Mutual inductance identification method and applicable mutual inductance calculation device thereof

Abstract

A mutual inductance identification method comprises the following steps: (S1) collecting primary side resonance current, secondary side resonance current and voltage, and filtering to obtain respective first and second harmonic components of the primary side resonance current, the secondary side resonance current and voltage; (S2) respectively modulating and demodulating first and second harmonic components of the primary side resonance current, the secondary side resonance current and the voltage to correspondingly calculate amplitudes of the first and second harmonic components of the primary side resonance current, the secondary side resonance current and the voltage and phase differences of the first and second harmonic components of the secondary side resonance voltage and the current; and (S3) calculating a mutual inductance parameter between the primary side circuit and the secondary side circuit according to the amplitudes of the first harmonic component and the second harmonic component of the primary side resonance current, the secondary side resonance current and the voltage and the phase difference of the first harmonic component and the second harmonic component of the secondary side resonance voltage and the current. The method is not related to circuit resonance states and load characteristics, adverse effects of other factors are avoided, and mutual inductance measurement precision is guaranteed. The invention relates to a mutual inductance calculation device.

Description

Technical Field

[0001] The present invention relates to the field of mutual induction technology, and in particular to a mutual induction identification method and a mutual induction calculation device applicable thereto. Background Art

[0002] Inductive Power Transfer (IPT) technology realizes power transmission without physical contact based on the principle of electromagnetic induction, effectively solving the problems of contact sparks, cumbersome plugging and unplugging, and power supply safety, and has therefore attracted more and more attention. However, a large number of studies have shown that the output power and transmission efficiency of inductive power transmission are greatly affected by the degree of coupling between the coupling coils, which makes the accurate identification of mutual inductance parameters in inductive power transmission systems or circuits increasingly important.

[0003] Taking wireless charging of electric vehicles (EV) as an example, its coupling coefficient mainly depends on the location where the vehicle is parked. In the actual application of inductive power transmission systems or circuits, the phenomenon of misalignment of coupling coils (i.e. primary and secondary coils) is usually difficult to avoid, which causes the mutual inductance parameters to change in real time during operation. The change in mutual inductance parameters causes changes in coupling parameters and energy transmission characteristics, affecting the operating conditions and transmission efficiency of the inductive power transmission system or circuit, resulting in unstable transmission efficiency.

[0004] Therefore, how to develop a mutual inductance recognition method and a mutual inductance calculation device applicable thereto that can improve the deficiencies of the above-mentioned prior art is a problem that the relevant technical field urgently needs to solve. Summary of the invention

[0005] The purpose of this case is to provide a mutual inductance identification method and a mutual inductance calculation device applicable thereto, so as to solve the problem that during the operation of a traditional inductive power system or circuit, due to the inability to accurately identify the mutual inductance parameters, the coupling parameters and energy transfer characteristics will change due to the change of the mutual inductance parameters, resulting in the operating conditions and transmission efficiency of the inductive power transmission system or circuit being affected, making the transmission efficiency of the inductive power transmission system or circuit unstable.

[0006] To achieve the above-mentioned purpose, a preferred embodiment of the present case is a mutual inductance identification method, which is applied to a wireless power transmission system. The wireless power transmission system includes a primary circuit, a resonant cavity and a secondary circuit. The mutual inductance identification method includes: (S1) collecting the primary resonant current of the primary circuit, and collecting the secondary resonant current and the secondary resonant voltage of the secondary circuit, and filtering the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively to obtain the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, wherein the frequency of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage is different from the frequency of the corresponding second harmonic component; (S2) modulating and demodulating the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively to obtain the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively. The mutual inductance parameter between the primary circuit and the secondary circuit is calculated according to the amplitude of the first harmonic component of the primary resonant current and the secondary resonant voltage, the amplitude of the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, the phase difference between the first harmonic component of the secondary resonant voltage and the first harmonic component of the secondary resonant current, and the phase difference between the second harmonic component of the secondary resonant voltage and the second harmonic component of the secondary resonant current; (S3) according to the amplitude of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, the amplitude of the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, the phase difference between the first harmonic component of the secondary resonant voltage and the first harmonic component of the secondary resonant current, and the phase difference between the second harmonic component of the secondary resonant voltage and the second harmonic component of the secondary resonant current.

[0007] To achieve the above-mentioned purpose, another preferred embodiment of the present case is a mutual inductance calculation device, which is arranged in a wireless power transmission system, and the wireless power transmission system also includes a primary circuit, a resonant cavity and a secondary circuit, and the mutual inductance calculation device includes: a sampling circuit, which collects the primary resonant current of the primary circuit, and collects the secondary resonant current and the secondary resonant voltage of the secondary circuit; a first filtering circuit, which filters the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively to obtain the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, wherein the frequency of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage is different from the frequency of the corresponding second harmonic component; an analog switch, which modulates the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively; a second filtering circuit, which demodulates the first harmonic component and the second harmonic component of the modulated primary resonant current, the secondary resonant current and the secondary resonant voltage respectively; and a micro control unit, which generates a first harmonic component according to the demodulated primary resonant current. The first harmonic components of the secondary resonant current and the secondary resonant voltage are obtained according to the amplitude of the first harmonic components of the primary resonant current, the secondary resonant current and the secondary resonant voltage, and the phase difference between the first harmonic component of the secondary resonant voltage and the first harmonic component of the secondary resonant current; the second harmonic components of the primary resonant current, the secondary resonant current and the secondary resonant voltage are obtained according to the amplitude of the second harmonic components of the primary resonant current, the secondary resonant current and the secondary resonant voltage, and the phase difference between the second harmonic component of the secondary resonant voltage and the first harmonic component of the secondary resonant current; The mutual inductance parameter between the primary circuit and the secondary circuit is calculated according to the phase difference of the second harmonic component of the secondary resonant current, and the amplitude of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, the amplitude of the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, the phase difference between the first harmonic component of the secondary resonant voltage and the first harmonic component of the secondary resonant current, and the phase difference between the second harmonic component of the secondary resonant voltage and the second harmonic component of the secondary resonant current. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 A schematic diagram of the steps of the mutual induction identification method according to the preferred embodiment of the present invention;

[0009] Figure 2 for Figure 1 A circuit diagram of a wireless power transmission system to which the mutual inductance identification method is applied;

[0010] Figure 3 for Figure 1 The equivalent circuit diagram of the wireless power transmission system shown;

[0011] Figure 4 for Figure 1 A detailed schematic diagram of the mutual induction computing device of the wireless power transmission system shown;

[0012] Figure 5 for Figure 1 The step S2 shown is a detailed flow chart of the first embodiment;

[0013] Figure 6 for Figure 1 A schematic flow chart of sub-steps of step (S2) of the mutual inductance identification method shown;

[0014] Figure 7 for Figure 1 The detailed flow chart of step S2 in the second embodiment is shown as follows: DETAILED DESCRIPTION

[0015] Some typical embodiments that embody the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various variations in different implementations without departing from the scope of the present invention, and the descriptions and drawings therein are essentially for illustrative purposes rather than for limiting the present invention.

[0016] See also Figure 1 , Figure 2 , Figure 3 and Figure 4 ,in Figure 1 This is a schematic diagram of the steps of the mutual induction identification method of the preferred embodiment of this case, Figure 2 for Figure 1 The circuit diagram of the wireless power transmission system to which the mutual inductance identification method is applied is shown. Figure 3 for Figure 1 The equivalent circuit diagram of the wireless power transmission system shown in Figure 4 for Figure 1 The mutual inductance calculation device of the wireless power transmission system shown in the figure is a detailed structural diagram. The mutual inductance identification method of the present case can be applied to the mutual inductance calculation device 5 of the wireless power transmission system 1, wherein the wireless power transmission system 1 further includes a primary circuit 2, a resonant cavity 3 and a secondary circuit 4. The primary circuit 2 receives an input voltage U in And input current I in , and convert it to output the primary resonant voltage With the primary resonant current The resonant cavity 3 is electrically connected between the primary circuit 2 and the secondary circuit 4 and includes a primary coil L P With secondary coil L S , primary coil L P With the secondary coil L S Electromagnetic coupling, and the primary coil L PElectrically connected to the primary circuit 2 to receive the primary resonant voltage With the primary resonant current Secondary coil L S is electrically connected to the secondary circuit 4, and the secondary coil L S Based on the primary resonant voltage With the primary resonant current The induction generates the secondary resonant voltage The secondary resonant current The secondary circuit 4 receives the secondary resonant voltage The secondary resonant current And convert it to output the output voltage U o With output current I o .

[0017] In some embodiments, the primary circuit 2 includes a first bridge switch circuit formed by connecting a first bridge arm and a second bridge arm in parallel, the first bridge arm includes a first primary switch S1 and a third primary switch S3 connected in series, and the second bridge arm includes a second primary switch S2 and a fourth primary switch S4 connected in series. The secondary circuit 4 includes a second bridge switch circuit formed by connecting a third bridge arm and a fourth bridge arm in parallel, the third bridge arm includes a first secondary switch Q1 and a third secondary switch Q3 connected in series, and the fourth bridge arm includes a second secondary switch Q2 and a fourth secondary switch Q4 connected in series. Of course, the primary circuit 2 is not limited to a full-bridge circuit structure, and can be any form of inverter structure, such as a half-bridge circuit structure. Similarly, the secondary circuit 4 is not limited to a full-bridge circuit structure, and can be any form of rectifier structure, such as a half-bridge, uncontrolled, half-controlled, fully controlled, and other circuit structures. In some embodiments, the first primary switch element S1, the second primary switch S2, the third primary switch S3, and the fourth primary switch S4 can be, for example, devices of the type of Si MOSFET, SiC MOSFET, etc. Similarly, the first secondary switch Q1 , the second secondary switch Q2 , the third secondary switch Q3 and the fourth secondary switch Q4 may be devices such as Si MOSFET, SiC MOSFET, power diode, etc.

[0018] In some embodiments, the resonant cavity 3 further includes a primary compensation capacitor C P And the secondary compensation capacitor C S , primary compensation capacitor C P Electrically connected to the primary circuit 2 and the primary coil L P Between, the secondary compensation capacitor C S Electrically connected to the secondary coil L S and the secondary circuit 4. In some embodiments, the wireless power transmission system 1 further includes an output capacitor C o , connected in parallel with the fourth bridge arm.

[0019] The mutual inductance calculation device 5 is electrically connected to the primary circuit 2, the resonant cavity 3 and the secondary circuit 4, and can measure parameters related to voltage and / or current in the primary circuit 2, the resonant cavity 3 and the secondary circuit 4, such as measuring the primary resonant voltage Secondary resonance voltage Primary resonant current and secondary resonant current Etc., and then calculate the mutual inductance parameter between the primary circuit 2 and the secondary circuit 4 according to the measurement results. Specifically, the mutual inductance calculation device 5 calculates the primary coil L according to the above measurement results. P And the secondary coil L S The mutual inductance parameter between them.

[0020] In addition, by Figure 3 The equivalent circuits of the primary circuit 2 and the secondary circuit 4 of the wireless power transmission system shown in the figure can be used with Kirchhoff's voltage formula to derive the following expressions (1) and (2):

[0021]

[0022] in is the primary resonant voltage, L P The primary coil L P The self-inductance value, C P is the primary compensation capacitor C P The capacitance value, is the primary resonant current, ω is the operating angular frequency, M is the primary coil L P With the secondary coil L S The mutual inductance parameter between (i.e. between the primary circuit 2 and the secondary circuit 4), is the secondary resonant voltage, L S The secondary coil L S The self-inductance value, C S is the secondary compensation capacitor C S The capacitance value, is the secondary resonant current, where the mutual inductance parameter M and the primary coil L P The self-inductance value and the secondary coil L S The self-inductance value is greatly affected by factors such as air gap and offset, and its value has a large fluctuation range and is usually regarded as an unknown quantity. The primary compensation capacitor C P The capacitance value of the secondary compensation capacitor C S The capacitance value of the primary resonant voltage hardly changes after the resonant parameters are determined (mostly using high stability material configuration) and is usually regarded as a known quantity. Secondary resonance voltage Primary resonant current and secondary resonant current It can be measured by the mutual inductance calculation device 5. Therefore, if the three unknown quantities, mutual inductance parameter M, primary coil L, are calculated by equations (1) and (2), P The self-inductance value and the secondary coil L S The self-inductance value can change the operating frequency of the wireless power transmission system 1 to increase the number of equations from equations (1) and (2). For example, two harmonic components of different frequencies (e.g., different frequencies f1 and f2) are taken to extend the following equations (3) and (4) from equations (1) and (2) at frequency f1, and extend the following equations (5) and (6) from equations (1) and (2) at frequency f2:

[0023]

[0024] Because the primary resonant voltage In practical applications, the amplitude is large and difficult to measure directly. Therefore, this case uses equations (4) and (6) to calculate the primary coil L P With the secondary coil L S The mutual inductance parameter M between them. In addition, the following general formula (7) can be obtained by integrating formulas (4) and (6):

[0025]

[0026] in is the secondary side resonant voltage The i-th harmonic component of is the primary resonant current The i-th harmonic component of is the secondary resonant current The i-th harmonic component, ω i is the operating angular frequency at the i-th harmonic component.

[0027] Since some parameters in equations (4) and (6) contain alternating quantities, and when measuring alternating quantities, both amplitude and phase need to be considered, equations (4) and (6) can be converted into the following equations (8) and (9):

[0028]

[0029] Where θ1 is the secondary resonant voltage when the operating frequency of the wireless power transmission system 1 is at frequency f1. Resonant current with secondary side The phase difference between them, θ2 is the secondary resonant voltage when the operating frequency of the wireless power transmission system 1 is at frequency f2. Resonant current with secondary side Therefore, from the above content, it can be known that by respectively obtaining the primary resonant current when the working frequency of the wireless power transmission system 1 is at frequency f1 and frequency f2, The amplitude Secondary resonant current The amplitude Secondary resonance voltage The amplitude Secondary resonance voltage Resonant current with secondary side The phase difference between them is θ1 and θ2, and combined with the known parameter secondary compensation capacitor C S The capacitance value of the primary coil L can be calculated P And the secondary coil L S The mutual inductance parameter M between them (the two unknown quantities, mutual inductance parameter M and secondary coil L, can be calculated using equations (8) and (9) S The self-inductance value). Since the primary circuit 2 is an inverter, the output voltage is a square wave signal. Combined with the certain filtering characteristics of the resonant cavity 3, the primary resonant current And the secondary resonant current The mixing signal dominated by the fundamental wave, the secondary resonant voltage It is a square wave signal, which contains sinusoidal components of various frequencies. Therefore, a filter can be used to extract the sinusoidal components of two frequencies to achieve the control of multiple frequencies. In addition, based on the two frequency signals (sine waves) obtained by filtering, the analog switch is used to modulate them respectively, and the output signal of the analog switch is low-pass filtered and then converted by an analog-to-digital converter (coherent demodulation), and the corresponding amplitude and phase of the sinusoidal components of the two frequencies are calculated accordingly. The following will introduce in detail the two solutions for the amplitude and phase of the sinusoidal components of the corresponding frequencies, which will not be repeated here.

[0030] In addition, equations (8) and (9) can be integrated into the following general equations (10) and (11):

[0031]

[0032] in, is the secondary side resonant voltage The i-th harmonic component of is the secondary resonant current The i-th harmonic component of is the primary resonant current The i-th harmonic component, ω i is the operating angular frequency of the i-th harmonic component, θ i is the secondary side resonant voltage The i-th harmonic component and the secondary resonant current The phase difference between the i-th harmonic components, is the secondary side resonant voltage The phase of the i-th harmonic component, is the secondary resonant current The phase of the i-th harmonic component of .

[0033] like Figure 4 As shown, in this case, the mutual inductance calculation device 5 includes a sampling circuit 50, a first filtering circuit 51, an analog switch 52, a second filtering circuit 53 and a micro control unit 54. The sampling circuit 50 is electrically connected to the primary circuit 2 and the secondary circuit 4 to collect the primary resonant current of the primary circuit 2. And collect the secondary resonant current of the secondary circuit 4 and secondary resonant voltage

[0034] The first filtering circuit 51 processes the primary resonant current sampled by the sampling circuit 50. Secondary side resonant current and secondary resonant voltage Filter them separately to obtain the primary resonant current Secondary side resonant current and secondary resonant voltage The first harmonic component and the second harmonic component of each, where the primary resonant current Secondary side resonant current and secondary resonant voltage The frequency of the first harmonic component of each is different from the frequency of the second harmonic component, so that equations (4) and (6) are respectively extended from the above equation (2), where the primary resonant current The first harmonic component and secondary resonant current The first harmonic component and secondary resonant voltage The frequencies of the first harmonic components are equal, and the primary resonant current The second harmonic component and secondary resonant current The second harmonic component and secondary resonant voltage The frequencies of the second harmonic components of the first and second harmonic components are all equal, and the frequencies of the first harmonic components of the first and second harmonic components are different from the frequencies of the corresponding second harmonic components. In some embodiments, the first filter circuit 51 may include an active high / low pass filter circuit, and to ensure performance, the operational amplifier used in the first filter circuit 51 should have a higher gain bandwidth product.

[0035] The analog switch 52 uses the received carrier signal to adjust the primary resonant current Secondary side resonant current and secondary resonant voltage The first harmonic component and the second harmonic component of each are modulated respectively. The second filter circuit 53 modulates the modulated primary resonant current Secondary side resonant current and secondary resonant voltage The first harmonic component and the second harmonic component of each are demodulated respectively. The modulation and demodulation methods will be described in detail below and will not be repeated here. In some embodiments, the second filter circuit 53 may include a low-pass filter circuit with a lower cut-off frequency, and an operational amplifier with a lower gain-bandwidth product may be used.

[0036] The micro control unit 54 generates a current according to the demodulated primary resonant current. Secondary side resonant current and secondary resonant voltage The first harmonic component of each corresponds to the primary resonant current Secondary side resonant current and secondary resonant voltage The amplitude of the respective first harmonic components and the secondary resonant voltage The first harmonic component and the secondary resonant current The micro control unit 54 determines the phase difference of the first harmonic component of the primary resonant current Secondary side resonant current and secondary resonant voltage The respective second harmonic components correspond to the primary resonant current Secondary side resonant current and secondary resonant voltage The amplitude of the respective second harmonic components and the secondary resonant voltage The second harmonic component and the secondary resonant current The phase difference of the second harmonic component and the primary resonant current Secondary side resonant current and secondary resonant voltage The amplitude of the first harmonic component and the primary resonant current Secondary side resonant current and secondary resonant voltage The respective second harmonic component amplitude and secondary resonant voltage The first harmonic component and the secondary resonant current The phase difference of the first harmonic component and the secondary resonant voltage The second harmonic component and the secondary resonant current The mutual inductance parameter between the primary circuit 2 and the secondary circuit 4 is calculated based on the phase difference of the second harmonic component.

[0037] In this case, the first method to calculate the amplitude and phase difference is based on the primary resonant current Secondary side resonant current and secondary resonant voltage Two DC components of the respective first harmonic component and two DC components of the respective second harmonic component are obtained.

[0038] Specifically, the second filter circuit 53 modulates the primary resonant current Secondary side resonant current and secondary resonant voltage The first harmonic component and the second harmonic component of each are demodulated respectively to obtain the primary resonant current Secondary side resonant current and secondary resonant voltage The two DC components of the respective first harmonic components and the two DC components of the respective second harmonic components, i.e., the primary resonant current The two DC components of the first harmonic component, the primary resonant current The two DC components of the second harmonic component; the secondary resonant current The two DC components of the first harmonic component, the secondary resonant current The two DC components of the second harmonic component; the secondary resonant voltage The two DC components of the first harmonic component, the secondary resonant voltage The microcontroller unit 54 is based on the primary resonant current The two DC components of the first harmonic component are used to calculate the primary resonant current The amplitude and phase of the first harmonic component of The two DC components of the second harmonic component are used to calculate the primary resonant current Similarly, the micro control unit 54 is based on the secondary resonant current The secondary resonant current is calculated from the two DC components of the first harmonic component The amplitude and phase of the first harmonic component of The secondary resonant current is calculated from the two DC components of the second harmonic component Similarly, the micro control unit 54 is based on the secondary resonant voltage The secondary resonant voltage is calculated from the two DC components of the first harmonic component The amplitude and phase of the first harmonic component of The secondary resonant voltage is calculated from the two DC components of the second harmonic component The microcontroller unit 54 determines the amplitude and phase of the second harmonic component of the secondary resonant voltage. and secondary resonant current The phase of the respective first harmonic components is used to calculate the secondary resonant voltage The first harmonic component and the secondary resonant current The micro control unit 54 determines the phase difference of the first harmonic component of the secondary resonant voltage Resonant current with secondary side The phase of the respective second harmonic components is used to calculate the secondary resonant voltage The second harmonic component and the secondary resonant current The phase difference of the second harmonic component of the primary resonant current is then calculated by the micro control unit 54. The amplitude of the first and second harmonic components and the secondary resonant current The amplitude of the first and second harmonic components and the secondary resonant voltage The amplitude of the first and second harmonic components and the secondary resonant voltage The first harmonic component and the secondary resonant current The phase difference of the first harmonic component and the secondary resonant voltage The second harmonic component and the secondary resonant current The phase difference of the second harmonic component is used to calculate the mutual inductance parameter between the primary circuit 2 and the secondary circuit 4 using formulas (8) and (9).

[0039] In some embodiments, the mutual inductance calculation device 5 further includes a differential amplifier 55 and an ADC conversion circuit 56. The differential amplifier 55 is used to convert the primary resonant current provided by the second filter circuit 53 into , secondary side resonant current and secondary resonant voltage The amplitudes of the two DC components of the respective first harmonic components and the amplitudes of the two DC components of the respective second harmonic components are adjusted. The ADC conversion circuit 56 is used to convert the amplitude-adjusted primary resonant current , secondary side resonant current and secondary resonant voltage The two DC components of the respective first harmonic components and the two DC components of the respective second harmonic components are converted into analog digital form, and the conversion results are provided to the micro control unit 54, so that the micro control unit 54 calculates the primary resonant current accordingly. , secondary side resonant current and secondary resonant voltage The amplitude and phase of the respective first harmonic components and the amplitude and phase of the respective second harmonic components, and according to the primary resonant current , secondary side resonant current and secondary resonant voltage The mutual inductance parameter between the primary circuit 2 and the secondary circuit 4 is calculated from the amplitude and phase of the respective first harmonic components and the amplitude and phase of the respective second harmonic components.

[0040] Please refer to Figure 1 ,The mutual inductance identification method of this case includes the following steps.

[0041] Step S1: The sampling circuit 50 collects the primary resonant current of the primary circuit 2. , and collect the secondary resonant current of the secondary circuit 4 and secondary resonant voltage , and the primary resonant current is filtered by the first filter circuit 51 , secondary side resonant current and secondary resonant voltage Filter them separately to obtain the primary resonant current , secondary side resonant current and secondary resonant voltage The first harmonic component and the second harmonic component of each.

[0042] Step S2: using the analog switch 52 and the second filter circuit 53 to filter the primary resonant current , secondary side resonant current and secondary resonant voltage The first harmonic component and the second harmonic component of each are modulated and demodulated respectively; the micro control unit 54 modulates and demodulates the primary resonant current according to the demodulated primary resonant current. , secondary side resonant current and secondary resonant voltage The first harmonic component of each corresponds to the calculation of the primary resonant current , secondary side resonant current and secondary resonant voltage The amplitude of the respective first harmonic components and the secondary resonant voltage The first harmonic component and the secondary resonant current The micro control unit 54 determines the phase difference of the first harmonic component according to the demodulated primary resonant current , secondary side resonant current and secondary resonant voltage The corresponding calculated primary resonant current of each second harmonic component , secondary side resonant current and secondary resonant voltage The amplitude of the respective second harmonic components and the secondary resonant voltage The second harmonic component and the secondary resonant current The phase difference of the second harmonic component.

[0043] Step S3, the micro control unit 54 generates a current according to the primary resonant current , secondary side resonant current and secondary resonant voltage The amplitude of the first harmonic component and the primary resonant current , secondary side resonant current and secondary resonant voltage The amplitude of the second harmonic component and the secondary resonant voltage The first harmonic component and the secondary resonant current The phase difference of the first harmonic component and the secondary resonant voltage The second harmonic component and the secondary resonant current The mutual inductance parameter between the primary circuit 2 and the secondary circuit 4 is calculated based on the phase difference of the second harmonic component.

[0044] Since higher-order harmonic components require more complex circuit structures and more expensive sampling circuits and filtering circuits for sampling and signal processing, in some embodiments, the first harmonic component and the second harmonic component described in step S1 are preferably harmonic components with frequencies below the fifth order. In this case, it is best to use the first harmonic component as the fundamental component and the second harmonic component as the third harmonic component. In this case, the primary resonant current The first harmonic component and secondary resonant current The first harmonic component and secondary resonant voltage The frequencies of the first harmonic components are equal, and the primary resonant current The second harmonic component and secondary resonant current The second harmonic component and secondary resonant voltage The frequencies of the second harmonic components are all equal, and the frequencies of the respective first harmonic components are different from the frequencies of the corresponding second harmonic components.

[0045] In some embodiments, the second filter circuit 53 is used to filter the primary resonant current , secondary side resonant current and secondary resonant voltage The first harmonic component and the second harmonic component of each are demodulated respectively to obtain the primary resonant current , secondary side resonant current and secondary resonant voltage The two DC components of the respective first harmonic components and the primary resonant current , secondary side resonant current and secondary resonant voltage The microcontroller unit 54 generates two DC components of the respective second harmonic components according to the primary resonant current. , secondary side resonant current and secondary resonant voltage The two DC components of the respective first harmonic components correspond to the calculation of the primary resonant current , secondary side resonant current and secondary resonant voltage The amplitude and phase of the respective first harmonic components; the micro control unit 54 is based on the primary resonant current , secondary side resonant current and secondary resonant voltage The two DC components of the respective second harmonic components correspond to the calculation of the primary resonant current , secondary side resonant current and secondary resonant voltage The magnitude and phase of the respective second harmonic components.

[0046] See also Figure 5 , which is Figure 1 The step S2 shown is a detailed flow chart of the first embodiment. The step S2 includes the following steps.

[0047] Step S2a, simulating the switch 52 to the primary resonant current , secondary side resonant current and secondary resonant voltage The first harmonic component and the second harmonic component of each are modulated respectively, and the second filter circuit 53 modulates the modulated primary resonant current , secondary side resonant current and secondary resonant voltage The first harmonic component and the second harmonic component of each are demodulated respectively to obtain the primary resonant current , secondary side resonant current and secondary resonant voltage The two DC components of the respective first harmonic components and the two DC components of the respective second harmonic components, i.e., the primary resonant current The two DC components of the first harmonic component, the primary resonant current The two DC components of the second harmonic component; the secondary resonant current The two DC components of the first harmonic component, the secondary resonant current The two DC components of the second harmonic component; the secondary resonant voltage The two DC components of the first harmonic component, the secondary resonant voltage The two DC components of the second harmonic component.

[0048] Step S2b, the micro control unit 54 generates a current according to the primary resonant current The two DC components of the first harmonic component are used to calculate the primary resonant current The amplitude and phase of the first harmonic component of The two DC components of the second harmonic component are used to calculate the primary resonant current Similarly, the micro control unit 54 is based on the secondary resonant current The secondary resonant current is calculated from the two DC components of the first harmonic component The amplitude and phase of the first harmonic component of The secondary resonant current is calculated from the two DC components of the second harmonic component Similarly, the micro control unit 54 is based on the secondary resonant voltage The secondary resonant voltage is calculated from the two DC components of the first harmonic component The amplitude and phase of the first harmonic component of The secondary resonant voltage is calculated from the two DC components of the second harmonic component The amplitude and phase of the second harmonic component.

[0049] Step S2c: the micro control unit 54 generates a voltage according to the secondary resonant voltage. and secondary resonant current The phase of the respective first harmonic components is used to calculate the secondary resonant voltage The first harmonic component and the secondary resonant current The micro control unit 54 determines the phase difference of the first harmonic component of the secondary resonant voltage Resonant current with secondary side The phase of the respective second harmonic components is used to calculate the secondary resonant voltage The second harmonic component and the secondary resonant current The phase difference of the second harmonic component.

[0050] See also Figure 6 , which is Figure 1 The sub-step flow chart of step S2 of the mutual inductance identification method shown in FIG. In some embodiments, step S2 is to determine the primary resonant current. , secondary side resonant current and secondary resonant voltage The respective first harmonic component and the second harmonic component are modulated separately and further include the following sub-steps.

[0051] In sub-step S20, the analog switch 52 receives the first carrier signal p1(t), the second carrier signal p2(t) and a modulated wave signal s(t), wherein the first carrier signal p1(t) and the second carrier signal p2(t) are square wave signals with a phase difference of 90°.

[0052] In sub-step S21, the analog switch 52 modulates the modulated wave signal s(t) by multiplying the first carrier signal p1(t) and the second carrier signal p2(t) respectively, and the following expressions are formed:

[0053]

[0054] Among them, the modulation wave signal s(t) represents the primary resonant current , secondary side resonant current and secondary resonant voltage Any of the first harmonic component and the second harmonic component of each, A is the amplitude of the modulation wave signal s(t), ω is the working angular frequency of the modulation wave signal s(t), is the phase of the modulated wave signal s(t), B k is the amplitude of the first carrier signal p1(t) and the second carrier signal p2(t), wherein k is an odd number and represents the frequency of the first carrier signal p1(t) and the second carrier signal p2(t), for example, k is equal to 3, which represents the frequency is 3. The first carrier signal p1(t) and the second carrier signal p2(t) can be obtained by, for example, performing Fourier transform on a square wave signal with the same frequency as the modulation wave s(t).

[0055] In some embodiments, step S2 modulates the primary resonant current , secondary side resonant current and secondary resonant voltage Demodulating the respective first harmonic component and the second harmonic component also includes the following sub-steps.

[0056] In sub-step S22 following sub-step S21, the second filter circuit 53 filters the primary resonant current , secondary side resonant current and secondary resonant voltage The results of multiplying the first harmonic component and the second harmonic component by the first carrier signal are filtered respectively to obtain the primary resonant current , secondary side resonant current and secondary resonant voltage The first DC component of the respective first harmonic component and the first DC component of the respective second harmonic component, wherein the first DC component is And B1 is a value where k is equal to 1. The first DC component is obtained by filtering the result of formula (12), as shown in the following formula (17):

[0057]

[0058] Step S23: The second filter circuit 53 filters the primary resonant current , secondary side resonant current and secondary resonant voltage The results of multiplying the first harmonic component and the second harmonic component of each signal with the second carrier signal are filtered respectively to obtain the primary resonant current. , secondary side resonant current and secondary resonant voltage The second DC component of the respective first harmonic component and the second DC component of the respective second harmonic component, wherein the second DC component is The second DC component is obtained by filtering the result of formula (13), as shown in the following formula (18):

[0059]

[0060] In some embodiments, in step S3, the micro control unit 54 calculates the primary resonant current using the following expression: , secondary side resonant current and secondary resonant voltage The amplitude and phase of the respective first harmonic components and the primary resonant current , secondary side resonant current and secondary resonant voltage The magnitude and phase of the respective second harmonic components:

[0061]

[0062] Where C1 is the primary resonant current , secondary side resonant current and secondary resonant voltage The first DC component of any of the first harmonic component and the second harmonic component, C2 is the primary resonant current corresponding to C1 , secondary side resonant current and secondary resonant voltage a second DC component of any one of the respective first harmonic component and the second harmonic component, and A are the primary resonant currents corresponding to C1 and C2 respectively , secondary side resonant current and secondary resonant voltage The phase and amplitude of any one of the respective first harmonic component and the second harmonic component. In other embodiments, the calculation of the phase and amplitude is not limited to formula (21) and formula (22), and this case does not limit this.

[0063] In some embodiments, in step S3, the differential amplifier 55 of the mutual inductance calculation device 5 can be used to calculate the primary resonant current , secondary side resonant current and secondary resonant voltage The two DC components of the respective first harmonic components and the primary resonant current , secondary side resonant current and secondary resonant voltage The amplitudes of the two DC components of the respective second harmonic components are adjusted, and then after analog-to-digital conversion by the ADC conversion circuit 56 of the mutual inductance calculation device 5, the primary resonant current is calculated by the micro control unit 54. , secondary side resonant current and secondary resonant voltage The amplitude and phase of the respective first harmonic components and the primary resonant current , secondary side resonant current and secondary resonant voltage The magnitude and phase of the respective second harmonic components.

[0064] In some embodiments, in step S4, the micro control unit 54 may , secondary side resonant current and secondary resonant voltage The amplitude of the first harmonic component of each, the primary resonant current , secondary side resonant current and secondary resonant voltage The amplitude of the respective second harmonic components, the secondary resonant voltage The first harmonic component and the secondary resonant current The phase difference of the first harmonic component and the secondary resonant voltage The second harmonic component and the secondary resonant current The phase difference of the second harmonic component is calculated to calculate the mutual inductance parameter between the primary circuit 2 and the secondary circuit 4. For example, the above parameters are substituted into formula (10) and formula (11) to calculate the mutual inductance parameter between the primary circuit 2 and the secondary circuit 4. For formula (10) and formula (11), i is equal to 1 and 2 respectively. When i is equal to 1, the i-th harmonic component is the first harmonic component; when i is equal to 2, the i-th harmonic component is the second harmonic component.

[0065] In some embodiments, such as non-ideal conditions, the square wave signal (such as the first carrier signal p1(t) and the second carrier signal p2(t)) received by the analog switch 52 may have a certain frequency difference Δf with the driving signal of the primary circuit 2, such as Δf≤100Hz, resulting in the output signal of the analog switch 52 still being a low-frequency AC component after passing through the second filter circuit 53. Instead of the ideal DC component, as shown in the following formula (23):

[0066]

[0067] Therefore, since the output signal of the analog switch 52 is a low-frequency AC component after passing through the second filter circuit 53, the present invention provides a method for obtaining the primary resonant current. , secondary side resonant current and secondary resonant voltage The amplitude of the first harmonic component and the primary resonant current , secondary side resonant current and secondary resonant voltage The amplitude of the second harmonic component and the secondary resonant voltage The first harmonic component and the secondary resonant current The phase difference of the first harmonic component and the secondary resonant voltage The second harmonic component and the secondary resonant current In the second method, the steps of the mutual inductance identification method and the mutual inductance calculation device are similar to those of the mutual inductance identification method and the mutual inductance calculation device in the first method, and the same component numbers represent the same components, structures and functions, which will not be repeated here.

[0068] See also Figure 7 , which is Figure 1 The step S2 shown is a detailed flow chart of the second embodiment. The step S2 in the second embodiment includes the following steps.

[0069] Step S2d: the second filter circuit 53 filters the primary resonant current , secondary side resonant current and secondary resonant voltage The first harmonic component and the second harmonic component of each are modulated and demodulated respectively to obtain the primary resonant current within a set time. , secondary side resonant current and secondary resonant voltage Multiple low-frequency AC components of respective first harmonic components and primary resonant current , secondary side resonant current and secondary resonant voltage A plurality of low frequency AC components with respective second harmonic components.

[0070] Step S2e, the micro control unit 54 generates a current according to the primary resonant current , secondary side resonant current and secondary resonant voltage The primary resonant current is calculated corresponding to the multiple low-frequency AC components of the respective first harmonic components. , secondary side resonant current and secondary resonant voltage The amplitude of the respective first harmonic components; the microcontroller unit 54 is based on the primary resonant current , secondary side resonant current and secondary resonant voltage The multiple low-frequency AC components of the respective second harmonic components correspond to the calculation of the primary resonant current , secondary side resonant current and secondary resonant voltage The amplitude of the respective second harmonic component.

[0071] Step S2f, the micro control unit 54 determines the secondary side resonant voltage within the set time. Any low-frequency AC component of the multiple low-frequency AC components of the first harmonic component and the secondary resonant current at the corresponding moment The secondary resonant voltage is calculated from the low-frequency AC component of the first harmonic component The first harmonic component and the secondary resonant current The micro control unit 54 sets the secondary resonant voltage within the set time. Any low-frequency AC component of the multiple low-frequency AC components of the second harmonic component and the secondary resonant current at the corresponding moment The secondary resonant voltage is calculated from the low-frequency AC component of the second harmonic component The second harmonic component and the secondary resonant current The phase difference of the second harmonic component.

[0072] For the primary resonant current , secondary side resonant current and secondary resonant voltage The amplitude of the respective first harmonic components and the primary resonant current , secondary side resonant current and secondary resonant voltage The amplitude of each second harmonic component can be determined, for example, by taking the low-frequency AC component within a set time. The maximum value of is obtained, where the setting time exists in a complete low-frequency AC cycle. In some embodiments, the setting time can be but not limited to 20 milliseconds. Formula (24) is used to obtain the secondary resonant voltage Taking the amplitude of the first harmonic component of as an example, it can be understood that formula (24) is also applicable to other parameters such as the secondary resonant current and secondary resonant voltage The amplitudes of the first and second harmonic components are obtained, which will not be described in detail in this case:

[0073]

[0074] Similarly, for the secondary resonant voltage The first harmonic component and the secondary resonant current The phase difference of the first harmonic component and the secondary resonant voltage The second harmonic component and the secondary resonant current The phase difference of the second harmonic component of can be obtained, for example, by the following method to obtain the secondary side resonant voltage The first harmonic component and the secondary resonant current For example, the phase difference of the first harmonic component of the secondary resonant voltage Any low-frequency AC component of the multiple low-frequency AC components of the first harmonic component and the secondary resonant current at the corresponding moment The inverse trigonometric function is used to calculate the instantaneous phase of the first harmonic component of the low-frequency AC component, as shown in the following formulas (25) and (26). The phase of the first harmonic component is related to the secondary resonant current The instantaneous phase difference of the first harmonic component of can be obtained, as shown in formula (27):

[0075]

[0076] The micro control unit 54 can further obtain the primary resonant current according to the second method. , secondary side resonant current and secondary resonant voltage The amplitude of the first harmonic component of each, the primary resonant current , secondary side resonant current and secondary resonant voltage The amplitude of the respective second harmonic components, the secondary resonant voltage The first harmonic component and the secondary resonant current The phase difference of the first harmonic component and the secondary resonant voltage The second harmonic component and the secondary resonant current The phase difference of the second harmonic component is calculated to calculate the mutual inductance parameter between the primary circuit 2 and the secondary circuit 4. For example, the above parameters are substituted into formula (10) and formula (11) to calculate the mutual inductance parameter between the primary circuit 2 and the secondary circuit 4. For formula (10) and formula (11), i is equal to 1 and 2 respectively. When i is equal to 1, the i-th harmonic component is the first harmonic component; when i is equal to 2, the i-th harmonic component is the second harmonic component.

[0077] The technical effects that can be achieved by the above mutual inductance identification method and mutual inductance calculation device 5 are shown in Table 1 below. P With the secondary coil L S When the distance between the primary coil L and the secondary coil L is large (≥20mm) or small (≤4mm), the measurement error of the mutual inductance parameter calculated in this case is about 3%. P With the secondary coil L S When the distance between the primary coil L and the secondary coil L is about 10 mm, the measurement error of the mutual inductance parameter calculated in this case is about 1%.P With the secondary coil L S When the distance between the primary coil L and the secondary coil L is greater than 10 mm, the mutual inductance parameter calculated in this case is slightly smaller than the actual value. P With the secondary coil L S When the distance is less than 6 mm, the mutual inductance parameter calculated in this case is slightly larger than the actual value. Therefore, the overall measurement error of the mutual inductance parameter calculated by the mutual inductance identification method and the mutual inductance calculation device 5 in this case does not exceed 3%, so it has good measurement accuracy.

[0078]

[0079] Table 1

[0080] In summary, this case provides a mutual inductance identification method and a mutual inductance calculation device applicable thereto. The mutual inductance identification method and the mutual inductance calculation device calculate the mutual inductance parameters in a manner that is independent of the circuit resonance state and the nature of the load size, and therefore can largely avoid the adverse effects of other factors (such as resonance point offset, load change, etc.), thereby ensuring that the mutual inductance measurement has good accuracy.

Claims

1. A mutual inductance identification method, applied to a wireless power transmission system, characterized in that: The wireless power transmission system includes a primary circuit, a resonant cavity and a secondary circuit, and the mutual inductance identification method includes: (S1) collecting a primary resonant current of the primary circuit, and collecting a secondary resonant current and a secondary resonant voltage of the secondary circuit, and filtering the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively to obtain a first harmonic component and a second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively, wherein the frequency of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively is different from the frequency of the corresponding second harmonic component; (S2) modulating and demodulating the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, respectively, to correspondingly obtain the amplitude of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, the amplitude of the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, the phase difference between the first harmonic component of the secondary resonant voltage and the first harmonic component of the secondary resonant current, and the phase difference between the second harmonic component of the secondary resonant voltage and the second harmonic component of the secondary resonant current; and (S3) Calculate a mutual inductance parameter between the primary circuit and the secondary circuit according to the amplitude of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, the amplitude of the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, the phase difference between the first harmonic component of the secondary resonant voltage and the first harmonic component of the secondary resonant current, and the phase difference between the second harmonic component of the secondary resonant voltage and the second harmonic component of the secondary resonant current.

2. The mutual induction identification method as claimed in claim 1, wherein step (S2) comprises: The first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage are modulated and demodulated respectively, so as to obtain two DC components of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage and two DC components of the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively; Calculate the amplitude and phase of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage according to the two DC components of the first harmonic component of each of the primary resonant current, the secondary resonant current and the secondary resonant voltage, and calculate the amplitude and phase of the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage according to the two DC components of the second harmonic component of each of the primary resonant current, the secondary resonant current and the secondary resonant voltage; as well as The phase difference between the first harmonic component of the secondary resonant voltage and the first harmonic component of the secondary resonant current is calculated according to the phase of the first harmonic component of the secondary resonant voltage and the secondary resonant current, and the phase difference between the second harmonic component of the secondary resonant voltage and the second harmonic component of the secondary resonant current is calculated according to the phase of the second harmonic component of the secondary resonant voltage and the secondary resonant current.

3. The mutual induction identification method as claimed in claim 1, wherein step (S2) comprises: The first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage are modulated and demodulated respectively, so as to obtain a plurality of low-frequency AC components of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage and a plurality of low-frequency AC components of the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage within a set time; Calculating the amplitude of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively according to the multiple low-frequency AC components of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively within the set time; Calculating the amplitude of the second harmonic component of each of the primary resonant current, the secondary resonant current and the secondary resonant voltage according to the multiple low-frequency AC components of the second harmonic component of each of the primary resonant current, the secondary resonant current and the secondary resonant voltage within the set time; as well as Calculating the phase difference between the first harmonic component of the secondary resonant voltage and the first harmonic component of the secondary resonant current according to any of the low-frequency AC components of the first harmonic component of the secondary resonant voltage within the set time and the low-frequency AC component of the first harmonic component of the secondary resonant current at a corresponding moment; The phase difference between the second harmonic component of the secondary resonant voltage and the second harmonic component of the secondary resonant current is calculated based on any low-frequency AC component of the second harmonic component of the secondary resonant voltage within the set time and the low-frequency AC component of the second harmonic component of the secondary resonant current at the corresponding moment.

4. The mutual inductance identification method as described in claim 3, wherein the maximum value among the multiple low-frequency AC components of the first harmonic component of each of the primary resonant current, the secondary resonant current and the secondary resonant voltage within the set time corresponds to the amplitude of the first harmonic component of each of the primary resonant current, the secondary resonant current and the secondary resonant voltage; the maximum value among the multiple low-frequency AC components of the second harmonic component of each of the primary resonant current, the secondary resonant current and the secondary resonant voltage within the set time corresponds to the amplitude of the second harmonic component of each of the primary resonant current, the secondary resonant current and the secondary resonant voltage.

5. The mutual inductance identification method as described in claim 3, wherein an inverse trigonometric function is performed on any one of the low-frequency AC components of the first harmonic component of the secondary resonant voltage within the set time and the low-frequency AC component of the first harmonic component of the secondary resonant current at the corresponding moment to obtain the phase difference between the first harmonic component of the secondary resonant voltage and the first harmonic component of the secondary resonant current; an inverse trigonometric function is performed on any one of the low-frequency AC components of the second harmonic component of the secondary resonant voltage within the set time and the low-frequency AC component of the second harmonic component of the secondary resonant current at the corresponding moment to obtain the phase difference between the second harmonic component of the secondary resonant voltage and the second harmonic component of the secondary resonant current.

6. The mutual inductance identification method as described in claim 1, wherein the frequencies of the first harmonic components of the primary resonant current, the secondary resonant current and the secondary resonant voltage are equal, the frequencies of the second harmonic components of the primary resonant current, the secondary resonant current and the secondary resonant voltage are equal, and the first harmonic component and the second harmonic component are harmonic components with frequencies below five times, respectively. 7 . The mutual inductance identification method as claimed in claim 6 , wherein the first harmonic component is a fundamental component, and the second harmonic component is a third harmonic component.

8. The mutual inductance identification method as claimed in claim 2, wherein the step (S2) of modulating the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage comprises the following sub-steps: (S20) receiving a first carrier signal p1(t), a second carrier signal p2(t) and a modulated wave signal s(t), wherein the first carrier signal p1(t) and the second carrier signal p2(t) are square wave signals with a phase difference of 90°; and (S21) The modulated wave signal s(t) is multiplied by the first carrier signal p1(t) and the second carrier signal p2(t), respectively, as follows: The modulation wave signal s(t) represents any one of the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, A is the amplitude of the modulation wave signal s(t), ω is the operating angular frequency of the modulation wave signal s(t), is the phase of the modulated wave signal s(t), B k are the amplitudes of the first carrier signal p1(t) and the second carrier signal p2(t), wherein k is an odd number and represents the frequency of the first carrier signal p1(t) and the second carrier signal p2(t).

9. The mutual inductance identification method as claimed in claim 8, wherein in the step (S2), respectively demodulating the first harmonic component and the second harmonic component of the modulated primary resonant current, the secondary resonant current and the secondary resonant voltage comprises the sub-steps of: (S22) filtering the results of multiplying the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage by the first carrier signal, respectively, and correspondingly obtaining the first DC component of the first harmonic component and the first DC component of the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage. Where B1 is the value of k equal to 1; and (S23) filtering the results of multiplying the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage by the second carrier signal, respectively, and obtaining the second DC component of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage and the second DC component of the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively.

10. The mutual inductance identification method as claimed in claim 9, wherein the step (S2) is to calculate the amplitude and the phase of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, and the amplitude and the phase of the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, respectively, using the following expression: in, C1 is the first DC component of any one of the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, C2 is the second DC component of any one of the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage corresponding to C1, and A are respectively the phase and the amplitude of any one of the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage corresponding to C1 and C2.

11. The mutual inductance identification method as described in claim 2, wherein the step (S2) also includes: adjusting the amplitudes of the two DC components of the first harmonic components of the primary resonant current, the secondary resonant current and the secondary resonant voltage, and the amplitudes of the two DC components of the second harmonic components of the primary resonant current, the secondary resonant current and the secondary resonant voltage, and after analog-to-digital conversion, obtaining the amplitude and phase of the first harmonic components of the primary resonant current, the secondary resonant current and the secondary resonant voltage, and the amplitude and phase of the second harmonic components of the primary resonant current, the secondary resonant current and the secondary resonant voltage by calculation.

12. The mutual inductance identification method as claimed in claim 1, wherein in step (S3), the mutual inductance parameter is calculated using the following expression: in, is the i-th harmonic component of the secondary resonant voltage, L S is the self-inductance of a secondary coil of the secondary circuit, C S is the capacitance value of a secondary compensation capacitor of the secondary circuit, is the i-th harmonic component of the secondary resonant current, M is the mutual inductance parameter, ω i is the operating angular frequency of the i-th harmonic component, is the i-th harmonic component of the primary resonant current, θ i is the phase difference between the i-th harmonic component of the secondary resonant voltage and the i-th harmonic component of the secondary resonant current, is the phase of the i-th harmonic component of the secondary resonant voltage, is the phase of the i-th harmonic component of the secondary resonant current, wherein i is equal to 1 and 2 respectively. When i is equal to 1, the i-th harmonic component is the first harmonic component; when i is equal to 2, the i-th harmonic component is the second harmonic component.

13. A mutual inductance calculation device, arranged in a wireless power transmission system, wherein the wireless power transmission system further comprises a primary circuit, a resonant cavity and a secondary circuit, wherein: The mutual induction computing device comprises: a sampling circuit for collecting a primary resonant current of the primary circuit, and collecting a secondary resonant current and a secondary resonant voltage of the secondary circuit; a first filtering circuit for filtering the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively to obtain a first harmonic component and a second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively, wherein the frequency of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively is different from the frequency of the corresponding second harmonic component; an analog switch for modulating the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively; a second filtering circuit for demodulating the first harmonic component and the second harmonic component of the modulated primary resonant current, the secondary resonant current and the secondary resonant voltage; and A microcontrol unit obtains the amplitude of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage and the phase difference between the first harmonic component of the secondary resonant voltage and the first harmonic component of the secondary resonant current according to the first harmonic component of the demodulated primary resonant current, the secondary resonant current and the secondary resonant voltage, and obtains the amplitude of the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage and the phase difference between the first harmonic component of the secondary resonant voltage and the first harmonic component of the secondary resonant current according to the second harmonic component of the demodulated primary resonant current, the secondary resonant current and the secondary resonant voltage. The phase difference between the second harmonic component of the primary resonant voltage and the second harmonic component of the secondary resonant current is calculated, and a mutual inductance parameter between the primary circuit and the secondary circuit is calculated according to the amplitude of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, the amplitude of the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, the phase difference between the first harmonic component of the secondary resonant voltage and the first harmonic component of the secondary resonant current, and the phase difference between the second harmonic component of the secondary resonant voltage and the second harmonic component of the secondary resonant current.

14. The mutual inductance calculation device as described in claim 13, wherein the second filtering circuit demodulates the first harmonic component and the second harmonic component of the modulated primary resonant current, the secondary resonant current and the secondary resonant voltage, respectively, to obtain two DC components of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, and two DC components of the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage; the microcontroller calculates the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage according to the two DC components of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage. The microcontrol unit calculates the amplitude and phase of the primary resonant current, the secondary resonant current and the secondary resonant voltage according to the two DC components of the second harmonic components of each of the primary resonant current, the secondary resonant current and the secondary resonant voltage, and the microcontrol unit calculates the phase difference between the first harmonic component of the secondary resonant voltage and the first harmonic component of the secondary resonant current according to the phase of the first harmonic component of each of the secondary resonant voltage and the secondary resonant current, and the microcontrol unit calculates the phase difference between the second harmonic component of the secondary resonant voltage and the second harmonic component of the secondary resonant current according to the phase of the second harmonic component of the secondary resonant voltage and the secondary resonant current.

15. The mutual inductance calculation device as claimed in claim 13, wherein the second filtering circuit modulates and demodulates the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively, so as to obtain a plurality of low-frequency AC components of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively, and a plurality of low-frequency AC components of the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively within a set time; The microcontrol unit calculates the amplitude of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage according to the multiple low-frequency AC components of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage within the set time, and the microcontrol unit calculates the amplitude of the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage according to the multiple low-frequency AC components of the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage within the set time; The microcontrol unit calculates the phase difference between the first harmonic component of the secondary resonant voltage and the first harmonic component of the secondary resonant current based on any one of the low-frequency AC components of the first harmonic component of the secondary resonant voltage within the set time and the low-frequency AC component of the first harmonic component of the secondary resonant current at the corresponding moment; the microcontrol unit calculates the phase difference between the second harmonic component of the secondary resonant voltage and the second harmonic component of the secondary resonant current based on any one of the low-frequency AC components of the second harmonic component of the secondary resonant voltage within the set time and the low-frequency AC component of the second harmonic component of the secondary resonant current at the corresponding moment.

16. The mutual inductance calculation device as described in claim 15, wherein the microcontroller unit determines that the maximum value among the multiple low-frequency AC components of the first harmonic component of each of the primary resonant current, the secondary resonant current and the secondary resonant voltage within the set time corresponds to the amplitude of the first harmonic component of each of the primary resonant current, the secondary resonant current and the secondary resonant voltage; the microcontroller unit determines that the maximum value among the multiple low-frequency AC components of the second harmonic component of each of the primary resonant current, the secondary resonant current and the secondary resonant voltage within the set time corresponds to the amplitude of the second harmonic component of each of the primary resonant current, the secondary resonant current and the secondary resonant voltage.

17. The mutual inductance calculation device as described in claim 15, the microcontroller unit performs inverse trigonometric function calculation on any one of the low-frequency AC components of the first harmonic component of the secondary resonant voltage within the set time and the low-frequency AC component of the first harmonic component of the secondary resonant current at the corresponding moment, so as to obtain the phase difference between the first harmonic component of the secondary resonant voltage and the first harmonic component of the secondary resonant current; the microcontroller unit performs inverse trigonometric function calculation on any one of the low-frequency AC components of the second harmonic component of the secondary resonant voltage within the set time and the low-frequency AC component of the second harmonic component of the secondary resonant current at the corresponding moment, so as to obtain the phase difference between the second harmonic component of the secondary resonant voltage and the second harmonic component of the secondary resonant current.

18. The mutual inductance calculation device as described in claim 13, wherein the frequencies of the first harmonic components of the primary resonant current, the secondary resonant current and the secondary resonant voltage are equal, the frequencies of the second harmonic components of the primary resonant current, the secondary resonant current and the secondary resonant voltage are equal, and the first harmonic component and the second harmonic component are harmonic components with frequencies below the fifth order, respectively.

19. The mutual inductance calculation device as claimed in claim 18, wherein the first harmonic component is a fundamental component, and the second harmonic component is a third harmonic component.

20. The mutual inductance calculation device as claimed in claim 14, wherein the analog switch receives a first carrier signal p1(t), a second carrier signal p2(t) and a modulated wave signal s(t), wherein the first carrier signal p1(t) and the second carrier signal p2(t) are square wave signals with a phase difference of 90°, and the analog switch multiplies the modulated wave signal s(t) with the first carrier signal p1(t) and the second carrier signal p2(t), respectively, as follows: The modulation wave signal s(t) represents any one of the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, A is the amplitude of the modulation wave signal s(t), ω is the operating angular frequency of the modulation wave signal s(t), is the phase of the modulated wave signal s(t), B k are the amplitudes of the first carrier signal p1(t) and the second carrier signal p2(t), wherein k is an odd number and represents the frequency of the first carrier signal p1(t) and the second carrier signal p2(t).

21. The mutual inductance calculation device as described in claim 20, wherein the second filtering circuit filters the results of multiplying the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage by the first carrier signal, respectively, and correspondingly obtains the first DC component of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, and the first DC component of the second harmonic component of each of the primary resonant current, the secondary resonant current and the secondary resonant voltage. Wherein B1 is a value where k is equal to 1, and the second filtering circuit filters the result of multiplying the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage by the second carrier signal, respectively, and correspondingly obtains the second DC component of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, and the second DC component of the second harmonic component of each of the primary resonant current, the secondary resonant current and the secondary resonant voltage.

22. The mutual inductance calculation device as claimed in claim 21, wherein the micro control unit calculates the amplitude and the phase of the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage respectively using the following expression: in, C1 is the first DC component of any one of the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, C2 is the second DC component of any one of the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage corresponding to C1, and A are respectively the phase and the amplitude of any one of the first harmonic component and the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage corresponding to C1 and C2.

23. The mutual inductance calculation device of claim 14, wherein the mutual inductance calculation device comprises a differential amplifier and an ADC conversion circuit, the differential amplifier adjusts the amplitudes of the two DC components of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage provided by the second filtering circuit, and the amplitudes of the two DC components of the second harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, respectively, and the ADC conversion circuit performs analog-to-digital conversion on the two DC components of the first harmonic component of the primary resonant current, the secondary resonant current and the secondary resonant voltage, respectively, and the two DC components of the second harmonic component, which have been adjusted in voltage amplitude, and provides the conversion results to the micro control unit.

24. The mutual inductance calculation device as claimed in claim 13, wherein the micro control unit calculates the mutual inductance parameter using the following expression: in, is the i-th harmonic component of the secondary resonant voltage, L S is the inductance of a secondary coil of the secondary circuit, C S is the capacitance value of a secondary compensation capacitor of the secondary circuit, is the i-th harmonic component of the secondary resonant current, M is the mutual inductance parameter, ω i is the operating angular frequency of the i-th harmonic component, is the i-th harmonic component of the primary resonant current, θ i is the phase difference between the i-th harmonic component of the secondary resonant voltage and the i-th harmonic component of the secondary resonant current, is the phase of the i-th harmonic component of the secondary resonant voltage, is the phase of the i-th harmonic component of the secondary resonant current, wherein i is equal to 1 and 2 respectively. When i is equal to 1, the i-th harmonic component is the first harmonic component; when i is equal to 2, the i-th harmonic component is the second harmonic component.

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