The present invention will be described in detail below with reference to the drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation mode and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.
 The circuit simulation model of the wireless power transmission WPT system is as figure 2 Shown. The joint simulation circuit of double-sided flat aluminum plate and WPT system is as image 3 Shown. In the figure, TX is the transmitting coil, T Al Is the equivalent circuit of the primary side aluminum plate, RX is the receiving coil, R Al Is the equivalent circuit of the secondary side aluminum plate, U ac High frequency power supply, R dc Is the internal resistance of the power supply, L 1 , L 2 Is the coil self-inductance, L f1 , L f2 Is the parasitic inductance, C 1 , C 2 Is the compensation capacitor, C f1 , C f2 Is the parasitic capacitance, R 1 , R 2 Is the coil resistance, M is the coil (TX, RX) and the aluminum plate (T Al , R Al ) Mutual inductance.
 The loop resonance equation of the WPT system can be expressed as:
 At resonance, the matrix equation of the WPT system is:
 Where R f1 , R Cf1 , R C1 , R 1 Respectively L f1 , C f1 , C 1 , L 1 Parasitic resistance, Z refl Is the circuit impedance of the secondary coil mapped to the primary coil, R f2 , R Cf2 , R C2 , R 2 Respectively L f2 , C f2 , C 2 , L 2 The parasitic resistance, the system transmission efficiency is:
 image 3 Medium, R 3 , L 3 Respectively T Al The equivalent resistance and equivalent inductance, R 4 , L 4 Respectively R Al The equivalent resistance and equivalent inductance of the system, the equivalent mutual inductance of the system is:
 T Al With R Al Almost no magnetic field coupling, its mutual inductance M 34 Close to zero, formula (4) can be simplified to:
 Based on the above analysis, the present invention provides a water tank type magnetic shield structure, such as Figure 15 As shown, the primary side shielding plate and the secondary side shielding plate are included. The primary side shielding plate includes a bottom plate portion and a side plate portion. The bottom plate portion is a flat plate with a hollow out. The side plate portion is arranged around the edge of the bottom plate portion, and the bottom plate and the side plate The part forms a trough-shaped structure. Both the primary side shielding plate and the secondary side shielding plate are made of aluminum plates. In some embodiments, the primary side shielding plate and the secondary side shielding plate may both have a square structure.
 The bottom plate can be a flat plate with a hollow in the middle, that is, shielding is only applied to the outer edge of the transmitting coil TX, and a shielding effect equivalent to that of a whole aluminum plate can also be obtained. The magnetic field incident on the aluminum plate on the primary side can induce eddy currents. Many eddy current loops can be equivalent to a coil with resistance and inductance in series (N=1, 2,...,n), and the coil is connected in parallel with the coil. The coil current is as Figure 4 Shown.
 The total resistance and total inductance of the eddy current equivalent circuit can be obtained by the following formula:
 It can be seen from formulas (6) and (7) that with the increase of the hollow area in the center of the primary side aluminum plate, that is, the reduction of the eddy current equivalent coil, the total resistance of the aluminum plate R eq (=R 3 ) And inductance L eq (=L 3 ) Gradually increase, mutual inductance M 13 , M 23 Gradually decrease; the secondary side aluminum plate size remains unchanged, L 4 , M 14 And M 24 Basically unchanged, it can be seen from formula (4) that the mutual inductance M TX-RX Gradually increase. The top view of the hollow center of the bottom plate of the primary side aluminum plate is as follows Figure 5 Shown.
 System mutual inductance such as Image 6 As shown, the x-axis is different hollow lengths, and the lines of different colors are different hollow widths. With the change of the hollow area in the center of the aluminum plate, the horizontal distance from the center of the coil edge when it reaches 6.25μT is as follows Figure 7 Shown.
 by Image 6 , Figure 7 It can be seen that when the hollow area of the primary side aluminum plate increases, the mutual inductance of the system is not much different, with the minimum value of 42.162 and the maximum value of 43.639.
 The introduction of aluminum plates can increase the attenuation rate of the magnetic field between the coils, resulting in a decrease in the mutual inductance of the system. The magnetic field of the WPT system is distributed symmetrically. For the convenience of observation, take 1/2 of the magnetic field distribution for observation, such as Figure 8 Shown. by Figure 8 (8a) shows that the magnetic field strength drops from 4.326mT to 2.439mT, and the attenuation rate is 43.62%; (8b) shows that the magnetic field strength drops from 4.125mT to 2.561mT, and the attenuation rate is 37.9%. Comparing the two figures, it can be seen that the attenuation rate of the magnetic field intensity of the primary side aluminum plate is reduced by 4.72% compared with the double-sided flat aluminum plate, which significantly reduces the attenuation rate of the magnetic field between the coils of the loosely coupled transformer.
 The side plate of the water tank type magnetic shielding structure of the present invention includes a side strip plate and an adjustable telescopic plate which are arranged in order from the bottom plate to the top. The side strip plate is perpendicular to the bottom plate, and the adjustable telescopic plate forms an angle with the bottom plate. Inclined setting, and the adjustable telescopic plate is inclined toward the middle of the bottom plate.
 1) Side strip plate
 The air gap between the coils of the loosely coupled transformer is large, and the magnetic leakage in the horizontal direction of the system is still serious. The double-sided flat aluminum plate can effectively reduce the magnetic leakage on the back of the loosely coupled transformer coil of the WPT system. In view of this, it is considered to introduce a strip-shaped aluminum plate on the side of the primary side aluminum plate to reduce the magnetic leakage in the horizontal direction of the WPT system. After introducing the side strip aluminum plate, the magnetic field distribution of the system is as follows Picture 9 As shown, the magnetic field in the horizontal direction on the edge of the coil is well suppressed, but the leakage of the magnetic field near the secondary side aluminum plate is still serious.
 2) Adjustable telescopic board
 The coupling magnetic field between the primary and secondary coils of a loosely coupled transformer is trapezoidally distributed, such as Picture 9 Shown. In order to further reduce the magnetic leakage at the secondary side aluminum plate, the tilt angle of the adjustable telescopic plate can be adjusted to make the magnetic field more concentrated in the trapezoidal area. The side view of the shielding structure with a side band and an inclination is as follows Picture 10 As shown, 1 is a side strip plate, and 2 is an adjustable telescopic plate. The angle α between the adjustable telescopic plate and the normal line of the bottom plate can be 0-75°. When the inclination angle changes, the coupling coefficient k, mutual inductance M and shielding effectiveness SE of the system are as follows: Picture 11 , 12 As shown, the magnetic field strength at measuring point A is as Figure 13 Shown.
 As α gradually increases between 0-34°, the side shielding plate 2’s ability to restrain the magnetic field is strengthened. At this time, α increases can promote magnetic field coupling; when α gradually increases between 34-75°, the side The shielding plate 2 can prevent the main energy of the magnetic field from propagating to the secondary coil, and at this time, a larger α can suppress the magnetic field coupling. From Picture 11 It can be seen that k is the maximum when α is 34°, which is 0.183; when α is 34°, M is the maximum, which is 43.41 μH. Such as Picture 12 As shown, when α is greater than 30°, the shielding effect of the system is poor, and the shielding efficiency is significantly reduced. When α is 50-60°, the shielding effect of the system is improved, but the magnetic leakage outside the system is serious.
 When the inclination angle α of the adjustable telescopic plate 2 is 30°, the magnetic field intensity of the system in the vertical direction at the measuring point A is small and the magnetic field distribution is relatively stable. At this time, the system k and SE are respectively 0.182 and 10.44, which are only lower than the maximum values of 0.01 and 0.1, such as Figure 13 Shown.
 The present invention also provides a flat coil wireless power transmission system, including the above-mentioned water tank type magnetic shield structure. Use MAXWELL simulation software to simulate the WPT system of the water trough-type magnetic shield structure. As a control, the double-sided flat-plate shield structure is also simulated and the simulation model is as follows: Figure 14 As shown, the simulation results are shown in Table 1. Figure 16 with Figure 17 Shown.
 Table 1 Self-inductance and coupling coefficient of coils of flat structure and trough structure
 It can be seen from Table 1 that after adding the aluminum shielding plate, the coupling coefficient and mutual inductance of the WPT system of the water tank type magnetic shielding structure are increased, and the internal magnetic field coupling of the system is strengthened. by Figure 16 It can be seen that compared with the flat magnetic shielding structure WPT system, the magnetic field attenuation rate in the horizontal direction of the center of the coil edge of the water trough is increased, and the magnetic radiation outside the system is reduced. by Figure 17 It can be seen that in the vertical direction at the measurement point A, the magnetic leakage of the WTP system with the double-sided flat-plate magnetic shield structure is much greater than that of the WPT system with the sink-type magnetic shield structure. From the above analysis, it can be seen that the water tank type magnetic shield structure can significantly reduce the magnetic leakage of the system while increasing the transmission efficiency of the system.
 The preferred embodiments of the present invention are described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and changes according to the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by those skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should fall within the protection scope defined by the claims.