APPLICATION-INDUCTION HEATING POWER ELECTRONICS APPLICATION-INDUCTION HEATING

POWER ELECTRONICS Power electronics is the applications of solid-state electronics for the control and conversion of electric power. Power electronics combine power, electronics, and control. Power electronics are based primarily on the switching of power semiconductor devices.

APPLICATIONS OF POWER ELECTRONICS Switch mode power supplies (SMPS) Uninterruptible power supply (UPS) systems Photo-voltaic and fuel-cell power conversion systems Rectifier supplies for electrochemical processes Heating and lighting, including high frequency illumination control Induction heating DC and AC servo drives High efficiency industrial/commercial drives Electric vehicle applications Electric traction Flexible AC transmission systems (FACTS)

INDUCTION HEATING Induction heating is a process which is used to bond, harden or soften metals or other conductive materials. For many modern manufacturing processes, induction heating offers an attractive combination of speed, consistency and control. The material to be heated is known as work piece and the coil wound around it is known as work coil.

INDUCTION HEATING PRINCIPLE When a high frequency ac voltage is applied across the work coil, a magnetizing current flows through it. this will generate flux in the work piece and induce voltage into the work piece. since the work piece is closed onto itself, eddy current flows into it. the work piece will be heated up due to finite resistance offered by the work piece to the flow of the eddy current. The heat loss in the work piece is normally confined to surface of the work piece (skin-effect). Maxwell Equation Electro magnetism fundamental Laws rot H =j +∂D/∂t  rot E= -∂B/∂t ; D=εE B=μH

Induction Heating Setup

IMPORTANT FACTORS TO CONSIDER The efficiency of an induction heating system for a specific application depends on several factors: the characteristics of the part itself, the design of the induction coil, the capacity of the power supply, and the degree of temperature change required for the application. The Characteristics of the Part METAL OR PLASTIC First, induction heating works directly only with conductive materials, normally metals. Plastics and other non-conductive materials can often be heated indirectly by first heating a conductive metal susceptor which transfers heat to the non-conductive material.

MAGNETIC OR NON-MAGNETIC It is easier to heat magnetic materials. In addition to the heat induced by eddy currents, magnetic materials also produce heat through what is called the hysteresis effect. During the induction heating process, magnetics naturally offer resistance to the rapidly alternating electrical fields, and this causes enough friction to provide a secondary source of heat. This effect ceases to occur at temperatures above the "Curie" point - the temperature at which a magnetic material loses its magnetic properties. The relative resistance of magnetic materials is rated on a “permeability” scale of 100 to 500; while non-magnetics have a permeability of 1, magnetic materials can have a permeability as high as 500.

THICK OR THIN With conductive materials, about 80% of the heating effect occurs on the surface or "skin" of the part; the heating intensity diminishes as the distance from the surface increases. So small or thin parts generally heat more quickly than large thick parts, especially if the larger parts need to be heated all the way through. Research has shown a relationship between the heating depth of penetration and the frequency of the alternating current. Frequencies of 100 to 400 kHz produce relatively high-energy heat, ideal for quickly heating small parts or the surface/skin of larger parts. For deep, penetrating heat, longer heating cycles at 5 to 30 kHz has been shown to be most effective.

RESISTIVITY Steel – along with carbon, tin and tungsten – has high electrical resistivity. Because these metals strongly resist the current flow, heat builds up quickly. Low resistivity metals such as copper, brass and aluminum take longer to heat. Resistivity increases with temperature, so a very hot piece of steel will be more receptive to induction heating than a cold piece.

INDUCTION HEATING CIRCUITS VOLTAGE-SOURCE SERIES RESONANT INVERTER- Here the output current is nearly sinusoidal at the switching freq slightly below the resonance. The power is controlled by a variable switching frequency control Voltage source inverter POWER FACTOR CORREC- -TION UN- CONTROLLED RECTIFIER AC LINE Cf Inductive coil+load Filter capacitor

CURRENT SOURCE PARALLEL RESONANT INVERTER –Here the output current source parallel resonant inverter, the output current is nearly sinusoidal at the switching freq slightly above the resonance POWER FACTOR CORRECTION CURRENT SOURCE INVERTER CONTRO- -LLED RECTIFIER Ac line INDUCTIVE COIL+LOAD

APPLICATIONS OF INDUCTION HEATING INDUCTION COOKING: The circulating currents in the metal pan on the top of the induction coil directly heats the pan. ANNEALING: process is used to soften metal for improved ductility and machinability, as well as to relieve residual stress. In contrast to hardening, annealing involves a much slower heating step followed by gradual cooling of the metal

BRAZING: is the process of joining two or more pieces of metal or ceramic material with a molten filler metal such as silver, aluminum alloy or copper. Brazing requires a higher temperature than soldering but produces a very strong bond which withstands shock, vibration and temperature change. SOLDERING: is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a relatively low melting point. Soft soldering is characterized by the melting point of the filler metal, which is below 400 °C (752 °F).[1] The filler metal used in the process is called solder.

SURFACE HARDENING: is the process of hardening the surface of a metal, often a low carbon steel, by infusing elements into the material's surface, forming a thin layer of a harder alloy.

INDUCTION HEATING APPLICATIONS

ADVANTAGES OF INDUCTION HEATING Heating speed linked to the possibility of obtaining very high power density. Exact location of the heating effect thanks to the inductor design and an operating frequency perfectly adapted to the part to be heated. The possibility to heat at very high temperatures with an efficiency practically independent of the temperature. A process perfectly adapted to industrial medium-sized and mass production requirements. Easy automation of equipment. Absence of thermal inertia (rapid start-up). Repeatability of operations carried out Often extremely high heating efficiency Absence of pollution from the source of heating (cold source) Good working conditions.

DISADVANTAGES OF INDUCTION HEATING A high frequency power source is required ,which is costly and complex.thus,initial cost required is more. The running cost or cost of operation is high Due to conversion of a.c supply into high frequency supply and low frequency of induction coil, this heating process is not efficient.

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