14MPE1032(SUBHAJIT) - Copy2

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.

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

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

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)


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)


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)


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.

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)

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.




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.




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.


discharging mode.

Fig. 15 Simulations results of Battery current Ib in battery

discharging mode.

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.


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.

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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14MPE1032(SUBHAJIT) - Copy2