Embed Size (px)
DESCRIPTION
Induction heating which is an efficient process of heating metals to improve their mechanical properties like ductility,tensile strength etc.,is now improved by means of connecting a frequency supply using resonant inverters. This process makes use of impedance matching inductor,dc blocking capacitor,bi-directional switches(MOSFET's) and a resonating tank circuit. THe working proncple involved here is same as that of transformer i.e., "MUTUAL INDUCTANCE".
Citation preview
INDUCTION HEATING BY HIGH FREQUENCY
RESONATING INVERTER CIRCUIT
Guide : G Mahesh
PRESENTED BY:
VAMSHI KRISHNA.NUDAY KUMAR.AADITHYA.B
INDUCTION HEATING BY HIGH FREQUENCY RESONATING INVERTER CIRCUIT
CONTENTS INTRODUCTION
WORKING PRINCIPLE
REQUIREMENTS OF INDUCTION HEATING
RESONATING CIRCUIT
POWER CONTROL METHODS
ADVANTAGES AND DISADVANTAGES
INTRODUCTION
IT IS AN ELECTRICAL PROCESS USED FOR HEATING METALS
NON-CONTACT HEATING PROCESS
IT USES HIGH FREQUENCY SUPPLY
Induction coil for Heating purpose
WORKING PRINCIPLE
IT WORKS ON THE PRINCIPLE OF MUTUAL INDUCTANCE
NEED OF HIGH FREQUENCY INVERTER
HYSTERSIS LOSSES HYSTERSIS LOSSES IS DIRECTLY PROPORTIONAL TO FREQUENCY
SHOULD BE ELECTRICALLY CONDUCTIVE MATERIAL
SKIN EFFECT
EDDY CURRENT LOSSES IS DIRECTLY PROPORTIONAL TO SQUARE OF FREQUENCY
EDDY CURRENT LOSSES
HENCE DUE TO ALL ABOVE FACTORS LARGE AMOUNT OFHEAT IS PRODUCED
REQUIREMENTS OF INDUCTION HEATING
A SOURCE OF HIGH FREQUENCY ELECTRICAL CIRCUIT
A WORK COIL TO GENERATE THE
ALTERNATING MAGNETIC FIELD AN ELECTRICAL CONDUCTIVE
MATERIAL WHICH IS TO BE HEATED
The alternating magnetic field induces a current flow in the conductive work piece.
The arrangement of the work coil and the work piece can be thought of as an electrical transformer.
The work coil is like the primary where electrical energy is fed in, and the work piece is like a single turn secondary that is short-circuited.
This causes tremendous currents to flow through the work piece. These are known as eddy currents.
Induction Burner
PROCESSES INVOLVED:
In addition to this, the high frequency used in induction heating applications gives rise to a phenomenon called skin effect.
This skin effect forces the alternating current to flow in a thin layer towards the surface of the workpiece.
The skin effect increases the effective resistance of the metal to the passage of the large current.
Therefore it greatly increases the heating effect caused by the current induced in the workpiece.
HALF BRIDGE INDUCTION HEATER USING“LCLR”
WORK COIL
PARALLEL RESONANT TANK CIRCUIT
POWER CONTROL METHODS
BY VARYING DC LINK VOLTAGE BY VARYING DUTY RATIO OF DEVICES
IN THE INVERTER BY VARYING THE OPERATING
FREQUENCY OF INVERTER BY USING IMPEDANCE MATCHING
TRANSFORMER
VARYING THE DC LINK VOLTAGE
The power processed by the inverter can be decreased by reducing the supply voltage to the inverter.
This can be done by running the inverter from a variable voltage DC supply such as a controlled rectifier using thyristors to vary the DC supply voltage derived from the mains supply.
Varying the DC link voltage allows full control of the power from 0% to 100%.
VARIATION OF DUTY RATIO OF THE INVERTER
The power processed by the inverter can be decreased by reducing the on-time of the switches in the inverter.
Power is only sourced to the work coil in the time that the devices are switched on.
The load current is then left to freewheel through the devices body diodes during the deadtime when both devices are turned off.
Varying the duty ratio of the switches also allows full control of the power from 0% to 100%.
However, a significant drawback of this method is the commutation of heavy currents between active devices and their free-wheel diodes.
For this reason duty ratio control is not usually used in high power induction heating inverters.
VARYING THE OPERATING FREQUENCY OF INVERTER
The power supplied by the inverter to the work coil can be reduced by detuning the inverter from the natural resonant frequency of the tank circuit incorporating the work coil.
As the operating frequency of the inverter is moved away from the resonant frquency of the tank circuit, there is less resonant rise in the tank circuit, and the current in the work coil diminishes.
Therefore less circulating current is induced into the workpiece and the heating effect is reduced.
IMPEDANCE MATCHING
L-C-L-R RESONANT
TANK CIRCUIT
FREQUENCY RESPONSEOF L-C-L-R CIRCUIT
ADVANTAGES AND DISADVANTAGES
ADVANTAGES :-
IT DOES NOT CONTAMINATE THE MATERIAL BEING HEATED
IT IS AN EFFECTIVE METHOD OF HEATING
HEAT CONTROL IS EASY
WE CAN CONTROL HEAT FROM 0% TO 100%
DISADVANTAGES:
NON –CONDUCTIVE MATERIALS CANNOT BE HEATED
COMPLEX CIRCUITARY
INITIAL COST IS MORE
ADAPTABILITY TO POOR
DIFFICULT TO GUARANTEE THE QUALITY OF SOME OF THE COMPLEX SHAPES OF WORK PIECE
INTERCHANGEABILITY OF INDUCTION COIL IS POOR
But obviously , the advantages outweighed the disadvantages.
Therefore, the induction heating is a better choice of metalworking for replacing coal heating, oil heating, gas heating, electric cooker, electric oven heating and other heating methods.
APPLICATIONS OF INDUCTION HEATING
INDUCTION FURNACEINDUCTION WELDINGINDUCTION SEALINGINDUCTION COOKINGINDUCTION BRAZINGPLASTIC PROCESSING
INDUCTION BRAZING & WELDING
INDUCTION COOKINGIn induction cooking an induction coil in the
cook-top heats the iron base of cookware. Copper-bottomed pans, aluminium pans and other non-ferrous pans are generally
unsuitable. The heat induced in the base is transferred to the food via (metal surface) conduction
Benefits of induction cookers include efficiency, safety (the induction cook-top is
not heated itself) and speed. Both permanently installed and portable
induction cookers are available.
INDUCTION COOKING-DOMESTIC PURPOSES
INDUCTION SEALING:
Induction heating is used in cap sealing of containers in the food and pharmaceutical industries.
A layer of aluminum foil is placed over the bottle or jar opening and heating by induction to fuse it to the container.
This provides a tamper-resistant seal, since altering the contents requires breaking the foil
INDUCTION CAP SEALING
USED IN SEALING FOOD CONTAINERS ALSO USED IN BEVERAGE INDUSTRIES TO PREVENT LEAKS AND EXTEND SHELF LIFE
PLASTIC PROCESSING:
Induction heating is used in plastic injection molding machines. Induction heating improves energy efficiency for injection and extrusion processes. Heat is directly generated in the barrel of the machine, reducing warm-up time and energy consumption. The induction coil can be placed outside thermal insulation, so it operates at low temperature and has a long life. The frequency used ranges from 30 kHz down to 5 kHz, decreasing for thicker barrels. The reduction in cost of inverter equipment has made induction heating increasingly popular.Induction heating can also be applied to molds, offering more even mold temperature and improved product quality.
QUERIES….???
