Adjustable Capacitance Value For Tuning Oscillatory Systems

Abstract

The present disclosure relates to tuning oscillatory systems. The teachings thereof may be embodied in a device having an adjustable capacitance value for tuning a first oscillatory system, connectable to a second oscillatory system having an unknown and weak coupling factor. The device may include: a first capacitor having a capacitance dependent upon a voltage; and a DC voltage source having a variable voltage applied to associated terminals; a series-connected arrangement of the DC voltage source and a decoupling element connected in parallel with terminals of the capacitor, to apply a variable bias voltage to the first capacitor. The voltage applied to the terminals of the DC voltage source may depend at least in part on a working frequency of the first oscillatory system.

Claims

1. A device having an adjustable capacitance value for tuning a first oscillatory system, provided for coupling with a second oscillatory system having an unknown and weak coupling factor, the device comprising: a first capacitor having a capacitance dependent upon a voltage; a DC voltage source having a variable voltage applied to associated terminals; further comprising a series-connected arrangement of the DC voltage source and a decoupling element is connected in parallel with terminals of the capacitor, to apply a variable bias voltage to the first capacitor; and wherein the voltage applied to the terminals of the DC voltage source depends at least in part on a working frequency of the first oscillatory system.

2. The device as claimed in claim 1, wherein the first capacitor comprises a plurality of parallel-connected capacitors.

3. The device as claimed in claim 1, wherein the decoupling element comprises an inductance.

4. The device as claimed in claim 1, further comprising the parallel-connected arrangement of the first capacitor and the series-connected arrangement of the DC voltage source and the decoupling element connected in series with a second capacitor.

5. The device as claimed in claim 4, wherein the second capacitor is frequency- and voltage stable.

6. The device as claimed in claim 4, wherein a capacitance value of the second capacitor is smaller than a capacitance value of the first capacitor.

7. The device as claimed in claim 1, wherein a coupling factor between the first oscillatory system and the second oscillatory system is less than 50%.

8. An oscillatory system for the transmission of energy to another weakly-coupled oscillatory system, comprising: an oscillating circuit having a frequency generator; a first coil; a first capacitor having a capacitance dependent upon a voltage; and a DC voltage source having a variable voltage applied to associated terminals; further comprising a series-connected arrangement of the DC voltage source and a decoupling element connected in parallel with terminals of the capacitor, to apply a variable bias voltage to the first capacitor; and wherein the voltage applied to the terminals of the DC voltage source depends at least in part on a working frequency of the first oscillatory system.

9. An oscillatory system for reception of energy from another weakly-coupled oscillatory system, comprising: a load; a second coil; a first capacitor having a capacitance dependent upon a voltage; and a DC voltage source having a variable voltage applied to associated terminals; further comprising a series-connected arrangement of the DC voltage source and a decoupling element connected in parallel with terminals of the capacitor, to apply a variable bias voltage to the first capacitor; and wherein the voltage applied to the terminals of the DC voltage source depends at least in part on a working frequency of the first oscillatory system.

10. An energy transmission system comprising: a first oscillatory system; and a second oscillatory system coupled with an unknown and weak coupling factor; wherein the first oscillatory system comprises: a first capacitor having a capacitance dependent upon a voltage; and a DC voltage source having a variable voltage applied to associated terminals; further comprising a series-connected arrangement of the DC voltage source and a decoupling element connected in parallel with terminals of the capacitor, to apply a variable bias voltage to the first capacitor; and wherein the voltage applied to the terminals of the DC voltage source depends at least in part on a working frequency of the first oscillatory system.

11. The energy transmission system as claimed in claim 10, wherein the second oscillatory system comprises: a first capacitor having a capacitance dependent upon a voltage; and a DC voltage source having a variable voltage applied to associated terminals; further comprising a series-connected arrangement of the DC voltage source and a decoupling element connected in parallel with terminals of the capacitor, to apply a variable bias voltage to the first capacitor; and wherein the voltage applied to the terminals of the DC voltage source depends at least in part on a working frequency of the first oscillatory system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention is described in greater detail hereinafter with reference to the exemplary embodiments in the drawing. Herein:

[0021] FIG. 1 shows a schematic representation of an energy transmission system,

[0022] FIG. 2 shows an equivalent electric circuit diagram of a first variant of a device according to the invention having an adjustable capacitance value,

[0023] FIG. 3 shows an equivalent electric circuit diagram of a second variant of a device according to the invention having an adjustable capacitance value,

[0024] FIG. 4 shows an equivalent electric circuit diagram of a third variant of a device according to the invention having an adjustable capacitance value,

[0025] FIG. 5 shows an equivalent electric circuit diagram of a fourth variant of a device according to the invention having an adjustable capacitance value.

DETAILED DESCRIPTION

[0026] The teachings of the present disclosure may be embodied in a device having an adjustable capacitance value for tuning a first oscillatory system, which is provided for coupling with a second oscillatory system having an unknown and weak coupling factor. The device comprises a first capacitor, the capacitance of which is dependent upon a voltage, and a DC voltage source, the voltage of which applied to the terminals thereof can be controlled. The series-connected arrangement of the DC voltage source and a decoupling element is connected in parallel with the terminals of the capacitor, to apply a variable bias voltage to the first capacitor. The voltage present on the terminals of the DC voltage source is or can be adjusted in accordance with a working frequency of the first oscillatory system.

[0027] The device described is associated with lower losses, in comparison with a variant having bidirectional switching elements. The device occupies a smaller space, and can be produced cost-effectively. Specifically, as the first capacitor, a comparatively low-cost capacitor with a “low-grade” ceramic can be employed. In this case, the term “low-grade” relates to the stability of its capacitance in relation to the voltage lost therefrom.

[0028] In some embodiments, the first capacitor can be comprised of a plurality of parallel-connected capacitors. The number of capacitors, which can vary according to the design of an energy transmission system, can be used to determine the magnitude of the capacitance value of the first capacitor. In a known manner, the higher the number of parallel-connected capacitors, the greater the capacitance value. In an automotive field application for the transmission of energy to a secondary coil, the number may lie between 30 and 40.

[0029] In some embodiments, the decoupling element is an inductance. This ensures that an alternating current flowing via the first capacitor does not flow in the parallel path via the low-resistance DC voltage source.

[0030] In some embodiments, the parallel-connected arrangement of the first capacitor and the series-connected arrangement of the DC voltage source and the decoupling element can be connected in series with a second capacitor. For example, the second capacitor may be a frequency- and voltage-stable capacitor. The presence and dimensioning of the second capacitor depend upon the maximum and minimum capacitance values to be achieved in the oscillatory system.

[0031] In some embodiments, the selected capacitance value of the second capacitor is smaller than the capacitance value of the first capacitor. Accordingly, by the series connection of the first and second capacitor, it is ensured that the voltage loss via the first capacitor is sufficiently small, such that the capacitance value of the first capacitor does not vary in response to the alternating voltage applied thereto. It would otherwise not be possible to maintain the constant capacitance value on the first capacitor.

[0032] The design of the capacitance values on the first oscillatory system may be based upon two criteria.

[0033] As a first criterion, maximum coupling between the first oscillatory system and the second oscillatory system is assumed. Maximum coupling is then achieved in the event of an optimum offset (e.g., a zero offset) between the coils of the first oscillatory system and the second oscillatory system, and a minimum air gap. In this case, the stray inductances of both coils in the two oscillating circuits will be at their minimum value. The total capacitance value, given by the capacitance value of the first capacitor and of the optionally-provided second capacitor which is serially-connected thereto, is then at a maximum.

[0034] As a second criterion, minimum coupling between the coils of the first and second oscillatory system is assumed. Minimum coupling then occurs in the event of a maximum air gap and likewise a maximum offset between the coils of the first and second oscillatory system. In this case, the stray inductances of the coils in the first and second oscillatory system will be at their maximum value. In this configuration, the capacitance value of the device, which is given by the capacitance value of the first variable capacitor and of the optionally-provided second capacitor, is at a minimum.

[0035] The adjustment of the capacitance value, by the corresponding adjustment of voltage in relation to the working frequency of the first oscillatory system, then proceeds between the minimum capacitance value and the maximum capacitance value, which have been determined, as described above.

[0036] In some embodiments, the coupling factor between the first oscillatory system and the second oscillatory system is smaller than 50%. The working frequency of the first oscillatory system specifically lies between 80 kHz and 90 kHz.

[0037] Some embodiments may include an oscillatory system for the transmission of energy to another weakly-coupled oscillatory system, comprising an oscillating circuit having a frequency generator (current source), a first coil and a device of the aforementioned type. The function of the device having an adjustable capacitance value is the setting of a fixed working frequency on the oscillatory system within a predefined frequency range, between 80 kHz and 90 kHz, where the oscillatory system is to be employed for inductive energy transmission in the field of charging of electric vehicles.

[0038] Some embodiments may include an oscillatory system for the reception of energy from another weakly-coupled oscillatory system, comprising a load, a second coil, and a device having an adjustable capacitance value, of the aforementioned type. By the adjustment of the capacitance value of the oscillatory system for the reception of energy, for example by the application of a MPP (maximum peak power) method, the transmittable energy to the load can be maximized.

[0039] In some embodiments, an energy transmission system includes a first oscillatory system and a second oscillatory system, which is coupled with an unknown and weak coupling factor, wherein the first oscillatory system for the transmission of energy to the other second oscillatory system comprises a device having an adjustable capacitance value for the tuning of the first oscillatory system.

[0040] In some embodiments, the second oscillatory system incorporates a device having an adjustable capacitance value for tuning the second oscillating circuit, in order to ensure a maximization of the transmittable power to the load by the application of the MPP method.

[0041] Reference in the present description to an “unknown” coupling factor is attributable to the circumstance of the preferred application. One application of the energy transmission system described herein is the wireless charging of electric vehicles. In this application, depending upon the parking position of the vehicle containing the secondary coil over a first coil, e.g., in the floor of a parking space, the air gap (dictated by the vehicle type) and the offset (dictated by the parking position) may be subject to variation. The aforementioned design criteria take account of this circumstance.

[0042] FIG. 1 shows a prior art energy transmission system, comprising a first oscillatory system 10 and a second oscillatory system 20. The first oscillatory system 10 comprises a frequency generator 11 (voltage source), a capacitor 12 with a capacitance value C.sub.1 and a coil 13 with an inductance L.sub.1. The first oscillatory system 10 constitutes a primary coil system of a device for the transmission of energy to the second oscillatory system 20. The first oscillatory system 10 can, for example, be set into the floor of a parking space, or arranged on the floor of the parking space.

[0043] The components of the second oscillatory system 20 comprise a load (an energy store), a second capacitor 22 with a capacitance value C.sub.2 and a second coil 23 with an inductance L.sub.2, and are, e.g., integrated in a vehicle. Where the vehicle is parked on the parking space, the coils are positioned one above the other, such that a mutual magnetic coupling K is constituted between the coils 13, 23 thereof, depending upon the parking position. As a result of the generally large air gap between the coils of the primary-side oscillatory system 10 and the secondary-side oscillatory system 20, in the range of 8 cm to 12 cm, coupling factors are generally lower than 50%.

[0044] The working frequency of the primary-side oscillatory system 10 is dictated by the inductance L.sub.1 of the transformer formed by the primary-side and the secondary-side coils 13, 23, and of the primary-side coil 13 in conjunction with the primary-side capacitance value C.sub.1. In order to ensure a fixed working frequency within a statutorily dictated frequency range between 80 kHz and 90 kHz for inductive vehicle charging systems, variable adjustment of the capacitance value C.sub.1 of the capacitor 12 may be required in response to a varying load 21 or a variation in the inductance L.sub.1 of the transformer or the coil 13.

[0045] The exemplary embodiments represented in FIGS. 2 to 5 permit the setting of the capacitance value C.sub.1 of the capacitor 12 of the primary-side oscillatory system between a minimum capacitance value and a maximum capacitance value. Accordingly, the requirement for the fixed working frequency f to be set in a fixed manner can be ensured, even in the event of a varying load 21 or in the inductance L.sub.1 or L.sub.2.

[0046] FIG. 2 shows an example configuration of a variable capacitance. As a corresponding variable, capacitance can also be provided in the second oscillatory system 20. The exemplary embodiments of the variable capacitance in FIGS. 2 to 5 are identified by the reference numbers 12, 22.

[0047] As shown in FIG. 2, the variable capacitance 12, 22 comprises a first capacitor C.sub.var, with a capacitance dependent upon a voltage, and a DC voltage source DC.sub.var, the voltage of which can be controlled. A series-connected arrangement of the DC voltage source DC.sub.var and a decoupling element L.sub.entk configured as an inductance are connected in parallel with the first capacitor C.sub.var. Accordingly, a variable bias voltage can be applied to the first capacitor C.sub.var. The voltage present on the terminals of the DC voltage source DC.sub.var is set in relation to a desired working frequency (between 80 kHz and 90 kHz) of the first oscillatory system 10. The first capacitor, which is highly voltage-dependent, is thus preloaded by means of the variable DC voltage source DC.sub.var, whereby the desired capacitance value setting is achieved. For the decoupling of the bias voltage of the components in the first oscillatory system, the inductance L.sub.entk is provided. For the setting of the variable capacitance 12, 22, a control function is employed, the manipulated variable of which is the DC voltage. The target value is thus derived from the desired working frequency of the first oscillatory system 10.

[0048] The exemplary embodiment according to FIG. 3 is distinguished from that in FIG. 2 in that the first capacitor C.sub.var is comprised of a plurality of parallel-connected capacitors C.sub.var,1, . . . , C.sub.var,n. The number of parallel-connected capacitors is selected in accordance with the design of the energy transmission system.

[0049] In the exemplary embodiments shown in FIGS. 4 and 5, additional to the variants represented in FIGS. 2 and 3, a second capacitor C.sub.fest is connected respectively in series with the parallel-connected arrangement of the first capacitor C.sub.var and the series-connected arrangement of the DC voltage source DC.sub.var and the decoupling element L.sub.entk. Conversely to the first capacitor C.sub.var, the second capacitor is frequency- and voltage-stable. Moreover, the capacitance value of the second capacitor C.sub.fest is smaller than the capacitance value of the first capacitor C.sub.var.

[0050] The magnitude of the capacitance value can be set by the number of parallel-connected capacitors of the first capacitor and the optional fixed capacitor. If the second frequency- and voltage-stable capacitor is additionally provided, an exceptionally highly variable capacitance value can be achieved. The design of the overall capacitance value is based upon two criteria:

[0051] As a first criterion, maximum coupling between the first oscillatory system and the second oscillatory system is assumed. Maximum coupling is then achieved in the event of an optimum offset (e.g., a zero offset) between the coils of the first oscillatory system and the second oscillatory system, and a minimum air gap. In this case, the stray inductances of both coils in the two oscillating circuits will be at their minimum value. The total capacitance value, given by the capacitance value of the first capacitor and of the optionally-provided second capacitor which is serially-connected thereto, is then at a maximum.

[0052] As a second criterion, minimum coupling between the coils of the first and second oscillatory system is assumed. Minimum coupling then occurs in the event of a maximum air gap and likewise a maximum offset between the coils of the first and second oscillatory system. In this case, the stray inductances of the coils in the first and second oscillatory system will be at their maximum value. In this configuration, the capacitance value of the device, given by the capacitance value of the first variable capacitor and of the optionally-provided second capacitor, is at a minimum.

[0053] The provision of a variable capacitance in the first oscillatory system is intended to ensure a fixed working frequency of the resonant converter in the event of varying load or inductance. The provision of a variable capacitance in the second oscillatory system can be employed in the interests of maximizing the power transmitted via the transformer. To this end, the capacitance value of the second oscillatory system—once the working frequency has been determined by the setting of the capacitance value on the first oscillatory system—can be varied to maximize the power transmittable to the load 21, by the application of the MPP (maximum peak power) method.