Wireless transmission system for coreless transmitting coil to multiple receiving coils

Abstract

The invention discloses a wireless transmission system of a coreless transmitting coil to a plurality of receiving coils, the system is used for supplying power to a light electric vehicle, the system comprises a transmitting end and a plurality of receiving ends, and an LCC compensation network in the transmitting end comprises a switched capacitor assembly connected in series with the transmitting coil; the transmitting end and the receiving end further comprise a first control module and a second control module which are used for respectively acquiring the input power and the output power of the system, and the first control module is used for acquiring the system transmission efficiency based on the input power and the output power of the system; and adjusting the equivalent capacitance of the switched capacitor assembly to realize dynamic tuning of the system. According to the invention, the energy transmission efficiency can be effectively improved under the condition of ensuring the electromagnetic safety standard.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wireless power transmission, and in particular to a wireless transmission system of a coreless transmitting coil to multiple receiving coils. BACKGROUND

[0002] The wireless charging technology for light electric vehicles can realize non-contact energy transmission between the transmitting coil and the vehicle through magnetic coupling, which has the advantages of convenience and flexibility. However, in practical applications, it is still mainly concentrated in small-scale point-to-point charging applications. This limited design approach not only reduces the flexibility of charging, but also makes it difficult to effectively support multiple devices charging at the same time. Therefore, a one-to-many wireless transmission system is provided in the related art.

[0003] However, the wireless transmission system in the related art cannot guarantee the safety of the human body of passengers and surrounding people from electromagnetic radiation when meeting the one-to-many condition, and does not consider the influence of metal vehicle body, metal foreign matter, parking position change and vehicle quantity on the parameters of the wireless transmission system, thereby causing the problem of system dynamic detuning. Therefore, it is necessary to provide a one-to-many wireless transmission system that can guarantee the safety of the human body of passengers and surrounding people from electromagnetic radiation and can dynamically tune in real time to ensure energy transmission efficiency. SUMMARY

[0004] The present application aims to at least partially solve the technical problems in the related art. To this end, the first object of the present application is to provide a wireless transmission system of a coreless transmitting coil to multiple receiving coils, which can guarantee the safety of the human body of passengers and surrounding people from electromagnetic radiation and can dynamically tune in real time to ensure energy transmission efficiency.

[0005] The second object of the present application is to provide a dynamic tuning method.

[0006] To achieve the above-mentioned objects, the present application realizes the following technical solutions:

[0007] A wireless transmission system of a coreless transmitting coil to multiple receiving coils, characterized by being used for power supply of light electric vehicles, the system comprising a transmitting end and multiple receiving ends, the transmitting end comprising a first rectifier, an inverter, an LCC compensation network and a transmitting coil connected in sequence with a power grid; each receiving end comprising a receiving coil, a receiving end compensation capacitor, a second rectifier and a load; the LCC compensation network comprising a switch capacitor assembly connected in series with the transmitting coil; the switch capacitor assembly comprising a first series compensation capacitor and a second series compensation capacitor and a switch tube, the switch tube being connected in parallel with the first series compensation capacitor and connected in series with the second series compensation capacitor; the transmitting end further comprising:

[0008] The first control module and the second control module are arranged at the transmitting end and the receiving end respectively and are wirelessly connected, the first control module is further connected with the control end of the switch tube, the first control module and the second control module are respectively used for acquiring the system input power and the system output power, the first control module is further used for comparing the system input power with the optimal system input power, judging whether the system is out of tune, and when it is determined that the system is out of tune, determining the system transmission efficiency according to the system input power and the system output power, and adjusting the duty cycle of the control signal of the switch tube based on the system transmission efficiency to adjust the equivalent capacitance of the switch capacitor assembly, so as to realize dynamic tuning of the system; wherein the optimal system input power is the input power when the system is in a resonant state.

[0009] In a possible implementation, the first control module is specifically configured to determine that the system is out of tune when the deviation value of the system input power and the optimal system input power is greater than a preset value.

[0010] In a possible implementation, the system parameters in the resonant state satisfy the following conditions:

[0011]

[0012] wherein, 、 、 are respectively the equivalent capacitance of the switch capacitor assembly, the series compensation inductance, and the parallel compensation capacitance in the LCC compensation network, 、 、 、 are respectively the receiving end compensation capacitance, the transmitting coil self-inductance, the receiving coil self-inductance, and the resonant angular frequency.

[0013] In a possible implementation, the switch capacitor assembly is used for dynamically tuning the system out of tune caused by at least one of the following factors: the metal vehicle body, the existence of metal foreign matter, the number change of light electric vehicles, or the parking position change.

[0014] In a possible implementation, for the light electric vehicle, the electromagnetic safety parameter of the system satisfies the following condition:

[0015] The transmitting coil is a rectangular coil, the length of the transmitting coil is 3 meters, and the width of the transmitting coil is 0.66 meters.

[0016] The working frequency of the transmitting coil is 1 MHz.

[0017] The maximum working current of the transmitting coil is not more than 11.8 A.

[0018] In a possible implementation, the electromagnetic safety parameter of the system is determined by the following method:

[0019] setting a magnetic field intensity safety threshold and an electric field intensity safety threshold;

[0020] determining the size of the transmitting coil according to the set magnetic field intensity safety threshold and the electric field intensity safety threshold;

[0021] After the size of the transmitting coil is determined, the operating current of the transmitting coil is set, and it is determined whether the magnetic field intensity at any point of the defined safety boundary surface is equal to the magnetic field intensity safety threshold; if not, the operating current of the transmitting coil is reset, until the magnetic field intensity at any point of the defined safety boundary surface is equal to the magnetic field intensity safety threshold, the corresponding operating current of the transmitting coil set is determined as the optimal operating current, and the optimal operating current does not exceed the corresponding current upper limit value; wherein the defined safety boundary surface is a space region defined with the transmitting coil as an electromagnetic field source for protecting the human body;

[0022] After the optimal operating current of the transmitting coil is determined, the operating frequency of the transmitting coil is set, and it is determined whether the electric field intensity at any point of the defined safety boundary surface is equal to the electric field intensity safety threshold; if not, the operating frequency of the transmitting coil is reset, until the electric field intensity at any point of the defined safety boundary surface is equal to the electric field intensity safety threshold, and the corresponding operating frequency of the transmitting coil set is determined as the optimal operating frequency.

[0023] In a possible implementation, the equivalent capacitance of the switched capacitor component is represented as follows:

[0024]

[0025] wherein, 、 、 、 respectively represent the equivalent capacitance of the switched capacitor component, the second series compensation capacitance in series with the transmitting coil, the first series compensation capacitance, and the control signal duty cycle of the switch tube.

[0026] To achieve the above object, the second aspect of the present application provides a dynamic tuning method applied to the wireless transmission system of the coreless transmitting coil to multiple receiving coils, and the method comprises:

[0027] collecting the system input power and the system output power;

[0028] comparing the system input power and the system optimal input power to determine whether the system is out of tune;

[0029] When it is determined that the system is out of resonance, the system transmission efficiency is determined according to the system input power and the system output power, and the control signal duty cycle of the switch tube is adjusted based on the system transmission efficiency to adjust the equivalent capacitance of the switched capacitor component, so that the system dynamic tuning is realized; wherein the system optimal input power is the input power when the system is in a resonant state.

[0030] The present application has at least the following technical effects:

[0031] The present application provides a coreless transmitting coil to multi-receiving coil wireless transmission system, which is provided with an LCC compensation network in the transmitting end, the LCC compensation network comprising a switched capacitor component connected in series with the transmitting coil, and first and second control modules provided in the transmitting end and the receiving end respectively, wherein the switched capacitor component comprises first and second series compensation capacitors and a switch tube, the switch tube is connected in parallel with the first series compensation capacitor and in series with the second series compensation capacitor, the first control module is further connected with the control end of the switch tube, when the first control module determines that the system is out of resonance by comparing the acquired system input power with the system optimal input power, the system transmission efficiency can be obtained according to the system output power sent by the second control module and the system input power acquired by the first control module, then the control signal duty cycle of the switch tube is adjusted step by step based on the system transmission efficiency or the system input power through the step method until the system transmission efficiency reaches the maximum transmission efficiency or the system input power reaches the system optimal input power, the corresponding control signal duty cycle is obtained by the adjustment, and the equivalent capacitance of the switched capacitor component is obtained, so that the system can recover to the complete resonant state under the equivalent capacitance, and the system can dynamically tune the system out of resonance caused by at least one factor of the metal vehicle body, the existence of metal foreign matter, the number change of light electric vehicles or the change of parking position in real time, and the energy transmission efficiency is improved. Moreover, the present application further provides a system electromagnetic safety parameter determination method, and the electromagnetic safety parameter meets the condition, which can ensure the human body safety of electromagnetic radiation to passengers and surrounding people.

[0032] Additional aspects and advantages of the present application will be made apparent by the following description. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a one-to-many electric bicycle wireless charging system schematic diagram for realizing non-contact transmission of electric energy according to an embodiment of the present application.

[0034] Figure 2 is a circuit topology schematic diagram of a coreless transmitting coil to multi-receiving coil wireless transmission system according to an embodiment of the present application.

[0035] Figure 3This is a schematic diagram of the equivalent circuit of a one-to-one wireless transmission system according to an embodiment of the present invention.

[0036] Figure 4 This is a flowchart of the optimal solution for electromagnetic safety of the transmission coil in an embodiment of the present invention.

[0037] Figure 5 This is a schematic diagram of the electric field distribution of a single capacitor and distributed capacitance compensation according to an embodiment of the present invention.

[0038] Figure 6 This is an equivalent circuit model diagram of a metallic foreign object according to an embodiment of the present invention.

[0039] Figure 7 This is a schematic diagram of the main metal components of a light electric vehicle according to an embodiment of the present invention.

[0040] Figure 8(a) is a schematic diagram of the pulse width modulation switched capacitor circuit model according to an embodiment of the present invention.

[0041] Figure 8(b) is a graph showing the functional relationship between the duty cycle and the equivalent capacitance in an embodiment of the present invention.

[0042] Figure 9 This is a flowchart of the system dynamic tuning process according to an embodiment of the present invention.

[0043] Figure 10(a) is a schematic diagram of the effect of the aluminum soda can on the self-inductance of the transmitting coil according to an embodiment of the present invention.

[0044] Figure 10(b) is a schematic diagram showing the relationship between the position of the soda can and the self-inductance of the transmitting coil in an embodiment of the present invention.

[0045] Figure 11(a) is a schematic diagram of the effect of X-axis offset on the self-inductance and mutual inductance of the transmitting coil according to an embodiment of the present invention.

[0046] Figure 11(b) is a schematic diagram of the effect of Y-axis offset on the self-inductance and mutual inductance of the transmitting coil according to an embodiment of the present invention.

[0047] Figure 12(a) is a schematic diagram of the output voltage and current waveforms of the transmitting coil under a duty cycle d=0 according to an embodiment of the present invention.

[0048] Figure 12(b) is a schematic diagram of the output voltage and current waveforms of the transmitting coil under a duty cycle of d=0.4 according to an embodiment of the present invention.

[0049] Figure 13 This is a diagram of an experimental setup for wireless power transmission according to an embodiment of the present invention.

[0050] Figure 14(a) is a schematic diagram of the system in the ZVS state according to an embodiment of the present invention.

[0051] Figure 14(b) is a schematic diagram of the output power and efficiency under single-load and dual-load conditions according to an embodiment of the present invention.

[0052] Figure 15 This is a flowchart of the dynamic tuning method according to an embodiment of the present invention. Detailed Implementation

[0053] The following describes this embodiment in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0054] The following description, with reference to the accompanying drawings, illustrates a coreless transmitting coil to multiple receiving coil wireless transmission system according to this embodiment.

[0055] This embodiment describes a coreless transmitting coil to multiple receiving coil wireless transmission system, primarily used for powering light electric vehicles, such as electric bicycles.

[0056] Figure 1 This is a schematic diagram of a wireless charging system for electric bicycles, enabling contactless power transmission in a one-to-many manner. The system includes a transmitter and multiple receivers, with an air gap between them. The transmitter is located on the ground beneath the bicycle and includes a first rectifier, an inverter, an LCC compensation network, and a transmitting coil, all connected sequentially to the power grid. Each receiver includes a receiving coil, a receiving compensation capacitor, a second rectifier, and a load. The mains frequency AC power supplied by the grid is converted to AC power at a frequency of 1MHz after passing through the first rectifier and inverter. After resonance in the LCC compensation network, based on Ampere's circuital law, the transmitting coil generates a time-varying electromagnetic field when AC power is applied. Based on Faraday's law of electromagnetic induction, the receiving coil, situated within this field, induces an electromotive force, thus enabling contactless power transmission from the transmitter to the receiver. The receivers are located inside the bicycle and are connected to the load (battery) through intermediate components such as the receiving compensation capacitor, rectifier, and filter.

[0057] It should be noted that the LCC compensation network includes a switched capacitor component in series with the transmitting coil; the switched capacitor component includes a first series compensation capacitor and a second series compensation capacitor and a switch tube, the switch tube is connected in parallel with the first series compensation capacitor and then connected in series with the second series compensation capacitor; the transmitting end further includes a first control module and a second control module, which are respectively arranged at the transmitting end and the receiving end and are wirelessly connected, and the first control module is further connected with the control end of the switch tube; the first control module and the second control module are respectively used for acquiring system input power and system output power, the first control module is used for comparing the system input power with the system optimal input power, judging whether the system is out of tune, and when it is determined that the system is out of tune, determining the system transmission efficiency according to the system input power and the system output power, and adjusting the duty cycle of the control signal of the switch tube based on the system transmission efficiency to adjust the equivalent capacitance of the switched capacitor component, so as to realize dynamic tuning of the system; wherein the system optimal input power is the input power when the system is in a resonant state. And when the first control module judges that the system is out of tune, it is specifically used for judging that the system is out of tune when the deviation value of the system input power and the system optimal input power is greater than the preset value, that is, the deviation exceeds the allowed range.

[0058] In the embodiment, when the metal vehicle body, metal foreign matter exists, the number of light electric vehicles changes or the parking position changes, the system parameters change and eventually the self-inductance of the transmitting coil, the mutual inductance of the transmitting coil and the receiving coil change, and then the system is out of tune and the energy transmission efficiency is reduced. Therefore, after the system is out of tune by comparing the system input power with the system optimal input power, the equivalent capacitance of the switched capacitor component is further adjusted by adjusting the duty cycle of the control signal of the switch tube, so that the system returns to the complete resonant state and realizes real-time dynamic tuning.

[0059] In addition, the present application also provides an electromagnetic safety parameter design method and an electromagnetic safety parameter limiting condition, which can ensure the safety of passengers and surrounding people under the limiting condition. The part and the above dynamic tuning part will be described in detail below.

[0060] Figure 2 The circuit topology diagram of the coreless transmitting coil of the wireless transmission system of the embodiment of the present application to multiple receiving coils is shown in Figure 2 As shown in the figure, the circuit includes an inverter, N-1 second rectifiers (N is at most 5), a transmitting coil and a magnetic coupling coil composed of N-1 receiving coils. The transmitting coil adopts an LCC compensation network. The receiving coil side adopts an S compensation, that is, a receiving end compensation capacitor is connected in series. The four power MOSFETs (metal semiconductor field effect transistors) of the full-bridge converter, that is, the inverter are labeled as S1-S4. f1 , C f1, C1 respectively represent series compensation inductance, parallel compensation capacitance and switched capacitor component in LCC compensation network; L1 represents transmitting coil, L2 represents 1st receiving coil, L N represents N-1st receiving coil; C2 represents 1st receiving end compensation capacitance, C N represents N-1st receiving end compensation capacitance; M n represents mutual inductance between transmitting coil and N-1st receiving coil, coupling coefficient is defined as K n =(L1L N ) 1 / 2 Further, the system further comprises first control module and second control module respectively arranged at transmitting end and receiving end, i.e. Figure 2 DSP (digital signal processor) in the first control module and the second control module, both of which are used to respectively acquire system input current, input voltage signal and system output current, output voltage signal collected by current sensor and voltage sensor at transmitting end and receiving end, so as to acquire system input power and system output power. The first control module can receive system output power information sent by the second control module through wireless communication mode.

[0061] Further, in the topology, since receiving coils are all in vertical direction of plane and the distance between planes is large, the coupling coefficient between them is very low and can be ignored. Therefore, only the relationship between a group of receiving coils and the transmitting coil needs to be analyzed. Taking the first receiving end on the top as an example, for a group of constant resonant frequency, the input voltage U AB of LCC compensation network is in phase with corresponding current i Lf1 , realizing zero phase angle (ZPA). The LCC compensation network on the transmitting coil side is T-type network (L f1 , C f1 , C1). The receiving coil side adopts S-type compensation, and series receiving end compensation capacitance C2 is adopted. In this case, the system shows constant voltage (CV) output characteristic, and the equivalent circuit is shown in Figure 3 , wherein Z ab represents load, and ω is system angular frequency. In the case of ignoring parasitic resistance of inductance and capacitance, the following matrix equation can be derived by using Kirchhoff's voltage law (KVL):

[0062] (1)

[0063] Wherein, X1 represents reactance of first loop composed of series compensation inductance and parallel compensation capacitance in LCC compensation network; X 12 represents capacitive reactance of parallel compensation capacitance, X2 represents reactance of second loop composed of parallel compensation capacitance, switched capacitor component and transmitting coil, X 23 represents reactance of mutual inductance, and X3 represents reactance of receiving end loop.f1 I1 represents the current on the switched capacitor assembly, and I2 represents the current on the load.

[0064] wherein:

[0065] (2)

[0066] wherein M is the mutual inductance between the transmitting coil and the receiving coil, and the following equation is used for system parameter design to keep the resonance frequency of the topology constant:

[0067] (3)

[0068] wherein: is the resonant angular frequency, which only depends on the inductance and capacitance in the system and is independent of the coupling coefficient and the load condition.

[0069] To meet the electromagnetic safety standards, for a light electric vehicle, the electromagnetic safety parameters of the system satisfy the following conditions: the transmitting coil is a rectangular coil, the length of the transmitting coil is 3 meters, and the width is 0.66 meters; the working frequency of the transmitting coil is 1 MHz; and the maximum working current of the transmitting coil is not more than 11.8 A.

[0070] Specifically, to achieve the optimal coil size while meeting the electromagnetic safety standards, a flowchart as shown in Figure 4 is designed to obtain the optimal solution. The final result is obtained under the conditions of a length a = 3 meters, a width b = 0.66 meters, a working frequency f of the transmitting coil = 1 MHz, and a maximum working current not more than 11.8 A. The HFSS simulation software is used to analyze the electric field and magnetic field distribution under the condition of 11.8 A current at 1 MHz frequency. According to the electromagnetic safety standards, the magnetic field strength should not exceed 21 A / m, and the electric field strength should not exceed 83 V / m. Figure 5 The electric field distribution result at a 10 cm plane (z = 10 cm) above the transmitting coil is shown. The maximum electric field strength of the single-capacitor-compensated transmitting coil far exceeds the safety limit. In contrast, the maximum electric field strength of the distributed-capacitor-compensated transmitting coil still has a certain margin from the safety limit, and the electric field distribution is uniform.

[0071] Figure 4The electromagnetic safety parameter design method shown is as follows: setting a magnetic field intensity safety threshold and an electric field intensity safety threshold; determining the size of the transmitting coil according to the set magnetic field intensity safety threshold and electric field intensity safety threshold; after determining the size of the transmitting coil, setting the working current of the transmitting coil, judging whether the magnetic field intensity at any place of the defined safety boundary surface is equal to the magnetic field intensity safety threshold, if not, returning to reset the working current of the transmitting coil, until the magnetic field intensity at any place of the defined safety boundary surface is equal to the magnetic field intensity safety threshold, the corresponding set working current of the transmitting coil is determined as the optimal working current, and the optimal working current does not exceed the corresponding current upper limit value; wherein the defined safety boundary surface is a space region drawn for protecting human body with the transmitting coil as an electromagnetic field source; after determining the optimal working current of the transmitting coil, setting the working frequency of the transmitting coil, judging whether the electric field intensity at any place of the defined safety boundary surface is equal to the electric field intensity safety threshold, if not, returning to reset the working frequency of the transmitting coil, until the electric field intensity at any place of the defined safety boundary surface is equal to the electric field intensity safety threshold, the corresponding set working frequency of the transmitting coil is determined as the optimal working frequency.

[0072] The embodiment gives an electromagnetic safety parameter determination method of the system, and a condition that the electromagnetic safety parameter meets, which can guarantee the human body safety of passengers and surrounding people from electromagnetic radiation.

[0073] Further, in the running process of the wireless charging system, its performance is easily affected by surrounding metal objects. When a vehicle body or metal foreign matter enters the charging area, eddy current and magnetic effect will be generated in the alternating magnetic field. At this time, the non-ferromagnetic metal object can be modeled as a closed coil coupled with the transmitting coil, which has series inductance and resistance characteristics. As shown in the following formula: Figure 6

[0074] Wherein, R coil and L coil represent the resistance and inductance of the transmitting coil in simulation, R metal and L metal represent the equivalent resistance and equivalent inductance of the metal foreign matter, M ’ is the mutual inductance between them. Set Z TX_eq as the equivalent impedance of the transmitting coil in simulation. According to the circuit theory principle, the following expressions can be derived:

[0075] (4)

[0076] (5)

[0077] (6)

[0078] Wherein, ​, The equivalent resistance and inductance of the metal foreign object, i.e. the equivalent circuit of the transmitting coil and the closed coil after coupling. For ferromagnetic metal, due to its magnetic effect, the equivalent inductance of the transmitting coil will increase, and its equivalent impedance can be derived from formula (4), and the expression is:

[0079] (7)

[0080] In the equation, L f represents the inductance generated by the magnetic effect of ferromagnetic metal. As shown in Figure 7 , considering the influence of the metal structure of the vehicle body, the metal components of the main parts of the vehicle body (frame, hub, brake assembly, fork, handlebar and seat tube) are simulated and analyzed using HFSS simulation software, and it is also found that it will affect the system parameters.

[0081] The presence of metal foreign objects, changes in the number of vehicles or changes in parking positions can change the system parameters. For the transmitting coil, when the system parameters change, the self-inductance and mutual inductance between the coils will be affected. According to formula (3), when the self-inductance L1 of the transmitting coil changes, the simplest way to restore the resonance state of the system is to adjust the value of the switch capacitor component C1, so that the system reenters the resonance state. Therefore, the embodiment proposes a method of using switch capacitor tuning, as shown in Figure 8(a), in which pulse width modulation (PWM) technology is used to control the switch capacitor component. The equivalent capacitance C eq of the switch capacitor component expressed in the fundamental component can be represented as:

[0082] (8)

[0083] Where, , , , represent the equivalent capacitance of the switch capacitor component, the second series compensation capacitance, the first series compensation capacitance and the duty cycle of the control signal within the period, i.e. the pulse width modulation duty cycle. Figure 8(b) shows the functional relationship of the equivalent capacitance C eq with the duty cycle when C0=10nF and C 10 =5nF, which shows that the equivalent capacitance changes linearly with the increase of the duty cycle.

[0084] The whole tuning process is as follows Figure 9The system is judged to be out of resonance by comparing the system input power P with the system optimal input power Pop. When the system is out of resonance, the system transmission efficiency based on the system input power and output power is gradually judged to reach the maximum transmission efficiency or the system input power is at the system optimal input power by gradually adjusting the duty cycle d. When the system transmission efficiency reaches the maximum transmission efficiency or the system input power is at the system optimal input power, the duty cycle d in this state is determined, and the equivalent capacitance of the switched capacitor assembly under the duty cycle d is obtained. Under the equivalent capacitance, the system can satisfy the resonance condition of formula (3) to make the system return to the fully resonant state. Thus, the control signal duty cycle of the switch tube is adjusted based on the system transmission efficiency, the equivalent capacitance of the switched capacitor assembly is adjusted, and the system dynamic tuning is realized.

[0085] The influence of the presence of metal foreign objects, the change in the number of vehicles, or the change in the parking position on the self-inductance and mutual inductance of the transmitting coil is simulated and verified.

[0086] Figure 10 (a) shows a schematic diagram of a soda can entering the center of the coil. The distance between the transmitting coil and the receiving coil is 10 cm, and the number of turns of the receiving coil is 10 turns. The size of the ferrite plate is 268 mm x 268 mm x 5 mm, the height of the soda can is 133 mm, and the diameter is 33 mm. The soda can is placed in the middle of the two coils. The analysis includes the case without foreign objects and the influence of the soda can in different positions. As shown in Figure 10 (b), when the aluminum soda can is placed between the coils, the self-inductance (LTx) of the transmitting coil will be reduced, and the offset amount (dx, dy) of the can body in different positions on the X-axis and Y-axis will have different effects on the self-inductance. This is consistent with the calculation results of equation (7).

[0087] Considering the influence of the metal body of the light electric vehicle on the coil parameters, the system parameter changes are analyzed for different numbers of light electric vehicles and five electric vehicles arranged in different positions along the X-axis and Y-axis. As shown in Table 1, the changes in system parameters under different working conditions are analyzed:

[0088] Table 1 Analysis of the influence of metal body and different number of vehicles on coil parameters

[0089]

[0090] The table data shows that for different numbers of vehicles, the self-inductance of the transmitting coil (LTx) changes by 3.23%, the self-inductance of the receiving coil (LRx) changes by 0.289%, and the mutual inductance between the coils changes by 0.326%. The receiving coil is less affected. This embodiment simulates and analyzes the effect of five light electric vehicles arranged at different positions along the X and Y axes on the coils. As shown in FIG. 11(a), M2 and M4 represent the mutual inductance between the two edge receiving coils and the transmitting coil, respectively. When moving along the X axis, the self-inductance of the transmitting coil decreases, while the mutual inductance M4 first increases and then decreases, because the receiving coils gradually move away from the transmitting coil. The mutual inductance M2 continuously decreases, because the corresponding receiving coil moves towards the center of the transmitting coil. FIG. 11(b) shows the movement of the vehicles along the Y axis, where M represents the mutual inductance between the middle vehicle and the transmitting coil. The experimental results show similar fluctuation trends as LTx and M4 in FIG. 11(a). The simulation results show that the mutual inductance and coupling coefficient between the receiving coils are extremely low, equivalent to only 1% of the values between the transmitting and receiving coils, and the coupling effect between the receiving coils is not considered in this embodiment. The focus is on analyzing the effect of the transmitting coil on the self-inductance and mutual inductance. Therefore, by adjusting the switched capacitor assembly, the system can be restored to full resonance after the system parameters change.

[0091] Further, a model is built in the LTspice simulation software using dynamic tuning technology. The switched capacitor configuration shown in FIG. 8(a) is used, and C0 and C 10 are set to 10 nF and 5 nF, respectively. As shown in FIG. 12, FIG. 12(a) shows the waveform when the duty cycle d = 0, and FIG. 12(b) shows the waveform when the duty cycle d = 0.4. The simulation results verify that the dynamic tuning technology can restore the system to resonance when the system parameters change.

[0092] Figure 13 A large square transmitting coil is shown, with dimensions of 3 meters in length and 0.66 meters in width. The transmitting coil uses the LCC-S compensation topology, with distributed compensation capacitors in series with the transmitting coil. The transmitting coil is divided into 14 segments, and the capacitors are distributed in proportion to achieve compensation. The inverter output signal passes through the LCC filter to attenuate high-order harmonics, ensuring that only the 1 MHz fundamental component remains in the transmitting coil. The receiving coil is a chamfered rectangular coil, 25 cm x 25 cm in size, with a total of 10 turns. After rectification, it is connected to an electronic load. The electrical parameters of the system are listed in Table 2.

[0093] Table 2 Electrical parameters of the system

[0094]

[0095] In this state, as shown in FIG. 14(a), the system is in a ZVS (zero voltage switching) state. FIG. 14(b) shows the transmission power and efficiency of the system under single load and double load conditions. The transmission efficiency reaches 69.957% under single load and 73.867% under double load.

[0096] The embodiment proposes and analyzes a wireless power transmission system based on a rectangular, coreless, large-area coil for charging light electric vehicles. By optimizing the electromagnetic field distribution, a 3m x 0.66m square coil is selected as the transmitting coil. Its self-inductance and mutual inductance with other coils remain stable, with no eddy current loss, low energy loss, and minimal risk of magnetic saturation. This design provides more uniform magnetic field distribution and larger charging area. Both experimental and simulation results show that the proposed system effectively meets the electromagnetic safety guidelines (ICNIRP 2020), with a magnetic field strength not exceeding 21 A / m and an electric field strength below 83 V / m, ensuring practical safety for human daily use. Through the proposed LCC-S compensation topology and distributed compensation method, the system can operate at a constant switching frequency, effectively reducing the influence of parasitic parameters and high-order harmonics, and achieving real-time dynamic tuning through a dynamic tuning method. The system has a single load transmission efficiency of 69.957% and a double load transmission efficiency of 73.867% at a frequency of 1 MHz. In addition, the transmission efficiency can be further improved as the input power and number of loads increase.

[0097] To achieve the above-mentioned purpose, the application further provides a dynamic tuning method applied to the coreless transmitting coil and multi-receiving coil wireless transmission system.

[0098] Figure 15 The flowchart of the dynamic tuning method of the embodiment of the application is shown in FIG. Figure 15 As shown, the method comprises:

[0099] Step S101: Collecting system input power and system output power.

[0100] Step S102: Comparing the system input power and the system optimal input power to determine whether the system is out of tune.

[0101] Step S103: When it is determined that the system is out of tune, determining the system transmission efficiency based on the system input power and the system output power, and adjusting the control signal duty cycle of the switching tube based on the system transmission efficiency to adjust the equivalent capacitance of the switching capacitor component, thereby realizing dynamic tuning of the system; wherein the system optimal input power is the input power when the system is in a resonant state.

[0102] It should be noted that the specific implementation of the dynamic tuning method of the embodiment can refer to the specific implementation of the wireless transmission system of the coreless transmitting coil to the multiple receiving coils described above, and details are not repeated here to avoid redundancy.

[0103] In summary, the application provides a wireless transmission system of a coreless transmitting coil to multiple receiving coils, which sets an LCC compensation network in the transmitting end, including a switch capacitor component in series with the transmitting coil, and sets a first control module and a second control module in the transmitting end and the receiving end respectively, wherein the switch capacitor component includes a first series compensation capacitor and a second series compensation capacitor and a switch tube, the switch tube is connected in parallel with the first series compensation capacitor and in series with the second series compensation capacitor, the first control module is further connected with the control end of the switch tube, when the first control module determines that the system is out of tune by comparing the obtained system input power with the optimal system input power, the system transmission efficiency can be obtained according to the system output power sent by the second control module and the system input power obtained by the first control module itself, and then the control signal duty cycle of the switch tube is adjusted by the step method based on the system transmission efficiency or the system input power, until the system transmission efficiency reaches the maximum transmission efficiency, or the system input power reaches the optimal system input power, the corresponding control signal duty cycle is obtained, and the equivalent capacitance of the switch capacitor component is obtained, so that the system can restore the complete resonance state under the equivalent capacitance, thereby the system can dynamically tune the system out of tune caused by at least one of the following factors: metal vehicle body, metal foreign matter, light electric vehicle quantity change or parking position change, and improve the energy transmission efficiency. Moreover, the application also provides a method for determining the electromagnetic safety parameters of the system, and the electromagnetic safety parameters meet the conditions, which can ensure the safety of the electromagnetic radiation to the passengers and the surrounding people.

[0104] The above-described apparatus embodiments are merely illustrative, wherein the units described as separate components can or can not be physically separate, and the components displayed as units can or can not be physical units, i.e., can be located in one place, or can be distributed on multiple network units. Part or all of the modules can be selected to achieve the purpose of the embodiment according to actual needs. Those skilled in the art can understand and implement without creative labor.

[0105] Those skilled in the art can clearly understand the implementation of the various embodiments by means of software and necessary general hardware platforms through the description of the above embodiments, and the various embodiments can also be implemented by hardware. Based on such understanding, the above technical solutions can be embodied in the form of a software product, and the computer software product can be stored in a computer readable storage medium, such as a ROM / RAM, a magnetic disk, an optical disk, etc., and includes a plurality of instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the method described in each embodiment or some parts of the embodiment.

[0106] Finally, it should be noted that the above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above embodiments, and any changes, modifications, substitutions, combinations, simplifications, etc. made without departing from the spirit and principles of the present application should be equivalent replacement methods and are included in the protection scope of the present application.

Claims

1. A coreless transmitting coil to multiple receiving coil wireless transmission system, characterized in that, For powering light electric vehicles, the system includes a transmitter and multiple receivers. Each transmitter includes a first rectifier, an inverter, an LCC compensation network, and a transmitting coil, all connected sequentially to the power grid. Each receiver includes a receiving coil, a receiving compensation capacitor, a second rectifier, and a load. The LCC compensation network includes a switched capacitor assembly connected in series with the transmitting coil. The switched capacitor assembly includes a first series compensation capacitor, a second series compensation capacitor, and a switching transistor. The switching transistor is connected in parallel with the first series compensation capacitor and then in series with the second series compensation capacitor. The transmitter also includes: A first control module and a second control module are respectively located at the transmitting end and the receiving end, and are wirelessly connected. The first control module is also connected to the control terminal of the switching transistor. The first control module and the second control module are used to acquire the system input power and the system output power, respectively. The first control module is also used to compare the system input power and the optimal system input power to determine whether the system is detuned. When the system is determined to be detuned, the first control module determines the system transmission efficiency based on the system input power and the system output power, and adjusts the duty cycle of the control signal of the switching transistor based on the system transmission efficiency to adjust the equivalent capacitance of the switched capacitor assembly, thereby achieving dynamic system tuning. The optimal system input power is the input power when the system is in a resonant state.

2. The system as described in claim 1, characterized in that, The first control module is specifically used to determine that the system has detuned when the deviation between the system input power and the system optimal input power is greater than a preset value.

3. The system as described in claim 1, characterized in that, When the system is in a resonant state, the system parameters satisfy the following conditions: ， in, , , These are the equivalent capacitances of the series compensation inductor, parallel compensation capacitor, and switched capacitor assembly in the LCC compensation network, respectively. , , , These are the receiving end compensation capacitor, the transmitting coil self-inductance, the receiving coil self-inductance, and the resonant angular frequency, respectively.

4. The system as described in claim 1, characterized in that, The switched capacitor assembly is used to dynamically tune the system for system detuning caused by at least one of the following factors: metal vehicle body, presence of metal foreign objects, changes in the number of light electric vehicles, or changes in parking location.

5. The system as described in claim 1, characterized in that, For light electric vehicles, the electromagnetic safety parameters of the system must meet the following conditions: The transmitting coil is a rectangular coil, with a length of 3 meters and a width of 0.66 meters; The operating frequency of the transmitting coil is 1 MHz; The maximum operating current of the transmitting coil does not exceed 11.8A.

6. The system as described in claim 5, characterized in that, The electromagnetic safety parameters of the system are determined by the following method: Set safety thresholds for magnetic field strength and electric field strength; The dimensions of the transmitting coil are determined based on the set safety thresholds for magnetic field strength and electric field strength; After determining the size of the transmitting coil, the operating current of the transmitting coil is set, and it is determined whether the magnetic field strength at any point on the defined safety boundary surface is equal to the magnetic field strength safety threshold. If not, the operating current of the transmitting coil is reset until the magnetic field strength at any point on the defined safety boundary surface is equal to the magnetic field strength safety threshold. The corresponding operating current of the transmitting coil is then determined as the optimal operating current, and the optimal operating current does not exceed the corresponding upper limit value. The defined safety boundary surface is a spatial area demarcated to protect the human body, with the transmitting coil as the electromagnetic field source. After determining the optimal operating current of the transmitting coil, the operating frequency of the transmitting coil is set, and it is determined whether the electric field strength at any point on the defined safety boundary surface is equal to the electric field strength safety threshold. If not, the operating frequency of the transmitting coil is reset until the electric field strength at any point on the defined safety boundary surface is equal to the electric field strength safety threshold. Then, the operating frequency of the corresponding transmitting coil is determined as the optimal operating frequency.

7. The system as described in claim 1, characterized in that, The equivalent capacitance of the switched capacitor assembly is expressed as follows: ， in, , , , These represent the equivalent capacitance of the switched capacitor assembly, the second series compensation capacitor connected in series with the transmitting coil, the first series compensation capacitor, and the duty cycle of the control signal of the switching transistor, respectively.

8. A dynamic tuning method, characterized in that, The method, applied to a coreless transmitting coil to multiple receiving coil wireless transmission system as described in any one of claims 1 to 7, comprises: The system input power and system output power are collected. Compare the system input power with the system's optimal input power to determine if the system has become detuned; When system detuning is determined, the system transmission efficiency is determined based on the system input power and the system output power, and the duty cycle of the control signal of the switching transistor is adjusted based on the system transmission efficiency to adjust the equivalent capacitance of the switched capacitor assembly, thereby achieving dynamic system tuning; wherein, the optimal system input power is the input power when the system is in the resonant state.

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