Ultrasonic transducer parallel resonance point frequency detection tracking adjustment method and device

Abstract

The invention relates to the field of ultrasonic power supplies, in particular to an ultrasonic transducer parallel resonance point frequency detecting, tracking and adjusting method and device. The ultrasonic power supply load parallel resonance point frequency phase lock adjusting device specifically comprises an ultrasonic power supply converter, a matching network circuit, a transducer load circuit and an adjuster. Parameters of the parallel inductor are matched by analyzing the characteristic relation between the ultrasonic power supply and the transducer load, the input current I2 at one end of the L0, the current I1 output to the ultrasonic transducer from the end and the current I0 of the inductor L0 are obtained through calculation, and the phase angle alpha between the I1 and the I2 is obtained through calculation according to the input current I2, the current I1 output to the ultrasonic transducer from the end and the current I0 of the inductor L0. And the frequency of the power supply or the input current I2 at one end of the inductor L0 is adjusted according to the cos alpha, so that the circuit is located at a resonance point. Compared with the prior art, the method can effectively solve the problem that the frequency cannot be adjusted in time by adapting to the load change during frequency adjustment, and enables the system to quickly respond to the frequency change of the load and to accurately work at the parallel resonance point.

Description

Technical Field

[0001] The invention relates to the field of ultrasonic power supplies, and in particular to a device and method for detecting, tracking and adjusting the frequency of a parallel resonance point of an ultrasonic transducer. Background Art

[0002] Ultrasonic power supplies are widely used in ultrasonic cleaning, welding, cutting and other fields. Existing ultrasonic systems are mainly composed of ultrasonic power supplies, transducers, horns, welding heads, etc. The function of ultrasonic power supplies is to convert electrical energy into high-frequency AC signals that match ultrasonic transducers, while transducers are devices that convert ultrasonic electrical energy into mechanical vibrations.

[0003] The transducer is generally equivalent to a series-parallel circuit of resistors, inductors and capacitors due to its structural design. The electrical energy in the entire system is loaded onto the transducer, and the transducer converts the electrical energy into ultrasonic energy. To achieve maximum power transmission, the electrical energy frequency is generally required to work at the parallel resonance point or series resonance point of the transducer equivalent circuit. During the operation of the system, due to the temperature of piezoelectric devices such as ultrasonic transducers, the size of welds, the wear of welding heads, and the sudden increase and decrease of loads, the equivalent capacitance, inductance and resistance of the ultrasonic load will change with the operation, and then the inherent resonant frequency point of the ultrasonic system will shift. If the power output frequency of the ultrasonic generator does not follow the change, the ultrasonic system will not work at the resonant point, reducing the working efficiency. In severe cases, the ultrasonic system will work in the resonant amplification area of ​​other frequencies, thereby damaging the ultrasonic transducer. Therefore, the inverter trigger frequency of the ultrasonic power supply needs to follow the resonant frequency of the transducer load.

[0004] The prior art discloses a method for tracking the resonant frequency of an ultrasonic power supply (publication number: CN113934137B), comprising the following steps: S1, constructing an LC series matching circuit, and connecting the LC series matching circuit between the ultrasonic power supply and the transducer; realizing initial adjustment of matching the output frequency of the ultrasonic power supply and the resonant frequency of the transducer through the LC series matching circuit; S2, detecting the current signal output by the transducer; S3, constructing a differential link phase-locked loop, and connecting the output end of the differential link phase-locked loop to the input end of a PWM signal generator; using the current signal output by the transducer in S2 as the input signal of the differential link phase-locked loop; according to the output signal of the differential link phase-locked loop, the PWM signal generator generates a driving signal; S4, the driving signal generated in S3 drives the switching tube in the ultrasonic power supply to turn on and off to adjust the output frequency of the ultrasonic power supply, so that the output frequency of the ultrasonic power supply changes with the change of the resonant frequency of the transducer. By constructing a differential phase-locked loop and using a DDS signal generator combined with a differential phase-locked loop to achieve closed-loop control, the output frequency of the ultrasonic power supply can quickly track the change of the resonant frequency of the transducer, so that the ultrasonic power supply works in a resonant state. However, this invention still has some defects. When tracking the frequency, it is difficult to ensure that the entire working circuit is in a resonant state in the presence of disturbances, and it is difficult to take into account the stability of the circuit when ensuring rapid frequency tracking. Summary of the invention

[0005] The purpose of the present invention is to solve the problem that the prior art cannot timely adjust the frequency to adapt to load changes during frequency adjustment, and proposes a device and method for detecting, tracking and adjusting the frequency of the parallel resonance point of an ultrasonic transducer.

[0006] On the one hand, the present invention provides a method for detecting, tracking and adjusting the frequency of a parallel resonance point of an ultrasonic power supply load, including an inductor L0 connected in parallel at both ends of an ultrasonic transducer, and comprising the following steps:

[0007] S1. Measure the input current I2 at one end of the inductor L0 and the current I1 output from the end to the ultrasonic transducer to obtain the current I0 flowing through the inductor L0;

[0008] S2. Calculate the phase angle α between I1 and I2

[0009]

[0010] Where: I2 is the input current at one end of the inductor L0, I1 is the current output from this end to the ultrasonic transducer, and I0 is the current of the inductor L0;

[0011] S3. If cosα>0 or cosα<0, the frequency of the power supply or the input current I2 at one end of the inductor L0 is operated.

[0012] Preferably, the current I0 flowing through the inductor L0 in S1 is obtained by directly measuring the inductor L0 through a detection unit to obtain the current I0, or by measuring the voltage V0 across the inductor L0 and then obtaining I0. The calculation process of I0 is as follows:

[0013]

[0014] Wherein: f is the frequency of the input power supply, V0 is the voltage across the inductor L0, and L0 is the inductance.

[0015] Preferably, the operation of the frequency of the power supply or the input current I2 at one end of the inductor L0 in S3 includes:

[0016] When cosα>0, the frequency of the input power supply is increased, or the input current I2 at one end of the inductor L0 is reduced;

[0017] When cosα<0, the frequency of the input power supply is reduced, or the input current I2 at one end of the inductor L0 is increased.

[0018] On the other hand, an ultrasonic transducer parallel resonance point frequency detection tracking and adjustment device includes an ultrasonic power converter, a matching network circuit, a transducer load circuit, and a regulator;

[0019] Preferably, the output end of the ultrasonic power converter is connected to the matching network circuit, and the output end of the matching network circuit is connected to the transducer load circuit; the regulator adjusts and controls the power output frequency according to the angle relationship between the power input current at the front end of the parallel inductor and the output current at the transducer end at the rear end of the parallel inductor;

[0020] The ultrasonic power converter is connected to a matching network;

[0021] The matching network is connected to an ultrasonic power converter and a transducer load circuit;

[0022] The transducer load circuit is connected to a matching network;

[0023] The ultrasonic power converter is composed of an inverter power module, and the output frequency of the power converter is changed by adjusting the PWM frequency;

[0024] The matching network is composed of capacitors and inductors, and is used to match the equivalent parameters of the transducer, achieve the matching system resonance point and filter the output of the inverter power module;

[0025] The transducer load circuit can be equivalent to an equivalent circuit composed of resistance, inductance and capacitance.

[0026] Further preferably, the equivalent circuit of the transducer load circuit specifically includes R as a resistor, C0 as a capacitor, C1 as a dynamic capacitor, and L1 as a dynamic inductor; the specific circuit is that the resistor R, the dynamic inductor L1 and the dynamic capacitor C1 are connected in series and then in parallel with the capacitor C0 to form the equivalent circuit of the transducer load circuit; the transducer load circuit is connected in parallel with the matching inductor L0 in the matching network circuit.

[0027] Preferably, the phase angle calculation of the resonance point frequency is realized, specifically comprising the following steps:

[0028] Step A, calculating the system impedance according to the equivalent circuit of the matching network circuit and the transducer load circuit, and calculating the transfer function between the front-end power input of the inductor L0 and the rear-end transducer output of the inductor L0 according to the system impedance;

[0029] Step B, input specific circuit parameters to calculate the phase angle between the power input current at the front end of the inductor L0 and the output current at the transducer end at the rear end of the inductor L0, and compare to obtain the phase angle that can make the transducer work in parallel resonance state.

[0030] Further preferably, the calculation of the system impedance is specifically as follows:

[0031]

[0032] Where: Z z is the system impedance, R is the resistance, s is the Laplace operator, C0 is the static capacitance, C1 is the dynamic capacitance, L0 is the matching inductor, and L1 is the dynamic inductor;

[0033] The power input at the front end of the inductor L0 is recorded as I2, and the output at the transducer end at the rear end of the inductor L0 is recorded as I1.

[0034] The transfer functions of I1 and I2 are obtained based on the calculated system impedance, as follows:

[0035]

[0036] Wherein: I2 is the power input current of the front end of the inductor L0, I1 is the output current of the transducer end of the rear end of the inductor L0, R is the resistance, S is the Laplace operator, C0 is the static capacitance, C1 is the dynamic capacitance, L0 is the matching inductor, and L1 is the dynamic inductor;

[0037] Further preferably, multiple groups of specific parameters are brought into the step Step B for calculation, and the obtained results prove that when the phase of I1 / I2 presents a 90-degree relationship, that is, when the cosine value of the phase angle is 0, it is in a parallel resonance point working state.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The present invention provides a device and method for detecting, tracking and adjusting the frequency of the parallel resonance point of an ultrasonic transducer. By analyzing the characteristic relationship between the ultrasonic power supply and the transducer load, matching the parallel inductance parameters, and calculating the input current I2 at one end of L0, the current I1 output from this end to the ultrasonic transducer and the current I0 of the inductance L0, and thereby calculating the phase angle α between I1 and I2, the frequency of the power supply or the input current I2 at one end of the inductance L0 is adjusted according to cosα, so that the circuit is at the resonance point. Compared with the prior art, the present invention adopts the method of using cosα as the adjustment basis, and cooperates with the circuit to adjust the frequency of the power supply or the input current I2 at one end of the inductance L0, which can effectively solve the problem of being unable to adjust the frequency in time to adapt to load changes when adjusting the frequency, so that the system can quickly respond to the frequency changes of the load and accurately work at the parallel resonance point. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of a regulator in an embodiment of the present invention.

[0041] Figure 2 It is a schematic diagram of the parallel matching inductor and transducer in an embodiment of the present invention.

[0042] Figure 3 1 is an equivalent circuit diagram of a parallel matching inductor and a transducer in an embodiment of the present invention.

[0043] Figure 4 is a vector diagram of the three currents I0, I1, and I2 in the embodiment of the present invention. DETAILED DESCRIPTION

[0044] The present invention is further described in detail below in conjunction with test examples and specific implementation methods. However, this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments, and all technologies realized based on the content of the present invention belong to the scope of the present invention.

[0045] Example 1

[0046] The purpose of the present invention is to solve the problem that the prior art cannot adapt to load changes during frequency adjustment, and to propose a device and method for detecting, tracking and adjusting the frequency of the parallel resonance point of an ultrasonic transducer.

[0047] A method for detecting, tracking and adjusting the frequency of a parallel resonance point of an ultrasonic transducer comprises the following steps:

[0048] S1. Calculate the system impedance of the equivalent circuit of the matching network circuit and the transducer load circuit, and calculate the transfer function between the front-end power input of the inductor L0 and the rear-end transducer output of the inductor L0 according to the system impedance;

[0049] S2, bring in specific parameters to calculate the phase angle between the power input at the front end of the inductor L0 and the output at the transducer end at the rear end of the inductor L0, and compare to obtain the phase angle that can make the transducer work in parallel resonance;

[0050] S3, measuring the input current I2 at one end of the inductor L0 and the current I1 output from the end to the ultrasonic transducer, and obtaining the voltage V0 flowing through the inductor L0.

[0051] S4, input the input current I2 at one end of the inductor L0, the current I1 output from the end to the ultrasonic transducer, and the voltage V0 across the inductor L0 into the conversion module, such as Figure 1 As shown;

[0052] S5. Perform judgment according to the result cosα calculated by the conversion module. If cosα>0 or cosα<0, operate the frequency of the power supply or the input current I2 at one end of the inductor L0.

[0053] The converter can calculate the current I0 of the inductor L0 according to the voltage V0 across the inductor L0, and obtain the phase angle α between I1 and I2. The calculation process includes:

[0054]

[0055] Where: I2 is the input current at one end of the inductor L0, I1 is the current output from this end to the ultrasonic transducer, and I0 is the current of the inductor L0;

[0056] By calculating cosα, a parameter reflecting the working state of the circuit can be obtained. According to the parameter, the present invention adjusts the frequency of the power supply in the circuit or the input current I2 at one end of the inductor L0 through a regulator to always maintain the resonant point frequency.

[0057] Wherein, by measuring the voltage V0 across the inductor L0, I0 is obtained, and the calculation process of I0 is as follows:

[0058]

[0059] Wherein: f is the frequency of the input power supply, V0 is the voltage across the inductor L0, and L0 is the inductance.

[0060] Furthermore, the method of obtaining the current I0 flowing through the inductor L0 also includes directly measuring the inductor L0 by a detection unit to obtain the current I0. According to both methods, the current I0 of the inductor L0 required for cosα can be calculated.

[0061] The operation of the frequency of the power supply or the input current I2 at one end of the inductor L0 in S5 includes:

[0062] When cosα>0, the frequency of the input power supply is increased, or the input current I2 at one end of the inductor L0 is reduced;

[0063] When cosα<0, the frequency of the input power supply is reduced, or the input current I2 at one end of the inductor L0 is increased.

[0064] Obtaining cosα by measuring and adjusting according to cosα can effectively solve the problem of the prior art that the frequency cannot be adjusted in time to adapt to load changes during frequency adjustment.

[0065] The present embodiment provides an ultrasonic transducer parallel resonance point frequency detection, tracking and adjustment device, including an ultrasonic power converter, such as Figure 2 As shown, a matching network circuit, a transducer load circuit, and a regulator are also included;

[0066] The step of implementing circuit regulation by the regulator includes:

[0067] S1. Measure the input current I2 at one end of the inductor L0 and the current I1 output from the end to the ultrasonic transducer to obtain the current I0 flowing through the inductor L0;

[0068] S2. Calculate the phase angle α between I1 and I2

[0069]

[0070] Where: I2 is the input current at one end of the inductor L0, I1 is the current output from this end to the ultrasonic transducer, and I0 is the current of the inductor L0;

[0071] S3. When cosα>0, increase the frequency of the input power supply, or reduce the input current I2 at one end of the inductor L0; when cosα<0, reduce the frequency of the input power supply, or increase the input current I2 at one end of the inductor L0.

[0072] The output end of the ultrasonic power converter is connected to the matching network circuit, and the output end of the matching network circuit is connected to the transducer load circuit;

[0073] The regulator adjusts and controls the power supply output frequency according to the angle relationship between the power supply input current at the front end of the parallel inductor and the output current at the transducer end at the rear end of the parallel inductor;

[0074] The ultrasonic power converter is composed of an inverter power module, and the output frequency of the power converter is changed by adjusting the PWM frequency;

[0075] The matching network is composed of capacitors and inductors, and is used to match the equivalent parameters of the transducer, achieve the matching system resonance point and filter the output of the inverter power module;

[0076] The transducer load circuit can be equivalent to an equivalent circuit composed of resistance, inductance and capacitance.

[0077] The ultrasonic power converter is composed of an inverter power module, and the output frequency of the power converter is changed by adjusting the PWM frequency. The matching network is generally composed of an inductor and a capacitor. By matching the equivalent parameters of the transducer, the purpose of matching the resonance point of the system and filtering the output of the inverter power module is achieved. L2 and C2 of the ultrasonic power system can match the resonance point of the transducer at a conventional frequency point, that is, the nominal center frequency of the transducer component can be selected for matching, and no precise matching is required. Even if the transducer frequency point is offset or there is a deviation in the component, the present invention can accurately track the offset resonance frequency point.

[0078] The ultrasonic transducer load can be equivalent to a static capacitor C0, a dynamic resistor R1, a dynamic inductor L1, and a dynamic capacitor C1. The specific circuit is that the resistor R, the dynamic inductor C1 and the dynamic capacitor L1 are connected in series and then in parallel with the capacitor C0 to form an equivalent circuit of the transducer load circuit. The equivalent circuit diagram is as follows: Figure 3 As shown;

[0079] The transducer load circuit is connected in parallel with the inductor L0 in the matching network circuit, such as Figure 3 shown.

[0080] Analyze the entire circuit, detect the I2 and I1 currents, and perform transfer function analysis on them:

[0081] Depend on Figure 3 The impedance of the entire system is obtained from the circuit in:

[0082]

[0083] The power input at the front end of the parallel inductor is I2, and the output at the transducer end at the rear end of the parallel inductor is I1. The relationship between I1 and I2 in this input and output situation can be obtained as follows:

[0084]

[0085] Simplifying gives the general transfer function form:

[0086]

[0087] All devices here are unknown, and the phase angle required for the resonant frequency cannot be verified. To achieve the best phase angle selection, the matching parameter L0 is selected according to the transducer parameters. This embodiment selects a set of parameters as an illustration to illustrate the basic principle algorithm. The selected transducer parameters are as follows:

[0088] L1=2730.94uH; R=30.1614Ω; C1=0.02336nF; C0=19.6417nF;

[0089] The matching inductor parameters are as follows:

[0090] L0=3.4mH;

[0091] According to the selected transducer parameters and matching inductor parameters, the transducer parallel resonant frequency is calculated as follows:

[0092]

[0093] It is calculated that the phase angle of the ratio I2 / I1 of the power input I2 at the front end of the parallel inductor and the output I1 at the transducer end at the rear end of the parallel inductor at the resonant frequency is:

[0094] θ=89.8°

[0095] In order to simulate the reversible parameter fluctuation under the actual working state, it is assumed that the matching inductance parameter L0 has a certain amplitude drop, and the matching inductance parameter L0 = 3.4 * 80% = 2.72mH, then the phase angle is:

[0096] θ=90.7°

[0097] Assuming that the matching inductance parameter L0 increases by a certain amount, becoming L0 = 3.4*120% = 4.08mH, the phase angle is:

[0098] θ=88.9°

[0099] According to the analysis of the calculation results, whether the matching inductance parameters decrease or increase by 20%, the impact on the final calculated phase angle result is within the error range. At the same time, the 20% amplitude fluctuation can cover the matching inductance parameter fluctuations in most actual working scenarios, so it can be determined that the change in the matching inductance parameters has a negligible impact on the angle of the resonant frequency point.

[0100] The calculation results show that, Figure 4As shown, when the phase angle of the ratio I2 / I1 of the power input I2 at the front end of the parallel inductor and the output I1 at the rear end of the transducer of the parallel inductor at the resonant frequency is 90 degrees, it must be in the parallel resonance point working state.

[0101] In the actual system, the ultrasonic power supply parameter matching corresponds to a certain frequency range for effective control. For example, for a 20kHz ultrasonic power supply, the resonant frequency range of the transducer load it can carry can be 20kHz±1kHz, which is the effective working range. This system performs phase identification of I2 and I1 within this frequency range, performs filtering and phase locking, and ultimately ensures that the phase difference between I2 and I1 is around 90°, thereby locking the parallel resonant frequency.

[0102] The above is just an example of a controller design method. You can also use a high-speed AD to sample the I1 and I2 currents, and then use Fourier calculation decomposition to get the phase between the I1 and I2 currents, and then adjust the frequency to reach 90°. The form is not limited, as long as the phase angle of I1 and I2 can be controlled to the control target of 90 degrees.

Claims

1. A method for detecting, tracking and adjusting the frequency of a parallel resonance point of an ultrasonic power supply load, comprising an inductor L0 connected in parallel at both ends of an ultrasonic transducer, characterized in that: The following steps are involved: S1. Measure the input current I2 at one end of the inductor L0 and the current I1 output from the end to the ultrasonic transducer to obtain the current I0 flowing through the inductor L0; S2. Calculate the phase angle α between I1 and I2 Where: I2 is the input current at one end of the inductor L0, I1 is the current output from this end to the ultrasonic transducer, and I0 is the current of the inductor L0; S3. If cosα>0 or cosα<0, the frequency of the power supply or the input current I2 at one end of the inductor L0 is operated.

2. The method for detecting, tracking and adjusting the frequency of a parallel resonance point of an ultrasonic power supply load according to claim 1, characterized in that: The method of obtaining the current I0 flowing through the inductor L0 in S1 is to directly measure the inductor L0 through a detection unit to obtain the current I0, or to measure the voltage V0 across the inductor L0 and then obtain I0. The calculation process of I0 is as follows: Wherein: f is the frequency of the input power supply, V0 is the voltage across the inductor L0, and L0 is the inductance.

3. The method for detecting, tracking and adjusting the frequency of an ultrasonic power supply load parallel resonance point according to claim 1, characterized in that: The operation of the frequency of the power supply or the input current I2 at one end of the inductor L0 in S3 includes: When cosα>0, the frequency of the input power supply is increased, or the input current I2 at one end of the inductor L0 is reduced; When cosα<0, the frequency of the input power supply is reduced, or the input current I2 at one end of the inductor L0 is increased.

4. An ultrasonic transducer parallel resonance point frequency detection, tracking and adjustment device comprises an ultrasonic power converter, a matching network circuit, and a transducer load circuit, characterized in that: A regulator is also included; The output end of the ultrasonic power converter is connected to the matching network circuit, and the output end of the matching network circuit is connected to the transducer load circuit; The ultrasonic power converter is composed of an inverter power module, and the output frequency of the power converter is changed by adjusting the PWM frequency; The matching network is composed of capacitors and inductors, and is used to match the equivalent parameters of the transducer, achieve the matching system resonance point and filter the output of the inverter power module; The transducer load circuit is equivalent to an equivalent circuit composed of resistance, inductance and capacitance; The regulator regulates and controls the frequency of the power supply or the input current at one end of the inductor according to the phase relationship between the power input current at the front end of the parallel inductor and the output current at the transducer end at the rear end of the parallel inductor.

5. The ultrasonic power supply load parallel resonance point frequency detection, tracking and adjustment device according to claim 4, characterized in that: The equivalent circuit of the transducer load circuit includes a resistor R, a capacitor C0, a dynamic capacitor C1, a dynamic inductor L1, The resistor R, the dynamic inductor C1 and the dynamic capacitor L1 are connected in series and then in parallel with the capacitor C0 to form an equivalent circuit of the transducer load circuit; The transducer load circuit is connected in parallel with the matching inductor L0 in the matching network circuit.

6. The ultrasonic power supply load parallel resonance point frequency detection, tracking and adjustment device according to claim 4, characterized in that: The phase angle calculation of the resonance point frequency is realized, which specifically includes the following steps: Step A, calculating the system impedance according to the equivalent circuit of the matching network circuit and the transducer load circuit, and calculating the transfer function between the front-end power input of the inductor L0 and the rear-end transducer output of the inductor L0 according to the system impedance; Step B, input specific circuit parameters to calculate the phase angle between the power input current at the front end of the inductor L0 and the output current at the transducer end at the rear end of the inductor L0, and compare to obtain the phase angle that can put the transducer in a parallel resonant working state.

7. The ultrasonic transducer parallel resonance point frequency detection, tracking and adjustment device according to claim 4, characterized in that: The calculation of the system impedance is as follows: Where: Z z is the system impedance, R is the resistance, s is the Laplace operator, C0 is the static capacitance, C1 is the dynamic capacitance, L0 is the matching inductor, and L1 is the dynamic inductor; The power input at the front end of the inductor L0 is recorded as I2, and the output at the rear end of the inductor L0 is recorded as I1. The transfer functions of I1 and I2 are obtained according to the calculated system impedance, which are as follows: Wherein: I2 is the power input current of the front end of the inductor L0, I1 is the output current of the transducer end of the rear end of the inductor L0, R is the resistance, s is the Laplace operator, C0 is the static capacitance, C1 is the dynamic capacitance, L0 is the matching inductor, and L1 is the dynamic inductor.

8. The ultrasonic power supply load parallel resonance point frequency detection, tracking and adjustment device according to claim 4, characterized in that: In the step Step B, multiple groups of specific parameters are brought into calculation, and the obtained results prove that when the phase of I1 / I2 presents a 90-degree relationship, that is, when the cosine value of the phase angle is 0, it is in a parallel resonance point working state.

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