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A Non-isolated Multi-input Multi-output DC–DC
Boost Converter
Subhajit Ghosh
M.Tech Power Electronics and Drives
VIT University, Chennai, TamilNadu
[email protected]
Nilanjan Tewari
School of Electrical Engineering
VIT University, Chennai, TamilNadu
[email protected]
Abstract—A new non-isolated multi-input multi-output dc-dc
boost converter is discussed in this paper. This converter is useful
for hybridizing different energy sources in electric vehicles. A
hybrid power generation system uses two or more sources to
balance the power supply. So advantages of different sources can
be possible to achieve. In this boost converter charging or
discharging of energy storages easily can be done. The proposed
converter has multiple outputs with different voltage level which
can be easily interface with multilevel inverter for harmonic
reduction. If it is used in electric vehicle then torque ripple of the
dc motor will be reduce. The proposed converter has two inputs
and two outputs with different voltage level. The proposed
converter has only one inductor.
Keywords—DC-DC converters, grids.
I. INTRODUCTION
Increasing rapidly population and energy consumption in
the world, increasing oil and natural gas prices, and the
depletion of fossil fuels are justifiable reasons for using electrical vehicles (EVs) instead of fossil-fuel vehicles. The
interest in developing the EVs with clean and renewable
energy sources as a replacement for fossil-fuel vehicles has
therefore steadily increased. The EVs are proposed as a
potential and attractive solution for transportation applications
to provide environmentally friendly operation with the usage
of clean and renewable energy sources [1], [2]. In the EVs, the
fuel cell (FC) stack usually used as clean energy source. The
FCs is energy sources that directly convert the chemical energy
reaction into the electrical energy. Currently, FCs is
acknowledged as one of the promising technologies to meet the future energy generation requirements. FCs generate
electric energy, rather than storing it. .
II. The Proposed Converter
As discussed in the introduction, in [2], a multi-output
converter is discussed. This is a single input converter. But
only one energy sources not enough to fulfill load requirement
because of the dynamic load and variable power. Then
hybridization of multiple sources is important. As discussed in
the introduction, in [3], a non isolated boost converter for
hybridization of energy sources is proposed with only one
inductor. In this paper a multi input multi output non-isolated
dc-dc converter based on the previous two converters is
proposed. The circuit diagram of the proposed converter is
presented in Fig.1. The converter has m input sources Vin1,
Vin2, Vin3, ....... Vinm. and the magnitude of the input voltages
are like that order. Vin1< Vin< Vin3 < ....... < Vinm. The proposed
converter has n number of outputs with n capacitors, only one
inductor and m+n switches. The load resistances are R1, R2,
R3, R4, R5........ Rn equivalent to power feeding to multilevel
inverter. Boost up of the input voltages also possible by proper
switching of switching pulses.
In this paper for analysis the proposed converter with two-output and two-input is shown in Fig. 2. In Fig. 2 R1 and R2 are
the load resistances and the voltage level across this two load
also different so different level of multilevel inverter can be
possible to connect with this converter. A diode placed in
between Vin1 and Vin2 so Vin1 can deliver power to the Vin2 but
Vin2 cannot deliver power to Vin1. If this converter used in
Electric Vehicle applications then Fuel Cell or PV which
cannot be charged must have to place where Vin1 placed in the
circuit and battery is located where Vin2 placed in the circuit. In
this converter four power switches S1, S2, S3, S4 are controlled
for power flow and output voltage control.
Fig.1. Proposed Converter.
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Fig.2. Proposed Converter with two-input and two-output.
In this paper PV used as a generating power and the battery
sometimes used as a power supplier and sometimes it stored
energy from PV cell. Depending on the battery charging and
discharging mode there is two power operation modes are
discussed for proposed converter. When requirement of the
load power is high then two input sources deliver power to the
load. In each mode only three switches are active and one
switch is not active. When battery operate at discharging
mode, in such condition, S2 is not active and switches S1, S3,
S4, are active and at battery charging mode, in such condition,
S3 is not active and switches S1 , S2 , S4, are active.
Fig.3. Steady state waveforms of proposed converter in battery discharging mode
III. PRINCIPLE OF OPERATION
A. First Operation Mode( Battery Discharging Mode)
In this mode, Vin1 (PV) and Vin2 (battery) supply power
to the loads. Here switch S1 is on to control battery
current to desired value by controlling inductor current.
Switch S3 regulate the total output voltage VT=V01+V02
and output voltage V01 is regulate by switch S4. In Fig. 3
inductor voltage, Inductor current and gate signal of the
switch waveforms are presented. In one switching period
there are four different operation modes:
1) Switching State 1 (0 < t < D3T): In this mode,
Switches S1 and S3 are active and Vin1<Vin2 so diode D0 is reverse biased. So, inductor L charges by Vin2
and inductor current increases. Because S1 is active
and diodes D1 and D2 are reverse biased Also, in this
mode, capacitors C1 and C2 supplies energy to the
load resistances R1 and R2. Equivalent circuit of this
switching state shown in Fig. 4(a). The equations of inductor and capacitors are as
follows:
Fig. 4(a) switching state 1
2) Switching State 2 (D3 T < t < D1 T):In this
state only switch S1 is ON and S3 is OFF, diodes D2 and D1 is reverse biased, so S4 is OFF. So, inductor L charges
by Vin1 and inductor current increases. In this mode also,
capacitors C1 and C2 supplies stored energy to the load
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resistances R1 and R2. Equivalent circuit of this switching
state shown in Fig. 4(a).
The equations of inductor and capacitors are as follows:
Fig. 4(b) switching state 2
3) Switching State 3 (D1T < t<D4 T): In this
mode, switch S1 is OFF and S3 also OFF. Diode D2
reverse biased. In this mode inductor L is started
discharging and inductor current decreases linearly
and capacitor C1 and resistor R1 are charged by stored
energy in inductor L. Capacitor C2 discharges its
stored energy to the load resistance R2. Equivalent
circuit of this switching state shown in Fig. 4(a) The equations of L, C1 and C2 are as follows:
Fig. 4(c) switching state 3
4) Switching State 4 (D4T < t<T): In this
mode, all switches are OFF. Diode D2 is forward
biased and inductor L is discharged through the
diode D2 and delivers its stored energy to
resistors R1, R2 and charges capacitors C1 and C2.
Equivalent circuit of this switching state shown
in Fig. 4(a). The equations of L, C1 and C2 are as follows:
Fig. 4(d) switching state 4
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B. Second Operation Mode (Battery Charging Mode)
In this mode, Vin1 supplies load as well as supplies Vin2 battery also. This condition occurs when load requirement is
low and battery has to be charge. When battery operates at
charging mode, in such condition, S3 is not active and switches
S1, S2, S4, are active. Here switch S2 is on to control battery
current to desired value by controlling inductor current. Switch
S1 regulate the total output voltage VT=V01+V02 and output
voltage V01 is regulate by switch S4. . In Fig. 5 inductor voltage,
Inductor current and gate signal of the switch waveforms are
presented. In one switching period there are four different
operation modes:
1) Switching State 1 (0 < t < D1 T): In this mode S1 is
active, so S4 and S2 reverse biased by reverse voltage and diode
D2 also reversely biased. So, inductor L charges by Vin2 and inductor current increases. In this mode, capacitors C1 and C2
supplies energy to the load resistances R1 and R2. Equivalent
circuit of this switching state shown in Fig. 6(a)
The equations of inductor and capacitors are as follows:
Fig. 6(a) switching state 1
Fig.5. Steady state waveforms of proposed converter in battery charging mode
2) Switching State 2 (D1 T < t<D2 T): In this mode,
switch S1 is OFF and switch S2 is active. Diode D1 and D2 are
OFF because of reversely biased.Vin1<Vin2, for this reason in
this mode inductor current decreases and delivered energy to
the battery (Vin2). In this mode, capacitors C1 and C2 get
discharged and supplies energy to the load resistances R1 and
R2. . Equivalent circuit of this switching state shown in Fig.
6(b)
The equations of inductor and capacitors are as follows:
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Fig. 6(b) switching state 2
3) Switching State 3 (D2 T < t<D4 T): In this mode,
Switch S1 and S2 is turned OFF and S4 is turned ON. So, diode
D2 is reversely biased. In this mode inductor L is started
discharging and inductor current decreases linearly and
capacitor C1 and resistor R1 are charged by stored energy in inductor L. Capacitor C2 discharges its stored energy to the
load resistance R2. Equivalent circuit of this switching state
shown in Fig. 6(c)
The equations of inductor and capacitors are as follows:
Fig. 6(c) switching state 3
3) Switching State 3 (D4 T < t<T): In this mode, all
switches are OFF. Diode D2 is forward biased and inductor L
is discharged through the diode D2 and delivers its stored
energy to resistors R1, R2 and charges capacitors C1 and C2. The
equivalent circuit of this switching state shown in Fig. 6(d)
The equations of L, C1 and C2 are as follows:
(8)
Fig. 6(d) switching state 4
IV. STEADY-STATE EQUATIONS A. Continuous Conduction Mode (Battery Discharging Mode)
The steady state values of inductor current and output
voltages can be find out by inductor volt-second balance
and capacitor charge balance principles.The steady state
performance of the MIMO boost converter at discharging
mode can be analyze by considering each switching
interval by T11,T10,T01,T00. Then total switching period at
discharging mode can be written as follows
T11+T10+T01+T00 = T (9)
T = total switching period of the discharging modes.
Based on the averaging techniques and waveforms shown in Fig. 3, in the steady state average inductor voltage across inductor is zero.
T11 (Vin2) +T10 (Vin1) +T01 (Vin1-V01) +T00 [Vin1- (V01+V02)] = 0 (10)
By the definition of duty cycle in equation (3) and substitute it in (2), the duty cycle equations can be written as follows
Vin2 (D3) +Vin1 ( =V01 (
) +V02 ( )
(12)
Again at steady state, the average current of the capacitor C1 and C2 over one cycle should be zero.
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From equations (4) to (6), derived steady state equations
are
During steady state operation, inductor current ripple (Δ )
is given by
TABLE I
SIMULATION AND PROTOTYPE PARAMETERS
Simulation & Prototype parameters Symbols
1.3mH L
470µF C1
470µF C2
35Vs Vin1
45V Vin2
50kHz fs
B. Continuous Conduction Mode (Battery charging Mode)
The steady state values of inductor current and output
voltages can be find out by inductor volt-second balance
and capacitor charge balance principles.The steady state
performance of the MIMO boost converter at charging mode can be analyze by considering each switching
interval by T11,T10,T01,T00. Then total switching period at
discharging mode can be written as follows
T11+T10+T01+T00 = T (17)
T = total switching period of the discharging modes.
Based on the averaging techniques and waveforms shown in Fig. 5, in the steady state average inductor voltage across inductor is zero.
T11 (Vin1) +T10 (Vin1- Vin2) +T01 (Vin1-V01) +T00
[Vin1-(V01+V02)] = 0 (18)
By the definition of duty cycle in equation (3) and substitute it in (2), the duty cycle equations can be written as follows
Vin1 +Vin2 (D2-D1) =V01 ( ) +V02 (
) (20)
Again at steady state, the average current of the capacitor C1 and C2 over one cycle should be zero.
From equations (4) to (6), derived steady state equations
are
V. DYNAMIC MODELING OF THE PROPOSED CONVERTER
The proposed converter can be controlled by switch S1, S2,
S, and S4.The duty cycle of the each switches also different and by regulating duty cycle of the each switches, battery charging
or discharging current, output voltages are adjustable. By
obtaining dynamic model, close loop controller of the
converter can be possible to design. For each mode there is
different dynamic model and consequently different controller
must be designed properly.
A. Dynamic Model of Battery Discharging Mode
Small-signal model is important for optimized controller
design. Especially for this MIMO converter, this model will be helpful for close loop control and also to optimize converter
dynamics. For this multiport converter transfer function is
higher order. Here dynamics of the plant can be presented as
matrix form. Thus state variables VO1, VO2, IL3 need to be
directly controlled. The design procedure of the converter
small signal model can be found in [8]. Based on this method
state variable, input voltage and duty ratio have two
components: dc values (X, D, V) and perturbations.
Here X is a matrix of state variables, U is a matrix of control
inputs and Y is a matrix of system outputs.
(24)
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A, B, C, D, matrices of the system are
(25)
VI. CONTROLLER DESIGN
A. Controller Design for Battery discharging mode
We have three transfer functions and for each transfer
function bode plot analysis obtained by MATLAB
software. The transfer function g11 is the ratio of V01(s)
and d4(s). Open loop bode diagram of the g11 shown in
Fig. 7. Phase margin of the plot is which is not sufficient. To increase the phase margin and system
stability a PI controller introduced.
Fig. 7 Simulated Bode plot of g11(s) before applying controller.
The PI controller Kp and KI value designed by robust
control method. Design value of Kp and KI are .0028 and 0.28.
After compensation the stability of the system also improves as
shown in Fig. 8.
The transfer function g22 is the ratio of Ib(s) and
d1(s).because battery current depends upon switch S1. Open
loop bode diagram of the g11 shown in Fig. 9.
The PI controller Kp and KI value designed by robust
control method. Design value of Kp and KI are .0054 and 0.54.
After compensation the stability of the system also improves as
shown in Fig. 10.
Fig. 8 Simulated Bode plot of g11(s) after applying
controller.
Fig. 9 Simulated Bode plot of g22(s) before applying
controller.
Fig. 10 Simulated Bode plot of g22(s) after applying
controller.
The transfer function g33 is the ratio of VT(s) and
d3(s).because battery current depends upon switch S3. Open
loop bode diagram of the g33 shown in Fig. 11.
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The PI controller Kp and KI value designed by robust
control method. Design value of Kp and KI are .0094 and 0.94.
After compensation the stability of the system also improves as
shown in Fig. 12.
Fig. 11 Simulated Bode plot of g33(s) before applying controller.
Fig. 12 Simulated Bode plot of g33(s) after applying controller.
VII. SIMULATIONS RESULT
The performance of the designed converter verified by
simulation on MATLAB software. The simulations parameters
are already given in TABLE I. The input voltage sources are
considered Vin1=35 V, Vin2=45 V.
Fig. 13 Simulations results of output voltage V01 in battery
discharging mode.
After disturbance also output voltages of the converter
must be regulated at reference value V01-REF=85 V, V02-REF=45
V, VT-REF=130 V. Load resistance of the load resistance
selected as R1= R2=40 ohm. The desired battery current is
Ib=3.75 A. After applying close loop controller simulations
results shown. To verify close loop result changes load resistance as R1= R2=17 ohm. Each switch is controlled by
designed controller. The output voltage V01 settled in 85 V as
shown in Fig. 13, also output voltage V02 settled in 45 V as
shown in Fig. 14. The battery current also tracked 3.75 A
correctly for controller action as shown in Fig. 16. Inductor
current is shown in Fig. 17.
For charging also simulations result of output voltage V01
and V02 shown in Fig. 18 and Fig.19. The output voltage is
maintained same in charging also by regulating duty cycle of
the S1, S2, S4. The output voltages of the charging conditions
V01=85 V and V02= 45 V respectively. For charging conditions battery charging current shows negative as shown in Fig. 21.
The load increases to R1= R2=70 ohm. So now current
drawing by load also reduces. The average battery current
reduces to 1.5 A as shown in Fig.21.
Fig. 14 Simulations results of output voltage V02 in battery
discharging mode.
Fig. 15 Simulations results of Battery current Ib in battery
discharging mode.
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Fig. 16 Simulations results of average battery current Ib in
battery discharging mode.
Fig. 17 Simulations results of inductor current IL in battery
discharging mode.
Fig. 18 Simulations results of output voltage V01 in battery charging mode.
Fig. 19 Simulations results of output voltage V02 in battery
charging mode.
Fig. 20 Simulations results of average battery current Ib
in battery charging mode.
Fig. 21 Simulations results of Battery current Ib in battery
charging mode.
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VIII. EXPERIMENTAL RESULT
The proposed converter effectiveness verified in laboratory
as shown in Fig. 18. Two inputs are taken from the fixed DC
supply and set inputs are 10 V and 20 volts. The hardware
setup is shown in Fig.22.
The proposed converter tested in open loop and in
discharging mode only. PICKIT-3 used to give control signal
to the switch. Gate pulses of the switches as shown in Fig.23.
The Output voltage of the converter is shown in Fig. 24.
Output current of the load R2 is shown in Fig. 24.
Fig. 22 Hardware setup of the proposed converter.
Fig. 23 Gate pulses of the three switches.
Fig. 24 Output voltages and current of the converter
Fig. 25 Switch pulse and Inductor current
Gate pulse of the switch S1 and Inductor current IL is shown in
Fig. 25. When switch S1 is on inductor started charging and
when switch is off inductor started discharging.
IX. CONCLUSION
The proposed converter has two input and two output so it can
be used for supplying power from different sources and it has
two different level output so it can be useful by supplying to
the multilevel inverter. If this converter used in Electric vehicle
then output from the multilevel inverter can be used to drive
induction motor so torque ripple will be also less. Also it can
be useful for interfacing PV and grid connected inverter for
renewable energy applications. Finally prototype converter experimentally verified in discharging mode.
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