WO2015125114A1

WO2015125114A1 - Charging circuit for a rechargeable battery with an increased output voltage

Info

Publication number: WO2015125114A1
Application number: PCT/IB2015/051295
Authority: WO
Inventors: Axel Krause
Original assignee: Brusa Elektronik Ag
Priority date: 2014-02-21
Filing date: 2015-02-20
Publication date: 2015-08-27
Also published as: DE112015000898A5

Abstract

The invention relates to a charging circuit (1, 1a..1e) for a rechargeable battery (A), having a transformer (T), a bridge rectifier (B) connected to a secondary coil (L2) of the transformer (T) via first opposite bridge points (P11, P21), and a charging output (a) connected to second opposite bridge points (P12, P22) of the bridge rectifier (B). A first capacitor (C1) is connected between a first bridge point (P11) and a second bridge point (P12). A second capacitor (C2) is also connected between this first bridge point (P11) and the other second bridge point (P22). The invention also relates to a mobile part (MT) for a contactless charging circuit, to a motor vehicle (2) having a mobile part (MT), to a motor vehicle charging system (3) and to a use of the charging circuit (1, 1a..1e).

Description

Charging circuit for an accumulator with increased output voltage

This application claims the benefit of European Applications No. EP14156254.6, filed on Feb. 21, 2014, and No. EP14167049.7, filed on May 5, 2014, the entirety of which is expressly and explicitly assigned by reference in their entirety and in any parts therewith, for all purposes and purposes, as incorporated herein, in the same manner as with identical complete inclusion in the subject application.

The invention relates to a charging circuit for a rechargeable battery, which comprises a transformer, a bridge rectifier connected to a secondary coil of the transformer via first opposing bridge points and a charging output connected to second opposing bridge points of the bridge rectifier. In addition, the charging circuit has a first capacitor connected between a first bridge point and a second bridge point and one between them

Bridge point and the other second bridge point connected second capacitor. Furthermore, the invention relates to a handset with the secondary-side components of a charging circuit of the type mentioned as well as a motor vehicle with such a handset. In addition, the invention relates to a motor vehicle charging system with such a charging circuit and such a motor vehicle. Finally, the invention relates to the use of a handset or a charging circuit of the type mentioned for loading a

Accumulator in a charging system for motor vehicles.

A charging circuit, a handset, a motor vehicle, a charging system and a use, as mentioned above, are basically known. For example, WO 2013/136409 A1 discloses a circuit comprising a transformer, a bridge rectifier connected to a secondary coil of the transformer via first opposite bridge points, a first capacitor connected between a first bridge point and a second bridge point, and a first bridge point between them and the other second bridge point connected second Capacitor. Similar circuits can also be found in GB 843 843 A and EP 0 633 652 A2.

A charging circuit of the type mentioned converts an input AC voltage in a conventional manner into a DC output voltage, whereby a connected to the output accumulator can be loaded. The following considerations relate in particular to charging circuits with a variable coupling between them

Primary side and its secondary side, which may occur, for example, inductive or contactless charging circuits. The output voltage of the charging circuits is generally proportional to the field strength and the coupling factor. An inductive charging circuit should therefore be dimensioned for the given nominal power to the maximum occurring output voltage with the smallest coupling factor. This maximum output voltage occurs especially in the final charge phase when the accumulator or the battery is almost fully charged. In particular, this dimensioning relates to the primary side of the charging circuit. If the charging circuit requires a smaller output DC voltage, which is the case during the majority of the charging time, or if the coupling is better than expected, the charging circuit is oversized for these specific operating points. An object of the present invention is therefore to provide an improved

Charging circuit to provide an improved handset, an improved motor vehicle, an improved automotive charging system and an improved use of the charging circuit. In particular, a high output voltage should be able to be generated while the power remains constant, without the field strength and thus the input current having to increase to the same extent.

The object is solved by the features of the independent claims.

Advantageous developments are in the figures and in the dependent

Claims set forth.

According to the invention, the capacitance value of the first and second lies

Capacitor in the charging circuit of the type mentioned in the range of P

c _{± 2} _

^L J ^υ t-DCmax

to

P

_{Ci 2} _

J ^ DCmax

where P indicates the rated power of the charging circuit, f the transmission frequency of the charging circuit and U2 _D cmax the maximum output DC voltage of the charging circuit. The additional capacitors results in a lower effective

Load voltage, the capacitors, especially in large

Output voltages are effective, however, are quickly reloaded at low output voltage and thus reduce the effective load voltage less. As a result, the ratio of maximum value to minimum value of the voltage at the secondary coil of the transformer is reduced in relation to the ratio of maximum value to minimum value of the DC output voltage. In the end, the charging circuit achieves higher output voltages with the same power and coupling compared to the prior art.

In particular, the charging circuit is formed contactless and has a secondary part of a charging circuit comprehensive handset and a separate therefrom the primary-side components of the charging circuit comprehensive stationary part.

In a contactless charging circuit, the advantages of the invention occur

especially when the coupling between the primary coil and the secondary coil can vary, that is, when the position of the primary coil to Sekundärspuie during charging due to the design of the operated device is not specified. The measures according to the invention result in reserves which enable a low-loss charging process even if the primary coil and the secondary coil are not optimally aligned with each other. These reserves can also be achieved in the partial load range at low

Advantageously use output voltages, because then due to the

Voltage doubling the required charging voltage already achieved with reduced primary current or reduced field strength. Such Reduction enables a reduction in losses and an improvement in efficiency.

Furthermore, the object of the invention is achieved with a motor vehicle comprising a handset of the type mentioned and connected to the charging output of the handset accumulator, which at least partially serves the drive of the motor vehicle.

In addition, the object of the invention with a motor vehicle charging system is solved which comprises a motor vehicle of the type mentioned and a primary side of the components of the charging circuit comprehensive stationary part, which is arranged outside this motor vehicle.

Finally, the object of the invention is achieved by using a mobile part according to the invention, the mobile part and a battery connected to the charging output of the handset accumulator, which at least partially serves the drive of the motor vehicle, are disposed within the motor vehicle.

Also, the object of the invention by a use of a

Solved charging circuit according to the invention in a motor vehicle charging system for motor vehicles, the handset and connected to the charging output of the handset accumulator, which at least partially serves the drive of the motor vehicle, are disposed within the motor vehicle and the stationary part is stationary outside this motor vehicle.

In general, the presented charging circuit for any inductive

or contactless charging systems are used with a stationary part and a handset. When using the featured

Charging circuit in a charging system for motor vehicles, the benefits of the invention but particularly apparent, since the coupling between the primary coil and secondary coil on the one hand can not be increased arbitrarily, on the other hand may vary depending on the position of the vehicle to the primary coil.

Inductive charging of electric vehicles via in-ground

Induction loops can be divided into two general categories, namely the stationary loading of the parked vehicle and the mobile loading while driving on laid in the roadway induction cables.

Via induction winding in the ground (primary coil) becomes a magnetic

Alternating field in the frequency range 25 ... 150kHz (preferably 85kHz) generated as soon as the system detects a ready to charge motor vehicle. A part of this field penetrates a "receiver coil" (secondary coil) in the vehicle and thus enables a contactless energy transfer as in a transformer.

The better the coupling between the induction loop installed in the ground and the receiver coil on the vehicle side, the smaller the required "reactive power" for generating the field.With a given distance between the road surface and the vehicle underbody, the greater the average diameter of the coupling Loop or the distance of the laid in the roadway lines.

At the same time, however, the part of the magnetic dipole field which is outside the vehicle and thus unusable increases sharply. Particularly in the case of high transmission powers, the permissible limit values for magnetic alternating fields can then be clearly exceeded in the accessible area next to the vehicle.

The interior of the vehicle, on the other hand, is magnetically well shielded by the sheet metal body, so there is no danger of exceeding the limit value here. In particular, at high power and frequencies but eddy currents can be generated in the body panel, which heat the vehicle underbody possibly inadmissible and the efficiency of

Significantly reduce the loading process. This warming is proportional to

Square of the generated field strength. One goal in a contactless charging system for electric vehicles is therefore to transmit as much power as possible with as little field strength as possible. This is realized by the measures according to the invention. Further advantageous embodiments and modifications of the invention will become apparent from the dependent claims and from the description in

Synopsis with the figures.

In particular, it is advantageous if the capacitance value of the first and second capacitor according to the formula

P

2 · f · U2 _DCmax

is calculated. As a result, the charging circuit achieves twice the output voltage for the same power and coupling compared to the prior art. A deviation of the capacitance value actually used from the calculated capacitance value of ± 10% only slightly changes the present conditions and is therefore to be regarded as included in the scope of protection.

In a favorable embodiment, the charging circuit comprises a third capacitor connected between a terminal of the secondary coil and a first bridge point. As a result, a resonant circuit is formed on the secondary side, as a result of which the charging circuit can be operated in particular well on voltage sources.

In a further advantageous embodiment, the charging circuit comprises a fourth capacitor connected between a terminal of a primary coil of the transformer and a terminal of a charging input.

As a result, a resonant circuit is also formed on the primary side, whereby the

Charging circuit in turn can be operated well on voltage sources. This is very advantageous in particular in the case of contactless energy transmission, since the reactive power required for the transmission field is taken over by this capacitor and does not burden the alternating voltage source.

It is also favorable if the charging circuit comprises a fourth capacitor connected in parallel with the primary coil of the transformer. As a result, instead of the primary-side resonant circuit is a primary-side

Parallel resonant circuit formed. This in turn results in advantageous conditions when operating the charging circuit to a voltage source.

In particular, results from the combination of series and parallel connection a capacitive voltage divider, which causes a reduction of the input current, whereby the input voltage source is relieved in an advantageous manner.

It is furthermore advantageous if the charging circuit comprises a fifth capacitor connected between the first bridge points. As a result, the voltage jump in the reversal of the current direction is avoided

or mitigated. As a result, the voltage harmonics at the secondary coil are also reduced.

A further advantageous charging circuit comprises a switch arranged between the first bridge point and the first capacitor or between the first bridge point and the second capacitor. For example, the switch may be formed by a relay contact.

But it is also particularly advantageous if the switch is formed by a transistor. Especially with good couplings between the primary coil and the secondary coil of the transformer cause the between the first

Bridge point and the second bridge point switched first capacitor and the between this first bridge point and the other second

Bridge point switched second capacitor a comparatively complex and undesirable behavior at the input of the inductive transmission system, specifically with regard to the phase response of the input current to the input voltage. In the mentioned operating state, however, the measures taken to increase the output voltage may be dispensable or the advantages do not outweigh the disadvantages.

Advantageously, the capacitor half-bridge comprising the two capacitors is made switchable with the switch in order to improve the phase characteristic of the input current.

An advantageous charging circuit further includes a controller which is adapted to open or close the switch depending on an operating state of the charging circuit. For example, the control of the switch based on a coupling between the

Primary coil and the secondary coil of the transformer, using a (especially with regard to the efficiency of the charging circuit) optimal

Operating point or based on a field strength of the primary coil done. In general, the control command can be determined on the secondary side or on the primary side or else based on operating parameters of both the primary side and the secondary side. It is also conceivable, in particular, that a command for opening or closing the switch is forwarded from the primary side to the secondary side, for example by radio.

When the charging circuit is designed as a contactless charging circuit, the handset having the secondary components of the charging circuit, in particular the secondary coil of the transformer, the bridge rectifier, the first and second capacitor, a charging output, and optionally the third and fifth capacitor, the switch and the controller comprise , If the charging circuit is used in a contactless motor vehicle charging system, the primary coil of the transformer as well as possibly the fourth capacitor can accordingly be arranged stationarily outside the motor vehicle.

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. The features mentioned in the claims and in the description may each be essential to the invention individually or in any desired combination.

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 shows a first embodiment of a charging circuit according to the invention;

FIG. 2 shows a time profile of secondary current and secondary voltage of the charging circuit according to FIG. 1; FIG. 3 shows a diagram of the DC output voltage as a function of the input current;

4 shows a diagram of the normalized secondary voltage as a function of the standardized DC output voltage for optimally dimensioned capacitors;

Fig. 5 as Fig. 4, but with half the size of capacitors;

Fig. 6 as in Fig. 4, but with twice as large capacitors;

7 is a graph of the normalized secondary voltage difference in FIG

Dependence of the capacitor values for different values of the normalized output DC voltage difference;

Fig. 8 shows a further embodiment of an inventive

Charging circuit with series resonant circuits in the primary circuit and in the secondary circuit;

Fig. 9 yet another embodiment of an inventive

Charging circuit with an additional capacitor in the

Bridge rectifier;

10 shows the time courses of secondary current and secondary voltage without the capacitor in the bridge rectifier;

11 shows the time profiles of secondary current and secondary voltage with the capacitor in the bridge rectifier;

12 shows an embodiment of a charging circuit according to the invention with an additional switch between bridge rectifier and capacitors;

FIG. 13, like FIG. 12, only with a field-effect transistor as a switch; FIG.

Fig. 14 shows an embodiment of a charging circuit according to the invention with a control for said switch and Fig. 15 is a schematically illustrated example of a charging system with a motor vehicle.

Fig. 1 shows a first embodiment of an inventive

Charging circuit 1a. The charging circuit 1a comprises a transformer T having a primary coil L1 and a secondary coil L2 inductively coupled thereto, one at the secondary coil L2 of the transformer T via first

opposite bridge points P1 1, P21 connected

Bridge rectifier B, which is formed here with four diodes D1..D4, and one with second opposite bridge points P12, P22 of

Bridge rectifier B connected charging output a. Between a first bridge point P1 1 and a second bridge point P12, a first capacitor C1 is additionally connected. Between this first bridge point P11 and the other second bridge point P22, a second capacitor C2 is connected.

At the output a connected to the second bridge points P12, P22, an accumulator A is connected in this example, which is indeed a possible but not mandatory component of the charging circuit 1a. In addition, a current source I connected to the input e connected to the primary coil L1, which is also possible but not mandatory part of the charging circuit 1 a.

The function of the charging circuit 1a shown in Fig. 1 will now be explained in more detail, the secondary coil L2 is considered for the following considerations as an ideal sine AC power source. That is, the secondary flow 12 is sinusoidal. Furthermore, the DC output voltage U2 _D c because of the accumulator A as (quasi) assumed constant. The diodes D1..D4 are considered ideal. At time t = 0 is also assumed UC1 = U2 _D c, UC2 = 0th Thus, the signal forms shown in FIG. 2 result for one oscillation period.

Initially diode D1 turns off due to the voltage on capacitor C1.

Likewise, the diodes D3 and D4 block because of the direction of the current 12. The current 12 thus flows at the beginning of the two capacitors C1 and C2, whereby the capacitor C1 is discharged and the capacitor C2 is charged. The reloading of the capacitors C1 and C2 takes place until the

Voltage at the first capacitor UC1 = 0. Further, the voltage across the first capacitor C1 can not fall but remains because of the diode D1, the time t starts to conduct ₀ constant to zero. Accordingly, the voltage at the second capacitor C2 remains constant at UC2 = U2 _D c- As a further consequence, the charging current no longer flows from the time t ₀ via the capacitor C1, but via the diode D1. Until the time t = T / 2, the voltages at the capacitors are thus UC1 = 0, UC2 = U2DC- After turning the current at t = T / 2, diodes Di and D2 are off.

Furthermore, the diode D4 blocks since the voltage UC2 = U2 _D c. Consequently, the current 12 now flows again across the capacitors C1 and C2, whereby the capacitor C1 is charged and the capacitor C2 is discharged. The reloading of the capacitors C1 and C2 takes place until the voltage at the second capacitor UC2 = 0. Next, the voltage on the second

Capacitor C2 does not sink, but remains constant at zero because of the diode D4, which begins to conduct from this point on. Accordingly, the remains

Voltage at first capacitor C1 constant at UC1 = U2 _DC . As a further consequence, the charging current no longer flows via the capacitor C2, but via the diode D4. Until the time t = T at which the cycle of

Starts anew, the voltages across the capacitors thus UC1 = U2 are _D c, UC2 = 0th

In FIG. 2, the voltages UC1 and UC2 are not shown directly, but the voltage U2. In the first half period, the voltage U2 corresponds to the voltage UC2, in the second half period the negative voltage UC1.

By the capacitors C1, C2 results over a pure

Charging circuit with only one rectifier B now a deeper effective

Load voltage U2, as shown in FIG. 2 clearly shows. The

Capacitors C1, C2 are effective especially at high output voltages U2 _D c, but at low output voltage U2 _D c they are quickly reloaded and thus reduce the effective load voltage U2 less. As a result, the ratio of maximum value to minimum value of the voltage U2 with respect to the ratio of maximum value to minimum value of

DC output voltage U2 _D c reduced. In the end, the

Charging circuit 1 a with the same power and coupling compared to the prior art thereby higher output voltages U2 _D c-

FIG. 3 shows an exemplary diagram of the DC output voltage U2DC as a function of the input current I1 or IAC _rms . in an inductive transmission system with weak coupling. Strichliert with short dashes is the rated current of the current source I (respectively a

Voltage source U), dashed with long lines a course of a

Charging circuit only with a rectifier B (and without capacitors C1 and C2) and finally drawn through the course of the presented charging circuit 1 a. It can clearly be seen that the charging circuit 1 a at low output DC voltage U 2 _D c initially as a charging circuit without

Capacitors C1 and C2 behaves, so these have little or no influence. However, as the DC output voltage U2DC increases, so does the influence of the capacitors C1 and C2, and the progression of the

DC output voltage U2 _D c over the input current 11 deviates more and more from a charging circuit according to the prior art. At the same

Input current 11 reaches the charging circuit 1 a in the example shown twice compared to a conventional charging circuit

Output voltages U2 _D c-

This case occurs when the capacitance value of the first and second capacitors C1, C2 according to the formula

P

^Cl ' ^{2 ~} 2 · / · U2 _D ² _Cmax

where P is the rated power of the charging circuit 1, 1 a..1 c, f is the transmission frequency of the charging circuit 1, 1 a..1 c and U2 _DCma x the maximum DC output voltage of the charging circuit 1, 1 a..1 c indicates.

In particular, this choice of the capacitance value at the power P and a secondary voltage U2 <U2ocmax ensures that at each full-wave of the transformer voltage both all diodes D1 ..D4, as well as the Capacitors C1, C2 carry a portion of the charging current. Only when U2 reaches or exceeds the value U2 _DCma x does no current flow anymore through the diodes D1, D4 connected in parallel to the capacitors C1, C2

Charging circuit 1, 1 a..1 c acts as pure, known from the literature, voltage doubler circuit.

Of course, a doubling of the output voltage U2 _D c is not mandatory for the invention. Compensation for this doubling can be achieved, for example, by halving the secondary turns of the

Transformers T done, accordingly, the curves shift to the left. As before, the output voltage range is limited

Input current 11 with the inventive circuit 1 a but twice as large as without them.

In general, the influence of the capacitors C1 and C2 on the charging circuit 1a is the greater the greater their capacitance value. Large capacitors C1 and C2 therefore lead to a greater increase in the output voltage U2 _D c than small capacitors C1 and C2. In general, therefore, the capacitance value of the first and second capacitors C1, C2 should be in the range of

P

i _{2 f} " ₂ 2

¹ / ^υ ^ DCmax

to

4 '/' U2 _DCmax

lie.

Figures 4 to 6 show additional diagrams of the normalized

Secondary voltage U2 / U2 _max depending on the normalized

DC output voltage U2 _D c U2DCmax- for different values of

Capacitors C1, C2. In Fig. 4 the course is for

2 - f ^■ U2 _DCmax shown. It can be clearly seen that the curve first approximates the value U2 / U2 _max = 1, but the curve at U2 _D c / U2 _D cmax = 1 bends upward. Will now for example, assume that 0.6 <U2 _D c / U2ocma ^ 1, 0, that is, that the DC output voltage U2DC is in the range of 60% of the maximum

DC output voltage U2DCmax up to 100% of the maximum

Output DC voltage U2 _D cmax may / should move, then results for the variation of the ratio U2 / U2 _max a range of

0.88 <U2 / U2max ^ 1, 0. That is, the secondary voltage U2 moves in a range of 88% of the maximum secondary voltage U2 _max to 100% of the maximum secondary voltage U2 _ma x-

In Fig. 5 is now the course for

P

Ci, 2-TTTJ _j W. As can be seen from FIG. 5, the kink in the graph moves to higher values of Δ by the change of the capacitance value to the right

U2 _DC / U2 _D cmax. Specifically, the graph bends upwards approximately at U2 _D c / U 2 _D cmax = 1, 4. The range of 0.6 <U 2 _D c / U 2 _D cmax ^ 1, 0 thus shifts to the steeper region of the characteristic curve. For the same area

Δζ U2 = _D c / U2 _D cmax = 0,6..1, 0 = 0.4 is now obtained for the variation of the ratio U2 / U2 _ma x, a range of 0.76 U2 / U2 _max <1, the 0th That means that

Secondary voltage U2 moves within a range of 76% of the maximum secondary voltage U2 _ma x to 100% of the maximum secondary voltage U2 _ma x.

In Fig. 6 is now the course for

P

^ 1,2 ~. <_ R r 2

u ^ DCmax shown. As can be seen from Fig. 6, the kink in the graph travels to the lower value of l by changing the capacitance value to the left

U2 _D c / U 2 _D cmax. Specifically, the graph bends away at approximately U2 _D c U2DCmax = 0.7 upwards. The range of 0.6 s U2Dc U2DCma ^ 1, 0 thus shifts partially into the linear range of the characteristic curve. For the same area Az =

U2 _DC / U2 _D cmax = 0.6..1, 0 = 0.4 results for the variation of the ratio

U2 / U2 _ma x now a range of 0.70 <U2 / U2 _max <1 0th That means that Secondary voltage U2 moves in a range of 70% of the maximum secondary voltage U2 _max to 100% of the maximum secondary voltage U2 _ma x.

Fig. 7 shows the relationships in a slightly different representation.

Specifically, the normalized secondary voltage difference AU2 / U2 _max in

Dependence of the normalized capacitance value of the capacitors C1 / C1 _o t,

C2 / C2 _op t for different values of the normalized

Output DC voltage difference Δζ = U2 _D c U2 _D cma> c shown, where:

P

Δ · J V £ DCmax

In addition, the operating points described in FIGS. 4 to 6 are plotted for the curve Δζ = 0.4. It can be clearly seen that the graphs at C1 / C1 _op t = C2 / C2 _op t = 1 have a minimum. That is, the normalized

Secondary voltage difference AU2 / U2 _max then becomes minimal when for the

Capacitors are selected above the capacitance _values C1 _0pt and C2 _opt , regardless of the normalized

DC output voltage difference Az = U2 _D c / _D U2 Cmax latter only affects the amount of normalized secondary voltage difference AU 2 / U2 _ma x, but not the position of the minimum in terms of the values chosen for the capacitors C1, C2. If C1, C2 goes to zero (the circuit then acts as a full-wave rectifier) or C1, C2 exceeds a certain value (the circuit then acts as a voltage doubler, ie the parallel diodes D1, D4 do not conduct), then AU2 / U2max = Δζ.

FIG. 8 now shows a further embodiment of a charging circuit 1b, which is very similar to the charging circuit 1a shown in FIG. In addition, however, this comprises a third capacitor C3a connected between one terminal of the secondary coil L2 and a first bridge point P1 1 and a third capacitor C3b connected between the other terminal of the secondary coil L2 and the other first bridge point P21. It would also be conceivable for a single, larger capacitor to be connected between a terminal of the secondary coil L2 and a first bridge point P1 1, P21 instead of the two third capacitors C3a and C3b. In addition, the charging circuit 1 b comprises one between a terminal of the primary coil L1 of the transformer T and a terminal of the

Ladeeingangs e fourth capacitor C4a and connected between the other terminal of the primary coil L1 of the transformer T and the other terminal of the charging input e fourth capacitor C4b. Again, it would be conceivable that instead of the two fourth capacitors C4a and C4b a single larger capacitor between a terminal of a

Primary coil L1 of the transformer T and a terminal of the charging input e is connected. As a result, a series resonant circuit is formed on the primary side and on the secondary side, as a result of which the charging circuit 1b can be operated in particular well on a voltage source U, as shown in FIG. 8. This is very advantageous, in particular in the case of contactless energy transmission, since the reactive power required for the transmission field is taken over by this capacitor and does not burden the alternating voltage source U. Despite the use of the voltage source U, the circuit acts on

Bridge input (ie at the bridge points P11 and P21) in turn as a current source, whereby the secondary current 12 is sinusoidal and the conditions shown in FIGS. 2 and 3 result. In this context, it would also be conceivable that instead of the

Primary-side resonant circuit a parallel resonant circuit is provided. For this purpose, instead of the capacitors C4a, C4b, a fourth capacitor is connected in parallel with the primary coil L1 of the transformer T. In particular, the combination of series and parallel connection results in a capacitive

Voltage divider, which causes a reduction of the input current 11, whereby the input voltage source U is advantageously relieved.

FIG. 9 shows yet another embodiment of a charging circuit 1c, which is very similar to the charging circuit 1b shown in FIG. In addition, however, this includes a fifth capacitor C5 connected between the first bridge points P1 1, P21. As a result, the voltage jump in the reversal of the current direction of the current 12 is avoided or mitigated. As a result, the voltage harmonics at the

Secondary coil L2 reduced.

FIG. 10 shows the time profiles of secondary current 12 and

Secondary voltage U2 without the fifth capacitor C5 in

Bridge rectifier B (see also Fig. 2), and Fig. 1 1 shows the time course of secondary current 12 and secondary voltage U2 with the fifth capacitor C5 in the bridge rectifier B. From Fig. 1 1 it can be seen that in Fig. 10 still occurring voltage jump when turning the current 12 now no longer occurs. Of course, the fifth capacitor C5 can also be used in a charging circuit 1a according to FIG.

FIG. 12 shows an example of a charging circuit 1d which has a switch S arranged between the first bridge point P1 1 and the first capacitor C1 or the second capacitor C2. The

Capacitors C1 and C2 cause a comparatively complex behavior at the input of the inductive transmission system, specifically with regard to the phase course of the current 11 with respect to the voltage U1. This is

especially in the case of good couplings. In this operating state, the measures taken to increase the output voltage U2oc but may be unnecessary. Advantageously, the capacitor half-bridge consisting of the capacitors C1 and C2 is now made switchable with the controlled switch S in order to increase the phase characteristic of the current 11

improve. The switch S can be designed, for example, as a relay contact. It is also conceivable that this, as in the example shown in Fig. 13, is formed by a transistor, in particular by a MOSFET or IGBT.

Fig. 14 shows in this connection an exemplary arrangement with a charging circuit 1e (or a charging circuit 1 d) and a controller CTR, which is connected to the switch S and provided for its activation. Furthermore, the arrangement comprises an optional, between the charging circuit 1 e and the accumulator A connected output filter F. The controller CTR controls the switch S in response to a Operating state of the charging circuit 1 e to. For example, the controller CTR can be set up to detect a coupling between the primary coil L1 and the secondary coil L2 of the transformer T and to close the switch S if the coupling falls below a predefinable threshold value and to open when the coupling exceeds a predefinable threshold value , It would also be conceivable that a command to open or close the switch S is determined on the primary side and forwarded (eg by radio) to the secondary side. For example, the state of the switch S may be changed in the course of a (primary) search for an optimal operating point. It would also be conceivable that the switch S is closed when a maximum field strength is exceeded in order to reduce this in turn with the aid of the realized voltage doubling at the output A again. In order to maximize the efficiency of the charging circuit 1e, it may be useful, in particular for small powers, to close the switch S despite good coupling, since only a comparatively low voltage is required at the secondary coil L2 because of the said voltage doubling. Thus, only a correspondingly small field strength must be generated at the primary coil L1, whereby the energy transfer is less lossy overall.

15 now shows a motor vehicle 2 which comprises the secondary components of a charging circuit 1 (ie the mobile part MT) and an accumulator A which is connected to the charging output a of the charging circuit 1 and at least partially serves to drive the motor vehicle 2. Specifically, the motor vehicle 2 includes the secondary coil L2 of the transformer T, the

Bridge rectifier B, the first and second capacitor C1, C2, the battery A connected to the charging output a and optionally the third and fifth capacitor C3a, C3b, C5.

With the primary-side components of the charging circuit 1, which are arranged stationarily outside this motor vehicle 2 (ie with the stationary part ST of the charging circuit 1) results in a charging system 3. Specifically, the

Primary coil L1 of the transformer T and optionally the fourth

Capacitor C4a, C4b stationarily outside the motor vehicle 2 arranged. When using the presented charging circuit 1, 1 a..1 e in one

Charging system 3 for motor vehicles 2 show the advantages of the invention particularly well, since the coupling between primary coil L1 and secondary coil L2 on the one hand can not be increased arbitrarily, on the other hand depending on the position of the vehicle 2 to the primary coil Li can vary.

Inductive charging of electric vehicles via in-ground

Induction loops can generally be distinguished into two categories, namely the stationary loading of the parked vehicle and the mobile charging while driving over induction lanes laid in the carriageway. Via induction winding in the ground (primary coil L1) becomes a magnetic

Alternating field in the frequency range 25 ... 150kHz (preferably with 85kHz) generated as soon as the system detects a ready to charge motor vehicle 2. A part of this field penetrates a "receiver coil" (secondary coil L2) in the vehicle 2, thus enabling contactless energy transmission as in a vehicle

Transformer T.

In general, a charge-less charging circuit 1, 1 a..1 e is not bound to the application in a motor vehicle 2, but can be used in general. The charging circuit 1, 1a..1 e then has a

secondary side components of the charging circuit 1, 1 a..1e comprehensive

Handset MT and a separate from the handset MT, the primary-side

Components of the charging circuit 1, 1 a. "1e comprehensive stationary part ST on. The handset does not necessarily comprise an accumulator A, but can the secondary coil L2 of the transformer T, the bridge rectifier B, the first and second capacitor C1, C2, the (free) charging output a, and

optionally comprising the third and fifth capacitors C3a, C3b, C5.

Finally, it should be noted that the charging circuit 1, 1a..1e can in reality also comprise more components than illustrated. Furthermore, it is noted that the above embodiments and developments of the invention can be combined in any manner. LIST OF REFERENCE NUMBERS

1, 1a..1e charging circuit

2 motor vehicle

3 charging system

A accumulator

a exit

B bridge rectifier

C1..C5 capacitor

CTR control

D, D1..D4 diode

e entrance

f frequency

F output filter

i power / current source

11, IAC primary current

! 2 secondary current

K optocoupler

L1 primary coil

L2 secondary coil

MT handset

P11..P22 bridge point

S switch

ST stationary part

T transformer

t time

T period

U voltage / voltage source

U2 secondary voltage

U2 _DC output _DC voltage

CO angular frequency

Claims

claims

1. charging circuit (1, 1a..1e) for an accumulator (A), comprising

a transformer (T);

a at a secondary coil (L2) of the transformer (T) via first opposite bridge points (P1 1, P21) connected

Bridge rectifier (B),

a charge output (a) connected to second opposing bridge points (P12, P22) of the bridge rectifier (B), and

a first capacitor (C1) connected between a first bridge point (P1 1) and a second bridge point (P12) and a second capacitor (C2) connected between these first bridge point (P1 1) and the other second bridge point (P22),

characterized in that

the capacitance value of the first and second capacitors (C1, C2) in the range of

P

d, =

1 * ^■ U2 _D ² _Cmax

to

C _{1 2} -

4 ^■ / ^■ U2 _max

where P is the rated power of the charging circuit (1, 1 a..1e), f the

Transmission frequency of the charging circuit (1, 1 a..1 e) and U2 _D cmax the maximum output DC voltage of the charging circuit (1, 1 a..1 e) indicates.

2. charging circuit (1, 1 a..1 e) according to claim 1, characterized in that the capacitance value of the first and second capacitors (C1, C2) according to the formula

is calculated.

3. charging circuit (1, 1 a..1 e) claim 1 or 2, characterized by a between a terminal of the secondary coil (L2) and a first bridge point (P1 1, P21) connected to the third capacitor (C3a, C3b).

4. charging circuit (1, 1 a..1e) according to one of claims 1 to 3,

characterized by a between a connection of a

Primary coil (L1) of the transformer (T) and a connection of a

Charging input (e) connected fourth capacitor (C4a, C4b).

5. charging circuit (1, 1 a..1e) according to one of claims 1 to 3,

characterized by a parallel to the primary coil (L1) of the

Transformer (T) connected fourth capacitor.

6. charging circuit (1, 1 a..1 e) according to one of claims 1 to 5,

characterized by a fifth capacitor (C5) connected between the first bridge points (P1 1, P21).

7. charging circuit (1, 1 a..1 e) according to one of claims 1 to 6,

characterized by a between the first bridge point (P1 1) and the first capacitor (C1) or the second

Capacitor (C2) arranged switch (S).

8. charging circuit (1, 1 a, .1 e) according to claim 7, characterized in that the switch (S) is formed by a transistor.

9. charging circuit (1, 1 a..1e) according to claim 7 or 8, characterized by a controller (CTR), which is adapted to the switch (S) in dependence of an operating state of the charging circuit (1, 1a..1e) to open or close.

10. charging circuit (1, 1 a..1 e) according to one of claims 1 to 9, characterized

characterized in that this is formed without contact and a secondary part of the charging circuit (1, 1 a..1e) comprising handset (MT) and a separate the primary-side components of the charging circuit (1, 1 a..1 e) comprising stationary part ( ST).

1 1. Handset (MT), characterized by the secondary coil (L2) of the

Transformer (T), the bridge rectifier (B), the first and second capacitor (C1, C2), a charging output (a), and optionally the Third and fifth capacitor (C3a, C3b, C5), the switch (S) and the controller (CTR) of a charging circuit (1, 1 a..1e) according to claim 10.

12. motor vehicle (2), characterized by a handset (MT) after

Claim 1 1 and one connected to the charging output (a) of the mobile part (MT) accumulator (A), softer at least partially the drive of the motor vehicle (2).

13. Motor vehicle charging system (3), characterized by a

Charging circuit (1, 1 a..1 e) according to claim 10 and a motor vehicle (2) according to claim 12, wherein the stationary part (ST) stationary outside this motor vehicle (2) is arranged.

14. motor vehicle charging system (3) according to claim 13, characterized in that the primary coil (L1) of the transformer (T) and optionally the fourth capacitor (C4a, C4b) are arranged stationarily outside the motor vehicle (2).

15. Use of a handset (MT) according to claim 1 1 for loading a

Accumulator (A) in a motor vehicle (2), characterized in that the mobile part (MT) as well as with the charging output (a) of the

Handset (MT) connected battery (A), which at least partially serves the drive of the motor vehicle (2), are arranged within the motor vehicle (2).

16. Use of a charging circuit (1, 1 a..1 e) claim 10 for charging a battery (A) in a motor vehicle charging system (3) for

Motor vehicles (2), characterized in that the mobile part (MT) and the one connected to the charging output (a) of the mobile part (MT)

Accumulator (A), which at least partially the drive of the

Motor vehicle (2) is used, are arranged within the motor vehicle (2) and the stationary part (ST) stationary outside this motor vehicle (2) is arranged.