Method for calculating loss of magnetic coupling mechanism of wireless power transmission system

Abstract

The application relates to the technical field of wireless power transmission, and particularly discloses a calculation method of a magnetic coupling mechanism loss of a wireless power transmission system. First, a circuit model of the system is established, and system parameters are determined; then, a coupling mechanism loss model is established, that is, the skin loss of primary and secondary side coils is calculated based on the current of the primary and secondary side coils, the coil parameters and the system working frequency; the proximity loss of the primary and secondary side coils is calculated based on the magnetic field intensity (obtained through simulation) of the primary and secondary side coils, the coil parameters and the system working frequency; the loss of the primary and secondary side magnetic cores is calculated based on the magnetic induction intensity (obtained through simulation) of the primary and secondary side magnetic cores, the magnetic core parameters and the system working frequency; and the loss of the primary and secondary side magnetic shielding plates is calculated based on the parameters of the primary and secondary side magnetic shielding plates and the magnetic field intensity (obtained through simulation) of the surfaces of the primary and secondary side magnetic shielding plates. The coupling mechanism loss is calculated through a finite element simulation software, and the simulation result is compared with the actual system measured efficiency, and the simulation result is consistent with the actual result.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wireless power transmission, and in particular to a method for calculating loss of a magnetic coupling mechanism of a wireless power transmission system. BACKGROUND

[0002] In recent years, electric vehicles have been widely used to alleviate the problems of fossil energy shortage and environmental pollution. Traditionally, electric vehicles use contact chargers. However, this power transmission method requires a charging cord and a socket, which may cause electric sparks and reduce safety levels. People hope to find a convenient, safe and reliable power transmission method. Compared with the traditional contact power transmission method, the wireless power transmission (WPT) technology not only avoids electric sparks caused by physical contact, but also greatly facilitates users. Currently, the WPT technology for electric vehicles has attracted widespread attention from countries around the world. The magnetic coupling mechanism is the most important part of realizing wireless power transmission. In the application of electric vehicle WPT, the distance between the transmitting end and the receiving end is usually large. In order to strengthen the coupling coefficient between the transmitting end and the receiving end, improve the transmission power and efficiency, and reduce the magnetic field leakage, a magnetic core is used in the WPT system. However, the magnetic core will cause additional magnetic core loss, which will reduce the efficiency of the prototype. At the same time, the coupling mechanism also has coil loss. Therefore, an accurate coupling loss model is an important basis for designing a WPT system.

[0003] The high-frequency current of the magnetic coupling wireless power transmission system will cause a high-frequency alternating magnetic field in the coupling mechanism, resulting in loss. An accurate loss model can provide guidance for the design of the coupling mechanism and reduce the generation of coupling mechanism loss. However, there is currently a lack of a relatively accurate method for calculating the loss of the magnetic coupling mechanism. SUMMARY

[0004] The present application provides a method for calculating the loss of the magnetic coupling mechanism of a wireless power transmission system, which solves the technical problem of how to accurately estimate the loss of the system magnetic coupling mechanism.

[0005] To solve the above technical problems, the present application provides a method for calculating the loss of the magnetic coupling mechanism of a wireless power transmission system, which includes:

[0006] establishing a circuit model of the wireless power transmission system and determining system parameters; the wireless power transmission system includes a magnetic coupling mechanism, which includes a primary side coil, a primary side magnetic core and a primary side magnetic shielding plate on the primary side, and a secondary side coil, a secondary side magnetic core and a secondary side magnetic shielding plate on the secondary side;

[0007] based on the determined system parameters and the circuit model of the wireless power transmission system, calculating the current of the primary side coil and the current of the secondary side coil;

[0008] calculating the skin loss of the primary side coil and the secondary side coil based on the current, coil parameters and system operating frequency f of the primary side coil and the secondary side coil;

[0009] obtaining the magnetic field intensity of the primary side coil or the secondary side coil through simulation;

[0010] calculating the proximity loss of the primary side coil and the secondary side coil based on the magnetic field intensity, coil parameters and system operating frequency f of the primary side coil and the secondary side coil;

[0011] obtaining the magnetic induction intensity of the primary side magnetic core and the secondary side magnetic core through simulation;

[0012] calculating the loss of the primary side magnetic core and the secondary side magnetic core based on the magnetic induction intensity, magnetic core parameters and system operating frequency f of the primary side magnetic core and the secondary side magnetic core;

[0013] obtaining the magnetic field intensity on the surface of the primary side magnetic shielding plate and the secondary side magnetic shielding plate through simulation;

[0014] calculating the loss of the primary side magnetic shielding plate and the secondary side magnetic shielding plate based on the parameters and the magnetic field intensity on the surface of the primary side magnetic shielding plate and the secondary side magnetic shielding plate;

[0015] summing all the calculated losses to obtain the loss of the magnetic coupling mechanism.

[0016] Further, the skin loss Pskin of the primary side coil or the secondary side coil is calculated by the following formula: skin

[0017]

[0018] wherein, l, N respectively represent the length and the number of strands of the litz wire used for winding the primary side coil or the secondary side coil, R DC represents the DC loss resistance of a single litz wire calculated based on the wire diameter d and the electrical conductivity γ of the litz wire, is the skin loss coefficient of the conductor of different shapes related to the system operating frequency f, I m is the peak current of the primary side coil or the secondary side coil.

[0019] Further, the primary side coil or the secondary side coil adopts a cylindrical litz wire, and the skin loss coefficient corresponding to the cylindrical litz wire is represented by F R (f) represents, F R (f) is calculated by the following formula:

[0020]

[0021] wherein, ξ is defined as ​δ represents the skin depth of a single Litz wire, the skin depth δ is calculated by the following formula:

[0022]

[0023] wherein μ0 is the permeability constant, μ r is the relative permeability of the copper wire, μ r = 1;

[0024] ber1(ξ), ber0(ξ) are the real parts of the first order, zero order first kind Kelvin functions bei1(ξ), bei0(ξ) are the imaginary parts of the first order, zero order first kind Kelvin functions i.e.:

[0025]

[0026] wherein Re() represents taking the real part, Im() represents taking the imaginary part, e is the natural base, and j is the imaginary unit.

[0027] Further, the proximity loss P proximity of the primary coil or the secondary coil is calculated by the following formula:

[0028] P proximity = NlR DC G R (f)H e 2

[0029] wherein G R (f) is the proximity loss coefficient of the cylindrical Litz wire related to the system working frequency f, H e is the amplitude of the external magnetic field strength of the primary coil or the secondary coil.

[0030] The coefficient G R (f) of the proximity loss is calculated by the following formula:

[0031]

[0032] wherein ber2(ξ), bei2(ξ) are the real part and the imaginary part of the second order first kind Kelvin functions

[0033] Further, the loss P v of the primary magnetic core or the secondary magnetic core per unit volume is calculated by the following formula:

[0034] P v = cf a B b

[0035] ​Wherein, B is the amplitude corresponding to the effective magnetic induction intensity in the primary side magnetic core or the secondary side magnetic core, the constants a, b, c are obtained by fitting the loss-frequency curve provided by the magnetic core data manual.

[0036] Further, the loss P of the primary side magnetic shielding plate or the secondary side magnetic shielding plate loss-Al is calculated by the following formula:

[0037]

[0038] Wherein, μ Al , γ Al are the permeability and conductivity of the primary side magnetic shielding plate or the secondary side magnetic shielding plate respectively, H rms is the magnetic field intensity of the surface of the primary side magnetic shielding plate or the secondary side magnetic shielding plate.

[0039] Further, the wireless power transmission system is a bidirectional wireless power transmission system using double LCC compensation network; the current I p of the primary side coil and the current I s of the secondary side coil are represented as:

[0040]

[0041] Wherein, U p,1 and U s,1 are the fundamental wave components of the alternating voltage output by the primary side full-bridge inverter and the secondary side full-bridge inverter respectively, L fp , L fs represent the primary side series resonance inductance and the secondary side series resonance inductance respectively, and ω is the working angular frequency of the system.

[0042] Further, U p,1 and U s,1 satisfy:

[0043]

[0044] Wherein, V dp is the primary side DC input voltage source, V ds is the secondary side DC output voltage source, and δ is the system's external phase angle, i.e. U s,1 lags behind U p,1 by an angle δ.

[0045] The application provides a method for calculating the loss of a magnetic coupling mechanism of a wireless power transmission system, which comprises the following steps: firstly, establishing a circuit model of the wireless power transmission system and determining system parameters; then, establishing a coupling mechanism loss model, i.e., calculating the skin loss of a primary coil and a secondary coil based on the current of the primary coil and the secondary coil, the coil parameters and the system operating frequency f; calculating the proximity loss of the primary coil and the secondary coil based on the magnetic field intensity (obtained through simulation) of the primary coil and the secondary coil, the coil parameters and the system operating frequency f; calculating the loss of a primary magnetic core and a secondary magnetic core based on the magnetic induction intensity (obtained through simulation) of the primary magnetic core and the secondary magnetic core, the magnetic core parameters and the system operating frequency f; calculating the loss of a primary magnetic shielding plate and a secondary magnetic shielding plate based on the parameters of the primary magnetic shielding plate and the secondary magnetic shielding plate and the magnetic field intensity (obtained through simulation) of the surface of the primary magnetic shielding plate and the secondary magnetic shielding plate; and summing up all the calculated losses to obtain the loss of the magnetic coupling mechanism. The loss of the coupling mechanism is calculated through a finite element simulation software, and the simulation result is compared with the actual system measured efficiency, and the simulation result is consistent with the actual result. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 is a flow chart of the method for calculating the loss of the magnetic coupling mechanism of the wireless power transmission system provided by the embodiment of the application;

[0047] Figure 2 is a circuit diagram of a bidirectional wireless power transmission system based on a double LCC provided by the embodiment of the application;

[0048] Figure 3 is a fundamental wave equivalent circuit diagram of the wireless power transmission system provided by the embodiment of the application; Figure 2

[0049] Figure 4 is a waveform diagram of the primary coil and the secondary coil provided by the embodiment of the application;

[0050] Figure 5 is a waveform diagram of the primary coil and the secondary coil provided by the embodiment of the application;

[0051] Figure 6 is a simulation model diagram of the coupling mechanism provided by the embodiment of the application;

[0052] Figure 7 is a magnetic flux density distribution diagram of the primary magnetic core and the secondary magnetic core provided by the embodiment of the application;

[0053] Figure 8 is a magnetic flux density distribution diagram of the primary coil and the secondary coil provided by the embodiment of the application;

[0054] Figure 9 is a magnetic flux density distribution diagram of the primary aluminum plate and the secondary aluminum plate provided by the embodiment of the application;

[0055] Figure 10 is a diagram of the relationship between the power loss of the magnetic core and the frequency provided by the embodiment of the application;

[0056] ​Figure 11 is a schematic diagram of the proportion of each part loss provided by the embodiment of the present application;

[0057] Figure 12 is a measured efficiency diagram of the system provided by the embodiment of the present application. DETAILED DESCRIPTION

[0058] The embodiments of the present application will be described in detail below with reference to the accompanying drawings. The embodiments are given only for the purpose of illustration and should not be understood as limiting the present application. The accompanying drawings are only for reference and illustration, and do not constitute a limitation on the scope of patent protection of the present application, because many changes can be made to the present application without departing from the spirit and scope of the present application.

[0059] The method for calculating the loss of the magnetic coupling mechanism of the wireless power transmission system provided by the embodiment of the present application, as shown in Figure 1 , includes the following steps:

[0060] S1, establishing a circuit model of the wireless power transmission system and determining system parameters; the wireless power transmission system includes a magnetic coupling mechanism, and the magnetic coupling mechanism includes a primary side coil, a primary side magnetic core and a primary side magnetic shielding plate on the primary side, and a secondary side coil, a secondary side magnetic core and a secondary side magnetic shielding plate on the secondary side;

[0061] S2, calculating the current of the primary side coil and the current of the secondary side coil based on the determined system parameters and the circuit model of the wireless power transmission system;

[0062] S3, calculating the skin loss of the primary side coil and the secondary side coil based on the current of the primary side coil and the secondary side coil, the coil parameters and the system operating frequency f;

[0063] S4, obtaining the magnetic field strength of the primary side coil or the secondary side coil through simulation;

[0064] S5, calculating the proximity loss of the primary side coil and the secondary side coil based on the magnetic field strength of the primary side coil and the secondary side coil, the coil parameters and the system operating frequency f;

[0065] S6, obtaining the magnetic induction strength of the primary side magnetic core and the secondary side magnetic core through simulation;

[0066] S7, calculating the loss of the primary side magnetic core and the secondary side magnetic core based on the magnetic induction strength of the primary side magnetic core and the secondary side magnetic core, the magnetic core parameters and the system operating frequency f;

[0067] S8, obtaining the magnetic field strength on the surface of the primary side magnetic shielding plate and the secondary side magnetic shielding plate through simulation;

[0068] S9, calculating the loss of the primary side magnetic shielding plate and the secondary side magnetic shielding plate based on the parameters of the primary side magnetic shielding plate and the secondary side magnetic shielding plate and the magnetic field strength on the surface;

[0069] S10, summing all the losses to obtain the loss of the magnetic coupling mechanism.

[0070] It should be noted that the order of execution of the above steps can be adjusted without affecting the calculation process.

[0071] This example takes a bidirectional wireless power transmission system as an example to more specifically describe steps S1 to S6.

[0072] The circuit diagram of the bidirectional wireless power transmission system based on double LCC is shown in Figure 2 . Among them, V dp is the original side DC input voltage source, C dp is the original side input filter capacitor; the original side full-bridge circuit is composed of switch tubes S1-S4; the original side resonance compensation network includes original side series resonance inductor L fp , original side parallel resonance capacitor C fp and original side series resonance capacitor C p ; L p and L s are the self-inductance of the original side coil and the secondary side coil respectively; the secondary side resonance compensation network includes secondary side series resonance inductor L fs , secondary side parallel resonance capacitor C fs and secondary side series resonance capacitor C s ; switch tubes T1-T4 constitute a secondary side full-bridge circuit; V ds is the secondary side DC output voltage source, C ds is the secondary side output filter capacitor; M is the mutual inductance between the original side coil and the secondary side coil. The currents of the original side series resonance inductor L fp , the secondary side series resonance inductor L fs , the original side coil L p , the secondary side coil L s are represented by I Lfp , I Lfs , I Lp , I Ls respectively. The original side output DC is represented by I dp , and the secondary side output DC is represented by I ds .

[0073] Because the high-order resonance network has low-pass filtering characteristics, the high-frequency components of the resonance network can be ignored, and the fundamental equivalent model of the system is shown in Figure 3 .

[0074] U p,1 and U s,1 are the fundamental components of the AC voltages output by the original and secondary side full-bridge circuits respectively. Taking the phase of U p,1 as the reference, it is denoted as U p,1 ∠0°. Define the external phase angle of the system as δ, U s,1 lags behind Up,1 angle δ, U p,1 and U s,1 The expression of U

[0075]

[0076] According to Kirchhoff's law, the loop KVL equation is written as follows:

[0077]

[0078] where ω is the system operating angular frequency, and satisfies:

[0079]

[0080] By combining equation (2) and equation (3), the loop current in step S2 can be obtained as follows:

[0081]

[0082] The loss of the coupling mechanism of the wireless power transmission system mainly includes three parts, which are coil loss, magnetic core loss and aluminum plate loss.

[0083] The coil loss is caused by the high-frequency alternating current passing through the coil, and is usually the main part of the coupling mechanism loss, which can be mainly divided into skin effect loss and proximity effect loss. In order to reduce the skin effect, the wireless power transmission system usually uses Litz wire (also known as Litz wire) with multiple cores.

[0084] Assuming that the number of Litz wire strands of the coil (primary coil or secondary coil) is N, the diameter of a single Litz wire is d, the total length of the Litz wire is l, d is much smaller than l, the resistivity of copper conductor is p, and the conductivity is g, the DC loss resistance R DC of a single Litz wire is:

[0085]

[0086] Where S represents the cross-sectional area of a single conductor.

[0087] The skin depth δ of a single Litz wire can be represented by the following formula:

[0088]

[0089] Where μ0 is the magnetic permeability constant, μ r is the relative magnetic permeability of copper conductor, μ r = 1, and f is the frequency of the sinusoidal current passing through the conductor, i.e. the operating frequency of the system.

[0090] The primary side coil and the secondary side coil in this example are both cylindrical Litz wire, so the skin loss of the primary side coil or the secondary side coil wound by N strands of cylindrical Litz wire is:

[0091]

[0092] where I m is the peak current of the primary side coil or the secondary side coil, is the skin loss coefficient of different shapes of conductors, used to describe the degree of impedance increase due to skin effect, R AC represents the alternating current impedance. F R (f) is the skin loss coefficient of cylindrical Litz wire, which is expressed as:

[0093]

[0094] where ξ is defined as:

[0095]

[0096] ber n (ξ) and bei n (ξ) are the real part and the imaginary part of the first kind of Kelvin function of order n about ξ, denoted as:

[0097]

[0098] where Re() represents taking the real part, Im() represents taking the imaginary part, e is the natural base, and j is the imaginary unit.

[0099] The expression of the N strands of Litz wire adjacent loss is:

[0100]

[0101] where H e is the amplitude of the external magnetic field strength, is the adjacent loss coefficient of different shapes related to the system operating frequency f, used to describe the coil loss due to the adjacent effect. Since the primary side coil and the secondary side coil in this example are both cylindrical Litz wire, the adjacent loss coefficient G R (f) is calculated by:

[0102]

[0103] Therefore, the total expression of the coil loss is:

[0104] P loss-Cu = P skin + P proximity (13) ​

[0105] There are three main physical loss mechanisms in magnetic cores: hysteresis loss, eddy current loss, and residual loss. Core losses can be calculated using a combination of finite element simulation and the Steinmetz formula. According to the Steinmetz formula, the core loss per unit volume is:

[0106] P v =cf a B b (14)

[0107] In the formula, P v The core loss per unit volume, expressed in kW / m. 3 f is the operating frequency in kHz, and B is the amplitude of the effective magnetic flux density in the primary or secondary core obtained through finite element simulation in tons (T). The coefficients a, b, and c can be obtained by fitting the loss curve with respect to frequency provided in the core datasheet.

[0108] Aluminum plates are widely used for electromagnetic shielding in electromagnetic coupling mechanisms. When they cover the back and surrounding area of ​​the coupling mechanism, the alternating magnetic field acting on the aluminum plate will generate eddy currents on the aluminum surface. In this example, both the primary and secondary magnetic shielding plates are made of aluminum plates. The eddy current loss of the aluminum plate can be calculated using the following formula:

[0109]

[0110] Where, μ Al γ is the permeability of aluminum. Al H is the electrical conductivity of aluminum. rms The magnetic field strength on the surface of the aluminum plate is obtained through finite element simulation.

[0111] The aluminum plate loss can be obtained by adding impedance boundary conditions to the surface of the aluminum plate and then performing an area integral on the built-in surface loss density using COMSOL finite element simulation.

[0112] Finally, the calculated coil loss, core loss, and aluminum plate loss are added together to obtain the total loss of the magnetic coupling mechanism.

[0113] The method for calculating the loss of the magnetic coupling mechanism in a wireless power transmission system provided in this invention first establishes a circuit model of the wireless power transmission system and determines the system parameters. Then, a loss model for the coupling mechanism is established, namely: calculating the skin loss of the primary and secondary coils based on the current, coil parameters, and system operating frequency f; calculating the proximity loss of the primary and secondary coils based on the magnetic field strength (obtained through simulation), coil parameters, and system operating frequency f; calculating the loss of the primary and secondary magnetic cores based on the magnetic induction intensity (obtained through simulation), core parameters, and system operating frequency f; calculating the loss of the primary and secondary magnetic shielding plates based on the parameters and surface magnetic field strength (obtained through simulation); and summing all the calculated losses to obtain the loss of the magnetic coupling mechanism.

[0114] The feasibility of the calculation method for the magnetic coupling mechanism loss of this wireless power transmission system is verified by simulation below.

[0115] The parameters of the 30kW bidirectional wireless power transfer system based on dual LCC are shown in Table 1:

[0116] Table 1

[0117] Parameter Value Parameter Value L fp / μH]]> 24 L fs / μH]]> 24 C fp / nF]] 145 C fs / nF]] 145 C p / nF]] 48 C s / nF]] 48 L p / μH 99.8 L s / μH 99.7 V dp / V]]> 650 V ds / V]]> 742

[0118] A bidirectional wireless power transfer system model with dual LCCs was built in Matlab / Simulink.

[0119] The waveforms of the primary and secondary AC and DC sides obtained through simulation are as follows: Figure 4 and Figure 5 As shown. Figure 4 Middle U AB I fp For the primary side AC output voltage and current, U ab I fs This refers to the AC input voltage and current on the secondary side. Figure 5 Chinese V dp I dp V represents the primary-side DC output voltage and current. ds I ds The secondary side DC output voltage and current are given. Through simulation, the current in each circuit is obtained as follows:

[0120]

[0121] A simulation model of the coupled mechanism is established in the finite element simulation software COMSOL, as follows: Figure 6 As shown in Table 2, the parameters of the coupling mechanism are as follows.

[0122] Table 2

[0123] Coil Parameter Primary Side Secondary Side Coil Outside Diameter (mm) 600 600 Coil Inside Diameter (mm) 330 330 Coil Turns 9 9 Magnetic Core Outside Diameter (mm) 700 700 Magnetic Core Inside Diameter (mm) 100 100 Aluminum Plate Outside Diameter (mm) 720 720

[0124] The magnetic flux density of the magnetic core of the coupling mechanism, the magnetic field mode of the coil, and the magnetic flux density distribution of the inner surface of the aluminum plate obtained by simulation are shown in Figure 7 , Figure 8 and Figure 9 .

[0125] Further, the following parameters are obtained:

[0126]

[0127] B m_Pri , B m_Sec respectively represent the amplitude of the effective magnetic induction intensity corresponding to the primary side, the secondary side, the primary side magnetic core or the secondary side magnetic core, H m_Pri , H m_Sec respectively represent the magnetic field intensity of the surface of the primary side and the secondary side aluminum plate.

[0128] The power loss of the magnetic core provided by the manufacturer and the frequency relationship diagram are shown in Figure 10 . Through curve fitting, the parameters a=2.1452, b=2.7652, and c=1.5498 are obtained. Further, through simulation software calculation, the following parameters are obtained:

[0129]

[0130] Among them, P v_Pri , P v_Sec respectively represent the loss of the primary side and the secondary side magnetic core, P loss_Al_Pri , P loss_Al_Sec respectively represent the loss of the primary side and the secondary side aluminum plate.

[0131] The number of strands of the Litz wire used is 2625, the wire diameter is 5.1*10 -5 m, and the total length of the coil is 16.74 m. Combined with the loss model of the coupling mechanism, F R (f)=0.5, G R (f)=2.0855*10 -11 can be calculated, and the coil loss can be calculated as follows:

[0132]

[0133] Among them, P loss_Cu_Pri , P loss_Cu_Sec respectively represent the loss of the primary side coil and the secondary side coil.

[0134] Therefore, the total loss of the coupling mechanism can be obtained as follows:

[0135] P loss =P v_Pri +P v_Sec +P loss_Al_Pri +P loss_Al_Sec +Ploss_Cu_Pri +P loss_Cu_Sec = 568.788 W (20)

[0136] The proportion of each part loss is shown in the following table. Figure 11

[0137] In addition, the resonant element and inverter loss is calculated to be about 178.79 W and 204.99 W. Therefore, the total loss of the system P Loss = 952.568 W, and the total input of the system P in = 31272.4 W, and the system efficiency is calculated to be about:

[0138] η = 1 - P Loss / P in × 100% = 96.95% (21)

[0139] The measured efficiency of the system is shown in the following table. Figure 12 The loss model efficiency and the measured efficiency only differ by 0.164% (97.114%-96.95%), which proves that the loss model has high accuracy and can provide a reference for loss estimation of the bidirectional wireless power transmission system.

[0140] In summary, the embodiment of the application carries out research on the loss modeling of the bidirectional wireless power transmission system with double LCC. Firstly, the characteristics of the bidirectional wireless power transmission system with double LCC are analyzed, and the current calculation formula of each branch of the system is given. Based on the finite element simulation, the coupling loss model of the system is established, and the calculation method of the loss of each part of the coupling mechanism is given. Finally, the simulation model of the 30kW bidirectional wireless power transmission system and the coupling mechanism is established, and the loss of each part is calculated. Compared with the measured efficiency, the efficiency only differs by 0.164%, which proves the correctness of the loss model.

[0141] The above embodiment is a preferred embodiment of the application, but the embodiment of the application is not limited by the above embodiment, and any change, modification, substitution, combination, simplification made without departing from the spirit and principle of the application should be an equivalent replacement method, which is included in the protection scope of the application.​

Claims

1. A method of calculating losses in a magnetic coupling mechanism of a wireless power transfer system, characterized by, The method comprises: establishing a circuit model of a wireless power transmission system and determining system parameters; the wireless power transmission system comprises a magnetic coupling mechanism, which comprises a primary side coil, a primary side magnetic core and a primary side magnetic shielding plate on the primary side, and a secondary side coil, a secondary side magnetic core and a secondary side magnetic shielding plate on the secondary side; calculating the current of the primary side coil and the current of the secondary side coil based on the determined system parameters and the circuit model of the wireless power transmission system; The skin loss of the primary side coil or the secondary side coil P is calculated based on the current, coil parameters and system operating frequency f of the primary side coil and the secondary side coil. skin The skin loss is calculated by the following formula: ， wherein, l, N represent the length and the number of strands of the litz wire used for winding the primary coil or the secondary coil, respectively, R DC represents the direct current loss resistance of a single litz wire calculated based on the wire diameter d and the conductivity γ of the litz wire, is the skin loss coefficient of the different shaped conductors related to the system operating frequency f, I m is the peak current of the primary coil or the secondary coil; obtaining the magnetic field intensity of the primary side coil or the secondary side coil through simulation; calculating the proximity loss of the primary side coil and the secondary side coil based on the magnetic field intensity of the primary side coil and the secondary side coil, the coil parameters and the system operating frequency f; obtaining the magnetic induction intensity of the primary side magnetic core and the secondary side magnetic core through simulation; calculating the loss of the primary side magnetic core and the secondary side magnetic core based on the magnetic induction intensity of the primary side magnetic core and the secondary side magnetic core, the magnetic core parameters and the system operating frequency f; obtaining the magnetic field intensity on the surface of the primary side magnetic shielding plate and the secondary side magnetic shielding plate through simulation; calculating the loss of the primary side magnetic shielding plate and the secondary side magnetic shielding plate based on the parameters of the primary side magnetic shielding plate and the secondary side magnetic shielding plate and the magnetic field intensity on the surface thereof; summing all the calculated losses to obtain the loss of the magnetic coupling mechanism.

2. The method of claim 1, wherein, The primary side coil or the secondary side coil adopts a cylindrical Litz wire, and a skin loss coefficient corresponding to the cylindrical Litz wire is represented by , is calculated by the following formula: ， where ξ is defined as δ represents the skin depth of a single Litz wire, the skin depth δ is calculated by the following equation: ， where μ0is the permeability constant, μ r is the relative permeability of the copper wire, μ r = 1. the real part of the first kind Kelvin function of order one, zero, , the imaginary part of the first kind Kelvin function of order one, zero, , i.e.:​ ， wherein, represents taking the real part, represents taking the imaginary part, e is the natural base, and j is the imaginary unit.

3. The method of claim 2, wherein, Proximity loss P of the primary coil or the secondary coil proximity is calculated by the following formula: ， wherein, is the proximity loss factor of a cylindrical Litz wire related to the system operating frequency f, H e is the amplitude of the external magnetic field strength of the primary coil or the secondary coil; coefficient of proximity loss is calculated from the equation: ， wherein are the real and imaginary parts of the second order first kind Kelvin function respectively.

4. The method of claim 1, wherein, The loss P in a unit volume of the primary side magnetic core or the secondary side magnetic core v is calculated by the following formula: ， Wherein, B is the amplitude corresponding to the effective magnetic induction intensity in the primary side magnetic core or the secondary side magnetic core, and the constants a, b and c are obtained by fitting the loss-frequency curve provided by the magnetic core data manual.

5. The method of claim 4, wherein, loss of the primary side magnetic shield plate or the secondary side magnetic shield plate calculated from the following formula: ， wherein μ Al , γ Al are the permeability and the electrical conductivity of the primary or secondary magnetic shielding plate, respectively, H rms is the magnetic field strength at the surface of the primary or secondary magnetic shielding plate, is the angular frequency of operation of the system.

6. The method of claim 5, wherein: The wireless power transmission system is a bidirectional wireless power transmission system using a double-sided LCC compensation network; the current of the primary side coil and the current of the secondary side coil is calculated by the following formula: ， wherein, and are the fundamental components of the AC voltages output by the primary side full-bridge inverter and the secondary side full-bridge inverter, respectively, L fp , L fs represent the primary side series resonant inductance and the secondary side series resonant inductance, respectively.

7. The method of claim 6, wherein, and satisfies: ， Wherein, V dp is the primary DC input voltage source, V ds is the secondary DC output voltage source, and δ is the phase angle of the system, i.e. the phase angle δ lags the phase angle δ.

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