Received October 2, 2021, accepted October 19, 2021, date of publication October 26, 2021, date of current version December 2, 2021.
Digital Object Identifier 10.1109/ACCESS.2021.3122877
Dual Output and High Voltage Gain DC-DC
Converter for PV and Fuel Cell Generators
Connected to DC Bipolar Microgrids
V. FERNÃO PIRES 1,3, (Senior Member, IEEE), ARMANDO CORDEIRO 2,3, DANIEL FOITO 1,4,
AND J. FERNANDO A. SILVA 3,5, (Senior Member, IEEE)
1SustainRD, ESTSetúbal, Polytechnic Institute of Setúbal, 2914-508 Setúbal, Portugal
2ISEL, Polytechnic Institute of Lisbon, 1959-007 Lisbon, Portugal
3INESC-ID, 1049-001 Lisbon, Portugal
4CTS-UNINOVA, New University of Lisbon, 2829-516 Caparica, Portugal
5IST, University of Lisbon, 1049-001 Lisboa, Portugal
Corresponding author: V. Fernão Pires (vitor.pires@estsetubal.ips.pt)
This work was supported by the National Funds through Fundação para a Ciência e a Tecnologia (FCT) under Grant UIDB/50021/2020
and Grant UIDB/00066/2020.
ABSTRACT This paper introduces a new topology for a DC-DC converter with bipolar output and high
voltage gain. The topology was designed with the aim to use only one active power switch. Besides the
bipolar multiport output and high voltage gain this converter has another important feature, namely, it has
a continuous input current. Due to the self-balancing bipolar outputs, the proposed topology is suitable for
bipolar DC microgrids. Indeed, the topology balancing capability can achieve the two symmetrical voltage
poles of bipolarDCmicrogrids. Furthermore, it is possible to create a midpoint in the output of the converter
that can be directly connected to the ground of the DC power supply, avoiding common-mode leakage
currents in critical applications such as transformerless grid-connect PV systems. The operating principle of
the proposed topology will be supported by mathematical analysis. To validate and verify the characteristics
of the presented topology, several experimental results are shown.
INDEX TERMS Photovoltaic (PV) systems, fuel Cell, DC-DC converter, bipolar DC microgrid,
single-switch.
I. INTRODUCTION
Energy conversion systems are extremely important for mod-
ern societies and are present in different forms in most
domestic, commercial and industrial applications [1]. With
the increasing challenges of CO2 reduction and proliferation
of solutions using clean and renewable resources (e.g. elec-
trification of transport or photovoltaic systems), the impor-
tance and interest around power electronic converters has
grown strongly over the last decades [2]. Numerous power
converters have been proposed over the years to overcome
different integration problems and, at the same time, improve
different economic and operational aspects of such sys-
tems. Among all power converters, the DC-DC converter
is currently one of the most important electronic circuit
in the overall decarbonization process allowing to mitigate
The associate editor coordinating the review of this manuscript and
approving it for publication was Bidyadhar Subudhi .
problems with integration of renewable energy sources
(RES) [3], smart grids [4], integration and optimization of
storage devices [5], electric vehicles [6], battery chargers [7]
and many others. Some of the most desired characteristics
of DC-DC converters are high-efficiency, cost effectiveness
and the voltage regulation capability in order to allow a
wide range of applicability. For certain applications, the
step-up voltage of the classic DC-DC converters can be
a simple and acceptable solution [8], [9]. However, for
applications where a high step-up ratio is required other
DC-DC converters have been reported in literature. In general
DC-DC converters are classified into two main categories:
isolated and non-isolated topologies [10]. Some isolated solu-
tions are based on a single-switch and a high frequency
transformer using either hard or soft-switching resonant
or quasi-resonant circuits [10], [11]. Other isolated solu-
tions using multiple switches, high frequency transformers,
quasi-Z source topologies and soft switching techniques can
157124 This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/ VOLUME 9, 2021
V. Fernão Pires et al.: Dual Output and High Voltage Gain DC-DC Converter for PV and Fuel Cell Generators
be found in [12]–[14]. Other topologies are based on the
boost full-bridge [15], [16], isolated push-pull boost [17]
and isolated inductor-feed boost converter [18]. Using iso-
lated converters, it is possible to achieve relatively high
voltage regulation ratios and, in some cases, high efficiency
by properly designing the transformer’s turn ratio and the
soft-switching circuits. The costs associated with the high
number of switching devices and transformers, in addition
to more complicated control schemes and more isolated
sensors are some of the main drawbacks of these isolated
topologies. Some existing isolated voltage-type converters
also present pulsed input current, which negatively impacts
the life of PV arrays. Several non-isolated topologies have
also been proposed to extend the output to input voltage
transfer ratio (voltage gain) of existing boost converters.
Some advantages and applications of non-isolated topologies
can be found in [9], [19]. Some topologies are based on the
integration of different DC-DC converters and use a single
switch [20]–[22]. Other high step-up voltage converters are
based on coupled inductors [23], [24]. These solutions repre-
sent a simple, effective, and promising alternative to achieve a
wide range of voltage conversion. Other high step-up voltage
converters are based on switched inductors and switched
capacitors cells [25]–[28]. Some solutions to achieve high
step-up voltage ratios are based on voltage-multiplier or
voltage-lift techniques [29]–[31]. Quadratic boost converters
and quasi-Z source topologies also provide another effective
method to obtain high-step-up voltage gains [32]–[36]. These
converters have usually less volume, simpler circuits and
are more suitable for extreme voltage applications. Despite
several advantages of non-isolated boost converters, some
require multiple switching devices to achieve high-step-up
voltage gains, which increase the cost and complexity. Some
converters require only a single switching device but present
limited voltage gain. In practical terms, due to large para-
sitic capacitors at the ground of the PV panels, the leakage
current in the non-isolated PV grid-connected system is an
important issue and a key problem. A review of non-isolated
high step-upDC-DC converters forPV applications regarding
these issues can be found in [37].
Very important applications of DC-DC converters can be
found in the context of theDCmicrogrids. Main architectures
of DC microgrids include the unipolar and bipolar wiring
configurations. The bipolar architecture microgrid has two
poles presenting symmetrical voltages regarding a ground
pole and is becoming attractive due to several advantages
such as, higher resilience, increased efficiency and power
supply with higher quality [38]. However, bipolar microgrids
can suffer from an important disadvantage, namely the bipo-
lar voltage unbalance. Unbalances are due to the connection
of loads with different power or characteristics to the two
poles whose voltage variation departs from the voltage sym-
metry. To eliminate or attenuate this disadvantage solutions
like the use of voltage balancers were proposed [39], [40].
However, this approach requires an extra power converter,
increasing the cost and losses of the system. Better solutions
require that the DC-DC generators balance the bipolar DC
microgrid voltages. To achieve this, the use of converters with
dual outputs, a common connection and symmetrical volt-
age outputs are needed [41]–[46]. However, these solutions
normally require extra switches and/or have limited voltage
gain.
In this paper a new DC-DC converter indicated to be used
in bipolar DC microgrids is proposed hereafter. To be able
to balance bipolar microgrids voltages the proposed topology
outputs dual symmetrical voltages. Besides, the converter has
also been designed to offer a very high voltage gain and
continuous input current using only a single active switch.
Therefore, the proposed converter is extremely suited for RES
such as PV and fuel cell generators. Also, the proposed design
allows a relatively reduced voltage stress across all power
semiconductors of theDC-DC converter. The topology is also
suitable for use in transformerless grid-connect solar PV and
fuel cell generators. The design and analysis of the converter
will be addressed in detail in the next sections. Some exper-
imental results from a laboratory prototype are presented to
confirm the theoretical validity of proposed converter.
FIGURE 1. Power circuit configuration of the proposed DC-DC converter
connected to bipolar DC microgrid.
II. DESCRIPTION OF THE PROPOSED DC-DC CONVERTER
To mitigate voltage unbalances in bipolar DC microgrids,
DC-DC converters of RES applications, like PV and fuel
cell generators, must be able to inject the power into the
two poles of the microgrid as a way to balance the bipolar
voltages. Thus, the proposed converter has dual outputs VCo1
and VCo2 illustrated in Fig. 1. Besides the important advan-
tage of self-balancing the bipolarDCmicrogrid, the proposed
converter has high voltage gain and continuous input current.
The proposed converter power circuit needs only a single
active switch (Sw), two inductors (L1 and L2), three capacitors
(C1, C2 and C3) and four diodes (D1 to D4). From circuit
VOLUME 9, 2021 157125
V. Fernão Pires et al.: Dual Output and High Voltage Gain DC-DC Converter for PV and Fuel Cell Generators
analysis it is verified that the active switch does not withstand
all the load voltage, given by the sum of the voltages across
the output capacitors Co1 and Co2.
The proposed circuit is also suited for applications like
grid connected solar PV and fuel cell generators. One of the
problems associated to the use of DC-DC converters in PV
and fuel cell applications with transformerless inverter is the
common mode leakage current. So, similar to previous case,
the ground of the PV panel (or fuel cell) is directly connected
to the neutral of the AC grid (green line of Fig. 2).
FIGURE 2. Connection of the proposed DC-DC converter to a half-bridge
three level single phase inverter for transformerless PV applications.
III. ANALYSIS AND OPERATING PRINCIPLE OF THE
PROPOSED DC-DC CONVERTER
As mentioned before, the circuit allows for continuous input
current and high voltage gain. This can be verified through the
analysis of the circuit in steady state behaviour and consid-
ering operation in the continuous conduction mode (CCM).
In accordance with these assumptions, there are two possible
operating modes, each one associated to one equivalent cir-
cuit (Fig. 4). Themainwaveforms of the voltages and currents
in this circuit that are associated to the two operating modes
are shown in Fig. 3.
From the analysis of the circuit the behaviour of the con-
verter for each operating mode is described as follows:
A. OPERATING MODE I (TIME INTERVAL to-t1)
During this interval the turn ON voltage is applied in the gate
of the transistor, resulting on the equivalent circuit of Fig. 4
a). Thus, inductors L1 and L2 have a positive voltage (input
voltage source plus C2 capacitor voltage and C1 capacitor
voltage) increasing their currents. The current in inductor L1
will flow through capacitor C1 (discharging it), transistor SW
and voltage source Vi. The current in the inductor L2 will flow
through transistor SW and capacitor C2 (discharging it). The
discharge of the capacitor C3 depends of the output buses.
Thus, if the voltage in capacitor Co1 is lower than capacitor
Co2, since the voltage of capacitor C3 is approximately equal
to the capacitor Co1 then there will be no discharge of capaci-
torC3 over the capacitorCo2 since diodeD4 is reverse biased.
Otherwise, capacitor C3 will discharge over Co2 flowing the
current through those capacitors and transistor SW (see ­
in Fig. 4 a)).
FIGURE 3. Main Waveforms associated to the operating modes of the
proposed DC-DC converter.
FIGURE 4. Equivalent circuits associated to each of the operating modes:
a) time interval (to < t < t1)(Mode 1), b) time interval
(t1 < t < T )(Mode 2).
From the analysis of this operating mode I, the following
expressions are obtained by:
vL1 = L1
diL1
dt
= Vi + vC1
vL2 = L2
diL2
dt
= vC2
vCo2 = vC3
(1)
B. OPERATING MODE II (TIME INTERVAL t1-T)
In this time interval the transistor SW is turnedOFF, originat-
ing the equivalent circuit presented in Fig. 4 b). The voltages
across the inductors are now negative, forcing the currents
in inductor L1 and L2 to decrease (discharge of the induc-
tors). The current in the inductor L1 will flow now through
157126 VOLUME 9, 2021
V. Fernão Pires et al.: Dual Output and High Voltage Gain DC-DC Converter for PV and Fuel Cell Generators
diode D1, capacitor C2(charging it) and voltage source Vi.
The current in the inductor L2 will flow through capacitor
C1 (charging it) and diode D1. The charge of the capacitor
Co1 depends on the output buses. Thus, if the voltage in
capacitor Co1 is lower than capacitor Co2 then (since the volt-
age of capacitor C3 is approximately equal to the capacitor
Co2) there will be no charge of capacitor C3 since diode D2
is reverse biased. In this condition there will be a current
flowing through this capacitor charging it (¬ in Fig. 4 b)).
Otherwise, there will be a current flowing through capacitor
C3 charging it (­ in Fig. 4 b)). In this operating mode the
following expressions are obtained by:
vL1 = L1
diL1
dt
= Vi − vC2
vL2 = L2
diL2
dt
= vC1
vCo1 = vC2 + vL2 = vC2 + L2
diL2
dt
(2)
The voltage gain of this power converter topology can be
determined from the analysis of the described two operating
modes. Taking into consideration these modes and that the
average value of voltages of the two inductors in steady-state
are equal to zero, it is possible to obtain:
1
T
T∫
0
vL1dt =
1
T
[
t1∫
0
(Vi + vC1 )dt +
T∫
t1
(Vi − vC2 )dt
]
= 0
1
T
T∫
0
vL2dt =
1
T
[
t1∫
0
vC2dt −
T∫
t1
vC1dt
]
= 0
(3)
Also considering that the capacitors C1 and C2 are suf-
ficiently large, it can be assumed that the voltages at their
terminals will change linearly, as well as, their average values,
given by:
VC1 =
1
T
T∫
0
vC1dt =
1
t1
t1∫
0
vC1dt =
1
T − t1
T∫
t1
vC1dt
VC2 =
1
T
T∫
0
vC2dt =
1
t1
t1∫
0
vC2dt
(4)
Using these last two equations in equations (3), it will be
derived the equations that are described by:{
t1
(
Vi + VC1
) + (T − t1) (Vi − VC2) = 0
t1 VC2 − (T − t1) VC1 = 0 (5)
From these equations and considering δ = (t1/T ) the duty
cycle associated to the switch Sw, the average voltages of VC1
and VC2 are obtained by:
VC1 =
t1
(T − t1)2 − t21
Vi = δ1− 2δVi
VC2 =
T − t1
(T − t1)2 − t21
Vi = 1− δ1− 2δVi
(6)
Using these equations with (1) and (2), the average value
of the output capacitor voltages (or pole voltages) function of
the input voltage will be determined by:
VCo1 = VCo2 =
1
1− 2δVi (7)
From the voltage gain given by this last equation it is
foreseen that the proposed topology extends the voltage gain
to the double of the conventional quasi-Z DC-DC converter,
or obtains two outputs with the same gain.
IV. DESIGN OF THE POWER CONVERTER COMPONENTS
To determine the power semiconductors ratings, it will be
considered again the converter operating in CCM with no
losses. Thus, in steady state operation the next relationship
is given:
Pi = Po = ViIi = VoIo (8)
where the current variables Ii and Io are the average value of
the input voltage source and output load current.
Considering the relationship of the last expression and
the gain voltage of the converter given by (7), the average
value of the input current source is a function of the duty
cycle and output load current, being given by equation (9).
This expression also gives the average value of the inductor
currents of the power converter.
Ii = IL1 = IL2 =
2
1− 2δ Io (9)
For the design of the inductors and capacitors, it will be
considered that they depend of the rated voltages and cur-
rents and that they ensure small ripple for the current in the
inductors and voltage across the capacitors. Thus, consider-
ing the differential equation that represents the evolution of
the current in the inductors (10) and the voltage across the
inductor almost constant, the linear solution (11) is obtained.
From this last equation considering equation (10) and
1iT = iT (t)- iT (to), the new relationship given by (12) is
obtained.
diL (t)
dt
= vL (t)
L
(10)
iL (t) = vLL t1 + iL (to) (11)
1iL
t1
= vL
L
(12)
L1 = t1
(
Vi + VC1
)
1IL1
= δ (1− δ) Vi
(1− 2δ) fs1IL1
L2 = t1VC2
1IL2
= δ (1− δ) Vi
(1− 2δ) fs1IL2
(13)
To size the capacitors, a similar approach is used. Thus,
considering the differential equation that mathematically rep-
resents the behavior of the capacitors voltage and the currents
through the capacitors constant during the operation interval,
the following relationship is obtained:
1vC
1t
= iC
C
(14)
VOLUME 9, 2021 157127
V. Fernão Pires et al.: Dual Output and High Voltage Gain DC-DC Converter for PV and Fuel Cell Generators
From the previous relationship, the capacitors depend on
average currents of the capacitors and the time interval (t1-T):
Co1 = Co2 = t1Io
1VCo1,o2
= δIo
fs1VCo1,o2
C1 = t1IC1
1VC1
= 2 δ Io
(1− 2δ) fs1VC1
C2 = t2IC2
1VC2
= (1− δ) Io
fs1VC2
C3 = t2IC2
1VC2
= (1− δ) Io
fs1VC2
(15)
The determination of the power semiconductors current
stress can be done considering the average values of the
currents in inductors and from the condition that the average
values of the currents in each of the capacitors are zero in a
switching cycle (T ), giving:
ISw =
(
4δ
1− 2δ +
1
δ
)
Io; ID1 =
[
4 (1− δ)
1− 2δ +
1
1− δ
]
Io
ID2 =
1
1− δ Io
ID3 =
1
1− δ Io
ID4 =
1
δ
Io
(16)
These equations show that the current in the switch is
higher than the load current, as expected since the switch
voltage stress is lower than the load voltage.
To determine the voltages stress across the semiconductors,
it is considered that the voltage ripple across the capacitors
can be neglected. The voltages in the power semiconductors
are dependent on the capacitors voltages as written in (17).
These expressions show that the voltage stresses of the power
semiconductors are only half of the converter output voltage.
VSW = VCo1 =
Vo
2
VD1 = VC1 + VC2 =
Vo
2
VD2 = VCo2 =
Vo
2
VD3 = VCo1 =
Vo
2
VD4 = VCo2 =
Vo
2
(17)
V. EFFECTS OF NON-IDEALITIES OF THE INDUCTORS
The non-idealities of the circuit components will affect the
voltage gain of the power converter. The elements that have
more impact on that are the inductors. To verify that impact,
the circuit will be analyzed considering that the losses in those
inductors can be represented by an equivalent resistance.
In this way, associated to those inductors will be considered
that the resistances of rL1 and rL2 are in serial connection
with the inductors L1 and L2, respectively. For the analysis
of the power circuit in non-ideal conditions with the previous
assumptions, the load was considered as an equivalent resis-
tance R0. Thus, with all these considerations it is obtained the
static voltage gain of the converter, expressed by:
VDC_bus
VSt
= 2
rL1
Ro
(4− 8δ)
(1− 2δ)2 +
rL2
Ro
(4− 8δ)
(1− 2δ)2 + (1− 2δ)
(18)
To verify the impact of the inductors and load resistances,
it is shown in Fig. 5 the voltage gain of the converter as a
function of the duty cycle for different values of rL1 / R0 =
rL2 / R0. From Fig. 5 it is seen that the voltage gain is limited.
This limitation is function of the resistors values. Considering
for example rL1 / R0 = rL2 / R0 = 0.001, the maximum
voltage gain will be around 11, while if it is considered rL1 /
R0 = rL2 / R0 = 0.005, the maximum voltage gain is
reduced to 5.
VI. COMPARISON WITH EXISTING SIMILAR CONVERTERS
To analyze the characteristics of the proposed converter,
a comparison with other topologies was also performed. For
this comparison it was considered equivalent topologies that
could be connected to a bipolar microgrid (with the possibil-
ity to connect to a positive and negative pole). Table 1 presents
a comparison between the characteristics of the proposed
solution and similar topologies available on literature. The
proposed converter (right column) presents the highest static
voltage gain. It is also one of the topologies that require min-
imal number of switches. Regarding the passive components,
it is the second topology that requires a smaller number of
inductors (only topology [46] requires less). It also provides
common ground between the neutral pole of the microgrid
and the ground of the input voltage source. The proposed
solution was developed to operate in hard switching which
could contribute to increasing the power losses. However, the
proposed topology can also be extended to a soft switching
solution.
VII. SIMULATION AND EXPERIMENTAL TESTS
The proposed DC-DC converter based on a quasi-Z topology
with extended voltage gain and dual output characteristic was
FIGURE 5. Static voltage gain ratio function of the duty-cycle in non-ideal
conditions.
157128 VOLUME 9, 2021
V. Fernão Pires et al.: Dual Output and High Voltage Gain DC-DC Converter for PV and Fuel Cell Generators
TABLE 1. Comparison of the proposed converter to similar solutions.
subject to simulation and experimental tests. For the experi-
mental tests it was developed a prototype with demonstrating
purposes regarding their operating principle and confirmation
of their features. The simulation and experimental tests were
made in accordance with Fig. 1, in which inductors L1 and L2
have 1,1 mH, and capacitors of 100 µF, 68 µF and 68 µF are
used for C1, C2 and C3 respectively. For the output capacitors
C01 and C02 have a capacitance of 470 µF. The load con-
nected to the power converter consists in a 540 resistor. The
power converter is supplied by a DC power source with 60 V
and was operated with a switching frequency of 20 kHz. The
duty cycle was adjusted to obtain an output voltage of 400 V.
A. SIMULATION TESTS
The obtained simulation results for a duty cycle of 0.35 are
presented in Figs. 6 to 8. Fig. 6 presents the voltage wave-
forms of the input (Vi) and outputs (VCo1, VCo2 and Vo) of
the proposed power converter. In accordance with the defined
duty cycle, it is expected a theoretical gain of 6.7. Analyzing
this figure is possible to verify that a similar gain is obtained.
Besides that, it is possible to confirm that the voltages of the
output capacitors (Co1 and Co2) have practically the same
average value equal to half of the total output voltage. The
voltages across the power semiconductors can be seen in
Fig. 7 where the waveforms that were obtained through this
simulation test are presented. The analysis of these wave-
forms confirms that the voltage across semiconductors is
lower than the output voltage. They are in accordance with
the described in the theoretical analysis, being half of the
total output voltage. The input current (also in the inductor
L1), inductor current L2 and output current are presented in
Fig. 8. From these waveforms obtained from the simulation
test, it is possible to confirm the continuous input current
of the power converter (CCM). Besides that, it can be seen
that the current in inductor L2 presents a similar behaviour
of the one in inductor L1, ensuring also CCM. Regarding the
output currents, io1 and io2 in Fig. 8, it is shown they are well
balanced as they have the same average and ripple values.
FIGURE 6. Simulation waveforms of the input (Vi ) and output (Vo, VCo1
and VCo2) voltages of the power converter.
FIGURE 7. Simulation waveforms of the voltages across the power
devices.
Therefore, the proposed converter will contribute to balance
the voltages of bipolar DC microgrids.
To test the capability of the proposed converter to inject
the power in an asymmetric way into the two poles in an
unbalanced situation, a new simulation with an unbalanced
resistive load was also realized. For this simulation, it was
initially considered the circuit with a balanced load (540 
and 540 ). However, suddenly the resistor connected to
the negative pole changed to 190  originating in this way
an asymmetry in the circuit output. The obtained output
voltages in this test can be seen in Fig. 9. This result shows
that although the load became unbalanced, the output pole
voltages remain balanced. Despite using only one switch,
the output currents appear in this situation as unbalanced
(Fig. 10). Moreover, the output current connected to the pole
VOLUME 9, 2021 157129
V. Fernão Pires et al.: Dual Output and High Voltage Gain DC-DC Converter for PV and Fuel Cell Generators
FIGURE 8. Simulation waveforms of the input current (iL1), inductor
current (iL2); output currents io1 and io2.
FIGURE 9. Simulation waveforms of the input (Vi ) and output (Vo, VCo1
and VCo2) voltages, for a suddenly change in the load of the negative pole.
FIGURE 10. Simulation waveforms of the output currents (io1 and io2),
for the situation of a suddenly change in the load of the negative pole.
with a higher load (io2) has higher value contributing in this
way to balance the microgrid voltages.
B. EXPERIMENTAL TESTS
The results obtained from the experimental tests real-
ized through the developed prototype are presented in
Figs. 11 to 13. As shown by Fig. 11 the output voltage was set
for 400 V. This voltage was obtained for a duty cycle of 0.36.
From this is possible to see that output/input voltage gain is
near to the expected theoretical gain. This figure also shows
the output capacitors voltages (Vo1 and Vo2) of the power
converter, being possible to confirm that they are practically
half of the total output voltage. The confirmation about the
reduction of the voltages across the power devices when
FIGURE 11. Experimental waveforms of the input (Vi ) and outputs (Vo,
VCo1 and VCo2) voltages of the power converter.
FIGURE 12. Experimental waveforms of the voltages across the power
semiconductors.
compared with the output voltage of the converter can be seen
in Fig. 12. From these voltages waveforms it is possible to see
that the maximum voltage that they must hold-off is half of
the total output voltage, confirming in this way the theoretical
expectations.
The confirmation about the main currents in the circuit can
be seen in Fig. 13. From the analysis of the waveforms of the
experimental currents it is possible to see that the input cur-
rent (also in the inductor L1) presents a continuous conduction
mode. The waveform of the experimental current in inductor
L2 also shows a similar behaviour with the one in inductor
L1. This figure also shows that the output currents (io1 and
io2) are balanced, like in the simulation. This confirms that in
a situation of a balancedDCmicrogrid the proposed converter
will not contribute to its unbalance.
157130 VOLUME 9, 2021
V. Fernão Pires et al.: Dual Output and High Voltage Gain DC-DC Converter for PV and Fuel Cell Generators
FIGURE 13. Experimental waveforms of the input current (iL1) and
inductor current (iL2).
FIGURE 14. Experimental waveforms of the input (Vi ) and output (Vo,
VCo1 and VCo2) voltages, for the situation of a suddenly change in the
load of the negative pole.
FIGURE 15. Experimental waveforms of the output currents (io1 and io2),
for the situation of a suddenly change in the load of the negative pole.
To experimentally confirm the capability of the proposed
converter to help in balancing the bipolar microgrid, a test
with an unbalanced resistive load was also performed. For
this test, an initially balanced load (with a resistor of 540 
in each of the poles) was suddenly unbalanced by paralleling
an extra load in the negative pole (to 190 ). Fig. 14 shows
the input and output voltages of the converter. The waveforms
of the positive and negative poles (VCo1 and VCo2) show that
they maintain the same voltage value even when the load is
unbalanced. This is ensured by the asymmetrical injection of
the converter output currents (io1 and io2) as shown in Fig. 15.
Indeed, the experimental waveforms of the converter output
currents shows that when the load became unbalanced the
currents also became unbalanced, since the output connected
to the pole with higher load presents a higher value. This
confirms that in an unbalanced situation the converter will
inject in an asymmetric way the power into the two poles
of the microgrid helping their balance, using only a single
switch.
Despite quite similar, the dynamic response of the con-
verter in the developed prototype regarding the output volt-
ages and capacitor voltages is not so good as the simulation
results. This is mainly due to parasitic elements introduced in
the circuit design of the prototype.
VIII. CONCLUSION
This study proposed a novel DC-DC power converter topol-
ogy that is especially suited for bipolar DC microgrids or
transformerless grid-connect PV and fuel cell generators. The
suitability to these applications is due to the fact that the
topology is characterized by a double output, allowing con-
nections to the positive, neutral and negative poles of bipolar
microgrids. The proposed converter contributes to balance the
voltages of the microgrid. The topology is also characterized
by a high input-output voltage gain and continuous input cur-
rent, which is very important for RES such as PV and fuel cell
generators. The proposed DC-DC converter was developed
with the purpose to maintain, as must as possible a reduced
number of components, using only a single active switch. One
of the features of the proposed DC-DC is the ability to create
an output midpoint that is directly connected to the ground
of the input DC power supply avoiding the common mode
leakage current. The operating principles of the proposed
DC-DC converter, as well, their component sizing were also
presented. The assumptions, theoretical analysis and design
were verified through the experimental results obtained from
a laboratory setup.
REFERENCES
[1] N. Bizon, N. M. Tabatabaei, F. Blaabjerg, and E. Kurt, ‘‘Energy harvesting
and energy efficiency,’’ in Technology, Methods, and Applications (Lecture
Notes in Energy). Cham, Switzerland: Springer, 2017.
[2] Y. Yang, K. A. Kim, F. Blaabjerg, and A. Sangwongwanich, Advances
in Grid-Connected Photovoltaic Power Conversion Systems. U.K.: Wood-
head Publishing, 2018.
[3] M. S. Agamy, S. Chi, A. Elasser, M. Harfman-Todorovic, Y. Jiang,
F. Mueller, and F. Tao, ‘‘A high-power-density DC–DC converter for dis-
tributed PV architectures,’’ IEEE J. Photovolt., vol. 3, no. 2, pp. 791–798,
Apr. 2013.
[4] H. Lee and J. Yun, ‘‘High-efficiency bidirectional buck-boost converter
for photovoltaic and energy storage systems in a smart grid,’’ IEEE Trans.
Power Electron., vol. 34, no. 5, pp. 4316–4328, May 2019.
[5] S. Inoue and H. Akagi, ‘‘A bidirectional DC–DC converter for an energy
storage system with galvanic isolation,’’ IEEE Trans. Power Electron.,
vol. 22, no. 6, pp. 2299–2306, Nov. 2007.
[6] M. Woldelibanos Beraki, J. Pedro F. Trovão, M. S. Perdigão, and
M. R. Dubois, ‘‘Variable inductor based bidirectional DC–DC con-
verter for electric vehicles,’’ IEEE Trans. Veh. Technol., vol. 66, no. 10,
pp. 8764–8772, Oct. 2017.
[7] L. Tan, B. Wu, S. Rivera, and V. Yaramasu, ‘‘Comprehensive DC power
balance management in high-power three-level DC–DC converter for elec-
tric vehicle fast charging,’’ IEEE Trans. Power Electron., vol. 31, no. 1,
pp. 89–100, Jan. 2016.
[8] M. Z. Hossain, N. A. Rahim, and J. Selvaraj, ‘‘Recent progress and devel-
opment on power DC-DC converter topology, control, design and appli-
cations: A review,’’ Renew. Sustain. Energy Rev., vol. 81, pp. 205–230,
Jan. 2018.
VOLUME 9, 2021 157131
V. Fernão Pires et al.: Dual Output and High Voltage Gain DC-DC Converter for PV and Fuel Cell Generators
[9] J.-M. Shen, H.-L. Jou, and J.-C. Wu, ‘‘Novel transformerless grid-
connected power converter with negative grounding for photovoltaic gener-
ation system,’’ IEEE Trans. Power Electron., vol. 27, no. 4, pp. 1818–1829,
Apr. 2012.
[10] M. Forouzesh, Y. P. Siwakoti, S. A. Gorji, F. Blaabjerg, and B. Lehman,
‘‘Step-upDC–DC converters: A comprehensive review of voltage-boosting
techniques, topologies, and applications,’’ IEEE Trans. Power Electron.,
vol. 32, no. 12, pp. 9143–9178, Dec. 2017.
[11] A. Emrani, E. Adib, and H. Farzanehfard, ‘‘Single-switch soft-switched
isolated DC–DC converter,’’ IEEE Trans. Power Electron., vol. 27, no. 4,
pp. 1952–1957, Apr. 2012.
[12] H. Tarzamni, F. Tahami,M. Fotuhi-Firuzabad, and F. Blaabjerg, ‘‘Improved
Markov model for reliability assessment of isolated multiple-switch PWM
DC-DC converters,’’ IEEE Access, vol. 9, pp. 33666–33674, 2021.
[13] O. Husev, L. Liivik, F. Blaabjerg, A. Chub, D. Vinnikov, and I. Roasto,
‘‘Galvanically isolated quasi-Z-source DC–DC converter with a novel
ZVS and ZCS technique,’’ IEEE Trans. Ind. Electron., vol. 62, no. 12,
pp. 7547–7556, Dec. 2015.
[14] H. Wang, Q. Sun, H. S. H. Chung, S. Tapuchi, and A. Ioinovici, ‘‘A
ZCS current-fed full-bridge PWM converter with self-adaptable soft-
switching snubber energy,’’ IEEE Trans. Power Electron., vol. 24, no. 8,
pp. 1977–1991, Aug. 2009.
[15] Y. Jang andM. Jovanovic, ‘‘Isolated boost converters,’’ IEEE Trans. Power
Electron., vol. 22, no. 4, pp. 1514–1521, Jul. 2007.
[16] M.-K. Nguyen, T.-D. Duong, Y.-C. Lim, and Y.-J. Kim, ‘‘Isolated boost
DC–DC converter with three switches,’’ IEEE Trans. Power Electron.,
vol. 33, no. 2, pp. 1389–1398, Feb. 2018.
[17] S. A. Gorji, M. Ektesabi, and J. Zheng, ‘‘Isolated switched-boost push–pull
DC–DC converter for step-up applications,’’ IET Electron. Lett., vol. 53,
no. 3, pp. 117–119, Feb. 2017.
[18] H. Jahangiri, S. Mohammadpour, and A. Ajami, ‘‘A high step-up DC-DC
boost converter with coupled inductor based on quadratic converters,’’ in
Proc. 9th Annu. Power Electron., Drives Syst. Technol. Conf. (PEDSTC),
Feb. 2018, pp. 13–15.
[19] M. Sagar Bhaskar, V. K. Ramachandaramurthy, S. Padmanaban, F. Blaab-
jerg, D. M. Ionel, M. Mitolo, and D. Almakhles, ‘‘Survey of DC-DC non-
isolated topologies for unidirectional power flow in fuel cell vehicles,’’
IEEE Access, vol. 8, pp. 178130–178166, 2020.
[20] V. F. Pires, D. Foito, F. R. B. Batista, and J. F. Silva, ‘‘A photovoltaic
generator system with a DC/DC converter based on an integrated Boost-
Ćuk topology,’’ Sol. Energy, vol. 136, pp. 1–9, Oct. 2016.
[21] S.-W. Lee and H.-L. Do, ‘‘Zero-ripple input-current high-step-up boost–
SEPIC DC–DC converter with reduced switch-voltage stress,’’ IEEE
Trans. Power Electron., vol. 32, no. 8, pp. 6170–6177, Aug. 2017.
[22] R. Moradpour, H. Ardi, and A. Tavakoli, ‘‘Design and implementation of
a new SEPIC-based high step-up DC/DC converter for renewable energy
applications,’’ IEEE Trans. Ind. Electron., vol. 65, no. 2, pp. 1290–1297,
Feb. 2018.
[23] A. Abramovitz and K. M. Smedley, ‘‘Analysis and design of a tapped-
inductor buck–boost PFC rectifier with low bus voltage,’’ IEEE Trans.
Power Electron., vol. 26, no. 9, pp. 2637–2649, Sep. 2011.
[24] H. Liu, H. Hu, H. Wu, Y. Xing, and I. Batarseh, ‘‘Overview of high-step-
up coupled-inductor boost converters,’’ IEEE J. Emerg. Sel. Topics Power
Electron., vol. 4, no. 2, pp. 689–704, Jun. 2016.
[25] Y. Ye and K. W. E. Cheng, ‘‘A family of single-stage switched-capacitor–
inductor PWM converters,’’ IEEE Trans. Power Electron., vol. 28, no. 11,
pp. 5196–5205, Nov. 2013.
[26] P. K. Peter and V. Agarwal, ‘‘Current equalization in photovoltaic strings
with module integrated ground-isolated switched capacitor DC–DC con-
verters,’’ IEEE J. Photovolt., vol. 4, no. 2, pp. 669–678, Mar. 2014.
[27] X. Wu, W. Shi, and J. Du, ‘‘Dual-switch boost DC–DC converter for use in
fuel-cell-powered vehicles,’’ IEEE Access, vol. 7, pp. 74081–74088, 2019.
[28] D. Bao, A. Kumar, X. Pan, X. Xiong, A. R. Beig, and S. K. Singh,
‘‘Switched inductor double switch high gain DC-DC converter for renew-
able applications,’’ IEEE Access, vol. 9, pp. 14259–14270, 2021.
[29] D. R. Espinoza Trejo, S. Taheri, J. L. Saavedra, P. Vazquez,
C. H. De Angelo, and J. A. Pecina-Sanchez, ‘‘Nonlinear control and
internal stability analysis of series-connected boost DC/DC converters in
PV systems with distributed MPPT,’’ IEEE J. Photovolt., vol. 11, no. 2,
pp. 504–512, Mar. 2021, doi: 10.1109/JPHOTOV.2020.3041237.
[30] M. Zhu and F. L. Luo, ‘‘Series SEPIC implementing voltage-lift tech-
nique for DC–DC power conversion,’’ IET Power Electron., vol. 1, no. 1,
pp. 109–121, Mar. 2008.
[31] M. S. Bhaskar, D. J. Almakhles, S. Padmanaban, F. Blaabjerg,
U. Subramaniam, and D. M. Ionel, ‘‘Analysis and investigation of hybrid
DC–DC non-isolated and non-inverting Nx interleaved multilevel boost
converter (Nx-IMBC) for high voltage step-up applications: Hardware
implementation,’’ IEEE Access, vol. 8, pp. 87309–87328, 2020.
[32] A. M. S. S. Andrade and M. L. D. S. Martins, ‘‘Quadratic-boost with
stacked zeta converter for high voltage gain applications,’’ IEEE J. Emerg.
Sel. Topics Power Electron., vol. 5, no. 4, pp. 1787–1796, Dec. 2017.
[33] V. F. Pires, D. Foito, and A. Cordeiro, ‘‘A DC–DC converter with
quadratic gain and bidirectional capability for batteries/supercapacitors,’’
IEEE Trans. Ind. Appl., vol. 54, no. 1, pp. 274–285, Feb. 2018.
[34] J. E. Valdez-Resendiz, J. C. Rosas-Caro, J. C. Mayo-Maldonado, and
A. Llamas-Terres, ‘‘Quadratic boost converter based on stackable switch-
ing stages,’’ IET Power Electron., vol. 11, no. 8, pp. 1373–1381, Jul. 2018.
[35] J. Liu, J. Wu, J. Qiu, and J. Zeng, ‘‘Switched Z-source/quasi-Z-source
DC-DC converters with reduced passive components for photovoltaic sys-
tems,’’ IEEE Access, vol. 7, pp. 40893–40903, 2019.
[36] J. Zhao, D. Chen, and J. Jiang, ‘‘Transformerless high step-up DC-DC
converter with low voltage stress for fuel cells,’’ IEEE Access, vol. 9,
pp. 10228–10238, 2021.
[37] W. Li and X. He, ‘‘Review of nonisolated high-step-up DC/DC converters
in photovoltaic grid-connected applications,’’ IEEE Trans. Ind. Electron.,
vol. 58, no. 4, pp. 1239–1250, Apr. 2011.
[38] H. Kakigano, Y. Miura, and T. Ise, ‘‘Low-voltage bipolar-type DC
microgrid for super high quality distribution,’’ IEEE Trans. Power Elec-
tron., vol. 25, no. 12, pp. 3066–3075, Dec. 2010.
[39] F. Wang, Z. Lei, X. Xu, and X. Shu, ‘‘Topology deduction and analysis of
voltage balancers for DC microgrid,’’ IEEE J. Emerg. Sel. Topics Power
Electron., vol. 5, no. 2, pp. 672–680, Jun. 2017.
[40] J. Lee, Y. Cho, and J. Jung, ‘‘Single-stage voltage balancer with high-
frequency isolation for bipolar LVDC distribution system,’’ IEEE Trans.
Ind. Electron., vol. 65, no. 5, pp. 3596–3606, May 2020.
[41] M. B. Ferrera, S. P. Litrán, E. D. Aranda, and J. M. A. Márquez, ‘‘A
converter for bipolar DC link based on SEPIC-Cuk combination,’’ IEEE
Trans. Power Electron., vol. 30, no. 12, pp. 6483–6487, Dec. 2015.
[42] Y. Zhang, L. Zhou,M. Sumner, and P.Wang, ‘‘Single-switch, wide voltage-
gain range, boost DC–DC converter for fuel cell vehicles,’’ IEEE Trans.
Veh. Technol., vol. 67, no. 1, pp. 134–145, Jan. 2018.
[43] V. F. Pires, D. Foito, and J. F. Silva, ‘‘A single switch hybrid DC/DC
converter with extended static gain for photovoltaic applications,’’ Elect.
Power Syst. Res., vol. 146, pp. 228–235, May 2017.
[44] A. K. Mishra and B. Singh, ‘‘Solar photovoltaic array dependent
dual output converter based water pumping using switched reluctance
motor drive,’’ IEEE Trans. Ind. Appl., vol. 53, no. 6, pp. 5615–5623,
Nov./Dec. 2017.
[45] K. Nathan, S. Ghosh, Y. Siwakoti, and T. Long, ‘‘A new DC-DC con-
verter for photovoltaic systems: Coupled-inductors combined Cuk-SEPIC
converter,’’ IEEE Trans. Energy Convers., vol. 34, no. 1, pp. 191–201,
Mar. 2019.
[46] S. Rezayi, H. Iman-Eini, M. Hamzeh, S. Bacha, and S. Farzamkia, ‘‘Dual-
output DC/DC boost converter for bipolar DC microgrids,’’ IET Renew.
Power Gener., vol. 13, no. 8, pp. 1402–1410, Jun. 2019.
V. FERNÃO PIRES (Senior Member, IEEE)
received the B.S. degree in electrical engineer-
ing from the Institute Superior of Engineering of
Lisbon, Portugal, in 1988, and the M.S. and Ph.D.
degrees in electrical and computer engineering
from theTechnical University of Lisbon, in 1995
and 2000, respectively.
Since 1991, he has been a member of the
teaching staff with the Electrical Engineer-
ing Department, Superior Technical School of
Setúbal—Polytechnic Institute of Setúbal. He is currently a Profes-
sor teaching power electronics and control of power converters. He is
also a Researcher with the Instituto de Engenharia de Sistemas e
Computadores—Investigação e Desenvolvimento em Lisboa (INESC-ID).
His work has resulted in more than 200 publications. His current research
interests include the areas of power-electronic converters, fault diagnosis
and fault tolerant operation, renewable energy, electrical vehicles, electrical
drives, and power quality.
157132 VOLUME 9, 2021
V. Fernão Pires et al.: Dual Output and High Voltage Gain DC-DC Converter for PV and Fuel Cell Generators
ARMANDO CORDEIRO was born in Portugal,
in 1976. He received the B.S. degree in elec-
trical engineering from the Instituto Superior de
Engenharia de Lisboa, in 1999, and the M.Sc.
and Ph.D. degrees in electrical engineering from
IST, Technical University of Lisbon, in 2004
and 2015, respectively. He has been a Professor
with the Department of Electrical Engineering and
Automation, Instituto Superior de Engenharia de
Lisboa for the area of Automation, since 2006.
He is currently a Researcher with the Instituto de Engenharia de Sistemas
e Computadores—Investigação e Desenvolvimento em Lisboa (INESC-ID).
His research interests include power electronics, variable speed drives,
automation systems, and electrical vehicles. His current research interests
include the areas of power-electronic converters, industrial automation, and
robotics.
DANIEL FOITO received the Dipl.Ing. and M.S.
degrees in electrical engineering from the Instituto
Superior Técnico, Technical University of Lisbon,
Lisbon, Portugal, in 1993 and 2002, respectively,
and the Ph.D. degree in electrical engineering from
the Faculty of Sciences and Technology, Universi-
dade Nova de Lisboa, in 2015. Since 1997, he has
been a member of the teaching staff with the Elec-
trical Engineering Department, Superior Techni-
cal School of Setúbal—Polytechnic Institute of
Setúbal. He is currently teaching power electronics and electric drives as an
Adjoint Professor. His research interests include renewable energy genera-
tion, electrical machines, electric drives, electric vehicle, fault diagnosis, and
fault tolerant operation.
J. FERNANDO A. SILVA (Senior Member, IEEE)
was born inMonção Portugal, in 1956. He received
the Dipl.Ing. degree in electrical engineering and
the Ph.D. degree in electrical and computer engi-
neering (power electronics and control) from
the Instituto Superior Técnico (IST), Universi-
dade Técnica de Lisboa (UTL), Lisbon, Portugal,
in 1980 and 1990, respectively. He is currently
a Full Professor in power electronics and energy
storage in the scientific area of energy with the
Department of Electrical and Computer Engineering, Instituto Superior
Técnico (IST), Universidade de Lisboa (UL). He is also a Senior Researcher
with the Instituto de Engenharia de Sistemas e Computadores—Investigação
e Desenvolvimento em Lisboa (INESC-ID) and also the Leader of the
research area Green Energy and Smart Converters. He was an Associate
Editor of IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, from 2000 to 2019.
He has been amember of the Industrial ElectronicsMagazine editorial board,
since 2010, and a member of the Portuguese Engineering Society.
VOLUME 9, 2021 157133