Primary-side power control for inductive power transfer
A method is provided for controlling the output voltage of a pickup in an inductive power transfer (IPT) system without any additional form of communications for feedback from the pickup to the power supply. The method comprising the steps of deriving an estimate of the output voltage of the pickup from the voltage across the primary conductive path, and adjusting the current in the primary conductive path so that the estimated pickup output voltage matches a required pickup output voltage. In particular, an estimate of the pickup output voltage is derived from the magnitude and phase angle of the voltage in the primary conductive path.
1. A method of controlling an output voltage of a pickup in an inductive power transfer (IPT) system comprising the pickup, a power supply, and a primary conductive path, the method comprising steps of:
deriving an estimate of the output voltage of the pickup from a real component of a voltage across the primary conductive path; and
adjusting a current in the primary conductive path so that the estimated pickup output voltage matches a required pickup output voltage, by controlling a voltage supplied to the primary conductive path by the power supply.
2. The method of claim 1 wherein the estimate of the output voltage of the pickup takes into account changes in both an output load and a mutual coupling between the pickup and the primary conductive path.
3. The method of claim 1 wherein the steps of deriving the estimate of the output voltage of the pickup comprises at least determining a phase angle between the voltage across the primary conduction path and the current in the primary conductive path, and using the phase angle to calculate the real component of the voltage across the primary conductive path.
4. The method of claim 3 wherein the steps of deriving the estimate of the output voltage of the pickup further comprises using the phase angle to calculate an imaginary component of the voltage across the primary conductive path, using the imaginary component to estimate a mutual coupling between the pickup and the primary conductive path, and using the phase angle and the mutual coupling to derive the estimate of the output voltage of the pickup.
5. A power controller adapted to perform the method according to claim 1 .
6. A power supply including the power controller according to claim 5 .
7. An inductive power transfer (IPT) system comprising the power supply according to claim 6 , pickup for inductive coupling with the power supply.
8. A power supply for inductive coupling with a pickup via a primary conductive path in an inductive power transfer (IPT) system, the power supply comprising:
an inverter;
a resonant tank electrically coupled with an output of the inverter and comprising a tuning capacitor and the primary conductive path; and
a power controller adapted to deriving an estimate of an output voltage of the pickup from a real component of a voltage across the primary conductive path.
9. The power supply of claim 8 , wherein the power controller is adapted to derive the estimate of the output voltage of the pickup by determining a phase angle between the voltage across the primary conduction path and a current in the primary conductive path, calculating a real component of the voltage across the primary conductive path using the phase angle, deriving the estimate of the output voltage of the pickup from the real component, and controlling a current supplied to the primary conductive path by varying an inverter output voltage such that the estimated pickup output voltage matches a required pickup output voltage.
10. The power supply of claim 9 , wherein the power controller is adapted to use the phase angle to calculate an imaginary component of the voltage across the primary conductive path, use the imaginary component to estimate a mutual coupling between the pickup and the primary conductive path, and use the phase angle and the mutual coupling to derive the estimate of the output voltage of the pickup.
11. The power supply of claim 9 , wherein the inverter comprises two pairs of switches in an H-bridge configuration, and the power controller operates each pair of switches using symmetric square wave driving signals and is adapted to control the inverter output voltage by phase shifting one driving signal with respect to another by an angle of between 180° and 360°.
12. The power supply of claim 9 , wherein the inverter output voltage is controlled using pulse-width modulation.
13. The power supply of claim 9 , wherein the inverter output voltage is controlled using a pre-regulator.
14. An inductive power transfer (IPT) system comprising the power supply according to claim 9 , the primary conductive path, and the pickup inductively coupled with the power supply via the primary conductive path.