WO2015125107A1

WO2015125107A1 - Inductive charging device

Info

Publication number: WO2015125107A1
Application number: PCT/IB2015/051279
Authority: WO
Inventors: Axel Krause
Original assignee: Brusa Elektronik Ag
Priority date: 2014-02-20
Filing date: 2015-02-19
Publication date: 2015-08-27
Also published as: DE112015000884T5

Abstract

The invention relates to an inductive charging device (1) for charging an electrical energy storage device (3) of a vehicle (2), comprising a primary coil (4) and an inverter (5) located upstream of the primary coil (4) for conversion of a direct-current voltage into an alternating voltage, wherein the rectifier (5) comprises a direct current voltage input (6) and an alternating voltage output (7) and wherein at least one switch stage (8, 9) and at least one filter (13) are switched between the direct current voltage input (8) and the alternating voltage output (7). In order to produce an alternating voltage which is as sinusoidal as possible without harmonics, where the efficiency of the power transmission should not be adversely affected, the filter (13) comprises a leakage transformer (10) having a first winding section (11) and a second winding section (12).

Description

Inductive charging device

This application claims the benefit of priority of prior European application no. EP14155956.7 filed on 20th February 2014 and prior Swiss application no. CH00950/14 filed on 23rd June 2014, and the entirety of European application no. EP14155956.7 and the entirety of Swiss application no. CH00950/14 is expressly incorporated herein by reference in their entirety and as to all their parts, for all intents and purposes, as if identically set forth in full herein.

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 as well as a method for operating an inductive charging device.

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

In such a system a magnetic alternating field in the frequency range from 25kHz to 150 kHz is usually generated, where the preferred frequency lies in the band between 80 and 90 kHz stipulated by the standards bodies. In this case, it must be noted that outside this frequency band the limiting values for the emission of electromagnetic waves are stipulated by internationally applicable standards. In order to adhere to these limiting values, it is crucial that the magnetic alternating field operates with the fundamental oscillation in the range from 25 kHz to 150 kHz and only contains a very small fraction of harmonics. On the other hand, however, the efficiency of the power

transmission should be as high as possible. This is why a rectangular signal having the fundamental frequency of the magnetic alternating field is generated with electronic switches, with the result that the losses can be kept low. However, the rectangular signal contains an appreciable fraction of undesired harmo-nics. The latter are filtered out in the prior art by means of a suitably dimensioned LC filter. However, such filters, particularly as a result of the dimensioning of the inductance, require an appreciable volume (space requirement) wherein lies one of the disadvantages resulting from the prior art. In addition, in many cases, the harmonics cannot be eliminated to a sufficient extent.

DE102010042395A1 discloses a method and systems for the inductive charging of a vehicle battery by means of inductively coupling a primary coil of a charging station to the vehicle's secondary coil. This reference, however, lacks to teach the use of an inverter arranged preceding the primary coil.

The US6362463B1 related to a totally different technical field and discloses a high frequency heater with a circuitry to operate a magnetron, e.g. a

microwave oven. The driver circuit comprises a direct current source, two switching elements, a leakage transformer with a primary and a secondary side, a rectifier and a magnetron. The latter is galvanically separated from the (direct current) source by the leakage transformer. This means that energy is transferred solely in inductive manner. On the secondary side the rectifier provides a high voltage for the magnetron. By the third coil of the leakage transformer, which is separated from the primary side galvanically, too, high frequency current is provided to the cathode of the magnetron. The leakage transformer does not constitute a filter within this circuitry, but is necessary for transmitting the high frequency voltage for the operation of the magnetron. Due to the (mere) inductive coupling of the leakage transformer, the whole electric energy of the primary side has to be transformed into magnetic energy (and vice-versa). Thus, the transformer has to be laid out powerful and therefore big (regarding spatial dimensions) and expensive. There is no teaching in this publication regarding the charging of an electrical energy storage for a vehicle.

It is therefore the object of the present invention to eliminate these

disadvantages and provide a charging device in which it is ensured that the harmonics are eliminated to a sufficient extent and the alternating voltage applied to the primary coil comes as close as possible to an ideal sinusoidal form. At the same time, the invention is intended to provide the possibility of dimensioning the charging device, in particular the inverter with the filter, in a space-saving manner with the result that the arrangement and/or application of an inductive charging device has higher flexibility.

This object is solved with an inductive charging device mentioned initially whereby the filter comprises a leakage transformer having a first winding section and a second winding section.

The first winding section and the second winding section are inductively coupled to one another and preferably wound on the same core. Basically the leakage transformer comprises coupled chokes. However, the coupling is in such a manner that only a portion of the flux produced by one winding section (or a choke) also passes through the other winding section (or the other choke) and conversely. The other portion of the flux (which does not pass through the respectively other choke) 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 in such a manner that they do not overlap (i.e. are not wound over one another). Particularly preferably the winding sections are spaced apart from one another on the core.

In connection with the present invention the term leakage transformer also comprises transformers in which the stray field or the leakage inductance has low values in relation to the total field or the total inductance. It is particularly preferred if the leakage inductance of the transformer or the respective winding sections lies in the range between 0.5% and 10% of its total inductance, quite 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 form, in particular a rectangular signal, for operation of an inductive charging system. This makes it possible to provide an almost sinusoidal output signal. At the same time, as a result of the use of a leakage transformer, the charging device can be constructed in a very compact and space-saving manner. Ultimately the simple and elegant wiring ensures a low-loss voltage conversion or transmission. Several advantages are obtained compared with a filter arrangement of the same type with two uncoupled chokes:

- Both windings (or winding sections) are wound on the common core, therefore in particular use the same magnetic yoke, which saves space and weight.

- The very high main inductance of the leakage transformer has the effect together with the filter capacitors that the common mode signals are virtually kept away from the charging coil which greatly reduces the spurious signals. A common mode filter choke additionally required otherwise is therefore omitted.

- As a result of the inductive coupling of the two winding sections, the semiconductors are acted upon with significantly lower current ripple, which minimizes the losses.

Switch stage is understood as a switch unit or a switching path which comprises at least one selectable switch, in particular semiconductor switches such as MOSFETs, IGBTs, transistors, etc., which delivers an output signal which is dependent on the triggering of the switch stage, e.g. a rectangular signal or a 'chopped' direct current voltage.

It is preferred that at least one switch stage (respectively its output on the transformer side or pole) is galvanically coupled with the alternating voltage output via a winding section of the leakage transformer. Thus, the current can flow from the output of the at least one switch stage on the transformer side via one of the windings of the leakage transformer directly to the alternating voltage output. Due to this measure only a (small) amount of electrical energy is transformed into magnetic energy in the leakage transformer. This allows for a much smaller, lightweight and economic dimensioned filter or leakage transformer, respectively. Simultaneously (and despite the advantageous dimensioning of the filter), the above mentioned advantages regarding to efficient filtering of the harmonics and thus the elimination of high frequency portions can be achieved by the circuit according to the invention. A preferred embodiment is characterized in that a first switch stage and a second switch stage are switched between the direct current voltage input and the alternating voltage output and that the first switch stage is connected to the alternating voltage output via the first winding section of the leakage

transformer and the second switch stage is connected to the alternating voltage output via the second winding section of the leakage transformer. In this way, two signal forms (in particular rectangular signals) formed by the respective switch stage can be combined with one another with the result that the output power can be regulated, e.g. by variation of the phase shift between the two signal forms.

Also with this embodiment it is preferred that the first winding portion of the leakage transformer forms a galvanic connection between the first switch stage and the alternating voltage output (or the first pole of the alternating voltage output, respectively) and/or that the second winding portion of the leakage transformer forms a galvanic connection between the second switch stage and the alternating voltage output (or the second pole of the alternating voltage output, respectively). That means that the switch stages (or their respective outputs or poles, respectively) are galvanically coupled to the alternating voltage output via a respective winding portion of the leakage transformer. By this measure, too, the above mentioned advantages can be achieved regarding space-saving, more lightweight and cost-effictive dimensioning of the filter, since not all electrical energy has to be transformed into magnetic energy (what would be the case by galvanic separation or mere inductive coupling, respectively).

A preferred embodiment is characterized in that the first winding section and the second winding section are connected in series (i.e. galvanically connected inside the leakage transformer) and that a tap between the first winding section and the second winding section forms a pole of the alternating voltage output or is connected to a pole of the alternating voltage output. A particularly simple circuit can thus be achieved in which the output voltage is approximately sinusoidal and in which the output currents can be significantly higher than the input currents. Also 'common mode" effects can be suppressed with such a circuit.

A preferred embodiment is characterized in that the primary coil is switched between the first winding section and the second winding section of the leakage transformer. That is, the end of the first winding section is connected to one pole of the alternating voltage output and the end of the second winding section is connected to the other pole of the alternating voltage output. The winding sections are therefore parallel to one another or galvanically separated from one another in the leakage transformer. This circuit has the advantage that no main field magnetization takes place and no direct current can flow through the windings. A stronger magnetic modulation is therefore possible.

A preferred embodiment is characterized in that the ratio between the leakage inductance relative to the respectively 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 relative to the respectively 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 in this case corresponds to a coupling factor of 0.99; the ratio 1 :20 corresponds to a coupling factor of 0.95.

It is therefore particularly preferred if the leakage inductance of the transformer or the respective winding sections lies 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 leakage transformer is configured symmetrically in regard to the first winding section and the second winding section. That is, both winding sections have the same number of windings. With symmetrical and identical input signals, in particular rectangular signals, a particularly good approximation to a sinusoidal signal is thereby achieved at the output.

A preferred embodiment is characterized in that the filter at least has a capacitance which together with the inductances formed by the leakage transformer forms an LC filter. As a result of its preferred characteristic, this filter particularly efficiently filters out harmonics. The term capacitance used in the present description naturally comprises capacitors; or a capacitance is achieved by a capacitor.

A preferred embodiment is characterized in that the filter comprises at least four capacitances which form a full bridge between the direct current voltage input and the alternating voltage output. The main inductances of the respective winding sections now together with these four capacitances form a filter which effectively prevents a common mode modulation of the primary coil.

The design with four capacitances of the same size is particularly favourable since as a result of the symmetrical current distribution thus achieved, the feedback effect on the direct current voltage intermediate circuit is particularly low.

A preferred embodiment is characterised in that a capacitive voltage divider (formed from resonant capacitances) is located downstream of the inverter. The impedance of the inductive transmission system can thereby be increased and thus adapted to the greater output impedance of the filter.

A preferred embodiment is characterized in that a capacitance is switched between the poles of the direct current voltage input. This is used to support the direct current voltage intermediate circuit. A preferred embodiment is characterized in that at least one switch stage of the inverter is formed from two semiconductor switch elements forming a half- bridge.

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

compatibility.

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

The object is also achieved by a method for operating an inductive charging device according to one of the embodiments described above, wherein a direct current voltage is applied to the direct current voltage input of the inverter and the at least one switch stage is triggered with a triggering signal in order to produce an alternating voltage at the alternating voltage output, where preferably the at least one switch stage is triggered in such a manner that the alternating voltage at the alternating voltage output has a frequency between 10 kHz and 180 kHz, preferably between 25 kHz and 150 kHz, where the preferred frequency lies in the band (stipulated by the standards bodies) between 80 and 90 kHz.

A preferred embodiment is characterized in that the two switch stages are operated with the same frequency, and phase-shifted with respect to one another, whereby a particularly 'near-sinusoidal' output signal is obtained. A preferred embodiment is characterized in that the frequency and the phase of the triggering signal are controllable. This increases the flexibility and the area of application of an inductive charging device.

A preferred embodiment is characterized in that the switch stages are triggered in such a manner that a substantially symmetrical rectangular signal, preferably having a duty cycle of substantially 50% is present in each case at the output thereof, whereby a low-harmonic and symmetrical output signal is also obtained.

A preferred embodiment is characterized in that the power available at the primary coil is adjusted by a variation of the phase shift between the triggering signals of the two switch stages. This enables a particularly simple regulation which as a result of the leakage transformer, makes it possible to achieve power-independent output signals having a very low harmonic fraction.

A preferred embodiment is characterized in that the frequency and/or the phase shift of the triggering signals is adjusted 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 are regulated at a defined or predefined value, preferably at a value greater than or equal to 0.95, e.g. 0.95, where the current slightly lags behind the voltage. This results in a particularly low current loading of the primary coil of the inductive transmission system which enables both a high efficiency and also keeps the magnetic field strength as low as possible and therefore below the permissible limiting values.

A preferred embodiment is characterized in that the resonant circuit formed by the filter is tuned to a frequency below the minimal working frequency of the inductive charging device, preferably to at most 85%, particularly preferably to at most 82% of the minimal working frequency. The tuned frequency can preferably be the resonance frequency or be slightly above this. As a result all the frequencies above the working frequency are particularly effectively filtered out, that is even the harmonics of the rectangular signals so that output voltage and current are almost sinusoidal.

Further advantages, features and details of the invention are obtained from the following description in which exemplary embodiments of the invention are described with reference to the drawings. In this case, the features mentioned in the claims and in the description are each essential to the invention individually by themselves or in any combination. The reference list is part of the disclosure. The figures are described cohesively and in an overlapping manner. The same reference numbers denote the same components, reference numbers having different indices indicate components which have the same function or which are similar.

In the figures in this case:

Fig. 1 shows schematically the basic principle for inductive charging of a vehicle,

Fig. 2 shows a section of a charging device according to the invention,

Fig. 3 shows an example of a leakage transformer,

Fig. 4 shows an equivalent circuit diagram of a leakage transformer,

Fig. 5 shows voltages and currents in or after the inverter,

Fig. 6 shows another embodiment of a charging device according to the invention,

Fig. 7 shows another embodiment of a charging device according to the invention,

Fig. 8 shows an example of an implementation in a complete system.

Figure 1 shows in schematic view an inductive charging device 1 for charging an electric energy storage device 3 of a vehicle 2. To this end, the energy is transferred from a primary coil 4 (Fig. 2) of the charging device to the secondary coil 21 located on the vehicle side. In the exemplary embodiment shown the secondary coil 21 is disposed in the bottom of the electric vehicle (only indicated purely schematically) and is connected to the energy storage device 3, in particular a battery or a rechargeable battery, via a rectifier (not shown). Figure 2 shows an exemplary embodiment of an inductive charging device 1 comprising a primary coil 4 and an inverter 5 located upstream of the primary coil 4 for conversion of a direct current voltage into an alternating voltage, where the inverter 5 comprises a direct current voltage input 6 and an alternating voltage output 7. Two switch stages 8, 9 and at least one filter 13 are switched between the direct current voltage input 6 and the alternating voltage output 7. The filter 13 comprises a leakage transformer 10 having a first winding section 1 1 and a second winding section 12. The winding sections 1 1 , 12 each form chokes which are inductively coupled to one another, where a fraction of the flux as stray flux does not pass through the respectively other winding section. Preferably the ratio between the leakage inductance relative to the respectively other winding section 12, 1 1 and the total inductance of one winding section 1 1 , 12 is at least 1 : 100, preferably at most 1 :20. Naturally this leakage inductance ratio can also have values below or above this preferred range.

A first switch stage 8 and a second switch stage 9 are switched between the direct current voltage input 6 and the alternating voltage output 7. The first switch stage 9 is connected to the alternating voltage output 7 via the first winding section 1 1 of the leakage transformer 10. The second switch stage 12 is connected to the alternating voltage output 7 via the second winding section 12 of the leakage transformer 10. The first winding section 1 1 and the second winding section 12 are connected in series. A tap between the first winding section 1 1 and the second winding section 12 forms a pole of the alternating voltage output 7 or is connected to a pole of the alternating voltage output 7.

In order to achieve a sinusoidal voltage as far as possible and therefore a small fraction of harmonics, the following circuit for example is used for the triggering of the primary coil 4:

The switch stages 8, 9 each form a controlled inverter subunit; both switch stages 8, 9 each deliver a substantially symmetrical rectangular signal U-i , U₂ having the same frequency (preferably having a duty cycle of 50%). The voltage signal Ui is phase-shifted with respect to the voltage signal U₂. Preferably both the frequency and the phase shift are adjustable by

corresponding triggering of the switch stages 8, 9.

One winding 1 1 , 12 each of a symmetrical leakage transformer 10 is connected at the output of each inverter subunit. This subunit is therefore constructed of two coils or inductances l_i, L₂ which are wound on a joint core. The leakage transformer 10 is configured symmetrically with regard to the first winding section 1 1 and the second winding section 12 (same number of windings).

Figure 3 shows a possible structure of a leakage transformer 10 and Fig. 4 shows the equivalent circuit diagram, where the ohmic resistances have been omitted for simplicity. To simplify the analyses, the leakage transformer 10 is shown as an 'ideal' transformer' having the 'ideal' inductances Lm, L_2H in addition to its leakage inductances Lis, L₂s- The leakage inductance comes about since the transformer is designed so that only a portion of the magnetic flux produced by the first winding passes through the second winding and conversely.

Regardless of the respective other preferred embodiment of the invention, the leakage transformer 10 can have the following preferred features: the leakage transformer 10 preferably comprises a core which has an annular contour. In addition, a projection can protrude from one (longitudinal) side of the core in the direction of 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 1 1 , 12 do not overlap in the embodiment shown (i.e. they are not wound over one another).The projection of the core is located in this case between the first winding section 1 1 and the second winding section 12, which are preferably spaced apart from one another by at least the width of the projection.

The filter 13 comprises at least one filter capacitance 14 which together with the inductances formed by the leakage transformer 10 forms an LC filter. In this case, the leakage inductances L_1S, L₂s together with the capacitor 14 form a resonant circuit which is preferably tuned to a frequency below the minimal working frequency of the inductive transmission system, preferably to at most 85% of the minimal working frequency, e.g. to about 82% of the minimal working frequency. As a result all the frequencies above the working frequency are filtered out, i.e. also the harmonics of the rectangular signals U-i , U₂, so that the output alternating voltage UA and the output alternating current l_A are almost sinusoidal. U_A is supplied to the inductive transmission system, i.e. the primary coil 4.

The frequency and the phase shift of Ui and U₂ are thus adjusted to that an optimal operation of the connected inductive transmission system is obtained. An essential advantage of the system according to the invention can be seen from the diagram shown in Fig. 5: as a result of the transformer coupling and the associated reduction, the amplitude of the output current l_A can be significantly higher than that of the input currents , . It can additionally be seen that the output alternating current l_A and the output alternating voltage U_A are almost sinusoidal although the input of the filter 13 is triggered with rectangular voltages Ui, l .

The triggering or the regulating method is accomplished as follows: the triggering is accomplished with two symmetrical rectangular signals (and a duty cycle of 50%). The power of the system is adjusted by a variation of the phase shift of the two input signals Ui, U₂. The frequency is 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 behave slightly

"inductively" (coscp > 0.95).

Figure 6 shows a variant of the invention in which the primary coil 4 is switched between the first winding section 1 1 and the second winding section 12 of the leakage transformer 10. Consequently the primary side of the inductive transmission system (i.e. the primary coil 4) is switched between the two transformer windings. In this case, in relation to the embodiment from Fig. 2 the second winding 12 is "turned" or runs in the opposite direction, i.e. the rectangular signals are fed in at the winding beginnings, the output voltage is applied between the two winding ends. This circuit has the advantage that no main field magnetization takes place and no direct current can flow through the windings 1 1 , 12. A stronger magnetic modulation is therefore possible.

In the embodiment shown in Fig. 6 as a further variant, a capacitive voltage divider 15 (downstream of the inverter 5) formed from resonance capacitances was indicated in the inductive transmission system (dashed capacitor). The impedance of the inductive transmission system can thus be increased and thus adapted to the greater output impedance of the filter 13.

In a further embodiment (Fig. 7) at least one switch stage 8, 9 of the inverter 5 is formed from two switch elements 17, 18; 19, 20 forming a half-bridge. In this case, the upper switching element 17 and the lower switching element 18 form one switch stage 8; and the upper switch element 19 and the lower switch element 20 form a switch stage 9 (see also Fig. 8). In Fig. 7 one switch stage of the inverter 5 comprises a half-bridge formed from IGBTs preferably with anti-parallel diodes and another switch stage forms a half-bridge formed from MOSFETs. In order to simplify the diagram, Li and L₂ are no longer divided into leakage and main inductance. The following differences exist compared with the embodiment from Fig. 6:

The original single filter capacitor 14 was divided into four capacitors 14 (Cm, C-i B, C₂A, C₂B) which are arranged as a full bridge, where the upper or lower terminal thereof are connected to the two poles of the direct current voltage input 6 (DC supply voltage). The main inductance of Li or L₂ now together with the capacitances 14 forms a filter 13 which effectively prevents a common mode modulation of the primary coil 4. The differential filter effect for producing the sinusoidal signal is based on the leakage inductances as in the circuit from Figs. 2 and 6.

The electronic switch states 8, 9 of the preceding embodiments were shown in an exemplary embodiments as an IGBT half-bridge (Qi_A, QI B) with anti-parallel diodes (Di_A, D _B) or as a MOSFET half-bridge (Q_2A, Q₂B)- Since in particular the switching elements Q_2A, Q₂B switch off at high currents, the steepness of the switching edge can be reduced by introducing capacitors C_3A> C₃B (connected in parallel to the respective switching elements) which improves the electromagnetic compatibility.

The capacitor 16 (direct current voltage intermediate circuit capacitance) between the poles of the direct current voltage input 6 is used to support the direct current voltage intermediate circuit.

As can be seen from Figs. 2, 6 and 7, the switch stages 8, 9 (or their outputs or poles on the transformer side, respectively) are galvanically connected with the alternating voltage output 7 in each case via a winding portion 1 1 , 12 of the leakage transformer 10. In the depicted embodiments the first winding portion 1 1 of the leakage transformer 10 forms a galvanic connection between the first switch stage 8 and one pole of the alternating voltage output 7 and the second winding portion 12 of the leakage transformer 10 forms a galvanic connection between the second switch stage 9 and the other pole of the alternating voltage output 7. Figure 8 shows the possible integration in a complete system. A mains filter 23 is located downstream of the main input 22. A mains rectifier 24 is connected between the mains filter 23 and a PFC (power correction factor) stage 25. The direct current voltage input 6 of the inverter 5 is connected to the output of the PFC stage 25. The reference number 26 designates the drivers for the switch stages 8, 9 or for the individual switching elements of the switch stages 8, 9. The drivers are controlled by a controller 27.

A preferred method for operating an inductive charging device 1 is described in detail in the following. In this case, a direct current voltage is applied to the direct current voltage input 6 of the inverter 5. This can be accomplished, for example, by rectifying an alternating voltage, e.g. from the socket. The switch stages or the switching elements thereof are triggered with a triggering signal in order to produce an alternating voltage at the alternating voltage output 7. Preferably the at least one switch stage is triggered in such a manner that the alternating voltage at the alternating voltage output has a frequency between 10 kHz and 180 kHz, preferably between 25 kHz and 150 kHz. The two switch stages 8, 9 are operated at the same frequency and phase- shifted with respect to one another. The frequency and the phase of the triggering signal of the switching elements are preferably variable.

The switch stages are triggered in such a manner that in each case a substantially symmetrical rectangular signal is applied to the output thereof, preferably with a duty cycle of substantially 50%.

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

The resonant circuit formed by the filter 13 is tuned to a frequency below the minimal working frequency of the inductive charging device 1 , preferably to at most 85%, particularly preferably at most about 82% of the minimal working frequency.

The invention is not restricted to the embodiments described and the aspects emphasized therein. On the contrary a plurality of modifications within the inventive idea which lie within the scope of action of the person skilled in the art are possible. It is also possible to implement further embodiments by combining the said means and features without departing from the framework of the invention.

Reference list

1 Inductive charging device

2 Vehicle

3 Electrical energy storage device

4 Primary coil

5 Inverter

6 Direct current voltage input

7 Alternating voltage output

8 First switch stage

9 Second switch stage

10 Leakage transformer

1 1 First winding section

12 Second winding section

13 Filter

14 Filter capacitance

15 Resonance capacitance / capacitive voltage divider

16 Direct current voltage intermediate circuit capacitance

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

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

19 (Upper) switching element of the second switch stage 9

20 (Lower) switching element of the second switch stage 9

21 Secondary coil

22 Mains input

23 Mains filter

24 Mains rectifier

25 PFC stage

26 Driver for the switching elements

27 Controller

Cm, C_1B, C_2A, C-2B, C_3A, C_3B Capacitances or capacitors

D , D-i B Diodes

L-i , L₂; LIH, L₂H; LIS, L₂S inductances

Ni , N₂ Winding numbers QIA, QIB; Q2A, Q2B Switching elements (MOSFETs, IGBTs) , I₂ Input currents

Ui, U2 Input voltages

Output alternating current

UA Output alternating voltage

Claims

Patent claims

Inductive charging device (1 ) for charging an electrical energy storage device (3) of a vehicle (2), comprising a primary coil (4) and an inverter (5) located upstream of the primary coil (4) for conversion of a direct-current voltage into an alternating voltage, wherein the rectifier (5) comprises a direct current voltage input (6) and an alternating voltage output (7) and wherein at least one switch stage (8, 9) and at least one filter (13) are switched between the direct current voltage input (6) and the alternating voltage output (7), characterized in that the filter (13) comprises a leakage transformer (10) having a first winding section (1 1 ) and a second winding section (12).

The charging device according to claim 1 , characterized in that the at least one switch stage (8, 9) is galvanically connected with the alternating voltage output (7) via a winding section (1 1 , 12) of the leakage transformer

(10).

The charging device according to claim 1 or 2, characterized in that a first switch stage (8) and a second switch stage (9) are switched between the direct current voltage input (6) and the alternating voltage output (7) and that the first switch stage (9) is connected to the alternating voltage output (7) via the first winding section (1 1 ) of the leakage transformer (10) and the second switch stage (12) is connected to the alternating voltage output (7) via the second winding section (12) of the leakage transformer (10).

The charging device according to claim 3, characterized in that the first winding section (1 1 ) of the leakage transformer (10) forms a galvanic connection between the first switch stage (8) and the alternating voltage output (7) and/or that the second winding section (12) of the leakage transformer (10) forms a galvanic connection between the second switch stage (9) and the alternating voltage output (7).

5. The charging device according to any one of the preceding claims, characterized in that the first winding section (1 1 ) and the second winding section (12) are connected in series and that a tap between the first winding section (1 1 ) and the second winding section (12) forms a pole of the alternating voltage output (7) or is connected to a pole of the alternating voltage output (7).

6. The charging device according to any one of the preceding claims,

characterized in that the primary coil (4) is switched between the first winding section (1 1 ) and the second winding section (12) of the leakage transformer (10).

7. The charging device according to any one of the preceding claims,

characterized in that the ratio between the leakage inductance relative to the respectively other winding section (12, 1 1 ) and the total inductance of a winding section (1 1 , 12) is at least 1 :200, preferably at least 1 :100 and/or that the ratio between the leakage inductance relative to the respectively other winding section (12, 11 ) and the total inductance of a winding section (1 1 , 12) is at most 1 :10, preferably at most 1 :20.

8. The charging device according to any one of the preceding claims,

characterized in that the leakage transformer (10) is configured symmetrically with regard to the first winding section (1 1 ) and the second winding section (12).

9. The charging device according to any one of the preceding claims,

characterized in that the filter (13) comprises at least one filter

capacitance (14) which together with the inductances formed by the leakage transformer (10) forms an LC filter, and that preferably the filter (13) comprises at least four filter capacitances (14) which form a full bridge between the direct current voltage input (6) and the alternating voltage output (7).

10. The charging device according to any one of the preceding claims, characterized in that a voltage divider (15) is located downstream of the inverter (10), and/or that a capacitance (16) is connected between the poles of the direct current voltage input (6). 1 1. The charging device according to any one of the preceding claims,

characterized in that at least one switch stage (8, 9) of the inverter (5) is formed from two switching elements (17, 18; 19, 20) which form a half- bridge.

The charging device according to any one of the preceding claims, characterized in that at least one switch stage of the inverter comprises a half-bridge formed from IGBTs preferably with anti-parallel diodes and/or that at least one switch stage comprises a half-bridge formed from

MOSFETs.

Method for operating an inductive charging device (1 ) according to any one of the preceding claims, characterized in that a direct current voltage is applied to the direct current voltage input (6) of the inverter (5) and the at least one switch stage (8, 9) is triggered with a triggering signal in order to produce an alternating voltage at the alternating voltage output (7), wherein preferably the at least one switch stage (8, 9) is triggered in such a manner that the alternating voltage at the alternating voltage output has a frequency between 10 kHz and 80 kHz, preferably between 25 kHz and 150 kHz, particularly preferably between 80 kHz and 90 kHz.

14. The method according to claim 13, characterized in that both switch

stages (8, 9) are operated at the same frequency and phase-shifted with respect to one another.

15. The method according to claim 13 or 14, characterized in that the

frequency and/or phase of the triggering signal of a switch stage (8, 9) are controllable and that preferably the power available at the primary coil (4) is adjusted by a variation of the phase shift between the triggering signals of the two switch stages (8, 9).

16. The method according to any one of claims 13 to 15, characterized in that the switch stages (8, 9) are triggered in such a manner that a substantially symmetrical rectangular signal is applied at the output thereof, preferably having a duty cycle of substantially 50%.

17. The method according to any one of claims 13 to 16, characterized in that the frequency of the triggering signals of the switch stages (8, 9) is adjusted so that at the output of the filter (13) or at the input of the primary coil (4) current and voltage are in phase or the cosine of the phase difference between current and voltage is regulated to a predefined value, preferably to a value greater than or equal to 0.95, e.g. 0.95, wherein the current lags slightly behind the voltage and/or that the resonant circuit formed by the filter (13) is tuned to a frequency below the minimal operating frequency of the inductive charging device (1 ), preferably to at most 85%, particularly preferably to at most about 82% of the minimal working frequency.