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

Abstract

The invention relates to the technical field of wireless power transmission, and particularly discloses a method for calculating loss of a magnetic coupling mechanism of a wireless power transmission system, which comprises the following steps of: firstly, establishing a circuit model of the system and determining system parameters; then establishing a coupling mechanism loss model, namely calculating skin loss of the primary and secondary coils based on current of the primary and secondary coils, coil parameters and system working frequency, and calculating proximity loss of the primary and secondary coils based on magnetic field intensity (obtained through simulation) of the primary and secondary coils, the coil parameters and the system working frequency; calculating the loss of the primary and secondary side magnetic cores 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 calculating the loss of the primary and secondary magnetic shielding plate based on the parameters of the primary and secondary magnetic shielding plate and the magnetic field intensity (obtained through simulation) of the surface. The loss of the coupling mechanism is calculated through finite element simulation software and compared with the actual measurement efficiency of an actual system, and the simulation result conforms to the reality.

Description

Technical Field

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

[0002] In order to alleviate the shortage of fossil energy and environmental pollution, electric vehicles have been widely used in recent years. Traditionally, electric vehicles use contact chargers. However, this method of power transmission requires charging cables and sockets, which may cause electric sparks and reduce the safety level. People hope to find a convenient, safe and reliable power transmission method. Compared with the traditional contact power transmission method, wireless power transmission (WPT) technology can not only avoid the electric sparks caused by physical contact, but also greatly facilitate users. At present, electric vehicle WPT technology has attracted widespread attention from countries around the world. The magnetic coupling mechanism is the most important part of realizing wireless power transmission. Usually, in the application of electric vehicle WPT, the distance between the transmitter and the receiver is relatively large. In order to strengthen the coupling coefficient between the transmitter and the receiver, 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 bring additional core loss and reduce the efficiency of the prototype. At the same time, there is also coil loss in the coupling mechanism. Therefore, an accurate coupling loss model is an important basis for designing a WPT system.

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

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

[0005] In order to solve the above technical problems, the present invention provides a method for calculating the loss of a magnetic coupling mechanism of a wireless power transmission system, comprising:

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

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

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

[0009] Acquire the magnetic field strength of the primary coil or the secondary coil through simulation;

[0010] Calculate proximity losses of the primary coil and the secondary coil based on magnetic field strengths of the primary coil and the secondary coil, coil parameters, and a system operating frequency f;

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

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

[0013] Acquire the magnetic field strength on the surface of the primary magnetic shielding plate and the secondary magnetic shielding plate through simulation;

[0014] Calculating the loss of the primary magnetic shielding plate and the secondary magnetic shielding plate based on the parameters of the primary magnetic shielding plate and the secondary magnetic shielding plate and the magnetic field strength on the surface;

[0015] The loss of the magnetic coupling mechanism is obtained by summing up all the calculated losses.

[0016] Furthermore, the skin loss P of the primary coil or the secondary coil is skin Calculated by the following formula:

[0017]

[0018] Wherein, l and N represent the length and number of strands of the Litz wire used to wind the primary coil or the secondary coil, respectively, and R DC It represents the DC 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 conductors of different shapes related to the system operating frequency f, I m is the current peak value of the primary coil or the secondary coil.

[0019] Furthermore, the primary coil or the secondary coil uses a cylindrical Litz wire, and the skin loss coefficient corresponding to the cylindrical Litz wire is denoted by F R (f) indicates that F R (f) is calculated by the following formula:

[0020]

[0021] Here, 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] Among them, μ 0 is the magnetic permeability constant, μ r is the relative magnetic permeability of the copper conductor, μ r =1;

[0024] ber 1 (ξ),ber 0 (ξ) are first-order and zero-order Kelvin functions of the first kind, respectively. The real part, bei 1 (ξ)、bei 0 (ξ) are first-order and zero-order Kelvin functions of the first kind, respectively. The imaginary part of , that is:

[0025]

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

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

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

[0029] Among them, G R (f) is the proximity loss coefficient of the 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;

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

[0031]

[0032] Among them, ber 2 (ξ)、bei 2 (ξ) are the second-order first-kind Kelvin functions The real and imaginary parts of .

[0033] Furthermore, the loss P per unit volume of the primary magnetic core or the secondary magnetic core is v 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 magnetic core or the secondary magnetic core, and the constants a, b, and c are obtained by fitting the loss curve with respect to frequency provided in the magnetic core data manual.

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

[0037]

[0038] Among them, μ Al , γ Al are the magnetic permeability and electrical conductivity of the primary magnetic shielding plate or the secondary magnetic shielding plate, respectively, H rms is the magnetic field strength on the surface of the primary magnetic shielding plate or the secondary magnetic shielding plate.

[0039] Furthermore, the wireless power transmission system is a bidirectional wireless power transmission system using a bilateral LCC compensation network; the current I p and the secondary coil current I s It is expressed as:

[0040]

[0041] Among them, U p,1 and U s,1 are the fundamental components of the AC voltage output by the primary full-bridge inverter and the secondary full-bridge inverter, L fp , L fs They represent the primary series resonant inductor and the secondary series resonant inductor respectively, and ω is the operating angular frequency of the system.

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

[0043]

[0044] Among them, V dp is the primary DC input voltage source, V ds is the secondary DC output voltage source, δ is the external phase shift angle of the system, i.e., U s,1 Hysteresis U p,1 Angle δ.

[0045] The method for calculating the loss of the magnetic coupling mechanism of the wireless power transmission system provided by the present invention first establishes a circuit model of the wireless power transmission system and determines the system parameters, and then establishes a coupling mechanism loss model, namely: the skin loss of the primary and secondary coils is calculated based on the current of the primary and secondary coils, the coil parameters and the system operating frequency f, the proximity loss of the primary and secondary coils is calculated based on the magnetic field strength of the primary and secondary coils (obtained through simulation), the coil parameters and the system operating frequency f, the loss of the primary and secondary magnetic cores is calculated based on the magnetic induction strength of the primary and secondary magnetic cores (obtained through simulation), the magnetic core parameters and the system operating frequency f; the loss of the primary and secondary magnetic shielding plates is calculated based on the parameters of the primary and secondary magnetic shielding plates and the surface magnetic field strength (obtained through simulation); and the loss of the magnetic coupling mechanism is obtained by summing up all the calculated losses. The coupling mechanism loss is calculated by finite element simulation software and compared with the actual system measured efficiency, and the simulation result is consistent with the actual. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0047] Figure 2 is a circuit diagram of a bidirectional wireless power transmission system based on dual LCC provided by an embodiment of the present invention;

[0048] Figure 3 The embodiment of the present invention provides Figure 2 Fundamental wave equivalent circuit diagram;

[0049] Figure 4 It is a waveform diagram of the primary and secondary AC sides provided by an embodiment of the present invention;

[0050] Figure 5 It is a waveform diagram of the primary and secondary DC sides provided by an embodiment of the present invention;

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

[0052] Figure 7 is a magnetic flux density distribution diagram of the primary and secondary magnetic cores provided by an embodiment of the present invention;

[0053] Figure 8 is a magnetic flux density distribution diagram of the primary and secondary coils provided in an embodiment of the present invention;

[0054] Fig. 9 It is a magnetic flux density distribution diagram of the primary and secondary aluminum plates provided by an embodiment of the present invention;

[0055] Fig.10 is a graph showing the relationship between core power loss and frequency provided by an embodiment of the present invention;

[0056] Fig.11 1. It is a schematic diagram of the loss ratio of each part provided by an embodiment of the present invention;

[0057] Fig.12 This is a diagram of the actual measured efficiency of the system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0058] The following specifically illustrates the implementation mode of the present invention in conjunction with the accompanying drawings. The embodiments are provided for illustrative purposes only and cannot be understood as limiting the present invention. The accompanying drawings are provided for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[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 invention is as follows: Figure 1 As shown, the steps include:

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

[0061] S2. calculating the current of the primary coil and the current of the secondary 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 coil and the secondary coil based on the current of the primary coil and the secondary coil, coil parameters and the system operating frequency f;

[0063] S4. Obtaining the magnetic field strength of the primary coil or the secondary coil through simulation;

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

[0065] S6. Obtain the magnetic induction intensity of the primary magnetic core and the secondary magnetic core through simulation;

[0066] S7, calculating the loss of the primary magnetic core and the secondary magnetic core based on the magnetic induction intensity of the primary magnetic core and the secondary 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 magnetic shielding plate and the secondary magnetic shielding plate through simulation;

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

[0069] S10. Sum all calculated losses to obtain the loss of the magnetic coupling mechanism.

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

[0071] This example takes a two-way wireless power transmission system as an example to explain steps S1 to S6 in more detail.

[0072] The circuit diagram of the bidirectional wireless power transmission system based on dual LCC is as follows Figure 2 As shown. Among them, V dp is the primary DC input voltage source, C dp is the primary input filter capacitor; the primary full-bridge circuit consists of the switch tube S 1 -S 4 Composition: The primary side resonant compensation network includes the primary side series resonant inductor L fp , primary parallel resonant capacitor C fp And the primary side series resonant capacitor C p ; L p and L s are the self-inductances of the primary coil and the secondary coil respectively; the secondary resonant compensation network includes the secondary series resonant inductor L fs , secondary side parallel resonant capacitor C fs And the secondary side series resonant capacitor C s Composition: Switching tube T 1 -T 4 Form a secondary full-bridge circuit; V ds is the secondary DC output voltage source, C ds is the secondary output filter capacitor; M is the mutual inductance between the primary coil and the secondary coil. fp , secondary side series resonant inductor L fs , primary coil L p , secondary coil L s The current is represented by I Lfp ,I Lfs ,I Lp ,I Ls The primary output DC is represented by I dp Indicates that the secondary output DC is I ds express.

[0073] Since the high-order resonant network has low-pass filtering characteristics, the high-frequency components of the resonant network can be ignored, and the fundamental wave equivalent model of the system is obtained as follows: Figure 3 shown.

[0074] U p,1 and U s,1 They are the fundamental components of the AC voltage output by the primary and secondary full bridges, respectively. p,1 The phase of is taken as the reference, denoted as Up,1 ∠0°. Define the system's external phase angle as δ, U s,1 Hysteresis U p,1 Angle δ, we can get U p,1 and U s,1 The expression of is shown in formula (1):

[0075]

[0076] According to Kirchhoff's law, the KVL equations of each loop are listed as shown:

[0077]

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

[0079]

[0080] By combining equations (2) and (3), we can get the current of each loop in step S2 as follows:

[0081]

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

[0083] Coil loss is caused by the high-frequency AC current flowing through the coil, which is usually the main part of the coupling mechanism loss. It can be mainly decomposed into skin effect loss and proximity effect loss. In order to reduce the skin effect, wireless power transmission systems usually use multi-core twisted Litz wire (or Litz wire).

[0084] Assume that the number of strands of the Litz wire in 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 the copper wire is ρ, and the conductivity is γ. At this time, the DC loss resistance R of a single Litz wire is DC The expression is:

[0085]

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

[0087] The skin depth δ of a single Litz line can be expressed as follows:

[0088]

[0089] Among them, μ 0 is the magnetic permeability constant, μ r is the relative magnetic permeability of the copper conductor, μ r=1, f is the frequency of the sinusoidal current passing through the wire, that is, the operating frequency of the system.

[0090] In this example, both the primary coil and the secondary coil are made of cylindrical Litz wire. Therefore, the skin loss of the primary coil or the secondary coil wound with N strands of cylindrical Litz wire can be obtained as:

[0091]

[0092] Among them, I m is the peak current of the primary coil or the secondary coil, is the skin loss coefficient of conductors of different shapes, which is used to describe the increase in impedance due to the skin effect. AC Indicates AC impedance. R (f) is the skin loss coefficient of cylindrical Litz wire, and its expression is:

[0093]

[0094] Where ξ is defined as:

[0095]

[0096] ber n (ξ) and bei n (ξ) is the nth order first kind Kelvin function with respect to ξ The real and imaginary parts of are expressed as:

[0097]

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

[0099] The expression of proximity loss of N Litz lines is:

[0100]

[0101] Among them, H e is the magnitude of the external magnetic field strength, is the proximity loss coefficient of different shapes related to the system operating frequency f, which is used to describe the coil loss caused by the proximity effect. Since both the primary coil and the secondary coil in this example use cylindrical Litz wire, the proximity loss coefficient G of the cylindrical Litz wire is R (f) is calculated by the following formula:

[0102]

[0103] Therefore, the overall expression for coil losses is:

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

[0105] There are three main physical loss mechanisms of the core: hysteresis loss, eddy current loss and residual loss. The loss of the core can be calculated by combining finite element simulation and Steinmetz formula. According to Steinmetz formula, the core loss per unit volume is:

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

[0107] Where P v is the core loss per unit volume, in kW / m 3 , f is the operating frequency, in kHz, and B is the amplitude corresponding to the effective magnetic induction intensity in the primary core or secondary core obtained by finite element simulation, in T. The coefficients a, b, and c can be obtained by fitting the loss curve with respect to frequency provided in the core data sheet.

[0108] Aluminum plates are widely used for electromagnetic shielding of electromagnetic coupling mechanisms. When they are covered on the back and around the coupling mechanism, the alternating magnetic field acts on the aluminum plate and generates eddy currents on the aluminum surface. In this example, both the primary magnetic shielding plate and the secondary magnetic shielding plate are made of aluminum plates. The eddy current loss of the aluminum plate can be calculated according to the following formula:

[0109]

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

[0111] Using COMSOL finite element simulation, impedance boundary conditions can be added to the surface of the aluminum plate, and the aluminum plate loss can be obtained by performing surface integral on the built-in surface loss density.

[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 of the wireless power transmission system provided by the embodiment of the present invention first establishes a circuit model of the wireless power transmission system and determines the system parameters, and then establishes a coupling mechanism loss model, namely: the skin loss of the primary and secondary coils is calculated based on the current of the primary and secondary coils, the coil parameters and the system operating frequency f, the proximity loss of the primary and secondary coils is calculated based on the magnetic field strength of the primary and secondary coils (obtained through simulation), the coil parameters and the system operating frequency f, the loss of the primary and secondary magnetic cores is calculated based on the magnetic induction strength of the primary and secondary magnetic cores (obtained through simulation), the magnetic core parameters and the system operating frequency f; the loss of the primary and secondary magnetic shielding plates is calculated based on the parameters of the primary and secondary magnetic shielding plates and the surface magnetic field strength (obtained through simulation); and all the calculated losses are summed to obtain the loss of the magnetic coupling mechanism.

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

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

[0116] Table 1

[0117] parameter Numeric parameter Numeric <![CDATA[L fp / μH]]> 24 <![CDATA[L fs / μH]]> 24 <![CDATA[C fp / nF]]> 145 <![CDATA[C fs / nF]]> 145 <![CDATA[C p / nF]]> 48 <![CDATA[C s / nF]]> 48 <![CDATA[L p / μH]]> 99.8 <![CDATA[L s / μH]]> 99.7 <![CDATA[V dp / V]]> 650 <![CDATA[V ds / V]]> 742

[0118] A dual LCC bidirectional wireless power transmission system model was established in Matlab / Simulink.

[0119] Through simulation, the waveforms of the primary and secondary AC and DC sides are as follows Figure 4 and Figure 5 shown. Figure 4 Middle U AB ,I fp is the primary AC output voltage and current, U ab ,I fs is the secondary side AC input voltage and current. Figure 5 Medium V dp ,I dp is the primary DC output voltage and current, V ds ,I ds is the DC output voltage and current of the secondary side. Through simulation, the current of each loop is obtained as follows:

[0120]

[0121] The simulation model of the coupling mechanism is established in the finite element simulation software COMSOL. Figure 6 The coupling mechanism parameters are shown in Table 2.

[0122] Table 2

[0123] Coil parameters Original Edge Secondary side Coil outer diameter (mm) 600 600 Coil inner diameter (mm) 330 330 Coil turns 9 9 Core outer diameter (mm) 700 700 Core inner diameter (mm) 100 100 Aluminum plate outer diameter (mm) 720 720

[0124] The simulation results show that the magnetic flux density of the coupling mechanism core, the magnetic field modulus of the coil and the magnetic flux density distribution on the inner surface of the aluminum plate are as follows: Figure 7 , Figure 8 and Fig. 9 shown.

[0125] Then we get the following parameters:

[0126]

[0127] B m_Pri , B m_Sec Respectively represent the amplitude of the effective magnetic induction intensity in the primary and secondary cores, H m_Pri , H m_Sec Respectively represent the magnetic field intensity on the primary and secondary aluminum plate surfaces.

[0128] The relationship between the core power loss and frequency provided by the manufacturer is as follows Fig.10 As shown. The parameters a=2.1452, b=2.7652, c=1.5498 were obtained through curve fitting. Then the following were calculated by simulation software:

[0129]

[0130] Among them, P v_Pri , P v_Sec Represent the loss of the primary and secondary cores, P loss_Al_Pri , P loss_Al_Sec Represent the losses of primary and secondary aluminum plates respectively.

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

[0132]

[0133] Among them, P loss_Cu_Pri , P loss_Cu_Sec Represent the losses of the primary coil and the secondary coil respectively.

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

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

[0136] The loss ratio of each part is Fig.11 shown.

[0137] In addition, the calculated resonant component and inverter losses are approximately 178.79W and 204.99W. Therefore, the total system loss P Loss =952.568W, at this time the total system input P in =31272.4W, it can be calculated that the system efficiency is approximately:

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

[0139] The system efficiency is measured as Fig.12 As shown, the difference between the loss model efficiency and the measured efficiency is only 0.164% (97.114%-96.95%), which proves that the loss model has high accuracy and can provide a reference for loss estimation of bidirectional wireless power transmission systems.

[0140] In summary, the embodiment of the present invention studies the loss modeling of the bidirectional wireless power transmission system of the dual LCC. First, the characteristics of the bidirectional wireless power transmission system of the dual LCC are analyzed, and the calculation formulas for the current of each branch of the system are given; based on finite element simulation, a loss model of the system coupling is established, and a calculation method for the loss of each part of the coupling mechanism is given; finally, a simulation model of a 30kW bidirectional wireless power transmission system and a coupling mechanism is established, and the loss of each part is calculated. Compared with the measured efficiency, the efficiency is only 0.164% different, which proves the correctness of the loss model.

[0141] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for calculating the loss of a magnetic coupling mechanism of a wireless power transmission system, characterized in that: include: Establishing a circuit model of a wireless power transmission system and determining system parameters; the wireless power transmission system includes a magnetic coupling mechanism, the magnetic coupling mechanism includes a primary coil, a primary magnetic core and a primary magnetic shielding plate located on the primary side, and a secondary coil, a secondary magnetic core and a secondary magnetic shielding plate located on the secondary side; Calculating the current of the primary coil and the current of the secondary coil based on the determined system parameters and a circuit model of the wireless power transmission system; Calculating the skin loss of the primary coil and the secondary coil based on the currents of the primary coil and the secondary coil, coil parameters and the system operating frequency f; Acquire the magnetic field strength of the primary coil or the secondary coil through simulation; Calculating proximity losses of the primary coil and the secondary coil based on magnetic field strengths of the primary coil and the secondary coil, coil parameters, and a system operating frequency f; Acquire the magnetic induction intensity of the primary magnetic core and the secondary magnetic core through simulation; Calculating the loss of the primary magnetic core and the secondary magnetic core based on the magnetic induction intensity, magnetic core parameters and system operating frequency f of the primary magnetic core and the secondary magnetic core; Acquire the magnetic field strength on the surface of the primary magnetic shielding plate and the secondary magnetic shielding plate through simulation; Calculating the loss of the primary magnetic shielding plate and the secondary magnetic shielding plate based on the parameters of the primary magnetic shielding plate and the secondary magnetic shielding plate and the magnetic field strength on the surface; The loss of the magnetic coupling mechanism is obtained by summing up all the calculated losses.

2. The method for calculating the loss of the magnetic coupling mechanism of the wireless power transmission system according to claim 1, characterized in that: The skin loss P of the primary coil or the secondary coil skin Calculated by the following formula: Wherein, l and N represent the length and number of strands of the Litz wire used to wind the primary coil or the secondary coil, respectively, and R DC It represents the DC 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 conductors of different shapes related to the system operating frequency f, I m is the current peak value of the primary coil or the secondary coil.

3. The method for calculating the loss of the magnetic coupling mechanism of the wireless power transmission system according to claim 2, characterized in that: The primary coil or the secondary coil uses a cylindrical Litz wire, and the skin loss coefficient corresponding to the cylindrical Litz wire is expressed by F R (f) indicates that F R (f) is calculated by the following formula: Here, ξ is defined as δ represents the skin depth of a single Litz wire. The skin depth δ is calculated by the following formula: Where μ0 is the magnetic permeability constant, μ r is the relative magnetic permeability of the copper conductor, μ r =1; ber1(ξ) and ber0(ξ) are the first-order and zero-order first-kind Kelvin functions respectively. The real part of the real part, bei1(ξ) and bei0(ξ) are the first-order and zero-order first-kind Kelvin functions, respectively. The imaginary part of , that is: Among them, Re() means taking the real part, Im() means taking the imaginary part, e is the natural base, j is the imaginary single Bit.

4. The method for calculating the loss of the magnetic coupling mechanism of the wireless power transmission system according to claim 3, characterized in that: The proximity loss P of the primary coil or the secondary coil proximity Calculated by the following formula: P proximity =NlR DC G R (f)H e 2 Among them, G R (f) is the proximity loss coefficient of the 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; The coefficient of proximity loss G R (f) is calculated by the following formula: Among them, ber2(ξ) and bei2(ξ) are the second-order first-kind Kelvin functions, respectively. The real and imaginary parts of .

5. The method for calculating the loss of the magnetic coupling mechanism of the wireless power transmission system according to claim 1, characterized in that: The loss P per unit volume of the primary magnetic core or the secondary magnetic core v Calculated by the following formula: P v =cf a B b Wherein, B is the amplitude corresponding to the effective magnetic induction intensity in the primary magnetic core or the secondary magnetic core, and the constants a, b, and c are obtained by fitting the loss curve with respect to frequency provided in the magnetic core data manual.

6. The method for calculating the loss of the magnetic coupling mechanism of the wireless power transmission system according to claim 5, characterized in that: The loss P of the primary magnetic shielding plate or the secondary magnetic shielding plate loss-Al Calculated by the following formula: Among them, μ Al , γ Al are the magnetic permeability and electrical conductivity of the primary magnetic shielding plate or the secondary magnetic shielding plate, respectively, H rms is the magnetic field strength on the surface of the primary magnetic shielding plate or the secondary magnetic shielding plate.

7. The method for calculating the loss of the magnetic coupling mechanism of the wireless power transmission system according to claim 6, characterized in that: The wireless power transmission system is a bidirectional wireless power transmission system using a bilateral LCC compensation network; the current I p and the secondary coil current I s Calculated by the following formula: Among them, U p,1 and U s,1 are the fundamental components of the AC voltage output by the primary full-bridge inverter and the secondary full-bridge inverter, L fp , L fs They represent the primary series resonant inductor and the secondary series resonant inductor respectively, and ω is the operating angular frequency of the system.

8. The method for calculating the loss of the magnetic coupling mechanism of the wireless power transmission system according to claim 7, characterized in that: U p,1 and U s,1 satisfy: Among them, V dp is the primary DC input voltage source, V ds is the secondary DC output voltage source, δ is the external phase shift angle of the system, i.e., U s,1 Hysteresis U p,1 Angle δ.

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