Failsafe safety circuits for wireless power transfer

Abstract

To provide safety circuits that decrease the likelihood of an electric shock caused by a high current source and a high voltage source.SOLUTION: A magnetic inductive resonance charging circuit includes: a resonant network 101 having an inductive secondary coil 104 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 115 may hold a pair of normally open switches 107, 108 of the synchronous rectifier off and a pair of normally closed switches 109, 110 of the synchronous rectifier on to shunt the AC current source when an over-voltage, over-current fault condition in a current and voltage sensor 113 or an over-temperature fault condition in a temperature sensor 117 is detected. The capacitive electromagnetic interference produced in the chassis of an electric vehicle is grounded when the resonant network is unbalanced.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This patent application claims the benefit of U.S. Provisional Patent Application No. 63 / 010,771, filed April 16, 2020, and U.S. Patent Application No. 16 / 952,933, filed November 19, 2020, entitled "Safety Circuit for Wireless Power Transmission," filed by Wolgemuth, John, and incorporated herein by reference in their entireties.

[0002] This disclosure relates to the transfer of electrical energy by resonant induction, and more particularly to system designs, circuit architectures, and safety circuit implementation details that maximize safety in high-power wireless power transfer systems. [Background technology]

[0003] Inductive power transfer has many important applications across many industries and markets. The use of inductive power transfer to charge capacitors such as batteries is becoming increasingly common in portable, low-power consumer devices.

[0004] Transferring power between coils using magnetic resonance is well known. As described by Faraday's law of induction and Lenz's law, alternating current in a primary (also called a transmitter) coil creates a magnetic field that propagates across an air gap and generates a corresponding, opposite current in a secondary (also called a receiver) coil. To charge a battery, the induced alternating current (AC) is converted to direct current (DC). A rectifier converts the alternating current (AC), which periodically reverses direction, into direct current (DC), which flows in only one direction.

[0005] Depending on the AC frequency, desired DC voltage, or desired efficiency, passive rectifiers (diode-based) or active rectifiers (MOSFET or switch-based) may be used. Rectifiers typically require additional circuitry to provide the uniform, steady-state voltage and / or voltage level (DC / DC) conversion required for battery charging.

[0006] As the demand for faster charging increases, the need for higher power charging leads to the use of higher voltages and currents. High current and voltage sources pose an increased safety hazard, and safety circuits are desired to reduce the chance of electric shock. Summary of the Invention [Means for solving the problem]

[0007] Various details regarding embodiments of the present subject matter are provided in the accompanying drawings and the detailed description that follows.

[0008] The systems and methods described herein enhance safety against electric shock during wireless power transfer by providing a mechanism for shunting power in the event of a fault. In an exemplary embodiment, a magnetic inductive resonant charging circuit is provided. The magnetic inductive resonant 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 produce a direct current (DC) signal for application to a load to be charged. The synchronous rectifier further includes means for shunting the AC waveform in the event of a fault. In an exemplary configuration, the secondary coil is attached to an electric vehicle and the load is a battery of the electric vehicle.

[0009] In an exemplary embodiment, the resonant network includes first and second balancing capacitors connected in series to each end of the secondary coil, such that the AC signal resonates in series with the first and second capacitors. The synchronous rectifier includes a pair of normally open switches and a pair of normally closed switches, one of the pair of normally open switches and one of the pair of normally closed switches connected to the first balancing capacitor, and the other of the pair of normally open switches and the other of the pair of normally closed switches connected to the second balancing capacitor. The shunting means includes the normally closed switches shunting the secondary coil in the event of the fault. The normally open switches are configured to prevent short-circuiting of the load in the event of the fault. A signal conditioning circuit may be provided to condition the DC signal and output a conditioned DC signal for application to the load.

[0010] In an exemplary embodiment, a first current and voltage sensor may be provided to monitor the AC signal input from the resonant circuit to the synchronous rectifier, and a second current and voltage sensor may be provided to monitor the regulated DC waveform applied to the load. A rectifier controller may be phase-locked to the AC signal output by the resonant network in response to values ​​measured by the first and second current and voltage sensors, and may provide control signals to control switching of the pair of normally open switches and the pair of normally closed switches in response to the measured values. A temperature sensor may be provided to detect an overtemperature fault condition of the synchronous rectifier and provide a detection signal to the rectifier controller.

[0011] In another exemplary embodiment, the charging circuit further includes a charge processor that receives the input AC signal amplitude, the input AC signal frequency, the regulated DC waveform voltage, the regulated DC waveform current, and / or the temperature of the synchronous rectifier from the rectifier controller and commands operation of the rectifier controller to, for example, provide protection from a detected fault condition. The charge processor instructs the rectifier controller to turn the pair of normally open switches and the pair of normally closed switches on and off approximately at zero crossings of the AC signal from the resonant network when the AC signal frequency is within an acceptable range, the root mean square of the AC signal is above a threshold, and no fault is detected. On the other hand, when a fault condition is detected, the charge processor disables the rectifier controller and holds the pair of normally open switches off and the pair of normally closed switches on. For example, if an over-voltage, over-current fault condition is detected by the second current and voltage sensor or an over-temperature fault condition is detected by the temperature sensor, the rectifier controller may hold the pair of normally open switches off and the pair of normally closed switches on.

[0012] In a further exemplary embodiment, the resonant network may include an alternating current (AC) current source, and the synchronous rectifier may include a first pair of diodes connected to first and second leads of the AC current source, respectively, and a second pair of diodes connected to the first and second leads of the AC current source, respectively. The shunting means may include 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 shunt the AC current source in the event of the fault.

[0013] In a further exemplary embodiment, the resonant network may include an alternating current (AC) current source, and the synchronous rectifier may include a first pair of diodes connected to first and second leads of the AC current source, respectively, and a second pair of diodes connected to the first and second leads of the AC current source, respectively. The shunting means may include 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 the fault.

[0014] In a further exemplary embodiment, the resonant network may include an alternating current (AC) current source, and the synchronous rectifier may include a first pair of normally open switches connected to first and second leads of the AC current source, respectively, and a second pair of normally open switches connected to the first and second leads of the AC current source, respectively. The shunting means may include a normally closed safety switch connected between the first and second pairs of normally open switches, the normally closed safety switch shunting the AC current source in the event of the fault.

[0015] In exemplary embodiments, the resonant network can be balanced or unbalanced. A variety of configurations can be used.

[0016] The resonant network may be a balanced parallel-parallel resonant network (PPRN) having 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.

[0017] The resonant network may be an unbalanced series-series resonant network (SSRN) having 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.

[0018] The resonant network may be an unbalanced parallel-series resonant network (PSRN) having 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.

[0019] The resonant network may be an unbalanced series-parallel resonant network (SPRN) having 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.

[0020] The resonant network may be a balanced PSRN having 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 induction coil, and a third resonant capacitor in series with the secondary coil at a second end of the secondary coil.

[0021] The resonant network may be a balanced SPRN having 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.

[0022] The resonant network may be a balanced SSRN having 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 the first end of the secondary coil, and a fourth resonant capacitor in series with the secondary coil at the second end of the secondary coil.

[0023] In an exemplary embodiment, the resonant network may further include an inductive primary coil having a rectangular coil winding, the rectangular coil winding being disposed on at least one side of an insulating substrate. The resonant capacitor may be connected in series with a first end of the rectangular coil winding, and a second end of the rectangular coil winding may be connected to ground. As a result, the rectangular coil winding has a common-mode voltage with respect to ground that is half the voltage of the resonant capacitor, which may cause the rectangular coil winding to act as a capacitive electromagnetic interference radiator.

[0024] In another exemplary embodiment, a first resonant capacitor may be connected in series with a first end of the rectangular coil winding, and a second resonant capacitor may be connected in series with a second end of the rectangular coil winding, such that the midpoint between the first and second ends of the rectangular coil winding is substantially at ground, thereby preventing the rectangular coil winding from radiating capacitive electromagnetic interference.

[0025] In further exemplary embodiments, techniques are provided for mitigating capacitive electromagnetic interference (EMI) radiated when the resonant network is unbalanced. According to a first technique, the electric vehicle is equipped with tires having conductive vias that ground the EMI during charging. According to a second technique, the electric vehicle includes a ground cable that grounds the EMI during charging. According to a third technique, the electric vehicle includes circuitry powered by the electric vehicle battery that cancels out-of-phase voltages during charging.

[0026] According to another aspect, a magnetic inductive resonant charging circuit for charging a battery of an electric vehicle is provided, the charging circuit including: a resonant network having an inductive secondary coil in an electric vehicle, the inductive secondary coil converting a magnetic field received from an inductive primary coil into an alternating current (AC) signal, the resonant network being unbalanced and thereby radiating capacitive electromagnetic interference (EMI); a synchronous rectifier rectifying the AC signal to generate a direct current (DC) signal for application to the battery of the electric vehicle; and means for grounding the EMI during charging. In an exemplary embodiment, the means for grounding the EMI during charging may include a tire of the electric vehicle, the tire including a conductive via for grounding the EMI during charging. Alternatively, the means for grounding the EMI during charging may include a ground cable connected to the electric vehicle to ground the EMI during charging. In another embodiment, the means for grounding the EMI during charging may include circuitry powered by the battery of the electric vehicle for canceling out-of-phase voltages during charging.

[0027] This Summary section is provided to introduce aspects of the inventive subject matter in a simplified form and follows the main body of the Detailed Description, which further describes the inventive subject matter. This Summary section is not intended to identify essential or required features of the claimed subject matter, nor is the particular combination and order of elements listed in this Summary section intended to limit the elements of the claimed subject matter. Rather, it will be understood that the following section provides summarized illustrations of some of the embodiments described in the Detailed Description below. [Brief explanation of the drawings]

[0028] The foregoing and other beneficial features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings. [Figure 1] FIG. 1 shows a high-level circuit embodiment of a safety-enhanced magnetically resonant inductive system. [Figure 2]Figure 2 shows a schematic diagram of a typical safety circuit for a voltage source with a reactive load. [Figure 3] FIG. 3 shows a schematic diagram of a typical safety circuit for a current source with a reactive load. [Figure 4A] FIG. 4A illustrates a schematic diagram of switch-based synchronous rectification of an AC voltage source with a complex load impedance. [Figure 4B] FIG. 4B illustrates a schematic diagram of switch-based synchronous rectification of an AC current source with a complex load impedance. [Figure 4C] FIG. 4C illustrates a schematic diagram of switch-based synchronous rectification of an AC voltage source with a DC voltage load. [Figure 4D] FIG. 4D illustrates a schematic diagram of switch-based synchronous rectification of an AC current source with a DC voltage load. [Figure 5A] FIG. 5A shows a schematic diagram of passive rectification of an AC voltage source with an impedance load. [Figure 5B] FIG. 5B shows a schematic diagram of passive rectification of an alternating current source with an impedance load. [Figure 5C] FIG. 5C shows a schematic representation of an alternative embodiment of passive rectification of an alternating current source with an impedance load. [Figure 6] FIG. 6 shows a schematic representation of an alternative embodiment of switch-based synchronous rectification of an alternating current source with an impedance load. [Figure 7A] FIG. 7A shows a schematic of a parallel-parallel resonant inductive circuit. [Figure 7B] FIG. 7B shows a schematic of an unbalanced series-series resonant inductive circuit. [Figure 7C] FIG. 7C shows a schematic of a hybrid parallel-unbalanced series resonant inductive circuit. [Figure 7D] FIG. 7D shows a schematic diagram of a hybrid unbalanced series-parallel resonant inductive circuit. [Figure 7E] FIG. 7E shows a schematic of a hybrid parallel-balanced series resonant inductive circuit. [Figure 7F] FIG. 7F shows a schematic diagram of a hybrid balanced series-parallel resonant inductive circuit. [Figure 7G] FIG. 7G shows a schematic of a balanced series-series resonant inductive circuit. [Figure 8] FIG. 8 shows the geometry of a coil for use in a magnetic resonant inductive power system. [Figure 9] FIG. 9 shows a schematic of an unbalanced circuit equivalent to a planar coil for use in a resonant inductive power system. [Figure 10] FIG. 10 shows a schematic of a balanced circuit equivalent to a planar coil used in a resonant inductive power system. [Figure 11] FIG. 11 shows the parasitic electric fields for a resonant inductive power system of an electric vehicle with an unbalanced resonant network. DETAILED DESCRIPTION OF THE INVENTION

[0029] Exemplary embodiments of the present invention are described with reference to the figures. The current source safety circuits and related methods described herein may be more readily understood by reference to the following detailed description, provided in connection with the accompanying drawings and examples that form a part of this disclosure. It will be understood that this description is not limited to the specific products, methods, conditions, or parameters described and / or illustrated herein, and that the terminology used herein is intended to describe particular embodiments by way of example only and is not intended to limit the claimed subject matter. Similarly, any descriptions of possible mechanisms or modes of action or reasons for improvement are for illustrative purposes only, and the subject matter described herein should not be limited by the correctness or incorrectness of such proposed mechanisms or modes of action or reasons for improvement. It will be understood that throughout this text, the description refers to both methods and systems / software for implementing such methods.

[0030] A detailed description of exemplary embodiments will now be provided with reference to Figures 1-11. While this description provides detailed examples of possible embodiments, it should be noted that these details are intended to be illustrative and in no way limit the scope of the inventive subject matter.

[0031] In wireless power transfer systems using open-air transformers, the resonant network (i.e., primary / transmitter and secondary / receiver) used for magnetic / wireless charging forms an AC current source for rectification in the vehicle. The presence of a current source nearly reverses the voltage-source-specific provisions of power supplies in domestic and industrial scenarios. The key difference between these scenarios is that in voltage sources, short circuits are bad. As a result, power conversion topologies are built with normally-off devices to avoid short circuits. However, with current sources, the opposite is true: open circuits are bad. This means that typical rectification techniques are undesirable. Straight passive (e.g., diode-based) rectifiers offer no protection. Traditional synchronous rectifiers can offer protection, but only if there is a reliable means of powering the device and turning it on.

[0032] FIG. 1 shows a high-level schematic diagram of a DC battery charging circuit using magnetic induction resonance. Resonant network 101 (also known as the receiver or secondary) includes an inductive secondary coil 104 and balancing capacitances 105 and 106. Secondary coil 104 converts a magnetic field from a charging transmitter (not shown) into an alternating current (AC) signal that resonates in series with balancing capacitances 105 and 106 in the voltage domain. As described below with respect to FIGS. 7A-7G, the primary side of the resonant network can be balanced or unbalanced. The AC signal from resonant network 101 is then rectified into a direct current (DC) signal in rectification stage 102. Rectification stage 102 includes a synchronous rectification circuit using a pair of normally open (NO) switches 107 and 108 and a pair of normally closed (NC) switches 109 and 110. As explained below, a pair of NC switches 109 and 110 function to shunt the secondary coil 104 in the event of a fault. The DC signal is passed to a conditioning circuit 111, which outputs a regulated DC signal that is used to charge a battery 112.

[0033] The rectifier controller 115 phase-locks to the resonant network current at the first current and voltage sensor 113 as a reference (e.g., with respect to detected zero crossings) for controlling the timing of the rectifier switches 107-110. The rectifier controller 115 (nominally a field-programmable gate array (FPGA) or conventional microcomputer) generates estimates of the amplitude, frequency, and instantaneous phase of the input AC waveform from the secondary coil 104 via the first current and voltage sensor 113, as long as the AC waveform has sufficient amplitude and the switching frequency is within its acquisition range. The rectifier controller 115 also monitors the amplitude of the output DC current waveform applied to the battery 112 via the second current and voltage sensor 114.

[0034] The vehicle charging processor 116 (typically implemented as software running on a microprocessor) can handle communication between internal subsystems (such as the wireless power transfer (WPT) system) and external vehicle systems via an interface (e.g., a controller area network (CAN) bus) and command the operation of the rectifier controller 115. For example, when queried by the vehicle charging processor 116, the rectifier controller 115 may report the amplitude of the input AC signal, the frequency of the input AC signal, the voltage and current of the DC output, and the temperature of the switching device. If the reported input switching frequency is within an acceptable closed range (e.g., 79 kHz to 90 kHz), the AC root mean square (RMS) exceeds a threshold (e.g., 5 amps), and no faults are detected, the vehicle charging processor 116 can instruct the rectifier controller 115 to turn the upper pair of NO switches 107 and 108 and the lower pair of NC switches 109 and 110 on and off at the appropriate zero crossings of the input AC waveform to maximize rectification efficiency. The nominal state is "start" or "safe," in which case the upper pair of NO switches 107 and 108 are open and the lower pair of NC switches 109 and 110 are closed. When the secondary coil 104 is producing a positive signal, the first set of switches 107 and 109 is open and the second set of switches 108 and 110 is closed. When the signal from the secondary coil 104 reverses, the first set of switches 107 and 109 is closed and the second set of switches 108 and 110 is open. This sequence is repeated to produce an output signal that is mathematically the absolute value of the input AC signal.

[0035] When disabled by vehicle charging processor 116, rectifier controller 115 holds the pair of upper NO switches 107 and 108 off and the pair of lower NC switches 109 and 110 on. Additionally, if an over-voltage, over-current fault condition is detected by current and voltage sensor 114, or an over-temperature fault condition is detected by temperature sensor 117, rectifier controller 115 holds the pair of upper NO switches 107 and 108 off and the pair of lower NC switches 109 and 110 on to shunt current from secondary coil 104.

[0036] The rectifier controller 115 monitors the output DC voltage from the rectifier stage 102 via a current and voltage sensor 114. The rectifier controller 115 also measures the output DC current via the current and voltage sensor 114 and reports the output DC current to the vehicle charging processor 116, allowing the system to calculate the total power delivered to the battery 112. Additionally, the rectifier controller 115 may monitor the temperature sensor or sensors (e.g., a thermistor or a network of thermistors) 117 that measure the temperature of the mounting plates of the rectifier switching devices 107-110. The mounting plate temperature represents the case temperature of the switching devices 107-110, which is related to the power dissipated by the switching devices 107-110.

[0037] When combined with a series-series resonant transmitter (not shown), resonant network 101 is an AC current source. An open-circuit condition of resonant network 101 would create a dangerous condition. However, the selection of NO switches 107 and 108 and NC switches 109 and 110 of synchronous rectifier stage 102 results in an intrinsically safe system. Under normal conditions, NC switches 109 and 110 can be closed accidentally or specifically controlled to shunt secondary coil 104, thus providing a means to shunt the AC current source of resonant network 101. NO switches 107 and 108 prevent shorting of output network 103, and in particular battery 112.

[0038] In the event of a fault, battery 112 is disconnected from signal conditioning circuit 111, the current into conditioning circuit 111 remains unchanged, but the current out of conditioning circuit 111 drops to zero. This causes the voltage across conditioning circuit 111 and rectification stage 102 to increase at a rate proportional to the rectified current and the impedance of conditioning circuit 111.

[0039] Rectifier controller 115 monitors voltage and / or current using current and voltage sensor 114 to detect disconnection of battery 112. In the event of a fault, rectifier controller 115 can respond by opening NO switches 107 and 108 and closing NC switches 109 and 110, which acts to disconnect resonant network 101 from regulation circuit 111 and battery 112. Power transfer will immediately cease when the flow of rectified current from rectification stage 102 to regulation circuit 101 and battery 112 is interrupted by NO switches 107 and 108 and current flow from resonant network 101 is shunted to NC switches 109 and 110.

[0040] In the passive state, with no control force operating the controller or synchronously commutating, NO switches 107 and 108 open output network 103 and NC switches 109 and 110 shunt resonant network 101. This protects the charger, load and service personnel from spurious energy picked up by resonant network 101, whether the spurious energy is accidental or intentional.

[0041] FIG. 2 shows a schematic of a typical safety circuit for a voltage source with a reactive load. Figure 2 illustrates a typical voltage source supply protection solution, in which voltage source 201 and load 202 share a common ground 203. Voltage source 201 provides a fixed voltage that remains constant relative to the source current. The source current is set by the load impedance of load 202. Current sensor 205 monitors the source current. If the source current exceeds an acceptable limit, current sensor 205 provides protection by triggering normally open switch 204 to an open state. Normally open switch 204 remains open until reset. When normally open switch 204 is triggered to disconnect, the voltage and current across load 202 are forced to zero. The normally open (NO) switch 204 and current sensor 205 shown herein are just one implementation option, with a variety of widely used relays, circuit breakers, and fuses. As shown in FIG. 2, virtually all power supply and distribution networks operate from a voltage source and implement some type of current limiting scheme using some form of breaker or fuse. It will be appreciated that in a voltage source power system, an open circuit is good and a short circuit is bad.

[0042] The current source supply embodiment shown in FIG. 3 is less common. A constant current power supply should faithfully represent the best practices for safety protection found in more common voltage source power supplies. It will be appreciated that in a current source power system, unlike a voltage source power system, an open circuit is not good and a shunt (intentional short circuit) is a good practice. Therefore, the different embodiments of the safety circuit described herein should be considered based on whether the power supply is a current source power system or a voltage source power system.

[0043] Figure 3 shows a schematic of a typical safety circuit for a current source with a reactive load. Current source 301 supplies current to reactive load 302 regardless of the voltage across it. In this example, all circuit paths share a common ground 303. Current source 301 provides a fixed current that is invariant with voltage and current.

[0044] A potential-sensitive disconnector is placed in parallel with the reactive load 302 to provide current shunting and isolation of the load from the source (and vice versa). The normally closed (NC) switch shunt 304 and voltage sensor 305 shown in Figure 3 are just one implementation option of commonly used shunting means involving various switches, relays, circuit breakers, and fuses. When the NC switch shunt 304 is triggered by the voltage sensor 305, the NC switch shunt 304 is opened, forcing the voltage and current flow through the reactive load 302 to zero.

[0045] 4A-4D all show alternative embodiments of the safety rectifier circuitry and additional subsystems required for wireless power transfer.

[0046] FIG. 4A illustrates a schematic diagram of switch-based synchronous rectification of an AC voltage source with a complex load impedance. Specifically, FIG. 4A illustrates a conventional AC voltage source and a safety-enhanced synchronous rectification circuit to form a direct current (DC) voltage source. AC voltage source 401 is synchronously rectified by a set of normally open (NO) switches 402, 403, 404, and 405. Power conditioning network 406 filters the rectified DC voltage to form a DC voltage source for load 407. In the event of a fault, the NO switches open as a fault, disconnecting and protecting load 407 from AC voltage source 401.

[0047] FIG. 4B schematically illustrates switch-based synchronous rectification of an AC current source with a complex load impedance in an exemplary embodiment. Specifically, FIG. 4B illustrates an AC current source and a safety-enhanced synchronous rectification circuit for forming a DC current source. AC current source 410 is synchronously rectified by a set of NO switches 403 and 404 and normally closed (NC) switches 408 and 409. Power conditioning network 406 filters the rectified current into a DC current source for load 407. AC current source 410 requires the set of NC switches 408 and 409 to be open to provide a means to shunt current in the event of a fault. Under a fault condition, closed switches 408 and 409 isolate load 407 from AC current source 410, preventing backfeed power.

[0048] FIG. 4C illustrates a schematic diagram of switch-based synchronous rectification of an AC voltage source with a DC voltage load. Specifically, FIG. 4C illustrates an AC voltage source and a safety-enhanced synchronous rectification circuit for forming a DC voltage source for battery charging. AC voltage source 401 is synchronously rectified by a set of NO switches 402, 403, 404, and 405. Power conditioning network 406 filters the rectified voltage into a DC voltage source for power conversion stage 411. Power conversion stage 411 adapts the DC voltage source to the voltage required to charge battery 412.

[0049] FIG. 4D schematically illustrates switch-based synchronous rectification of an AC source with a DC voltage load in an exemplary embodiment. Specifically, FIG. 4D illustrates an AC current source and a safety-enhanced synchronous rectification circuit for forming a DC voltage source for battery charging. AC current source 410 is synchronously rectified by a set of NO switches 402 and 403 and NC switches 408 and 409. Power conditioning network 406 filters the rectified current into a DC current source for battery 412. AC current source 410 requires the set of NC switches 408 and 409 to provide a means to shunt the current in the event of a fault. However, because this system is powered by the current source, power conversion stage 411 of FIG. 4C is not required for battery charging.

[0050] FIG. 5A schematically illustrates passive rectification of an AC voltage source with an impedance load. Specifically, FIG. 5A schematically illustrates a conventional passive full-wave rectifier circuit for AC voltage source 501. Diodes 502, 503, 504, and 505 function as unidirectional gates to generate full-wave rectification of the AC signal. Power conditioning stage 506 serves to smooth the rectifier voltage output applied to load 507, allowing it to charge.

[0051] As with all diode circuits, the reverse recovery time and voltage drop under forward bias conditions affect the efficiency of the rectifier circuit. Passive rectifier circuits do not require a controller stage. However, in the event of a fault, the AC voltage source 501 remains connected to the load 507 through the power conditioning stage 506, exposing the load 507 to the voltage source fault (and vice versa).

[0052] FIG. 5B schematically illustrates passive rectification of an AC current source with an impedance load in an exemplary embodiment. Specifically, FIG. 5B illustrates a hybrid embodiment of a safety-enhanced circuit for rectifying an AC current source 508. Full-bridge passive rectifier diodes 502, 503, 510, and 512 are supplemented by normally closed (NC) switches 509 and 511. Diodes 502, 503, 510, and 512 function as unidirectional gates to generate full-wave rectification. NC switches 509 and 511 act as shunts in the event of a fault, preventing overvoltage damage between AC current source 508 and diodes 502, 503, 510, and 512. Power conditioning stage 506 helps smooth the rectifier voltage output applied to load 507, allowing for charging of load 507.

[0053] As with all diode-based rectifier circuits, the reverse recovery time and voltage drop under forward bias conditions affect the efficiency of the rectifier circuit. This passive rectifier circuit does not require a controller stage, but does require a controller (e.g., rectifier controller 115) to command the NC switches 509 and 511.

[0054] FIG. 5C schematically illustrates an alternative passive rectification of an AC current source with an impedance load in an exemplary embodiment. FIG. 5C illustrates an alternative semi-passive embodiment of a safety-enhanced full-wave rectifier circuit for an AC current source 508. Diodes 502, 503, 510, and 512 function as unidirectional gates to generate full-wave rectification. Power conditioning stage 506 helps smooth the rectifier voltage output applied to load 507, allowing it to charge. In this embodiment, a normally closed (NC) shunt switch 513 is placed in the circuit. In the event of a fault or command event, shunt switch 513 shunts the current in the rectifier circuit, preventing damage to power conditioning stage 506 and load 507.

[0055] This embodiment is a cheaper implementation with simpler control, but it is less efficient. Additionally, it results in high dV / dt across the isolated control boundary of the shunt switch 513. As with all diode-based rectifier circuits, the reverse recovery time and voltage drop under forward bias conditions affect the efficiency of the rectifier circuit.

[0056] FIG. 6 schematically illustrates an alternative switch-based synchronous rectification of an AC current source with an impedance load in an exemplary embodiment. Specifically, FIG. 6 illustrates an alternative safety circuit for active rectification of an AC current source 601. A power conditioning stage 606 serves to smooth the rectifier voltage output for application to a charged load 607. Full-wave rectification is achieved by alternating at the zero crossings of the sinusoidal output of the AC current source 601. A normally closed (NC) safety switch 608 is installed between upper normally open (NO) rectifier switches 602 and 604 and lower normally open (NO) rectifier switches 603 and 605 to provide a means for shunting current within the rectifier circuit in the event of a fault or command option, preventing damage to the power conditioning stage 606 and the load 607.

[0057] In the event of a fault condition or loss of commutation control, NO commutation switches 602, 603, 604, and 605 fail open (or are commanded open), while NC safety switch 608 fails closed. Thus, current is shunted back to AC current source 601 while the load is isolated by NC safety switch 608. This embodiment reduces the demand on normally closed (NC) switches by using an additional switch 608.

[0058] In resonant inductive wireless charging, there are four possible two-pole networks: parallel-parallel resonant network (PPRN) and series-series resonant network (SSRN). Galvanic isolation also allows for the formation of parallel-series resonant network (PSRN) and series-parallel resonant network (SPRN). PPRN, PSRN, and SPRN all behave as AC voltage-controlled voltage sources (VCVS) when the load impedance is large compared to the network impedance, and as AC voltage-controlled current sources (VCCS) when the load impedance is small compared to the network impedance. SSRN, on the other hand, behaves as a VCCS for all load impedances. A constant-voltage load, such as a battery, behaves as a variable load impedance as the power level changes. A battery behaves as a high-impedance load at low power and as a low-impedance load at high power. At high power, all four resonant networks behave as VCCSs.

[0059] When operating as a VCCS, the transconductance (G) of the PPRN is k / (w*L) in units of Amperes / Volt, where k is the magnetic coupling coefficient of the primary and secondary inductors in the range 0 to 1 and is unitless. w is the resonant frequency of the network in radians / second, and L is the geometric mean of the primary and secondary inductors in Henrys. When operating as a VCCS, the G of the PSRN, SPRN, and SSRN is 1 / (w*L*k). This means that for a fixed G, the PPRN inductors have a value of k 2 and the PPRN capacitor is k -2 This is undesirable because the capacitor is a much more expensive component.

[0060] A resonant network resonates an amount of power, S, proportional to P / k, where P is the power passing through the network. For typical values ​​of k (e.g., 0.05 to 0.2), S is 5 to 20 times higher than P. In the parallel resonant branch, the resonant power is seen as a current through the capacitive and inductive elements. In the series resonant branch, the resonant power is seen as an additional voltage across the capacitive and inductive elements. For example, in a 500V, 125A system with k=0.1, parallel resonance resonates at 125A / 0.1 or 1,250A across the inductor and capacitor, while series resonance resonates at 500V / 0.1 or 5,000V across the inductor and capacitor. Series resonance is preferable because higher voltages require more insulation, while higher currents require more conductors; higher voltages allow for lighter, more compact products.

[0061] With these considerations in mind, the PSRN, SPRN, and SSRN can each have both balanced and unbalanced topologies. The PPRN has only a balanced topology. Each of these topologies is shown in Figures 7A-7G.

[0062] 7A shows a schematic diagram of a balanced PPRN circuit in an exemplary embodiment. The resonant network includes a ground induction coil 701, a ground parallel resonant capacitor 703, a vehicle induction coil 702, and a vehicle parallel resonant capacitor 704.

[0063] 7B shows a schematic diagram of an unbalanced SSRN circuit in an exemplary embodiment. The resonant network includes a ground induction coil 701, a ground series resonant capacitor 705, a vehicle induction coil 702, and a vehicle series resonant capacitor 706.

[0064] 7C shows a schematic diagram of an unbalanced PSRN circuit in an exemplary embodiment. The resonant network includes a ground induction coil 701, a ground parallel resonant capacitor 707, a vehicle induction coil 702, and a vehicle series resonant capacitor 708.

[0065] 7D shows a schematic diagram of an unbalanced SPRN circuit in an exemplary embodiment. The resonant network includes a ground induction coil 701, a ground series resonant capacitor 709, a vehicle induction coil 702, and a vehicle parallel resonant capacitor 710.

[0066] 7E shows a schematic of a balanced PSRN circuit in an exemplary embodiment. The resonant network includes a ground induction coil 701, a ground parallel resonant capacitor 711, a vehicle induction coil 702, and a pair of vehicle series resonant capacitors 712 and 713.

[0067] 7F shows a schematic of a balanced SPRN circuit in an exemplary embodiment. The resonant network includes a ground induction coil 701, a pair of ground series resonant capacitors 714 and 715, a vehicle induction coil 702, and a vehicle parallel resonant capacitor 716.

[0068] 7G shows a schematic of a balanced SSRN circuit in an exemplary embodiment. The resonant network includes a ground induction coil 701, a pair of ground series resonant capacitors 717 and 718, a vehicle induction coil 702, and a pair of vehicle series resonant capacitors 719 and 720.

[0069] FIG. 8 illustrates the geometry of a planar coil 801 for use as a primary coil in a magnetically resonant inductive power system in an exemplary embodiment. While shown as a rectangular coil, other shapes (e.g., a classic round coil or a rectangle) are possible. The coil windings 803 are disposed on an insulating substrate 805 and may include individual conductive ribbons (e.g., a printed circuit board), insulated wire strands (e.g., Litz wire), etc. Vias 802 and 804 allow connection to other coils on the other side of the insulating substrate 805.

[0070] FIG. 9 shows a schematic diagram of an unbalanced circuit equivalent to planar coil 801 used in a series resonant network 901 in an exemplary embodiment. Series resonant network 901 is a transmitter. Terminals 906 and 907 of the network are connected to an inverter. Resonant capacitor 905 has a high-voltage, high-frequency voltage across it when series resonant network 901 resonates. This same voltage appears across inductor 903. First terminal 904 of inductor 903 is effectively held at ground potential. Second terminal 902 of inductor 903 is exposed to the full voltage of resonant capacitor 905 relative to ground. That is, the voltage across inductor 903 has a common-mode voltage, relative to ground, that is half the voltage across resonant capacitor 905, making inductor 903 a capacitive electromagnetic interference (EMI) radiator. In this configuration, techniques to mitigate EMI emissions are desirable, as discussed below with respect to FIG. 11.

[0071] FIG. 10 shows a schematic diagram of a balanced circuit equivalent to planar coil 801 used in series resonant network 1001 in an exemplary embodiment. Series resonant network 1001 is also a transmitter. Terminals 1007 and 1008 of the network are connected to an inverter. Capacitors 1005 and 1006 have high-voltage, high-frequency voltages across them when series resonant network 1001 resonates. The sum of these voltages appears across inductor 1003. However, because series resonant network 1001 is balanced, the midpoint of inductor 1003 between terminals 1002 and 1004 is essentially grounded. Therefore, there is a differential voltage across inductor 1003, but no high-frequency common-mode voltage to ground. Inductor 1003 does not radiate capacitive EMI and does not require any EMI handling mechanisms.

[0072] FIG. 11 illustrates the parasitic electric fields for a resonant inductive power system of an electric vehicle 1101 with an unbalanced resonant network that leads to EMI radiation in an exemplary embodiment. The electric vehicle 1101 has a small amount of conductance between the chassis 1106 and ground 1108 through the tires 1102. The high-frequency admittance between the chassis 1106 and ground 1108 is dominated by the capacitance between the chassis 1106 and ground 1108. Common-mode capacitive EMI generated by the transmitter 1104 or receiver 1103 must be minimized because the electric field 1105 generated across the gap 1107 between the chassis 1106 and ground 1108 excites the capacitance and induces a voltage on the chassis 1106. At the very least, this capacitive coupling can exacerbate EMI problems and, at worst, can pose a shock hazard.

[0073] Chassis voltage can be reduced by adding a conductive path to ground, which acts as a means of grounding EMI during charging. The tire's already conductive material (carbon black) can be reinforced by adding low resistance conductive vias to the tire material. Chassis voltage can also be reduced during charging by placing a "tail" on the ground cable or wire. Chassis voltage can also be reduced by adding circuitry powered by the wireless charging system or vehicle battery system that cancels out-of-phase voltages during charging.

[0074] Those skilled in the art will appreciate that the embodiments described herein provide various means for shunting the DC waveform in the event of a fault to minimize the possibility of electric shock during charging. This technique can be used with balanced or unbalanced resonant network topologies. The rectifier circuit may include diodes and / or switches in a configuration designed to shunt power in the event of a fault, leading to improved safety during the charging process, particularly in high-power transmission applications such as charging electric vehicles.

[0075] As described herein, logic, commands, or instructions implementing aspects of the methods described herein can be provided in computing systems, including any number of computing system form factors, such as desktop or notebook personal computers, mobile devices such as tablets, netbooks, and smartphones, as well as client terminals and server-hosted machine instances. Other embodiments described herein include incorporating the techniques described herein into other forms, including other forms of programmed logic, hardware configurations, or distinct components or modules comprising apparatuses with respective means for performing the functions of such techniques. Each algorithm used to perform the functions of such techniques may include some or all of the sequences of electrical operations described herein, or other aspects shown in the accompanying drawings and the following detailed description. Such systems and computer-readable media containing instructions implementing the methods described herein also constitute exemplary embodiments.

[0076] In one embodiment, the monitoring and control functions described herein may be implemented in software. Software may consist of computer-executable instructions stored on one or more computer-readable media or storage devices, such as one or more non-transitory memories or other types of hardware-based storage devices, local or networked. Furthermore, such functions correspond to modules, which may be software, hardware, firmware, or any combination thereof. Where appropriate, multiple functions may be performed by one or more modules, and the described embodiment is merely exemplary. Software may be executed on a digital signal processor, ASIC, microprocessor, or other type of processor operating on a computer system, such as a personal computer, server, or other computer system, transforming such a computer system into a specifically programmed machine.

[0077] An embodiment as described herein may include or operate with a processor, logic, or a number of components, modules, or mechanisms (herein "modules"). A module is a tangible entity (e.g., hardware) capable of performing specific operations and may be configured or arranged in a particular manner. In one example, a circuit may be arranged (e.g., internally or relative to an external entity, such as other circuitry) in a manner designated as a module. In one example, all or part of one or more computer systems (e.g., standalone, client, or server computer systems) or one or more hardware processors may be configured by firmware or software (e.g., instructions, application portions, or applications) as modules that operate to perform specified operations. In one example, the software may reside on a machine-readable medium. The software, when executed by the underlying hardware of the module, causes the hardware to perform the specified operations.

[0078] Thus, the term "module" is understood to include a tangible hardware and / or software entity that is physically constructed, specifically configured (e.g., hardwired), or configured (e.g., programmed) for a limited period of time (e.g., temporarily) to operate in a specified manner or to perform some or all of the operations described herein. Considering examples in which modules are temporarily configured, each module need not be instantiated at any one time. For example, if the modules have a general-purpose hardware processor configured using software, the general-purpose hardware processor may be configured as different respective modules at different times. Thus, the software may configure the hardware processor, for example, to configure certain modules at some times and other modules at other times.

[0079] Those skilled in the art will appreciate that the topology and circuit implementation methodology described herein allow for effective realization as a single application-specific integrated circuit. Furthermore, while the disclosure contained herein relates to providing power to a vehicle, it should be understood that this is only one of many possible applications, and that other embodiments are possible, including non-vehicle applications. For example, those skilled in the art will appreciate that there are many applications for providing current source safety circuits, such as inductive charging applications other than vehicles, e.g., chargers for portable consumer electronics such as those used to charge toothbrushes, cell phones, and other devices (e.g., Powermat®). Accordingly, these and other such applications are intended to be encompassed by the following claims.

Claims

1. A magnetic induction resonant charging circuit, a resonant network having an inductive secondary coil that converts a magnetic field received from the inductive primary coil into an alternating current (AC) signal; a synchronous rectifier for rectifying the AC signal to produce a direct current (DC) signal for application to a load to be charged, the synchronous rectifier including means for shunting the AC signal in the event of a fault; A charging circuit having

2. 10. The charging circuit of claim 1, wherein the resonant network is an AC current source.

3. 2. The charging circuit of claim 1, wherein the resonant network further comprises first and second balancing capacitors connected in series to each end of the secondary coil, whereby the AC signal resonates in series with the first and second capacitors.

4. 4. The charging circuit of claim 3, wherein the synchronous rectifier has a pair of normally open switches and a pair of normally closed switches, one of the pair of normally open switches and one of the pair of normally closed switches connected to the first balancing capacitor, the other of the pair of normally open switches and the other of the pair of normally closed switches connected to the second balancing capacitor, and the shunting means includes the normally closed switches that shunt the secondary coil in the event of the fault.

5. 5. The charging circuit of claim 4, wherein the normally open switch is configured to prevent shorting of the load in the event of the fault.

6. 5. The charging circuit of claim 4, further comprising a signal conditioning circuit that conditions the DC signal and outputs a conditioned DC signal for application to the load.

7. 7. The charging circuit of claim 6, further comprising a first current and voltage sensor monitoring the AC signal input from the resonant circuit to the synchronous rectifier, and a second current and voltage sensor monitoring the regulated DC signal applied to the load.

8. 8. The charging circuit of claim 7, further comprising a rectifier controller that phase-locks the AC signals output by the resonant network in response to values ​​measured by the first current and voltage sensor and the second current and voltage sensor, and provides control signals that control switching of the pair of normally open switches and the pair of normally closed switches in response to the measured values.

9. 9. The charging circuit of claim 8, further comprising a temperature sensor for detecting an over-temperature fault condition of the synchronous rectifier and providing a detection signal to the rectifier controller.

10. 10. The charging circuit of claim 9, further comprising a charging processor that receives at least one of an input AC signal amplitude, an input AC signal frequency, a regulated DC waveform voltage, a regulated DC waveform current, and a temperature of the synchronous rectifier from the rectifier controller and commands operation of the rectifier controller.

11. 11. The charging circuit of claim 10, wherein the charging processor instructs the rectifier controller to turn the pair of normally open switches and the pair of normally closed switches on and off approximately at a zero crossing of the AC signal from the resonant network when the AC signal frequency is within an acceptable range, the root mean square of the AC signal is above a threshold, and no fault is detected.

12. 11. The charging circuit of claim 10, wherein when a fault condition is detected, the charging processor disables the rectifier controller to hold the pair of normally open switches off and the pair of normally closed switches on.

13. 11. The charging circuit of claim 10, wherein the rectifier controller holds the pair of normally open switches off and the pair of normally closed switches on when an over-voltage, over-current fault condition is detected by the second current and voltage sensor or an over-temperature fault condition is detected by the temperature sensor.

14. 3. The charging circuit of claim 2, wherein the synchronous rectifier comprises a first pair of diodes connected to first and second leads of the AC current source, respectively, and a second pair of diodes connected to the first and second leads of the AC current source, and 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 the fault.

15. 3. The charging circuit of claim 2, wherein the synchronous rectifier comprises a first pair of diodes connected to first and second leads of the AC current source, respectively, and a second pair of diodes connected to the first and second leads of the AC current source, and 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 the fault.

16. 3. The charging circuit of claim 2, wherein the synchronous rectifier comprises a first pair of normally open switches connected to first and second leads of the AC current source, respectively, and a second pair of normally open switches connected to the first and second leads of the AC current source, and the shunting means comprises a normally closed safety switch connected between the first pair of normally open switches and the second pair of normally open switches, the normally closed safety switch shunting the AC current source in the event of the fault.

17. 2. The charging circuit of 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.

18. 2. The charging circuit of 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.

19. 2. The charging circuit of 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.

20. 2. The charging circuit of 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.

21. 2. The charging circuit of claim 1, wherein the resonant network includes 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.

22. 2. The charging circuit of 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.

23. 2. The charging circuit of 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, a third resonant capacitor in series with the secondary coil at the first end of the secondary coil, and a fourth resonant capacitor in series with the secondary coil at the second end of the secondary coil.

24. 10. The charging circuit of claim 1, wherein the resonant network further comprises an inductive primary coil having a rectangular coil winding, the rectangular coil winding disposed on at least one side of an insulating substrate.

25. 25. The charging circuit of claim 24, further comprising a resonant capacitor connected in series with a first end of the rectangular coil winding, the second end of the rectangular coil winding being connected to ground, the rectangular coil winding having a common mode voltage with respect to ground that is half the voltage of the resonant capacitor, thereby making the rectangular coil winding a capacitive electromagnetic interference radiator.

26. 25. The charging circuit of claim 24, further comprising a first resonant capacitor connected in series to a first end of the rectangular coil winding and a second resonant capacitor connected in series to a second end of the rectangular coil winding, wherein a midpoint between the first end and the second end of the rectangular coil winding is substantially at ground, thereby preventing the rectangular coil winding from radiating capacitive electromagnetic interference.

27. 2. The charging circuit of claim 1, wherein the secondary coil is attached to an electric vehicle and the load is a battery of the electric vehicle.

28. 28. The charging circuit of claim 27, wherein the resonant network is unbalanced and thereby radiates capacitive electromagnetic interference (EMI), and the electric vehicle has tires with conductive vias that ground the EMI during charging.

29. 28. The charging circuit of claim 27, wherein the resonant network is unbalanced and thereby radiates capacitive electromagnetic interference (EMI), and the electric vehicle includes a ground cable that grounds the EMI during charging.

30. 28. The charging circuit of claim 27, wherein the resonant network is unbalanced and thereby radiates capacitive electromagnetic interference (EMI), and the electric vehicle includes circuitry powered by a battery of the electric vehicle that cancels out-of-phase voltages during charging.

31. A magnetic induction resonant charging circuit for charging a battery of an electric vehicle, comprising: a resonant network in an electric vehicle having an inductive secondary coil, the inductive secondary coil converting a magnetic field received from the inductive primary coil into an alternating current (AC) signal, the resonant network being unbalanced and thereby radiating capacitive electromagnetic interference (EMI); a synchronous rectifier that rectifies the AC signal to generate a direct current (DC) signal for application to the battery of the electric vehicle; means for grounding said EMI during charging; A charging circuit having

32. 32. The charging circuit of claim 31, wherein the means for grounding the EMI during charging comprises a tire of the electric vehicle, the tire including a conductive via for grounding the EMI during charging.

33. 32. The charging circuit of claim 31, wherein the means for grounding the EMI during charging comprises a ground cable connected to the electric vehicle to ground the EMI during charging.

34. 32. The charging circuit of claim 31, wherein the means for grounding the EMI during charging comprises circuitry powered by a battery of the electric vehicle for canceling out-of-phase voltages during charging.

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