Method for operating an apparatus for wirelessly transferring energy in the direction of an electrical consumer by means of inductive coupling, apparatus and system

Abstract

A method for operating a device for wirelessly transmitting energy in the direction of an electrical consumer by inductive coupling, wherein the device is: - A rectifier for generating DC voltage from power supply system voltage, - An inverter configured to generate a pulse width modulated driving signal supplied from a DC voltage, and - A coil driven by a pulse width modulated driving signal, comprising said coil, wherein the coil is capable of generating an alternating magnetic field for the purpose of transferring energy. The method is, - Includes a step of controlling the actual power output by the inverter to a predefined target power, wherein the frequency and duty cycle of the pulse width modulated driving signal serve as the operating variables of the control, and - To adjust to the target power, a) Step to set the starting frequency (f_0), b) A step of setting the starting duty cycle (DC_1) in such a way that the target power is undershooted, c) A step of measuring the actual power output by the inverter when the start frequency (f_0) is set and the start duty cycle (DC_1) is set, d) A step of selecting an adjusted target power that is less than or equal to the target power, e) A step of calculating the duty cycle (DC_2) computationally corresponding to the adjustment target power, f) Step of setting the calculated duty cycle (DC_2), g) A step of measuring the actual power output by the inverter when the frequency (f_0) is set and the duty cycle (DC_2) is set, and h) Steps d) through g) are repeated while increasing the adjusted target power until the deviation between the target power and the actual power falls below a predefined threshold.

Description

Background Technology

[0001] The present invention relates to a method, device, and system for operating a device for wirelessly transmitting energy in the direction of an electrical consumer by inductive coupling. The problem to be solved

[0002] The present invention is based on the objective of providing a method, apparatus, and system for operating a device for wirelessly transferring energy in the direction of an electrical consumer by inductive coupling, enabling operation that is as reliable and flexible as possible. means of solving the problem

[0003] The method serves to operate a device for wirelessly transferring energy toward electrical consumers by inductive coupling, which is also referred to as WPT (Wireless Power Transfer). Regarding the principles of WPT, relevant technical literature should also be consulted. Preferably, the device operates according to the WPC (Wireless Power Consortium) Ki (Cordless Kitchen) method.

[0004] A device for wirelessly transmitting energy in the direction of an electrical consumer by inductive coupling may also be referred to as a transmitter, and the electrical consumer may be referred to as a receiver.

[0005] The device includes, in particular, a conventional single-phase or multi-phase rectifier for generating a DC voltage from a sinusoidal power supply system voltage.

[0006] The device includes an inverter supplied from a DC voltage. The inverter may be, for example, a half-bridge inverter or a full-bridge inverter. The inverter is configured to generate a pulse-width modulated driving signal, particularly in the form of a pulse-width modulated driving voltage.

[0007] The device includes a conventional coil or transmitter coil configured to generate an alternating magnetic field for the purpose of transmitting energy, driven by an inverter or its pulse width modulated driving signal.

[0008] The method includes the following steps.

[0009] The actual power output by the inverter is controlled to a predefined target power, where the frequency and duty cycle of the pulse-width modulated drive signal serve as the operating variables of the control. In the case of an inverter with a half-bridge, the duty cycle of the pulse-width modulated drive signal generated by the inverter, which constitutes a periodic sequence of pulses in this case, specifies the ratio of the pulse duration to the period duration. The duty cycle is specified as a ratio number of a dimension number with a value range of 0 to 1 or 0 to 100%. In the case of an inverter with a full-bridge, the duty cycle represents, for example, the phase angle of two rectangular waveform signals generated by the associated bridge branches and can assume values ​​between 0° and 360°.

[0010] For example, starting from an actual power of 0 W, the following steps are performed to adjust to the target power.

[0011] In step a), the starting frequency of the pulse width modulated driving signal is first set.

[0012] In step b), the starting duty cycle of the pulse width modulated driving signal is set in such a way that the target power is definitely undershooted. This starting duty cycle can be determined, for example, by experiments and / or computation, where a 15% duty cycle constitutes a suitable starting value according to the above criteria in many cases. The starting duty cycle can be selected depending on the target power. The higher the target power, the higher the starting duty cycle can, of course, be selected.

[0013] Step c) involves measuring the actual power output by the inverter when the start frequency and start duty cycle are set. The power output by the inverter can be determined, for example, by conventional voltage and current measurements and appropriate calculations of the measured variables. Otherwise, relevant technical literature should be consulted in this regard.

[0014] Step d) involves selecting an adjustment target power that is less than or equal to the target power. Preferably, it is selected so that the difference between the previously measured actual power and the next adjustment target power is not too large. For example, the initial adjustment target power may, in principle, correspond to a predefined or predefined ratio of the target power or the previously measured actual power, and may, for example, correspond to ± 80% of the previously measured actual power.

[0015] In step e), the duty cycle of the pulse width modulated driving signal is calculated, which computationally corresponds to the adjustment target power.

[0016] In step f), the calculated duty cycle is set.

[0017] Step g) involves determining the actual power output by the inverter when the frequency is set and the duty cycle is set.

[0018] Step h) involves repeating steps d) through g) while continuously increasing the adjusted target power until the deviation between the established actual power and the target power falls below a predefined threshold. The threshold may be predefined in absolute or relative terms and, for the sake of reference only to exemplary numerical values, may be, for example, 2% of the target power or 30 watts.

[0019] The increase in the adjustment target power can be selected in such a way that the number of iterations is limited to 3 iterations, particularly 2 iterations, particularly 1 iteration.

[0020] The method according to the present invention allows for very rapid adjustment of actual power to target power and limits overshoot that can cause overvoltage in consumer goods. Furthermore, the method according to the present invention imposes only minor requirements regarding knowledge of the actual behavior of the transmission path.

[0021] In an embodiment, at step e), the duty cycle computationally corresponding to the adjustment target power is calculated based on the duty cycle calculated in the aforementioned step f), the actual power measured in the aforementioned step g), and the current or instantaneous adjustment target power.

[0022] The calculation of the duty cycle is explained below with an example.

[0023] The following holds true:

[0024]

[0025] port represents the phase angle between current and voltage. For frequencies close to the resonance frequency is. In the case of a constant operating frequency. can be estimated as a constant, and therefore the term in the following calculations It may be ignored as in.

[0026]

[0027] In this case, DC represents the duty cycle. U_N represents the root-mean-square value of the sinusoidal power supply system voltage rectified by the rectifier. U_DC represents the root-mean-square value of the pulse-width modulated drive voltage generated by the inverter during a given duty cycle (DC).

[0028] Control-level-independent linear and time-invariant impedance It is assumed for the calculation. The operating frequency between the two stages is Since it typically behaves nonlinearly with respect to frequency changes, it must be the same. If the operating frequency is intended to change after one step, it is necessary once again to select an initial duty cycle and measure the new power for the new frequency before the mentioned calculation formulas are allowed to be applied again.

[0029] Hereinafter, the duty cycle calculated in the aforementioned step e) is designated as DC_old. The actual power measured in the aforementioned step g) is designated as P_old. The frequency set in the aforementioned step is designated as f_old. The selected adjustment target power in the current or momentary step d) is designated as P_new. The duty cycle to be calculated is designated as DC_new. The mean square value of the pulse width modulated driving voltage generated by the inverter in the aforementioned step is designated as U_DC_old. The mean square value of the pulse width modulated driving voltage generated by the inverter in the current step is designated as U_DC_new.

[0030] Preferably, P_new is selected to be between 2.5 times and 2 times P_old at most to keep errors resulting from the nonlinearity of the real part of Z(f) (amplitude, temperature, share of higher harmonic oscillations, switching delay, etc.) within acceptable limits. The ratio of P_new to P_old can be selected to be progressively smaller for each subsequent iteration.

[0031] The following holds true:

[0032] silver

[0033] It is established in the case of

[0034] silver

[0035] It holds when f_old = f_new and U_N = constant

[0036] The above formula can finally be solved for DC_new by applying the inverse function arc sine.

[0037] In an embodiment, the adjustment target power for the iteration of steps d) to g), particularly the first, is limited to 2.5 times, particularly 2 times, the adjustment target power selected in the aforementioned step d). Accordingly, the adjustment target power selected for the first time, i.e., the adjustment target power selected before the iteration of steps d) to g), can be limited to 2.5 times, particularly 2 times, the actual power measured in step c).

[0038] In an embodiment, once the deviation between the target power and the actual power falls below a predefined threshold, the frequency and duty cycle are changed while the target power is theoretically maintained the same until an operating point formed from the frequency and duty cycle that satisfies the optimization criteria is established.

[0039] In the embodiment, the optimization criterion is the minimum power loss of the inverter.

[0040] In an embodiment, the operating point satisfying the optimization criterion has a duty cycle greater than 40% in the case of a half-bridge inverter, and in particular has a duty cycle close to 50%. In the case of a full-bridge inverter, the operating point satisfying the optimization criterion has a phase angle between two bridge branches of the full-bridge that is > 150°, in particular close to 180°. In an embodiment having multiple inverters, synchronization with respect to a common operating frequency can constitute the optimization criterion.

[0041] In an embodiment, the starting frequency is based on data communicated to the device by an electrical consumer. Additional data that may be used for the size of the coil diameter of the receiver, its rated output, or system characterization enables the device to estimate, for example, a transfer function P(f) and select a suitable starting frequency f_0 along with the target power.

[0042] In an embodiment, at step g), at least one switching current when switching off the semiconductor switch of the inverter is determined by adding it to the actual power, and the frequency for subsequent repetitions of steps d) to g) is increased when the switching current exceeds a capacitive limit value. In this case, capacitance means that the current after sign change to the parallel diode related to the switch is forced so that the next switch can no longer be switched on in a current-free manner. The larger the switching current, the greater the loss. If the switching current for a given duty cycle is too high, this indicates that the operating frequency has been selected to be too low.

[0043] The device according to the present invention serves to wirelessly transmit energy in the direction of an electrical consumer by inductive coupling and is configured to perform the method described above.

[0044] The device comprises: a rectifier for generating a DC voltage from a power supply system voltage; an inverter supplied from the DC voltage; a coil driven by the inverter, said coil capable of generating an alternating magnetic field for the purpose of transferring energy by said coil; and a control unit configured to drive the inverter in a manner in which the method described above is performed.

[0045] In an embodiment, the device is part of an induction hob.

[0046] A system according to the present invention includes the device described above for wirelessly transmitting energy in the direction of an electric consumer by inductive coupling, and an electric consumer. Brief explanation of the drawing

[0047] The present invention is described in detail below with reference to the drawings, wherein: FIG. 1 schematically illustrates a system including a device for wirelessly transmitting energy in the direction of an electrical consumer by inductive coupling and an electrical consumer supplied by said device, and FIG. 2 illustrates an exemplary transfer function characterizing power transferable by a device in the direction of an electrical consumer through frequency, and schematically a sequence of steps according to the present invention for adjusting power output by the device to a set target power. Specific details for implementing the invention

[0048] FIG. 1 schematically illustrates a system comprising a device (100) and an electric consumer (200) for wirelessly transmitting energy or power in the direction of an electric consumer (200) by inductive coupling. Systems of this type are known in principle and are also referred to as WPT systems.

[0049] The device (100) may be, for example, part of an induction hob or form an induction hob.

[0050] The device (100) includes a conventional rectifier (101) for generating a DC voltage (UG) from a single-phase sinusoidal power supply system voltage (UN). The rectifier (101) can be realized, for example, as a bridge rectifier.

[0051] The device (100) further includes a half-bridge inverter (102) supplied from a DC voltage (UG). The inverter (102) includes two semiconductor switching means (106 and 107) looped in series between the outputs of the rectifier (101).

[0052] The device (100) further includes a coil (103) driven by an inverter (102), and an alternating magnetic field can be generated by the coil for the purpose of transferring energy. To this end, the inverter (102) generates a pulse width modulated driving signal (AS) that serves to drive the coil (103) or a resonant circuit (104) including the coil (103).

[0053] The coil (103) is inductively coupled to the receiver coil (201) of the electric consumer (200), and the rectifier (202) of the electric consumer (200) and also the resonant capacitor and additional components—not specifically exemplified—are connected downstream of the receiver coil (201). Otherwise, reference should also be made to the relevant technical literature in this regard. The consumer (200) typically includes an operator control section that allows an operating mode to be selected. Depending on the operating mode, a target power is selected and delivered to the device. In the configuration phase, additional system parameters of the consumer may be communicated to the device.

[0054] The device (100) further includes two capacitors (108 and 109) looped in series between the outputs of the rectifier (101). A coil (103) is looped between the connection node of the semiconductor switching means (106 and 107) and the connection node of the capacitors (108 and 109). Otherwise, regarding this term as it is known by itself, reference should also be made to the relevant technical literature.

[0055] Furthermore, the device (100) includes a control unit (105), for example in the form of a conventional microprocessor, which controls the operation of the device (100) as described below.

[0056] The control unit (105) controls the actual power output by the inverter (102) to a predefined target power, wherein the frequency and duty cycle of the pulse width modulated driving signal (AS) serve as the operating variables of the control. In this regard, reference should also be made to the relevant technical literature.

[0057] FIG. 2 illustrates a transfer function P(f), where the transfer function P(f) characterizes the power (P) that can be transferred by the device (100) in the direction of the electric consumer (200) through frequency f in the case of a 50% duty cycle.

[0058] The process of adjustment to the target power according to the present invention is described below.

[0059] In the following descriptions, the target power to be adjusted is assumed to be 1.5 kW, for example.

[0060] Furthermore, in the following descriptions, the device (100) for wirelessly transmitting energy is referred to as a transmitter and the electrical consumer (200) is referred to as a receiver. Accordingly, the coil (103) of the device or transmitter (100) is referred to as the transmitter coil and the corresponding coil (201) of the electrical consumer or receiver (200) is referred to as the receiver coil.

[0061] The control unit (105) or its controller does not know the transfer function P(f) at the start of the control. Nevertheless, it is intended to make adjustment toward the required target power in a small number of control steps by setting the frequency and duty cycle of the drive signal (AS) appropriately. In this case, only three steps are required for adjustment toward the target power, and efficiency optimization steps may also follow while the power is kept constant.

[0062] The transmitter (100) can roughly estimate which operating frequency f typically produces the desired power based on its installation conditions, the known coupling range, known rating and target power, and also the size of the receiver coil (201).

[0063] In the first step sequence (S1), a starting frequency (f_0) is selected, which is typically slightly lower than the optimal frequency to keep the power reserve available. In this case, for example, a frequency of 28 kHz is selected as the starting frequency f_0. By monitoring the switching current of the inverter (102), it is possible to identify an incorrectly selected starting frequency (f_0) and then select a different one.

[0064] Consequently, in the first step sequence (S1), the starting frequency (f_0) of the pulse width modulated driving signal (AS) of 28 kHz is set, and the starting duty cycle (DC_1) is set in such a way that the actual power of the result is definitely smaller than the target power. For example, a starting duty cycle (DC_1) of 15% can be set. The smaller the target power, the smaller the starting duty cycle (DC_1) should be selected.

[0065] The first step sequence (S1) subsequently involves measuring the actual power output by the inverter (102) when the start frequency (f_0) is set and the start duty cycle (DC_1) is set. In this case, the measured actual power is 500 W.

[0066] In the subsequent step sequence (S2), an adjusted target power of 1250 W is then selected, which is close to the target power of 1500 W but slightly less than that target power. The adjusted target power of 1250 W corresponds to 2.5 times the previously measured actual power.

[0067] In step sequence (S2), given linearity, a duty cycle (DC_2) resulting in a selected adjustment target power of 1250 W is then calculated and set, i.e., computationally corresponding to the adjustment target power - linearity is assumed. In this case, this duty cycle (DC_2) is 25%.

[0068] The step sequence (S2) involves measuring the actual power output by the inverter (102) once again when the next frequency (f_0) is set and the duty cycle (DC_2) is set. Due to nonlinearity, the measured power is only 1150 W, not 1250 W.

[0069] In the subsequent step sequence (S3), an adjustment target power of 1500 W is selected, which corresponds to a target power of 1500 W. Unacceptable overshooting of the output power due to the selected adjustment target power of 1500 W can be excluded because the change in power between the two steps is intended to be limited and sufficient linearity may be assumed within the remaining power range between 1250 W and 1500 W.

[0070] In step sequence (S3), given linearity, a duty cycle (DC_3) resulting in a selected adjustment target power of 1500 W is then calculated and set, i.e., computationally corresponding to the adjustment target power - linearity is assumed. In this case, the duty cycle (DC_3) is 32%.

[0071] The step sequence (S3) involves measuring the actual power output by the inverter (102) when the next frequency (f_0) is set and the duty cycle (DC_3) is set. In this case, the measured actual power corresponds to the target power.

[0072] Accordingly, subsequently, at the operating point of the driving signal (AS) having frequency (f_0) and duty cycle (DC_3), the operating point of the driving signal (AS) having frequency (f_op1) and duty cycle (DC_op1) of 50% is approached in a plurality of step sequences (S4 to Sn), in each case, the frequency (f) is gradually increased and the duty cycle (DC) is adjusted.

[0073] For the case of a constant duty cycle (DC), the variable (dP / df) shows how the transfer function P(f) proceeds with respect to frequency f, for example, making it possible to identify the minimums (minima) and frequencies on the left side of the peak of the transfer function P(f).

Claims

Claim 1 A method for operating a device (100) for wirelessly transmitting energy in the direction of an electrical consumer (200) by inductive coupling, wherein the device comprises: - a rectifier (101) for generating a DC voltage (UG) from a power supply system voltage (UN); - an inverter (102) configured to generate a pulse width modulated driving signal (AS) supplied from the DC voltage (UG); and - a coil (103) driven by the pulse width modulated driving signal (AS), wherein the coil (103) is capable of generating an alternating magnetic field for the purpose of transmitting the energy, and the method comprises: - a step of controlling the actual power output by the inverter (102) to a predetermined target power, wherein the frequency and duty cycle of the pulse width modulated driving signal (AS) serve as operating variables of the control, and, for adjustment to the target power, a) a step of setting a starting frequency (f_0); b) a starting in such a manner that the target power is undershooted A step of setting a duty cycle (DC_1); c) a step of measuring the actual power output by the inverter (102) when the starting frequency (f_0) is set and the starting duty cycle (DC_1) is set; d) a step of selecting an adjustment target power that is less than or equal to the target power; e) a step of calculating a duty cycle (DC_2) that computationally corresponds to the adjustment target power; f) a step of setting the calculated duty cycle (DC_2); g) a step of measuring the actual power output by the inverter (102) when the frequency (f_0) is set and the duty cycle (DC_2) is set; and h) a step of repeating steps d) through g) while increasing the adjustment target power until the deviation between the target power and the actual power falls below a predefined threshold value, and - in step e),A method for operating a device (100) for wirelessly transmitting energy in the direction of an electric consumer (200) by inductive coupling, wherein a duty cycle (DC_3) computationally corresponding to the above adjustment target power is calculated based on the duty cycle (DC_2) calculated in the above step (f), the actual power measured in the above step g), and the above adjustment target power. Claim 2 A method for operating a device (100) for wirelessly transmitting energy in the direction of an electric consumer (200) by inductive coupling, wherein, in claim 1, the adjustment target power for the repetition of steps d) to g) is limited to 2.5 times the adjustment target power selected in the aforementioned step d). Claim 3 A method for operating a device (100) for wirelessly transferring energy in the direction of an electric consumer (200) by inductive coupling, wherein, when the deviation between the target power and the actual power falls below the predefined threshold value, the frequency and the duty cycle are changed while the target power remains the same until an operating point formed from the frequency (f_op1) and the duty cycle, which satisfies the optimization criteria, is established. Claim 4 In claim 3, the optimization criterion is the minimum power loss of the inverter (102), a method for operating a device (100) for wirelessly transmitting energy in the direction of an electric consumer product (200) by inductive coupling. Claim 5 In claim 4, the operating point satisfying the above optimization criteria is a method for operating a device (100) for wirelessly transferring energy in the direction of an electric consumer (200) by inductive coupling, having a duty cycle greater than 40% in the case of a half-bridge inverter (102). Claim 6 In claim 1, - the starting frequency (f_0) is based on data communicated to the device (100) by the electric consumer (200), a method for operating the device (100) to wirelessly transmit energy in the direction of the electric consumer (200) by inductive coupling. Claim 7 A method for operating a device (100) for wirelessly transferring energy in the direction of an electric consumer (200) by inductive coupling, wherein, in step g), at least one switching current is determined by adding to the actual power when switching off the semiconductor switches (106, 107) of the inverter (102), and the frequency for subsequent repetitions of steps d) to g) is increased when the switching current exceeds a limit value. Claim 8 A method for operating a device (100) for wirelessly transmitting energy in the direction of an electric consumer (200) by inductive coupling, wherein the adjustment target power for the repetition of steps d) to g) is limited to twice the adjustment target power selected in the aforementioned step d). Claim 9 In claim 4, the operating point satisfying the above optimization criteria is a method for operating a device (100) for wirelessly transferring energy in the direction of an electric consumer (200) by inductive coupling, having a duty cycle close to 50% in the case of a half-bridge inverter (102). Claim 10 A method for operating a device (100) for wirelessly transferring energy in the direction of an electrical consumer (200) by inductive coupling, wherein, in step g), at least one switching current is determined by adding to the actual power when switching off the semiconductor switches (106, 107) of the inverter (102), and the frequency for subsequent repetitions of steps d) to g) is increased when the switching current exceeds a capacitive limit value. Claim 11 A device (100) for wirelessly transmitting energy in the direction of an electric consumer (200) by inductive coupling, wherein the device is configured to perform the method described in any one of claims 1 to 10, and comprises: a rectifier (101) for generating a DC voltage (UG) from a power supply system voltage (UN); an inverter (102) supplied from the DC voltage (UG); a coil (103) driven by the inverter (102), wherein the coil (103) is capable of generating an alternating magnetic field for the purpose of transmitting the energy; and a control unit (105) configured to drive the inverter (102) in such a manner that the method described in any one of claims 1 to 10 is performed. Claim 12 In claim 11, the device (100) is a part of an induction hob, a device (100) for wirelessly transmitting energy in the direction of an electric consumer product (200) by inductive coupling. Claim 13 A system comprising: a device (100) for wirelessly transmitting energy in the direction of an electric consumer (200) by inductive coupling as described in claim 11; and an electric consumer (200).

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