Bidirectional wireless power transfer

Abstract

A bidirectional wireless power transfer (WPT) system includes a WPT resonator, a power transfer connection for coupling to a battery, a bidirectional power converter coupled to the WPT resonator and to the power transfer connection, a communication interface for communicating with another bidirectional WPT system to which the WPT resonator is configured to be coupled, and a controller. The controller is configured to determine first, second, and third control parameters, control the bidirectional power converter based on the first and second control parameters, and communicate the third control parameter to the other bidirectional WPT system. The controller may operate in a power-controlled mode when delivering power to a vehicle battery, and in a voltage controlled mode when transferring power from the vehicle battery to a load or the Grid.

Description

WiTricity Ref. No. P0470WO-W-NPR1 Bidirec^onal Wireless Power Transfer TECHNICAL FIELD

[0001] This applica^on relates to bidirec^onal wireless power transfer, and, in par^cular, to bidirec^onal wireless power transfer between an electric vehicle and an external load, or the electrical Grid. BACKGROUND

[0002] Wireless power transfer (WPT) for charging the trac^on ba^eries of electric vehicles (EVs) has been standardized and is beginning to be available on the market. Plug-in or “wired” charging systems capable of bidirec^onal power transfer, such as vehicle-to-load (V2L) or vehicle-to-grid (V2G), generally V2X, are also available, but are not yet standardized. Among other things, whether conversion from the direct current (DC) voltage of a ba^ery to the alterna^ng current (AC) voltage of the Grid should be done by the on board charger (OBC) of the vehicle or in an external power electronics system remains an open ques^on. Bidirec^onal wireless power transfer has been suggested and has been achieved in consumer electronic devices such as mobile phones. SUMMARY

[0003] In general, in some aspects, a bidirec^onal wireless power transfer (WPT) assembly includes a WPT resonator, a power transfer connec^on for coupling to a ba^ery, a bidirec^onal power converter coupled to the WPT resonator and to the power transfer connec^on, a communica^on interface for communica^ng with another bidirec^onal WPT system to which the WPT resonator is configured to be coupled, and a controller. The controller is configured to determinefirst, second, and third control parameters, control the bidirec^onal power converter based on thefirst and second control parameters, and communicate the third control parameter to the other bidirec^onal WPT system.

[0004] In general, in some aspects, a bidirec^onal wireless power transfer (WPT) controller includes an output for providing control commands to a bidirec^onal power converter, an input for 1 A^orney Ref. No. P0470USWNPR1WiTricity Ref. No. P0470WO-W-NPR1 receiving opera^ng parameters of the bidirec^onal power converter and a target output value, and a communica^on interface for communica^ng with another bidirec^onal WPT system. The controller is configured to determinefirst, second, and third control parameters, communicate the first and second control parameter to the bidirec^onal power converter, and communicate the third control parameter to the other bidirec^onal WPT system. The opera^ng parameters include output voltage and output power of the bidirec^onal power converter, the target output value is selected from one of output power or output voltage of the bidirec^onal power converter, thefirst control parameter is based on the output power, and the second and third parameters are based on whichever of output voltage or output power is selected as the target output value.

[0005] Implementa^ons may include one or more of the following, in any order or combina^on. The bidirec^onal WPT assembly is installed in a vehicle, and, during a vehicle charging mode of opera^on, is configured to determine the control parameters based on output power of the bidirec^onal WPT assembly. The bidirec^onal WPT assembly is installed in a wireless electric vehicle charging sta^on (WEVC), and, during a V2x mode of opera^on, is configured to determine thefirst control parameter based on output power and determine the second and third control parameters based on output voltage of the bidirec^onal WPT assembly. Thefirst control parameter includes a target phase shiA between a current and voltage input at the bidirec^onal power converter. The controller includes a zero voltage switching (ZVS) controller, which receives as input afirst input parameter represen^ng power at an output of the bidirec^onal power converter, and outputs the first control parameter. Thefirst input parameter includes a product of current and voltage measured at the output of the bidirec^onal power converter. The second control parameter includes a target duty cycle of the bidirec^onal power converter. The controller further includes a power controller, which receives as input a second input parameter comprising a difference between the first input parameter and a third input parameter including a requested amount of power, and outputs the second control parameter. The ZVS controller further receives as input the second control parameter, as output from the power controller. The power controller further outputs the third control parameter, and the third control parameter includes a target coil current in a WPT resonator of the other WPT assembly. The controller is further configured to generate an ini^al value of the third control parameter, and to control whether the ini^al value of the third control parameter or a value output by the power controller is provided to the other WPT assembly. The controller is 2 A^orney Ref. No. P0470USWNPR1WiTricity Ref. No. P0470WO-W-NPR1 configured to generate the ini^al value of the third control parameter from a measured value of current into the bidirec^onal power converter and a minimum current value. The second control parameter includes a target duty cycle of the bidirec^onal power converter, the third control parameter includes a target coil current in a WPT resonator of the other WPT assembly, and the controller is configured to update thefirst control parameter more frequently than it updates the second and third control parameters. The controller is configured to determine the second and third control parameters together. The controller is configured to determine the second and third control parameters independently of each other.

[0006] In general, in some aspects, a method of controlling a bidirec^onal wireless power transfer (WPT) assembly is disclosed. The method includes determiningfirst, second, and third control parameters for a bidirec^onal power converter coupled to a WPT resonator and to a power transfer connec^on, controlling the bidirec^onal power converter based on thefirst and second control parameters; and communica^ng the third control parameter to another bidirec^onal WPT assembly.

[0007] Implementa^ons may include one or more of the following, in any order or combina^on. The determining thefirst control parameter includes determining a target phase shiA between a current and voltage input at the bidirec^onal power converter based on afirst input parameter represen^ng power at an output of the bidirec^onal power converter. Thefirst input parameter includes a product of current and voltage measured at the output of the bidirec^onal power converter. The determining the second control parameter includes determining a target duty cycle of the bidirec^onal power converter based on a second input parameter including a difference between thefirst input parameter and a third input parameter including a requested amount of power. The second control parameter includes a target duty cycle of the bidirec^onal power converter, the third control parameter includes a target coil current in a WPT resonator of the other WPT assembly, and the method further includes upda^ng thefirst control parameter more frequently than the second and third control parameters are updated.

[0008] Various embodiments can include one or more of the foregoing features, in any combina^on. 3 A^orney Ref. No. P0470USWNPR1WiTricity Ref. No. P0470WO-W-NPR1 BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 illustrates a wireless electric vehicle charging sta^on and a vehicle.

[0010] Figures 2, 3, 4, and 6 are block diagrams of wireless power transfer systems.

[0011] Figure 5 is aflow chart showing an example order of opera^ons for control loops. DETAILED DESCRIPTION

[0012] Wireless power transfer (WPT) for charging electric vehicles is described in detail in patents such as U.S. Patents 8,933,594, ^tled “Wireless energy transfer for vehicles,” and 9,561,730, ^tled “Wireless power transmission in electric vehicles,” which are incorporated here by reference in their en^rety. Wireless electric vehicle charging (WEVC) systems according to the SAE J2954 standard, as of the date offiling of this applica^on, provide up to 22 kW of power at each charging sta^on. Lower power levels, such as 11 kW and 7 kW, are commonly used, due to their compa^bility with household and industrial electrical systems. At the same ^me, higher power levels are also used, especially for charging heavier-duty vehicles, like busses or trucks, or for charging light duty vehicles at a higher rate, and proposals have been made to extend exis^ng WEVC standards to such power levels. Lower-power vehicles, such as scooters, golf carts, neighborhood electric vehicles (NEVs), or industrial vehicles like forkliAs and automated ground vehicles (AGVs) may also be charged using WPT, but standards for doing so do not currently exist, though several are in development. References herein to “AC power,” “DC power,” or “AC” and “DC” alone should be understood as referring to power that is transferred as electricity having the corresponding current waveform.

[0013] Wireless vehicle charging uses power converters on both sides of the WPT connec^on, to convert 50 Hz or 60 Hz AC power from the Grid to, for example, 85 kHz power (referred to as low- frequency, LF, power) for conversion from electric current to a magne^cfield on the transmi^er side, and then from the LF magne^cfield to LF electric current and then to DC power within the vehicle for charging the ba^ery. Wireless power transfer through an electromagne^cfield inherently isolates the vehicle electrical system from the Grid, while wired charging solu^ons require an isola^on stage in the vehicle, in the external charger, or both. Some^mes the isola^on is implemented within a power conversion stage, such as an isola^on transformer as part of a DC-DC converter. In some examples, as described in U.S. Patents 9,561,730 and 9,381,821 and co-pending applica^on 4 A^orney Ref. No. P0470USWNPR1WiTricity Ref. No. P0470WO-W-NPR1 [Provisional App 63 / 556601], all incorporated here by reference, various power converters or components of the power converters are shared between wired and wireless charging systems.

[0014] For bidirec^onal power transfer, the general assump^on has been that simply making each stage of power conversion itself bidirec^onal, such as by using a switching rec^fier rather than a diode bridge for AC to DC conversion, is sufficient to make the en^re power transfer chain bidirec^onal. This disclosure discusses details of the control logic for a bidirec^onal system, which are not necessarily the same for V2G and G2V opera^on, and which may improve ordinary G2V opera^on by virtue of the addi^onal control capabili^es of a bidirec^onal system.

[0015] Figure 1 shows an example of a parking facility 100 with wireless power transfer services. A vehicle 102 is parked over a WPT pad 104. Although shown as car in Figure 1, any type of vehicle, such as a golf cart, neighborhood electric vehicle, delivery van, bus, AGV, etc., can be charged in the same way. WPT pad 106 in the vehicle is connected to a power converters 108. The power converter 108 converts power received by the pad 106 to a form suitable for charging the vehicle’s trac^on ba^ery, not shown. In some examples, the power converter 108 may be integrated with power converters used for plug-in charging of the vehicle, commonly called on-board chargers (OBC), or other on-board vehicle components. The ground-side WPT pad 104 is shown with an external power converter 110 connected to a power supply cable 112. The power supply cable 112 is in turn connected to a power converter 114. In some examples, the power converter 114 provides DC power over the cable 112 and the external power converter 110 includes inverters, such as the mul^-level inverter (MLI) described in U.S. Patent Applica^ons 18 / 486,830 and 18 / 486,835, bothfiled October 13, 2023, and incorporated here by reference. The inverters provide low-frequency (LF) power signals, such as the 85 kHz signals used for wireless charging according to the SAE J2954 standard, to the pad 104, to turn into magne^cfields for wireless power transfer. In other examples, inverters included in the power converter 114 provide the LF power signals over the cable 112, and the power converter 110 may be omi^ed, or may provide only limited features, such as impedance matching. The power converter 110 may also be integrated into the pad 104. In some examples, the pad 104 is referred to as the Ground Assembly Resonator (GAR), and the combina^on of the GAR with the power converter 110 or any other ground-side electronics is referred to as a Ground Assembly (GA), whether integrated or housed separately. Similarly, the WPT pad 106 may be referred to as the 5 A^orney Ref. No. P0470USWNPR1WiTricity Ref. No. P0470WO-W-NPR1 Vehicle Assembly Resonator (VAR) and the combina^on of the VAR and the power converter 108 or any other vehicle-side electronics as a Vehicle Assembly (VA), again, whether integrated or housed separately. Each of the connec^ons shown may be bi-direc^onal, allowing the vehicles to discharge power from their ba^eries to the power converter 114 in a V2x arrangement.

[0016] Figure 2 is a schema^c diagram of exemplary components of a wireless power transfer system 200 such as that shown in Figure 1. The wireless power transfer system 200 includes a base resonant circuit (e.g., GAR 206) including a coil 204 having an inductance L1. The wireless power transfer system 200 further includes an electric vehicle resonant circuit (e.g., VAR 222) including a coil 216 having an inductance L2. Implementa^ons may use capaci^vely loaded conductor loops (e.g., mul^-turn coils) forming a resonant structure that is capable of efficiently coupling energy from a primary structure (transmi^er) to a secondary structure (receiver) via a magne^c or electromagne^c nearfield if both the transmi^er and the receiver are tuned to a common resonant frequency. The coils may be used for the coil 216 and the coil 204. Using resonant structures for coupling energy may be referred to as “magne^cally coupled resonance,” “electromagne^cally coupled resonance,” or “resonant induc^on.”

[0017] A power supply 208 supplies power PSto the base power converter 236 to transfer energy to the electric vehicle. The base power converter 236 may include circuitry such as an AC-to-DC converter configured to convert power from standard Grid-supplied AC to DC power at a suitable voltage level, and a DC-to-LF converter configured to convert DC power to LF power at an opera^ng frequency suitable for wireless power transfer. The base power converter 236 supplies power P1to the GAR 206 including tuning capacitor C1in series with coil 204 to emit an electromagne^cfield at the opera^ng frequency. The series-tuned resonant circuit shown for GAR 206 should be construed as exemplary. In another implementa^on, the capacitor C1 may be coupled with the coil 204 in parallel. In yet other implementa^ons, tuning may be provided by several reac^ve elements in any combina^on of parallel or series topology. The capacitor C1 may be provided to form a resonant circuit with the coil 204 that resonates substan^ally at the opera^ng frequency. The coil 204 receives the power P1 and wirelessly transmits power at a level sufficient to charge or power the electric vehicle. For example, the level of power provided wirelessly by the coil 204 may be on the order of 6 A^orney Ref. No. P0470USWNPR1WiTricity Ref. No. P0470WO-W-NPR1 kilowa^s (kW) (e.g., anywhere from 1 kW to 500 kW, although actual levels may be or higher or lower).

[0018] The GAR 206 (including the coil 204 and tuning capacitor C1) and the VAR 222 (including the coil 216 and tuning capacitor C2) may be tuned to substan^ally the same frequency. The coil 216 may be posi^oned within the near-field of the base power transfer element and vice versa, as further explained below. The coil 204 and the coil 216 become coupled to one another such that power may be transferred wirelessly from the coil 204 to the coil 216. The series capacitor C2forms a resonant circuit with the coil 216 that resonates substan^ally at the opera^ng frequency. The series- tuned resonant circuit shown for VAR 222 should be construed as being exemplary. In another implementa^on, the capacitor C2may be coupled with the coil 216 in parallel. In yet other implementa^ons, the VAR 222 may be formed of several reac^ve elements in any combina^on of parallel or series topology. Element k(d) represents the mutual coupling coefficient resul^ng at coil separa^on d. Equivalent resistances Req,1and Req,2represent the losses that may be inherent to the coils 204 and 216 and the tuning (an^-reactance) capacitors C1 and C2, respec^vely. The VAR 222, including the coil 216 and capacitor C2, receives and provides the power P2to an electric vehicle power converter 238 of an electric vehicle charging system 214.

[0019] The electric vehicle power converter 238 may include, among other things, a LF-to-DC converter configured to convert power at an opera^ng frequency back to DC power at a voltage level of the load 218 that may represent the electric vehicle ba^ery unit. The electric vehicle power converter 238 provides the converted power PLDCto the load 218.

[0020] The coil 216 and the coil 204, as described throughout the disclosed implementa^ons, may be referred to or configured as “conductor loops”, and more specifically, “mul^-turn conductor loops” or coils. The base and electric vehicle power transfer elements (e.g., coil 204 and coil 216) may also be referred to herein or be configured as “magne^c” couplers. The term “coupler” is intended to refer to a component that may wirelessly output or receive energy for coupling to another “coupler.”

[0021] As discussed above, efficient transfer of energy between a transmi^er and receiver occurs during matched or nearly matched resonance between a transmi^er and a receiver. However, even 7 A^orney Ref. No. P0470USWNPR1WiTricity Ref. No. P0470WO-W-NPR1 when resonance between a transmi^er and receiver are not matched, energy may be transferred at a lower efficiency.

[0022] Figure 3 shows an example bidirec^onal WPT system in greater detail. The power converters offigure 2 are replaced by bidirec^onal switching inverter / rec^fiers 336, 338, which we may generally be referred to as inverters or rec^fiers based on their mode of opera^on in a given situa^on. Control signals PWM1through PWM8control the switching of the metal-oxide- semiconductorfield-effect transistors (MOSFETS) Q1 through Q8 in the inverter / rec^fiers 336, 338. The control schemes are described later in this disclosure. In this example, impedance matching and filtering is provided by two inductors L3sA / B, L3dA / B, and three capacitors C1sA / B, C2s, C1dA / B on each side of the WPT coils L1s, L1d. This example assumes DC input to the ground-side inverter / rec^fier 336, shown as VBUS. Such input may be provided, for example, by a bidirec^onal power-factor-correc^ng converter (PFC). Thefigure iden^fies two values used below: the current I3dinto the vehicle-side inverter / rec^fier 338 in charging (G2V) mode, and the voltage Vacdacross the input terminals of the same inverter / rec^fier.

[0023] Figure 4 shows the control logic used to operate the system of Figure 3. The internal switches Q1 … Q8 of the inverter / rec^fiers 336 are now shown. The control signals PWM1through PWM4for the ground-side switches are represented as PWMGAprovided by a ground-side Inverter Controller 402. Note that the VBUS fromfigure 3 is replaced by Vgridand a Bidirec^onal PFC 404, with its own controller 406. On the vehicle side, the Inverter controller 408 is shown in more detail. The control signals PWM5through PWM5for the ground-side switches are represented as PWMVAand are provided by a modulator 410. The Modulator receives input messages ΦVAand βVAfrom corresponding controllers 412, 414. The modulator 410 also receives as input a sync signal based on the Iacd,sense measurement of inverter input current. The Φ controller 412 is noted as also being a zero voltage switching (ZVS) controller, and receives as its input a parameter Pba^, the product of Iba^,sense and Vba^,sense, current and voltage measured at the ba^ery. The β controller receives as its input the difference of Pba^ and a power command message Pcmd. Pcmd may be provided by the onboard charger (OBC) or other ba^ery management system (BMS) and represents the power that should be provided to the ba^ery. That is, the input to the β controller is the difference between power being supplied to the ba^ery and the power requested. 8 A^orney Ref. No. P0470USWNPR1WiTricity Ref. No. P0470WO-W-NPR1

[0024] As shown, the β controller 414 is combined with a GA coil current controller 416 in a Power Controller 418. The GA coil current command message IGA_cmd is sent from the GA coil current controller to the GA over a WiFi link 420. Within the GA, a command processing unit 422 decomposes the IGA_cmdmessage into a Vbus_cmdmessage sent to the PFC controller, indica^ng the voltage that should be provided to the GA inverter (e.g., inverter / rec^fier 336, and a βGA_cmdmessage sent to the GA inverter controller 402. The coil current is determined by the input voltage Vbusand inverter duty cycle βGAaccording to Equa^on (1): ^ ^^^^^^^^√^ ^^ = ^^^^ ×^^^ × 2 ×^ Equa^on (1)

[0025] In Equa^on (1), XGAisof the GA side of the system. In both the GA and VA, β and the associated commands refers to the duty cycle of the inverter / rec^fier. The symbol Φ and associated messages refers to the phase shiA between the current and voltage input at the VA inverter / rec^fier 338. By opera^ng the switches of the inverter / rec^fier in synchrony with the zero-crossing of the input current, the voltage can be made to lag or lead the current, thus controlling ΦVA.

[0026] For Grid-to-Vehicle (G2V) mode (e.g., vehicle charging), it is desired to operate in a constant power mode. For this, the GA is operated to control coil current as requested by the VA, while the VA is operated to control the duty cycle of the rec^fier, β. Both inverter / rec^fiers are operated as phase-shiAed full-bridge devices, which allows all switches to operate with zero voltage switching, and to share losses equally. Maintaining ΦVA between values of 90°–β and 90° maintains zero voltage switching in the rec^fier 338. Specifically, for any value of β, Φ=90°–β represents the boundary of where ZVS can be achieved. Controlling ΦVA also helps to increase power output of the system at weak coupling condi^ons.

[0027] As noted, IGA and βVA together determine the power output of the system. The two controllers 414, 416 can run sequen^ally or concurrently to implement power control. In some examples, the βVA control loop can run faster than the IGA loop, as the βVA loop directly regulates output power, while the IGA control loop is limited by WiFi delay. In some examples, the βVA loop controls output power with a bandwidth between 5 and 50 Hz, while the IGA loop has a bandwidth 9 A^orney Ref. No. P0470USWNPR1WiTricity Ref. No. P0470WO-W-NPR1 less than 5 Hz. At the same ^me, the ΦVAcontrol loop can operate at 500 Hz to assure ZVS for good efficiency and maximum power output.

[0028] Theflow chart in Figure 5 shows an example order of opera^ons for the control loops. Ini^ally, in afirst, ini^al rec^fier current phase 502 of start-up, a power command 504 is received. This command indicates that the present mode is G2V, with a requested power Pba^and Vba^to be delivered to the ba^ery. VA rec^fier input current Iacdis then increased, 506, and compared, 508, to a minimum value Iac-min. During this loop, the value of GA current target IGA-refis increased, 510, un^l Iacdis less than Iac-min.

[0029] Once Iacdis greater than Iac-min, the lower-power phase 512 of start-up begins. In this phase, βVAand ΦVAare tuned together, 514 – βVAis set to achieve the desired power output, and ΦVAis set along the ZVS boundary 90°–βVA. During this phase, ba^ery power Pba^is compared 516 to the command Pcmd. If the difference is less than a threshold ε, the start-up process loops un^l the Pcmdcommand is changed, or for some other reason the output power deviates from the target, or un^l the charging process is stopped, 518. When more power is needed, βVAcommand is adjusted un^l Pba^exceeds 3 kW (520), at which point start-up phase can be exited. In full-power opera^on, ΦVAis ini^ally increased, 522, to increase power output. As noted above, βVAand IGA,cmdare updated at lower frequencies than ΦVA. Whenever it is ^me to update one or both of them, 524, these parameters are tuned to match output Pba^to the target Pcmd, 526. Un^l instructed to stop charging, 528, the output power Pba^ is compared to the target Pcmd, 530. If output power remains or has fallen more than ε below the target, or the target has been updated, the tuning steps are repeated. If output power falls below 3 kW (520), the low-power phase of startup is reentered. As long as output power is within the threshold ε of the target, the system con^nues charging un^l told to stop, at which point charging ends.

[0030] Figure 6 shows the control logic used to operate the system of Figure 3 in vehicle-to-grid (V2G) mode. Specifically, the details of the GA power controller 608, which were abstracted as Math block (e.g., command processing unit 422) in Figure 4, are shown in more detail. This control block is largely the mirror image of the VA power controller 408 infigure 4, except that it operates in a voltage control mode, rather than power control. That is, while Pbus, the DC output powerflowing from the inverter / rec^fier 336 to the bidirec^onal PFC 404, again provides the input to the Φ 10 A^orney Ref. No. P0470USWNPR1WiTricity Ref. No. P0470WO-W-NPR1 controller 612, the bus voltage Vbus, rather than the Vbus× Ibusproduct Pbus, is compared to a Vbus,cmdtarget and the difference used as the input to the power controller 618. As in Figure 4, the difference from the target is again used by the GA β controller 614 to set a βGA value for the duty cycle of the inverter 556, and by the GA-side VA coil current controller 616 to set the value of IVA,cmdto request coil current in the VA (now opera^ng as the power transmi^er). The process of upda^ng the control commands in Figure 6 may be essen^ally the same as that shown in Figure 5, with a change from power control to voltage control.

[0031] The Bidirec^onal PFC 404 and the power system connected to it – shown as Vgridin Figure 6, may be Grid-^ed or islanded. In Grid-^ed mode, for V2G opera^on, the PFC provides power to the Grid at the frequency dictated by its Grid connec^on. For islanded mode, for V2L (load), V2B (building), V2x, etc., opera^on, the PFC itself determines the voltage and sets the AC frequency for whatever loads are connected to it. Unlike the vehicle charging scenario of Figure 4, where the power requirements of the ba^ery are expected to be stable and predictable according to the ba^ery’s charging curve, the Grid, in V2G situa^ons, or other loads, in V2x modes, may cause unpredictable spikes or dips in demand. Controlling ΦGAallows rapid response to changes in the demand at the PFC and can reduce how much power is required by way of βGAor IVAadjustment. Addi^onally, a capacitor bank 604 provides some measure of buffer, sustaining the required output voltage during the transi^on ^me required by the rela^vely slow WiFi connec^on 420 and response ^me of the vehicle charging system to deliver requested increases in power.

[0032] Figure 6 also shows a coupling check block 630, which corresponds to a coupling check 430 on the vehicle side in Figure 4. The coupling check may confirm that the two WPT systems are aligned with each other by comparing the current through one of the inductors to that provided to the transmit coil on the other side. In some cases, the coupling check may be performed by the same system (VA or GA) in both G2V and V2G / x modes. In other cases, measurements may be made on one side but the calcula^ons are performed on the other. For example, measurements may be made on the vehicle side during G2V, and on the ground side during V2G, but the computa^ons performed by the vehicle in both cases.

[0033] The various illustra^ve logical blocks, modules, circuits, and methods described in connec^on with the examples disclosed above may be implemented as electronic hardware, 11 A^orney Ref. No. P0470USWNPR1WiTricity Ref. No. P0470WO-W-NPR1 computer soAware, or combina^ons of both. To clearly illustrate this interchangeability of hardware and soAware, various illustra^ve components, blocks, modules, circuits, and steps have been described above generally in terms of their func^onality. Whether such func^onality is implemented as hardware or soAware depends upon the par^cular applica^on and design constraints imposed on the overall system. The described func^onality may be implemented in varying ways for each par^cular applica^on, but such implementa^on decisions should not be interpreted as causing a departure from the scope of the described aspects.

[0034] The various illustra^ve blocks, modules, and circuits described in connec^on with disclosed controllers may be implemented or performed with a general-purpose hardware processor, a Digital Signal Processor (DSP), an Applica^on-Specific Integrated Circuit (ASIC), a Field- Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combina^on thereof designed to perform the func^ons described herein. A general-purpose hardware processor may be a microprocessor, but in the alterna^ve, the hardware processor may be any conven^onal processor, controller, microcontroller, or state machine. A hardware processor may also be implemented as a combina^on of compu^ng devices.

[0035] The steps of a method and func^ons described above may be embodied directly in hardware, in a soAware module executed by a hardware processor, or in a combina^on of the two. If implemented in soAware, the func^ons may be stored on or transmi^ed as one or more instruc^ons or code on a tangible, non-transitory, computer-readable medium. A soAware module may reside in Random Access Memory (RAM),flash memory, Read-Only Memory (ROM), or any other form of storage medium known in the art. A storage medium is coupled to the hardware processor such that the hardware processor can read informa^on from, and write informa^on to, the storage medium. In another example, the storage medium may be integral to the hardware processor. The hardware processor and the storage medium may reside in an ASIC.

[0036] Unless context dictates otherwise, items represented in the accompanyingfigures and terms may represent one or more items or terms, and thus reference may be made interchangeably to single or plural forms of the items and terms in this wri^en descrip^on. Although subject ma^er has been described in language specific to structural features or methodological opera^ons, it is to 12 A^orney Ref. No. P0470USWNPR1WiTricity Ref. No. P0470WO-W-NPR1 be understood that the subject ma^er defined in the appended claims is not necessarily limited to the specific features or opera^ons described above, including not necessarily being limited to the organiza^ons in which features are arranged or the orders in which opera^ons are performed. For example, the context of the above descrip^on is wireless charging of electric vehicles, but these techniques may be used in other situa^ons where it is desired to distribute power between various sources and loads.

[0037] A number of implementa^ons have been described. Nevertheless, it will be understood that addi^onal modifica^ons may be made without depar^ng from the scope of the concepts described herein, and, accordingly, other embodiments are within the scope of the following claims. 13 A^orney Ref. No. P0470USWNPR1

Claims

WiTricity Ref. No. P0470WO-W-NPR1 What is claimed is:

1. A bidirec^onal wireless power transfer (WPT) assembly, comprising: a WPT resonator; a power transfer connec^on for coupling to a ba^ery; a bidirec^onal power converter coupled to the WPT resonator and to the power transfer connec^on; a communica^on interface for communica^ng with another bidirec^onal WPT assembly to which the WPT resonator is configured to be coupled; and a controller configured to: determine control parameters includingfirst, second, and third control parameters; control the bidirec^onal power converter based on thefirst and second control parameters; and communicate the third control parameter to the other bidirec^onal WPT assembly.

2. The bidirec^onal WPT assembly of claim 1, wherein: the bidirec^onal WPT assembly is installed in a vehicle, and, during a vehicle charging mode of opera^on, is configured to determine the control parameters based on output power of the bidirec^onal WPT assembly.

3. The bidirec^onal WPT assembly of claim 1, wherein: the bidirec^onal WPT assembly is a component of a wireless electric vehicle charging sta^on (WEVC), and, during a V2x mode of opera^on, is configured to: determine thefirst control parameter based on output power; and determine the second and third control parameters based on output voltage of the bidirec^onal WPT assembly. 14 A^orney Ref. No. P0470USWNPR1WiTricity Ref. No. P0470WO-W-NPR1 4. The bidirec^onal WPT assembly of claim 1, wherein: thefirst control parameter comprises a target phase shiA between a current and voltage input at the bidirec^onal power converter.

5. The bidirec^onal WPT assembly of claim 4, wherein: the controller comprises a zero voltage switching (ZVS) controller, which receives as input afirst input parameter represen^ng power at an output of the bidirec^onal power converter, and outputs thefirst control parameter.

6. The bidirec^onal WPT assembly of claim 5, wherein: thefirst input parameter comprises a product of current and voltage measured at the output of the bidirec^onal power converter.

7. The bidirec^onal WPT assembly of claim 5, wherein: the second control parameter comprises a target duty cycle of the bidirec^onal power converter.

8. The bidirec^onal WPT assembly of claim 7, wherein: the controller further comprises a power controller, which receives as input a second input parameter comprising a difference between thefirst input parameter and a third input parameter comprising a requested amount of power, and outputs the second control parameter.

9. The bidirec^onal WPT assembly of claim 8, wherein: the ZVS controller further receives as input the second control parameter, as output from the power controller. 15 A^orney Ref. No. P0470USWNPR1WiTricity Ref. No. P0470WO-W-NPR1 10. The bidirec^onal WPT assembly of claim 8, wherein: the power controller further outputs the third control parameter, and the third control parameter comprises a target coil current in a WPT resonator of the other WPT assembly.

11. The bidirec^onal WPT assembly of claim 10, wherein: the controller is further configured to generate an ini^al value of the third control parameter, and to control whether the ini^al value of the third control parameter or a value output by the power controller is provided to the other WPT assembly.

12. The bidirec^onal WPT assembly of claim 11, wherein: the controller is configured to generate the ini^al value of the third control parameter from a measured value of current into the bidirec^onal power converter and a minimum current value.

13. The bidirec^onal WPT assembly of claim 4, wherein: the second control parameter comprises a target duty cycle of the bidirec^onal power converter; the third control parameter comprises a target coil current in a WPT resonator of the other WPT assembly; and the controller is configured to update thefirst control parameter more frequently than it updates the second and third control parameters.

14. The bidirec^onal WPT assembly of claim 1, wherein: the controller is configured to determine the second and third control parameters together. 16 A^orney Ref. No. P0470USWNPR1WiTricity Ref. No. P0470WO-W-NPR1 15. The bidirec^onal WPT assembly of claim 1, wherein: the controller is configured to determine the second and third control parameters independently of each other.

16. A method of controlling a bidirec^onal wireless power transfer (WPT) assembly, comprising: determiningfirst, second, and third control parameters for a bidirec^onal power converter coupled to a WPT resonator and to a power transfer connec^on; controlling the bidirec^onal power converter based on thefirst and second control parameters; and communica^ng the third control parameter to another bidirec^onal WPT assembly.

17. The method of controlling a bidirec^onal WPT assembly of claim 16, wherein: determining thefirst control parameter comprises determining a target phase shiA between a current and voltage input at the bidirec^onal power converter based on afirst input parameter represen^ng power at an output of the bidirec^onal power converter.

18. The method of controlling a bidirec^onal WPT assembly of claim 17, wherein: thefirst input parameter comprises a product of current and voltage measured at the output of the bidirec^onal power converter.

19. The method of controlling a bidirec^onal WPT assembly of claim 17, wherein: determining the second control parameter comprises determining a target duty cycle of the bidirec^onal power converter based on a second input parameter comprising a difference between thefirst input parameter and a third input parameter comprising a requested amount of power. 17 A^orney Ref. No. P0470USWNPR1WiTricity Ref. No. P0470WO-W-NPR1 20. The method of controlling a bidirec^onal WPT assembly of claim 16, wherein: the second control parameter comprises a target duty cycle of the bidirec^onal power converter, the third control parameter comprises a target coil current in a WPT resonator of the other WPT assembly, and the method further includes upda^ng thefirst control parameter more frequently than the second and third control parameters are updated. 18 A^orney Ref. No. P0470USWNPR1WiTricity Ref. No. P0470WO-W-NPR1 21. A bidirec^onal wireless power transfer (WPT) controller, comprising: an output for providing control commands to a bidirec^onal power converter; an input for receiving opera^ng parameters of the bidirec^onal power converter and a target output value; and a communica^on interface for communica^ng with another bidirec^onal WPT assembly, wherein: the controller is configured to: determinefirst, second, and third control parameters; communicate the first and second control parameter to the bidirec^onal power converter; and communicate the third control parameter to the other bidirec^onal WPT assembly; the opera^ng parameters include output voltage and output power of the bidirec^onal power converter; the target output value is selected from one of the output power or the output voltage of the bidirec^onal power converter; thefirst control parameter is based on the output power; and the second and third control parameters are based on whichever of the output voltage or the output power is selected as the target output value. 19 A^orney Ref. No. P0470USWNPR1

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