Key measuring point selection method applied to electromagnetic safety assessment of dynamic WPT system

Abstract

The invention provides a key measuring point selection method applied to electromagnetic safety assessment of a dynamic WPT system. The key measuring point selection method is used for solving the problem that an existing key measuring point selection method for electromagnetic safety assessment of the dynamic WPT system is lacked. The method comprises the following steps: determining mutual inductance change of a system and a receiving coil current expression; dividing a magnetic field sampling area and a magnetic field safety evaluation area, performing equivalent excitation by adopting the current effective values of the transmitting and receiving coils, and extracting magnetic field data of the magnetic field sampling area and the safety evaluation area; analyzing the correlation between the field intensity of the measuring points of the sampling area and the average field intensity of the safety assessment area, and obtaining key measuring points influencing the average field intensity of the safety assessment area according to correlation sorting; and calculating a regression equation for predicting the average field intensity of the safety assessment area based on the key measuring points. The method is suitable for electromagnetic safety assessment of the dynamic WPT system under different working conditions, and the selected key measuring points can predict the average field intensity of the electromagnetic safety assessment area more accurately.

Description

Technical Field

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

[0002] Inductive power transmission based on the principle of near-field electromagnetic coupling is a safe, flexible, and emerging power supply technology without wire contact, and can adapt to a variety of severe weather environments. The problems of electromagnetic radiation and electromagnetic compatibility are the problems that must be solved for its industrial application. At present, small and medium-power static inductive power transmission technology has been widely used in consumer electronic devices, implantable medical devices, household appliances, electric vehicles and other fields, forming a series of electromagnetic compatibility safety-related standards such as PMA, Qi (Part 4), A4WP, IEC PAS63184, SAE J2954 (Parts 9 and 10), GB / T 38775 (Parts 4 and 5). It can be seen that the electromagnetic safety of small and medium-power static inductive power transmission technology. After effectively solving the problems of system power improvement and power supply efficiency optimization, dynamic wireless power transmission technology also provides a practical way to solve the needs of mobile power supply scenarios. In recent years, with the rapid development of electrification of transport vehicles such as AGV logistics vehicles, port tractors, electric buses, trams, and maglev trains under the "dual carbon" environment, the application demand for dynamic inductive power transmission technology has become increasingly urgent and the prospects are broad.

[0003] Under dynamic moving conditions, the electromagnetic exposure safety assessment of the system is a problem that needs to be solved. However, due to the uneven magnetic field distribution and transient impulse current caused by segmented power supply and receiving coil segmentation, the system may be exposed to the magnetic field. Therefore, how to effectively measure the potential dangerous areas of the dynamic system is crucial for electromagnetic safety assessment. At present, there is no effective method for selecting measurement points for the magnetic field exposure problem caused by transient impulse current in dynamic induction power transmission systems. Summary of the invention

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

[0005] 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, and the method specifically includes 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 change of the mutual inductance of the system when the receiving coil moves in the segmented area of ​​the transmitting coil, derive the expression of the receiving coil current at different speeds, and analyze the transient characteristics of the receiving coil current under the change of 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 the key measuring points and the average field intensity in the safety assessment area, and 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 in 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, the transmitting coil i+1 and the 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 mutual inductance change law and the expression of receiving coil current, the transient characteristics of receiving coil current under mutual inductance change are analyzed.

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

[0016] According to the spatial physical relationship between the transmitting coil, the receiving coil and their segmented areas, and considering 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 respectively, 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, where: the magnetic field sampling area V1 is used to collect magnetic field strength data points, and the safety assessment area V2 is used to select key measuring points for magnetic field strength 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 use DC excitation to replace the AC excitation method, that is, the AC current effective value i r_rms (t) The receiving coil is equivalently excited with an AC current effective value 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 mobile 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 measuring 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] In the formula, B avg represents the linear regression equation fitted with the magnetic field intensity at key points a and b as independent variables, B a represents the magnetic field strength at the key point a, B b It represents the magnetic field intensity at the key point b coordinate. α, β and γ are the constant coefficients of the linear regression equation respectively. The origin of the coordinate point 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 measuring points in quasi-static fields. The selected key measuring points can more accurately predict the average field strength in the electromagnetic safety assessment area.

[0033] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings of the present invention are as follows.

[0035] Figure 1 It is a flow chart of the key measurement point selection method for electromagnetic safety assessment of 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 in the evaluation area at different speeds of the present invention.

[0040] Figure 6 The present invention is Figure 5 Flow chart for selecting key measurement points in a 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] Fig. 9 It is a comparison diagram between the fitting values ​​and the 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 in conjunction with the accompanying drawings and embodiments.

[0045] Embodiment 1:

[0046] like Figure 2 and Figure 3 A dynamic WPT system shown includes a transmitting end and a receiving end, wherein the receiving end is arranged on a moving vehicle body, and the transmitting end includes a plurality of transmitting modules arranged in sequence along a moving path of the moving vehicle body;

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

[0048] In this embodiment, all the 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 respectively include a transmitting coil L ti and L t(i+1) The high-frequency inverters of the i-th and i+1-th transmitting modules include four switch tubes S1 to S4 and four switch tubes S5 to S8, respectively, and 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 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 The internal resistance, R ti and R t(i+1) They 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 Respectively represent the output current and voltage of the high-frequency inverter of the i-th and i+1-th transmitter modules, i r Represents the receiving coil current, M tit(i+1) Indicates the transmitting coil L ti and the transmitting coil L t(i+1) The 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 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 the transmitting coil i, the self-impedance of the loop of the transmitting coil i and the self-impedance of the loop of the receiving coil respectively, and ω represents the operating angular frequency of the system.

[0058] Embodiment 2:

[0059] like Figure 1 A key measurement point selection method for electromagnetic safety assessment of a dynamic WPT system is shown, which is applied to the dynamic WPT system described in Example 1, and 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 of ​​the transmitting coil i and the transmitting coil i+1, the receiving coil is coupled with the transmitting coil i and the transmitting coil i+1 at the same time. Therefore, the minimum working unit circuit topology of the dynamic WPT system is determined to include 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] In the formula, 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 transmitting module.

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

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

[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 induced voltage expressions of the system transmitting coil i, transmitting coil i+1 and receiving coil are obtained as follows:

[0069]

[0070] In the dynamic WPT system, when the receiving coil passes through the segmented area of ​​the transmitting coil i and the 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 by the root mean square are:

[0071]

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

[0073]

[0074] It can be concluded that the effective value of the induced voltage at the receiving end is:

[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: 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; the specific steps are:

[0080] S3.1: First, a three-dimensional finite element electromagnetic simulation model of a dynamic WPT system including key components such as segmented transmitting coils, receiving coils, and receiving-end loads is constructed; based on the spatial physical relationship between the transmitting coils, receiving coils, and their segmented areas, and considering 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:

[0081]

[0082] Where V 1_x is the length of the magnetic field sampling area V1 in the X direction, V 1_y is the width of the magnetic field sampling area V1 in the Y direction, V 1_z is the height of the magnetic field sampling area 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, where: the magnetic field sampling area V1 is used to collect magnetic field strength data points, and the safety assessment area V2 is used to select key measuring points for magnetic field strength measurement.

[0083] In this embodiment, if Figure 4 As shown, set V 1_x 、V 1_y and V 1_z The sizes are 1000mm, 1000mm and 1500mm respectively.

[0084] S3.2: The transmitting coil and the receiving coil use a DC excitation method instead of an AC excitation method, that is, the AC current effective value i r_rms (t) The receiving coil is equivalently excited with an AC current effective value i ti_rms (t) and i t(i+1)_rms (t) Equivalently excite the transmitting coil i and the transmitting coil i+1 respectively;

[0085] According to the mobile 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.

[0086] 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 sorting; 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, g=1001.

[0089] The 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 measuring points with the strongest correlation is as follows Figure 6 shown.

[0091] S5: Fit the mathematical relationship between the magnetic field intensity at key measuring points and the average field intensity in the safety assessment area, and obtain the regression equation for predicting the average field intensity in the safety assessment area based on key measuring 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] In the formula, B avg represents the linear regression equation fitted with the magnetic field intensity at key points a and b as independent variables, B a represents the magnetic field strength at the key point a, B b It represents the magnetic field intensity at the key point b coordinate. α, β and γ are the constant coefficients of the linear regression equation respectively. The origin of the coordinate point is the starting point of the magnetic field sampling area.

[0095] In this embodiment, the accuracy of the average magnetic field strength in the evaluation area by the key measuring points of the magnetic field of the system is verified, and the effect of the method can be verified. Specifically, it includes: analyzing and comparing the conformity of the characteristic phenomenon of the receiving coil segmented by the transmitting coil with the theoretical analysis at different speeds; and analyzing and comparing the influence of the measuring point selection method of the present invention and the traditional three-point measurement method on the accuracy of the average magnetic field strength in the evaluation area.

[0096] S6: Simulate and verify the dynamic system:

[0097] Build as Figure 3 The dynamic WPT wireless power transmission system shown in Figure 1 includes two transmitting coils and one receiving coil. The capacitors are tuned according to the system resonant frequency so that each coil is in a resonant state. The frequency of this system is 85kHz. The coil inductance, compensation capacitor and coil internal resistance are shown in Table 1. The mutual inductance changes during the system coupling process are shown in Figure 2 shown.

[0098] Table 1 Dynamic WPT system parameters

[0099] <![CDATA[L t1 (μH)]]> <![CDATA[L t2 (μH)]]> <![CDATA[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)]]> <![CDATA[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 and the DC input voltage is shown in equation (1), and the equivalent load composed of the rectifier, filter capacitor and load is shown in equation (2).

[0101] 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:

[0102]

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

[0104]

[0105] Next, based on step S3 and step S4, a three-dimensional finite element electromagnetic simulation model of the dynamic WPT system is established as follows: Figure 4 As shown, the mobile speed range of the receiving end determines the minimum number of time sampling points and the number of space sampling points in the magnetic field sampling area at different speeds, forming a magnetic field sampling data set for selecting key measuring points.

[0106] The correlation distribution fan diagram at different speeds is obtained by formula (13): Figure 5 As shown in the figure, all spatial measurement 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 measurement points with the strongest correlation, and multiple independent variables with low linear correlation are selected as key measurement points. The specific flow chart is as follows Figure 6 shown.

[0107] The regression equation with strong generalization ability obtained by the multivariate 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, and the fitting degree is only 0.608, which verifies the effectiveness of selecting the measurement points of the present invention from the algorithm.

[0115] By establishing an experimental device, the magnetic field strength of the measuring point of the present invention and the traditional measuring point and 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, such as Fig. 9 shown. Fig. 9 (a) is a comparison chart of the fitting values ​​and experimental values ​​obtained at the key measurement points of the present invention, Fig. 9 (b) is a comparison chart of the fitting values ​​and experimental values ​​obtained at the traditional measurement points. Fig. 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 μΤ, while the traditional measuring points have low accuracy, with a maximum difference of 78 μΤ. Based on this, the effectiveness of selecting the measuring points of the present invention is experimentally verified.

[0116] Analyze and compare the characteristics of the receiving coil segmentation 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 respectively, 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 will change 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 measuring points in quasi-static fields. The selected key measuring 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 rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant 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 within 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 comprises a receiving end and a plurality of transmitting modules arranged in sequence, wherein the receiving end comprises a receiving coil, and the transmitting module comprises a transmitting coil, wherein: 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 change of the mutual inductance of the system when the receiving coil moves in the segmented area of ​​the transmitting coil, derive the expression of the receiving coil current at different speeds, and analyze the transient characteristics of the receiving coil current under the change of 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 sorting; S5: Fit the mathematical relationship between the magnetic field intensity at the key measuring points and the average field intensity in the safety assessment area, and obtain a regression equation for predicting the average field intensity in the safety assessment area based on the key measuring points.

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

3. According to claim 1, a key measurement point selection method for electromagnetic safety assessment of dynamic WPT system 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 in 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 according to Kirchhoff's law, the receiving coil current i at different speeds is derived. r_rms Based on the expression of mutual inductance change law and the expression of receiving coil current, the transient characteristics of receiving coil current under mutual inductance change are analyzed.

4. According to claim 3, a key measurement point selection method for electromagnetic safety assessment of dynamic WPT system 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: According to the spatial physical relationship between the transmitting coil, the receiving coil and their segmented areas, and considering 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 respectively, 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, where: the magnetic field sampling area V1 is used to collect magnetic field strength data points, and the safety assessment area V2 is used to select key measuring points for magnetic field strength measurement.

5. According to claim 4, a key measurement point selection method for electromagnetic safety assessment of dynamic WPT system is characterized in that: The specific method of 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 use DC excitation to replace the AC excitation method, that is, the AC current effective value i r_rms (t) The receiving coil is equivalently excited with an AC current effective value 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 mobile 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. According to claim 1, a key measurement point selection method for electromagnetic safety assessment of a dynamic WPT system is characterized in that: In step S4, the correlation m between the field strength at the measuring point in the sampling area and the average field strength in the safety assessment area is: In the formula, 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. A key measurement point selection method for electromagnetic safety assessment of dynamic WPT system according to claim 6, characterized in that: The specific steps of 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 key measurement point selection method for electromagnetic safety assessment of dynamic WPT system according to claim 1 is 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 In the formula, B avg represents the linear regression equation fitted with the magnetic field intensity at key points a and b as independent variables, B a represents the magnetic field strength at the key point a, B b It represents the magnetic field intensity at the key point b coordinate. α, β and γ are the constant coefficients of the linear regression equation respectively. The origin of the coordinate point is the starting point of the magnetic field sampling area.

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