Analysis of High Frequency Multi-Phase Multi

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Analysis of High Frequency Multi-Phase Multi-Stage Boost Converter
Karuna Mudliyar
Manipal Institute of
Technology
Manipal, India
[email protected]
Suryanarayana K
Dept. of Electrical and
Electronics Engineering
NMAM Institute of
Technology
Karkala, India
[email protected]
H.V.Gururaj Rao
Dept. of Electrical and
Electronics Engineering
Manipal Institute of
Technology
Manipal, India
[email protected]
Abstract-A novel approach to achieve a high static gain in nonisolated dc-dc converter is presented in this paper. The
conventional boost converter is cascaded to step-up the voltage
to higher level and the first boost stage is multi-phased to avoid
high input current stress on the switch. The multi-phase
configuration significantly reduces the current ripple and the
voltage ripple due to the operation of the parallel paths and
hence reducing the filter size. This technique allows the
operation with a high static gain and high efficiency, making
possible to design a compact circuit. The operational principle,
the design procedure and the simulation results obtained are
presented for multi-phase, multi-stage and integrated multiphase multi-stage boost converter.
L.V. Prabhu, Krishnaprasad
Technical Director
HEXMOTO Controls Pvt. Ltd
Mysore, India
[email protected]
[email protected]
A new alternative for the implementation is proposed in
this paper by cascading the boost converter to get high stepup [13] and multi-phasing to avoid current stress on
semiconductor switches [9], thus designing a highly efficient
converter with simpler structure. With increase in ripple
frequency due to multi-phasing the filter size will reduce
significantly.
II.MULTIPHASE BOOST CONVERTER
The concept of interleaving is that of increasing the effective
pulse frequency of any periodic power source by
synchronizing several smaller converters and operating them
with relative phase shifts [10]. In high power applications, the
voltage and current stress can easily go beyond the range that
one power device can handle. Multiple power devices
connected in parallel and/or series could be one solution.
However, voltage sharing and/or current sharing are still the
concerns. Instead of paralleling power devices, paralleling
power converters is another solution which could be more
beneficial. Furthermore, with the power converter paralleling
architecture, interleaving technique comes naturally. Benefits
like harmonic cancellation, better efficiency, better thermal
performance, and high power density can be obtained [13].
With these multi-modular converters the current stress can be
divided to a level that can be handled by semiconductor
switches and reduces the ohmic component of their
conduction losses. In many applications, one major concern
is the input and output filters rely almost exclusively on
tantalum capacitors due to the highest available energystorage-to-volume ratio [10]. However, the ESR of this filter
capacitor causes high level thermal stress from the high
switching pulsed current. The input and output filter
capacitance is usually determined by the required number of
capacitors sufficient to handle the dissipation losses due to
the ripple current. Interleaving multiple converters can
significantly reduce the switching pulsed current go through
the filter capacitor. By properly choosing the channel number
and considering the duty cycle, the ripple current may be
reduced to zero. Furthermore, interleaving increases the
ripple frequency to be n (n is the total number of phase) times
the individual switching frequency.
Keywords: high step-up gain, multi-stage, multi-phase, ripple
cancellation.
I. INTRODUCTION
With the growth of battery powered application, there is a
huge demand for highly efficient, small size, low cost and
high static gain dc-dc converter. Typical applications are
hybrid vehicle, uninterrupted power supply [4] and renewable
energy system such as solar.
The step-up stage normally is the critical point for the
design of high efficiency converters due to the operation with
high input current and high output voltage, thus a detailed
study should be carried out, in order to define the topology
for a high step-up application.
Magnetic coupled classic converter such as flyback or
push-pull converter can be used to achieve high static gain
[4]. However, volume of power transformer will greatly
influence the size of converter. The leakage inductance can
produce voltage stress; high switching frequency will bring
down the efficiency of the transformer itself and will cause
electromagnetic Interference (EMI), thereby reducing the
converter efficiency. Non-isolated conventional boost
converter, can provide high step-up voltage gain but with the
penalty of high voltage and current stress, high duty cycle
operation.
However, new non-isolated dc–dc converter topologies is
proposed, showing that it is possible to obtain high static gain
with low current stress and low losses, improving the
performance with respect to conventional dc-dc converter.
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International Journal of Advanced Electrical and Electronics Engineering, (IJAEEE)
L13
current is increased by the number of the phase.
D13
L13
L12
D12
L12
L11
D11
R
L11
R
C
Vin
S11
S12
S13
C
Vin
Fig.1. Three-Phase boost converter
S11
S12
S13
Fig.4. Phase-3 Open, Phase-1 and Phase-2 closed
L13
L13
L12
L12
L11
C
R
L11
Vin
S11
S12
S13
Vin
Fig.2. Phase-1, 2, 3 closed
L13
S13
Thus the factors, such as reduced ripple current, increased
ripple frequency contribute to a smaller output filter capacitor
for the same ripple voltage requirement, thereby reducing the
size and cost of the filter components. This results in
improved dynamic response to load transients [13].
L11
C
S11
C
S12
Fig.5. Phase-1 Open, Phase-2 and Phase-3 closed
L12
Vin
S11
S12
R
S13
A) Circuit description and operational analysis of MultiPhase Boost Converter.
Fig.3. Phase-2 Open, Phase-1 and phase-3 closed.
The ESR of the tantalum capacitors is inversely proportional
to the frequency. Interleaving technique can effectively
reduce the filter capacitor size and weight. Another concern
of this application is packaging. Due to the thermal
management issues, the power loss of non-interleave
converter exceeds the typical power dissipation capability. In
addition, the substantial bulky converter usually requires a
larger heat sink module. Interleaving technique can divide the
power transfer into multiple modules, lighter and smaller.
With the interleaving architecture, increased output power
may be supplied by adding additional identical modules.
Use of multi-phase boost converter is an optimal solution
for high input current dc-dc converter such as conventional
boost where the current is shared among different phases
[12]. The multi-phase booster can be achieved by adding
more parallel legs to the conventional boost converter. The
Fig.1.shows a three-phase boost converter, where two more
legs connected in parallel with the conventional one. The
multi-phase boost converter interleaves the clock signals of
the paralleled power stages, reducing input and output ripple
current without increasing the switching frequency. Because
of the phase difference in clocking between the converters,
the inductor ripple currents in the different phases tend to
cancel each other, resulting in a smaller ripple current getting
to the output capacitor. The frequency of the output ripple
The basic structure of three-phase boost converter can be
constructed by adding two parallel legs to conventional boost
converter. It is possible to add more number of parallel legs
to have more phases, where the input current is shared among
different phases. The converter is operating in continuous
conduction modes for better operational characteristics
results. Thus, the different operational stages and the
theoretical waveforms are represented for CCM and
considering three phases only. Different stage operations can
be explained with reference to the Figs.2 – 6. The three-phase
boost converter operates in six stages. The Table no.1 figures
out the status of the three-phase boost converter for different
switching conditions.
In three-phase boost converter, the clock for the switches is
phase shifted by 120 degree as shown in Fig.6. The three
phase ripple current waveforms are shown with solid, dashed
and dotted lines with reference to their clock signals, the
ripple cancellation among different phase’s results in reduced
magnitude and increase in frequency by three times [13].
The voltage transformation of three-phase boost converter is
same as that of conventional boost converter. Due to
interleaving of the clock pulses, all the three switches are
2
closed for the duration 𝐷 − . 𝑇, three times a period with
3
the interval of 1 − 𝐷 . 𝑇
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R
International Journal of Advanced Electrical and Electronics Engineering, (IJAEEE)
T – Switching period.
The resultant peak-to-peak ripple current through the
capacitor, is given by
Where, D and T are duty ratio and switching period of the
converter.
Table no. 1 Switching status of Three-Phase Boost Converter
PHASE I
Stages
S11
S12
S13
First
[Fig.2]
ON
ON
ON
Second
[Fig.3]
ON
OFF
ON
Third
[Fig.2]
ON
ON
ON
Fourth
[Fig.4]
ON
ON
OFF
ON
ON
ON
OFF
ON
ON
Status
PHASE II
PHASE III
INDUCTOR
CURRENTS
RESULTANT
RIPPLE CURRENT
Fig.6. Theoretical three-phase Inductor currents
B) Design Consideration for Multi-Phase Boost Converter.
Fifth
[Fig.2]
Sixth
[Fig.5]
The design equations for Multi-Phase Boost converter
operating in continuous conduction mode is presented with
an example. Considering the following specifications,
ΔIripple =
2
3
L phase
All the three phase inductors
stores energy, the stored
energy in the output capacitor
is supplied to load
The stored energy in the
inductor L12 is transferred to
load through diode D12.
Similar to stage 1, where all
the three phases inductors
stores energy.
The stored energy in the
inductor L13 is transferred to
load through diode D13.
Similar to stage 1 and 3.
The stored energy in the
inductor L11 is transferred to
load through diode D11.
V in D− T
= 5.56 A
(4)
3
Input voltage: Vin = 12 V.
Output voltage: Vout = 40 V.
Output power: P = 1KW.
Switching frequency: F = 100 kHz.
The rated load for given output power: R = 1.6 Ω
4) Filter capacitance: For 20% ripple voltage, the
capacitance value is given by,
2
C=
1) Static gain: The static gain of Multi-Phase booster is as
that of conventional booster.
V
Vout = in
(1)
V out D−3 T
ΔV out .R
= 1.04 μF
(5)
By considering the inductor copper loss and semiconductor
loss [7], output voltage equation for three-phase booster is
given by,
1−D
Vo
Where D is switch duty cycle ratio.
Therefore, the nominal duty cycle is 0.7
V in
=
1
D
1−
D.V D
1
V in
R +D .R on +D .R D
1+ L
2
(6)
3.R .D
Parasitic element values are same for all the phases, as it is
identical multi-modular structure.
VD − diode voltage drop
R L − Inductor DC resistance
R ON − Switch ON resistance
2) Inductor current: The inductor current through each phase
is given by,
V
IL_phase = out = 27.78 A
(2)
N×R.D
N – Number of phases.
D= 1−D
Similarly, the efficiency of three-phase booster can be
computed as,
3) Inductance: Considering 70% peak to peak ripple,
ΔIL_phase = 38.89 A
η= 1−
D .V D
1
V in
R +D .R on +D .R D
1+ L
2
(7)
3.R .D
Therefore, inductance in each phase is given by
Lphase =
V in .D.T
ΔI L _phase
= 2.16 μH
(3)
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C) Simulation result of Multi-Phase Boost Converter.
OFF time in one switching period, the same duty cycle is
maintained for all the stages.
The design procedure that developed was verified with
simulation results. The simulations include semiconductor
and copper loss. The Fig.7 shows the phase inductor current
and resultant ripple current waveforms. The output voltage
and current waveforms are shown in Fig.8.
100 A
1) Switch ON [Fig.10]: During the ON duration of switching
period, all the three switches are closed. The capacitor C1
and C2 are charged with voltage V1 and V2 respectively.
Thus, the input voltage Vin will cause the inductor current IL1
D1
Resultant ripple current
D2
L1
80 A
D3
L2
L3
60 A
IL3
IL2
IL1
C1
S1
40 A
S2
C2
C3
S3
R
Vin
20 A
Stage 1
0A
502 us
506 us
510 us
Time
514 us
Stage3
Stage2
Fig.9. Three-Stage boost Converter
518 us
Fig.7. Three phase Inductor currents.
L1
60 V
L2
L3
50 V
Vout
40 V
40 A
30 V
R
C3
30 A
20 V
20 A
10 V
10 A
0.2 ms
C2
C1
Vin
Iout
0.4 ms
Time
0.6 ms
0.8 ms
Stage 1
Stage2
Stage3
Fig.10. All Switches ON
1 ms
Fig.8. Output Voltage and Current.
L3
L2
L1
III.MULTISTAGE BOOST CONVERTER
R
C2
C1
In order to attain a higher boosting in conventional dc-dc
converter the required duty cycle will be very high. The
switch has to be closed for a long time so that the inductor
will store energy. But the OFF time will be in fractions,
compared to ON time. The inductor has to collapse, within
the given OFF time. Very close to 100% duty cycle will
always be a threat to the system such as when the load
fluctuates or rises, the system tries to compensate the load by
increasing the duty cycle which may lead to duty ratio of 1,
means the switch has to be closed all the time, the current in
the inductor and as well in switch will continue to increase.
Thus, causing the semiconductor devices to get damaged as
the rated power dissipation exceeds [3].
Multi-Stage boost converter is a cascaded boost
converter that results in the output voltage increasing in a
geometric progression [8]. The output voltage of one stage
will act as input voltage to the next stage, and thus steps up.
The Fig.9 shows the structure of three-stage boost converter
to achieve a very high static gain.
C3
Vin
Stage 1
Stage2
Stage3
Fig.11. All Switches OFF
to increase during the ON period, thereby storing the energy.
Same with the inductor currents, IL2 and IL3, the voltages
V1 and V2 cause the inductors L2 and L3 to store energy.
The capacitor C3 will be supplying to load [8].
2) Switch OFF [Fig.11]: During the OFF duration of the
switching period all the switches are made open, the voltage
across the first stage inductor L1, V1-Vin, will cause the
inductor current to decrease, thereby releasing the stored
energy and charging the capacitor C1 through diode D1 [8].
Similarly, with the inductor currents IL2 and IL3, charging
the capacitor C2 and C3 and supplying to load through diodes
D2 and D3.
Thus for three-stage booster, the voltage transformation is
given as.
A) Circuit description and operational analysis of MultiStage Boost Converter.
V3 =
The structure of three-stage boost converter is achieved by
cascading three discrete conventional boost converters. It is
possible to add more stages for higher static gain. The
converter circuit can be resolved for two conditions, ON and
1
1−D
V2 =
1
1−D
2
V1 =
1
1−D
3
Vin
(8)
Where, V1 , V2 , V3 are output voltages of first, second and
third stage respectively.
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Similarly, the current relation is given by,
Io = 1 − D IL3 = 1 − D 2 IL2 = 1 − D 3 IL1
Io − output current
IL1 − first stage inductor currents.
IL2 − second stage inductor currents.
IL3 − third stage inductor currents.
3) Inductance: Considering 70% peak to peak ripple, the
inductor values are given by [7],
(9)
L1 =
T – Switching period.
L2 =
800V
600V
Vout_3
L3 =
400V
Vout_1
0.2ms
0.4ms
0.6ms
0.8ms
1ms
C1 =
Time
Fig.12. Output voltage of each stage
300 A
150 A
0A
100 A
50 A
0A
30 A
15 A
ΔI L 1
V 1 .D.T
ΔI L 2
V 2 .D.T
ΔI L 3
= 0.72 μH
(16)
= 8.01 μH
(17)
= 88.86 μH
(18)
4) Capacitance: For 20% ripple voltage [7], the capacitance
value is given by,
Vout_2
200V
V in .D.T
IL1
C2 =
IL2
C3 =
IL3
V 1 .D.T
ΔV 1 R eq 1
V 2 .D.T
ΔV 2 R eq 2
V 3 .D.T
ΔV 3 R eq 3
= 21.06 μF
(19)
= 1.96 μF
(20)
= 0.17 μF
(21)
C) Simulation result of Multi-stage Boost Converter.
0A
0.2 ms
0.4 ms
Time
0.6 ms
0.8 ms
1 ms
The design procedure that developed was verified with
simulation results. The Fig.12 shows the output voltage of
every stage. The Fig.13 shows the inductor current of all the
three stages.
Fig.13. Inductor current for all stages
B) Design Consideration for Multi-Stage Boost Converter.
The design equations for Multi-Stage Boost converter
operating in continuous conduction mode is presented with
an example. Considering the following specifications,
Input voltage: Vin = 12 V.
Output voltage: Vout = 444 V.
Output power: P = 1KW.
Switching frequency: F = 100 kHz.
The rated load for given output power: R = 197.13 Ω
1) Static gain: The static gain of Three-stage booster is given
by,
1
IV. MULTI-PHASE MULTI-STAGE BOOST
CONVERTER
Generally, the problem with high static gain dc-dc converter
is very high input current, power equality law [1]. The high
static gain dc-dc converter posses a high input current stress
on the switch. Thus the power semiconductor device at the
input side is always stressed by high current. In case of
Multi-stage boost converter, the first stage power
semiconductor switches are more stressed than any other. The
multi-phase booster is integrated with multi-stage booster, in
order to achieve the advantage of both modalities. Thus, the
first stage in three stage boost converter can be multi-phased,
so that the high input current can be shared among all the
phases [13]. The Fig.14 shows a three-phase three-stage
boost converter, the converter provides a high static gain and
posses much less stress to the initial stage components. More
than one stage can be multi-phased if required. Thus it makes
possible to have low rated components to be used. The
increase in the number of components in multi-phase multistage booster is compensated by better efficiency. The heat
sink module required at high current input stage is
considerably reduced.
The design procedure is the same as discussed above
for multi-phase and multi-stage booster. The number of
stages and the number of phase in each stage will depend on
the application, the static gain and the duty cycle.
3
Vout =
Vin
1−D
Where D is switch duty cycle.
Therefore, the nominal duty cycle is 0.7
(10)
2) Intermediate Inductor currents and capacitor voltages:
First stage output capacitance voltage,
1
V1 =
Vin = 40 V
(11)
1−D
Second stage output capacitance voltage,
2
1
V2 =
Vin = 133.33 V
1−D
First stage inductor current,
1
3
IL1 =
Io = 83.33 A
1−D
Second stage inductor current,
1
(13)
2
IL2 =
Io = 25 A
1−D
Third stage inductor current,
IL3 =
(12)
1
1−D
Io = 7.5 A
(14)
(15)
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International Journal of Advanced Electrical and Electronics Engineering, (IJAEEE)
L2
D13
L13
L12
L3
D2
D3
D12
L11
D11
S12
S11
Vin
S13
S2
C1
C2
S3
C3
R
Fig.14.Multi-phase Multi-stage boost converter
compact system. Thus, for the application requiring very high
static gain, multi-phase multi-stage booster topology will be
best suitable being an efficient system.
800 V
600 V
Vout_3
400 V
REFERENCES
Vout_2
200 V
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Eduardo F. Romaneli, and Roger Gules, “Voltage Multiplier Cells
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of a low-stress Buck-Boost Converter in Universal-Input PFC
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Vout_1
2 ms
4 ms
6 ms
8 ms 10 ms
Time
12 ms 14 ms 16 ms 18 ms
Fig.15.Each stage output voltages
The simulation result for the integrated three-phase
three-stage boost converter is shown in Fig.15 and Fig.16,
the output voltage of each stage and first stage three-phase
currents respectively.
100 A
Resultant ripple current
80 A
60 A
IL3
IL2
IL1
40 A
20 A
0A
612 us
616 us
620 us
Time
624 us
628 us
Fig.16. First stage- Three Phase currents
V.CONCLUSION
The shortcomings of conventional boost converter can be
easily overcome by multi-phase and multi-stage boost
converter. The high input current was divided by identical
parallel modality in multi-phase boost converter. With
average duty cycle very high static gain can be achieved by
multi-stage boost converter. The above two advantage can be
achieved by integrating multi-phase and multi-stage booster.
The inductor current ripple cancellation leads to reduced
ripple with increased frequency in multi-phase booster. This
makes the way to have a smaller filter size, leading to a
ISSN (Print): 2278-8948, Volume-2, Issue-1, 2013
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International Journal of Advanced Electrical and Electronics Engineering, (IJAEEE)
ISSN (Print): 2278-8948, Volume-2, Issue-1, 2013
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