Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B6/00—Heating by electric, magnetic or electromagnetic fields
  • H05B6/02—Induction heating
  • H05B6/10—Induction heating apparatus, other than furnaces, for specific applications
  • H05B6/12—Cooking devices
  • H05B6/129—Cooking devices induction ovens
• • A—HUMAN NECESSITIES
  • A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
  • A47J—KITCHEN EQUIPMENT; COFFEE MILLS; SPICE MILLS; APPARATUS FOR MAKING BEVERAGES
  • A47J37/00—Baking; Roasting; Grilling; Frying
  • A47J37/06—Roasters; Grills; Sandwich grills
  • A47J37/0623—Small-size cooking ovens, i.e. defining an at least partially closed cooking cavity
  • A47J37/0629—Small-size cooking ovens, i.e. defining an at least partially closed cooking cavity with electric heating elements
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B6/00—Heating by electric, magnetic or electromagnetic fields
  • H05B6/02—Induction heating
  • H05B6/06—Control, e.g. of temperature, of power
  • H05B6/062—Control, e.g. of temperature, of power for cooking plates or the like
  • H05B6/065—Control, e.g. of temperature, of power for cooking plates or the like using coordinated control of multiple induction coils

Definitions

• the present invention generally relates to a cooking oven for cooking food.
• the present invention has particular, although not exclusive application to domestic ovens.
• Fan forced ovens have somewhat improved the foregoing heat distribution problem, but still suffer from heat distribution problem, requiring frequent user’s supervision to evenly cook food.
• Figure 1 it is not uncommon for different heating levels within a cooking chamber of an oven 100 whereby the rear 102 of the oven 100 is hotter than the front 104 of the oven 100 resulting in uneven cooking of the food 104.
• the graphs in Figure 2 show the temperature of the fan forced airflow, that will eventually impact on the food surfaces, ranging from 210°C to 300°C for a 200°C oven temperature setting (Fig. 2a) and from 184°C to 264°C for the 180°C oven temperature setting (Fig. 2b).
• a conventional heated oven utilizes typical electric resistive heating elements that reach 650°C, while the cooking temperature requirements ranges from 100 to 250°C. As shown in Figure 3, food needs to be distanced from the resistive heating elements 300 to avoid burning by the 650°C temperature.
• the preferred embodiment provides for more even heating of food.
• Precision heating is a desirable functionality for many oven applications. It has the capability to control the temperature across a heated object (workpiece) and thus can achieve a uniform temperature distribution.
• Reference [1] proposed an induction heating system with physically adjustable heating coils.
• Reference [2] used bidirectional switching network to control each heating coil individually.
• Reference [3] suggested that a single inverter with varied operation frequency can selectively control the heat distribution of multiple heating coils of which resonant frequencies are with tuned distinctively.
• a zone control induction heating (ZCIH) system was invented to perform high quality precision heating using multiple coils wound around a single workpiece, operated by multiple inverters [4], The ZCIH system detects and controls all coil currents at the same time at the same frequency to overcome the mutual magnetic coupling between the coils. This approach was proven to be effective, however the cost is significant and thus it is only really suitable for high power applications.
• the preferred embodiment provides cost reduction of precision heating at lower power for a household oven.
• pure copper wire has melting point of 1085°C and it starts to loose mechanical strength or begins to soften above 150°C.
• a cooking oven including: a heating body defining a cooking chamber; and an induction coil surrounding the heating body and for exciting to heat the heating body.
• the induction coil surrounds the heating body and the heating body may be evenly heated for even cooking of food.
• the heating body may not be heated more than oven thermostatic temperature setting during cooking.
• the oven may include an insulator located between the heating body and the induction coil.
• the insulator cay be a ceramic insulator.
• the insulator may be an electrical and/or heat insulator.
• the body may be endless.
• the body preferably includes heating panels.
• the panels may be heated in the range of 50°C to 480°C.
• Each panel may include carbon steel with vitreous enamel coating.
• each panel may be layered.
• Each layered panel may include an outer ferric stainless steel layer, and an inner aluminum layer.
• the oven may further include a power supply for supplying power to the induction coil.
• the power supply may be an alternating current (AC) power supply.
• the AC power supply may provide AC power with a frequency of at least 20kHz.
• the oven may further include a thermostat for deactivating the power supply to regulate the temperature in the cooking chamber.
• the oven may further include one or more other induction coils surrounding the heating enclosure and for exciting to heat the heating body.
• the induction coils may be separately excited to heat separate zones of the body.
• the induction coils may be sequentially or sporadically excited.
• the oven may further include an electromagnetic radiation shield for shielding electromagnetic radiation.
• the shield may surround the coil to shield outwardly emanating radiation.
• the shield may be located withing the coil to shield inwardly emanating radiation.
• the shield may include aluminium.
• a power supply including: a DC to AC inverter for supplying AC power to one or more induction coils surrounding a heating body.
• the coils may form heating zones to deliver precision heating at lower power for a household oven.
• Each heating zone may include a respective temperature sensor.
• the DC to AC inverter may be configured to supply AC power at varying frequencies or at a synchronized frequency.
• the DC to AC inverter may be configured to switch between exciting respective coils.
• the DC to AC inverter may be configured to vary the time in exciting respective coils to accommodate for varying temperature in corresponding zones in the oven.
• the DC to AC inverter may be configured to excite respective coils concurrently.
• the DC to AC inverter may include one or more half bridge inverters driving respective induction coils. Alternatively, the DC to AC inverter may include a full bridge inverter.
• the power supply may further include an AC to DC converter for supplying DC power to the DC to AC inverter.
• the AC to DC converter may be supplied by mains power (e.g. 230V, 50Hz).
• an induction coil including: a conductor having a number of turns; and an insulator located between the turns.
• the coil further includes an insulator between filaments.
• the insulator may be a thermal insulator and thermally protect the conductor from a heated oven.
• the insulator is an electrical insulator.
• the insulator may include filament passing between the turns.
• the filament may be woven between the turns.
• the filament may alternately pass between the turns.
• the filament may pass between the turns in rows. Adjacent rows may be staggered.
• the filament may include silica.
• the filament may include glass.
• the coil may further include a coating for coating the insulator.
• the filaments may include Sol-Gel insulating coatings.
• the conductor may include copper wire.
• the conductor may include a Litz (i.e. multicore) wire.
• the Litz wire may be coated or saturated with moisture resistant substance.
• the insulator may include a coating for coating the conductor.
• the coating may be a ceramic coating.
• the turns may form an array.
• the induction coil may include another insulator for insulating the array.
• the other insulator may include a coating for coating the array.
• an electromagnetic radiation shield for shielding electromagnetic radiation, the shield including at least one layered panel, and preferably four in interconnected layered panels.
• one of the layers of the panel may be excited whereas another layer of the panel may not be excited by an induction coil of an oven.
• Each layered panel may include an outer heating layer, and an inner shielding layer.
• the outer heating layer may include ferric material, preferably including steel or ferric stainless steel.
• the inner shielding layer may include aluminum.
• the outer heating layer may be perforated.
• Each layered panel may include locking joints.
• Figure 1 shows uneven cooking of food in a known oven owing to poor heat distribution
• Figure 2a is a graph of temperature over time in a known fan forced oven with thermostat temperature set to 200°C;
• Figure 2b is a graph of temperature over time in a known fan forced oven with thermostat temperature set to 180°C;
• Figure 3 is a schematic front view of a known fan forced convection oven
• Figure 4 is a schematic front view of an induction oven in accordance with an embodiment of the present invention.
• Figure 5 is a close-up sectional view of the induction oven of Figure 4;
• Figure 6a is an upper perspective view of an induction coil of the induction oven of Figure 4 and 5;
• Figure 6b is an upper perspective view of a dual induction coil arrangement in accordance with another embodiment
• Figure 6c is an upper perspective view of a triple induction coil arrangement in accordance with another embodiment
• Figure 7 is a schematic of a power supply for driving the triple induction coil arrangement of Figure 6c;
• Figure 8 is a schematic showing the switching operating principle of the power supply of Figure 7;
• Figure 9 is a schematic showing a half bridge inverter of the power supply of Figure 7.
• Figure 10 a schematic showing a full bridge inverter of the power supply of Figure 7;
• the geometry of the cooking chamber 404 affects the design of the electronics operating systems, as exemplified in the table below.
• the coil 500 needs to be variable in length to accommodate the various turns around the above listed cooking chambers perimeter.
• the area sizes that need to be heated, while maintaining the system operating electrical current ranges between 2000W and 3500W at 240V, requires manufacture of a single or multi-zones induction heating oven 400 with induction coils 500, 600a, 600b, 602a, 602b, 602c specifically designed for the cooking chamber 404 as described above.
• a power supply 700 is provided for supplying power to the induction coils 602a, 602b, 602c.
• the power supply 700 includes a DC to AC inverter 702 for supplying AC power to the induction coils 602a, 602b, 602c surrounding the heating body 402.
• the adjacent coils 602a, 602b, 602c form respective heating zones to deliver precision heating at lower power for the household oven 400.
• Each coil 602a, 602b, 602c controls the temperature of its proximate heating area i.e., heating “zone.”
• the oven temperature is measured by three temperature sensors in respective zones and sent to a feedback controller of the power supply 700 to achieve a uniform temperature distribution across the oven 400. There is no need to detect coil currents, thus lowering the cost and control complexity for the power supply 700 when compared with other known systems.
• the power supply 700 further includes an AC to DC converter 704 for supplying DC power to the DC to AC inverter 702.
• the AC to DC converter 704 is supplied by residential mains power 706 (e.g. 230V, 50Hz).
• the oven thereby operates from the household electrical grid, e.g., 230V, 50Hz with the oven 400 having from 2.3kW to 3.5kW heating power capability.
• the DC to AC inverter 702 can be configured to supply AC power at varying frequencies when the coils 602a, 602b, 602c are operating alone, or at a synchronized frequency when the coils 602a, 602b, 602c are operating together.
• the DC to AC inverter 702 can be configured to switch between exciting respective coils 602a, 602b, 602c.
• the 3-coil heating oven 400 operates in intermittently sequential cycles. In a normal setting, each coil 602a, 602b, 602c operates from approx. 2.3 kW to 3.5kW for a limited time interval before switching to another coil 602a, 602b, 602c. This sequence will repeat to keep a consistent heat generation across the oven 400. Due to the sporadic operation, each coil 602a, 602b, 602c only handles a part of the full power on average.
• coils 1 , 2, 3 operate in a sequence with equal time intervals, assuming a uniform temperature distribution across the oven 400.
• the DC to AC inverter 702 can be configured to vary the time in exciting respective coils 602a, 602b, 602c to accommodate for varying temperature in corresponding zones in the oven 400.
• the DC to AC inverter 702 can be configured to excite coils 602a, 602b, 602c concurrently.
• FIG. 9 shows the detailed structure of the DC-to-AC inverter 702 where a distributed half-bridge system is used with 3 separated half-bridge inverters 900a, 900b, 900c connected to the 3 heating coils 602a, 602b, 602c.
• a single half-bridge inverter 900 can deliver 2.3kW to a single coil 602 in a sequence interval, and then turns to open/short circuit to let the other half-bridge operate.
• each halfbridge inverter 900 only delivers approximately a third of the full power (767W) in average.
• the DC to AC inverter 702 can include a distributed full bridge inverter as shown in Figure 10.
• Figure 11 shows an induction coil 500 (or 600, 602) of the oven 400.
• the coil 500 includes a looped copper conductor 1100 having a number of turns 1102.
• An electrical insulator 1104 is located between the turns 1102.
• the insulator 1104 is also a thermal insulator and thermally protects the conductor 1100 from the heated oven 400.
• the insulator 1 104 includes woven filament 1200 passing between the turns 1102.
• the filament 1200 alternately passes, over and under, between the turns 1 102.
• the filament 1200 forms rows, with adjacent rows being staggered.
• the coil 500 manufacture involves weaving sixteen turns 1 102 of uncoated copper conductor 1100 with Silica (yarn) filament 1200.
• Silica material characteristics are as per the following data:
• the E-CR-Glass which is an alumino- lime silicate composite version, has even better electric insulation characteristics.
• Figure 12 illustrates the physical separation of each turn 1102 of wire by weaving 0.1 mm silica or glass-fibre yarn filament 1200 between them.
• a ribbon can be subsequently wrapped in glass fibre braid to completely cover and encapsulate the copper wire turns 1102.
• the coil 500 may further include a ceramic glass coating 1202 for coating the insulator 1104.
• the conductor 1100 can include a Litz (i.e. multicore) wire.
• the Litz wire may be coated or saturated with moisture resistant substance. Humidity contamination of the Litz wire coil 500 can occur during the operation of the final product. The consequential risk could result in an electrical insulation failure between the Litz wire, compromising the electromagnetic flux efficiency or electrical insulation integrity and safety of the coil 500.
• a solution is to spray the litz/glass-fibre coil 500 with a thin coat of moisture resistant ceramic or saturate it with silicone such as Aremco Silicone P4010.
• the silica and or Glass Fiber woven copper filament conductor assembly as final stage, can be coated with Alumina-Glass coating 1202 as shown in Figure 12. Also, can be coated with Sol-Gel
• Figures 13 and 14 shows a glass coating ribbon, and high temperature resistant and water-proof induction Litz wire coil 1300.
• An insulator 1302 coats the conductor 1100, being greater than 0.2mm in diameter, and is located between the turns 1 102.
• the electrical insulator 1302 is a ceramic coating.
• the diameter of the copper conductor 1100 can vary and it is conditioned by the design, whether single core or multicore (Litz wire), to achieve an electromagnetic flux magnitude and power rating and energy efficiency objectives.
• the first stage is to coat the electric metal conductor 1 100 with the ceramic coating insulator 1302 as shown in Figure 13.
• the second stage is to loop and position the coated conductor 1100 as required, whereby the ceramic coating insulator 1302 will ensure correct spacing between the copper turns 1102.
• the turns 1102 form a grid array.
• the third stage is to coat and encase the electrical ceramic insulated conductors 1100, arranged in an array, with > 0.01 mm thick ceramic glass encapsulating coating 1400 (i.e. another insulator) as illustrated in Figure 14.
• Figures 13 and 14 illustrate a variable arrangement of copper filaments per row and superimposed number of rows.
• the final design of the induction of the coil 1300 will depend on the application purpose of the induction heating in terms of power rating, electromagnetic flux and skin depth objectives.
• Figure 15 illustrates a single core coil arrangement, this variation it will a more economical induction heating solution, however its resulting electromagnetic flux is limited by the copper conductor surface area.
• Figure 16 illustrates illustrates a multicore arrangement, with 0.65mm diameter copper turns 1102, to increase the resulting coil electromagnetic flux and the heating efficiency.
• the encapsulating coating 1400 can include Borosilicate Glass or Aluminosilicate Glass.
• Borosilicate Glass has a melting point temperature of 1 ,648°C, with a transition temperature of Approx. 820°C.
• Alumino-silicate Glass transition temperature is >820°C.
• the apply glass coating 1400 is applied, at transition temperature, into stages as follows:
• stage one A ribbon >10 micron thick molten glass, is placed onto special designed precision ceramic conveyor chain belt. A heating duct station will keep the glass at a transition temperature.
• stage two copper wires with gap between individual strands of > 0.1 mm or a singular core system, are positioned on top of the glass base.
• a special designed ceramic conveyor will position the copper wire filament on top of the very thin glass.
• a heating duct module keeps the glass and the copper at a suitable temperature.
• stage three a layer of >10 micron thick transition temperature glass, is position on top of the copper filament with special design precision conveyor chain belt.
• a heating duct module follows the final stage to cool down the ribbon and or the single core copper wire.
• the induction heating oven 400 needs to be safe for the consumers who will be exposed to radiation that will be emitted and propagate into the ambient from the heating coils 500 (or 600, 602). [000107]
• the range of frequencies the induction oven 400 operates is typically limited to 30-100 kHz, which corresponds to a wavelength from 9,993 to 2,898 meters. Therefore, the induction-heating oven 400 operates at low frequency (LF) of 25 to 100 KHz, and it is classified as a Non-Ionizing Radiation.
• LF low frequency
• the potential electromagnetic (EM) astray radiation in the induction heating oven 400 can emanate from the panels 406 of the heating body 402, and from external surfaces as well as the internal surface.
• the external EM stray radiation is actually emanated by the induction coils 500 (or 600, 602) themselves, being located on the external face of the heating body 402 defining the cooking chamber 404.
• the internal EM stray radiation emanates from the exited cooking chamber panels 406, which then propagates to the ambient through the glass door of the oven 400.
• One solution to the external EM shield solution is to provide a simple thick aluminum foil wrapped outside the insulation 502 or the induction coils 500 (or 600, 602).
• a solution is also provided to impede the EM radiation into the cooking chamber 404.
• Ferric stainless steel can be effectively inducted or excited at a frequency 30KHz, while Aluminum can only be inducted or excited at around 100KHz.
• aluminum can be an effective EM radiation shield at around the 30KHz frequency range.
• an electromagnetic radiation shield 1800 including four interconnected layered panels 406.
• Each layered panel may include an outer ferric stainless steel heating layer 1802, and an inner aluminum shielding layer 1804.
• the induction coils 500 (or 600, 602) excite the Ferric Stainless steel layer 1802, but not the aluminum layer 1804.
• the Ferric Stainless steel layer 1802 located on the external face of the body 402 defining the cooking chamber 404, will heat up by the induction process and transfer the heat to the Aluminum layer 108, Aluminum being a good thermal conductor by thermodynamic convection. EM stray will be shielded by the aluminum layer 108 which is positioned on the internal face of the cooking chamber 404.
• a Thermo-Mechanical Bonding Lamination manufacturing process is used in forming the radiation shield 1800 with the following technical parameters:
• perforated stainless steel 1802 is used as shown in Figures 20 and 21 (with dimensions in mm), to allow heated aluminum 1804 to be pressed and to protrude through these perforations 2200 and create a mechanical key bond as shown in Figure 22.
• the flat sheet of stainless steel 1802 measures from > 0.5mm thick, 400mm wide and with variable lengths as required according to the cooking chamber 404 being selected.
• the stainless steel 1802 is perforated with holes measuring 3.5mm diameter arranged in a matrix, and not necessarily limited to this configuration.
• a protruding design of the orifices 2200 maximize surface contact area between the stainless steel 1802 and the aluminum sheet 1804 and also will create a mechanical locking and frictional bonding.
• the laminating manufacturing process involves the following steps:
• oven cooking chambers 404 The only common size in oven cooking chambers 404 is its depth, which measures 438mm. Logically, the perimeter of the cooking chamber 404 varies according to its final width and height as detailed in the following table (dimensions in mm):
• Figure 25 shows that the oven 400 can further include an outer electromagnetic radiation shield 2500, surrounding the coil 500, for shielding outward electromagnetic radiation.
• the shield 2500 is for a 60 cm built in oven 400, featuring an aluminum outer casing to mitigate induction EM propagating into the ambient.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Food Science & Technology (AREA)
• General Induction Heating (AREA)

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• 2023
  • 2023-05-04 EP EP23799047.8A patent/EP4520135A4/de active Pending
  • 2023-05-04 WO PCT/AU2023/050373 patent/WO2023212779A1/en not_active Ceased
  • 2023-05-04 AU AU2023264639A patent/AU2023264639A1/en active Pending

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