CN104614595A - Non-contact Measurement Method of Natural Frequency and Quality Factor of Resonant Coil - Google Patents

Abstract

A non-contact measurement method for natural frequency and quality factor of a resonance coil relates to a measurement technology for the natural frequency and the quality factor of the self-resonance coil by using self-distributed capacitance in a magnetic coupling resonance wireless power transmission system. The method aims to solve the problems that when the natural frequency and the quality factor of the resonant coil are measured by adopting a direct measurement method, errors are introduced, and the impedance is too large, so that the measurement result is inaccurate. The invention uses a primary magnetic field generated by a small standard coil to excite the coil to be measured so as to obtain impedance parameters. The impedance information of the coil to be measured can be obtained by calculating the impedance characteristic of the standard coil and comparing the impedance characteristic when the coil to be measured is not added, so that the natural frequency f of the self-resonance coil is measured and calculated₀And a figure of merit method. The method has the characteristics of small introduced error, high measurement precision and convenience in measurement. The accuracy is improved by at least 20% compared to the direct measurement method.

Description

Non-contact Measurement Method of Natural Frequency and Quality Factor of Resonant Coil

technical field

The invention relates to the measurement technology of the natural frequency and quality factor of the resonant coil in the magnetic coupling resonant wireless power transmission system.

Background technique

The transmission coil applied to the magnetically coupled resonant wireless power transmission system is responsible for the mutual conversion of magnetic field and electric field energy, and its own resonance is mainly realized by the resonant circuit composed of coil inductance and resonant capacitor. The natural frequency of the resonant circuit determines the operating frequency of the system, and the quality factor of the resonant circuit is an important parameter that affects the transmission efficiency. Since the use of concentrated capacitance has solder joint resistance and its own internal resistance, it is easy to reduce the quality factor of the coil, so the use of the distributed capacitance of the coil itself to realize the self-resonance of the coil has a great impact on the efficiency of wireless power transmission. However, there are several problems when directly measuring the parameters of this self-resonant coil: 1. The distribution parameters at the contact point between the coil and the probe will have a great impact on the measurement results of the system; 2. The distributed capacitance is equivalent to a lumped The parameter is a structure connected in parallel with the inductor, the impedance at the resonance is extremely large (infinitely large when there is no internal resistance), and the reflection loss is high, which makes the measuring instrument unable to measure accurately, and the measurement results are not even reliable.

Contents of the invention

The purpose of the present invention is to solve the problem that when the natural frequency and quality factor of the resonant coil are measured by the direct measurement method, errors will be introduced, and the impedance is too large, resulting in inaccurate measurement results. contact measurement method.

The non-contact method for measuring the natural frequency and quality factor of the resonant coil of the present invention comprises the following steps:

Step 1. Connect the impedance measuring device to measure the standard coil;

Step 2, utilizing the impedance measuring device to measure the curves of the real part Real (Z _S (f)) and the imaginary part Imag (Z _S (f)) of the standard coil impedance as a function of frequency, and the range of the frequency is 0 ~ 20M;

Step 3. Coupling the standard coil and the coil to be tested through a weak magnetic field strength;

Step 4, utilize the impedance measuring device to measure the curves of the real part Real (Z ₀ (f)) and the imaginary part Imag (Z ₀ (f)) of the standard coil impedance as a function of frequency, f represents the frequency, and the range of the frequency is 0 ~20M;

Step five, calculate Real(Z _C (f)) and Imag(Z _C (f));

Real(Z _C (f))=Real(Z ₀ (f))-Real(Z _S (f)), Imag(Z _C (f))=Imag(Z ₀ (f))-Imag(Z _S ( f));

Step 6, make Imag(Z _C (f))=0, calculate the natural frequency f ₀ of the coil to be tested;

Step 7. Construct a new impedance complex number Z _C : Z _C =Real(Z _C (f))+i×Imag(Z _C (f)), and calculate the modulus of Z _C and the maximum value of the modulus of Z _C , where i stands for imaginary number;

Step 8. Calculate the two frequency points f ₁ and f ₂ corresponding to when the mode of Z _C drops to (1/2) ^(1/2) times of the maximum value, and calculate the 3db bandwidth Δf of the mode of Z _C ＝f ₁ -f ₂ , finally calculate the quality factor Q of the coil to be tested:

$\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; \&Delta;f</span>}}<span\; class="notranslate">\; .</span>$

The above method uses a primary magnetic field generated by a small standard coil to excite the coil under test to obtain impedance parameters. By calculating the impedance characteristics of the standard coil and comparing the impedance characteristics when the coil under test is not added, the impedance information of the coil under test can be obtained, thereby measuring the natural frequency f ₀ and quality factor of the coil. This method has the characteristics of small error, high measurement accuracy and convenient measurement. Accuracy is improved by at least 20% compared to direct measurement methods.

Description of drawings

Fig. 1 is the schematic diagram of the principle of the non-contact method for measuring the natural frequency and quality factor of the resonant coil according to the present invention;

Fig. 2 is the curve of the real part and the imaginary part of the impedance measured in step 2 as a function of frequency, wherein 2 represents the imaginary part and 3 represents the real part;

Fig. 3 is the curve of the real part and the imaginary part of the impedance measured in step 4 as a function of frequency, wherein 4 represents the real part and 5 represents the imaginary part;

Fig. 4 is the curve that the real part and the imaginary part of impedance complex number Z _C vary with frequency in step 7; wherein 6 represents the real part, and 7 represents the imaginary part;

Fig. 5 is the curve that the modulus of impedance complex number Z _C changes with frequency in step 7;

In FIGS. 2 to 5 , the abscissa represents the angular frequency, and the ordinate represents the values of the real and imaginary parts of the impedance.

Detailed ways

Specific Embodiment 1: This embodiment is described in conjunction with FIG. 1. The non-contact method for measuring the natural frequency and quality factor of the resonant coil described in this embodiment includes the following steps:

Step 1, connect the standard coil 1 of the impedance measuring device;

Step 2, using the impedance measuring device to measure the curves of the real part Real (Z _S (f)) and the imaginary part Imag (Z _S (f)) of the impedance of the standard coil 1 as a function of frequency, and the range of the frequency is 0 ~ 20M; Z means impedance;

Step 3. Coupling the standard coil 1 and the coil to be tested through a weak magnetic field strength;

Step 4, utilize the impedance measuring device to measure the curve of the real part Real (Z ₀ (f)) and the imaginary part Imag (Z ₀ (f)) of the impedance of the standard coil 1 as a function of frequency, f represents the frequency, and the range of the frequency is 0~20M;

Step five, calculate Real(Z _C (f)) and Imag(Z _C (f));

Real(Z _C (f))=Real(Z ₀ (f))-Real(Z _S (f)), Imag(Z _C (f))=Imag(Z ₀ (f))-Imag(Z _S ( f));

Step 6: Let Imag(Z _C (f))=0, and calculate the natural frequency f ₀ of the coil to be tested; the calculation process here is actually to find the Imag(Z _C (f))=0 or the closest to 0 Frequency point, this frequency point is f ₀ ;

Step 7. Construct a new impedance complex number Z _C : Z _C =Real(Z _C (f))+i×Imag(Z _C (f)), and calculate the modulus of Z _C and the maximum value of the modulus of Z _C , where i stands for imaginary number;

Step 8. Calculate the two frequency points f ₁ and f ₂ corresponding to when the mode of Z _C drops to (1/2) ^(1/2) times of the maximum value, and calculate the 3db bandwidth Δf of the mode of Z _C ＝f ₁ -f ₂ , finally calculate the quality factor Q of the coil to be tested:

$\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; \&Delta;f</span>}}<span\; class="notranslate">\; .</span>$

In this embodiment, a standard coil 1 is coupled with the coil to be tested to obtain the characteristic parameters of the coil to be tested, ie, the natural frequency f ₀ and the quality factor Q, through the coupling of a weak magnetic field. The standard coil 1 is a small single-turn coil whose natural frequency is greater than 100 MHz. The coil to be tested is a self-resonant coil for magnetically coupled resonant wireless power transmission, its coil self-inductance is its own distributed inductance, and its resonant capacitance is its own distributed capacitance. The natural frequency of the self-resonant coil is the lowest frequency point among the multiple natural frequency points of the self-resonant coil. There is magnetic field coupling between the coil to be tested and the standard coil 1, and its coupling coefficient is not less than 0.05. The standard coil 1 is connected with an impedance measuring device. Since there is no electrical contact between the standard coil 1 and the coil to be tested, the problems caused by the direct measurement method can be avoided, and the accuracy of the measurement result is increased by 20%. Figures 2 to 5 show the measurement and calculation results.

Specific Embodiment 2: This embodiment is a further limitation of the non-contact measurement method for the natural frequency and quality factor of the resonant coil described in Embodiment 1. In this embodiment, the impedance measurement device is an impedance analyzer or a network analyzer instrument.

Specific Embodiment 3: This embodiment is a further limitation of the non-contact measurement method for the natural frequency and quality factor of the resonant coil described in Embodiment 1. In this embodiment, the connection between the impedance measuring device and the standard coil 1 adopts coaxial cable or twisted pair.

Specific Embodiment 4: This embodiment is a further limitation of the non-contact measurement method for the natural frequency and quality factor of the resonant coil described in Embodiment 1. In this embodiment, the standard coil 1 in step 3 and the coil to be tested The coupling coefficient is 0.01~0.5.

Claims (4)

1. The non-contact measuring method of natural frequency and quality factor of resonant coil, it is characterized in that: the method comprises the following steps: Step 1, connecting the measuring standard coil (1) of the impedance measuring device; Step 2, utilize the impedance measuring device to measure the curve of the real part Real (Z _S (f)) and the imaginary part Imag (Z _S (f)) of the standard coil (1) impedance as a function of frequency, and the range of the frequency is 0～ 20M; Step 3, coupling the standard coil (1) and the coil to be tested with each other through a weak magnetic field strength; Step 4, utilize impedance measuring device to measure the curve of real part Real (Z ₀ (f)) and imaginary part Imag (Z ₀ (f)) of standard coil (1) impedance as a function of frequency, f represents frequency, and the curve of described frequency The range is 0~20M; Step five, calculate Real(Z _C (f)) and Imag(Z _C (f)); Real(Z _C (f))=Real(Z ₀ (f))-Real(Z _S (f)), Imag(Z _C (f))=Imag(Z ₀ (f))-Imag(Z _S ( f)); Step 6, make Imag(Z _C (f))=0, calculate the natural frequency f ₀ of the coil to be tested; Step 7. Construct a new impedance complex number Z _C : Z _C =Real(Z _C (f))+i×Imag(Z _C (f)), and calculate the modulus of Z _C and the maximum value of the modulus of Z _C , where i stands for imaginary number; Step 8. Calculate the two frequency points f ₁ and f ₂ corresponding to when the mode of Z _C drops to (1/2) ^(1/2) times of the maximum value, and calculate the 3db bandwidth Δf of the mode of Z _C ＝f ₁ -f ₂ , finally calculate the quality factor Q of the coil to be tested: $\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; \&Delta;f</span>}}<span\; class="notranslate">\; .</span>$ 2. The non-contact method for measuring the natural frequency and quality factor of the resonant coil according to claim 1, wherein the impedance measuring device is an impedance analyzer or a network analyzer. 3. The non-contact method for measuring the natural frequency and quality factor of the resonant coil according to claim 1, characterized in that: the connection between the impedance measuring device and the standard coil (1) adopts a coaxial cable or a twisted pair. 4. The non-contact method for measuring the natural frequency and quality factor of the resonant coil according to claim 1, characterized in that: in step 3, the coupling coefficient between the standard coil (1) and the coil to be tested is 0.01-0.5.