Passive Safety Circuits for Wireless Power Transfer

Abstract

A magnetic inductive resonance charging circuit includes a resonant network having an inductive secondary coil that converts a magnetic field received from an inductive primary coil into an alternating current (AC) signal and a synchronous rectifier that rectifies the AC signal to generate a direct current (DC) signal for application to a load. The synchronous rectifier includes a variety of configurations for shunting the AC waveform of an AC current source in the event of a fault. For example, a rectifier controller may hold a pair of normally open switches of the rectifier off and a pair of normally closed switches of the rectifier on to shunt the AC current source when an over-voltage, over-current fault condition or an over-temperature fault condition is detected. Configurations are provided for grounding the capacitive electromagnetic interference produced in the chassis of an electric vehicle when the resonant network is unbalanced.

What is claimed is: 
     
         1 . A magnetic inductive resonance charging circuit, comprising:
 a resonant network comprising an AC current source including an inductive secondary coil that converts a magnetic field received from an inductive primary coil into an alternating current (AC) signal;   a first pair of diodes respectively connected to first and second leads of the AC current source and a second pair of diodes respectively connected to the first and second leads of the AC current source that rectify the AC signal to generate a direct current (DC) signal for application to a load to be charged; and   means for shunting an AC signal current flow out of the AC current source in an event of a fault or loss of rectification control being detected during rectification by the first and second pair of diodes.   
     
     
         2 . A charging circuit as in  claim 1 , wherein the shunting means comprises a first normally closed switch connected in parallel with a first diode of the second pair of diodes and a second normally closed switch connected in parallel with a second diode of the second pair of diodes, the first and second normally closed switches shunting the AC current source in the event of a fault or loss of rectification control. 
     
     
         3 . A charging circuit as in  claim 1 , wherein the shunting means comprises a normally closed safety switch connected between the first and second pairs of diodes, the normally closed safety switch shunting the AC current source in the event of a fault or loss of rectification control. 
     
     
         4 . A charging circuit as in  claim 1 , wherein the resonant network is disconnected from the load and the current flow out of the resonant network is shunted when no power is applied to the first and second pairs of diodes. 
     
     
         5 . A charging circuit as in  claim 1 , wherein the resonant network further comprises first and second balanced capacitors connected in series to respective ends of the secondary coil whereby the AC signal series resonates with the first and second capacitors. 
     
     
         6 . A charging circuit as in  claim 5 , wherein the resonant network comprises an inductive primary coil, a first resonant capacitor in parallel with the primary coil, the secondary coil, a second resonant capacitor in series with the secondary coil at a first end of the secondary coil and a third resonant capacitor in series with the secondary coil at a second end of the secondary coil. 
     
     
         7 . A charging circuit as in  claim 5 , wherein the resonant network comprises an inductive primary coil, a first resonant capacitor in series with the primary coil at a first end of the primary coil, a second resonant capacitor in series with the primary coil at a second end of the primary coil, the secondary coil, a third resonant capacitor in series with the secondary coil at a first end of the secondary coil, and a fourth resonant capacitor in series with the secondary coil at a second end of the secondary coil. 
     
     
         8 . A charging circuit as in  claim 1 , further comprising signal conditioning circuitry that conditions the DC signal into a conditioned DC signal for application to the load. 
     
     
         9 . A charging circuit as in  claim 1 , wherein the resonant network comprises an inductive primary coil, a first resonant capacitor in parallel with the primary coil, the secondary coil, and a second resonant capacitor in parallel with the secondary coil. 
     
     
         10 . A charging circuit as in  claim 1 , wherein the resonant network comprises an inductive primary coil, a first resonant capacitor in series with the primary coil, the secondary coil, and a second resonant capacitor in series with the secondary coil. 
     
     
         11 . A charging circuit as in  claim 1 , wherein the resonant network comprises an inductive primary coil, a first resonant capacitor in parallel with the primary coil, the secondary coil, and a second resonant capacitor in series with the secondary coil. 
     
     
         12 . A charging circuit as in  claim 1 , wherein the resonant network comprises an inductive primary coil, a first resonant capacitor in series with the primary coil, the secondary coil, and a second resonant capacitor in parallel with the secondary coil. 
     
     
         13 . A charging circuit as in  claim 1 , wherein the resonant network comprises an inductive primary coil, a first resonant capacitor in series with the primary coil at a first end of the primary coil, a second resonant capacitor in series with the primary coil at a second end of the primary coil, the secondary coil, and a third resonant capacitor in parallel with the secondary coil. 
     
     
         14 . A charging circuit as in  claim 1 , wherein the resonant network further comprises an inductive primary coil comprising a coil winding disposed on at least one side of an insulative substrate. 
     
     
         15 . A charging circuit as in  claim 14 , further comprising a resonant capacitor connected in series to a first end of the coil winding and a second end of the coil winding being connected to ground or driven by an inverter, the coil winding having a common mode voltage relative to ground of one half a voltage across the resonant capacitor whereby the coil winding is a capacitive electromagnetic interference radiator. 
     
     
         16 . A charging circuit as in  claim 14 , further comprising a first resonant capacitor connected in series to a first end of the coil winding and a second resonant capacitor connected in series to a second end of the coil winding, a midpoint of the coil winding between the first and second ends of the coil winding being virtually ground whereby the coil winding does not capacitively radiate electromagnetic interference. 
     
     
         17 . A charging circuit as in  claim 1 , wherein the secondary coil is mounted on an electric vehicle and the load is a battery of the electric vehicle. 
     
     
         18 . A charging circuit as in  claim 17 , wherein the resonant network is unbalanced so as to radiate capacitive electromagnetic interference (EMI) and the electric vehicle comprises tires having conductive vias that ground the EMI during charging. 
     
     
         19 . A charging circuit as in  claim 17 , wherein the resonant network is unbalanced so as to radiate capacitive electromagnetic interference (EMI) and the electric vehicle comprises a grounding cable that grounds the EMI during charging.