GB2501609A

GB2501609A - A non-contact energy transmitter periodically increases Q factor in order to detect foreign objects

Info

Publication number: GB2501609A
Application number: GB1305957.1A
Authority: GB
Inventors: Juergen Mack; Dragan Krupezevic
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2012-04-05
Filing date: 2013-03-02
Publication date: 2013-10-30
Anticipated expiration: 2033-03-02
Also published as: CN103368276A; GB201305957D0; CN103368276B; GB2501609B; DE102012205693A1

Abstract

A wireless energy transmitter 100 comprises a resonance transformer 105 with transmitting coil 120, a controller 165 which changes the quality (Q) factor of the transformer 105 between a lower value for energy transmission and a higher value for foreign object detection. A determiner 185 detects a foreign object dependent on an electrical parameter (e.g. current, voltage, resonant frequency or Q factor) of the transformer 105. A second transmitting coil 135 may be provided, connected either in series or in parallel with the first coil 125 for low or high Q factor transmission respectively. The coils 125, 135 may transmit at low power with high Q factor, or high power with low Q factor. The coils 125, 135 may transmit at high frequency with high Q factor, or low frequency with low Q factor. The high Q factor mode may be enabled periodically, for a period much shorter than that of the low Q factor mode. The transmitter 100 may transmit power by magnetic induction.

Description

Wireless energy transmission The invention relates to a wireless energy transmission. In -particular, the invention relates to a transmitter for inductive enérg' transmission and a method for controlling the transmitter.

Prior art -

A small electrical apparatus comprises a load and an accumulator, in order to allow cableless use. In order to charge the accumulator, energy may.bewirelessly transmitted from a power unit to the small apparatus by utilising n electromagnetic field for energy transmission.

For this purpose, the power unit and the small apparatus each comprise a coil which may be positioned at a small.

distance from each other and thus tdether essentially form * a transformer.

If an electrically conductive object cothes into the region of the electromagnetic field, then eddy currents may form which heat up the object 1f the object is magnetisable, then the object may also be heated up by irpn losses or hysteresis losses. The heating may be considerable, with, * * 25 the result that operational reliabilityofthe transmitter -.or the receiver may not be ensured. Moreover, the object

may withdraw energy from field,

disrupting the energy transmission to the receiver.

It is possible to detect the presence of the object by determining the influence of the object on the inductance * of the transmitting coil. However, it the object is * relatively small or relatively far away from the transmitting coil, then a reliable detection of the object may be difficult.

The Object Ofl which the invention is based, therefore, is to specify a device, a system and a method, by means of which a sensitive, reliable and selective determination of the objectcan be carried out, in order to enable a reaction to the presence pf the object. The invention solves the stated problems by means of a transmitter, an energy transmission system and a method haviig the features of the independent claims. Subclaim give prefetred eodiments.

Disclosure of the invention

A transmitter according to the invention for a wireless energy trhsmissiofl comprises a resonance ransformer having a transmitting coil for providing an electromagnetic alternating fjeld. A determining -device for detecting an object in the region of the transmitting coil in dependence on an electrical parameter at the resonance transformer is provided. Furthermore, the ransmitter comprises a control device for changing a quality factor of the esonance transformer, in order to allow an energy transmission at a low quality factor and a detection of the object at a high quality factor.

It is thereby possible to create improved conditions adapted in each case, for the energy transmission and the detection of the object. BythiE difftrentiatiOfl of different modes of operation, the energy transmission or the object detection or both may be realisable in an improved manner. , * In a particularly preferred embodiment, the transmitter comprises a further transmitting coil and the control device is configured to, connect the transmitting coils in parallel for a high quality factor and in series for a. low quality factor. In this way, the quality factor of the resonance tansformer may be easily and reproducibly changeable. Furthermora, both.for the energy transmission and for the object detection, both transmitting coils may be used. An improved energy transmission or an improved object detection or both may result.

In one embodiment, the transmitting coils comprise equal inductances and equal ohmic resistances. As a result, coils of identical construction may be used, whereby a production may be made more cost-effective. Furthermore, the quality factor may thereby bèeasily increased or educed by a well manageablefactor of two.

In a particularly preferred embodiment, both transmitting coils are wound on a common core. As a result, the transmitting coils ma' be arranged as close as pbssible to each other, so that they may behave in an improved manner as. a single coil of the resonance transformer. 25.

The control device may be configured to feed the resonance transformer at a high quality factor with a low power and ata low quality factor with a high power. While the high power may be conducive to the energy tfansrnission, the determinatioci of the object at low pcwer ma be carried out in an energ-saving manner and with low heating of the object. The transmitting coils áonnected in parallel may furthermore be protected by the reduded power from H: A overloading, for example by overvoltage. Moreover, emisSion control may be # forded by the reduced power.

The control device may be configured to operate *the resonance transformer at a high quality factor with a high -, working frequency and at a low quality factor with a low working frequency. The working frequency may change in the opposite manner to the quality faator when the transmitting coils are connected in parallel or in series. Through the different activations, it is possible for powers and working frequencies of the resonance transformer and of the * transmitter to be chosen such that electromagnetic compatibility values (ENC) are observed, Observing an * emission contrpl standard may thus be possible in a simplified manner.

In a particularly preferred embodiment, the control device is configured to periodically increase the quality factor of the resonance transformer for the detection of the object, a ratio of the operating time with low quality factor to the operating time with high quality factor being large. In general, the ratio is chosen ath large as possible, depending on a desired frequency and required duration for the object reccgnition. Advantageous are values of at least 10 to 1, preferably at least' 100 to 1.

In a particularly preferred embodiment, the detecting * device is configured to detect the object on the basis of a current, a voltage, a resonant frequency or a quality factor, at the. resonance transformer. The particular.

parameter may be compared with a threshold value, the object being detected when the parameter lies beyond the Lhreshold value. . In one embodiment, each of the transmitting coils has a first and a second terminal and the control device comprises three switching devices,' namely a first switching device for connecting the first terminal of the first transmitting coi to the first, terminal of the second transmitting coil, a' second switchinq devie for connecting.

the secdnd terminal of the first transmitting coil to.the second terminal of the second transmitting coil, and a -.

hird switching device for connecting the second terminal of the first transmitting coil to the first terminal of the * second transmitting coil. In this case, the control device is configured to open and close the first' switching device and the second switching device in the same direction and th third switching device in the opposite direction thereto. . As a result, the second transmitting coil may be connected in parallel or in series to the first transmitting coil in a simple and, efficient manner. The first terminal,of the first transmitting coil and the second terminal of the second transmitting coil may be used as termin1s of a combined transmitting coil which may be sviitched ove± and comprises both'individual transmitting coils. The switching devices described may be employed,in a corresponding manner also between the second and an additional third transmitting coil, so that also three or more transmitting coils may be connected in parallel or in series with one another. -* A system'according to the invention for wireless energy transmission comprises the above-described transmitter and * : a receiver which is configured to convert a magnetic alternating field, in particular that which-is provided in the region of the transmitting coil, into an electric current. The.receiver may also comprise one or More loads * for the-electric current, for example an accumulator or a * .5 charging control for the accuMulator.

A method according to the invention fOr detecting an object at a transmitter for wireless energy transmission, the transmitter comprising a resonance transformer which has a transmitting coil, comprises steps of operating the resonance transformer with a high quality factor, sensing an electrical parameter-at the resonance transformer, detecting the object on the basis of the sensed parameter, and operating the resonande transformer with alow quality * factor for energy transmission.

Brief description df the figures

The invention will now be described in more detail with reference to the appended figures, in which: Figure 1 shows a transmitter for wireless energy - transmission, and -Figure 2 shows a flow diagram of amethod for determining an object in the region of the transmitting coil * of the tranSmitter of Figure 1.

Detailed description of-exemplary embodiments

Figure 1 shows a transmitter 100 for wireless energy- * transmission. The transmitter 100 comprises a resonance * transformer 105, which comprises a resonance capacitor 110 and a combined transmitting coil 115, which are connected to. one another in series. In this case, the combined transmitting coil 115 comprises a first transmitting coil 120, which is forjned from a first inductor 125 and, a first * , resistor 139 in the equivalent circuit diagram illustrated, and also a second transmittin coil 135, which is formed from a second inductbt 140 and a second resistor 145.

Arranged between Lerminals of the first transmitting coil 120 and the second transmitting coil 135 are a first switching device 150, a second switching device 155 and a third switching device 16D, which may each be realised by a relay or a transistor. The first switching device 150 is * connected to-the upper terminals of the trahsitting coils 120 and 135, and the second switching device 155 is connected to the lower terminals of the transmitting coils and 135. The third switching device 160 lies between the lower terminal of the first transmitting coil 120 and the upper terminal of the' scond transmitting coil 135. The switching devices 150, 155 and 160 are controllable by a control device. 165.

Windings of the transmitting coils 120 and 135 preferably lie lose to each other and have the same winding sense as marked by the dots on the transmitting coils 120 and 135.

In particular, the windings of both transmitting coils 120, may be placed on a common core' 170. The' core 170 can improve an inductive coupling of the combined transmitting coil 115 with a receiving coil 175 of a receiver 177 (not illustrated) . An object 180 may be arranged in an electromagnetic region of influence of the combined transmitting coil 115, which, H. object absorbs some of the energy of the electric field, and may heat up in doing so: *To detect the object. 180, there is provided a detecting,dev±ce 1.85, which senses an * electrical parameter at the..resonance transformer 105, in order to infer the presence of the Qbject 180 on the basis* of this parameter. Preferably, the determining device 185 is connected to the control device 165.: The resonance transformet 105 may be supplied with energy and excited to oscillate by one of its terminals being periodically alternately cgnnected to a positive and a negative potential. For this purpose, in the embodiment illustrated in Figure 1, there is provided a half bridge 190, which is constricted by way of example by means of two transistors. The half bridge 190 thay be controlled by means of a clock generator 195, which in one embodiment is coupled back to the resonance transformer -105, in order to set the resonance transformer 105 into a resonant osáillation. . The control device 165 is configured to jointly open or close the first switching device 150 and the second switchinç device 155 and to simultaneously actuate the third switching devIce 160 in the opposite direction1 that 25, is to say to open it, when. the switching device 150 and 155 are closed, and vice versa. If the first two switching deyices 150, 155 are closed and the third switching device is open, then the transmitting coils 120 and 135'are connected to one another In parallel. Conversely, if the first and the-second switchin device 150, 155 are open and -. th,e third sw.itching device 160 is closed, then the transmitting coils 120 and 135 are connected to one another in series. The connection of the twb transmitting coils 120 and 135 which is shown may be extended in a corresponding * manner to three or more transmitting coils 120, 135 by designing the illustrated connection a plurality of times in succession. The upper terminal of the first fransmitting coil 120 and the lower terminal of the last transmitting coil 135 in this case constitute the terminals of the combined transmitting coil 115.

The dynamic properties of the combined transmittinq coil 115 depend on its effectiië indutaflce and: itseffective electrical resistanóe. Both the inductance and the resistance are dependent on whether the transmitting coils and 135 are connected to one another in series or in parallel.

To determine the resonant frequency of the reonance transformer 1051the following formula applies: ." (equation 1) 20: . . where L is the effective induction of the combined -transmitting coil 115 and C is the resonance capacitance 110. The quality factorof the resonance transformer 105 is determined as -. 25. . . . . ifLI. . (equation 2) where S is the ohthic resistance of the combined transmitting coil 115. The ohm-ic resistances -R of the transmitting coils 120 and 135 are modelled by the resistors 130 and 145,. respectively, and the effective * inductances L are modelled by the inductors 125 and 140, respectively.

If the transmitting coils 120 and 135 are connected in series, so tha the inductors 125 and 140 add up to an effective inductance and the resistors 130 and 145 add up to an effective resistahce, then for resonant frequency and the quality factor, respectively; the following formulae apply: *10 * series connection: * 1 = (equation 3) fi,J(L1+L2)C 1 1 ____ (equation 4) RSVC R1-i-R2 C * 15 If the transmitting coils 120 and 135 are connected to one another in parallel, so that the effective inductance Is formed as a quotient from the product and the sum of the inductors 125 and 140 and the effective resisanceis formed as a quotient frbm the product and the sum of the resLstors 130 and 145, then for reonant frequency and --quality factor the following apply: * -parallel connection: = 1 = _____ * (equatton 5) PvfeIlL2c H -* * -Q 1R1+R2 (equation 6) ° C R1R2 1(L1+L2)C.

If the tánsmitting coils 120 and 135 are of identical construction to each other, sp that the inductors 125 and 140 and the resistors 130 and 145, respectively, correspond to each other in pairs, theh the above-stated equations 3 to 6 are implified and it can be seen that *in the parallel connection the resonant frequehcy and the quality factor is in each case twice as high as the resonant frequency and the quality factor in the series connection.

-Regardless of the embodiment of the two transmitting coils and 135, the quality factor of the combined transmitting coil 115 may be increased by parallel connection of the transmitting coils 120 and 135, and reduced by series connection of the two transmittincoils 120, 135. A low quality factor is advantageous especially for energy transmission between the combined transmitting coil 115 and the receiving coil.175, while detection of the object 180 can be carried out especially with.a high quality factor.

Advantageously, the working frequency at which the clock * generator 195 excites the resonance transfotner. 105 by means of the half bridge 190 is adapted to the parallel or series connection of the coils 120, 135 in accordance with * the stated formulae: It is further. preferred to carry out * the detection of the object 180 with a reduced * * electromagnetic field of the combined transmitting coil 115. For this.purpose, for example,a. voltage at the resonance transfprmer.105 can be reduced, for instance by * . 12 abtivating the switching devices of the half bridge 190 for a shorter time, so that they are.both open for an increased part of a complete period of oscillatioP.

The object 180 may be detected by means of the detecting device 185 by the latter sensing an electrical páramet?r in particular a current or a voltage, at the resonance transforner 105 and determining whether the sensed.

parameter is influenced by the presente of the object 180.

For this purpose, the sensed pararheter maybe compared With a predetermined threshold value. -In a preferred embodiment, a periodic determination of the presence of the object 180 takes place, for which the energy transmission from the transmitter 100 to the receiver is interrupted. In order to àhieve an efficiency which is asthigh as possible, it is preferred to keep the operating time during the object detectioti as short as possible compared with the operating time during the energy transmission. A atio of the operating time during the * eriergy transmission to the operating time during ttie object detection preferably lies above 10, particularly preferably above 100. * . * * * ..

30. .* S: .13 * The following tabl.e summarises the combinations of relative * parameters at the transmitter 100: Series connection Parallel for. connection for Energy. Object detection transmission Quality factor -. . + Resonant frequency. . + Power + Operating time. + -

(Table 1)

Figure.2 shows a flow diagram of a method 200 for determining the object 180 in the region of the transmitting coil 115 of the transmitter100 from Figure 1.

The method 200 begins at a step 205. In a following step 210,. the transmitting coils 120 and 135 are connected tq one another in parallel. In a further following step 215, the combined transmitting coil 115 is operated with a low IDower and a high working frequency. This state is advantageous for an object determination which is carried out from the following step 220. For determination of the Object 180, in a step 225 firstly an electrical parameter at the resonance transformer 105 is sensed and compared with a threshold value. If the sensed parameter lies beyond the threshoidvalue, then in a following step 230 the presence of the. object 180 in the region of. the combined transmitting coil 115 is inferred, If an object 180 is present, then in a step.235 a suitable measure is taken, for exafuple bi stopping or limiting the * 14 operation of the tranSmitter iOO. Additionally or alternatively, a warning may be issued to a user for * example in visual or audible form.

* 5 If no object 180 is present, then an energy transmission from the transmitter 100 to the wireless receiver 177 is initiated. For this purpose, in a step 240 the coils 120 and 135 are connected in series. In a: following step 245, the combined transmitting coil.115 is operated with a high -10 power and a low working frequency. This gives rise, in a step 250, to an energy transmission to the receiver 177 for wireless energy transmission.

* -Preferably, after a predetermined time has elapsed or on * 15 the basis of an external-event, the method may return to the first step 205 and run again. Preferably, a time during which the steps 215 to 235 are performed is kept-as short as possible, in order tb spend a largest propottion of the operating time of the method 200 as possible in the step * 20 250. * * * .15