Constant voltage / constant current charging EC-WPT system and parameter design method for drones

Abstract

The present invention provides a constant voltage / constant current charging EC-WPT system for unmanned aerial vehicles and a parameter design method, comprising a transmitting end and a receiving end, wherein the transmitting end is provided with a DC power supply, a high-frequency inverter, a variable-structure LC resonant network and two energy transmitting plates; the receiving end is provided with two energy receiving plates, a CLC-Π type resonant network, a rectifier filter circuit and an electrical load; the variable-structure LC resonant network includes an inductor L1, a capacitor C 1c , capacitor C 1v and switch element K; when the system requires constant current output, the switch element K is disconnected, and the high-frequency inverter operates at the first system operating angular frequency ω cc Output high-frequency inverter signal; when the system requires constant voltage output, the switch element K is closed, and the high-frequency inverter operates at the second system operating angular frequency ω cv Output high-frequency inverter signal. The effect is that the system can not only achieve constant output when the load changes, but also can achieve constant output when the coupling mechanism is offset.

Description

Technical Field

[0001] The present invention relates to wireless power transmission technology, and in particular to a constant voltage / constant current charging EC-WPT system for unmanned aerial vehicles and a parameter design method. Background Art

[0002] A drone is a reusable unmanned aerial vehicle that can be controlled by programming or wireless remote control to perform multiple tasks. It is referred to as a drone (UAV). Drones have the advantages of low cost, low loss, safety and flexibility. Whether in the civil, military or scientific research fields, drones are playing an increasingly important role. Among the many technical indicators for evaluating the performance of drones, endurance is undoubtedly one of the most critical technologies for drones. For drones, having a longer endurance means that it can complete the assigned tasks more quickly and efficiently, avoiding risks such as crashes caused by insufficient power. From an energy perspective, power can be replenished multiple times during the drone's mission. If the charging technology is based on the traditional electrical contact conduction method, the electrical contact points will be exposed. Obviously, this method is insufficient in terms of safety and reliability.

[0003] Wireless Power Transfer (WPT) technology combines power electronics technology with modern control theory and technology, and realizes wireless transmission of electric energy through carriers such as magnetic field, electric field, microwave, and laser. The common wireless charging method is magnetic coupling wireless power transfer technology (MC-WPT), but the weight of the coupling mechanism will increase the weight of the drone. For drones, the weight is a key factor that directly affects the portability and flight speed of drones. The coupling mechanism of electric field coupling wireless power transfer technology (EC-WPT) has the characteristics of low cost, light weight, and changeable shape, which is more suitable for wireless charging of drones. Compared with MC-WPT technology, the research work on the application of EC-WPT technology in drones is still in its infancy. References: MOSTAFA TM, MUHARAM A, HATTORI R. Wireless battery charging system for drones via capacitive power transfer: IEEE, 2017. Using a coupling capacitor with a size of 500pF parallel plate, an EC-WPT system with a transmission power of 12W was designed to charge drones. The designed system operates at a frequency of 6.8MHz and has a transmission efficiency of 50%. References: KIM D, AHN D. Optimization of Capacitive Wireless Power Transfer System for Maximum Efficiency [J]. Journal of Electrical Engineering & Technology, 2020, 15 (1): 343-352. Using the bilateral LC resonant network, a UAV EC-WPT charging system was designed, and a method for calculating the inductance and capacitance in the LC resonant network at the receiving end was proposed to maximize the efficiency.

[0004] Drones are generally powered by lithium batteries. During the charging process of such batteries, the charging mode is constant current first and then constant voltage. In the initial stage, the system needs to work in constant current mode, and the voltage rises rapidly. When the voltage rises to the rated value, the system needs to switch to constant voltage mode. Therefore, in order to make the charging process meet the above requirements, the EC-WPT system should have constant current / constant voltage output characteristics.

[0005] In the relevant research on EC-WPT technology, the existing literature mainly revolves around two methods to achieve constant output of the system. The first method is to set a detection circuit at the output end of the system, and feed back the detected load voltage to the control circuit at the transmitting end to achieve constant output. The second method is to use the characteristics of the resonant network to achieve constant output characteristics. Relatively speaking, the latter does not need to set up detection and complex control circuits, and the complexity and cost of the system are lower, which has greater advantages. Chinese patents 201710143436.X and 201710143425.1 respectively use double-sided F-CLCL resonant networks and T-Π composite resonant networks to make the system output voltage not change with changes in load size. Chinese patent 201910164956.8 also proposes a T-type CLC resonant network that can make the voltage output constant. However, the above resonant networks can only achieve constant voltage output or constant current output in a single way, facing the needs of practical application of constant current / constant voltage power supply and its mode switching; Chinese patent 201810032336.4 proposes a FF / T variable structure resonant network to achieve the switching of system constant current / constant voltage working mode; Chinese patent 202010309224.6 adopts a variable structure LC-CLCL resonant network to enable the system to achieve constant current / constant voltage working mode switching. These two topologies have more components at the receiving end, and the switching switch is also installed at the receiving end. If applied to drone charging, the flight load of the drone will be relatively large.

[0006] In addition, when drones are performing autonomous wireless charging, there will often be a certain deviation due to inaccurate positioning or the influence of environmental factors; the receiving end of the drone charging system should also be designed to be lightweight to reduce the load on the drone during normal operation. Existing technologies cannot fully meet the above requirements, so further optimization of the drone constant voltage / constant current charging system is needed. Summary of the invention

[0007] Based on the above requirements, the present invention first proposes a constant voltage / constant current charging EC-WPT system for drones. By adding a switch and a switching capacitor at the transmitting end, the topology is changed while changing the frequency to achieve switching of the output characteristics, so that the output can be constant not only when the load changes, but also when the coupling mechanism is offset.

[0008] In order to achieve the above object, the specific technical solution adopted by the present invention is as follows:

[0009] A constant voltage / constant current charging EC-WPT system for unmanned aerial vehicles, comprising a transmitting end and a receiving end, wherein the transmitting end is provided with a DC power supply, a high-frequency inverter, a variable structure LC resonant network and two energy transmitting plates; the receiving end is provided with two energy receiving plates, a CLC-Π type resonant network, a rectifier filter circuit and an electrical load;

[0010] The variable structure LC resonant network includes an inductor L 1 , capacitor C 1c , capacitor C 1v and switch element K; where the inductor L 1 and capacitor C 1c Connected in series between the two output terminals of the high-frequency inverter, the capacitor C 1c The two ends of the capacitor C are connected to the two energy emitting plates respectively; 1v With capacitor C 1c In parallel, the capacitor C is controlled by the switch element K 1v The switching on and off of the parallel branch realizes the change of the LC resonant network structure;

[0011] When the system requires constant current output, the switch element K is disconnected, and the high-frequency inverter operates at the first system operating angular frequency ω cc Output high-frequency inverter signal;

[0012] When the system requires constant voltage output, the switch element K is closed, and the high-frequency inverter operates at the second system operating angular frequency ω cv Output high frequency inverter signal.

[0013] Optionally, two sections of metal foil are attached to the outer wall of the drone body in a corresponding up and down position relationship as the two energy receiving plates; a charging slot is provided on the drone charging seat, and two sections of metal foil are attached to the inner wall of the charging slot in a corresponding up and down position relationship as the two energy emitting plates; when the drone docks on the drone charging seat, the two energy emitting plates correspond one-to-one with the two energy receiving plates to form a coupling capacitor.

[0014] Optionally, the two energy emitting plates and the two energy receiving plates are both arranged in a cylindrical shape, and the inner diameter of the energy emitting plate is greater than the outer diameter of the energy receiving plate.

[0015] Optionally, the CLC-Π type resonant network is composed of a capacitor C 2 、Inductance L 2 and capacitor C 3 When the system needs constant current output, the operating angular frequency of the first system satisfies:

[0016] Among them, C 1c , C2 , C 3 They correspond to the capacitance C 1c , capacitor C 2 and capacitor C 3 Capacitance value; L 1 , L 2 Corresponding to the inductance L 1 and inductor L 2 The self-sensing value.

[0017] Optionally, when the system requires constant voltage output, the operating angular frequency of the second system satisfies:

[0018] Among them, C 1v is the capacitance C 1v Capacitance value.

[0019] Optionally, a communication link for transmitting an operating mode switching instruction is provided between the transmitting end and the receiving end; when the transmitting end receives the operating mode switching instruction from the receiving end, the switching element K and the high-frequency inverter are controlled to perform corresponding actions.

[0020] Based on the above system design, the present invention also proposes a parameter design method for a constant voltage / constant current charging EC-WPT system for a drone, comprising the following steps:

[0021] S1: Determine the power load R according to application requirements L Variation range, current i in constant current working mode L And the voltage u in constant voltage working mode L , and determine the coupling capacitance C according to the energy transmitting plate and the energy receiving plate s ;

[0022] S2: Set DC power supply E dc The initial value of

[0023] S3: Set the first system operating frequency f according to engineering experience cc and capacitor C 1c The initial value of

[0024] S4: Determine the first capacitance ratio k based on the constant current output relationship 1 , and determine the second capacitance ratio k according to the constant voltage output relationship 2 The value of

[0025] S5: Determine whether P is satisfied out_实际 ≥αP out , where P out_实际 Indicates the actual output power, P out represents the target output power, α is the margin coefficient; if it is satisfied, then go to step S6; if it is not satisfied, then increase the DC power supply Edc And return to step S2;

[0026] S6: Determine the second system operating angular frequency f cv ;

[0027] S7: Determine the inductance L 1 、Inductance L 2 The self-inductance value and capacitance C 1v , capacitor C 2 , capacitor C 3 Capacitance value;

[0028] S8: Determine whether L is satisfied 2 ≤L max If it is not satisfied, increase the operating frequency f of the first system cc And return to S3; if satisfied, go to step S9, where L max is the maximum inductance value under the system weight constraint;

[0029] S9: Obtain a set of parameters as the final parameters of the system.

[0030] Optionally, in step S4, the first capacitance ratio k is determined 1 When Calculation: Determine the second capacitance ratio k 2 When calculate;

[0031] in, It indicates the effective value of the voltage across the load equivalent resistance in the system equivalent circuit in the constant voltage working mode; for u o The vector representation of ; It indicates the effective value of the current passing through the load equivalent resistance in the system equivalent circuit under the constant current working mode. for i o The vector representation of ; is the vector expression of the effective value of the current after the coupling mechanism; X 1c is the capacitance C 1c Impedance; It is the vector expression of the effective value of the inverter output voltage.

[0032] Optionally, in step S6, Determine the operating angular frequency of the second system.

[0033] Optionally, in step S7:

[0034]

[0035]

[0036] Determine the inductance L 1 、Inductance L 2 The self-inductance value and capacitance C 1v , capacitor C 2 , capacitor C 3 Capacitance value.

[0037] The effects of the present invention are:

[0038] The present invention proposes a constant voltage / constant current charging EC-WPT system and parameter design method for drones. A switching element and a switching capacitor are added to the transmitting end of the system. The topology is changed while the frequency is changed to achieve the switching of the output characteristics. The advantage of the present invention is that it does not require complex feedback control to achieve constant current charging or constant voltage charging of the battery according to the charging requirements of the drone, and the system still has good constant current / constant voltage output characteristics under a large range of load changes and a large offset of the coupling mechanism. The system is simple to implement, and the coupling mechanism and the receiving end are lightweight, which is conducive to reducing the load of the drone. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the specific implementation of the present invention or the technical solution in the prior art, the drawings required for use in the specific implementation or the description of the prior art will be briefly introduced below.

[0040] Figure 1 The circuit topology of the constant voltage / constant current charging EC-WPT system for UAVs proposed by the present invention;

[0041] Figure 2 It is a schematic diagram of the coupling mechanism structure in a specific embodiment of the present invention;

[0042] Figure 3 This is a topology diagram of a variable structure LC-II type EC-WPT system for a UAV in a specific embodiment of the present invention;

[0043] Figure 4 for Figure 3 Equivalent circuit diagram of

[0044] Figure 5 This is the system equivalent circuit diagram under constant current mode;

[0045] Figure 6 It is the system equivalent circuit diagram under constant voltage mode;

[0046] Figure 7 Design a flow chart for the system's parameters;

[0047] Figure 8 It is the simulation waveform of load current and voltage in constant current mode;

[0048] Fig. 9It is the simulation waveform of load current and voltage in constant voltage mode. DETAILED DESCRIPTION

[0049] The following embodiments of the technical solution of the present invention are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore only used as examples, and cannot be used to limit the protection scope of the present invention.

[0050] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in this application should have the common meanings understood by those skilled in the art to which the present invention belongs.

[0051] like Figure 1 As shown, this embodiment provides a constant voltage / constant current charging EC-WPT system for drones, including a transmitting end and a receiving end, wherein the transmitting end is provided with a DC power supply, a high-frequency inverter, a variable structure LC resonant network, and two energy transmitting plates; the receiving end is provided with two energy receiving plates, a CLC-Π type resonant network, a rectifier filter circuit, and an electrical load;

[0052] Taking the structure of the current coaxial twin-rotor UAV as an example, two sections of metal foil are attached to the outer wall of the UAV fuselage in a corresponding up and down position relationship as the two energy receiving plates; a charging slot is provided on the UAV charging seat, and two sections of metal foil are attached to the inner wall of the charging slot in a corresponding up and down position relationship as the two energy emitting plates; in order to better avoid the problem of short circuit caused by direct contact between the energy emitting plate and the energy receiving plate and to ensure the safety of the system, metal foil with insulating film is used in the coupling mechanism. When the UAV is docked on the UAV charging seat, the two energy emitting plates correspond to the two energy receiving plates one by one to form a coupling capacitor, thereby forming a structure such as Figure 2 The cylindrical coupling mechanism shown is very light and will not increase the size and weight of the drone excessively, nor will it cause wind resistance when the drone is flying.

[0053] Figure 2 The middle emitting end plates P1 and P2 are composed of two pieces with a radius of r 1 The receiving plates P3 and P4 are made of metal plates with a radius of r 2 copper foil, the transmission distance between the transmitter and the receiver is r 2 -r 1 , P1 and P3 plates are facing each other with a height of h, P2 and P4 plates are facing each other with a height of h, and the vertical distance between the two sets of facing plates is d.

[0054] The circuit topology of the system is as follows: Figure 3 As shown, where E dc is the DC input voltage; S 1 -S 4It is a high-frequency full-bridge inverter circuit composed of 4 MOSFETs; the transmitting end is a variable structure LC resonant network; the receiving end is a CLC-Π type resonant network composed of two capacitors and one inductor; D 1 -D 4 It is a full-bridge rectifier circuit composed of 4 diodes; C f is the filter capacitor; R L It is the load equivalent resistance. The DC power supply generates an alternating voltage through a high-frequency inverter, which is filtered by the LC network at the transmitting end and the voltage is pumped up to the high excitation voltage required by the coupling mechanism. When the receiving plate of the coupling mechanism is placed near the transmitting plate, an alternating electric field is generated between the two plates. Under the action of the alternating electric field, a displacement current "flows" through the plates, realizing wireless transmission of electric energy. The rectifier filter converts AC power into DC power to power the drone battery.

[0055] from Figure 3 As can be seen, the variable structure LC resonant network includes the inductor L 1 , capacitor C 1c , capacitor C 1v and switch element K; where the inductor L 1 and capacitor C 1c Connected in series between the two output terminals of the high-frequency inverter, the capacitor C 1c The two ends of the capacitor C are connected to the two energy emitting plates respectively; 1v With capacitor C 1c In parallel, the capacitor C is controlled by the switch element K 1v The switching of the parallel branch realizes the structural change of the LC resonant network; in specific implementation, when the system requires constant current output, the switch element K is disconnected, and the high-frequency inverter is operated at the first system operating angular frequency ω cc Output high-frequency inverter signal; when the system requires constant voltage output, the switch element K is closed, and the high-frequency inverter operates at the second system operating angular frequency ω cv Output high frequency inverter signal.

[0056] Without considering the inductor internal resistance and the equivalent series resistance of the capacitor, the system can be equivalent to Figure 4 The circuit shown. Figure 4 The capacitance C formed by the two sets of facing plates in the coupling mechanism s1 and C s2 Series connection is equivalent to C s , that is, C s =(C s1 C s2 ) / (C s1 +C s2), it is worth mentioning that, usually the coupling mechanism can be equivalent to a six-capacitor model due to the existence of cross-coupling capacitance between each plate. However, in the coupling mechanism in this article, since the plates P1 and P3 are very close to each other, and the plates P2 and P4 are very close to each other, their cross-coupling capacitance is very small and can be ignored. Figure 3 The rectifier, filter capacitor and load R L Can be equivalent to resistance R eq , satisfying R eq =8R L / π 2 . Figure 4 middleu in is the inverter output voltage, that is Figure 4 The input voltage in is expanded by the Fourier trigonometric series formula, namely:

[0057]

[0058] Where ω is the operating angular frequency of the system, and satisfies ω=2πf with the operating frequency f. Since the resonant compensation network of the system can filter out most of the high-order harmonics, the fundamental harmonics approximation (FHA) method can be used to analyze the circuit, and then we can get:

[0059]

[0060] It can be expressed in vector form as:

[0061]

[0062] Similarly, the rectifier input voltage and current have the same relationship with the output voltage and current:

[0063]

[0064] In formula (4), u L and i L Respectively, the resistor R L The voltage across the terminals and the current flowing through them, U o and I o is the equivalent circuit R eq The effective value of the voltage across the two ends and the effective value of the current flowing through.

[0065] For constant current output, when the system operating frequency is ω cc When switch K is disconnected, the system equivalent circuit is as follows: Figure 5 As shown. First, analyze the transmitter, and according to Kirchhoff's voltage law, we can get the following equations:

[0066]

[0067] Where X L1 , X 1c Separate inductance L 1 and capacitor C 1c The impedance of the coupling mechanism can be obtained from equation (5):

[0068]

[0069] From the above formula, we can know that when the system input voltage is constant, the current flowing through the coupling mutual capacitance should be Not affected by impedance Z x The impact of the change, that is, the impact of the change in coupling capacitance and receiving end, needs to meet the following requirements:

[0070] X L1 +X 1c =0 (7)

[0071] at this time for:

[0072]

[0073] Therefore, under the action of the input voltage, when the LC resonant network at the transmitting end satisfies the resonant condition in equation (7), a constant current source can be provided for the receiving end. Analyzing the receiving end, according to Kirchhoff's voltage law, we can obtain:

[0074]

[0075] Where X c2 , X c3 , X L2 Respectively represent the capacitance C 2 , C 3 and inductor L 2 Impedance. Definition is the output current, and from formula (9) we can get for:

[0076]

[0077] From the above formula, we can see that in the constant current source In order to make the system output current not change with the load under the effect of, it is necessary to meet the following conditions:

[0078] X L2 +X c3 +X c2 =0 (11)

[0079] At this time, the output current for:

[0080]

[0081] where k 1 =C 3 / C 2 .

[0082] Based on the above analysis, when the system parameters meet the resonance conditions in equations (7) and (11), the LC circuit resonant network at the power transmitter can provide a constant current for the receiver, and the CLC-Π type resonant network at the power receiver can output a constant current under the input of the constant current source provided by the transmitter. From equations (7) and (11), the operating frequency ω of the system at this time can be obtained: cc satisfy:

[0083]

[0084] For constant voltage output, when the system operating frequency is ω cv When switch K is turned on, the system equivalent circuit is as follows: Figure 6 As shown, Figure 6 Middle C 1 =C 1v +C 1c According to the analysis above, if the transmitter meets the following conditions:

[0085] X L1 +X c1 =0 (14)

[0086] Where X c1 is the equivalent capacitance C 1 The impedance of the coupling mutual capacitance is for:

[0087]

[0088] Similarly, the receiving end is analyzed according to Figure 6 The output voltage of the system can be obtained for:

[0089]

[0090] From the above formula, we can see that in the constant current source In order to make the system output voltage not change with the load under the effect of, it is necessary to meet the following conditions:

[0091] X c2 +X L2 =0 (17)

[0092] At this time the output voltage for:

[0093]

[0094] where k2 =(C 1c +C 1v ) / C 2 .

[0095] Based on the above analysis, when the system parameters meet the resonance conditions in equations (14) and (17), the LC circuit resonant network at the power transmitter can provide a constant current for the receiver, and the CLC-Π type resonant network at the power receiver can output a constant voltage under the constant current source input provided by the transmitter. From equations (14) and (17), the operating frequency ω of the system at this time can be obtained: cv satisfy:

[0096]

[0097] In summary, without considering the equivalent series resistance of the inductor and the capacitor, the system can achieve constant current / constant voltage output by changing the frequency and the topology at the same time.

[0098] In a specific implementation, a communication link for transmitting an operating mode switching instruction may be further provided between the transmitting end and the receiving end; when the transmitting end receives the operating mode switching instruction from the receiving end, the switching element K and the high-frequency inverter are controlled to perform corresponding actions.

[0099] Based on the above system design, this embodiment also provides a parameter design method for a constant voltage / constant current charging EC-WPT system for a drone.

[0100] According to formula (13), formula (19) and R eq The expression of constant current and constant voltage can be obtained in two working modes: the output power P cc and P cv They are:

[0101]

[0102] At present, the operating frequency of most EC-WPT systems is within 2MHz. According to engineering experience, the operating frequency is greater than 500kHz. Moreover, from equations (13) and (19), it can be seen that the constant current operating frequency is greater than the constant voltage operating frequency. After conversion, we have So take 500kHz <f cc <2MHz; Capacitor C 1c If the value is too small, the voltage across the system will be very large when it is working, which may easily break down the capacitor. If the value is too large, the inductance L will increase. 1 The parameter sensitivity of C 1c The value of is generally taken as the coupling capacitor C s2 to 4 times of. Since formula (20) is obtained by ignoring the equivalent series resistance of the inductor and capacitor in the circuit, considering the existence of component loss in the actual circuit and the loss of some energy in the inverter and rectifier, a margin coefficient α should be multiplied before the output power, α is usually 110% to 120%;

[0103] According to the above analysis, the process of the parameter design method of the UAV EC-WPT system is as follows: Figure 7 As shown. Set R according to actual application conditions and load requirements. L The range of change, the current i in constant current working mode L The value of the constant voltage working mode voltage u L In addition, since the receiving end of the drone charging system is mainly light, a larger inductor will weigh more and make the system heavier. Therefore, the inductor L of the system design needs to be 2 Less than L max , whose value depends on the weight and efficiency requirements of the actual application. Then follow Figure 7 The parametric design flow shown determines the other parameters.

[0104] Specifically, the following steps are included:

[0105] S1: Determine the power load R according to application requirements L Variation range, current i in constant current working mode L And the voltage u in constant voltage working mode L , and determine the coupling capacitance C according to the energy transmitting plate and the energy receiving plate s ;

[0106] S2: Set DC power supply E dc The initial value of

[0107] S3: Set the first system operating frequency f according to engineering experience cc and capacitor C 1c The initial value of

[0108] S4: Determine the first capacitance ratio k according to the constant current output relationship agreed upon in formula (11) 1 , and determine the second capacitance ratio k according to the constant voltage output relationship agreed by formula (17) 2 The value of

[0109] S5: Determine whether P is satisfied out_实际 ≥αP out , where P out_实际 Indicates the actual output power, P out represents the target output power, α is the margin coefficient; if it is satisfied, then go to step S6; if it is not satisfied, then increase the DC power supply E dcAnd return to step S2;

[0110] S6: According to the first system operating frequency f cc ,according to Determine the operating angular frequency of the second system Determine the operating angular frequency of the second system f cv ;

[0111] S7: According to formula (13) and formula (19), the inductance L can be determined 1 、Inductance L 2 The self-inductance value and capacitance C 1v , capacitor C 2 , capacitor C 3 Capacitance value;

[0112] S8: Determine whether L is satisfied 2 ≤L max If it is not satisfied, increase the operating frequency f of the first system cc And return to S3; if satisfied, go to step S9, where L max is the maximum inductance value under the system weight constraint;

[0113] S9: Obtain a set of parameters as the final parameters of the system.

[0114] according to Figure 2 The schematic diagram of the coupling mechanism in the figure is shown in Table 1. After determining the size of the coupling mechanism, it is simulated using the Maxwell simulation software. The thickness of each electrode plate is 1 mm. The coupling capacitance C formed by the two sets of opposite electrodes when the coupling mechanism is not offset is obtained. s1 and C s2 are 578.68pF and 612.57pF respectively, then C s =297.6pF. When the coupling mechanism has a horizontal offset of 1mm, C s =345pF. In order to verify the effectiveness of the above system and method, this embodiment also Figure 3 The circuit shown in the figure was simulated and analyzed, and the corresponding simulation model was established using the PLECS simulation platform. The simulation takes a drone lithium battery with a rated power of 1896W and a rated voltage of 158V as an example. L The maximum and minimum values ​​of are set to 5Ω and 15Ω respectively. According to the above parameter design method, the main parameters of the system can be obtained as shown in Table 2.

[0115] Table 1 Coupling mechanism dimensions

[0116]

[0117] Table 2 System parameters

[0118]

[0119] In the constant current working mode, the system load current i L and load voltage u L The simulation waveform under dynamic switching is as follows Figure 8 At the switching point a, the load resistor R L When switching from 5Ω to 9Ω, the load current changes from 12.75A to 12.11A. At the switching point b, the load resistance R L Switching from 9Ω to 13Ω, the load current changes from 12.11A to 12.1A; at the switching point c, the load resistance R L Switching from 13Ω to 9Ω, the load current changes from 12.11A to 12.43A; at the switching point d, the coupling capacitor C s Switching from 297.6pF to 345pF, the load current changes from 12.43A to 12.42A. It can be seen that when the load resistance changes by 61.54%, the load current only changes by 2.57%. s When the coupling capacitance and load change by 12%, the load current changes by only 0.08%. Therefore, the proposed system can achieve a nearly constant current output when the coupling capacitance and load change in constant current mode.

[0120] In the constant voltage working mode, the system load current i L and load voltage u L The simulation waveform under dynamic switching is as follows Fig. 9 At the switching point e, the load resistor R L When switching from 13Ω to 15Ω, the load voltage changes from 158.56V to 158.15V. At the switching point f, the load resistance R L Switching from 15Ω to 9Ω, the load voltage changes from 158.15V to 158.04V; at the switching point g, the coupling capacitor C s Switching from 297.6pF to 345pF, the load voltage changes from 158.04V to 159.91V. It can be seen that when the load resistance changes by 46.15%, the load voltage only changes by 0.32%. s The load current changes by only 1.18% when the coupling capacitance changes by 12%. Therefore, the proposed system can achieve a nearly constant voltage output when the coupling capacitance and load change in constant voltage operation mode.

[0121] In summary, it can be seen that the constant voltage / constant current charging EC-WPT system and parameter design method for drones proposed in the present invention can not only achieve constant output when the load changes, but also achieve constant output when the coupling mechanism is offset.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some or all of the technical features can be replaced by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and such changes should be included in the scope of the claims and description of the present invention.

Claims

1. A constant voltage / constant current charging EC-WPT system for unmanned aerial vehicles, comprising a transmitting end and a receiving end, characterized in that: The transmitting end is provided with a DC power supply, a high-frequency inverter, a variable-structure LC resonant network and two energy transmitting plates; the receiving end is provided with two energy receiving plates, a CLC-Π type resonant network, a rectifier filter circuit and an electrical load; The variable structure LC resonant network includes an inductor L1, a capacitor C 1c , capacitor C 1v and switch element K; among which, inductor L1 and capacitor C 1c Connected in series between the two output terminals of the high-frequency inverter, the capacitor C 1c The two ends of the capacitor C are connected to the two energy emitting plates respectively; 1v With capacitor C 1c In parallel, the capacitor C is controlled by the switch element K 1v The switching on and off of the parallel branch realizes the structural change of the LC resonant network; When the system requires constant current output, the switch element K is disconnected, and the high-frequency inverter operates at the first system operating angular frequency ω cc Output high-frequency inverter signal; When the system requires constant voltage output, the switch element K is closed, and the high-frequency inverter operates at the second system operating angular frequency ω cv Output high-frequency inverter signal; The CLC-Π type resonant network is composed of capacitor C2, inductor L2 and capacitor C3, and when the system requires constant current output, the first system operating angular frequency satisfies: Among them, C 1c , C2, C3 correspond to capacitors C 1c , the capacitance of capacitor C2 and capacitor C3; L1 and L2 correspond to the self-inductance of inductor L1 and inductor L2 respectively; When the system requires constant voltage output, the second system operating angular frequency satisfies Among them, C 1v is the capacitance C 1v Capacitance value.

2. The constant voltage / constant current charging EC-WPT system for drones according to claim 1, characterized in that: Two sections of metal foil are attached to the outer wall of the drone body in a corresponding up-and-down relationship as the two energy receiving plates; a charging slot is provided on the drone charging seat, and two sections of metal foil are attached to the inner wall of the charging slot in a corresponding up-and-down relationship as the two energy emitting plates; when the drone docks on the drone charging seat, the two energy emitting plates correspond one-to-one with the two energy receiving plates to form a coupling capacitor.

3. The constant voltage / constant current charging EC-WPT system for drones according to claim 1 or 2, characterized in that: The two energy emitting plates and the two energy receiving plates are both arranged in a cylindrical shape, and the inner diameter of the energy emitting plate is greater than the outer diameter of the energy receiving plate.

4. The constant voltage / constant current charging EC-WPT system for drones according to claim 1, characterized in that: A communication link for transmitting the working mode switching instruction is provided between the transmitting end and the receiving end; when the transmitting end receives the working mode switching instruction from the receiving end, the switching element K and the high-frequency inverter are controlled to perform corresponding actions.

5. A parameter design method for a constant voltage / constant current charging EC-WPT system for a drone as claimed in claim 1, characterized in that: The following steps are involved: S1: Determine the power load R according to application requirements L Variation range, current i in constant current working mode L And the voltage u in constant voltage working mode L , and determine the coupling capacitance C according to the energy transmitting plate and the energy receiving plate s ; S2: Set DC power supply E dc The initial value of S3: Set the first system operating frequency f according to engineering experience cc and capacitor C 1c The initial value of S4: determining a first capacitance ratio k1 according to a constant current output relationship, and determining a value of a second capacitance ratio k2 according to a constant voltage output relationship; S5: Determine whether P is satisfied out_实际 ≥αP out , where P out_实际 Indicates the actual output power, P out represents the target output power, α is the margin coefficient; if it is satisfied, then go to step S6; if it is not satisfied, then increase the DC power supply E dc And return to step S2; S6: Determine the second system operating angular frequency f cv ; S7: Determine the self-inductance of inductor L1, inductor L2 and capacitor C 1v , capacitance of capacitor C2 and capacitor C3; S8: Determine whether L2≤L max If it is not satisfied, increase the operating frequency f of the first system cc And return to S3; if satisfied, go to step S9, where L max is the maximum inductance value under the system weight constraint; S9: Obtain a set of parameters as the final parameters of the system.

6. The parameter design method of the constant voltage / constant current charging EC-WPT system for unmanned aerial vehicles according to claim 5 is characterized in that: When the first capacitance ratio k1 is determined in step S4, Calculation: To determine the second capacitance ratio k2, press calculate; in, It indicates the effective value of the voltage across the load equivalent resistance in the system equivalent circuit in the constant voltage working mode; for u o The vector representation of ; It indicates the effective value of the current passing through the load equivalent resistance in the system equivalent circuit under the constant current working mode. for i o The vector representation of ; is the vector expression of the current after passing through the coupling mechanism; X 1c is the capacitance C 1c Impedance; It is the vector expression of the inverter output voltage.

7. The parameter design method of the constant voltage / constant current charging EC-WPT system for unmanned aerial vehicles according to claim 5 or 6, characterized in that: In step S6, Determine the operating angular frequency of the second system.

8. The parameter design method of the constant voltage / constant current charging EC-WPT system for unmanned aerial vehicles according to claim 7, in step S7, according to: Determine the self-inductance of inductor L1, inductor L2 and capacitance C 1v , the capacitance of capacitor C2 and capacitor C3.

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