Multi-parameter Target Optimization Method for a Resonant Electric Vehicle Wireless Charging System and Its Coils

Abstract

The present invention relates to a resonant electric vehicle wireless charging system, which includes an AC voltage source. The AC voltage source is connected to the input end of the transmitting-end circuit. The output end of the transmitting-end circuit is connected to the transmitting-end main coil. The transmitting-end main coil transmits energy to the receiving-end main coil through coil coupling. The receiving-end main coil is connected to the input end of the receiving-end circuit. Both the transmitting-end main coil and the receiving-end main coil adopt square DD-type coils. The winding directions of the coils are the same, the energizing directions are the same, and chamfering is performed on each right angle of the coils. The present invention also discloses a multi-parameter target optimization method for the coils of the resonant electric vehicle wireless charging system. The present invention optimizes the structure and spatial arrangement of the DD-type main coil, enhances the coupling ability between the coils while reducing the coil loss, i.e., copper loss, and without increasing the cost. The improved main coil is compared with the conventional DD-type coil, improving the wireless charging efficiency and enhancing the anti-offset characteristic of the coil.

Description

Technical Field

[0001] The present invention relates to the technical field of electric vehicle charging, in particular to a resonant electric vehicle wireless charging system and a multi-parameter target optimization method for its coil. Background Art

[0002] In recent years, electric vehicles have received extensive attention due to their good advantages such as economy and environmental protection. However, due to problems such as large volume, large mass, small storage capacity of the current electric vehicle batteries and potential safety hazards in charging, the promotion and application of electric vehicles are restricted. The wireless charging technology of electric vehicles provides a solution to the above problems.

[0003] Currently, wireless charging technologies mainly include electric field coupling type, magnetic field coupling type and electromagnetic radiation type. Among them, the magnetic field coupling type is the mainstream of current wireless charging technology, and can be further divided into inductive type and resonant type. The mechanism of the inductive type is similar to that of a separable transformer without a compensation circuit. Its characteristic is that the transmission efficiency is very high within a very short distance, but the efficiency will decrease significantly as the transmission distance increases. Therefore, it is generally used in centimeter-level scenarios. The resonant charging technology is based on the principle of electromagnetic resonance. By setting the parameters of the transmitting circuit and the receiving circuit, the two have the same resonant frequency. Under the action of the power supply excitation at this resonant frequency, the entire circuit reaches a "resonance" state to achieve the directional transmission of electric energy. It generally consists of an inverter source located on the ground, a transmitting end compensation network, a transmitting coil, and a vehicle-mounted receiving coil, a receiving end compensation network and a receiving end power conversion device. Due to its good performance, it is the main implementation means of current wireless charging.

[0004] Aiming at problems such as low efficiency and poor robustness of current wireless charging vehicles, as the core part of wireless charging vehicles, the coil is particularly important for improving the system performance. Affected by road conditions and driving skills, the receiving end will inevitably shift laterally relative to the transmitting end. As the offset distance increases, both the output power and the transmission efficiency will decrease, and the anti-offset characteristics of the coil are generally poor. Summary of the Invention

[0005] To solve the problems of low charging efficiency and poor anti-offset characteristics of the coil in the current electric vehicle wireless charging system, the primary object of the present invention is to provide a resonant electric vehicle wireless charging system that optimizes and improves the coil to enhance the transmission efficiency and anti-offset performance of the electric vehicle wireless charging system.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A resonant wireless charging system for electric vehicles includes an AC voltage source for powering the entire system, a transmitting end circuit, a transmitting end main coil, a receiving end main coil, and a receiving end circuit. The AC voltage source is connected to the input end of the transmitting end circuit, the output end of the transmitting end circuit is connected to the transmitting end main coil, and the transmitting end main coil transmits energy to the receiving end main coil through coil coupling. The receiving end main coil is connected to the input end of the receiving end circuit; the transmitting end circuit is composed of a transmitting end protection circuit, a rectifying circuit, a high-frequency inverter circuit, and a transmitting end compensation network. The receiving end circuit is composed of a receiving end compensation network, a rectifying and filtering circuit, a receiving end protection circuit, and a power storage device. Both the transmitting end main coil and the receiving end main coil adopt square DD-shaped coils, with the same winding direction and the same power-on direction, and chamfers are made at all right angles of the coils.

[0007] The transmitting end compensation network and the receiving end compensation network adopt a bilateral LCC resonant compensation topology. The transmitting end compensation network includes a transmitting end compensation coil and two compensation capacitors, and the receiving end compensation network includes a receiving end compensation coil and two compensation capacitors.

[0008] The transmitting end compensation coil, a transmitting end iron plate, and a transmitting end aluminum plate are sequentially arranged downward under the transmitting end main coil. The receiving end compensation coil, a receiving end iron plate, and a receiving end aluminum plate are sequentially arranged upward above the receiving end main coil. The transmitting end main coil and the receiving end main coil are located on the same central axis.

[0009] Another object of the present invention is to provide a multi-parameter target optimization method for the coils of a resonant wireless charging system for electric vehicles. This method includes the following steps in sequence:

[0010] (1) Optimize the coil structure, specifically including the following steps:

[0011] (1a) By deriving the coupling coefficient k of a single-turn rectangular planar coil during high-frequency operation, with the side lengths of the single-turn rectangular planar coil being a and b respectively, it is obtained that when the area s = a*b of the rectangular planar coil remains unchanged, the closer the side length ratio a / b of the rectangular planar coil is to 1, the stronger the coupling ability, i.e., the coupling coefficient k, between the rectangular planar coils, and the smaller the winding loss of the rectangular planar coil.

[0012] (1b) Conduct simulation verification: Place two identical multi-turn rectangular planar coils coaxially, fix the number of turns and wire diameter of the rectangular planar coils, keep the horizontal area of the rectangular planar coils unchanged, and take the side lengths of the rectangular planar coils as the only variable for simulation analysis. Increase the side lengths in sequence to obtain the corresponding winding loss and coupling coefficient results. The results show that the closer the aspect ratio is to 1, the smaller the winding loss, i.e., the copper loss, of the rectangular planar coil, and the larger the coupling coefficient k.

[0013] (1c) Expand the single multi-turn rectangular planar coil into a bipolar coil, namely the DD coil. Taking the side length of the rectangular planar coil as the only variable for simulation analysis, similar to the simulation results of the unipolar rectangular planar coil, when the aspect ratio is closer to 1, the winding loss of the rectangular planar coil, that is, the copper loss, is smaller, and the coupling coefficient k is larger.

[0014] (1d) By observing the magnetic field distribution of the rectangular planar coil, it is found that the closer the angle at the corner is to a right angle, the more obvious the magnetic field non-uniformity at the corner. Since the magnetic field change of the circular coil is not very sensitive to spatial changes, the circular coil is combined with the rectangular planar coil, and the right angle of the rectangular planar coil is set as a rounded corner. It can be seen from the simulation that the magnetic field distribution is greatly improved. Finally, it is determined that the main coils at the transmitting end and the receiving end are square DD coils, and chamfers are made at all right angles of the coils.

[0015] (2) Optimize the spatial position of the coil, which specifically includes the following steps:

[0016] (2a) Analyze the magnetic flux distribution diagram of the DD coil in a conventional wireless charging system. The relationship between the coupling coefficient and the magnetic flux is as follows:

[0017]

[0018] Among them, Φ m is the main magnetic flux; Φ σ1 and Φ σ2 are the leakage magnetic fluxes. To enhance the coupling ability between the coils, that is, the coupling coefficient k, it is achieved by increasing the main magnetic flux Φ m ; for a planar coil, the magnetic flux is not uniformly excited from the plane of the transmitting coil. The closer to the center of the coil, the stronger the magnetic flux. Therefore, the magnetic coupling between the coils mainly focuses on the center of the coils. And the size of the main receiving coil in the DD coil of a conventional wireless charging system is smaller than that of the main transmitting coil.

[0019] Ohm's law of magnetic circuit is:

[0020]

[0021] Among them, R is the magnetic resistance; F is the magnetomotive force; l is the length of the magnetic flux path; S is the cross-sectional area of the magnetic flux space; μ 0 is the permeability of free space, Φ is the magnetic flux. Translating the two sides of the main receiving coil in the direction away from each other can shorten the length l of the magnetic flux path of the main magnetic flux Φ m , and then the magnetic resistance R m of the main magnetic flux is reduced, and the main magnetic flux Φ m increases, so as to achieve the purpose of enhancing the coupling ability between the coils. When the centers of the main transmitting coil and the main receiving coil are completely perpendicular to the coil plane, the coupling ability reaches the maximum.

[0022] (2b) Based on the above optimization of the coil structure, the coupling coefficient k and the winding loss corresponding to the coil offset on both sides of the main coil at the receiving end are obtained through simulation.

[0023] As can be seen from the above technical solutions, the beneficial effects of the present invention are as follows: First, the technology of the present invention optimizes the structure and spatial arrangement of the main coil of the DD type, enhancing the coupling ability between coils while reducing the coil loss, i.e., copper loss, without increasing costs; Second, the present invention compares the improved main coil with the conventional DD type coil in the past, improving the wireless charging efficiency and enhancing the anti-offset characteristics of the coil. Description of the Drawings

[0024] Figure 1 is the circuit block diagram of the resonant type wireless electric vehicle charging system;

[0025] Figure 2 is the structural schematic diagram of the main coil at the transmitting end and the main coil at the receiving end in the present invention;

[0026] Figure 3 is the graph of the change of the coupling coefficient k and the winding loss analyzed with the side length of the bipolar square coil (DD coil) as the only variable;

[0027] Figure 4 is the theoretical schematic diagram of the coil translation;

[0028] Figure 5 is the structural schematic diagram of the installation of the main coil at the transmitting end and the main coil at the receiving end;

[0029] Figure 6 is the comparison diagram of the full alignment coupling of the main coil;

[0030] Figure 7 is the comparison diagram of the offset of the main coil in the x direction;

[0031] Figure 8 is the comparison diagram of the offset of the main coil in the y direction;

[0032] Figure 9 is the comparison diagram of the offset of the main coil in the z direction;

[0033] Figure 10 is the method flow chart of the present invention. Detailed Embodiments

[0034] Such as Figure 1 、 2As shown in the figure, a resonant wireless charging system for electric vehicles includes an AC voltage source for powering the entire system, a transmitting-end circuit, a transmitting-end main coil 4, a receiving-end main coil 5, and a receiving-end circuit. The AC voltage source is connected to the input end of the transmitting-end circuit, the output end of the transmitting-end circuit is connected to the transmitting-end main coil 4, and the transmitting-end main coil 4 transfers energy to the receiving-end main coil 5 through coil coupling. The receiving-end main coil 5 is connected to the input end of the receiving-end circuit. The transmitting-end circuit consists of a transmitting-end protection circuit, a rectifier circuit, a high-frequency inverter circuit, and a transmitting-end compensation network. The receiving-end circuit consists of a receiving-end compensation network, a rectifier and filter circuit, a receiving-end protection circuit, and a power storage device. The transmitting-end main coil and the receiving-end main coil 5 both adopt square DD-type coils with the same winding direction and the same energizing direction, and chamfers are made at all right angles of the coils. The rectifier circuit and the high-frequency inverter circuit convert the 50Hz AC voltage source of the power frequency into high-frequency alternating current to meet the resonant frequency of the compensation network and achieve the maximum transmission efficiency.

[0035] The transmitting-end compensation network and the receiving-end compensation network adopt a bilateral LCC resonant compensation topology. The transmitting-end compensation network includes a transmitting-end compensation coil 3 and two compensation capacitors, and the receiving-end compensation network includes a receiving-end compensation coil 6 and two compensation capacitors. The resonant compensation topology can increase the transmission power of the system, improve the transmission efficiency of the coil, and reduce the reactive power demand.

[0036] As Figure 2 Shown in the figure are the transmitting-end main coil 4 (large) and the receiving-end main coil 5 (small) with optimized coil structures and spatial positions. Both coils are square DD coils and have been chamfered. The two single coils of the receiving-end main coil 5 are translated in directions away from each other. When the center connection line between the transmitting-end main coil 4 and the receiving-end main coil 5 is completely perpendicular to the coil plane, the coupling ability of the coils reaches the maximum.

[0037] As Figure 3 Shown in the figure, two identical DD coils are coaxially placed. The number of turns of the coil is two, the wire diameter is 4mm, the coupling distance is 40mm, and the horizontal area of the coil is 8×10 -2 mm 2 (The area of the DD coil is the sum of the areas of two identical single rectangular plane coils, 4×10 -2 mm 2 +4×10 -2 mm 2) The peak value of the input alternating current is 5 A, and the frequency is 85 kHz. Keeping the number of turns and wire diameter of the coil fixed and the horizontal area of the coil unchanged, the side length of the rectangular coil is taken as the only variable for simulation analysis. The side length is increased successively to obtain the corresponding winding loss and coupling coefficient results. The results show that the closer the aspect ratio is to 1, the smaller the winding loss (i.e., copper loss) of the coil, and the larger the coupling coefficient k.

[0038] As Figure 4 shown, during the process of the main coil 5 at the receiving end moving horizontally to both sides, the magnetic path length l of the main magnetic flux Φ m is reduced, resulting in a decrease in the magnetic resistance R m of the main magnetic flux, an increase in the main magnetic flux Φ m , and ultimately an improvement in the coupling ability between the coils. When the centers of the main coil 4 at the transmitting end and the main coil 5 at the receiving end are completely perpendicular to the coil plane, the coupling ability of the coils reaches the maximum.

[0039] As Figure 5 shown, the main coil 4 at the transmitting end is successively provided with a transmitting end compensation coil 3, a transmitting end iron plate 2, and a transmitting end aluminum plate 1 downward, and the main coil 5 at the receiving end is successively provided with a receiving end compensation coil 6, a receiving end iron plate 7, and a receiving end aluminum plate 8 upward. The main coil 4 at the transmitting end and the main coil 5 at the receiving end are located on the same central axis. Figure 5 The coil system model formed by them. The aluminum plate and the iron plate are used for magnetic shielding to improve the magnetic focusing ability. The main coil 4 at the transmitting end and the main coil 5 at the receiving end should meet the electric vehicle charging standard, and the air gap is 150 mm.

[0040] As Figure 6 shown is the efficiency change diagram when the main coil 4 at the transmitting end and the main coil 5 at the receiving end are completely aligned and coupled. Compared with the conventional coil system model in the past, the efficiency of the present invention has been greatly improved.

[0041] As Figure 7 , 8 , and 9 shown are the diagrams of the change of the transmission efficiency of the system when the main coil has a certain offset in the x, y, and z directions respectively. According to the comparison, the anti-offset ability of the coil improved by the present invention has been significantly improved.

[0042] As Figure 10 shown, the present method includes the following steps in sequence:

[0043] (1) Optimize the coil structure, specifically including the following steps:

[0044] (1a) By deriving the coupling coefficient k of a single-turn rectangular planar coil during high-frequency operation, with the side lengths of the single-turn rectangular planar coil being a and b respectively, it is obtained that when the area s = a*b of the rectangular planar coil remains unchanged, the closer the ratio a / b of the side lengths of the rectangular planar coil is to 1, the stronger the coupling ability between the rectangular planar coils, that is, the coupling coefficient k, and the smaller the winding loss of the rectangular planar coil.

[0045] (1b) Conduct simulation verification: Place two identical multi-turn rectangular planar coils coaxially, fix the number of turns and wire diameter of the rectangular planar coils, keep the horizontal area of the rectangular planar coils unchanged, and use the side lengths of the rectangular planar coils as the only variable for simulation analysis. Increase the side lengths in sequence to obtain the corresponding winding loss and coupling coefficient results. The results show that when the aspect ratio is closer to 1, the winding loss, that is, the copper loss, of the rectangular planar coil is smaller, and the coupling coefficient k is larger.

[0046] (1c) Expand a single multi-turn rectangular planar coil into a bipolar coil, that is, a DD coil, and conduct simulation analysis with the side lengths of the rectangular planar coil as the only variable. Similar to the simulation results of the single-pole rectangular planar coil, when the aspect ratio is closer to 1, the winding loss, that is, the copper loss, of the rectangular planar coil is smaller, and the coupling coefficient k is larger.

[0047] (1d) By observing the magnetic field distribution of the rectangular planar coil, it is found that the closer the angle at the corner is to a right angle, the more obvious the magnetic field non-uniformity at the corner. Since the magnetic field change of the circular coil is not very sensitive to spatial changes, the circular coil is combined with the rectangular planar coil, and the right angle of the rectangular planar coil is set as a rounded corner. It can be seen from the simulation that the magnetic field distribution is greatly improved. Finally, it is determined that the transmitting end main coil 4 and the receiving end main coil 5 are selected as square DD coils, and chamfers are made at all right angles of the coils.

[0048] (2) Optimize the spatial position of the coils, which specifically includes the following steps:

[0049] (2a) Analyze the magnetic flux distribution diagram of the DD coil in a conventional wireless charging system. The relationship between the coupling coefficient and the magnetic flux is as follows:

[0050]

[0051] Among them, Φ m is the main magnetic flux; Φ σ1 and Φ σ2 are the leakage magnetic fluxes. To enhance the coupling ability between the coils, that is, the coupling coefficient k, it is achieved by increasing the main magnetic flux Φ m . For planar coils, the magnetic flux is not uniformly excited from the plane of the transmitting coil. The closer to the center of the coil, the stronger the magnetic flux. Therefore, the magnetic coupling between the coils mainly focuses on the center of the coils. And the size of the receiving end main coil 5 of the DD coil in the conventional wireless charging system is smaller than that of the transmitting end main coil 4.

[0052] Ohm's law of magnetic circuit is as follows:

[0053]

[0054] Wherein, R is the magnetic resistance; F is the magnetomotive force; l is the length of the magnetic flux path; S is the cross-sectional area of the magnetic flux space; μ 0 is the permeability of vacuum, Φ is the magnetic flux. Translating the two sides of the main coil 5 of the receiving end in the direction away from each other can shorten the length l of the magnetic flux path of the main magnetic flux Φ m and thus the magnetic resistance R of the main magnetic flux m is reduced, and the main magnetic flux Φ m is increased, so as to achieve the purpose of enhancing the coil coupling ability until the centers of the main coil 4 of the transmitting end and the main coil 5 of the receiving end are completely perpendicular to the coil plane, and the coupling ability reaches the maximum;

[0055] (2b) On the basis of the above coil structure optimization, the results of the coupling coefficient k and winding loss corresponding to the offset of the coils on both sides of the main coil 5 of the receiving end are obtained through simulation.

[0056] As Figure 10 shown, first determine the sizes of the two main coils, then keep the main coil 4 of the transmitting end stationary, and translate the main coil 5 of the receiving end to both sides respectively. When the centers of the two main coils are completely aligned, determine the spatial positions of the main coils; then, through the method of controlling variables, determine the sizes of the ferrite and aluminum plates when the coupling ability of the main coils reaches the maximum. Finally, by analyzing the relationships such as resistance and the number of turns of the compensation coil, determine the size of the compensation coil. After the coil system is built, observe whether the coupling ability of the coil system model is improved. If it is improved, the coil system model is successfully built; if not, it is necessary to recheck the design

[0057] In summary, the technology of the present invention optimizes the structure and spatial arrangement of the main coils of the DD type, enhances the coupling ability between the coils while reducing the coil loss, i.e., copper loss, and without increasing the cost; the present invention compares the improved main coils with the conventional DD type coils in the past, improves the wireless charging efficiency, and enhances the anti-offset characteristics of the coils.

Claims

1. A multi-parameter target optimization method for the coils of a resonant electric vehicle wireless charging system. The resonant electric vehicle wireless charging system includes an AC voltage source for powering the entire system, a transmitting-end circuit, a transmitting-end main coil, a receiving-end main coil, and a receiving-end circuit. The AC voltage source is connected to the input end of the transmitting-end circuit, the output end of the transmitting-end circuit is connected to the transmitting-end main coil, and the transmitting-end main coil transmits energy to the receiving-end main coil through coil coupling. The receiving-end main coil is connected to the input end of the receiving-end circuit. The transmitting-end circuit consists of a transmitting-end protection circuit, a rectifying circuit, a high-frequency inverter circuit, and a transmitting-end compensation network. The receiving-end circuit consists of a receiving-end compensation network, a rectifying and filtering circuit, a receiving-end protection circuit, and a power storage device. Both the transmitting-end main coil and the receiving-end main coil adopt square DD-type coils with the same winding direction and the same energizing direction, and chamfers are made at all right angles of the coils. The transmitting-end main coil is sequentially provided with a transmitting-end compensation coil, a transmitting-end iron plate, and a transmitting-end aluminum plate from top to bottom. The receiving-end main coil is sequentially provided with a receiving-end compensation coil, a receiving-end iron plate, and a receiving-end aluminum plate from bottom to top. The transmitting-end main coil and the receiving-end main coil are located on the same central axis. It is characterized in that: This method includes optimizing the coil structure, specifically including the following steps: (1a) By deriving the coupling coefficient k of a single-turn rectangular planar coil during high-frequency operation, with the side lengths of the single-turn rectangular planar coil being a and b respectively, it is obtained that when the area s = a*b of the rectangular planar coil remains unchanged, the closer the side length ratio a / b of the rectangular planar coil is to 1, the stronger the coupling ability, i.e., the coupling coefficient k, between the rectangular planar coils, and the smaller the winding loss of the rectangular planar coil. (1b) Conduct simulation verification: Place two identical multi-turn rectangular planar coils coaxially, fix the number of turns and wire diameter of the rectangular planar coils, keep the horizontal area of the rectangular planar coils unchanged, and use the side lengths of the rectangular planar coils as the only variable for simulation analysis. Increase the side lengths in sequence to obtain the corresponding winding loss and coupling coefficient results. The results show that the closer the aspect ratio is to 1, the smaller the winding loss, i.e., the copper loss, of the rectangular planar coil, and the larger the coupling coefficient k. (1c) Expand a single multi-turn rectangular planar coil to a bipolar coil, i.e., a DD coil, and conduct simulation analysis with the side lengths of the rectangular planar coil as the only variable. Similar to the simulation results of the single-pole rectangular planar coil, the closer the aspect ratio is to 1, the smaller the winding loss, i.e., the copper loss, of the rectangular planar coil, and the larger the coupling coefficient k. (1d) By observing the magnetic field distribution of the rectangular planar coil, it is found that the closer the angle at the corner is to a right angle, the more obvious the magnetic field non-uniformity at the corner. Since the magnetic field change of a circular coil is not very sensitive to spatial changes, a circular coil is combined with the rectangular planar coil, and the right angles of the rectangular planar coil are set as rounded chamfers. It can be seen from the simulation that the magnetic field distribution is greatly improved. Finally, it is determined that the transmitting-end main coil and the receiving-end main coil are selected as square DD coils, and chamfers are made at all right angles of the coils.

2. The multi-parameter target optimization method for the coil of the resonant electric vehicle wireless charging system according to claim 1, characterized in that: The optimization of the coil spatial position specifically includes the following steps: (2a) Analyze the magnetic flux distribution diagram of the DD coil of the conventional wireless charging system. The relationship between the coupling coefficient and the magnetic flux is as follows: Among them, Φ m is the main magnetic flux; Φ σ1 and Φ σ2 are leakage magnetic fluxes. Enhancing the coupling ability between coils, i.e., the coupling coefficient k, is achieved by increasing the main magnetic flux Φ m ; for planar coils, the magnetic flux is not uniformly excited from the plane of the transmitting coil. The closer to the center of the coil, the stronger the magnetic flux. Therefore, the magnetic coupling between coils mainly concentrates at the center of the coil, while the size of the main receiving coil of the DD coil in a conventional wireless charging system is smaller than that of the main transmitting coil; Ohm's law of magnetic circuit is: Among them, R is the magnetic resistance; F is the magnetomotive force; l is the length of the magnetic flux path; S is the cross-sectional area of the magnetic flux space; μ 0 is the permeability of free space, Φ is the magnetic flux. Translating the two sides of the main coil at the receiving end in the direction away from each other can shorten the length l of the magnetic flux path of the main magnetic flux Φ m and further reduce the magnetic resistance R of the main magnetic flux m and increase the main magnetic flux Φ m so as to achieve the purpose of enhancing the coupling ability of the coil. When the centers of the main coils at the transmitting end and the receiving end are completely perpendicular to the coil plane, the coupling ability reaches the maximum; (2b) On the basis of the above coil structure optimization, obtain the results of the coupling coefficient k and the winding loss corresponding to the coil offset on both sides of the receiving end main coil through simulation.

3. The multi-parameter target optimization method for the coil of the resonant electric vehicle wireless charging system according to claim 1, characterized in that: The transmitting end compensation network and the receiving end compensation network adopt a bilateral LCC resonant compensation topology structure. The transmitting end compensation network includes a transmitting end compensation coil and two compensation capacitors, and the receiving end compensation network includes a receiving end compensation coil and two compensation capacitors.

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