A LOW COST DESIGN SOLUTION- DSP BASED

ACTIVE POWER FACTOR CORRECTOR

FOR SMPS(SINGLE PHASE)

ABSTRACT

The main objective of the project is to achieve unity power factor. It is

important to reduce the current harmonics in the ac line current drawn by

SMPS connected to AC mains as source. Active power factor corrector

topology is used to achieve the unity power factor. It is implemented as front

end power interface between SMPS and AC Mains source. This project

explores low cost design solution-DSP based APFC for industry involved in

manufacturing/supply for SMPS. The active power factor corrector topology

used is interleaved boost converter.

.

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TABLE OF CONTENTS

CHAPTER NO. TITLE PAGE NO.

ABSTRACT v

LIST OF TABLES viii

LIST OF FIGURES viii

ABBREVIATION ix

1 INTRODUCTION

1.1 CHAPTER OVERVIEW…………………………………….1

1.2 PROJECT IDEA………………………………………… .... 1

1.3 POWER FACTOR…………………………………………...2

1.3.1 Power factor in linear circuit………………….…3

1.3.2 Definition and

calculation……………….3 1.3.3 Linear

load……………………………....5

1.3.4 Power factor correction of linear load…………...6

1.3.5 Non linear load…………………………………..8

1.3.6 Non sinusoidal components……………………...8

1.3.7 Measuring power factor………………………….9

2 ACTIVE POWER FACTOR CORRECTOR

2.1 ACTIVE PFC…………….........................................................11

2.2 INTERLEAVED BOOST CONVERTER…………………...11.

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2.3 MODES OF OPERATION…………......................................13

2.3.1 continuous vs discontinuous mode……………....14

2.4 ADVANTAGE OF INTERLEAVED BOOST CONVERTER15

3 SWITCHED MODE POWER SUPPLY 3.1 SMPS…………………………………………………...........16

3.2 CLASSIFICATION…………………………….……………18

3.3 APPLICATION……………………………………………..19

4 SIMULATION RESULTS4.1 CHAPTER OVERVIEW…………………………………....20

4.2 CURRENT CONTROLLER ALGORITHM……………..…20

4.3 SIMULATION RESULTS………………………………..…23

5 HARDWARE IMPLEMENTATION5.1 CHAPTER OVERVIEW…………………………………....31

5.2 COMPONENT LIST……………………………………..…31

5.3 POWER SUPPLY……………………………………….... .32

5.3.1 Transformer…………………………………….....32

5.3.2 Bridge Rectifier…………………………………...33

5.4 Optocoupler………...…………………………………….…34

5.5 Power Supply circuit…..…………………………………...36

5.6 Interleaved boost converter circuit…………………………37

5.7 DSP controller……………………………………………....38

6 RESULT AND DISCUSSION……………………………………45

7 CONCLUSION7.1 Chapter Overview…………………………………………. 46

7.2 Project Summary………………………………………… . .46

7.3 Conclusions from Project…………………………………. 47

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7.4 Scope for future work…………………………………… . 47

List of References……………………………………………….... 48

Appendix…………………………………………………………. ...49

List of TablesTables Page

4.1 Design specification ……………………………………………….................36

5.1 Hardware Requirements………………………………………………………38

List of Figures

Figure 2.1 Interleaved boost converter……………………………………………………….13

2.2 Inductor current waveform………………………………………………………15

2.3 Waveforms of interleaved boost converter……………………………………….16

3.1 switched mode power supply…………………………………………………… .18

4.3.1 Boost converter………………………………………………………………….23

4.3.2 Rectified input voltage for boost converter………………………………….… 24

4.3.3 Output voltage for boost converter……………………………………………...24

4.3.4 Output current for boost converter……………………………………………...25

4.3.5 Power factor for boost converter………………………………………………..26

4.3.6 Interleaved boost converter……………………………………………………..27

4.3.7 Rectified input voltage for interleaved boost converter……………………..…27

4.3.8 Output voltage for interleaved boost converter………………………………...28

4.3.9 Output current for interleaved boost converter…………………………………28

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4.3.10 Power factor for interleaved boost converter…………………………………..29

5.1 Transformer………..…………………………………………………………….32

5.2 Bridge rectifier ………………………………………………………………..….33

5.3 Pin diagram for optocoupler………………………………………………………35

5.4 Optocoupler circuit diagram………………………………………………………35

5.5 N- channel Mosfet………………………………………………………………..36

5.6 Interleaved boost converter……………………………………………………….37

5.7 Pin diagram of TMS 320F28335………………………………………………..39

5.8 Functional block diagram……………………………………………………….40

5.9 TMS 320F28335…………………………………………………………………41

5.10 Interleaved boost converter with DSP controller….............................................42

6.1 Pulse from DSP controller………………………………………………………..43

6.2 Input current from interleaved boost converter…………………………………..44

6.3 Input voltage from interleaved boost converter…………………………………..45

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LIST OFABBREVIATION

APFC - Active Power Factor Corrector

SMPS - Switched Mode Power Supply

PF - Power Factor

CCM - Continuous current mode

DCM - Discontinuous current mode

AC - Alternating current

DC - Direct current

P - Real power

S - Apparent power

Q - Reactive power

EMI - Electromagnetic interference

RFI - Radio Frequency interference

Mosfet - Metallic oxide semiconductor field effect transistor

PWM - Pulse Width Modulation.

CCS - Code composer studio

DSP - Digital signal processor

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CHAPTER 1

1 INTRODUCTION

1.1 Chapter Overview

In this chapter, Section 1.2 provides brief discussion of this project. In

Section 1.3,Power factor is discussed. In Section 1.3.1 power factor in linear

circuit is discussed and in section 1.3.2 refers to definition and calculation of

power factor.

Section 1.3.3 briefly discuss the linear load 1.3.4 discuss the power

factor correction of linear load. In this chapter, power factor of non linear

load and non sinusoidal components are also discussed. Power factor

measurement are referred.

1.2 Project Idea

In this project, to achieve unity power factor active power factor

corrector topology is used. The active power factor corrector topology used

is interleaved boost converter. APFC is implemented as the front end power

interface between SMPS and AC mains source. Typical SMPS is built with

uncontrolled bridge rectifier with a filter capacitor providing a narrow pulse

current that contains significant amount of harmonics polluting utility which

makes the input power factor is low and so it is in-efficient. To reduce the

current harmonics in the AC line current interleaved boost converter

operation is performed. Here Comparing the operation of both interleaved

boost converter and the boost converter. To increase the efficiency of the

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SMPS and to achieve the power factor as 1, interleaved boost operation is

performed.

1.3 Power factor

The power factor of an AC electric power system is defined as the

ratio of the real power flowing to the load to the apparent power , and is a

number between 0 and 1 (frequently expressed as a percentage, e.g. 0.9 pf =

90% pf).

Apparent power is the product of the current and voltage of the circuit. Due

to energy stored in the load and returned to the source, or due to a non-linear

load that distorts the wave shape of the current drawn from the source, the

apparent power can be greater than the real power.

In an electric power system, a load with low power factor draws more

current than a load with a high power factor for the same amount of useful

power transferred. The higher currents increase the energy lost in the

distribution system, and require larger wires and other equipment. Because

of the costs of larger equipment and wasted energy, electrical utilities will

usually charge a higher cost to industrial or commercial customers where

there is a low power factor.

Linear loads with low power factor (such as induction motors) can be

corrected with a passive network of capacitors or inductors. Non-linear

loads, such as rectifiers, distort the current drawn from the system. In such

cases, active power factor correction is used to counteract the distortion and

raise power factor. The devices for correction of power factor may be at a

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central substation, or spread out over a distribution system, or built into

power-consuming equipment.

1.3.1 Power factor in linear circuit

In a purely resistive AC circuit, voltage and current waveforms are in step

(or in phase), changing polarity at the same instant in each cycle. Where

reactive loads are present, such as with capacitors or inductors, energy

storage in the loads result in a time difference between the current and

voltage waveforms. This stored energy returns to the source and is not

available to do work at the load. Thus, a circuit with a low power factor will

have higher currents to transfer a given quantity of real power than a circuit

with a high power factor. A linear load does not change the shape of the

waveform of the current, but may change the relative timing (phase)

between voltage and current.

Circuits containing purely resistive heating elements (filament lamps, strip

heaters, cooking stoves, etc.) have a power factor of 1.0. Circuits containing

inductive or capacitive elements (compact fluorescent lamps,lamp ballasts,

motors, etc.) often have a power factor below 1.0.

1.3.2 Definition and calculation

AC power flow has the three components: real power (P), measured in watts

(W); apparent power (S), measured in volt-amperes (VA); and reactive

power (Q), measured in reactive volt-amperes (VAr).

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The power factor is defined as:

In the case of a perfectly sinusoidal waveform, Real power(P),

Apparent power (S) and Reactive power(Q) can be expressed as

vectors that form a vector triangle such that:

S = P² + Q²

If φ is the phase angle between the current and voltage, then the power

factor is equal to COS φ , and

P = S COS φ

Since the units are consistent, the power factor is by definition a

dimensionless number between 0 and 1. When power factor is equal to 0, the

energy flow is entirely reactive, and stored energy in the load returns to the

source on each cycle. When the power factor is 1, all the energy supplied by

the source is consumed by the load. Power factors are usually stated as

"leading" or "lagging" to show the sign of the phase angle.

Distortion power factor is the distortion component associated with

harmonics voltage and currents present. It is defined as the ratio of the

fundamental component of the AC line current to the total line current.

If a purely resistive load is connected to a power supply, current and voltage

will change polarity in step, the power factor will be unity (1), and the

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electrical energy flows in a single direction across the network in each cycle.

Inductive loads such as transformers and motors (any type of wound coil)

consume reactive power with current waveform lagging the voltage.

Capacitive loads such as capacitor banks or buried cable generate reactive

power with current phase leading the voltage. Both types of loads will

absorb energy during part of the AC cycle, which is stored in the device's

magnetic or electric field, only to return this energy back to the source

during the rest of the cycle.

For example, to get 1 kW of real power, if the power factor is unity, 1 kVA

of apparent power needs to be transferred (1 kW ÷ 1 = 1 kVA). At low

values of power factor, more apparent power needs to be transferred to get

the same real power. To get 1 kW of real power at 0.2 power factor, 5 kVA

of apparent power needs to be transferred (1 kW ÷ 0.2 = 5 kVA). This

apparent power must be produced and transmitted to the load in the

conventional fashion, and is subject to the usual distributed losses in the

production and transmission processes.

1.3.3 Linear loads

Electrical loads consuming alternating current power consume both real

power and reactive power. The vector sum of real and reactive power is the

apparent power. The presence of reactive power causes the real power to be

less than the apparent power, and so, the electric load has a power factor of

less than 1.

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1.3.4 Power factor correction of linear loads

It is often desirable to adjust the power factor of a system to near 1.0. This

power factor correction is achieved by switching in or out banks of inductors

or capacitors. For example the inductive effect of motor loads may be offset

by locally connected capacitors. When reactive elements supply or absorb

reactive power near the load, the apparent power is reduced.

Power factor correction may be applied by an electrical power transmission

utility to improve the stability and efficiency of the transmission network.

Correction equipment may be installed by individual electrical customers to

reduce the costs charged to them by their electricity supplier. A high power

factor is generally desirable in a transmission system to reduce transmission

losses and improve voltage regulation at the load.

Power factor correction brings the power factor of an AC power circuit

closer to 1 by supplying reactive power of opposite sign, adding capacitors

or inductors which act to cancel the inductive or capacitive effects of the

load, respectively. For example, the inductive effect of motor loads may be

offset by locally connected capacitors. If a load had a capacitive value,

inductors (also known as reactors in this context) are connected to correct

the power factor. In the electricity industry, inductors are said to consume

reactive power and capacitors are said to supply it, even though the reactive

power is actually just moving back and forth on each AC cycle.

The reactive elements can create voltage fluctuations and harmonic noise

when switched on or off. They will supply or sink reactive power regardless

of whether there is a corresponding load operating nearby, increasing the

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system's no-load losses. In a worst case, reactive elements can interact with

the system and with each other to create resonant conditions, resulting in

system instability and severe overvoltage fluctuations. As such, reactive

elements cannot simply be applied at will, and power factor correction is

normally subject to engineering analysis.

An automatic power factor correction unit is used to improve power

factor. A power factor correction unit usually consists of a number of

capacitors that are switched by means of contactors. These contactors are

controlled by a regulator that measures power factor in an electrical network.

To be able to measure 'power factor', the regulator uses a CT (Current

transformer) to measure the current in one phase.

Depending on the load and power factor of the network, the power factor

controller will switch the necessary blocks of capacitors in steps to make

sure the power factor stays above 0.9 or other selected values (usually

demanded by the energy supplier).

Instead of using a set of switched capacitors, an unloaded synchronous

motor can supply reactive power. The reactive power drawn by the

synchronous motor is a function of its field excitation. This is referred to as a

synchronous condenser. It is started and connected to the electrical network.

It operates at full leading power factor and puts VARs onto the network as

required to support a system’s voltage or to maintain the system power

factor at a specified level. The condenser’s installation and operation are

identical to large electric motors. Its principal advantage is the ease with

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which the amount of correction can be adjusted; it behaves like an

electrically variable capacitor. Unlike capacitors, the amount of reactive

power supplied is proportional to voltage, not the square of voltage; this

improves voltage stability on large networks. Synchronous condensors are

often used in connection with high voltage direct current transmission

projects or in large industrial plants such as steel mills.

1.3.5 Non-linear load

A non-linear load on a power system is typically a rectifier (such as used in a

power supply), or some kind of arc discharge device such as a fluorescent

lamp, electric welding machine, or arc furnace. Because current in these

systems is interrupted by a switching action, the current contains frequency

components that are multiples of the power system frequency.

1.3.6 Non-sinusoidal components

Non-linear loads change the shape of the current waveform from a sine wave

to some other form. Non-linear loads create harmonic currents in addition to

the original (fundamental frequency) AC current. Addition of linear

components such as capacitors and inductors cannot cancel these harmonic

currents, so other methods such as filters or active power factor correction

are required to smooth out their current demand over each cycle of

alternating current and so reduce the generated harmonic currents.

In circuits having only sinusoidal currents and voltages, the power factor

effect arises only from the difference in phase between the current and

voltage. This is narrowly known as "displacement power factor". The

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concept can be generalized to a total, distortion, or true power factor where

the apparent power includes all harmonic components. This is of importance

in practical power systems which contain non-linear loads such as rectifiers,

some forms of electric lighting, electric arc furnaces, welding equipment,

switched-mode power supplies and other devices.

A typical multimeter will give incorrect results when attempting to measure

the AC current drawn by a non-sinusoidal load. A true RMS multimeter

must be used to measure the actual RMS currents and voltages (and

therefore apparent power). To measure the real power or reactive power, a

wattmeter designed to properly work with non-sinusoidal currents must be

used.

1.3.7 Measuring power factor

Power factor in a single-phase circuit (or balanced three-phase circuit) can

be measured with the wattmeter-ammeter-voltmeter method, where the

power in watts is divided by the product of measured voltage and current.

The power factor of a balanced polyphase circuit is the same as that of any

phase. The power factor of an unbalanced polyphase circuit is not uniquely

defined.

A direct reading power factor meter can be made with a moving coil meter

of the electrodynamic type, carrying two perpendicular coils on the moving

part of the instrument. The field of the instrument is energized by the circuit

current flow. The two moving coils, A and B, are connected in parallel with

the circuit load. One coil, A, will be connected through a resistor and the

second coil, B, through an inductor, so that the current in coil B is delayed

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with respect to current in A. At unity power factor, the current in A is in

phase with the circuit current, and coil A provides maximum torque,driving

the instrument pointer toward the 1.0 mark on the scale. At zero power

factor, the current in coil B is in phase with circuit current, and coil B

provides torque to drive the pointer towards 0. At intermediate values of

power factor, the torques provided by the two coils add and the pointer takes

up intermediate positions.

Another electromechanical instrument is the polarized-vane type.In this

instrument a stationary field coil produces a rotating magnetic field, just like

a polyphase motor. The field coils are connected either directly to polyphase

voltage sources or to a phase-shifting reactor if a single-phase application. A

second stationary field coil, perpendicular to the voltage coils, carries a

current proportional to current in one phase of the circuit. The moving

system of the instrument consists of two vanes which are magnetized by the

current coil. In operation the moving vanes take up a physical angle

equivalent to the electrical angle between the voltage source and the current

source. This type of instrument can be made to register for currents in both

directions, giving a 4-quadrant display of power factor or phase angle.

Digital instruments can be made that either directly measure the time lag

between voltage and current waveforms and so calculate the power factor, or

by measuring both true and apparent power in the circuit and calculating the

quotient. The first method is only accurate if voltage and current are

sinusoidal; loads such as rectifiers distort the waveforms from the sinusoidal

shape.

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CHAPTER 2

ACTIVE POWER FACTOR CORRECTOR

2.1 Active PFC

An Active Power Factor Corrector (active PFC) is a power electronic

system that controls the amount of power drawn by a load in order to obtain

a Power factor as close as possible to unity. In most applications, the active

PFC controls the input current of the load so that the current waveform is

proportional to the mains voltage waveform (a sinewave).

Some types of active PFC are

1. Boost

2. Buck

3. Buck-boost

4. Interleaved boost .

Active power factor correctors can be single-stage or multi-stage.

In the case of a switched-mode power supply, a boost converter is inserted

between the bridge rectifier and the main input capacitors. The boost

converter attempts to maintain a constant DC bus voltage on its output while

drawing a current that is always in phase with and at the same frequency as

the line voltage. Another switchmode converter inside the power supply

produces the desired output voltage from the DC bus. This approach requires

additional semiconductor switches and control electronics, but permits

cheaper and smaller passive components. It is frequently used in practice.

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For example, SMPS with passive PFC can achieve power factor of about

0.7–0.75, SMPS with active PFC, up to 0.99 power factor, while a SMPS

without any power factor correction has a power factor of only about 0.55–

0.6. Due to their very wide input voltage range, many power supplies with

active PFC can automatically adjust to operate on AC power from about 100

V (Japan) to 240 V (UK). That feature is particularly welcome in power

supplies for laptops.

Millions of computers in the world operate around the hour which makes their efficiency a very critical issue. A trial of improving the efficiency by using power electronics circuits have been simulated and tested. In this case an active power factor corrector (active PFC) has been used. Additionally, the active PFC will improve the power factor to a value close to unity which means eliminating the reactive power drawn by the power supply.2.2 Interleaved boost converter

Mutual Inductance

Mosfet 1

gm

DS

Mosfet

gm

DS

Diode 1

Diode

DC Voltage Source

C2

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fig 2.1 interleaved boost converter

Fig 2.1 shows the functional diagram of a interleaved boost converter, which

comprises two boost converters operating 180° out of phase. The input

current is the sum of the two inductor currents, IL1 and IL2. Because the

inductor's ripple currents are out of phase, they cancel each other out and

reduce the input-ripple current that the boost inductors cause. The best input-

inductor-ripple-current cancellation occurs at 50% duty cycle. The output-

capacitor current is the sum of the two diode currents, I1+I2, minus the dc-

output current, which reduces the output-capacitor ripple, IOUT, as a function

of duty cycle. As the duty cycle approaches 0, 50, and 100%, the sum of the

two diode currents approaches dc. At this point, the output capacitor has to

filter only the inductor-ripple current.

2.3 Modes of Operation

The mode of operation can be analyzed by based on the energy delivered to the load during each switching period. The interleaved boost converter can be classified into continuous or discontinuous conduction mode. If all the energy stored in the inductor is delivered to the load during each switching cycle, then the mode of operation is said to be discontinuous conduction mode (DCM).In this mode the inductor current ramps down to zero during switch-off time. If only part of energy stored in the inductor is delivered to the load , then the mode of operation is said to be continuous conduction mode (CCM).

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The mode of operation is fundamental factor in determining the electrical characteristics of the converter. The characteristics vary significantly from one mode to the other.

fig 2.2 Inductor current waveforms

2.3.1 Continuous Versus Discontinuous Mode

Both modes of operation have advantages and disadvantages. The switch and output diode peak currents are larger when the converter is operating in DCM mode. Larger peak currents cause greater EMI/RFI problems. Most modern designs use CCM because higher power densities are possible. For these reasons, this design is based on continuous conduction mode.

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The main disadvantage in using CCM is inherent stability problems caused by the right-half-plane zero in the transfer function.

fig 2.3 waveforms of interleaved boost converter

2.4 Advantage of Interleaved boost converter There is reduction in ripple currents in both input and output circuits. Higher efficiency is realized by splitting the output current into two paths, substantially reducing I²R

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losses and inductor AC losses. Also there is shrink in the size of capacitor and inductor.

CHAPTER 3 3.1 Switched mode power supply

A switched-mode power supply (also switching-mode power supply and

SMPS) is an electronic power supply unit (PSU) that incorporates a

switching regulator. While a linear regulator maintains the desired output

voltage by dissipating excess power in a pass power transistor, the switched-

mode power supply switches a power transistor between saturation (full on)

and cutoff (completely off) with a variable duty cycle whose average is the

desired output voltage. It switches at a much-higher frequency (tens to

hundreds of kHz) than that of the AC line (mains), which means that the

transformer that it feeds can be much smaller than one connected directly to

the line/mains. Switching creates a rectangular waveform that typically goes

to the primary of the transformer; typically several secondaries feed

rectifiers, series inductors, and filter capacitors to provide various DC

outputs with low ripple.

The main advantage of this method is greater efficiency because the

switching transistor dissipates little power in the saturated state and the off

state compared to the semiconducting state (active region). Other advantages

include smaller size and lighter weight (from the elimination of low

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frequency transformers which have a high weight) and lower heat generation

due to higher efficiency. Disadvantages include greater complexity, the

generation of high amplitude, high frequency energy that the low-pass filter

must block to avoid electromagnetic interference (EMI), and a ripple voltage

at the switching frequency and the harmonic frequencies thereof.

Figure 3.1 swiched mode power supply

A particularly important class of non-linear loads is the millions of personal

computers that typically incorporate switched-mode power supplies (SMPS)

with rated output power ranging from a few watt to more than 1 kW.

Historically, these very-low-cost power supplies incorporated a simple full-

wave rectifier that conducted only when the mains instantaneous voltage

exceeded the voltage on the input capacitors. This leads to very high ratios

of peak-to-average input current, which also lead to a low distortion power

factor and potentially serious phase and neutral loading concerns.

A typical switched-mode power supply first makes a DC bus, using a bridge

rectifier or similar circuit. The output voltage is then derived from this DC

bus. The problem with this is that the rectifier is a non-linear device, so the

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input current is highly non-linear. That means that the input current has

energy at harmonics of the frequency of the voltage.

This presents a particular problem for the power companies, because they

cannot compensate for the harmonic current by adding simple capacitors or

inductors, as they could for the reactive power drawn by a linear load. Many

jurisdictions are beginning to legally require power factor correction for all

power supplies above a certain power level.

Regulatory agencies such as the EU have set harmonic limits as a method of

improving power factor. Declining component cost has hastened

implementation of two different methods. To comply with current EU

standard EN61000-3-2, all switched-mode power supplies with output power

more than 75 W must include passive PFC, at least. 80 PLUS power supply

certification requires a power factor of 0.9 or more.

Although the term "power supply" has been in use since radios were first

powered from the line/mains, that does not mean that it is a source of power,

in the sense that a battery provides power. It is simply a device that (usually)

accepts commercial AC power and provides one or more DC outputs. It

would be more correctly referred to as a power converter, but long usage has

established the term.

3.2 Classification

SMPS can be classified into four types according to the input and output

waveforms:

AC in, DC out: rectifier, off-line converter input stage

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DC in, DC out: voltage converter, or current converter, or DC to DC

converter

AC in, AC out: frequency changer, cycloconverter

DC in, AC out: inverter

3.3 Application

Switched-mode power supply in domestic products such as personal

computers often have universal inputs, meaning that they can accept power

from most mains supplies throughout the world, with rated frequencies from

50 Hz to 60 Hz and voltages from 100 V to 240 V (although a manual

voltage range switch may be required). In practice they will operate from a

much wider frequency range and often from a DC supply as well. In 2006, at

an Intel Developers Forum, Google engineers proposed the use of a single

12 V supply inside PCs, due to the high efficiency of switch mode supplies

directly on the PCB.

Most modern desktop and laptop computers already have a DC-DC

converter on the motherboard, to step down the voltage from the PSU or the

battery to the CPU core voltage, as low as 0.8 V for a low voltage CPU to

1.2-1.5 V for a desktop CPU as of 2007. Most laptop computers also have a

DC-AC inverter to step up the voltage from the battery to drive the

backlight, typically around 1000 Vrms.

Certain applications, such as in automobile industry and in some industrial

settings, DC supply is chosen to avoid hum and interference and ease the

integration of capacitors and batteries used to buffer the voltage. Most small

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aircraft use 28 V DC, but larger aircraft often use 120 V AC at 400 Hz,

though they often have a DC bus as well. Some submarines like the Soviet

Alfa class submarine utilized two synchronous generators providing a

variable three-phase current, 2 x 1500 kW, 400 V, 400 Hz.

.

CHAPTER 4

4 SIMULATION RESULTS

4.1 Chapter OverviewThe previous two chapters introduced the theory behind the project is

presented. In this chapter, some of the theoretical and experimental results

will be presented. In Section 4.2, a general discussion of each step in the

research process will be provided. Section 4.3 provides the idea of control

signals to interleaved boost converter.

4.2 Current controller AlgorithmThe voltage mode controller senses APFC output voltage, increases the Inductor current from the AC line if out put voltage tends to decrease from the set value Vo(specified voltage) and decreases the current from the AC line when the output voltage tends to increase. The current mode controllersees the Inductor current has the desired wave shape as the voltage waveform and the amplitude as commanded by voltage mode controller.

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Now we shall see how the PWM (switch ON/OFF time) can be designed to achieve the controller objectives. We operate the circuit under current modecontrol and, to make the reference current (instantaneous value of Inductor current) equals instantaneously desired sine wave current. This approach leads to Input current to APFC that approximated to a rectified sinusoid in phase with voltage.Now, Vi = Vm sin t/TL

Where Vm= Amplitude of AC line,TL = frequency of AC line.If the circuit operates properly and PF=1, there must exist a linear relationship in each switching cycle between the average value of Inductor current and Input voltage, IL = gi Vi and analogously between the lowfrequency components, these quantities In (t) = gi vi(t)……………………………………………………………. (1)Here gi denotes the proportionality factor being the input conductance of the circuit (valid for low frequency components). The proportionality factor gi isvaried one cycle to other i.e. every TL second (line period) so as to regulate output voltage Vo around specified value. For a steady state operation, gi must be constant independent of the considered cycle.In inner current mode controller, we assume,

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Iref (t) = I (t)………………………………………………………………(2)For inductor continuous current mode operation,Vi = (1-D) Vo ……………………………………………………………(3)Therefore,(1)equation Becomes In(t) = gi Vo (1-D)……………………………… (4)If Vi and Vo are fixed, Inductor current and the output power can be adjusted by controlling dTs (which in turn alters gi).The average switch current can be related with Inductor current i.e.IS = D In(t)………………………………………………………………. (5)From (4) & (5), it can be shown IS = Vo gi (1-D) = gi Vo (1-dTs)…………………………………………(6)(6) gives the required relationship between IS and dTs in order to keep gi constant in a steady state operation independent of the considered cycle.For practical implementation, from (2)Iref (t)= gi Vo (1-dTs) = vc. Vramp……………………………………… (7)The waveform Iref(t) is similar to ramp function of classical PWM switching mode converter, but the amplitude is adjustable and is controlled by vc(t). Thus the switch current

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can be compared with Iref(t) so that dTs will be determined in accordance with the above relationship.As shown in (7), Iref(t) is derived from the product of feed back controller input vc(t) which gives the control action (gi Vo) in steady state, and a standard ramp function vramp(t) that generates a function of (1- dTs) is called PWM of the switch. Also it is known that Inductor current to follow sine wave voltage Vi in phase at start of line half cycle, Zero crossing detector (ZCD) is used to detect current reference start point. Input voltage variations and Dc load variations are considered as disturbance input of APFC. Hence APFC controller is to regulate output voltage and track inductor current in phase with AC Mains through PWM switching forany step change in the disturbance. This is the current controller algorithm is to be implemented on TMS 320F28335.Vc is the voltage controller output and Iref is reference current generation synchronized with active power factor corrector input voltage Vi. Kp is proportional constant and Is(t) is sampling current. C is the DSP compare unit.

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fig 4.1 current controller algorithm

4.3 Simulation Results The Simulation process are done by using Matlab software.

4.3.1Boost converter

powergui

Continuous

Vin

VL2

v+-

VL1

v+-

VL

v+-

Scope 5

Scope 4

Scope 3

Scope 2

Scope 1 Saturation

RelationalOperator 1

<=

Rectifier

A

B

+

-

PI

PI

Mosfet

gm

DS

Load

LIs1

i+ -

Is

i +-

Gain -K-

Diode

Constant

200

C2C1

xxx

fig 4.3.1 Boost converter

Rectified Input voltage for boost converter

fig 4.3.2 Rectified input voltage for boost converter

Output voltage for boost converter

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fig 4.3.3 Output voltage for boost converter

Output current for boost converter

fig 4.3.4 Output current for boost converter

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Power factor for Boost Converter

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fig 4.3.5 Power factor for boost converter

Calculation of power factor

20 ms 360

2.95ms x

X=53.1

Power factor for boost converter=0.6

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Interleaved Boost Converter

powergui

Continuous

Vin

VL2

v+-

VL1

v+-

VL

v+-

Scope 5

Scope 4

Scope 3

Scope 2

Scope 1

RelationalOperator 1

>=

Rectifier

A

B

+

-

PI

PI

Mutual Inductance

Mosfet 1

gm

DS

Mosfet

gm

DS

LogicalOperator

NOT

Is1

i +-

Is

i +-

Gain 1

Diode 1

Diode

Constant

200

C2C1

fig 4.3.6 Interleaved boost converter

Rectified Input voltage for Interleaved Boost converter

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fig 4.3.7 rectified input voltage for interleaved boost converter

Output voltage for interleaved Boost converter

fig 4.3.8 output voltage for interleaved boost converter

Output current for interleaved boost converter

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fig 4.3.9 output current for interleaved boost converter

Power factor for interleaved Boost converter

fig 4.3.10 power factor for interleaved boost converter

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DESIGN SPECIFICATION

Design specification Boost converter Interleaved boost

converter

Input voltage

Output voltage

Peak-peak output ripple

Output power

Switching frequency

Inductor

Capacitor (c1)

Capacitor (c2)

Switch

Power factor

85v-135v AC

200v DC +\- 2%

< 5 %

400W

20Khz

150mH

1000uF

150uF

Mosfet

0.6

85v-135v AC

200v DC +\- 2%

< 5 %

400W

20Khz

150mH

1000uF

150uF

Mosfet

0.99

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CHAPTER 5

5 HARDWARE IMPLEMENTATION

5.1 Chapter Overview

In this chapter the hardware implementation of Interleaved boost

converter is discussed. In Section 5.2 components required for the hardware

implementation are provided. Section 5.3 provides information about the

Power supply circuit. Section 5.4 briefly discusses the Opto-coupler circuit.

In Section 5.5 power circuit will be discussed. Section 5.6 will present the

idea of using DSP controller for the generation of control signals.

5.2 Components List

To implement the Interleaved Boost converter in an effective way,

the following components are required.

Components Specification Quantity

MOSFET IRF250 2

Opto-coupler MCT2E 2

DSP controller TMS 320LF28335 1

Bridge Rectifier ------ 1

Transformer 230 V/12 V 1

Transformer 230 V/ 9 V 1

Table 5.1 – Hardware Requirements

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Transformers, Bridge Rectifiers and Voltage Regulators are used to

form 12V DC supply for opto-couplers. Opto-couplers form the driver

circuit for MOSFETs. The output from driver circuits is given across the

gate and emitter of the MOSFETs. The output can be seen in a cathode ray

oscilloscope (CRO).

5.3 Power Supply Circuit

5.3.1 Transformers

A transformer is a device that transfers electrical energy from one

circuit to another through inductively coupled electrical conductors. A

changing current in the first circuit (the primary) creates a changing

magnetic field; in turn, this magnetic field induces a changing voltage in the

second circuit (the secondary). By adding a load to the secondary circuit,

one can make current flow in the transformer, thus transferring energy from

one circuit to the other. The main advantage of using transformers is that it

provides electrical isolation. A number of transformers can be connected in

parallel with isolation of secondary sides.

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Fig 5.1 transformer

5.3.2 Bridge RectifierA diode bridge or bridge rectifier is an arrangement of four diode

connected in a bridge circuit that provides the same polarity of output

voltage for any polarity of the input voltage. When used in its most common

application, for conversion of alternating current (AC) input into direct

current (DC) output, it is known as a bridge rectifier. The bridge rectifier

provides full wave rectification from a two wire AC input (saving the cost of

a center tapped transformer) but has two diode drops rather than one

reducing efficiency over a center tap based design for the same output

voltage.

The essential feature of this arrangement is that for both polarities of

the voltage at the bridge input, the polarity of the output is constant.

fig 5.2 Bridge rectifier

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When the input connected at the left corner of the diamond is positive

with respect to the one connected at the right hand corner, current flows to

the right along the upper path to the output, and returns to the input supply

via the lower one.

5.4 Opto-couplerIn electronics, an opto-isolator (or optical isolator, optocoupler,

photocoupler, or photoMOS) is a device that uses a short optical

transmission path to transfer a signal between elements of a circuit, typically

a transmitter and a receiver, while keeping them electrically isolated – since

the signal goes from an electrical signal to an optical signal back to an

electrical signal, electrical contact along the path is broken.

A common implementation involves a LED and a phototransistor,

separated so that light may travel across a barrier but electrical current may

not. When an electrical signal is applied to the input of the opto-isolator, its

LED lights, its light sensor then activates, and a corresponding electrical

signal is generated at the output. Unlike a transformer, the opto-isolators

allow for DC coupling and generally provide significant protection from

serious over voltage condition in one circuit affecting the other.

With a photodiode as the detector, the output current is proportional to

the amount of incident light supplied by the emitter. The diode can be used

in a photovoltaic mode or a photoconductive mode. In photovoltaic mode,

the diode acts like a current source in parallel with a forward-biased diode.

The output current and voltage are dependent on the load impedance and

light intensity.

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In photoconductive mode, the diode is connected to a supply voltage,

and the magnitude of the current conducted is directly proportional to the

intensity of light. An opto-isolator can also be constructed using a small

incandescent lamp in place of the LED; because the lamp has a much slower

response time than a LED, will filter out noise or half-wave power in the

input signal. In so doing, it will also filter out any audio or higher frequency

signals in the input. It has the further disadvantage, that incandescent lamps

have relatively short life spans. Thus, such an unconventional device is of

extremely limited usefulness, suitable only for applications such as science

projects. The optical path may be air or a dielectric waveguide. The

transmitting and receiving elements of an optical isolator may be contained

within a single compact module, for mounting, for example, on a circuit

board; in this case, the module is often called an opto-isolator or opto-

coupler. The photo sensor may be a photocell, phototransistor, or an

optically triggered SCR or Triac. Occasionally, this device will in turn

operate a power relay or contactor. The pin diagram of MCT2E opto-coupler

IC is shown in figure.

NC – No connection

fig 5.3 MCT2E Pin Diagram

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fig 5.4 optocoupler circuit

The package consists of a gallium-arsenide infrared-emitting diode and an

npn silicon phototransistor mounted on a 6-lead frame encapsulated within

an electrically nonconductive plastic compound. The case can withstand

soldering temperature with no deformation and device performance

characteristics remain stable when operated in high-humidity conditions.

Unit weight is approximately 0.52 grams.

5.5 Power CircuitThe power circuit is formed using MOSFETs (IRF250). A metal

oxide semiconductor field effect transistor (MOSFET) is a three-terminal

power semiconductor device, noted for high efficiency and fast switching. It

switches electric power in many modern appliances: electric cars, variable

speed refrigerators, air-conditioners, and even stereo systems with digital

amplifiers. Since it is designed to rapidly turn on and off, amplifiers that use

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it often synthesize complex waveforms with pulse width modulation and

low-pass filters.

fig 5.5 IRF250 – N-Channel MOSFET

5.6 Interleaved boost converter circuit

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fig 5.6 interleaved boost circuit

5.7 DSP ControllerThis universal DSP Controller offers a low cost yet powerful solution for a

wide variety of power conversion or power electronic applications such as

motor drives (induction motor, brushless, DC or AC), power factor

correction, active filters, single or three phase inverters, converters (AC/DC,

DC/AC, AC/AC, DC/DC), SCR controlled converters and others. The dsp

controller TMS 320F28335 is used to generate pulse signal and it is

transferred through opto-coupler circuit to trigger Mosfet .

Features of TMS320F28335

• Digital Signal Controller TMS320F28335 operating at 150 MHz

• 256K word on-chip Flash program memory

• 34K word on-chip data/program of RAM memory

• 128K word on-board data/program of RAM memory

• RS-232 serial communication port

• Opto - isolated CAN communication interface

• Standard I/O connector (3.3V – MC-BUS) for simultaneous links with two power modules

• Access to 58 Individually Programmable GPIO DSP pins

• 16 channels of 12-bit accuracy A/D inputs

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• 2 channels of 12-bit accuracy D/A outputs

• DSC address / data expansion bus connector

• Single DC power supply: 5V

• Dimensions: 104x63 mm

Pin diagram for TMS 320F28335

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fig 5.7 pin diagram for TMS 320F28335

Functional block Diagram for TMS 320F28335

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fig 5.8 functional block diagram

TMS 320F28335

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fig 5.9 TMS 320f28335

l

HARDWARE

fig 5.10 interleaved boost converter with DSP controller

li

CHAPTER 6

6 RESULTS AND DISCUSSION

6.1 Output from the DSP controller

The output that is obtained from the DSP controller are the two pulses

which are given to the anode of the corresponding opto-coupler. The output

pulses can be seen using a CRO or DSO by connecting the positive terminal

of the CRO or DSO to the emitter of the opto-coupler and the negative

terminal to the ground.

fig 6.1 Pulse from dsp controller

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6.2 Output from Interleaved boost converter

The output from interleaved boost converter can be obtained by connecting

positive terminal of Multimeter to the one point of the resistive load and the

negative terminal to the another point of the same resistive load as shown in

the figure.

fig 6.2 Input current of interleaved boost converter

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fig 6.3 Input voltage of interleaved boost converter

6.3 Power factor

The input power factor is obtained by connecting one of the probe across the

supply voltage and another probe to the supply current (By connecting series

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resistor across the voltage as shown in fig) in the CRO/DSO . The output

obtained in DSO is shown in the following figure.

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CHAPTER 7

7 CONCLUSION

7.1 Chapter Overview

The purpose of this chapter is to provide some concluding remarks. In

Section 7.2, a brief summary of the project will be given. From this

summary, some conclusions regarding the project will be made in Section

7.3. Section 7.4 will provide suggestions for possible future research in the

area of interleaved boost converters.

7.2 Project Summary

Chapters 1 and 2 served to provide both an introduction to interleaved

boost converters as well as some background information regarding the

project. In Chapter 1, a brief summary of the project to be presented was

first provided. A general definition of power factor and how to measure the

power factor was given. Power factor on linear load and power factor on

non-linear load was discussed. The importance of power factor in distributed

system was discussed.

In Chapter 2, the methods use to improve the power factor was given.

The active power factor corrector topology was discussed. Advantage of

using interleaved boost converter and the modes of operation of interleaved

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boost converter was given. The inductor current waveform for continuous

and discontinuous mode was discussed.

In Chapter 3, the various issues of Switched mode power supply was

detailed. The classification of switched mode power supply was given and

the application of SMPS in various fields are discussed.

The Chapter 4 was to present some of the collected theoretical and

experimental results. A general discussion of each step in the project process

was presented first. The simulation result for interleaved boost and boost

converters was compared.

In Chapter 5, hardware implementation of Interleaved boost converter

is presented.

7.3 Conclusions from Project

The simulation of boost converter is compared with interleaved boost

converter and the results suggest the interleaved boost converter is more

efficient. The output voltage is regulated and the boost operation was

verified for interleaved boost converter. The power factor of interleaved

boost converter is achieved almost unity. Ripple currents are reduced in both

input and output circuit of the interleaved boost converter.

7.4 Scope for future work

One suggestion for future research would be to extend the interleaved

boost converter for three phase and to reduce the current harmonics in three

phase AC. In this project SMPS application is considered, it can also

lvii

implemented for UPS application. The PIC controller can also implemented

instead of DSP controller. The PIC controller act as driver to trigger pulses

in the mosfet.

List of ReferencesC.H. Chan and M.H. Pong ‘Interleaved Boost Power Factor Corrector Operating in Discontinuous-Inductor-Currrent Mode’-The University of Hong Kong @1997 Vol 405-410.

Yungtaek Jang and Milan M. Jovanović ‘Interleaved PFC Boost Converter with Intrinsic Voltage-Doubler Characteristic’ 37th IEEE Power Electronics Specialists Conference / June 18 - 22, 2006, Jeju, Korea .Vol 1888-1894.

Laszlo Balogh and Richard Redl ‘Power-Factor Correction with Interleaved BoostConverters in Continuous-Inductor-Current Mode’ @ 1993 IEEE Vol 168-174.

Samia Pillai Pitchai and B.Umamaheswari ‘A Low Cost Design Solution - DSP Based Active Power Factor Corrector for SMPS/ UPS( Single Phase)’ American Journal of Applied Sciences 3 (1): 1675-1681, 2006 ISSN 1546-9239 © 2006 Science Publications.

Ron Crews ‘LM5032 Interleaved Boost Converter’ National SemiconductorApplication Note 1820 May 22, 2008 © 2008 National Semiconductor Corporation.

  

Ron Crews, Principal Applications Engineer, and Kim Nielson, Senior Engineering Technician, National semiconductor,phoenix ‘Interleaving is Good for Boost Converters’, Too Vol 24-29.

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