DE102014012703B4 - Receiving unit, inductive energy transmission system, method for inductive energy transmission and use - Google Patents

Abstract

Receiving unit (200) for an inductive energy transmission system (500), comprising: - a receiving coil (16) for inductively generating an AC voltage; - a rectifier circuit (30) for rectifying the generated AC voltage, the rectifier circuit (30) having a switch (40). , with which the rectifier circuit (30) can be operated in a first and a second operating mode, the first operating mode being matched to a first reception power and the second operating mode being coordinated to a second reception power, the first reception power differing from the second reception power ; and - a control unit for controlling the switch (40), wherein the control unit is designed to determine the received power, to compare the determined received power with a predetermined comparison value, and to open the switch (40) if the determined received power is at least as great as is the predetermined comparison value and to close the switch (40) if the received power determined is less than the predetermined comparison value.

Description

The present invention relates to a receiving unit for an inductive energy transmission system, an inductive energy transmission system, a method for inductive energy transmission and a use of the receiving unit or the inductive energy transmission system.

Inductive energy transfer is the most widespread method of contactless energy transfer. Especially with regard to the expansion of electromobility, inductive energy transmission is of great importance. For example, electric vehicles can be charged using inductive energy transfer without using a cable.

For inductive energy transmission, an alternating magnetic field is generated in a transmission unit or transmitter. This is done with the help of a transmission coil or transmitter coil through which an alternating current flows. An associated receiving unit or an associated receiver also contains a coil, the receiving coil. This is penetrated by part of the alternating magnetic field. This induces a voltage in the receiving coil. If an electrical load is connected to the receiving coil, current flows through the load due to the induced voltage, i.e. energy is transmitted inductively, i.e. wirelessly, from the transmitter to the receiver. If the load is a battery or a rechargeable battery, for example, it can be charged inductively via the transmitter. The operating principle corresponds to that of a transformer with weak coupling of the coils.

Transmission systems or charging stations are currently being developed for the inductive charging of electric vehicles, which transmit a power of approx. 20 kW. There are also systems or charging stations with an output of approx. 3 kW, some of which are already available on the market or will be on the market in the foreseeable future. Compatibility between a receiver unit installed in an electric vehicle and the charging stations available on the market is therefore particularly important for the end user. In particular, vehicles with, for example, a 20 kW receiver unit should also be able to use a charging station with, for example, a 3 kW rated output.

However, an inductive energy transmission system that is designed for a specific rated power requires a disproportionately large reactive power when operated with significantly lower power compared to a system that is optimized for the lower power. The high reactive power consequently generates high losses, which in turn greatly reduces the efficiency of the system.

A previous approach to operating a receiving unit of an inductive energy transmission system in an efficiency-optimized manner even at significantly lower power than its nominal power is to use a DC/DC converter on the receiving side. As a result, the voltage level at the receiving coil can be adapted to the transmitted power and the system can thus be operated close to the optimum point. However, an additional DC/DC converter makes the receiving unit more expensive, heavier and larger. Especially the higher weight and the larger space requirement are extremely unfavorable in vehicle construction.

The pamphlet DE 10 2011 119 261 A1 discloses a secondary-side rectifier of an inductive energy transmission system, the energy transmission system having a single-phase resonant circuit with at least one inductance and at least one capacitance, which can be magnetically coupled to a primary-side resonant circuit. The rectifier on the secondary side has a B2 bridge circuit made up of four diodes, which is connected on the input side to the resonant circuit on the secondary side and whose output voltage is smoothed by at least one smoothing capacitor. A switching device, by means of which the diode can be short-circuited, is connected in parallel with one of the four diodes.

The pamphlet DE 10 2009 021 797 A1 discloses a vehicle with an energy store and a charging arrangement, the charging arrangement comprising at least one inductive energy transmission.

It is an object of the present invention to improve the previous inductive energy transmission systems, in particular the receiving unit of an inductive energy transmission system, with regard to interoperability. In particular, it is an object of the present invention to keep the receiving unit of an inductive energy transmission system inexpensive, light and compact, while still ensuring good compatibility with different charging stations or transmitting units.

This problem is solved by the subjects of the independent claims. Advantageous embodiments are the subject matter of the dependent claims.

In the context of the present description, the terms “primary side” or “primary side” refer to the transmission unit and the terms “secondary side” or “secondary side” refer to the receiving unit of an inductive energy transmission system.

• - eine Empfangsspule zum induktiven Erzeugen einer Wechselspannung;
• - eine Gleichrichterschaltung zum Gleichrichten der erzeugten Wechselspannung, wobei die Gleichrichterschaltung einen Schalter aufweist, mit dem die Gleichrichterschaltung in einem ersten und einem zweiten Betriebsmodus betrieben werden kann, wobei der erste Betriebsmodus auf eine erste Empfangsleistung abgestimmt ist und der zweite Betriebsmodus auf eine zweite Empfangsleistung abgestimmt ist, wobei sich die erste Empfangsleistung von der zweiten Empfangsleistung unterscheidet; und
• - eine Steuereinheit zum Steuern des Schalters, wobei die Steuereinheit ausgelegt ist, die Empfangsleistung zu ermitteln, die ermittelte Empfangsleistung mit einem vorgegebenen Vergleichswert zu vergleichen, und den Schalter zu öffnen, wenn die ermittelte Empfangsleistung mindestens so groß wie der vorbestimmte Vergleichswert ist und den Schalter zu schließen, wenn die ermittelte Empfangsleistung kleiner als der vorbestimmte Vergleichswert ist.

A first independent aspect of solving the problem relates to a receiving unit for an inductive energy transmission system, comprising:

• - A receiving coil for inductively generating an AC voltage;
• - a rectifier circuit for rectifying the AC voltage generated, the rectifier circuit having a switch with which the rectifier circuit can be operated in a first and a second operating mode, the first operating mode being matched to a first received power and the second operating mode being matched to a second received power is, wherein the first reception power differs from the second reception power; and
• - A control unit for controlling the switch, wherein the control unit is designed to determine the reception power, to compare the reception power determined with a predetermined comparison value, and to open the switch when the reception power determined is at least as great as the predetermined comparison value and the switch to close when the determined received power is less than the predetermined comparison value.

An alternating voltage can be generated inductively in the receiving coil on the basis of an alternating magnetic field generated by a transmitting unit or a transmitting coil. The AC voltage generated is converted into a DC voltage with the rectifier circuit, with which a load can be supplied. In particular, the converted DC voltage can be used to charge an energy store.

The rectifier circuit is designed so that it can be operated in at least a first and a second operating mode. In particular, the rectifier circuit is designed to be operated in exactly one first and one second operating mode. In principle, however, it is also possible for the rectifier circuit to be designed to be operated in a third, fourth, fifth, etc. operating mode.

For the purposes of this description, received power is understood to mean power received by the receiving unit or the receiving coil of the receiving unit, in particular magnetic power, which is inductively transmitted, for example, from a transmitting unit to the receiving unit. In the ideal case, the reception power corresponds to the transmission power of the transmission unit. However, the reception power can also be slightly lower than the transmission power of the transmission unit due to transmission losses. This means that the reception power can be equal to the transmission power minus a transmission power loss P _loss . For example, the transmission power can be about 3 kW, 3.6 kW, 7 kW or 20 kW. The received power is then also 3 kW, 3.6 kW, 7 kW or 20 kW in a first approximation. If a transmission power loss is taken into account, the corresponding transmission power loss must be subtracted from the transmission power in order to obtain the reception power. The transmission power loss can also depend on the transmission power. For example, a first transmission power can be approximately 20 kW and a second transmission power can be approximately 3 kW. In the ideal case or in a first approximation, the first reception power is therefore also approximately 20 kW and the second reception power is approximately 3 kW. If any transmission losses are taken into account, the first reception power is 20 kW - P _loss,20kW and the second reception power is 3 kW - P _loss,3kW . For the purposes of this description, the terms reception power and transmission power generally refer to a nominal power.

The property that an operating mode is matched to a reception power means in particular that the energy transmission from a transmission unit to the reception unit is optimized. For example, tuning achieves higher efficiency in energy transmission.

Due to the different operating modes, the receiving unit according to the invention can thus be adapted or adjusted in an efficiency-optimized manner to different transmission units or charging stations, in particular to transmission units or charging stations with different transmission power. In other words, the receiving unit according to the invention is compatible with several, in particular two, different transmitting units, in that the receiving unit has several, in particular two, optimized operating points. Each optimized operating point can be optimized for one of the transmission units, ie for a transmission power or reception power of one of the transmission units. Compatibility with a number of transmission units is thus ensured without the efficiency significantly changing or deteriorating when using the different transmission units, ie when using different transmission powers or reception powers of the different transmission units. With the help of the receiving unit according to the invention, it is also possible to dispense with an additional DC/DC stage, which is necessary in conventional receiving units in order to make them compatible with different transmitting units. The invent The receiving unit according to the invention can thus be adapted or adjusted in an efficiency-optimized manner to different transmission units or charging stations, in particular to transmission units or charging stations with different transmission powers. And yet the receiving unit remains inexpensive, light and compact.

The rectifier circuit is preferably connected between a receiving coil and a load, for example an energy store, in particular a battery or an accumulator.

In a preferred embodiment of the receiving unit according to the invention, the rectifier circuit is designed to reduce the reactive power of the energy transmission system for the first received power in comparison to the reactive power of the energy transmission system for the second received power in the first operating mode, and/or to reduce the reactive power of the energy transmission system for the second received power in the second operating mode to reduce compared to the reactive power of the energy transmission system for the first reception power.

Due to the electromagnetic coupling between the transmitting unit, i.e. the primary side of the inductive energy transmission system, and the receiving unit, i.e. the secondary side of the inductive energy transmission system, the operating mode of the rectifier circuit of the receiving unit also affects the reactive power of the transmitting unit. The reactive power of the energy transmission system thus represents the sum of the reactive power of the transmitting unit and the reactive power of the receiving unit.

Alternatively or additionally, the rectifier circuit is designed to reduce the reactive power of the energy transmission system in the first operating mode compared to the reactive power of the energy transmission system in the second operating mode for the first received power.

Alternatively or additionally, the rectifier circuit is designed to reduce the reactive power of the energy transmission system in the second operating mode compared to the reactive power of the energy transmission system in the first operating mode for the second received power.

The respective reduction in the reactive power of the energy transmission system in the various operating modes of the receiving unit or the rectifier circuit thus enables an increase in the efficiency and effectiveness of the energy transmission independently of the received power, i.e. independently of the transmission power of a transmission unit.

In a further preferred embodiment of the receiving unit according to the invention, the first operating mode is a full-bridge mode and the second operating mode is a half-bridge mode.

In other words, the rectifier circuit functions as a full-bridge rectifier in the first operating mode and as a half-bridge rectifier in the second operating mode.

The respective operating mode, i.e. full-bridge mode or half-bridge mode, determines the characteristics of the entire energy transmission system. In particular, when operating in half-bridge mode, the optimal operating point is at a transmitted power which corresponds to approximately a quarter of the power when operating in full-bridge mode. It is thus possible in a simple manner to adapt the receiving unit to a transmitting unit. For example, the reception unit or its components can be designed for a reception power or transmission power of approximately 20 kW in the first operating mode. If the transmission unit has a transmission power of 20 kW, then the reception unit can be operated in the first operating mode in order to achieve a high or optimum level of efficiency. However, if the transmission unit has a transmission power of only 3 kW, for example, then the reception unit can be operated in the second operating mode in order to again achieve a high or optimal efficiency.

The optional operation of the rectifier circuit as a full-bridge rectifier or half-bridge rectifier makes it possible to reduce the reactive power requirement of the entire energy transmission system even when operating with a lower received power. As a result, an unnecessary oversizing of components of the inductive energy transmission system, in particular of components of the transmission unit such as the transmission coil and/or any compensation components, can be avoided. In addition, the efficiency of the inductive energy transmission system can be increased.

In a further preferred embodiment of the receiving unit according to the invention, the rectifier circuit includes a switch for setting the operating mode. The rectifier circuit functions or behaves as a full-bridge rectifier when the switch is open and as a half-bridge rectifier when the switch is closed.

The operating mode of the rectifier circuit and thus the behavior of the receiving unit or of the entire inductive energy transmission system can thus be changed using the switch. In other words, the switch serves to Switching the rectifier circuit between a full bridge mode and a half bridge mode.

The switch may be a mechanical switch or a semiconductor switch, for example a MOSFET, i.e. a metal-oxide-semiconductor field effect transistor, or an IGBT, i.e. an insulated gate bipolar transistor.

In a further preferred embodiment of the receiving unit according to the invention, the rectifier circuit comprises four diodes, in particular rectifier diodes, with the switch being connected in parallel with one of the four diodes.

With the help of the four diodes, an alternating voltage (AC voltage), which is e.g. induced in the receiving coil of the receiver unit, can be rectified, i.e. converted into a direct voltage (DC voltage). The converted DC voltage is preferably such that it can supply or operate a load and/or charge an energy store.

The rectifier circuit also includes a switch which is arranged and/or connected in parallel with one of the four diodes. When the switch is open, the rectifier circuit acts as a full bridge rectifier. If the switch is closed, the diode connected in parallel with the switch is bridged, so that the rectifier circuit functions as a half-bridge rectifier.

In a preferred embodiment of the receiving unit according to the invention, the four diodes are arranged and connected according to a so-called Graetz circuit.

The Graetz circuit is a bridge rectifier circuit with four diodes. According to one embodiment, two of the four diodes are connected in series with the same polarity direction and form a first bridge branch. Same direction of polarization means that the anode of the first diode is connected to the cathode of the second diode. The other two of the four diodes are also connected in series with the same polarization direction and form a second bridge branch. The first bridge arm is connected in parallel to the second bridge arm in such a way that the cathode of a diode in the first bridge arm is connected to the cathode of a diode in the second bridge arm and/or the anode of a diode in the first bridge arm is connected to the anode of a diode in the second bridge arm.

The rectifier circuit preferably has a voltage input, in particular an AC voltage input, and a voltage output, in particular a DC voltage output. A first connection of the voltage input is formed between the diodes of the first bridge arm on the first bridge arm. A second connection of the voltage input is formed between the diodes of the second bridge arm on the second bridge arm. The terminals of the voltage output are each formed between the bridge branches. In other words, the converted DC voltage can be tapped off between the bridge arms.

The receiving unit according to the invention also includes a control unit for controlling the switch of the rectifier circuit, the control unit being designed to determine the received power and to actuate the switch on the basis of the determined received power, i.e. to close or open it.

For example, the control unit has a signal receiver with which information can be received from an associated signal transmitter of a transmission unit or charging station. The control unit can thus be designed to receive the transmission power generated by a transmission unit and thus the reception power via the signal receiver, in particular as a signal. In other words, the control unit can receive a signal, after processing the signal by the control unit or based on the received signal, the control unit is or is prompted to put the switch into the state or to leave it in the state that corresponds to the received power corresponds, i.e. is advantageous or optimized for the reception performance. The rectifier circuit can thus be operated in the operating state that corresponds to the received power.

Alternatively or additionally, the control unit can have a measuring device with which the received power can be measured or detected.

The control unit is designed to compare the received power determined with a predetermined comparison value and to open the switch or leave it in an open state if the received power determined is at least as great as the predetermined comparison value and to close the switch or leave it in a closed state Leave state when the received power is less than the predetermined comparison value.

The comparison value is preferably determined by the fact that during operation of the receiving unit or the inductive energy transmission system characteristic ratio is as close to 1 as possible. Alternatively or additionally, the comparison value can be determined by the characteristic ratio preferably being less than 2, more preferably less than 1.5, even more preferably less than 1.3, in particular less than 1.2 during operation of the receiving unit or the inductive energy transmission system or 1.1 and most preferably less than or equal to 1. In the context of the invention, it was recognized that the closer the characteristic ratio is to 1, the greater the efficiency of the inductive energy transmission system. Furthermore, it was recognized that a characteristic ratio significantly greater than 1 can lead to problems with the resonant control of the transmitter coil, since the inductive energy transmission system has several stable system-related resonance frequencies in this range, which differ from the desired resonance frequency, the so-called design frequency ω _D , deviate. Consequently, the stability of the system is generally higher when the characteristic ratio satisfies the conditions given above. For example, if the transmission power of a first transmission unit is 3 kW and the transmission power of a second transmission unit is 20 kW, the comparison value can be 5 kW, for example.

The receiving unit according to the invention can be connected to an energy store and/or comprise an energy store. Thus, at least part of the energy transmitted by the energy transmission system, i.e. the energy transmitted from a charging station or an associated transmission unit to the receiving unit, can be stored. The energy store can include, for example, one or more rechargeable batteries or accumulators.

The receiving coil and the diodes of the rectifier circuit are preferably dimensioned or designed in such a way that the rectifier circuit generates a DC voltage that lies within a charging voltage range of the energy store. If the energy store is a car battery, the charging voltage range is usually 250 V to 500 V, in particular 280 V to 420 V.

In a further preferred embodiment, the receiving unit according to the invention also includes a reactive power compensation unit for reducing the reactive power of the receiving unit.

The reactive power compensation unit can include, for example, one or more reactive power compensation capacitors or reactive power compensation capacities. The reactive power compensation unit can be designed as a series connection or as a parallel connection. The reactive power compensation unit is preferably connected in series with the receiving coil. Alternatively, the reactive power compensation unit can also be connected in parallel with the receiving coil. If the reactive power compensation unit is connected in parallel to the receiving coil, then the reactive power compensation unit preferably has additional smoothing components, in particular a choke.

With the help of the reactive power compensation unit, the losses due to reactive power can be reduced and the efficiency and/or efficiency of the inductive energy transmission system can be increased.

• - eine Sendeeinheit zum Erzeugen von Energie in Form eines magnetischen Wechselfeldes; und
• - eine erfindungsgemäße Empfangseinheit zum Empfangen und/oder Speichern zumindest eines Teils der von der Sendeeinheit erzeugten Energie.

Another independent aspect of solving the task relates to an inductive energy transmission system comprising:

• - A transmission unit for generating energy in the form of an alternating magnetic field; and
• - A receiving unit according to the invention for receiving and/or storing at least part of the energy generated by the transmitting unit.

• - eine Energiequelle und/oder einen Anschluss bzw. eine Anbindung an eine Energiequelle, insbesondere einen Anschluss bzw. eine Anbindung an ein Stromnetz, zum Erzeugen und/oder Aufnehmen bzw. Abgreifen von Energie;
• - eine Sendespule zum Erzeugen eines magnetischen Wechselfeldes
• - einen AC/DC Wandler als PFC-Stufe (Power Factor Correcting Stage) zur Anpassung der Sendeeinheit an die Energiequelle, insbesondere an das Stromnetz;
• - einen DC/DC-Wandler zum Einstellen der Sendeleistung der Sendeeinheit;
• - einen DC/AC-Wandler zur Erzeugung einer Wechselspannung bzw. eines Wechselstroms für die induktive Kopplung;
• - eine primärseitige Blindleistungskompensationseinheit zur Kompensation der Blindleistung in der Sendeeinheit;
• - einen Signalsender zum Senden von Informationen, insbesondere zum Senden der Information über die Sendeleistung des Signalsenders.

The transmission unit preferably includes one or more of the following primary-side components:

• - an energy source and/or a connection or a connection to an energy source, in particular a connection or a connection to a power grid, for generating and/or absorbing or tapping off energy;
• - A transmitter coil for generating an alternating magnetic field
• - An AC/DC converter as a PFC stage (Power Factor Correcting Stage) for adapting the transmission unit to the energy source, in particular to the power grid;
• - A DC/DC converter for adjusting the transmission power of the transmission unit;
• - A DC/AC converter for generating an alternating voltage or an alternating current for the inductive coupling;
• - A primary-side reactive power compensation unit for compensating for the reactive power in the transmission unit;
• - A signal transmitter for sending information, in particular for sending information about the transmission power of the signal transmitter.

With the help of the receiving unit according to the invention, a high efficiency of the inductive Energy transmission system can be achieved regardless of the transmission power of the transmitter unit.

wobei k ein vorbestimmter Kopplungsfaktor zwischen der Sendeeinheit und der Empfangseinheit, ω_D eine vorbestimmte Resonanzfrequenz und R_L ein vorbestimmter Ersatzlastwiderstand ist.In a preferred embodiment of the energy transmission system according to the invention, the receiving coil has an inductance L ₂ so that the following applies to a characteristic relationship of the energy transmission system: $$\frac{k{\omega }_D{L}_2}{R_L}\approx 1$$

where k is a predetermined coupling factor between the transmitting unit and the receiving unit, ω _D is a predetermined resonant frequency, and R _L is a predetermined equivalent load resistance.

bestimmt werden, wobei L₁ die Selbstinduktivität der Sendespule, L₂ die Selbstinduktivität der Empfangsspule und M die Gegeninduktivität ist. Die sogenannte Design-Frequenz ω_D ist eine der Resonanzfrequenzen des gesamten Energieübertragungssystems, welche immer existiert. Sie wird auch zur Auslegung der Kompensationskondensatoren verwendet. Der Ersatzlastwiderstand R_L charakterisiert einen effektiven Widerstand sowohl der Gleichrichtungsschaltung als auch der Last, d.h. des Energiespeichers.The coupling factor k between the transmitter unit and receiver unit or between the transmitter coil of the transmitter unit and the receiver coil of the receiver unit can be $$k=\frac{M}{\sqrt{L_1{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="DE102014012703B4\_0027.png,DE102014012703B4\_0029.png"\; state="\{\{state\}\}">L</figure-callout>}}_2}}$$

be determined, where L ₁ is the self-inductance of the transmitting coil, L ₂ is the self-inductance of the receiving coil and M is the mutual inductance. The so-called design frequency ω _D is one of the resonant frequencies of the entire energy transmission system, which always exists. It is also used to design the compensation capacitors. The equivalent load resistance R _L characterizes an effective resistance of both the rectification circuit and the load, ie the energy store.

im Wesentlichen gleich 1 ist.In the context of the present invention, the inventors recognized that the total reactive power of the inductive energy transmission system is lowest and the best efficiency is therefore achieved when the characteristic ratio $\frac{k{\omega }_D{L}_2}{R_L}$

is essentially equal to 1.

• - Bereitstellen einer erfindungsgemäßen Empfangseinheit;
• - Betätigen des Schalters der Gleichrichterschaltung der Empfangseinheit derart, dass der Schalter geöffnet ist bzw. wird, wenn eine Empfangsleistung mindestens so groß wie ein vorgegebener bzw. vorbestimmter Vergleichswert ist und der Schalter geschlossen ist bzw. wird, wenn die Empfangsleistung kleiner als der vorbestimmte Vergleichswert ist.

Another independent aspect of solving the problem relates to a method for the inductive transmission of energy, comprising the steps:

• - Providing a receiving unit according to the invention;
• - Actuating the switch of the rectifier circuit of the receiving unit in such a way that the switch is or will be open when a received power is at least as great as a specified or predetermined comparison value and the switch is or will be closed when the received power is less than the predetermined comparison value is.

The switch can be operated, i.e. opened and closed, manually. Alternatively or additionally, the switch can be actuated automatically with the aid of a control unit.

• - Ermitteln der Empfangsleistung;
• - Vergleichen der ermittelten Empfangsleistung mit einem vorgegebenen Vergleichswert;
• - Betätigen des Schalters auf Basis des Vergleichsergebnisses.

In particular, actuating the switch can include one or more of the following steps:

• - Determining the reception power;
• - Comparing the determined received power with a predetermined reference value;
• - Operating the switch based on the comparison result.

The steps mentioned above can be carried out, for example, by the control unit, in particular by a microprocessor or microcontroller.

For example, the switch can be closed or left in a closed state when the determined power is less than the specified comparison value or equal to the specified comparison value. Accordingly, the switch can be opened or left in an open state when the power determined is greater than the specified comparison value. The transmission power or reception power is preferably set before the start of the inductive energy transmission and the switch is then switched accordingly. Thus, advantageously, switching does not occur during operation, i.e. during energy transfer.

A further independent aspect for solving the problem relates to using the receiving unit according to the invention and/or the inductive energy transmission system for inductively charging an electric vehicle or its energy store.

The receiving unit can be part of the vehicle, i.e. integrated or built into the vehicle.

The statements made above or below regarding the embodiments of the first aspect also apply to the above-mentioned further independent aspects and in particular to preferred embodiments in this regard.

In the following, individual embodiments for solving the problem are described by way of example with reference to the figures. In this case, the individual embodiments described in part Features that are not absolutely necessary to implement the claimed subject matter, but which provide desired properties in certain applications. Thus, embodiments that do not have all the features of the embodiments described below are also to be regarded as being disclosed as falling under the technical teaching described. Furthermore, in order to avoid unnecessary repetition, certain features are only mentioned in relation to individual embodiments described below. It is pointed out that the individual embodiments should therefore not only be considered individually, but should also be viewed as a whole. Based on this synopsis, those skilled in the art will recognize that individual embodiments can also be modified by incorporating individual or multiple features of other embodiments. It is pointed out that a systematic combination of the individual embodiments with one or more features that are described in relation to other embodiments can be desirable and useful and should therefore be considered and also be regarded as covered by the description.

character list

• 1 shows a schematic circuit diagram of a conventional inductive energy transmission system;
• 2 shows a schematic circuit diagram of a receiving unit according to the invention for an inductive energy transmission system according to a preferred embodiment, which allows two different operating modes;
• 3 shows a schematic circuit diagram of an inductive energy transmission system according to the invention according to a preferred embodiment;
• 4 shows a schematic equivalent circuit diagram of an inductive energy transmission system for calculating reactive power;
• 5 shows diagrams of simulation results of the characteristic ratio depending on the battery voltage for different coupling factors k using an example system with the values L ₁ = 30 µH, L ₂ = 18 µH and ω _D = 140 kHz, where:
  • 5a shows the curves for P _Bat = 20 kW using the full bridge mode of the rectifier circuit according to the invention;
  • 5b shows the curves for P _Bat = 3 kW using the full bridge mode of the rectifier circuit according to the invention;
  • 5c shows the curves for P _Bat = 3 kW using the half-bridge mode of the rectifier circuit according to the invention;
• 6 shows diagrams of the simulation results of the total reactive power of the inductive energy transmission system depending on the battery voltage for different coupling factors k using an example system with the values L ₁ = 30 µH, L ₂ = 18 µH and ω _D = 140 kHz, where:
  • 6a shows the curves for P _Bat = 20 kW using the full bridge mode of the rectifier circuit according to the invention;
  • 6b shows the curves for P _Bat = 3 kW using the full bridge mode of the rectifier circuit according to the invention;
  • 6c shows the curves for P _Bat = 3 kW using the half-bridge mode of the rectifier circuit according to the invention;
• 7 shows diagrams of the simulation results of the standardized total reactive power component of the inductive energy transmission system as a function of the battery voltage for various coupling factors k using an example system with the values L ₁ = 30 µH, L ₂ = 18 µH and ω _D = 140 kHz, where:
  • 7a shows the curves for P _Bat = 20 kW using the full bridge mode of the rectifier circuit according to the invention;
  • 7b shows the curves for P _Bat = 3 kW using the full bridge mode of the rectifier circuit according to the invention;
  • 7c shows the curves for P _Bat = 3 kW using the half-bridge mode of the rectifier circuit according to the invention.

Detailed description of the drawings

The 1 shows a schematic circuit diagram of a conventional inductive energy transmission system 50. The inductive energy transmission system comprises a primary side or a transmitting unit 10 and a secondary side or a receiving unit 20.

The transmission unit 10 comprises an energy source 1, a DC/DC converter 2, a DC/AC converter 4, a primary coil or transmission coil 6 and a reactive power compensation unit or a reactive power compensation capacitor 8. The energy source 1 can be a power grid, for example. With the DC/DC converter 2, the transmission power of the transmission unit 10 can be defined or set via the output voltage level. The DC/AC converter 4 converts the DC voltage output from the DC/DC converter 2 into an AC voltage. The alternating voltage generates an alternating current in the transmitter coil 6, so that the transmitter coil 6 generates an alternating magnetic field which is used for inductive energy transmission. The reactive power compensation capacitor 8 is used to compensate for the reactive power occurring in the transmission coil 6 .

The receiving unit comprises a secondary coil or a receiving coil 16, a reactive power compensation unit or a reactive power compensation capacitor 18, an AC/DC converter 14 and a DC/DC converter 12. The receiving unit is connected to an energy store or a rechargeable battery 11 in order to to charge them. The reactive power compensation capacitor 18 is used to compensate for the reactive power generated in the receiving unit 20 . The magnetic alternating field of the transmitting coil 6 flows through the receiving coil 16 and consequently generates an induced alternating voltage. This alternating voltage is rectified using the AC/DC converter 14 . The DC/DC converter is conventionally required in order to be able to operate the inductive energy transmission system 50, which is designed for a specific nominal power, with a different power, e.g. a significantly lower power, in an efficiency-optimized manner. Without the DC/DC converter, the system would require a disproportionately large amount of reactive power in the compensation capacities when operated with significantly lower power than a system that is optimized for the lower power. This would thus cause high losses and correspondingly reduce the efficiency of the system. With the help of the DC/DC converter 12 on the receiving side, the voltage level at the receiving coil is conventionally adapted to the transmitted power, so that the system can be operated close to the optimal point. However, the receiving unit becomes more expensive, heavier and larger because of the additionally required DC/DC converter.

The 2 shows a schematic circuit diagram of a receiving unit 200 according to the invention for an inductive energy transmission system according to a preferred embodiment. The receiving unit 200 includes a receiving coil 16, a reactive power compensation unit 18 and an AC-DC converter or a rectifier circuit 30. The receiving unit is connected to an energy store or a rechargeable battery 11 in order to charge it. The rectifier circuit 30 serves to rectify the AC voltage generated by the receiving coil 16 . The rectifier circuit 30 thus represents an improvement on the AC-DC converter 14 of FIG 1 represent.

The receiving unit 30 includes four diodes 32, 34, 36, 38, which are arranged in a Graetz circuit. As an extension of this B2 two-pulse bridge circuit, the receiving unit 30 also includes a switch 40 which is connected in parallel with the diode 32 . However, the switch could just as well be connected in parallel with one of the other diodes 34, 36 or 38. If the receiving unit 30 is operated with a significantly lower power, i.e. received power, than the nominal power, the switch 40 is closed. Closing switch 40 changes the behavior of rectifier circuit 30 from a full-bridge rectifier (switch open) to a half-bridge rectifier (switch closed). The rectifier circuit 30 thus has two operating modes, namely a full-bridge mode when the switch is open and a half-bridge mode when the switch is closed. Closing switch 40 changes the characteristics of the entire system in that the optimal operating point is now at a transmitted power or received power that corresponds to a quarter of the power when the switch is open. This eliminates the need for an additional DC/DC stage.

The optional operation of the rectifier as a full-bridge or half-bridge rectifier reduces the reactive power requirement of the entire inductive energy transmission system when operating with significantly lower power, e.g. when operating with 3 kW or 6 kW instead of operating at a nominal power or transmission power or reception power of 20 kW. In this way, in particular, an unnecessary oversizing of the primary coil and reactive power compensation unit on the primary side can be avoided, and the efficiency and efficiency of the inductive energy transmission system can be increased.

The invention thus provides an electrical circuit or a receiving unit which can be used in particular for the inductive charging of electric vehicles and enables very good interoperability between different systems, e.g. between a 20 kW system and a 3 kW system. Conventional inductive energy transmission systems or inductive energy transmission systems with conventional receiving units, on the other hand, cause higher losses and reduce efficiency or require an additional DC/DC stage.

The 3 shows a schematic circuit diagram of an inductive energy transmission system 500 according to the invention according to a preferred embodiment. The energy conversion according to the invention The transmission system 500 includes a transmitter unit 10 and a receiver unit 200 according to the invention, which have already been described above. In addition, transmitter unit 10 and receiver unit 200 can be equipped with a, in particular wireless, communication system (in 3 not shown). That is to say that the transmission unit 10 and the reception unit 200 can each have a transmitter and/or receiver which enable information to be exchanged. For example, the transmission unit 10 can transmit information on the transmission power or reception power used to the reception unit 200 .

The 4 shows a schematic equivalent circuit diagram of an inductive energy transmission system, on the basis of which calculations or simulations can be carried out. For example, based on the equivalent circuit diagram, the reactive powers of the transmitter unit, receiver unit and the entire system made up of transmitter unit and receiver unit can be calculated or simulated.

In the following model calculations, the variable j designates the imaginary unit. Underlined quantities are complex quantities, while quantities that are not underlined and capitalized represent effective values or magnitudes of the complex quantities. Lowercase quantities are time-dependent quantities. For the sake of simplicity, the ohmic resistance of the coils is neglected.

wird als Kopplungsfaktor bezeichnet. Zur Berechnung des grundlegenden Verhaltens des Systems wurde nur die Grundschwingung einer einzelnen sinusförmigen Spannungsquelle 1 betrachtet. Der sekundärseitige Gleichrichter, d.h. die Gleichrichterschaltung der Empfangseinheit, wurde einschließlich der Last, d.h. der Batterie 11, als sogenannter Ersatzlastwiderstand R_L modelliert. Die Werte der Kondensatoren 8 und 18 der primärseitigen und sekundärseitigen Blindleistungskompensationseinheit wurden jeweils mit der gleichen Designfrequenz ω_D, wie in der 4 dargestellt, dimensioniert.The coil system can be described by three parameters, namely the self-inductances L ₁ and L ₂ of the transmitter coil 6 and receiver coil 16, respectively, and the mutual inductance M. The size $k=\frac{M}{\sqrt{L_1{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="DE102014012703B4\_0027.png,DE102014012703B4\_0029.png"\; state="\{\{state\}\}">L</figure-callout>}}_2}}$

is called the coupling factor. To calculate the basic behavior of the system, only the fundamental frequency of a single sinusoidal voltage source 1 was considered. The rectifier on the secondary side, ie the rectifier circuit of the receiving unit, including the load, ie the battery 11, was modeled as a so-called equivalent load resistance R _L . The values of the capacitors 8 and 18 of the primary-side and secondary-side reactive power compensation units were respectively calculated with the same design frequency ω _D as in FIG 4 shown, dimensioned.

$$\frac{I_2}{I_1}=\left|\frac{{\underset{\_}{I}}_2}{{\underset{\_}{I}}_1}\right|=\frac{{\omega }_{D}M}{R_L}$$

$$\frac{U_2}{I_1}=={\omega }_{D}M$$

$$\frac{I_2}{U_1}=\frac{1}{{\omega }_{D}M}$$

$$\frac{U_2}{U_1}=\frac{R_L}{{\omega }_{D}M}$$

Using Kirchhoff's laws on the secondary side of the equivalent circuit of the 4 the following relationships result at an operating frequency ω = ω _D : $$\frac{{\underset{\_}{I}}_2}{{\underset{\_}{I}}_1}=\text{j}\cdot \frac{{\omega }_{D}M}{R_L}$$

$$\frac{I_2}{I_1}=\left|\frac{{\underset{\_}{I}}_2}{{\underset{\_}{I}}_1}\right|=\frac{{\omega }_{D}M}{R_L}$$

$$\frac{u_2}{I_1}=={\omega }_{D}M$$

$$\frac{I_2}{{\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="DE102014012703B4\_0030.png,DE102014012703B4\_0031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1}=\frac{1}{{\omega }_{D}M}$$

$$\frac{u_2}{{\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="DE102014012703B4\_0030.png,DE102014012703B4\_0031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1}=\frac{R_L}{{\omega }_{D}M}$$

I ₁ symbolizes the current through the primary coil and U ₁ the voltage of the primary coil. Correspondingly, I ₂ symbolizes the current through the secondary coil and U ₂ the voltage of the secondary coil.

The reactive power of the entire inductive energy transmission system is calculated to $$Q_{Ges}=I_1^2{\mathrm{<figure-callout\; id="1"\; label="\omega \; D\; L"\; filenames="DE102014012703B4\_0030.png,DE102014012703B4\_0031.png"\; state="\{\{state\}\}">\omega </figure-callout>}}_D{L}_{}{}_1+I_2^2{\mathrm{<figure-callout\; id="2"\; label="\omega \; D\; L"\; filenames="DE102014012703B4\_0027.png,DE102014012703B4\_0029.png"\; state="\{\{state\}\}">\omega </figure-callout>}}_D{L}_{}{}_2$$

With equation (4) we get $$Q_{Ges}=\left(\frac{R_L}{k{\mathrm{<figure-callout\; id="2"\; label="\omega \; D\; L"\; filenames="DE102014012703B4\_0027.png,DE102014012703B4\_0029.png"\; state="\{\{state\}\}">\omega </figure-callout>}}_D{L}_{}{}_2}+\frac{k{\omega }_D{L}_2}{R_{\text{L}}}\right)\cdot \frac{1}{k}\cdot \frac{{\mathrm{<figure-callout\; id="2"\; label="u"\; filenames="DE102014012703B4\_0027.png,DE102014012703B4\_0029.png"\; state="\{\{state\}\}">u</figure-callout>}}_2{}^2}{R_{\text{L}}}$$

ab. Wegen min [x+1/x] = 2 für x = 1, folgt für die minimale Blindleistung des induktiven Energieübertragungssystems: $$Q_{\text{min}}=Q_{\text{ges}}\left(\frac{k{\omega }_D{L}_2}{R_{\text{L}}}=1\right)=\frac{2}{k}\cdot \frac{U_2{}^2}{R_{\text{L}}}$$

The total reactive power depends strongly on the so-called characteristic ratio $\frac{k{\omega }_D{L}_2}{R_L}$

away. Because min [x+1/x] = 2 for x = 1, it follows for the minimum reactive power of the inductive energy transmission system: $$Q_{\text{at least}}=Q_{\text{total}}\left(\frac{k{\omega }_D{L}_2}{R_{\text{L}}}=1\right)=\frac{2}{k}\cdot \frac{{\mathrm{<figure-callout\; id="2"\; label="u"\; filenames="DE102014012703B4\_0027.png,DE102014012703B4\_0029.png"\; state="\{\{state\}\}">u</figure-callout>}}_2{}^2}{R_{\text{L}}}$$

The highest efficiency can be achieved when the total reactive power, i.e. the reactive power of the entire inductive energy transmission system is minimal. Thus, the inductive energy transmission system works most efficiently in nominal operation when the characteristic ratio is as close to 1 as possible.

Depending on whether the rectifier circuit is operated in full-bridge mode or in half-bridge mode, different currents or voltages result at the battery. In general, the current through the battery is calculated as follows: $$I_{Bat}=\frac{1}{T}{\displaystyle \underset{0}{\overset{T}{\int }}\left|i_2\left(t\right)\right|\text{i.e}t}$$

This results in the full bridge mode: $$I_{\text{Bat}}=\frac{2\sqrt{2}}{\pi }\cdot I_2\approx 0.9\cdot I_2$$

For the half-bridge mode we get: $$I_{\text{Bat}}=\frac{\sqrt{2}}{\pi }\cdot I_2\approx 0.45\cdot I_2$$

$$U_{\text{Bat}}=\frac{I_2}{I_{\text{Bat}}}\cdot U_2$$

The power balance gives: $$I_{\text{Bat}}\cdot u_{\text{Bat}}=I_2\cdot {\mathrm{<figure-callout\; id="2"\; label="u"\; filenames="DE102014012703B4\_0027.png,DE102014012703B4\_0029.png"\; state="\{\{state\}\}">u</figure-callout>}}_2$$

$$u_{\text{Bat}}=\frac{I_2}{I_{\text{Bat}}}\cdot {\mathrm{<figure-callout\; id="2"\; label="u"\; filenames="DE102014012703B4\_0027.png,DE102014012703B4\_0029.png"\; state="\{\{state\}\}">u</figure-callout>}}_2$$

Thus it follows for the full bridge: $$u_{\text{Bat}}=\frac{\mathrm{<figure-callout\; id="2"\; label="\pi "\; filenames="DE102014012703B4\_0027.png,DE102014012703B4\_0029.png"\; state="\{\{state\}\}">\pi </figure-callout>}}{2\sqrt{2}}\cdot {\mathrm{<figure-callout\; id="2"\; label="u"\; filenames="DE102014012703B4\_0027.png,DE102014012703B4\_0029.png"\; state="\{\{state\}\}">u</figure-callout>}}_2\approx 1.11\cdot {\mathrm{<figure-callout\; id="2"\; label="u"\; filenames="DE102014012703B4\_0027.png,DE102014012703B4\_0029.png"\; state="\{\{state\}\}">u</figure-callout>}}_2$$

And for the half bridge: $$u_{\text{Bat}}=\frac{\mathrm{<figure-callout\; id="2"\; label="\pi "\; filenames="DE102014012703B4\_0027.png,DE102014012703B4\_0029.png"\; state="\{\{state\}\}">\pi </figure-callout>}}{\sqrt{2}}\cdot {\mathrm{<figure-callout\; id="2"\; label="u"\; filenames="DE102014012703B4\_0027.png,DE102014012703B4\_0029.png"\; state="\{\{state\}\}">u</figure-callout>}}_2\approx 2.22\cdot {\mathrm{<figure-callout\; id="2"\; label="u"\; filenames="DE102014012703B4\_0027.png,DE102014012703B4\_0029.png"\; state="\{\{state\}\}">u</figure-callout>}}_2$$

Thus, the equivalent load resistance R _L can be calculated as follows: $$R_{\text{L}}=\frac{u_2}{{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="DE102014012703B4\_0027.png,DE102014012703B4\_0029.png"\; state="\{\{state\}\}">I</figure-callout>}}_2}$$

The equivalent load resistance R _L for the full bridge results in: $$R_{\text{L}}\approx 0.81\cdot \frac{u_{\text{Bat}}}{I_{\text{Bat}}}$$

And for the half bridge, the equivalent load resistance R _L results in: $$R_{\text{L}}\approx 0.20\cdot \frac{u_{\text{Bat}}}{I_{\text{Bat}}}$$

von ungefähr 1. Bei vorgegebenem Kopplungsfaktor k, Designfrequenz ω_D und Ersatzlastwiederstand R_L, sollte also die Selbstinduktivität der Empfangsspule als einstellbarer Parameter entsprechend gewählt werden. Bei einer Batteriespannung von 290 V bis 410 V, einem Kopplungsfaktor von 0,25 bis 0,35, einer konstanten Sende- bzw. Empfangs- bzw. Ladeleistung von 20 kW und einer Resonanzfrequenz von 140 kHz, kann die Selbstinduktivität L₂ der Empfangsspule z.B. etwa 18 µH betragen.As can be seen from equation (10), the system works most efficiently at a characteristic ratio $\frac{k{\omega }_D{L}_2}{R_L}$

of approximately 1. With a given coupling factor k, design frequency ω _D and equivalent load resistance R _L , the self-inductance of the receiving coil should be selected accordingly as an adjustable parameter. With a battery voltage of 290 V to 410 V, a coupling factor of 0.25 to 0.35, a constant transmission or reception or charging power of 20 kW and a resonant frequency of 140 kHz, the self-inductance L ₂ of the receiving coil, for example be about 18 µH.

in Abhängigkeit der Batteriespannung für verschiedene Kopplungsfaktoren k mit L₁ = 30 µH, L₂ = 18 µH und ω_D = 140 kHz. Dabei wurde bei der Simulation der 5a eine Empfangsleistung bzw. Batterie-Ladeleistung von P_Bat = 20 kW angenommen und die Simulation für den Vollbrückenmodus der erfindungsgemäßen Gleichrichterschaltung durchgeführt. Bei der Simulation der 5b wurde die Empfangsleistung bzw. Batterie-Ladeleistung auf P_Bat = 3 kW reduziert und die Simulation ebenfalls für den Vollbrückenmodus der erfindungsgemäßen Gleichrichterschaltung durchgeführt. Bei der Simulation der 5c wurde die Empfangsleistung bzw. Batterie-Ladeleistung von P_Bat = 3 kW beibehalten, dafür aber die Simulation für den Halbbrückenmodus der erfindungsgemäßen Gleichrichterschaltung durchgeführt.The 5a until 5c show diagrams of simulation results of the characteristic ratio $\frac{k{\omega }_D{L}_2}{R_L}$

depending on the battery voltage for different coupling factors k with L ₁ = 30 µH, L ₂ = 18 µH and ω _D = 140 kHz. In the simulation, the 5a a received power or battery charging power of P _Bat = 20 kW assumed and carried out the simulation for the full bridge mode of the rectifier circuit according to the invention. When simulating the 5b the received power or battery charging power was reduced to P _Bat =3 kW and the simulation was also carried out for the full-bridge mode of the rectifier circuit according to the invention. When simulating the 5c the received power or battery charging power of P _Bat = 3 kW was retained, but the simulation was carried out for the half-bridge mode of the rectifier circuit according to the invention.

As can be seen from the diagrams of 5a and 5b results, the characteristic ratio deviates noticeably from the ideal value 1 when the transmission or receiving power of 20 kW ( 5a) to 3 kW ( 5b) is reduced and the rectifier circuit continues to be operated in full-bridge mode. If, on the other hand, the rectifier circuit is operated at 3 kW in half-bridge mode ( 5c ), the characteristic ratio moves closer to 1 again. By switching the rectifier circuit according to the invention from the full-bridge mode to the half-bridge mode, it can thus be achieved that the efficiency of the inductive energy transmission system is significantly increased.

The 6a until 6c show diagrams of simulation results of the total reactive power of the inductive energy transmission system depending on the battery voltage for different coupling factors k with L ₁ = 30 µH, L ₂ = 18 µH and ω _D = 140 kHz. In the simulation, the 6a a received power or battery charging power of P _Bat = 20 kW assumed and carried out the simulation for the full bridge mode of the rectifier circuit according to the invention. When simulating the 6b the received power or battery charging power was reduced to P _Bat =3 kW and the simulation was also carried out for the full-bridge mode of the rectifier circuit according to the invention. When simulating the 6c the received power or battery charging power of P _Bat = 3 kW was retained, but the simulation was carried out for the half-bridge mode of the rectifier circuit according to the invention.

As can be seen from the diagrams of 6a until 6c results, the total reactive power is reduced, ie the reactive power Q _tot of the entire inductive energy transmission system when the transmission or reception power is reduced from 20 kW to 3 kW. However, when the rectifier circuit is operated in half-bridge mode, Q _tot is ( 6c ) significantly smaller than Q _tot when operating the rectifier circuit in full-bridge mode ( 6b) .

In the 7a until 7c are the same simulations as in the 6a until 6c shown, but the total reactive power Q _tot was normalized to the transmission or reception or battery charging power. Thus, the curves can be better compared in terms of the efficiency of the inductive energy transfer system.

As can be seen from the diagrams of 7a and 7b results, the reactive power component Q _tot / P _Bat increases significantly when the transmission or receiving power of 20 kW ( 7a) to 3 kW ( 7b) is reduced and the rectifier circuit is operated in full bridge mode. If, on the other hand, the rectifier circuit is operated at 3 kW in half-bridge mode ( 7c ), the reactive power component Q _tot /P _Bat is significantly smaller than in full-bridge mode. By switching the rectifier circuit according to the invention from the full-bridge mode to the half-bridge mode, the efficiency of the inductive energy transmission system can be significantly increased.

reference list

1

Energy source / power grid

2

Primary side DC/DC converter

4

Primary side DC/AC converter

6

Primary coil / transmitter coil

8th

Primary side reactive power compensation unit

10

Primary circuit / transmitter unit

11

load / energy storage / battery or accumulator

12

Secondary side DC/DC converter

14

Secondary side AC/DC converter / rectifier circuit

16

Secondary coil / receiving coil

18

Secondary reactive power compensation unit

20

Secondary circuit / receiving unit

30

Secondary side AC/DC converter / rectifier circuit

32

diode

34

diode

36

diode

38

diode

40

Switch

50

Inductive energy transmission system

200

Secondary circuit / receiving unit

500

Inductive energy transmission system

Claims (10)

Receiving unit (200) for an inductive energy transmission system (500), comprising: - A receiving coil (16) for inductively generating an AC voltage; - a rectifier circuit (30) for rectifying the AC voltage generated, the rectifier circuit (30) having a switch (40) with which the rectifier circuit (30) can be operated in a first and a second operating mode, the first operating mode being switched to a first received power is tuned and the second mode of operation is tuned to a second received power, wherein the first received power differs from the second received power; and - a control unit for controlling the switch (40), the control unit being designed to determine the received power, to compare the determined received power with a predetermined comparison value, and to open the switch (40) if the determined received power is at least as great as the predetermined comparison value and to close the switch (40) when the received power determined is less than the predetermined comparison value. Receiving unit (200) after claim 1 , wherein the rectifier circuit (30) is designed, in the first operating mode, to reduce the reactive power of the inductive energy transmission system (500) for the first received power compared to the reactive power of the inductive energy transmission system (500) for the second received power, and/or wherein the rectifier circuit (30 ) is designed to reduce the reactive power of the inductive energy transmission system (500) for the second reception power in comparison to the reactive power of the inductive energy transmission system (500) for the first reception power in the second operating mode. Receiving unit (200) after claim 1 or 2 , wherein the first mode of operation is a full-bridge mode and the second mode of operation is a half-bridge mode. Receiving unit (200) according to any one of the preceding claims, wherein the rectifier circuit (30) acts as a full-bridge rectifier when the switch (40) is open, and wherein the rectifier circuit (30) acts as a half-bridge rectifier when the switch (40) is closed. Receiving unit (200) after claim 4 , wherein the rectifier circuit (30) comprises four diodes (32, 34, 36, 38) and the switch (40) is connected in parallel with one of the four diodes (32, 34, 36, 38). Receiving unit (200) after claim 5 , wherein the four diodes (32, 34, 36, 38) are arranged and connected according to a Graetz circuit. Inductive energy transmission system (500) comprising: - A transmitter unit (10) for generating energy in the form of an alternating magnetic field; and - A receiving unit (200) according to any one of the preceding claims for receiving and / or storing at least part of the energy generated by the transmitting unit (10). Inductive energy transmission system (500) according to claim 7 , wherein the comparison value is determined such that a characteristic ratio $\frac{k{\omega }_D{L}_2}{R_L}$

of the inductive energy transmission system (500) is less than 2, where k is a predetermined coupling factor between the transmitting unit (10) and the receiving unit (200), ω _D is a predetermined resonance frequency, L ₂ is an inductance of the receiving coil (16) and R _L is a predetermined equivalent load resistance is. Method for the inductive transmission of energy, comprising the steps: - providing a receiving unit (200) according to one of Claims 1 until 6 ; and - actuating the switch (40) of the rectifier circuit (30) of the receiving unit (200) using the control unit in such a way that the switch (40) is or becomes open when the received power is at least as great as the predetermined comparison value and the switch (40) is closed when the received power is less than the predetermined comparison value. Use of the receiving unit (200) according to one of Claims 1 until 6 and/or the inductive energy transmission system (500). claim 7 or 8th for inductive charging of an electric vehicle.

Images