Download 1.3.7 Measuring power factor

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.
1
TITLE
PAGE NO.
ABSTRACT
v
LIST OF TABLES
viii
LIST OF FIGURES
viii
ABBREVIATION
ix
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.
2.3 MODES OF OPERATION…………......................................13
ii
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 RESULTS
4.1 CHAPTER OVERVIEW…………………………………....20
4.2 CURRENT CONTROLLER ALGORITHM……………..…20
4.3 SIMULATION RESULTS………………………………..…23
5
HARDWARE IMPLEMENTATION
5.1 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
CONCLUSION
7.1 Chapter Overview…………………………………………. 46
7.2 Project Summary………………………………………… . .46
7.3 Conclusions from Project…………………………………. 47
7.4 Scope for future work…………………………………… . 47
iii
List of References……………………………………………….... 48
Appendix…………………………………………………………. ...49
List of Tables
Tables
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
4.3.10 Power factor for interleaved boost converter…………………………………..29
iv
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
v
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
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).
3
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.
11
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
Diode 1
D
g
Diode
D
g
Mutual Inductance
C2
fig 2.1 interleaved boost converter
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S
m
S
Mosfet 1
m
DC Voltage Source
Mosfet
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 inputinductor-ripple-current cancellation occurs at 50% duty cycle. The outputcapacitor current is the sum of the two diode currents, I1+I2, minus the dcoutput 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).
13
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.
Ip
CCM
0
Ip
DCM
0
Ip
Boundary
Condition
0
DTS
TS=1/fs
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.
14
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 losses and inductor AC losses. Also there is shrink
in the size of capacitor and inductor.
15
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 switchedmode 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
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.
16
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 fullwave 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
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
17
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

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
18
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
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.
.
19
CHAPTER 4
4 SIMULATION RESULTS
4.1 Chapter Overview
The 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 Algorithm
The 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 controller
sees the Inductor current has the desired wave shape as the voltage
waveform and the amplitude as commanded by voltage mode controller.
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 mode
control 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.
20
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 low
frequency 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 is
varied 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,
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)
21
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 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 for
any 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.
22
fig 4.1 current controller algorithm
4.3 Simulation Results
The Simulation process are done by using Matlab software.
4.3.1Boost converter
Continuous
powergui
Scope 2
+ v
-
VL 1
Scope 3
+ v
-
VL 2
Is1
B
g
C2
Mosfet
C1
Vin
+ v
-
D
+
-
Load
VL
Scope 5
S
A
Diode
m
+
i
-
L
Is
Rectifier
i
-
+
Scope 4
Gain
Relational
Operator 1
Scope 1
-K-
<=
Saturation
PI
Constant
PI
200
fig 4.3.1 Boost converter
23
Rectified Input voltage for boost converter
fig 4.3.2 Rectified input voltage for boost converter
Output voltage for boost converter
fig 4.3.3 Output voltage for boost converter
24
Output current for boost converter
fig 4.3.4 Output current for boost converter
25
Power factor for Boost Converter
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
26
Interleaved Boost Converter
Continuous
powergui
+
v
-
Scope 3
VL1
Scope 2
Mutual Inductance
C2
-
+ v
-
VL
Scope 4
S
B
Mosfet 1
m
Mosfet
C1
Vin
D
+
S
A
Diode
g
+
g
i
-
D
VL2
Diode 1
Is1
m
+
v
-
Is
Rectifier
i
-
+
Scope 5
NOT
Scope 1
Logical
Gain
Operator
Relational
Operator 1
>=
1
PI
PI
Constant
200
fig 4.3.6 Interleaved boost converter
27
Rectified Input voltage for Interleaved Boost converter
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
28
Output current for interleaved boost converter
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
29
DESIGN SPECIFICATION
Design specification
Boost converter
Interleaved boost
converter
Input voltage
85v-135v AC
85v-135v AC
Output voltage
200v DC +\- 2%
200v DC +\- 2%
Peak-peak output ripple
<5%
<5%
Output power
400W
400W
Switching frequency
20Khz
20Khz
150mH
150mH
Capacitor (c1)
1000uF
1000uF
Capacitor (c2)
150uF
150uF
Mosfet
Mosfet
Inductor
Switch
Power factor
0.6
0.99
30
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
31
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.
Fig 5.1 transformer
32
5.3.2 Bridge Rectifier
A 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
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-coupler
In electronics, an opto-isolator (or optical isolator, optocoupler,
photocoupler, or photoMOS) is a device that uses a short optical
33
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.
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
34
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 optocoupler. 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
fig 5.4 optocoupler circuit
35
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 Circuit
The 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
it often synthesize complex waveforms with pulse width modulation and
low-pass filters.
fig 5.5 IRF250 – N-Channel MOSFET
36
5.6 Interleaved boost converter circuit
fig 5.6 interleaved boost circuit
5.7 DSP Controller
This 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 .

37
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
• 2 channels of 12-bit accuracy D/A outputs
• DSC address / data expansion bus connector
• Single DC power supply: 5V
• Dimensions: 104x63 mm
38
Pin diagram for TMS 320F28335
fig 5.7 pin diagram for TMS 320F28335
39
Functional block Diagram for TMS 320F28335
fig 5.8 functional block diagram
40
TMS 320F28335
fig 5.9 TMS 320f28335
41
HARDWARE
fig 5.10 interleaved boost converter with DSP controller
42
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
43
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
44
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
45
resistor across the voltage as shown in fig) in the CRO/DSO . The output
obtained in DSO is shown in the following figure.
46
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
47
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
48
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 References
C.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 Boost
Converters 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 Semiconductor
Application 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.
49
50