Abstract:
A power transfer apparatus including a first device and a second device having a first coil and a second coil, respectively, is provided. The first device is configured to produce primary power through the primary coil upon being supplied with external power and to be controlled by a provided control signal so that the primary power decreases and increases upon the control signal representing a first value and a second value, respectively. The second device is configured to be joined with the first device so that the secondary coil is electromagnetically coupled with the primary coil. The second device is configured to produce secondary power upon the secondary coil being driven through the electromagnetic coupling. The second device is configured to provide the first device with the control signal representing the first value and the second value upon the secondary power being greater and smaller than a reference value, respectively.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-305041 filed on Nov. 28, 2008; the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a power transfer apparatus and a method for transferring electric power, and in particular to a power transfer apparatus adapted for contactless power transfer not through an electrical contact. The power transfer apparatus is configured to feed a secondary output voltage back to a primary side so as to make the secondary output voltage stable. 
         [0004]    2. Description of the Related Art 
         [0005]    An apparatus configured to transfer electric power by means of electromagnetic induction of a transformer is known, as disclosed in Japanese examined patent application publication (Toroku), No. B-3416863. According to paragraphs 0167-0168 and FIG. 22 of JP-B-341 6863, the apparatus transfers electric power from a primary side to a secondary side through a transformer, and transfers a signal from the secondary side to the primary side through the transformer. transformer. As to the signal transfer, the apparatus converts a secondary output voltage into a frequency signal as a load condition signal by using a V-f conversion and so on, and transfers the frequency signal to the primary side. The apparatus thereby controls an oscillating circuit of the primary side for a feedback control so as to make the secondary output voltage stable. The apparatus can be applied to a use for which the primary side of the transformer can be easily put on and taken off the secondary side in a case where, e.g., the primary and secondary sides are a battery charger and a mobile phone, respectively. The apparatus transfers the electric power and the signal while the mobile phone is being put on the battery charger. 
         [0006]    Another apparatus configured to similarly transfer electric power by means of electromagnetic induction of a transformer is known, as disclosed in Japanese patent publication of unexamined applications (Kokai), No. A-2003-348775. According to  FIGS. 1-2  and paragraphs 0031-0033 of JP-A-2003-348775, the apparatus transfers electric power from a primary side to a secondary side through an output transformer  103 , and transfers a signal from the secondary side to the primary side through an optical communication circuit  108 . As to the signal transfer, the apparatus converts a secondary output voltage into a digital signal and transfers the digital signal to the primary side through the optical communication circuit  108 . The apparatus thereby controls the primary side for a feedback control so as to make the secondary output voltage stable. The apparatus can be applied not to a use for which the primary side of the transformer can be easily put on and taken off the secondary side but to a use for which the primary side is always put on the secondary side in a case where, e.g., the primary and secondary sides are a main body of a vehicle and a steering wheel. The apparatus transfers the electric power and the signal while the steering wheel is always put on the main body of the vehicle. Thus, the output transformer  103  need not have an internal configuration that can be divided, put on and taken off. The optical communication circuit  108  need not have an internal configuration that can be divided, put on and taken off, either. 
         [0007]    According to JP-B-3416863, as the secondary output voltage is converted into a frequency signal by using a V-f conversion and so on, the signal transfer through the transformer requires a broad frequency bandwidth corresponding to an output voltage variation. The signal transfer of JP-B-3416863 is required to be stable in the required frequency bandwidth. 
         [0008]    According to JP-A-2003-348775, as digital data corresponding to the secondary output voltage is serially exchanged, the signal transfer through the optical communication requires significant time upon the data size being large. The signal transfer of JP-A-2003-348775 may thereby cause a time lag, and is possibly unable to react to a steep change of the secondary output voltage. 
       SUMMARY OF THE INVENTION 
       [0009]    Accordingly, an advantage of the present invention is to provide a power transfer apparatus configured to transfer a signal for feeding a secondary output voltage transferred through contactless power transfer back to the primary side without a need of a broad frequency bandwidth. The power transfer apparatus is configured to reduce a time lag by reducing digital data to be transferred. The power transfer apparatus is configured to immediately react to a steep change of the secondary output voltage. 
         [0010]    To achieve the above advantage, one aspect of the present invention is that a power transfer apparatus including a first device and a second device having a first coil and a second coil, respectively, is provided. The first device is configured to produce primary power through the primary coil upon being supplied with external power and to be controlled by a provided control signal so that the primary power decreases and increases upon the control signal representing a first value and a second value, respectively. The second device is configured to be joined with the first device so that the secondary coil is electromagnetically coupled with the primary coil. The second device is configured to produce secondary power upon the secondary coil being driven through the electromagnetic coupling. The second device is configured to provide the first device with the control signal representing the first value and the second value upon the secondary power being greater and smaller than a reference value, respectively. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a block diagram of a power transfer apparatus  100  of a first embodiment of the present invention. 
           [0012]      FIG. 2  is a block diagram of a power transfer apparatus  100  of a second embodiment of the present invention. 
           [0013]      FIG. 3  shows a structure of an optical communication portion of the power transfer apparatus  100  of the second embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]      FIG. 1  is a block diagram of a power transfer apparatus  100  of a first embodiment of the present invention. The power transfer apparatus  100  includes a battery charger  10  (first device on the primary side) and a mobile communication device  20  (second device on the secondary side). The mobile communication device  20  can be easily put on and taken off the battery charger  10 . The power transfer apparatus  100  transfers electric power and a signal while the mobile communication device  20  is being put on the battery charger  10 . 
         [0015]    An upper half of  FIG. 1  shows a portion of the power transfer apparatus  100  for transferring electric power from the battery charger  10  to the mobile communication device  20 . A lower half of  FIG. 1  shows a portion of the power transfer apparatus  100  for transferring a signal from the mobile communication device  20  to the battery charger  10  so as to control feedback for making an output of the power transferred to the mobile communication device  20  stable. 
         [0016]    The configuration of the power transfer apparatus  100  will be described in detail below. The battery charger  10  is constituted by a dc power supply  1 , a variable output oscillator  2 , a transformer coil  3  (first coil), a transformer coil  4  (fourth coil), a frequency/voltage converter  5  and so on. The mobile communication device  20  is constituted by a transformer coil  21  (second coil), a regulating circuit  22 , a smoothing circuit  23 , a comparator  24 , a voltage/frequency converter  25 , a transformer coil  6  (third coil) and so on. 
         [0017]    The battery charger  10  is connected to an external ac power source and produces dc power by means of the dc power supply  1 . The variable output oscillator  2  is supplied by the dc power supply  1  with the dc power, oscillates at a frequency f 1  and drives the transformer coil  3  (first coil on the primary side) with an output of the oscillation. The battery charger  10  transfers electric power to the transformer coil  21  (second coil on the secondary side) of the mobile communication device  20 . 
         [0018]    An output of the transformer coil  21  (second coil on the secondary side) of the mobile communication device  20  is regulated by the regulating circuit  22 , and then smoothed by the smoothing circuit  23  so that a dc output  23 A is obtained. The dc output  23 A is provided to a charge control circuit (not shown) included in the mobile communication device  20  so as to charge a battery (not shown). 
         [0019]    The comparator  24  compares the dc output  23 A with a reference voltage  24 A so as to produce a waveform-shaped binary up/down signal  24 B. 
         [0020]    The up/down signal  24 B represents one bit digital data having a value of “0” corresponding to “down” and a value of “1” corresponding to “up” upon the dc output  23 A being greater and smaller than the reference voltage  24 A, respectively. 
         [0021]    The voltage/frequency converter  25  is provided with the binary signal of the up/down signal  24 B as an input, performs a voltage-to-frequency conversion process and drives the transformer coil  6  (third coil) by using a frequency-converted output. The output of the voltage/frequency converter  25  has a frequency of f 2 +? and f 2 −? upon the up/down signal  24 B having a value of “1” and a value of “0”, respectively. The frequency f 2  is different from the frequency f 1  for power transfer. The frequencies f 2 +? and f 2 −? are almost same as f 2  as the value ? is very small. 
         [0022]    Upon being driven, the transformer coil  26  (third coil) transfers a signal to the transformer coil  4  (fourth coil) through electromagnetic induction at the frequencies f 2 +? and f 2 −?. The above frequency range is just around the frequency f 2 , and it is enough to cause electromagnetic induction only around the frequency f 2 . 
         [0023]    An output of the transformer coil  4  (fourth coil) is provided to the frequency/voltage converter  5  so that an up/down signal  5 A of a voltage level corresponding to the input frequency value is obtained. As the frequency has two values, f 2 +? and f 2 −?, the output of the frequency/voltage converter  5  is binary. 
         [0024]    The up/down signal  5 A similarly has a value of “0” and a value of “1” upon the up/down signal  24 B having a value of “0” corresponding to “down” and a value of “1” corresponding to “up”, respectively. 
         [0025]    The variable output oscillator  2  controls a decrease and an increase in an output of the variable output oscillator  2  by using the up/down signal  5 A. That is, the power transfer apparatus  100  performs a feedback control such that the output of the variable output oscillator  2  decreases and increases upon the dc output  23 A being greater and smaller than the reference voltage  24 A, respectively. The dc output  23 A is thereby made stable around the reference voltage  24 A. 
         [0026]    The comparator  2  is, but not limited to, an ordinary comparator as described above, and may be a comparator having a hysteresis characteristic such as a Schmitt comparator. In such a case, the feedback control works such that the repetition of the decrease and increase of the output of the variable output oscillator  2  slows down. 
         [0027]    Although the mobile communication device  20  (second device) can be easily put on and taken off the battery charger  10  (first device) as described above, the present invention can be applied to another power transfer apparatus constituted by a first device and a second device integrated with and fixed to each other. 
         [0028]    According to the first embodiment of the present invention, as the signal transfer through the electromagnetic induction is performed on the binary basis, the power transfer apparatus only needs the two frequencies, f 2 +? and f 2 −?, for the electromagnetic induction. As the frequency remains in a narrow range around the frequency f 2 , it is enough to make sure of the electromagnetic induction around the frequency f 2 . The power transfer apparatus can thereby enhance reliability of the signal transfer. 
         [0029]      FIG. 2  is a block diagram of a power transfer apparatus  100  of a second embodiment of the present invention. Each of portions which is a same as the corresponding one of the first embodiment (shown in  FIG. 1 ) is given a same reference numeral, and remaining portions different from the portions of the first embodiment will be mainly explained. An upper half of  FIG. 2  shows a same portion of the power transfer apparatus  100  as shown in the upper half of  FIG. 1  for transferring electric power from the battery charger  10  to the mobile communication device  20 , and its explanation is omitted. A lower half of  FIG. 2  shows a portion configured to transfer a signal for output stability, similarly as the corresponding portion of the first embodiment, but by using optical communication for the signal transfer. 
         [0030]    The configuration of the power transfer apparatus  100  will be described in detail below. The battery charger  10  is constituted by the dc power supply  1 , the variable output oscillator  2 , the transformer coil  3  (first coil), a photo receiver  6  for optical communication, a communication controller  7  that is a demodulator and so on. The mobile communication device  20  is constituted by the transformer coil  21  (second coil), the regulating circuit  22 , the smoothing circuit  23 , the comparator  24 , a communication controller  27  that is a modulator, a photo emitter  28  for the optical communication and so on. 
         [0031]    The portion of the power transfer apparatus  100  for power transfer is a same as the corresponding portion of the first embodiment (shown in  FIG. 1 ), and its explanation is omitted. The portion of the power transfer apparatus  100  for the signal transfer will be explained below. The communication controller  27  is provided with the up/down signal  24 B (binary) as an input, performs a modulation process for the optical communication, drives the photo emitter  28  and sends an optical signal to the photo receiver  6  of the battery charger  10 , i.e., the optical communication. 
         [0032]    The photo receiver  6  of the battery charger  10  provides the communication controller  7  with an optical-electric conversion output. The communication controller  7  demodulates the optical-electric conversion output so as to produce an up/down signal  7 A of a voltage level. As the up/down signal  24 B is binary, the up/down signal  7 A, which is demodulated from the signal binary-modulated by using the binary up/down signal  24 B, is also binary. 
         [0033]    The up/down signal  7 A similarly has a value of “0” and a value of “1” upon the up/down signal  24 B having a value of “0” corresponding to “down” and a value of “1” corresponding to “up”, respectively. 
         [0034]    The variable output oscillator  2  controls a decrease and an increase in an output of the variable output oscillator  2  by using the up/down signal  7 A. That is, the power transfer apparatus  100  performs a feedback control such that the output of the variable output oscillator  2  decreases and increases upon the dc output  23 A being greater and smaller than the reference voltage  24 A, respectively. The dc output  23 A is thereby made stable around the reference voltage  24 A. 
         [0035]      FIG. 3  shows a structure of an optical communication portion of the power transfer apparatus  100  of the second embodiment of the present invention. A lightshield  30  is provided so that the optical communication between the photo emitter  28  and the photo receiver  6  is not affected by external light upon the mobile communication device  20  being put on the battery charger  10 . The power transfer apparatus  100  can thereby perform stable optical communication without being affected by external light. 
         [0036]    The photo emitter  28  and the photo receiver  6  are configured to be separate and the one of them can be easily put on and taken off the other of them so that the mobile communication device (second device) can be put on and taken off the battery charger  110  (first device). For another power transfer apparatus constituted by a first device and a second device integrated with and fixed to each other, though the photo emitter  28  and the photo receiver  6  may form a photo coupler and so on by being Integrated with each other. The photo coupler is not affected by external light, and thus needs no lightshield. 
         [0037]    The power transfer apparatus  100  is provided with, but not limited to, the optical communication subsystem for the signal transfers and may be provided with another communication subsystem as long as the transmitter and receiver sides are electrically isolated from each other. 
         [0038]    According to the second embodiment of the present invention, the optical signal transfer needs only one bit data of the up/down signal  24 B, and thus can save time required for the signal transfer. The power transfer apparatus  100  can thereby reduce a time lag of the feedback control and can thereby react to an abrupt change of the output voltage on the secondary side. 
         [0039]    The particular hardware or software implementation of the present invention may be varied while still remaining within the scope of the present invention. It is therefore to be understood that within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described herein.