International Conference on Electrical, Electronics, and Optimization Techniques (ICEEOT) - 2016
A Novel Single Stage Buck Boost Inverter For
Photovoltaic Applications
Muhammed Nishad T , Muhammedali Shafeeque K
Electrical and Electronics Engineering,
MEA Engineering College,
Perinthalmanna, Kerala, India
nsdthottungal@gmail.com
Abstract— This paper propose a novel single stage buck-boost
inverter with various line conditions and working in both buck
and boost modes. This novel topology is derived from
conventional buck boost converter. The output voltages of
photovoltaic (PV) systems are vary in wide ranges due to
environmental changes. So the inverter system needs to operate
in both buck and boost modes. This topology suitable for wide
range of inputs and the inverter provide accurate outputs. The
configuration uses lesser components making it compact and less
weight. Operational analysis of both buck and boost modes are
presented, MATLAB Simulink model is developed and the closed
loop control scheme applied in the system. Simulation results are
included to verify this topology.
Keywords—buck boost; photovoltaic; single stage inverter.
I. INTRODUCTION
Nowadays, the demand of electrical energy increases day
by day. Worldwide use of dependable fossil fuels has resulted
in the emission of greenhouse gases, mainly emission of
carbon dioxide and methane that terrors the effects of global
warming. Over the years, scientists and investigators have
devised by doing research and studies in order to come up
with new ideas and proposal to reduce the looming threat from
the emissions of carbon dioxide. To overcome the energy
shortage and to protect the environment, a clean and copious
energy substitute is required. Renewable energy sources play a
vital role now a day in electric power generation due to its
eco-friendly and pollution free clean energy[1]. Photovoltaic
(PV) energy is one of the prospective sources of renewable
energy, which gets more preference due to its availability,
simplicity, lesser maintenance and reliability choices.
It is predicted that the solar energy shall subsidize up to
64% of total global energy requirement by the end of this
century. Solar energy from the PV modules needs to be
converted into an appropriate form which is compatible with
the load. Majority of existing loads are AC, hence the PV
inverters should perform DC-AC conversion and that are the
major functional unit of most solar PV plants[2]. It has been a
continuous exertion of researcher to develop low cost, highly
efficient and compact inverters.
978-1-4673-9939-5/16/$31.00 ©2016 IEEE
The output voltage of photovoltaic system varies in wide
ranges due to the environmental variations, such as light,
temperature, and so on. Hence the inverter system must need
to perform both buck and boost operation in order to generate
constant AC voltage at the output. There are different types of
inverters are used for the dc-ac power conversion, like voltage
source inverter, current source inverter etc. They accomplish
either buck or boost conversion. To overcome this constraint
number of modifications are developed. The diode-assisted
buck–boost VSI can perform a wide range buck and boost
conversion with additional passive and active elements, has a
unique X-shaped diode capacitor network [3]. The main
drawback of the system are number of passive & active
elements are high and only two stage conversion is possible.
The Z-source inverter (ZSI) consists of an X-shaped
passive impedance network to couple the main power
converter and the power source[4]. By properly exploiting the
shoot-through state of the inverter bridge, ZSI can either
stepping up or stepping down the input voltage. But these
inverters have many passive components which are not good
for integration and the voltage boost ratio is limited. Also the
size and weight of the overall system is very high and they are
not suitable for low power applications[5]. The switched boost
inverter (SBI) is introduced with the Z source inverter and it
consists of an active switch and diode[6].It has the advantage
of less inductors and capacitors. SBI has only one L-C pair
which leads significant reduction in the size, weight and cost.
The major drawback of SBI is the boost factor, which is (1-D)
times that of ZSI. The Active Buck-Boost Inverter (ABI) can
boost the voltage with Active Boost Network, performs the
voltage buck and boost conversion in a single-stage
inverter[7]. The AC\AC unit composed of active switches
performs like a step up transformer and boost the output ac
voltage. Increase in number of switching devices is the main
drawback of ABI.
In this paper, the control of a novel buck-boost inverter is
discussed. It is derived from buck boost converter. A Full
bridge inverter is connected as the input voltage source and it
is connected to the buck boost circuit. It performs the voltage
buck and boost conversion in a quasi-single-stage inverter, and
has the advantages of compact structure, improved power
density, and efficiency without utilization of a line-frequency
transformer and additional passive elements.
A brief overview of the structure and operation of the
improved topology is given in section II. Section II describes
about the circuit and Section III describes about the operating
principle. Section IV deals with the simulation results. Section
V deals with the conclusion.
II. DERIVATION OF PROPOSED SYSTEM
Fig. 1 shows the conventional buck boost converter. By
controlling the duty ratio of the switch, the system will
perform either buck or boost operation. The input voltage
source is replaced by a single phase full bridge inverter, to
perform the operation of buck boost inverter.
Then, a novel single-stage buck-boost full-bridge inverter
is derived, as shown in Fig. 2. It consists of a full bridge
inverter and a buck boost circuit. Buck boost circuit includes
one inductor, capacitor and a pairs of switches and diodes. The
inverter and buck boost circuit share the inductor and
capacitor, hence it can reduce the number additional passive
elements. In this proposed topology, only one powerprocessing stage exists. Hence it is a quasi-single-stage buckboost inverter.
The output voltage of the buck boost circuit is
V
o
=
V *D
1 −D
in
(2)
Where M is the modulation index and D is the duty ratio.
Inverter has buck operation when D is less than 0.5 as well as
boost operation when D is greater than 0.5.
A. During Positive half cycle
Fig. 3 shows that during positive half cycle, switches S1 &
S3 having high frequency SPWM and switch S5 is always on.
During on time of S1 & S3 inductor charges through Vi - S1 L - S3 Vi. During off time, inductor discharges through L - CD2 - S5 - L and load.
B. During Negative half cycle
Fig. 4 shows that during negative half cycle, switches S2 &
S4 having high frequency SPWM and switch S6 is always on.
During on time of S2 & S4 inductor charges through Vi - S4 L - S2 - Vi. During off time, inductor discharges through L D1 - S6 - C - L and load.
III. OPERATING PRINCIPLE AND WORKING OF
PROPOSED SYSTEM
The legs of single phase full bridge inverter is controlled by
Sinusoidal Pulse Width Modulation (SPWM) technique. The
output voltage of the inverter is
(1)
=
V
in
M V Sinwt
i
Fig. 1. Conventional buck boost converter
Fig. 3. During positive half cycle.
discharging path
Fig. 2. Novel single stage buck boost inverter
(a) Inductor charging path (b) Inductor
IV. SIMULATION RESULTS
Simulation has been done by using Matlab/Simulink model
as shown in Fig. 7. The parameters are used as follows: Input
voltage Vi = 200-250V dc, Output voltage Vo = 230V(rms), the
carrier frequency is set at 1kHz.Fig.6. Shows the switching
signals generated for inverter legs S1- S4. Table 1. Indicates
the simulation parameters used for the MATLAB simulation.
Fig.8 shows the Switching signals for S5 & S6. THD and
harmonic order of the output voltage of the proposed inverter
shown in Fig.9. it shows that THD value is only 1.64%. Both
buck and boost operations are achieved by using step input
voltage (200-250V) as shown in Fig. 10.
Fig. 4. During negative half cycle. (a) Inductor charging path (b) Inductor
discharging path
Fig. 6. Switching signals for inverter legs. (a) S1 & S3 (b) S2 & S4
TABLE I.
Fig. 5. Modulation scheme for the system
The modulation scheme used for generating switching
signals of inverter legs and controlling switches are shown in
Fig. 5. Sinusoidal pulse width modulation (SPWM) signals are
generated by comparing sine wave and high frequency
triangular wave. During positive half cycle switch S5 is
always on and switch S6 is always off. SPWM signals are
given to switches S1 & S6. During negative half cycle switch
S6 is turn on and switch S5 is permanently off. SPWM
signals are given to switches S1 & S6 as shown in Fig. 6.
SIMULATION PARAMETERS
Parameters
Value
Input voltage
200-250V
Rated current , Io
1.25 A
Inductor, L
9 mH
Capacitor, C
5 μF
Switching Frequency
1 kHz
Filter Inductor
50mH
Load Resistance, R
250 Ω
Fig. 7. MATLAB Simulink model of the proposed novel buck boost inverter.
Fig. 8. Switching signals for S5 & S6. (a) S5.
(b) S6.
Fig. 10. Closed loop Voltage wave forms. (a) Output AC voltage.
Step input voltage.
(b)
V. CONCLUSION
Fig. 9. THD and harmonic order of the output voltage of the proposed
inverter
A novel buck boost inverter has been proposed in this
paper. The topological derivation, the operating principle,
and the modulation strategy have been presented. This paper
introduces a new closed loop control of the buck-boost
inverter for photovoltaic applications. This inverter achieves
both buck and boost mode of operation with a wide range of
inputs. The THD value is only 1.64%. It is useful in
reducing system volume, increasing the system efficiency,
reducing the cost and also increasing the system power
density.
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