阅读说明：本技术 一种基于模糊pi的频率跟踪搜索方法 (Fuzzy PI-based frequency tracking search method ) 是由 练圣哲 王�忠 于 2020-07-22 设计创作，主要内容包括：本发明公开了一种基于模糊PI的频率跟踪搜索方法,包括：根据超声换能器两端电压电流的相位差计算当前时刻超声换能器的相位差变化率；根据当前时刻的所述相位差和相位差变化率模糊推理得到频率变化标识符；根据所述频率变化标识符判断变步长级别,并在所述变步长级别内指数化PI参数；根据所述PI参数确定超声换能器下一步步长的变化量,并计算超声换能器下一步的输出频率。本发明采用模糊PI全频域搜索和跟踪,使用者不需要设定初始频率,也不需要了解换能器的谐振频率,即能直接快速搜索到谐振频率。(The invention discloses a frequency tracking search method based on fuzzy PI, which comprises the following steps: calculating the phase difference change rate of the ultrasonic transducer at the current moment according to the phase difference of the voltage currents at the two ends of the ultrasonic transducer; obtaining a frequency change identifier according to the phase difference and the phase difference change rate fuzzy inference at the current moment; judging a variable step size level according to the frequency change identifier, and indexing a PI parameter in the variable step size level; and determining the variable quantity of the next step of the ultrasonic transducer according to the PI parameter, and calculating the next step of output frequency of the ultrasonic transducer. The invention adopts the fuzzy PI full frequency domain search and tracking, and the user can directly and quickly search the resonant frequency without setting the initial frequency and knowing the resonant frequency of the transducer.)

1. A frequency tracking search method based on fuzzy PI is characterized by comprising the following steps:

calculating the phase difference change rate of the ultrasonic transducer at the current moment according to the phase difference of the voltage currents at the two ends of the ultrasonic transducer;

obtaining a frequency change identifier according to the phase difference and the phase difference change rate fuzzy inference at the current moment;

judging a variable step size level according to the frequency change identifier, and indexing a PI parameter in the variable step size level;

and determining the variable quantity of the next step of the ultrasonic transducer according to the PI parameter, and calculating the next step of output frequency of the ultrasonic transducer.

2. The method according to claim 1, wherein the calculation formula of the phase difference change rate of the ultrasonic transducer is:

in the formula (I), the compound is shown in the specification,is the rate of change of the phase difference of the ultrasound transducer,the phase difference of the voltage and the current at two ends of the ultrasonic transducer at the current moment,the phase difference of the voltage and the current at two ends of the ultrasonic transducer at the previous moment.

3. The method for searching for frequency tracking based on fuzzy PI as claimed in claim 1, wherein said frequency variation identifier is obtained by: and (4) reasoning by adopting a gravity center method according to a preset fuzzy rule.

4. The frequency tracking search method based on the fuzzy PI as claimed in claim 3, wherein the preset fuzzy rule is

。

5. The method of claim 1, wherein indexing the PI parameters comprises: and calculating a proportional coefficient of PI regulation and a differential coefficient of PI regulation.

6. The method as claimed in claim 5, wherein the PI-adjusted scaling factor is calculated by the following formula:

the calculation formula of the differential coefficient of the PI regulation is as follows:

in the formula, Kp is proportional coefficient of PI regulation, Ki is differential coefficient of PI regulation, flag is frequency change identifier, and the change range of flag is [0,7.5 ]]K is a change direction identifier, and Z is an adjustment coefficient; when flag is greater than 4, k is 2; when flag is < 4, k is 1, whenWhen the flag is set to be =4,stopping frequency searching; flag is in [0,2.5 ]]U[5.5,7.5]When internal, Z is 5; flag in [2.5,5.5 ]]And when inside, Z is 4.

7. The method as claimed in claim 1, wherein the calculation formula of the variation of the next step size of the ultrasonic transducer is:

in the formula, df is the variation of the next step length of the ultrasonic transducer, Kp is the proportional coefficient of PI regulation, Ki is the differential coefficient of PI regulation,the phase difference of the voltage and the current at two ends of the ultrasonic transducer at the current moment,the phase difference of the voltage and the current at two ends of the ultrasonic transducer at the previous moment.

8. The method as claimed in claim 1, wherein the following formula of the output frequency of the ultrasonic transducer is:

in the formula (I), the compound is shown in the specification,for the next step of the output frequency of the ultrasound transducer,is ultraThe current output frequency of the transducer, df, is the amount of change in the next step of the ultrasound transducer.

Technical Field

The invention belongs to the technical field of ultrasonic frequency tracking, and particularly relates to a frequency tracking search method based on fuzzy PI.

Background

Ultrasonic waves refer to sound waves having a frequency greater than 20kHz and are known as ultrasonic waves because they exceed the upper limit of human hearing. At present, ultrasonic waves can generate mechanical effect, cavitation effect, chemical effect and thermal effect, and are widely applied to the fields of cleaning, detection, processing, welding and the like.

When the ultrasonic transducer works in a resonance state, the output power of the ultrasonic transducer is the maximum, and an impedance matching technology and a frequency tracking technology become two key technologies for the ultrasonic transducer to work in the resonance state, and the ultrasonic technology just utilizes the principle to generate ultrasonic waves. Due to the influences of various factors such as load change of the ultrasonic transducer, aging of the ultrasonic transducer and the like, dynamic parameters or static parameters of the ultrasonic transducer can change, and the ultrasonic transducer is in a detuning state. Therefore, in order to make the ultrasonic transducer work in a resonance state for a long time, frequency tracking of the ultrasonic transducer becomes a big hot problem in the field of ultrasonic research.

Wahlin, Liuli morning and the like use a PI-DDS algorithm to realize frequency tracking, and the tracking method is high in speed and good in performance, but the tracking range is small. Licharlin, Quibada and the like adopt a fuzzy control algorithm to track the frequency, and noble and the like adopt a maximum likelihood estimation method to estimate the parameters of the transducer, so that the tracking algorithm for the frequency is realized, and the parameters are inaccurate due to the limitation of sampling. Summer xu peak, autumn lin et al propose a fuzzy PI-based frequency tracking algorithm, but because of the design deficiency of fuzzy language clarity, the initial frequency can only be realized by a fast frequency sweep. Although the dichotomy proposed by Pengxiang et al and the variable-step frequency sweeping method proposed by Lechang et al solve the frequency sweeping problem, the frequency sweeping speed is too slow.

Disclosure of Invention

The invention aims to provide a frequency tracking search method based on fuzzy PI, which overcomes the defects of the prior art in frequency tracking speed and frequency tracking range and breaks the mutual restriction between the frequency tracking speed and the frequency tracking range.

The purpose of the invention is realized by the following technical scheme: a frequency tracking search method based on fuzzy PI comprises the following steps:

calculating the phase difference change rate of the ultrasonic transducer at the current moment according to the phase difference of the voltage currents at the two ends of the ultrasonic transducer;

obtaining a frequency change identifier according to the phase difference and the phase difference change rate fuzzy inference at the current moment;

judging a variable step size level according to the frequency change identifier, and indexing a PI parameter in the variable step size level;

and determining the variable quantity of the next step of the ultrasonic transducer according to the PI parameter, and calculating the next step of output frequency of the ultrasonic transducer.

Preferably, the calculation formula of the phase difference change rate of the ultrasonic transducer is as follows:

in the formula (I), the compound is shown in the specification,is the rate of change of the phase difference of the ultrasound transducer,the phase difference of the voltage and the current at two ends of the ultrasonic transducer at the current moment,the phase difference of the voltage and the current at two ends of the ultrasonic transducer at the previous moment.

Preferably, the method for acquiring the frequency change identifier includes: and (4) reasoning by adopting a gravity center method according to a preset fuzzy rule.

Preferably, the preset fuzzy rule is

。

Preferably, the indexed PI parameters include: and calculating a proportional coefficient of PI regulation and a differential coefficient of PI regulation.

Preferably, the calculation formula of the proportional coefficient for PI adjustment is as follows:

the calculation formula of the differential coefficient of the PI regulation is as follows:

in the formula, Kp is proportional coefficient of PI regulation, Ki is differential coefficient of PI regulation, flag is frequency change identifier, and the change range of flag is [0,7.5 ]]K is a change direction identifier, and Z is an adjustment coefficient; when flag is greater than 4, k is 2; when flag < 4, k is 1, when flag =4,stopping frequency searching; flag is in [0,2.5 ]]U[5.5,7.5]When internal, Z is 5; flag in [2.5,5.5 ]]And when inside, Z is 4.

Preferably, the calculation formula of the variation of the next step size of the ultrasonic transducer is as follows:

in the formula, df is the variation of the next step length of the ultrasonic transducer, Kp is the proportional coefficient of PI regulation, Ki is the differential coefficient of PI regulation,the phase difference of the voltage and the current at two ends of the ultrasonic transducer at the current moment,the phase difference of the voltage and the current at two ends of the ultrasonic transducer at the previous moment.

Preferably, the following calculation formula of the output frequency of the ultrasonic transducer is:

in the formula (I), the compound is shown in the specification,for the next step of the output frequency of the ultrasound transducer,df is the amount of change in the next step of the ultrasonic transducer, which is the current output frequency of the ultrasonic transducer.

The invention has the beneficial effects that:

(1) the invention adopts the fuzzy PI full frequency domain search and tracking, and a user can directly and quickly search the resonant frequency without setting the initial frequency and knowing the resonant frequency of the transducer;

(2) the transducer state is identified through the phase difference and the phase difference change rate, so that the step length is adjusted, and the condition that the parallel resonance point is tracked cannot occur;

(3) the method can search the vicinity of the resonant frequency in 18 steps, and then dynamically track the resonant frequency; starting from any frequency, the search efficiency is about 40% higher than that of the ordinary PI variable step size search;

(4) the performance of the method is superior to that of the common PI variable step tracking, because the parameters of the method are in dynamic adjustment, the method has the advantages of both step length adjustment and adjustment precision; the ordinary PI variable step tracking algorithm is fixed with parameters in a certain range, so that the tracking step change rate is limited;

(5) the exponential change step of this patent can make the change step change between 1Hz to 100 kHz.

Drawings

FIG. 1 is a flow chart of a fuzzy PI based frequency tracking search method;

FIG. 2 is a schematic block diagram of fuzzy PI control;

FIG. 3 is a plot of a fuzzy function of phase difference of voltage current across an ultrasonic transducer;

fig. 4 is a graph of a blurring function of a rate of change of phase difference of an ultrasonic transducer.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.

Referring to fig. 1 to 4, the present invention provides a frequency tracking search method based on a fuzzy PI:

as shown in fig. 1, a frequency tracking search method based on fuzzy PI includes:

and S1, calculating the phase difference change rate of the ultrasonic transducer at the current moment according to the phase difference of the voltage current at the two ends of the ultrasonic transducer.

The calculation formula of the phase difference change rate of the ultrasonic transducer is as follows:

in the formula (I), the compound is shown in the specification,is the rate of change of the phase difference of the ultrasound transducer,the phase difference of the voltage and the current at two ends of the ultrasonic transducer at the current moment,the phase difference of the voltage and the current at two ends of the ultrasonic transducer at the previous moment.

And S2, obtaining a frequency change identifier according to the phase difference and the phase difference change rate fuzzy inference at the current moment.

As shown in fig. 2, the input fuzzification in the present embodiment uses a typical function design, fuzzifies the input function according to the phase change characteristics of the ultrasonic transducer, and fine-tunes the parameters in actual debugging. The phase difference of the voltage current at two ends of the ultrasonic transducer is in the range of [ -1.57,1.57], the domain of ambiguity is [ NB NM NS ZO PS PB ], and the curve of the ambiguity function is shown in FIG. 3. After the phase difference change rate of the ultrasonic transducer is amplified, the change range is [ -2,2], the ambiguity domain is [ NB NMNS ZO PS PB ], and the ambiguity function curve is shown in FIG. 4.

The method for acquiring the frequency change identifier comprises the following steps: and (4) reasoning by adopting a gravity center method according to a preset fuzzy rule.

The preset fuzzy rule is

。

Fuzzy rules take the form of fuzzy conditional inference if E is NM and EC is NS, Then U is NM. In order to avoid searching the parallel resonance frequency, when a fuzzy rule is established, the parallel resonance frequency characteristic is judged, namely, when the fuzzy controller tracks the parallel resonance frequency, the frequency range can be avoided.

And S3, judging a variable step size level according to the frequency change identifier, and indexing the PI parameter in the variable step size level.

The indexed PI parameters include: and calculating a proportional coefficient of PI regulation and a differential coefficient of PI regulation.

The calculation formula of the proportional coefficient regulated by the PI is as follows:

the calculation formula of the differential coefficient of the PI regulation is as follows:

in the formula, Kp is proportional coefficient of PI regulation, Ki is differential coefficient of PI regulation, flag is frequency change identifier, and the change range of flag is [0,7.5 ]]K is a change direction identifier, and Z is an adjustment coefficient; when flag is greater than 4, k is 2; when flag < 4, k is 1, when flag =4,stopping frequency searching; flag is in [0,2.5 ]]U[5.5,7.5]When internal, Z is 5; flag in [2.5,5.5 ]]And when inside, Z is 4.

The variation of the next step of the ultrasonic transducer in this embodiment can be increased (df can be in the range of 1-106). When large-step search is needed, the step length is large enough; when small step tracking is required, the step size can be taken small enough. Therefore, the method can realize the quick search of the full frequency and the tracking of the resonant frequency neighborhood.

And S4, determining the variable quantity of the next step length of the ultrasonic transducer according to the PI parameter, and calculating the next step output frequency of the ultrasonic transducer.

The calculation formula of the variation of the next step length of the ultrasonic transducer is as follows:

in the formula, df is the variation of the next step length of the ultrasonic transducer, Kp is the proportional coefficient of PI regulation, Ki is the differential coefficient of PI regulation,the phase difference of the voltage and the current at two ends of the ultrasonic transducer at the current moment,the phase difference of the voltage and the current at two ends of the ultrasonic transducer at the previous moment.

The calculation formula of the next output frequency of the ultrasonic transducer is as follows:

in the formula (I), the compound is shown in the specification,for the next step of the output frequency of the ultrasound transducer,df is the amount of change in the next step of the ultrasonic transducer, which is the current output frequency of the ultrasonic transducer.

The foregoing is illustrative of the preferred embodiments of this invention, and it is to be understood that the invention is not limited to the precise form disclosed herein and that various other combinations, modifications, and environments may be resorted to, falling within the scope of the concept as disclosed herein, either as described above or as apparent to those skilled in the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.