Abstract:
An inductive power transfer system including a synchronous drive system having a resonance control module. The resonance control module includes a primary coil module with a primary LC circuit. The resonance control module seeks and detects the resonant frequency of the primary LC circuit. The synchronous drive system further includes a switching coil amplifier for selectively energizing the primary coil to keep the primary LC circuit operating at or as close as possible to its natural resonant frequency. The inductive power transfer system may further include a secondary receiving unit. The secondary receiving unit includes a secondary LC circuit coupled with the primary LC circuit for inductively receiving power. The secondary LC circuit includes an LC filter and a rectifier unit for operating the secondary LC circuit at a mutual resonance with the primary LC circuit.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject of the invention relates to an inductive power transfer system and more specifically to a synchronous system for inductively transferring power. 
     2. Description of the Prior Art 
     Inductive power transfer can be used to power a device and/or charge a remotely located battery without the need for any electrical connection between the device and a power source. Inductive power transfer typically uses a primary coil and a secondary coil. The primary coil may be contained within a primary unit or source connected to an AC (Alternating Current) power source. The secondary coil may be contained in a secondary or receiving system, which may be directly included in, for example a cordless consumer device. When the cordless device is placed near the primary unit, such that the primary coil is in proximity to the secondary coil, power is inductively transferred from the primary coil to the secondary coil. The energy stored by the secondary coil can be utilized to power and/or charge the consumer device. 
     One problem with inductive power transfer is the lack of spatial freedom between the primary coil and the secondary coil. The efficiency at which the primary coil transfers power to the secondary coil is limited by the distance between the primary unit and the device, including the secondary unit. Operating the primary coil and the secondary coil at mutual frequencies, at or close to resonance, increases the efficiency of the power transfer. It is additionally desirable to adjust the magnitude of oscillation existing at the primary coil to control the magnitude of power transfer from the primary coil to the secondary coil. However, adjusting frequency to operate at resonance and simultaneously controlling amplitude can be problematic. Additionally, using voltage pulses to control the resonance frequency and amplitude can easily generate undesired electromagnetic emissions when inductively coupling a primary coil to a secondary coil. Furthermore, primary and secondary coils intended to couple with a high degree of spatial freedom can easily radiate unwanted electromagnetic energy due to the pulsing form of the control, especially if the secondary coil includes a rectifier circuit having sudden changes in current flowing through the secondary coil. These electromagnetic energies may affect a variety of devices, such as radios in vehicles. 
     SUMMARY OF THE INVENTION AND ADVANTAGES 
     The inductive power transfer system including a synchronous drive system provides for a resonance control module having a primary coil module with a primary LC circuit. The resonance control module seeks the resonant frequency of the primary LC circuit and selectively powers the primary LC circuit to keep the primary LC circuit operating at or as close as possible to its natural resonant frequency while varying the magnitude of the power signal delivered to the primary LC circuit. 
     Not only does the resonance control module seek the resonant frequency to operate the primary LC circuit at or as close as possible to its natural resonance, the primary unit includes the synchronous drive system that controls the magnitude of a power signal used to power the primary LC circuit. Accordingly, the magnitude of the power signal can be adjusted to efficiently transfer power to a device to sufficiently operate the device and/or charge a battery without substantial frequency variations. Additionally, undesired electromagnetic emissions generated by the power signal and emitted by the primary LC circuit are reduced. 
     Further scope of applicability of the present invention will become apparent from the following detailed description, claims, and drawings. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1  is a block diagram of the inductive power transfer system including a synchronous drive system in proximity with a secondary receiving system; 
         FIG. 2  are electronic circuit schematics of the resonance control module and the primary coil module; and 
         FIG. 3  is detailed electronic circuit schematic of a secondary receiving circuit. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, an inductive power transfer system is generally shown for adjusting the conduction angle of an oscillating circuit. Referring to  FIG. 1 , the inductive power transfer system  20  includes a primary unit  24  and a secondary unit  22 . The primary unit  24  includes a synchronous drive system  26  and the secondary unit  22  includes a secondary receiving system  30 . The synchronous drive system  26  inductively powers the secondary receiving system  30 , as discussed in greater detail below. The synchronous drive system  26  may further include a receiver module  28  that communicates with the secondary receiving system  30  to receive a status signal (STATUS) indicating power conditions within the secondary unit  22 . The secondary unit  22  may include a battery  32  and/or a consumer device that can be charged and/or powered by the secondary receiving system  30 . The secondary unit  22  may further include a transmitter module  34  that communicates with the receiver module  28  on the synchronous drive system  26  to communicate the status signal (STATUS). Various methods of communicating the status signal (STATUS) may be used including, but not limited to, RF (radio frequency), Bluetooth, etc. 
     The synchronous drive system  26  includes a condition module  36  in communication with the receiver module  28  to receive the status signal (STATUS). The condition module  36  outputs a desired oscillation level signal (V DESIRE ) for setting a desired voltage level of resonance in the primary coil circuit based on status signal (STATUS). 
     Referring to  FIG. 2 , the synchronous drive system  26  further includes a resonance control module  40  and a primary coil module  38 . The resonance control module  40  is in communication with the condition module  36  and receives the desired resonance amplitude signal (V DESIRE ). The resonance control module  40  outputs a pre-amplified switching source voltage (V PREAMP ) based on the signal (V DESIRE ), as discussed in greater detail below. 
     The primary coil module  38  communicates with the resonance control module  40  for generating an amplified switching source voltage (V AMP ) based on the pre-amplified source voltage (V PREAMP ). The primary coil module  38  includes a switching coil amplifier  42  for amplifying the pre-amplified source voltage (V PREAMP ). The switching coil amplifier  42  includes an amplifier input for receiving the pre-amplified source voltage (V PREAMP ) and includes an amplifier output for outputting the amplified source voltage (V AMP ). 
     The primary coil module  38  further includes an EMC (electromagnetic compatibility) filter  44  and a primary LC (inductor capacitor) circuit  52 . The EMC filter  44  utilizes an EMC coil  46  and an EMC capacitor  48  to filter electronic noise from the amplified source voltage (V AMP ). The EMC capacitor  48  has one end connected to reference point, such as a ground point, and an opposite end connected to one end of the EMC coil  46 . The opposite end of the EMC coil  46  is connected to the amplifier output of the switching coil amplifier  42 . The EMC filter  44  suppresses unwanted noise generated by the switching coil amplifier  42  from reaching the tank coil  50  where it can radiate and generate undesired electromagnetic energy. 
     The primary LC circuit  52  includes a tank capacitor  54  and a tank coil  50 . In some embodiments, the tank coil  50  is also referred to as a primary coil. The tank capacitor  54  has one end connected to a reference point and an opposite end in communication with one end of the tank coil  50 . The opposite end of the tank coil  50  communicates with one end of each of the EMC coil  46  and the EMC capacitor  48  for receiving the amplified source voltage (V AMP ). 
     The amplified source voltage (V AMP ) induces a current through the tank coil  50 . As current flows through the tank coil  50 , a magnetic field is generated. A secondary coil  56  can be placed in proximity to the magnetic field to induce a current in the secondary coil  56 . The current induced in the secondary coil  56  can be utilized to charge the battery  32  and/or power a device. A natural resonant frequency exists due to the arrangement of the tank coil  50  and the tank capacitor  54 . When the tank coil  50  and the tank capacitor  54  operate at resonance, variations in frequency are small, thereby increasing the efficiency of the inductive power transfer between the tank coil  50  and the secondary coil  56 . By delivering the amplified source voltage (V AMP ) at a frequency that oscillates approximately at the resonance frequency of the primary LC circuit, an efficient inductive power transfer for charging the battery  32  and/or powering a device can be achieved. Additionally, by controlling the amplitude of (V AMP ) the power delivered to a secondary coil  56  can compensate for changes in spatial conditions, battery conditions, and differing power demands of various devices according to information communicated in the status signal. Furthermore, the primary LC circuit can maintain the amplitude of oscillation and power at the secondary with fluctuations in the voltage of the energy source. 
     The resonance control module  40  includes a phase angle prediction module  57 , an AC/DC converter module  60 , an error module  62 , a phase comparator  64 , an oscillation module  66 , and a conduction angle module  68 . The phase angle prediction module  57  includes a sawtooth PNP transistor  70  and a sawtooth capacitor  72  to predict the phase angle of the primary LC circuit  52  during oscillation. The sawtooth capacitor  72  includes a ground end in communication with a reference point and a transistor end in communication with the collector of the sawtooth PNP transistor  70 . The voltage across the sawtooth capacitor  72  generates a predicted phase angle signal (V SAW ). The magnitude of the predicted phase angle signal (V SAW ) represents the angle of the primary LC circuit  52  sinusoidal oscillation. Although a sawtooth generator is utilized to predict the phase angle of the primary LC circuit  52 , another means of predicting the phase angle may be used. 
     The AC/DC converter module  60  converts the AC (alternating current) voltage signal generated across the tank capacitor  54  into a scaled DC (direct current) voltage signal. Specifically, the AC/DC converter module  60  has an AC/DC input in communication with the tank capacitor  54  for receiving a tank capacitor AC voltage signal (V TANK ). The AC/DC converter module  60  converts the AC voltage magnitude into a DC voltage. The AC/DC converter module  60  has an AC/DC output for outputting the actual scaled signal (V ACTUAL ) that indicates the DC tank voltage value of the AC tank voltage of the tank capacitor  54 . The AC/DC converter module  60  is particularly fast at converting the AC magnitude to a useful DC signal. The high-speed signal response allows for stable feedback control and also wide tolerance to variations in energy sources and/or supply voltage for charging secondary loads. 
     The error module  62  generally indicated has an error amplifier  74  with a non-inverting input for receiving the desired resonance amplitude signal (V DESIRE ). The error amplifier  74  further includes an inverting input for receiving the actual resonance amplitude signal (V ACTUAL ) indicating the actual oscillation level of a primary LC circuit. The error module  62  computes the difference between the voltage level of the desired resonance amplitude signal (V DESIRE ) and the voltage level of the actual resonance amplitude signal (V ACTUAL ). The error module  62  includes an output for outputting an error feedback signal (V ERROR ) that is influenced by the voltage magnitude difference between (V DESIRE ) and (V ACTUAL ). The error feedback signal (V ERROR ) is used to regulate the amplitude of oscillation of the primary LC circuit  52  in spite of load, supply voltage, and damping disturbances. 
     The phase comparator  64  generally indicated has an inverting phase input and a non-inverting phase input. The phase comparator  64  includes a phase output in communication with each of the collector of the sawtooth PNP transistor  70  and the transistor end of the sawtooth capacitor  72 . The phase comparator  64  selectively operates in a high impedance state and a low impedance state. Specifically, the phase comparator  64  operates in a high impedance state when the sawtooth voltage across the sawtooth capacitor  72  increases. When the voltage across the sawtooth capacitor  72  decreases, the phase comparator  64  operates in a low impedance state. 
     The oscillation module  66  generally indicated has an oscillation comparator  76 . The oscillation comparator  76  has a non-inverting oscillation input and an inverting oscillation input. The non-inverting oscillation input is in communication with each of the error output of the error amplifier  74  and the non-inverting phase input of the phase comparator  64  and a reference voltage. The inverting oscillation input is in communication with the inverting phase input of the phase comparator  64  and with an oscillation output for outputting the pre-amplified source voltage (V PREAMP ). The LC resonant circuit includes a feedback network that communicates with the oscillation module  66 . The feedback network includes a feedback resistor  78 , a first feedback capacitor  80 , and a second feedback capacitor  82 . Specifically, the feedback resistor  78  has one end in communication with one the tank capacitor  54 . The feedback resistor  78  has an opposite end in communication with one end of each of the first feedback capacitor  80  and the second feedback capacitor  82 . The first feedback capacitor  80  has an opposite end in communication with each of the inverting feedback input of the oscillation module  66  and the inverting phase input of the phase comparator  64 . The feedback network provides a signal path for delivering the tank capacitor  54  AC voltage signal (V TANK ) to the oscillation comparator  76  of the oscillation module  66 . The second feedback capacitor  82  has an opposite end in communication with a reference point for filtering the tank capacitor  54  AC voltage signal (V TANK ). 
     The conduction angle module  68  (CAM) generally indicated has a conduction angle comparator  84  for comparing the predicted phase angle signal (V SAW ) with the error feedback signal (V ERROR ). The conduction angle module  68  includes a non-inverting CAM input and an inverting CAM input. The non-inverting CAM input communicates with the error output of the error module  62  for receiving the error feedback signal (V ERROR ). The inverting CAM input communicates with the collector of the sawtooth PNP transistor  70  for receiving the predicted phase angle signal (V SAW ). The conduction angle module  68  has a conduction angle output for outputting a drive termination signal (TERM) to terminate the pre-amplified source voltage (V PREAMP ) output by the oscillation comparator  76  of the oscillation module  66  when the predicted phase angle signal (V SAW ) equals the error feedback signal (V ERROR ). By selectively terminating the pre-amplified source voltage (V PREAMP ), the resonance control module can selectively energize the primary LC circuit  52  in order to continuously operate the primary LC circuit  52  at the natural resonance frequency and simultaneously and at the desired AC amplitude of oscillation. 
     Referring to  FIG. 3 , the secondary unit  22  is illustrated in greater the detail. The secondary unit  22  includes the secondary receiving system  30 . A battery  32  and/or consumer device may be included in the secondary unit  22  for being charged and/or powered by the secondary receiving system  30 . 
     The secondary receiving system  30  includes a secondary coil module  86  and a rectifier module  88 . The secondary coil module  86  generally indicated can be disposed in proximity of the primary coil module  38  of the synchronous drive system  26 . The synchronous drive system  26  can inductively transfer power to the secondary receiving system  30 , which in turn charges a battery  32  and/or powers a consumer device  33 , as discussed in greater detail below. 
     As stated above, the secondary unit  22  may include a battery  32  for powering a consumer device  33 . The secondary coil module  86  generates a pre-rectified charging voltage (V pre—rec ), as discussed in greater detail below. The rectifier module  88  generally indicated communicates with the secondary coil module  86  for rectifying the pre-rectified charging voltage (V pre—rec ). The rectified charging voltage (V REC ) is output by the rectifier module  88  and can be used to charge and/or power the battery  32  and/or the consumer device  33 . Various rectifier designs may be used including, but not limited to, a half-wave diode rectifier and a full-wave bridge rectifier. An exemplary embodiment of the rectifier module  88  may include a first rectifier diode  90 , a second rectifier diode  92 , and a rectifier capacitor  94 . The anode of the first rectifier diode  90  is in communication with a reference point and the cathode is in communication with secondary coil module  86 . The cathode of the second rectifier diode  92  is in communication with the positive terminal of the battery  32  and the anode is in communication with both the cathode of the first rectifier diode  90  and secondary coil module  86 . The rectifier capacitor  94  has one end in communication with a reference point and has an opposite end in communication with one end of the second rectifier diode  92  and the positive terminal of the battery  32 . The secondary receiving system  30  may further include a status module  96  that communicates with the rectifier module  88  and computes power conditions within the secondary unit  22 . The status module  96  outputs a status signal (STATUS) that can indicate the charge status of the battery  32  and/or power status of the device  33 . 
     The secondary coil module  86  includes a secondary LC circuit  98  and an LC filter  100 . The secondary LC circuit  98  generally indicated communicates with both the primary LC circuit  52  and the LC filter  100 . The secondary LC circuit  98  includes a secondary coil  56  having one end in communication with the rectifier module  88  for being disposed in proximity with the magnetic field to induce a current through the secondary coil  56 . The secondary LC circuit  98  generates the pre-rectified charging voltage (V pre—rec ) that is delivered to the rectifier module  88 . The secondary capacitor  102  has one end communicating with a reference point and has an opposite end communicating with one end of the secondary coil  56 . 
     The LC filter  100  generally indicated has a filter coil  104  and a filter capacitor  106 . The filter coil  104  has one end in communication with one end of the secondary coil  56 , the cathode of the first rectifier diode  90 , and the anode of the second rectifier diode  92 . The opposite end of the filter coil  104  communicates with one end of the filter capacitor  106 . The opposite end of the filter capacitor  106  communicates with a reference point. The LC filter  100  suppresses undesired electrical noise generated by the switching action of the first and second rectifier diodes  90 ,  92  before delivering the pre-rectified charging voltage (V pre—rec ) to the rectifier module  88 . Additionally, the LC filter  100  inhibits unwanted electromagnetic emission generated by the secondary coil  56  that is typically caused by the sudden changes in diode current flowing through the first and second rectifier diodes  90 ,  92 . 
     A mutual resonant frequency can be determined based on the component values and the mutual coupling between the primary LC circuit  52  and the secondary LC circuit  98 . By operating both the primary LC circuit  52  and the secondary LC circuit  98  at resonance, undesirable EMC emissions that can affect secondary receiving system  30  are reduced. Additionally, operating the primary LC circuit  52  and the secondary LC circuit  98  in mutual resonance improves the power transfer to the secondary receiving system  30  when the coupling between primary and secondary coils  56  is reduced by spatial separation. Further, the improved coupling allows a battery  32  and/or consumer device to be charged and/or powered at greater distances from the primary unit  24 . 
     The foregoing discussion discloses and describes an exemplary embodiment of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the true spirit and fair scope of the invention as defined by the following claims.