Combination cooking appliance and method for cooking food in a combination cooking appliance

Abstract

The invention relates to a method for cooking food (20) in a combination cooking appliance (10) with a fan (28) and a semiconductor microwave unit (24) for generating microwaves. The method comprises the following steps: - determining an angular position of the fan (28), - selecting an excitation vector for the semiconductor microwave unit (24) based on the determined angular position from a set of different excitation vectors, wherein the excitation vector includes at least control parameters for the phase of the microwaves to be generated, and - operating the semiconductor microwave unit (24) with the selected excitation vector. A combination cooking appliance (10) is also described.

Description

[0001] The invention relates to a method for cooking food in a combination cooking appliance comprising a fan and a semiconductor microwave unit for generating microwaves. The invention further relates to a combination cooking appliance for cooking food.

[0002] Cooking appliances are known from the prior art that, in addition to conventional energy sources such as a hot air device and a steam generator, also have a microwave unit. This microwave unit can introduce energy into the food in the cooking chamber to cook it. Such cooking appliances are also called combination cooking appliances because they combine several different energy sources. Combination cooking appliances are typically used in professional kitchens, for example, in canteens or restaurants.

[0003] Combination ovens are divided into two classes, distinguished by the type of microwave unit they use. The first class, representing the traditional approach, employs magnetrons as microwave units. However, semiconductor microwave units, also known as SSC ("Solid State Cooking" hardware), can be used instead of magnetrons. In this case, the semiconductor components replace the traditionally used magnetrons to generate the microwaves.

[0004] Regardless of their specific type, combination ovens feature a fan that rotates during operation to circulate the air within the cooking chamber, ensuring the desired energy transfer of hot air and / or steam to the food. However, the rotating fan also significantly impacts the microwave field generated by the microwave unit, as this too is affected by the turbulence. In effect, the fan acts as a mode mixer.

[0005] While first-class combination ovens, which use a magnetron as their microwave unit, can utilize the rotating fan to ensure a consistent energy input from the microwaves, the rotating fan has a disruptive effect in second-class combination ovens, i.e., those with a semiconductor microwave unit. This is because, unlike the magnetron, which always operates at its optimal point, the semiconductor microwave unit can only react to the changing microwave field with a delay, as a suitable operating point must first be determined.

[0006] The microwave field in the cooking chamber changes with the speed of the fan, resulting in rapid fluctuations that the semiconductor microwave unit cannot easily keep up with. Consequently, it can no longer operate at its optimal point, thus reducing efficiency. A large portion of the input power is therefore reflected directly back out of the cooking chamber and absorbed by the semiconductor microwave unit, which in the worst case leads to such a high level of reflection that the semiconductor microwave unit shuts down for safety reasons.

[0007] For this reason, it is known from the prior art that in combination ovens with a semiconductor microwave unit, the fan is shielded to minimize its influence on the microwave field in the cooking chamber. The microwave field in the cooking chamber is not affected, or only minimally affected, by the rotating fan, as the shielding prevents any influence from the rotating fan. Any changes in the microwave field that do occur are therefore not due to the rotation of the fan, but solely to other factors, such as the expansion of the inner housing and / or changes in the food being cooked due to the increasing temperature in the cooking chamber. However, these are slow processes compared to the rotation of the fan, to which the semiconductor microwave unit can respond with algorithms, as semiconductor microwave units are specifically designed to follow these slow changes.

[0008] However, the shielding makes the manufacturing and maintenance of the combination oven more complex and requires more effort. For example, the shielding must be electrically connected to an inner housing of the oven that defines the cooking chamber. The shielding also affects the operation of the oven, particularly its hot air performance, as it influences the evenness and velocity of the airflow.

[0009] German patent DE 10 2019 201 332 A1 relates to a household cooking appliance with an integrated microwave unit comprising a semiconductor-based microwave generator and a rotating antenna or wobbler. Microwave radiation is directed into a cooking chamber via the rotating antenna or wobbler. Furthermore, the microwave unit is designed to adjust at least one parameter to alter the field distribution within the cooking chamber. This parameter may be the phase of the microwave radiation or the rotational speed of the rotating antenna or wobbler.

[0010] A method for operating a household microwave oven is known from DE 102019 210 119 A1. In this method, microwaves are fed into the cooking chamber, settings for the microwave field distribution in the cooking chamber are changed, and microwave leakage radiation escaping from the cooking chamber is measured. A mode variation of the microwave radiation is then performed based on the measured leakage radiation.

[0011] Furthermore, a method for detecting at least one loading parameter of a cooking chamber using electromagnetic radiation is known from DE 10 2018 105 232 A1. In this method, the angular position of the fan wheel is determined using coherent electromagnetic radiation. The phase and amplitude of the microwaves can also be changed via a control and evaluation unit associated with the cooking appliance.

[0012] Therefore, the object of the invention is to provide an improved operation of the combination cooking appliance as well as an improved combination cooking appliance, wherein simultaneous operation of the semiconductor microwave unit and the fan wheel is possible without the aforementioned disadvantages.

[0013] The problem is solved according to the invention by a method for cooking food in a combination cooking appliance with a fan wheel and a semiconductor microwave unit for generating microwaves. The method comprises the following steps: Determining an angular position of the fan wheel, selecting an excitation vector for the semiconductor microwave unit based on the determined angular position from a set of different excitation vectors, wherein the excitation vector includes at least control parameters for the phase of the microwaves to be generated, and operating the semiconductor microwave unit with the selected excitation vector.

[0014] Furthermore, the object of the invention is achieved by a combination cooking appliance for cooking food, comprising a fan wheel, a control and evaluation unit, and a semiconductor microwave unit. The control and evaluation unit is configured to determine the current angular position of the fan wheel. The semiconductor microwave unit is configured to operate in several different operating modes. The control and evaluation unit is further configured to control the semiconductor microwave unit based on the determined angular position such that the semiconductor microwave unit is in a selected operating mode based on the determined angular position.

[0015] The basic idea of ​​the invention is that, based on the determined angular position of the fan wheel, the semiconductor microwave unit is controlled accordingly. This allows, for example, the generation of a microwave field adapted to the fan wheel's angular position by the semiconductor microwave unit, enabling it to operate at its optimal operating point. In other words, the rotating fan wheel is divided into numerous individual snapshots during operation, each related to the fan wheel's angular position. A corresponding excitation vector for the semiconductor microwave unit can be provided for each of these snapshots. The appropriate excitation vector can then be selected to control the semiconductor microwave unit for the specific snapshot of the fan wheel, i.e., the respective angular position of the fan wheel.

[0016] This allows the food to be cooked or heated more evenly, as the microwaves are generated according to the specific angle of the fan. At the same time, it is not necessary to shield the fan, thus improving the energy input from at least one conventional energy source, i.e., the hot air and / or steam function. This is possible because the semiconductor microwave unit is controlled based on the angle of the fan. The different excitation vectors available are therefore angle-dependent, as they depend on the angle of the fan.The angle-dependent excitation vectors are specified in a sequence within the set of excitation vectors, since each excitation vector is assigned to an angular segment of the fan wheel's rotation. These segments necessarily follow one another because the fan wheel cannot change its angular position abruptly. An angular segment is understood to be a range of angles, for example, a rotation of the fan wheel by 10°, 3°, or 0.9°.

[0017] In principle, a semiconductor microwave unit comprises a control module and at least one power module, and in particular, several power modules. The control module contains corresponding algorithms that are selected according to the chosen cooking program or cooking process to provide energy input via microwaves. These algorithms serve to establish a basic setting for the semiconductor microwave unit based on the selected cooking program or process. The algorithms react to slowly changing conditions caused by the heating of the cooking chamber and / or the food being cooked. In contrast, the rotating fan wheel represents a rapid and periodic change that cannot be represented by the algorithms in the control module.

[0018] The control module controls at least one power module, with the corresponding control being angle-dependent, i.e., dependent on the detected angular position of the fan wheel. This angle-dependent control of the at least one power module ensures that the rapid changes occurring due to the rotating fan wheel can be compensated for.

[0019] The control and evaluation unit of the combination cooking appliance can be provided by the control module.

[0020] In addition to the phase control parameter, the excitation vectors can also include control parameters for amplitude, pulse width, excitation frequency, and / or frequency of the microwaves to be generated. Accordingly, the control module adjusts the phase, amplitude, pulse width, excitation frequency, and / or frequency of the microwaves depending on the detected angular position.

[0021] The basic principle is that an excitation vector, based on the determined angular position of the fan wheel, is assigned to a defined time slot corresponding to the period of the fan wheel's rotation. This time slot represents the duration the fan wheel requires to traverse the corresponding angular segment. Therefore, the time slot depends on the period (or speed) of the fan wheel and the number of segments. The excitation vector is then applied to the time slot corresponding to the period.

[0022] The invention utilizes the fact that the rotation of the fan wheel is a cyclical process for controlling the semiconductor microwave unit, so that differently matched excitation vectors can be used for the different angular positions, which ensure the optimal operating point of the semiconductor microwave unit at the respective angular position of the fan wheel.

[0023] The optimal operating point depends on the desired purpose. Therefore, the optimal operating point can be one that is optimal in terms of energy input, meaning the semiconductor microwave unit delivers the highest energy input. The operating point can also be optimal in terms of efficiency, ensuring maximum efficiency at that point. Efficiency is frequency-dependent. Similarly, the optimal operating point can be chosen for uniformity, thus avoiding so-called "sweet spots." This can be achieved by selectively using different excitation frequencies, thereby preventing the formation of a "sweet spot."

[0024] The semiconductor microwave unit also has different operating modes that can be selected depending on the operating mode of the combination cooking appliance, with an additional selection based on the determined angular position of the fan wheel, so that angle-dependent control of the semiconductor microwave unit takes place.

[0025] The entire rotation of the fan wheel can be divided into several angular segments, with each of these segments corresponding to a specific operating mode of the semiconductor microwave unit. Therefore, it is possible for the semiconductor microwave unit to operate in several different modes during a single rotation of the fan wheel, ensuring efficient cooking of the food.

[0026] One aspect stipulates that the set of distinct excitation vectors covers a complete rotation of the fan wheel, which is divided into several angular segments. Accordingly, one period of the fan wheel, i.e., the time the fan wheel requires to complete one full rotation, is divided into several time intervals, also referred to as time slots. Each of these time slots is assigned a unique excitation vector from the set of distinct excitation vectors. This ensures that an excitation vector is available for each angular segment, guaranteeing the operation of the semiconductor microwave unit at its optimal operating point.

[0027] Another aspect stipulates that the selected excitation vector is constant for a defined angular segment of the rotating fan wheel, where the angular segment is less than 360°, in particular less than 10°, preferably less than 1°. A complete rotation of the fan wheel is divided into different angular segments, which can be of equal or different sizes. Each of the different angular segments is assigned a corresponding excitation vector that is constant over the respective angular segment. Thus, if the angular segment covers a range of 10°, it is ensured that the excitation vector of the semiconductor microwave unit is kept constant during the duration of the fan wheel rotation required for the 10° angular range.

[0028] The angular position of the fan wheel can be measured using a rotary encoder, calculated based on the fan wheel's rotational speed and a reference pulse, or derived from measurements of scattering parameters at a fixed frequency over the duration of one fan wheel revolution. Thus, various methods are available for determining the respective angular position of the fan wheel. The rotary encoder, which can also be called an angle encoder, is either integrated into the fan wheel's drive mechanism or mounted on a drive shaft that powers the fan wheel. The rotary encoder can provide a signal from which the fan wheel's direction of rotation, the number of complete revolutions, and / or individual angular increments can be directly derived.The corresponding signal from the rotary encoder, i.e., the rotary encoder signal, is processed, for example, by the semiconductor microwave unit to select the appropriate operating mode, in particular the respective excitation vector.

[0029] This creates a coupling between the semiconductor microwave unit and the rotary encoder, which ensures real-time control of the semiconductor microwave unit.

[0030] For example, the rotary encoder signal provides a large number of pulses per revolution of the fan wheel, which are aggregated into a smaller number of pulses, thus reducing the resolution accordingly. This results in a simplified control of the semiconductor microwave unit. For example, the carrier signal provides 4096 pulses, which are converted into 400 pulses per revolution of the fan wheel, so that a full revolution of the fan wheel is divided into 400 angular segments, each correspondingly assigned 400 different excitation vectors. In other words, the set of different excitation vectors thus comprises 400 different excitation vectors, so that one angular segment is smaller than 1°, namely 0.9°.

[0031] Alternatively, the respective angular position can be calculated via the rotational speed of the fan wheel, which is known to the combination cooking appliance, in particular the control and evaluation unit, since the combination cooking appliance controls the fan wheel accordingly, as well as a reference pulse.

[0032] An absolute angle value can be determined, although a relative angle value is sufficient for controlling the semiconductor microwave unit.

[0033] Alternatively, the angular position of the fan wheel can be derived from measurements of scattering parameters (S-parameters), although this is an estimate. The waves used to calculate the scattering parameters must be measured at a fixed frequency over the duration of a complete rotation of the fan wheel and then analyzed; that is, the forward-propagating waves (emitted waves) and the backward-propagating waves (reflected waves). In the time domain, distinct or prominent points can be observed in the scattering parameters that correspond to angular positions of the fan wheel, so that the rotational speed and the angle can be derived from their periodicity. Using the measured scattering parameters, the best excitation vectors for the respective angular position can then be selected.

[0034] Another aspect involves determining the direction of rotation of the fan wheel, whereby this determined direction dictates the sequence of excitation vectors within the set of different excitation vectors. In this sense, the excitation vectors of a set are arranged in a defined order, so that the excitation vectors of the set are processed sequentially. This occurs based on a clock signal that depends on the determined angular position of the fan wheel. If the direction of rotation of the fan wheel changes during operation, for example, in reversible operation, the sequence of excitation vectors also changes accordingly. Thus, with the change in the direction of rotation of the fan wheel, the processing direction of the set of excitation vectors also changes.

[0035] In other words, the excitation vectors are continuously indexed, with the excitation vectors with increasing indices used for counterclockwise rotation of the fan wheel. If the fan wheel rotates clockwise after a change in direction, the excitation vectors with decreasing indices are used.

[0036] The rotary encoder signal can generally consist of two trigger signals, which can be used to determine the direction of rotation of the fan wheel. Depending on whether the first trigger signal is detected before the second, the corresponding direction of rotation of the fan wheel can be determined.

[0037] The rotary encoder can be designed as an incremental encoder.

[0038] Another aspect involves the calculation or updating of the excitation vectors based on a control system. This allows the system to react to slow changes, such as those caused by the heating of an inner chamber of the combination oven or the heating of the food being cooked. In such cases, the intended excitation vectors are recalculated or updated by the control system (control algorithm). This ensures stable operation of the semiconductor microwave unit.

[0039] Another aspect involves selecting the set of different excitation vectors from several different sets. These sets can differ from each other in just one excitation vector, i.e., a differently controlled angular segment during the fan wheel's rotation. In principle, the different excitation vectors for a single angular segment, and especially the different sets of excitation vectors, can be used to ensure increased diversity, resulting in more uniform heating of the food. The set can be switched between the individual fan wheel rotations, for example, alternately.

[0040] Furthermore, the number of excitation vectors can vary between the different sets, so that, for example, 400 excitation vectors are provided for a first set, whereas only 200 excitation vectors are provided for a second set.

[0041] The different sets can also react to acceleration or deceleration of the fan wheel and the associated change in its rotational speed. For example, when the fan wheel is stationary or just before it comes to a standstill, a set with fewer excitation vectors is used. Typically, however, the length of the time slots changes during acceleration or deceleration, so they are compressed or stretched accordingly. The absolute number of time slots, however, remains constant.

[0042] Basically, the different sets are intended to react to the slow changes that are calculated or determined accordingly by the algorithms.

[0043] Selecting the respective set can also be referred to as updating the excitation vectors or updating the change vectors.

[0044] Furthermore, the corresponding set can be reselected from several different sets based on a predetermined time, a change in a dielectric property within the cooking chamber of the combination oven, and / or continuously. This allows the system to react to slow changes within the cooking chamber, updating the angle-dependent excitation vectors, and in particular the corresponding sets. This update of the excitation vectors can be achieved using three different mechanisms.

[0045] If the update occurs after a specific time, for example, 30 seconds, the excitation vectors are updated rigidly, which can be linked to an ongoing cooking program. However, this method cannot react to changes that fall outside the initial assumptions. To be able to react to such changes, a change in the dielectric properties within the cooking chamber of the combination oven can be taken into account, enabling appropriate monitoring. For example, changes in the scattering parameters are also considered, with a change in the excitation vectors being required if the change exceeds a threshold value.

[0046] Even if the reflected power in a time slot is significantly higher than expected, especially if it exceeds a threshold, an update can be requested for that time slot. For example, the input and reflected power are measured with each application of the excitation vector, i.e., with each rotation, and transmitted to the control and evaluation unit.

[0047] As explained above, the update can also be limited to individual angular segments, i.e., individual excitation vectors. Alternatively, a continuous update can be performed, whereby the corresponding angular segments of the fan wheel are continuously remeasured, i.e., in a measurement operation mode of the semiconductor microwave unit. It is also possible to remeasure only one angular segment at a time to avoid excessively reducing the energy input from the semiconductor microwave unit. In particular, a small number of angular segments are remeasured.

[0048] One aspect stipulates that the several different operating modes of the semiconductor microwave unit include an idle operating mode, a measurement operating mode, and a heating operating mode.

[0049] In heating mode, the semiconductor microwave unit is operated in such a way that a microwave field is generated to heat the food by means of the excitation vectors.

[0050] In measurement mode, microwaves are fed into the cooking chamber via the semiconductor microwave unit to perform, for example, a scattering parameter measurement. This scattering parameter measurement can be used to calculate the excitation vectors to be used in the heating mode. Similarly, measurement mode can be used to determine whether the dielectric properties of the cooking chamber have changed, for example, due to a change in the properties of the food being cooked or a new load being added to the cooking chamber.

[0051] A change in the dielectric properties of the cooking chamber can also be detected due to a change in the resonance behavior of a sensor, for example due to a change in the resonance behavior of a temperature sensor, in particular a core temperature probe.

[0052] In idle mode, the semiconductor microwave unit is not activated, so no energy is fed from the semiconductor microwave unit into the cooking chamber. Likewise, no microwaves used for scanning or sensing are fed into the cooking chamber in idle mode.

[0053] As explained above, the semiconductor microwave unit can operate in different modes during a single rotation of the fan wheel. For example, in the first time slot or angular segment, the semiconductor microwave unit operates in a measurement mode, while in the subsequent time slot or angular segment, it operates in a heating mode. This can depend, in particular, on the required power output of the semiconductor microwave unit. For instance, with a power requirement of 75%, 75% of the available angular segments are used for heating the food (heating mode), while the remaining 25% are used for the measurement mode.The corresponding assignment of the operating modes to the available angular segments is dynamic, particularly depending on the performance requirements.

[0054] Therefore, the control and evaluation unit can be configured to vary the operating modes of the semiconductor microwave unit within a complete rotation of the fan wheel and / or to vary the operating modes for the same angular segment of two consecutive rotations of the fan wheel. This implements a correspondingly efficient power control of the semiconductor microwave unit, as the allocation of angular segments is based on the desired power output. For example, a specific angular segment can be active in a certain number of the available sets of excitation vectors, whereas that same angular segment is not active for other sets.

[0055] Another aspect stipulates that the semiconductor microwave unit comprises a control module and several power modules, each of which communicates with the control module. Each power module is assigned a set of different excitation vectors. The control module is configured to provide the power modules with a common frequency reference and to control them using a clock signal dependent on the detected angular position, in order to select an excitation vector from the set of different excitation vectors.

[0056] This concerns the heating operation mode of the semiconductor microwave unit, in which the control module of the semiconductor microwave unit controls the power modules to provide the selected excitation vectors for generating the microwaves. The detected angular position of the fan wheel is used to generate the clock signal with which the control module controls the individual power modules. This results in a clock-wise switching of the excitation vectors from the set of different excitation vectors at each power module. In other words, the sequence of excitation vectors is processed clock-wise, namely in response to the clock signal. The clock signal depends on the speed of the fan wheel, so the clock signal is adjusted or scaled when the fan wheel rotates faster or slower.

[0057] The power modules can each have at least one sensor configured to detect forward-propagating and / or reverse-propagating waves. A suitable directional coupler can be provided for this purpose to isolate the forward-propagating and reverse-propagating waves. This allows for the measurement of relevant scattering parameters, particularly angle-dependent ones, i.e., dependent on the angular position of the fan wheel.

[0058] In principle, each power module within each angular segment can emit a microwave signal, with the other power modules of the semiconductor microwave unit receiving the corresponding reflected signal. The frequency at which the transmitting power module transmits is set or predefined by the control module, so that the set frequency applies to the entire angular segment. The subsequent angular segment, in which a corresponding scattering parameter measurement can also be performed, may already have a different frequency.

[0059] It is also possible to measure several frequencies sequentially within a single angular segment. This is particularly feasible at low fan speeds.

[0060] During each angular segment, the forward-propagating wave from the transmitting power module is measured, as is the reverse-propagating wave at all other power modules. The scattering parameters can then be calculated from this data, specifically from the ratio of reflected to forward waves. The resulting data, which describe the scattering parameters, can be forwarded to the control module, which calculates or updates the existing excitation vectors based on these parameters. Similarly, any dielectric load present in the cooking chamber, or changes in it, can be detected, effectively creating a virtual sensor.

[0061] If an angular segment is to be measured for several different frequencies, this angular segment must be measured in successive or multiple revolutions of the fan wheel. For example, if 100 different frequency points are to be measured for the same angular segment, 100 revolutions of the fan wheel are necessary to obtain the corresponding data.

[0062] Alternatively, the obtained measurement data can be interpolated or extrapolated along the frequency axis or along the time axis, thereby reducing the required measurement time to achieve the desired frequency resolution. For example, a frequency is measured only in every second time slot, with interpolation taking place in between.

[0063] As already explained, at slow speeds or when the fan wheel is stationary, it is also possible to measure several frequencies in one angular segment or one after the other.

[0064] The control module of the semiconductor microwave unit executes the respective algorithms asynchronously to the clock signal. If a heating or measurement operation mode is to be executed, for example, due to a recipe or control by the control and evaluation unit of the combination oven, corresponding control commands for selected angular segments are sent to the power modules, and a corresponding frequency reference is provided, which sets the frequency appropriate for the angular segment. The next time the corresponding angular segment occurs, for example, during the next rotation of the fan wheel, the corresponding control command is executed, such as the corresponding excitation vector in heating mode.

[0065] The semiconductor microwave unit can be modularly designed, allowing the number of power modules to be varied. In particular, additional power modules can be subsequently integrated into the semiconductor microwave unit; these are coupled to and controlled by the control module.

[0066] The power module can comprise at least one power amplifier, one circulator, and / or one directional coupler. The power module can be coupled via the directional coupler to an evaluation section of the control module, in particular the control and evaluation unit, so that the corresponding coupled waves are made available.

[0067] In principle, reflected power can be monitored during heating operation. This allows for the detection of whether the reflected power exceeds an expected value or a limit value within a given angular segment. If this occurs, a new measurement of the scattering parameters is triggered, resulting in an update of the excitation vector.

[0068] Once the angular position of the fan wheel has been determined, the scattering parameter at that angular position can be measured to calculate the excitation vector. Alternatively, a predefined excitation vector can be used first.

[0069] Further advantages and features of the invention will become apparent from the following description and the drawings, to which reference is made. The drawings show: Figure 1 a schematic representation of a combination cooking appliance according to the invention, Figure 2a representation that exemplifies a segmentation of a period of the fan wheel, Figure 3 a schematic representation of a semiconductor microwave unit used in the combination cooking appliance according to the invention, Figure 4 a power module of the semiconductor microwave unit according to Figure 3 , Figure 5 an overview of the control parameters encompassed by an excitation vector, Figure 6 an overview that clarifies the measurement operation mode of the semiconductor microwave unit, Figure 7 an overview that clarifies the heating operation mode of the semiconductor microwave unit, Figure 8 a representation of a rotary encoder that can be used in the combination cooking appliance according to the invention to determine the angular position of the fan wheel, and Figure 9 An overview showing another way to determine the angle of the fan wheel.

[0070] In Figure 1A combination cooking appliance 10 is shown, comprising a housing 12 that surrounds a cooking chamber 14 and a technical compartment 16. A food carrier 18 is provided in the cooking chamber 14, on which the food to be cooked 20 is arranged.

[0071] The food 20 is cooked using at least one conventional energy source 22, which may be, for example, a heating device and / or a steam device. The conventional energy source 22 is assigned to the cooking chamber 14, whereby a cooking chamber climate is created in the cooking chamber 14 by means of the conventional energy source 22, by means of which the food 20 is cooked.

[0072] In addition to the conventional energy source 22, the combination cooking appliance 10 also has a semiconductor microwave unit 24, by means of which the food 20 is additionally cooked using microwaves. In this respect, microwaves are fed into the cooking chamber 14 to transfer the corresponding energy to the food 20.

[0073] In the illustrated embodiment, the combination cooking appliance 10 also has a control and evaluation unit 26, which is designed separately from the semiconductor microwave unit 24. Therefore, the control and evaluation unit 26 is a separate control and evaluation unit, for example, a higher-level control and evaluation unit of the combination cooking appliance 10, which controls all components of the combination cooking appliance 10.

[0074] Alternatively, the control and evaluation unit 26 can also be integrated into the semiconductor microwave unit 24, as will be explained below.

[0075] Furthermore, it is assumed that Figure 1It is shown that the combination cooking appliance 10 has a fan wheel 28, which is assigned to the cooking chamber 14. The fan wheel 28 is driven by a drive 30 and a drive shaft 32. This ensures that the cooking chamber climate provided by the conventional energy source 22 is circulated within the cooking chamber 14 to ensure even heating of the food 20 by means of hot air and / or steam.

[0076] A rotary encoder 34 is assigned to the fan wheel 28, which is, for example, integrated into the drive 30. The rotary encoder 34 allows the angular position of the fan wheel 28 to be detected during operation, i.e., while the drive 30 is powering the fan wheel 28. The rotary encoder can be an incremental encoder.

[0077] For example, the rotary encoder 34 is designed as an optical encoder, as shown in Figure 8The rotary encoder 34 can transmit a corresponding rotary encoder signal to the control and evaluation unit 26, from which the control and evaluation unit 26 determines the angular position of the fan wheel 28. Alternatively, the rotary encoder signal is transmitted to the semiconductor microwave unit 24.

[0078] As an alternative to the rotary encoder signal, which is in Figure 8 As shown, the rotary encoder 34 can output two trigger signals, which are evaluated by the control and evaluation unit 26 or the semiconductor microwave unit 24 to determine the angular position of the fan wheel 28, in particular also the direction of rotation of the fan wheel 28, as exemplified in Figure 9 shown.

[0079] In the upper area of ​​the Figure 9 A rotation of the fan wheel 28 in clockwise direction is shown, whereas in the middle area of ​​the Figure 9The figure shows the rotation of the fan wheel 28 in counterclockwise direction. It can be seen that the two different trigger signals are output at different times depending on the direction of rotation, thus enabling the direction of rotation of the fan wheel 28 to be detected.

[0080] As explained above, the rotary encoder 34 associated with the fan wheel 28 can be integrated into the drive 30 or assigned to the drive shaft 32, so that the angular position of the fan wheel 28 can be determined. The respective angular position of the fan wheel 28 can be a relative angular position, meaning that an absolute angular position of the fan wheel 28 does not necessarily have to be determined. However, the absolute angular position can be determined using a corresponding reference pulse, as described in Figure 8 This is clarified. The reference pulse specifies a starting or zero point of the fan wheel 28, from which the absolute angular position can then be determined.

[0081] As an alternative to the rotary encoder 34, the angular position of the fan wheel 28 can also be calculated by the control and evaluation unit 26 based on a rotational speed of the fan wheel 28, which is specified by the control and evaluation unit 26 due to a running cooking program. The control and evaluation unit 26 thus controls the drive 30 in such a way that a desired rotational speed of the fan wheel 28 is achieved. If a trigger signal or reference pulse is detected by the fan wheel 28, the relative angular position of the fan wheel 28 can be determined, in particular based on the elapsed time since the last reference pulse, taking into account the rotational speed of the fan wheel 28. This calculation can also be performed by the semiconductor microwave unit 24, provided it receives the corresponding information.

[0082] In the Figure 1In the embodiment shown, the angle information, i.e. the determined angular position of the fan wheel 28, is transmitted to the semiconductor microwave unit 24, which processes it accordingly in order to set or select a corresponding operating mode of the semiconductor microwave unit 24, i.e. depending on the detected angular position of the fan wheel 28.

[0083] The semiconductor microwave unit 24 has a control module 36 which receives the angular position of the fan wheel 28 from the control and evaluation unit 26 or, if the control and evaluation unit 26 is integrated in the semiconductor microwave unit 24, determines it itself accordingly, as already explained above.

[0084] In any case, the control module 36 of the semiconductor microwave unit 24 controls corresponding power modules 38 of the semiconductor microwave unit 24 depending on the determined angular position of the fan wheel 28, whereby a corresponding operating mode of the respective power module 38 can be set here. In particular for the respective angular position of the fan wheel 28.

[0085] The power modules 38, which can also be referred to as microwave power stages, are connected to the cooking chamber 14 via antennas 40, so that microwaves provided by the semiconductor microwave unit 24 can be coupled into the cooking chamber 14 via the antennas 40, for example to cook the food 20. A power output of 250 W or 500 W can be provided per power module 38. For example, four power modules 38 with a power output of 250 W each are provided, thus forming four power stages.

[0086] The control of the individual power modules 38 is angle-dependent, as already explained above.

[0087] For example, in Figure 2 It has been shown that a complete rotation of the fan wheel 28 can be divided into 20 angular segments (n=0 to n=19). This results in 20 different possibilities for controlling the power modules 38 during a single rotation of the fan wheel 28. A larger number of angular segments is usually provided, for example 400.

[0088] For example, the period T p of the fan wheel 28 is between 30 and 240 milliseconds, depending on the rotational speed or rotational speed of the fan wheel 28.

[0089] The period T p is divided into N time slots, so that the complete revolution of the fan wheel 28, i.e. a 360° revolution of the fan wheel 28, is divided into correspondingly N angular segments.

[0090] The N angular segments can cover the same angular range or vary in their angular range. The duration of the corresponding time slot ts, for example, is between 0.625 milliseconds and 10 milliseconds, depending on the number of time slots N and the period Tp.

[0091] If the semiconductor microwave unit 24 is operated entirely in heating mode during one revolution of the fan wheel 28, this results in N different excitation vectors with which the semiconductor microwave unit 24 is operated during the revolution of the fan wheel 28. The excitation vectors are indexed with an index n, so that the indices "0" to "N-1" are provided. The excitation vectors are each different from one another and take into account the respective angular position of the fan wheel 28, thus ensuring that the semiconductor microwave unit 24 always has an optimal operating point during operation.

[0092] Based on the Figures 3 to 5 The heating operation mode of the semiconductor microwave unit 24 is described.

[0093] In Figure 3The semiconductor microwave unit 24 is shown in more detail, in particular the control module 36 and the individual power modules 38 which are controlled by the control module 36.

[0094] The control module 36 receives information regarding the angular position of the fan wheel 28 from the control and evaluation unit 26 or calculates it itself based on the received data, for example based on the angle encoder 34.

[0095] This enables the control module 36 to provide a clock signal with period ts, via which the individual power modules 38 are controlled, as will be explained below.

[0096] In addition, the control module 36 provides a frequency reference f ref [n] which is transmitted to all power modules 38.

[0097] The power modules 38 are each equipped with corresponding sets of excitation vectors, which are controlled by the control module 36 using the clock signal or selected by the control module 36 clock by clock. In other words, an incoming clock edge of the clock signal is converted by the corresponding power module 38 so that the next excitation vector is used.

[0098] The respective sentences are in the Figures 3 and 4 denoted by W j, where each set comprises several different excitation vectors W j [n], namely excitation vectors from W j [0] to W j [N-1], each of which is fixedly assigned to one of the several angular segments or time slots, as shown above based on the Figure 2 has been explained.

[0099] The excitation vectors Wj[n] are also arranged in a predefined sequence, so that they are switched through sequentially by means of the clock signal. The direction in which the excitation vectors Wj[n] are switched through or selected clockwise depends on the direction of rotation of the fan wheel 28, which can be detected by means of the rotary encoder 34.

[0100] The control module 36 controls the individual power modules 38 by means of the clock signal or the trigger signal with period ts such that the correspondingly assigned excitation vector W j [n] is used in the respective angular segments or time slots. In the respective angular segment or time slot, the control parameters for the phase of the microwaves to be generated, which are assigned to the excitation vector, are provided and processed together with the frequency reference by the respective power module 38 in order to generate the microwaves accordingly. For this purpose, the power modules 38 have an IQ modulator or IQ demodulator 42 and at least one amplifier 44, so that the desired microwave signal is generated.

[0101] In Figure 5It has been shown, for example, that an excitation vector comprises several control parameters, namely for the phase, the amplitude, the pulse width, and the frequency. This ensures efficient and optimal heating of the food 20 by means of microwaves for each angular segment. In addition to the control parameters shown, the excitation frequency can also be provided as a control parameter, i.e., how often heating should occur in a specific time slot within a defined number of revolutions, for example, in the next 100 revolutions. In other words, the excitation frequency determines how often the excitation vector is activated within a specific number of subsequent revolutions. This can also be referred to as power scaling.

[0102] Basically, it is ensured that the semiconductor microwave unit 24 is always operated at the optimal operating point, since the angle-dependent control of the semiconductor microwave unit 24 takes place.

[0103] As explained above, the control module 36 switches the different excitation vectors W j [n] of the corresponding set in real time to react to the rotating fan wheel 28. This is controlled by at least one trigger signal, i.e. the clock signal ts .

[0104] The algorithms on the control module 36, which are used to compensate for slow changes and generally to determine the optimal operating point or the corresponding excitation vector, are executed asynchronously and update, as required, part (or the entire) set of excitation vectors of the respective power module 38.

[0105] In Figure 7The corresponding heating operation mode is shown within an angular segment, where the selection of the appropriate excitation vector takes place. In the example of the Figure 7 This is shown for the time slot t s0, which in the example has a duration of 75 µs.

[0106] Within a time slot, the desired excitation vector is set. A control loop ensures that the excitation vector is implemented correctly. For example, thermal effects are taken into account. Several control cycles can be executed within a single time slot.

[0107] In principle, the time slot can have a duration between 75 µs and 300 µs, depending on the fan speed, which can range from 0 to 2000 revolutions per minute, provided 400 time slots are to be generated, as shown in the example. Accordingly, the complete rotation of the fan wheel 28 is divided into 400 angular segments, which are correspondingly assigned to 400 time slots ts.

[0108] Out of Figure 7 It becomes clear that the angular segments follow one another in a specific order due to the predetermined rotation of the fan wheel 28, which also repeats periodically, namely with the period of the fan wheel 28.

[0109] Within the single time slot t s0 or the associated angular segment, the power modules 38 are controlled via the control module 36 according to the lower section of the Figure 7 depicted process.

[0110] Among other things, a "hardware access" is provided, which lasts for 6 µs. During the "hardware access," the amplitude and phase are set in the form of DAC values. The necessary measurement is then performed to verify the set amplitude and phase.

[0111] After the measurement, a software control loop ("software control algorithm") runs, which provides corrected DAC values ​​to more accurately achieve the desired amplitude and phase.

[0112] These values ​​are then reset and measured in the subsequent "hardware access," whereupon the control loop calculates corrected values. This process repeats until the time slot ends. This allows temperature effects to be compensated for.

[0113] In the background, the desired excitation vector can be continuously active if this is desired or necessary due to the desired power requirement, so that a heating power can be continuously available to heat the food 20.

[0114] A pulse width modulation (PWM) would then switch off the excitation vector before the end of the time slot. The duration of the time slot, ts, is known, so with a pulse width of 80%, the system would switch off after 0.8*ts and wait for the next trigger signal.

[0115] In this area, the power modules 38 are operated according to the intended excitation vectors, i.e., the phase and other parameters are set accordingly. To keep the excitation vectors stable, a control algorithm can also be implemented within an angular segment, as described in Figure 7 is shown.

[0116] The control algorithm is typically executed as often as possible within the time slot or the time of the angular segment, depending on the power requirement of the semiconductor microwave unit 24. The control values ​​determined in the control algorithm are stored for the next revolution of the fan wheel 28, so that they are directly available and can be used as a starting value.

[0117] In the illustrated embodiment, a total of three sub-segments ("HW access") are provided within an angular segment. These sub-segments are used to set the DAC values ​​and measure the actual amplitude and phase: once for approximately 6 µs and twice for approximately 5 µs. The remaining 59 µs of the 75 µs time slot are therefore reserved for the control algorithm, which is executed multiple times, specifically each time after the "HW access." However, the DAC values ​​set during the first "HW access" remain active in the background; that is, the excitation vector / operating point is also active for the entire duration of the time slot.

[0118] In Figure 6 An alternative operating mode of the semiconductor microwave unit 24 is shown, which is a measurement operating mode.

[0119] The semiconductor microwave unit 24 is used in measurement operation mode such that one of the several line modules 38 emits a microwave signal at a set frequency, with the other power modules 38 receiving a corresponding reflected signal from the cooking chamber 14.

[0120] In this process, the forward-propagating and reverse-propagating waves are coupled out at the corresponding power modules 38, in particular at the connections between the power modules 38 and the antennas 40, in order to determine the corresponding scattering parameters. Accordingly, each power module 38 can have a directional coupler via which the differently propagating waves can be coupled out.

[0121] In a subsequent angular segment, a different frequency can already be used to determine the scattering parameters before another angular segment and a different frequency.

[0122] If multiple frequencies are to be measured for the same angular segment, the measurements are performed at the corresponding number of revolutions of the fan wheel 28. For example, if 101 frequency points of an angular segment are to be measured, 101 revolutions of the fan wheel 28 are used to obtain the measurement data. Alternatively, the measurement time can be shortened by interpolating or extrapolating the scattering parameters along a frequency axis or the fan wheel angle or the time slots.

[0123] At low rotational speeds, it is also conceivable to measure several frequencies within a single time slot. The measurement takes approximately 25 µs, for example, so that with a time slot duration of 300 µs, multiple measurements are possible.

[0124] In principle, the data acquired in the measurement mode can be used to calculate or determine the excitation vectors for the heating mode, in particular to respond to slowly changing dielectric properties that arise due to the heating of the food 20 or an inner box of the combination oven 10 surrounding the cooking chamber 14. The power modules 38 can therefore be configured to measure scattering parameters (S-parameters) in a defined angular segment or over the entire angular range. The optimal excitation vector is determined from these measurements. Suitable algorithms for a fixed time slot are identical to those for a shielded cooking chamber 14. The optimal excitation vector can be optimized according to its purpose, for example, maximum energy input, highest efficiency, or greatest uniformity.

[0125] Likewise, the measurement operation mode may include the determination of a dielectric load of the cooking chamber 14 in order to detect, for example, the cooking state of the food 20, its progress, newly introduced food into the cooking chamber 14, a type of food or cooking accessories such as the food carrier 18 present in the cooking chamber 14.

[0126] During sensing, the electric field distribution in the respective object acts like a volumetric weight of the object's material properties. The rotating fan wheel 28 alters the field patterns in the cooking chamber 14, resulting in different field distributions within the object, thus enabling a more uniform scanning of the corresponding material properties. Combining the scattering parameters from all angular positions increases the information content about the object.

[0127] The information is continuously updated through cyclical measurement of the scattering parameters, i.e., measurement for one angular segment per revolution of the fan wheel 28. Heating operation does not need to be interrupted. Only the time during which microwave power is applied is reduced by the proportion of time spent measuring one angular segment to the total revolution. This cyclical measurement allows the excitation vectors in the angular segment to be automatically updated.

[0128] The measurement data or waves obtained in measurement operation mode are generally transmitted to the control module 36, for example, the waves coupled out by the directional coupler. The control module 36 evaluates the received measurement data or waves to determine the scattering parameters. Therefore, the control module 36 has at least one evaluation section that is used to evaluate and determine the scattering parameters. As described above, the control module 36 can generally include the control and evaluation unit 26.

[0129] In principle, the semiconductor microwave unit 24 can also be operated in an idle operation mode in which no microwaves are generated via the semiconductor microwave unit 24, i.e. neither for heating the food 20 nor for sensing the cooking chamber 14.

[0130] In the Figure 2In the example shown, 20 angular segments were provided, which divided the entire rotation of the fan wheel 28 accordingly. A specific operating mode could be provided in each angular segment, i.e., an idle operating mode, a measuring operating mode, or a heating operating mode.

[0131] In particular, successive angular segments can have different operating modes. This can depend on the cooking program or the power requirement of the semiconductor microwave unit 24. For example, the in Figure 2 The angle segments shown, 0 to 15, are used for heating the food 20, whereas angle segments 16 to 19 are used for sensing, for example to update the excitation vectors or to implement a control algorithm. If the power requirement increases, more angle segments can be assigned to the heating operation mode.

[0132] In principle, the efficiency of the power modules 38 scales with the amplitude, so that the best efficiency is achieved at maximum amplitude. Therefore, the power modules 38 are operated at maximum amplitude, whereby their switch-on times or the assigned time slots are varied accordingly, i.e., the respective operating mode of the individual angular segments.

[0133] For example, an angular segment is only activated in x / 100 of revolutions, allowing the power of the angular segment to be scaled, specifically in 1% increments in the example given. With a value of x = 10, the corresponding angular segment would therefore be active for 10% of the time, which corresponds to a power scaling to 10%. Instead of 1% increments, a finer or coarser resolution can also be set, for example, 5% increments with activation at x / 20 of revolutions. This is also understood as the excitation frequency of the excitation vector.

[0134] The amplitude of the individual power modules 38 is always set at the maximum or most efficient output power for the corresponding frequency. The excitation vectors are then controlled solely via the phases. The appropriate coupling of the microwave into the cooking chamber 14 is therefore controlled exclusively via the phases.

[0135] It is generally possible to operate the semiconductor microwave unit 24 efficiently due to the angle-dependent control, while at the same time the conventional energy source 22 can be used without restriction, for example the heating device and / or the steam device, since no interfering shielding is required, which also increases the manufacturing and service effort.

Claims

1. A method of cooking food to be cooked in a combination cooking appliance (10) having a fan wheel (28) and a semiconductor microwave unit (24) for generating microwaves, comprising the following steps: - determining an angular position of the fan wheel (28); - selecting an excitation vector for the semiconductor microwave unit (24) based on the determined angular position from a set of different excitation vectors, wherein the excitation vector at least comprises drive parameters for the phase of the microwaves to be generated, and - operating the semiconductor microwave unit (24) with the selected excitation vector.

2. The method according to claim 1, characterized in that the set of different excitation vectors covers a complete revolution of the fan wheel (28), which is subdivided into a plurality of angular segments.

3. The method according to claim 1 or 2, characterized in that the selected excitation vector is constant for a defined angular segment of the rotating fan wheel (28), the angular segment being less than 360°, in particular less than 10°, preferably less than 1°.

4. The method according to any of the preceding claims, characterized in that the angular position of the fan wheel (28) is measured by means of a rotary encoder (34), or in that the angular position of the fan wheel (28) is calculated based on a speed of the fan wheel (28) and a reference pulse, or in that the angular position of the fan wheel (28) is derived from measurements of scattering parameters at at least a fixed frequency over the duration of one revolution of the fan wheel (28).

5. The method according to any of the preceding claims, characterized in that the direction of rotation of the fan wheel (28) is determined, wherein the determined direction of rotation of the fan wheel (28) determines an order of the excitation vectors of the set of different excitation vectors.

6. The method according to any of the preceding claims, characterized in that at least one excitation vector is calculated or is updated on the basis of a control.

7. The method according to claim 6, characterized in that the at least one excitation vector is calculated based on measured scattering parameters at an angular position of the fan wheel (28) or is updated on the basis of a control.

8. The method according to any of the preceding claims, characterized in that the set of different excitation vectors is selected from a plurality of different sets of different excitation vectors.

9. The method according to claim 8, characterized in that a re-selection of the appropriate set from the plurality of different sets is performed on the basis of a predetermined time, a change in a dielectric property in a cooking chamber (14) of the combination cooking appliance (10), and / or continuously.

10. A combination cooking appliance for cooking food to be cooked (20), comprising a fan wheel (28), a control and evaluation unit (26), and a semiconductor microwave unit (24), wherein the control and evaluation unit (26) is configured to determine a present angular position of the fan wheel (28), wherein the semiconductor microwave unit (24) is configured to be operated in a plurality of different operating modes, wherein the control and evaluation unit (26) is further configured to drive the semiconductor microwave unit (24) based on the determined angular position such that, based on the determined angular position, the semiconductor microwave unit (24) is in a selected operating mode.

11. The combination cooking appliance according to claim 10, characterized in that the plurality of different operating modes of the semiconductor microwave unit (24) comprise an idle operating mode, a measuring operating mode, and a heating operating mode.

12. The combination cooking appliance according to claim 11, characterized in that the control and evaluation unit (26) is configured to vary the operating modes of the semiconductor microwave unit (24) within one complete revolution of the fan wheel (28) and / or to vary the operating modes for the same angular segment of two successive revolutions of the fan wheel (28).

13. The combination cooking appliance according to any of claims 10 to 12, characterized in that the semiconductor microwave unit (24) comprises a drive module (36) and a plurality of power modules (38), which are each in communication connection with the drive module (36), wherein each power module (38) has a set of different excitation vectors assigned to it, and wherein the drive module (36) is configured to specify a common frequency reference to the power modules (38) and to drive the power modules (38) by means of a clock signal dependent on the detected angular position in order to select an excitation vector from the set of different excitation vectors.

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