Wireless power transmission system primary side inverter waveform frequency control method and system

Abstract

The application discloses a wireless power transmission system primary side inverter waveform frequency control method and system, wherein the primary side inverter waveform frequency control system comprises a wireless energy transmitting end, a high-frequency inverter circuit, a compensation circuit and a transmitting end control circuit arranged at the end, further comprises a voltage sensor installed between the high-frequency inverter circuit and the compensation network, which collects voltage signals according to time sequence; the transmitting end control circuit comprises a waveform detection circuit module and a feedback control circuit module connected with the module, the waveform detection circuit module obtains the collected signal function X(t) through Fourier transform of the detected voltage signal data, obtains the theoretical signal function Y(t) through Fourier transform of the current input frequency, calculates the correlation coefficient ρ of the two functions xy and selects the frequency of the point with the maximum correlation coefficient as the optimal input frequency under the current input, which is transmitted to the high-frequency inverter circuit through the feedback control circuit module to perform optimal control on the primary side waveform.

Description

Technical Field

[0001] This invention belongs to the field of wireless power transmission technology, specifically relating to a method and system for controlling the frequency of the primary-side inverter waveform in a wireless power transmission system based on Fourier transform. Background Technology

[0002] With the booming development of high-tech industries such as electric vehicles, high-speed rail, and wireless sensor networks, and the increasing application of electronic devices in more and more situations, traditional wired power supply methods have exposed many limitations. Compared with traditional wired charging methods, wireless power transmission systems have the advantages of being flexible and convenient to use, requiring less maintenance, adapting to harsh environments, and easily achieving unmanned automatic power supply and mobile power supply.

[0003] Wireless power transfer systems utilize electromagnetic fields for energy transmission and generally consist of two parts: a wireless power transmitter and a wireless power receiver. At the transmitter, the DC power, after power conversion, is transformed into a square wave by a high-frequency inverter circuit and output to a magnetic coupling mechanism composed of a resonant compensation circuit and a power transfer coil. However, due to manufacturing errors in components such as capacitors, inductors, and coils, the actual operating resonant frequency of the system deviates from the rated frequency, causing ringing in the inverter output waveform and preventing it from achieving the theoretical output waveform. This makes it difficult to meet the requirements for efficient and safe charging. Therefore, in actual operation, it is necessary to adjust the input frequency to find the optimal operating frequency for efficient wireless power transfer. Traditional frequency modulation methods require parameter identification, phase acquisition, and phase-locked loops, resulting in complex hardware circuitry. Therefore, this invention, based on the Fourier transform principle and considering practical application scenarios, establishes an automatic inverter frequency control method for wireless power transfer systems. Summary of the Invention

[0004] This invention addresses the issue of oscillation in the output waveform of existing magnetically coupled primary-side inverter modules, which necessitates frequency modulation. However, current frequency modulation methods rely on hardware, resulting in complex circuitry. This invention proposes a frequency control method and system for the primary-side inverter waveform in a wireless power transfer system without adding additional hardware circuitry. This enables the wireless charging system to automatically operate at its optimal resonant frequency. Based on the principles of wireless power transfer technology, this invention addresses the oscillation problem in the primary-side inverter output waveform by acquiring voltage signals to obtain waveform characteristics. Using Fourier transform, the inverter waveform is represented as a characteristic function. Considering the characteristics of waveforms at different frequencies, correlation coefficients are used to calculate the fit and select the optimal waveform for feedback control, thereby achieving automatic control of the optimal resonant frequency of the wireless charging system.

[0005] The technical solution of this invention is:

[0006] A method for controlling the frequency of the primary-side inverter waveform in a wireless power transmission system includes the following steps:

[0007] D1: Feature signal acquisition steps: In the wireless power transmission system, after setting the current input parameters such as current input frequency, voltage and duty cycle, voltage feature signal acquisition is performed at the transmitting end. The voltage signal is acquired according to the time sequence to obtain the original voltage signal dataset. The original input function P(t) is obtained by fitting the acquired voltage signal data.

[0008] D2: Function fitting steps: Expand the waveform function P(t) based on Fourier transform to obtain the trigonometric function form of the acquired signal function X(t); then, based on the current input frequency, obtain the perfect inverted waveform function: the theoretical signal function Y(t);

[0009] D3: Steps for calculating the correlation coefficient: Define the correlation coefficient between two functions X(t) and Y(t) as ρ xy Calculate the correlation coefficient ρ between X(t) and Y(t). xy This allows us to determine the degree of correlation between the two functions;

[0010] D4: Feedback control steps: Set the required control parameters, and calculate the correlation coefficient of each input frequency by iterating through all values ​​in the interval according to the set control limit and control accuracy. The point with the largest correlation coefficient is the point where the input signal is closest to the theoretical perfect waveform, which is also the optimal input frequency under the current input frequency. The optimal input frequency is transmitted to the inverter circuit for feedback control.

[0011] In D1, the current input frequency is set to p, the voltage to u, and the duty cycle to f. The fitting method is interpolation, which obtains the original waveform function P(t). The interpolation formula is:

[0012]

[0013] In D2, the Fourier transform theory formula is:

[0014]

[0015] Based on the Fourier transform principle, the original function P(t) is expanded and transformed into the trigonometric function form of the acquired signal function X(t):

[0016]

[0017] Based on the current input parameters, the theoretical perfect waveform of the signal can be obtained. This waveform is a periodic square wave, and the square wave signal function is defined as the theoretical signal function Y(t). The square wave function is then expanded based on the Fourier transform principle:

[0018]

[0019] Thus, the acquired signal function X(t) and the theoretical signal function Y(t) are obtained.

[0020] In D3, when the theoretical signal function y(t) approximates the acquired signal x(t), x(t) can be expressed as:

[0021] x(t)=a xy y(t)+x e (t)

[0022] Among them, a xy x is the coefficient. e (t) represents the error signal. The smaller the energy of the error signal, the higher the approximation. To minimize the energy of the error signal, the energy of the error signal must be such that it corresponds to the coefficient a. xy The partial differential is 0, thus obtaining the optimal coefficient a. xy for:

[0023]

[0024] Therefore ρ xy The expression is:

[0025]

[0026] When x(t) and y(t) are both deterministic signals, ρ xy are real numbers and |ρ xy |<1. When the waveforms of signals x(t) and y(t) are the same, |ρ xy |=1; when two signals x(t) and y(t) have no similarity, |ρ xy |=0, at which point the two signals are linearly independent. Therefore, ρ xy This indicates the degree of similarity between two signals, 0 < |ρ|. xy |<1,|ρ xy The closer the value is to 1, the higher the similarity between the two signals; conversely, the closer the value is to 1, the lower the similarity is to 1.

[0027] Define the input frequency as pk, the control precision as j, and select the control precision j within the range of [(p-1)k~(p+1)k], with J (J=10 -j Divide all intervals into intervals, calculate the correlation coefficient of all points in the selected interval, and select the point with the largest correlation coefficient as the optimal frequency under the current input.

[0028] A primary-side inverter waveform frequency control system for a wireless power transmission system includes a wireless power transmitter and a high-frequency inverter circuit, a compensation circuit, and a transmitter control circuit disposed at the transmitter. The system is characterized by further including a voltage sensor installed between the high-frequency inverter circuit and the compensation network, which acquires voltage signals according to a time sequence. The transmitter control circuit includes a waveform detection circuit module and a feedback control circuit module connected to the waveform detection module. The waveform detection circuit module is electrically connected to the voltage sensor. It obtains the acquired signal function X(t) by performing a Fourier transform on the detected voltage signal dataset, obtains the theoretical signal function Y(t) by performing a Fourier transform on the current input frequency, and calculates the correlation coefficient ρ between the two functions. xy It iterates through all points within the selected interval, selects the frequency corresponding to the point with the largest correlation coefficient as the optimal input frequency under the current input, and transmits the optimal input frequency to the high-frequency inverter circuit through the feedback control circuit module for optimal control of the primary side waveform.

[0029] The voltage signal dataset is first obtained by interpolation to obtain the original waveform function P(t), and then Fourier transform is performed. The interpolation formula is:

[0030]

[0031] The Fourier transform theory formula is as follows:

[0032]

[0033] The acquired signal function is:

[0034] The theoretical signal function Y(t) is:

[0035]

[0036] The correlation coefficient ρ xy The formula is:

[0037]

[0038] When x(t) and y(t) are both deterministic signals, ρ xy are real numbers and |ρ xy |<1; When the waveforms of signals x(t) and y(t) are the same, |ρ xy |=1; when two signals x(t) and y(t) have no similarity, |ρ xy | = 0, at this time the two signals are linearly independent; 0 < |ρ xy |<1,|ρ xy The closer the value is to 1, the higher the similarity between the two signals; conversely, the closer the value is to 1, the lower the similarity is to 1.

[0039] The advantages of this invention are:

[0040] 1. The method of the present invention obtains two waveform functions by performing Fourier transforms on the original input function obtained from the current input frequency voltage signal and the perfect square wave based on the input frequency, respectively. The optimal frequency under the current input frequency is obtained by calculating the correlation coefficient of the two functions, thereby performing feedback adjustment. Therefore, the present invention can adjust the resonant frequency according to the current input frequency without complex circuit structure, quickly and automatically realize the optimal inverter waveform and resonant frequency, and improve the efficiency of wireless power transmission.

[0041] 2. The function control method provided by this invention can serve as a reference for waveform control methods in wireless power transmission. Attached Figure Description

[0042] Figure 1 : This is a schematic diagram of a wireless power transmission system having the primary-side inverter waveform frequency control system of the wireless power transmission system of the present invention;

[0043] Figure 2 This is a flowchart of a method for controlling the frequency of a primary-side inverter waveform in a wireless power transmission system according to the present invention. Detailed Implementation

[0044] See appendix Figure 1 and 2 The present invention discloses a method for controlling the frequency of a primary-side inverter waveform in a wireless power transmission system, comprising the following steps:

[0045] D1: Characteristic Signal Acquisition Steps: In the wireless power transfer system, after setting the current input parameters such as current input frequency, voltage, and duty cycle, voltage characteristic signals are acquired at the transmitting end. Specifically, a voltage sensor is installed between the high-frequency inverter circuit and the compensation network. (See...) Figure 1 The circles on the line between the high-frequency inverter circuit and the compensation network represent voltage sensors. The voltage signals collected by these sensors are transmitted to the transmitting control circuit for processing. The sensor acquires the voltage signal according to a timing sequence. The waveform detection circuit module in the transmitting control circuit obtains the raw voltage signal dataset. The original input function P(t) is obtained by fitting this acquired voltage signal data. The current input frequency can be set to p, the voltage to u, and the duty cycle to f (the dead time can be set, and is generally very short). The voltage signal data fitting uses interpolation, and the interpolation formula is:

[0046]

[0047] D2: Function fitting steps: Expand the waveform function P(t) based on Fourier transform, and collect the signal function X(t) expressed by trigonometric functions; then obtain the perfect inverted waveform function: theoretical signal function Y(t) according to the current input frequency.

[0048] Specifically: Based on the characteristics of electrical energy transmission, the original function P(t) is a periodically changing waveform, an approximate square wave with slight oscillations. According to Fourier transform theory, a function with a periodic waveform can be formed by a linear combination of trigonometric functions or their integrals. The Fourier transform formula is:

[0049]

[0050] Therefore, based on the principle of Fourier transform, the original function P(t) is expanded and transformed into a trigonometric function X(t):

[0051]

[0052] Based on the characteristics of the current input signal, the current input frequency p, input voltage u, and duty cycle are approximately 50%. Under these current signal characteristics, the theoretical perfect waveform of the signal is a periodic square wave, and the signal function of this square wave is defined as Y(t). This square wave function is expanded based on the Fourier transform principle:

[0053]

[0054] This yields the theoretical signal function and the acquired signal function.

[0055] D3: Steps for calculating the correlation coefficient: Define the correlation coefficient between two functions X(t) and Y(t) as ρ xy Calculate the correlation coefficient ρ between X(t) and Y(t). xy This allows us to determine the degree of correlation between the two functions;

[0056] To determine whether the acquired signal waveform matches the preset theoretical waveform and meets practical application requirements, waveform similarity calculation is necessary. For two defined waveform signals, the correlation coefficient can describe their similarity. The correlation coefficient between two functions x(t) and y(t) is defined as ρ. xy When x(t) is approximated by the signal function y(t), x(t) can be expressed as:

[0057] x(t)=a xy y(t)+x e (t)

[0058] Among them, a xy x is the coefficient. e (t) represents the error signal. The smaller the energy of the error signal, the higher the approximation, because to minimize the energy of the error signal, the energy of the error signal must be such that it approximates the coefficient a. xy The partial differential is 0, thus obtaining the optimal coefficient a. xy for:

[0059]

[0060] Therefore ρ xy The expression is:

[0061]

[0062] When x(t) and y(t) are both deterministic signals, ρ xy are real numbers and |ρ xy |<1. When the waveforms of signals x(t) and y(t) are the same, |ρ xy |=1; when two signals x(t) and y(t) have no similarity, |ρ xy |=0, at which point the two signals are linearly independent. Therefore, ρ xy This indicates the degree of similarity between two signals, 0 < |ρ|. xy |<1,|ρ xy The closer the value is to 1, the higher the similarity between the two signals; conversely, the closer the value is to 1, the lower the similarity is to 1.

[0063] D4: Feedback control steps: Set the required control parameters, and calculate the correlation coefficient of each input frequency by iterating through all values ​​in the interval according to the set control limit and control accuracy. The point with the largest correlation coefficient is the point where the input signal is closest to the theoretical perfect waveform, which is also the optimal input frequency under the current input frequency. The optimal input frequency is transmitted to the inverter circuit for feedback control.

[0064] Let the control precision be j and the control limit be m. Then, the input frequency range is [pm, p+m]. Using p0 = pm as the initial value and j as the parameter increment, we iterate through all points within this range, taking each point as the input frequency. Based on the calculation method described above, we perform signal acquisition and function calculation to obtain the ρ values ​​for all points. xy ,|ρ xy The point with the largest value is the point where the acquired input signal is closest to the theoretical perfect waveform, which is also the optimal frequency under the current input frequency.

[0065] Figure 1 A wireless power transmission system includes a primary-side inverter waveform frequency control system, comprising a wireless power transmitter and a high-frequency inverter circuit, a compensation circuit, and a transmitter control circuit installed at the transmitter. The primary-side inverter waveform frequency control system further includes a voltage sensor installed between the high-frequency inverter circuit and the compensation network, which acquires voltage signals according to a time sequence. The transmitter control circuit includes a waveform detection circuit module and a feedback control circuit module connected to the waveform detection module. The waveform detection circuit module is electrically connected to the voltage sensor, and obtains the acquired signal function X(t) by Fourier transforming the detected voltage signal dataset, and obtains the theoretical signal function Y(t) by Fourier transforming the current input frequency, and calculates the correlation coefficient ρ between the two functions. xyThe correlation coefficient with all points within the selected interval is used to select the frequency corresponding to the point with the largest correlation coefficient, which is the optimal input frequency under the current input. The optimal input frequency is then transmitted to the high-frequency inverter circuit through the feedback control circuit module for optimal control of the primary side waveform.

[0066] The voltage signal dataset first obtains the original waveform function P(t) through interpolation and then performs a Fourier transform. The interpolation formula is as described above, but other interpolation formulas are also possible.

[0067] The acquired signal function is:

[0068]

[0069] The theoretical signal function Y(t) is:

[0070]

[0071] The correlation coefficient ρ xy The formula is:

[0072]

[0073] When x(t) and y(t) are both deterministic signals, ρ xy are real numbers and |ρ xy |<1; When the waveforms of signals x(t) and y(t) are the same, |ρ xy |=1; when two signals x(t) and y(t) have no similarity, |ρ xy | = 0, at this time the two signals are linearly independent; 0 < |ρ xy |<1,|ρ xy The closer the value is to 1, the higher the similarity between the two signals; conversely, the closer the value is to 1, the lower the similarity is to 1.

[0074] Figure 2 In the control flow, the input frequency is first set to p, the voltage to u, the duty cycle to f, the control precision to j, and the control limit to m. Then, p0 = pm is set as the initial value. i For input frequencies ∈ [pm, p+m], the sensor acquires a voltage signal, fits it to obtain a waveform function P(t), performs a Fourier transform on it to obtain the acquired signal function X(t), and then obtains a square wave function Y(t) fitted to the setpoint based on the current input frequency. The correlation coefficient ρ is then calculated using these two functions. xy If p i If ≤p+m, then let p i =p i-1 +j, then return to the sensor's signal acquisition and continue the calculation, iterating through all values ​​within the interval. If it is greater than, then select |ρ. xyThe frequency of the maximum value is the optimal input frequency. This result is transmitted to the inverter circuit for feedback control, so that the primary side automatically operates at the optimal waveform frequency.

Claims

1. A method for controlling the frequency of a primary-side inverter waveform in a wireless power transmission system, comprising the following steps: D1: Feature signal acquisition steps: In the wireless power transmission system, after setting the current input parameters such as current input frequency, voltage and duty cycle, voltage feature signal acquisition is performed at the transmitting end. The voltage signal is acquired according to the time sequence to obtain the original voltage signal dataset. The original input function P(t) is obtained by fitting the acquired voltage signal data. D2: Function fitting steps: Expand the waveform function P(t) based on Fourier transform to obtain the trigonometric function form of the acquired signal function X(t); then, based on the current input frequency, obtain the perfect inverted waveform function: the theoretical signal function Y(t); D3: Steps for calculating the correlation coefficient: Define the correlation coefficient between two functions X(t) and Y(t) as ρ xy Calculate the correlation coefficient ρ between X(t) and Y(t). xy This allows us to determine the degree of correlation between the two functions; D4: Feedback control steps: Set the required control parameters, and calculate the correlation coefficient of each input frequency by iterating through all values ​​in the interval according to the set control limit and control accuracy. The point with the largest correlation coefficient is the point where the input signal is closest to the theoretical perfect waveform, which is also the optimal input frequency under the current input frequency. The optimal input frequency is transmitted to the inverter circuit for feedback control.

2. The method for controlling the frequency of the primary-side inverter waveform in a wireless power transmission system according to claim 1, characterized in that... In D1, the current input frequency is set to p, the voltage to u, and the duty cycle to f. The fitting method is interpolation, which obtains the original waveform function P(t). The interpolation formula is: 。 3. The method for controlling the frequency of the primary-side inverter waveform in a wireless power transmission system according to claim 2, characterized in that... In D2, the Fourier transform theory formula is: Based on the Fourier transform principle, the original function P(t) is expanded and transformed into the trigonometric function form of the acquired signal function X(t): Based on the current input parameters, the theoretical perfect waveform of the signal can be obtained. This waveform is a periodic square wave. The square wave signal function is defined as the theoretical signal function Y(t). The square wave function is expanded based on the Fourier transform principle: Thus, the acquired signal function X(t) and the theoretical signal function Y(t) are obtained.

4. The method for controlling the frequency of the primary-side inverter waveform in a wireless power transmission system according to claim 3, characterized in that... In D3, when the theoretical signal function y(t) approximates the acquired signal x(t), x(t) can be expressed as: x(t)=a xy y(t)+x e (t) Among them, a xy x is the coefficient. e (t) represents the error signal. The smaller the energy of the error signal, the higher the approximation. To minimize the energy of the error signal, the energy of the error signal must be such that it corresponds to the coefficient a. xy The partial differential is 0, thus obtaining the optimal coefficient a. xy for: Therefore ρ xy The expression is: When x(t) and y(t) are both deterministic signals, ρ xy are real numbers and |ρ xy |<1; When the waveforms of signals x(t) and y(t) are the same, |ρ xy |=1; when two signals x(t) and y(t) have no similarity, |ρ xy When | = 0, the two signals are linearly independent, therefore ρ can be used. xy This indicates the degree of similarity between two signals, 0 < |ρ|. xy |<1,|ρ xy The closer the value is to 1, the higher the similarity between the two signals; conversely, the closer the value is to 1, the lower the similarity is to 1.

5. The method for controlling the frequency of the primary-side inverter waveform in a wireless power transmission system according to claim 4, characterized in that... Define the input frequency as pk and the control precision as j. Within the range of [(p-1)k~(p+1)k], select the control precision j, divide all intervals with J (J=10-j) as the interval, calculate the correlation coefficient of all points in the selected interval, and select the point with the largest correlation coefficient as the optimal frequency under the current input.

6. A primary-side inverter waveform frequency control system for a wireless power transmission system, comprising a wireless power transmitter and a high-frequency inverter circuit, a compensation circuit, and a transmitter control circuit disposed at the transmitter, characterized in that, It also includes a voltage sensor installed between the high-frequency inverter circuit and the compensation network, which acquires voltage signals according to a timing sequence; the transmitter control circuit includes a waveform detection circuit module and a feedback control circuit module connected to the waveform detection circuit module. The waveform detection circuit module is electrically connected to the voltage sensor, and obtains the acquired signal function X(t) by Fourier transforming the detected voltage signal dataset, and obtains the theoretical signal function Y(t) by Fourier transforming the current input frequency, and calculates the correlation coefficient ρ between the two functions. xy It iterates through all points within the selected interval, selects the input frequency corresponding to the point with the largest correlation coefficient as the optimal input frequency under the current input, and transmits the optimal input frequency to the high-frequency inverter circuit through the feedback control circuit module for optimal control of the primary side waveform.

7. The primary-side inverter waveform frequency control system for a wireless power transmission system according to claim 6, characterized in that: The voltage signal dataset is first obtained by interpolation to obtain the original waveform function P(t), and then Fourier transform is performed. The interpolation formula is: 。 8. The primary-side inverter waveform frequency control system for a wireless power transmission system according to claim 7, characterized in that: The Fourier transform theory formula is as follows: 。 9. The primary-side inverter waveform frequency control system for a wireless power transmission system according to claim 8, characterized in that: The acquired signal function is: The theoretical signal function Y(t) is:

10. The primary-side inverter waveform frequency control system for a wireless power transmission system according to claim 9, characterized in that: The correlation coefficient ρ xy The formula is: When x(t) and y(t) are both deterministic signals, ρ xy are real numbers and |ρ xy |<1; When the waveforms of signals x(t) and y(t) are the same, |ρ xy |=1; when two signals x(t) and y(t) have no similarity, |ρ xy | = 0, at this time the two signals are linearly independent; 0 < |ρ xy |<1,|ρ xy The closer the value is to 1, the higher the similarity between the two signals; conversely, the closer the value is to 1, the lower the similarity is to 1.

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