ISSN: 2277-3754

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International Journal of Engineering and Innovative Technology (IJEIT)

Volume 2, Issue 11, May 2013

76

Analysis and Simulation of Interleaved Boost Converter

for Automotive Applications

Farag. S. Alargt **

, Ahmed. S. Ashur *

*Department of Electrical and Electronic Engineering

University of Tripoli / Tripoli - Libya. **

Centre for Solar Energy Research and Studies / Tripoli-Libya

Abstract - This paper studies a design and simulation of

multi-phase interleaved boost DC-DC converter. The control

strategy of the converter is based on a voltage mode-controlled

Pulse Width Modulation (PWM) with a Proportional-Integral-

Derivative (PID) controller. The proposed converter has a 1KW

power and 42V output voltage to satisfy the requirements of

usage in 14/42 power system used in automotive applications.

This architecture is considered to be technically a viable solution

for automotive dual-voltage power system for passenger car in

the near further. The conception, analysis and simulation of a

multi-phase interleaved DC-DC boost converter for 42V power

systems are presented. One kilowatt interleaved three-phase

boost converter designed to operate in a Discontinuous

Conduction Mode (DCM). The impact of parameter variation on

the performance capabilities of the converter is described.

Simulation results are provided to illustrate the advantages of

the proposed converter and controller scheme. All the

advantages of interleaving, such as higher efficiency and

reduced input and output ripple for voltage/current, are also

Achieved in the proposed boost converter. The results show that

the system is stable and well behaved under input voltage

variations and the output voltage remains within the desired

specified limits presented in automotive standards.

Index Terms – DC-DC converters; interleaved boost

converter.

I. INTRODUCTION

A switching converter is an electronic power system

which transforms an input voltage level into another for a

given load by switching action of semiconductor devices. A

high power efficient dc-dc converter is strongly desired and

has found widespread applications. Examples include

aerospace, sea and undersea vehicles, electric vehicles (EV),

Hybrid Electric Vehicle (HEV), portable electronic devices

like pagers, and microprocessor voltage regulation [1].

In dual-voltage power systems, the dc-to-dc converter is

required to step-up voltage provided from the low-voltage

bus or back up part for the existing high-power devices in

the application that use this power system. A power system

consisting of fuel cell, battery and possibly other energy

storage components used in electric vehicles and stationary

power system applications, which normally require a high-

power boost converter for energy management that employs

an energy storage component to assist the slow-responding

fuel cell. Multiphase converter with interleaved control is

essential for the high-power boost converter in order to

reduce the ripple current and to reduce the size of passive

component. So far few literatures related to the controller

design of the high-power interleaved boost converter can be

found [4].

There have been many papers describing the use of

multiphase buck converters, especially for high-performance

high-power applications [1,9,10]. However, all the

advantages of interleaving, such as higher efficiency and

reduced input and output ripple for voltage/current, are also

realized in the boost topology. Most of the controllers used

in buck applications apply equally well when configured for

use in an interleaved boost application. In [1] multi-phase

buck converter controlled by PID is presented.

This paper following the same approach used in buck

converters and applied it on boost converter, PID is

configured using „Ziegler–Nichols‟ tuning method, where

the individual effects of P, I, and D is tuned on the closed-

loop response to give the required characteristics.

In sections ii and iii respectively, principles of modeling

and design steps to select components are presented for

boost converter. Interleaved multiphase boost converter and

control design are introduced in section iv, and v.

Simulation and results of work reported and computed in

section vi. A brief conclusion is drawn in section vii.

II. PRINCIPLES OF MODELING AND DESIGN

BOOST CONVERTER

The circuit of the PWM boost dc–dc converter is shown

in Fig. 1, its output voltage Vo is always higher than the

input voltage Vi for steady-state operation. It boosts the

voltage to a higher level. The converter consists of an

inductor L, a power MOSFET, a diode D1, a filter capacitor

C, and a load resistor RL. The switch S is turned on and off

at the switching frequency fs = 1/T with the ON duty ratio D

= ton/T, where ton is the time interval when the switch S is

ON [2]. The Equivalent circuit when the switch is ON and

the diode is OFF and the reverse case are shown in fig. 1(b)

and fig. 1(c), respectively.

The principle of operation of the converter are depicted

in Fig. 2, for the time interval 0 < t ≤ DT, the switch is ON.

Therefore, the voltage across the diode is VD = -Vo, causing

the diode to be reverse biased. The voltage across the

inductor is VL = Vi. As a result, the inductor current

increases linearly with a slope of Vi /L. The switch current is

equal to the inductor current. At t = DT, the switch is turned

off by the gate-to-source voltage. The inductor acts as a

current source and turns the diode on. The voltage across

the inductor is VL = Vi – Vo < 0 . Hence, the inductor current

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decreases with a slope of (Vi – Vo )/L . The diode current

equals the inductor current. During this time interval, the

energy is transferred from the inductor L to the filter

capacitor C and the load resistance RL. At time t = T, the

switch is turned on again, terminating the cycle [2,6,5].

Fig 1. PWM boost converter. (a) Circuit. (b) Equivalent

circuit when the switch is ON and the diode is OFF. (c)

Equivalent circuit when the switch is OFF and the diode is ON

[2].

Fig 2. Idealized current and voltage waveforms in the PWM

boost converter work in CCM [6].

A mathematical model of the system helps us to realize

the controller design. Hence, we will derive the equations

concerning the DC/DC boost converter model from basic

laws.

Fig 3. Boost converter operation states [2].

When the switch is closed, the equivalent circuit that is

applicable is shown in Fig. 3.b.The source voltage is applied

across the inductor and the rate of rise of inductor current is

dependent on the source voltage Vi and inductance L. The

differential equation describing this condition is [2]:

( )L

i

di tL V t

dt (1)

If the source voltage remains constant, the rate of rise

of inductor current is positive and remains fixed, so long as

the inductor is not saturated. Then equation (1) can be

expressed as:

( )L idi t V

dt L (2)

When the switch is open, the circuit that is applicable is

shown in Figure 3.a. Now the voltage across the inductor is:

 L i ov V V (3)

Given that the output voltage is larger than the source

voltage, the voltage across the inductor is negative and the

rate of rise of inductor current, described by equation (4)

[2], is negative. Hence if the switch is held OFF for a time

interval equal to (1-D)T, the change in inductor current can

be computed as given in equation (5)

( ) i oLV Vdi t

dt L

(4)

Δ 1i oL

V Vi t D T

L

(5)

The change in inductor current reflected by equation (5)

has a negative value, since Vo >Vi. Since the net change in

inductor current over a cycle period is zero when the

response iL(t) is periodic, the sum of changes in inductor

current expressed by (3) and (5) should be zero. That yields

1

io

VV

D

(6)

the value of the inductance needed to ensure that the

converter remains in Discontinuous Conduction Mode

(DCM) of operation i.e. the inductor current is zero during

part of the switching period and both semiconductor devices

are OFF during some part of each cycle, inductor value

must be less than critical L, which can be determined as

follow[2].

critical 

1

2

i

o

D V D TL

I

(7)

Where,

critical L L

And

oo

o

PI

V (8)

Where, Po is the output power.

The peak inductor current can be calculated as:

pk iV DT

IL

(9)

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The average inductor current can be found out by

equating the power drawn from the source to the power

delivered to the load resistor. Again the ripple in output

voltage is ignored and it is assumed justifiably that the

output voltage remains steady at its average value Vo. Po

absorbed by load resistor is then: 2( )O

o

VP

R (10)

The average value of inductor current IL is also the

average value of source current Ii, then: 2

L 

( )O

i

VI

V R

(11)

Similarly, the output capacitance selection is also

considered to make sure that output voltage ripple is within

the desired boundary. It is proven that the minimum

capacitance required for output voltage ripple is given by

[8],

min 

ripple

DTC

R V

(12)

However, the standard dc-dc converter with single

structure is not practicable due to the high current (71A),

and high power (1KW) required for automotive

applications. Therefore, the power stage of the converter

would have to be built in parallel for practical

implementation. A common approach in technical literature

and industry practice is to use interleaved multi-phase

technique instead of a single larger converter [1]. This

approach will be discussed in the next section.

III. COMPONENT SELECTION

For low voltage/high current power converter, the usage

of MOSFETs switching devices with low on-resistance is

required for more efficient and practical power conversion.

The inductors and capacitors play important roles in the

design of the power converter. Inductor is an energy storage

element while the capacitor is the main buffer for absorbing

the ripple current generated by the switching action of the

power stage. The switching frequency of the power

electronics used in automotive industry ranges from 82 kHz

to 200 kHz with 100 kHz as a typical value used for most

operation of dc/dc converters [1]. Components was

calculated from equations above with Vi = 14V, Vo = 42V,

and Po = 1000W, the calculated and selected component

summarized in table (1).

TABLE 1 Calculated And Selected Component

Component/

parameters

calculated selected equation

R 1.764ohm 1.764ohm (10)

L 0.65µH .3 µH (7) in (8)

C 3.779mF 3.9mF (12)

IV. MULTIPHASE SWITCHING OF DC-TO-DC

CONVERTER

To realize power conversion by a simple system

configuration, a multi-cells boost converter topology

designed for DCM of operation is employed. Fig. 4 shows

the developed Simulink diagram of three-cell interleaved

boost converter with PID Controller.

Fig 4. Simulink implementation of the interleaved three-

phase boost converter circuit with PID controller

To design this converter, the following automotive

specifications for dual-voltage automotive electrical systems

must be fulfilled and are tabulated in table (2) [1,11].

TABLE 2 Design Specifications For A Power Converter In

A Dual-Voltage Automotive Electrical System

Description Parameter Value

Operation output

voltage

Vo 30V<42V<50

V

Operation input

voltage

Vi 11V<14V<16

V

Power rating Po 1KW

Operation temperature

range

T -40C<T<90C

Output ripple voltage Vripple 300mV

Output ripple current Iripple 1A

The three-cell interleaved boost converter is connected in

parallel to a common output capacitor and sharing a

common load with the associated control system. In this

interleaved three-cell dc/dc converter architecture, the cells

are switched with the same duty ratio, but with a relative

phase shift or time interleaved of 120° introduced between

each cell in order to reduce the magnitude of the ripple at

the output port of the converter. The overall output current

is achieved by the summation of the output currents of the

cells. With the phase shift of 120°, the output of the

converter is found to be continuous. Due to the equal

sharing of the load current between cells, the overwork on

the semiconductor switches is reduced and thereby

reliability is improved.

Another advantage is the ability to operate the converter

when a failure occurs in one cell as well as the possibility to

add new cells to the converter with minimum efforts [1].

Since this is a three-phase interleaving converter, the power

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stage inductance of each phase is therefore equal to. 0.885

µH (note that L required for one stage converter is 0.3 µH,

as shown in table 1). The output capacitor is another

important element, which may reduce the system cost in

multi-phase converter system and is needed to keep the

output voltage ripple Vripple within the allowable output

voltage range. To meet these constraints of the design

specification, a capacitor value of 3.9mFis sufficient.

V. CONTROL DESIGN

Feedback is used in control systems to change the

dynamic behaviour of the system, whether mechanical,

electrical, or biological, and to maintain their stability. The

control strategy of the proposed converter is based on a

voltage-mode-controlled Pulse Width Modulation (PWM)

with a Proportional-Integral-Derivative (PID) which takes

its control signal from the output voltage of the switching

converter.

A Simulink model for the internal structure of the PID

used to control the converter is shown in Figure 5.

Fig 5. A PID controller represented by a Simulink block

diagram

The aim is to regulate the output voltage of the converter

Vo across the load resistance RL to match a precise stable

reference voltage Vref . This is achieved by subtracting the

desired reference voltage Vref from the sensed output

Voltage Vo of the converter. The voltage-error thus obtained

is passed through a PID controller to obtain the desired

signal. The function of the PID controller is to take the input

signal, compute its derivative and integral, and then

compute the output as a combination of input signal,

derivative and integral. The individual effects of P, I, and D

tuning on the closed-loop response are summarized in table

3[1].

Table 3 effect of independent P, I, and D during the tuning

process

Closed

Loop

response

Rise

time

Oversho

t

Settling

time

Steady

state error

Increasing

P

Decreas

e Increase

Small

increase Decrease

Increasing

I

Small

decreas

e

Increase Increase Large

decrease

Increasing

D

Small

decreas

e

Decreas

e Decrease

Minor

decrease

The desired output generated signal of the PID controller

is fed to the Pulse Width Modulation (PWM) unit, where it

is compared with a constant frequency sawtooth voltage.

The frequency of sawtooth voltage is the switching

frequency fs of the converter which is 100 kHz. The output

signal from the PWM is the switching control signal, which

represents a sequence of pulses that drives the

semiconductor switch, as shown in Figure 6.

Fig 6. Implementation of Pulse Width Modulation in

Simulink

The proposed converter necessitates a phase-shift of 120°

between the cells to generate the three-switching control

signal which are used to drive the three active MOSFET

switching devices of the converter system. Figure 7 and 8

show the implementation of the three-phase interleaving

circuit in Simulink and the three phase control signal

waveforms respectively.

Fig 7. Three phases of interleaving in Simulink

Fig 8. Three phase control signals in Simulink

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V. SIMULATION AND RESULTS

The complete model of the Simulink implementation of

the internal structure of the interleaved three-phase boost

converter system is shown in Figure 9. The converter system

is divided into three main parts; the three-cell boost

converter, the PID controller including the voltage mode

PWM and the phase shift circuit. The multi-phase converter

has been simulated to obtain the necessary waveforms that

describe converter system operation under steady-state and

transient conditions, using the design parameters tabulated

in table 4.

Fig 9. Simulink schematic diagram illustrating the

implementation of interleaved tree-phase boost converter

circuit with a PID controller

Table 4. The parameters of converter

parameter symbo

l

value unit

Input voltage Vi 14 V

Output voltage Vo 42 V

Number of phases N 3 -

Inductor value L 0.885 μH

Capacitor value C 3.9 mF

Load resistance RL 1.764 ohm

Switching

frequency

fs 100 kHz

A. Ripple Cancellation

The first step in the analysis of the multi-phase

interleaved converter system is to investigate the

effectiveness of ripple cancellation related to the variation

of current and voltage as a function of the number of cells.

As can be seen the converter achieves a very good current

and voltage ripple cancellation for three-cells and above.

Though, six or eight cells produce a better ripple

cancellation, however the cost outweigh the gains in

accuracy.

It can be seen from Figures 10 and 11, which the ripple of

output voltage is 8.8mV, and the ripple of the total output

current of the converter is 5mA, and they are better than the

desired specified limits.

Fig 10. Output Voltage Ripples

Fig 11. Output Current Ripples

Figure 12 shows the steady-state waveforms of the

individual cell currents, the simulated results show that

inductor current of each cell rises to 70.86A during each

switching period and goes through an interval in the

discontinuous conduction mode.

Fig 12. The individual cell currents waveform

Fig 13 and 14 show the total output current and the

output voltage of the converter system, the operation of the

power converter system is stable and accurate. The

converter is able to respond and produce the desired stable

output voltage and deliver the required total output current

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to the load with very low ripple. As a result, no negative

effect on the loads connected to the converter.

Fig 13. The output voltage of the converter

Fig 14. The total output current of the converter

B. Transient Simulation for Load Variation

The interleaved dc/dc boost converters are used as power

source to resistive and dynamic loads in passenger car and

these loads could be categorized into [1].

Small motors

Very small motors

Lighting system

Key-off loads

other loads

The electrical loads demand varies and depends upon the

weather and the driving conditions. A full load condition is

rarely present for a prolonged period of time and most of the

devices run at light loads (stand-by-mode) for most of the

time. To study the effect of the load variation on the

dynamic behaviour of the converter system, the load at the

output of the converter system is suddenly changed from

25% to 50% to 75% and to 100% and then back from 100%

to 75% to 50% and 25% of the full load at time t = 0.05,

0.08, 0.11, 0.13, 0.16 and 0.19s, respectively. The simulated

results are shown in Figure 15.

Fig15. Transient response of the output voltage to step

change in load

It can be seen that the output voltage overshoot to 44.5V,

43.09V and 42.6V, when the load at the output of the

converter system was rapidly changed from 25% to 50%,

from 50% to 75% and from 75% to full load (1kW).

The results show that the performance of the system is

stable and well behaved under load variations and the output

voltage remains within the desired specified limits presented

earlier in table (2).

C. Transient Simulation for Input Voltage Variation

In real conditions, the alternator output voltage ranges

from 11V to 16V during normal operation, with nominal

voltage of 14V. To study this line of variation, a step change

in the input voltage from 9V to 24V is applied to the model.

Figure 16 shows a transient response of the output

voltage behaviour waveform due to sudden changes in the

input voltage of the power converter system.

Fig 16. Output voltage and output current due to input

voltage variations

It can be seen that the output voltage overshoots to

42.69V, 44.09V and decreases to 38.276V, then overshoots

to 43.29V finally voltage overshooting to 43.42V when the

input voltage of the converter system is rapidly changed

from 14V to 16V to 24V to 9V to 11V and to 14V, at time

t= 0.05s, 0.08s, 0.11s, 0.13s, 0.16s and 0.19s,

respectively.

It can be observed that the designed system has a low

sensitivity to the variations of input voltage. These

variations have only small influence on the output voltage

and load current and still respect the specifications of the

automotive standard. It can be concluded that from the

results obtained the proposed converter can maintain the

desired output voltage independently of load and supply-

voltage variations. This may lead to the elimination or

reducing of protection connected to the 42V bus in the

power system.

VI. CONCLUSION

In this paper, analysis, design and simulation of 14V/42V

interleaved three-phase dc/dc boost converter system with

one kilowatt output power is presented. This system is a part

of the dual voltage architecture that will be used in future

passenger car power system. Based on the simulation

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results, the performance of the dc-to-dc boost converter

system provides a number of features that do not exist in

today's electrical systems. All the advantages of

interleaving, such as higher efficiency and reduced input

and output ripple for voltage/current, are also Achieved in

the proposed boost converter.

The results show that the system is stable and well

behaved under input voltage variations and the output

voltage remains within the desired specified limits presented

in automotive standards.

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AUTHOR BIOGRAPHY

Ahmed Said Ashur (M 2009) obtained his BSc

from the University of Al-Fatah in 1975, his MSc

from the Southern California University (USC) in

1981, and his PhD from University of Nottingham

in 1996. He is a faculty member at the University

of Tripoli since 1981. His area of interest is digital

signal processing algorithms, systems,

applications, and communications. He has more

than 19 publications in reputable journals, and international conferences.

Farag S. Alargt was born in Zliten, Libya, in

1982. He received the B.S. degree in electrical

and electronic engineering from Almergb

University, Alkhoms, Libya, in 2007. He is

currently working toward the M.S. degree in

electrical engineering in Tripoli University,

Tripoli, Libya. Since 2012, he has been a

Researcher at Centre for Solar Energy Research

and Studies. His research interests include modeling and control of

switching dc–dc converters and renewable energy technology.