Design and Analysis of Multi - input Buck -Boost … and Analysis of Multi - input Buck -Boost Converter with Less Number of Switches Mudadla Dhananjaya 1, Swapnajit Pattnaik 2 1,2

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.

[email protected],

[email protected]

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

129

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


131

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)


132

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].


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


134

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)


135

(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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Documents

Design and Analysis of Multi - input Buck -Boost … and Analysis of Multi - input Buck -Boost Converter with Less Number of Switches Mudadla Dhananjaya 1, Swapnajit Pattnaik 2 1,2