Abstract:
A power transfer system includes: a transmitting device having a transmitting coil and a receiving device having a receiving coil, the two coils being inductively coupleable to one another for the purpose of transferring power, so that a power transfer path exists between them; an electrical load for connecting with terminals of the receiving coil; a detection device for detecting an electrical parameter which indicates the inductance of the transmitting coil while the electrical load is connected to the receiving coil; and a determination device for determining an object in the area of the power transfer path on the basis of the detected parameter.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally relates to a wireless power transfer, and the present invention particularly relates to a system and a method for detecting an object on a power transfer path of a wireless power transfer. 
         [0003]    2. Background of the Invention 
         [0004]    A small power device includes a consumer and an accumulator in order to allow for wireless utilization. To charge the accumulator, power may be transferred wirelessly from a power supply to the small device by using an electromagnetic field to transfer power. For this purpose, the power supply and the small device each include a coil, the coils being positioned at a small distance from one another and thus essentially together forming a transformer. 
         [0005]    If an electrically conductive object gets into the area of the electromagnetic field, eddy currents may form which heat the object. If the object is magnetizable, the object may also be heated through core or hysteresis losses. The heating may be considerable, so that an operational reliability of the transmitter or of the receiver cannot be ensured. Moreover, the object may withdraw power from the electromagnetic field, so that the power transfer to the receiver is interfered with. 
         [0006]    It is possible to detect the presence of the object by determining the influence of the object on the inductance of the transmitter coil. If, however, the object is relatively small or relatively far away from the transmitting coil, it may be difficult to reliably detect the object. 
         [0007]    The object underlying the present invention is therefore to provide a system, a method, and a computer program product, with the aid of which a preferably precise, reliable, and highly sensitive determination of the object may be carried out, in order to enable a response to the presence of the object. The present invention achieves the objects indicated above with the aid of a power transfer system, a method, and a computer program product. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    A power transfer system according to the present invention includes a transmitting device having a transmitting coil and a receiving device having a receiving coil, the coils being inductively coupleable to one another for the purpose of transferring power, so that a power transfer path exists between them. The power transfer system furthermore includes an electrical load for connecting with terminals of the receiving coil, a detection device for detecting an electrical parameter which indicates the inductance of the transmitting coil while the electrical load is connected to the receiving coil, and a determination device for determining an object in the area of the power transfer path on the basis of the detected parameter. 
         [0009]    By providing an electrical load at the terminals of the receiving coil, a voltage which is induced in the receiving coil acts similarly to a current source, so that the receiving coil generates or intensifies its own magnetic field. If a magnetizable object is present in the area of the power transfer path, in particular close to the receiving coil, it may thus be exposed to an intensified magnetic field. The power which the object withdraws from the magnetic field due to the eddy currents, hysteresis losses or core losses, may be increased as a result. Accordingly, an effect of the object on the inductance of the transmitting coil may also be increased. This change may be detectable in an improved manner, so that the object may be detected with improved accuracy. Moreover, a smaller object or an object which is less susceptible to the magnetic field may also be detectable with the aid of the system described above. 
         [0010]    In one preferred specific embodiment, the electrical load includes a short circuit. It is preferred in any case to increase the electrical load of the receiving coil in relation to a usual charging operation, so that an increased current flows through the receiving coil, while the electrical load is connected to the receiving coil. A short circuit may contribute to maximizing this current without providing an additional load. 
         [0011]    In one specific embodiment, the receiving coil includes multiple windings and the electrical load is configured to be connected to the terminals of only one winding of the receiving coil. In this way, the magnetic field generated by the receiving coil may be controllable in an improved manner. In particular, the winding which is connectable with the electrical load may be configured to allow for an increased current flow rate without damage, e.g., by using a correspondingly thicker wire for this winding. 
         [0012]    In one refinement, a separating device may be provided for separating the terminals of at least one of the other windings from electrical loads. In this way, the determination may take place under conditions which are better controllable and better reproducible. With the aid of the separating device, a useful load may, in particular, be separated from the receiving coil, the power supply of which is the purpose of the power transfer. 
         [0013]    In one specific embodiment, the power transfer system includes a resonance transformer which includes a resonance capacitor and the transmitting coil, the detecting device being configured to detect the electrical parameters at the resonance transformer. 
         [0014]    A change in the inductance of the transmitting coil may result in a changed vibration behavior of the resonance transformer, the resonance behavior being easily determinable by measurement. 
         [0015]    The electrical parameter may include one of a current, a frequency, a phase or an attenuation. Some of these parameters may be advantageously determinable at the above-described resonance transformer. Instead of the attenuation, a quality factor of the resonance transformer may also be determined. Here it holds: 
         [0000]    
       
         
           
             
               D 
               = 
               
                 1 
                 Q 
               
             
             , 
           
         
       
     
         [0000]    where D is the attenuation and Q is the quality factor (the quality). 
         [0016]    A method according to the present invention for detecting an object in the area of an inductive power transfer path, which exists between a transmitting coil and a receiving coil which is inductively coupleable with the transmitting coil, includes the steps of connecting an electrical load with the terminals of the receiving coil, detecting an electrical parameter which indicates the inductance of the transmitting coil, and determining the object on the basis of the detected parameter. 
         [0017]    The method may be implementable in a conventional inductive power transfer system. If an object was determined, the power transfer may be throttled or stopped in order to prevent overheating of the object and to reduce an accident risk associated with that. 
         [0018]    The magnetic field, to which the object is exposed, may be advantageously controlled by the transmitting device, and the effect of a potentially present object in the area of the power transfer path may be detected at the same time, also by the transmitting device. 
         [0019]    In one preferred specific embodiment, the object is determined on the basis of a change of the electrical parameter during a change of voltage at the terminals of the transmitting coil. 
         [0020]    The voltage at the transmitting coil may be changed continuously or abruptly, a periodic change also being possible. For example, objects of different sizes or susceptibilities may be detectable. In particular, it may be avoided that for the purpose of determining its effect, the object is exposed to a strong enough magnetic field for dangerous overheating to occur already during the determination. 
         [0021]    In another specific embodiment, which may be combined with the latter specific embodiment, the object is determined on the basis of a change of the electrical parameter during a change of the electrical load of the receiving coil. The advantages mentioned above may also be achieved with this specific embodiment. 
         [0022]    A computer program product according to the present invention includes program code means for carrying out the described method when the computer program product runs on a processing device or is stored on a computer-readable data carrier. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  shows a system for wireless power transfer. 
           [0024]      FIG. 2  shows a detail of the system from  FIG. 1 . 
           [0025]      FIG. 3  shows an equivalent circuit diagram for a magnetic flux in the area illustrated in  FIG. 2 . 
           [0026]      FIG. 4  shows a flow chart of a method for determining an object in the system of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]      FIG. 1  shows a system  100  for wireless power transfer. System  100  includes a transmitting device  105  and a receiving device  110  between which a power transfer path  115  is defined. In the area of power transfer path  115 , an object  120  may be present. Object  120  is conductive or magnetizable, so that a changing magnetic field could cause eddy currents, hysteresis losses, or core losses in object  120  which heat object  120 . It is the object of illustrated system  100  to determine the existence of object  120 . 
         [0028]    Transmitting device  105 , which may be included in a power supply, for example, includes a transmitting coil  125  for converting an electric current in a magnetic field in the area of power transfer path  115 . Transmitting coil  125  is connected to a voltage source  130  which makes available an alternating current. Voltage source  130  may be connected to a conventional power supply system. A resonance capacitor  135  is preferably connected to transmitting coil  125  in series with voltage source  130 , so that resonance capacitor  135  forms a resonance transformer  140  together with transmitting coil  125 . Resonance capacitor  135  may, however, also be connected in parallel to transmitting coil  125 . A resonance frequency of resonance transformer  140  is a function of the inductance of transmitting coil  125  as well as the capacitance of resonance capacitor  135 . 
         [0029]    A receiving coil  145  of receiving device  110  is situated at the other end of power transfer path  115 . In known receiving devices, receiving coil  145  is directly connected to a useful load which includes a charge controller  150  for an accumulator  155 , as an example, in the illustration of  FIG. 1 . In contrast, a switching device  160  is also provided in the present case in order to connect an electrical load  165  to terminals of receiving coil  145 . Electrical load  165  may, in particular, include a low-resistance load or a short circuit. In one specific embodiment, the useful load, i.e., charge controller  150  and/or accumulator  155  in this case, may remain connected to the terminals of receiving coil  145 . In another specific embodiment, the useful load is separated from receiving coil  145  at least on one side, while electrical load  165  is applied to receiving coil  145 . 
         [0030]    In the illustrated specific embodiment, receiving coil  145  includes multiple windings, the ends of which are separated as terminals at receiving coil  145 . Switching device  160  is configured to connect electrical load  165  to only one of the windings of receiving coil  145 . A separating device  170  is preferably provided for the purpose of separating one or more of the remaining windings from electrical loads, in particular the useful load, while another winding of receiving coil  145  is connected to electrical load  165 . 
         [0031]    A transfer device  175  is preferably provided for the purpose of being able to control switching device  160  and, if necessary, also separating device  170  with the aid of transmitting device  105 . Transfer device  175  may be implemented to be wired or wireless, an information transfer with the aid of a variation of the magnetic field in the area of power transfer path  115  being provided in one specific embodiment. 
         [0032]    On the side of transmitting device  105 , transfer device  175  is connected to a control unit  180  which controls system  100  for the purpose of determining object  120 . Control unit  180  is preferably also configured to control a conventional power transfer process from transmitting device  105  to receiving device  110 . For this purpose, control device  180  may be connected to voltage source  130 . Furthermore, control device  180  may be linked to transmitting coil  125  or resonance transformer  140  in such a way that control device  180  may scan an electrical parameter which indicates the inductance of resonance transformer  140 . This parameter may include an electric current, an electrical voltage, a frequency, attenuation, or a quality factor at transmitting coil  125  or resonance transformer  140 . 
         [0033]    Control unit  180  is configured to activate receiving device  110  in such a way that electrical load  165  is connected to receiving coil  145 . In one preferred specific embodiment, voltage source  130  may be activated simultaneously or subsequently to change the voltage at transmitting coil  125 . Object  120  may be determined on the basis of a change of the electrical parameter or on the basis of an absolute value of the electrical parameter which indicates the inductance of transmitting coil  125 . 
         [0034]      FIG. 2  shows a section from power transfer path  115  from  FIG. 1 . The illustration corresponds to a part of an exemplary physical configuration of transmitting coil  125  and receiving coil  145  as the parts of transmitting device  105  and receiving device  110 , respectively. Power transfer path  115  is indicated between coils  125  and  145 . Moreover, magnetic field lines are indicated between coils  125  and  145 . Object  120  is situated between delimitations  205  which represent sections of the housings of transmitting device  105  or receiving device  110 , as an example. 
         [0035]      FIG. 3  shows a magnetic equivalent circuit diagram for the area illustrated in  FIG. 2 . In this case, resistance symbols represent magnetic resistances and voltage source symbols represent magnetic through flows. The illustration is true to position with regard to the illustration of  FIG. 2 . 
         [0036]    A first magnetic through flow  305  represents the magnetic inductance (B field) which is formed by actively energized transmitting coil  125 . Magnetic resistances  310 ,  315 ,  320  and  325  represent the resistances in the horizontal and the vertical areas around transmitting coil  125 . Beyond housing  205  of transmitting device  105 , a vertically running magnetic resistance  330  represents magnetic dispersion losses. Magnetic resistances  335  and  340  represent resistances in the horizontal direction between housings  205 . A magnetic resistance  345  represents the magnetic flux through object  120 . Beyond second housing  205 , on the right in  FIG. 3 , other magnetic resistances  350  through  365 , as well as a second magnetic through flow  370 , are denoted which correspond to elements  305  through  325 . 
         [0037]    The illustrated equivalent circuit diagram applies only if receiving coil  110  is in idle state, i.e., when no electrical consumer is connected to receiving coil  110 . Due to the electrical load, the voltage induced in receiving coil  145  is immediately converted back into a magnetic field, so that second magnetic through flow  370  may be understood to mean a controllable source, the magnetic flux of which is proportional to the magnetic flux of first magnetic through flow  305 . 
         [0038]    If electrical load  165  is low, as is the case during a normal charging operation of system  100 , second magnetic through flow  370  is also low. The greater electrical load  165 , the greater is magnetic through flow  370 . The inductance of transmitting coil  125  decreases with increasing through flow  370 , which may be determined based on an increasing resonance frequency of resonance transformer  140 , for example. 
         [0039]    In order to increase the inductance of transmitting coil  125 , the magnetic flux of first magnetic through flow  305  may be increased on the one hand, and, on the other hand, the magnetic resistance of second through flow  370  may be reduced. In order to increase the magnetic flux, the winding number of transmitting coil  125  or the current flowing through transmitting coil  125  may be increased. In order to increase the magnetic flux, receiving coil  145  may also be electrically loaded or short-circuited, whereby the magnetic flux through object  120  or through magnetic resistance  345  of object  120  increases as a whole. 
         [0040]      FIG. 4  shows a flow chart of a method  400  for determining an object  120  in the system of  FIG. 1 . Method  400  is in particular configured to control system  100  through control unit  180 . In one specific embodiment, a computer program product for controlling a programmable microcomputer is involved which is included in control unit  180 . 
         [0041]    The method starts in a step  405  in which a usual charging operation takes place, during which electrical energy is transported from transmitting coil  125  to receiving coil  145  on power transfer path  115  with the aid of a magnetic alternating field. 
         [0042]    In order to determine object  120 , receiving coil  145  is separated from useful load  150 ,  155  in a step  410 . This step may also be skipped. 
         [0043]    Subsequently, receiving coil  145  is connected to an electrical load  165 , so that the current flowing through receiving coil  145  is increased. 
         [0044]    Furthermore, an excitation for transmitting coil  125  is determined in a step  420  by activating voltage source  130  to make available a predetermined voltage. Subsequently, transmitting coil  125  is excited in a step  425 , preferably using an alternating voltage. The alternating voltage may be predetermined by a resonance frequency of resonance transformer  140 . 
         [0045]    Subsequently, an electrical parameter is detected at transmitting coil  125  or resonance transformer  140  in a step  430 . On the basis of the detected parameter, it is determined in a step  435  whether object  120  is present in the area of transfer path  115 . If this is the case, a corresponding measure, such as a reduction of the transferred power or a discontinuation of the power transfer, may be taken in a step  440 . Subsequently, receiving coil  145  is again separated from electrical load  165  in a step  445  and connected to the original load, e.g., useful load  150 ,  155 , if necessary. Subsequently, the method may return to step  405  and be repeated. 
         [0046]    If it was determined in step  435  that an object  120  is not present, it is checked in a subsequent step  450  whether all intended excitations of transmitting coil  125  have already been applied. If this is the case, object  120  cannot be determined and method  400  returns to step  405  via step  445 . 
         [0047]    Otherwise, the excitation is changed in a step  455  before method  400  proceeds with step  425 . If only one excitation is used, steps  450  and  455  may be dispensed with.