Induction Cooker Theory

8/11/2019 Induction Cooker Theory

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Induction Cooking Theory and Operation

By S. S. Kulkarni


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1 R-L-C FUNDAMENTALS, ENERGY STORAGE EQUATIONS

2 MAGNETIC CIRCUIT FUNDAMENTALS & MAGNETIC MATERIALS

3 DC, AC CIRCUITS & THEORY OF LOSSES IN MAGNETICCIRCUITS DUE TO HYSTERESIS, EDDY CURRENTS AND SKIN EFFECTS.

4 MAGNETIC MATERIALS FOR HIGH FREQUENCY OPERATIONS DISCUSSIONS , Q & A

5a Diode/Transistor Characteristics and Transistor Linear/saturation mode )

6 RECTIFIER CIRCUITS, LINEAR/NON-LINEAR LOAD & HARMONICGENERATION

7 EFFECT OF HARMONICS & ELECTRICAL/MAGNETIC INTERFERENCE 8 MAINS FILTER TO ATTENUATE HARMONICS

DISCUSSIONS, Q & A

9 LINEAR/SWITCHING CIRCUITS & COMPONENTS LIKE BJT, IGBT, MOSFET

10 BJT, IGBT, MOSFET INPUT/OUTPUT CHARACTERISTICS

11 GATE DRIVER CIRCUITS & SWITCHING LOSSES

12 BUCK, BOOST & FLY-BACK TOPOLOGIESDISCUSSIONS, Q & A

13 POWER FACTOR CORRECTION CIRCUITS

14 INVERTE - CIRCUITS- SINGLE SWITCH, HALF BRIDGE & FULL BRIDGE

15 PWM TECHNIQUE TO CONTROL VOLTAGE * REDUCE LOSSES

16 APPLICATIONS OF RESONANT CIRCUITS FOR DC/AC CONVERTION DISCUSSIONS, Q & A

5b AC->DC & DC->AC CONVERTIONS (RECTIFIERS & INVERTERS)


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32 DEVELOPING TEST PROCEDURE FOR QUALITY CONTROL & SERVICING DISCUSSIONS, Q & A

17 THERMAL MANAGEMENT, HEATSINK DESIGN

18 PRINCIPLE OF INDUCTION HEATING

19 ADVANTAGES & DISADVANTAGES OF INDUCTION HEATING

20 INDUCTION HEATING CIRCUITS TOPOLOGIES & ADVANTAGES

/ DISADVANTAGES, DISCUSSIONS, Q & A 21 INDUCTION HEATER COMPONENTS

22 CIRCUIT WAVEFORM, MEASUREMENT OF POWER EFFICIENCY

23 INSTRUMENTATIONS: - MEASUREMENT OF VOLTAGE, CURENT,POWER, INDUCTANCE, CAPACITANCE, FLUX & TEMPERATURE.

24 SENSORS FOR CURRENT, FLUX, TEMPERATURE

DISCUSSIONS, Q & A 25 BASICS OF MICROCONTROLLER

26 MICROCONTROLLER DATA/ADDRESS BUS, MEMORY MANAGEMENT,I/O PORTS, PWM, COMMUNICATIONS

27 DISPLAY TECHNOLOGY: - LED, LCD, CHARACTER AND GRAPHIC DISPLKAY

28 TOUCH MEMBRANE SWITCHES AND INTERFACING TO MICROCONTROLLER

DISCUSSIONS, Q & A 29 BASICS OF MICROCONTROLLER PROGRAMMING

30 CORELATING THEORY TO EXISTING INDUCTION COOKER CIRCUITS

31 QUALITY CONTROL MEASURES TO BE TAKEN


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Definitions of LCR

andHence average power across capacitor in circuit is Zero.Also capacitor current increases as frequency of voltageapplied across capacitor increases. At very high frequencycapacitor act as short circuit.

V = I*R So if applied voltage across resistor is sinusoidal thenCurrent is also sinusoidal and in phase with voltage

across itCapacitance is a property of dielectric material to store electriccharge and given by equation as

dT dV

C dT dQ

Q = CV; andV

C Q

d

Ar 0=C

so if applied voltage is sinusoidal across capacitorthen the current through the capacitor leads by90 0 to voltage.

for parallel plate capacitor


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dt dV

C I then

22

21

21 CV dt

dt dV C dt

dt dV V C dt

dt dV VC VIdt E

where E is energy stored in joules in the capacitor.

Think what happens when current is passed through a

capacitor? Does it store charge? If yes which polarity? Can Capacitor store energy if disconnected from charging circuit?

Inductance is a property of coil and measured as I

N L

and hence dT d N dT dI L and according to faradays law

is induced voltage. So induced voltagedT dI

LV

and voltage induced across inductor because of dc current is Zero.

dT

d N

and voltage induced across inductor because of dc current is Zero.


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Inductor current will lag by 90 0 to inductor voltage whenexcited by AC voltage.

Also DC voltage cant be applied across inductorContinuously otherwise it will act as a short circuit.

dt dI

LV 22

21

21

LI dt dt

dI Ldt

dt dI

I Ldt dt dI

LI VIdt E If

then where E is energy stored in joules in the Inductor.

Can Inductor hold back energy if current is disconnected?


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Classification of Magnetic Materials

(a) Orbital Magnetic Moment m0 & (b) Spin Magnetic Moment ms of an electron.

Relationship of magnetisation vector M, magnetic flux densityB, and permeability m

The magnetic flux density corresponding to M is Bm = 0 M . In the presence of an applied magnetic field H, the total magnetic fluxdensity in the magnetic material is given asB = 0 H + 0 M = 0 (H +M), and M = m H where is called magneticsusceptibility


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Diamagnetism: r < 1

no remanenceorbit distortione.g., copper, mercury, gold, zinc

Paramagnetism:

r > 1no remanenceorbit and spin alignmente.g., aluminum, titanium, platinum

Ferromagnetism: r >> 1remanence, coercivity, hysteresisself-amplifying paramagnetismCurie temperature

e.g., iron, nickel, cobalt

Types of magnetic materials


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(a) Un-magnetised domains. (b) Magnetised domains.


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3 Magnetic recording materials

Ferromagnetic materials

1 Soft magnetic materials

2 Hard magnetic materials

Soft magnetic materialsSoft magnetic materials have high permeability and lowcoercivity. = ( B / H) ; B = 0 H + I & = 0 + H / I = 0 +

For obtaining soft magnetic propertiesa) Materials with low magnetic anisotropy, low magnetostriction

and high saturation magnetizationb) Annealing for reducing defects in a material,

which makes domain wall move easily.c) Ring shape for reducing magnetic shape anisotropy.

1. Fe-Si alloys: 3%Si-Fe, 6.5% Si- Fe (s ~ 0 ) 2. Pemalloy: K1 ~ 0, s ~ 0 for 78%Ni-Fe , 4%Mo-79%Ni-Fe4. Spinal ferrites such as Mn0.5Zn0.5Fe2O4, Ni0.3Zn0.7Fe2O4

for high frequency applications5. YIG: Microwave applications

6. Amorphous alloys7. Nanocrystals


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Ferromagnetism

(i) magnetic polarization is produced by collectiveaction of similarly oriented spins withinmagnetic domains

(ii) very high permeability(iii) magnetic hysteresis(v) remnant magnetic polarization (remanence)(vi) coercive magnetic field (coercivity)(iv) depolarization above the (magnetic) Curie

temperature

H

B

Br

Hc

first magnetization


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Magnetic Properties

para- and diamagnetic materials: 0 ( ) B H M M H

0 r B H r 1

ferromagnetic materials: 0 0( , ) ( , ) p p B B H M H M H M

-1.5

-1

-0.5

0

0.5

1

1.5

-5 -4 -3 -2 -1 0 1 2 3 4 5Magnetic Field [kA/m]

F l u

x D e n s i t y

[ T e s

l a ] hardened steel

soft iron


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3%Si-Fe alloy

This material is for power and distribution transformers, whichare used under the AC with a lower frequency. The energy lossin these transformers generally consists of magnetic core lossand coil loss due to joule heating in the copper coils.

Core loss = classical eddy current loss +eddy current loss due to domain wall movement

+ acoustic loss due to magnetostrictive deformation ofthe core under changing flux.

For reducing core loss, decreasing laminationthickness, increasing resistivity, decreasing domainsize and decreasing magnetostriction are effective.


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Figure 1: Law relating the current direction and the resultantflux direction - cork-screw rule

When the current i amperes flows through a conductor, theflux wraps around in a similar manner as that of a direction

of travel of cork-screw when turned in clockwise direction.F =B XI FBI Rule

where B is direction of flux density, I isdirection of current flow and F is resultantforce experienced by current carrying conductor

Magnetic Circuits

Production of Magnetic Field: In order to determine thedirection of flux created due flow of current in a conductor;

consider the diagram in figure 1.


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Production of Magnetic Field (continued)Consider the magnetic core shown in the diagram of Figure 2. Ithas a winding carrying a current of i amperes and N turns. Itgenerates a magneto motive force (MMF) F of N.i ampere (A).

Figure 2: A simple magnetic Core

Since the number of turns, Nis dimensionless; the SI unitfor MMF is just ampere,denoted by A.

The MMF creates a magnetic fieldin core having an intensity of Hampere-turns / meter along thelength of the magnetic path. Uponintegrating the magnetic field

intensity along themagnetic path,we get,

H dl = N.i ampere (A) ..(1)


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The above is the Ampere's law governing the production of amagnetic field by a current carrying coil. If the path ofintegration is the mean path length of the core lc , Amperes lawbecomes;

Production of Magnetic Field (Continued) This MMF F drives through the magnetic core, a flux

Webers. The flux can be related as: = N.i/R = F/R .. (3)

H.l c = N.i (2)

The term R refers to reluctance of the magnetic core. TheMMF has to drive the flux against this reluctance R . Thereluctance of the magnetic core may be given by the

following expression:R = l c / . A c (4)

Wherel c refers to the mean length of the magnetic path in meters

Ac refers to the cross-sectional area of the flux path in meter 2

and the term refers to the permeability of the magnetic material.


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Production of Magnetic Field (Continued)The unit for R is 1/henry or 1/H. The unit for is H/m. Thepermeability of free space or air is 0 and is given by;

0 = 4 x10-7 H/m .. (5)Remember that each ferromagnetic material has its ownrelative permeability ( r ) and can befound from manufacturer where;

= 0 x r (6)

A simple magnetic core Relative permeability is a convenientway to compare the magnetizability different materials. ForExample, the steels used in modern machines have relativepermeability in the range 2000 to 6000. This means that, for a

given amount of current, 2000 to 6000 times more flux isestablished in a piece of steel than in a corresponding area ofair. Obviously, the metal in a transformer or amotor core may plays an extremely important role inincreasing and concentrating the magneticflux in the device.


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Since the permeability of iron is much higher than that of Air,a major portion of the flux in configuration, likes that of Figure2, remains inside the core instead of travelling through thesurrounding Air, which has lower permeability. The small

portion of flux that does not travel through the iron core, buttravels through Air path is called leakage flux . Treatment ofleakage flux is very important in transformer and motors. Production of Magnetic Field (Continued) The flux density B may be defined as B = / A c (7) Where dS is the differential unit of the cross-sectional area. If the

flux density vector B is perpendicular to a plane of area A c , and ifthe flux density B is constant throughout the area, then thisequation reduces to

= B.Ac ..(8)


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Thus, the total flux in the core in Figure 2 due to the currenti in the winding is

)9..(..........

c

C C l

NiA BA

Magnetic Field Intensity, Relative Permeability andReluctance In the previous lecture basics of magnetic circuits are coveredwith display of the similarities between magnetic and electric

circuits parameters, such as current I is analogues to flux, etc...

Magnetic flux behaves in the same manner as the currentflowing in closed loops and many of magnetic circuitsapplications are of different shapes, sizes, and may

come in unified or composite ferromagnetic materials.Example 1: N turns of wire are wound around a toroidal coreof a ferromagnetic material with permeability . Determine B f,in the ferromagnetic core; H f in the core; and H g in the air gap.

S l ti


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Figure 3 Magnetic circuit of Example 1

SolutionApplying Amperes circuital law

If flux leakage is neglected, thesame total flux will flow in boththe ferromagnetic core and in theair gap. If the fringing effect of

NI=Hdl

the flux in the air gap is neglected, the magnetic flux density Bin both the core and the air gap will also be the same.If the radius of the cross section of the core is much smallerthan the mean radius of the toroid, the magnetic flux density Bin the core is approximately constant, and the magnetic flux inthe circuit is = BS

where the f and g denote ferromagneticand gap, respectively. In theferromagnetic core and in the air gap,


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Both Rf and Rg are called reluctance.

Fig. 4 Equivalent magnetic and electric circuit of the example1

It has to be noted that all the formulae and methods of circuitanalysis learned in electric circuits analysis eg. current/voltagedivision rules, superposition, series and parallel, etc are to be applied in solving magnetic circuits.


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Similar to Kirchhoffs voltage law, we may write, for any closed path in a magnetic circuit,

N I = R

Around a closed path in a magnetic circuit the algebraic sum ofampere-turns is equal to the algebraic sum of the products ofthe reluctances and fluxes.

It has to be noted that all the formulae and methods of circuitAnalysis concerning electric circuits analysis eg. current/voltage

division rules, superposition, series and parallel, etc are to beapplied in solving magnetic circuits.

Example 2 the magneticcircuit in Fig. 5 (a)

Figure 5 Magnetic circuits for Example 2


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Solution The reluctances are:

The two loop equations are

Solving these simultaneous equations, we have

One of the reasons we make a narrow gap is that As the air gap ofa coil is increased, the linear inductance region of the coil will alsoincrease, and the coil will not saturate for the same excitation current;which would cause saturation if the air gap was not included.

H i


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Hysteresis

The magnetisation behaviour of the ferromagnetic materials is described by the B-H magnetisation curve (hysteresis loop) as shown in figure below.

down to zero, the curve will move from point "a" to point b. At this point, it can be seenthat some magnetic flux remains in the material even though the magnetising force is zero.This is referred to as the point of retentivity on the graph and indicates the remanence orlevel of residual magnetism in the material. (Some of the magnetic domains remain alignedbut some have lost there alignment.)

The loop is generated by measuring themagnetic flux B of a ferromagnetic materialwhile the magnetising force H is changed. Aferromagnetic material that has neverbeen previously magnetised or has beenthoroughly demagnetised will follow thedashed line as H is increased. As the line

demonstrates, the greater the amount ofcurrent applied (H+), the stronger themagnetic field in the component (B+).

At point a almost all of the magnetic domains are aligned and an additional increase inthe magnetising force will produce very little increase in magnetic flux. The material hasreached the point of magnetic saturation. When H is reduced


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As the magnetising force is reversed, the curve moves to point c,where the flux has been reduced to zero. This is called the point ofcoercivity on the curve. (The reversed magnetising force has flippedenough of the domains so that the net flux within the material is

zero.) The force required to remove the residual magnetism from thematerial, is called the coercive force or coercivity of the material.

Eddy Current LossesWhen a changing magnetic field cuts through a sample of metal ormagnetic materials that is not connected to a circuit, by Faradayslaw, a circulating current is induced. This current is known as eddycurrent, it is localised within that material and has a flow patternas shown in fig. Below


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This circulating current creates a magnetic field that opposes theexternal magnetic field. The direction of the eddy current is describedby Lenzs law. The stronger of the external magnetic field or thegreater of the electrical conductivity of the material, the eddy currentthat is developed will be stronger and also yields stronger opposingforce. Eddy current creates losses through Joule heating, and itreduces the efficiency of device that operates under alternatingmagnetic field condition such as iron core of transformers andalternating current motors.

This power loss is known as eddy current loss due to the inducededdy current in the metal or magnetic materials. In order to reducethe eddy current loss, the resistivity of the material is increased byadding silicon in the metal or ferromagnetic materials. Anothereffective way to achieve low eddy current loss is by using laminationof electrical metal sheets. These metal sheets are coated withinsulator which breaks the eddy currents path.

The power due to the eddy current loss is given asP e = k d 2 f 2 B p 2 , unit: W/m3


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Diodes and transistors are non -linear device: V IR!

Rectifier Circuit

+9V

-5V

ORing Circuit

+6.3v

R11k

D3

D2

D1

0.000ms 0.500ms 1.000ms 1.500ms 2.00

100.0 V

80.00 V

60.00 V

40.00 V

20.00 V

0.000 V

-20.00 V

Rectifier Circuit

A

1kHz

D4

D3

D2

D1

R1


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R4

10K

+10V

100K

R3

10V

R21K

hfe = 100Q1 2N2222


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Single-phase Half-wave rectifiersIn half wave rectification of a single-phase supply, either the positiveor negative half of the AC wave is passed, while the other half isblocked. Because only one half of the input waveform reaches theoutput, mean voltage is lower. Half-wave rectification requires asingle diode in a single-phase supply , or three in a three-phasesupply . Rectifiers yield a unidirectional but pulsating direct current;half-wave rectifiers produce far more ripple than full-wave rectifiers,and much more filtering is needed to eliminate harmonics of the ACfrequency from the output.

Half-wave rectifierThe no-load output DC voltage of an ideal half wave rectifier for asinusoidal input voltage is:

Where: V dc , V av - the DC or average output voltage,

V peak , the peak value of the phase input voltages,V rms , the root-mean-square value of output voltage.

Electric Shock, Isolation & Protection
http://en.wikipedia.org/wiki/Single-phase_electric_powerhttp://en.wikipedia.org/wiki/Three-phase_electric_powerhttp://en.wikipedia.org/wiki/Three-phase_electric_powerhttp://en.wikipedia.org/wiki/File:Halfwave.rectifier.en.svghttp://en.wikipedia.org/wiki/File:Halfwave.rectifier.en.svghttp://en.wikipedia.org/wiki/File:Halfwave.rectifier.en.svghttp://en.wikipedia.org/wiki/File:Halfwave.rectifier.en.svghttp://en.wikipedia.org/wiki/File:Halfwave.rectifier.en.svghttp://en.wikipedia.org/wiki/File:Halfwave.rectifier.en.svghttp://en.wikipedia.org/wiki/File:Halfwave.rectifier.en.svghttp://en.wikipedia.org/wiki/File:Halfwave.rectifier.en.svghttp://en.wikipedia.org/wiki/File:Halfwave.rectifier.en.svghttp://en.wikipedia.org/wiki/File:Halfwave.rectifier.en.svghttp://en.wikipedia.org/wiki/File:Halfwave.rectifier.en.svghttp://en.wikipedia.org/wiki/File:Halfwave.rectifier.en.svghttp://en.wikipedia.org/wiki/File:Halfwave.rectifier.en.svghttp://en.wikipedia.org/wiki/File:Halfwave.rectifier.en.svghttp://en.wikipedia.org/wiki/File:Halfwave.rectifier.en.svghttp://en.wikipedia.org/wiki/Three-phase_electric_powerhttp://en.wikipedia.org/wiki/Three-phase_electric_powerhttp://en.wikipedia.org/wiki/Three-phase_electric_powerhttp://en.wikipedia.org/wiki/Three-phase_electric_powerhttp://en.wikipedia.org/wiki/Single-phase_electric_powerhttp://en.wikipedia.org/wiki/Single-phase_electric_powerhttp://en.wikipedia.org/wiki/Single-phase_electric_powerhttp://en.wikipedia.org/wiki/File:Halfwave.rectifier.en.svg


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p

dc p

rmsV

V V

V &2

Full-wave rectificationA full-wave rectifier converts the whole of the input waveform to one of constantpolarity (positive or negative) at its output. Full-wave rectification converts bothpolarities of the input waveform to pulsating DC (direct current), and yields a higheraverage output voltage. Two diodes and a center tapped transformer , or four diodes ina bridge configuration and any AC source (including a transformer without center tap),

are needed. Single semiconductor diodes, double diodes with common cathode orcommon anode, and four-diode bridges, are manufactured as single components.

For single-phase AC, if the transformer is center-tapped, then two diodes back-to-back(cathode-to-cathode or anode-to-anode, depending upon output polarity required)

can form a full-wave rectifier. Twice as many turns are required on the transformersecondary to obtain the same output voltage than for a bridge rectifier, but the powerrating is unchanged.
http://en.wikipedia.org/wiki/Center_taphttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Diode_bridgehttp://en.wikipedia.org/wiki/File:Fullwave.rectifier.en.svghttp://en.wikipedia.org/wiki/File:Gratz.rectifier.en.svghttp://en.wikipedia.org/wiki/Diode_bridgehttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Center_tap


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0.000ms 5.000ms 10.00ms 15.00ms 20.00ms 25.00ms 30.00ms 35.00m

100.0 A

50.00 A

0.000 A

-50.00 A

-100.0 A

A: d1_kB: v1#branch

Rectifier Circuit

C

B

A +

C12200uF

50 Hz

D4

D3

D2

D1

R1

Full-wave rectifier using a center tap transformer and 2 diodes.

THD = 43.5%
http://en.wikipedia.org/wiki/Center_taphttp://en.wikipedia.org/wiki/File:Fullwave.rectifier.en.svghttp://en.wikipedia.org/wiki/Center_taphttp://en.wikipedia.org/wiki/File:Gratz.rectifier.en.svg


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Unity Power Factor Rectifiers


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Fairchild PPT on EMI, EMC Compliance

EFFECT OF HARMONICS on ELECTRICAL &MAGNETIC INTERFERENCE

Induction Cooker Theory

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