Method for in-phase wireless energy supply of multi-base station local area wireless power transfer system

Abstract

The present application relates to the technical field of multi-base station local area wireless power transmission system, and specifically discloses a same-phase wireless energy supply method of a multi-base station local area wireless power transmission system, which controls the amplitude and phase of the power supply voltage of each base station in cooperation, so that the current of each base station can realize same-phase energy output under comprehensive consideration of all cross-coupling conditions in the wireless power transmission network, thereby realizing maximum power output, improving the power level, and maintaining high transmission efficiency at the same time. Compared with the existing local area wireless power transmission network working mechanism, the present application has the following advantages: the amplitude and phase of the power supply voltage of each base station are controlled in cooperation to ensure that the excitation currents are in the same phase, maximum power transmission is realized, and the effective power transmission range is wide; the cross-coupling among all coils is comprehensively considered to ensure that the system is in the maximum energy efficiency working frequency, the transmission efficiency is high, and the energy efficiency position robustness is strong; the multi-base station cooperates in power supply, the energy link reliability is high, and the anti-interference is strong.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of multi-base station local area wireless power transmission system, and particularly relates to a same-phase wireless energy supply method of a multi-base station local area wireless power transmission system. BACKGROUND

[0002] Wireless power transmission is a research hotspot in the field of electrical engineering and automation at present, and has advantages of safety, reliability, flexibility, convenience and the like, and has been successfully applied to the fields of household electrical appliances, consumer electronics, electric vehicles and the like.

[0003] With the development of technology and the expansion of application fields, the demand for multi-degree-of-freedom wireless power transmission within a certain range like a WiFi hotspot is becoming more and more intense. It is an inevitable development trend to establish a multi-base station local wireless power network (LPN).

[0004] Unlike a local wireless communication network (LCN) which belongs to far-field coupling and each node is independent and does not exist coupling, wireless power transmission belongs to near-field power transmission and there is strong magnetic field coupling between nodes, so the LPN exists strong cross coupling. The addition, removal and movement of a terminal will have a great influence on the selection of an energy link and the transmission energy efficiency.

[0005] The LPN has attracted the attention of domestic and foreign researchers, but the current research is relatively less. Most of the current research is based on a traditional working mode, that is, the working frequency of the system and the inherent frequency of each node circuit are set to be consistent, a corresponding algorithm is used to select a single node as a transmitting node and select 0 to multiple nodes as relay nodes to form a corresponding energy link. The energy link constructed by this mode has poor stability and anti-interference ability, because once a node in the energy link is broken, the entire energy link cannot work normally. More importantly, due to the strong cross coupling and multi-stage oscillation of the LPN, the dynamic behavior of the system is complex, not only exists frequency splitting phenomenon, but also exists frequency offset phenomenon, and the traditional working mechanism is not the maximum energy efficiency mechanism, so the energy efficiency is low. At the same time, since each node itself consumes a certain amount of energy, the energy efficiency of the terminal of the traditional multi-stage energy link mode will be very low.

[0006] Multiple transmission methods are an effective way to improve the stability and anti-interference of power links. Currently, there is considerable research on multiple-transmitter wireless power transfer systems, but most studies focus on modeling and characteristic analysis, investigating the dynamic behavior of multi-coil architectures and their maximum energy-efficient operating frequency while ignoring cross-coupling. Research on multi-excitation coordinated control is scarce. In 2017, Ahn Deok-ju of South Korea proposed two coordinated control methods for dual-transmitter systems: one method, when the currents at both transmitters are equal, determines whether to use one or two transmitters based on the coupling ratio between the two transmitter coils and the receiver coil, thereby optimizing efficiency; the other method, when the currents at both transmitters are adjustable, adjusts the transmitter currents based on the coupling ratio between the two transmitter coils and the receiver coil, ultimately optimizing system efficiency. The first method, by setting the current amplitude ratio to be the same and selecting the number of excitation sources, does not qualify as coordinated control. The second method only coordinates the current ratio without considering complex dynamic behaviors such as frequency splitting; the control quantity is singular, making it difficult to simultaneously balance power and efficiency. Summary of the Invention

[0007] This invention provides a method for supplying in-phase wireless power to a multi-base station local wireless power transmission system. The technical problem it solves is that the commonly used working mechanism of local wireless power transmission networks has low energy efficiency, poor location robustness, and fragile power links.

[0008] To address the above technical problems, this invention provides a method for supplying in-phase wireless power to a multi-base station local wireless power transmission system. This system includes n transmitting base stations on the primary side and one terminal device on the secondary side. Each transmitting base station i includes a power supply U. i Base station series compensation capacitor C i and transmitting coil L pi The terminal equipment includes a receiving coil L s1 Secondary series compensation inductor L s2 Secondary-side series compensation capacitor C s and load R L , i = 1, 2, ..., n, n ≥ 2; where each transmitting coil L pi Given, and each transmitting coil L pi The self-induction is equal, that is, L p1 =L p2 =…=L pn The internal resistances are equal, i.e., R p1 =R p2 =…=R pn Each transmitting coil L pi Mutual induction between M ij Given j = 1, 2, ..., n, i ≠ j and M ij =M ji The self-inductance of the receiving coil Ls1 The internal resistance R of the receiving coil ps Load R L Given each transmitting coil L pi With receiving coil L s1 Mutual induction between M is Given, let L pi =L i =L p R pi =R i =R p L s =L s1 +L s2 R s =R ps +R L The key lies in the fact that this in-phase wireless power supply method includes the following steps:

[0009] S1: Determine the inherent frequency ω0 of each transmitting base station i based on the actual system frequency band range, according to... Determine the series compensation capacitor C for each base station i ;

[0010] S2: Determine the current amplitude ratio a between transmitting base stations 2, ...,n and transmitting base station 1 based on application requirements. k1 k = 2, ..., n;

[0011] S3: The currents I1, I2, ..., I at each transmitting base station i n Under the conditions that all phases are in sync, the system satisfies the real eigenstate frequency, and the system operating frequency is set at the zero-phase frequency, according to L1, M 1j a k1 L s1 Determine L s2 And determine C based on C1 s ;

[0012] S4: According to L s R s C s M is a k1 Determine the system's operating angular frequency ω and the system's operating frequency.

[0013] S5: Determine the power supply voltage of base station 1 as U1 based on application requirements, and determine the voltage based on U1, R1, and R... s Determine the current I1 of transmitting base station 1 based on U1, R1, R s a k1 Determine the currents I2,…,I n And according to U1, R1, R s a k1, ω, M is L s C s Determine the receiving coil current I s ;

[0014] S6: Using U1 as the reference voltage, determine the power supply U according to the system's KVL relationship. i The amplitude and phase.

[0015] Furthermore, in step S3, the secondary side is connected in series with the compensation inductor L. s2 =L1+M 12 a 21 +···+M 1n a n1 -L s1 C s =C1.

[0016] Furthermore, in step S4, the system operating angular frequency ω is:

[0017]

[0018] in, L i =L p =L,R pi =R i =R p =R, k is Indicates transmitting coil L pi The coupling coefficient between the receiver coil and the receiver coil, and

[0019] Further, in step S5, according to U1, R1, R s The current I1 of transmitting base station 1 is determined as follows:

[0020]

[0021] Further, in step S5, according to U1, R1, R s a k1 Determine the currents I2,…,I n for:

[0022]

[0023] Further, in step S5, according to U1, R1, R s a k1 , ω, M is L s Cs determining the receiving coil current I s is:

[0024]

[0025] wherein,

[0026] Further, in step S6, the power supply U i is determined according to the system KVL relationship

[0027]

[0028] wherein,

[0029] The application provides a same-phase wireless energy supply method of a multi-base-station local area wireless power transmission system. For an LPN, the amplitude and phase of the voltage of each base station power supply are cooperatively controlled, so that the currents of each base station can realize same-phase energy output under comprehensive consideration of all cross couplings in the wireless power transmission network, so as to realize maximum power output, improve the power level, and also maintain high transmission efficiency. Compared with the existing local area wireless power transmission network working mechanism, the application has the following advantages:

[0030] 1) The amplitude and phase of the voltage of each base station power supply are cooperatively controlled, the currents of each base station are guaranteed to be in the same phase, maximum power transmission is realized, and the effective power transmission range is wide;

[0031] 2) The cross couplings among all coils are comprehensively considered, the system is guaranteed to be in a maximum energy efficiency working frequency, the transmission efficiency is high, and the energy efficiency position robustness is strong;

[0032] 3) Multi-base-station cooperative power supply, high energy link reliability, and strong anti-interference. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a circuit topology diagram of a multi-base-station local area wireless power transmission system provided by the embodiment of the application;

[0034] Figure 2 is a circuit topology diagram of a dual-base-station local area wireless power transmission system provided by the embodiment of the application;

[0035] Figure 3 is a curve diagram of the power and efficiency of the system provided by the embodiment of the application when the position is determined, and the power and efficiency change with a 12 ;

[0036] Figure 4 is a curve diagram of the power and efficiency of the system provided by the embodiment of the application, and the power and efficiency change with the distance. DETAILED DESCRIPTION

[0037] The embodiments of the present application are described below in detail with reference to the accompanying drawings, the examples are given only for the purpose of illustration and should not be construed as limiting the present application, the accompanying drawings are used for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present application, because many changes can be made to the present application without departing from the spirit and scope of the present application.

[0038] In view of the single control variable of the traditional cooperative control, it is difficult to promote to an arbitrary multi-coil architecture system, all cross couplings are comprehensively considered, and each base station voltage amplitude, phase and frequency are controlled in real time, so that the system can work in the maximum energy efficiency frequency state, the energy efficiency problem caused by complex dynamic behaviors such as frequency splitting and frequency deviation can be eliminated, and the phase of each base station current is the same, and the power and efficiency are further improved. Specifically, the embodiment of the present application provides a same-phase wireless energy supply method of a multi-base station local area wireless power transmission system, wherein the circuit topology of the multi-base station local area wireless power transmission system is as shown in Figure 1 The multi-base station local area wireless power transmission system includes n transmitting base stations on the primary side and one terminal device on the secondary side, the transmitting base station i includes a power supply U i , a base station series compensation capacitor C i and a transmitting coil L pi , the terminal device includes a receiving coil L s1 , a secondary side series compensation inductor L s2 , a secondary side series compensation capacitor C s and a load R L , i = 1, 2, …, n, n ≥ 2.

[0039] Wherein, for a given local area wireless power transmission network, the positions of each base station are fixed, and the transmitting coils of each base station are generally the same, so that the self-inductance of each transmitting coil L pi is given, and the self-inductance of each transmitting coil L pi is equal, that is, L p1 = L p2 = … = L pn , the internal resistance is equal, that is, R p1 = R p2 = … = R pn , the mutual inductance M pi between each transmitting coil L ij is given, j = 1, 2, …, n, i ≠ j and M ij = M ji , the self-inductance of the receiving coil L s1 , the receiving coil internal resistance R ps and the load R L are given, the mutual inductance M pi between each transmitting coil L s1 and the receiving coil L is is given, in order to facilitate calculation, Lpi =L i =L p R pi =R i =R p L s =L s1 +L s2 R s =R ps +R L .

[0040] according to Figure 1 The KVL equations of the system can be obtained as follows:

[0041]

[0042] in, ω represents the system operating frequency, I1, I2, ..., I n This indicates the current of each transmitting base station.

[0043] According to equation (1), the current I of the receiving coil can be determined. s The expression and load R L The power P is expressed as:

[0044]

[0045] From the above formula, we can know that I1, I2, ..., I n When all phases are in phase, the power of the receiving load is maximized, therefore we can set:

[0046] I2=a 21 I1,I3=a 31 I1,···,I n =a k1 I1 (3)

[0047] a k1 This represents the ratio of the current amplitude of transmitting base stations 2, ..., n to that of transmitting base station 1.

[0048] when a 21 ,a 31 ,···,a k1 When the value is a positive real number, the primary current is in phase, which can achieve energy compensation for the receiving load. Under this condition, according to equation (1):

[0049] 0=jωM 1s I1+jωM 2s a 21 I1+···+jωM ns a n1 I1+(R s +jX s )Is (4)

[0050] Solving this gives the current relationship between the receiving side and the first transmitting coil:

[0051]

[0052] Applying real eigenstate theory to arbitrary multi-coil circuits, namely:

[0053]

[0054] The solution yields the real eigenstate frequency condition for a multi-coil system:

[0055]

[0056] in, L i =L p =L,R pi =R i =R p =R, ω0 represents the inherent frequency of each transmitting base station i, k is Indicates transmitting coil L pi The coupling coefficient between the receiver coil and the receiver coil, and

[0057] for Figure 1 For the MC-WPT system shown, zero phase angle has excellent energy efficiency characteristics. Therefore, setting the operating frequency at the zero phase angle frequency ensures high-efficiency energy compensation. Based on equations (1), (3), and (5), the equivalent impedance of the system is:

[0058] Z eq =R eq +jX eq (8)

[0059] Among them, R eq X represents the equivalent resistance. eq The equivalent reactance is expressed as follows:

[0060] R eq =R1+R s (9)

[0061] X eq =X1+ωM 12 a 21 +···+ωM 1n a n1 -X s (10)

[0062] In the zero phase angle condition, the equivalent input impedance of the system is purely resistive, i.e. Z eq = R eq , X eq = 0, at this time the primary voltage and current are in phase, and we have:

[0063] X1+ ωM 12 a 21 + ··· + ωM 1n a n1 - X s = 0 (11)

[0064] According to the above formula, the parameter conditions for the system to operate in the zero phase angle condition are:

[0065]

[0066] In combination with the given parameters, the parameter conditions can finally be summarized as follows:

[0067]

[0068] Under the zero phase angle condition,

[0069] Z eq = R1+ R s (14)

[0070] Then we have:

[0071]

[0072] Since U1 is given and the system coil electrical parameters are also determined, according to the above formula and in combination with formula (1), the voltage source amplitude and phase of all transmitting sources in the multi-coil system can be determined.

[0073] Under the above parameter conditions, the energy efficiency expression of the system is as follows:

[0074]

[0075] As can be seen from the above formula, after selecting appropriate positive real numbers a 21 , a 31 , ···, a n1 , the power received by the load is related to the mutual inductance between the transmitting coil and the receiving coil, but regardless of the change in mutual inductance, the power level received by the load is considerable. The efficiency of the system is also related to the mutual inductance between the transmitting coil and the receiving coil, and is greatly affected by the size ratio of mutual inductance. However, since the internal resistance is very small, the energy efficiency remains at a high level, and the electrical energy transmission performance of the system is very good.

[0076] On the basis of the above theoretical analysis, for Figure 1The multi-base station local wireless power transmission system shown in this embodiment provides a method for supplying in-phase wireless power to the multi-base station local wireless power transmission system, specifically including the following steps:

[0077] S1: Determine the inherent frequency ω0 of each transmitting base station i based on the actual system frequency band range, according to... Determine the series compensation capacitor C for each base station i ;

[0078] S2: Determine the current amplitude ratio a between transmitting base stations 2, ...,n and transmitting base station 1 based on application requirements. k1 k = 2, ..., n;

[0079] S3: The currents I1, I2, ..., I at each transmitting base station i n Under the condition that all phases are in sync and the system operating frequency is set at the zero-phase frequency, according to L1, M 1j a k1 L s1 Determine L s2 =L1+M 12 a 21 +···+M 1n a n1 -L s1 And determine C based on C1 s =C1;

[0080] S4: According to L s R s C s M is a k1 Determine the system's operating angular frequency. and system operating frequency in, L i =L p =L,R pi =R i =R p =R, ω0 represents the inherent frequency of each transmitting base station i, k is Indicates transmitting coil L pi The coupling coefficient between the receiver coil and the receiver coil, and

[0081] S5: Based on application requirements, the power supply voltage of transmitting base station 1 is determined to be U1. Then, based on U1, R1, R... s The current of transmitting base station 1 can be calculated. According to U1, R1, R s a k1 The current can be calculated and according to U1, R1, R s , a k1 , ω, M is , L s , C s The receiving coil current I can be calculated

[0082] S6: According to the system KVL relationship, the amplitude and phase of the power supply U i of U1 as the reference voltage are determined, and the system KVL relationship is:

[0083]

[0084] wherein,

[0085] Thus, the amplitude and phase of the power supply voltage of each base station, and the system operating frequency f r , and other unknown parameters of the system are determined, so that each base station current can realize in-phase energy output under comprehensive consideration of all cross-coupling in the wireless energy transmission network, so as to realize maximum power output, improve power level, and also maintain high transmission efficiency. Compared with the existing local wireless energy transmission network working mechanism, the present application has the following advantages:

[0086] 1) Cooperate to control the amplitude and phase of the power supply voltage of each base station, ensure that the excitation currents are in phase, realize maximum power transmission, and the effective energy transmission range is wide;

[0087] 2) Comprehensive consideration of the cross-coupling between all coils ensures that the system is at the maximum energy efficiency operating frequency, the transmission efficiency is high, and the energy efficiency position is robust;

[0088] 3) Multi-base station cooperative power supply, high energy link reliability, strong anti-interference.

[0089] Taking a double-base station local wireless power transmission system as an example, the effect of the method is simulated and verified, and the receiving coil is taken as an example. The schematic diagram is as shown in Figure 2

[0090] Wherein, the voltage source V1 of the transmitting end where the transmitting coil 1 is located is fixed, the amplitude and phase of the voltage source V2 of the transmitting end where the transmitting coil 2 is located need to be adjusted according to formula (15) and formula (1), and the compensation inductance of the receiving end is determined after a 12 (the current amplitude ratio of the transmitting coil 2 to the transmitting coil 1) and the positions of the two transmitting ends are determined. The specific parameter design refers to formula (13).

[0091] According to formula (16), the energy efficiency expression of the three-coil system is as follows:

[0092] ​

[0093] where R p1 = R1, R p2 = R2, R s = R3, is a constant, power is positively related to a 12 and efficiency is not monotonic with respect to a 12 The analysis is as follows:

[0094] Let take the derivative of efficiency with respect to a 12 ,

[0095] The extreme point is obtained Then we have:

[0096]

[0097] Since the internal resistance of the two transmitting ends is the same, the optimal range of a 12 is (0, 1).

[0098] The first group of simulations first determines the size of a 12 , determines a set of coil distances (the distance between the two transmitting coils is 40 cm, and the distance between the receiving coil is 30 cm and 10 cm, respectively), that is, a set of mutual inductances (the mutual inductance between transmitting coil 1 and transmitting coil 2 is M 12 , the mutual inductance between transmitting coil 1 and the receiving coil is M 13 , and the mutual inductance between transmitting coil 2 and the receiving coil is M 23 ), and the simulation parameters are shown in Table 1, and the corresponding simulation diagram is shown in Figure 3 .

[0099] Table 1: Parameter table for selecting the optimal a 12 of the system

[0100] Electrical parameter name Parameter value 10V ​ 10V [L1, L2] 398 μH [C1,C2,C3] 10 nF [R p1 ,R p2 ]]> 0.24 Ω [R p3 ]]> 0.25 Ω [R L ]]> 10 Ω M 12 ]]> 12.38 μH M 13 ]]> 23.598 μH M 23 ]]> 129.247 μH

[0101] From the Figure 3 curve, it can be seen that under the existing data, the trend of energy efficiency is consistent with the theory, the power is monotonically increasing, and the efficiency has an extreme value when a 12 is about 0.6.

[0102] The second group of simulations verifies the energy efficiency. In the simulation, the distance between the two transmitting ends is fixed at 40 cm (mutual inductance is 12.38H), the transmission distance D between transmitting coil 1 and the receiving coil is gradually changed from 20 cm to 38 cm at a step of 2 cm, a 12 is selected as 0.6, and the simulation data is shown in Table 2, and the corresponding simulation diagram is shown in Figure 4 .

[0103] Table 2: a 12 Parameter table of =0.6

[0104] Electrical parameter name Parameter value 10V ​ 10V [L1, L2] 398 μH [[ L s ]]> 404.19 μH [C1,C2,C3] 10 nF [R p1 ,R p2 ]]> 0.24 Ω [R ps ]]> 0.25 Ω [R L ]]> 10 Ω M 12 ]]> 12.38 μH

[0105] As can be seen from Figure 4 , under the condition that a 12 is determined, the receiving power and system efficiency are related to the ratio M 23 / M 13 , and the larger M 23 / M 13 , the larger the receiving power and the higher the efficiency.

[0106] In summary, the in-phase wireless energy supply method of the multi-base-station local-area wireless power transmission system provided by the embodiments of the present application is aimed at the LPN, and through the cooperative control of the amplitude and phase of the power supply voltage of each base station, the current of each base station can realize in-phase energy output under the comprehensive consideration of all cross-coupling conditions in the wireless power transmission network, so as to realize maximum power output, improve the power level, and also maintain a very high transmission efficiency. Compared with the existing local-area wireless power transmission network working mechanism, the present application has the following advantages:

[0107] 1) The amplitude and phase of the power supply voltage of each base station are cooperatively controlled to ensure that the excitation currents are in phase, maximum power transmission is realized, and the effective power transmission range is wide;

[0108] 2) The cross-coupling between all coils is comprehensively considered to ensure that the system is in the maximum energy efficiency working frequency, the transmission efficiency is high, and the energy efficiency position is robust;

[0109] 3) Multi-base-station cooperative power supply, high energy link reliability, and strong anti-interference.

[0110] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above embodiments, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, and all are included in the protection scope of the present application.

Claims

1. A method for in-phase wireless energy supply of a multi-base-station local-area wireless power transfer system, the multi-base-station local-area wireless power transfer system comprising n transmitting base stations on a primary side and one terminal device on a secondary side, the transmitting base station i comprising a power supply U i , a base-station series compensation capacitor C i , and a transmitting coil L pi , the terminal device comprising a receiving coil L s1 , a secondary-series compensation inductor L s2 , a secondary-series compensation capacitor C s , and a load R L , i = 1, 2, …, n, n ≥ 2; wherein Each transmitting coil L pi Given, and each transmitting coil L pi The self-induction is equal, that is, L p1 =L p2 =…=L pn The internal resistances are equal, i.e., R p1 =R p2 =…=R pn Each transmitting coil L pi Mutual induction between M ij Given j = 1, 2, ..., n, i ≠ j and M ij =M ji The self-inductance of the receiving coil L s1 The internal resistance R of the receiving coil ps Load R L Given each transmitting coil L pi With receiving coil L s1 Mutual induction between M is Given, let L pi =L i =L p R pi =R i =R p L s =L s1 +L s2 R s =R ps +R L The method is characterized by comprising the following steps: S1: Determine the inherent frequency ω0 of each transmitting base station i according to the actual system frequency range, and determine the inherent frequency ω0 of each base station according to the C i = 1 / ω02L pi Determine the series compensation capacitor C of each base station i ; S2: determining the current amplitude ratio a of the transmitting base stations 2,..., n to the transmitting base station 1 depending on the application requirements k1 k = 2,..., n; S3: the current I1, I2,..., In of each transmitting base station is determined according to the current I1, I2,..., In of each transmitting base station i and the current I1, I2,..., In of each receiving base station j n Under the conditions that all phases are in phase, the system satisfies the real eigenstate frequency, and the system operating frequency is set at the zero phase angle frequency, L1, M 1j , a k1 , L s1 is determined according to L1, M s2 , and C s is determined according to C1; S4: According to L s , R s , C s , M is , a k1 , determine the system operating angular frequency ω and the system operating frequency S5: Determine the power supply voltage of base station 1 as U1 based on application requirements, and determine the voltage based on U1, R1, and R... s Determine the current I1 of transmitting base station 1 based on U1, R1, R s a k1 Determine the currents I2,…,I n And according to U1, R1, R s a k1 , ω, M is L s C s Determine the receiving coil current I s ; S6: According to the system KVL relationship, determine the amplitude and phase of the power supply U i with U1 as the reference voltage.

2. The method of claim 1, wherein the in-phase wireless energy supply of the multi-base station local area wireless power transfer system is characterized by: In step S3, the secondary side series compensation inductance L s2 = L1+ M 12 a 21 + ··· + M 1n a n1 - L s1 , C s = C1.

3. The method of claim 2, wherein the method further comprises: In step S4, the system operating angular frequency ω is: wherein L i = L p = L, R pi = R i = R p = R, k is denotes the coupling factor between the transmitting coil L pi and the receiving coil, and 4. The method of claim 3, wherein the method further comprises: In step S5, the current I1 of the transmitting base station 1 is determined as: s The current I1 of the transmitting base station 1 is determined as:

5. The method of claim 3, wherein the method further comprises: In step S5, the currents I2,..., I s are determined as: k1 I2= U1- R1- R2 n I3= U1- R1- R2- R3 6. The method of claim 3, wherein the method further comprises: In step S5, according to U1, R1, R s a k1 , ω, M is L s C s Determine the receiving coil current I s for: wherein 7. The method of claim 3, wherein the method further comprises: In step S6, the magnitude and phase of the power U are determined from the system KVL relationship i are given by: wherein

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