DE112015000884T5 - Inductive charging device - Google Patents

Abstract

The invention relates to an inductive charging device (1) for charging an electrical energy store (3) of a vehicle (2), comprising a primary coil (4) and an inverter (5) connected upstream of the primary coil (4) for converting a DC voltage into an AC voltage , wherein the inverter (5) comprises a DC voltage input (6) and an AC voltage output (7) and wherein between the DC voltage input (6) and the AC output (7) at least one switch stage (8, 9) and at least one filter (13) are connected , In order to generate as sinusoidal alternating voltage without harmonics, wherein the efficiency of the power transmission should not be affected, the filter (13) comprises a stray field transformer (10) having a first winding section (11) and a second winding section (12).

Description

This application takes the priority of the preceding European patent application no. EP14155956.7 filed on 20 February 2014 and the priority of Swiss patent application no. CH00950 / 14 , which was registered on June 23, 2014. The entirety of both applications are hereby incorporated by reference expressly and explicitly in their entirety and in all arbitrary parts, for all purposes and purposes, in the same manner as in identical complete inclusion in the subject application.

The invention relates to an inductive charging device for charging an electrical energy storage device of a vehicle according to the preamble of claim 1 and to a method for operating an inductive charging device.

Due to their flexibility and user-friendliness, inductive energy transfer systems are increasingly being used for contactless charging of electric vehicles. In this case, energy is transmitted from a primary coil subjected to alternating voltage to a secondary coil arranged on the vehicle side with a downstream rectifier.

In such a system, an alternating magnetic field is usually generated in the frequency range of 25 kHz to 150 kHz, with the preferred frequency in the band set by the standardization bodies being between 80 and 90 kHz. It should be noted that outside of this frequency band, the limits for the emission of electromagnetic waves are defined by internationally valid standards. To comply with these limits, it is crucial that the alternating magnetic field works with the fundamental in the range of 25 kHz to 150 kHz and contains only a very small proportion of harmonics. On the other hand, however, the efficiency of the power transmission should be as high as possible. Therefore, a square wave signal with the fundamental frequency of the alternating magnetic field is generated with electronic switches, whereby the losses can be kept low. However, the square wave signal contains a significant amount of unwanted harmonics. The latter are filtered out in the prior art by means of a suitably dimensioned LC filter. However, such filters, in particular due to the dimensioning of the inductance, require a considerable volume (space requirement), which is one of the disadvantages resulting from the prior art. In addition, the harmonics can often not be eliminated sufficiently.

The DE102010042395A1 discloses a method and systems for inductively charging a battery of a vehicle by means of an inductive coupling of a primary coil of a charging station to a secondary coil of the vehicle. However, DE102010042395A1 does not disclose any inverter upstream of the primary coil.

The US6362463B1 refers to a completely different field and discloses a high-frequency heating apparatus with a circuit for operating a magnetron, z. B. a microwave oven. The driver circuit comprises a DC voltage source, two switching elements, a stray field transformer with a primary and secondary side, a rectifier and a magnetron. The magnetron is galvanically isolated from the (DC) voltage source by the stray field transformer, ie the transmission of the energy is exclusively inductive. On the secondary side, a high-volt voltage for the magnetron is provided by the rectifier. High-frequency current is conducted to the cathode of the magnetron via a third coil of the stray field transformer, which is also galvanically isolated from the primary side. The stray field transformer is not a filter in this circuit; rather, the transmission of the high-frequency voltage for the operation of the magnetron ("high-frequency heating") is required. Due to the (purely) inductive coupling of the stray field transformer, the entire electrical energy of the primary side must be converted into magnetic energy (and reconverted again). This requires that the transformer must be powerful and thus large (space demanding) and costly dimensions. For loading an electrical energy storage device of a vehicle this document is no lesson.

The object of the present invention is thus to eliminate these disadvantages and to provide a charging device which ensures that the harmonics are sufficiently eliminated and the alternating voltage applied to the primary coil comes as close as possible to an ideal sinusoidal shape. At the same time to be created with the invention, the possibility of dimensioning the charging device, in particular the inverter with the filter, space-saving, whereby the arrangement and / or application of an inductive charging device has higher flexibility.

This object is achieved with an inductive charging device mentioned above in that the filter comprises a stray field transformer having a first winding section and a second winding section.

The first winding section and the second winding section are mutually inductive coupled and preferably wound on the same core. Basically, the stray field transformer is a coupled choke. However, the coupling is such that only a part of the flow generated by one winding section (or a throttle) also penetrates the other winding section (or the other throttle) and vice versa. The other (the other non-penetrating) part of the river is called leakage flux or stray field.

In a preferred embodiment, the first winding section and the second winding section of the transformer are wound on a core so that they do not overlap (i.e., are not wound over each other). Particularly preferably, the winding sections are spaced apart on the core.

In the context of the present invention, the term stray field transformer also encompasses transformers in which the stray field or the stray inductance assumes small values in relation to the total field or to the total inductance. It is preferred if the leakage inductance of the transformer or of the respective winding sections lies in the range between 0.5% and 10% of its total inductance, very particularly preferably between 1% and 5% of its total inductance.

This particular embodiment of the filter in an inverter ensures efficient filtering of the harmonics of an incoming signal, in particular a rectangular signal, for the operation of an inductive charging system. This allows the provision of a nearly sinusoidal output signal. At the same time, the charging device can be built very compact and space-saving due to the use of a stray field transformer. Finally, the simple and elegant shading ensures low-loss voltage conversion or transmission.

• – Beide Wicklungen (bzw. Wicklungsabschnitte) werden auf den gemeinsamen Kern gewickelt, benutzen also insbesondere denselben magnetischen Rückschluss, was Platz und Gewicht spart.
• – Die sehr große Hauptinduktivität des Streufeld-Transformators bewirkt zusammen mit den Filterkondensatoren, dass die Gleichtakt-Signale von der Ladespule praktisch ferngehalten werden, was die Störsignale stark verringert. Eine sonst zusätzlich erforderliche „Common Mode Filterdrossel” entfällt damit.
• – Durch die induktive Kopplung der beiden Wicklungsabschnitte werden die Halbleiter mit deutlich geringerem Stromrippel beaufschlagt, was die Verluste minimiert.

Compared to a similar filter arrangement with two uncoupled throttles, there are several advantages:

• - Both windings (or winding sections) are wound on the common core, so in particular use the same magnetic yoke, which saves space and weight.
• - The very large main inductance of the stray field transformer, together with the filter capacitors, that the common mode signals are kept practically away from the charging coil, which greatly reduces the interference signals. An otherwise additionally required "common mode filter choke" is thus eliminated.
• - Through the inductive coupling of the two winding sections, the semiconductors are subjected to significantly lower current ripple, which minimizes the losses.

Switch level is understood to mean a switching unit or a switching path which has at least one controllable switch, in particular semiconductor switches, such as MOSFETs, IGBTs, transistors, etc., which supplies an output signal which is dependent on the activation of the switch stage, e.g. B. a square wave signal or a 'chopped' DC voltage.

When the at least one switch stage (or its transformer-side output or pole) is galvanically connected to the AC voltage output via a winding section of the stray field transformer, it is preferred. The current can thus flow continuously from the transformer-side output of the at least one switch stage via one of the windings of the stray field transformer to the alternating voltage output. This measure has the effect that only a (small) part of the electrical energy in the stray field transformer is converted into magnetic energy. As a result, the filter or the stray field transformer can be dimensioned much smaller, lighter and more cost-effective. At the same time (i.e., despite the advantageous dimensioning of the filter), the circuit according to the invention can achieve the already mentioned advantages with regard to efficient filtering of the harmonics, thus elimination of high-frequency components.

A preferred embodiment is characterized in that between the DC voltage input and the AC output, a first switch stage and a second switch stage are connected and that the first switch stage is connected to the AC output via the first winding section of the leakage transformer and the second switch stage with the AC output via the second Winding portion of the stray field transformer is connected. In this way, two, formed by the respective switch stage waveforms (in particular rectangular signals) are combined with each other, whereby the output power, z. B. via variation of the phase shift between the two waveforms, is adjustable.

Also in this embodiment it is preferred if the first winding section of the stray field transformer makes a galvanic connection between the first Forming switch stage and the AC voltage output (or the first pole of the AC voltage output) and / or the second winding section of the stray field transformer forms a galvanic connection between the second switch stage and the AC output (or the second pole of the AC output). Ie. the switch stages (or their transformer-side outputs or poles) are galvanically connected to the AC output in each case via a winding section of the stray field transformer. Also by this measure, the above-mentioned advantages in terms of space-saving, lighter and more cost-effective dimensioning of the filter, since not the entire electrical energy must be converted into magnetic energy (as would be the case with a galvanic isolation or a purely inductive coupling) ,

A preferred embodiment is characterized in that the first winding section and the second winding section are connected in series (ie galvanically connected within the stray field transformer) and that a tap between the first winding section and the second winding section forms one pole of the AC output or with one pole of the AC output is connected. Thus, a particularly simple circuit can be realized in which the output voltage is almost sinusoidal and in which the output currents can be significantly higher than the input currents. Also, with such a circuit, common-mode effects can be suppressed.

A preferred embodiment is characterized in that the primary coil is connected between the first winding section and the second winding section of the stray field transformer. Ie. the end of the first winding section is connected to one pole of the AC output and the end of the second winding section is connected to the other pole of the AC output. The winding sections are thus parallel to each other or galvanically separated from each other in the stray field transformer. This circuit has the advantage that there is no main field magnetization and no direct current can flow through the windings. For a stronger magnetic modulation is possible.

A preferred embodiment is characterized in that the ratio between the leakage inductance related to the respective other winding section and the total inductance of a winding section is at least 1: 200, particularly preferably at least 1: 100.

In a preferred embodiment, the ratio between the leakage inductance related to the respective other winding section and the total inductance of a winding section is at most 1:10, particularly preferably at most 1:20.

The ratio 1: 100 corresponds to a coupling factor of 0.99; the ratio 1:20 a coupling factor of 0.95.

It is therefore particularly preferred if the leakage inductance of the transformer or the respective winding sections is in the range between 0.5% and 10%, particularly preferably between 1% and 5% of its total inductance.

A preferred embodiment is characterized in that the stray field transformer is formed symmetrically with respect to the first winding section and the second winding section. Ie. both winding sections have the same number of windings. With symmetrical and identical input signals, in particular square-wave signals, this achieves a particularly good approximation to a sinusoidal signal at the output.

A preferred embodiment is characterized in that the filter comprises at least one capacitor which forms an LC filter together with the inductances formed by the stray field transformer. Due to its preferred characteristic, this filters out harmonics particularly efficiently. The term capacitance used in the present specification naturally includes capacitors; or a capacity is realized by a capacitor.

A preferred embodiment is characterized in that the filter comprises at least four capacitances which form a full bridge between the DC voltage input and the AC voltage output. The main inductances of the respective winding sections together with these four capacitances now form a filter which effectively prevents common mode modulation of the primary coil. Particularly favorable is the design with four equal capacities, because by the symmetrical current distribution thus achieved, the reaction to the DC link is particularly low.

A preferred embodiment is characterized in that the inverter is followed by a capacitive voltage divider (formed from resonance capacitors). Thus, the impedance of the inductive transmission system can be increased and adapted to the larger output impedance of the filter.

A preferred embodiment is characterized in that between the poles of the DC input, a capacity is switched. This serves to support the DC intermediate circuit.

A preferred embodiment is characterized in that at least one switch stage of the inverter is formed from two, a half-bridge forming semiconductor switching elements.

Preferably, at least one switch stage half bridge has antiparallel diodes.

Preferably, at least one switch stage half-bridge has capacitors connected in parallel to the individual switch elements of the half-bridge. In view of the fact that individual switching elements can switch off at high currents, the steepness of the switching edge can be reduced by introducing these capacitors (or capacitors), which improves the electromagnetic compatibility.

A preferred embodiment is characterized in that at least one switch stage of the inverter comprises a half bridge formed of IGBTs, preferably with anti-parallel diodes, and / or that at least one switch stage comprises a half bridge formed of MOSFETs, preferably with capacitors connected in parallel to the individual switch elements of the half bridge , includes.

The object is also achieved with a method for operating an inductive charging device according to one of the embodiments described above, wherein a DC voltage is applied to the DC input of the inverter and the at least one switch stage is driven by a drive signal to generate an AC voltage at the AC output, preferably the at least one switch stage is controlled in such a way that the AC voltage at the AC output has a frequency between 10 kHz and 180 kHz, preferably between 25 kHz and 150 kHz, the preferred frequency being between 80 and 90 kHz in the band (defined by the standard committees) ,

A preferred embodiment is characterized in that the two switch stages are operated at the same frequency and out of phase with one another, which results in a particularly 'sinusoidal' output signal.

A preferred embodiment is characterized in that the frequency and the phase of the drive signal are controllable. This increases the flexibility and scope of an inductive charging device.

A preferred embodiment is characterized in that the switch stages are controlled such that at their output in each case a substantially symmetrical square wave signal is applied, preferably with a duty cycle of substantially 50%, which also results in a harmonic-poor and symmetrical output signal.

A preferred embodiment is characterized in that the power available at the primary coil is set by a change in the phase shift between the drive signals of the two switch stages.

This allows a particularly simple control, which allows output signals with a very low harmonic content due to the stray field transformer, independent of power.

A preferred embodiment is characterized in that the frequency and / or the phase shift of the control signals of the switch stages is set so that at the output of the filter or at the input of the inductive transmission system (primary coil) current and voltage are in phase or the cosine of the phase difference between current and voltage to a defined or predetermined value, preferably to a value greater than or equal to 0.95, z. B. 0.95, with the current lagging slightly behind the voltage. This results in a particularly low current load of the primary coil of the inductive transmission system, which both enables high efficiency and keeps the magnetic field strength as low as possible and thus below the permissible limits.

A preferred embodiment is characterized in that the resonant circuit formed by the filter is tuned to a frequency below the minimum operating frequency of the inductive charging device, preferably at most 85%, more preferably at most about 82% of the minimum operating frequency. The tuned frequency may preferably be the resonant frequency or slightly above it. As a result, all frequencies above the operating frequency are filtered out particularly effectively, including the harmonics of the square wave signals, so that output voltage and current are practically sinusoidal.

Further advantages, features and details of the invention will become apparent from the following description in which embodiments of the invention are described with reference to the drawings. In this case, the features mentioned in the claims and in the description each individually by itself or in any combination essential to the invention.

The list of reference numerals is part of the disclosure. The figures are described coherently and comprehensively. The same reference symbols denote the same components, reference symbols with different indices indicate functionally identical or similar components.

It shows:

1 schematically the basic principle in the inductive charging of a vehicle,

2 a detail of a loading device according to the invention,

3 an example of a stray field transformer,

4 an equivalent circuit diagram of a stray field transformer,

5 Voltages and currents in and after the inverter,

6 a further embodiment of a loading device according to the invention,

7 a further embodiment of a loading device according to the invention,

8th an example of an implementation in an overall system.

1 shows a schematic representation of an inductive charging device 1 for charging an electrical energy store 3 of a vehicle 2 , This is done by the energy from a primary coil 4 ( 2 ) of the charging device on the vehicle side arranged secondary coil 21 transfer. In the illustrated embodiment, the secondary coil 21 in the bottom of the (only schematically indicated) electric vehicle and arranged with the energy storage 3 , in particular a battery or a rechargeable battery, connected via a (not shown) rectifier.

2 shows an embodiment of an inductive charging device 1 comprising a primary coil 4 and one of the primary coil 4 upstream inverter 5 for converting a DC voltage into an AC voltage, wherein the inverter 5 a DC input 6 and an AC output 7 includes. Between the DC input 6 and the AC output 7 are two switch stages 8th . 9 and at least one filter 13 connected. The filter 13 includes a stray field transformer 10 with a first winding section 11 and a second winding section 12 , The winding sections 11 . 12 each represent chokes, which are inductively coupled to each other, wherein a portion of the flow as leakage flux does not penetrate the respective other winding section. Preferably, the ratio between the on the other winding section 12 . 11 related stray inductance and the total inductance of a winding section 11 . 12 at least 1: 100, preferably at most 1:20. Of course, this leakage inductance ratio can also assume values below or above this preferred range.

Between the DC input 6 and the AC output 7 are a first switch stage 8th and a second switch stage 9 connected. The first switch stage 9 is with the AC output 7 over the first winding section 11 of the stray field transformer 10 connected. The second switch stage 12 is with the AC output 7 over the second winding section 12 of the stray field transformer 10 connected.

The first winding section 11 and the second winding section 12 are connected in series. A tap between the first winding section 11 and the second winding section 12 forms a pole of the AC output 7 or is one pole of the AC output 7 connected.

In order to achieve the most sinusoidal voltage possible and thus less harmonic content, is used for the control of the primary coil 4 For example, the following circuit is used:
The switch stages 8th . 9 each form a controlled inverter subunit; both switch stages 8th . 9 each deliver a substantially symmetrical square wave signal U ₁ , U ₂ with the same frequency (preferably with a duty cycle of 50%). The voltage signal U ₁ is phase-shifted with respect to the voltage signal U ₂ . Preferably, both the frequency and the phase shift by appropriate control of the switch stages 8th . 9 adjustable.

At the output of each inverter subunit is one winding each 11 . 12 a symmetrical stray field transformer 10 connected. This is thus composed of two coils or inductors L ₁ , L ₂ , which are wound on a common core. The stray field transformer 10 is with respect to the first winding section 11 and the second winding section 12 symmetrically formed (same number of turns).

3 shows a possible structure of a stray field transformer 10 and 4 shows that Equivalent circuit diagram, wherein the ohmic resistances have been omitted for the sake of simplicity. To simplify the considerations, the stray field transformer is 10 as an 'ideal transformer' with the 'ideal' inductors L _1H , L _2H additionally shown with its leakage inductances L _1S , L _2S . The leakage inductance is due to the fact that the transformer is designed such that only part of the magnetic flux generated by the first winding penetrates the second winding and vice versa.

Regardless of the respective other preferred embodiments of the invention, the stray field transformer 10 have the following preferred features: The stray field transformer 10 preferably comprises a core having an annular contour. In addition, from one (longitudinal) side of the core, a protrusion may protrude toward the other (longitudinal) side of the core (in FIG 3 from top to bottom). In this case, an air gap is preferably provided between the projection and the other (longitudinal) side of the core. The winding sections 11 . 12 do not overlap in the illustrated embodiment (ie, they are not wrapped over each other). The projection of the core is located between the first winding section 11 and the second winding section 12 , which are preferably spaced from each other by at least the width of the projection.

The filter 13 includes at least one filter capacity 14 , which together with through the stray field transformer 10 formed inductors forms an LC filter. The stray inductances L _1S , L _2S form together with the capacitor 14 a resonant circuit, which is preferably tuned to a frequency below the minimum operating frequency of the inductive transmission system, preferably at most 85% of the minimum operating frequency, z. B. to about 82% of the minimum operating frequency. As a result, all frequencies are filtered away above the working frequency, including the harmonics of the square wave signals U ₁ , U ₂ , so that the AC output voltage U _A and the AC output current I _{A are} practically sinusoidal. U _A is the inductive transmission system, ie the primary coil 4 , fed.

The frequency and the phase shift of U ₁ and U ₂ are adjusted so that an optimal operation of the connected inductive transmission system results.

From the in 5 represented diagram is a significant advantage of the system according to the invention can be seen: by the transformer coupling and the associated reduction, the amplitude of the output current I _{A can be} significantly higher than that of the input currents I ₁ , I ₂ . It can also be seen that the output AC current I _A and the output AC voltage U _{A are} practically sinusoidal, although the input of the filter 13 is driven with rectangular voltages U ₁ , U ₂ .

The control or the control method is as follows: The control is carried out with two symmetrical square wave signals (and a duty cycle of 50%). The performance of the system is adjusted by changing the phase shift of the two input signals U ₁ , U ₂ . The frequency is thus preferably adjusted so that at the input of the filter 13 or the resonant circuit formed therefrom, the current and the voltage are in phase or slightly "inductive" behavior (cosφ> 0.95).

6 shows a variant of the invention, in which the primary coil 4 between the first winding section 11 and the second winding section 12 of the stray field transformer 10 is switched. Thus, the primary side of the inductive transmission system (ie, the primary coil 4 ) connected between the two transformer windings. The second winding 12 is doing in relation to the embodiment 2 "Reversed" or runs in opposite directions, ie the supply of rectangular signals takes place at the winding beginnings, the output voltage is between the two winding ends.

This circuit has the advantage that there is no main field magnetization and no DC current through the windings 11 . 12 can flow. For a stronger magnetic modulation is possible.

In the in 6 illustrated embodiment was a further variant of a (the inverter 5 downstream) formed from resonant capacitances capacitive voltage divider 15 Indicated in inductive transmission system (dashed capacitor). Thus, the impedance of the inductive transmission system can be increased and so on the larger output impedance of the filter 13 be adjusted.

In a further embodiment ( 7 ) is at least one switch stage 8th . 9 of the inverter 5 from two, a half-bridge forming switching elements 17 . 18 ; 19 . 20 educated. In this case, the upper switching element 17 and the lower switching element 18 a switch stage 8th ; and the upper switching element 19 and the lower switching element 20 a switch stage 9 (see also 8th ). In 7 includes a switch stage of the inverter 5 a half-bridge formed of IGBTs preferably with anti-parallel diodes and another switch stage a half-bridge formed of MOSFETs. To simplify the illustration, L ₁ and L ₂ did not more divided into stray and main inductance. Compared to the embodiment 6 the following differences exist:
The original one filter capacitor 14 was on four capacitors 14 (C _1A , C _1B , C _2A , C _2B ) are arranged, which are arranged as a full bridge, wherein the upper and lower terminal to the two poles of the DC input 6 (DC supply voltage) are connected. The main inductance of L ₁ and L ₂ now forms together with the capacitances 14 a filter 13 , which is a common-mode modulation of the primary coil 4 effectively prevented. The differential filtering effect for generating the sine signal is based on the leakage inductances as in the circuit 2 and 6 ,

The electronic switch stages 8th . 9 of the previous embodiments have been illustrated in an exemplary embodiment as an IGBT half-bridge (Q _1A , Q _1B ) with anti-parallel diodes (D _1A , D _1B ) and as a MOSFET half-bridge (Q _2A , Q _2B ). In particular, since the switching elements Q _2A , Q _2B turn off at high currents, the transconductance of the switching edge can be reduced by introducing capacitors C _3A , C _3B (parallel to the respective switching elements), which improves the electromagnetic compatibility.

The capacitor is used to support the DC link 16 (DC link capacitance) between the poles of the DC input 6 ,

Like from the 2 . 6 and 7 the switch stages are visible 8th . 9 (or their transformer-side outputs or poles) with the AC voltage output 7 each over a winding section 11 . 12 of the stray field transformer 10 galvanically connected. In the illustrated embodiments, the first winding section forms 11 of the stray field transformer 10 a galvanic connection between the first switch stage 8th and one pole of the AC output 7 and forms the second winding section 12 of the stray field transformer 10 a galvanic connection between the second switch stage 9 and the other pole of the AC output 7 ,

8th shows the possible integration into an overall system. The network entrance 22 is a line filter 23 downstream. Between the mains filter 23 and a PFC (power correction factor) stage 25 is a power rectifier 24 connected. With the output of the PFC stage 25 is the DC input 6 of the inverter 5 connected. With the reference number 26 are the drivers for the switch stages 8th . 9 or for the individual switching elements of the switch stages 8th . 9 designated. The drivers are from a controller 27 controlled.

The following is a preferred method for operating an inductive charging device 1 described in more detail. It is at the DC voltage input 6 of the inverter 5 a DC voltage applied. This can be z. B. be done by an AC voltage z. B. from the socket, is rectified. The switch stages or their switching elements are driven with a drive signal to the AC output 7 to generate an AC voltage. Preferably, the at least one switch stage is controlled such that the AC voltage at the AC output has a frequency between 10 kHz and 180 kHz, preferably between 25 kHz and 150 kHz.

The two switch stages 8th . 9 are operated at the same frequency and out of phase with each other. The frequency and the phase of the drive signal of the switching elements are preferably variable.

The switch stages are controlled such that at their output in each case a substantially symmetrical square wave signal is applied, preferably with a duty cycle of substantially 50%.

The at the primary coil 4 available power can be adjusted by changing the phase shift between the drive signals of the two switch stages. The frequency of the drive signals of the switch stages is preferably adjusted so that at the input of the filter 13 formed oscillator circuit current and voltage in phase or the cosine of the phase difference between current and voltage is greater than 0.95.

The through the filter 13 The resonant circuit formed is at a frequency below the minimum operating frequency of the inductive charging device 1 tuned, preferably to at most 85%, more preferably at most about 82% of the minimum operating frequency.

The invention is not limited to the described embodiments and the aspects highlighted therein. Rather, within the concept of the invention a variety of modifications are possible, which are within the scope of expert action. It is also possible, by combining the means and features mentioned to realize further embodiments, without departing from the scope of the invention.

LIST OF REFERENCE NUMBERS

1

Inductive charging device

2

vehicle

3

Electric energy storage

4

primary coil

5

inverter

6

DC input

7

AC output

8th

First switch level

9

Second switch level

10

Leakage transformer

11

First winding section

12

Second winding section

13

filter

14

Filter capacity

15

Resonant Capacitance / Capacitive Voltage Divider

16

DC voltage intermediate circuit capacitor

17

(Upper) switching element of the first switch stage 8th

18

(Lower) switching element of the first switch stage 8th

19

(Upper) switching element of the second switch stage 9

20

(Lower) switching element of the second switch stage 9

21

secondary coil

22

power input

23

Line filter

24

Mains rectifier

25

PFC stage

26

Driver for the switching elements

27

controller

C _1A , C _1B , C _2A , C _2B , C _3A , C _3B

Capacitors or capacitors

D _1A , D _1B

diodes

L ₁ , L ₂ ; L _1H , L _2H ; L _1S , L _2S

inductors

N ₁ , N ₂

winding numbers

Q _1A , Q _1B ; Q _2A , Q _2B

Switching elements (MOSFETs, IGBTs)

I ₁ , I ₂

input currents

U ₁ , U ₂

input voltages

I _A

AC output

U _A

AC output voltage

Claims (17)

Inductive charging device ( 1 ) for charging an electrical energy store ( 3 ) of a vehicle ( 2 ) comprising a primary coil ( 4 ) and one of the primary coil ( 4 ) upstream inverter ( 5 ) for converting a DC voltage into an AC voltage, wherein the inverter ( 5 ) a DC input ( 6 ) and an AC output ( 7 ) and wherein between the DC input ( 6 ) and the AC output ( 7 ) at least one switch stage ( 8th . 9 ) and at least one filter ( 13 ), characterized in that the filter ( 13 ) a stray field transformer ( 10 ) with a first winding section ( 11 ) and a second winding section ( 12 ). Loading device according to claim 1, characterized in that the at least one switch stage ( 8th . 9 ) with the AC output ( 7 ) via a winding section ( 11 . 12 ) of the stray field transformer ( 10 ) is galvanically connected. Charging device according to claim 1 or 2, characterized in that between the DC voltage input ( 6 ) and the AC output ( 7 ) a first switch stage ( 8th ) and a second switch stage ( 9 ) and that the first switch stage ( 9 ) with the AC output ( 7 ) over the first winding section ( 11 ) of the stray field transformer ( 10 ) and the second switch stage ( 12 ) with the AC output ( 7 ) over the second winding section ( 12 ) of the stray field transformer ( 10 ) connected is. Loading device according to claim 3, characterized in that the first winding section ( 11 ) of the stray field transformer ( 10 ) a galvanic connection between the first switch stage ( 8th ) and the AC output ( 7 ) forms and / or that the second winding section ( 12 ) of the stray field transformer ( 10 ) a galvanic connection between the second switch stage ( 9 ) and the AC output ( 7 ). Charging device according to one of the preceding claims, characterized in that the first winding section ( 11 ) and the second winding section ( 12 ) are connected in series and that a tap between the first winding section ( 11 ) and the second winding section ( 12 ) one pole of the AC output ( 7 ) or with one pole of the AC output ( 7 ) connected is. Loading device according to one of the preceding claims, characterized in that the primary coil ( 4 ) between the first winding section ( 11 ) and the second winding section ( 12 ) of the stray field transformer ( 10 ) is switched. Loading device according to one of the preceding claims, characterized in that the ratio between the on the other winding section ( 12 . 11 ) related leakage inductance and the total inductance of a winding section ( 11 . 12 ) is at least 1: 200, preferably at least 1: 100, and / or that the ratio between the on the other winding section ( 12 . 11 ) related leakage inductance and the total inductance of a winding section ( 11 . 12 ) is at most 1:10, preferably at most 1:20. Loading device according to one of the preceding claims, characterized in that the stray field transformer ( 10 ) with regard to the first winding section ( 11 ) and the second winding section ( 12 ) is formed symmetrically. Loading device according to one of the preceding claims, characterized in that the filter ( 13 ) at least one filter capacity ( 14 ), which together with the stray field transformer ( 10 ) forms an LC filter, and that preferably the filter ( 13 ) at least four filter capacities ( 14 ) connected between the DC input ( 6 ) and the AC output ( 7 ) form a full bridge. Charging device according to one of the preceding claims, characterized in that the inverter ( 10 ) a capacitive voltage divider ( 15 ), and / or that between the poles of the DC input ( 6 ) a capacity ( 16 ) is switched. Charging device according to one of the preceding claims, characterized in that at least one switch stage ( 8th . 9 ) of the inverter ( 5 ) of two, a half-bridge forming switching elements ( 17 . 18 ; 19 . 20 ) is formed. Charging device according to one of the preceding claims, characterized in that at least one switch stage of the inverter comprises a half-bridge formed of IGBTs preferably with anti-parallel diodes and / or that at least one switch stage comprises a half bridge formed of MOSFETs. Method for operating an inductive charging device ( 1 ) according to one of the preceding claims, characterized in that at the DC input ( 6 ) of the inverter ( 5 ) a DC voltage is applied and the at least one switch stage ( 8th . 9 ) is driven with a drive signal to the AC output ( 7 ) to generate an alternating voltage, wherein preferably the at least one switch stage ( 8th . 9 ) is driven such that the AC voltage at the AC output has a frequency between 10 kHz and 180 kHz, preferably between 25 kHz and 150 kHz, more preferably between 80 kHz and 90 kHz. Method according to claim 13, characterized in that the two switch stages ( 8th . 9 ) are operated at the same frequency and out of phase with each other. A method according to claim 13 or 14, characterized in that the frequency and / or the phase of the drive signal of a switch stage ( 8th . 9 ) are controllable, and that preferably at the primary coil ( 4 ) available power by a change in the phase shift between the drive signals of the two switch stages ( 8th . 9 ) is set. Method according to one of claims 13 to 15, characterized in that the switch stages ( 8th . 9 ) are driven such that at their output in each case a substantially symmetrical square wave signal is applied, preferably with a duty cycle of substantially 50%. Method according to one of claims 13 to 16, characterized in that the frequency of the drive signals of the switch stages ( 8th . 9 ) is adjusted so that at the output of the filter ( 13 ) or at the input of the primary coil ( 4 ) Current and voltage in phase or the cosine of the phase difference between current and voltage to a predetermined value, preferably to a value greater than or equal to 0.95, z. B. 0.95, wherein the current of the voltage lags slightly, and / or that by the filter ( 13 ) resonant circuit to a frequency below the minimum operating frequency of the inductive charging device ( 1 ), preferably at most 85%, more preferably at most about 82% of the minimum operating frequency.

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