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TRANSILVANIA UNIVERSITY OF BRAŞOV

FACULTY OF ELECTRICAL ENGINEERING

AND COMPUTER SCIENCE

Interleaved Boost Converter

PROJECT SEUE

Students:

Ing. Ungureanu Andrei

Ing. Lăpădat Andrei

Grupa 4736

Anul II SEA

2014 – 2015



2

Table of contents

1.Abstract

2.Introduction

3.Theory

4.The Linear Mode conversion method

5.The Switched Mode conversion method

6.Conventional DC-DC Boost Converter Topology

7.Differences between a single phase and a multiphase converter

8.Interleaved Boost converter Operation

9.Operating principle

10.Continuous mode

11.Discontinuous mode

12.Two channel interleaved Boost converter

13.PWM Signals Generation Technique

14.Theoretical Waveforms for an interleaved Boost Converter

15.Main application of interleaved dc-dc converter

16.Voltage source Invertor

17.Invertor switching states

18.Three phrase rectifier

19.Tehnical calculations

20.Simulation schematic

21. Waveforms



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Interleaved Boost Converter

1. Abstract

Interleaved power converters can be very beneficial for high performance electrical equipment

applications. Reductions in size and electromagnetic emission along with an increase in

efficiency, transient response, and reliability are among the many advantages to using such

converters. The theoretical derivations and simulations results clearly showed that interleaved

designs can provide significant benefit when utilized for high power applications.

In addition to the electrical performance benefits, coupled inductor interleaved boost converters

can be smaller and lighter compared to conventional converter topologies.

These study results have been organized during the course of this project. In this technical report.

2. Introduction

This projects main aim is to show Interleaved boost Converter topology, features

operating modes acording given parameters by solving technical calculations and simulation

results are obtained using MATLAB/Simulink

Minimum ripple can be achieved in both the input and output current. This can be achieved by

carefully investigating the effect of combing two or three phase of boost converters when the

duty circle and the phase are shifted over a switching time. An algorithm is produced with an

input made up of the duty circle and the different phases for the different boost converters.

3.Theory

THE BOOST CONVERTER.

DC-DC converters are power electronics circuits that are capable of converting direct current

(DC) from a particular voltage level to another. The applications of this converter are

numerous and still on the increase, areas of applications include: laptops computers, cell

phones, automobiles e.g. electric power steering systems etc. DC-DC converters are usually

operated with a source voltage from batteries and recently from fuel cells and even



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photovoltaic solar panels. The converters are either required to increase the inputted voltage

or reduce the input voltage i.e. regulate the voltage to meet the requirement of the load.

The DC-DC converters are basically made up of power electronics switches, such as bi-polar

junction transistors (BJT), MOSFET, diodes etc and energy storage devices like inductors

and capacitors. The desired outputs are achieved by controlling the turn on and turn off time

of the switches. There are two conversion method employed by DC-DC converters i.e. Linear

mode and switched mode conversion method.

The Linear Mode conversion method.

The linear mode DC-DC converters are only efficient when the required output voltage is

lesser than the input voltage. They become inefficient as the drop in voltage and output

current increases in comparison to the input voltage. The inefficiency of the linear mode

conversion method is due to the fact that they have to dissipate the heat equivalent to the

difference in voltage and the output current In consequence to this, larger, more expensive

and higher rated components are required to cater for this losses and also a lot of

consideration has to be given to the cooling of the components. They do have some

advantage, especially when used in application where less voltage drop is required and a

good heat sink is used. They are less expensive, reliable and less complex as compared to the

switched mode conversion method. They also have the capacity to provide low noise output

voltage.

The Switched Mode conversion method

Switched mode DC-DC converts DC voltage from one voltage level to another by first

storing the input energy temporarily in a magnetic field storage component such as inductor

or an electrical field storage device such as capacitor and later releasing the stored energy at a

different voltage level. Switched mode conversion methods are more efficient than the linear

mode method. They are capable of achieving 90% efficiency. They accomplish this by

switching a power electronics switch with a variable duty circle. Some disadvantages of the

switching mode conversion method include; they are expensive, they make use of a more

complex control system and they can also be a source electromagnetic interference (EMI).

Interleaved Boost Converter topology consists of:



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Three phrase rectifier

Two chanel interleved Boost converter

Voltage source inverter

Conventional DC-DC Boost Converter Topology

Equation (1) reflects the fact that a large duty ratio is required for a large voltage boost, which

places a practical limit on the achievable voltage step-up due to the large volume and weight of

the required capacitance. For example, if the switch duty ratio (D) is greater than 0.5 (50%), the

capacitor, C, supplies all of the output current for a longer portion of each period compared to

the energy storage inductor. Therefore, in order to maintain acceptably small output ripple

voltages, a prohibitively large capacitance is required to ensure that the output voltage does not

sag as the stored energy is supplied by C during the duration D. Furthermore, since both dc and

ac current are being sourced through the inductor, the inductor must be designed such that the

cores will not saturate during high power operation. In addition, elevated temperatures typically

lower the saturation flux threshold of the inductor core material, making this requirement a more

significant design consideration. In order to address these concerns, an interleaved design

involving parallel operation of two boost converters, was evaluated as a means to reduce the

burden on the output capacitor as well as the form factor and weight of the inductor. Additional

benefits of interleaving include high power capability, modularity, and improved reliability of



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the converter. An interleaved topology, however, improves converter performance at the cost of

additional inductors, power switching devices, and output rectifiers. Since the inductor is the

largest and heaviest component in a power boost converter, the use of a coupled inductor, where

a core is shared by multiple converters instead of using multiple discrete inductors, offers a

potential approach to reducing parts count, volume, and weight. Coupled inductor topologies can

also provide additional advantages such as reduced core and winding loss as well as improved

input and inductor current ripple characteristics. Properly implemented, the coupled inductor can

also yield a decrease in electromagnetic emission, an increase in efficiency, and improved

transient response. Inductor flux coupling can be realized using either direct or indirect winding

configurations and is a primary design consideration for the interleaved topology. Descriptions

of the benefits and disadvantages of each configuration are more fully described below.

A generalized steady state analysis of multiphase interleaved boost converters has been

previously reported in detail in [3]. Useful design equations for operation of an interleaved boost

converter along with the effects of inductor coupling on the key converter performance

parameters such as inductor ripple current, input ripple current, minimum load current

requirement

Differences between a single phase and a multiphase converterA multiphase converter consists of paralleled power stages, which drive a common load. By

phase shifting the PWM signals to the converter power stages, or “channels”, several advantages

over a single power stage including lower current ripple on the input and output capacitors, faster

transient response to load steps, improved power handling capabilities, and higher system

efficiency are obtained.



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Interleaved Boost converter Operation

Fig. 2 shows the schematic of the dual interleaved boost dc-dc converter. The interleaved boost

dc-dc converter consists of two parallel connected boost converter units, which are controlled by

a phase-shifted switching function (interleaved operation). To illustrate interleaving operation,

Fig. 3 shows the timing diagram of control signals to the switches Since this converter has two

parallel units, the duty cycle for each unit is equal to (Vout-Vin)/Vout, and it is same for each

unit due to parallel configuration. A phase shift should be implemented between the timing

signals of the first and the second switch. Since there are two units parallel in this converter, the

phase shift value is 180O.

The states of operation of this converter are explained as follows. In order to simplify the

calculation, it is assumed that the inductance value of both inductor are L1 and L2, where

L1=L2=L, and the duty cycle of Q1 and Q2 denoted as D1and D2, with D1=D2=D.

1). State a:

At time t0, Q1 is closed and Q2 is opened. The current of the inductor L1 starts to rise, while L2

continues to discharge. The rate of change of iLl is diLl/dt = Vi/L, while the rate of change of

iL2 is diL2/dt = (Vi – Vo)/L.



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2). State b:

At time t1, Q1 and Q2 are opened. The inductors L1 and L2 discharge through the load. The rate

of change of iLl and iL2 are diLl/dt = diL2/dt = (Vi – Vo)/L.

3). State c:

At time t2, Q2 is closed while Q1 still opened. The current of the inductor L2 starts to rise, while

L1 continues to discharge. The rate of change of iL2 is diL2/dt = Vi/L, while the rate of change

of iL1 is diL1/dt = (Vi – Vo)/L.

4). State d:

At time t3, Q2 is opened and Q1 still opened. The situation is same as state b. The inductors L1

and L2 discharge

through the load. The rate of change of iLl and iL2 are diLl/dt = diL2/dt = (Vi – Vo)/L.

Due to the symmetry of the circuit, the next state is similar to the previous.

Operating principle

Continuous mode

When a boost converter operates in continuous mode, the current through the inductor (I_L)never falls to zero. Figure 3 shows the typical waveforms of currents and voltages in a converter

operating in this mode. The output voltage can be calculated as follows, in the case of an ideal

converter (i.e. using components with an ideal behaviour) operating in steady conditions

During the On-state, the switch S is closed, which makes the input voltage (V_i) appear across

the inductor, which causes a change in current (I_L) flowing through the inductor during a time

period (t) by the formula:



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D is the duty cycle. It represents the fraction of the commutation period T during which the

switch is On. Therefore D ranges between 0 (S is never on) and 1 (S is always on). During the

Off-state, the switch S is open, so the inductor current flows through the load. If we consider

zero voltage drop in the diode, and a capacitor large enough for its voltage to remain constant,

the evolution of IL is:

Waveforms of current and voltage in a boost converter operating in continuous mode.

Discontinuous mode

If the ripple amplitude of the current is too high, the inductor may be completely discharged

before the end of a whole commutation cycle. This commonly occurs under light loads. In this

case, the current through the inductor falls to zero during part of the period (see waveforms in

figure 4). Although slight, the difference has a strong effect on the output voltage equation. It can

be calculated as follows:



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Waveforms of current and voltage in a boost converter operating in discontinuous mode.

Two channel interleved Boost converter



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12

PWM Signals Generation Technique

The pwm duty cycle signals are generated by comparing a level control signal (Vc) with a

constant peak repetitive triangle signal (Vst). The frequency of the repetitive triangle signal

establishes the switching frequency.

Since the interleaved boost converter requires two pwm signals to drive both of switches, the

additional work necessary to generate two of pwm signals from single duty cycle formula. Fig. 4

shows the pwm signals generation technique. The first pwm signal is produce when the control

signal V1 is less than Vst and the second pwm signal is produce when the control signal V2 is

greater than Vst.

The value of the desired level control signal (Vc) is got from controller output. The values of

control signal V1 and V2 are given in (1) and (2), while the PWM signals are generated by v1

= vc

Theoretical Waveforms for a interleaved Boost Converter



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Main application of interleaved dc-dc converter in photovoltaic (PV) modular system has been

presented. In the multi-string technology, several PV strings are interfaced with their own dc-dc

converter to a common dc-ac inverter. Enlargements are easily achieved since a new string with

dc-dc converter can be plugged into the existing platform. This paper proposes a simple method

to connect various PV modules in order to improve power quality. Thanks to the proposed digital

control method, the PV interleaving becomes simple and efficient in terms of dynamic

performances, steady-state condition and well regulated output voltage.



14

Voltage source Invertor

The inverter is composed of six groups of active switches,1

S to6

S . Depending on the DC

operating voltage of the inverter, each switch is an IGBT switching device.

Three-phase inverters are used for variable-frequency drive applications and for high power

applications such as HVDC power transmission. A basic three-phase inverter consists of three

single-phase inverter switches each connected to one of the three load terminals. For the most

basic control scheme, the operation of the three switches is coordinated so that one switch

operates at each 60 degree point of the fundamental output waveform. This creates a line-to-line

output waveform that has six steps. The six-step waveform has a zero-voltage step between the

positive and negative sections of the square-wave such that the harmonics that are multiples of

three are eliminated as described above. When carrier-based PWM techniques are applied to six-

step waveforms, the basic overall shape, or envelope, of the waveform is retained so that the 3rd

harmonic and its multiples are cancelled.

3-phase inverter switching circuit showing 6-step switching sequence and waveform of voltage

between terminals A and C (23-2 states)



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Three-Phase Inverter with RL Load

Phase Voltages for 180 Conduction



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Waveforms for 180 Conduction



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Inverter switching states

Stage I of the inverter:

Stage II of the inverter:

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Stage IV of the inverter:

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Three phrase rectifier

Three- phase rectifiers are commonly used in industry to produce a dc voltage and current

for large loads.

The three-phase voltage source is balanced and has phase sequence a-b-c.

The source and the diodes are assumed to be ideal in the initial analysis of the circuit.

Only one diode in the top half of the bridge may conduct at one time (D1, D3, or D5).

Only one diode in the bottom half of the bridge may conduct at one time (D2, D4, or D6).

D1 and D4 cannot conduct at the same time. Similarly, D3 and D6 cannot

conduct simultaneously, nor can D5 and D2.

The output voltage across the load is one of the line-to-line voltages of the

source. For example, when D1 and D2 are on, the output voltage is vac.

he diodes that are on are determined by which line-to-line voltage is the

highest at that instant.

There are six combinations of line-to-line voltages (every 60°).

Because of the six transitions that occur for each period of the source

voltage the circuit is called a six- pulse rectifier.



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the fundamental frequency of the output voltage is 6*w (w is grid freq.)



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Waveforms of the input voltages

Waveforms of the output terminal voltages specified by (2.5) and (2.6) are

presented in Fig. 2-3. These waveforms are periodic, with the period equal to

one third of the line period; thus their spectral components are located at

triples of the line frequency. Fourier series expansion of the waveform of the

positive output terminal leads to:



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Waveforms of the output terminal vA and vB



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Tehnical calculations

Requirements

A two-channel boost converter is used in a 1.2 MW, 690 V, 50 Hz PMSG wind energy

conversion system as shown below. The boost converter transfers the power from the

generator to the grid of 690 V/50 Hz via a diode rectifier and a two-level voltage source

inverter. The inductance L1(L 2 = L 1 ) and capacitance Co of the boost converter are

270 µH and 2300 µF, respectively. The switching frequency of the boost converter is

2000 Hz. The output voltage Vo of the boost converter is set by the inverter to 1220 V.

At a given wind speed, the generator is delivering the rated power to the grid and its line-

to-line stator voltage is found to be 690 V. Calculate/answer the following:

a) The input voltage and power to the boost converter

b) The boundary inductor and output currents for each channel, operating mode, and

duty cycle.

c) The peak-to-peak and average inductor currents in each channel.

d) The peak-to-peak and average input currents.

e) The percentage inductor and input current ripples.

f) The percentage output voltage ripple if the boost converters are interleaved and not

interleaved.

g) Simulate the circuit using Simulink



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Main circuit schematic



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Tehnical calculations acording our parameters are in the pdf file atached



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Simulation schematic



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Simulation results :

Main Scope

Ouput waveforms for voltage and curent

Scope 1



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PWM discrette generator pulses

Scope 2

Voltage waveform for first phrase after the rectifier and capacitive filter

Scope 3



Voltage waveform between phrases before the inverter

Scope 4

Input voltage waveforms between second and third phrase

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