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DESIGN OF THREE PORT BIDIRECTIONAL DC TO DC
CONVERTER FOR PHOTOVOLTAIC APPLICATIONS
K.R.Sunil Raj 1, Dr.G. Themozhi 2 and Dr. A. Kalaimurugan 3
1Research Scholar, Anna University, Chennai, India.
2Professor, AMET (Deemed to be, University), Chennai, India.
3Professor, Agni College of Technology, Chennai, India.
Corresponding E. Mail: [email protected]
Abstract
The applications of Bidirectional DC to DC converter mainly include renewable energy
systems and also many other DC applications. This paper deals with characteristics and control
structure of a Full Bridge three port bidirectional DC to DC converter(FB-TPBDC) for high
voltage applications (400V, 5KW). It consists of a interleaved boost converter. The control
methods used are Pulse width modulation (PWM) and Phase shift control (PSC). By using PSC,
the switches attain Zero Voltage Switching (ZVS) without any additional snubber circuit in
addition to higher efficiency, low EMI , less harmonics and low switching noise. The operation
principles of the proposed converter are analyzed. The existing FB-TPBDC circuit uses parallel
inductor which gives an efficiency of 90%. The parallel inductor is replaced with a coupled
inductor in the proposed FB-TPBDC circuit resulting in an efficiency of 92%. Also the usage of
coupled inductor makes the circuit more compact. In order to verify the theoretical principles,
simulation of the proposed FB-TPBDC is done in MATLAB/Simulink software environment and
tested under various scenarios
Keywords: Storage; Three-port Converter; Voltage Control; Zero-Voltage-Switching.
1. Introduction
Bidirectional power transfer is needed in power electronic applications such as plugin
hybrid-vehicles (P-HEV) [4], uninterruptible power supply (UPS) systems, and micro-grids [2]-
[5]. Also In addition, if an application needs both bidirectional power transfer and galvanic
isolation, then the obvious choice is a bidirectional dual active bridge (DAB) DC-DC converter
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[4]. Another significant feature of DC-DC converters is their ability to smoothly supply loads,
especially in case of intermittent renewable energy sources. This calls for energy storage systems
such as batteries [1]-[3]. So far the hybrid PV -storage based distributed generation networks
consist of several DC-DC converters, which results in higher cost, lower efficiency, and lower
power density mainly because of several power conversion stages. This can be avoided by the
implementation of multi-port converters (MPC) where a unified control system is performed in
an integrated topology. A lot of MPC topologies which are classified in three main categories as
follows: non-isolated, partly-isolated and fully isolated topologies have been introduced for
different applications. By the way, compared to single-input single output DC-DC converters,
MPC topologies are more complicated to control due to additional active and/or passive elements
which are added to satisfy the requirements of topology and control structure [8], [11]. One of
the popular converters of industrial applications is full-bridge converter which has the feature of
zero-voltage switching (ZVS) [3]. According to the phase-shifted control and inductive current
flowing through switches with the benefit of low voltage stress characteristic, ZVS can be
guaranteed [3], [5], [9]. On the other hand, the possible power transfer tracks in the primary side
are not employed entirely. It means that the primary side can play the role of Boost converters
which can be connected to different sources with added inductors. Through the duty cycle
adjustment, the battery system, can be charged and discharged by a renewable energy source
which is the input of the Boost converter. In this way, the full-bridge converter can be turned to
the MPC topologies [2], [5].
2 Circuit Description
Fig. 1 shows the proposed FB-TPBDC which consists of a PV source and a battery
system as the input ports on the primary side and the output port is connected to a load or
medium-voltage direct current (MVDC) network. The circuit has a voltage fed full-bridge on the
primary side and a full-bridge active rectifier on the secondary side. From battery to the output
port, the FB - TPBDC acts as a DAB converter. To control the energy/voltage between PV
source and battery system, it also has a bidirectional interleaved boost converter which is made
of switches S1~S4 and mutual inductor (LM). It is integrated into the primary side of proposed
converter. Hence, the active switches are used by the DAB converter and the bidirectional a
interleaved boost converter simultaneously. Using the SSPS control scheme leads to eliminate
the output filter inductor in the conventional phase-shift converters to simplify the topology. Lf is
the transformer leakage inductance and it is determined by the maximum transferred power of
the converter. If the practical leakage inductance of transformer is not large enough to provide
circuit operation requirements, an external inductor will be added.
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Figure 1. Proposed FB – TPBDC for hybrid PV – storage system
2.1 Working Modes
The power of the PV panels, battery system and output load are denoted as PPV, PBAT
and Po, respectively. If the PV power is higher than the output power (Ppv >Po), the extra power
charges the battery. Considering the power relations between the ports, the FB-TPBC has three
operation modes: (1) dual output (DO) mode when Ppv> Po, the PV source generates power for
both the load and battery system simultaneously, and the battery is charged; (2) dual-input (01)
mode when 0 < Ppv< Po, the battery system and PV source supply the output load together; (3)
single-input single-output(SISO) mode if Ppv=0, the load is solely supplied by the battery
system (SISO BAT), and if PPV = Po, the load is solely supplied by the PV system (SISO PV).
Mode: 1
In the Primary Side, the voltage across the points A and B (VAB) is positive .Hence the switches
S1 and S4 are in forward bias. In the secondary side due to voltage across the points C and D(VCD ) the
switches S6 and S7 are triggered and as a result current will flow through the load from the leakage
inductance(ILf) of the primary side(Lf). This stage ends when ILf reaches its peak value is shown in the
figure (a) and (2).
iPV
ib
iL1
iL2
L1
L2
iLf
Li L
0
M
i0
.
.
iDC
Vb
VPV
C2
C1
C0 R
0
+
_
V0
Figure (a). Mode 1 of FB – TPBDC
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t
t
t
t
t
t
t
t
t
t
t
t
t
t0
t1
t2
t3
t
ILf
Vg1
Vg2
Vg3
Vg4
Vg5,8
Vg6,7
VL1
VL2
IL1
IL2
VAB
VCD
VLf
Figure. 2. Waveforms of the proposed FB-TPBDC
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Mode 2
In the Primary Side, the voltage across the points A and B (VAB) is positive .Hence the
switches S1 and S4 are in forward bias. In the secondary side due to voltage across the
points C and D(VCD ) the switches S5 and S8 are triggered and as a result current Idc will
flow in the positive direction. .However the leakage inductance (ILf) decreases because of
negative voltage across Lf is shown in the figure (b) and (2).
iPV
ib
iL1
iL2
L1
L2
iLf
Li L
0
M
i0
.
.V
b
VPV
C2
C1
C0 R
0
+
_
V0
iDC
Figure (b). Mode 2 of FB – TPBDC
Mode3
In the Primary Side, at t2 the switches S2 and S4 turn on. The current ILf decreases linearly and
reaches zero at the end of this mode due to the negative voltage across Lf is shown in the figure
(c)and (2).
iPV
ib
iL1
L1
L2
iLf
Li L
0
M
i0
.
.V
b
VPV
C2
C1
C0 R
0
+
_
V0
iL2
iDC
Figure (c). Mode 3 of FB – TPBDC
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3 FULL-BRIDGE THREE-PORT BIDIRECTIONAL CONVERTER
SIMULATION DIAGRAM AND RESULTS
In order to verify the analysis and controller structure presented in this paper, the
proposed converter is simulated using parameters as defined in Table. 1. The simulation of
convertor is done under two scenarios.
Case 1: Three – Port bi-directional DC - DC converter for boost operation
Case 2: Three – Port bi-directional DC - DC converter for buck operation.
Table I Key Parameters Of Circuit
Cases Circuit Parameter Value
Boost Mode
Input voltage VPV = 48V
Vb = 48 V
Output voltage V0 =400V
Nominal output power P0 = 5000W
Buck Mode
Input voltage V = 400V
Output voltage V0 = 48V
Nominal output power P0 = 5600
Other Parameters
Transformer T N1/N2 =0.135
Inductor Lf Lf = 11.7 µH
Capacitor CPV; C1 = 1000 µF
Capacitor Co C0 = 100µF
Switching frequency fs = 8Hz
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Case1: Three – Port Bi-Directional Dc - Dc Converter for Boost Operation
Fig.3. shows the simulation diagram of Full Bridge three port bidirectional DC to DC
converter(FB-TPBDC) for boost operation. The corresponding results are shown in the fig.3(a – g)
which indicates the parameters such as input voltage, current through the mutual inductor, Current and
voltage through primary and secondary side of the transformer, Output voltage. It also shows the
comparison between the input voltage, output voltage, power, efficiency of parallel inductor over coupled
inductor of bidirectional DC – DC converter.
Figure.3. DC - DC converter boost mode
Figure.3 (a). Battery input voltage
Figure.3 (b). Current through Mutual inductor (ML)
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Figure.3 (c). Current through primary and secondary side transformer
Figure.3 (d). Transformer primary and secondary side voltage
Figure.3 (e). Output voltage
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Figure.3 (f). Input Vs Output voltage and power
Figure.3 (g). Input voltage Vs Efficiency
Case2: Three – Port Bi-Directional Dc - Dc Converter for Buck Operation
Fig.4. shows the simulation diagram of Full Bridge three port bidirectional DC to DC
converter(FB-TPBDC) for buck operation. The corresponding results are shown in the fig.4(a – h)
which indicates the parameters such as input voltage, current through the mutual inductor, Current and
voltage through primary and secondary side of the transformer, Output voltage. It also shows the
comparison between the input voltage, output voltage, power, and efficiency of parallel inductor over
Ou
tpu
t P
ow
er
(W
)
Input Voltage (V)
Input Voltage VS Output Power
Pout_CP
% E
ffic
ien
cy
Input Voltage (V)
Input Voltage VS Efficiency
Eff_CP
Eff_N
Ou
tpu
t V
olt
age
(V
)
Input Voltage (V)
Input Voltage VS Output Voltage
Vout_N
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coupled inductor of bidirectional DC – DC converter
Figure.4. DC - DC converter buck mode
Figure.4 (a). Photovoltaic input voltage
Figure.4 (b). Current through Mutual inductor (ML)
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Figure.4 (c). Current through primary and secondary side transformer
Figure.4 (d). Transformer primary and secondary side voltage
Figure.4 (e). Output voltage 1
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Figure.4 (f). Output voltage 2
Figure.4 (g). Input voltage Vs Output Voltage and Power
Figure.4 (h). Input voltage Vs Efficiency
Ou
tpu
t P
ow
er
(W
)
Input Voltage (V)
Input Voltage VS Output Power
Pout_CUP
% E
ffic
ien
cy
Input Voltage (V)
Input Voltage VS Efficiency
Eef_CUP
Eef_N
Ou
tpu
t V
olt
age
Input Voltage (V)
Input Voltage VS Output Voltage
Vout_…
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5 Conclusion
This paper presents an efficient Full Bridge Three Port Bidirectional Convertor by
combining interleaved boost convertor and SSPS full bridge convertor. ZVS operation of
switches and single stage conversion between any two of the three ports helps in achieving
higher efficiency. The system is simple in structure and has lesser components. It also weighs
less and has higher power density. This convertor uses PWM+SSPS control scheme to achieve
ZVS. The operation of the convertor with the control scheme is simulated in MATLAB and the
results are verified.
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