A key measuring point selection method applied to electromagnetic safety evaluation of dynamic WPT system

Abstract

The application provides a key measuring point selection method applied to electromagnetic safety evaluation of a dynamic WPT system, and is used for solving the problem of lack of the key measuring point selection method of the electromagnetic safety evaluation of the existing dynamic WPT system. The steps are as follows: determining mutual inductance variation and a current expression of a receiving coil of the system; dividing a magnetic field sampling area and a magnetic field safety evaluation area, using current effective values of the transmitting and receiving coils for equivalent excitation, and extracting magnetic field data of the magnetic field sampling area and the safety evaluation area; analyzing the correlation between the field strength of the sampling area measuring point and the average field strength of the safety evaluation area, and obtaining the key measuring point affecting the average field strength of the safety evaluation area according to the correlation ranking; and calculating a regression equation for predicting the average field strength of the safety evaluation area based on the key measuring point. The application is suitable for electromagnetic safety evaluation of the dynamic WPT system under different working conditions, and the selected key measuring point can more accurately predict the average field strength of the electromagnetic safety evaluation area.

Description

Technical Field

[0001] The present invention relates to the field of wireless power transmission, and in particular to a method for selecting key measurement points for electromagnetic safety assessment of a dynamic WPT system. Background Art

[0002] Inductive power transmission (IPT) based on near-field electromagnetic coupling is a safe, flexible, and wire-free power supply technology that can adapt to a variety of harsh weather conditions. However, electromagnetic radiation and electromagnetic compatibility (EMC) issues are essential for its industrial application. Currently, low- and medium-power static inductive power transmission (SIT) technology has been widely used in consumer electronics, implantable medical devices, home appliances, electric vehicles, and other fields. A series of EMC safety-related standards have been established, including PMA, Qi (Part 4), A4WP, IEC PAS63184, SAE J2954 (Parts 9 and 10), and GB / T 38775 (Parts 4 and 5). This demonstrates the electromagnetic safety of SIT technology. After effectively addressing issues such as increasing system power and optimizing power supply efficiency, dynamic wireless power transmission (DWT) technology also provides a practical and feasible approach to addressing the needs of mobile power supply scenarios. In recent years, with the rapid development of electrified transportation vehicles such as AGVs, port tractors, electric buses, trams, and maglev trains under the "dual carbon" environment, the demand for DIT technology has become increasingly urgent, and the prospects are promising.

[0003] Under dynamic motion conditions, system electromagnetic exposure safety assessment is a critical issue. However, due to segmented power supply and uneven magnetic field distribution caused by over-segmented receiving coils, as well as transient surge currents, the system may be at risk of magnetic field exposure. Therefore, effectively measuring potential hazardous areas in dynamic systems is crucial for electromagnetic safety assessment. Currently, there is no effective method for selecting measurement points to address the magnetic field exposure caused by transient surge currents in dynamic induction power transmission systems. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for selecting key measurement points for electromagnetic safety assessment of dynamic WPT systems, so as to solve the technical problem of the lack of a method for selecting key measurement points for electromagnetic safety assessment of dynamic WPT systems.

[0005] A method for selecting key measurement points for electromagnetic safety assessment of a dynamic WPT system is disclosed. The dynamic WPT system includes a receiving end and a plurality of transmitting modules arranged in sequence. The receiving end includes a receiving coil, and the transmitting module includes a transmitting coil. The method specifically comprises the following steps:

[0006] S1: Based on the segmented power supply coil activation strategy of the dynamic WPT system, determine the topology of the minimum working unit circuit of the dynamic WPT system;

[0007] S2: Analyze the changes in the mutual inductance of the system when the receiving coil moves in the segmented area of ​​the transmitting coil, derive the expressions of the receiving coil current at different speeds, and analyze the transient characteristics of the receiving coil current under the changes in mutual inductance;

[0008] S3: Divide the magnetic field sampling area and the magnetic field safety assessment area, use the effective value of the current of the transmitting coil and the receiving coil for equivalent excitation, and extract the magnetic field data of the magnetic field sampling area and the safety assessment area;

[0009] S4: Analyze the correlation between the field strength of the sampling area measurement points and the average field strength of the safety assessment area, and obtain the key measurement points that affect the average field strength of the safety assessment area according to the correlation ranking;

[0010] S5: Fit the mathematical relationship between the magnetic field intensity at key measuring points and the average field intensity in the safety assessment area to obtain a regression equation for predicting the average field intensity in the safety assessment area based on the key measuring points.

[0011] Optionally, the minimum working unit circuit topology of the dynamic WPT system determined in step S1 includes a receiving end circuit, an i-th transmitting module circuit and an i+1-th transmitting module circuit, where: i∈(1~n), n is the number of transmitting modules.

[0012] Optionally, the specific steps of step S2 are:

[0013] S2.1: Determine the mutual inductance expression of the system when the receiving coil moves within the segmented area of ​​the transmitting coil, where: the mutual inductance expression is a function of the mutual inductance with respect to the position and velocity of the receiving coil;

[0014] S2.2: According to Faraday's law of electromagnetic induction, the relationship between the induced voltage of the system transmitting coil i, transmitting coil i+1 and receiving coil is derived, and according to Kirchhoff's law, the receiving coil current i at different speeds is derived. r_rms Based on the expression of (s), the transient characteristics of the receiving coil current under the change of mutual inductance are analyzed based on the variation law of mutual inductance and the expression of receiving coil current.

[0015] Optionally, the specific method for dividing the magnetic field sampling area and the magnetic field safety assessment area in step S3 is:

[0016] Based on the spatial physical relationship between the transmitting coil, receiving coil and their segmented areas, and taking into account the characteristics of human activities, the magnetic field sampling area V1 and the safety assessment area V2 are determined. The relationship between the two areas is:

[0017]

[0018] Where V 1_x 、V 1_y and V1_z are the dimensions of the magnetic field sampling area V1 in the X, Y, and Z directions, a is the length of the receiving coil, b is the length of the transmitting coil, c is the gap between the transmitting coils, and d is the height threshold. The magnetic field sampling area V1 is used to collect magnetic field intensity data points, and the safety assessment area V2 is used to select key measurement points for magnetic field intensity measurement.

[0019] Optionally, the specific method for extracting the magnetic field data of the magnetic field sampling area and the safety assessment area in step S3 is:

[0020] The transmitting coil and the receiving coil adopt the DC excitation method to replace the AC excitation method, that is, the AC current effective value i r_rms (t) Equivalently excite the receiving coil with the effective value of the AC current i ti_rms (t) and i t(i+1)_rms (t) Equivalently excite the transmitting coil i and the transmitting coil i+1 respectively;

[0021] According to the moving speed range of the receiving end, the minimum number of time sampling points and the number of spatial sampling points in the magnetic field sampling area at different speeds are determined to form a magnetic field sampling data set for selecting key measuring points.

[0022] Optionally, in step S4, the correlation m between the field strength at the measurement point in the sampling area and the average field strength in the safety assessment area is:

[0023]

[0024] Where, X i is the magnetic field intensity of any spatial sampling point in the magnetic field sampling area at the i-th moving time point, is the average magnetic field intensity of any spatial sampling point in the magnetic field sampling area within the time sampling range, Y i is the average magnetic field strength at the i-th moving time point in the safety assessment area, is the average value of the average magnetic field intensity in the safety assessment area within the time sampling range, and g is the number of measuring points in the sampling area.

[0025] Optionally, the specific steps of obtaining the key measurement points that affect the average field strength of the safety assessment area in step S4 are:

[0026] A level threshold of correlation m is set, all spatial measurement points are classified according to the level threshold, and all spatial measurement points are sorted according to correlation levels such as strong correlation, medium correlation, weak correlation, and no correlation. Multiple linear correlation analysis is further carried out on the electromagnetic measurement points with the strongest correlation, and multiple independent variables with low linear correlation are selected as key measurement points.

[0027] Optionally, the specific method in step S5 is:

[0028] According to the independent variable factors, the magnetic field sampling data at different speeds are used as training data, and the magnetic field sampling data at other speeds are used as verification data. The regression equation with strong generalization ability is obtained through the multivariate linear regression algorithm:

[0029] B avg =αB a +βB b +γ

[0030] Where B avg represents the linear regression equation fitted with the magnetic field intensity at key points a and b as independent variables, B a Indicates the magnetic field intensity at the key point a, B b represents the magnetic field intensity at the key point b coordinate, α, β, and γ are the constant coefficients of the linear regression equation, and the coordinate point origin is the starting point of the magnetic field sampling area.

[0031] Due to the adoption of the above technical solution, the present invention has the following advantages:

[0032] This application is applicable to the electromagnetic safety assessment of dynamic WPT systems under different working conditions such as acceleration, deceleration, and uniform speed. It breaks through the limitations of traditional electromagnetic measurement points in quasi-static fields. The selected key measurement points can more accurately predict the average field strength in the electromagnetic safety assessment area.

[0033] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings of the present invention are described below.

[0035] Figure 1 This is a flow chart of the key measurement point selection method for the electromagnetic safety assessment of the dynamic WPT system of the present invention.

[0036] Figure 2 It is a diagram of the dynamic coupling process in the dynamic WPT system of the present invention.

[0037] Figure 3 It is a circuit structure diagram of the dynamic WPT system of the present invention.

[0038] Figure 4 It is a three-dimensional finite element electromagnetic simulation model of the dynamic WPT system of the present invention.

[0039] Figure 5 It is a fan-shaped distribution diagram of the correlation between the magnetic field sampling points and the average magnetic field intensity of the evaluation area at different speeds in the present invention.

[0040] Figure 6 The present invention is Figure 5 Flowchart showing the selection of key measurement points in the correlation fan chart.

[0041] Figure 7 It is a difference diagram and a fitting diagram of the predicted value and the actual value in the regression equation fitted by the key measurement points of the present invention.

[0042] Figure 8 It is a waveform diagram of the system voltage and receiving current of the receiving coil passing through the segmented area of ​​the transmitting coil at different speeds of the present invention.

[0043] Figure 9 It is a comparison diagram of the fitting values ​​and experimental values ​​obtained at the key measurement points and the traditional measurement points under the experimental conditions of the present invention. DETAILED DESCRIPTION

[0044] The present invention will be further described below with reference to the accompanying drawings and examples.

[0045] Example 1:

[0046] like Figure 2 and Figure 3 A dynamic WPT system shown includes a transmitter and a receiver. The receiver is disposed on a mobile vehicle, and the transmitter includes a plurality of transmitter modules sequentially disposed along a motion path of the mobile vehicle.

[0047] The transmitting module is connected in sequence to a DC power supply, a high-frequency inverter, a primary-side compensation circuit, and a transmitting coil. The receiving end includes a receiving coil, a secondary-side compensation circuit, a rectifier and filter circuit, and a load connected in sequence. The primary-side compensation circuit and the secondary-side compensation circuit have an LCC-S topology.

[0048] In this embodiment, all switching elements in the inverter are assumed to be lossless ideal switching elements. Since the fundamental wave component is much larger than the harmonic component generated by the resonant network, when the receiving end moves between the i-th and i+1-th transmitting modules, based on the fundamental wave analysis method, the equivalent model of the system is obtained as follows: Figure 3 As shown. Figure 3 As shown, the i-th and i+1-th transmitting modules respectively include a DC power supply U dci and U dc(i+1) The i-th and i+1-th transmitting modules each include a transmitting coil L ti and L t(i+1) The high-frequency inverters of the i-th and i+1-th transmitter modules include four switch tubes S1 to S4 and four switch tubes S5 to S8, respectively. Their output currents and voltages are i i 、U i and i i+1 、Ui+1 The primary compensation circuit of the i-th transmitting module includes the transmitting coil L ti The series compensation capacitor C ti and compensation inductor L i , and the transmitting coil L ti Parallel compensation capacitor C i The primary compensation circuit of the i+1th transmitting module includes the transmitting coil L t(i+1) The series compensation capacitor C t(i+1) and compensation inductor L i+1 , and the transmitting coil L t(i+1) Parallel compensation capacitor C i+1 .like Figure 3 As shown, the receiving end includes a receiving coil L r and load R L , the secondary side compensation circuit includes capacitor C r The rectifier filter circuit includes four diodes D1 to D4 and a filter capacitor C d .

[0049] Figure 3 In, R r Represents the receiving coil L r Internal resistance, R ti and R t(i+1) Represent the transmitting coil L ti and the transmitting coil L t(i+1) The internal resistance, i i 、U i and i i+1 、U i+1 Represent the output current and voltage of the high-frequency inverter of the i-th and i+1-th transmitter modules, respectively. r Represents the receiving coil current, M tit(i+1) Indicates the transmitting coil L ti and the transmitting coil L t(i+1) Mutual inductance between tr_i and M tr_i+1 They represent the transmitting coil L ti and the transmitting coil L t(i+1) With the receiving coil L r The mutual inductance between them.

[0050] In this embodiment, the relationship between the output voltage of the high-frequency inverter and the DC input voltage can be expressed as:

[0051]

[0052] The equivalent load consisting of the rectifier filter circuit and the load can be expressed as:

[0053]

[0054] DC load R L The current and voltage are expressed as U L and I L .

[0055] Under the premise of ignoring the cross-coupling between transmitting coils, the relationship between the self-inductance of each coil and the compensation capacitance should be satisfied when the WPT system resonates:

[0056]

[0057] X ti 、X i and X r They represent the self-impedance of the compensation loop of transmitting coil i, the self-impedance of the loop of transmitting coil i, and the self-impedance of the loop of receiving coil i, respectively, and ω represents the operating angular frequency of the system.

[0058] Example 2:

[0059] like Figure 1 The method for selecting key measurement points for electromagnetic safety assessment of a dynamic WPT system is shown and is applied to the dynamic WPT system described in Example 1. The specific steps are as follows:

[0060] S1: Based on the segmented power supply coil activation strategy of the dynamic WPT system, the minimum working unit circuit topology of the dynamic WPT system is determined.

[0061] In this embodiment, when the receiving coil is located in the segmented area between transmitting coil i and transmitting coil i+1, the receiving coil is coupled to both transmitting coil i and transmitting coil i+1. Therefore, the minimum operating unit circuit topology of the dynamic WPT system includes the receiving end circuit, the i-th transmitting module circuit, and the i+1-th transmitting module circuit, where: i∈(1-n), n is the number of transmitting modules. Ignoring the cross-coupling between the transmitting coils, the transmitting coil current expression is:

[0062]

[0063] Where, is the current of the i-th transmitting coil, is the current of the i+1th transmitting coil, u i_rms is the effective value of the AC input voltage of the i-th transmitter module, u (i+1)_rms is the effective value of the AC input voltage of the i+1th transmitter module.

[0064] S2: Analyze the changes in the mutual inductance of the system when the receiving coil moves in the segmented area of ​​the transmitting coil, derive the expressions of the receiving coil current at different speeds, and analyze the transient characteristics of the receiving coil current under the changes in mutual inductance; the specific steps are:

[0065] S2.1: When the receiving end moves rapidly along the positive half of the x-axis through the segmented area of ​​the transmitting coil, the mutual inductance of the system changes as follows:

[0066] M tr_i (t)=f(x(t),v x (t)) i=1,2,...,n (5)

[0067] Where x(t) is the position of the transmitting coil on the positive half of the x-axis at time t, v x (t) is the velocity of the transmitting coil at time t;

[0068] S2.2: According to Faraday's law of electromagnetic induction, the expressions for the induced voltages of the system's transmitting coil i, transmitting coil i+1, and receiving coil are:

[0069]

[0070] In a dynamic WPT system, when the receiving coil passes through the segmented area of ​​transmitting coil i and transmitting coil i+1, the inductance and capacitance of each loop in the minimum working unit topology are completely resonant, and the current phases differ by 90 degrees. The time domain expressions of each voltage and current expressed in root mean square are:

[0071]

[0072] The expressions of the induced voltages of the transmitting coil and the receiving coil are combined to obtain the simplified forms of the induced voltages of the transmitting coil and the receiving coil, and u r The cosine term of (t) can be neglected, so:

[0073]

[0074] The effective value of the induced voltage at the receiving end is obtained as follows:

[0075] u r_rms (t)=ω[M tr_i (t)i ti_rms (t)+M tr_i+1 (t)i t(i+1)_rms (t)] (10)

[0076] Starting from the equivalent circuit of the receiving end, according to KVL and KCL, write the time domain differential equations to derive and determine the receiving coil current i r_rms (s) and u r_rms The mathematical relationship between (s):

[0077]

[0078] According to the variation law of mutual inductance and the expression of receiving coil current, the transient characteristics of receiving coil current under the variation of mutual inductance are obtained.

[0079] S3: dividing the magnetic field sampling region and the magnetic field safety evaluation region, using the current effective value of the transmitting coil and the receiving coil for equivalent excitation, and extracting the magnetic field data of the magnetic field sampling region and the safety evaluation region; the specific steps are:

[0080] S3.1: first, a three-dimensional finite element electromagnetic simulation model of the dynamic WPT system containing key components such as segmented transmitting coils, receiving coils, and receiving end loads is constructed; according to the spatial physical relationship of the transmitting coils, receiving coils, and their segmented regions, and considering the characteristics of human activities, the magnetic field sampling region V1 and the safety evaluation region V2 are determined, and the relationship between the two regions is:

[0081]

[0082] In the formula, V 1_x is the length of the magnetic field sampling region V1 in the X direction, V 1_y is the width of the magnetic field sampling region V1 in the Y direction, V 1_z is the height of the magnetic field sampling region V1 in the Z direction, a is the length of the receiving coil, b is the length of the transmitting coil, c is the gap between the transmitting coils, and d is the height threshold, wherein: the magnetic field sampling region V1 is used to collect magnetic field intensity data points, and the safety evaluation region V2 is used to select key measurement points for measuring the magnetic field intensity.

[0083] In this embodiment, as shown in Figure 4 , the dimensions of V 1_x , V 1_y , and V 1_z are set to 1000mm, 1000mm, and 1500mm, respectively.

[0084] S3.2: the transmitting coil and the receiving coil use a direct current excitation method to replace an alternating current excitation method, that is, the receiving coil is excited by the alternating current effective value i r_rms (t), the transmitting coil i is excited by the alternating current effective value i ti_rms (t), and the transmitting coil i+1 is excited by the alternating current effective value i t(i+1)_rms (t);

[0085] According to the moving speed range of the receiving end, the minimum time sampling point number and the spatial sampling point number of the magnetic field sampling region under different speeds are determined to form a magnetic field sampling data set for selecting key measurement points.

[0086] S4: analyzing the correlation between the field intensity of the sampling region measurement points and the average field intensity of the safety evaluation region, and obtaining the key measurement points affecting the average field intensity of the safety evaluation region according to the correlation ranking; wherein the correlation expression is:

[0087]

[0088] Where, X i is the magnetic field intensity of any spatial sampling point in the magnetic field sampling area at the i-th moving time point, is the average magnetic field intensity of any spatial sampling point in the magnetic field sampling area within the time sampling range, Y i is the average magnetic field strength at the i-th moving time point in the safety assessment area, is the average value of the average magnetic field intensity in the safety assessment area within the time sampling range, g is the number of measuring points in the sampling area, and g = 1001.

[0089] A level threshold of correlation m is set, and all spatial measurement points are classified and sorted according to the correlation levels such as strong correlation, medium correlation, weak correlation, and no correlation; multiple linear correlation analysis is further carried out on the electromagnetic measurement points with the strongest correlation, and multiple independent variables with low linear correlation are selected as key measurement points.

[0090] In this embodiment, the level thresholds of the correlation m at different speeds are set as follows: Figure 5 In this embodiment, the specific flow chart of further carrying out multiple linear correlation analysis on the electromagnetic measurement points with the strongest correlation is as follows Figure 6 shown.

[0091] S5: Fit the mathematical relationship between the magnetic field intensity at key measurement points and the average field intensity in the safety assessment area to obtain a regression equation for predicting the average field intensity in the safety assessment area based on key measurement points. The specific method is:

[0092] According to the independent variable factors, the magnetic field sampling data at different speeds are used as training data, and the magnetic field sampling data at other speeds are used as verification data. The regression equation with strong generalization ability is obtained through the multivariate linear regression algorithm:

[0093] B avg =αB a +βB b +γ (14)

[0094] Where B avg represents the linear regression equation fitted with the magnetic field intensity at key points a and b as independent variables, B a Indicates the magnetic field intensity at the key point a, B b represents the magnetic field intensity at the key point b coordinate, α, β, and γ are the constant coefficients of the linear regression equation, and the coordinate point origin is the starting point of the magnetic field sampling area.

[0095] In the embodiment, the key measuring points of the system magnetic field are studied to verify the accuracy of the average magnetic field strength in the evaluation area, and the effect of the method can be verified. Specifically, the representation phenomenon of the receiving coil at the segmented position of the transmitting coil under different speeds is analyzed and compared with the theoretical analysis; and the influence of the measuring point selection method of the application and the traditional three-point measurement method on the accuracy of the average magnetic field strength in the evaluation area is analyzed and compared.

[0096] S6: Simulation verification of dynamic system:

[0097] A dynamic WPT wireless power transmission system as shown in Figure 3 is constructed, which includes two transmitting coils and one receiving coil. The capacitances are matched according to the system resonance frequency, so that each coil is in a resonant state. The frequency of the system is 85 kHz. The inductance of the coil, the compensation capacitance and the coil resistance are shown in Table 1, and the mutual inductance change in the coupling process of the system is shown in Figure 2 .

[0098] Table 1 Dynamic WPT system parameters

[0099] <![CDATA[L t1 (μH)]]> <![CDATA[L t2 (μH)]]> L r (μH) <![CDATA[C r (nF)]]> <![CDATA[R t1 (Oh)]]> <![CDATA[C1(nF)]]> <![CDATA[C t1 (nF)]]> 65.66 65.4 23.97 146.6 0.167 149.79 82.96 <![CDATA[L2(μH)]]> [C2(nF)] <![CDATA[C t2 (nF)]]> <![CDATA[L1(μH)]]> <![CDATA[R t2 (Oh)]]> <![CDATA[R r (Oh)]]> / 23.41 149.79 83.49 23.41 0.164 0.069 /

[0100] The relationship between the output voltage of the inverter side and the DC input voltage is shown in equation (1), and the equivalent load composed of the rectifier, the filter capacitor and the load is shown in equation (2).

[0101] Under the precondition of ignoring the cross-coupling between the transmitting coils, the WPT system should satisfy the relationship between the self-inductance of each coil and the compensation capacitance when resonating:

[0102]

[0103] Based on this, the transmitting coil current of the system is represented as:

[0104]

[0105] Next, based on steps S3 and S4, a three-dimensional finite element electromagnetic simulation model of the dynamic WPT system is established as shown in Figure 4 , the moving speed range of the receiving end is determined, the minimum time sampling point number and the spatial sampling point number of the magnetic field sampling area under different speeds are determined, and the magnetic field sampling data set for selecting the key measuring points is formed.

[0106] The correlation distribution sector diagram under different speeds is obtained by equation (13) as shown in Figure 5 , wherein all spatial measuring points are classified and sorted according to the correlation levels such as strong correlation, medium correlation, weak correlation and no correlation, and multiple linear correlation analysis is further carried out on the electromagnetic measuring points with the strongest correlation, and multiple independent variables with low linear correlation are selected as key measuring points, and the specific flow chart is as follows Figure 6 shown.

[0107] The regression equation with strong generalization ability obtained by the multiple linear regression algorithm is:

[0108] B avg2_1 =1.11B a +1.93B b -15.72 (17)

[0109] In the same steps, the expression of the relationship between the three-point coordinate magnetic field intensity and the average magnetic field in the evaluation area by fitting the traditional three-point measurement method is as follows:

[0110]

[0111] Select mean absolute error MAE, mean square error MSE, root mean square error RMSE and determination coefficient R 2 The generalization ability of the two regression equations is evaluated, and the generalization ability evaluation table of the two regression equations of the validation set for key measurement points and traditional measurement points is shown in Table 2:

[0112] Table 2 Generalization ability evaluation table of two regression equations

[0113] parameter MAE MSE RMSE <![CDATA[R 2 ]]> <![CDATA[B avg_1 ]]> 7.16 62.09 7.87 0.972 <![CDATA[B avg_2 ]]> 27.22 1035.26 32.17 0.608

[0114] As can be seen from Table 2, the regression equation of the key measurement points obtained by correlation sorting has the strongest generalization ability, with a fitting degree of 0.972. The difference between the predicted value and the actual value in the regression equation is shown in the figure below. Figure 7 As shown in (a), the fitting diagram of the predicted value and the actual value in the regression equation is as follows Figure 7 However, if only the three-point coordinates of the traditional three-point measurement method are used to fit the equation, the generalization ability is the weakest, with a fitting degree of only 0.608. This verifies the effectiveness of the measurement point selection of the present invention from an algorithmic perspective.

[0115] By establishing an experimental device, the magnetic field strength of the measuring point of the present invention and the traditional measuring point as well as the average magnetic field strength of the evaluation area are measured respectively, and the fitting values ​​obtained by inserting them into the respective fitting equations are compared with the experimental value of the average magnetic field strength of the evaluation area, as shown in FIG. Figure 9 shown. Figure 9 (a) is a comparison chart of the fitting values ​​and experimental values ​​obtained at the key measurement points of the present invention, Figure 9 (b) is a comparison chart of the fitting values ​​and experimental values ​​obtained at the traditional measurement points. Figure 9 It can be seen that by comparing the accuracy of the average magnetic field intensity in the evaluation area between the measuring points of the present invention and the traditional measuring points, the measuring points of the present invention have high accuracy, with a maximum difference of 1.2 μT, while the traditional measuring points have low accuracy, with a maximum difference of 78 μT. Based on this, the effectiveness of selecting the measuring points of the present invention is verified experimentally.

[0116] Analyze and compare the characteristics of the receiving coil segmented by the transmitting coil at different speeds and the consistency with the theoretical analysis, such as Figure 8 As shown. Figure 8 It can be seen that when the receiving coil passes through the transmitting coil segment area at speeds of 0.3m / s and 0.6m / s, the maximum current of the receiving coil is 1.95A and 2.23A respectively. It can be seen that the maximum current of the receiving coil changes with the speed when passing through the transmitting coil segment at different speeds, which is consistent with the theoretical analysis.

[0117] It can be seen from the experimental results that the key measurement point selection method for electromagnetic safety assessment of dynamic WPT systems provided by the present invention is very effective in predicting the average magnetic field intensity in the assessment area, and provides a reference for subsequent dynamic system measurement methods.

[0118] In summary, this application is applicable to the electromagnetic safety assessment of dynamic WPT systems under different working conditions such as acceleration, deceleration, and uniform speed. It breaks through the limitations of traditional electromagnetic measurement points in quasi-static fields. The selected key measurement points can more accurately predict the average field strength in the electromagnetic safety assessment area.

[0119] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A method for selecting key measurement points for electromagnetic safety assessment of a dynamic WPT system, wherein the dynamic WPT system includes a receiving end and a plurality of transmitting modules arranged in sequence, wherein the receiving end includes a receiving coil, and the transmitting module includes a transmitting coil, characterized in that: The specific steps of the method are: S1: Based on the segmented power supply coil activation strategy of the dynamic WPT system, determine the topology of the minimum working unit circuit of the dynamic WPT system; S2: Analyze the changes in the mutual inductance of the system when the receiving coil moves in the segmented area of ​​the transmitting coil, derive the expressions of the receiving coil current at different speeds, and analyze the transient characteristics of the receiving coil current under the changes in mutual inductance; S3: Divide the magnetic field sampling area and the magnetic field safety assessment area, use the effective value of the current of the transmitting coil and the receiving coil for equivalent excitation, and extract the magnetic field data of the magnetic field sampling area and the safety assessment area; S4: Analyze the correlation between the field strength of the sampling area measurement points and the average field strength of the safety assessment area, and obtain the key measurement points that affect the average field strength of the safety assessment area according to the correlation ranking; S5: Fit the mathematical relationship between the magnetic field intensity at key measuring points and the average field intensity in the safety assessment area to obtain a regression equation for predicting the average field intensity in the safety assessment area based on the key measuring points.

2. The key measurement point selection method for dynamic WPT system electromagnetic safety assessment according to claim 1 is characterized in that: In step S1, the minimum working unit circuit topology of the dynamic WPT system is determined to include a receiving end circuit, an i-th transmitting module circuit, and an i+1-th transmitting module circuit, where: i∈(1-n), n is the number of transmitting modules.

3. The key measurement point selection method for dynamic WPT system electromagnetic safety assessment according to claim 1 is characterized in that: The specific steps of step S2 are: S2.1: Determine the mutual inductance expression of the system when the receiving coil moves within the segmented area of ​​the transmitting coil, where: the mutual inductance expression is a function of the mutual inductance with respect to the position and velocity of the receiving coil; S2.2: According to Faraday's law of electromagnetic induction, the relationship between the induced voltage of the system transmitting coil i, the transmitting coil i+1 and the receiving coil is derived, and the receiving coil current i at different speeds is derived according to Kirchhoff's law. r_rms Based on the expression of (s), the transient characteristics of the receiving coil current under the change of mutual inductance are analyzed based on the variation law of mutual inductance and the expression of receiving coil current.

4. The method for selecting key measurement points for electromagnetic safety assessment of a dynamic WPT system according to claim 3 is characterized in that: The specific method of dividing the magnetic field sampling area and the magnetic field safety assessment area in step S3 is: Based on the spatial physical relationship between the transmitting coil, receiving coil and their segmented areas, and taking into account the characteristics of human activities, the magnetic field sampling area V1 and the safety assessment area V2 are determined. The relationship between the two areas is: Where V 1_x 、V 1_y and V 1_z are the dimensions of the magnetic field sampling area V1 in the X, Y, and Z directions, a is the length of the receiving coil, b is the length of the transmitting coil, c is the gap between the transmitting coils, and d is the height threshold. The magnetic field sampling area V1 is used to collect magnetic field intensity data points, and the safety assessment area V2 is used to select key measurement points for magnetic field intensity measurement.

5. The method for selecting key measurement points for electromagnetic safety assessment of a dynamic WPT system according to claim 4 is characterized in that: The specific method for extracting the magnetic field data of the magnetic field sampling area and the safety assessment area in step S3 is: The transmitting coil and the receiving coil adopt the DC excitation method to replace the AC excitation method, that is, the AC current effective value i r_rms (t) Equivalently excite the receiving coil with the effective value of the AC current i ti_rms (t) and i t(i+1)_rms (t) Equivalently excite the transmitting coil i and the transmitting coil i+1 respectively; According to the moving speed range of the receiving end, the minimum number of time sampling points and the number of spatial sampling points in the magnetic field sampling area at different speeds are determined to form a magnetic field sampling data set for selecting key measuring points.

6. The key measurement point selection method for dynamic WPT system electromagnetic safety assessment according to claim 1 is characterized in that: The correlation m between the field strength at the measurement point in the sampling area and the average field strength in the safety assessment area analyzed in step S4 is: Where, X i is the magnetic field intensity of any spatial sampling point in the magnetic field sampling area at the i-th moving time point, is the average magnetic field intensity of any spatial sampling point in the magnetic field sampling area within the time sampling range, Y i is the average magnetic field strength at the i-th moving time point in the safety assessment area, is the average value of the average magnetic field intensity in the safety assessment area within the time sampling range, and g is the number of measuring points in the sampling area.

7. The method for selecting key measurement points for electromagnetic safety assessment of a dynamic WPT system according to claim 6, characterized in that: The specific steps for obtaining the key measurement points that affect the average field strength in the safety assessment area in step S4 are: A level threshold of correlation m is set, all spatial measurement points are classified according to the level threshold, and all spatial measurement points are sorted according to correlation levels such as strong correlation, medium correlation, weak correlation, and no correlation. Multiple linear correlation analysis is further carried out on the electromagnetic measurement points with the strongest correlation, and multiple independent variables with low linear correlation are selected as key measurement points.

8. The method for selecting key measurement points for electromagnetic safety assessment of a dynamic WPT system according to claim 1, characterized in that: The specific method in step S5 is: According to the independent variable factors, the magnetic field sampling data at different speeds are used as training data, and the magnetic field sampling data at other speeds are used as verification data. The regression equation with strong generalization ability is obtained through the multivariate linear regression algorithm: B avg =αB a +βB b +γ Where B avg represents the linear regression equation fitted with the magnetic field intensity at key points a and b as independent variables, B a Indicates the magnetic field intensity at the key point a, B b represents the magnetic field intensity at the key point b coordinate, α, β, and γ are the constant coefficients of the linear regression equation, and the coordinate point origin is the starting point of the magnetic field sampling area.

Images