Abstract
An isolation transformer and an energy transfer device having an isolation transformer are disclosed. In an embodiments an isolation transformer includes an input winding, an output winding, a third winding, a capacitive element and a resistive element, wherein the capacitive element, the resistive element and the third winding are connected in series, and wherein the input winding, the output winding and the third winding are magnetically coupled.
Claims
1. An isolation transformer comprising: an input winding; an output winding; a third winding; a capacitive element; and a resistive element, wherein the capacitive element, the resistive element and the third winding are connected in series, wherein the input winding, the output winding and the third winding are magnetically coupled, and wherein a capacitance C of the capacitive element and an electrical resistance R of the resistive element are chosen such that resonances of matching elements formed by parasitic reactance elements are reduced and an electromagnetic contamination of an area surrounding the output winding is reduced.
2. The isolation transformer according to claim 1, further comprising a transformer core, wherein the input winding is wound onto the transformer core, wherein the output winding is wound onto the transformer core, and where the third winding is wound onto the transformer core.
3. The isolation transformer according to claim 2, wherein the input winding and/or the third winding cover the output winding.
4. The isolation transformer according to claim 1, wherein the capacitive element, the resistive element and the third winding form an attenuation circuit for the resonances.
5. The isolation transformer according to claim 1, wherein 1 ohm (Ω)≤R≤20 Ω, wherein 0.5 nanofarad (nF)≤C≤10 nF, and wherein the third winding has a number of turns N, where 5≤N≤40.
6. The isolation transformer according to claim 5, wherein the input winding and the output winding have N.sub.1=N.sub.2=29 turns, R=10 ohm (Ω), C=2.2 nanofarad (nF) and N=23.
7. The isolation transformer according to claim 1, wherein the input winding and the output winding have an equal number of turns.
8. The isolation transformer according to claim 1, wherein the input winding has an inductance L.sub.I, where 1 millihenry (mH)≤L.sub.I≤10 mH.
9. The isolation transformer according to claim 1, wherein the input winding has an inductance L.sub.I=3.67 millihenry (mH).
10. The isolation transformer according to claim 1, wherein 0.5≤N.sub.3/N.sub.1≤1.0, wherein N.sub.1 is the number of turns of the input winding and N.sub.3 is the number of turns of the third winding.
11. An energy transfer device comprising: the isolation transformer according to claim 1; an inverter connected in series with the isolation transformer; and a common-mode choke connected in series between the inverter and the isolation transformer.
12. A system for wireless energy transfer comprising: the energy transfer device according to claim 11; a rectifier connected in series with the isolation transformer; a receiving winding connected in series between the rectifier and the isolation transformer; and a transmitting winding connected in series between the receiving winding and the isolation transformer.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Essential principles of the isolation transformer and/or of the energy transfer device are shown using schematic figures.
(2) In said figures:
(3) FIG. 1 shows an equivalent circuit diagram of the isolation transformer with an attenuation circuit;
(4) FIG. 2 shows the equivalent circuit diagram of an isolation transformer which is coupled to a common-mode choke;
(5) FIG. 3 shows the circuit of the isolation transformer with an inverter;
(6) FIG. 4 shows the circuit of an isolation transformer with a common-mode choke and an inverter;
(7) FIG. 5 shows the equivalent circuit diagram of a wireless energy transfer device with a transmitting winding and a receiving winding;
(8) FIG. 6 shows the additional use of a rectifier;
(9) FIG. 7 shows the use of the rectifier for charging an energy source;
(10) FIG. 8 shows the basic design of a test system;
(11) FIG. 9 shows the insertion loss (matrix element S.sub.12) of an isolation transformer, split into a common-mode signal and a differential-mode signal; and
(12) FIG. 10 shows further measured voltage values and associated permitted limit values.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
(13) FIG. 1 shows an equivalent circuit diagram of an improved isolation transformer IT which has an input winding WP and an output winding WA. The input winding WP and the output winding WA are magnetically coupled by means of a transformer core K. In addition, the isolation transformer TT has an attenuation circuit DK which has a third turn W3, a capacitive element KE and a resistive element RE. The third turn W3 is also magnetically coupled to the input winding WP and to the output winding WA by means of the transformer core K. The transformer core K is schematically illustrated. The transformer core K can be of rod-shaped design or form a magnetically closed circuit, for example, a U-shaped core with a yoke.
(14) The attenuation circuit DK of the transformer core TT attenuates critical frequencies, so that critical resonances, which would lead to unwanted resonance, cannot even be produced in the first place.
(15) FIG. 2 shows the optional circuit of the isolation transformer TT with a common-mode choke GD. The common-mode choke GD comprises a choke core K and two turns W. The dimensions of the core K and of the turns W are selected such that common-mode interference are suppressed to the maximum extent.
(16) This produces an energy transfer device EÜ in which common-mode interference and critical resonances, for example, due to differential-mode signals, are greatly reduced.
(17) FIG. 3 shows the circuit of the energy transfer device EÜ with an inverter WR. The inverter receives electrical energy in the form of a direct current and passes an AC signal to the isolation transformer IT. The inverter WE can have a switch arrangement of NH configuration (H-bridge) here. The switches can be semiconductor switches. The applied AC current signal can then be, for example, a square wave with steep voltage edges. The operating frequency of the isolation transformer which is connected downstream of the inverter can be, for example, 85 kHz.
(18) FIG. 4 shows a form of the energy transfer device in which the common-mode choke GD is interconnected between the isolation transformer TT and the inverter WR. FIG. 5 shows a system for wireless energy transfer. The wireless energy transfer device DEÜ has a transmitting winding WT in addition to the inverter WE, the common-mode choke GD and the isolation transformer TT. A magnetic or electromagnetic power signal can be output by means of the transmitting winding WT. This magnetic or electromagnetic power can be received and output to an area surrounding the circuit by means of a receiving winding WREC. The physical distance between the transmitting coil WT and the receiving coil WR can be between 3 and 20 cm.
(19) FIG. 6 shows a wireless energy transfer device in which a rectifier GR is connected to the receiving winding WREC. The AC signal in the kilohertz range is converted by the rectifier GR back into a DC signal for use in a further circuit.
(20) Here, the rectifier can be a cross-type rectifier with four diodes and possibly smoothing capacitors.
(21) FIG. 7 shows the use of the wireless energy transfer device for coupling the electrical power into an electrical energy storage device, for example, the rechargeable battery of an automobile or of a mobile communication system.
(22) FIG. 8 shows the physical arrangement of the components of a test setup in which the transmitting winding WT and the receiving winding WREC are arranged situated opposite one another but are physically separate from one another. The isolation transformer TT is arranged in the housing of the transmitting winding WT and is fed by an amplifier AMP. An electrical insulator, which can have a thickness of 10 cm, is arranged beneath the transmitting winding WT. A copper sheet at ground potential GND is arranged below the insulator INS. The receiving winding WREC is arranged above the transmitting winding WT. An electromagnetic shield S which is composed of aluminum and has a length of 1 m and a width of 1 m is arranged above said transmitting winding. The shield S is connected to a copper sheet at ground potential GND. The receiving winding WREC is interconnected to a rectifier GR, wherein a 5 cm-thick insulation layer INS is arranged between the rectifier GR and the copper sheet. The vertical offset between the shield S and the lower section of the copper sheet at ground potential GND, which copper sheet is connected to said shield, is greater than 20 cm. The horizontal section between the copper sheet below the transmitting winding WT and the section of the copper sheet below the rectifier GR at the same height is more than 0.4 m.
(23) FIG. 9 shows the insertion loss of the isolation transformer in a frequency-dependent manner for the common-mode signal (solid line, at the bottom) and for the differential-mode signal (dashed line, at the top). In a frequency region around 85 kHz, the isolation transformer is virtually transmissive to differential-mode signals, while common-mode signals are attenuated to a great extent.
(24) FIG. 10 shows a typical voltage spectrum with peak P. The top curve shows the peak values measured by a peak value detector. The bottom curve shows the mean values measured by a mean value detector. Measurements were taken at the input of the inverter here. The suppression of resonance can be clearly seen, especially at 1 MHz. In addition, the second harmonic OW2 of 85 KHz is suppressed to a great extent. The frequency range GAB of approximately 10.sup.5.7 Hz to 10.sup.6.3 Hz is a particularly suitable operating range.
(25) The isolation transformer and the energy transfer device are not limited to the forms shown. Energy transfer devices and isolation transformers with additional circuit elements are likewise covered by the scope of the invention.
