induction heating based on IGBT-No Mosfet
you will learn how a new invention, IGBT-based induction heating, works and how it differs from other types of heating. Unlike other heaters, this one operates using only IGBT technology, without the use of MOSFETs, diodes, resistors or coils. The result is greater energy efficiency and a more sustainable heating solution. By watching this video you will learn the details of this innovative technology and get a glimpse into the future of heating technology.
Induction heating is a non-contact heating process. It uses high frequency electricity to heat materials that are electrically conductive. Since it is non-contact, the heating process does not contaminate the material to be heated. It is also very efficient because the heat is actually generated inside the room. This can be contrasted with other methods where heat is generated in a heating flame or heating element, which is then applied to the workpiece. For these reasons Induction heating lends itself to some unique applications in industry.
A high frequency power source is used to drive a large alternating current through a coil. This coil is known as the working coil. See the photo opposite.
The passage of a current through this coil generates a very intense and rapidly changing magnetic field in space within the work coil. The part to be heated is placed in this intense magnetic field.
Depending on the nature of the part material, a number of things happen...
The alternating magnetic field induces a current in the conductive part. The arrangement of the work winding and the part can be considered as an electrical transformer. The work coil looks like the primary where electrical power is fed into, and the part looks like a single secondary turn that is shorted. This causes huge currents to flow through the room. They are called eddy currents.
Also, the high frequency used in induction heating applications gives rise to a phenomenon called the skin effect. This skin effect causes the alternating current to flow in a thin layer over the surface of the part. The skin effect increases the effective resistance of the metal for the passage of the large current. Therefore, it greatly increases the thermal effect caused by the induced current in the workpiece
(Although heating due to eddy currents is desirable in this application, it is worth noting that transformer manufacturers go to great lengths to avoid this phenomenon in transformers. Laminated transformer cores, powdered iron cores and ferrites are used to prevent eddy currents from flowing inside transformer cores.Inside a transformer the passage of eddy currents is highly undesirable as it causes heating of the magnetic core and represents the power that is lost.)
What about ferrous metals?
For ferrous metals like iron and some types of steel, there is an additional heating mechanism that takes place along with the eddy currents mentioned above. The intense alternating magnetic field inside the work coil magnetizes and de-magnetizes the iron crystals repeatedly. This rapid reversal of the magnetic domains causes considerable friction and heating inside the material. Heating due to this mechanism is known as hysteresis loss and is most significant for materials that have a large surface area inside their B-H curve. This can be a big contributing factor to the heat produced during induction heating, but only occurs inside ferrous materials. This is why ferrous materials lend themselves more easily to induction heating than non-ferrous materials.
Interestingly, steel loses its magnetic properties when heated above approximately 700°C. This temperature is called the Curie temperature. This means that there is no heating of the material due to hysteresis losses above 700°C. Any overheating of the material must be due to induced eddy currents alone. This makes heating steel above 700°C more of a challenge for induction heating systems. The fact that Copper and Aluminum are non-magnetic and very good electrical conductors, can also make these materials a challenge to heat efficiently. (We will see that the best course of action for these materials is to increase the frequency to exaggerate the peeffects due to the skin effect).
What is Induction Heating used for?
Induction heating can be used for any application where we want a heat conducting material in a clean, efficient and controlled way.
One of the most common applications is for sealing jammed tamper seals at the top of beverage and medicine bottles. A lid covered with "hot-melt glue" is inserted into the plastic cap and screwed onto the top of each bottle during manufacture. These seals are then heated rapidly as the bottles pass under induction heating on the single sheet production line. The heat melts the glue and seals the foil to the top of the bottle. When the cap is removed, the foil remains providing a tight seal and preventing any tampering or contamination of the bottle's contents until the customer pierces the foil.
p style = "text-dash: 0px;"> Another common application is the "Get accessor shot" to remove contamination from evacuated tubes, such as TV CRTs, vacuum tubes, and various gas discharge lamps . A ring of conductive material called a "getter" is placed inside the evacuated glass container. Since induction heating is a non-contact process it can be used to heat getter which is already sealed inside a vessel. A work inductor is located near the Get accessor on the outside of the pipe and the source is turned on. Within seconds of starting the induction heater, the getter is heated to white heat and the chemicals in its coating react with any gas in a vacuum. As a result, the Get accessor absorbs any last remaining traces of the gas inside the vacuum tube and increases the purity of the vacuum.
Yet another common application for induction heating is a process called Zone Purification used in the semiconductor manufacturing industry. It is a process in which the silicon is purified by means of a moving zone of molten material. An internet search is sure to bring up more details about this process which I know little about.
Other applications include melting, welding and brazing or metals. Induction cooking and rice cookers. Hardening of metal ammunition, gear teeth, saw blades and drive shafts, etc. are also common applications because the induction process heats the metal surface very quickly. Therefore, it can be used for surface hardening and hardening of localized areas of metal parts by "policing" the thermal conduction of heat deeper into the part or surrounding area. The non-contact nature of induction heating also means that it can be used to heat materials in analytical applications without the risk of sample contamination. Similiarly, metal medical instruments can be sterilized by heating them to a high temperature, while they are still sealed inside a known sterile environment, in order to kill germs.
What is needed for Induction Heating?
In theory only 3 things are essential to implement induction heating:
A high frequency electrical power source,
A work coil to generate the alternating magnetic field,
A conductive part to be heated,
That said, practical induction heating systems are usually a bit more complex. For example, an impedance matching network is often required between the high frequency source and the work coil to ensure proper power transfer. Water cooling systems are also common in high power induction heaters to remove waste heat from the work coil, its corresponding network and power electronics. Finally control electronics are generally used to control the intensity of the heating action and the time of the heating cycle to ensure consistent results. The control electronics also protect the system from being damaged by a number of adverse operating conditions. However, the operating principle of induction heating remains identical to that described above.
Practical implementation
In practice the work coil is usually incorporated into a tank resonant circuit. This has a number of advantages. First, it makes the current or the voltage waveform become sinusoidal. This minimizes inverter losses by allowing it to benefit from voltage-zero switching or zero-current-switching depending on the arrangement.
exact investment chosen. Also, the sine waveform at the working winding represents a cleaner signal and causes less Radio Frequency interference to nearby equipment. This point later becomes very important in strong powerful systems. We will see that there are a number of resonance regimes that the designer of an induction heater can choose from for the work coils:
Series Reservoir Resonant Circuit
The work coil made to resonate at the intended operating frequency by means of a capacitor placed in series with it. This causes the current in the work coil to be sinusoidal. The series resonance also increases the voltage on the work coil, significantly higher than the output voltage of the inverter alone. The inverter sees a sinusoidal load current, but it has to carry the full current flowing through the work coil. For this reason the work coil often consists of many turns of wire with only a few amps or tens of amps flowing. Significant heating power is obtained by raising the resonant voltage on the work coil in the series resonant arrangement while keeping the current in the coil (and inverter) at a reasonable level.
This arrangement is commonly used in things like rice cookers where the power level is low, and the inverter is located next to the object to be heated. The main disadvantages of the series resonance arrangement are that the inverter must carry the same current that flows through the work coil. Additionally, the voltage rise due to series resonance can become very pronounced if there is not a distinctly large piece present in the coil from the work of circuit moisture. This is not a problem in applications like rice cookers where the part is always the same vessel, and its properties are well known at the time of system design.
The reservoir capacitor is usually rated for high voltage because of the resonant voltage rise experienced in the tuned series resonant circuit. It must also carry the current full CA rried coil through the job, although this is generally not a problem in low power applications.
Parallel resonant resonant circuit
The working coil made to resonate at the intended operating frequency by means of a capacitor placed in parallel with it. This causes the current in the work coil to be sinusoidal. The parallel resonance also amplifies the current through the work coil, much higher than the output current capability of the inverter alone. The inverter sees a sinusoidal load current. However, in this case it only needs the part of the actual load current that actually works. The inverter does not have to carry full current into the coil of the circulating work. This is very important, since power factors in induction heating applications are generally low. This property of the parallel resonant circuit can make a tenfold reduction in the current which must be sustained by the inverter and the wires to be connected to the work coil. Conduction losses are generally proportional to current squared, so a tenfold reduction in load current represents a significant saving in conduction losses in the inverter and associated wiring. This means that the work coil can be placed in a location away from the inverter without incurring massive losses in the power leads.
Coils working using this technique often consist of only a few turns of thick copper wire, but flowing with large currents of hundreds or thousands of amps. (This is necessary to get the required intensity turns to do induction heating). Water cooling is common for all but the smallest of systems. This is necessary to remove the excess heat generated by the passage of the large high frequency current through the work coil and its associated reservoir capacitor.
In parallel resonant tank circuit the work coil can be thought of as an inductive load with "power factor correction" capacitor connected across it. The PFC capacitor provides reactive current equal and opposite to the large inductive current drawn by the work coil. The key thing to remember is that this large current is localized to the work winding and its capacitor and simply represents the reactive power swaying back and forth between the two. The only real current flow of the inverter is therefore the relatively small amount to overcome the losses in the capacitor "
Impedance matching
Or simply “Matching”. This is the electronics that sits between the high frequency power source and the work coil that we use for heating. In order to heat a piece of metal by induction heating, we need to cause a huge current to flow across the surface of the metal. However, this can be compared with the inverter which generates the high frequency power. The inverter generally works better (and the design is a bit easier) if it runs on relatively high voltage but low current. (Typically problems are encountered in power electronics when we try to switch large currents on and off in very short times.) Increasing the voltage and decreasing the current allow common switch mode MOSFETs (or fast IGBTs) to be used. The relatively low currents make the inverter less susceptible to layout issues and parasitic inductance. This is the work of the corresponding grid and the work coil transforming itself from the high-voltage/low-current of the inverter to the low-voltage/high-current needed to heat the workpiece efficiently.
induction heating based on IGBT-No Mosfet
you will learn how a new invention, IGBT-based induction heating, works and how it differs from other types of heating. Unlike other heaters, this one operates using only IGBT technology, without the use of MOSFETs, diodes, resistors or coils. The result is greater energy efficiency and a more sustainable heating solution. By watching this video you will learn the details of this innovative technology and get a glimpse into the future of heating technology.
Induction heating is a non-contact heating process. It uses high frequency electricity to heat materials that are electrically conductive. Since it is non-contact, the heating process does not contaminate the material to be heated. It is also very efficient because the heat is actually generated inside the room. This can be contrasted with other methods where heat is generated in a heating flame or heating element, which is then applied to the workpiece. For these reasons Induction heating lends itself to some unique applications in industry.
A high frequency power source is used to drive a large alternating current through a coil. This coil is known as the working coil. See the photo opposite.
The passage of a current through this coil generates a very intense and rapidly changing magnetic field in space within the work coil. The part to be heated is placed in this intense magnetic field.
Depending on the nature of the part material, a number of things happen...
The alternating magnetic field induces a current in the conductive part. The arrangement of the work winding and the part can be considered as an electrical transformer. The work coil looks like the primary where electrical power is fed into, and the part looks like a single secondary turn that is shorted. This causes huge currents to flow through the room. They are called eddy currents.
Also, the high frequency used in induction heating applications gives rise to a phenomenon called the skin effect. This skin effect causes the alternating current to flow in a thin layer over the surface of the part. The skin effect increases the effective resistance of the metal for the passage of the large current. Therefore, it greatly increases the thermal effect caused by the induced current in the workpiece
(Although heating due to eddy currents is desirable in this application, it is worth noting that transformer manufacturers go to great lengths to avoid this phenomenon in transformers. Laminated transformer cores, powdered iron cores and ferrites are used to prevent eddy currents from flowing inside transformer cores.Inside a transformer the passage of eddy currents is highly undesirable as it causes heating of the magnetic core and represents the power that is lost.)
What about ferrous metals?
For ferrous metals like iron and some types of steel, there is an additional heating mechanism that takes place along with the eddy currents mentioned above. The intense alternating magnetic field inside the work coil magnetizes and de-magnetizes the iron crystals repeatedly. This rapid reversal of the magnetic domains causes considerable friction and heating inside the material. Heating due to this mechanism is known as hysteresis loss and is most significant for materials that have a large surface area inside their B-H curve. This can be a big contributing factor to the heat produced during induction heating, but only occurs inside ferrous materials. This is why ferrous materials lend themselves more easily to induction heating than non-ferrous materials.
Interestingly, steel loses its magnetic properties when heated above approximately 700°C. This temperature is called the Curie temperature. This means that there is no heating of the material due to hysteresis losses above 700°C. Any overheating of the material must be due to induced eddy currents alone. This makes heating steel above 700°C more of a challenge for induction heating systems. The fact that Copper and Aluminum are non-magnetic and very good electrical conductors, can also make these materials a challenge to heat efficiently. (We will see that the best course of action for these materials is to increase the frequency to exaggerate the peeffects due to the skin effect).
What is Induction Heating used for?
Induction heating can be used for any application where we want a heat conducting material in a clean, efficient and controlled way.
One of the most common applications is for sealing jammed tamper seals at the top of beverage and medicine bottles. A lid covered with "hot-melt glue" is inserted into the plastic cap and screwed onto the top of each bottle during manufacture. These seals are then heated rapidly as the bottles pass under induction heating on the single sheet production line. The heat melts the glue and seals the foil to the top of the bottle. When the cap is removed, the foil remains providing a tight seal and preventing any tampering or contamination of the bottle's contents until the customer pierces the foil.
p style = "text-dash: 0px;"> Another common application is the "Get accessor shot" to remove contamination from evacuated tubes, such as TV CRTs, vacuum tubes, and various gas discharge lamps . A ring of conductive material called a "getter" is placed inside the evacuated glass container. Since induction heating is a non-contact process it can be used to heat getter which is already sealed inside a vessel. A work inductor is located near the Get accessor on the outside of the pipe and the source is turned on. Within seconds of starting the induction heater, the getter is heated to white heat and the chemicals in its coating react with any gas in a vacuum. As a result, the Get accessor absorbs any last remaining traces of the gas inside the vacuum tube and increases the purity of the vacuum.
Yet another common application for induction heating is a process called Zone Purification used in the semiconductor manufacturing industry. It is a process in which the silicon is purified by means of a moving zone of molten material. An internet search is sure to bring up more details about this process which I know little about.
Other applications include melting, welding and brazing or metals. Induction cooking and rice cookers. Hardening of metal ammunition, gear teeth, saw blades and drive shafts, etc. are also common applications because the induction process heats the metal surface very quickly. Therefore, it can be used for surface hardening and hardening of localized areas of metal parts by "policing" the thermal conduction of heat deeper into the part or surrounding area. The non-contact nature of induction heating also means that it can be used to heat materials in analytical applications without the risk of sample contamination. Similiarly, metal medical instruments can be sterilized by heating them to a high temperature, while they are still sealed inside a known sterile environment, in order to kill germs.
What is needed for Induction Heating?
In theory only 3 things are essential to implement induction heating:
A high frequency electrical power source,
A work coil to generate the alternating magnetic field,
A conductive part to be heated,
That said, practical induction heating systems are usually a bit more complex. For example, an impedance matching network is often required between the high frequency source and the work coil to ensure proper power transfer. Water cooling systems are also common in high power induction heaters to remove waste heat from the work coil, its corresponding network and power electronics. Finally control electronics are generally used to control the intensity of the heating action and the time of the heating cycle to ensure consistent results. The control electronics also protect the system from being damaged by a number of adverse operating conditions. However, the operating principle of induction heating remains identical to that described above.
Practical implementation
In practice the work coil is usually incorporated into a tank resonant circuit. This has a number of advantages. First, it makes the current or the voltage waveform become sinusoidal. This minimizes inverter losses by allowing it to benefit from voltage-zero switching or zero-current-switching depending on the arrangement.
exact investment chosen. Also, the sine waveform at the working winding represents a cleaner signal and causes less Radio Frequency interference to nearby equipment. This point later becomes very important in strong powerful systems. We will see that there are a number of resonance regimes that the designer of an induction heater can choose from for the work coils:
Series Reservoir Resonant Circuit
The work coil made to resonate at the intended operating frequency by means of a capacitor placed in series with it. This causes the current in the work coil to be sinusoidal. The series resonance also increases the voltage on the work coil, significantly higher than the output voltage of the inverter alone. The inverter sees a sinusoidal load current, but it has to carry the full current flowing through the work coil. For this reason the work coil often consists of many turns of wire with only a few amps or tens of amps flowing. Significant heating power is obtained by raising the resonant voltage on the work coil in the series resonant arrangement while keeping the current in the coil (and inverter) at a reasonable level.
This arrangement is commonly used in things like rice cookers where the power level is low, and the inverter is located next to the object to be heated. The main disadvantages of the series resonance arrangement are that the inverter must carry the same current that flows through the work coil. Additionally, the voltage rise due to series resonance can become very pronounced if there is not a distinctly large piece present in the coil from the work of circuit moisture. This is not a problem in applications like rice cookers where the part is always the same vessel, and its properties are well known at the time of system design.
The reservoir capacitor is usually rated for high voltage because of the resonant voltage rise experienced in the tuned series resonant circuit. It must also carry the current full CA rried coil through the job, although this is generally not a problem in low power applications.
Parallel resonant resonant circuit
The working coil made to resonate at the intended operating frequency by means of a capacitor placed in parallel with it. This causes the current in the work coil to be sinusoidal. The parallel resonance also amplifies the current through the work coil, much higher than the output current capability of the inverter alone. The inverter sees a sinusoidal load current. However, in this case it only needs the part of the actual load current that actually works. The inverter does not have to carry full current into the coil of the circulating work. This is very important, since power factors in induction heating applications are generally low. This property of the parallel resonant circuit can make a tenfold reduction in the current which must be sustained by the inverter and the wires to be connected to the work coil. Conduction losses are generally proportional to current squared, so a tenfold reduction in load current represents a significant saving in conduction losses in the inverter and associated wiring. This means that the work coil can be placed in a location away from the inverter without incurring massive losses in the power leads.
Coils working using this technique often consist of only a few turns of thick copper wire, but flowing with large currents of hundreds or thousands of amps. (This is necessary to get the required intensity turns to do induction heating). Water cooling is common for all but the smallest of systems. This is necessary to remove the excess heat generated by the passage of the large high frequency current through the work coil and its associated reservoir capacitor.
In parallel resonant tank circuit the work coil can be thought of as an inductive load with "power factor correction" capacitor connected across it. The PFC capacitor provides reactive current equal and opposite to the large inductive current drawn by the work coil. The key thing to remember is that this large current is localized to the work winding and its capacitor and simply represents the reactive power swaying back and forth between the two. The only real current flow of the inverter is therefore the relatively small amount to overcome the losses in the capacitor "
Impedance matching
Or simply “Matching”. This is the electronics that sits between the high frequency power source and the work coil that we use for heating. In order to heat a piece of metal by induction heating, we need to cause a huge current to flow across the surface of the metal. However, this can be compared with the inverter which generates the high frequency power. The inverter generally works better (and the design is a bit easier) if it runs on relatively high voltage but low current. (Typically problems are encountered in power electronics when we try to switch large currents on and off in very short times.) Increasing the voltage and decreasing the current allow common switch mode MOSFETs (or fast IGBTs) to be used. The relatively low currents make the inverter less susceptible to layout issues and parasitic inductance. This is the work of the corresponding grid and the work coil transforming itself from the high-voltage/low-current of the inverter to the low-voltage/high-current needed to heat the workpiece efficiently.
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