Device for inductive energy transfer

Abstract

Device (1) for inductive energy transfer to an object (3), wherein energy is induced in the object (3) by means of an alternating electromagnetic field, comprising a half-bridge circuit (2) for a primary current circuit with a first and a second switching device (S1, S2), wherein the half-bridge circuit (2) operates the first and second switching devices (S1, S2) at a switching frequency (SF), a coil arrangement (L) connected to the half-bridge circuit (2) for transferring the energy to the object (3), and a control unit (PCU) for controlling the switching frequency (SF), wherein a unit (10) is provided for determining or estimating a current resonance frequency (RFa) and / or a current maximum load point (max LP) and / or a current maximum load current (Ith) of the primary current circuit of the half-bridge circuit (2), the unit (10) communicating with the control unit (PCU),and the control unit (PCU) controls the switching frequency (SF) depending on the determination or estimation of the current resonance frequency (RFa) and / or the current maximum load point (max LP) and / or the current maximum load current (Ith).

Description

[0001] The present invention relates to a device for inductive energy transmission to an object according to the preamble of claim 1. Technological background

[0002] Inductive energy transfer is used for many different technical applications. These include, in particular, the inductive charging of mobile phones or vehicles, induction cooktops, and induction furnaces. Each of these applications is based on the transfer of energy from a coil arrangement to an object, e.g., a mobile phone, a vehicle, cooking utensils, or a material to be melted, using an alternating electromagnetic field. Typically, a device for inductive energy transfer comprises a half-bridge circuit, with the half-bridge circuit comprising the coil arrangement and switching devices. The switching devices of the half-bridge circuit are controlled at a switching frequency, so that the coil arrangement is operated with an alternating current.

[0003] To achieve particularly high efficiency, the maximum energy should be transferred to the object. Maximum energy is achieved when the switching frequency with which the coil arrangement is controlled corresponds to the resonant frequency of the half-bridge circuit. The resonant frequency is influenced by the components of the half-bridge circuit and by the type of object and its position relative to the coil arrangement.

[0004] If the position of an object relative to the coil arrangement is suddenly changed, for example, by moving or removing the object, the resonant frequency of the half-bridge circuit shifts. If the switching frequency remains constant, there is a risk of damage to the half-bridge circuit due to undesirable effects. This is particularly relevant for induction cooktops.

[0005] A half-bridge circuit for induction hobs is known, for example, from ON Semiconductor, “Induction Cooking Everything You Need to Know”, AND9166 / D October, 2014 - Rev. 2. Object of the present invention

[0006] The object of the present invention is to provide a device for inductive energy transmission which enables improved control of the device with reduced computational effort. Solution to the task

[0007] The above object is achieved by a device for inductive energy transfer to an object according to claim 1. Advantageous embodiments of the invention are claimed in the dependent claims.

[0008] According to the invention, the device comprises a unit for determining or estimating a current, i.e., current operating, resonant frequency and / or a current, i.e., current operating, maximum load point and / or a current, i.e., current operating, maximum load current of a primary circuit of the half-bridge circuit. The unit communicates with a control unit of the device, wherein the control unit controls, in particular increases, the switching frequency depending on the determination or estimation of the current resonant frequency and / or the current maximum load point and / or the current maximum load current. The determination or estimation of the current resonant frequency and / or the current maximum load point and / or the current maximum load current makes it possible to determine when the position of the object relative to the coil arrangement is changed or when the object is removed.Therefore, in this case, the control unit can intervene in the control of the half-bridge circuit in such a way that the switching frequency is changed to prevent damage to the half-bridge circuit. In particular, the switching frequency can be increased, thus reducing the power of the half-bridge circuit. Compared to sampling at a high sampling rate, this can be achieved with comparatively low computational effort.

[0009] Preferably, the unit comprises a first signal path with a maximum value detector, wherein the maximum value detector outputs a current, i.e., operational, maximum value that correlates with the primary current of the primary circuit. This maximum value detector thus makes it possible to determine when the device is emitting the maximum energy depending on the object.

[0010] Conveniently, the maximum value output by the maximum value detector is a voltage signal. Conveniently, the voltage signal remains essentially the same or constant after reaching the maximum value.

[0011] In particular, the voltage signal is a signal from a secondary circuit connected to the primary circuit via a voltage transformer. The voltage transformer is preferably a transformer with a specific transformation ratio, i.e., a specific ratio of the number of turns of the primary and secondary windings of the transformer.

[0012] Advantageously, a measurement voltage signal can be supplied to the maximum value detector, which represents the current primary current of the primary circuit. The measurement voltage signal is a signal from the secondary circuit that represents the primary current, in particular the resonant waveform of the primary circuit. This allows even particularly high primary currents to be evaluated. The measurement voltage signal depends in particular on a secondary current of the secondary circuit, with the secondary current being generated by the current transformer as a function of the primary current.

[0013] Preferably, the voltage signal output by the maximum value detector is fed to a microcontroller of the unit or the control unit, in particular via an analog-to-digital converter.

[0014] The unit preferably determines or estimates a first time period, wherein the first time period corresponds to the time between a first time of activation of the half-bridge circuit, i.e., a switching of the half-bridge circuit, and a second time point at which the maximum value of the signal dependent on the primary current, in particular the measurement voltage signal, is reached in the respective switching cycle. Based on the second time period, the current resonant frequency can be determined or estimated. The current resonant frequency preferably corresponds to twice the first time period, converted into a frequency value. The first time period can preferably be stored in the unit.

[0015] By specifying a second time period following the first time period, the current maximum load point and / or the current maximum load current can be determined or estimated depending on the first time period and the second time period. In particular, the value of the second time period depends on the half-bridge circuit, e.g., the elements installed therein, and / or the current resonant frequency and / or a frequency shift between the current resonant frequency and the switching frequency at the maximum load point. The second time period preferably determines how far the maximum load point should be located from the resonant frequency.

[0016] The current maximum load point can be determined or estimated, in particular, as a function of the resonant frequency determined or estimated using the first time period and the second time period converted into a frequency. Alternatively, the first time period and the second time period can be added together and converted into a frequency corresponding to the switching frequency at the maximum load point.

[0017] The current maximum load current can be determined or estimated in particular depending on the determined or estimated current maximum load point.

[0018] Preferably, the current maximum load point and / or the current maximum load current are determined or estimated as a function of a predetermined frequency shift and the resonance frequency. The frequency shift corresponds in particular to the intended distance between the switching frequency at the maximum load point and the current resonance frequency.

[0019] The switching frequency at the maximum load point can thus be easily determined or estimated, for example, by adding the resonant frequency and the frequency shift. The maximum load point can be determined or estimated using the switching frequency determined or estimated as a function of the resonant frequency and the frequency shift. The maximum load current is preferably determined as a function of the maximum load point.

[0020] Preferably, the unit comprises a second signal path, wherein the second signal path is connected in particular in parallel with the first signal path. The output signals are used to determine or estimate the current resonance frequency and / or the current maximum load point and / or the current maximum load current. The second signal path can be used to perform additional, particularly redundant, signal evaluation.

[0021] Conveniently, the same measurement voltage signal is supplied to the first and second signal paths. This allows the same measurement voltage signal to be evaluated using the first signal path and the second signal path.

[0022] Since the second signal path preferably comprises a signal buffer, the signal dependent on the primary current of the half-bridge circuit can be preprocessed, in particular amplified or attenuated.

[0023] Preferably, the determination or estimation of the current resonance frequency and / or the current maximum load point and / or the current maximum load current can be carried out using an algorithm based on the signals of the first and second signal paths. The algorithm preferably determines the dependency between the measurement voltage signal and the voltage signal of the maximum value detector. In particular, the algorithm is implemented by the microcontroller or the control unit.

[0024] The current maximum load point and / or the current maximum load current can expediently be determined or estimated as a function of the first time period and the second predetermined time period following the first time period, and of the output signal, in particular the measurement voltage signal, of the second signal path. In particular, the magnitude of the output signal of the second signal path is preferably determined or estimated at a third point in time. The third point in time depends in particular on the first time period and the second time period and is the point in time at which the first time period and the second time period following the first time period have elapsed. When determining the maximum load current and / or the maximum load point, the effects or influences of other components of the unit, e.g. a transformation ratio of a current transformer or a resistor, are preferably taken into account.

[0025] Advantageously, the current resonance frequency and / or the current maximum load point and / or the current maximum load current are stored in the unit or the control unit. This allows the stored values to be used, preferably, for comparison with future values.

[0026] By comparing the current resonance frequency and / or the current maximum load point and / or the current maximum load current with, in particular, predetermined and / or empirically determined, reference values and / or stored values, the unit or the control unit can detect a change in the respective values particularly easily. If the current resonance frequency and / or the current maximum load point and / or the current maximum load current do not correspond, in particular, to the respective reference values or the previously determined or estimated values, a change can be detected, whereby the switching frequency is changed, in particular increased.

[0027] Preferably, the current resonant frequency and / or the current maximum load point and / or the current maximum load current can be determined or estimated dynamically. In particular, the resonant frequency and / or the maximum load point and / or the maximum load current can be determined or estimated for each switching cycle of the switching devices of the half-bridge circuit. This allows for a particularly rapid response to a change in at least one of the values.

[0028] Since the unit can in particular comprise a rectifier, preferably a bridge rectifier, the secondary current can be rectified. The rectifier expediently comprises several diodes. Preferably, an evaluation of the primary current or of the signals dependent on the primary current can be performed using a direct current.

[0029] The secondary current is expediently converted into the measurement voltage signal, in particular via a resistor. The measurement voltage signal is preferably fed to the first signal path and / or the second signal path.

[0030] The unit preferably comprises a microcontroller, which preferably determines or estimates the current resonance frequency and / or the current maximum load point and / or the current maximum load current. The microcontroller is preferably connected to the first signal path and / or the second signal path. At least one analog-to-digital converter is expediently provided to convert the signals of the first signal path and / or the second signal path into a digital signal. The analog-to-digital converter can be provided as a standalone component or integrated into the microcontroller.

[0031] The microcontroller can also be part of the device's control unit.

[0032] Conveniently, the device for inductive energy transfer is an induction hob, the object being a piece of cookware. Description of the invention using exemplary embodiments

[0033] Advantageous embodiments of the present invention are explained in more detail below with reference to the drawing figures. They show: Fig. 1 is a schematic representation of an example of a device for inductive energy transfer to an object; Fig. 2 an exemplary resonance curve when operating the device with an object according to Fig. 1; Fig. 3a a schematic representation of an example of a unit for determining or estimating a current resonance frequency and / or a current maximum load point and / or a current maximum load current of the primary circuit of the half-bridge circuit as a component of a device according to Fig. 1 according to a first embodiment; Fig. 3b a schematic representation of an example of a unit for determining or estimating a current resonance frequency and / or a current maximum load point and / or a current maximum load current of the primary circuit of the half-bridge circuit as a component of a device according to Fig. 1 according to a second embodiment; Fig. 3c a schematic representation of an example of a unit for determining or estimating a current resonance frequency and / or a current maximum load point and / or a current maximum load current of the primary circuit of the half-bridge circuit as a component of a device according to Fig. 1 according to a third embodiment; Fig. 4 shows an example of a time course of a voltage signal dependent on a primary current (resonance current) of the device in the region of a minimum load point for determining the maximum value of the voltage signal; Fig. 5 shows an example of a time course of a voltage signal dependent on a primary current (resonance current) of the device in the region of a maximum load point for determining the maximum value of the voltage signal; Fig. 6 an example of a time course of the signal detected by a maximum value detector of the unit according to Fig. 3a-3c output voltage signal; and Fig. 7 the time course of the voltage signal after Fig. 5 to determine a maximum load current.

[0034] Reference number 1 in Fig. 1 denotes a device for inductive energy transmission to an object 3. The device 1 is connected to a DC power supply via a cable or busbar. The DC power supply can be provided in particular by rectifying an alternating current, in particular from a power grid.

[0035] Device 1 is, in particular, an induction hob. Device 1 can also be a device for inductive charging or an induction oven. Object 3 is, for example, a piece of cooking utensil, a mobile phone, a vehicle, or a material to be melted, to each of which energy is to be transferred from device 1.

[0036] The device 1 comprises a so-called half-bridge circuit 2 as the primary circuit, which comprises a first switching device S1, a second switching device S2 and a coil arrangement L. In addition, the half-bridge circuit 2 comprises two capacitors C1, C2 and a control unit PCU.

[0037] The two switching devices S1, S2 are switched by the control unit PCU at a switching frequency SF. This generates a change in the primary current (I1) at a frequency corresponding to the switching frequency SF. The half-bridge circuit also includes two snubber capacitors or damping capacitors C4, C5, which dampen particularly disruptive high-frequency oscillations or voltage spikes.

[0038] The primary current (I1) generated by the switching devices S1, S2 is applied to the coil arrangement L, which generates a corresponding alternating electromagnetic field. The object 3, to which the energy of the alternating electromagnetic field is transferred, is arranged on the coil arrangement L.

[0039] In an induction hob, the alternating electromagnetic field in the object 3 (e.g. in a cooking pot) causes heat through induced eddy currents and remagnetization losses, which causes the object 3 to heat up.

[0040] For example, to achieve particularly high efficiency or the fastest possible heating rate in an induction hob, the maximum energy is normally transferred to object 3. Maximum energy is transferred when the switching frequency SF of the half-bridge circuit 2 approximately corresponds to a resonant frequency RF. The resonant frequency is influenced by the components of the half-bridge circuit 2 and the object 3, as well as its position relative to the coil arrangement L.

[0041] Fig. 2 shows an example resonance curve. The half-bridge circuit 2 can be operated in three different operating modes depending on the switching frequency SF. In a first operating mode, the switching frequency SF corresponds to the resonance frequency RF, whereby the transmitted energy has a maximum value, the so-called resonance frequency point RFP. In a second operating mode, the switching frequency SF is greater than the resonance frequency RF. In this operating mode, the transmitted energy decreases as the switching frequency SF increases. In the second operating mode, the half-bridge circuit 2 is in an inductive region of the resonance curve. In a third operating mode, the switching frequency SF is lower than the resonance frequency RF, whereby the half-bridge circuit 2 is in a capacitive region. In this operating mode, the transmitted energy decreases as the switching frequency SF decreases.If the half-bridge circuit 2 is operated in the third operating mode, the half-bridge circuit 2 may be damaged, for example due to capacitive effects.

[0042] For maximum energy transfer, it is therefore advantageous if the switching frequency SF essentially corresponds to the resonant frequency RF. To avoid possible damage, it is particularly advantageous if the half-bridge circuit 2 is operated with a switching frequency SF that is greater than the resonant frequency RF. This ensures that the switching frequency SF is in the inductive range of the resonance curve even with a slight fluctuation of the resonant frequency RF. For this purpose, a frequency shift ΔF, in particular a predetermined one, is provided, which defines the minimum distance between the switching frequency SF and the resonant frequency RF. The frequency shift ΔF from the resonant frequency RF to Fig. The switching frequency shifted to the right represents the minimum switching frequency SF1 at which half-bridge circuit 2 operates. A maximum load point max LP is defined in the range of the minimum switching frequency SF1. Furthermore, a minimum load point min LP is provided, which is assigned to a maximum switching frequency SF2.

[0043] If the position of the object 3 (e.g. a cooking pot) relative to the coil arrangement L is changed by moving or removing the object 3 from the ideal position on the coil arrangement L, the resonance frequency RF increases and shifts in the Fig. 2 to the right. If the switching frequency SF were left unchanged in this case and not adjusted to the shifted resonant frequency RF, there would be a risk that the shifted resonant frequency RF would reach a higher frequency than the switching frequency SF. In this case, the half-bridge circuit 2 would operate in the capacitive range, which could lead to damage to the half-bridge circuit 2.

[0044] In order to detect such a shift of the resonance frequency RF and to take rapid countermeasures, according to the invention a unit 10, in particular a measuring unit, for measuring or estimating a current resonance frequency RFa and / or a current maximum load point max LP and / or a current maximum load current I thThe unit 10 communicates with the control unit PCU, which, depending on the measurement or estimation of the current resonance frequency RFa and / or the current maximum load point max LP and / or the current maximum load current I th the switching frequency SF of the half-bridge circuit 2 is changed. The switching frequency SF can be increased for the previously described case, shifting the switching frequency SF toward the minimum load point min LP. Thus, the switching frequency SF can be adjusted when the current resonant frequency RFa is shifted, preventing operation of the half-bridge circuit 2 in the capacitive range.

[0045] The unit 10 forms a secondary circuit and comprises a microcontroller MCU and a current transformer 11 and is connected to the primary circuit or the half-bridge circuit 2 via the connection points x and z, cf. Fig. 1 and Fig. 3a. The current transformer 11 is, in particular, a transformer. The current transformer 11 converts the primary current I1 of the half-bridge circuit 2 into the secondary current I2 of the secondary circuit. The current transformer 11 comprises a predetermined transformation ratio, which corresponds, in particular, to the ratio of the number of turns of the transformer. The secondary current I2 is then fed to a rectifier D1 with several diodes, in particular a bridge rectifier, which rectifies it.

[0046] The rectified current I3 is converted into a measurement voltage signal U3 by means of a resistor RS. The measurement voltage signal U3 is thus dependent on the primary current I1 or represents it. The measurement voltage signal U3 also represents the resonant waveform of the primary current I1. The measurement voltage signal U3 is then fed to a maximum value detector B, which is arranged in a first signal path 12 of the unit 10.

[0047] The measuring voltage signal U3 supplied to the maximum value detector B is in the Fig. 4 and Fig. 5 is shown as a continuous line. Fig. 4 the measuring voltage signal U 3, min at the maximum switching frequency SF2 in the range of the minimum load point min LP. The measuring voltage signal U 3, min is essentially a triangular signal. In Fig. 5, however, the measuring voltage signal U 3, max at the minimum switching frequency SF1 in the range of the maximum load point max LP. The measuring voltage signal U 3, max is an essentially sinusoidal signal.

[0048] The measuring voltage signal U3 increases when the respective switching device S1, S2 is activated at time T1 as a function of the primary current I1. The maximum value detector B outputs a voltage signal U4 (dashed line in the Fig. 4 and Fig. 5), which increases with the voltage increase of the measuring voltage signal U3. The maximum value of the measuring voltage signal U3 is reached at time T2. As soon as the maximum value of the measuring voltage signal U3 is reached, the measuring voltage signal U3 decreases again. The voltage signal U4 output by the maximum value detector B, on the other hand, does not decrease, but remains constant for a certain time after reaching the maximum value. The output voltage signal U4 is reset again by a reset signal RST that is generated before the next activation of one of the switching devices S1, S2. The reset signal RST can be generated by the microcontroller MCU or by the maximum value detector B.

[0049] The output voltage signal U4 is fed to the microcontroller MCU, in particular via an analog-to-digital converter ADC. The microcontroller MCU determines or estimates a first time period Ta between the time T1 of activation of the switching devices S1, S2 and the time T2 at which the measurement voltage signal U3 has reached its maximum value.

[0050] Based on the first time period Ta, the current resonance frequency RFa of the half-bridge circuit 2 is determined or estimated using the following equation: 12⋅Ta=RFa

[0051] Thus, based on the first time period Ta, the current resonance frequency RFa can be easily determined.

[0052] In addition, a second predetermined time period Tb can be specified, cf. Fig. 6. The second time period Tb depends in particular on the half-bridge circuit 2, e.g., on the elements installed there, and the current resonant frequency RFa. The second time period Tb defines, based on an estimate, how far the switching frequency SF1 or the maximum load point max LP is from the current resonant frequency RFa or the resonant frequency point RFP, see. Fig. 2. The second time period Tb follows the first time period Ta.

[0053] The second time period Tb can be converted into a frequency corresponding to the frequency shift ΔF between the switching frequency SF1 and the current resonant frequency RFa. This allows the switching frequency SF1 to be determined or estimated, for example, by adding the second time period Tb converted into a frequency and the current resonant frequency RFa. Alternatively, the switching frequency SF1 can also be determined or estimated as a function of the sum of the time periods Ta and Tb converted into a frequency.

[0054] As an alternative to the predetermined second time period Tb, the frequency shift ΔF, cf. Fig. 2, so that the switching frequency SF1 can be determined or estimated by directly adding the current resonance frequency RFa to the frequency shift ΔF.

[0055] The switching frequency SF1 can thus be used to determine the current maximum load point max LP and / or the current maximum load current I th determined or estimated.

[0056] According to a second embodiment, the unit 10 comprises a second signal path 13, cf. Fig. 3b. The second signal path 13 is connected in parallel to the first signal path 12, with the measurement voltage signal U3 also being fed to the second signal path. According to a third embodiment according to Fig. 3c, the second signal path 13 comprises a signal buffer A, which is provided for amplifying or attenuating the measuring voltage signal U3.

[0057] According to the second embodiment, cf. Fig. 3b, the measurement voltage signal U3 is fed to both the first signal path 12 and the second signal path 13. The measurement voltage signal U3 is thus also fed directly to the microcontroller MCU. As a result, the microcontroller MCU processes the voltage signal U4 of the maximum value detector B on the one hand and the measurement voltage signal U3 of the second signal path 13 on the other.

[0058] As in Fig. As shown in Figure 7, using the time duration Ta and Tb, a voltage U th of the measuring voltage signal U3 at a time T3. The voltage U th of the measuring voltage signal U3 corresponds to the voltage at the end of the first and second time periods Ta and Tb. Starting from the voltage U th Depending on the resistance RS and the transformation ratio of the current transformer 11, the maximum load current I th determined or estimated. The maximum load current I thcorresponds to the primary current at the time of the maximum load point max LP. Starting from the maximum load current I th the maximum load point max LP can be determined or estimated.

[0059] As a result, the microcontroller MCU can determine the current resonance frequency RFa, and / or the current maximum load point max LP and / or the current maximum load current I th Determine or estimate. The measured values are conveniently determined or estimated dynamically. This allows the determined or estimated values in unit 10 to be immediately adapted to changing conditions.

[0060] It is advisable to measure the current resonance frequency RFa, and / or the current maximum load point max LP and / or the current maximum load current I th stored in the microcontroller MCU or unit 10 so that they are available as comparison values.

[0061] As a result, the microcontroller MCU can compare the current resonance frequency RFa with a stored resonance frequency and / or the current maximum load point max LP with a stored maximum load point and / or the current maximum load current I th compare with a stored load current and thereby determine whether the values have changed.

[0062] In particular, the microcontroller MCU can compare the current resonance frequency RFa with a stored resonance frequency and / or the current maximum load point max LP with a stored maximum load point and / or the current maximum load current I th using an algorithm. The algorithm determines the dependence between the measurement voltage signal U3 and the voltage signal U4 of the maximum value detector B.

[0063] Alternatively or in addition to continuously saving the current comparison values, at least one, e.g., empirical, reference value of the resonance frequency and / or the maximum load point and / or the maximum load current can be provided in the microcontroller MCU or in the unit 10. The determined or estimated current values, i.e., the current resonance frequency RFa, and / or the current maximum load point max LP and / or the current maximum load current I th , are compared with corresponding reference values so that a change can be detected.

[0064] In particular, the unit 10 communicates the determined or estimated values to the control unit PCU. Alternatively, only changes are transmitted to the control unit PCU. As soon as changes in the current resonance frequency RFa and / or the current maximum load point max LP and / or the current maximum load current I thare detected, the switching frequency SF is changed, in particular increased, by the control unit PCU. This expediently shifts the switching frequency SF toward the minimum load point min LP, thereby preventing operation of device 1 in the capacitive region of the resonance curve. As a result, device 1 is effectively protected from damage.

[0065] Depending on the circuit design, the microcontroller MCU can also be part of the control unit PCU or its functionality can be integrated into the control unit PCU. LIST OF REFERENCE SYMBOLS 1 facility 2 half-bridge circuit 3 consumers (pot, metals, vehicles) 10 units 11 current transformers 12 Signal path 13 Signal path A signal buffer ADC analog-to-digital converter B Maximum value detector C1 capacitor C2 capacitor C4 Damping capacitor C5 Damping capacitor D1 rectifier DC power supply ΔF frequency shift I1-I3 current I th maximum load current L Coil arrangement max LP maximum load point MCU microcontroller min LP minimum load point PCU control unit RF resonance frequency RFa resonance frequency RFP resonance frequency point RS resistance RST reset signal S1 switching device S2 switching device SF switching frequency SF1 minimum switching frequency SF2 maximum switching frequency T 1-3 time Ta, Tb duration U3 voltage U 3, min Tension U 3, max Tension U4 voltage x, z connection points QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited non-patent literature

[0000] ON Semiconductor, “Induction Cooking Everything You Need to Know”, AND9166 / D October, 2014 - Rev. 2

[0005]

Claims

[1] Device (1) for inductive energy transfer to an object (3), wherein energy is induced into the object (3) by means of an alternating electromagnetic field, comprising a half-bridge circuit (2) for a primary circuit having a first and a second switching device (S1, S2), wherein the half-bridge circuit (2) operates the first and second switching devices (S1, S2) at a switching frequency (SF), a coil arrangement (L) connected to the half-bridge circuit (2) for transmitting the energy to the object (3), and a control unit (PCU) for controlling the switching frequency (SF), characterized by , that a unit (10) for determining or estimating a current resonance frequency (RFa) and / or a current maximum load point (max LP) and / or a current maximum load current (I th ) of the primary circuit of the half-bridge circuit (2), the unit (10) communicates with the control unit (PCU), and the control unit (PCU) depending on the determination or estimation of the current resonance frequency (RFa) and / or the current maximum load point (max LP) and / or the current maximum load current (I th ) controls the switching frequency (SF). [2] Device (1) according to claim 1, characterized by that the unit (10) comprises a first signal path (12) with a maximum value detector (B), wherein the maximum value detector (B) outputs a current maximum value which correlates with the primary current (I1) of the primary circuit. [3] Device (1) according to claim 2, characterized by that the maximum value is a voltage signal (U4). [4] Device (1) according to claim 3, characterized bythat the voltage signal (U4) is a signal of a secondary circuit which is connected to the primary circuit via a current transformer (11). [5] Device (1) according to claim 3 or 4, characterized by that a measuring voltage signal (U3) is fed to the maximum value detector (B), which represents the current primary current (I1) of the primary circuit. [6] Device (1) according to one of claims 3-5, characterized by that the voltage signal (U4), in particular via an analog-digital converter (ADC), is fed to a microcontroller (MCU) of the unit (10) or the control unit (PCU). [7] Device (1) according to one of the preceding claims, characterized bythat the unit (10) determines or estimates a first time period (Ta) which corresponds to the time between a time (T1) of activation of the half-bridge circuit (2) and a time (T2) of reaching the maximum value of the signal dependent on the primary current (I1), and based on the first time period (Ta) the current resonance frequency (RFa) is determined or estimated. [8] Device (1) according to claim 7, characterized by that a second time period (Tb) is specified, which follows the first time period (Ta), and that depending on the first time period (Ta) and the second time period (Tb) the current maximum load point (max LP) and / or the current maximum load current (I th ) determined or estimated. [9] Device (1) according to one of the preceding claims, characterized bythat a frequency shift (ΔF) is specified which follows the current resonance frequency (RFa), and that depending on the frequency shift (ΔF) and the current resonance frequency (RFa) the current maximum load point (max LP) and / or the current maximum load current (I th ) determined or estimated. [10] Device (1) according to one of the preceding claims, characterized by that the unit (10) comprises a second signal path (13), wherein the second signal path (13) is connected in particular in parallel to the first signal path (12), and wherein the output signals of the first and second signal paths (12, 13) are used to determine or estimate the current resonance frequency (RFa) and / or the current maximum load point (max LP) and / or the current maximum load current (I th ) be used. [11] Device (1) according to claim 10, characterized bythat the measuring voltage signal (U3) is fed to the first and second signal path (12, 13). [12] Device (1) according to claim 10 or 11, characterized by that the second signal path (13) comprises a signal buffer (A). [13] Device (1) according to one of claims 10-12, characterized by that the evaluation of the signals of the first and second signal paths (12, 13) is carried out by means of an algorithm. [14] Device (1) according to one of claims 10-13, characterized by that depending on the first time period (Ta) and a predetermined second time period (Tb) following the first time period (Ta), and the output signal of the second signal path (13) the current maximum load point (max LP) and / or the current maximum load current (I th ) determined or estimated. [15] Device (1) according to one of the preceding claims, characterized bythat the current resonance frequency (RFa) and / or the current maximum load point (max LP) and / or the current maximum load current (I th ) in the unit (10) or the control unit (PCU). [16] Device (1) according to one of the preceding claims, characterized by that the unit (10) or the control unit (PCU) detects the current resonance frequency (RFa) and / or the current maximum load point (max LP) and / or the current maximum load current (I th ) with reference values and / or previous determined or estimated values. [17] Device (1) according to one of the preceding claims, characterized by that the current resonance frequency (RFa) and / or the current maximum load point (max LP) and / or the current maximum load current (I th ) can be determined or estimated dynamically. [18] Device (1) according to one of the preceding claims, characterized bythat the unit (10) comprises a rectifier (D1) for rectifying a secondary current (I2) of the secondary circuit. [19] Device (1) according to claim 18, characterized by that the secondary current (I2) is converted into the measuring voltage signal (U3) which is fed to the first signal path (12) and / or the second signal path (13). [20] Device (1) according to one of the preceding claims, characterized by that the device (1) is an induction hob.

Images