9781509011476/16/$31.00©2016IEEE
TABLE I. CONVERSION RATIO
New Buck Boost Converter
Voltage Conversion Ratio
BBC or L Converter
D/(1-D)
SI BBC or 2L Converter
2D/1-D
VLSI BBC or 2LC Converter
1+D/1-D
modified VLSI or 2LCm Converter
1+D/1-D
X-Y Converter Family: A New Breed of Buck
Boost Converter for High Step-up Renewable
Energy Applications
S. B. Mahajan
, Member, IEEE, P. Sanjeevikumar, Senior Member, IEEE, Patrick Wheeler, Senior Member, IEEE, Frede
Blaabjerg
, Fellow, IEEE, Marco Rivera, Member, IEEE, Rishi Kulkarni, Student Member, IEEE
Abstract—A New breed of a buck boost converter, named
as the XY converter family is proposed in this article. In the
XY family, 16 topologies are presented which are highly
suitable for renewable energy applications which require a
high ratio of DC-DC converter; such as a photovoltaic
multilevel inverter system, high voltage automotive
applications and industrial drives. Compared to the traditional
boost converter and existing recent converters, the proposed
XY converter family has the ability to provide a higher output
voltage by using less number of power devices and reactive
components. Other distinct features of the XY converter
family are i) Single control switch ii) Provide negative output
voltage iii) Non-isolated topologies iv) High conversion ratio
without making the use of high duty cycle and v) modular
structure. XY family is compared with the recent high step-up
converters and the detailed description of XY converter family
and its topologies are presented. The simulation results are
provided and it confirms the feasibility, functionality and
validity of the concepts of the proposed XY converter family.
Index Terms— DC-DC converter toplogies; High Conversion
ratio; Non-isolated; Renewable Energy.
I. INTRODUCTION
N THE CURRENT scenario, the rising energy demand
increases the need for renewable energy sources. The
rapidly rising energy demand has reached a level where the
world will face severe crisis of energy. This is because the
energy sources required for the massive power generation
are exhaustible. On the other hand, renewable energy
sources are reliable and plentiful and can be locally
produced and therefore are not vulnerable to any kind of
risks [1]-[4]. Hence energy management focus on the
widespread use of renewable energy resources for power
generation. Several renewable energy applications such as a
photovoltaic multilevel inverter system, high voltage
automotive applications and industrial drives require a high
step-up and non isolated converter [1]-[35]. Series
connection of solar arrays is not practical solution to
achieve high voltage. Generally for applications involving
photovoltaic systems, DC-DC converters with high
conversion ratio are employed. The performance of a boost
converter deteriorates with the increase in the duty cycle of
the power switch and also due to the leakage resistance of
the inductor. Because of these practical difficulties, the
traditional DC-DC converter is not a suitable solution to
achieve high voltage. Hence it is impossible to use
traditional converters when the required conversion ratio is
greater than four [3]-[35]. Another major drawback of using
the traditional buck-boost converter is discontinuous input
current which proves the minimum utilization of input
source. A classical approach to overcome the problem of
leakage resistance is by increasing the converter’s switching
frequency for a certain value of acceptable ripple. The finite
switching time in a normal power device limits the
switching frequency if the duty ratio is either too high or
too small. In order to overcome the above drawback and to
simultaneously increase the voltage without using the
extreme values of duty cycles, isolated converters can be
employed.
Numerous isolated converter topologies that make use
of transformers and coupled inductors have been proposed
in the literature [15]-[19]. The switching losses and
electromagnetic interference (EMI) problem are caused by
high voltage stress due to transformer leakage inductance,
overall reducing the converter efficiency. Comparing the
hard switching converter the voltage stress is higher, thus
increasing the cost and circuit complexity. Hence, for
isolated topologies size, weight and losses of power
transformer are limiting factors. In [15]-[19], Switched
capacitor (SC) and Switched Inductor (SI), Voltage Lift
Switched Inductor (VLSI), modified VLSI principles are
used along with a combination of coupled inductors, voltage
multipliers or Switched capacitor multipliers [21]-[25]. Fig.1
(a)-(d) shows the inductor, SI, VLSI and modified VLSI. In
order to attain a higher boost ratio, cascaded approach is
used. Several industries are required to design a Cascaded
Boost Converter (CBC) which is the most complex part and
quite hard to encapsulate [20, 21]. In addition to that, high
ripple current and losses prove to be obstacles to attain the
high conversion ratio and efficiency [26, 27]. Quadratic
Boost converter (QBC) is proposed to obtain high voltage
gain by just using a single switch. However, in Quadratic
Boost converter, the voltage stress on the switch is equal to
the total output voltage. This requires high voltage rated
power switch with higher R
DS-
ON [20, 21]. In the recent
past, several DC-DC multilevel topologies have been
proposed to overcome the limitations of cascaded converter
S. B. Mahajan is with the Dept. of Electrical and Electronics Engg.,
Marathwada Institute of Technology, Aurangabad, India. (email:
sagar25.mahajan@gmail.com).
P. Sanjeevikumar is with the Dept. of Electrical & Electronics Engg.,
University of Johannesburg, Auckland Park, South Africa. Research &
Development, Chennai, India. (email: sanjeevi_12@yahoo.co.in).
Patrick Wheeler is with the Power Electronics, Machines and Control
(PEMC) Group, Dept. of Electrical & Electronics Engg., Nottingham
University, United Kingdom. (email: pat.wheeler@nottingham.ac.uk).
Frede Blaabjerg is with the Center for Reliable Power Electronics
(CORPE), Dept. of Energy Technology, Aalborg University, Denmark.
(email: fbl@et.aau.dk).
Marco Rivera is with the Dept. of Electrical Engineering, Faculty of
Engg., Universidad de Talca, Chile. (email: marcoriv@utalca.cl).
Rishi Kulkarni is with the Dept. of Electrical and Electronics Engg.,
Marathwada Institute of Technology, Aurangabad, India. (email:
kulkarni.rishi123@gmail.com).
I
and isolated topologies. However, a large number of
capacitors and diodes are required to design DC-DC
multilevel converter [22]-[35].
In this paper a new breed of a buck boost converter,
named as the XY converter family is proposed. In the XY
family, 16 topologies are presented which are highly suitable
for renewable energy applications which require a high ratio
of DC-DC converter. The proposed XY converter family has
the ability to provide a higher output voltage by using less
number of power devices and reactive components. Other
distinct features of the XY converter family are i) Single
control switch ii) Provide negative output voltage iii) Non-
isolated topologies iv) High conversion ratio without making
the use of high duty cycle and v) modular structure.
II. XY Converter Family
A. Generalized structure of XY converter Family
New Buck Boost Converters are designed by using
inductor, SI, VLSI and mVLSI for boost applications. Fig2
shows (a) traditional Buck Boost Converter (BBC or L
Converter) (b) Switched Inductor Buck Boost Converter (SI
BBC or 2L Converter) (c) Voltage Lift Switched Inductor
Converter (VLSI BBC or 2LC Converter) and (d) modified
Voltage Lift Switched Inductor Converter (modified VLSI
or 2LC
m
Converter). The voltage conversion ratio of above
designed Buck Boost Converters is determined and
provided in Table-I. The generalized structure of the XY
converter family is shown in Fig.3. XY converter consists
of two separate converters named as X converter and Y
converter. The input voltage source is directly attached to
the X converter and input of Y converter is a series
connection of input voltage source and output voltage of X
converter. The total output voltage of the XY converter
family is equal to the inverting sum of output voltage of X
converter and Y converter as in (1).
Vo Vx Vy
(1)
B. XY Converter topologies
Various suitable combinations of the new Buck Boost
Converter are designed and total 16 topologies are formed
named as the XY family. The detail description of suitable
combinations of X converter and Y converter is provided in
Table-II. Fig.4 (a)-(p) shows the XY converter topologies.
The operation mode of XY converter topologies is divided
into mode two modes-one when the switch is conducting
and other when switch is not conducting. To explain the
modes of operation 2LC
m
-2LC
m
converter topology is
considered.
C. 2LC
m
-2LC
m
converter topology
2LC
m
-2LC
m
converter topology is shown in Fig.4 (p).
The 2LCm-2LCm converter is a combination of two 2LC
m
converters. 4 inductor, 4 capacitors and 7 diodes along with
single switch are needed to design the 2LC
m
-2LC
m
converter. In order to analyse converter, it is assumed that
the converter is operating in steady state and following
assumptions are considered during one switching state: i)
Pure DC input supply ii) All power devices are ideal, thus
100% efficient component iii) L
X1
and L
X2
is inductors with
the same rating and identical iv) L
Y1
and L
Y2
are inductors
with the same ratings and identical v) All capacitors have
very small ripple at the operating switching frequency f
S
.
When switch S is conducting, input voltage charges the
inductors L
X1
and L
X2
in parallel through diode D
X2
and D
X3
respectively. At the same time, series connection of input
voltage and voltage across capacitor C
X
charges inductor
L
Y1
and L
Y2
through diode D
Y1
and D
Y2
. Capacitor of X, C
1
is charged by input voltage through diode D
X2
and D
X3
.
Similarly capacitor of Y, C
2
is charged by series connection
of input voltage and voltage across C
X
. The output voltage
of the 2LC
m
-2LC
m
converter is equal to the negative sum of
(a) (b) (c) (d)
Fig.1 (a) Single Inductor (b) Switched Inductor (c) Voltage Lift Switched Inductor (VLSI) (d) modified Voltage Lift Switched Inductor (mVLSI).
(a) (b) (c) (d)
Fig.2 (a) Traditional Buck Boost Converter (BBC or L Converter) (b) Switched Inductor Buck Boost Converter (SI BBC or 2L Converter) (c) Voltage Lift
Switched Inductor Converter (VLSI BBC or 2LC Converter) (d) modified Voltage Lift Switched Inductor Converter (modified VLSI or 2LCm Converter).
TABLE II. XY CONVERTER FAMILY
XY Converter
Y DC-DC Converter
BBC (L)
SI (2L)
VLSI BBC (2LC)
Modified VLSI BBC (2LC
m
)
X DC-DC
Converter
BBC (L)
L-L Converter
L-2L Converter
L-2LC Converter
L-2LC
m
Converter
SI BBC (2L)
2L-L Converter
2L-2L Converter
2L-2LC Converter
2L-2LC
m
Converter
VLSI BBC (2LC)
2LC-L Converter
2LC-2L Converter
2LC-2LC Converter
2LC-2LC
m
Converter
Modified VLSI BBC (2LC
m
)
2LC
m
-L Converter
2LC
m
-2L Converter
2LC
m
-2LC Converter
2LC
m
-2LC
m
Converter
voltage across C
X
and C
Y
. Fig.4 (p. 1) shows ON state
equivalent circuit of the 2LCm-2LCm converter.
12
1 2 1
;
XX
Y Y X
L L in
L L in C C in
V V V
V V V V V V
2
-
X
XY
C in C
O C C
V V V
V V V
ON-State (2)
When Switch S is not conducting, input supply is
disconnected from the power circuit. Both inductor L
X1
and
L
X2
discharges in series with a capacitor of X, C
1
through
load and simultaneously charges the capacitor C
X
. Similarly
inductor L
Y1
and L
Y2
discharges in series with capacitor of
Y, C
2
to charge the capacitor C
Y
. Fig.4 (p. 2) shows the
OFF state equivalent circuit of the 2LCm-2LCm converter.
12
1 2 2
1
2 2 -
2 2 -
XX
Y Y Y
L L C CX
L L C C
V V V V
V V V V
Fig.3 Generalized structure of XY converter family (a) (b) (c)
(d) (e) (f) (g) (h)
(i) (j) (k) (l) (m)
(n) (o) (P) (P.1) (P.2)
Fig.4 XY Converter Topologies (a) L-L Converter (b) L-2L Converter (c) L-2LC Converter (d) L-2LC
m
Converter (e) 2L-L Converter (f) 2L-2L Converter (g) 2L-
2LC Converter (h) 2L-2LC
m
Converter (i) 2LC-L Converter (j) 2LC-2L Converter (k) 2LC-2LC Converter (l) 2LC-2LC
m
Converter (m) 2LC
m
-L Converter (n)
2LC
m
-2L Converter (o) 2LC
m
-2LC Converter (p) 2LC
m
-2LC
m
Converter (P.1) ON state equivalent circuit of 2LC
m
-2LC
m
converter (P.2) OFF state equivalent
circuit of 2LC
m
-2LC
m
converter.
TABLE III. VOLTAGE CONVERSION RATIO OF XY CONVERTER FAMILY
AND RECENT TOPOLOGY.
No.
Converter Topology
Conversion Ratio
1. XY Converter Family
L-L Converter
(D
2
-2D) /(1-D)
2
L-2L Converter
(D
2
-3D)/(1-D)
2
L-2LC Converter
(D
2
-2D-1)/(1-D)
2
L-2LC
m
Converter
(D
2
-2D-1)/(1-D)
2
2L-L Converter
(D
2
-3D)/(1-D)
2
2L-2L Converter
-4D/(1-D)
2
2L-2LC Converter
(D
2
-4D-1)/(1-D)
2
2L-2LC
m
Converter
(D
2
-4D-1)/(1-D)
2
2LC-L Converter
(D
2
-2D-1)/(1-D)
2
2LC-2L Converter
(D
2
-4D-1)/(1-D)
2
2LC-2LC Converter
(D
2
-2D-3)/(1-D)
2
2LC-2LC
m
Converter
(D
2
-2D-3)/(1-D)
2
2LC
m
-L Converter
(D
2
-2D-1)/(1-D)
2
2LC
m
-2L Converter
(D
2
-4D-1)/(1-D)
2
2LC
m
-2LC Converter
(D
2
-2D-3)/(1-D)
2
2LC
m
-2LC
m
Converter
(D
2
-2D-3)/(1-D)
2
2
Conventional Boost Converter
1/(1-D)
3
Switched Inductor (SI) Boost Converter
1+D/(1-D)
4
Single switch Quadratic Boost
Converter
1/(1-D)
2
5
Conventional Three Level Boost
Converter
2/(1-D)
6
Quadratic Three Level Boost Converter
1/(1-D)
2
7
Converters using bootstrap capacitors
and boost inductors
3+D/1-D
8
Switched Capacitor Based Boost
Converter
1+D/1-D
9
Two-phase quadrupled interleaved
boost converter
4/(1 − D)
9
High-voltage gain two-phase
interleaved boost converter using one
VMC
((VMC + 1)/1 − D)
10
Extra high voltage (HV) dc-dc
converter
4/(1-D)
1
2
(1 ) /(1- )
2 /(1- )
-
XY
C in
C in
O C C
V D V D
V V D
V V V
OFF-State (3)
From (2) and (3) the input to output voltage conversion
ratio of the 2LC
m
-2LC
m
converter can be determined as
2
2
0
(1 ) / (1 )
2(1 ) / (1 )
(3 )(1 ) / (1 )
X
Y
C in
C in
in
V D D V
V D D V
V D D D V
(4)
The input to output voltage conversion ratio of XY
converter family and recent converter topologies is
determined and is also given in Table-III. The current
waveform of inductors present in all XY Converter
topologies is analyzed and shown in Fig.5 (a) -(p). It is
observed that inductors present in XY converter are charged
when the switch is conducting and discharged when the
switch is not conducting.
III. SIMULATION RESULTS
All the proposed XY Converter topologies are simulated
for 10V input supply, 100W and 60% duty cycle and 50
kHz switching frequency in MATLAB. Output voltage
waveforms of all the XY converter topologies are provided
in Fig.6 (a)-(p). It is observed that all the XY converter
topologies give negative output voltage and the conversion
ratio is higher than the existing recent converters. It is
investigated that 2LC-2LC Converter, 2LC-2LC
m
Converter, 2LC
m
-2LC Converter and 2LC
m
-2LC
m
Converter have a maximum conversion ratio in XY
converter family and it convert the input, voltage output
voltage with a conversion ratio 24 at 60% duty cycle.
IV. CONCLUSIONS
A new breed of buck Boost converter named as XY
converter family is proposed for high step-up renewable
applications. All the XY converter topologies have negative
conversion ratio and have ability to provide a higher output
voltage by using less number of power devices and reactive
components. Other distinct features of the XY converter
family are i) Single control switch ii) Provide negative
output voltage iii) Non-isolated topologies iv) High
conversion ratio without making the use of high duty cycle
and v) modular structure. Detailed analysis of the
conversion ratio of XY family is discussed. The simulation
results are provided and it confirms the feasibility,
functionality and validity of the concepts of the proposed
XY converter family.
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(a) (b) (c) (d)
(e) (f) (g) (h)
(i) (j) (k) (l)
(m) (n) (o) (p)
Fig.5 Inductor waveform of XY Converter Topologies (a) L-L Converter (b) L-2L Converter (c) L-2LC Converter (d) L-2LC
m
Converter (e) 2L-L Converter (f)
2L-2L Converter (g) 2L-2LC Converter (h) 2L-2LC
m
Converter (i) 2LC-L Converter (j) 2LC-2L Converter (k) 2LC-2LC Converter (l) 2LC-2LC
m
Converter (m)
2LC
m
-L Converter (n) 2LC
m
-2L Converter (o) 2LC
m
-2LC Converter (p) 2LC
m
-2LCm Converter. [Colour indication Green: Inductor waveform of L converter,
Brown: Inductor waveform 2L Converter, Orange: Inductor waveform 2LC Converter, Violet: Inductor waveform 2LCm Converter].