Method for operating a device for wirelessly transmitting energy to an electrical load by means of inductive coupling, device and system

Description

[0001] The invention relates to a method for operating a device for wirelessly transmitting energy towards an electrical consumer by means of inductive coupling, a device and a system.

[0002] US 2016 / 0181818 A1 and US 2017 / 0149286 A1 each disclose a device for wirelessly transmitting energy to an electrical load by means of inductive coupling. The device comprises an inverter powered by a supply voltage. The device further comprises capacitors and a power coil, wherein the capacitors and the power coil are interconnected to form an oscillating circuit. The inverter is configured to generate a control signal for the power coil from the supply voltage. The device further comprises a communication coil configured separately from the power coil and configured to exchange data bidirectionally with the electrical load.During a data exchange via the communication coil, the power coil is controlled in such a way that data exchange via the communication coil is possible despite the alternating magnetic field generated by the power coil.

[0003] US 2014 / 0333145 A1 discloses a method for load detection in an electrical consumer that is supplied with energy wirelessly.

[0004] US 2012 / 0112554 A1 discloses a method for wirelessly transmitting energy towards an electrical load by means of inductive coupling and an associated method for controlling a transmitted power.

[0005] The invention is based on the object of providing a method for operating a device for wirelessly transmitting energy towards an electrical consumer by means of inductive coupling, a device and a system which enable the most reliable and flexible operation possible.

[0006] The device is used for the wireless transmission of energy towards an electrical consumer by means of inductive coupling.

[0007] The device comprises a low-voltage power supply, wherein the low-voltage power supply serves to generate a supply voltage with a first level.

[0008] The device comprises a rectifier for generating the supply voltage with a second level, wherein the low-voltage power supply is connected to an output of the rectifier via a decoupling diode and wherein the first level is smaller than the second level,

[0009] The device comprises an inverter or converter powered by the supply voltage. The supply voltage is preferably a direct current. The inverter can, for example, comprise a conventionally connected inverter branch with two semiconductor switching devices. Alternatively, the device can also comprise two inverter branches in a full-bridge configuration. In this regard, reference is also made to the relevant specialist literature.

[0010] The device further comprises at least one capacitor and a power coil, wherein the at least one capacitor and the power coil are connected in such a way that they form a parallel or series resonant circuit.

[0011] The inverter is designed to generate an excitation voltage, particularly a pulse-width modulated one, for the resonant circuit from the supply voltage. The pulse-width modulated excitation voltage is typically a square-wave voltage with a constant or variable duty cycle and a constant or variable period or frequency. In this regard, reference is also made to the relevant specialist literature.

[0012] The inverter further comprises a communication coil formed separately from the power coil, which is designed to exchange data bidirectionally with the electrical consumer.

[0013] The inverter further comprises a control unit which is designed to control the inverter in such a way that the inverter is supplied from the supply voltage having the first level during the data exchange via the communication coil, and the inverter is supplied from the supply voltage having the second level outside of the data exchange via the communication coil.

[0014] The method is used to operate a device described above for wirelessly transmitting energy to an electrical load using inductive coupling, also known as wireless power transfer (WPT). For the fundamentals of WPT, please refer to the relevant technical literature. The device is preferably operated according to the WPC (Wireless Power Consortium) Ki (Cordless Kitchen) method.

[0015] The device for wirelessly transmitting energy towards an electrical consumer by means of inductive coupling can also be referred to as a transmitter and the electrical consumer can be referred to as a receiver.

[0016] According to the invention, during a data exchange or data transmission via the communication coil, the power coil is controlled in such a way that, despite the alternating magnetic field generated by the power coil, a data exchange via the communication coil is still possible.

[0017] In one embodiment, during the data exchange via the communication coil, the power coil is controlled such that an amount of a voltage induced in the communication coil due to the alternating magnetic field remains less than a predetermined threshold value, for example less than 2 V.

[0018] In one embodiment, the first level is less than 60 V, in particular less than or equal to 24 V. Preferably, a low-voltage power supply or a source is used to generate the first level, which is already present in the device for controlling IGBT drivers of the inverter or for controlling a fan.

[0019] In one embodiment, the second level corresponds to a rectified AC mains voltage.

[0020] In one embodiment, the data exchange is carried out cyclically.

[0021] In one embodiment, a value of an electrical parameter of an oscillating circuit comprising the power coil is determined during the data exchange.

[0022] In one embodiment, during the data exchange, the value of the electrical parameter is determined in the form of a value of the impedance of the power coil and / or a value of the impedance of the resonant circuit comprising the power coil, and / or during the data exchange, the value of the electrical parameter is determined in the form of a power that is fed into the power coil and / or into the resonant circuit comprising the power coil.

[0023] In one embodiment, the value of the electrical parameter is determined for a plurality of different frequencies to determine a frequency response of the parameter value.

[0024] In one embodiment, based on the parameter values ​​determined for the plurality of different frequencies, an operating frequency is determined with which the power coil is controlled, in particular outside of the data exchange.

[0025] In one embodiment, a maximum transmittable power is determined based on the parameter values ​​determined for the plurality of different frequencies, wherein the determined maximum transmittable power is communicated to the electrical consumer by means of the communication coil.

[0026] In one embodiment, a difference is formed between two parameter values ​​determined at different frequencies, wherein the formed difference is communicated to the electrical consumer by means of the communication coil.

[0027] In one embodiment, unwanted metallic foreign bodies are detected based on the parameter values ​​determined for the plurality of different frequencies.

[0028] In one embodiment, a natural resonance frequency of an oscillating circuit comprising the power coil is determined during the data exchange.

[0029] In one embodiment, unwanted metallic foreign bodies are detected based on the determined natural resonance frequency.

[0030] In one embodiment, any detected metallic foreign bodies are communicated to the electrical consumer by means of the communication coil.

[0031] The system comprises a device as described above and an electrical consumer.

[0032] Wireless Power Transfer (WPT) is intended to provide a power supply for wireless devices or electrical consumers that can be used with the same flexibility as a power outlet. The device according to the invention for wirelessly transmitting power to an electrical consumer is also referred to as a transmitter, and the electrical consumer is referred to as a receiver.

[0033] Energy transfer in WPT occurs via magnetic coupling between a power coil in the transmitter and a corresponding power coil in the receiver, both of which are preferably tuned to the same or at least a similar resonant frequency using capacitors. This results in a frequency-dependent transfer function from the receiver to the transmitter. The transfer function can be represented, for example, as the power P_Load(f) drawn in the receiver, the transmitted voltage U_Load(f) or current I_Load(f) in the receiver, or the total impedance Z_tot(f), each dependent on the operating frequency f of the transmitter.

[0034] A transmitter can, for example, be integrated into an induction hob or installed as a concealed supply unit beneath a kitchen countertop or tabletop. Portable transmitters for flexible use of wireless receivers are also possible.

[0035] The receiver is typically integrated into a wireless device, particularly a kitchen appliance, whereby the devices can include a wide variety of functions such as heating, stirring, mixing, chopping or combinations of functions. The power requirements and diameter of the devices can vary greatly, for example from 50 to 2400 watts or power coil diameters in the receiver of, for example, 8 to 23 cm, which leads to very different transmission functions and operating points of the inverter in the transmitter.

[0036] Operation is preferably carried out on the receiver, which requires auxiliary power from the transmitter if a battery in the receiver is to be avoided. Data exchange between the receiver and transmitter is also required so that settings, etc., can be exchanged.

[0037] Antennas in the form of short-range communication coils are preferably used for communication, as this ensures clear assignment from the receiver to the transmitter and prevents confusion with a neighboring transmitter, as would be the case with BLE communication, for example. With suitable near-field communication, the communication coils are operatively connected to the power coils; for example, they are located between the power coils. This is why these communication coils can also transmit a small amount of auxiliary power to activate at least simple operation and display, thus enabling battery-free operation. A disadvantage of this arrangement, however, is that power coils and communication coils influence each other, which is why normally only either communication or power supply can be active at the same time.

[0038] The power that can be transmitted from a transmitter to a receiver is limited, among other things, by the magnetic coupling between the transmitter's power coil and the receiver's power coil. For a given inverter size, the current in the transmitter must be increased if the coupling deteriorates. This means that the maximum transmittable power depends on the coupling and the maximum current carrying capacity of the transmitter-inverter, but this also depends on the receiver's design parameters.

[0039] With poor coupling, the magnetic field in the area around the transmitter and receiver also increases. Therefore, it would be desirable to be able to measure the coupling during operation of the transmitter. This, in combination with the design parameters communicated by the receiver, allows for the determination of sufficient coverage of the receiver over the transmitter and / or the calculation of the transfer function, from which suitable operating parameters for efficient energy transfer or unsuitable operating points or control parameters (gain of the system) can be derived.

[0040] Alternatively or in addition to determining the entire transfer function, one or more operating points adjacent to the current operating point can also be measured. This allows the partial slope at the operating point to be determined and, for example, a controller step size to be adjusted accordingly. Multiple substitute parameters can be calculated from multiple measurement points. For example, substitute parameters for the receiver can be calculated by the transmitter independently of the data communicated by the receiver itself, thus determining control parameters for the entire system.

[0041] Furthermore, the use of additional devices for detecting foreign objects can be dispensed with if they can be detected using an impedance measurement with the transmitter's power coil. With WPT, it is necessary to check before and, if necessary, during power transmission to the receiver for any foreign objects above the transmitter. If these are made of metal and would therefore be undesirably heated by the transmitter's magnetic field, these must be checked.

[0042] Since the power coils and the communication coils can conventionally only be operated alternately, impedance measurements cannot be performed with the transmitter's power coil during communication times. This limitation is due to the fact that the power coils are powered by the mains voltage, and especially when a converter / inverter in the transmitter is switched on, the peak voltage of the mains voltage is usually applied to the converter / inverter, resulting in relatively large currents during converter operation, which would disrupt communication.

[0043] According to the invention, during data exchange, the transmitter is connected to a supply voltage of less than 60 V, in particular less than 24 V, 16 V or 12 V, instead of to the mains voltage, so that the current through the power coil of the transmitter remains small enough during an impedance measurement to determine the transfer function or at least one or more operating points on the transfer function so as not to disrupt the communication and its supply or the receiver circuit, so that simultaneous measurement operation with the power coils is possible during communication. Instead of or in addition to the impedance measurement, a self-resonance measurement can also be carried out during communication, which can be used to determine the coupling between the receiver and transmitter and / or as foreign object detection.

[0044] In summary, an impedance measurement of the transmitter's power coil with a limited voltage level can be carried out to measure operationally relevant parameters simultaneously with the communication and / or energy transfer via the communication coils.

[0045] The invention is described in detail below with reference to the drawings. Fig. 1 a system with a device for wirelessly transmitting energy towards an electrical consumer by means of inductive coupling and the electrical consumer, and Fig. 2 a power coil of the Fig. 1 shown device as a function of a frequency of a control signal of the power coil for various coupling factors that represent a magnetic coupling between the power coil of the device and a corresponding power coil of the electrical consumer.

[0046] Fig. 1 shows a system with a device 100 for wirelessly transmitting energy towards an electrical load 200 by means of inductive coupling and an electrical load 200.

[0047] The device 100 can also be referred to as a transmitter. The electrical load can also be referred to as a receiver.

[0048] The device 100 is powered by an alternating current network 300.

[0049] The device 100 comprises a line filter 107 and a downstream rectifier 108 for generating a DC supply voltage U_S with a second level. A switch 115 is connected between the line filter 107 and the rectifier 108, the function of which is described below.

[0050] The device 100 further comprises a low-voltage power supply 113, which is connected to the output of the rectifier 108 via a decoupling diode 114. The low-voltage power supply 113 serves to generate the DC supply voltage U_S with a first level that is lower than the second level generated by the rectifier 108. As long as the DC supply voltage U_S is generated with the first level, the switch is open; otherwise, it is closed.

[0051] The device 100 further comprises an inverter 102 which is supplied from the DC supply voltage U_S.

[0052] The device 100 further comprises capacitors 104, 105 which are connected in series between output terminals of the rectifier 108 and the supply voltage U_S, respectively.

[0053] The device 100 further comprises a power coil 101, wherein the capacitors 104, 105 and the power coil 101 are connected in such a way that they form an oscillating circuit 103. For this purpose, one terminal of the power coil 101 is electrically connected to a connection node of semiconductor switching means 109, 110 of the inverter 102, and another terminal of the power coil 101 is electrically connected to a connection node of the capacitors 104, 105.

[0054] It is understood that the inverter and resonant circuit topology shown is merely exemplary. Within the scope of the present invention, for example, a full-bridge inverter may be used, or differently connected series or parallel resonant circuits may be used, etc.

[0055] The inverter 102 is designed to generate a pulse-width modulated control signal A_S in the form of a control voltage for the resonant circuit 103 from the DC supply voltage U_S.

[0056] The device 100 further comprises a control unit or a controller 106 which is designed to control the operation of the device 100.

[0057] The device 100 further comprises measuring means 116 which are designed to measure all variables necessary for the operation of the device 100, in particular to measure a current I_P through the power coil 101 and to measure a voltage across the coil 101, so that the control unit 106 can determine an active electrical power fed into the power coil 101 and an effective value of an alternating current fed into the power coil 101.

[0058] The device 100 further comprises a communication device 111 coupled to a communication coil 112. The communication device 111, in conjunction with the communication coil 112, serves for bidirectional data exchange with the electrical load 200.

[0059] The electrical load 200 has a power coil 201 and a downstream passive LC resonant circuit 202.

[0060] The electrical consumer 200 further comprises an electrical load 203 fed from the LC resonant circuit 202, for example in the form of an ohmic consumer 203a or an electric motor 203b, for example in the form of a single-phase series-wound motor.

[0061] The electrical load 200 further comprises a measuring device 204 which is designed to measure all variables relevant to the operation of the electrical load 200, for example a voltage applied to the load 203 and a current flowing into the load 203.

[0062] The electrical consumer 200 further comprises a control unit or a controller 205 which is designed to control the operation of the electrical consumer 200.

[0063] The electrical load 200 further comprises a communication device 206 coupled to a communication coil 207. The communication device 206, in conjunction with the communication coil 207, serves for bidirectional data exchange with the device 100.

[0064] Fig. 2 shows the influence of the magnetic coupling on a transfer function P(f) of an electrical consumer 200 with a nominal power of 2.2 kW. The transfer function P(f) shows a magnetic field introduced into the power coil 101 of the Fig. 1 The electrical active power fed into the device 100 shown is dependent on a frequency f of the control signal A_S. The transfer function P(f) is represented as a family of parameters for various coupling factors k. The coupling factor k quantifies a magnetic coupling between the power coils 101 and 201.

[0065] Fig. 2 shows, in addition to the transfer function P(f), also the voltage U_L (or its effective value) at the power coil 201 of the electrical consumer 200. The maximum of the voltage U_L occurs with a resistive load at frequencies of the left maximum of the power.

[0066] For an electrical load 200 designed for high power, a transfer function P(f) with two local maxima can occur, provided the magnetic coupling k between power coil 101 and receiver coil 201 is sufficiently high. According to the design rules for Ki, the left maximum at the lower frequency is larger than the maximum at the higher frequency, which is why this operating range must be used to transmit high power. The load 200 shown exhibits two peaks at couplings of 0.75 and 0.6, but only one peak at a coupling of 0.3. At a coupling of 0.45, the transfer function has inflection points but no second local maximum.

[0067] The operation of the system is described below.

[0068] According to the invention, during a data exchange via the communication coils 112, 207, the power coil 101 is controlled in such a way that, despite the alternating magnetic field generated by the power coil 101, a data exchange or data transmission via the communication coils 112, 207 is possible. For this purpose, during the data exchange, the inverter 102 is powered by the DC voltage U_S at the first level. Outside of the data exchange, the inverter 102 is powered by the DC voltage U_S at the second level. The first level is less than 60 V, in particular less than 20 V. The second level corresponds to the level of a rectified AC mains voltage.

[0069] Data exchange is typically carried out cyclically or periodically.

[0070] According to the invention, during the data exchange, a value of the impedance of the resonant circuit 103 having the power coil 101 is determined and / or a value of the impedance of the power coil 101 is determined, and / or during the data exchange, a value of a power that is fed into the resonant circuit 103 having the power coil 101 is determined.

[0071] The value of the electrical parameter is determined for a variety of different frequencies in order to determine a frequency response of the parameter value, as shown, for example, in Fig. 2 is shown.

[0072] Based on the frequency response, for example, an operating frequency of a control signal can be determined with which the power coil 101 of the device 100 is acted upon, in particular outside of the data exchange.

[0073] Based on the frequency response, for example, a maximum transmittable power can be determined, wherein the determined maximum transmittable power is communicated to the electrical consumer 200 by means of the communication coil 112.

[0074] Furthermore, a difference can be formed between two parameter values ​​determined at different frequencies, wherein the formed difference is communicated to the electrical consumer 200 by means of the communication coil 112.

[0075] Based on the frequency response, unwanted metallic foreign bodies can be detected, for example.

[0076] During the data exchange, a natural resonance frequency of the resonant circuit 103 having the power coil 101 can be determined, wherein undesired metallic foreign bodies are also detected based on the determined natural resonance frequency.

[0077] Detected metallic foreign bodies can be communicated to the electrical consumer 200 via the communication coil 112.

Claims

1. Apparatus (100) for wirelessly transferring energy in the direction of an electrical consumer (200) by means of inductive coupling, comprising: - an inverter (102) fed from a supply voltage (U_S), - at least one capacitor (104, 105), - a power coil (101), - wherein the at least one capacitor (104, 105) and the power coil (101) are interconnected in such a way that they form a resonant circuit (103), and - wherein the inverter (102) is configured to generate a drive signal (A_S) for the power coil (101) from the supply voltage (U_S), and - a communication coil (112) which is separate from the power coil (101) and which is configured to exchange data bidirectionally with the electrical consumer (200), characterized in that the apparatus (100) further comprises: - a low-voltage power supply unit (113), wherein the low-voltage power supply unit (113) is used to generate the supply voltage (U_S) at a first level, - a rectifier (108) for generating the supply voltage (U_S) at a second level, wherein the low-voltage power supply unit (113) is connected via a decoupling diode (114) to an output of the rectifier (108) and wherein the first level is lower than the second level, and - a control unit (106) which is configured to drive the inverter (102) in such a way that - the inverter (102) is supplied with the first level from the supply voltage (U_S) during the data exchange via the communication coil (112), and - the inverter (102) is supplied with the second level from the supply voltage (U_S) outside the data exchange via the communication coil (112).

2. Method for operating the apparatus (100) for wirelessly transferring energy in the direction of the electrical consumer (200) by means of inductive coupling according to Claim 1, characterized in that - during data exchange via the communication coil (112), the power coil (101) is driven in such a way that a magnitude of a voltage induced in the communication coil (112) by the alternating magnetic field remains lower than a predetermined threshold value.

3. Method according to Claim 2, characterized in that - the first level is lower than 60 V.

4. Method according to Claim 3, characterized in that - the first level is suitable for supplying IGBT drivers of the inverter and / or for driving a fan of the apparatus (100).

5. Method according to any one of Claims 2 to 4, characterized in that - the second level corresponds to a rectified AC mains voltage.

6. Method according to any one of Claims 2 to 5, characterized in that - the data is exchanged cyclically.

7. Method according to any one of Claims 2 to 6, characterized in that - during the data exchange, a value of an electrical parameter of a resonant circuit (103) comprising the power coil (101) is determined.

8. Method according to Claim 7, characterized in that - during the data exchange, a value of the impedance of the power coil (101) is determined and / or a value of the impedance of the resonant circuit (103) comprising the power coil (101) is determined, and / or - during the data exchange, a value of a power which is fed into the power coil and / or into the resonant circuit (103) comprising the power coil (101) is determined.

9. Method according to Claim 7 or 8, characterized in that - the value of the electrical parameter is determined for a plurality of different frequencies in order to determine a frequency response of the parameter value.

10. Method according to Claim 9, characterized in that - an operating frequency at which the power coil (101) is driven is determined based on the parameter values determined for the plurality of different frequencies.

11. Method according to Claim 9 or 10, characterized in that - a maximum transferable power is determined based on the parameter values determined for the plurality of different frequencies, wherein the determined maximum transferable power is communicated to the electrical consumer (200) by means of the communication coil (112).

12. Method according to any one of Claims 9 to 11, characterized in that - a difference is formed between two parameter values determined at different frequencies, wherein the difference formed is communicated to the electrical consumer (200) by means of the communication coil (112).

13. System, comprising: - an apparatus (100) for wirelessly transferring energy in the direction of an electrical consumer (200) by means of inductive coupling according to Claim 1, and - an electrical consumer (200).