Circuit for inductively transferring electrical energy

Abstract

A circuit for inductively transferring electrical energy from a primary side to a secondary side has a primary-sided autoresonant power oscillator compensated in parallel having a primary inductivity and serially compensated secondary sides each having a secondary inductivity.

Claims

1. A circuit for inductively transferring electrical energy from a primary side to a secondary side, comprising a primary-sided autoresonant power oscillator compensated in parallel having a primary inductivity (205) and a plurality of serially compensated secondary sides each having a secondary inductivity (225, 235, 245), wherein the circuit is designed to place an operating point of each recipient on the secondary side in a region of a constant voltage transfer function at the resonance frequency, so that a coupling factor between the secondary-sided recipient and the primary side is low.

2. The circuit according to claim 1, wherein the primary-sided autoresonant power oscillator compensated in parallel is an autoresonant Royer oscillator.

3. The circuit according to claim 1, wherein the serially compensated secondary sides each have a rectifier.

4. The circuit according to claim 1, wherein the primary side and the secondary side are tuned to a resonance frequency that can be predetermined.

5. The circuit according to claim 1, wherein the winding number of the secondary inductivities (225, 235, 245) can be varied dependent on a power to be evoked.

6. A circuit for inductively transferring electrical energy from a primary side to a secondary side, comprising a primary-sided autoresonant power oscillator compensated in parallel having a primary inductivity (205) and a plurality of serially compensated secondary sides each having a secondary inductivity (225, 235, 245), wherein the primary-sided autoresonant power oscillator and the secondary sides are designed in such a way that the averaged electrical energy, which all secondary sides extract, is less than or equal to the energy available on the primary side, and the operating point of all secondary sides can be found condensed in the range R2>R2,c, wherein the circuit is designed to place the operating point of each recipient on the secondary side in a region of a constant voltage transfer function at the resonance frequency, so that a coupling factor between the secondary-sided recipient and the primary side is low.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other objects and features of the invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.

(2) In the drawings,

(3) FIG. 1 shows a circuit known from the prior art of a Royer oscillator;

(4) FIG. 2 shows the circuit according to the invention for inductively transferring electrical energy from a primary side to recipients on the secondary side;

(5) FIG. 3a shows the system behavior of the circuit depicted in FIG. 2; and

(6) FIG. 3b shows the frequency response of the circuit depicted in FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(7) In FIG. 1, a Royer oscillator known from the prior art is depicted, which is realized with MOSFETs. Such a Royer oscillator constitutes an autoresonant power oscillator; it emerges, for example, from DE 20 2007 011 745 U1, to which reference is presently made.

(8) FIG. 2 shows a circuit according to the invention for inductively transferring electrical energy from a primary side 201 to three recipients 220, 230, 240 arranged on the secondary side.

(9) The primary side is realized as an autoresonant Royer oscillator having a primary inductivity 205, which transfers electrical energy to inductivities 225, 235, 245 on the secondary side. Each secondary side 220, 230, 240 has its own compensation circuit and its own rectifier. A single load R2.1, R2.2, R2.3 is attached to each secondary side 220, 230, 240. The secondary sides can be operated completely independently of one another. A criterion, which must be fulfilled, is a tuning to an identical design resonance frequency between the secondary-sided recipients and the primary side. The transferred power between the individual secondary-sided recipients can vary. To do so, the inductivities 225, 235, 245 of the recipients can be adjusted independently of one another, for example by changing the winding number of the windings on the secondary side. However, the change must take place in such a way that the tuning to the same design resonance frequency takes place.

(10) All recipients must be compensated in series, a parallel compensation having several recipients is not possible because of the system behavior.

(11) The system behavior is depicted in FIG. 3a. FIG. 3b shows the frequency response of the system compensated in parallel on the primary side and in series on the secondary side, referred to as 1p2s-system for short. The voltage transfer function and the current transfer function M.sub.u are depicted in FIG. 1a. The voltage transfer function and the current transfer function of the system for the resonance frequency ω_r0 are

(12) $.Math.{\underset{\_}{Z}}_{\mathrm{IN}}.Math.=\frac{R_2{L}_1}{L_2{k}^2}$$M_U=k\sqrt{\frac{L_2}{L_1}}$
and for the resonance frequencies ω_r1r2 are

(13) $.Math.{\underset{\_}{Z}}_{\mathrm{IN}}.Math.=\frac{{\omega }_d^2{L}_1{L}_2\left(1-k^2\right)}{R_2}$$M_U=\frac{R_2}{{\omega }_d\sqrt{L_1{L}_2\left(1-k^2\right)}}.$

(14) The design resonance frequency ωd is determined by

(15) $C_{1p}=\frac{1}{{\omega }_d^2{L}_1}$$\mathrm{and}$$C_{2x}=\frac{1}{{\omega }_d^2{L}_2\left(1-k^2\right)}.$

(16) So that the resonance frequency remains constant, the operation with a load resistance of R2>R2,c is necessary according to FIG. 3b, wherein index c stands for the characteristic resistance, at which it results in case analysis of the resonance frequencies wr0, wr1, wr2. The sum of all load resistances (parallel circuit) must therefore fulfil the criterion R2>R2,c so that the resonance frequency for all recipients is identical. In exceptional or erroneous cases, for example a short circuit, individual recipients can violate the criterion R2>R2,c if the energy decrease of the individual recipients is small in comparison to the available overall power of the primary side.

(17) As depicted in FIG. 4, the operating point of the circuit on the right side is to be chosen with the resonance frequency ω=ω_r0. In this, the starting voltage is constant and only one function of the coupling factor. This does not constitute any problem, since the coupling factor is virtually constant for the desired system, and small deviations can be eliminated by an inherently known voltage stabilisation device not depicted here.

(18) As depicted in FIGS. 3a and 3b, there is only one resonance frequency on the right side, to which all recipients can be tuned (compensated).

(19) The system design and the choice of the compensation capacitors also aim for the resonance frequency to be independent of the load. This means that the autoresonant power oscillator does not change its operating frequency if the load does not fall below the characteristic resistance. This must be taken into consideration with the system design. This means that the operating point of each recipient is placed in the region of the constant voltage transfer function, which is depicted in FIGS. 3a and 3b on the right when ω=ω_r0. During the switching-on process or in the case of a short circuit, this criterion is indeed violated. However, because of the design of the primary side for n recipients, the case of a short circuit of a recipient does not lead to a noticeable change of the operating frequency, since the idle power on the primary side in the system is much larger than in a recipient on the secondary side. If several recipients on the secondary side were to fall below the load resistance, this would result in a tangible frequency change dependent on load (ω_r1,r2 is a resonance frequency dependent on load), which then leads to a problem with matching with recipients having a load resistance larger than R2,c, as depicted above.

(20) Due to the system design, in particular the low coupling factor, the problem of the frequency change is already avoided by the design. The influence of the secondary side on the primary side giving the frequency increases with increasing coupling between secondary and primary side. Since the coupling between one single secondary-sided recipient and the primary side is nevertheless low, the influence on the frequency change is also low in an erroneous case. Furthermore, the secondary side can be designed in such a way that it is of high impedance in the erroneous case.

(21) The depicted circuit according to the invention makes it possible to supply one or more secondary-sided recipients with a primary-sided autoresonant power electronic system without additional regulation measures, wherein each recipient is operated in the nominal operating point and can reduce an arbitrary amount of power without influencing the other recipients if the nominal operating point of all secondary sides is in the ω=ω_r0 range. (Parallel circuit of individual recipients results in smaller R2_“overall”, 8 recipients with R2=R2c would not work since the resulting resistance, which sees the primary side, is then much smaller than R2,c.)

(22) Although only a few embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.