Magnetic coupling resonant wireless power transmission system of unmanned aerial vehicle

Abstract

The invention belongs to the technical field of unmanned aerial vehicle endurance, and particularly relates to an unmanned aerial vehicle magnetic coupling resonant wireless power transmission system which comprises a magnetic coupling mechanism, a coupling mechanism anti-offset characteristic, design of a circuit compensation structure, circuit design and simulation analysis and a system closed-loop control strategy. According to the coupling mechanism, a receiving coil is wound on a U-shaped frame on one side of the unmanned aerial vehicle, a transmitting coil is arranged in the charging station, the height of the receiving coil is H1, the length of the receiving coil is L2, the value is fixed and equal to the length of a rack, the length of the transmitting coil is L1, the width of the transmitting coil is W1, the length of a magnetic core in the middle of the transmitting coil is L3, the width of the magnetic core in the middle of the transmitting coil is W3, and the coupling coefficient is k. A bipolar transmitting device is adopted, a U-shaped ferrite iron core is arranged at a receiving end to guide magnetic flux, a transmitting coil adopts a double-D-shaped coil, and the coil at the receiving end is uniformly wound at a landing leg of the unmanned aerial vehicle in multiple turns, so that the distance between coupling coils is effectively reduced, and the system coupling capability is enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of unmanned aerial vehicle endurance, and specifically relates to a magnetically coupled resonant wireless power transmission system for unmanned aerial vehicles. Background Art

[0002] Magnetic coupling resonance wireless power transmission is one of many wireless power transmission technologies. It is based on the principle of electromagnetic induction, combined with modern power electronics technology and control theory. It converts electrical energy into electromagnetic field energy through a transmitter, transmits it over a certain distance, and then converts the electromagnetic field energy into electrical energy through a receiver, thus realizing wireless transmission of electrical energy.

[0003] The traditional drone charging method has the following problems:

[0004] 1. Traditional wired charging methods also have drawbacks such as easy sparks, leakage, easy wear, and possible heating of contacts. The carrier platform will face certain wave disturbances during the charging process, causing dynamic dislocation of the platform, which has a certain impact on the safety of the charging system;

[0005] 2. In actual use, the prior art device adjusts the drone, and the coupling position cannot be fixed. The drone is usually supported by the landing gear during wireless charging, and the support function of the frame itself cannot fix the existing charging position of the drone, causing the drone to be hit by external objects or external forces during the charging process, causing the charging position to be misaligned with the charging module, resulting in poor coupling between the drone and the charging module and reduced charging efficiency.

[0006] Therefore, to address the above problems, a magnetically coupled resonant wireless power transmission system for UAVs is proposed. Summary of the invention

[0007] 1. Technical issues to be resolved

[0008] In view of the shortcomings of the prior art, the present invention provides a magnetically coupled resonant wireless power transmission system for unmanned aerial vehicles, which solves the drawbacks of the prior art such as easy spark generation, leakage, easy wear, possible heating of contacts, and the problem that the drone may be affected by collision with external objects or external forces during the charging process, causing its charging position to be misaligned with the charging module, resulting in poor coupling effect between the drone and the charging module and reduced charging efficiency.

[0009] (II) Technical solution

[0010] To achieve the above-mentioned object, the present invention provides the following technical solutions: a magnetically coupled resonant wireless power transmission system for unmanned aerial vehicles, including a magnetic coupling mechanism, anti-drift characteristics of the coupling mechanism, design of a circuit compensation structure, circuit design and simulation analysis, and a system closed-loop control strategy;

[0011] The coupling mechanism: a receiving coil is wound on a U-shaped frame on one side of the drone, a transmitting coil is arranged in the charging station, and the height of the receiving coil is H 1 , the receiving coil length is L 2 , the value is fixed, equal to the rack length, the length of the transmitting coil is L 1 , the width of the transmitting coil is W 1 , the length of the magnetic core in the transmitting coil is L 3 and width W 3 , the coupling coefficient is k;

[0012] The coupling coefficient is an important parameter that affects the output characteristics of the system. Based on the finite element simulation software COMSOL, the self-inductance L of the primary coil is obtained. p1 , the secondary coil self-inductance L s1 The coupling coefficient can be calculated based on the mutual inductance according to formula (3.1), and the optimal range of the coupling coefficient k suitable for the wireless charging system can be found.

[0013]

[0014] When L 1 When it reaches 170mm, the coupling coefficient has reached its maximum value, indicating that the receiving coil has received the maximum magnetic flux. 1 The continued increase of makes the leakage magnetic field of the coupling mechanism increase, and the coupling coefficient k gradually decreases. Therefore, the length L of the transmitting coil 1 Select 170mm;

[0015] The W 1 As W increases, the coupling coefficient k increases because 1 As W increases, the height of the main magnetic flux path increases, and more and more magnetic flux passes through the receiving coil. 1 When it is 60mm-70mm, k reaches the maximum value and changes little. The width W of the transmitting coil 1 Select 70mm;

[0016] The H 1 As H increases, the k value increases first and then decreases. Since the height of the transmitting magnetic field is limited, if the receiving coil is set too high, the leakage inductance of the receiving device will increase, but the effective magnetic flux receiving area will not increase. 1 The more the receiving coil cannot receive the leakage magnetic flux, the more leakage magnetic flux passes through the soft magnetic core, which will also reduce the magnetic resistance of the leakage magnetic circuit. The coupling coefficient k changes by only 0.3% in the receiving width range of 50-80mm, and the change is not obvious. Therefore, the height H of the receiving coil 1 Select 50mm.

[0017] Furthermore, the anti-drift characteristic of the coupling mechanism: the coupling mechanism has good anti-drift characteristic in the X-axis direction, and in the Y-axis and 45° direction, when the offset is small, it still has certain anti-drift characteristic.

[0018] Furthermore, the design of the circuit compensation structure includes a DC power supply, an inverter circuit, a coupling mechanism, a rectifier circuit and a battery part, and adopts a wireless power transmission system based on an LCC-S compensation topology, wherein the left structure is a full-bridge inverter circuit, the middle structure is an LCC-S coupling structure, and the right structure is a full-bridge uncontrolled rectifier circuit;

[0019] Circuit compensation structure, the L at the transmitter in its equivalent circuit p1 , L 1 , C 1 and C p are coil self-inductance, compensation inductance, compensation capacitance and resonant capacitance respectively, L S1 and C s are coil self-inductance and compensation capacitance respectively;

[0020] Assume the inverter works at an angular frequency of ω and the secondary equivalent impedance Z s It can be expressed as:

[0021]

[0022] The secondary side needs to meet the resonance condition, and we can get:

[0023]

[0024] Convert the secondary side impedance to the reflected impedance Z of the primary side r , when it satisfies the resonance condition (3.3), its value can be expressed as:

[0025]

[0026] The equivalent input impedance Z of the primary side in It is expressed as:

[0027]

[0028] According to circuit theory, the input impedance Z in The imaginary part of is zero, which satisfies pure resistance. At this time, the reactive power generated by the system is zero, and the system efficiency is optimal.

[0029] Further, the circuit design and simulation analysis: The inverter circuit can convert DC into high-frequency AC, and the design of the voltage-type inverter circuit is relatively simple. This design adopts a full-bridge inverter circuit, which outputs the target AC waveform by controlling the inverter phase shift angle. After the AC output reaches the receiving end through the compensation network, it passes through the bridge uncontrolled rectifier circuit to obtain the required output voltage and power according to different loads;

[0030] The system input current and voltage through the inverter are in phase with the output current and voltage before the rectifier circuit, which shows that the system is in a resonant state.

[0031] Furthermore, the closed-loop control strategy of the system: adopts the PWM phase-shift closed-loop control method. After the sampling module collects the charging voltage and power at both ends of the battery, it sends the data to the stm32 controller through the serial port and compares it with the target value. The deviation between the two is used as the control quantity. By controlling the four-way PWM phase angle sent by the stm32 timer, the effective value or amplitude of the voltage after the DC power passes through the inverter is changed to realize closed-loop control. The specific process is divided into the following four steps:

[0032] (1) Initialize each module of the system and assign values ​​to the comparators; the target value is set to the charging voltage required by the drone battery, 11.1V;

[0033] (2) According to the voltage output at the load end, the system value under the required output voltage is determined by calculating and converting it into the phase shift control angle of the inverter;

[0034] (3) The primary side master control calculates and changes the phase shift angle of the rectifier drive signal through the PI controller so that the actual output voltage is the same as the target value;

[0035] (4) The output voltage is collected and judged again. If it is the same as the target value, the system outputs a constant voltage at this time;

[0036] When the system offset is large, a closed-loop control system is introduced, and the system can still maintain a stable constant voltage output. When the coupling mechanism is offset in the Y-axis direction, the load voltage changes in the open-loop and closed-loop states of the system. In the open-loop state, the Y-axis offset is in the range of 8-20mm, and the load voltage decreases sharply with the increase of the offset, and the maximum change rate is 34.3%. At this time, the system cannot maintain a constant voltage output state and is highly sensitive to the offset. However, when the system adds closed-loop control, it can be clearly seen that the Y-axis offset is in the range of 0-20mm, the output voltage is basically constant, and the maximum change rate is only 5.0%. That is, when the coupling mechanism offset is large, the introduction of closed-loop control can effectively improve the output characteristics of the system and maintain a stable constant voltage output.

[0037] (III) Beneficial effects

[0038] Compared with the prior art, the present invention provides a magnetically coupled resonant wireless power transmission system for drones, which has the following beneficial effects:

[0039] 1. This UAV magnetically coupled resonant wireless power transmission system adopts a bipolar transmitting device and a U-shaped ferrite core at the receiving end to guide the magnetic flux. The transmitting coil adopts a double D-type coil, and the receiving end coil is evenly wound around the UAV legs with multiple turns, which effectively reduces the distance between the coupling coils and enhances the system coupling capability.

[0040] 2. This is a magnetically coupled resonant wireless power transmission system for drones. By combining the working characteristics of drones, this wireless charging platform can complete the task of automatic charging of drones after landing, and achieve high-efficiency power transmission through a closed-loop control system, truly realizing unmanned operation.

[0041] 3. This UAV magnetically coupled resonant wireless power transmission system reduces the volume and weight of the receiving side loop by adopting an LCC-S compensation structure, and reduces the impact on the UAV's flight state through the design of the receiving coil, and has no effect on the UAV's extended functions such as the installation of the gimbal, thereby improving its structural adaptability.

[0042] 4. This magnetically coupled resonant wireless power transmission system for drones adopts an LCC-S structure. When the offset increases, the system will not have safety problems caused by overcurrent, and the leakage magnetic field generated by the magnetic coupling mechanism has little effect on the drone, so high-efficiency and safe charging can be achieved.

[0043] 5. This kind of UAV magnetic coupling resonant wireless power transmission system, through the design and optimization of the magnetic coupling mechanism and the design of the circuit compensation structure, when the system is offset within a certain scale, the coupling coefficient changes within a small range and the system transmission power does not change much. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0045] Figure 1 It is a schematic diagram of the main view of the three-dimensional structure of the present invention;

[0046] Figure 2 is a schematic top view of the three-dimensional structure of the coupling mechanism of the present invention;

[0047] Figure 3 is a schematic side view of the three-dimensional structure of the coupling mechanism of the present invention;

[0048] Figure 4 It is a data graph of the transmission distance of the coupling mechanism of the present invention;

[0049] Figure 5 It is a data graph of the length of the transmitting coil of the present invention;

[0050] Figure 6 is a data graph of the width of the transmitting coil of the present invention;

[0051] Figure 7 is a data graph of the width of the receiving coil of the present invention;

[0052] Figure 8 It is a data diagram of the magnetic flux density distribution in the YZ cross section of the present invention;

[0053] Fig. 9 It is a data diagram of the X-axis offset of the present invention;

[0054] Fig.10 It is a data graph of the Y-axis offset of the present invention;

[0055] Fig.11 It is a data graph of the 45° anti-drift characteristic curve of the present invention;

[0056] Fig.12 It is a research and development model diagram of the work of the present invention;

[0057] Fig.13 This is the LCC-S compensation circuit diagram of the present invention;

[0058] Fig.14 is the LCC-S equivalent circuit of the present invention;

[0059] Fig.15 It is a comparison diagram of the PWM waveform of the present invention;

[0060] Fig.16 It is the voltage and current waveform diagram of the inverter output terminal of the present invention;

[0061] Fig.17 It is a waveform diagram of voltage and current of the secondary coil at the receiving end under the resonant state of the present invention;

[0062] Fig.18 It is a comparison diagram of the inverter output voltage waveform and the receiving voltage waveform under the resonant state of the present invention;

[0063] Fig.19 It is a data diagram of load voltage variation curve under different loads when the present invention is open-loop;

[0064] Fig. 20 is a load voltage data diagram when the system is offset along the X-axis when the loop is open;

[0065] Fig.21 It is a load voltage data diagram when the system is offset along the Y axis when the loop is open;

[0066] Fig. 22 It is a control circuit diagram of the present invention;

[0067] Fig.23 It is a control flow chart of the present invention;

[0068] Fig.24 It is a flow chart of the closed-loop control module of the present invention;

[0069] Fig.25 It is a flow chart of the power calculation module of the present invention;

[0070] Fig.26 It is a constant voltage output data diagram under different loads of the present invention;

[0071] Fig. 27 It is a load voltage variation diagram when the open and closed loop of the present invention is offset along the Y axis. DETAILED DESCRIPTION

[0072] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0073] Specific examples are given below.

[0074] See also Figure 1-Figure 27 , the present invention provides a magnetically coupled resonant wireless power transmission system for unmanned aerial vehicles, including a magnetic coupling mechanism, anti-drift characteristics of the coupling mechanism, design of a circuit compensation structure, circuit design and simulation analysis, and a system closed-loop control strategy;

[0075] Coupling mechanism: The receiving coil is wound on the U-shaped frame on one side of the drone, and a transmitting coil is set in the charging station. The height of the receiving coil is H 1 , the receiving coil length is L 2 , the value is fixed, equal to the rack length, the length of the transmitting coil is L 1 , the width of the transmitting coil is W 1 , the length of the magnetic core in the transmitting coil is L 3 and width W 3 , the coupling coefficient is k;

[0076] The coupling coefficient is an important parameter that affects the output characteristics of the system. Based on the finite element simulation software COMSOL, the self-inductance L of the primary coil is obtained. p1 , the secondary coil self-inductance L s1 The coupling coefficient can be calculated based on the mutual inductance according to formula (3.1), and the optimal range of the coupling coefficient k suitable for the wireless charging system can be found;

[0077]

[0078] When L 1 When it reaches 170mm, the coupling coefficient has reached its maximum value, indicating that the receiving coil has received the maximum magnetic flux. 1 The continued increase of makes the leakage magnetic field of the coupling mechanism increase, and the coupling coefficient k gradually decreases. Therefore, the length L of the transmitting coil 1 Select 170mm;

[0079] W 1 As W increases, the coupling coefficient k increases because 1 As W increases, the height of the main magnetic flux path increases, and more and more magnetic flux passes through the receiving coil. 1 When it is 60mm-70mm, k reaches the maximum value and changes little. The width W of the transmitting coil 1 Select 70mm;

[0080] H 1 As H increases, the k value increases first and then decreases. Since the height of the transmitting magnetic field is limited, if the receiving coil is set too high, the leakage inductance of the receiving device will increase, but the effective magnetic flux receiving area will not increase. 1 The more the receiving coil cannot receive the leakage magnetic flux, the more leakage magnetic flux passes through the soft magnetic core, which will also reduce the magnetic resistance of the leakage magnetic circuit. The coupling coefficient k changes by only 0.3% in the receiving width range of 50-80mm, and the change is not obvious. Therefore, the height H of the receiving coil 1 Select 50mm;

[0081] Anti-drift characteristics of the coupling mechanism: The coupling mechanism has good anti-drift characteristics in the X-axis direction. In the Y-axis and 45° direction, when the offset is small, it still has certain anti-drift characteristics;

[0082] The design of the circuit compensation structure includes a DC power supply, an inverter circuit, a coupling mechanism, a rectifier circuit and a battery. A wireless power transmission system based on an LCC-S compensation topology is adopted. The left structure is a full-bridge inverter circuit, the middle structure is an LCC-S coupling structure, and the right structure is a full-bridge uncontrolled rectifier circuit.

[0083] Circuit compensation structure, the L at the transmitter in its equivalent circuit p1 , L 1 , C 1 and C p are coil self-inductance, compensation inductance, compensation capacitance and resonant capacitance respectively, L S1 and C s are coil self-inductance and compensation capacitance respectively;

[0084] Assume the inverter works at an angular frequency of ω and the secondary equivalent impedance Zs It can be expressed as:

[0085]

[0086] The secondary side needs to meet the resonance condition, and we can get:

[0087]

[0088] Convert the secondary side impedance to the reflected impedance Z of the primary side r , when it satisfies the resonance condition (3.3), its value can be expressed as:

[0089]

[0090] The equivalent input impedance Z of the primary side in It is expressed as:

[0091]

[0092] According to circuit theory, the input impedance Z in The imaginary part of is zero, which satisfies pure resistance. At this time, the reactive power generated by the system is zero, and the system has the best efficiency. Therefore, it needs to satisfy:

[0093]

[0094] Therefore, the conditions for resonance of this system can be known;

[0095] Write the KCL equation for the primary circuit, and we have:

[0096]

[0097] Based on the resonant condition of the system, the loop KVL equation is:

[0098]

[0099] Combining the above formula, we can get the system output current for:

[0100]

[0101] Then the system output voltage is obtained for:

[0102]

[0103] Since the internal resistance of the coil is small, its resistance value RL<<R2, so the above formula can be further simplified as:

[0104]

[0105] In this formula, the expression of output voltage U is related to load R L It does not matter, when the input voltage U in When it is determined, the output voltage U can be approximated as a constant value;

[0106] Circuit design and simulation analysis: The inverter circuit can convert DC into high-frequency AC, and the design of the voltage-type inverter circuit is relatively simple. This design uses a full-bridge inverter circuit to output the target AC waveform by controlling the inverter phase shift angle. After the AC output reaches the receiving end through the compensation network, it passes through the bridge uncontrolled rectifier circuit to obtain the required output voltage and power according to different loads;

[0107] After analysis, it can be known that the DC voltage input range of the inverter circuit is provided by an adjustable DC power supply, which is 0~60V, and the voltage at the load end is also 0~60V. The waveform of this simulation takes 15V as an example, and the required output is 11.1V;

[0108] Assume the inverter output effective value is 0.9U d , according to the above resonance analysis, the actual rectified input voltage U 1 for:

[0109]

[0110] After passing through the rectifier, its voltage is U 2 , which can be expressed as:

[0111]

[0112] Finally, substitute the data to get the theoretical value of the output voltage, measure the corresponding voltage and current on the load, and the power can be obtained by P = UI;

[0113] If the given DC power supply voltage is 15V, then L 1 and C 1 Determined by the power level, L can be obtained through analysis 1 =20uH and C 1 =0.175uF, the inverter operating frequency is 85kHz, the angular frequency ω = 2 × 3.14 × 85kHz = 533800rad / s. According to the formula, C s1 =0.1638uF; According to the formula, C P =0.055uF, it can be seen that by adjusting the shift angle α, U 2 The output voltage is 11.1V;

[0114] The system input current and voltage through the inverter are in phase with the output current and voltage before the rectifier circuit, which shows that the system is in a resonant state;

[0115] System closed-loop control strategy: PWM phase-shift closed-loop control method is adopted. After the sampling module collects the charging voltage and power at both ends of the battery, it sends the data to the STM32 controller through the serial port and compares it with the target value. The deviation between the two is used as the control quantity. By controlling the four-way PWM phase angle sent by the STM32 timer, the effective value or amplitude of the voltage after the DC power passes through the inverter is changed to realize closed-loop control. The specific process is divided into the following four steps:

[0116] (1) Initialize each module of the system and assign values ​​to the comparators; the target value is set to the charging voltage required by the drone battery, 11.1V;

[0117] (2) According to the voltage output at the load end, the system value under the required output voltage is determined by calculating and converting it into the phase shift control angle of the inverter;

[0118] (3) The primary side master control calculates and changes the phase shift angle of the rectifier drive signal through the PI controller so that the actual output voltage is the same as the target value;

[0119] (4) The output voltage is collected and judged again. If it is the same as the target value, the system outputs a constant voltage at this time;

[0120] When the system offset is large, a closed-loop control system is introduced, and the system can still maintain a stable constant voltage output. When the coupling mechanism is offset in the Y-axis direction, the load voltage changes in the open-loop and closed-loop states of the system. In the open-loop state, the Y-axis offset is in the range of 8-20mm, and the load voltage decreases sharply with the increase of the offset, and the maximum change rate is 34.3%. At this time, the system cannot maintain a constant voltage output state and is highly sensitive to the offset. However, when the system adds closed-loop control, it can be clearly seen that the Y-axis offset is in the range of 0-20mm, the output voltage is basically constant, and the maximum change rate is only 5.0%. That is, when the coupling mechanism offset is large, the introduction of closed-loop control can effectively improve the output characteristics of the system and maintain a stable constant voltage output.

[0121] Specifically, the invention uses a bipolar orthogonal coupling coil to solve the problem of low charging efficiency of the UAV in an offset state, and uses an experimental method to quantitatively verify the relationship between its charging voltage, charging efficiency and offset parameters, and solves the problem of non-constant charging voltage caused by changes in load resistance parameters of the battery due to factors such as heat during the charging process, which is beneficial to improving the efficiency and safety of wireless charging. Combined with the shape characteristics of the UAV, the LCC-S compensation structure is adopted to reduce the volume and weight of the receiving side loop, and the design of the receiving coil reduces the impact on the flight state of the UAV, and has no effect on the extended functions of the UAV such as the installation of the gimbal, thereby improving its structural adaptability.

[0122] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A magnetically coupled resonant wireless power transmission system for unmanned aerial vehicles, including the design of magnetic coupling mechanism, anti-drift characteristics of coupling mechanism, circuit compensation structure, circuit design and simulation analysis, and system closed-loop control strategy; The coupling mechanism: a receiving coil is wound on a U-shaped frame on one side of the drone, a transmitting coil is arranged in the charging station, the height of the receiving coil is H1, the length of the receiving coil is L2, the value is fixed and equal to the length of the frame, the length of the transmitting coil is L1, the width of the transmitting coil is W1, the length of the middle magnetic core of the transmitting coil is L3 and the width is W3, and the coupling coefficient is k; The coupling coefficient is an important parameter that affects the output characteristics of the system. Based on the finite element simulation software COMSOL, the self-inductance L of the primary coil is obtained. p1 , the secondary coil self-inductance L s1 The coupling coefficient can be calculated based on the mutual inductance according to formula (3.1), and the optimal range of the coupling coefficient k suitable for the wireless charging system can be found; When L1 reaches 170 mm, the coupling coefficient has reached its maximum value, indicating that the magnetic flux received by the receiving coil has reached its maximum value. Then, as L1 continues to increase, the magnetic leakage of the coupling mechanism increases, and the coupling coefficient k gradually decreases. Therefore, the length L1 of the transmitting coil is selected to be 170 mm. When W1 increases, the coupling coefficient k increases, because as W1 increases, the height of the main magnetic flux path increases, and more and more magnetic flux passes through the receiving coil. When W1 is 60mm-70mm, k reaches the maximum value and does not change much. The width W1 of the transmitting coil is selected to be 70mm. As H1 increases, the k value first increases and then decreases. Since the height of the transmitting magnetic field is limited, if the receiving coil is set too high, the leakage inductance of the receiving device will increase, but the effective magnetic flux receiving area will not increase. As H1 continues to decrease, the more leakage magnetic flux that the receiving coil cannot receive, the more leakage magnetic flux passes through the soft magnetic core, which will also reduce the magnetic resistance of the leakage magnetic circuit. The coupling coefficient k changes by only 0.3% within the receiving width range of 50-80mm, and the change is not obvious. Therefore, the height H1 of the receiving coil is selected to be 50mm.

2. The magnetically coupled resonant wireless power transmission system for unmanned aerial vehicles according to claim 1, characterized in that: The anti-drift characteristic of the coupling mechanism: the coupling mechanism has good anti-drift characteristic in the X-axis direction, and still has certain anti-drift characteristic in the Y-axis and 45° direction when the offset is small.

3. The magnetically coupled resonant wireless power transmission system for unmanned aerial vehicles according to claim 1, characterized in that: The design of the circuit compensation structure includes a DC power supply, an inverter circuit, a coupling mechanism, a rectifier circuit and a battery part, and adopts a wireless power transmission system based on an LCC-S compensation topology. The left structure is a full-bridge inverter circuit, the middle structure is an LCC-S coupling structure, and the right structure is a full-bridge uncontrolled rectifier circuit. Circuit compensation structure, the L at the transmitter in its equivalent circuit p1 , L1, C1 and C p are coil self-inductance, compensation inductance, compensation capacitance and resonant capacitance respectively, L S1 and C s are coil self-inductance and compensation capacitance respectively; Assume the inverter works at an angular frequency of ω and the secondary equivalent impedance Z s It can be expressed as: The secondary side needs to meet the resonance condition, and we can get: Convert the secondary side impedance to the reflected impedance Z of the primary side r , when it satisfies the resonance condition (3.3), its value can be expressed as: The equivalent input impedance Z of the primary side in It is expressed as: According to circuit theory, the input impedance Z in The imaginary part of is zero, which satisfies pure resistance. At this time, the reactive power generated by the system is zero, and the system efficiency is optimal.

4. The magnetically coupled resonant wireless power transmission system for unmanned aerial vehicles according to claim 1, characterized in that: Circuit design and simulation analysis: The inverter circuit can convert DC into high-frequency AC, and the design of the voltage-type inverter circuit is relatively simple. This design uses a full-bridge inverter circuit to output the target AC waveform by controlling the inverter phase shift angle. After the AC output reaches the receiving end through the compensation network, it passes through the bridge uncontrolled rectifier circuit to obtain the required output voltage and power according to different loads; The system input current and voltage through the inverter are in phase with the output current and voltage before the rectifier circuit, which shows that the system is in a resonant state.

5. The magnetically coupled resonant wireless power transmission system for unmanned aerial vehicles according to claim 1, characterized in that: The closed-loop control strategy of the system: adopts PWM phase-shift closed-loop control method. After the sampling module collects the charging voltage and power at both ends of the battery, it sends the data to the stm32 controller through the serial port and compares it with the target value. The deviation between the two is used as the control quantity. By controlling the four-way PWM phase angle sent by the stm32 timer, the effective value or amplitude of the voltage after the DC power passes through the inverter is changed to realize closed-loop control. The specific process is divided into the following four steps: (1) Initialize each module of the system and assign values ​​to the comparators; the target value is set to the charging voltage required by the drone battery, 11.1V; (2) According to the voltage output at the load end, the system value under the required output voltage is determined by calculating and converting it into the phase shift control angle of the inverter; (3) The primary side master control calculates and changes the phase shift angle of the rectifier drive signal through the PI controller so that the actual output voltage is the same as the target value; (4) The output voltage is collected and judged again. If it is the same as the target value, the system outputs a constant voltage at this time; When the system offset is large, a closed-loop control system is introduced, and the system can still maintain a stable constant voltage output. When the coupling mechanism is offset in the Y-axis direction, the load voltage changes in the open-loop and closed-loop states of the system. In the open-loop state, the Y-axis offset is in the range of 8-20mm, and the load voltage decreases sharply with the increase of the offset, and the maximum change rate is 34.3%. At this time, the system cannot maintain a constant voltage output state and is highly sensitive to the offset. However, when the system adds closed-loop control, it can be clearly seen that the Y-axis offset is in the range of 0-20mm, the output voltage is basically constant, and the maximum change rate is only 5.0%. That is, when the coupling mechanism offset is large, the introduction of closed-loop control can effectively improve the output characteristics of the system and maintain a stable constant voltage output.

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