NL1041080B1

NL1041080B1 - An inductive power transfer system, a method and a computer program product.

Info

Publication number: NL1041080B1
Application number: NL1041080A
Authority: NL
Inventors: Bauer Pavol; Prasanth Venugopal; Ralino Elias Gomes Prazeres Jose
Original assignee: Univ Delft Tech
Priority date: 2014-12-04
Filing date: 2014-12-04
Publication date: 2016-10-11

Abstract

The invention relates to an inductive power transfer system. The system comprises a transmitter circuit and a receiver circuit, each being provided with a resonant tank including a coil structure with a coil for transmitting and receiving magnetic energy, respectively. The coil structure of the transmitter resonant tank and/or the coil structure of the receiver resonant tank includes a multiple number of coils. Further, coils of a coil structure are driven at mutually different operating frequencies.

Description

Title: An inductive power transfer system, a method and a computer program product

The invention relates to an inductive power transfer system, comprising a transmitter circuit and a receiver circuit, each being provided with a resonant tank including a coil structure with a coil for transmitting and receiving magnetic energy, respectively, wherein the coil structure of the transmitter resonant tank and/or the coil structure of the receiver resonant tank includes a multiple number of coils.

An Inductive Power Transfer (IPT) system is one wherein wireless power transfer is achieved across large air gaps between a transmitter and a receiver. Such technology can be used for high power applications (in the order of 100 kW or more) such as for charging electric vehicles, and also for low power applications (in the order of 10 W) such as for charging mobile phones and consumer electronic devices. Presently known inductive power transfer systems (also known as wireless/contactless power transfer), although frequency dependent, are designed to transfer power using a harmonic signal.

It appears, in practice, that when using multiple primary and secondary coils, de-tuning of mutually coupled coils may occur within the primary and the secondary or high induced currents which flow into an input power supply.

Primary systems that have multiple mutually coupled coils such as for example, a three phase primary system, experience adverse problems due to inter-coil mutual inductance as explained below. It is well known from literature and various studies that the performance of IPT systems are affected when the primary has more than one independent coil powered by an independent inverter or inverter leg. In these systems, depending on the type of primary compensation topology used, e.g. Series, LCL etc, the inter coil mutual inductance can cause detuning of the system and can also cause large induced currents. If the primary system is detuned, the efficiency of power transfer to the secondary reduces. If large induced currents flow into the primary coils, the voltage across the input DC link capacitances rise causing problems in the control of the inverter.

Secondary systems that have multiple mutually coupled coils also get detuned and exhibit a resonance frequency that depends on the magnitude of the currents flowing in the coils. This is an undesirable characteristic as the induced secondary currents depend on the coupling between the primary transmitter and the secondary receiver which is in turn dependent on the relative alignment between the transmitter and the receiver. In general, due to many possible alignment conditions, the coupling between the primary and the secondary is not constant.

It is an object of the invention to provide an inductive power transfer system according to the preamble wherein the above-identified drawback of detuning of mutually coupled coils is reduced. Thereto, according to an aspect of the invention, the system is arranged such that, during operation of the transfer system, coils of a coil structure are driven at mutually different operating frequencies.

By using multiple frequencies, power may be transferred through the same medium, the air gap, via a multiple number of frequencies in an independent way, such that one frequency system does not interact with another. The adverse effects caused by inter coil mutual inductance are reduced or even removed. Further, by combining a transmitter coil with a corresponding receiver coil into a coil pair that is driven at a frequency that is not used by other coil pair, multiple coils at the transmitter and/or receiver side can be decoupled by virtue of the fact that they are carrying currents of mutually different frequencies. Then, major challenges in the design of IPT systems with multiple primary and/or secondary coils, such as de-tuning of mutually coupled coils within the primary and the secondary or high induced currents which flow into the input power supply, can be solved.

As an example, the transmitter circuit may include two transmitter coils while the receiver circuit also includes two receiver coils, thus forming two coil pairs, each coil pair operating at a distinct frequency.

As a further example, the transmitter circuit may include a single transmitter coil while the receiver circuit includes a multiple number of receiver coils, e.g. two, three, four or more receiver coils. Alternatively, the receiver circuit includes a single receiver coil while the transmitter circuit includes a multiple number of transmitter coils. Then, the multiple number of coils of the receiver circuit or the transmitter circuit, or a subset of said multiple number of coils, are operated at mutually different operating frequencies. Further, both the transmitter circuit and the receiver circuit may include a multiple number of coils.

In an advantageous embodiment, a transmitter coil forms a coil pair with a corresponding receiver coil such that, during operation of the transfer system, the coil pair is driven at an operating frequency that is different from operating frequencies of other coils, thereby reducing and/or counteracting the occurrence of an inter coil mutual inductance.

Preferably, the number of transmitter coils is equal to the number of receiver coils, and each of the transmitter coils forms a coil pair with a corresponding receiver coil such that, during operation of the transfer system, the coil pairs are driven at mutually different operating frequencies, thereby optimizing efficient energy transfer.

Thus, inductive power transfer can be achieved from a transmitter to a receiver over a large air gap by using at least two frequencies with an independent input frequency - amplitude relation. A primary coil system can be designed wherein two coils, although having a finite mutual inductance between them, can operate independently and without interference. Hence, power can be transferred to a secondary system over a large air gap at high efficiencies. Also, reduction of inverter conduction losses can be achieved, due to power splitting between the two or more frequencies. In addition, the operational reliability of the IPT system can be improved when compared to a conventional single inverter single frequency Inductive Power Transfer system. This is possible as power is transferred via at least two frequencies and if one frequency system is faulty, all the power can be transferred via the at least one other frequency.

Two primary coils can be used having a finite mutual inductance between them. The secondary system can also have two coils with a finite mutual inductance and can be designed to operate independently. By operating the coils at different frequencies, the IPT system can even be used if there is a finite mutual inductance between the coils, thereby providing an advantage over prior art IPT coil systems having multiple coils in the primary and the secondary which are designed in such a way that the multiple coils are spatially decoupled by means of their relative positions.

The system of multiple coils can have coils oriented in any positon over/close to each other. The system can nullify the effects of mutual inductance due to resonance operating as a low pass filter and rejecting frequencies beyond a short band. Also, the coils can be wound over a magnetic material to further improve coupling to the pickup.

By using the above-described multi-frequency IPT system, inverter conduction losses decrease. Further, the reliability of the entire system increases. The system can increase misalignment tolerances by using multiple frequency decoupled coils in the secondary. Further, power can be transferred to different secondary systems that are mutually coupled. Also, the system provides more control to transfer power as the system can choose how to share the power transfer between the at least two frequencies.

The system is potentially relevant in low power segments, e.g. focused on making wireless-inductive charge pads for mobile phone, tablets, laptops, smartphones, TV units and other portable consumer electronics. The system is also applicable in a smart table where appliances can plug and play with seamless energy transfer between the table and the device.

The invention also relates to a method.

Further, the invention relates to a computer program product. A computer program product may comprise a set of computer executable instructions stored on a data carrier, such as a flash memory, a CD or a DVD. The set of computer executable instructions, which allow a programmable computer to carry out the method as defined above, may also be available for downloading from a remote server, for example via the Internet, e.g. as an app.

Other advantageous embodiments according to the invention are described in the following claims.

By way of example only, embodiments of the present invention will now be described with reference to the accompanying figures in which

Fig. 1 shows a diagram of an inductive power transfer system according to the invention;

Fig. 2 shows a diagram of a dual half bridge inverter;

Fig. 3 shows a schematic view of coils of the system in Fig. 1, and

Fig. 4 shows a flow chart of an embodiment of a method according to the invention.

The figures merely illustrate preferred embodiments according to the invention. In the figures, the same reference numbers refer to equal or corresponding parts.

Figure 1 shows a diagram of an inductive power transfer system 1 according to the invention. The system 1 has a transmitter circuit 2 and a receiver circuit 3. Both the transmitter circuit 2 and the receiver circuit 3 have a resonant tank including a coil structure and capacitances. The coil structure is provided with a multiple number of coils for transmitting and receiving magnetic energy, respectively.

In the shown embodiment, the resonant tank of the transmitter circuit 2 includes two partial resonant tank circuits. A first partial resonant tank circuit has a first transmitter capacitance Cip arranged in series with a first transmitter coil Lip., for resonating at a first frequency fi. A first and second end port a, N of the first partial resonant tank circuit are connectable to an inverter circuitry described below. Similarly, a second partial resonant tank circuit has a second transmitter capacitance C2P arranged in series with a first transmitter coil Li2P) for resonating at a second frequency f2, different form the first frequency fi. Also the second partial resonant tank circuit is connectable to an inverter circuitry described below, with its first and second end port b, N. The resonant tank is designed such that the first and second partial resonant tank circuits have a common second end port N.

Further, in the shown embodiment, the resonant tank of the receiver circuit 3 includes two separate partial resonant tanks circuits. A first partial resonant tank circuit includes a first receiver capacitance Cis arranged in series with a first receiver coil Lis, for resonating at said first frequency fi. Similarly, a second, separate, partial resonant tank circuit includes a second receiver capacitance C2s arranged in series with a first receiver coil L2S, for resonating at a second frequency f2, different form the first frequency fi. The first partial resonant tank circuit has end ports a’, N’i connected to a first load impedance Zli, while the second partial resonant tank circuit has end ports b’, N’2 connected to a second load impedance Zl2.

Generally, the number of transmitter coils is equal to the number of receiving coils, in the shown embodiment two coils at the transmitter circuit and two coils at the receiver circuit. Further, each of the transmitter coils forms a coil pair with a corresponding receiver coil such that, during operation of the transfer system 1, the coil pairs are driven at mutually different operating frequencies. In the shown embodiment, the first transmitter coil Lip and the first receiver coil Lis form a first coil pair operating at a first frequency fi, while the second transmitter coil L2P and the second receiver coil L<2s form a second coil pair operating at a second frequency f2. The transmittance between the coil pair components Lip, Lis; L,2P, L2s are denoted by the symbols Mipis and M2P2s, respectively.

Figure 2 shows a diagram of a dual half bridge inverter 10 including a control unit 12, a voltage source Vin, a series of two capacitors Ci, C2 arranged parallel to the voltage source Vin, and a dual half bridge circuitry DB including four switches SWl, SW2, SW3, SW4 arranged as two parallel bridge chains 14, 16, parallel to the voltage source Vin, and operated by the control unit 12. The inverter 10 is provided with connection ports a, b, N positioned between switches in the parallel bridge chains 14, 16 and between the two capacitors Ci, C2.

Figure 3 shows a schematic view of the coils Lip, L,2P, Lis, L,2S of the system 1 described referring to Fig. 1. The coils are implemented as electrically conducting spiral shaped metal patterns formed on a dielectric plate material. The primary coils, i.e. the transmitter coils Lip, Lis, are positioned on a transmitter plate 18, while the secondary coils, i.e. the receiver coils Lis, L2S, are positioned on a receiver plate 20. In a specific embodiment, the transmitter circuit and/or the receiver circuit, or at least parts thereof, are implemented using micro-strip technology so that the system can be manufactured in a reliable and cost effective manner.

During operation of the system 1, magnetic flux lines Di, D2 are formed in a closed loop, between the respective coil pairs, i.e. between the first transmitter coil Lip and the first receiver coil Lis and between the second transmitter coil L,2P and the second receiver coil L.2s, respectively. Since the operating frequencies fi, f2 of the coil pairs are mutually different, the magnetic flux lines Di, D2 do not interact which each other, or merely as a secondary order effect. In other words, the magnetic interaction between the first transmitter coil Lip and the second receiver coil L2S, and between the second transmitter coil L,2P and the second receiver coil Lis is at least an order smaller than the magnetic transmittance of the coils in the above mentioned coil pairs.

Figure 4 shows a flow chart of an embodiment of a method according to the invention. The method is used for transferring inductive power, and comprises a step of providing 110 a transmitter circuit and a receiver circuit, each being provided with a resonant tank including a coil structure with a multiple number of coils for transmitting and receiving magnetic energy, respectively, wherein the number of transmitter coils is equal to the number of receiver coils, and wherein each of the transmitter coils forms a coil pair with a corresponding receiver coil, and a step of driving 120 the coil pairs at mutually different operating frequencies.

The method of transferring inductive power can be performed using dedicated hardware structures, such as computer servers or control units. Otherwise, the method can also at least partially be performed using a computer program product comprising instructions for causing a processor of a computer system or a control unit to perform the step of driving the coil pairs at mutually different operating frequencies. All (sub)steps can in principle be performed on a single processor. However, it is. noted that at least one step can be performed on a separate processor. A processor can be loaded with a specific software module. Dedicated software modules can be provided, e.g. from the Internet.

The invention is not restricted to the embodiments described herein. It will be understood that many variants are possible.

As an example, more than two transmitter coils and/or more than two receiver coils can be used, e.g. three transmitter coils and three receiver coils. Further, another inverter circuitry can be applied for generating the signals with mutually different frequencies, e.g. a full-bridge inverter.

These and other embodiments will be apparent for the person skilled in the art and are considered to fall within the scope of the invention as defined in the following claims. For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments. However, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described.

Claims

An inductive energy transfer system, comprising a transmit circuit and a receive circuit, each comprising a resonance tank having a coil structure with a coil for respectively transmitting and receiving magnetic energy, the coil structure of the transmit resonance tank and / or the coil structure of the receiving resonance tank comprises a plurality of coils such that, during operation of the transmission system, coils of a coil structure are applied at mutually different operating frequencies.

An inductive energy transfer system according to claim 1, wherein the coil structure of the transmit resonance tank comprises a single coil and wherein the coil structure of the receive resonance tank comprises a multiple number of receive coils.

The inductive energy transfer system of claim 1, wherein the coil structure of the receive resonance tank comprises a single coil and wherein the coil structure of the transmit resonance tank comprises a plurality of transmit coils.

An inductive energy transfer system according to any one of the preceding claims, wherein the coil structure of both the transmit resonance tank and the receive resonance tank comprises a plurality of coils.

The inductive energy transfer system of claim 4, wherein a transmit coil forms a coil pair with a corresponding receive coil such that, during operation of the transmission system, the coil pair is applied to an operating frequency that differs from operating frequencies of other coils.

An inductive energy transfer system according to claim 4 or 5, wherein the number of transmission coils is equal to the number of reception coils, and wherein each of the transmission coils forms a coil pair with a corresponding receiving coil such that, during operation of the transmission system, the coil pairs are applied to mutually different operating frequencies.

An inductive energy transfer system according to any one of the preceding claims, wherein the resonant tank of the transmission circuit comprises a dual half bridge inverter or a full bridge inverter for generating the different operating frequencies.

The inductive energy transfer system according to any of the preceding claims, wherein the transmit circuit and / or the receive circuit are implemented using microstrip technology.

9. Method for transmitting inductive energy, comprising the steps of: - providing a transmitting circuit and a receiving circuit, each comprising a resonance tank having a coil structure with a coil for respectively transmitting and receiving magnetic energy, the coil structure of the transmit resonance tank and / or the coil structure of the receive resonance tank comprises a multiple number of coils, and - applying coils of a coil structure at mutually different operating frequencies.

A computer program product for transmitting inductive energy, the computer program product comprising a computer readable code that causes a processor to perform a process comprising the step of: - controlling a transmitting circuit and a receiving circuit, each provided with a resonance tank having a coil structure with a coil for respectively transmitting and receiving magnetic energy, the coil structure of the transmit resonance tank and / or the coil structure of the receive resonance tank comprising a plurality of coils such that, during use of the transmission system, coils of a coil structure can be applied to mutually different operating frequencies.