design and analysis of multi - input buck -boost converter...
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Design and Analysis of Multi-input Buck-Boost Converter
with Less Number of Switches
Mudadla Dhananjaya1,
Swapnajit Pattnaik 2
1,2Department of Electrical Engineering,
National Institute of Technology,
Raipur, India.
April 14,15 - 2017
Abstract
Power electronics offer a cost effective solution for
connecting components at either source end or load
end based on multiple converter configurations. This
paper presents a non-isolated multi input buck-
boost converter (MIBBC) with less number of
switches there by reducing the switching losses. The
voltage and current stresses on a particular switch
have been analyzed for proper selection of switches.
The effect of change in output voltage with respect
to delay in the turning on of switches has been
investigated. Further, using of a single inductor
reduces the cost and complexity of the system. A
laboratory prototype have been developed for
experimental validation which shows the efficiency
and effectiveness of the presented topology by using
dSPACE controller (1104).
Key Words:Multi input, buck-boost converter,
efficiency.
1. Introduction In recent years, there has been a vast increase in the demand of
renewable energy sources due to depletion of fossil fuels in the
International Journal of Pure and Applied MathematicsVolume 114 No. 7 2017, 129-139ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu
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near future and also increase in global warming, greenhouse
effect, environmental pollution and problems associated with the
conventional sources of energy [1-3]. There has been an increased
utilization of fuel cell stack over the wind and PV systems [4]. In
order to meet the energy demands, hybridization of the energy
systems is gaining more importance for various applications like
hybrid vehicles and household applications [5]. But this needs a
proper interfacing circuitry to combine various energy systems to
meet the power demand [6-7].
Multiport converter have grabbed attention in recent years as the
system with single input source has the drawback of less power
density [8]. Moreover, in hybrid system the V-I characteristics of
energy sources differ from each other and hence in order to
obtain the required output voltage, multiport converters are to be
used [9]. The advantages of these converter include simple circuit
topologies, centralized control, high reliability, low
manufacturing cost and size [4]. Also, the multiport converter
has the benefit of integrating a number of converters either in
the input DC-DC converter stage or in the isolation stage, in
addition to the commonly shared output stage [10].
The output voltage of the renewable sources such as fuel cell,
photovoltaic unit is quite low and fluctuating which prevents the
direct connection of these units to the load as they need a
constant DC voltage. Power electronic converter plays a vital role
for voltage conversion. A buck-boost converter can be used to
maintain a constant DC voltage [11-12].
Multiinput single output (MISO) converter have been well
established in the literature. Early MISO were designed by
connecting the input voltage source in series to obtain a multi-
input topology [13-14]. To prevent input sources to get shorted,
an active switch is connected in series with each input source
such that only one source can transfer energy to the load at a
time [15].
DC-DC converters can be either isolated structure or non-isolated
[10]. Several types of DC-DC isolated converters have been
proposed [16-17], their drawbacks include leakage loss due to
which the conversion efficiency gets lowered, induces high
voltage stress in the switches and also increases the switching
losses along-with increased Electro-magnetic interference (EMI)
problems. The solution to the above mentioned problems is the
active clamp circuit which recycles the leakage energy, but
increases the circuit complexity [18]. Hence various multi input
topologies were proposed based on non-isolated structures [19-
23].
A non-isolated multi-input buck/boost converter time sharing
concept has been proposed in [14]. A four switch bidirectional
buck boost converter, with similar concept is proposed [19]. In
[20], an auxiliary circuit was used to achieve soft switching for
International Journal of Pure and Applied Mathematics Special Issue
130
series connected boost converters. In [21], a general derivation
for non-isolated parallel integrated multi-input converters
including SEPIC and Cuk has been proposed. In [22], a different
approach based on switched capacitor converter has been
reported.
In this paper, a multi input buck-boost converter is presented
which has an advantage of using less number of switches as
compared to the other topologies (Table 1). This reduction in the
number of switches reduces the switching and conduction losses
thereby increasing the efficiency of the converter. The input
power delivered by different DC sources can be regulated
individually. This topology employs only one inductor which
indeed reduces the complexity as well as cost of the system. The
key features of the presented topology include
Less number of switches compared with few other
topologies
Low cost and simple design
High efficiency
This paper is organized as follows. Section 2 describes the
presented topology and its operation. Whereas Section 3 shows
the calculation of loss and efficiency. Simulation and
experimental results are shown in Section 4 followed by
conclusion in Section 5.
2. Circuit topology and operation of
multiport buck-boost converter
The Multi-input DC-DC converter is shown in Fig. 1. With VDC1,
VDC2 (VDC1>VDC2) as input voltage sources. The voltage sources are
interfaced through a diode. A common inductance, L has been
shared by the energy sources and the output capacitance is C [24-
26].
VDC2VDC1
L
RD
C
D1
D2
SW1
SW2
Fig. 1. Schematic of multi-input DC-DC converter.
Modes of operation
Mode1 10 tt
In this interval power switch SW1 is ON, SW2 is OFF and diode is
International Journal of Pure and Applied Mathematics Special Issue
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reverse-biased. The inductor is energized by the input power VDC1
as shown in Fig. 2(a).
VDC2VDC1
L
RD
C
D1
D2
SW1
SW2 VDC2VDC1
L
RD
C
D1
D2
SW1
SW2 VDC2VDC1
L
RD
C
D1
D2
SW1
SW2
(a) (b) (c)
Fig. 2(a), (b), (c) Equivalent circuit of operation during Modes
1,2,3 and 4.
Mode2 21 ttt
In the second interval, SW1 is turned OFF and to avoid the
simultaneous conduction of both the switches, SW2 is not turned
ON immediately. By providing delay between the active periodsof
the two sources of the converter. In this mode the energized inductor
transfer its energy to the load. The equivalent circuit of Mode II is in
the Fig. 2(c).
Mode3 32 ttt
In this mode, as shown in Fig. 2(b) switch SW2 is ON, VDC2
supplies the energy to the inductor, and it is energized, switch SW1
and diode are in to OFF state.
Mode4 43 ttt
In this interval power switches SW1, SW2 are OFF, Diode will be
forward-biased through load and capacitor is charged reversely by
the demagnetization of inductor (L). The equivalent circuit of the
converter is shown in Fig. 2c.
The conduction time for both power switches in the respective
modes of operation can be determined by the values of duty ratio of
the switches.
Applying volt - second balance principle to four modes of the
operation
00 3423121 ttdt
diLtt
dt
diLtt
dt
diLt
dt
diL LLLL
(1)
03402321211 ttVttVttVtV DCODC (2)
sTdt 11 , sTdtt 1
12 , sTdtt 223 and sTdtt 11
34
(3)
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011
022
1
011 ssDCssDC TdVTdVTdVTdV (4)
111
2211
0dd
dVdVV DCDC
(5)
where
d1 is the delay time between switches,
d11 is the duty ratio of the OFF time
d1+ d11 gives the total OFF state of the switches
2.2Calculation of voltage and current stress
The voltage across each switch is calculated as follows [9].
In Mode1 according to Fig. 2(a) the voltage across the switch SW1 is
zero. Applying KVL to the loop with VDC1, VDC2, SW1, and SW2 the
voltage across the switch SW2 is as follows.
1212 dDCDCSW VVVV
(6)
Similarly in Mode3 according Fig. 2(b) voltage across switch SW2 is
zero. Applying KVL to the loop with VDC1, VDC2, SW1, and SW2 the
voltage across the switch SW1 is as follows
2121 dDCDCSW VVVV
(7)
In Mode2 and Mode4 the switches SW1, and SW2 should block the
respective source voltages, VDC1 and VDC2 respectively i.e.
11 DCSW VV (8)
and
22 DCSW VV
(9)
Let current passing through the power switches and diode be
indicated as isw1, isw2 and iD respectively
1
1
1
0 1
L s
SW
s
i d Ti
d T
(10)
2
2
2
0 1
L s
SW
s
i d Ti
d T
(11)
1 2
1 2
0 ,
i 1 T
s s
D
L s
d T d Ti
d d
(12)
3. Calculation of power loss and
efficiency
Power losses across the switch mainly include conduction and
switching losses. In the ON state, the IGBT conducts a current for
an interval ton for every switching period, TS. Conduction losses are
calculated considering the duty ratio(d) of the switch [5], [29].
International Journal of Pure and Applied Mathematics Special Issue
133
dtIVT
Pont
SC
S
swc 0
_
1
(13)
VC is the voltage drop across the switch when it conducts and ISis
current through the switch
Diode losses are calculated as
dtIVT
Pont
FF
S
DC 0
_
1
(14)
VF is forward voltage drop, IF is the forward current of diode
In DC-DC converter at high switching frequencies switching
losses play an important role in determining the efficiency of the
converter. Switching loss are calculated as
fttIVP offonBSW 6
1
(15)
where
VB- is the blocking voltage of the switch, I- is the current through
the switch, ton - on time, toff - off time of the IGBT, obtained from
data sheet of STGW30NC120HD, f - is the switching frequency of
the converter
The efficiency of the converter is given by
_ _
out
out C SW SW C D
P
P P P P
(16)
Table 1 Comparison of various components in presented topology
with other existing multi-input topologies
Table 1 shows that the presented topology having less number of
device count leads to reduce cost, complexity, size, simple controlling
and using less number of switches there by reduction in the
switching loss to get the higher efficiency.
Topology
Proposed
No. of
sources(N)
No.of
switches
No.of
Diodes
Total
switches Inductor Capacitor
Expected
efficiency
(%)
Khaligh A
et.al [19] 2 N+3 0 5 1 1 78-90
Kumar L
et. al [5] 2 N+2 2 6 1 1 82-92
S. Rezaee
et. al [28] 2 N+1 0 3 3 3 80-97
Gavris et.
al [27] 2 N 6 8 3 3 90-95
Presented 2 N 3 5 1 1 85-95
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4. Simulation and experimental results
The simulation of the converter is performed in
MATLAB/SIMULINK using SimPower Toolbox. For input
voltages VDC1=50V, VDC2=40V the output voltage and the various
responses of the system are shown in the figures. Fig. 3(a)
shows the output voltage of the presented converter. Fig. 3(b)
shows the inductor current of the presented converter at
different modes operation.
(a) (b)
Fig. 3. (a) Output voltage, (b) Inductor current
Experimental results
A low voltage hardware setup is developed to verify the
feasibility of the presented converter. The selection of the
components and the values of input voltages are VDC1=50,
VDC2=40, IGBT= STGW30NC120HD, inductor=5mH and
capacitor=10uF. The control signals for power switches are
generated using dSPACE controller. Switching pulses are
generated in accordance with the modes of operation with
appropriate duty ratios as shown in Fig. 4(a) and the output
voltage of the converter is shown Fig. 4(b) the variation of
inductor current in different modes of operation as shown in Fig.
4(c) the efficiency of the converter is plotted as shown in the Fig.
4(d). Voltage and current stress of the two switches are with in
stress tolerance as show in the Fig. 4(e) and (f) and it has small
switching loss which can be reduced by using soft switching
techniques.
(a) (b)
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(c) (d)
(e) (f)
5. Conclusion A non-isolated multi input BBC has been presented. The
advantages of this converter include less number of switches
there by decreasing the power loss and increasing the efficiency
of the converter, using single inductor reduced the cost and
complexity of the system. The operation of the presented
converter has been studied and analyzed with two inputs.
Simulation and experimental results clearly justifies the
effectiveness and efficiency of the presented converter.
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