WO2023163595A1

WO2023163595A1 - An inductive power transfer system for wirelessly charging a battery with either half or double the nominal battery voltage for the same output power as well as a corresponding method

Info

Publication number: WO2023163595A1
Application number: PCT/NL2023/050094
Authority: WO
Inventors: Francesca GRAZIAN; Thiago Batista Soeiro; Pavol Bauer
Original assignee: Technische Universiteit Delft
Priority date: 2022-02-25
Filing date: 2023-02-27
Publication date: 2023-08-31
Also published as: NL2031085B1

Abstract

An inductive power transfer system, comprising a first power converter for converting an input to a first output, a second power converter for converting said input to a second output, a controller arranged for controlling said first power converter and said second power converter, a first set of magnetically coupled coils, wherein a first coil of said first set of magnetically coupled coils is connected to said first power converter for receiving said first output, a second set of magnetically coupled coils, wherein a first coil of said second set of magnetically coupled coils is connected to said second power converter for receiving said second output, rectifying means connected to said second coil of said first set of magnetically coupled coils and to said second coil of said second set of magnetically coupled coils, wherein said rectifying means are arranged for providing an output power to a battery, wherein said rectifying means are configured for either connecting said second coil of said first set of magnetically coupled coils and said second coil of said second set of magnetically coupled coils in series such that said second coils shares the same current for providing said output to said battery which nominal voltage is double, or connecting said second coil of said first set of magnetically coupled coils and said second coil of said second set of magnetically coupled coils in parallel for adding currents flowing through said second coils for providing said output to said battery which nominal voltage is half.

Description

Title

An inductive power transfer system for wirelessly charging a battery with either half or double the nominal battery voltage for the same output power as well as a corresponding method.

Technical field

The present disclosure is directed to the field of inductive power transfer systems for wirelessly charging a battery and, more specifically, to an inductive power transfer system that is capable to cope with different nominal battery voltages.

Background

T ransportation consists of one of the primary sources of greenhouse gas emissions. To limit these emissions, there is a collective effort to switch from gasbased vehicles to electric vehicles, EVs, powered by clean-energy sources. This electrification process is part of a greater worldwide phenomenon called the energy transition.

So far, some of the main concerns related to large-scale usage of EVs are linked to the EV energy storage, i.e. the drivers’ anxiety for the limited battery range and the relatively long duration of one battery charging cycle. Wireless charging has been gaining interest in the EV industry for several reasons. First, wireless charging stations can be integrated more easily into the streets than conventional- wired charging points. Then, it would solve the drivers’ inconvenience in handling charging cables making the process more autonomous. Additionally, it could create more opportunity for charging spots in, for example, congested streets, crossings, or busy intersections with traffic lights. EV wireless charging systems are composed of two main parts: the transmitter circuit, which is the power source embedded in, for example, the street, and the receiver circuit placed on board of the vehicle and which is connected to the battery of the vehicle.

As more EV models crowd the streets, it is noticeable that their nominal battery voltage is not necessarily the same. The nominal voltage of EV batteries is, typically, 400 Volts or 800 Volts. Wireless charging transmitters should be able to supply power efficiently to multiple EV battery classes. This need becomes fundamental when considering applications such as public parking, taxi pick-up locations in front of stations or airports, corporate fleets, car rental, or sharing facilities. Additionally, to ensure that wireless charging is a sustainable and cost-effective solution, the power loss in the circuit during one charging cycle must be minimal.

The above translates into the demand for high-power transfer efficiency. Usually, EV wireless charging systems achieve high power transfer efficiency when operating at the nominal operating condition for a certain power level, i.e. when they charge the battery class for which they have been designed. Charging a battery with either double or half the nominal voltage would dramatically worsen the system efficiency for the same output power.

Summary

A summary of aspects of certain examples disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects and/or a combination of aspects that may not be set forth.

It is an object of the present disclosure to provide an inductive power transfer system that is capable of operating with EV battery classes of either double or half the nominal voltage for the same output power while maintaining high power transfer efficiency. It is a further object of the present disclosure to provide for a corresponding method.

In a first aspect of the present disclosure, there is provided an inductive power transfer system, comprising: a first power converter (M1-M4) for converting an input to a first output; a second power converter (M5-M8) for converting said input to a second output; a controller arranged for controlling said first power converter (M1-M4) and said second power converter (M5-M8); a first set of magnetically coupled coils (L1-L3), wherein a first coil (L1) of said first set of magnetically coupled coils is connected to said first power converter for receiving said first output; a second set of magnetically coupled coils (L2-L4), wherein a first coil (L2) of said second set of magnetically coupled coils is connected to said second power converter for receiving said second output; rectifying means connected to said second coil (L3) of said first set of magnetically coupled coils and to said second coil (L4) of said second set of magnetically coupled coils, wherein said rectifying means are arranged for providing an output power to a battery, wherein said rectifying means are configured for: connecting said second coil (L3) of said first set of magnetically coupled coils and said second coil (L4) of said second set of magnetically coupled coils in series such that said second coils (L3-L4) share the same current for providing said output power to said battery, for example with a double nominal voltage (e.g. 800V); connecting said second coil (L3) of said first set of magnetically coupled coils and said second coil (L4) of said second set of magnetically coupled coils in parallel for adding currents flowing through said second coils (L3-L4) for providing said output power to said battery, for example with half a nominal voltage (e.g. 400V).

This present disclosure is directed to an inductive power transfer system that can operate either as voltage doubler or current doubler for the same output power while maintaining high power transfer efficiency.

The rectifying means are construed such that the second coils of the two sets of magnetically coupled coils are either effectively connected in series or in parallel.

The inductive power transfer system operates as a voltage doubler when the second coils of the two sets of magnetically coupled coils are connected in series. That is, the series connection of the second coils of the first set of magnetically coupled with the second coil of the second set of magnetically coupled coils results in the secondary coils conducting the same nominal current which makes the system, for the said output power, suitable for batteries with double the nominal voltage (e.g. 800V).

The inductive power transfer system operates as a current doubler when the second coils of the two sets of magnetically coupled coils are connected in parallel. That is, the nominal current flowing through the second coil of the first set of magnetically coupled coils is added to the nominal current flowing through the second coil of the second set of magnetically coupled coils at the output. The output to the battery thus comprises the sum of both currents resulting in double the battery current compare to the above described voltage doubler mode. This particular mode is thus suitable for batteries with half the nominal voltage (e.g. 400V).

In accordance with the present disclosure, it is noted that the inductive power transfer system may be split into a transmitter part and a receiver part. The transmitter part may be construed as the two power converters and the first coils of the two sets of magnetic coupled coils. The first coils may thus be viewed as the primary windings of both the two sets of magnetic coupled coils.

The receiver part may be construed as the rectifying means as well as the second coils of the two sets of magnetic coupled coils. The second coils may thus be viewed as the secondary windings of both the two sets of magnetic coupled coils.

The transmitter may be provided in a charging station. The receiver may be implemented in a vehicle and may be connected to the battery of the vehicle.

The inventors have found that it may be beneficial if the control of the inductive power transfer system is implemented at the transmitter side. This would mean that the receiver side only comprises passive components. As such, the rectifying means may not need to comprise active components in the sense that these components do not need to be controlled by a controller, for example.

The rectifying means may be implemented in such a way that the polarity of the voltages at the secondary windings of the magnetic coupled coils determine whether the secondary windings are connected in series or in parallel. The polarity of these voltages can be controlled by the controller. The controller may be arranged to control the outputs of the two power converters and thereby the polarity of the output voltages.

It is noted that compensation capacitors may be added in series to the second coils of the respective sets of magnetically coupled coils to reduce the circulation of reactive power in the system and to ensure that both the first and the second power converter operates in a soft-switching condition. These capacitors are also highlighted in the appending figures with reference numerals C1 , C2, C3 and C4.

The input of the inductive power transfer system may be a regular Alternating Current, AC, mains power supply, for example a 230Vac mains power supply. It is noted that, in accordance with the present disclosure, the input may be a Direct Current, DC, input or an Alternating Current, AC, input.

In accordance with the present disclosure, the controller may be any of a microcontroller, Field Programmable Gate Array, FPGA, an Application Specific Integrated Circuit, ASIC, or anything alike.

It is noted that, in accordance with the present disclosure, intentional or unintentional magnetic coupling may occur between any of: the first coil of the first set of magnetically coupled coils and the second coil of the second set of magnetically coupled coils, and/or the first coil of the second set of magnetically coupled coils and the second coil of the first set of magnetically coupled coils.

In an example, the controller is further arranged for: controlling said first power converter and said second power converter such that said rectifying means connect said second coil (L3) of said first set of magnetically coupled coils and said second coil (L4) of said second set of magnetically coupled coils either in series or in parallel.

The above described example is directed to the functionality of the controller. The controller may control the polarity of the outputs of the two power converters such that, at the secondary side, i.e. the receiver side, the second coils are either connected in series or in parallel.

In a further example, the first power converter and said second power converter are both full-bridge inverters.

A full bridge inverter is a switching device that generates a square wave AC output voltage on the application of an input by adjusting the switch turning ON and OFF based on the appropriate switching sequence, where the output voltage generated is of the form of the input voltage, the reversed input voltage or even zero.

It is noted that the two full-bridge inverter may operate independently. The first full-bridge inverter may operate in such a way that the output resembles the positive input voltage for the first half of the switching period and the negative input voltage for the remaining half. The second full-bridge inverter may operate in such a way that the output is either the same or the opposite to the output from the first fullbridge inverter.

Controlling the second full-bridge inverter in such a way that its output is the same as, i.e. follows, the output of the first full-bridge inverter may result in a situation wherein the secondary coils of the corresponding sets of magnetic coupled coils are effectively connected in series, thereby sharing the same nominal current which is suitable for said battery with double nominal voltage (e.g. 800V).

Controlling the second full-bridge inverter in such a way that its output is the opposite to the output of the first full-bridge inverter, from a polarity perspective, may result in a situation wherein the secondary coils of the corresponding sets of magnetic coupled coils are effectively connected in parallel, thereby doubling the output current of the inductive power transfer system which is suitable for said battery with half nominal voltage (e.g. 400V)..

In a further example, the controller is arranged to any of: control said first power converter and said second power converter such that corresponding output currents of said first and second power converter flow in a same direction through said first coil (L1) of said first set of magnetically coupled coils and said first coil (L2) of said second set of magnetically coupled coils; control said first power converter and said second power converter such that corresponding output currents of said first and second power converter flow in opposite direction through said first coil (L1) of said first set of magnetically coupled coils and said first coil (L2) of said second set of magnetically coupled coils.

In a further example, the second terminal of said second coil (L3) of said first set of magnetically coupled coils is connected to a first terminal of said second coil (L4) of said second set of magnetically coupled coils, wherein said rectifying means comprise: a first diode (D1) having an anode connected to a first terminal of said second coil (L3) of said first set of magnetically coupled coils, and wherein a cathode of said first diode (D1) is connected to a first terminal of said output (+); a third diode (D3) connected in series with a sixth diode (D6), wherein a centre tap c) is connected to a second terminal of said second coil (L4) of said second set of magnetically coupled coils, and wherein a cathode of said third diode (D3) is connected to said first terminal of said output (+), and wherein an anode of said sixth diode (D6) is connected to a second terminal of said output (-); a fifth diode (D5) having an anode connected to said second terminal of said output (-) and having a cathode connected to a centre tap (b) of said connection between said second terminal of said second coil (L3) of said first set of magnetically coupled coils and said first terminal of said second coil (L4) of said second set of magnetically coupled coils.

The above described example provides for a detailed implementation of a particular implementation of the rectifying means. It is noted that the rectifying means may also be implemented in a different manner. One of the aspects of the rectifying means is that they operate in such a manner that the two second coils of the sets of magnetic coupled coils are either effectively connected in series or in parallel, depending on the polarity of the voltages across the second coils.

In a further example, the rectifying means further comprises: a fourth diode (D4) having an anode connected to said second terminal of said output (-) and having a cathode connected to said anode of said first diode (D1), such that there is centre tap (a) in said connection between said fourth diode (D4) and said first diode (D10, said centre tap (a) being connected to said first terminal of said second coil (L3) of said first set of magnetically coupled coils.

In another example, the rectifying means further comprises: a second diode (D2) having an anode connected to said centre tap (b) of said connection between said second terminal of said second coil (L3) of said first set of magnetically coupled coils and said first terminal of said second coil (L4) of said second set of magnetically coupled coils, and having a cathode connected to said first terminal of said output (+);

In accordance with the present disclosure, the controller may be arranged to control said first power converter and said second power converter such that an output voltage of said output to said battery is either between 300Volt - 500Volt or 700Volt - 900Volt. Typically, a battery of an electric vehicle may have a nominal battery voltage of either 400Volts or 800Volts.

In a second aspect of the present disclosure, there is provided a method of operating an inductive power transfer system in accordance with any of the previous examples, wherein said method comprises the steps of: converting, by said first power converter (M1-M4), said input to said first output; converting, by said second power converter (M5-M8), said input to said second output; controlling, by said controller, said first power converter (M1-M4) and said second power converter (M5-M8); providing, by said rectifying means, said output to said battery, wherein said providing comprises any of: connecting said second coil (L3) of said first set of magnetically coupled coils and said second coil (L4) of said second set of magnetically coupled coils in series such that said second coils (L3-L4) share the same output current for providing said output power to said battery; connecting said second coil (L3) of said first set of magnetically coupled coils and said second coil (L4) of said second set of magnetically coupled coils in parallel for adding currents flowing through said second coils (L3-L4) for providing said output power to said battery.

It is noted that the advantages as explained with reference to the first aspect of the present disclosure, being the inductive power transfer system, are also applicable to the second aspect of the present disclosure, being the method of operating such an inductive power transfer system.

In an example, the method comprises the step of: controlling, by said controller, said first power converter and said second power converter such that said rectifying means connect said second coil (L3) of said first set of magnetically coupled coils and said second coil (L4) of said second set of magnetically coupled coils either in series or in parallel.

In a further example, the first power converter and said second power converter are both full-bridge inverters. In another example, the method comprises any of the steps of: controlling, by said controller, said first power converter and said second power converter such that corresponding output currents of said first and second power converter flow in a same direction through said first coil (L1) of said first set of magnetically coupled coils and said first coil (L2) of said second set of magnetically coupled coils; controlling, by said controller, said first power converter and said second power converter such that corresponding output currents of said first and second power converter flow in opposite direction through said first coil (L1) of said first set of magnetically coupled coils and said first coil (L2) of said second set of magnetically coupled coils.

In an example, the rectifying means may be provided with a plurality of diodes, as indicated with reference numerals D1 , D2, D3, D4, D5 and D6 in the appending figures. The working principle of these diodes may be explained as follows.

When the currents flowing through both first coils (L1 , L2) of said sets of magnetically coupled coils flow in the same direction, this results in a series connection of the second coils (L3, L4) of said sets of magnetically coupled coils. This is considered the voltage doubler mode. In this particular case, the diodes D2 and D5 do not conduct any current. In particular, Diode D1 and Diode D6 conduct current when the square voltage between the centre taps (a) and (c) is positive. On the other hand, diode D3 and diode D4 conduct current when the square voltage between the centre taps (a) and (c) is negative.

When the currents flowing through both first coils (L1 , L2) of said sets of magnetically coupled coils flow in an opposite direction, this results in a parallel connection of the second coils (L3, L4) of said sets of magnetically coupled coils. This is considered the current doubler mode. In that particular case, the Diodes D1 , D3 and D5 conduct current when the square voltage between the centre taps (a) and (b) is positive. On the other hand, diode D2, diode D4 and diode D6 conduct when the square voltage between the centre taps (a) and (b) is negative.

In a further example, the method comprises the step of: controlling, by said controller, the input to said first power converter and said second power converter such that an output current of said output to said battery is constant during the battery charging profile in which the voltage of the battery varies either between 300Volt - 500Volt or 700Volt - 900Volt.

In a third aspect of the present disclosure, there is provided a computer program product comprising a computer readable medium having instructions stored thereon which, when executed by a controller of an inductive power transfer system, cause said controller to implement the method steps associated with the controller in any of the examples as provided above.

The present disclosure is described in conjunction with the appended figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

The above and other aspects of the disclosure will be apparent from and elucidated with reference to the examples described hereinafter.

Brief description of the drawings

Figure 1a discloses an example of an implementation of an inductive power transfer system in accordance with the present disclosure;

Figure 1 b discloses a further example of an inductive power transfer system in accordance with the present disclosure;

Figure 2a discloses an example of an equivalent circuit of figure 1 when operating as a voltage doubler;

Figure 2b discloses an example of an equivalent circuit of figure 1 when operating as a current doubler;

Figure 3a discloses an example of an S-S compensated 1-to-1 coil system;

Figure 3b discloses an example of a DC-DC converter at the battery; Figure 4 discloses two examples of a coils arrangement in accordance with the two sets of magnetic coupled coils in accordance with the present disclosure;

Figure 5 shows a pragmatic example of an implementation of an indicative power transfer system in association with an electric vehicle, EV;

Figure 6 shows an example of a power transfer system in accordance with the present disclosure when the controller operates it as a current doubler;

Figure 7 shows an example of a power transfer system in accordance with the present disclosure when the controller operates it as a voltage doubler.

Detailed Description

It is noted that in the description of the figures, same reference numerals refer to the same or similar components performing a same or essentially similar function.

A more detailed description is made with reference to particular examples, some of which are illustrated in the appended drawings, such that the manner in which the features of the present disclosure may be understood in more detail. It is noted that the drawings only illustrate typical examples and are therefore not to be considered to limit the scope of the subject matter of the claims. The drawings are incorporated for facilitating an understanding of the disclosure and are thus not necessarily drawn to scale. Advantages of the subject matter as claimed will become apparent to those skilled in the art upon reading the description in conjunction with the accompanying drawings.

The ensuing description above provides preferred exemplary embodiment(s) only, and is not intended to limit the scope, applicability or configuration of the disclosure. Rather, the ensuing description of the preferred exemplary embodiment(s) will provide those skilled in the art with an enabling description for implementing a preferred exemplary embodiment of the disclosure, it being understood that various changes may be made in the function and arrangement of elements, including combinations of features from different embodiments, without departing from the scope of the disclosure.

Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to." As used herein, the terms "connected," "coupled," or any variant thereof means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, electromagnetic, or a combination thereof. Additionally, the words "herein," "above," "below," and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word "or," in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

These and other changes can be made to the technology in light of the following detailed description. While the description describes certain examples of the technology, and describes the best mode contemplated, no matter how detailed the description appears, the technology can be practiced in many ways. Details of the system may vary considerably in its specific implementation, while still being encompassed by the technology disclosed herein. As noted above, particular terminology used when describing certain features or aspects of the technology should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the technology with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the technology to the specific examples disclosed in the specification, unless the Detailed Description section explicitly defines such terms. Accordingly, the actual scope of the technology encompasses not only the disclosed examples, but also all equivalent ways of practicing or implementing the technology under the claims.

Figure 1a discloses an example of an implementation of an inductive power transfer system 1 in accordance with the present disclosure.

The inductive power transfer system 1 comprises two full-bridge inverters. The first full-bridge inverter is indicated with the Metal Oxide Semiconductor, MOS, Field Effect Transistors, FETs, Power Si MOSFETs, Power SiC MOSFETs, having reference numerals M1 , M2, M3 and M4. The second full-bridge inverter is indicated with the MOSFETs having reference numerals M5, M6, M7 and M8.

The controller is not shown in figure 1 but is arranged to control the gates of the MOSFETs.

A first set of magnetic coupled coils is indicated with the reference numerals L1 , L3, wherein the magnetic coupling is indicated with reference numeral M13. A first coil L1 of the first set of magnetic coupled coils is connected to the output of the first full-bridge inverter.

A second set of magnetic coupled coils is indicated with the reference numerals L2, L4, wherein the magnetic coupling is indicated with reference numeral M24. A first coil L2 of the second set of magnetic coupled coils is connected to the output of the second full-bridge inverter.

It is noted that there might be additional unintentional coupling between any of L1 with L4, L2 with L3, L1 with L4 and L3 with L4. Such unintentional coupling does not affect the working principles of the inductive power transfer system in accordance with the present disclosure.

The rectifying means is implemented as the circuit that is connected to the secondary sides of the two magnetic coupled coils.

As shown in figure 1 , the second terminal of the coil L3 is connected to the first terminal of coil L4. Other types of components may be present in this particular connection, for example R3, C3, C4 and R4, but are, for simplicity reasons, not further discussed in this particular disclosure.

It is noted that the above described the compensation is not limited to this specific implementation, but could also consist, for example, of parallel compensation capacitors or any connection of compensation inductors and capacitors. When considering the four coils, they do not need to be compensated in the same way, but any combinations of the previously mentioned compensations are possible.

The output of the inductive power transfer system 1 is indicated with the reference numeral V_out, and may be connected to a battery. As mentioned above, the rectifying means may be implemented in an electric vehicle such that the output is connected to the battery that is present in the electric vehicle.

The rectifying means are arranged for connecting the coil L3 effectively in series with the coil L4 in case the inductive power transfer system is to double the voltage. The rectifying means are arranged for connecting the coil L3 effectively in parallel with the coil L4 in case the inductive power transfer is to double the output current. This is explained in more detail with reference to figures 2a and 2b.

Following the above, the inductive power transfer system may operate as either a voltage doubler or current doubler for the same output power depending on the modulation strategy of the two full-bridge inverters.

When the half-bridge legs with mid-point A and C have the same modulation, the secondary coils L3, L4 are effectively provided in a series connection. This is a consequence of the fact that, in the rectification stage, only the diode D1 and D6 of the rectifying means conduct during the positive half-wave of the voltage between point a and point c, while the diodes D3 and D4 conduct in the negative one.

Due to the series connection of the corresponding series-compensated secondary coils L3, L4, this modulation corresponds to the voltage doubler mode. An equivalent circuit is shown in figure 2a, where the battery and power handling are replaced by the equivalent first-harmonic load R_ac.

On the other hand, when the half-bridge legs with mid-point A and D have the same modulation, the secondary coils result in a parallel connection. In this particular case, the diodes D1 , D3 and D5 conduct during the positive half-wave of the voltage between points a and b while the diodes D2, D4 and D6 conduct during the negative one. The parallel connection of the secondary coils L3, L4 results in a load current that is double compared to the previous modulation. For the same output power, this corresponds to the current doubler mode, of which the equivalent figure is shown in figure 2b.

The present disclosure is directed to a scheme for controlling the power converters in such a way that either the voltage is doubled at the secondary side, or that the current is doubled at the secondary side. There is no need to provide active control in the secondary, by utilizing diodes. However, it is possible to provide such active control, for example by utilizing switches like MOSFETs.

One of the aspects of the present disclosure is that the controller at the primary side is able to ensure that the output voltage is doubled or that the output current is doubled. The controller does so by controlling the H-bridges, i.e. power converters, such that the outputs are “in sync” or have opposite polarity. In accordance with the present disclosure, the wording connected to, may mean directly or indirectly connected to.

In essence, the current and/or voltage doubler may be explained in a bit more detail, with a bit more nuance, as follows.

There is a controllability on the output current by changing the modulation of the power converters. The voltage doubler mode is suitable for 800V batteries since the modulation of the power converters result in an equivalent series connection between the receiving coils, meaning that they conduct the same nominal current that flows into the battery.

On the other hand, the current doubler mode is suitable for 400V batteries since the modulation of the H-bridge inverters result in an equivalent parallel connection between the receiving coils, meaning that they still conduct the same nominal current but their parallel connection makes the battery current double than in the previous mode.

In this way, the same selected output power can be efficiently delivered to 400V and 800V batteries. In essence, the voltage is not doubled by the circuitry since that is given by the battery. The circuitry either sends a nominal current or double that current to the load, i.e. the battery.

Figure 1 b discloses a further example of an inductive power transfer system 2 in accordance with the present disclosure.

For completeness reasons, input and output capacitors, i.e. bus-bar capacitances, are shown in both figure 1a and figure 1 b.

The main difference of the implementation shown in figure 1a and the implementation shown in figure 1 b is related to the rectifying means.

In figure 1A diodes are used in the rectification stage, i.e. the diodes with the reference numerals D1 , D2, D3, D4, D5, D6. However, it is noted that other means may be utilized for performing the same function. For example, these diodes may be replaced by switches, like MOSFETs, operating with the same modulation scheme, achieving synchronous rectification. This example is shown in figure 1 b, where the diodes are replaced by the MOSFETs having reference numerals M9, M10, M 11 , M12, M13, M14. Figure 2a discloses an example of an equivalent circuit of figure 1 when operating as a voltage doubler. Figure 2b discloses an example of an equivalent circuit of figure 1 when operating as a current doubler.

The equivalent circuit in figure 2a is described by the Kirchhoff voltage law:

The equivalent circuit in figure 2b is described by the Kirchhoff voltage law:

The impedance Zj of each resonant circuit is defined as:

The mutual inductances M12 and M24 are expressed as:

VAB is taken as reference according to the phasor convention and, together with R_ac, they are defined as follows through the first-harmonic approximation:

For a given processed power, the efficiency of the inductive power transfer system may be defined as:

The parameters of the inductive power transfer system 1 may be chosen to ensure high power transfer efficiency. For simplicity, the parameters’ selection criteria may take into account the following symmetry:

The choice of the coils’ self-inductance Lid, l-2d, and the mutual inductance MD follows from the following equations:

The first condition in the top equation ensures that the conduction losses in the primary and the secondary circuits are balanced. To achieve that, the ratio between RID and R2D must be dependent on the ratio between Vm and V_out which has been derived from the equation:

The second condition above has been found by assuming that the coils’ quality factor QID, Q2D differs of the constant ‘a’ which depends on the coils’ geometry. Finally, the target MD can be approximated in the above provided third equation as well as known from the S-S compensation.

MD depends on the maximum DC input voltage V .max available, the nominal battery voltage V_out, the target output power P_out and the resonant frequency fo=wo/2TT . From the equations provided above, the resulting L1 D and L2D are shown

here below:

Figure 3a discloses an example of an S-S compensated 1-to-1 coil system. Figure 3b discloses an example of a DC-DC converter at the battery. To evaluate the advantages of the proposed inductive power transfer system, its efficiency is compared analytically to the one resulting from a conventional 1 -to-1 coil system with S-S compensation represented in figure 3A. The latter employs half of the passive components, and it has the highest power transfer efficiency for a specific nominal value of EV battery voltage. As stated from the circuit terminals in figure 1 , this system uses the same amount of MOSFETs and diodes as the inductive power transfer system in figure 1 such that they have equal semiconductor cost.

Moreover, this system is provided of a 99% efficient DC/DC converter as shown Fig. 3B, which would conduct only in the case that the current EV battery voltage differs from the nominal one. The comparison between the inductive power transfer system in accordance with the present disclosure and the 1-to-1 coil system has been performed considering the input parameters and semiconductor devices as listed in Table I.

Table 1.

Table 2.

For the 1-to-1 coil system, two designs have been considered: one with 400 V as nominal battery voltage, and the other with 800 V. The 1 -to-1 coil circuit parameters have been chosen in terms of the inductive power transfer system ones which are shown in Table II. Thereby, both options of the 1-to-1 coil system have coils which quality factor is about 41 .4% higher than the one of the inductive power transfer systems coils. This result from the assumptions:

• a=1 — > QI D = Q2D = QD;

• MD, MAB are computed via the equation provided above and KAB = ko.

• the current density J = l/A is the same in each coil, where A is the cross-sectional area of the winding;

• the relationship between the coil’s inductance L, number of turns N, and length of the winding I is: L <x N² <x I²;

• the coils’ resistance is approximated as R = pl/A where p is the resistivity of the material. This is valid if Litz wire is used and if allocating enough space between two consecutive turns that minimize the proximity effect. The resistance of the compensation capacitors has neglected since it is generally much less than the coils’ resistance.

From an analysis of the model it is understood that the losses of the resonant circuit stays the same at both 400 V and 800 V. However, when considering the power conversion stages, there is a difference between the computed efficiency at 400 V and 800 V. In the case of the inductive power transfer system, the current doubler mode (400 V) has more losses since the number of diode conducting are twice that of the voltage doubler mode (800 V). Similarly, when considering the 1-to-1 coils system, the designs with 800 V as nominal Vout are more efficient than the ones at 400 V since the current flowing through the diodes is half for the same power.

When comparing the two different systems, coupled coils with relatively high QD and ko result in inductive power transfer systems being more efficient (over 1%) than the 1 -to-1 coil system at both values of V_out. Moreover, higher values of ko (generally shorter air gaps) require lower values of QD for which inductive power transfer systems become more convenient.

Figure 4 discloses an example of a coils arrangement in accordance with the two sets of magnetic coupled coils in accordance with the present disclosure.

EVs with different nominal battery voltage values complicate the design and the operation of wireless charging systems. A conventional way to address this issue is connecting a DC/DC converter to the battery to supply the target power at the nominal battery voltage. However, the DC/DC converter adds control complexity onboard the EV and lowers the overall efficiency when operated.

The present disclosure discloses a topology defined as voltage/current doubler for EV wireless charging that supplies the same power with high efficiency to both 400V and 800V batteries. The inductive power transfer system comprises two sets of series-compensated coupled coils connected to a dedicated full-bridge converter. The control is implemented at the primary side by operating the two fullbridge inverters with either the same or opposite modulation. The secondary circuit is composed of only passive devices. It has been found that the inductive power transfer system can be more advantageous also in terms of computed power transfer efficiency, for example over 1%, compared to the conventional 1-to-1 coil series- compensated system that uses a 99% efficient DC/DC converter for coils’ quality and coupling factors typical used in inductive power transfer systems. Finally, the inductive power transfer system in accordance with the present disclosure has been experimentally verified for a power level of 7.7kW. Considering that the battery voltage could be either 400V or 800V, the peak DC-to-DC efficiency of 97.11% and 97.52% were measured, respectively.

Following the above, one of the advantages of the present disclosure is that the controller at the primary side of the inductive power transfer is able to determine whether the inductive power transfer system is to operate as a voltage doubler or as a current doubler.

The controller is able to do this by controlling the polarity of the outputs of the first power converter and the second power converter.

Figure 5 shows a pragmatic example 1 of an implementation of an indicative power transfer system in association with an electric vehicle, EV.

The inductive power transfer system is shown with its receiver side having reference numeral 52. The receiver side is arranged to receive the power from a transmitter side 53. The transmitter side 53 thus comprises the two power converters and the primary sides of the two sets of magnetically coupled coils 54, 55. The receiver side comprises the rectifying means, the battery as well as the secondary sides of the two sets of magnetically coupled coils 54, 55.

The input of the inductive power transfer system may be a regular Alternating Current, AC, mains power supply, for example a 230Vac mains power supply. It is noted that, in accordance with the present disclosure, the input may be a Direct Current, DC, input or an Alternating Current, AC, input. Depending on the nature of the input, an initial power conversion stage might need to generate the proper DC input voltage for the two power converters.

For example, the conversion might be AC to DC, or DC to DC. That stage might also be in charge of setting different DC input voltage levels. After that, the first and second power converters are connected to each of the primary coils and their compensation. The compensation can be made of any passive component as explained above, for example capacitors or combination between capacitors and inductors.

The primary coils are coupled to the secondary coils whose main coupling for the operation of the system is L1-L3, L2-L4. However, the presence of unintentional magnetic-cross couplings between the coils, namely L1-L4, L2-L3, L1-4, L3-L4, is not excluded.

Passive components may compensate each secondary coil. These are then connected to the same rectifying circuit, i.e. rectifying means, comprising diodes or MOSFETs. Finally, the rectification stage can be directly connected to the EV battery and its passive filtering. Alternatively, there could be another power conditioning stage between the battery and the rectifying circuit.

Figure 6 shows an example of a power transfer system in accordance with the present disclosure when the controller operates it as a current doubler.

In this particular case, the diodes D1 , D5 and D3 will be active at the secondary side of the system. The current that flows through the diode D1 is then added to the current that flows through the diode D3.

In this particular case, the diodes D1 and D3 will be active at the secondary side of the system. The current that flows through the secondary side of the magnetic coupling L3 will then also flow through the secondary side of the magnetic coupling L4. The current is then not added, but the voltages over both secondary windings L3 and L4 are added to one another.

To reduce the number of claims, certain aspects of the technology are presented below in certain claim forms, but the applicant contemplates the various aspects of the technology in any number of claim forms. For example, while some aspect of the technology may be recited as a computer-readable medium claim, other aspects may likewise be embodied as a computer-readable medium claim, or in other forms, such as being embodied in a means-plus-function claim.

In the description above, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of implementations of the disclosed technology. It will be apparent, however, to one skilled in the art that embodiments of the disclosed technology may be practiced without some of these specific details.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope thereof.

Claims

1. An inductive power transfer system, comprising: a first power converter (M1-M4) for converting an input to a first output, the first power converter being a full-bridge inverter; a second power converter (M5-M8) for converting said input to a second output, the second power converter being a full bridge inverter; a controller arranged for controlling said first power converter (M1-M4) and said second power converter (M5-M8); a first set of magnetically coupled coils (L1-L3), wherein a first coil (L1) of said first set of magnetically coupled coils is connected to said first power converter for receiving said first output; a second set of magnetically coupled coils (L2-L4), wherein a first coil (L2) of said second set of magnetically coupled coils is connected to said second power converter for receiving said second output; rectifying means connected to said second coil (L3) of said first set of magnetically coupled coils and to said second coil (L4) of said second set of magnetically coupled coils, wherein said rectifying means are arranged for providing an output power to a battery, wherein said rectifying means are configured for: connecting said second coil (L3) of said first set of magnetically coupled coils and said second coil (L4) of said second set of magnetically coupled coils in series such that said second coils (L3-L4) share a same current for providing said output power to said battery; connecting said second coil (L3) of said first set of magnetically coupled coils and said second coil (L4) of said second set of magnetically coupled coils in parallel for adding currents flowing through said second coils (L3-L4) for providing said output power to said battery.

2. An inductive power transfer system in accordance with claim 1 , wherein said controller is further arranged for: controlling said first power converter and said second power converter such that said rectifying means connect said second coil (L3) of said first set of magnetically coupled coils and said second coil (L4) of said second set of magnetically coupled coils either in series or in parallel.

3. An inductive power transfer system in accordance with claim 2, wherein said first power converter and said second power converter are both full-bridge inverters.

4. An inductive power transfer system in accordance with claim 3, wherein said controller is arranged to any of: control said first power converter and said second power converter such that corresponding output currents of said first and second power converter flow in a same direction through said first coil (L1) of said first set of magnetically coupled coils and said first coil (L2) of said second set of magnetically coupled coils; control said first power converter and said second power converter such that corresponding output currents of said first and second power converter flow in opposite direction through said first coil (L1) of said first set of magnetically coupled coils and said first coil (L2) of said second set of magnetically coupled coils.

5. An inductive power transfer system in accordance with any of the previous claims, wherein a second terminal of said second coil (L3) of said first set of magnetically coupled coils is connected to a first terminal of said second coil (L4) of said second set of magnetically coupled coils, wherein said rectifying means comprise: a first diode (D1) having an anode connected to a first terminal of said second coil (L3) of said first set of magnetically coupled coils, and wherein a cathode of said first diode (D1) is connected to a first terminal of said output (+); a third diode (D3) connected in series with a sixth diode (D6), wherein a centre tap c) is connected to a second terminal of said second coil (L4) of said second set of magnetically coupled coils, and wherein a cathode of said third diode (D3) is connected to said first terminal of said output (+), and wherein an anode of said sixth diode (D6) is connected to a second terminal of said output (-); a fifth diode (D5) having an anode connected to said second terminal of said output (-) and having a cathode connected to a centre tap (b) of said connection between said second terminal of said second coil (L3) of said first set of magnetically coupled coils and said first terminal of said second coil (L4) of said second set of magnetically coupled coils.

6. An inductive power transfer system in accordance with claim 5, wherein said rectifying means further comprises: a fourth diode (D4) having an anode connected to said second terminal of said output (-) and having a cathode connected to said anode of said first diode (D1).

7. An inductive power transfer system in accordance with claim 4, wherein said controller is arranged to control said first power converter and said second power converter such that the said output power to said battery is supplied when the battery voltage ranges either between 300Volt - 500Volt or 700Volt - 900Volt.

8. A method of operating an inductive power transfer system in accordance with any of the previous claims, wherein said method comprises the steps of: converting, by said first power converter (M1-M4), said input to said first output; converting, by said second power converter (M5-M8), said input to said second output; controlling, by said controller, said first power converter (M1-M4) and said second power converter (M5-M8); providing, by said rectifying means, said output to said battery, wherein said providing comprises any of: connecting said second coil (L3) of said first set of magnetically coupled coils and said second coil (L4) of said second set of magnetically coupled coils in series such that the said second coils (L3-L4) shared a same current for providing said output power to said battery; connecting said second coil (L3) of said first set of magnetically coupled coils and said second coil (L4) of said second set of magnetically coupled coils in parallel for adding currents flowing through said second coils (L3-L4) for providing said output power to said battery.

9. A method in accordance with claim 8, wherein said method comprises the step of: controlling, by said controller, said first power converter and said second power converter such that said rectifying means connect said second coil (L3) of said first set of magnetically coupled coils and said second coil (L4) of said second set of magnetically coupled coils either in series or in parallel.

10. A method in accordance with claim 9, wherein said first power converter and said second power converter are both full-bridge inverters.

11. A method in accordance with claim 10, wherein said method comprises any of the steps of: controlling, by said controller, said first power converter and said second power converter such that corresponding output currents of said first and second power converter flow in a same direction through said first coil (L1) of said first set of magnetically coupled coils and said first coil (L2) of said second set of magnetically coupled coils; controlling, by said controller, said first power converter and said second power converter such that corresponding output currents of said first and second power converter flow in opposite direction through said first coil (L1) of said first set of magnetically coupled coils and said first coil (L2) of said second set of magnetically coupled coils.

12. A method in accordance with any of the claims 8 - 11 , wherein a second terminal of said second coil (L3) of said first set of magnetically coupled coils is connected to a first terminal of said second coil (L4) of said second set of magnetically coupled coils, wherein said rectifying means comprise: a first diode (D1) having an anode connected to a first terminal of said second coil (L3) of said first set of magnetically coupled coils, and wherein a cathode of said first diode (D1) is connected to a first terminal of said output (+); a third diode (D3) connected in series with a sixth diode (D6), wherein a centre tap c) is connected to a second terminal of said second coil (L4) of said second set of magnetically coupled coils, and wherein a cathode of said third diode (D3) is connected to said first terminal of said output (+), and wherein an anode of said sixth diode (D6) is connected to a second terminal of said output (-); a fifth diode (D5) having an anode connected to said second terminal of said output (-) and having a cathode connected to a centre tap (b) of said connection between said second terminal of said second coil (L3) of said first set of magnetically coupled coils and said first terminal of said second coil (L4) of said second set of magnetically coupled coils.

13. A method in accordance with claim 12, wherein said rectifying means further comprises: a fourth diode (D4) having an anode connected to said second terminal of said output (-) and having a cathode connected to said anode of said first diode (D1).

14. A method in accordance with any of the claims 8 - 13, wherein said method comprises the step of: controlling, by said controller, said first power converter and said second power converter such that said output power is delivered while an output voltage of said output to said battery is either between 300Volt - 500Volt or 700Volt - 900Volt.

15. A computer program product comprising a computer readable medium having instructions stored thereon which, when executed by a controller of an inductive power transfer system, cause said controller to implement the method steps associated with the controller in any of the claims 8 - 14.