Abstract:
The invention relates to a method for the contactless charging or discharging of a battery-operated object ( 4 ) via a magnetically coupled coil pair, comprising a primary coil ( 6 ) of a charging/discharging station ( 2 ) and a secondary coil ( 8 ) of the object ( 4 ), wherein: in a first step, the object ( 4 ) is transferred into a reference position in relation to the charging/discharging station ( 2 ); in a second step, a reference parameter is determined in the reference position; in a third step, a lateral desired offset of the object ( 4 ) to the charging/discharging station ( 2 ) is determined, based on the reference parameter; and in a fourth step, based on the lateral desired offset, the object ( 4 ) is transferred into a charging/discharging position in relation to the charging/discharging station ( 2 ) in which position the contactless charging or discharging is carried out. The invention also relates to a computer program, a system ( 100 ), a charging/discharging station ( 2 ) and an object ( 4 ), which are designed to carry out the method.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a method for the contactless charging or discharging of a battery-operated object, for example an electric vehicle or an electric bike. Further applications can relate, for example, to electric tools or consumer appliances. 
         [0002]    A computer program, a system and also a charging/discharging station and a battery-operated object, which are designed to carry out the method, are further specified. 
         [0003]    During the contactless charging or discharging process of a battery-operated object, electrical power is transmitted across an air gap. A coil pair, the coils of which are inductively coupled to one another by means of an alternating magnetic field, is used for this purpose. 
         [0004]    The magnetically coupled coil pair can be modelled as a transformer with a large air gap. The size of the air gap influences the magnitude of stray inductances of the system and determines the degree of coupling between the coils of the coil pair, this coupling being represented as a coupling factor within the scope of the invention. 
         [0005]    One object of the invention is to provide a method and a system for the contactless charging or discharging of a battery-operated object by means of a magnetically coupled coil pair, wherein the number of control components required in the system should be kept low. 
         [0006]    A further object of the invention is to provide a method of this kind and a system of this kind which allow a wide range of use with a low level of complexity and low costs. 
       SUMMARY OF THE INVENTION 
       [0007]    In a method according to the invention for the contactless charging or discharging of a battery-operated object by means of a magnetically coupled coil pair which comprises a primary coil, a charging/discharging station and a secondary coil of the object, it is provided that 
         [0008]    the object is moved to a reference position with respect to the charging/discharging station in a first step, 
         [0009]    a reference parameter is ascertained in the reference position in a second step, 
         [0010]    a lateral desired offset and/or a vertical desired height of the object in relation to the charging/discharging station are/is ascertained on the basis of the reference parameter in a third step, and 
         [0011]    the object is moved to a charging/discharging position with respect to the charging/discharging station, in which charging/discharging position the contactless charging or discharging takes place, on the basis of the lateral desired offset and/or the vertical desired height in a fourth step. 
         [0012]    A position of the object with respect to the charging/discharging station can be determined using methods known from the prior art, for example with the aid of GPS, indoor GPS, optical or ultrasonic sensors, a video system or a combination thereof. A measurement of the electrical and/or magnetic parameters of the coil pair can also be used as a reference. 
         [0013]    The object can likewise be moved to the reference position in a known manner, possibly by controlling a drive system of the battery-operated object and/or by displaying positioning instructions to persons. In the case of electric vehicles, it is possible, for example, for the means of a parking assistant to be accessed in the process. The reference position can be determined by an optimum orientation or position of the coils in relation to one another. 
         [0014]    According to one embodiment, the reference parameter is a coupling factor or a mutual inductance which describes the quality of the magnetic coupling of the coil pair. The coupling factor or the mutual inductance can be measured by means of a current and/or voltage measurement when a reference signal is applied, that is to say when a defined current or voltage profile is applied. In this case, the defined current or voltage profile can be applied both by the battery-operated object and, as is preferred, by the charging/discharging station. The respective systemic counterpart, that is to say the charging/discharging station or the battery-operated object, measures the received current or voltage profile by means of a suitable sensor system for voltage and current. The coupling factor is ascertained from the ratio of transmitted current or voltage to received current or voltage. 
         [0015]    According to a further embodiment of the invention, the reference parameter is a height of the object above the charging/discharging station. In the abovementioned model, the height of the object above the charging/discharging station can determine a size of an air gap between the object and the charging/discharging station, in particular between the primary and secondary coils, and therefore can be critical for the magnitude of the stray inductance. The height of the object above the charging/discharging station can be determined with the aid of a known sensor system, for example with the aid of GPS, indoor GPS or in an optical or acoustic manner, for example with the aid of camera data or ultrasound. 
         [0016]    According to one embodiment, a lateral desired offset, that is to say a deliberate spatial offset from the reference parameter, is ascertained, for example, on the basis of a lookup table. The objective here may be to allow a relatively constant coupling factor over a changing air gap or over a changing transmission partner. This is achieved by using the lateral desired offset between the primary coil and secondary coil, which lateral desired offset is set such that a constant coupling factor is produced. The relationship between the coupling factor and the relative offset can be in the form of a functional relationship here and can be stored in the lookup table. The functional relationship between the height of the object above the charging/discharging station and the lateral desired offset can also be stored in lookup tables of this kind. 
         [0017]    In addition or as an alternative to the lateral desired offset, the desired height of the object in relation to the charging station given an existing actuator system is set. In the case of a vehicle, said actuator system may be, for example, an existing pneumatic suspension. The relationship between the coupling factor and the desired height can be in the form of a functional relationship here and can be stored in the lookup table. The functional relationship between the height of the object above the charging/discharging station and the desired height can also be stored in lookup tables of this kind. 
         [0018]    After ascertaining the lateral desired offset and/or the desired height from the reference parameter, the object is moved to the charging/discharging position with respect to the charging/discharging station, for example by applying the lateral desired offset to the reference position. The means of a parking assistant may, for example, be accessed in this case. It can be provided to initiate the contactless charging or discharging after this. 
         [0019]    As an alternative, the described method is applied once again after the lateral desired offset and/or the desired height of the object have been applied to the reference position. If the ascertained reference parameter is above or below a specific threshold value, a further lateral desired offset and/or a further desired height is ascertained on the basis of the reference parameter. The method can therefore be carried out in an iterated manner. A termination criterion may be that an ascertained reference parameter is above or below the threshold value, as a result of which the charging/discharging position with respect to the charging/discharging station is defined. 
         [0020]    As soon as the ascertained reference value is within the desired limits, the contactless charging or discharging is initiated. 
         [0021]    According to the invention, a computer program is further proposed, one of the methods described in this document being carried out in accordance with said computer program, wherein the computer program is run on a programmable computer device. The computer program may be, for example, a software module, a software routine or a software subroutine for implementing a charging/discharging system comprising a battery-operated object and a charging/discharging station. The computer program can be stored in the battery-operated object or in the charging/discharging station or distributed between them, in particular in permanent or rewritable machine-readable storage media or in association with a computer device, for example, in a portable memory, such as a CD-ROM, DVD, Blu-ray Disc, a USB stick or a memory card. In addition or as an alternative to this, the computer program can be provided on a computer device, such as, for example, on a server or a cloud server, for downloading, for example via a data network, such as the Internet, or via a communication connection, such as a telephone line or a wireless connection. In the case of an electric vehicle, the computer program can be stored in a control unit in the vehicle. 
         [0022]    According to a further aspect of the invention, a system comprising a charging/discharging station, a battery-operated object and a control unit is provided, wherein the control unit is designed to move the object to a reference position with respect to the charging/discharging station, to ascertain a reference parameter in the reference position, to ascertain a lateral desired offset and/or a vertical desired height of the object in relation to the charging/discharging station on the basis of the reference parameter, to move the object to a charging/discharging position with respect to the charging/discharging station on the basis of the lateral desired offset and/or the vertical desired height, and to initiate contactless charging or discharging of the object by means of a magnetically coupled coil pair, wherein the charging/discharging station has a primary coil and the object has a secondary coil, which primary coil and secondary coil form the coil pair. 
         [0023]    The system is preferably designed and/or set up for carrying out the described methods. Therefore, the features which are described within the scope of the methods accordingly apply to the system and, conversely, the features which are described within the scope of the system accordingly apply to the methods. 
         [0024]    In this case, the control unit can be associated with the charging/discharging station or with the battery-operated object. As an alternative, it can be provided that both the battery-operated object and the charging/discharging station are equipped with control units which jointly carry out the method according to the invention. In particular, it can be provided that the control unit can communicate with further driver assistance systems, in particular with a parking assistant, or can access the resources of said further driver assistance systems. 
         [0025]    According to further aspects of the invention, a charging/discharging station and also a battery-operated object are provided for use in a system of this type. 
         [0026]    The terms “battery” and “battery-operated” are used for “rechargeable battery” and “rechargeable battery-operated”, respectively, in the present description, in accordance with common parlance. In the battery, the battery cells are preferably grouped together spatially and are connected to one another in a circuit, for example interconnected in series or in parallel to form modules, in order to be able to provide the required power data using the battery cells. However, in principle, any other electrical energy storage means, for example double-layer capacitors, is conceivable. 
         [0027]    In particular, the battery-operated object can be a motor vehicle, wherein the battery of said motor vehicle is connected to a drive system of the motor vehicle. The motor vehicle can be designed as a pure electric vehicle and can exclusively comprise an electric drive system. As an alternative, the motor vehicle can be designed as a plug-in hybrid vehicle which comprises an electric drive system and an internal combustion engine, wherein the energy storage means can be charged externally. 
         [0028]    One advantage of the invention is that the described method and the system allow an approximately constant coupling factor over a changing air gap and/or over different transmission partners. This makes it easier to design the power electronics components in the charging/discharging station and also the coil pair. As a result, cost and/or installation space can be reduced. 
         [0029]    Reducing the size of the value range for the coupling factor by defining a position of the battery-operated object with respect to the charging/discharging station or between them makes it possible to save costs and complexity of the system. Specific components in the system, for example additional DC/DC converters, can be entirely dispensed with owing to the presented approach, and similarly complex control strategies, for example control at both ends, that is to say a combination of active electronics systems on the primary and the secondary side, are not absolutely necessary. In this case, the additional expenditure on the invention can be rated as low since existing systems with inductive contactless energy transmission are often already equipped with positioning devices. 
         [0030]    Furthermore, the minimum degree of efficiency of the inductive charging/discharging system given unfavorable positioning of the coil pair can be increased without additional expenditure since it can be designed for the smaller parameter range in a more targeted manner. Averaging the degree of efficiency results in a minimum/maximum response of the system being significantly reduced. 
         [0031]    A further advantage is that the invention can be applied to a transmitter which is based on any desired principle, in particular in terms of the topology of the power electronics system and the type of primary and secondary coils used. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    Exemplary embodiments of the invention are illustrated in the drawings and explained in greater detail in the following description. 
           [0033]    In the drawings: 
           [0034]      FIG. 1  shows a system comprising a battery-operated object and a charging/discharging station according to one embodiment of the invention, 
           [0035]      FIG. 2  is a schematic illustration of primary and secondary circuits according to one embodiment of the invention, 
           [0036]      FIG. 3  is a further schematic illustration of primary and secondary circuits according to one embodiment of the invention, 
           [0037]      FIG. 4  is a graph showing the dependence of the coupling factor on lateral offset and height, 
           [0038]      FIG. 5  is a graph showing the dependence of the lateral offset on the height, 
           [0039]      FIG. 6  is a graph showing the dependence of the degree of efficiency and the coupling factor on the air gap, and 
           [0040]      FIGS. 7A-7D  show current and voltage profiles during the contactless charging or discharging according to the prior art and with the measures of the invention in comparison. 
       
    
    
       [0041]    In the following description of the exemplary embodiments of the invention, identical or similar components are provided with the same or similar reference symbols, wherein said components are not repeatedly described in certain cases. The figures illustrate the subject matter of the invention only schematically. 
       DETAILED DESCRIPTION 
       [0042]      FIG. 1  shows a system  100  according to the invention comprising a battery-operated object  4 , for example an electric vehicle, and a charging/discharging station  2  which are arranged in a specific spatial position in relation to one another. The battery-operated object  4  is also called object  4  for short in the text which follows. In this example, the spatial position in relation to one another is described by a size h of an air gap and by a lateral offset which is measured by dx in a first direction and by dy in a second direction. The size h of the air gap can correspond to a height of the object  4  above the charging/discharging station  2 . 
         [0043]    In this embodiment, the charging/discharging station  2  has a planar primary coil  6  which is arranged in a base. The object  4  likewise has a planar secondary coil  8  by means of which a battery (not illustrated) can be charged or discharged. The primary coil  6  and the secondary coil  8  are positioned exactly one above the other for optimum energy transmission. The size h of the air gap can correspond to a size of a vertical spacing of the coils  6 ,  8  in relation to one another. 
         [0044]    The power electronics systems  18 ,  24  in the charging/discharging station  2  and in the object  4  are typically designed for a nominal operating point and for a specific coupling factor. However, in reality, the actual operating point differs from the nominal operating point since the size h of the air gap is dependent on the site of installation of the secondary coil  8  and, for example, in the case of an electric vehicle is also dependent on the loading of the vehicle. The actual operating point or actual coupling factor also differs owing to the actual lateral offset of the coils  6 ,  8  in relation to one another. This makes it more difficult to design the power-electronics components and the coil pair and results in the system response having a strongly preferred operating point without the measures according to the invention, but with other operating points being put at a significant disadvantage, for example in respect of the degree of efficiency. 
         [0045]    In the system  100  according to the invention, a control unit  100  is provided, as illustrated, for overcoming said disadvantages, said control unit being connected firstly to one of the coils  6 ,  8  and secondly to sensors  11 , for example ultrasonic sensors. 
         [0046]    The control unit  10  is set up to ascertain one or more reference parameters and to ascertain a lateral desired offset of the object  4  in relation to the reference position with respect to the charging/discharging station  2  on the basis of the reference parameter or reference parameters. 
         [0047]    The control unit  10  can determine, for example, a coupling factor k, which is established by the actual position of the object  4  in relation to the charging/discharging station  2 , as a reference parameter by means of the connection of the control unit  10  to one of the coils  6 ,  8 . As an alternative or in addition to this, the control unit  10  can determine the size h of the air gap as a further reference parameter by means of the sensors  11 . 
         [0048]    Furthermore, the control unit  10  is set up to move the object  4  to a charging/discharging position on the basis of the ascertained lateral desired offset. This can be done either in an iterative process or in a direct process. 
         [0049]    In  FIG. 1 , the control unit  10  is arranged on the side of the object  4 . It goes without saying that some of the functions which are assigned to the control unit  10  within the scope of the invention can also run on a further control unit (not illustrated) which is associated with the charging/discharging station  2 . In particular, the control unit  10  of the object  4  and the further control unit, not illustrated, of the charging/discharging station  2  can communicate with one another in order to carry out the method according to the invention. 
         [0050]      FIG. 2  shows a circuit according to one embodiment of the invention. A primary circuit  12  comprises a supply system  16  which comprises a current or voltage source or a plurality of interconnected current or voltage sources, for example a public power supply system. The supply system  16  is connected to a primary-side power electronics system  18  which can comprise a rectification electronics system and also possibly protective and fuse circuits. The primary circuit  12  comprises a primary-side resonant network  20  which is connected to the primary-side power electronics system  18 . The primary-side resonant network  20  is connected to the primary coil  6  which represents the interface for energy transmission to the battery-operated object  4 . 
         [0051]    Within the scope of the invention, the battery-operated object  4  is referred to as being on the secondary side and the charging/discharging station  2  is referred to as being on the primary side. However, this actually applies only for the charging process. In the discharging process, the roles of the object  4  and the charging/discharging station  2  are reversed. 
         [0052]    The secondary circuit  14  comprises the secondary coil  8  which, with the primary coil  6 , forms a magnetically coupled, that is to say inductively coupled, coil pair. A secondary-side resonant network  22  is connected to the secondary coil  8 . A secondary-side power electronics system  24 , which comprises a rectification electronics system and possibly protective and fuse circuits, is connected to the secondary-side resonant network  22 . The load  26 , in particular a battery of the object  4 , which battery is to be charged or discharged, is connected to the secondary-side power electronics system  24 . 
         [0053]      FIG. 3  shows a detailed view of the primary circuit  12  and the secondary circuit  14  according to one embodiment of the invention. 
         [0054]    The primary circuit  12  has, as supply system  16 , a voltage source which provides an intermediate circuit voltage U 0  to the system. Said voltage source may be, for example, a rectifier with a power factor correction (PFC) filter. 
         [0055]    Here, the primary-side power electronics system  18  comprises, by way of example, four directing elements  28  which each have a switchable transistor  30 , typically an IGBT or MOSFET, and a diode  32 , which transistor and diode are connected back-to-back in parallel to one another. The diode  32  can either be designed separately or integrated into a housing with the IGBT, or said diode may also be an intrinsic body diode of a MOSFET. The transistors  30  are controlled by an electronics system, not illustrated. From amongst the four directing elements  28 , in each case two are connected in series with one another. The two series circuits of the directing elements  28  are connected in parallel with one another, so that a full bridge arrangement is produced overall. In each case between the two directing elements  28  which are connected in series, the voltage is supplied to the primary-side resonant network  20  which merely comprises a capacitor  38  in the form of a series resonant capacitor in this case. The primary-side resonant network  20  is fed by the first series circuit of the directing elements  28  at one end and by the second series circuit of the directing elements  28  at the second end. The primary coil  6  is located at the output end of the primary-side resonant network  20 . 
         [0056]    A capacitor  40  of the secondary-side resonant network  22  is connected to the secondary coil  8  on the side of the secondary circuit  14 . 
         [0057]    It goes without saying that the coils  6 ,  8  are functionally connected to the resonant networks  20 ,  22  in such a way that, in other words, the coils  6 ,  8  can be counted as belonging to the resonant networks  20 ,  22 . 
         [0058]    The current is supplied to the secondary-side power electronics system  24  at the output end of the secondary-side resonant network  22 , said secondary-side power electronics system comprising four diodes  34  in the illustrated exemplary embodiment, said four diodes being connected to one another substantially in the same manner as the directing elements  28  in the primary-side power electronics system  18 , so that a passive bridge rectifier is formed. 
         [0059]    The secondary-side power electronics system  24  also comprises a capacitor  36  which is connected in parallel with the diodes  34 , the purpose of said capacitor being to smooth the output voltage and the output current. The battery of the battery-operated object  4 , the voltage U bat  and the current I bat  being provided to said battery, is located on the output side as load  26 . Further filter elements, such as inductors or further capacitors, can be provided between an output capacitor and the battery for reasons of electromagnetic compatibility (EMC). 
         [0060]    The secondary-side power electronics system  24  fulfils the task of rectifying the received AC signal of the secondary-side resonant network  22 . 
         [0061]      FIG. 4  shows the qualitative dependence of the coupling factor k on a lateral offset dx or dy. Said figure shows three curves of coupling factors which relate to a different height h of the object  4  above the charging/discharging station  2 . A relatively small magnetic air gap and, as a result, a relatively high coupling factor k are produced at the minimum height h min . The smallest coupling factor at which transmission of the rated power is still possible is produced at the maximum height h max . 
         [0062]    The coupling factor k exhibits a non-linear response with a monotonic fall in relation to the increasing lateral offset dx or dy. 
         [0063]    With the method according to the invention, the lateral spacing dx or dy is set such that an approximately constant coupling factor is established even given different air gaps, as shown by line  43 . Instead of this, it is also possible to provide a region in which the coupling factor is intended to be located before the charging/discharging process can be initiated. 
         [0064]    In order to achieve a situation of the coupling factor k being constant or at least falling in the specified range, the vehicle is moved from an initial position when the air gap is too small, wherein the initial position is typically a position in which optimum energy transmission takes place, that is to say at which the coils  6 ,  8  are aligned with one another in an optimum manner. If, however, the air gap is large, the vehicle is positioned exactly above the primary coil  6 . Although different vehicles with different ground clearances are therefore intended to be charged in these two cases, a similar coupling factor can be set in both cases. 
         [0065]      FIG. 5  shows a dependence of a desired offset dx* or dy* on the size h of the air gap. The curve shows a non-linear monotonically falling response of the desired offset dx* or dy* from a minimum value of the size h min  to a maximum value of the size h max . The system determines the desired offset dx* or dy*, which is applied to the current position of the object  4 , from the measurement of the size h, for example on the basis of an illustrated response of the dependence, which response is stored in the lookup table. 
         [0066]      FIG. 6  shows the effect which the application of the desired offset dx* or dy* has on the current position of the object  4 . The dependence of a degree of efficiency del_eta on the size h of the air gap is illustrated in an upper region  46 , and the dependence of the coupling factor k on the size h of the air gap is illustrated in a lower region  48 . The degree of efficiency with application of the method according to the invention is illustrated as eta n  here. The degree of efficiency eta n  is substantially constant, whereas the degree of efficiency eta o  without application of the method according to the invention is dependent on the size h of the air gap. Similarly, the coupling factor k n  after application of the method according to the invention is substantially constant, whereas the coupling factor k o  without application of the method according to the invention exhibits a non-linear dependence on the size h of the air gap. 
         [0067]      FIGS. 7A to 7D  illustrate current and voltage profiles in graphs, wherein  FIGS. 7A and 7B  show a system  100  without application of the invention, and  FIGS. 7C and 7D  show a system  100  with application of the invention. The solid lines represent the voltage and the dotted lines represent the current.  FIGS. 7A and 7C  represent the signal in the primary circuit  12 , and  FIGS. 7B and 7D  represent the signal in the secondary circuit  14 . Both systems  100  are each designed such that the full rated power can be transmitted both given the minimum air gap h min  and also given the maximum air gap h max . 
         [0068]    In this case, all profiles are based on a maximum air gap h max  at which the charging or discharging is still functional. 
         [0069]      FIGS. 7A and 7C  show that the current in the system  100  according to the invention is considerably reduced by the primary coil  6  since the primary coil  6  can be designed with a relatively large number of turns in an optimum manner for this operating point. The primary-side power electronics system  18  switches close to the current zero crossing, which leads to substantially lower losses in the system  100 . The degree of efficiency can therefore be increased and the expenditure in the primary-side power electronics system  18  can be reduced, in particular with respect to used semiconductor area of the transistors and the expenditure on cooling. 
         [0070]    However, when the system  100 , as shown in  FIGS. 7A and 7B , is designed for a large coupling factor range, an unfavorable operating point for the primary-side power electronics system  18  and the primary-side resonant network  20  is established given the maximum air gap h max . The current in the inverter is at maximum and leads to high losses in the power semiconductors. 
         [0071]    However, when the system  100  is designed only for a small coupling factor range, as illustrated in  FIGS. 7C and 7D , a more favorable operating point is produced given the maximum air gap h max , even if the absolute coupling factor in both cases is identical. 
         [0072]    The invention is not restricted to the exemplary embodiments described here and the aspects highlighted therein. Rather, a large number of modifications which are within the capabilities of a person skilled in the art are possible within the scope specified by the claims.