Electronic control method for a planar inductive battery charging apparatus
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.
1. The 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 of 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.