Method for the load-dependent adjustment of a microwave power in a cooking device

Abstract

The invention relates to a method for load-dependent adjustment of a microwave power in a cooking appliance (10) having a cooking chamber (14) and a microwave module (16), comprising the steps of: - determining a number of dielectric unit volumes in the cooking chamber (14); - determining a target microwave power based on the number of dielectric unit volumes; and - adjusting the microwave power of the microwave module (16) based on the determined target microwave power. The invention further relates to a cooking appliance (10).

Description

[0001] The invention relates to a method for adjusting microwave power in a cooking appliance based on the load. Furthermore, the invention relates to a cooking appliance.

[0002] Many traditional cooking appliances that heat food primarily with hot air or similar heating devices deliver reproducible cooking results, particularly regardless of the load size. This is due to the fact that users have an intuitive understanding of how a cooking process carried out using hot air needs to be adapted to a changed load size and / or how a cooking process needs to be extended if a target cooking chamber climate or target heating output cannot be achieved, provided an intelligent cooking process is used. In simple terms, a user gets at least approximately the same cooking results with different cooking processes, regardless of whether they place, for example, half a tray of steaks (= 3 steaks) or 3 trays of steaks (= 18 steaks) in the cooking chamber. This is because the energy input into the food or the heating element is constant.The food is scaled to the surface using hot air, allowing the user to make the necessary adjustments. If the desired cooking chamber climate is achievable, the adjustment can be made automatically, particularly taking into account a recipe selection and / or a measured (core) temperature profile of the food(s).

[0003] However, in professional and commercial kitchens, cooking appliances that can cook food in different or combined ways are increasingly being used. In addition to traditional methods such as convection and / or steam, modern cooking appliances often also use microwave sources (additionally) that introduce energy into the food(s) using electromagnetic radiation to (additionally) heat them. Magnetrons and semiconductor components can be used as microwave sources.

[0004] If microwaves are (additionally) used in the cooking chamber, the reproducibility of the cooking results deteriorates for different load sizes. This is due to the lack of a linear scalability between microwave energy and load size, which is not intuitive for the user. Ultimately, this phenomenon is due to the competitive behavior of the foods being cooked among each other in the microwave field and the load-dependent efficiency.

[0005] For example, with 2 kW of available microwave power, half a tray of steaks (3 steaks) absorbs approximately 600 W (approximately 200 W per steak) of microwave power. Three trays of 6 steaks each, in contrast, absorb approximately 1500 W (approximately 80 W per steak). In other words, the three trays of steaks absorb less than half the power per steak compared to a load of only half a tray of steaks.

[0006] This example shows that even if a recipe works well for cooking a certain amount of food using microwaves, the amount of food cannot simply be varied. In particular, even if the recipe works well, reducing the amount of food can lead to overcooking the food(s). Increasing the load, on the other hand, carries the risk of undercooking.

[0007] The object of the invention is therefore to provide a simple and cost-effective way of ensuring a good and reproducible cooking result for different load quantities when cooking food using microwave energy.

[0008] The object is achieved according to the invention by a method for load-dependent adjustment of a microwave power in a cooking appliance with a cooking chamber and a microwave module, comprising the steps: Determining a number of dielectric unit volumes in the cooking chamber; determining a target microwave power based on the number of dielectric unit volumes; and adjusting the microwave power of the microwave module based on the determined target microwave power.

[0009] The basic idea of ​​the invention is to use a dielectric unit volume that absorbs a certain microwave power in order to be able to compare different loading scenarios (type, size, geometry and number of items to be cooked).

[0010] Based on the number of dielectric unit volumes in the cooking chamber, the microwave power required to achieve the desired cooking result can be determined. In this context, the term "number" should be understood to include fractions, especially less than 1. Thus, half a dielectric unit volume can also be present or determined.

[0011] If the same microwave power is fed into the cooking chamber per unit volume, for example, 70 W, then the individual items in the cooking chamber will each absorb the same microwave power, and the same cooking result will be achieved (assuming the same thermal environment). In other words, a reproducible cooking result is achieved regardless of the load size, even if (additional) microwave energy is fed in.

[0012] In particular, the microwave power can be self-regulating in relation to the load placed in the cooking chamber. This means that the microwave power is automatically adjusted to the amount of food in the cooking chamber. The amount is preferably detected automatically. Alternatively, it can also be specified by a user. Self-regulation reduces the effort required by the user and reduces the risk of incorrect microwave power settings.

[0013] In a variant of the method, a quality factor Q of the cooking chamber is determined in a loaded state. Based on this quality factor, the number of dielectric unit volumes in the cooking chamber is then determined.

[0014] The quality can be an approximate parameter that is determined from the scattering parameters S of the microwaves entering or leaving the cooking chamber.

[0015] The scattering parameters, in turn, are characteristic quantities of the microwave system and quantify the transmission and reflection behavior of the microwaves in the cooking chamber.

[0016] To determine the scattering parameters S, the incoming power waves a and outgoing power waves b can be measured at at least one antenna of the microwave module. The formula b=S*a applies.

[0017] For a plurality of antennas, a scattering parameter matrix results.

[0018] The approximate quality factor Q (for simplicity, we will only refer to the quality factor below) quantifies variations in the scattering parameters.

[0019] It can be determined using the following formula: Q = 1 n f ∗ n a 2 ∑ f ∑ i , k d df s ik f

[0020] These include n f the number of frequencies considered (at least one), n a the number of antennas (at least one) and s ik the entries in the scatter parameter matrix (i-th row and k-th column).

[0021] By varying the frequency, different microwave modes can be excited, each of which delivers more or less power to the food, depending, for example, on the loading scenario—i.e., the load size and the location of the food in the cooking chamber. This can be compared to scanning the food.

[0022] The consideration of the mean value over the frequencies and scattering parameter entries can be understood as a homogenization of the electric field.

[0023] The quality is therefore a parameter which characterises the absorption behaviour of the loaded or unloaded cooking chamber in a simple numerical value and which is therefore ideally suited for carrying out the method according to the invention.

[0024] In principle, it is known how the quality is determined, whereby different methods can be used for this purpose, as described, among others, in DE 10 2020 104 763 A1, DE 10 2019 127 620 A1 or DE 10 2021 131 619 A1.

[0025] Of course, the method described above for determining the (approximate) quality factor is not intended to be limiting. Other methods for determining the quality factor are also conceivable, for example, by solving Maxwell's equations.

[0026] As already explained, the quality factor can be used to determine the number of dielectric unit volumes.

[0027] A dielectric unit volume can characterize the microwave power that can be absorbed by a defined body of a material under given conditions.

[0028] For example, the dielectric unit volume can represent the same dielectric load as a water cube with an edge length of 4 cm. Of course, this is only an example and should not be considered limiting. The dielectric unit volume can be freely chosen in terms of its shape and size.

[0029] In particular, the dielectric unit volume can also characterize the dielectric load of a cuboid, especially a cube, or a sphere made of a specific material. Any cooking product can, in turn, be considered a body consisting of a defined number of unit volumes.

[0030] The use of comparatively simple geometric shapes when defining the dielectric unit volume is advantageous because this leads to less (computational) effort when carrying out the method.

[0031] It is conceivable that the dielectric unit volume is a calculated parameter, in particular determined by means of a simulation, or experimentally determined.

[0032] For example, the dielectric unit volume can be determined by calculating the total microwave power absorbable in the underlying body (cuboid, sphere, etc.). This, in turn, results from the shape of the body itself and its dielectric properties.

[0033] The dielectric unit volume can be determined, for example, by a finite element method (FEM)-based numerical simulation of the high-frequency properties (HF-FEM) of the food being cooked and / or by calculating a volume integral over the norm of the electric field in the food. For simplicity, it can be assumed that the microwaves are incident plane waves.

[0034] To improve the accuracy of the method, it is also conceivable to consider the absorption properties of the empty cooking chamber when determining the number of dielectric unit volumes. This can be achieved by determining the number of dielectric unit volumes based on a ratio of the quality factor of the cooking chamber in a loaded state to the quality factor of the cooking chamber in an unloaded state.

[0035] In a variant of the method, the number of dielectric unit volumes is determined based on a defined, in particular experimentally determined, relationship between the quality of the cooking chamber and a dielectric volume of the cooking chamber or the food to be cooked.

[0036] The dielectric volume characterizes the microwave power that can be absorbed by the (loaded) cooking chamber.

[0037] The relationship between the quality of the cooking chamber and the dielectric volume of the cooking chamber can be stored as a table or graph in the cooking appliance's memory. If the scattering parameters and the resulting quality of the loaded cooking chamber are determined based on measurements of the incoming and outgoing microwaves during (or before) a cooking process, the dielectric volume or the number of dielectric unit volumes can be directly determined by relying on the known relationship.

[0038] The number of dielectric unit volumes in the cooking chamber can therefore be determined automatically without any user intervention, which simplifies the cooking process overall.

[0039] If the number of unit volumes is known, the target microwave power can be determined based on a specified microwave target power for a single dielectric unit volume. This is technically simple to implement and less prone to errors. The target power can be a value stored in the cooking appliance's memory and / or a value specified by a user.

[0040] In one embodiment of the method, if the target microwave power is greater than a nominal power or a control-specific limit for the microwave power of the at least one microwave module, an extended cooking time is determined and set. This reliably prevents undercooking with large loads.

[0041] In this context, it is also conceivable that a heating and / or steaming device of the cooking appliance is operated at reduced power during the extended cooking time. Preferably, the power of the heating and / or steaming device is reduced so much that the food is always cooked with the same ratio of cooking energy supplied by the different energy sources. In simple terms, this prevents the food from absorbing too much heat (e.g., from hot air) during the extended cooking time, which could lead to drying out and / or overcooking.

[0042] The invention further relates to a cooking appliance with a cooking chamber and at least one microwave module, which is designed and configured to feed electromagnetic radiation into the cooking chamber in order to cook food placed in the cooking chamber using microwave energy. The cooking appliance has a control and / or evaluation unit, which is designed and configured to execute a computer program with program code means for carrying out a method according to the invention. The advantages discussed for the method apply correspondingly to the cooking appliance.

[0043] Further features and advantages of the invention will become apparent from the following description and the drawings, to which reference is made. In the drawings: Fig. 1 a schematic representation of a cooking appliance according to the invention, loaded with a food to be cooked; and Fig. 2 a graphical plot of an experimentally determined course of a dielectric volume of a cooking chamber versus the quality of the cooking chamber.

[0044] In Fig. 1 An embodiment of a cooking appliance 10 according to the invention is shown, which is loaded with several items 12 to be cooked. For simplicity, the following always refers to "the item 12" even when loaded with several items 12.

[0045] The cooking appliance 10 has a cooking chamber 14 and at least one (preferably several) microwave module(s) 16. For simplification, Fig. 1 only one microwave module 16 is shown.

[0046] The at least one microwave module 16 comprises a semiconductor microwave source ("Solid State Microwave Generator" - SSMG) and is designed and configured to feed microwave beams into the cooking chamber 14. The microwave beams can have a frequency suitable for heating the food 12 to be cooked in the cooking chamber 14. For example, the frequency is between 2.1 GHz and 2.8 GHz, in particular 2.4 GHz to 2.5 GHz, preferably approximately 2.45 GHz.

[0047] For feeding into the cooking chamber 14, the at least one microwave module 16 can be equipped with an antenna 18 and a directional coupler (not shown). However, multiple antennas 18 and directional couplers can also be provided per microwave module 16.

[0048] In addition, the at least one microwave module 16 may comprise further components or parts, for example a modulator, an amplifier, a demodulator and / or a controller (not shown).

[0049] In the exemplary embodiment, the cooking appliance 10 is a combination appliance that, in addition to the at least one microwave module 16, has various additional components for cooking the food 12, in particular hot air and / or steam sources 20 and infrared heating sources 22. Of course, this is not to be understood as limiting. Other types of heating devices are also conceivable.

[0050] Furthermore, the cooking appliance 10 in the exemplary embodiment comprises a temperature sensor 24, with which the cooking chamber temperature can be measured, as well as a fan wheel 26, which is preferably operable reversibly to homogeneously mix the cooking chamber atmosphere. This is, of course, not to be understood as limiting. Cooking appliances 10 according to the invention without a fan wheel 26 or with more than one fan wheel are also conceivable.

[0051] Furthermore, the Fig. 1 The cooking appliance 10 shown has an input device 28, for example a touch display, with which a user can make inputs, in particular to manually select a cooking program or to set and / or adjust desired cooking parameters.

[0052] In the exemplary embodiment, the cooking appliance 10 also has a control and / or evaluation unit 30 connected to the at least one microwave module 16, as well as a memory 32 in which a computer program with program code is stored. When the computer program is executed by a processor unit (not shown) of the cooking appliance 10, it causes the control and / or evaluation unit 30 to perform a method for adjusting a microwave power level depending on the load. This method is described in more detail below.

[0053] At the start of the process, the food 12 to be cooked is placed in the cooking chamber 14 of the cooking appliance 10 or is already in it.

[0054] In an initial step of the method, the control and / or evaluation unit 30 causes the at least one microwave module 16 to feed microwave radiation into the cooking chamber 14 via the at least one antenna 18, i.e., to radiate microwaves. The antenna 18 is essentially a coupling structure, i.e., a structure for coupling the microwaves.

[0055] Waves or microwaves arriving and departing via antenna 18 are detected (using the associated directional coupler). The information obtained is transmitted to the control and / or evaluation unit 30.

[0056] In a further step of the method, the control and / or evaluation unit 30 determines an (approximate) quality Q of the loaded cooking chamber 14 based on the information about the incoming and outgoing microwaves, for example based on the formulas mentioned above.

[0057] In addition, the control and / or evaluation unit 30 retrieves a previously determined quality Q 0 of the empty cooking chamber 14 from the memory 32 and forms a ratio Q / Q 0 .

[0058] The quality of the empty cooking chamber 14 can be an experimentally determined value that is permanently stored in the memory 32 of the cooking appliance 10. Alternatively, the quality of the empty cooking chamber 14 can also be determined by an empty measurement immediately before loading with food 12 and / or after (automatic) cleaning. This has the advantage of taking into account any additional components introduced into the cooking chamber 14, but is somewhat more complex for the user.

[0059] In alternative embodiments, it is also conceivable for a user to specify the quality of the loaded and / or unloaded cooking chamber 14 via the input device 28.

[0060] In a further step of the method, the control and / or evaluation unit 30 retrieves a previously defined dielectric unit volume V mw,0 from the memory 32. Alternatively, the dielectric unit volume can also be specified by a user via the input device 28.

[0061] In particular, the dielectric unit volume can also depend on the selected cooking program. For example, if steaks are being prepared during the cooking process, the dielectric unit volume can, figuratively speaking, refer to one or more steaks.

[0062] The dielectric unit volume is characterized by the microwave power that can be absorbed by a defined body (for example in the form of a sphere, a cuboid or a typical steak shape) made of a defined material (for example water, meat, etc.) under given conditions (for example at a certain microwave frequency or in a certain frequency range and / or at a certain temperature).

[0063] Put simply, the dielectric unit volume can correspond to the dielectric load of the defined body. A corresponding cooking product can then correspond to a number of such defined bodies, i.e., in terms of dielectricity or dielectric load.

[0064] In the exemplary embodiment, the dielectric unit volume is an experimentally determined parameter stored in the memory 32 of the cooking appliance 10. Alternatively, it can also be a calculated parameter, in particular a parameter determined by simulation.

[0065] Of course, several different dielectric unit volumes can also be stored in the memory 32, for example those for different cooking products such as meat, fish, pastries, etc.

[0066] In a further step of the method, the control and / or evaluation unit 30 determines a number n of dielectric unit volumes in the loaded cooking chamber 14 (i.e., for example, three trays of steaks).

[0067] For this purpose, the control and / or evaluation unit 30 in the exemplary embodiment retrieves from the memory 32 a known relationship (in this case an experimentally determined relationship) between the quality Q of the cooking chamber 14 and a dielectric volume V mw of the cooking chamber 14.

[0068] Fig. 2 shows this relationship, which was experimentally determined from several measurements, schematically using a graph 34.

[0069] Specifically, Fig. 2 the experimentally determined relationship between the dielectric volume V mw / V mw,0 normalized to the unit volume and the quality factor Q / Q 0 normalized to the empty cooking chamber 14. The measuring points 36 of the various measurements are also shown.

[0070] If the quality Q of the loaded cooking chamber 14 (determined in the process by measuring the incoming and outgoing microwaves or power waves) and thus the ratio Q / Q 0 are determined, then the Fig. 2The number n of dielectric unit volumes can be directly deduced from the relationship shown, since this corresponds directly to the dielectric volume V mw / V mw,0 normalized to the unit volume.

[0071] In other words, dielectric load detection is possible, i.e. detection of the dielectric load in the cooking chamber 14, since the number n of dielectric unit volumes can be determined.

[0072] Of course, the method of determining the number of unit volumes described above is not intended to be limiting. Alternatively, the number can also be determined by specifying or measuring the weight and / or volume of the food 12 being cooked and correlating this value(s) with the dielectric unit volume.

[0073] In a further step of the method, the control and / or evaluation unit 30 determines a target microwave power P soll of the at least one microwave module 16 based on the determined number of dielectric unit volumes.

[0074] To this end, the control and / or evaluation unit 30 first retrieves from the memory 32 a target power P target to be absorbed per dielectric unit volume, at which a good cooking result is expected. Alternatively, the target power can also be specified by a user via the input device 28 and / or specified by a recipe. In particular, the target power can be an experimentally determined value or a user-generated value.

[0075] Subsequently, the control and / or evaluation unit 30 determines, on the basis of the previously determined number n of unit volumes and the target power P target, a total power P food to be absorbed by the food 12, for example using the formula P food =n* P target.

[0076] The target microwave power P soll can then be determined from the total power P food to be absorbed by the food 12 and the quality Q / Q 0 standardized to the empty cooking chamber 14, for example using the formula P soll =P food / (1-Q / Q empty ).

[0077] In the event that the target microwave power P target is less than or equal to a nominal power PN of the at least one microwave module 16 (for example 2 kW), the control and / or evaluation unit 30 sets the microwave power of the at least one microwave module 16 based on the target microwave power in a further step of the method.

[0078] However, if the target microwave power is greater than the rated power of the at least one microwave module 16, the control and / or evaluation unit 30 redetermines an extended cooking time t . This ensures that the food 12 is undercooked due to the limited power of the at least one microwave module 16 and an excessively short cooking time.

[0079] In particular, it can be provided that the at least one microwave module 16 is operated at the rated power during the extended cooking time.

[0080] In the exemplary embodiment, the control and / or evaluation unit 30 recalculates the extended cooking time t based on the cooking time t soll originally intended for the cooking process or by the selected recipe, as well as the target microwave power P soll . For this purpose, the same energy quantities to be input are assumed for the originally intended and the extended cooking process, and the formula P soll *t soll = PN *t is reapplied.

[0081] Taking into account the relationships between the individual parameters explained above, the formula is: t new = t target * n*P target / PN (1-Q / Q empty).

[0082] In the exemplary embodiment, the hot air and / or steam sources 20 and the infrared heating sources 22 (collectively also referred to as heating and / or steam devices 38) are operated at reduced power during the extended cooking time. This ensures that the food 12 does not dry out or overcook during cooking with the extended cooking time.

[0083] Preferably, all of the aforementioned steps of the method run automatically, for example, by the control and / or evaluation unit (30) of the cooking appliance 10. This allows the microwave power to self-regulate in relation to the load placed in the cooking chamber 14. This significantly reduces the risk of incorrect settings. Furthermore, the user is not faced with the problem of adjusting the microwave power in a way that is not intuitive for them.

[0084] This allows for reproducible cooking results without additional user input. In particular, this also enables precise target temperature cooking for different load scenarios (e.g., heating 100 ml of milk or 1 liter of milk to a specified temperature) without having to specify the load size separately.

[0085] Of course, alternative embodiments are also conceivable in which one or more individual specifications are made by a user.

Claims

1. A method for load-dependent adjustment of a microwave power in a cooking appliance (10) having a cooking chamber (14) and a microwave module (16), comprising the steps of: - determining a number of dielectric unit volumes in the cooking chamber (14); - determining a target microwave power based on the number of dielectric unit volumes; and - adjusting the microwave power of the microwave module (16) based on the determined target microwave power.

2. Method according to claim 1, wherein the microwave power is self-regulating with respect to a load introduced into the cooking chamber (14).

3. The method according to claim 1 or 2, wherein a quality of the cooking chamber (14) in a loaded state is determined, and wherein the number of dielectric unit volumes in the cooking chamber (14) is determined based on the quality.

4. Method according to one of the preceding claims, wherein the dielectric unit volume is characterized by a microwave power absorbable by a defined body of material under predetermined conditions.

5. A method according to any one of the preceding claims, wherein the dielectric unit volume is a calculated parameter.

6. The method according to claim 5, wherein the dielectric unit volume has been determined by calculating a volume integral over the norm of the electric field in the food to be cooked.

7. The method of claim 5, wherein the dielectric unit volume is a parameter calculated by means of a simulation.

8. The method according to claim 7, wherein the dielectric unit volume has been calculated by a numerical simulation of high-frequency properties of the food to be cooked based on the finite element method.

9. The method according to any one of claims 1 to 4, wherein the dielectric unit volume is an experimentally determined parameter.

10. Method according to one of the preceding claims, wherein the number of dielectric unit volumes is determined based on a defined relationship between the quality of the cooking chamber (14) and a dielectric volume of the food to be cooked (12).

11. Method according to claim 10, characterized in that the relationship is an experimentally determined relationship.

12. Method according to one of the preceding claims, wherein the desired microwave power is determined based on a microwave target power specified for a single dielectric unit volume.

13. Method according to one of the preceding claims, wherein in the event that the target microwave power is greater than a nominal power of the microwave module (16), an extended cooking time is determined and set.

14. The method according to claim 13, wherein during the extended cooking time a heating and / or steaming device (38) of the cooking appliance (10) is operated at reduced power.

15. Cooking appliance with a cooking chamber (14), at least one microwave module (16) which is designed and configured to feed electromagnetic radiation into the cooking chamber (14) in order to cook a food item (12) placed in the cooking chamber (14) by means of microwave energy, and a control and / or evaluation unit (30) which is designed and configured to execute a computer program with program code means for carrying out a method according to one of claims 1 to 14.

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