The present invention refers to wireless power transfer systems for electric vehicles (EV).
Wireless power transfer (WPT) using magnetic resonance is the technology which could set humans free from the annoying wires. In fact, the WPT adopts the same basic theory which has already been developed for at least 30 years with the term inductive power transfer. WPT technology has been developing rapidly in recent years. At kilowatts power level, the transfer distance increases from several millimeters to several hundred millimeters with a grid to load efficiency above 90%. The advances make the WPT very attractive to the electric vehicle (EV) charging applications in both stationary and dynamic charging scenarios. By introducing WPT in EVs, the obstacles of charging time, range, and cost can be easily mitigated and battery technology is not as relevant in the EVs market.
Conventionally, in power conversion, when AC is converted to low voltage DC, or AC from one frequency to another, the AC is usually rectified and smoothed to obtain a fixed voltage at fixed frequency. Once this is accomplished, the power is then routed to an inverter to obtain the final output with variable voltage and variable frequency. The DC voltage that is fed into the inverter is called the DC link. As the name implies, the two sources are linked together with a filter capacitor.
In electric vehicle (EV) applications, the DC link capacitor is used as a load-balancing energy storage device. The DC link capacitor may be placed between the DC battery and the AC, i.e. the load side of the voltage inverter. The capacitor is placed parallel to the battery and to a DC-to-DC battery charger, maintaining a solid voltage across the inverter. The DC link capacitor helps protecting the inverter network from momentary voltage spikes, surges and EMI.
A known WPT system (100) for an EV (120) is shown in
The GA (101) of the WPT system (100) comprises an AC/DC converter (104) with power factor correction (PFC) that converts the single or three phase power source (103) to a regulated DC power source. The GA (101) of the WPT system (100) also comprises a DC to high frequency (HF) AC converter (105) that generates a square wave voltage with a nearly constant frequency and duty cycles. The GA (101) comprises a primary compensation circuit (106) which is a passive circuit network that compensates the transmitting coil inductance in order to reduce the amount of reactive power delivered by the DC to HF AC converter (105).
The WPT system (100) comprises an inductive charging coil assembly (112) comprising a transmitting GA coil (107) in the ground side, GA (101) and a receiving VA coil (108) located at the vehicle side, VA (102).
The VA (102) comprises a secondary compensation circuit (109) which is a passive circuit network that compensates the receiving coil inductance in order to maximize the transferred power at electrical resonance. The VA (102) comprises an AC/DC Rectifier (110) and/or a DC/DC battery charger (205) (shown in
The charging of the high voltage battery (111) can potentially be handled by both assemblies the GA (101) and the VA (102) of the WPT system (100), which design can determine an optimal WPT architecture.
Typically, the VA inductive charging of the WPT systems is designed without considering the potential existing conductive charger in the EV. Therefore the charging modules in the WPT are not optimized in terms of cost, volume and weight, because some of the basic functionalities of the charging modules in the VA (102) are likely to be duplicated in the conductive and inductive charging stages of the EV (120).
For instance, existing systems elements of the inductive charger of the VA as e.g. a current-doubler rectifier, an interleaved secondary control and/or an output filter stages may not be shared with the conductive charger of the VA. In these systems, it is likely that a conductive on-board charger (OBC) is connected in parallel to the battery duplicating the functionality of the aforementioned stages as shown in
The VA (102) of the WPT system (100) comprises the receiving VA coil (108) located at the vehicle side of the inductive charging coil assembly (112), the secondary compensation circuit (109) to compensate the receiving coil inductance, the AC/DC Rectifier (110), a DC link capacitor (204) and a DC/DC battery charger (205).
Hence, it can be seen from
Therefore, a battery charging system that uses inductive and conductive charging but avoids at least the aforementioned duplicities to reduce volume, weight and cost of the vehicle assembly of the EV is desired.
This invention deals with a wireless power transfer (WPT) system that can be integrated with an already existing conductive on-board battery charger (OBC) for electric vehicles. The invention has the potential of sharing the conductive on-board charger modules with the WPT system, thus reducing volume, weight and cost of the vehicle assembly.
This invention proposes a WPT architecture including the associated power converter topologies with proposed compensation and control strategies that allow integrating the WPT system with charging modules of an already existing conductive charging system in the EV, thus optimizing the EV volume, weight and cost.
In a first aspect, it is proposed an example of a WPT system for an EV according to the present invention. The WPT system comprises a GA and a VA. The GA comprises a GA transmitter coil and the VA comprises a VA receiver coil magnetically coupled to the GA transmitter coil. This WPT system can correspond to
The WPT comprises a compensation strategy. The compensation strategy comprises a parallel-series compensation network that permits obtaining a voltage VVA in the VA receiver coil which amplitude is proportional to an effective current Ip_rms flowing through the GA transmitter coil. A parallel-series compensation network is shown in
The voltage VVA in the VA receiver coil can be converted into a continuous voltage with a rectifier comprised in the VA of the EV. Hence, a continuous Vdc_VA of the voltage source VVA is obtained in the VA receiver coil of the WPT.
The WPT comprises a control strategy stage to adjust the continuous voltage Vdc_VA in order to reach a reference DC link voltage. For this action, the control strategy stage comprises two nested control loops: a voltage control loop receiving as inputs the continuous Vdc_VA and the reference DC link voltage and a current control loop receiving as inputs the current Ip_rms and the output of the voltage control loop. The reference DC link voltage is the required voltage in the DC link of the conductive charger of the EV.
Hence, the DC link of the conductive charger of the EV can be regulated with the adjusted Vdc_VA during an inductive charging process of the EV. Therefore, upon the use of the proposed compensation and control strategies, the proposed WPT can use the battery charging modules/DC link of the conductive charger during an inductive charging process of the EV and hence, duplicities in the vehicle assembly can be avoided.
The GA of the WPT can comprise a DC-to-AC converter that converts a DC source to a square wave voltage source. A duty cycle of the DC-to-AC converter may vary depending upon a control command received from the control strategy stage to obtain the adjusted Vdc_VA.
Additionally, the WPT comprises a DC blocking and impedance matching network (IMN) stage that comprises a capacitor Cc for blocking DC current that may saturate an IMN transformer. An inductor Lc can convert the square wave voltage source from the DC-to-AC converter to a current source. The IMN transformer can adapt the impedance and voltage levels to values required by the GA coil and the VA coil in the WPT.
In a second aspect, it is proposed another example of a WPT system for an EV. The WPT comprises a GA and a VA. The GA comprises a GA transmitter coil. The VA comprises a VA receiver coil magnetically coupled to the GA transmitter coil.
This WPT also comprises a compensation strategy that comprises a parallel-series compensation network to obtain a voltage VVA in the VA receiver coil proportional to an effective current Ip_rms in the GA transmitter coil.
The WPT also comprises a control strategy stage to adjust Vdc_VA based on the reference DC link voltage. As in the first WPT, the reference DC link voltage is the required voltage in the DC link of the conductive charger of the EV.
The control strategy stage comprises two nested control loops: a voltage control loop receiving the Vdc_VA and the reference DC link voltage as inputs and a current control loop receiving the current Ip_rms and an output from the voltage control loop.
A power factor correction (PFC) stage of a conductive charger of the EV can be supplied with VVA during an inductive charging process of the EV to obtain a continuous Vdc_VA. Hence, the continuous Vdc_VA can be used to regulate a DC link of the conductive charger of the EV. Therefore, the proposed second example of WPT uses the battery charging modules/DC link of the conductive charger during an inductive charging process. Furthermore, this WPT also uses the PFC of the conductive charger as a rectifier to obtain the continuous Vdc_VA. Hence, DC charging stages of a conventional WPT are no longer needed with the proposed WPT. The WPT of the second aspect according to the present invention can correspond to the embodiment shown in
Similar to the first aspect, WPT comprises the DC-to-AC converter regulated with a control command of the control strategy stage to obtain the adjusted Vdc_VA and a DC blocking and impedance matching network (IMN).
In a third aspect according to the present invention, it is proposed an electrical vehicle that comprises a conductive charging stage having a DC link and the proposed WPT.
In a fourth aspect, it is proposed a method for charging an EV with a WPT system according to the present invention, the system comprising a GA and a VA, the method comprises a step for applying an effective current Ip_rms to a GA transmitter coil of the WPT, a second step for obtaining a voltage VVA in a VA receiver coil of the WPT proportional to the Ip_rms, a third step for obtaining a continuous voltage Vdc_VA in the VA of the WPT, a fourth step for adjusting Vdc_VA to reach a reference DC link voltage value, a fifth step for regulating a DC link of a conductive charging of the EV with the adjusted Vdc_VA. This method may be performed by the WTP according to the first WPT described in the present disclosure.
In a fifth aspect, it is proposed a method for charging an EV with a WPT system, the system comprising a GA and a VA, the method comprises a first step for applying a effective current Ip_rms to a GA transmitter coil of the WPT, a second step for obtaining a voltage VVA in a VA receiver coil of the WPT proportional to the Ip_rms, a third step for adjusting Vdc_VA to reach a reference DC link voltage, a fourth step for supplying a PFC of conductive charger of the EV with the VVA to obtain a continuous adjusted Vdc_VA, and a fifth step for regulating a DC link of the conductive charging of the EV with the continuous adjusted Vdc_VA. This method may be performed by the second WTP described in the present disclosure.
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.
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).
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.
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 VVA is generated in the VA receiver coil (308) having an amplitude proportional to an effective current Ip_rms in the GA transmitting coil (307). A preferred parallel-series compensation network is shown in
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
The GA (401) comprises a DC-to-AC converter (404) that would correspond to the AC converter (305) in
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).
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 VVA at the VA coil Ls (408) which amplitude depends upon the effective current Ip_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 Ip_rms in the GA (401).
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.
The VA (402) comprises a HF rectifier (410). The HF rectifier (410) converts the high frequency signal across the VA coil to DC.
As shown in
Vda_VA* represents the reference DC link voltage, i.e. the required DC link voltage in the DC link. Vdc_VA is the actual DC link voltage, i.e. the voltage measured in real time. Vdc_VA is the DC value of the voltage VVA 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 Vda_VA* and the actual DC link voltage Vdc_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 Vdc_VA equal to the reference DC link voltage Vda_VA*. Therefore the subtraction of Vdc_VA and Vda_VA* is 0 at steady state and the DC link of the conductive charger of the EV can be regulated with the adjusted Vdc_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 Ip_rms to obtain a Vdc_VA equal to Vda_VA*.
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 Ip_rms. Therefore, this is the electrical relationship between the GA coil current Ip_rms and the VA coil voltage VVA. Therefore, as the inductor L2 is cancelled out with the series capacitor C2, this voltage VVA can be placed directly across the terminals of the HF rectifier (410).
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.
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).
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).
An alternative solution is shown in
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.
Number | Date | Country | Kind |
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19382083.4 | Feb 2019 | EP | regional |