A cooking appliance with multiple heating modes

Abstract

The application discloses a multi-heating-mode cooking utensil, which comprises a pot body, an inner pot arranged in the pot body, an electromagnetic coil and a main control circuit board. The electromagnetic coil comprises a first coil arranged at the bottom of the inner pot and a second coil arranged at the side of the inner pot. The first coil and the second coil are arranged separately. The main control circuit board drives the first coil to generate an alternating magnetic field with a first frequency to form a bottom heating mode. The main control circuit board drives the second coil to generate an alternating magnetic field with a second frequency to form a side heating mode. The main control circuit board simultaneously drives the first coil and the second coil to generate an alternating magnetic field with a third frequency to form a full heating mode. The third frequency is greater than the first frequency and / or the second frequency. The coil inductance value of the second coil is greater than the coil inductance value of the first coil. The application drives the coil to generate alternating magnetic fields with different frequencies, realizes frequency conversion heating, improves energy efficiency and adapts to various cooking scenes.

Description

Technical Field

[0001] This application belongs to the field of cooking appliance technology, specifically relating to a cooking appliance with multiple heating modes. Background Technology

[0002] With the improvement of living standards, users have placed higher demands on the cooking effect, heating efficiency, and energy consumption of cooking appliances such as rice cookers. Electromagnetic induction heating (IH) technology, due to its characteristics of fast heating speed and high temperature control potential, has been widely used in the field of cooking appliances such as rice cookers.

[0003] The core component of existing induction heating systems (IH) in cooking appliances is an electromagnetic coil, which typically uses a single coil structure and is usually only positioned at the bottom of the inner pot. In actual cooking, IH heating with a single bottom coil has significant limitations: it can only heat the bottom of the pot. For foods requiring overall heating, such as soups and porridges, the bottom temperature is often too high while the surface temperature is insufficient, leading to uneven cooking of the ingredients, sometimes resulting in burnt bottom food and undercooked top food. For cooking methods requiring precise localized heating, such as frying, stir-frying, and baking, while a single bottom coil can act on the bottom of the pot, it cannot flexibly adjust the heating area according to cooking needs, making it difficult to achieve ideal localized heating. Especially when cooking rice in a rice cooker, appliances with a single bottom coil can only heat the bottom of the inner pot, resulting in high temperatures for the bottom food and low temperatures for the top food, easily leading to burnt bottom and undercooked top rice, resulting in poor cooking quality.

[0004] In existing technologies, to address the problem of poor cooking results caused by cooking appliances using a single bottom coil that can only heat the bottom of the inner pot, a solution has been proposed to install side coils on the sides of the inner pot. This allows for overall heating of the cooking appliance by using the bottom coil and side coils to heat the food alternately or together.

[0005] However, from the perspective of thermal response and energy efficiency, most IH heating methods currently using bottom and side coils employ fixed frequencies for both. Based on the principles of electromagnetic induction and the characteristics of electromagnetic heating, a fixed frequency cannot meet the needs of different cooking scenarios and cannot balance energy efficiency and thermal response. If both the bottom and side coils use lower frequencies, such as close to 20kHz, while some heat penetration can be achieved and the temperature difference between the upper and lower layers of food reduced, the thermal response is slow, requiring a long heating time and failing to meet the demand for rapid temperature increases, especially during the initial boiling stages of water or rice. Furthermore, the heat loss due to current passing through the coil resistance and the relatively high hysteresis or eddy current losses in the inner pot's iron core result in lower energy efficiency for the cooking appliance. However, if the bottom coil and side coil use a higher frequency, such as close to 30kHz, although the thermal response is fast and the energy efficiency is improved, the heat is concentrated on the surface of the inner pot, which can easily lead to the problem of "hot surface and cold inside". In addition, the requirements for the thickness of the inner pot material and the compatibility of the coil parameters are extremely high. If the inner pot thickness is too thin, such as less than 2mm, or if there is a slight deviation in the coil parameters, it may cause problems such as power fluctuation, increased coil heating, and even high-frequency noise.

[0006] In summary, existing cooking appliances using a single bottom coil cannot achieve flexible switching between localized and overall heating, making it difficult to adapt to diverse cooking scenarios and fully meet users' needs for refined cooking. On the other hand, the overall heating solution using bottom and side coils, which uses a fixed frequency for heating, makes it difficult to balance thermal response and energy efficiency. Summary of the Invention

[0007] This application provides a cooking appliance with multiple heating modes, which adopts a variable frequency heating technology solution to solve the problems of low energy efficiency and uneven heating when traditional electromagnetic heating cooking appliances only heat at one frequency.

[0008] The technical solution adopted in this application is as follows:

[0009] A multi-heating mode cooking appliance includes a pot body, an inner pot disposed within the pot body, an electromagnetic coil, and a main control circuit board. The main control circuit board is electrically connected to the electromagnetic coil, causing the electromagnetic coil to generate an alternating magnetic field. The inner pot couples with the alternating magnetic field to generate an induced current to achieve heating. The electromagnetic coil includes a first coil located at the bottom of the inner pot and a second coil located on the side of the inner pot. The first coil and the second coil are separately disposed. The main control circuit board drives the first coil to generate an alternating magnetic field of a first frequency to form a bottom heating mode. The main control circuit board drives the second coil to generate an alternating magnetic field of a second frequency to form a side heating mode. The main control circuit board simultaneously drives the first coil and the second coil to generate an alternating magnetic field of a third frequency to form a full heating mode. The third frequency is greater than the first frequency and / or the second frequency, and the coil inductance value of the second coil is greater than the coil inductance value of the first coil.

[0010] The cooking appliance in this application uses a first coil separately located at the bottom of the inner pot and a second coil located on the side of the inner pot as electromagnetic coils for IH heating. By driving the first coil to generate an alternating magnetic field of a first frequency, the cooking appliance can form a bottom heating mode. By driving the second coil to generate an alternating magnetic field of a second frequency, the cooking appliance can form a side heating mode. When both the first and second coils are driven to generate an alternating magnetic field of a third frequency, the cooking appliance can form a full heating mode. The third frequency is greater than the first and / or second frequencies, enabling the electromagnetic coils of the cooking appliance to achieve variable frequency heating, rather than fixed frequency heating. When the cooking appliance requires bottom heating or side heating, driving the first or second coil to generate an alternating magnetic field of a relatively low frequency, that is, heating at a relatively low frequency, results in localized heating of the inner pot. The low-frequency heating can achieve deep heating of localized areas of the inner pot, resulting in more thorough local heating. When the alternating magnetic field of the third frequency is used to form a full heating mode, the bottom and side walls of the inner pot of the cooking appliance are heated. The high-frequency heating can quickly raise the temperature of the inner pot and its contents, achieving rapid heating or boiling.

[0011] Furthermore, according to the principle of electromagnetic induction energy conversion, frequency affects the energy coupling efficiency between the coil and the inner pot. Therefore, a relatively high third frequency allows for tighter energy coupling between the coil and the inner pot, resulting in faster heating of the inner pot and quicker temperature increase for the food. The bottom heating mode and side heating mode use relatively low frequencies, allowing for localized deep heating of the inner pot. When switching to full heating mode, sufficient time is given for the heat from the full heating mode to be conducted to the food inside the inner pot. In other words, when switching from full heating mode to bottom heating mode or side heating mode, time is given for heat to be conducted locally, greatly improving the efficiency of heat utilization and thus enhancing the energy efficiency of the cooking appliance. Moreover, compared to traditional fixed-frequency heating such as 20kHz, this application utilizes a relatively high third frequency, resulting in greater energy savings and reduced energy consumption for the same cooking time.

[0012] In other words, the cooking appliance of this application generates alternating magnetic fields of different frequencies by driving an electromagnetic coil, enabling the appliance to switch between different heating modes. The full heating mode uses a relatively high frequency, improving the thermal response speed and thus increasing energy efficiency and reducing energy consumption, achieving a balance between thermal response and energy efficiency. The bottom heating mode and side heating mode use relatively low frequency heating, enabling the cooking appliance to achieve uniform heating while effectively reducing total energy consumption. Although the energy efficiency of low-frequency heating is slightly lower than that of high-frequency heating, it is low-power heating, keeping the total energy consumption of the cooking appliance at a low level, and the advantage of uniform heating far outweighs the impact of minor differences in energy efficiency.

[0013] Furthermore, when the cooking appliance needs to heat a localized area of ​​the bottom of the inner pot, the first coil is driven to generate an alternating magnetic field of the first frequency, operating in bottom heating mode to ensure even heating of the food at the bottom of the pot, making the cooking appliance suitable for frying, stir-frying, and grilling. When the cooking appliance needs to heat a localized area of ​​the side of the inner pot, the second coil is driven to generate an alternating magnetic field of the second frequency, operating in side heating mode to heat the food on the upper or side, avoiding the problem of the bottom burning while the surface is uncooked during stewing or boiling, ensuring even cooking of the food in the pot, achieving better cooking results. When the cooking appliance needs to heat both the bottom and side of the inner pot simultaneously, the first and second coils can be driven simultaneously to generate an alternating magnetic field of the third frequency, operating in full heating mode to achieve overall heating of the inner pot, which can quickly increase the overall temperature inside the pot, making the cooking appliance suitable for cooking scenarios that require rapid temperature increases, such as boiling water and simmering. Therefore, the cooking appliance of this application generates alternating magnetic fields of different frequencies by driving an electromagnetic coil, which can realize the automatic switching of three heating modes: bottom heating, side heating, and full heating. This makes the cooking appliance adaptable to a variety of cooking scenarios such as frying, stir-frying, baking, stewing, boiling, and braising. It breaks through the limitation of existing cooking appliances with poor adaptability to cooking scenarios, improves the precision of cooking effects, and thus enhances the user's product experience.

[0014] Furthermore, this implementation controls the inductance value of the second coil to be greater than that of the first coil. This results in a larger inductance value for the second coil located on the side of the inner pot, leading to a more stable alternating magnetic field. For example, when cooking rice, the rice grains tend to sink to the bottom more due to gravity, adhering more closely to the bottom of the inner pot. Therefore, they are less sensitive to changes in the operating frequency of the electromagnetic coil during heating mode switching and are less affected by these changes. However, the rice grains on the side of the inner pot are more sparsely packed, only resting against the side. Therefore, making the inductance value of the second coil on the side greater than that of the first coil at the bottom ensures a more stable alternating magnetic field on the side. This results in a smoother frequency transition for the second coil on the side when switching heating modes, leading to a more stable temperature on the side of the inner pot and preventing overheating of the sparse rice grains. This results in more even heating of the entire pot of rice, resulting in better rice quality.

[0015] In one possible implementation of this application, the first coil and the second coil are wrapped around the outside of the inner pot, the first coil having 30-40 turns and the second coil having 18-28 turns.

[0016] In this implementation, by wrapping the first and second coils around the outer edge of the inner pot, the alternating magnetic field generated by the first and second coils is ensured to act on the inner pot as much as possible, improving the heating efficiency of the electromagnetic coil and enhancing energy efficiency. Furthermore, this implementation limits the number of turns of the first coil to 30-40 turns and the number of turns of the second coil to 18-28 turns. This range of turns effectively controls the heating of the bottom by the first coil and the heating of the sides by the second coil. Since the area available for winding the electromagnetic coil on the bottom of the inner pot is smaller than the area available on the sides, having more turns in the first coil than in the second coil makes the overall electromagnetic coil easier to wind and results in a more reasonable winding layout.

[0017] In one possible implementation of this application, the first coil and / or the second coil are tightly wound around the outside of the inner pot, and the number of layers of the first coil and / or the second coil is greater than or equal to two.

[0018] In this embodiment, at least one of the first and second coils is tightly wound around the outside of the inner pot. This tight winding results in more concentrated coupling between each turn of the coil, effectively increasing the inductance of the electromagnetic coil. Under the same parameter conditions, tight winding can effectively increase the inductance of the electromagnetic coil, thereby improving its heating efficiency and energy efficiency. Furthermore, at least one of the first and second coils has two or more layers, increasing the equivalent cross-sectional area of ​​the electromagnetic coil and resulting in stronger magnetic field superposition. This also increases the inductance of the corresponding portion of the electromagnetic coil. Preferably, the second coil has more or more layers than the first coil.

[0019] In one possible implementation of this application, the length of the first coil is 9-12m, and the length of the second coil is 14-18m.

[0020] In this implementation, limiting the length range of the first and second coils helps to effectively control the inductance value of the second coil to be greater than that of the first coil. Preferably, the length of the first coil is 10.6m and the length of the second coil is 15.9m, thus ensuring that the inductance value of the second coil is greater than that of the first coil. This prevents the electromagnetic coils in various parts from being too long to wind properly or too short, resulting in an inductance value that does not meet the requirements.

[0021] In one possible implementation of this application, the cross-sectional area of ​​the first coil is 2-2.5 mm, which is equal to the combined cross-sectional area of ​​the first coil and the second coil. 2 .

[0022] In this implementation, while ensuring that the length range of the first coil is less than or equal to the length range of the second coil, the cross-sectional area of ​​each coil is reasonably controlled to ensure that the inventive purpose of this application is achieved while reducing waste.

[0023] In one possible implementation of this application, the first coil and the second coil are made of 63-78 strands of aluminum wire, each strand of which has a diameter of 0.1-0.2 mm.

[0024] In this implementation, the first and second coils are made of aluminum wire with a reasonable number of strands, which "concentrates and strengthens" the magnetic field, thereby increasing the inductance of each coil. Furthermore, the use of aluminum wire reduces manufacturing costs and the likelihood of damage to the electromagnetic coils due to the properties of aluminum. In other possible implementations, the first and second coils can be supported by copper wire.

[0025] In one possible implementation of this application, a magnetic strip is also included. The magnetic strip is disposed on the side of the electromagnetic coil away from the inner pot and spans the electromagnetic coil. The number of magnetic strips corresponding to the first coil is 4-6, and the number of magnetic strips corresponding to the second coil is 5-7.

[0026] In this implementation, the magnetic strips and their placement ensure that the magnetic field generated by the electromagnetic coil is more concentrated towards the inner pot, while reducing electromagnetic radiation leakage outwards. Specifically, the magnetic strips spanning the electromagnetic coil are positioned such that their ends extend beyond the inner and outer sides of the coil, resulting in a larger coverage area and better concentration of the alternating magnetic field. Specifically, the number of magnetic strips in the first coil is controlled to be 4-6, and the number in the second coil is 5-7. This allows for better placement of the magnetic strips outside the electromagnetic coil, and by rationally controlling the number of strips, manufacturing costs are reduced while achieving the desired magnetic field concentration. Furthermore, since the diameter of the second coil located on the side of the inner pot is typically larger, it is preferable to have 5 magnetic strips in the first coil and 6 magnetic strips in the second coil to meet the required number of magnetic strips.

[0027] In one possible implementation of this application, the bottom heating mode and the side heating mode operate alternately, and the first frequency is different from the second frequency.

[0028] In this implementation, the first frequency and the second frequency are different. Different parts of the inner pot of a cooking appliance usually have different thicknesses, and the difference between the first and second frequencies allows the bottom heating mode and the side heating mode to adapt to the different thicknesses of the bottom and sides of the inner pot.

[0029] Furthermore, alternating between bottom heating and side heating modes creates convection currents within the pot, increasing the evenness of heating. For example, when cooking rice, alternating between bottom and side heating modes allows for convection, ensuring the rice grains fully absorb water and heat. The alternation also prevents the rice from burning at the bottom and remaining undercooked at the top, a common problem with traditional bottom-only heating methods. This ensures even heating of the rice, improving cooking results. Additionally, the alternating heating prevents the rice at the bottom from overheating and prematurely gelatinizing, hindering water absorption and resulting in a better overall cooking outcome. Similarly, during the boiling stage, bottom heating causes the food at the bottom to tumble upwards, while side heating causes the food at the edges to flow towards the center, ensuring thorough boiling and bubbling. Especially for soups and porridges, the alternating operation of bottom and side heating creates convection currents in the ingredients, effectively stirring them. This allows the ingredients to fully interact and release more flavor compounds, resulting in a better texture and taste. Simultaneously, the side heating mode pushes ingredients from the edges towards the center, preventing the boiling and overflowing phenomenon that often occurs with traditional bottom-heated systems. Furthermore, the alternating bottom and side heating modes reduce energy consumption compared to full heating and avoid overheating issues caused by concentrated heating in either the bottom or side coils, thus extending the coil's lifespan.

[0030] In one possible implementation of this application, the heating power of the bottom heating mode is different from that of the side heating mode, and both the first frequency and the second frequency are in the range of 20kHz to 30kHz.

[0031] In this implementation, since the area covered by the second coil on the side of the inner pot is larger than the area covered by the first coil on the bottom, achieving uniform heating of the entire inner pot requires that the heat output per unit area be the same for both the bottom and sides. Therefore, the heating power of the bottom heating mode and the side heating mode are designed to be different. Both the first and second frequencies are within the range of 20kHz to 30kHz, which ensures that the first and second frequencies remain consistent or nearly consistent. The power output of the first and second coils can be made different while their frequencies are similar by adjusting the inductance of the electromagnetic coils.

[0032] The first and second coils are typically switched via IGBTs, using a frequency range of 20kHz to 30kHz. This avoids both excessively low frequencies, which would lead to prolonged IGBT conduction time, excessive heat generation, and potential burnout, and also prevent continuous heating of the bottom of the inner pot, potentially burning the food. Conversely, excessively high frequencies would cause the IGBTs to discharge prematurely during frequent switching, increasing switching losses and reducing energy efficiency. Based on the commonly used inner pots of cooking appliances, a frequency range of 20kHz to 30kHz is chosen, with 21-26kHz being preferable. This ensures that the frequency is not too low to prevent excessive heat generation and IGBT burnout, while also ensuring that the IGBTs can conduct at or near zero voltage, enhancing safety. Furthermore, the 20kHz to 30kHz frequency range allows for deep heating of the bottom of the inner pot, minimizing temperature differences between the top and bottom layers and ensuring even heating of the food. It also allows for gentle heating of food on the sides, resulting in uniform heating of the entire contents of the pot.

[0033] In one possible implementation of this application, the heating power of the side heating mode is greater than the heating power of the bottom heating mode.

[0034] In this implementation, because the area of ​​the side of the inner pot is larger than the area of ​​the bottom of the inner pot, the area covered by the second coil on the side of the inner pot is larger than the area covered by the first coil on the bottom of the inner pot. Therefore, this application requires that the heating power of the side heating mode and the heating power of the bottom heating mode be different, and that the heating power of the side heating mode be greater than the heating power of the bottom heating mode, so that the heat generation per unit area of ​​the side and bottom of the inner pot is balanced. This ensures that when the side heating mode and the bottom heating mode are running alternately, the convection effect on the food in the pot is the same, ensuring that the food is fully turned and achieving a better cooking effect.

[0035] In one possible implementation of this application, when the cooking appliance performs a cooking program, the heating process is changed at least once. The heating process includes running a bottom heating mode, a side heating mode, or a full heating mode, as well as alternating between bottom heating mode and side heating mode.

[0036] In one possible implementation of this application, the cooking process includes at least a water absorption stage, a heating stage, and a boiling stage; in the water absorption stage and the boiling stage of the cooking process, the heating process includes alternating between a bottom heating mode and a side heating mode; and in the heating stage of the cooking process, the heating process includes operating a full heating mode.

[0037] In this implementation, taking the cooking of rice in a cooking appliance as an example, the cooking process includes a water absorption stage, a heating stage, and a boiling stage. During the water absorption stage, bottom heating and side heating modes are alternately operated. Because the heating frequencies used in bottom heating and side heating modes are relatively low, the temperature difference between the upper and lower layers of rice in the pot is small, allowing the rice to be heated evenly. The alternating operation of the side heating mode also heats the rice on the sides, ensuring that the entire rice in the pot is heated evenly. Simultaneously, the alternating operation of bottom and side heating causes convection in the rice within the pot. During the water absorption stage, the rice grains flow with this convection, allowing them to fully absorb water, achieving both even heating and thorough water absorption. Furthermore, the alternating operation of bottom and side heating prevents the bottom temperature from becoming too high, which could cause the outer starch layer to gelatinize prematurely, forming a "hard shell" that hinders water absorption. During the heating phase, a full heating mode is used. In this mode, the electromagnetic coil uses a relatively high frequency to heat the bottom and sides of the inner pot simultaneously and rapidly, quickly raising the overall temperature inside the pot and shortening the heating time. This also reduces the high-frequency operation time of the electromagnetic coil, improving energy efficiency and speeding up heating, while reducing the time the electromagnetic coil operates at high power, lowering heat generation, and extending its service life. During the boiling phase, bottom heating and side heating modes are alternated. On one hand, this creates convection in the rice inside the pot, increasing the tumbling effect during boiling, ensuring the rice boils thoroughly and the starch on the outer layer of the rice grains gelatinizes more completely, improving the texture of the cooked rice. At the same time, bottom heating causes the food in the pot to tumble upwards, while side heating pushes the food towards the center, forming a "bottom pushing - side guiding" cycle. This avoids excessive tumbling and overflowing of rice water that can occur with heating only one area, ensuring the rice boils thoroughly while preventing overflow.

[0038] In one possible implementation of this application, before the boiling stage, the bottom heating mode and the side heating mode are operated alternately at an interval of T1, and during the boiling stage, the bottom heating mode and the side heating mode are operated alternately at an interval of T2, wherein T2 < T1.

[0039] In this implementation, a longer interval is used to alternate between bottom heating and side heating modes before the boiling stage, which creates relatively gentle convection within the pot. For example, during the water absorption stage, ingredients such as rice grains can fully contact water and heat through gentle convection, allowing for more complete water absorption. During the boiling stage, a relatively shorter interval is used to alternate between bottom heating and side heating modes. This shortens the alternation time between the upward tumbling of ingredients due to bottom heating and the inward pushing due to side heating, resulting in more frequent upward tumbling and inward pushing. This ensures more complete boiling, releasing the flavor compounds of the ingredients and achieving better cooking results.

[0040] In one possible implementation of this application, the cooking process includes at least a water absorption stage, a heating stage, and a boiling stage; in the water absorption stage of the cooking process, the heating process includes operating a bottom heating mode or a side heating mode; in the heating stage of the cooking process, the heating process includes alternating between bottom heating mode and side heating mode; and in the boiling stage of the cooking process, the heating process includes operating a full heating mode.

[0041] In this implementation, taking rice cooking as an example, the bottom heating mode or side heating mode is used during the water absorption stage. Both modes employ relatively low heating frequencies, reducing the temperature difference between the upper and lower layers of the pot and ensuring that ingredients on the sides are also heated. This allows the rice grains to be heated evenly and fully absorb water during the absorption stage. Because the bottom or side heating mode is used during the water absorption stage, no convection occurs within the pot, meaning the rice grains are essentially in a static state absorbing water. The gelatinization of the starch on the outer layer of the rice grains can easily lead to clumping. Therefore, to break up the clumps and ensure optimal cooking results, the bottom and side heating modes are alternately used during the heating stage. This creates convection within the pot, breaking up any potential clumps. Simultaneously, the alternating use of bottom and side heating modes during the heating stage allows the rice grains to come into full contact with water through convection, further facilitating water absorption and resulting in more elastic and better-cooked rice. During the boiling stage, the full heating mode is activated, which uses a relatively high frequency of heating to improve energy efficiency and keep the temperature inside the pot at a high level, thereby increasing the boiling intensity.

[0042] In one possible implementation of this application, when the cooking appliance is cooking rice, the heating power of the bottom heating mode and / or side heating mode and / or full heating mode is adjusted according to the type of rice and / or the variety of rice.

[0043] In this implementation, the cooking appliance typically handles different types of rice and different types of cooked rice. Different types of rice may require slightly different cooking procedures or characteristics; for example, indica rice requires a stronger boiling point, while japonica rice requires a longer water absorption time. Therefore, by adjusting the heating power of the bottom heating mode and / or side heating mode and / or full heating mode, the cooking appliance of this application can adapt to the cooking needs of various rice types, improving its adaptability. Furthermore, because the electromagnetic coil in this application is driven by a variable frequency drive, meaning the frequency of the magnetic coil heating is adjustable, adjusting the heating power of the bottom heating mode and / or side heating mode and / or full heating mode can be achieved by adjusting the alternating magnetic fields of different frequencies generated when driving the first coil and / or driving the second coil and / or simultaneously driving the first and second coils. This adjusts the heating power, improving the adaptability of the cooking appliance to different types of rice and / or different types of cooked rice, while also improving the energy efficiency and reducing energy consumption.

[0044] In one possible implementation of this application, the main control circuit board includes at least one insulated gate bipolar transistor (IGBT) and two relays, with the two relays electrically connected to the first coil and the second coil, respectively; when the bottom heating mode and the side heating mode are alternately operated, the IGBT is first turned off, and then the relay electrically connected to the corresponding coil of the original heating mode is turned off.

[0045] In this implementation, the alternating operation of bottom heating mode and side heating mode actually involves switching between the two modes. The bottom heating mode is generated by driving the first coil to produce an alternating magnetic field of a first frequency, while the side heating mode is generated by driving the second coil to produce an alternating magnetic field of a second frequency. Therefore, switching between the bottom heating mode and side heating mode is essentially switching between the first and second coils. This switching is achieved using one IGBT and two relays. The two relays are connected to the branches of the first and second coils, respectively. When switching between bottom heating mode and side heating mode is required, the IGBT is first turned off, and then the relay connected to the corresponding coil of the original heating mode is turned off. For example, if the current heating mode is bottom heating mode and a switch to side heating mode is needed, the IGBT is first turned off, and then the relay connected to the branch of the first coil is turned off. In this way, on the one hand, arc-free interruption of the relay can be achieved, protecting the relay: when the IGBT is turned off first, the current in the coil can decay to zero through a safe path. At this time, when the relay switches again, no current flows between the contacts, avoiding arcing, greatly reducing contact erosion, significantly extending the mechanical and electrical life of the relay, and reducing maintenance costs. On the other hand, it also avoids the fatal induced voltage spikes of the IGBT, preventing the IGBT from being damaged: the relay that is turned off first will forcibly cut off the inductive load current, generating a high voltage spike. However, if the IGBT is turned off first, its matching protection circuit, such as the freewheeling diode and the absorption circuit, can effectively clamp and absorb the induced voltage generated during turn-off, ensuring that the IGBT operates within a safe voltage range and preventing overvoltage breakdown. On the other hand, turning off the IGBT first and then the relay can improve the overall stability and reliability of the system, making the switching process of the heating mode controllable and orderly: the IGBT is responsible for precisely controlling the power on and off, while the relay is only responsible for switching the path in the absence of current, choosing whether to connect the first coil or the second coil. Each performs its own function, which can reduce electromagnetic interference, avoid unpredictable circuit states, and make the system work more stable and reliable. Attached Figure Description

[0046] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0047] Figure 1A schematic diagram showing the positions of the first and second coils;

[0048] Figure 2 A schematic diagram of the heating process of a cooking appliance at each stage;

[0049] Figure 3 This is another schematic diagram of the heating process of a cooking appliance at each stage.

[0050] Figure 4 This is a cross-sectional schematic diagram of the inner pot of a cooking appliance in conjunction with an electromagnetic coil.

[0051] Figure 5 This is a bottom view of the interior of a cooking appliance.

[0052] Figure label:

[0053] 10 - First coil; 20 - Second coil; 30 - Inner pot; 40 - Magnetic strip. Detailed Implementation

[0054] To more clearly illustrate the overall concept of this application, a detailed explanation is provided below with reference to the accompanying drawings.

[0055] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Therefore, the scope of protection of this application is not limited to the specific embodiments disclosed below.

[0056] Furthermore, it should be understood in the description of this application that the terms "top", "bottom", "inner", "outer", "axial", "radial", "circumferential", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0057] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0058] In this application, unless otherwise expressly specified and limited, the "above" or "below" of the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. In the description of this specification, references to terms such as "implementation," "example," "a particular embodiment," "example," or "specific example," etc., indicate that the specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples.

[0059] The cooking appliance described in this application employs an induction heating (IH) method, such as a rice cooker or electric rice pot. The appliance includes a pot body, an inner pot for holding food, an electromagnetic coil, and a main control circuit board. In existing technology, the electromagnetic coil is typically located at the bottom of the inner pot. The main control circuit board is electrically connected to the electromagnetic coil and can output alternating current to drive the electromagnetic coil to generate an alternating magnetic field. The inner pot generates an alternating current due to electromagnetic response within the alternating magnetic field, thereby achieving bottom heating.

[0060] To achieve both localized and overall heating in cooking appliances, some appliances currently incorporate two electromagnetic coils within the pot. One coil is located at the bottom of the inner pot for heating the bottom, while the other is positioned on the side for heating the side. However, both coils currently operate at a fixed frequency, such as 30kHz, which offers faster thermal response and improved energy efficiency compared to lower frequencies. This results in heat concentrating on the surface of the inner pot, placing extremely high demands on the inner pot material and coil parameters, requiring advanced inner pot manufacturing processes. If the inner pot is too thin, power fluctuations and increased coil heating can occur, affecting the appliance's normal operation. Therefore, most current dual-coil heating methods use a frequency of 20kHz. However, 20kHz is too low, resulting in slow heating and a slow thermal response, making it difficult to meet the need for rapid heating. Furthermore, 20kHz heating leads to relatively high copper losses in the coil and iron losses in the inner pot, resulting in low energy efficiency and high energy consumption.

[0061] To solve this problem, such as Figure 1As shown, the electromagnetic coil in this application is composed of a first coil 10 and a second coil 20, which are separately arranged. The first coil 10 is located at the bottom of the inner pot 30. The main control circuit board drives the first coil 10 to generate an alternating magnetic field of a first frequency, which can heat the bottom of the inner pot 30, enabling the cooking appliance to form a bottom heating mode. The second coil 20 is located on the side of the inner pot 30. Optionally, the second coil 20 is arranged around the side of the inner pot 30. The main control circuit board drives the second coil 20 to generate an alternating magnetic field of a second frequency, which can heat the side of the inner pot 30, enabling the cooking appliance to form a side heating mode. When the main control circuit board drives the first coil 10 and the second coil 20 simultaneously, it can generate an alternating magnetic field of a third frequency, simultaneously heating the bottom and side of the inner pot, enabling the cooking appliance to form a full heating mode. The inductance value of the second coil 20 is greater than that of the first coil 10.

[0062] It should be noted that the number of turns and winding density of the bottom coil can be designed according to the bottom area of ​​the inner pot and the bottom heating power requirements. It can fit tightly against the outer side of the bottom of the inner pot to ensure that the alternating magnetic field can act efficiently on the bottom area of ​​the inner pot. The side coils are arranged around the outer side of the inner pot, and their coil height is adapted to the height of the inner pot side wall. The winding density can be adjusted according to the side heating power requirements to ensure that a uniform alternating magnetic field is formed over the food on the side of the pot, so as to achieve uniform heating of the food on the side.

[0063] Furthermore, the third frequency is greater than the first and / or second frequencies. That is, when the main control circuit board of this application drives the electromagnetic coil, it causes the electromagnetic coil to generate an alternating magnetic field with a variable frequency, achieving variable frequency heating instead of fixed frequency heating. When the cooker requires bottom or side heating, the first or second coil is driven to generate an alternating magnetic field with a relatively low frequency, i.e., heating at a relatively low frequency. This achieves uniform heating while effectively reducing energy consumption. When the cooker requires full heating mode operation, both the first and second coils are driven simultaneously to generate an alternating magnetic field with a third frequency. This relatively high third frequency improves the thermal response speed of the cooker, allowing for rapid temperature increases in the inner pot and its contents, achieving rapid heating or boiling.

[0064] Furthermore, according to the principle of electromagnetic induction energy conversion, frequency affects the energy coupling efficiency between the coil and the inner pot. Therefore, a relatively high third frequency allows for tighter energy coupling between the coil and the inner pot, resulting in lower copper losses in the coil and iron losses in the inner pot. This, in turn, improves the energy efficiency of the cooking appliance and reduces energy consumption. The bottom heating mode and side heating mode use relatively low-frequency heating, which can heat the inner pot locally. When switching to the full heating mode, this allows sufficient time for the heat from the full heating mode to be conducted to the food inside the inner pot. In other words, when switching from the full heating mode to the bottom heating mode or side heating mode, it allows time for heat to be conducted locally, greatly improving the efficiency of heat energy utilization and thus improving the energy efficiency of the cooking appliance.

[0065] Furthermore, compared to traditional fixed-frequency heating such as 20kHz, this application utilizes a relatively higher third frequency for heating, resulting in greater energy savings and reduced energy consumption for the same cooking time. While the bottom heating and side heating modes employ low-frequency heating, leading to slightly lower energy efficiency compared to the high-frequency heating of the full heating mode, this low frequency ensures that the bottom and side heating modes operate at low power, maintaining a relatively low overall energy consumption. Moreover, the advantage of uniform heating far outweighs the impact of minor differences in energy efficiency.

[0066] In one example, the main control circuit board has a built-in frequency adjustment module, power control module, and mode switching module, which can drive the first coil and the second coil to work at different frequencies according to cooking needs, i.e., variable frequency operation, to achieve the following three heating modes:

[0067] Bottom heating mode: The main control circuit board only conducts the first coil circuit through the mode switching module. The frequency adjustment module controls the first coil to pass an alternating current of the first frequency, generating an alternating magnetic field of the first frequency, with a power range of 500-1000W. The first frequency is preferably 20KHZ±2KHZ. At this frequency, for stainless steel inner pots with a thickness of 3-5mm commonly used in cooking appliances such as rice cookers, the induced current generated by the magnetic field of the inner pot coupling coil can penetrate to a slightly deeper layer of the inner pot. Heat is conducted from the inside of the inner pot to the outside, resulting in a small temperature difference between the upper and lower layers of the food inside the pot. This is suitable for scenarios that require uniform bottom heating, such as rice absorbing water, cooking porridge, braising, boiling, frying, and grilling.

[0068] Side heating mode: The main control circuit board only conducts the second coil circuit. The frequency adjustment module controls the second coil to receive an alternating current of the second frequency, generating an alternating magnetic field of the second frequency, with a power range of 700-1300W. The second frequency is also preferably 20KHZ±2KHZ. At this frequency, the alternating magnetic field generated by the second coil acts on the side of the inner pot, which can gently and evenly heat the food on the side of the pot, avoiding delayed cooking due to insufficient heating of the food on the side. It is suitable for stewing soups, keeping warm, and other scenarios that require even heating of the side.

[0069] Full heating mode: The main control circuit board connects the first and second coils in parallel via a mode switching module. The frequency adjustment module controls the two coils to receive an alternating current of a third frequency, generating an alternating magnetic field of the third frequency, with a power range of 1300-2000W. The third frequency is greater than the first and / or second frequencies, preferably 30kHz ± 2kHz, and this frequency is closer to the optimal resonant frequency of the IH system. At a frequency of 30kHz, the eddy current depth generated by the magnetic field of the inner pot coupling coil is approximately 0.2-0.3mm, concentrating heat on the outer surface of the inner pot, resulting in a rapid temperature rise. Simultaneously, the two parallel coils form an overall alternating magnetic field covering the bottom and sides of the inner pot, achieving rapid overall heating. This is suitable for scenarios requiring rapid heating, such as boiling water, the initial boiling stage of rice, and quickly reheating cold rice.

[0070] Therefore, the cooking appliance of this application generates alternating magnetic fields of different frequencies by driving an electromagnetic coil, enabling automatic switching between three heating modes: bottom heating, side heating, and full heating. This allows the appliance to adapt to diverse cooking scenarios such as frying, stir-frying, grilling, stewing, boiling, and braising, improving the precision of cooking results and thus enhancing the user experience. Furthermore, the power control module on the main control circuit board can adjust the output power in real time according to different heating modes and cooking needs, ensuring a stable output of the target power at different frequencies.

[0071] As one possible implementation of this application, the first coil 10 and the second coil 20 are wound around the outside of the inner pot. The first coil 10 has 30-40 turns, and the second coil 20 has 18-28 turns, thereby better ensuring that the coil inductance of the second coil 20 is greater than that of the first coil 10. Figure 1 , Figure 4 and Figure 5 As shown, both the first coil 10 and the second coil 20 are tightly wound around the outside of the inner pot. In other implementations, at least one of the first coil 10 and the second coil 20 is ensured to be tightly wound, thereby increasing the strength of the alternating magnetic field generated by the electromagnetic coil, allowing it to act more on the inner pot and improving heating efficiency. Furthermore... Figure 1 and Figure 4 In this design, both the first coil 10 and the second coil 20 have two layers. Having two or more layers increases the effective cross-sectional area of ​​the electromagnetic coil, resulting in a stronger magnetic field superposition. Preferably, the number of layers in the second coil is greater than or equal to the number of layers in the first coil to better ensure that the inductance of the second coil 20 is greater than that of the first coil 10. Further, the number of turns in the first coil 10 is preferably 31-38 turns, and the number of turns in the second coil is preferably 23-24 turns.

[0072] As one possible implementation of this application, see [link to relevant documentation]. Figure 5It also includes magnetic strips 40, which are positioned on the side of the electromagnetic coil away from the inner pot 30 and span the electromagnetic coil. The first coil 10 has 4-6 magnetic strips, and the second coil 20 has 5-7 magnetic strips. This satisfies the heating requirements of most existing cooking appliances while avoiding waste and reducing manufacturing costs. Preferably, the first coil 10 has five magnetic strips 40, and the second coil 20 has six magnetic strips, forming an array to fully utilize the function of the magnetic strips 40 and save materials.

[0073] As one possible implementation of this application, the cooking appliance alternates between bottom heating mode and side heating mode. In bottom heating mode, the first coil heats the bottom of the inner pot, causing the food inside to tumble upwards. In side heating mode, the second coil acts on the side of the inner pot, heating the food on the side and causing it to flow towards the center. Alternating between bottom and side heating modes creates convection as the food alternates between tumbling upwards and being pushed towards the center. This convection ensures the food is fully in contact with water and heat, guaranteeing adequate heating and water absorption, thus improving cooking results. Furthermore, compared to full heating mode, alternating between bottom and side heating modes reduces overall energy consumption because the first and second frequencies generated by the electromagnetic coils are lower than the third frequency. The alternating heating of the first and second coils also avoids the overheating caused by a single coil continuously concentrating heat, extending the lifespan of both coils.

[0074] In one example, cooking appliances typically go through low-temperature, medium-high-temperature, and heat-preserving stages, alternating between bottom heating and side heating modes to create convection within the pot, resulting in high cooking efficiency at each stage. Specifically, in the low-temperature stage, such as the rice water absorption stage: the bottom heating mode is initially used. When the bottom temperature reaches the target threshold, such as 50-60℃ during rice water absorption, the system switches to side heating mode. Once the side temperature catches up with the bottom temperature, for example, the temperature difference is ≤5℃, it switches back to bottom heating mode. The core design principle here is to prevent excessively high temperatures at the bottom or sides, which could cause premature gelatinization of the food, such as premature gelatinization of the outer starch layer of rice hindering water absorption. This stage can be switched every 30-60 seconds to allow the food to slowly absorb water or preheat in a relatively stable temperature field, avoiding frequent switching that causes temperature fluctuations and affects the water penetration of the food cells. For example, rice requires a stable environment of around 50℃ for water absorption; frequent switching can cause localized temperature fluctuations, affecting the water absorption of the rice grains. During the medium-high temperature stage, such as the rice heating period: first run the bottom heating mode. When the bottom heating causes the center of the pot to begin to simmer, switch to the side heating mode. Use the side heat to push the food at the edges towards the center. When the edges start to churn noticeably, switch back to the bottom heating mode to create a "center-edge" cyclical convection. This stage can be switched every 10-20 seconds to strengthen the "bottom heating - center heating - side heating - edge heating" cycle, creating continuous convection within the pot. Food such as rice and porridge will be heated more evenly during churning, avoiding the problem of "vigorous boiling in the center and insufficient temperature at the edges" and layering. During the heat preservation stage, such as the rice simmering stage: when the overall temperature inside the pot drops to the lower limit of the heat preservation threshold, such as 65℃ when simmering rice, first activate the bottom heating mode to raise the temperature to the upper limit of the threshold, such as 70℃, and then switch to the side heating mode to maintain the temperature. This avoids "localized overheating and aging" caused by prolonged heating of a single area, which can affect the cooking effect, such as the rice becoming burnt at the bottom. This stage can be switched every 2-5 minutes, because the heat preservation stage only needs to maintain the overall temperature stability and does not require convection. Switching at longer intervals can reduce energy consumption and avoid the life loss caused by frequent start-stop of the coil.

[0075] Furthermore, by alternating between bottom heating and side heating modes, the temperature difference between the bottom and sides drives natural convection of the food inside the pot, solving the problems of overheating at the bottom and underheating at the sides that are common with traditional single heating modes. This addresses issues like rice easily burning at the bottom and undercooked at the top, resulting in more even heating of each grain of rice. Simultaneously, the convection effect simulates "gentle stirring," allowing ingredients in soups or porridges to fully collide and blend, releasing more flavor compounds and improving the texture. For rice, the convection allows the grains to absorb water evenly, preventing the outer layer from becoming too soft and the inner layer too hard. Moreover, alternating bottom and side heating avoids simultaneous high-power operation of both coils, reducing overall energy consumption by 10%-15% compared to full heating mode. Compared to single-coil operation, the heat concentration is reduced, and the coil temperature can be lowered by 5-8℃, helping to extend the coil's lifespan.

[0076] In addition, the first and second frequencies are different. Different parts of the inner pot of a cooking appliance typically have different thicknesses. The difference between the first and second frequencies allows the bottom heating mode and side heating mode to adapt to the different thicknesses of the bottom and sides of the inner pot. For example, the first frequency is lower than the second frequency. At a lower frequency, the eddy current generated by the magnetic field of the inner pot's coupling coil is relatively deeper. Therefore, the bottom of the inner pot can be designed to be thicker than the sides, thus ensuring uniform heating of the entire inner pot.

[0077] As one possible implementation of this application, since the area of ​​the side of the inner pot is larger than the area of ​​the bottom of the inner pot, the area covered by the second coil on the side of the inner pot is larger than the area covered by the first coil on the bottom of the inner pot. Therefore, this implementation requires that the heating power of the side heating mode and the heating power of the bottom heating mode are different, and the heating power of the side heating mode is greater than the heating power of the bottom heating mode, so that the heat generation per unit area of ​​the side and bottom of the inner pot is balanced. This ensures that when the side heating mode and the bottom heating mode are running alternately, the convection effect on the food in the pot is the same, ensuring that the food is fully turned and achieving a better cooking effect.

[0078] Furthermore, both the first and second frequencies are within the range of 20kHz to 30kHz. On one hand, since the area covered by the second coil on the side of the inner pot is larger than the area covered by the first coil on the bottom, achieving uniform heating of the entire inner pot requires that the heat output per unit area be the same for both the bottom and sides. Therefore, the heating power of the bottom heating mode and the side heating mode are designed to be different. Since both the first and second frequencies are within the range of 20kHz to 30kHz, this frequency range ensures that the first and second frequencies remain consistent or nearly consistent. The power output of the first and second coils can be made different while their frequencies are similar by adjusting the inductance of the electromagnetic coils. On the other hand, the first and second coils are generally switched by IGBTs, using a frequency range of 20kHz to 30kHz. This avoids making the first and second frequencies too low, which would result in long IGBT conduction times, excessive heat generation, and potential burnout of the IGBTs, and also prevents the bottom of the inner pot from being continuously heated, causing the food at the bottom of the inner pot to burn. At the same time, it also avoids making the first and second frequencies too high, which would cause the IGBTs to discharge prematurely during frequent switching, increasing switching losses and reducing energy efficiency.

[0079] The optimal frequency range for cooking appliance inner pots is 21-26kHz, within the 20kHz to 30kHz range. This ensures the frequency isn't too low, preventing excessive heat that could damage the IGBTs, while also preventing the IGBTs from conducting at or near zero voltage, enhancing safety. Furthermore, the 20kHz to 30kHz frequency range allows for deep heating of the bottom of the inner pot, minimizing temperature differences between the top and bottom layers and ensuring even heating of the food. It also allows for gentle heating of food on the sides, resulting in uniform heating of all ingredients within the pot.

[0080] As one possible implementation of this application, the cooking appliance has multiple cooking scenarios, and different cooking programs need to be executed under different cooking scenarios. Each cooking program includes multiple cooking stages, and the cooking program differs depending on the stage. In this implementation, the heating process is changed at least once when the cooking appliance executes a cooking program. Optionally, the heating process can be a single operation of bottom heating mode, a single operation of side heating mode, a single operation of full heating mode, or an alternating operation of bottom heating mode and side heating mode. For example, operating the bottom heating mode at a low temperature stage and alternating between bottom heating mode and side heating mode at medium and high temperature stages is equivalent to changing the heating process once during the cooking program. That is, the cooking appliance in this implementation can operate a single bottom heating mode, side heating mode, or full heating mode at different cooking stages, or it can alternate between bottom heating mode and side heating mode, so that there can be multiple combinations of heating processes in a cooking program containing multiple cooking stages, thereby enabling the cooking appliance to adapt to multiple different cooking scenarios. However, the specific heating mode or multiple heating modes used in the overall cooking process can be adjusted according to actual cooking needs and cooking scenarios. This implementation does not limit this, but is only used to illustrate that cooking appliances or cooking programs can combine different heating processes.

[0081] As one possible implementation of this application, taking the cooking of rice in a cooking appliance as an example, the process includes a water absorption stage, a heating stage, and a boiling stage. The heating requirements differ significantly between these stages. For instance, the water absorption stage requires gentle penetration, while the heating stage requires rapid temperature increase. Therefore, a single heating process, such as only operating bottom heating, side heating, or full heating modes, or only alternating between bottom heating and side heating modes, cannot cover the entire process optimization. Combining different heating processes in stages is the optimal choice. The specific adaptation logic is as follows:

[0082] Firstly: such as Figure 2As shown, during the water absorption stage, bottom heating and side heating modes are alternately operated. Because the heating frequencies used in bottom and side heating modes are relatively low, the temperature difference between the upper and lower layers of rice in the pot is small, allowing for even heating. The alternating operation of the side heating mode also heats the rice on the sides, ensuring uniform heating of the entire pot of rice. Simultaneously, the alternating operation of bottom and side heating creates convection currents within the rice, allowing the rice grains to fully absorb water during the water absorption stage, achieving both uniform heating and thorough water absorption. Furthermore, the alternating operation of bottom and side heating prevents the bottom temperature from becoming too high, which could cause premature gelatinization of the outer starch layer, forming a "hard shell" that hinders water absorption. During the heating stage, a full heating mode is used. In full heating mode, the electromagnetic coil uses a relatively high frequency to heat, allowing the bottom and sides of the inner pot to heat up rapidly and simultaneously. This results in a fast thermal response and improved energy efficiency, enabling the cookware to balance both thermal response and energy efficiency. Simultaneously, the rapid increase in the overall temperature inside the pot shortens the time required for the heating phase, reducing the time the electromagnetic coil operates at high frequency and power, thus lowering heat generation and extending its lifespan. During the boiling phase, bottom heating and side heating modes alternate. On one hand, this creates convection within the rice, increasing the tumbling effect during boiling and ensuring thorough boiling. This leads to more complete gelatinization of the starch on the outer layer of the rice grains, improving the texture. On the other hand, bottom heating causes the food to tumble upwards, while side heating pushes it towards the center, creating a "bottom pushing - side guiding" cycle. This avoids excessive tumbling and overflowing of rice water that can occur with heating only one area, ensuring the rice boils thoroughly while preventing overflow.

[0083] Furthermore, in the above process, both the water absorption stage and the boiling stage employ alternating bottom heating and side heating modes. However, the water absorption stage uses a longer interval (T1) for alternating bottom and side heating modes, creating a relatively gentle convection within the pot. This allows the rice grains to fully contact the water and heat during convection, resulting in more thorough water absorption. Conversely, the boiling stage uses a relatively short interval (T2) for alternating bottom and side heating modes. This shortens the alternation time between the upward tumbling of the food under bottom heating and the inward pushing under side heating, resulting in more frequent upward tumbling and inward pushing. This leads to more complete boiling, releasing the flavor compounds of the food and achieving better cooking results. In other words, the shorter alternation time in the boiling stage compared to the water absorption stage results in greater convection intensity during boiling, making the convection gentler in the water absorption stage and the tumbling more intense in the boiling stage.

[0084] Secondly: such as Figure 3As shown, either bottom heating or side heating mode is used during the water absorption stage. Both bottom and side heating modes use relatively low heating frequencies, which reduces the temperature difference between the upper and lower layers of the pot, allowing the food on the sides to also be heated. This ensures that the rice grains are heated evenly and fully absorb water during the water absorption stage. Because bottom or side heating mode is used during the water absorption stage, no convection occurs inside the pot, meaning the rice grains are essentially in a static water absorption state. The starch gelatinization on the outer layer of the rice grains can easily cause them to clump together. Therefore, to break up the clumps and ensure the final cooked rice, bottom and side heating modes are alternately used during the heating stage. This creates convection inside the pot, breaking up any potential clumps. Simultaneously, alternating between bottom and side heating modes during the heating stage also allows the rice grains to come into full contact with water through convection, further facilitating water absorption and ensuring the rice is fully hydrated. This results in more elastic cooked rice with a better cooking effect. During the boiling stage, the full heating mode is activated, using a relatively high frequency of heating to improve energy efficiency while keeping the temperature inside the pot at a high level, thereby increasing the boiling intensity and achieving full boiling.

[0085] It should be noted that the above examples are merely illustrative and are not intended to limit the implementation method. In actual cooking scenarios, the cooking program may also adopt other combinations of bottom heating mode, side heating mode, full heating mode, and alternating bottom heating mode and side heating mode to adapt to different cooking scenarios and cooking needs.

[0086] In addition to the above, the rice cooking process can also include a simmering stage or a keep-warm stage. During these stages, bottom heating and side heating modes can be alternated. However, the purpose of the keep-warm stage is not to create convection, but to maintain a certain temperature so that the rice can soften during this process. Therefore, when bottom and side heating modes are alternated, the interval between them should be greater than 2 minutes. This avoids frequent alternation and prevents the bottom rice from burning when only bottom heating is used. The side heating mode supplements the heat to the sides, preventing the rice at the edges from becoming hard due to low heat, thus improving the overall cooking effect. Alternatively, during the keep-warm or simmering stages, it is also possible to choose not to alternate between bottom and side heating modes, but to use only side heating or only bottom heating. These two heating modes have a relatively low heating frequency, ensuring even heating of the rice in the pot, maintaining the keep-warm effect, and reducing the overall energy consumption of the cooking appliance.

[0087] For example, the core objective of the water absorption stage is to ensure that the rice grains absorb water evenly and prevent the outer layer of the grains from gelatinizing. Therefore, an alternating bottom heating mode and a side heating mode are used, alternating every 30-60 seconds. During this stage, the temperature needs to be stabilized at the optimal temperature for starch water absorption, 50-60℃. Alternating bottom and side heating with a power of 500-1200W creates gentle convection within the pot, allowing the rice grains to evenly contact water and heat during the flow. This prevents the outer starch of the bottom grains from prematurely gelatinizing due to prolonged heating, forming a "hard shell" that hinders further water absorption. Data shows that when alternating bottom and side heating modes, the difference in water absorption rate can be controlled within 5%, far lower than the 15%-20% with single bottom heating. The goal of the heating stage is to quickly reach the gelatinization temperature within the pot, shortening the heating time; therefore, a full heating mode is used. The gelatinization of rice starch requires a rapid breakthrough of the gelatinization initiation temperature of 70℃. In full heating mode, the heating frequency is 30kHz, and the power is 1300-2000W. Utilizing the overall magnetic field coverage of the dual coils, the bottom and sides of the inner pot are simultaneously and rapidly heated, raising the internal temperature from 60℃ to 100℃ within 3-5 minutes. This saves 40% of the time compared to bottom heating alone, improving energy efficiency. Simultaneously, the 30kHz high-frequency "concentrated surface heating" characteristic quickly raises the surface temperature of the inner pot, promoting rapid water circulation and preparing for subsequent boiling. The goal of the boiling stage is continuous boiling to ensure complete starch gelatinization while avoiding localized overflow. Therefore, alternating bottom and side heating modes are used, switching frequently at 10-20 second intervals. The boiling temperature needs to be maintained at around 100℃, but continuous strong boiling that could cause rice water to overflow must be avoided. Alternating heating, such as 900W at the bottom and 1200W at the sides, creates a "bottom-push - side-guide" cycle: bottom heating causes the rice water in the center to rise, while side heating pulls the rice water from the edges towards the center. This ensures thorough boiling and more complete gelatinization of the starch in the rice grains, while avoiding overflow caused by strong boiling in a single area. Simultaneously, the power control module on the main control circuit board can adjust the heating power in real time according to the boiling intensity. For example, if boiling is too strong, the heating power is reduced to 600W or 500W to balance gelatinization and safety. The goal of the simmering or heat-keeping stage is to lock in moisture and make the rice grains plump and elastic. Therefore, this stage primarily uses bottom heating, supplemented by side heating, and alternates between bottom and side heating modes, but with a long interval between the alternations, preferably every 2-3 minutes. During the simmering stage, the temperature needs to be lowered to 70-80℃ to allow the rice grains to "soften" during heat preservation, meaning the starch molecules rearrange themselves. The system primarily uses bottom heating at 500-600W to prevent the top grains from drying out due to rapid heat loss, while side heating at 300-600W supplements the heat to the sides, preventing the edges from becoming hard in the center due to low temperature. Experiments have shown that alternating between bottom and side heating modes during this stage can control the moisture content difference of the cooked rice to within 3%, increasing the plumpness of the rice grains by 20%.

[0088] As one possible implementation of this application, when cooking rice, the cooking appliance typically handles different types of rice and / or different types of cooked rice. Different types of rice may require slightly different cooking procedures or characteristics; for example, indica rice requires a stronger boiling point, while japonica rice requires a longer water absorption time. Therefore, by adjusting the heating power of the bottom heating mode and / or side heating mode and / or full heating mode, the cooking appliance of this application can adapt to the cooking needs of various different types of rice, improving its adaptability. Of course, the cooking appliance can also be adapted to various different types of rice or cooked rice by adjusting the duration of each cooking stage.

[0089] As one possible implementation of this application, when alternating between bottom heating mode and side heating mode, the actual operation involves switching between the two modes. The bottom heating mode is generated by driving the first coil to produce an alternating magnetic field of a first frequency, while the side heating mode is generated by driving the second coil to produce an alternating magnetic field of a second frequency. Therefore, switching between the bottom heating mode and side heating mode is essentially switching between the first and second coils. This switching is achieved using one IGBT and two relays. The two relays are connected to the branches of the first and second coils, respectively. When switching between bottom heating mode and side heating mode is required, the IGBT is first turned off, and then the relay connected to the corresponding coil of the original heating mode is turned off. For example, if the current heating mode is bottom heating mode and a switch to side heating mode is needed, the IGBT is first turned off, and then the relay connected to the branch of the first coil is turned off. In this way, on the one hand, arc-free interruption of the relay can be achieved, protecting the relay: when the IGBT is turned off first, the current in the coil can decay to zero through a safe path. At this time, when the relay switches again, no current flows between the contacts, avoiding arcing, greatly reducing contact erosion, significantly extending the mechanical and electrical life of the relay, and reducing maintenance costs. On the other hand, it also avoids the fatal induced voltage spikes of the IGBT, preventing the IGBT from being damaged: the relay that is turned off first will forcibly cut off the inductive load current, generating a high voltage spike. However, if the IGBT is turned off first, its matching protection circuit, such as the freewheeling diode and the absorption circuit, can effectively clamp and absorb the induced voltage generated during turn-off, ensuring that the IGBT operates within a safe voltage range and preventing overvoltage breakdown. On the other hand, turning off the IGBT first and then the relay can improve the overall stability and reliability of the system, making the switching process of the heating mode controllable and orderly: the IGBT is responsible for precisely controlling the power on and off, while the relay is only responsible for switching the path in the absence of current, choosing whether to connect the first coil or the second coil. Each performs its own function, which can reduce electromagnetic interference, avoid unpredictable circuit states, and make the system work more stable and reliable.

[0090] This application, through a split coil structure and variable frequency heating mode design, combined with the law of electromagnetic induction, solves many defects of existing IH heating coils, with the following specific benefits:

[0091] In bottom heating mode / side heating mode, preferably, f1 = 20kHz, f2 = 20kHz:

[0092] The vortex can penetrate to a slightly deeper layer of the inner pot, and the heat is conducted from the inside of the inner pot to the outside, avoiding the temperature difference problem of "the surface heating up first and the inside heating up later". For example, during the water absorption stage of rice, a certain heating depth can allow the heat from the bottom and sides of the inner pot to penetrate evenly into the rice grains, ensuring that each grain of rice absorbs water fully; when cooking porridge, gentle deep heating can prevent the bottom grains from burning due to localized high temperature, and the surface porridge from being half-cooked due to insufficient heating, completely solving the core pain points of traditional heating: "half-cooked" or "burnt bottom".

[0093] Full heating mode, preferably, f3 = 30kHz:

[0094] The vortex and heat are highly concentrated on the surface of the inner pot, significantly increasing the power density, or heat per unit area. For example, when boiling water, the concentrated heat on the surface can quickly raise the water temperature on the surface of the inner pot, thereby driving the overall water temperature to rise rapidly. Combined with the overall coverage of the bottom and side dual coils, it achieves "rapid surface heat conduction and synchronous overall heating", perfectly meeting the needs of cooking scenarios such as rapid boiling and quick reheating of cold rice.

[0095] This application achieves flexible selection of the heating area through a separate design of the first and second coils: In bottom heating mode, the first coil, for example at a frequency of 20kHz, heats the bottom of the inner pot slightly deeper, with a small temperature difference between the upper and lower layers, allowing for precise frying, stir-frying, and searing of the food at the bottom of the pot, ensuring even heating; in side heating mode, the second coil, for example at a frequency of 20kHz, gently heats the food on the sides, preventing the bottom from burning while the surface remains uncooked during stewing; in full heating mode, the two coils are connected in parallel, for example at a frequency of 30kHz, forming overall heating, quickly raising the overall temperature inside the pot to meet the needs of boiling water and rapid boiling. The automatic switching between these three heating modes allows the rice cooker to adapt to diverse cooking scenarios such as frying, stir-frying, searing, stewing, boiling, and braising, breaking the limitations of poor adaptability of existing cooking appliances, improving the precision of cooking results, and enhancing the user experience.

[0096] Specifically, the cooking appliance of this application can also achieve:

[0097] Optimized thermal response speed, balancing rapid heating and stable temperature control: The full heating mode uses a third frequency of 30kHz. At this frequency, the power density is concentrated on the surface of the inner pot, allowing the surface temperature to rise rapidly and resulting in a fast thermal response. Experimental data shows that, at the same power (e.g., 1200W), using the 30kHz full heating mode to boil 2L of water from 25℃ to 100℃ is reduced by approximately 20%-25% compared to the existing single 20kHz bottom coil. This quickly meets the needs of scenarios requiring rapid reheating, such as briefly raising the temperature to enhance aroma during rice cooking or quickly compensating for voltage fluctuations. The bottom heating and side heating modes use the first and second frequencies of 20kHz, respectively. The current is more dispersed within the metal inner pot, resulting in a relatively lower power density and a slower temperature rise. Although the thermal response is slower, temperature fluctuations are smaller, with the fluctuation range controllable within ±2℃. During the later stages of rice gelatinization, the temperature can be stably maintained at around 100℃, effectively preventing scorching and meeting the requirements for precise temperature control.

[0098] Reduced energy consumption and improved energy efficiency: According to the principle of electromagnetic induction energy conversion, frequency affects the energy coupling efficiency between the coil and the inner pot. The 30kHz frequency in full heating mode is closer to the optimal resonant frequency of the IH system, resulting in tighter energy coupling between the coil and the inner pot, and lower copper and iron losses. Experimental tests show that at an output power of 1200W, the energy efficiency ratio (the ratio of effective heat to input electrical energy) at 30kHz is about 5%-8% higher than that at 20kHz, saving 5%-8% of energy consumption in the same cooking time. While the bottom heating and side heating modes use a 20kHz frequency, their energy efficiency is slightly lower than that of 30kHz. However, these modes mainly involve low-power continuous heating, such as cooking porridge or keeping warm, so their total energy consumption remains low. Moreover, the advantage of uniform heating far outweighs the impact of slight differences in energy efficiency.

[0099] For any parts not mentioned in this application, existing technologies may be used or referenced.

[0100] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0101] The above description is merely an embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A cooking appliance with multiple heating modes, comprising a pot body, an inner pot disposed within the pot body, an electromagnetic coil, and a main control circuit board, wherein the main control circuit board is electrically connected to the electromagnetic coil to generate an alternating magnetic field, and the inner pot couples with the alternating magnetic field to generate an induced current to achieve heating, characterized in that, The electromagnetic coil includes a first coil located at the bottom of the inner pot and a second coil located on the side of the inner pot. The first coil and the second coil are separately arranged. The main control circuit board drives the first coil to generate an alternating magnetic field of a first frequency to form a bottom heating mode. The main control circuit board drives the second coil to generate an alternating magnetic field of a second frequency to form a side heating mode. The main control circuit board simultaneously drives the first coil and the second coil to generate an alternating magnetic field of a third frequency to form a full heating mode. The third frequency is greater than the first frequency and / or the second frequency. The coil inductance value of the second coil is greater than the coil inductance value of the first coil.

2. A cooking appliance with multiple heating modes according to claim 1, characterized in that, The first coil and the second coil are wrapped around the outside of the inner pot, the first coil having 30-40 turns and the second coil having 18-28 turns.

3. A cooking appliance with multiple heating modes according to claim 2, characterized in that, The first coil and / or the second coil are tightly wound around the outside of the inner pot, and the number of layers of the first coil and / or the second coil is greater than or equal to two.

4. A cooking appliance with multiple heating modes according to claim 1, characterized in that, The length of the first coil is 9-12m, and the length of the second coil is 14-18m.

5. A cooking appliance with multiple heating modes according to claim 1, characterized in that, The cross-sectional area of ​​the first coil and the second coil is 2-2.5 mm2.

6. A cooking appliance with multiple heating modes according to claim 5, characterized in that, The first coil and the second coil are made of 63-78 strands of aluminum wire, each strand of which has a diameter of 0.1-0.2 mm.

7. A cooking appliance with multiple heating modes according to claim 1, characterized in that, It also includes magnetic strips, which are disposed on the side of the electromagnetic coil away from the inner pot and span the electromagnetic coil. The number of magnetic strips corresponding to the first coil is 4-6, and the number of magnetic strips corresponding to the second coil is 5-7.

8. A cooking appliance with multiple heating modes according to claim 1, characterized in that, The heating power of the bottom heating mode is different from that of the side heating mode, and both the first frequency and the second frequency are in the range of 20KHZ to 30KHZ.

9. A cooking appliance with multiple heating modes according to claim 7, characterized in that, The heating power of the side heating mode is greater than that of the bottom heating mode.

10. A cooking appliance with multiple heating modes according to claim 1, characterized in that, The main control circuit board includes at least one insulated gate bipolar transistor (IGBT) and two relays, with the two relays electrically connected to the first coil and the second coil, respectively.

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