Primary-side power control for inductive power transfer
View Patent ↗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 with an unknown or variable mutual coupling between the pickup and the primary conductive path, the method comprising steps of:
deriving an estimate of the unknown or variable mutual coupling between the primary conductive path and the pickup from a voltage across the primary conductive path;
deriving an estimate of the output voltage of the pickup based at least in part on the voltage across the primary conductive path and the estimated unknown or variable mutual coupling; 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 the unknown or variable 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 and the current in the primary conductive path, using the phase angle to calculate a real component of the voltage across the primary conductive path, and deriving the estimate of the output voltage of the pickup from 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 the unknown or variable mutual coupling between the pickup and the primary conductive path, and using the phase angle and unknown or variable mutual coupling to derive the estimate of the output voltage of the pickup.
5. A power supply comprising an inverter, a resonant tank electrically coupled with an output of the inverter, and a power controller adapted to control operation of the inverter to control an output voltage of a pickup inductively coupled with the power supply, wherein the power controller is adapted to:
derive an estimate of an unknown or variable mutual coupling between a primary conductive path and the pickup from a voltage across the primary conductive path;
derive an estimate of the output voltage of the pickup based at least in part on the voltage across the primary conductive path and the estimated unknown or variable mutual coupling; and
adjust 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.
6. An inductive power transfer (IPT) system comprising a power supply and a pickup for inductive coupling with the power supply, wherein the power supply comprises an inverter, a resonant tank electrically coupled with an output of the inverter, and a power controller adapted to control operation of the inverter to control an output voltage of the pickup inductively coupled with the power supply wherein the power controller is adapted to:
derive an estimate of an unknown or variable mutual coupling between a primary conductive path and the pickup from a voltage across the primary conductive path;
derive an estimate of the output voltage of the pickup based at least in part on the voltage across the primary conductive path and the estimated unknown or variable mutual coupling; and
adjust 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.
7. A power supply for inductive coupling with a pickup via a primary conductive path in an inductive power transfer (IPT) system with an unknown or variable mutual coupling between the pickup and the primary conductive path, 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 derive from a voltage across the primary conductive path an estimate of the unknown or variable mutual coupling between the primary conductive path and the pickup inductively coupled with the power supply in use, and derive an estimate of an output voltage of the pickup based at least in part on the estimated unknown or variable mutual coupling and the voltage across the primary conductive path.
8. The power supply of claim 7 , wherein the power controller is further adapted to derive the estimate of the output voltage of the pickup by determining a phase angle between the voltage across 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 the 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.
9. The power supply of claim 8 , 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 the unknown or variable mutual coupling between the pickup and the primary conductive path, and use the phase angle and unknown or variable mutual coupling to derive the estimate of the output voltage of the pickup.
10. The power supply of claim 7 , 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 an inverter output voltage by phase shifting one driving signal with respect to another by an angle of between 180° and 360°.
11. The power supply of claim 7 , wherein an inverter output voltage is controlled using pulse-width modulation.
12. The power supply of claim 7 , wherein an inverter output voltage is controlled using a pre-regulator.
13. An inductive power transfer (IPT) system comprising the power supply according to claim 7 , the primary conductive path, and the pickup inductively coupled with the power supply via the primary conductive path.