The present invention relates to an inductive energy transfer system with a primary-side coil arrangement and a secondary-side coil arrangement, which in each case together with capacities form resonant circuits.
In the case of contactless energy transfer, a good coupling between the primary-side and the secondary-side coil arrangement is important for the degree of effectiveness of the energy transfer. Insofar as energy should be transferred between a vehicle and a charging station, the charging station is most often placed on the ground, whereas the secondary-side pickup is mounted under the vehicle. The coil arrangements are most often formed by planar coils, whereby the charging station and the pickup can be formed in a plate-shaped manner. The magnetic coupling is in this regard substantially determined by the distance of the coil arrangements in the vertical direction as well as the horizontal offset thereof. The vertical distance is in this regard substantially predetermined by the vehicle type, whereas the horizontal offset of the coil arrangements to each other depends on the park position of the vehicle relative to the charging station.
An attractive coil configuration for the secondary-side pickup is the double winding, consisting of the coils LS1 and LS2, as it is depicted by way of example in FIG. 1a together with the associated equivalent circuit diagram. The primary-side charging station most often comprises a similar coil arrangement and is depicted in FIG. 1a merely by the conductor LP1 with the current Ip flowing through the latter. In FIG. 1a, the primary and secondary-side coils are optimally arranged i.e. without horizontal offset to each other such that an optimal coupling results and the currents LS1 and LS2 flow in the secondary-side coils LS1 and LS2 in the push-pull operation. It lends itself in this regard to connect the coils LS1 and LS2 in series, as depicted in FIG. 2, since both currents LS1 and LS2 are in phase and equal in size. The magnetic coupling noticeably changes if the primary and secondary-side coil arrangements are offset horizontally to the optimal alignment according to FIG. 1a, as is depicted in FIG. 1b. In this case, the flow portions penetrating the two coils LS1 and LS2 are not phase-shifted by 180° to each other such that the coils LS1 and LS2 can no longer be connected in series, as depicted in FIG. 2.
In order to decouple the coil currents IS1 and IS2, the coils LS1 and LS2 can be interconnected, as depicted in FIG. 3. The coil currents IS1 and IS2 can comprise different phase positions and amplitudes in the case of this circuit and are rectified by the rectifier circuit GL and smoothed by the smoothing capacitor CGL. In the case of this circuit, a vulnerability, however, results in the case of a horizontal offset of primary-side and secondary-side coil arrangement since due to the coupling of the coils LS1 and LS2, it leads to an unbalance of the entire resonant circuit. FIG. 4 shows the equivalent circuit diagram for the circuit according to FIG. 3. As long as no horizontal offset relative to the optimal alignment of the primary-side and secondary-side coil arrangements exists, the magnetic circuit works in the push-pull operation and the current I1 equal to minus I2. The coils act, as if they were connected in series and have a positive feedback, wherein the entire inductance is greater than the sum of both partial inductances LS1 and LS2.
However, as soon as the horizontal position of the primary and secondary-side coil arrangements deviates from the optimal position, the currents have a common mode portion, whereby the entire inductance is reduced since the coils comprise a negative feedback in the common mode operation. In the extreme case I1=I2, both currents mutually cancel each other in the main inductance, whereby IN=and I2=O. The entire inductance thus changes with the positioning of the secondary circuit over the primary circuit, whereby it leads to an unbalance of the resonant circuit and thus to a deterioration of the transfer properties.
The object of the present invention is thus to provide a solution for the above-mentioned problem.
This object is solved according to the invention in that either the primary-side coil system comprises two coils connected in series, the connection point of which is connected via a primary-side impedance with the centre point/centre tap of a voltage divider, or with the plus or minus pole of the intermediate circuit of the circuit suppling the primary-side resonant circuit, in particular in the form of a controlled inverter and/or in that the secondary-side coil system comprises two coils connected in series, the connection point of which is connected via a secondary-side impedance with the centre point/centre tap of a voltage divider or with the plus or minus pole of a circuit downstream of the secondary-side resonant circuit, in particular in the form of an rectifier.
The provision of an additional impedance according to the invention causes the inductance in the series resonant circuit of the primary and/or secondary-side coils connected in series to increase in the case of an offset to the optimal horizontal alignment, whereby an adaptation of the resonant frequency of the resonant circuit to the system frequency takes place.
The circuit supplying the primary-side resonant circuit is in this regard preferably a controlled bridge inverter, wherein each primary-side coil is connected in series with a capacity and forms a series resonant circuit with the latter and the series circuit of the series resonant circuits is connected to the AC voltage connection of the controlled bridge inverter. The impedance forms in this regard a centre tap between the primary-side coils and serves to adapt the resonant frequency of the primary-side resonant circuits to the system frequency.
The circuit downstream of the secondary-side resonant circuit is preferably a rectifier, in particular a bridge rectifier, wherein in the case of a bridge rectifier, each secondary-side coil is connected in series with a capacity and forms a series resonant circuit with the latter and the series circuit of the series resonant circuits is connected to the AC voltage connection of the bridge rectifier. The additional impedance forms in this regard a centre tap between the secondary-side coils and serves to adapt the resonant frequency of the secondary-side resonant circuits to the system frequency.
It is of course possible that both on the primary side as well as on the secondary side, in each case an additional impedance can be provided. It is also possible that an additional impedance is only provided on the secondary side or on the primary side. Generally, the additional impedance can be equal to the mutual inductance of the coils coupled to each other.
Below the invention is explained in greater detail by means of the Figures. They show:
FIG. 1
a and 1b: Inductive energy transfer system with two secondary-side coils according to the prior art, in addition to equivalent circuit diagrams; FIG. 2: Possible interconnection of the secondary-side coils according to FIG. 1a;
FIG. 3: Decoupling circuit for coil arrangement according to FIG. 1b, in the case of horizontal offset;
FIG. 4: Equivalent circuit diagram for circuit according to FIG. 3;
FIG. 5: Circuit according to the invention with additional impedance for secondary side of the inductive energy transfer system;
FIG. 6: Circuit according to the invention with additional impedance for primary side of the inductive energy transfer system;
FIGS. 7 and 8: Circuits according to FIGS. 5 and 6, wherein additional impedance is connected to centre tap of a capacitive divider;
FIGS. 9 and 10: Circuits with additional changeable impedance for the secondary side of the inductive energy transfer system;
FIG. 11: Inductive energy transfer system according to the prior art with two planar secondary-side coils, which are arranged on a ferrite plate;
FIG. 12: Inductive energy transfer system according to the prior art of secondary-side U-Pickup;
FIG. 13: Equivalent circuit diagram for illustrating the inventive idea.
FIG. 5 shows a circuit according to the invention with additional impedance LSM for the secondary side of the inductive energy transfer system, wherein the secondary-side coils LS together with the capacitors C form series resonant circuits RESS. The series circuit of the series resonant circuits RESS is connected to the AC voltage connection of the rectifier GL. The additional impedance LSM is connected with its one pole LSM1 to the connection point VS and with its other pole LSM2 to the plus or minus pole (4) of the downstream rectifier GL.
FIG. 6 shows a circuit according to the invention with additional impedance LPM for the primary side of the inductive energy transfer system, wherein the primary-side coils LP together with the capacitors C form series resonant circuits RESP. The series circuit of the series resonant circuits RESp is connected to the AC voltage connection of the inverter 1. The additional impedance LPM is connected with its one pole LPM1 to the connection point VP of the resonant circuits RESP and with its other pole LPM2 to the plus or minus pole (3) of the intermediate circuit of the inverter 1 feeding the primary-side resonant circuit (RESp).
FIGS. 7 and 8 show circuits according to FIGS. 5 and 6, wherein the additional impedance LPM or LSM is not connected to a plus or minus pole, but to the centre tap MTP or MTS of a capacitive voltage divider CGL1, CGL2.
FIGS. 9 and 10 show developments of the circuit according to FIG. 5, which enable it to change the value or the secondary additional impedance LSM. As depicted in FIG. 9, the capacitor CSM can be connected parallel to the impedance L′SM by means of the switching means S1, as required. It is hereby possible to adapt the resonant frequency of the secondary resonant circuits RESS in the case of different horizontal offsets between the primary and secondary coil arrangement of the primary-side frequency. Of course, it is possible to connect a plurality of capacitors in parallel, as required such that an even finer tuning of the resonant frequency is possible.
As is depicted in FIG. 10, it is also possible to connect a capacitor in series. This occurs by the switching means S2, S3 locking. Insofar as the capacitor CSM should be disabled, the switching means S2 and S3 can be connected in a conductive manner.
FIGS. 11 and 12 show a flat pickup with planar coils as well as a U-shaped pickup in cooperation with a primary arrangement indicated as the line conductors. The depictions correspond to the FIGS. 1a and 1b, wherein the field lines and the ferrite cores are depicted for clarification.
FIG. 13 serves to explain the mode of action of the additional impedance. The magnetic T-equivalent circuit diagram for a common mode operation is depicted to the left. Through the common mode operation, the currents Is1 and Is2 cancel each other in the coils (see FIG. 1a) such that the inductance Lsh is dispensed with, as is depicted in the centre circuit diagram. The equivalent coil-inductance Leq is Ls1 and no longer Ls1+2Lsh as in the push-pull operation. The resonant capacitor is, however, designed for the push-pull operation such that an increase of the coil-inductance by 2Lsh is necessary here. This is implement by the “reverse” of one of the leakage inductances for the common mode operation in order to emulate the magnetic T-equivalent circuit diagram (depicted right) in a discrete circuit with an additional inductance Lsm. As a result, a circuit results, which, for the common mode operation, comprises the same impedance as the magnetic equivalent circuit diagram in the push-pull mode.
Patent Application
20160020615
