DE102016207929A1 - Secondary unit with voltage adjustment for inductive charging - Google Patents

Abstract

A secondary unit (120) for an inductive charging system for charging an electrical energy store (103) of a vehicle (100) is described. The secondary unit (120) comprises a secondary coil (121) in which a secondary current (352) is generated in response to a magnetic charging field. In addition, the secondary unit (120) comprises a bridge rectifier (301) connected to the secondary coil (121) via input bridge points (311, 312) and arranged at output bridge points (321, 322) on the basis of the secondary current (352) Bridge rectifier (301) to generate a rectified charging current (353) for charging the energy storage (103). Furthermore, the secondary unit (120) comprises a first capacitor (341) and a second capacitor (342). The secondary unit (120) further comprises at least one switching element (302, 501, 502) and a control unit (370) for controlling the at least one switching element (302, 501, 502).

Description

The invention relates to a secondary unit with a device for adjusting the charging voltage during inductive charging of an electrical energy storage device of a motor vehicle.

Electric vehicles typically have a battery in which electrical energy can be stored to operate an electric machine of the vehicle. The battery of the vehicle can be charged with electrical energy from a power grid. For this purpose, the battery is coupled to the power grid to transfer the electrical energy from the power grid into the battery of the vehicle. The coupling can be wired (via a charging cable) and / or wireless (based on an inductive coupling between a charging station and the vehicle).

One approach to automatically, wirelessly, inductively charging the battery of the vehicle is to transmit electrical energy to the battery from the floor to the underbody of the vehicle via magnetic induction via the underbody clearance. This is exemplary in 1 shown. In particular shows 1 a vehicle 100 with a memory 103 for electrical energy (eg with a rechargeable battery 103 ). The vehicle 100 includes a secondary coil 121 in the vehicle underbody, with the secondary coil 121 via an impedance matching (not shown) and a rectifier 101 with the memory 103 connected to electrical energy. The secondary coil 121 is typically part of a so-called "Wireless Power Transfer" (WPT) vehicle unit 120 or secondary unit 120 ,

The secondary coil 121 the WPT vehicle unit 120 can over a primary coil 111 be positioned, the primary coil 111 eg on the floor of a garage. The primary coil 111 is typically part of a so-called WPT ground unit 110 or primary unit 110 , The primary coil 111 is with a power supply 113 connected. The power supply 113 may include a radio-frequency generator that provides an alternating current in the primary coil of the WPT ground unit 110 is generated (which is also referred to in this document as a primary current), whereby a magnetic field (in particular an electromagnetic charging field) is induced. The magnetic charging field may have a predefined charging field frequency range. The charging field frequency of the magnetic charging field can be in the range of 80-90 kHz (in particular at 85 kHz).

With sufficient magnetic coupling between primary coil 111 the WPT ground unit 110 and secondary coil 121 the WPT vehicle unit 120 about the underbody freedom 130 becomes by the magnetic field a corresponding voltage and thus also a current in the secondary coil 121 (also referred to as secondary current in this document). The induced current in the secondary coil 121 the WPT vehicle unit 120 is through the rectifier 101 rectified and in memory 103 saved. So, electric power can be wireless from the power supply 113 to the energy store 103 of the vehicle 100 be transmitted. The charging process can be in the vehicle 100 through a charging control unit 105 to be controlled. The charging control unit 105 may be set up for this purpose, eg wireless, with the WPT ground unit 110 to communicate.

To maximize field strengths of the magnetic charging field for bridging the underbody clearance 130 To be able to produce resonant systems can be used. Here are both the primary coil 111 as well as the secondary coil 121 integrated into resonant circuits, via the primary coil 111 and the secondary coil 121 coupled together.

In EP2911264A1 a charging system is described, which is a voltage Doppler circuit in the secondary unit 120 includes, with the charging voltage to the energy storage 103 can be raised or the secondary voltage to the secondary coil 121 can be reduced. Thus, even with relatively low primary currents in the primary coil 111 and with relatively low field strengths of the charging field, high charging powers are provided. As with increasing state of charge of the energy storage 103 typically the voltage across the energy store 103 increases, the use of a voltage Doppler circuit is particularly advantageous at relatively high charge states. The use of a voltage Doppler circuit can, however, at relatively low charge states to reduced charging power and / or increased demands on the current carrying capacity of the secondary coil 121 to lead.

This document deals with the technical problem, a secondary unit 120 for an inductive charging system for charging the energy storage 103 of a vehicle 100 provide energy, cost and space efficient way charging the energy storage 103 allows for different states of charge.

The object is solved by the independent claims. Advantageous embodiments are described i.a. in the dependent claims.

According to one aspect, a secondary unit for an inductive charging system for charging an electrical energy storage device of a vehicle is described. The inductive charging system typically includes a vehicle-external primary unit configured to generate a magnetic charging field at a particular charging field frequency (eg, 81.38 to 90 kHz according to the FCC, Frequency Table). Furthermore, the inductive charging system typically comprises a secondary unit which is set up to generate a (rectified) charging current for charging the electrical energy store as a function of the magnetic charging field. For this purpose, the primary unit comprises a primary coil for generating the magnetic charging field as a function of a primary current, ie as a function of an alternating current with the charging field frequency. The secondary unit comprises a secondary coil which is magnetically coupled to the primary coil to generate a secondary current (ie, an alternating current with the charging field frequency) based on the magnetic charging field. The secondary coil can thus be used to inductively receive electrical energy from the primary coil.

The secondary unit may comprise a resonant capacitor which together with the secondary coil forms a resonant circuit for generating a secondary current in response to a magnetic charging field. The secondary unit further comprises a rectifier which is set up to generate a rectified charging current for charging the energy store on the basis of the secondary current.

Furthermore, the secondary unit comprises a bridge rectifier which is connected to the secondary coil via input bridge points (in particular via a first and a second input bridge point) and which is set up based on the secondary current at output bridge points (in particular at a first and a second output Bridge point) of the bridge rectifier to generate a rectified charging current for charging the energy storage. The bridge rectifier typically includes a first diode disposed forwardly between the first input bridge point and the first output bridge point, and a second diode disposed in the reverse direction between the first input bridge point and the second output bridge point. In addition, the bridge rectifier may include a third diode disposed forwardly between the second input bridge point and the first output bridge point and a fourth diode disposed in the reverse direction between the second input bridge point and the second output bridge point ,

The secondary unit further comprises a first capacitor and a second capacitor. The first capacitor can substantially have the same capacitance value as the second capacitor.

Furthermore, the secondary unit comprises at least one switching element which is set up to switch the first capacitor between the first input bridge point and the first output bridge point or to decouple it from the first input bridge point or the first output bridge point. The at least one switching element is further configured to switch the second capacitor between the first input bridge point and the second output bridge point or to decouple from the first input bridge point or the second output bridge point. The at least one switching element may e.g. comprise one or more switching transistors. By means of the at least one switching element, a voltage boost can thus be activated or deactivated by means of the first and second capacitor.

The secondary unit further comprises a control unit configured to drive the at least one switching element such that the first capacitor is connected between the first input bridge point and the first output bridge point and the second capacitor is connected between the first input bridge point and the second output -Brückpunkt is switched when a (rectified) charging voltage at the output bridge points is greater than a charging voltage threshold. In other words, at relatively high charging voltages, the voltage boost can be activated by means of the first and second capacitors. Thus it can be effected that relatively low primary currents can be used even at relatively high charging voltages.

The control unit is further configured to drive the at least one switching element in such a way that the first capacitor is decoupled from the first input bridge point or the first output bridge point and the second capacitor is decoupled from the first input bridge point or the second output bridge point. when the charging voltage is less than the charging voltage threshold. In other words, at relatively low charging voltages, the voltage boost may be deactivated by means of the first and second capacitors. Thus it can be effected that relatively low secondary currents can be used even at relatively low charging voltages.

The charging voltage-dependent activation or deactivation of the voltage boost thus allows over a wide range of states of charge of the energy storage, high charging power with reduced requirements for the primary coil and the secondary coil of the charging system.

The secondary unit may comprise a first switching element (eg a first switching transistor) arranged to switch the first capacitor between the first input bridge point and the first output bridge point or from the first input bridge point or the first output bridge point. Decouple bridge point. In this case, the first switching element can be arranged in series with the first capacitor such that a current through the first capacitor corresponds to the current through the first switching element. Thus, the requirements for the current resistance of the switching element can be limited or reduced.

The secondary unit may comprise a second switching element (eg, a second switching transistor) configured to switch the second capacitor between the first input bridge point and the second output bridge point or from the first input bridge point or the second output bridge point. Decouple bridge point. The second switching element may be arranged in series with the second capacitor such that a current through the second capacitor corresponds to the current through the second switching element. Thus, the requirements for the current resistance of the switching element can be limited or reduced.

The first switching element (in series with the first capacitor) may comprise a transistor (in particular a field effect, FET, transistor) with an inverse diode or body diode, which is arranged in the forward direction between the first input bridge point and the first output bridge point (and thus together with the first capacitor) is arranged parallel to the first diode of the bridge rectifier). In an analogous manner, the second switching element may comprise a transistor (in particular a field effect, FET, transistor) with an inverse diode or body diode which is arranged in the reverse direction between the first input bridge point and the second output bridge point (and thus together with the second capacitor is arranged in parallel to the second diode of the bridge rectifier). Thus, an efficient implementation of the switching elements can be effected (by only one transistor at a time).

The secondary unit may include a plurality of first capacitors and a corresponding plurality of second capacitors. Furthermore, the secondary unit may comprise a plurality of switching elements. By the plurality of switching elements, in each case a first capacitor between the first input bridge point and the first output bridge point can be switched or decoupled from the first input bridge point or the first output bridge point. In addition, by the plurality of switching elements in each case a second capacitor between the first input bridge point and the second output bridge point can be switched or decoupled from the first input bridge point or the second output bridge point. In this case, the switching element for a pair of a first capacitor and a second capacitor may be arranged such that the switching element is traversed by the buzzer of the capacitor currents of the capacitor pair.

Alternatively, the secondary unit for the plurality of first capacitors may comprise a corresponding plurality of first switching elements, wherein in each case a corresponding first capacitor is connected between the first input bridge point and the first output bridge point or from the first input bridge point or through the first switching elements can be decoupled from the first output bridge point. In particular, in each case a first capacitor and a first switching element may be connected in series. In a corresponding manner, the secondary unit for the plurality of second capacitors may comprise a corresponding plurality of second switching elements, wherein in each case a corresponding second capacitor is connected between the first input bridge point and the second output bridge point by the second switching elements or from the first input terminal. Bridge point or the second output bridge point can be decoupled. In particular, in each case a second capacitor and a second switching element may be connected in series.

The control unit may be configured to control the plurality of (possibly first and second = switching elements such that with increasing charge voltage, a number of first capacitors which are connected between the first input bridge point and the first output bridge point (and thus parallel to each other) , and a number of second capacitors, which are connected between the first input bridge point and the second output bridge point (and thus parallel to each other), increases by the use of a plurality of first and second capacitors, a maximum value of the Secondary voltage and a maximum value of the primary current can be further reduced.

In particular, the control unit may be set up at a plurality of different, relatively increasing Charging voltage thresholds each to connect a further first capacitor between the first input bridge point and the first output bridge point and to connect a further second capacitor between the first input bridge point and the second output bridge point. This gradual activation of the capacitors may be such that, at a charging voltage above a highest of the plurality of charging voltage thresholds, all first capacitors of the plurality of first capacitors are connected between the first input bridge point and the first output bridge point and all second ones Capacitors of the plurality of second capacitors are connected between the first input bridge point and the second output bridge point. By stepwise activation of the plurality of first and second capacitors, a maximum value of the secondary voltage and a maximum value of the primary current can be further reduced while the total capacity is unchanged.

The capacitance values of the plurality of first capacitors and the plurality of second capacitors as well as the plurality of charging voltage threshold values may be designed such that a predetermined maximum value of the secondary current is not exceeded.

The control unit may be configured to control the at least one switching element such that a predetermined maximum value of the secondary current is not exceeded up to a predetermined maximum value of the charging voltage.

Furthermore, the control unit may be configured to increase the charging voltage in a charging period such that the energy storage is charged during the charging period with a constant target charging power. For this purpose, the charging voltage can be steadily raised.

In addition, the control unit may be configured to send a control signal to a primary unit of the inductive charging system, which is configured to generate the magnetic charging field. In this case, the control signal indicate that the at least one switching element has been switched or switched. Alternatively or additionally, the control unit may be configured to receive a control signal from the primary unit, which indicates that the at least one switching element is to be switched. Through the communication between the primary unit and the secondary unit, charging can be effected with a certain (constant) target charging power (even if the voltage boosting is activated).

In another aspect, a charging system is described that includes the secondary unit described in this document.

According to a further aspect, a vehicle, in particular a road vehicle such as e.g. a passenger car, a truck, a bus or a motorbike, comprising the secondary unit described in this document.

It should be understood that the devices and systems described herein may be used alone as well as in combination with other devices and systems described in this document. Furthermore, any aspects of the devices and systems described in this document may be combined in a variety of ways. In particular, the features of the claims can be combined in a variety of ways.

Furthermore, the invention will be described in more detail with reference to exemplary embodiments. Show

1 exemplary components of an inductive charging system;

2 exemplary components of a WPT ground unit and a WPT vehicle unit;

3 a secondary unit with a switchable voltage Doppler;

4a and 4b exemplary curves of the RMS values of the secondary current or the secondary voltage as a function of the charging voltage;

5a exemplary switching elements for activating or deactivating the voltage Doppler;

5b and 5c exemplary switchable voltage Doppler having a plurality of capacitor strings; and

6 an exemplary profile of the RMS value of the secondary voltage as a function of the charging voltage when using a plurality of capacitor strings.

As set forth above, the present document is concerned with the provision of a cost, energy and space efficient secondary unit or WPT vehicle unit 120 that charge a store of energy 103 of a vehicle 100 with the highest possible charging power at different states of charge of the energy storage 103 allows.

ergibt. Die Ladefeld-Frequenz ist bevorzugt nahe an der Resonanzfrequenz f₀, um einen möglichst hohen Primärstrom zu erzeugen (durch eine Resonanz). Ein hoher Primärstrom ist typischerweise erforderlich, da der Kopplungsfaktor k zwischen Primärspule 111 ist, z.B. k~0.1. und Sekundärspule 121 aufgrund der großen Unterbodenfreiheit 130 relativ klein 2 shows a circuit diagram of a WPT ground unit 110 and a WPT vehicle unit 120 , The WPT ground unit 110 includes an inverter 213 , which is adapted to generate from a direct current (eg at a DC voltage of about 500V) an alternating current with a charging field frequency. This alternating current is referred to in this document as the primary current I ₁ . Furthermore, the WPT ground unit includes 110 the primary coil 111 (commonly referred to as inductive unit) and a primary capacitor 212 (commonly referred to as capacitive unit). It is also in 2 an example of a filter (eg 4th order) 214 the WPT ground unit 110 shown. The WPT ground unit 110 thus includes a series resonant circuit (also referred to herein as the primary resonant circuit), the resonant frequency of the total capacitance C (in particular the capacitance of the capacitor 212 ) and the total inductance L (in particular the inductance of the primary coil 111 when

results. The charging field frequency is preferably close to the resonance frequency f ₀ in order to generate the highest possible primary current (by a resonance). A high primary current is typically required because the coupling factor k between the primary coil 111 is, eg k ~ 0.1. and secondary coil 121 due to the large underbody clearance 130 relatively small

Analogously, the WPT vehicle unit includes 120 a resonant circuit (also referred to here as secondary resonant circuit), which consists of the secondary coil 121 (commonly referred to as inductive unit) and a secondary capacitor 222 (generally referred to as capacitive unit) is formed. The resonant frequency of this secondary resonant circuit is preferably at the resonant frequency of the primary resonant circuit of the WPT ground unit 110 adapted to achieve the best possible transmission. It is also in 2 a filter capacitor 224 , a rectifier 101 and an energy store to be charged 103 shown. Through the charging field is over the coupled coils 111 . 121 a secondary voltage and a secondary current in the WPT vehicle unit 120 induced. This is done by the rectifier 101 rectified to a rectified charging current and charging voltage for charging the energy storage 103 provide.

3 shows a charging system with a WPT vehicle unit or a secondary unit 120 comprising a voltage Doppler circuit or a circuit for raising the charging voltage, by means of a switching element 302 can be activated or deactivated. The rectifier 101 the secondary unit 120 is in the in 3 illustrated example as a bridge rectifier 301 with two input bridge points 311 . 312 and two exit bridge points 321 . 322 educated. At the entrance bridge points 311 . 312 are the secondary voltage 362 with the secondary current 352 on, and at the output bridge points 321 . 322 be the charging current 353 with the charging voltage 363 provided.

The voltage Doppler circuit comprises a first capacitor 341 that is between a first output bridge point 321 and a first entrance bridge point 311 is arranged, and a second capacitor 342 that is between the first entrance bridge point 311 and a second output bridge point 322 is arranged. The voltage doubling occurs when the in 3 illustrated switching element 302 the connection point between the first capacitor 341 and the second capacitor 342 with the first entrance bridge point 311 coupled. On the other hand, the voltage doubling can be deactivated by the connection point between the capacitors 341 . 342 from the first entrance bridge point 311 is decoupled.

The secondary unit 120 includes a control unit 370 that is set up, the switching element 302 to control the voltage boost through the capacitors 341 . 342 to activate or deactivate. In particular, the control unit 370 be set up, information relating to the state of charge of the energy storage 103 to investigate. For this purpose, for example, the energy storage 103 from the secondary unit 120 be decoupled to the quiescent voltage of the energy storage 103 to investigate. The quiescent voltage of the energy storage 103 typically shows the state of charge (ie, the state of charge, SOC) of the energy store 103 at. The switching element 302 can then be controlled as a function of the rest voltage. Alternatively or additionally, the charging current 353 or the secondary current 352 and / or the charging voltage 363 or the secondary voltage 362 be determined. The switching element 302 can then depend on the charging current 353 or the secondary current 352 and / or the charging voltage 363 or the secondary voltage 362 be controlled.

4a shows the amount or rms value of the secondary current 352 as a function of the charging voltage 363 during a charging process. The secondary current 352 is typically at a maximum value 451 limited, with the maximum value 451 from the design of the secondary coil 121 depends. As a result, the charging power in the areas A, B of the charging process is reduced. From a charging voltage 363 which has a first charging voltage threshold 471 exceeds, can be loaded with a certain (constant) target charging power. To the target charging power even with increasing state of charge of the energy store 103 maintain the charging voltage 363 which in turn increases the magnitude or RMS value of the secondary voltage 362 requires. This in turn requires an increase in the field strength of the charging field, which in turn increases the magnitude or RMS value of the primary current 351 requires. With an increase in the primary current 351 or the field strength of the charging field to be generated in turn increase the requirements and thus the costs for the primary coil 111 ,

For this reason, from reaching a second charging voltage threshold 472 the voltage Doppler circuit are activated (at the switching point 402 ), so that the rms value of the secondary voltage 362 at constant charging voltage 363 decreases, and the rms value of the secondary current 352 in a corresponding manner (with the same target charging power) increases (eg from the minimum value 452 to the maximum value 451 ).

4b shows the the 4a corresponding course of the rms value of the secondary voltage 362 , the activation of the voltage Doppler circuit of a minimum value 461 to a maximum value 462 increases. By deactivating or activating the voltage Doppler circuit at a certain charging voltage threshold 472 can thus be achieved that at a relatively low state of charge, the rms value of the secondary current 352 to a maximum value 451 can be limited, and that at a relatively high state of charge, the rms value of the primary current 351 can be limited to a maximum value. Thus, with reduced demands on the coils 111 . 121 allow the charging system over a wide range of charging a certain target charging power.

The capacity of the capacitors 341 . 342 and the switching point 402 can be chosen such that the points C and E have the same minimum value 452 for the RMS value of the secondary current 352 and / or the same maximum value 462 for the RMS value of the secondary voltage 352 exhibit. In this case, the activation of the voltage doubler circuit takes place at point C. At point E is a maximum charging voltage 363 reached and / or the charging finished.

This in 3 illustrated switching element 302 can be implemented by using at least two switching transistors (in particular field effect, eg, MOS, metal oxide semiconductor, transistors), which each have mutually opposite inverse diodes or body diodes. These switching transistors must be designed for the entire current between the connection point of the capacitors 341 . 342 and the first entrance bridge point 311 flows.

5a shows a first switching element 501 (In particular, a first switching transistor), which is arranged, the first capacitor 341 from the first entrance bridge point 311 and from the connection point 503 to decouple. Further shows 5a a second switching element 502 that is set up, the second capacitor 342 from the first entrance bridge point 311 and from the connection point 503 to decouple. The control unit 370 can be set up, the respective switching elements 501 . 502 head for. Through the two switching elements 501 . 502 only the respective capacitor current flows 551 . 552 , and not the entire capacitor current 553 so that the switching elements 501 . 502 compared to switching elements between the connection point 503 and the first entrance bridge point 311 have reduced requirements in terms of current carrying capacity. In this case, the switching elements 501 . 502 each on the, the connection point 503 facing, side of the respective capacitor or on the, the connection point 503 facing away, be arranged side of the respective capacitor. The arrangement of the second switching element 502 for the second capacitor 342 on the, the connection point 503 remote, side of the second capacitor 342 can in particular for the implementation of the second switching element 502 be beneficial.

Instead of the total current 553 can thus by the arrangement according to 5a two streams that are half as big 551 and 552 be switched. In this case, each individual transistor must only block in a single direction, since in the respective opposite direction after reaching the charging voltage 363 in the respective capacitor 341 . 342 no further current flow is possible. The switching elements 501 . 502 Thus, each can be implemented by using a single switching transistor. These preferably have a dielectric strength which is at least twice the charging voltage threshold value 472 equivalent. A switching of the switching transistors at a certain switching point 402 prevents the conduction of the reverse diodes of the respective switching transistors. In an arrangement of switching transistors according to 3 Two twice as powerful switching transistors would have to be switched antiparallel. Consequently, with an arrangement according to 5a the size, cost and losses of the switching elements 302 be reduced to enable or disable the voltage boost.

With increasing capacitance value of the capacitors 341 . 342 typically increases the value of the charging voltage 363 or the rms value of the secondary voltage 362 at the one substantial increase in voltage takes place. In particular, a substantial increase in voltage typically only occurs when the charging voltage at a certain target charging power 363 and the capacitance values of the capacitors 341 . 342 reach or exceed a certain ratio threshold. To the voltage Doppler circuit already at relatively low charging voltages 363 to enable (and thereby the maximum value 451 of the secondary current 362 can be further reduced), a plurality of parallel-arranged capacitor strings can be used, wherein the individual capacitor strings with increasing charging voltage 363 gradually activated (see 5b ). Each of the capacitor strings includes a first capacitor 341 and a second capacitor 342 , via respective switching elements 501 . 502 with the connection point 503 and the first entrance bridge point 311 can be coupled. So can gradually with increasing charging voltage 363 the effective capacitance values of the capacitors 341 . 342 increase. As a result, the maximum value 462 the secondary voltage 362 and the maximum value of the primary current 351 be further reduced.

5c illustrates the use of a plurality of parallel arranged capacitor strings in connection with switching elements 302 , by each of which a capacitor string can be activated or deactivated as a whole. The switching element 302 a capacitor string is thereby the sum of the first capacitor current 551 through the first capacitor 341 and the second capacitor current 552 through the second capacitor 342 flowed through the respective capacitor string.

6 shows the course of the rms value of the secondary voltage 362 as a function of the charging voltage 363 when using a voltage Doppler circuit with three capacitor strings, each at one of the switching points 402 to be activated. As the number of capacitor strings increases, the maximum value can increase 462 more and more to the minimum value 461 the secondary voltage 362 be reduced. The individual capacitor strings lead in each case only partial currents 551 . 552 of the total current 553 , so that with increasing number of capacitor strings the requirements for the switching elements 501 . 502 decline.

The number of capacitor pairs or capacitor strings and / or the capacitance values of the capacitors 341 . 342 can be determined in an iterative procedure. In a first step, a maximum value 462 the secondary voltage 362 be determined. From the ratio of the maximum charging power and the maximum permissible secondary current 451 the minimum value results 461 the secondary voltage 362 , The first switching point 402 , in which the first capacitor string is switched on, takes place when the secondary voltage 362 the predetermined maximum value 462 has reached. In a first approximation corresponds in this case, the charging voltage 363 the predetermined maximum value 462 (ie the charging voltage threshold 472 corresponds to the predetermined maximum value in a first approximation 462 the secondary voltage 362 ).

The required capacitance values of the capacitors 341 . 342 of the first capacitor string can then be determined such that, after connecting the first capacitor string, the minimum value 461 the secondary voltage 362 results. The capacitance values are typically also from the charging field frequency or from the frequency of the secondary current 353 dependent.

In an analogous way, the capacitance values of the capacitors 341 . 342 the one or more further capacitor strings are determined until the maximum required charging voltage 363 is reached. If the maximum charging voltage 363 can not be achieved with a certain number of capacitor strings, the number of capacitor strings can be increased and / or the maximum value 462 the secondary voltage 362 increase. This procedure can be repeated until the capacitance values of a sufficient number of capacitor strings have been determined.

It thus becomes a secondary unit 120 described at the capacitors 341 . 342 , which cause a voltage boost, by dedicated switches 501 . 502 can be switched on and off. The capacitance values of the capacitors 341 . 342 and the switching thresholds 472 to activate the capacitors 341 . 342 can be dimensioned such that at a predetermined maximum value of the charging current 353 or the secondary current 352 the secondary voltage 362 at the entrance of the rectifier 101 . 301 during the entire charging a predetermined maximum value 462 does not exceed. There is thus a switchable voltage Doppler circuit to increase the charging voltage 363 described to both the primary stream 351 (through the primary coil 111 ) as well as the secondary current 352 (through the secondary coil 121 ) to a certain respective maximum value 451 to limit. The switching transistors 501 . 502 to activate / deactivate the individual capacitors 341 . 342 can be arranged such that no inverse current flow through the reverse diodes of the transistors 501 . 502 takes place, and thus no "antiserial" switched transistors are required. This can be done by a suitable choice of the switching point 402 be guaranteed, in which the capacitors 341 . 342 with the first entrance bridge point 311 be coupled.

The capacitors 341 . 342 and switching transistors 501 . 502 can be split into multiple sub-capacitors and sub-switches to provide parallel voltage Doppler circuits, allowing for more flexible switching. The division does not increase the sum of the capacitance values and the required current carrying capacity of the switching transistors. When using a plurality of Doppler circuits, the dimensioning of the partial capacitors 341 . 342 be chosen such that the difference between a minimum rectifier input voltage 461 and a maximum rectifier input voltage 462 is reduced, resulting in a reduction of the primary coil current 351 leads.

Possibly. can change the capacitance values of each capacitor 341 . 342 in relation to a certain maximum value of the charging voltage 363 oversized. Thus, relatively large tolerances in the choice of capacitors 341 . 342 allowing, in turn, the use of cost-effective capacitors 341 . 342 allows.

The described secondary unit 120 thus allows a reduction of the primary current 351 without increasing the secondary current 352 , So can costs and space for the coils 111 . 121 (in particular HF strand and ferrites) can be saved. Furthermore, the switching elements 501 . 502 for the activation / deactivation of the voltage Doppler circuit arranged such that only current in one direction must be disabled, which allows a reduction of costs, space and energy consumption. In addition, the described secondary unit 120 a high degree of robustness to fluctuations or tolerances of the element values of the individual circuit components.

The present invention is not limited to the embodiments shown. In particular, it should be noted that the description and figures are intended to illustrate only the principle of the proposed devices and systems.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 2911264 A1 [0007]

Claims (10)

Secondary unit ( 120 ) for an inductive charging system for charging an electrical energy store ( 103 ) of a vehicle ( 100 ), the secondary unit ( 120 ), - a secondary coil ( 121 ) in which, in response to a magnetic charging field, a secondary current ( 352 ) is generated; - one at the secondary coil ( 121 ) via entry bridge points ( 311 . 312 ) connected bridge rectifier ( 301 ), which is set up based on the secondary current ( 352 ) at output bridge points ( 321 . 322 ) of the bridge rectifier ( 301 ) a rectified charging current ( 353 ) for charging the energy store ( 103 ) to generate; A first capacitor ( 341 ) and a second capacitor ( 342 ); and - at least one switching element ( 302 . 501 . 502 ), which is set up, - the first capacitor ( 341 ) between the first entrance bridge point ( 311 ) and the first output bridge point ( 321 ) or from the first input bridge point ( 311 ) or the first exit bridge point ( 321 ) to decouple; and - the second capacitor ( 342 ) between the first entrance bridge point ( 311 ) and the second exit bridge point ( 322 ) or from the first input bridge point ( 311 ) or the second exit bridge point ( 322 ) to decouple; and a control unit ( 370 ), which is set up, the at least one switching element ( 302 . 501 . 502 ) such that - the first capacitor ( 341 ) between the first entrance bridge point ( 311 ) and the first output bridge point ( 321 ) and the second capacitor ( 342 ) between the first entrance bridge point ( 311 ) and the second exit bridge point ( 322 ) is switched when a charging voltage ( 363 ) at the exit bridge points ( 321 . 322 ) greater than a charging voltage threshold ( 472 ); and - the first capacitor ( 341 ) from the first entrance bridge point ( 311 ) or the first exit bridge point ( 321 ) is decoupled and the second capacitor ( 342 ) from the first entrance bridge point ( 311 ) or the second exit bridge point ( 322 ) is decoupled when the charging voltage ( 363 ) smaller than the charging voltage threshold ( 472 ). Secondary unit ( 120 ) according to claim 1, wherein - the secondary unit ( 120 ) a first switching element ( 501 ) arranged to connect the first capacitor ( 341 ) between the first entrance bridge point ( 311 ) and the first output bridge point ( 321 ) or from the first input bridge point ( 311 ) or the first exit bridge point ( 321 ) to decouple; and - the secondary unit ( 120 ) a second switching element ( 502 ) configured to connect the second capacitor ( 342 ) between the first entrance bridge point ( 311 ) and the second exit bridge point ( 322 ) or from the first input bridge point ( 311 ) or the second exit bridge point ( 322 ) to decouple; and - the control unit ( 370 ), the first switching element ( 501 ) and the second switching element ( 502 ) head for. Secondary unit ( 120 ) according to claim 2, wherein - the first switching element ( 501 ) in series with the first capacitor ( 341 ) is arranged that a stream ( 551 ) through the first capacitor ( 341 ) the stream ( 551 ) by the first switching element ( 501 ) corresponds; and - the second switching element ( 502 ) in series with the second capacitor ( 342 ) is arranged that a stream ( 552 ) through the second capacitor ( 342 ) the stream ( 552 ) by the second switching element ( 502 ) corresponds. Secondary unit ( 120 ) according to one of claims 2 to 3, wherein - the bridge rectifier ( 301 ) comprises a first diode which is connected in the forward direction between the first input bridge point ( 311 ) and the first exit bridge point ( 321 ) is arranged; The first switching element ( 501 ) has a transistor with an inverse diode, which in the forward direction between the first input bridge point ( 311 ) and the first exit bridge point ( 321 ) is arranged; - the bridge rectifier ( 301 ) comprises a second diode which is connected in the reverse direction between the first input bridge point ( 311 ) and the second exit bridge point ( 322 ) is arranged; and - the second switching element ( 502 ) has a transistor with an inverse diode, which in the reverse direction between the first input bridge point ( 311 ) and the second exit bridge point ( 322 ) is arranged. Secondary unit ( 120 ) according to one of the preceding claims, wherein - the secondary unit ( 120 ) a plurality of first capacitors ( 341 ) and a plurality of second capacitors ( 342 ); - the secondary unit ( 120 ) a plurality of switching elements ( 302 . 501 . 502 ), by each of which - a first capacitor ( 341 ) between the first entrance bridge point ( 311 ) and the first output bridge point ( 321 ) or from the first input bridge point ( 311 ) or the first exit bridge point ( 321 ) can be decoupled; - in each case a second capacitor ( 342 ) between the first entrance bridge point ( 311 ) and the second exit bridge point ( 322 ) or from the first input bridge point ( 311 ) or the second exit bridge point ( 322 ) can be decoupled; and - the control unit ( 370 ), the plurality of switching elements ( 302 . 501 . 502 ) such that with increasing charge voltage ( 362 ) a number of first capacitors ( 341 ) between the first entrance bridge point ( 311 ) and the first output bridge point ( 321 ), and a number of second capacitors ( 342 ) between the first entrance bridge point ( 311 ) and the second exit bridge point ( 322 ), increases. Secondary unit ( 120 ) according to claim 5, wherein the control unit ( 370 ) is arranged at a plurality of different, relatively increasing charging voltage thresholds ( 472 ) each have a further first capacitor ( 341 ) between the first entrance bridge point ( 311 ) and the first output bridge point ( 321 ) and in each case a further second capacitor ( 342 ) between the first entrance bridge point ( 311 ) and the second exit bridge point ( 322 ), so that at a charging voltage ( 362 ) above a highest one of the plurality of charging voltage thresholds ( 472 ) all first capacitors ( 341 ) of the plurality of first capacitors ( 341 ) between the first entrance bridge point ( 311 ) and the first output bridge point ( 321 ) and all second capacitors ( 342 ) of the plurality of second capacitors ( 342 ) between the first entrance bridge point ( 311 ) and the second exit bridge point ( 322 ) are switched. Secondary unit ( 120 ) according to claim 6, wherein the capacitance values of the plurality of first capacitors ( 341 ) and the plurality of second capacitors ( 342 ) as well as the plurality of charging voltage thresholds ( 472 ) are designed such that a predetermined maximum value ( 451 ) of the secondary current ( 352 ) is not exceeded. Secondary unit ( 120 ) according to one of the preceding claims, wherein the control unit ( 370 ) is arranged, the at least one switching element ( 302 . 501 . 502 ) in such a way that up to a predetermined maximum value of the charging voltage ( 363 ) a predetermined maximum value ( 451 ) of the secondary current ( 352 ) is not exceeded. Secondary unit ( 120 ) according to one of the preceding claims, wherein the control unit ( 370 ), the charging voltage ( 363 ) in such a load period to raise that the energy storage ( 103 ) is charged at a constant target charging power during the charging period. Secondary unit ( 120 ) according to one of the preceding claims, wherein the control unit ( 370 ), - a control signal to a primary unit ( 110 ) of the inductive charging system configured to generate the magnetic charging field; wherein the control signal indicates that the at least one switching element ( 302 . 501 . 502 ) has been switched or switched; and / or - a control signal from the primary unit ( 110 ), which indicates that the at least one switching element ( 302 . 501 . 502 ) should be switched.

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