Modular Marx Topology for High Boost Ratio DC/DC Boost Converter

Modular Marx Topology for High Boost Ratio DC/DC Boost Converter
Asmarashin Ponniran*
Koji Orikawa*
Jun-ichi Itoh*
*Nagaoka University of Technology
1. Introduction
DC/DC converter with high boost ratio is required for some
industrial applications, such as for X-ray generation plasma
generation and others. In Marx circuits which are usually used for
high voltage pulse generator, high conduction losses and copper
losses due to large input current are significant problems.
In this paper, a new Marx topology DC/DC boost converter
with charging choppers is proposed for a high boost ratio. In the
proposed circuit, the parallel connection is applied at the input
side and the multistage connection is applied at the output side.
Therefore, a high efficiency boost converter can be achieved. For
the prototype development, only three-stage Marx topology
DC/DC boost converter is considered in order to confirm the
converter operation and the design method of the input inductors.
Fig. 1. Three-stage Marx topology boost converter.
Table 1. Stage capacitors operation.
2. Circuit topology
In a conventional DC/DC boost converter, the high boost ratio
can be achieved by connecting those converters in series or in
cascade connection [1]. However, this topology has low
efficiency due to the required number of the DC/DC converters.
Besides that generally DC/DC converters using high frequency
transformers are also can be considered in order to obtain a high
boost ratio. However, this kind of converters usually suffers from
the bulkiness, large losses and leakage current due to the parasitic
capacitance between the transformer windings. On the other hand,
switched capacitor DC/DC converters also can achieve a high
boost ratio. However, in this topology output voltage stress on the
output capacitor is very high due to high output voltage [2,3].
Fig. 1 shows a circuit diagram of a Marx topology boost
converter (MTBC) of three-stage. Each stage of the MTBC
consists of a conventional boost DC/DC converter, a capacitor
and two additional switches. The converter is designed based on
a principle of the Marx generator whereby a high-output voltage
is generated from a low-voltage DC source [4]. This principle can
be realized by charging a number of capacitors in parallel and
then suddenly connecting those capacitors in series. Therefore by
arranging the combination of capacitors in the proposed converter,
a high-output voltage can be generated. By piling stages, the
Marx topology boost converter generates high voltage from a
low-voltage DC power source. It is noted that 10 to 20 stages
might be required in order to reduce input currents stress,
switching devices voltage rating and stage capacitor voltages
stress in the actual application,.
The relationship between the input voltage Vin and the output
voltage Vout can be expressed as follows:
 D 
Vout = 
nVin ............................................................... (1)
1− D 
where D is the duty ratio for the switches S1a, S1b, S2a, S2b, S3a
and S3b and n is the number of stage. For the prototype, only
three-stage of the Marx topology boost converter is considered.
Fig. 2 shows the operation mode of the three-stage Marx
topology boost converter. Table 1 and Fig. 2(b) show that the
(a) Switching pattern.
L3
S3a
L3
D3
C3
S3b
Lout
D3
S3a
C3
S3c
L2
S2a
S2b
S2c
L1
Vin
S1a
Cout
D2
S2a
Vout
C2
L1
S1b
Vin
C1
S3a
Mode II
Dead-time Td condition
S1a, S2a and S3a – ON
L3
D3
C3
Lout
D3
S3a
C3
S3c
L2
S2a
L2
S2b
S2c
L1
Vin
S1a
Cout
Lout
C2
S2b
S2c
L1
S1b
D2
S2a
Vout
D1
C1
S3b
S3c
D2
C2
S1b
S1c
Mode I
S1a, S2a and S3a – ON
S1b, S2b and S3b – ON
S3b
Vout
Cout
D1
S1a
S1c
L3
S2b
S2c
D1
C1
Lout
S3c
L2
D2
C2
S3b
Vin
Cout
Vout
D1
C1
S1a
S1c
S1b
S1c
Mode III
Additional delay-time Ta condition
S1a, S2a and S3a – ON
S1c, S2c and S3c – ON
Mode IV
S1c, S2c and S3c – ON
(b) Equivalent circuit.
Fig. 2. Operation modes of the three-stage Marx topology boost.
stage capacitors C1, C2 and C3 are charged when those capacitors
are connected in parallel. Then those stage capacitors are
Table 2. Specifications of the experimental prototype circuit.
connected in series during discharging condition. Thus from these
conditions, the output voltage can be boost-up by advantage of a
series connection of the stage capacitors. Therefore a high boost
ratio can be achieved. The voltage stresses on the switching
devices Sna (S1a, S1b and S1c), Snb (S2a, S2b and S2c) and Snc (S3a,
S3b and S3c) are equal to the stage capacitor voltages VC1, VC2 and
VC3, respectively. Meanwhile voltages stresses on the D1, D2 and
D3 are equal to the VC1, 2VC2, and 3VC3, respectively.
In this paper, the inductor current of each stage in the MTBC
is designed to be operated in continuous current mode (CCM) in
order to minimize the peak input current. Thus the minimum
inductor current of each stage should be more than zero to ensure
a CCM condition is achieved. The minimum inductance of the
input inductor of each stage Lin(m) for CCM operation can be
expressed as follows:
2
n (Vin ) D
Lin (m ) >
................................................................. (2)
2 Pout f sw
where n is the stage, Pout is the output power and fsw is the
switching frequency.
Meanwhile the inductor current ripple of each stage ∆ILin(m)
can be expressed as follows:
V D
∆I Lin(m ) = in
................................................................ (3)
f swLin(m )
3. Experimental Results
Table 2 shows the specifications of the experimental
prototype circuit. The inductance of each stage of the input
inductor is designed by using (2). The designed inductance of
each stage is 500 µH in this prototype. According to (3), the
designed input inductor current ripple on each stage is 2.8 A.
Fig. 3 shows the experimental results of the input inductor
ripple currents of IL1 and IL2 are 2.8 A, respectively. In Fig. 3, the
output power is 500 W and the average input current is 11.1 A.
Besides that, the experimental results of the inductor current
ripples of the IL1, IL2 and IL3 are according to the designed value
though IL3 is not shown in Fig. 3. As a result, both the designed
and the experimental results show a good agreement. In addition,
in Fig. 3, the experimental results of the inductor currents of IL1
(stage 1) and IL2 (stage 2) are shown. The average inductor
currents for the IL1 and IL1 are 3.7 A meanwhile the average
inductor current of IL3 (stage 3) is also 3.7 A because the input
current is divided by three due to three-stage arrangement in a
parallel connection at the input side. Therefore if many stages are
considered, the input current will divided by the factor of the
stage number and consequently the input current stress, the
conduction loss and the copper loss will be reduced. On the other
hand, the stage capacitor voltage VC1 is 193 V and the stage
capacitor voltages of the VC2 and VC3 show good agreements with
the stage capacitor voltage VC1. Besides it is experimentally
confirmed that the output voltage of 400 V is achieved.
Fig. 4 shows the efficiency of the Marx topology converter.
The input and output voltages are fixed at 48 V and 400 V,
respectively. The measured maximum efficiency is 92.2 % at the
output power of 500 W and 600 W. In addition, the efficiency is
increased when the output power is increased. From this
characteristic, the conduction loss and copper loss which are
increased directly the squared of the current are not dominant in
the total power loss when the output power is high. On the other
Fig. 3. Experimental waveforms of the output voltage, the capacitor
voltage (stage 1), the inductor current (stage 1) and the inductor current
(stage 2).
93
92
91
90
89
88
87
86
200
300
400
500
600
Fig. 4. The converter efficiency characteristic.
hand, during low output power, the power loss are dominated by
the switching loss and the iron loss. As a result, the efficiency is
low during low output power.
4. Conclusion
This paper presented the high boost ratio of the Marx
topology converter whereby the parallel connection at the input
side and the multistage connection at the output side are applied.
Therefore the high efficiency converter is achieved. The
operation of the converter is confirmed by the three-stage Marx
topology converter prototype. The achieved maximum efficiency
is 92.2 % at the output power of 500 W and 600 W.
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