Electronic control method for a planar inductive battery charging apparatus

Abstract

This invention provides an electronic control method for a planar inductive battery charging apparatus on which one or more electronic loads such as mobile phones, MP3 players etc can be placed and charged simultaneously. The power control circuit of the charging pad consists of two power conversion stages. Depending on the nature of the input power supply, the first power stage is an AC-DC power converter with variable output voltage control and a second stage is a DC-AC power inverter with constant current control. The combination of the two stages provides power control of the charging pad and generates AC magnetic flux of ideally constant magnitude over the charging areas within a group of primary windings that are excited.

The invention claimed is: 
     
       1. A planar battery charging system comprising;
 a primary power transmission side formed of an array of primary windings adapted to generate magnetic flux substantially perpendicular to a charging surface; and 
 a secondary power receiving side comprising a secondary winding associated with a battery to be charged and being adapted to receive said magnetic flux when a said secondary winding is placed on said charging surface; 
 wherein a said primary winding is energized by a control circuit comprising a first-stage power converter and a second-stage power inverter, both being on the primary power transmission side, wherein the first-stage power converter is controlled to provide a controlled variable DC-link voltage on the primary power transmission side, and wherein the second-stage power inverter generates a controlled fixed-frequency constant AC current to said primary winding. 
 
     
     
       2. The planar battery charging system as claimed in  claim 1 , wherein the first-stage power converter is current controlled. 
     
     
       3. The planar battery charging system as claimed in  claim 1 , wherein the first-stage power converter is voltage-controlled. 
     
     
       4. The planar battery charging system as claimed in  claim 1 , wherein the current fed to said primary winding is monitored to provide a feedback control of said variable DC-link voltage. 
     
     
       5. The planar battery charging system as claimed in  claim 1 , wherein a step-down transformer is provided between the output off said second-stage power inverter and the primary winding. 
     
     
       6. The planar battery charging system as claimed in  claim 1 , wherein said second-stage power inverter comprises a resonant tank that sets the frequency of said AC current supplied to said winding. 
     
     
       7. The planar battery charging system as claimed in  claim 6 , wherein said second-stage power inverter is switched at a constant frequency that is equal to the frequency of the resonant tank. 
     
     
       8. The planar battery charging system as claimed in  claim 1 , wherein the secondary side is adapted to receive power at an excitation frequency of the primary winding. 
     
     
       9. The planar battery charging system as claimed in  claim 1 , wherein the first-stage power converter comprises one of a boost converter, a buck converter, a flyback converter, a Cuk converter, and a Sepic converter. 
     
     
       10. The planar battery charging system as claimed in  claim 1 , wherein the second-stage power inverter comprises one of a full-bridge type, a half-bridge type, a Class D type, and a Z-source type inverter. 
     
     
       11. The planar battery charging system as claimed in  claim 1 , wherein each primary winding has the same excitation frequency and generates the same AC magnetic flux. 
     
     
       12. The planar battery charging system as claimed in  claim 1 , wherein the AC current supplied to the primary winding is sinusoidal. 
     
     
       13. A planar battery charging system comprising;
 a primary power transmission side formed of an array of primary windings adapted to generate magnetic flux substantially perpendicular to a charging surface;   wherein a said primary winding is energized by a control circuit comprising a first-stage power converter and a second-stage power inverter, both being on the primary power transmission side, wherein the first-stage power converter is controlled to provide a controlled variable DC-link voltage on the primary power transmission side, and wherein the second-stage power inverter generates a controlled fixed-frequency constant AC current to said primary winding.   
     
     
       14. The planar battery charging system as claimed in claim 13, wherein the first-stage power converter is current controlled. 
     
     
       15. The planar battery charging system as claimed in claim 13, wherein the first-stage power converter is voltage-controlled. 
     
     
       16. The planar battery charging system as claimed in claim 13, wherein the current fed to said primary winding is monitored to provide a feedback control of said variable DC-link voltage. 
     
     
       17. The planar battery charging system as claimed in claim 13, wherein a step-down transformer is provided between the output of said second-stage power inverter and the primary winding. 
     
     
       18. The planar battery charging system as claimed in claim 13, wherein said second-stage power inverter comprises a resonant tank that sets the frequency of said AC current supplied to said winding. 
     
     
       19. The planar battery charging system as claimed in claim 18, wherein said second-stage power inverter is switched at a constant frequency that is equal to the frequency of the resonant tank. 
     
     
       20. The planar battery charging system as claimed in claim 13, wherein the first-stage power converter comprises one of a boost converter, a buck converter, a flyback converter, a Cuk converter, and a Sepic converter. 
     
     
       21. The planar battery charging system as claimed in claim 13, wherein the second-stage power inverter comprises one of a full-bridge type, a half-bridge type, a Class D type, and a Z-source type inverter. 
     
     
       22. The planar battery charging system as claimed in claim 1, wherein each primary winding has the same excitation frequency and generates the same AC magnetic flux. 
     
     
       23. The planar battery charging system as claimed in claim 1, wherein the AC current supplied to the primary winding is sinusoidal. 
     
     
       24. The planar battery charging system as claimed in claim 1, wherein the magnetic flux is adapted to be received by a secondary winding of a physically separate secondary power receiving side when said secondary winding is placed on said charging surface, the magnetic flux thereby charging a battery of the second power receiving side. 
     
     
       25. A planar battery charging system comprising;
 a primary-side control circuit adapted to power a physically separate secondary side comprising:
 a first-stage power converter coupled to a primary-side input voltage and configured to generate a variable DC-link output voltage while the power converter is operating in a specified control mode; 
 a second-stage power inverter configured to receive the variable DC-link output voltage from the first-stage power converter and to generate an inverter output current having a constant alternating current (AC) and a fixed frequency; 
   an active group of primary windings included in an array of primary windings, the active group of primary windings configured to receive the output current of the second-stage power inverter to generate magnetic flux in a direction substantially perpendicular to a charging surface of the planar battery charging system.   
     
     
       26. The planar battery charging system as claimed in claim 25, wherein the specified control mode is a current control mode. 
     
     
       27. The planar battery charging system as claimed in claim 25, wherein the specified control mode is a voltage control mode. 
     
     
       28. The planar battery charging system as claimed in claim 25, further comprising a sensor to detect current supplied to the active group of primary windings and provide a feedback control of the variable DC-link output voltage of the first-stage power converter. 
     
     
       29. The planar battery charging system as claimed in claim 25, wherein the second-stage power inverter comprises a resonant tank that sets the frequency of the inverter output current. 
     
     
       30. The planar battery charging system as claimed in claim 29, wherein the second-stage power inverter is switched at a frequency that is equal to the frequency of the resonant tank. 
     
     
       31. The planar battery charging system as claimed in claim 25, wherein the first-stage power converter comprises one of a boost converter, a buck converter, a flyback converter, a Cuk converter, and a Sepic converter. 
     
     
       32. The planar battery charging system as claimed in claim 25, wherein the first-stage power inverter comprises one of a full-bridge type, a half-bridge type, a Class D type, and a Z-source type inverter.