WIRELESS POWER TRANSFER SYSTEMS FOR ELECTRIC VEHICLES

Abstract

A wireless power transfer (WPT) system for an electrical vehicle (EV) may include a ground assembly (GA) having a GA transmitter coil, a vehicle assembly (VA) having a VA receiver coil magnetically coupled to the GA transmitter coil, a compensation strategy stage including a parallel-series compensation network to obtain a voltage V.sub.VA in the VA receiver coil proportional to an effective current I.sub.p_rms in the GA transmitter coil, a rectifier in the VA to obtain a continuous voltage V.sub.dc_VA, and a control strategy stage with a voltage control loop and a current control loop. The control strategy stage may provide a control command to regulate voltage in the VA to adjust the continuous voltage V.sub.dc_VA based on a reference DC link voltage. A DC link of a conductive charger of the EV may be regulated with the adjusted continuous voltage V.sub.dc_VA during an inductive charging process of the EV. The rectifier may be connected to the DC link of the conductive charger of the EV.

Claims

1. A wireless power transfer (WPT) system for an electrical vehicle (EV), the system comprising: a ground assembly (GA) having a GA transmitter coil; a vehicle assembly (VA) having a VA receiver coil magnetically coupled to the GA transmitter coil; a compensation strategy stage including a parallel-series compensation network to obtain a voltage V.sub.VA in the VA receiver coil proportional to an effective current I.sub.p_rms in the GA transmitter coil; a rectifier in the VA to obtain a continuous voltage V.sub.dc_VA; and a control strategy stage with a voltage control loop and a current control loop; wherein the control strategy stage provides a control command to regulate voltage in the VA to adjust the continuous voltage V.sub.dc_VA based on a reference DC link voltage; wherein a DC link of a conductive charger of the EV is regulated with the adjusted continuous voltage V.sub.dc_VA during an inductive charging process of the EV; and wherein the rectifier is connected to the DC link of the conductive charger of the EV.

2. The WPT system for an EV according to claim 1, wherein the GA comprises a DC-to-AC converter regulated with the control command of the control strategy stage.

3. The WPT system for an EV according to claim 1, wherein the GA comprises an AC/DC converter with power factor correction (PFC).

4. The WPT system for an EV according to claim 1, wherein the GA comprises a DC blocking and impedance matching network (IMN).

5. The WPT system for an EV according to claim 1, wherein the GA and the VA comprise wireless communicator for at least transmitting the continuous voltage V.sub.dc_VA and the reference DC link voltage from the VA to the GA.

6. A wireless power transfer (WPT) system system for an EV, the system comprising: a ground assembly (GA) having a GA transmitter coil; a vehicle assembly (VA) having a VA receiver coil magnetically coupled to the GA transmitter coil a compensation strategy including a parallel-series compensation network to obtain a voltage V.sub.VA in the VA receiver coil proportional to an effective current I.sub.p_rms in the GA transmitter coil; and a control strategy stage with a voltage control loop and a current control loop; wherein the control strategy stage provides a control command to regulate voltage in the VA to adjust a continuous voltage V.sub.dc_VA based on a reference DC link voltage; wherein a power factor correction (PFC) stage of a conductive charger of the EV is supplied with the voltage V.sub.VA during an inductive charging process of the EV; and wherein the continuous voltage V.sub.dc_VA is the voltage measured at a DC link of the conductive charger of the EV.

7. The WPT system for an EV according to claim 5, wherein the GA comprises a DC-to-AC converter regulated with a control command of the control strategy stage.

8. The WPT system for an EV according to claim 5, wherein the GA comprises an AC/DC converter with PFC.

9. The WPT system for an EV according to claim 5, wherein the GA comprises a DC blocking and impedance matching network (IMN).

10. The WPT system for an EV according to claim 6, wherein the GA and the VA comprise wireless communicators for transmitting the continuous voltage V.sub.dc_VA and the reference DC link voltage from the VA to the GA.

11. An electric vehicle, comprising: a conductive charging stage having a DC link; and a WPT system having: a ground assembly (GA) having a GA transmitter coil; a vehicle assembly (VA) having a VA receiver coil magnetically coupled to the GA transmitter coil; a compensation strategy including a parallel-series compensation network to obtain a voltage V.sub.VA in the VA receiver coil proportional to an effective current I.sub.p_rms in the GA transmitter coil; and a control strategy stage with a voltage control loop and a current control loop; wherein the control strategy stage provides a control command to regulate voltage in the VA to adjust the continuous voltage V.sub.dc_VA based on a reference DC link voltage; wherein one of: the WPT system further includes a rectifier in the VA to obtain a continuous voltage V.sub.dc_VA, a DC link of a conductive charger of the EV is regulated with the adjusted continuous voltage V.sub.dc_VA during an inductive charging process of the EV, and the rectifier is connected to the DC link of the conductive charger of the EV; or a power factor correction (PFC) stage of a conductive charger of the EV is supplied with the voltage V.sub.VA during an inductive charging process of the EV, and the continuous voltage V.sub.dc_VA is the voltage measured at a DC link of the conductive charger of the EV; and wherein the WPT system regulates the DC link of the conductive charging stage.

12. A method for charging an electric vehicle (EV) with a wireless power transfer (WPT) system having a ground assembly (GA) and a vehicle assembly (VA), the method comprising: applying an effective current I.sub.p_rms to a GA transmitter coil of the WPT system, obtaining a voltage V.sub.VA in a VA receiver coil of the WPT system proportional to the I.sub.p_rms; obtaining a continuous voltage V.sub.dc_VA in the VA of the WPT system; adjusting the continuous voltage V.sub.dc_VA based on a reference DC link voltage; and regulating a DC link of a conductive charger of the EV with the adjusted continuous voltage V.sub.dc_VA.

13. A method for charging an electric vehicle (EV) with a wireless power transfer (WPT) system having a ground assembly (GA) and a vehicle assembly (VA), the method comprising: applying an effective current I.sub.p_rms to a GA transmitter coil of the WPT system; obtaining a voltage V.sub.VA in a VA receiver coil of the WPT system proportional to the I.sub.p_rms; supplying a power factor correction (PFC) stage of a conductive charger of the EV with the voltage V.sub.VA; obtaining an adjusted continuous voltage V.sub.dc_VA; adjusting the continuous voltage V.sub.dc_VA based on a reference DC link voltage; and regulating a DC link of the conductive charger of the EV with the adjusted continuous voltage V.sub.dc_VA; wherein the continuous voltage V.sub.dc_VA is the voltage measured at the DC link of the conductive charger of the EV; and wherein the rectifier is connected to the DC link of the conductive charger of the EV.

14. The method according to claim 12, further comprising: transmitting the continuous voltage V.sub.dc_VA and the reference DC link voltage from the VA to the GA of the WPT systems.

15. The method according to claim 13, further comprising: transmitting the continuous voltage V.sub.dc_VA and the reference DC link voltage from the VA to the GA of the WPT systems.

16. The WPT system for an EV according to claim 6, wherein the GA comprises an AC/DC converter with PFC.

17. The WPT system for an EV according to claim 6, wherein the GA comprises a DC blocking and impedance matching network (IMN).

18. The WPT system for an EV according to claim 7, wherein the GA and the VA comprise wireless communicators for transmitting the continuous voltage V.sub.dc_VA and the reference DC link voltage from the VA to the GA.

19. The WPT system for an EV according to claim 8, wherein the GA and the VA comprise wireless communicators for transmitting the continuous voltage V.sub.dc_VA and the reference DC link voltage from the VA to the GA.

20. The WPT system for an EV according to claim 9, wherein the GA and the VA comprise wireless communicators for transmitting the continuous voltage V.sub.dc_VA and the reference DC link voltage from the VA to the GA.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] For a better understanding the above explanation and for the sole purpose of providing an example, some non-limiting drawings are included that schematically depict a practical embodiment.

[0036] FIG. 1 shows a conventional WPT system for an EV.

[0037] FIG. 2 shows a conventional WPT system in combination with a conductive charger of an EV.

[0038] FIG. 3 shows a first example of a WPT and a conductive charger according to the present invention.

[0039] FIG. 4 shows the first example of the WPT according to the present invention.

[0040] FIG. 5 shows an example of a parallel-series compensation network.

[0041] FIG. 6 shows the behavior of coupled coils.

[0042] FIG. 7 shows a second example of a WPT according to the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

[0043] FIG. 3 shows a first example of a WPT system (300) according to the present invention in combination with a conductive charging stage that comprises the OBC (200) with the DC link capacitor (202) for an EV. The WPT system (300) comprises a GA (301) and a VA (302) for inductive charging of the EV. Furthermore, the EV comprises an OBC (200) for conductive charging as the one shown in FIG. 2.

[0044] The WPT system (300) comprises an inductive charging coil assembly (312) comprising a transmitting coil (307) in the GA (301) and a receiving coil (308) in the VA (302).

[0045] The GA (301) of the WPT system (300) comprises an AC/DC converter (304) with power factor correction (PFC) that converts the three phase power source (303) to a regulated DC power source. The GA (301) of the WPT system (300) comprises an AC converter (305) generates a square wave voltage with a nearly constant frequency and duty cycles.

[0046] The WPT system (300) further comprises a compensation circuit having a primary compensation circuit (306) for the GA (301) and a secondary compensation circuit (309) for the VA (302). The compensation circuit is a parallel-series compensation network used to achieve a proposed compensation strategy according to the present invention. The proposed compensation strategy permits the inductive charging of the EV in the VA (302) to take advantage of the conductive battery charger by regulating the DC link voltage of the DC link capacitor (202) in the OBC (200). Hence, the compensation circuit (309) permits the receiving coil (308) to behave as a voltage source. Hence, a voltage V.sub.VA is generated in the VA receiver coil (308) having an amplitude proportional to an effective current I.sub.p_rms in the GA transmitting coil (307). A preferred parallel-series compensation network is shown in FIG. 5.

[0047] The VA (302) of the WPT system (300) comprises a secondary compensation circuit (309) as part of the parallel-series compensation network which causes the receiving coil (308) of the coil assembly (312) to behave as a voltage source. The VA (302) of the WTP system (300) lacks the DC link capacitor and the DC/DC battery charger previously shown in FIG. 2. The output of the HF rectifier (310) can be loaded in the DC link capacitor (202). Hence, the DC link capacitor (202) and the DC/DC battery charger (203) of the OBC (200) can be shared between the conductive stage OBC (200) and the VA (302) of the WPT system (300). Therefore, the proposed WPT system (300) avoids duplicities of the charging modules/DC links in the EV (120).

[0048] FIG. 4 shows a GA (401) and VA (401) wireless charging stages of a more detailed example of a WPT (400) according to the present disclosure. FIG. 4 also shows the control strategy stage (445) used to obtain a desired voltage to regulate a DC link/battery charger in a conventional conductive charger of an EV.

[0049] The GA (401) comprises a DC-to-AC converter (404) that would correspond to the AC converter (305) in FIG. 3 and which converts a DC source V.sub.dc_GA to a square wave voltage source which main frequency depends upon an applicable technical standard, e.g. SAE standard (e.g. 81.38 kHz to 90 kHz), and which duty cycle may vary depending upon regulation circuit input command from the control strategy stage (445). The DC-to-AC converter (404) can be designed to minimize switching loses by means of zero voltage switching (ZVS) or zero current switching (ZCS) techniques.

[0050] The GA (401) comprises DC blocking and Impedance Matching Network (IMN) stage (405) that includes a capacitor Cc (405a) for blocking DC current that may saturate the IMN transformer. An inductor Lc (405b) converts the square wave voltage source to a current source and an IMN transformer adapts the impedance and voltage levels to values required by the WPT coils (407), (408).

[0051] The GA (401) comprises a GA coil Lp (407) and a primary compensating network (406). The VA (402) comprises a VA coil Ls (408) and a secondary compensating network (409). The compensation network (406), (409) is a parallel-series compensation circuit. As previously mentioned, the parallel-series compensation circuit advantageously permits to generate a voltage source V.sub.VA at the VA coil Ls (408) which amplitude depends upon the effective current I.sub.p_rms flowing through the GA coil Lp (407). Because the DC link voltage of the conductive charging in the DC/DC battery charge (403) shall be regulated within certain boundaries to ensure the proper operation of the on-board DC-to-DC battery charger, the parallel-series compensation circuit permits regulating the DC link voltage by controlling the GA coil current I.sub.p_rms in the GA (401).

[0052] Hence, the GA coil Lp (407) transfers energy from the GA (401) to the VA (402). The compensating network (406) allows the reactive power to be locally provided (i.e. the DC-to-AC converter (404) delivers only the active power). The VA coil Ls (408) is magnetically coupled with the GA coil Lp (407) and receives the energy transferred wirelessly from the GA coil Lp (407) which is maximized.

[0053] The VA (402) comprises a HF rectifier (410). The HF rectifier (410) converts the high frequency signal across the VA coil to DC. FIG. 4 also shows a DC link capacitor Cdc (420) of the conductive charging of the EV. The WPT (400) also shows a block diagram of the proposed control strategy stage (445) used to obtain a desired continuous voltage that regulates the DC link/battery charger in the conductive charger of the EV.

[0054] As shown in FIG. 4, the control strategy stage (445) is composed of 2 nested control loops based on the regulation of the voltage source V.sub.dc_VA and the GA coil current I.sub.p_rms. For this particular implementation, the control strategy stage comprises two PI regulators (450), (455) for the voltage and current control.

[0055] V.sub.da_VA* represents the reference DC link voltage, i.e. the required DC link voltage in the DC link. V.sub.dc_VA is the actual DC link voltage, i.e. the voltage measured in real time. V.sub.dc_VA is the DC value of the voltage V.sub.VA at the VA coil Ls (408) after rectification. Furthermore, the WPT (400) comprises wireless communication means between the VA (402) and the GA (401). Hence, the reference DC link voltage V.sub.da_VA* and the actual DC link voltage V.sub.dc_VA can be sent from the VA (402) to the GA (401) wirelessly by using online communication as e.g. WIFI and/or offline communication as e.g. Bluetooth, NFC or the like. After some time (usually in the range of seconds or milliseconds for this application), the PI regulators (450), (455) can make the actual DC link voltage V.sub.dc_VA equal to the reference DC link voltage V.sub.da_VA*. Therefore the subtraction of V.sub.dc_VA and V.sub.da_VA* is 0 at steady state and the DC link of the conductive charger of the EV can be regulated with the adjusted V.sub.dc_VA during an inductive charging process of the EV. Hence, the control strategy stage (445) can command the DC-to-AC converter (404) to regulate I.sub.p_rms to obtain a V.sub.dc_VA equal to V.sub.da_VA*.

[0056] FIG. 5 shows a parallel-series compensation circuit (500) that can be used in the proposed WPT's according to the present invention. The VA coil model in the VA (302) includes a parasitic R2 and an inductor L2. If a capacitor C2 is placed in series with the inductor L2 (compensation network) and its value is properly chosen, the impedance of the series connection of L2 and the capacitor C2 is null at the operating frequency, where the wireless transfer happens at a fixed frequency f=85 Khz.

[0057] Interestingly enough, the amplitude of this voltage depends upon the signal frequency which is constant, the coupling term, M which is also constant for a given position of the EV car relative to the GA coil L1, and the GA current I.sub.p_rms. Therefore, this is the electrical relationship between the GA coil current I.sub.p_rms and the VA coil voltage V.sub.VA. Therefore, as the inductor L2 is cancelled out with the series capacitor C2, this voltage V.sub.VA can be placed directly across the terminals of the HF rectifier (410).

[0058] FIG. 6 explains the electrical behaviour of coupled coils. In this figure, a voltage source in series with the coil inductance is shown, which models more accurately the behaviour of the coupled coils (the parasitic resistance has been neglected in this figure). The compensation of the VA coil makes L.sub.s to disappear from the model, thus leaving just the voltage source, which is proportional to the frequency, the coupling term M and the primary coil current I.sub.p.

[0059] FIG. 7 shows an alternative example of a WPT (700) according to the present invention.

[0060] Similarly, the GA (701) of the WPT (700) comprises an AC/DC converter (704) with power factor correction (PFC) that converts the three phase power source (103) to a regulated DC power source. The GA (701) of the WPT (700) comprises an AC converter (705) that generates a square wave voltage with a nearly constant frequency and duty cycles.

[0061] The WPT (700) comprises an inductive charging coil assembly (712) comprising a transmitting coil (707) in the GA (701) and a receiving coil (708) in the VA (713).

[0062] The inductive charging coil assembly (712) in the GA (701) comprises a GA coil (707) and a primary compensating network (706). The VA (702) comprises the VA coil (708) and a secondary compensating network (709). The compensation network (706), (709) is also a parallel-series compensation circuit. As previously mentioned, the parallel-series compensation circuit advantageously permits to generate a voltage source at the VA coil (708) which amplitude depends upon the effective current flowing through the GA coil (707).

[0063] FIG. 7 also shows the conductive charging stage OBC (200) for conductive charging of the EV. The OBC (200) of the VA (702) comprises the three phase PFC stage (201) for the three phase power source (103), the DC link comprising the DC link capacitor (202) and the isolated DC/DC battery charger (203).

[0064] An alternative solution is shown in FIG. 7, the output of the VA compensation network (709) is connected to the input of the conductive charger three phase PFC stage (201) in the conductive charging OBC (200). Because the three phase PFC stage (201) can be composed of 3 half bridges based on MOSFETs (each of them including a parasitic body diode in parallel), the three phase PFC stage (201) stage can be used as a simple rectifier in order to obtain an adjusted continuous voltage (V.sub.dc_VA) that can be used to regulate the DC link of the conductive charger of the EV during an inductive charging process of the EV, thus affording the dedicated rectifier shown in the original solution as well as the DC link.

[0065] Even though reference has been made to a specific embodiment of the invention, it is obvious for a person skilled in the art that the WPT architectures described herein are susceptible to numerous variations and modifications, and that all the details mentioned can be substituted for other technically equivalent ones without departing from the scope of protection defined by the attached claims.