost inductor current. If the PFC is
commutating at high voltage levels, part of the input power
will be directly supplied into the load when Q2 is on, and it
can be found as,
Plotting (4) and (5) will give rise to the time domain
waveforms of power distribution shown in Fig. 3, and it is
clear that the shaded area enclosed by pin and pbatt_H
indicates the active power pdc that needs to be processed by
the buck converter.
Fig 3: Instantaneous power distribution in the PFC converter and the buck converter, given fixed gird voltage, output voltage, and dc-link
In addition to the buck operation, the proposed PFC can also
function as a boost and this operation mode is triggered when
VIN<VL<VH. In this case, the modulation scheme discussed
above is still applicable. According to (2), the duty cycle of Q 2
International Journal of Multidisciplinary Research and Development
will be greater than 1, implying that Q2 is always on.
Therefore, the proposed circuit is simplified as a conventional
two-level PFC that is comprised of Q1 and D1 only, and the
buck converter is only used for ripple power compensation.
5. System Controller Design
The control system of the proposed three-level AC/DC
converter will be relatively more complicated than that of a
conventional boost PFC, because it requires at least two
voltage control loops to regulate the output voltage VL and the
dc-link voltage VH, respectively. Also, the intermittent
operation of Q1 and Q2 imposes a disturbance to the system,
and a fast control loop must be designed to reject this periodic
disturbance. In order to realize these control objectives, two
independent control loops are designed for controlling the
PFC stage.
Fig 4: Circuit diagram of controller circuit for PFC converter.
Fig. 4 consist of PI controller, microcontroller AVR require
5volt Supply, which is provides by 230/12 volt transformer,
this 12 volt transformer output voltage can be regulated in 5
volt by the voltage regulator. Gate pulses to Q1, Q2, Q3 & Q4
can be provides from the out-put port of microcontroller PB0,
PB 1, PB 2, PB3.
In order to realize these control objectives, must be designed
to reject this periodic disturbance. Two independent control
loops are designed for controlling the PFC stage and the buck
stage, respectively
Where Kpv is the proportional gain to adjust control
bandwidth, and τv is the time constant of the integral term to
achieve high DC compensation gain.
In order to prevent the dc-link ripple voltage from distorting
the reference of inner current control loop, a second order
notch filter tuned at 2ω is added at the output of the PI
5.1 PFC Converter Control
A classic cascaded control structure is employed to regulate
the PFC converter. Its outer voltage control loop is tasked at
balancing input and output power, and the dc-link voltage VH
is chosen as the control variable because the charging power
into the dc-link capacitor CH is directly proportional to input
power as long as VL, Vin, and VH are fixed. This voltage
control loop will also maintain the average value of VH to be
constant, whereas its instantaneous value is not necessary to
be constant, because the dc-link capacitor CH has to absorb the
double line frequency harmonic in this single-phase system.
The control loop is therefore of slow response and its control
bandwidth is set below 20Hz as per usual design, and this is
realized by tuning the parameters of a proportional-integral
(PI) regulator Gv(s) as follow,
Where K2 is a coefficient that determines the quality factor of
this notch filter. Large K2 can give rise to more attenuation of
double line frequency harmonic, but in the meantime, it may
reduce the phase margin of the control loop, and thus
deteriorate system dynamic response. The transfer function of
duty cycle-to-inductor current Gid_PFC(s) can be simply
regarded as a first order inertial element in the high frequency
through the small signal modeling approach, and in this case it
can be written as,
where Vdc is the output voltage that may change between VL
and (VH-VL), depending on the operation mode of the PFC. It
is worth noting that this voltage change is undesired in the
system, because it may give rise to a variable bandwidth of the
current control loop and affect its regulation performance. In
International Journal of Multidisciplinary Research and Development
order to have a fixed control bandwidth for the inner current
loop, a dynamic gain compensator is implemented as shown in
the right bottom part of Fig. 5, and an upper saturation is set to
limit the gain value Gdy in case that VL is approaching VH. In
this case, the inner current loop can be easily controlled by
another PI regulator,
where Kpc is its proportional gain and τc is the time constant.
These two coefficients should be tuned such that the
bandwidth of the current control loop is around one tenth of
the system switching frequency. In order to achieve accurate
current tracking and make the control system robust against
line voltage change, a duty cycle feed-forward control scheme
is also implemented in the current loop.
5.2 Buck Converter Control
As mentioned earlier, the output voltage of the buck converter
should be as constant as possible because it is directly
connected to end loads. Therefore, a single voltage control
loop is designed for this power stage to expedite its dynamic
response and also to save a current transducer. Another reason
for pursuing fast response of this voltage control loop is that it
has to reject the periodic disturbance induced by its
intermittent operation. the equivalent load resistance Rload is
much larger than the ESRs and the filter inductance Ldc, the
control duty cycle-to-output voltage transfer function Gvd_dc(s)
of the bidirectional buck converter can be derived as,
where ωo is the LC resonant frequency introduced by the
output filter. RCL is the ESR of the output capacitor CL and it
introduces a zero ωz in the open loop gain. RLdc is the ESR of
the boost inductor and these two ESRs together determine the
quality factor Q of this second order system and they can
provide damping effect to the LC resonance. Using the
parameters listed in Table I, the system is closed-loop control
system is inherently stable even a simple proportional gain is
used. However, if the crossover frequency of this control loop
is tuned to be less than one tenth of the switching frequency,
e.g. 1 kHz the system phase margin is only 17°, which is
obviously insufficient and may cause transient oscillations.
Furthermore, this system has limited DC gain, and its steadystate tracking error may not be zero.
In order to solve these issues, a type III compensator is then
designed to control this buck converter and its standard form
can be written as,
Clearly, the integral term is to produce infinite DC gain for
zero steady-state tracking error, and the two zeros ωz1 and ωz2
should be placed around the LC resonance frequency ωo so
that phase boost can be obtained. The first high frequency pole
ωp1 is to cancel the ESR zero introduced by the output
capacitor, while the other pole ωp2 acts as a low pass filter
(LPF) which increases gain attenuation at high frequencies. A
common way is to set ωp2 to be around half of the switching
frequency. By using type III compensator confirms its stable
operation and fast transient response.
Fig 5: Overall control block diagram for the proposed three-level PFC converter.
International Journal of Multidisciplinary Research and Development
6. Simulation & Simulation Result
Three Phase Grid
Grid Voltage
Converted Pole Voltage
Current Measurement2
Gate 2
- +
i +
Voltage Measurement5
Conv erted Pole Voltage
Current Measurement1
Series RLC Branch5
Series RLC Branch2
- v Grid Voltage
- v
Current Measurement5
Series RLC Branch3
Voltage Measurement6
+ i
Voltage Measurement3
DC Current
Series RLC Branch7
Gate 1
Series RLC
RLC Branch1
A Single-Stage PFC Half-Bridge Converter
Voltage Measurement4
- +
Output DC Voltage
v Branch8
Series RLC Branch6
AC Voltage Source2
AC Voltage Source1
AC Voltage Source
Current Measurement4
Output DC Voltage
Voltage Measurement7
Ts = 5e-005 s.
PI Controller
ref current generator1
I Angle
Power Factror
Power Factor Meter
Power factor angle (degrees)
rm s
Load Current (A)
Fig 6: Simulation for Three level-Quasi-Two Stage PFC converter
Simulation study was carried out in Matlab/Simulink
environment and the circuit parameters are listed in Table 1.
Simulation for Three level-Quasi-Two Stage PFC converter is
shown in Fig.6. The steady-state operation waveforms are
presented in Fig.7. It can be seen that Q1 and Q2 operate
alternatively and may produce the desired three-level
converter pole voltage VAB. The high level bus voltage is not
constant because the dc-link capacitor needs to absorb the
system double line frequency harmonic. This fluctuation
voltage has basically no impact to the regulation of the boost
inductor current, because it can be easily compensated by the
fast current control loop. Thanks to the feed-forward
mechanism of the open loop duty cycle, the grid current is
almost sinusoidal and in phase with the grid voltage, and its
ripple component is very small because of the three-level
output voltage.
Table 1: Circuit Parameters used for Simulation and Experiment
Grid voltage
Line frequency
Output voltage
Switching frequency
Nominal load
ESR of Inductor
ESR of capacitors
As mentioned before, the buck converter theoretically does not
need to switch when D2 is blocking. However, in order to deal
with the system harmonic power and ensure constant load
440 √2 V
50 Hz
230 V
2.2 KΩ
0.66 mH
25 µF
voltage, the buck converter still has to work during this
operation mode.
International Journal of Multidisciplinary Research and Development
Fig 7: Simulation Steady state waveform under 430/2 KW operation, Converted pole voltage, three phase grid, grid voltage, output DC voltage,
Gate pulses respectively.
7. Hardware Result
A 2kW prototype circuit was built in the laboratory for
experimental validation of the proposed PFC converter and the
circuit parameters are basically the same as those used in
simulation, despite some very slight differences due to the
tolerance of passive components. The key active and passive
components used for the tested prototype are summarized in
Table 2.
Table 2: Key Components Used for the Experimental Prototype
Diode Rectifier bridge
0.66 mH,2*18/20W, Core, Crompton Greaves
25 µf /440 VAC, HITRON Capacitor
The proposed topology was first tested with standard
430V/50Hz high line AC input and its corresponding steadystate experimental waveforms are presented in Fig. 8 & 9. It is
obvious that they can match well with those simulated ones
presented in Fig. 7. It should be noted that there is very slight
current distortion during the mode transition period, and this is
due to the limited compensation gain of the controller.
Fig 9: Gate pulses
Fig 8: Converter Pole Voltage
The load transient can be handled by the high voltage bus and
the output voltage remains undisturbed. In order to examine
the line frequency ripple component in the output voltage, its
spectrum is plotted in Fig. 10 and compared with that of the
high DC bus. From Fig. 10, it is clear that the high DC bus can
absorb most of the second order harmonics and therefore, the
load voltage can be kept as ripple free during both steady-state
and dynamic process.
International Journal of Multidisciplinary Research and Development
because the proposed PFC essentially becomes equivalent to
the conventional two-stage PFC and the characteristic of
three-level switching is lost.
It should be noted that the power losses induced by the gate
drivers were not included in the efficiency measurement.
Since the required gate charge is low and the adopted
switching frequency is also relatively slow, these power losses
are insignificant to the system overall efficiency and the
performance comparison presented above is still reasonable.
Fig 10: Harmonic contents of the output voltage and high DC bus
voltage under 440V/2kW operation.
The proposed PFC converter is also compared with a
conventional two-stage solution, i.e. a boost PFC cascaded
with a DC/DC buck converter and its circuitry is obtained by
removing D1 and Q2 shown in Fig. 1. Therefore, the proposed
three-level PFC will have higher cost than the conventional
one, and it is complicated with one fast recovery diode (D 1),
one switch (Q2) and one isolated gate driver. The remaining
active and passive components in the two-stage PFC are
exactly the same as those in the proposed one and therefore, a
fair performance comparison can be conducted.
The efficiency tests were performed by a Fluke Norma 5000
power analyzer. Different tests under universal input voltage
conditions (85Vrms to 265Vrms) were conducted for the two
topologies. The output voltage and load power were fixed at
230V and 2kW, respectively, and the recorded efficiency
curves are presented in Fig. 11. As shown, the proposed PFC
features higher efficiency than the conventional one under all
input conditions. During standard 230V high line operation,
1% efficiency improvement can be obtained over the entire
load range and this confirms the superior performance of the
proposed topology.
Fig 11: Efficiency curves of the proposed PFC converter under
universal input voltages, shown in comparison with the conventional
two-stage solution.
In addition to the efficiency versus input voltage curves, the
efficiency versus output voltage curve is also plotted in Fig.
12, and in this test, the converters were operated with 430V
input voltage and nominal load power. Fig. 12 shows that the
proposed PFC can maintain much higher efficiency when the
output voltage is low. However, as the output voltage
increases, the efficiency improvement will be less significant
Fig 12: Efficiency curve of the proposed PFC converter under
different output voltages, shown in comparison with the conventional
two-stage solution.
8. Application
1. It has flexible output voltage and can be used for singlephase PHEV charger applications, where the battery
voltage can be either lower or higher than the peak AC
input voltage.
2. Used to reduce conduction losses.
3. Used in industries which have low power factor problems.
4. It is also used for low-output voltage applications, such as
telecommunication or computer industry.
5. Used to improve Power factor & reduce total harmonic
9. Conclusion
In this paper, A three-level quasi two-stage three phases PFC
converter is presented.
1. It has flexible output voltage and can be used for singlephase PHEV charger applications, where the battery
voltage can be either lower or higher than the peak AC
input voltage.
2. The proposed converter features high quality input current,
three-level output voltage, and improved conversion
3. By designing a fast regulation loop for the buck converter,
the inherent fluctuating power issue in single phase
systems can also be resolved, and the load voltage will be
fairly constant and insensitive to load changes and external
4. Moreover, a dynamic gain compensator is implemented in
the current control loop and in this case, its control
bandwidth can be kept relatively constant irrespective of
the DC bus voltage change during two different operation
modes. Therefore, the grid current can be well regulated
with low THD and high power factor.
5. The proposed PFC may have 1% efficiency gain under
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high line operation as compared to a conventional
cascaded two-stage solution.
6. This efficiency improvement is partly contributed by the
reduced switching voltage in the PFC stage, and also partly
by the reduced power conversion in the DC/DC buck
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