1. The working frequency optimization method of the wireless power transmission system based on the three-coil structure is characterized in that: step one, determining the resonance angular frequency w of an optimized wireless power transmission system₀；

Step two, setting the angular frequency of the sending coil as a first peak angular frequency w₂Or a second peak angular frequency w₃As shown in formula (9);

wherein L is₃An inductance value of the receiving coil; r₃Parasitic resistance of the receiving coil; r_LIs the impedance of the load; k is a radical of₂₃Is the coupling coefficient between the relay coil and the receiving coil.

2. The operating frequency optimizing method of a wireless power transmission system based on a three-coil structure according to claim 1, wherein: the transmitting coil, the relay coil and the receiving coil are all rectangular single-turn printing directional coils; the transmitting coil, the relay coil and the receiving coil are coaxially arranged.

3. The operating frequency optimizing method of a three-coil structure-based wireless power transmission system according to claim 1 or 2, wherein: inductance L of the receiving coil₃Calculating according to the coil inductance value expression, as shown in formula (1);

wherein, L is the coil inductance value; mu.s₀Is the permeability of free space; w is the line width of the coil; t is the wire thickness of the coil; d is the diameter of the coil.

4. The operating frequency optimizing method of a three-coil structure-based wireless power transmission system according to claim 1 or 2, wherein: parasitic resistance R of receiving coil₃Calculating according to the parasitic resistance expression of the coil, as shown in formula (2);

wherein R is_acIs a parasitic resistance; delta is skin depth and is expressed asMu is the magnetic permeability of the conductor; σ is the conductivity of copper;is a first type of complete elliptic integral;

5. the operating frequency optimizing method of a wireless power transmission system based on a three-coil structure according to claim 1, wherein: calculating the efficiency eta of the optimized wireless electric energy transmission system as shown in the formula (8);

wherein ref₁₂、ref₁₃、ref₂₃Respectively the impedance of the transmitting coil reflecting relay coil, the impedance of the transmitting coil reflecting receiving coil and the impedance of the relay coil reflecting receiving coil; z₁、Z₂、Z₃Circuit impedances of the transmitting coil, the relay coil and the receiving coil are respectively; r_LIs the load impedance.

6. The operating frequency optimizing method of a wireless power transmission system based on a three-coil structure according to claim 5, wherein: impedance ref of the transmitter coil reflective relay coil₁₂The transmitter coil reflecting the impedance ref of the receiver coil₁₃And the impedance ref of the relay coil reflection receiving coil₂₃The expression of (b) is shown in formula (6);

7. the operating frequency optimizing method of a wireless power transmission system based on a three-coil structure according to claim 5, wherein: simplified impedance ref of the transmitter coil reflective relay coil₁₂The transmitter coil reflecting the impedance ref of the receiver coil₁₃And the impedance ref of the relay coil reflection receiving coil₂₃The expression of (b) is shown in formula (7);

ref₁₃＝0 (7)。

8. the operating frequency optimizing method of a three-coil structure-based wireless power transmission system according to claim 5, 6 or 7, wherein: mutual inductance M between transmission coil and relay coil₁₂(ii) a Mutual inductance M between relay coil and receiving coil₁₂(ii) a Mutual inductance M between relay coil and receiving coil₂₃Calculated from the expression of the mutual inductance between the two coils, as shown in equation (3)

Wherein a and c are the wire radiuses of the two coils respectively; z is the distance between the two coils; mu.s₀Is the permeability of free space.

9. The operating frequency optimizing method of a three-coil structure-based wireless power transmission system according to claim 5, 6 or 7, wherein: impedance Z of transmitting coil, relay coil and receiving coil₁、Z₂、Z₃Is represented by formula (4):

wherein the content of the first and second substances,I₁、I₂、I₃working currents of the transmitting coil, the relay coil and the receiving coil are respectively; v is the voltage of the emission source, and the expression is shown in formula (5):

where j is an imaginary symbol.

10. The operating frequency optimizing method of a three-coil structure-based wireless power transmission system according to claim 1 or 2, wherein: the optimized wireless power transmission system comprises a resonant wireless power transmitting circuit, a resonant wireless power relay circuit and a resonant wireless power receiving circuit; the resonant wireless power transmitting circuit comprises a transmitting source V connected in series_sLoss R of driving source_sAn external capacitor C₁And a transmitting coil L₁(ii) a The resonant wireless power relay circuit comprises relay coils L connected in series₂And outsideAdding capacitor C₂(ii) a The resonant wireless power receiving circuit comprises a receiving coil L connected in series₃An external capacitor C₃And a load R_L。

Background

With the progress of science and technology, the wireless power transmission technology gets rid of the inconvenience of wire connection because of the characteristic that the wireless power transmission technology can transmit power without contact, and is widely applied to the fields of industrial electronics, implantable medical electronics, smart homes and the like. The medical device has a particularly remarkable effect in the field of implantable medical treatment, and helps people to solve the problems that the power supply of implantable medical devices needs regular operation for replacing batteries in vivo, and inflammation infection, cell necrosis and other injuries are easily caused due to fussy operation.

In implantable medical applications, it is often desirable to achieve efficient energy transfer within a limited implantation space in order to maintain a stable and efficient electrical energy supply. The most widely used wireless energy transmission mode at present is the magnetic coupling resonance type wireless energy transmission technology. The transmission technology utilizes the resonant coil with high quality factor as a receiving and transmitting antenna, utilizes the transmitting frequency of the high-frequency power source to keep consistent with the resonant frequency of the transmitting and receiving end coils to achieve resonance, can realize high-power and high-efficiency energy transmission within a medium transmission distance, is slightly influenced by the surrounding environment, and is safer for human bodies. Many studies have shown that the transmission efficiency can be effectively improved by adding a relay coil between a wireless transmitting coil and a wireless receiving coil. Therefore, a relay coil and a receiving coil can be implanted in a human body, a wireless transmitting coil is arranged outside the human body, and three coil structures are coupled with each other, so that high-efficiency wireless energy supply is realized.

Generally, when the magnetic coupling resonance system has a two-coil structure and the operating frequency of the magnetic coupling resonance system is close to the resonance frequency of the transceiver coil, the transmission efficiency is the highest, that is, the transmission efficiency and frequency curve has only one peak. However, in practical applications, the wireless transmission system with a three-coil structure often has a frequency splitting phenomenon due to various factors such as load, distance between coils, or size. The so-called frequency splitting phenomenon, i.e. the transmission efficiency versus frequency curve of the magnetically coupled resonance, shows a number of peaks. When the system is operating at a resonant frequency, the efficiency is greatly reduced.

Many current improvements to this phenomenon that result in reduced efficiency are to suppress frequency splitting phenomena such as impedance matching, changing coil size, changing coil spacing to reduce coupling, changing load size, etc. However, for the implanted wireless power transmission system, the implanted wireless power transmission system is limited by the close arrangement of tissue structures in the human body, the space is small, and the implanted wireless power transmission system is easy to be injured. Therefore, the distance between the coil structures and the coil size cannot be changed at will, and the size of the load of a specific implant device is difficult to change, so that the specific application is inconvenient.

Disclosure of Invention

In order to overcome the problem of low efficiency caused by the existing frequency splitting phenomenon, the invention provides a frequency optimization method of a three-coil structure to improve the transmission efficiency. The transmission efficiency is improved by adjusting the operating frequency of the transmission source by calculating and measuring frequency split points that may occur in a three coil configuration.

The working frequency optimization method of the wireless power transmission system based on the three-coil structure comprises the following specific steps:

step one, determining a resonant frequency f of an optimized wireless power transmission system, and obtaining a resonant angular frequency w according to the resonant frequency f₀。

Step two, setting the angular frequency of the sending coil as a first peak angular frequency w₂Or secondPeak angular frequency w₃As shown in formula (9).

Wherein L is₃An inductance value of the receiving coil; r₃Parasitic resistance of the receiving coil; r_LIs the impedance of the load; k is a radical of₂₃Is the coupling coefficient between the relay coil and the receiving coil.

Preferably, the transmitting coil, the relay coil and the receiving coil are all rectangular single-turn printing direction coils. The transmitting coil, the relay coil and the receiving coil are coaxially arranged.

Preferably, the transmitting coil, the relay coil and the receiving coil are all multi-turn circular coils.

Preferably, the inductance L of the receiving coil₃And (4) calculating according to the coil inductance value expression, as shown in formula (1).

Wherein, L is the coil inductance value; mu.s₀Is the permeability of free space; w is the line width of the coil; t is the wire thickness of the coil; d is the diameter of the coil.

Preferably, the parasitic resistance R of the receiving coil₃And (4) calculating according to the coil parasitic resistance value expression, as shown in formula (2).

Wherein R is_acIs a parasitic resistance; delta is skin depth and is expressed asMu is the magnetic permeability of the conductor; σ is the conductivity of copper;is a first type of complete elliptic integral;

preferably, the efficiency η of the wireless power transmission system optimized by calculation is shown as equation (8).

Wherein ref₁₂、ref₁₃、ref₂₃Respectively the impedance of the transmitting coil reflecting relay coil, the impedance of the transmitting coil reflecting receiving coil and the impedance of the relay coil reflecting receiving coil; z₁、Z₂、Z₃Circuit impedances of the transmitting coil, the relay coil and the receiving coil are respectively; r_LIs the load impedance.

Preferably, the transmitting coil reflects the impedance ref of the relay coil₁₂The transmitter coil reflecting the impedance ref of the receiver coil₁₃The relay coil reflecting the impedance ref of the receiver coil₂₃And the total reflected impedance ref of the system_ToIs represented by the formula (6).

Preferably, the simplified transmitting coil reflects the impedance re of the relay coilf₁₂The transmitter coil reflecting the impedance ref of the receiver coil₁₃And the impedance ref of the relay coil reflection receiving coil₂₃Is represented by the formula (7).

ref₁₃＝0 (7)

Preferably, the mutual inductance M between the transmission coil and the relay coil₁₂(ii) a Mutual inductance M between relay coil and receiving coil₁₂(ii) a Mutual inductance M between relay coil and receiving coil₂₃Calculated from the expression of the mutual inductance between the two coils, as shown in equation (3)

Wherein a and c are the wire radiuses of the two coils respectively; z is the distance between the two coils; mu.s₀Is the permeability of free space.

Preferably, the impedances Z of the transmitter coil, the relay coil and the receiver coil₁、Z₂、Z₃Is represented by formula (4):

wherein the content of the first and second substances,I₁、I₂、I₃working currents of the transmitting coil, the relay coil and the receiving coil are respectively; v is the voltage of the emission source, and the expression is shown in formula (5):

where j is an imaginary symbol.

Preferably, the optimized wireless power transmission system includes a resonant wireless power transmission circuit, a resonant wireless power relay circuit, and a resonant wireless power reception circuit. The resonant wireless power transmitting circuit comprises a transmitting source V connected in series_sLoss R of driving source_sAn external capacitor C₁And a transmitting coil L₁. The resonant wireless power relay circuit comprises relay coils L connected in series₂And an external capacitor C₂. The resonant wireless power receiving circuit comprises a receiving coil L connected in series₃An external capacitor C₃And a load R_L。

The invention has the beneficial effects that:

the invention establishes the efficiency calculation method of the three-coil structure by the reflection impedance principle, and realizes the improvement of the wireless transmission efficiency by only adjusting the working frequency of the external transmitting power source under the condition of avoiding changing the factors such as load, coil size structure, distance and the like. When the wireless power supply is applied to implantable medical treatment, the defect that the parameters of the in-vivo coil are difficult to adjust can be overcome under the condition that the efficiency is reduced due to the frequency splitting phenomenon, and high-efficiency wireless power supply of implantable medical treatment is realized.

Drawings

FIG. 1 is a schematic view of a single turn printed directional coil used in the present invention;

FIG. 2 is an equivalent circuit diagram of a three coil configuration of the present invention;

FIG. 3 is an equivalent circuit diagram of a three coil structure equivalent to a two coil structure;

FIG. 4 is a comparison graph of Matlab calculated values, Hfss simulated values, and experimental results with frequency changes according to the present invention.

Detailed Description

In order to make the technical content and advantages of the present invention more apparent, the present invention is further described with reference to the accompanying drawings. It should be emphasized that the following description is merely exemplary in nature and is not intended to limit the scope of the invention or its application.

A working frequency optimization method of a wireless power transmission system based on a three-coil structure is characterized in that three optimized coils are all single-turn printing directional coils, and the cross sections of the three optimized coils are rectangular; fig. 1 shows a plan view of the planar coil.

As shown in fig. 2, the wireless power transmission system corresponding to the optimization method includes a resonant wireless power transmission circuit, a resonant wireless power relay circuit, and a resonant wireless power receiving circuit. The resonant wireless power transmitting circuit comprises an emission source V_sLoss R of driving source_sAn external capacitor C₁And a transmitting coil L₁. Transmitting coil L₁Having a parasitic resistance R₁. The resonant wireless power relay circuit comprises a relay coil L₂And an external capacitor C₂. Relay coil L₂Having a parasitic resistance R₂. The resonant wireless power receiving circuit comprises a receiving coil L₃An external capacitor C₃And a load R_L. Receiving coil L₃Having a parasitic resistance R₃。

The optimization method comprises the following specific steps:

step one, according to the specific application of implantable medical treatment, coaxially placing three coils, and determining the distance h between a relay coil and a transmitting coil₁₂Distance h between relay coil and receiving coil₂₃The resonant frequency f, and the line width w, wire thickness t and diameter d of the three coils.

Step two, working frequency in millimeter-grade implanted medical treatment usually uses high frequency of hundred megahertz level, skin depth at the moment is far less than thickness t and diameter d of the coil, current distribution and direct current distribution are different, and therefore the square single-turn coil with the rectangular section is deduced by direct current conditions and is possibly inaccurate at high frequency. The following inductance formula is used to more accurately describe the coil inductance L in the implantable medical field, as shown in formula (1).

Wherein, mu₀Is the permeability of free space. This formula is generally applicable to the order of hundred megahertz, and d is less than or equal to 30mm in the data source at the time of fitting.

Optionally, the coil structure is not limited to a single-turn rectangular printed coil, but may be a circular multi-turn coil or other coils, and the appropriate inductance value is used. The method is also applicable to the frequency splitting phenomenon of the non-implanted large-size wireless power transmission coil structure.

Step three, establishing a parasitic resistance value R under high-frequency application_acIs represented by the formula (2).

Wherein, delta is skin depth and the expression isMu is the magnetic permeability of the conductor, sigma is the electrical conductivity of copper,is a first type of complete elliptic integral. When in useThe error is within 4%.

And step four, establishing an expression of mutual inductance between the two coils as shown in the formula (3).

Where 2a is the diameter of the first coil, 2c is the diameter of the second coil, and z is the distance between the two coils.According to the formula, the mutual inductance M between the transmitting coil and the relay coil can be calculated₁₂Mutual inductance M between the relay coil and the receiver coil₂₃Mutual inductance M between transmitter coil and receiver coil₁₃。

And step five, establishing impedance expressions of the three coils. Using kirchhoff's law, equation (4) is obtained as follows:

wherein Z is₁、Z₂、Z₃Circuit impedances of the transmitting coil, the relay coil and the receiving coil; I₁、I₂、I₃the working currents of the transmitting coil, the relay coil and the receiving coil are respectively. V is the voltage of the emission source.

The expression of the voltage V of the emission source is obtained from the above equation as follows:

where j is an imaginary symbol.

Definition of ref_ToExpressed as the total reflected impedance of the circuitIncluding the total impedance reflected by the relay coil and the receive coil to the transmit coil.

In the same way, ref can be obtained₁₂，ref₁₃And ref₂₃，ref_ijThe impedance of the jth coil reflecting the ith coil is shown as follows:

if the distance between the transmitting coil and the receiving coil is relatively long, the coupling capability is relatively weak and can be approximately ignored, namely M₁₃At this time, the expression of formula (6) can be simplified to formula (7).

ref₁₃＝0 (7)

The efficiency η of the whole system can be expressed as equation (8) by the reflection impedance.

Wherein Re (. cndot.) is the operation of the real part.

Step six, whenA frequency splitting phenomenon occurs. As shown in fig. 2 and 3, if the impedance of the receiving coil is reflected to the relay coil, the three-coil structure is equivalent to a two-coil structure. Therefore, let the imaginary impedance of the equivalent relay coil structure be 0Solving the resulting three angular frequency solutions w₁、w₂、w₃As shown in formula (9).

Wherein, w₀Is the resonance angular frequency point, k₂₃Is the coupling coefficient between the relay coil and the receiving coil. At this time, w₂And w₃Are respectively at w₁Two sides; at this time, the operating angular frequency of the transmitting coil is set to w₂And w₃The efficiency of operation of the transmitting coil will be higher than at the resonant frequency. Adjusting the operating angular frequency of an extracorporeal transmit power source to w₂Or w₃A frequency w compared to the resonance frequency can be obtained₁Higher transmission efficiency.

To verify the effect of improving efficiency by optimizing the operating frequency using the present invention. The following comparative tests were performed.

Parameters of three coils: selecting three identical coil sizes; the metal material is copper; the coil diameter is 28 mm; the line width is 1 mm; the thickness is 35 um; the resonant frequency is 103MHz, the capacitance is 27pf, and the load is 2050 omega in parallel; the relay coil is 45mm away from the transmitting coil and 15mm away from the receiving coil. Finally, can find w₂Is 109.5M, w₃97.512M. As can be seen from fig. 4, the calculated results are more accurate compared to the simulation and experimental results. And then, the frequency can be optimized by adjusting the working frequency to the splitting point, so that the efficiency is effectively improved.