induction cooking theory & operation_ part iii

8/12/2019 Induction Cooking Theory & Operation_ Part III

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Induction Cooking Theory and Operation Part III


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Resonant Circuits

.IC

CMD1

0V+ V1

100V

L1

1mH

C1

1uF

R1

20A

0.000ms 0.200ms 0.400ms 0.600ms 0.800ms 1.000ms

200.0 V

175.0 V

150.0 V

125.0 V

100.0 V

75.00 V

50.00 V

25.00 V

0.000 V

D1

DIODE

S1

C1

1uF

L1

1mH

+ V1

100V

.IC

CMD1

0V

R1

20


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Inverter Circuits

Single Switch
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Two Switch Inverter

Four Switch Inverter
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Compared efficiencies

The efficiency is the ratio that exists between

consumed energy (gas or electricity) and

energy converted into heat. Large differencesexist between induction, range-top appliance,

and other cooking modes. These efficiencies

may vary depending on the diameter and

quality of the container used.

Exceptional high speedThanks to the available power and

high efficiency, this hob is much

more rapid than an electrical or gas

hob. Time necessary to increase

the temperature of two litres of

water from 20C to 95C:

Savings : Removing the container from a source is sufficient to stop the cooking

immediately, there is no energy waste. As long as there is no container on a source,

the source does not heat, the power indicator lights are flashing. This hob consumes

thus much less energy than hobs fitted with traditional gas or electricity hobs.


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Information

Very flexible to use, it reacts instantaneously to controls. The power available on

a source can vary from 50 to 2800 W (and more in certain cases!)

Safety

The induction principle makes thatheat is produced directly in the

container. The temperature of the

glass top is much lower and risk of

burn is reduced, especially for

children. Return to 60C after

boiling of one litre of water:

THE SAUCEPANS

- Compatible containers

Induction requires appropriate saucepans. As cooking is performed by magnetic

field, conductive materials are necessary. A simple means is

used to check whether an implement is compatible or not: A magnet shouldstick to the bottom.

During cooking, some pans can emit some noise (jangling). This is normal and

due to the magnetic field. There is no risk, neither for the hob, nor for the pan.

The containers compatible with the induction are:


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Containers in enamelled steel with or without non-stick coating.

-Advantages:

Compatibility guaranteed with induction (good efficiency) Low noise. Wide range of cooking possible.- Disadvantages:

Worse heat distribution pan diameters < 230mm. Cleaning is more difficult. Bad reaction if the pan is empty bottom distortion, possible breaking ofthe enamel

Cast-iron containers with or without enamelled bottom.

- Advantages :

Compatibility guaranteed with induction (good efficiency) Good heat distribution (with low cooking power). Reduced noise of the pan.

Easy cleaning Good to cook lovingly- Disadvantages :

The non enamelled bottom may scratch the glass. Bad reaction if the pan is empty Cast iron doesnt move but can break. Please note: Do a preheating systematically before a full power cooking


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Certain containers in stainless steel: multilayer stainless steel, ferritic

stainless steel. Most

stainless steel containers are suitable if they pass the magnet test. (Saucepans,

stew pots, frying pans, deep fryers...).

- Advantages : Very good heat distribution (For the pan with a stuck bottom). Good reaction if the pan is empty --> Stainless steel becomes blue Easy to clean. Wide range of cooking.-Disadvantage :

Bad heat distribution (For the pan without a stuck bottom). Compatibility is not always guaranteed: Some stainless steels give badresults.

When the hob recognizes a poor reaction of the pan, the power isautomatically reduced.

Advice: Use an enamelled pan to do some tests

The pan is noisier.

Aluminium containers with special bottoms.

Aluminium containers are used more and more. Unfortunately, the qualityand the thickness of the stainless steel are not always good. Containers with a

thick flat base for uniform cooking have to be decided upon (heat is better

distributed).


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Glass, earthenware, ceramic, copper and aluminium containers without

special bottoms are not compatible.

INSTALLATION

Flush mounting

A minimum dimension shall be measured from the wall and sidewalls (back and/or

sides).

Protection of cuts: Chipboards used for making working planes inflate relativelyrapidly in contact with humidity.

Apply to the cut edge a varnish or special glue to protect it from steam or

condensation waters that can rise under the working plane.

A seal ensures water tightness with the working plane. It must be glued under the

hob periphery. Clips supplied together with the hob are used to fix the hob.

Ventilation

Many after-sales department problems are related to bad ventilation. The induction hob is

fitted with a cooling fan that sucks the air through the rear and discharges it to the front. It is

necessary, during the installation, to scrupulously observe the recommendations provided by

the user manual. Depending on the kitchen layout, the hob will be installed: Over a furniture with door or with drawer Over an oven of same brand Over an oven of other brand Over a dishwasherIt should not be fitted over a washing machine, refrigerator or a freezer.


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22

11

12

2

21

12

21

22

22

11

11

2

22

1

11

2

1

1

w

l

w

l

a

l

a

l

R

R

Aluminium has of 2.8 .cm and r of 1Stainless steel 410 has of 62.2 .cm r of 1000

1492

1

R

R

Aluminium has of 2.8 .cm and r of 1

Electrical steel has of 47.2 .cm r of 4000260

2

1

R

R

= resistivity; = permeability of the object;and

= frequency of the currentflowing through object.

2

At a 20KHz frequency, and for a steel saucepan (magnetic ferriticmaterial), the thickness of the saucepan in which the induced currentsflow is approximately 35 m. This allows generating a current in only apart of the saucepan bottom. The resistance becomes significant and theheating consequent therein.

For a non-ferritic material, such as aluminium, the thickness is appr.. 590 m,

SKIN EFFECT


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Magnetic susceptibility and permeability data for selected materials

MediumSusceptibility m(volumetric SI)

Permeability [H/m] Relative permeability /0Magnetic field Frequency max.

Metglas 1.26 1000000[7] at 0.5 T 100 kHz

Iron(99.95% pure Feannealed in H)

0.25 200000[8]

Nanoperm 0.1 80000[9] at 0.5 T 10 kHz

Mu-metal 2.5102 20000[10] at 0.002 TMu-metal 6.3102 50000[11]Cobalt-Iron (high

permeability stripmaterial)

2.3102 18000[12]

Permalloy 8000 1.0102 8000[10] at 0.002 TIron(99.8% pure) 6.3103 5000[8]Electrical steel 5.0103 4000[10] at 0.002 TFerritic stainless steel(annealed)

1.26103- 2.26103 10001800[13]

Martensitic stainless steel(annealed)

9.42104- 1.19103 750950[13]

Ferrite (manganese zinc) >8.0104 640 (or more) 100 kHz ~ 1 MHz

Ferrite(nickel zinc) 2.01058.0104 16640 100 kHz ~ 1 MHz[citationneeded]Carbon Steel 1.26104 100[10] at 0.002 T

Nickel 1.26104- 7.54104 100[10]600 at 0.002 T

Martensitic stainless steel(hardened)

5.0105- 1.2104 4095[13]

Austenitic stainless steel 1.260106- 8.8106 1.0037 [13][14][note 1]

Neodymium magnet 1.32106 1.05[15]

Platinum 1.256970106

1.000265Aluminum 2.22105[16] 1.256665106 1.000022Wood 1.25663760106 1.00000043[16]Air 1.25663753106 1.00000037 [17]Concrete(dry) 1[18]

Vacuum 0 4 107(0) 1, exactly[19]Hydrogen 2.2109[16] 1.2566371106 1.0000000Teflon 1.2567106[10] 1.0000Sapphire 2.1107 1.2566368106 0.99999976

Copper6.4106or 9.2106[16]

1.256629106 0.999994

Water 8.0106 1.256627106 0.999992

Bismuth 1.66104

1.25643106

0.999834Superconductors 1 0 0
http://en.wikipedia.org/wiki/Metglashttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Mu-metalhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Mu-metalhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permalloyhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Electrical_steelhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Ferrite_(magnet)http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Steelhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Nickelhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Neodymium_magnethttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Platinumhttp://en.wikipedia.org/wiki/Aluminumhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Woodhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Airhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Concretehttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Teflonhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Sapphirehttp://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Bismuthhttp://en.wikipedia.org/wiki/Superconductorhttp://en.wikipedia.org/wiki/Superconductorhttp://en.wikipedia.org/wiki/Bismuthhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Sapphirehttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Teflonhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Concretehttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Airhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Woodhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Aluminumhttp://en.wikipedia.org/wiki/Platinumhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Neodymium_magnethttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Nickelhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Steelhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Ferrite_(magnet)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Electrical_steelhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permalloyhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Mu-metalhttp://en.wikipedia.org/wiki/Mu-metalhttp://en.wikipedia.org/wiki/Mu-metalhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Mu-metalhttp://en.wikipedia.org/wiki/Mu-metalhttp://en.wikipedia.org/wiki/Mu-metalhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Metglas


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THE OPERATING PRINCIPLE

Analogy with the transformer

An induction hob operates due to the electromagnetic properties of most containers used on

traditional hobs.

one can compare this hob with a transformer of which the secondary winding would have been

shorted. A significant internal current arises therein and causes quick heating.

TRANSFORMER INDUCTION HOB

Magnetic conductor 1 Saucepan

Secondary winding shorted 2 Saucepan

Gap 3 Glass-ceramic plate

Primary winding 4 Inductor

Magnetic conductor 5 Ferrite

Magnetic field 6 Magnetic field


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Topology of Power SystemHard Switching

Generally, semiconductor switching devices operate in Hard Switch Mode in

various types of Pulse Width Modulation (PWM) DC-DC converters and DC-AC

inverter topologies employed in power systems. In this mode, a specific currentis turned on or off at a specific voltage whenever switching occurs, as shown in

Figure 3. This process results in switching loss. The higher the frequency, the

greater the switching loss, which obstructs efforts to raise the frequency.

Switching loss can be calculated as shown in Equation below. Switching also

causes an EMI problem, because a large amount of di/dt and dv/dt is

generated. =(1/2)(on+)

Waveform of a Switching Device


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The total amount of energy stored in the circuit during resonance remains unchanged.

This total amount is the same as the amount of energy stored at peak in the conductor or

capacitor.

=2=(1/)=(2/) []=(1/2)

2=22 [] (9)

=(1/2)2=(2/2)2=22 []

+=2

(2

2

)=2

=2

/(02

) []

Soft Switching :-Higher energy conversion efficiency at high-frequency switching can be

obtained by manipulating the voltage or current at the moment of switching to become

zero. This is called softswitching,which can be subcategorized into two methods: Zero-Voltage Switching (ZVS) and Zero-Current Switching (ZCS). ZVS refers to eliminating the

turn-on switching loss by having the voltage of the switching circuit set to zero right

before the circuit is turned on. ZCS avoids the turn-off switching loss by allowing nocurrent to flow through the circuit right before turning it off. The voltage or current

administered to the switching circuit can be made zero by using the resonance created

by an L-C resonant circuit. This is a ResonantConverterTopology.


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Transformer Equivalent Circuit and Maximum Power Transfer for Series Resonant

N

L

RL

Lm

L2L1

N

L

X

L3

22)( XLVI

XIXP 2)(

LKwhereXK

XVXP

.......)(22

2

P(X) is power dissipated as heat which is

Function of resistor X

Power is maximum when X = K


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R1L1 C1I1

00

1

jCjL 0is resonant frequency

At resonant frequency parallel combination Of L&C acts as

open circuit and all the current passes through Eddyresistance Giving maximum power.

RLC

Ic IL IR

+ Vc(0+) I0

Ic= IL+ IR (1)

= I

C

( ) (4

sLIL(s) LI0=VC(s).(5)

-sCVC(s) CV0=IC(s)(6)

.(2) .(3)

VC(s)/R = IR(s).(7)

Ic(s) = IL(s) + IR(s)(8) -sCVC(s) CV0= [LI0+ VC(s)]/sL + VC(s)/R(9)

CV0I0/s = [sC + 1/R +1/sL] VC(s)(10)

sRLCV0RLI0= [s2RLC + sL +R] VC(s)(12)

sV0I0/C = [s2+ s/RC +1/LC] VC(s)(11)

where 20= 1/RC

sV0I0/C = [s2+ 20s +

202+ (1- 2)0

2]VC(s)(13)

sV0I0/C = [(s + 0)2+ (1- 2)0

2] VC(s)(15)

sV0I0/C = [(s + 0)2+ 2] VC(s)(14)

where =

V0e-

0tcost I0e

-

0tsint/C = VC(t)(16)

0


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The Single Ended Parallel ResonantConverterThe single ended parallel resnant (SEPR)converter (basic schematic and operating

waveforms are shown in figure 3), consistsprimarily of a parallel inductor and capacitorresonant tank network, formed by Lr and Crin the schematic; typically a singleIGBT/Diode Co-pak device, and a smallcapacitor, shown as Cf, placed to help as an

EMI filter and to provide a path, togetherwith the Diode for the inductors resonantcurrent flow. The main power source of thisconverter is the rectified, but not filtered,line voltage to achieve near unity powerfactor at the mains voltage.

For power levels close to 2.0kW, and for a reasonable IH cooker design,voltages up to or above 1200V and currents close to 60Apkmust easilybe supported by the converter as shown in the operating waveformsfigure. A switching frequency control scheme is typically used,operating from ~20kHz to 60kHz switching frequencies in order to avoid

acoustic noise; starting at the higher frequency for soft start operationand reaching the maximum power at the lower frequency.


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Operating Theory of IH Rice Cooker

Half-Bridge Series Resonant InverterSingle Switch Quasi-Resonant Inverter


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http://openschemes.com/wp-content/uploads/2010/10/4_Coil.jpghttp://openschemes.com/wp-content/uploads/2010/10/10_PCB_Bare.jpg


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Supervisory Power Supply


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Current peak, current phase and alarm


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Optimal Switching Waveform with nearZero-Voltage and Zero-Current turn-on

Over resonant application

with capacitive load


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Overvoltage Protection

A serious problem in the single-ended topology is the case of an overvoltage that cannot

be filtered. To reduce the voltage surge a varistor is commonly used, but it does not

absorb the whole energy. To avoid a destruction of the IGBT protection features should

be integrated in the circuit. Also the voltage safety margin of the IGBT should bechooses high enough to avoid avalanche destruction. To suppress an overvoltage surge

the IGBT can be turned on actively with a series of zener diodes connected to the

collector and the gate. Other possibilities to clamp the collector-emitter voltage are

shown in Fig. below.


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induction cooking theory & operation_ part iii

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