DC-DC Converter for household Applications

abtechnosolutions

Grid-Connected PV-Wind-Battery based Multi-Input
Transformer Coupled Bidirectional DC-DC
Converter for household Applications
B. Mangu, Member, IEEE, S. Akshatha, Student Member, IEEE, D. Suryanarayana, Member, IEEE, and B. G.
Fernandes, Member, IEEE
Abstract—In this paper, a control strategy for power flow
management of a grid-connected hybrid PV-wind-battery based
system with an efficient multi-input transformer coupled bidirectional
dc-dc converter is presented. The proposed system
aims to satisfy the load demand, manage the power flow from
different sources, inject surplus power into the grid and charge
the battery from grid as and when required. A transformer
coupled boost half-bridge converter is used to harness power
from wind, while bidirectional buck-boost converter is used to
harness power from PV along with battery charging/discharging
control. A single-phase full-bridge bidirectional converter is used
for feeding ac loads and interaction with grid. The proposed
converter architecture has reduced number of power conversion
stages with less component count, and reduced losses compared
to existing grid-connected hybrid systems. This improves the
efficiency and reliability of the system. Simulation results obtained
using MATLAB/Simulink show the performance of the proposed
control strategy for power flow management under various modes
of operation. The effectiveness of the topology and efficacy of
the proposed control strategy are validated through detailed
experimental studies, to demonstrate the capability of the system
operation in different modes.
Keywords—Hybrid system, solar photovoltaic, wind energy, transformer
coupled boost dual-half-bridge bidirectional converter, bidirectional
buck-boost converter, maximum power point tracking, fullbridge
bidirectional converter, battery charge control.
I. INTRODUCTION
RAPID depletion of fossil fuel reserves, ever increasing
energy demand and concerns over climate change motivate
power generation from renewable energy sources. Solar
photovoltaic (PV) and wind have emerged as popular energy
sources due to their eco-friendly nature and cost effectiveness.
However, these sources are intermittent in nature. Hence, it is
a challenge to supply stable and continuous power using these
sources. This can be addressed by efficiently integrating with
energy storage elements.
The interesting complementary behaviour of solar insolation
and wind velocity pattern coupled with the above mentioned
advantages, has led to the research on their integration resulting
in the hybrid PV-wind systems. For achieving the integration of
The authors are with the Department of Electrical Engineering,Department
of Energy Science and Enginnering, Indian Institute of Technology Bombay,
Mumbai 400076, India (email: bmangu@iitb.ac.in; akshathas@ee.iitb.ac.in;
suryad@iitb.ac.in; bgf@ee.iitb.ac.in
multiple renewable sources, the traditional approach involves
using dedicated single-input converters one for each source,
which are connected to a common dc-bus [1] – [15]. However,
these converters are not effectively utilized, due to the intermittent
nature of the renewable sources. In addition, there are
multiple power conversion stages which reduce the efficiency
of the system.
Significant amount of literature exists on the integration of
solar and wind energy as a hybrid energy generation system
with focus mainly on its sizing and optimization [7], [8]. In [7],
the sizing of generators in a hybrid system is investigated. In
this system, the sources and storage are interfaced at the dclink,
through their dedicated converters. Other contributions
are made on their modeling aspects and control techniques for
a stand-alone hybrid energy system in [9] – [15]. Dynamic
performance of a stand-alone hybrid PV-wind system with
battery storage is analyzed in [9]. In [14], a passivity/sliding
mode control is presented which controls the operation of
wind energy system to complement the solar energy generating
system.
Not many attempts are made to optimize the circuit configuration
of these systems that could reduce the cost and
increase the efficiency and reliability. In [16] – [19], integrated
converters for PV and wind energy systems are presented.
PV-wind hybrid system, proposed by Daniel et al. [16], has
a simple power topology but it is suitable for stand-alone
applications. An integrated four-port topology based on hybrid
PV-wind system is proposed in [18]. However, despite simple
topology the control scheme used is complex. In [19], to feed
the dc loads, a low capacity multi-port converter for a hybrid
system is presented.
Hybrid PV-wind based generation of electricity and its
interface with the power grid are the important research areas.
Chen et al. in [20], [21] have proposed a multi-input hybrid
PV-wind power generation system which has a buck/buckboost
fused multi-input dc-dc converter and a full-bridge dcac
inverter. This system is mainly focused on improving the
dc-link voltage regulation. In the six-arm converter topology
proposed by H. C. Chiang et al. [22], the outputs of a PV array
and wind generators are fed to a boost converter to match
the dc-bus voltage. The steady-state performance of a gridconnected
hybrid PV and wind system with battery storage
is analyzed in [4]. This paper focuses on system engineering,
such as energy production, system reliability, unit sizing, and
cost analysis. In [5], a hybrid PV-wind system along with
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This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JESTPE.2016.2544789, IEEE
Journal of Emerging and Selected Topics in Power Electronics
2
Fig. 1. Grid-connected hybrid PV-wind-battery based system for household
applications.
a battery is presented, in which both sources are connected
to a common dc-bus through individual power converters. In
addition, the dc-bus is connected to the utility grid through an
inverter.
The use of multi-input converter (MIC) for hybrid power
systems is attracting increasing attention because of reduced
component count, enhanced power density, compactness and
centralized control. Due to these advantages, many topologies
are proposed and they can be classified into three groups,
non-isolated, fully-isolated and partially-isolated multi-port
topologies.
All the power ports in non-isolated multi-port topologies
share a common ground. To derive the multi-port dc-dc converters,
a series or parallel configuration is employed in the
input side [23] – [27]. Some components can be shared by each
input port. However, a time-sharing control scheme couples
each input port, and the flexibility of the energy delivery is
limited. The series or parallel configuration can be extended at
the output to derive multi-port dc-dc converters [28]. However,
the power components cannot be shared. All the topologies
in non-isolated multi-port are mostly combinations of basic
topology units, such as the buck, the boost, the buck-boost
or the bidirectional buck/boost topology unit. These timesharing
based multi-port topologies promise low-cost and easy
implementation. However, a common limitation is that power
from multiple inputs cannot be transferred simultaneously to
the load. Further, matching wide voltage ranges will be difficult
in these circuits. This made the researchers to prefer isolated
multi-port converters compared to non-isolated multi-port dcdc
converters.
The magnetic coupling approach is used to derive a multiport
converter [29] – [32], where the multi-winding transformer
is employed to combine each terminal. In fully isolated multiport
dc-dc converters, the half-bridge, full-bridge, and hybridstructure
based multi-port dc-dc converters with a magnetic
coupling solution can be derived for different applications,
power, voltage, and current levels. The snubber capacitors and
transformer leakage inductance are employed to achieve softswitching
by adjusting the phase-shift angle. However, the
circuit layout is complex and the only sharing component is
the multi-winding transformer. So, the disadvantage of time
sharing control to couple input port is overcome. Here, among
multiple inputs, each input has its own power components
which increases the component count. Also, the design of
multi-winding transformer is an involved process.
In order to address the above limitations, partially isolated
multi-port topologies [33] – [39] are becoming increasingly
attractive. In these topologies, some power ports share a
common ground and these power ports are isolated from
the remaining, for matching port voltage levels. A tri-modal
half-bridge topology is proposed by Al-Atrash et al. in [33]
and [34]. This topology is essentially a modified version of
the half-bridge topology with a free-wheeling circuit branch
consisting of a diode and a switch across the primary winding
of the transformer. The magnetizing inductance of the
transformer is used to store energy, and to interface the
sources/storage devices. Wuhua Li et.al. [37] – [38], have
proposed a decoupled controlled tri-port dc-dc converter for
multiple energy interface. The power density is improved and
circuit structure is simplified. However, it can interface only
one renewable source and energy storage element. Further,
the pulse width modulation plus phase-shift control strategy
is introduced to provide two control freedoms and achieve the
decoupled voltage regulation within a certain operating range.
All the state of the art on converter topologies presented
so far can accommodate only one renewable source and one
energy storage element. Whereas, the proposed topology is
capable of interfacing two renewable sources and an energy
storage element. Hence, it is more reliable as two different
types of renewable sources like PV and wind are used either
individually or simultaneously without increase in the component
count compared to the existing state of the art topologies.
The proposed system has two renewable power sources,
load, grid and battery. Hence, a power flow management
system is essential to balance the power flow among all these
sources. The main objectives of this system are as follows:
• To explore a multi-objective control scheme for optimal
charging of the battery using multiple sources.
• Supplying un-interruptible power to loads.
• Ensuring evacuation of surplus power from renewable
sources to the grid, and charging the battery from grid
as and when required.
The grid-connected hybrid PV-wind-battery based system
for household applications is shown in Fig. 1, which can work
either in stand-alone or grid connected mode. This system is
suitable for household applications, where a low-cost, simple
and compact topology capable of autonomous operation is
desirable. The core of the proposed system is the multiinput
transformer coupled bidirectional dc-dc converter that
interconnects various power sources and the storage element.
Further, a control scheme for effective power flow management
to provide uninterrupted power supply to the loads, while
injecting excess power into the grid is proposed. Thus, the
proposed configuration and control scheme provide an elegant
integration of PV and wind energy source. It has the following
advantages:
• MPP tracking of both the sources, battery charging
control and bidirectional power flow are accomplished
2168-6777 (c) 2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JESTPE.2016.2544789, IEEE
Journal of Emerging and Selected Topics in Power Electronics
3
with six controllable switches.
• The voltage boosting capability is accomplished by
connecting PV and battery in series which is further
enhanced by a high frequency step-up transformer.
• Improved utilization factor of the power converter, since
the use of dedicated converters for ensuring MPP operation
of both the sources is eliminated.
• Galvanic isolation between input sources and the load.
• The proposed controller can operate in different modes
of a grid-connected scheme ensuring proper operating
mode selection and smooth transition between different
possible operating modes.
• Enhancement in the battery charging efficiency as a
single converter is present in the battery charging path
from the PV source.
The basic philosophy and preliminary study of a compact and
low-cost multi-input transformer coupled dc-dc converter capable
of interfacing multiple sources for a stand-alone application
is presented in [40]. In the present paper, the integration of
renewable sources to the grid, detailed analysis, exhaustive
simulation and experimental studies have now been included.
This paper is organised as follows: In section II, the power
circuit configuration of the grid-connected hybrid PV-windbattery
system is described along with its analysis. Control
strategy for effective power flow management and various
operating modes of the system are explained in section III.
In sections IV & V, simulation and experimental results are
presented to validate the performance of the proposed system.
Finally, the conclusions are summarised in section VI.
II. PROPOSED CONVERTER CONFIGURATION
The proposed converter consists of a transformer coupled
boost dual-half-bridge bidirectional converter fused with bidirectional
buck-boost converter and a single-phase full-bridge
inverter. The proposed converter has reduced number of power
conversion stages with less component count and high efficiency
compared to the existing grid-connected schemes. The
topology is simple and needs only six power switches. The
schematic diagram of the converter is depicted in Fig. 2(a).
The boost dual-half-bridge converter has two dc-links on both
sides of the high frequency transformer. Controlling the voltage
of one of the dc-links, ensures controlling the voltage of
the other. This makes the control strategy simple. Moreover,
additional converters can be integrated with any one of the
two dc-links. A bidirectional buck-boost dc-dc converter is
integrated with the primary side dc-link and single-phase fullbridge
bidirectional converter is connected to the dc-link of
the secondary side.
The input of the half-bridge converter is formed by connecting
the PV array in series with the battery, thereby incorporating
an inherent boosting stage for the scheme. The boosting
capability is further enhanced by a high frequency step-up
transformer. The transformer also ensures galvanic isolation to
the load from the sources and the battery. Bidirectional buckboost
converter is used to harness power from PV along with
battery charging/discharging control. The unique feature of
this converter is that MPP tracking, battery charge control and
voltage boosting are accomplished through a single converter.
Transformer coupled boost half-bridge converter is used for
harnessing power from wind and a single-phase full-bridge
bidirectional converter is used for feeding ac loads and interaction
with grid. The proposed converter has reduced number of
power conversion stages with less component count and high
efficiency compared to the existing grid-connected converters.
The power flow from wind source is controlled through a
unidirectional boost half-bridge converter. For obtaining MPP
effectively, smooth variation in source current is required
which can be obtained using an inductor. In the proposed topology,
an inductor is placed in series with the wind source which
ensures continuous current and thus this inductor current can
be used for maintaining MPP current. When switch T 3 is ON,
the current flowing through the source inductor increases. The
capacitor C1 discharges through the transformer primary and
switch T 3 as shown in Fig. 2(b). In secondary side capacitor
C3 charges through transformer secondary and anti-parallel
diode of switch T 5. When switch T 3 is turned OFF and T 4
is turned ON, initially the inductor current flows through antiparallel
diode of switch T 4 and through the capacitor bank.
The path of current is shown in Fig. 2(c). During this interval,
the current flowing through diode decreases and that flowing
through transformer primary increases. When current flowing
through the inductor becomes equal to that flowing through
transformer primary, the diode turns OFF. Since, T 4 is gated
ON during this time, the capacitor C2 now discharges through
switch T 4 and transformer primary. During the ON time of
T 4, anti-parallel diode of switch T 6 conducts to charge the
capacitor C4. The path of current flow is shown in Fig. 2(d).
During the ON time of T 3, the primary voltage VP = −VC1.
The secondary voltage VS = nVp = −nVC1 = −VC3, or
VC3 = nVC1 and voltage across primary inductor Lw is Vw.
When T 3 is turned OFF and T 4 turned ON, the primary voltage
VP = VC2. Secondary voltage VS = nVP = nVC2 = VC4
and voltage across primary inductor Lw is Vw −(VC1 +VC2).
It can be proved that (VC1 + VC2) = Vw
(1−Dw) . The capacitor
voltages are considered constant in steady state and they settle
at VC3 = nVC1, VC4 = nVC2. Hence the output voltage is
given by
Vdc = VC3 + VC4 = n
Vw
(1 − Dw)
(1)
Therefore, the output voltage of the secondary side dc-link is
a function of the duty cycle of the primary side converter and
turns ratio of transformer.
In the proposed configuration as shown in Fig. 2(a), a
bidirectional buck-boost converter is used for MPP tracking
of PV array and battery charging/discharging control. Further,
this bidirectional buck-boost converter charges/discharges the
capacitor bank C1-C2 of transformer coupled half-bridge boost
converter based on the load demand. The half-bridge boost
converter extracts energy from the wind source to the capacitor
bank C1-C2. During battery charging mode, When switch T 1
is ON, the energy is stored in the inductor L. When switch
T 1 is turned OFF and T 2 is turned ON, energy stored in L is
transferred to the battery. If the battery discharging current is
more than the PV current, inductor current becomes negative.
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This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JESTPE.2016.2544789, IEEE
Journal of Emerging and Selected Topics in Power Electronics
4
Fig. 2. Operating modes of proposed multi-input transformer coupled bidirectional dc-dc converter. (a) Proposed converter configuration. (b) Operation when
switch T3 is turned ON. (c) Operation when switch T4 ON, charging the capacitor bank. (d) Operation when switch T4 ON, capacitor C2 discharging.
Fig. 3. Proposed control scheme for power flow management of a grid-connected hybrid PV-wind-battery based system.
Here, the stored energy in the inductor increases when T 2 is
turned on and decreases when T 1 is turned on. It can be proved
that Vb = D
1−DVpv. The output voltage of the transformer
coupled boost half-bridge converter is given by,
Vdc = n(VC1 + VC2) = n(Vb + Vpv) =
nVw
(1 − Dw)
(2)
This voltage is n times of primary side dc-link voltage. The
primary side dc-link voltage can be controlled by half-bridge
boost converter or by bidirectional buck-boost converter. The
relationship between the average value of inductor, PV and
battery current over a switching cycle is given by IL = Ib + Ipv.
It is evident that, Ib and Ipv can be controlled by controlling
IL. Therefore, the MPP operation is assured by controlling IL,
while maintaining proper battery charge level. IL is used as
inner loop control parameter for faster dynamic response while
for outer loop, capacitor voltage across PV source is used for
ensuring MPP voltage. An incremental conductance method is
used for MPPT.
A. Limitations and Design issues
The output voltage Vdc of transformer coupled boost dual
half-bridge converter, depends on MPP voltage of PV array
VPV mpp, the battery voltage Vb and the transformer turns
ratio n. Since the environmental conditions influence PV array
voltage and the battery voltage depends on its charge level,
the output dc-link voltage Vdc is also influenced by the same.
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This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JESTPE.2016.2544789, IEEE
Journal of Emerging and Selected Topics in Power Electronics
5
However, the PV array voltage exhibits narrow variation in
voltage range with wide variation in environmental conditions.
On the other hand, the battery voltage is generally stiff and it
remains within a limited range over its entire charge-discharge
cycle. Further, the SOC limits the operating range of the
batteries used in a stand-alone scheme to avoid overcharge
or discharge. Therefore, with proper selection of n, PV array
and battery voltage the output dc-link voltage Vdc can be kept
within an allowable range, though not controllable. However,
when there is no PV power, by controlling the PV capacitor
voltage the output dc-link voltage Vdc can be controlled.
III. PROPOSED CONTROL SCHEME FOR POWER FLOW
MANAGEMENT
A grid-connected hybrid PV-wind-battery based system consisting
of four power sources (grid, PV, wind source and
battery) and three power sinks (grid, battery and load), requires
a control scheme for power flow management to balance the
power flow among these sources.
The control philosophy for power flow management of the
multi-source system is developed based on the power balance
principle. In the stand-alone case, PV and wind source generate
their corresponding MPP power and load takes the required
power. In this case, the power balance is achieved by charging
the battery until it reaches its maximum charging current limit
Ibmax. Upon reaching this limit, to ensure power balance, one
of the sources or both have to deviate from their MPP power
based on the load demand. In the grid-connected system both
the sources always operate at their MPP. In the absence of
both the sources, the power is drawn from the grid to charge
the battery as and when required. The equation for the power
balance of the system is given by:
VpvIpv + VwIw = VbIb + VgIg (3)
The peak value of the output voltage for a single-phase fullbridge
inverter is,
bv = maVdc (4)
and the dc-link voltage is,
Vdc = n(Vpv + Vb) (5)
Hence, by substituting for Vdc in (4), gives,
Vg =
1
p2
man(Vpv + Vb) (6)
In the boost half-bridge converter,
Vw = (1 − Dw)(Vpv + Vb) (7)
Now substituting Vw and Vg in (3),
VpvIpv+(Vpv+Vb)(1−Dw)Iw = VbIb+
1
p2
man(Vpv+Vb)Ig
(8)
After simplification,
Ib = Ipv

1 − Dpv
Dpv

+Iw

1 − Dw
Dpv

−Ig

man
p2Dpv
!
(9)
TABLE I. SIMULATION PARAMETERS
Parameter Value
525 W
Solar PV power (Impp = 14.8 A)
(Vmpp = 35.4 V)
300 W
Wind power (Impp = 8 A)
(Vmpp = 37.5 V)
Switching frequency 15 kHz
Transformer turns ratio 5.5
Inductor-half bridge boost converter, Lw 500 μH
Inductor-bidirectional converter L 3000 μH
Primary side capacitors C1-C2 500μF
secondary side capacitors C3-C4 500μF
Secondary side capacitor for the entire dc-link 2000 μF
Battery capacity & voltage 400 Ah, 36 V
From the above equation it is evident that, if there is a change
in power extracted from either PV or wind source, the battery
current can be regulated by controlling the grid current Ig.
Hence, the control of a single-phase full-bridge bidirectional
converter depends on availability of grid, power from PV and
wind sources and battery charge status. Its control strategy is
illustrated using Fig. 3. To ensure the supply of uninterrupted
power to critical loads, priority is given to charge the batteries.
After reaching the maximum battery charging current limit
Ibmax, the surplus power from renewable sources is fed to
the grid. In the absence of these sources, battery is charged
from the grid.
IV. SIMULATION RESULTS AND DISCUSSION
Detailed simulation studies are carried out on MATLAB/
Simulink platform and the results obtained for various
operating conditions are presented in this section. Values of
parameters used in the model for simulation are listed in
Table I.
The steady state response of the system during the MPPT
mode of operation is shown in Fig. 4. The values for source-
1 (PV source) is set at 35.4 V (Vmpp) and 14.8 A (Imppp),
and for source-2 (wind source) is set at 37.5 V (Vmpp) and
8 A (Imppp). It can be seen that Vpv and Ipv of source-1,
and Vw and Iw of source-2 attain set values required for MPP
operation. The battery is charged with the constant magnitude
of current and remaining power is fed to the grid.
The system response for step changes in the source-1
insolation level while operating in MPPT mode is shown in
Fig. 5. Until 2 s, both the sources are operating at MPPT and
charging the battery with constant current and the remaining
power is fed to the grid. At instant 2 s, the source-1 insolation
level is increased. As a result the source-1 power increases
and both the sources continue to operate at MPPT. Though the
source-1 power has increased, the battery is still charged with
the same magnitude of current and power balance is achieved
by increasing the power supplied to the grid. At instant 4 s,
insolation of source-1 is brought to the same level as before 2
s. The power supplied by source-1 decreases. Battery continues
to get charged at the same magnitude of current, and power
injected into the grid decreases. The same results are obtained
for step changes in source-2 wind speed level. These results
2168-6777 (c) 2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JESTPE.2016.2544789, IEEE
Journal of Emerging and Selected Topics in Power Electronics
6
Fig. 4. Steady state operation in MPPT mode.
Fig. 5. Response of the system for changes in insolation level of source-1
(PV source) during operation in MPPT mode.
are shown in Fig. 6.
The response of the system in the absence of source-1 is
shown in Fig. 7. Till time 2 s, both the sources are generating
the power by operating at their corresponding MPPT and
charging the battery at constant magnitude of current, and
the remaining power is being fed to the grid. At 2 s, source-
1 is disconnected from the system. The charging current of
the battery remains constant, while the injected power to the
grid reduces. At instant 4 s, source-1 is brought back into the
system. There is no change in the charging rate of the battery.
The additional power is fed to grid. The same results are
obtained in the absence of source-2. These results are shown
in Fig. 8. Fig. 9 shows the results in the absence of both PV
t]
Fig. 6. Response of the system for changes in wind speed level of source-2
(wind source) during operation in MPPT mode.
Fig. 7. Response of the system in the absence of source-1 (PV source) while
source-2 continues to operate at MPPT.
and wind power, battery is charged from the grid.
V. EXPERIMENTAL VALIDATION
To verify the simulation results, experimental tests are
carried out on a laboratory prototype shown in Fig. 10. The
specifications of experimental set up are given in Table II.
The control strategy is implemented by employing Texas
Instruments floating-point DSP, TMS320F28335.
A. Design of multi-input transformer coupled dc-dc converter
The MPP voltage of the PV is considered as 36 V (Vmpp).
The nominal voltage level of the battery is chosen as 36 V
(Vb). The voltage across the dc-bus at the primary side of the
transformer is (V c1 + V c2) which is equal to (Vpv+Vb). It
implies that this dc-bus voltage depends on the magnitude of
Vpv and Vb. An overall variation of ± 10 V on (Vpv+Vb) is
considered for design purpose and thus overall variation in this
dc-bus is in the range of 62-82 V.
The dc-bus voltage at the transformer secondary side, Vdc is
2168-6777 (c) 2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JESTPE.2016.2544789, IEEE
Journal of Emerging and Selected Topics in Power Electronics
7
Fig. 8. Response of the system in the absence of source-2 (wind source)
while source-1 continues to operate at MPPT.
Fig. 9. Response of the system in the absence of both the sources and
charging the battery from grid.
required to be maintained at 350 V. Since, the dc-link voltage at
secondary side is ‘n times the dc-link voltage at primary side,
‘n turns out to be 5.65 (=350/62). Now, considering voltage
drops at transformer primary and secondary sides, the turns
ratio is chosen to be 6. During ON/OFF operation of switches
T3 and T4 (Fig.2), each of the capacitors, C1 and C2, appear
across the transformer primary winding. Considering the range
of variation of voltage of the wind source as 36-44 V, the
capacitors C1 and C2 will experience a voltage in the range
of 18-46 V (calculation is given below). Therefore, by keeping
a small safety factor, the transformer primary voltage is chosen
as 50 V. Thus, the secondary voltage rating is chosen as, 6 × 50 V = 300 V. The transformer chosen has a capacity of 1
kVA.
The range for Vw=36-44 V, and the range for the dc-bus on
the transformer primary side, Vbus (Vc1 + Vc2) is 62-82 V.
The relationship between Vw and Vbus is, Vbus = Vw
1−D, where
D is duty ratio of switch T3. For Vw=44 V, and Vbus = 82 V,
D = 1 −

Vw
Vbus

= 0.46. (10)
TABLE II. SPECIFICATIONS OF EXPERIMENTAL SET UP
Parameter Value Part number
Solar PV power 250 W
Wind power 250 W
Total load power 500 W
MOSFET- T1-T4 200 V, 90 A IRFP4668PbF
IGBT- S1-S4 1200 V, 20 A IRG7PH35UD1PbF
Diode- D1-D2 1000 V,60 A STTH6010W
Capacitor- Cb 1000μF, 100 V SLPX102M100A3P3
Capacitor- C1-C2 560μF, 100 V 100ZLJ560M
Capacitor- C3-C4 560μF, 400 V MCLPR400V567M
Capacitor- Cw 1000μF, 63 V ECA1JHG102
Capacitor- Cpv 2000μF, 200 V CGS202T200V4C
Inductor- L 3000μH, 40 A
Inductor -Lw 500μH, 50 A
Inductor -Lb 1000μH, 30 A
Battery 12 X 3 V, 7.2 Ah
Solar Emulator
Wind Emulator
Oscilloscope
Sensing circuit
Power circuit
HF transformer
Batteries
Load
Inverter
Fig. 10. Experimental setup of the proposed grid-connected hybrid PV-windbattery
based system
In steady state,
DV c1 − (1 − D)V c2 = 0, (11)
and V c1 + V c2 = Vbus. From these equations, various values
for V c1 and V c2 considering all extreme cases are given in
Table III.
TABLE III. RANGES OF Vc1 AND Vc2 FOR VALUES OF Vw AND Vbus
Vw (V) Vbus (V) D 1 − D Vc1 (V) Vc2 (V)
44 82 0.46 0.53 44 38
36 82 0.56 0.44 36 46
44 62 0.29 0.71 44 18
36 62 0.42 0.58 36 26
The steady state response of the system during the MPPT
mode of operation is shown in Fig. 11. The values for source-1
(PV source) and source-2 (wind source), are set at 40 V (Vmpp)
and 5 A (Imppp) respectively and both the sources attain the
set value required for MPP operation. The battery is charged
at a constant magnitude of current and remaining power is fed
to the grid.
The system response for step changes in the source-1
insolation level while operating in MPPT mode is shown in
Fig. 12. Until time t1, both the sources are operating at MPPT,
battery is charged at a constant current and the remaining
power is fed to the grid. At time t1, source-1 insolation level
is increased. As a result the source-1 power increases. Both
2168-6777 (c) 2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JESTPE.2016.2544789, IEEE
Journal of Emerging and Selected Topics in Power Electronics
8
Fig. 11. Steady state operation in MPPT mode (vpv=10V/div; ipv=2A/div;
vw=20V/div; iw=2A/div; vg=200V/div; ig=2A/div; ib=2A/div). Zoomed version
of vg & ig during steady state operation.
Fig. 12. Response of the system for changes in insolation level of source-
1 (PV source) during operation in MPPT mode (vpv=10V/div; ipv=1A/div;
vw=50V/div; iw=5A/div; vg=200V/div; ig=2A/div; ib=2A/div). Zoomed version
of vg & ig during step change in insolation.
Fig. 13. Response of the system in the absence of source-1 (PV source)
while source-2 continues to operate at MPPT (vpv=10V/div; ipv=2A/div;
vw=20V/div; iw=2A/div; vg=200V/div; ig=2A/div; ib=2A/div). Zoomed version
of vg & ig in the absence of source-1.
Fig. 14. Response of the system for changes in wind speed level of
source-2 (wind source) during operation in MPPT mode (vpv=10V/div;
ipv=1A/div; vw=10V/div; iw=1A/div; vg=200V/div; ig=2A/div; ib=2A/div).
Zoomed version of vg & ig during step change in insolation.
Fig. 15. Response of the system in the absence of source-2 (wind source)
while source-1 continues to operate at MPPT (vpv=10V/div; ipv=1A/div;
vw=10V/div; iw=1A/div; vg=200V/div; ig=2A/div; ib=2A/div). Zoomed version
of vg & ig in the absence of source-2.
the sources continue to operate at MPP. Though the source-1
power has increased, the battery is still charged at the same
magnitude of current. The additional power is fed to the grid.
At time t2, source-1 is brought to the same insolation level as
before t1. The power generated by the source-1 decreases, and
there is no change in charging current of the battery. The power
injected to the grid decreases. The same results are obtained
for step changes in source-2 wind speed level. These results
are shown in Fig. 14.
The response of the system without source-1 is shown in
Fig. 13. Till time t1, both the sources are present in the system,
operating at their corresponding MPP and charging the battery
at constant magnitude of current. The remaining power is fed to
the grid. At time t1, source-1 is disconnected from the system.
However, the battery continues to get charged at the same rate,
and the power injected into the grid reduces. At time t2, source-
1 is brought back into the system. This additional power is
injected into the grid. The same results are obtained in the
absence of source-2. These results are shown in Fig. 15.
2168-6777 (c) 2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JESTPE.2016.2544789, IEEE
Journal of Emerging and Selected Topics in Power Electronics
9
Fig. 16. Response of the system during changes of the operating
mode from grid-connected without injection to grid-connected with injection
(vpv=10V/div; ipv=1A/div; vw=10V/div; iw=1A/div; vg=200V/div;
ig=2A/div; ib=2A/div). Zoomed version of vg & ig during mode transition.
Fig. 16 shows that when the battery reaches its float voltage
Vbref , it goes to constant voltage mode. The surplus power
from the renewable sources is fed to the grid. It is clear that
before the battery reaches its float voltage the current injected
into grid is zero, and it increases thereafter.
VI. CONCLUSION
A grid-connected hybrid PV-wind-battery based power evacuation
scheme for household application is proposed. The
proposed hybrid system provides an elegant integration of PV
and wind source to extract maximum energy from the two
sources. It is realized by a novel multi-input transformer coupled
bidirectional dc-dc converter followed by a conventional
full-bridge inverter. A versatile control strategy which achieves
better utilization of PV, wind power, battery capacities without
effecting life of battery and power flow management in a
grid-connected hybrid PV-wind-battery based system feeding
ac loads is presented. Detailed simulation studies are carried
out to ascertain the viability of the scheme. The experimental
results obtained are in close agreement with simulations and
are supportive in demonstrating the capability of the system
to operate either in grid feeding or stand-alone mode. The
proposed configuration is capable of supplying un-interruptible
power to ac loads, and ensures evacuation of surplus PV and
wind power into the grid.
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B. Mangu (M’15) was born in Warangal, India,
in 1975. He received B.E. and M.E. degrees from
University College of Engineering, Osmania University,
Hyderabad, India in the year 2000 and
2005 respectively. Since 2001, he has been with
the Department of Electrical Engineering, University
College of Engineering, Osmania University, Hyderabad,
where he is currently a Associate Professor.
He is currently working towards the Ph.D. degree,
in the Department of Electrical Engineering, Indian
Institute of Technology Bombay, Mumbai, India. His
research interests include design of converters for integration of renewable
sources.
S. Akshata (S’16) received the B.E. degree from
Visvesvaraya Technological University, Belgaum, India
and M.Tech. degree from National Institute of
Technology, Surathkal, India, in 2005 and 2012 respectively.
From 2012 to 2014, she was with Sukam
Power Systems Ltd., India, as Design Engineer.
Her research interests include power electronic converter
topologies for integration of renewable energy
sources with ac grids. She is currently working
towards the Ph.D. degree at Indian Institute of Technology
Bombay, Mumbai, India.
D. Suryanarayana (M’06) is currently an Associate
Professor at the Indian Institute of Technology
Bombay, where he teaches and directs research in
power electronics and power systems as a faculty
member of the Energy Science and Engineering
Department. He is currently serving as Associate
Editor for Electric Power Components and Systems,
Editorial Board Member for International Journal of
Sustainable Energy (Taylor & Francis Journals) and
Associate Editor for IEEE Transactions on Industrial
Applications. His research interest include Grid integration
of distributed energy resources, Smartgrids, Microgrids, Converter
topologies and control, Communication protocol for power systems..
B. G. Fernandes (M’95) graduated from National
Institute of Technology, Surathkal in 1984. He has
received M.Tech and Ph.D. from I.I.T., Kharagpur
and I.I.T., Bombay in 1989 and 1993 respectively.
He joined the Department of Electrical Engineering
at I.I.T., Kanpur in 1993 as Assistant Professor. In
Dec. 1998, he joined I.I.T., Bombay, India where he
is currently a Professor. His present research interests
include motors for electric vehicles, reactive power
compensation and power electronic interfaces for
non conventional energy sources.