Ultrasonic power supply load parallel resonance point frequency phase locking adjustment method and device

Abstract

The invention relates to the field of ultrasonic power supplies, in particular to an ultrasonic power supply load parallel resonance point frequency phase locking adjusting method and device. The ultrasonic power supply load parallel resonance point frequency phase-locked adjusting device specifically comprises an ultrasonic power supply converter, a matching network circuit, a transducer load circuit and a phase-locked loop. A fixed phase relation is obtained by calculating and analyzing the system impedance and substituting different specific numerical values, it is guaranteed that the system is in a parallel resonance point working state under the phase relation, phase-locked adjustment is designed according to the phase relation, and the phase-locked state is adjusted. The parallel inductor front-end power supply input and the parallel inductor rear-end transducer output are subjected to XOR processing to obtain an XOR signal, and after the XOR signal is processed by a digital filter, a phase difference is output to a PI controller to realize phase locking control. Compared with the prior art, the invention can filter the interference influence of zero square wave comparison of the final output current output from the rear end to the transducer, so that the system can quickly respond to the frequency change of the load and 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 frequency phase-locked adjustment device and method for a parallel resonance point of an ultrasonic power supply load. 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 an ultrasonic power supply based on a phase-locked loop (publication number: CN209345032U), which includes an oscillator, a driving circuit, a power amplifier circuit, an impedance matching circuit, an ultrasonic transducer, a voltage sampling circuit, a current sampling circuit and a power supply module; the oscillator uses a phase-locked loop CD4046, the output end of the oscillator is connected to the input end of the driving circuit, and the output end of the driving circuit is connected to the input end of the power amplifier circuit; the output end of the power amplifier circuit is divided into two paths: one path is connected to the input end of the impedance matching circuit, and the other path is connected to the input end of the voltage sampling circuit, the output end of the voltage sampling circuit is connected to the input end of the oscillator, the output end of the impedance matching circuit is divided into two paths: one path is connected to the input end of the ultrasonic transducer, and the other path is connected to the input end of the current sampling circuit, and the output end of the current sampling circuit is connected to the input end of the oscillator; the power supply module is respectively connected to the oscillator, the driving circuit, the voltage sampling circuit and the current sampling circuit for power supply. The ultrasonic power supply achieves frequency tracking to a certain extent, thereby ensuring the stability of the ultrasonic transducer drive, a larger amplitude and the output power of the ultrasonic power supply, but the frequency tracking performance and anti-disturbance capabilities are relatively weak, and there is a lack of guarantee that the working circuit is at the resonant frequency. Summary of the invention

[0005] 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 frequency phase-locked adjustment device and method for a parallel resonance point of an ultrasonic power supply load.

[0006] On the one hand, the present invention provides a method for phase-locking frequency adjustment 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, and comprising the following steps:

[0007] S1. Measure the input current I1 at one end of the inductor L0 and the current I2 output from the end to the ultrasonic transducer, and calculate the zero-crossing square wave comparison signal of the currents I1 and I2;

[0008] S2. performing an XOR operation on the zero-crossing square wave comparison signal, and obtaining the phase difference between the currents I1 and I2 after filtering;

[0009] S3. Use a reference value to perform closed-loop control on the phase difference between I1 and I2 to achieve phase locking, so that the phase difference is maintained at 90°.

[0010] The phase-locked loop is adjusted according to the calculated phase difference, and the power input at the front end of the parallel inductor and the output at the transducer end at the back end of the parallel inductor are XOR-processed to obtain an XOR signal. After being processed by a digital filter, the phase difference is output to the PI controller to realize phase-locked control.

[0011] Preferably, in step S2, the zero-crossing square wave signals of the currents I1 and I2 are filtered, specifically, noise glitches distributed on the transition edges of the zero-crossing square wave comparison signals are eliminated by integral filtering;

[0012] Among them, filtering can filter out the interference effect of the zero-point square wave comparison of the final output current output from the back end to the transducer, so that the system can quickly respond to the frequency change of the load and accurately operate at the parallel resonance point.

[0013] Preferably, the reference value for maintaining the phase difference at 90° in step S3 is specifically 0.5;

[0014] When the offset is added, the reference value becomes an arbitrary value.

[0015] On the other hand, an ultrasonic power supply load parallel resonance point frequency phase-locked adjustment device includes an ultrasonic power supply converter, a matching network circuit, a transducer load circuit, and also includes a closed-loop controlled phase-locked loop;

[0016] 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;

[0017] The phase-locked loop tracks and adjusts the frequency of the power input at the front end of the parallel inductor and the output at the transducer end at the rear end of the parallel inductor;

[0018] The ultrasonic power converter is connected to a matching network;

[0019] The matching network is connected to an ultrasonic power converter and a transducer load circuit;

[0020] The transducer load circuit is connected to a matching network;

[0021] 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;

[0022] 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;

[0023] The transducer load circuit can be equivalent to an equivalent circuit composed of resistance, inductance and capacitance.

[0024] Preferably, the equivalent circuit of the transducer load circuit specifically includes R as a resistor, C0 as a capacitor, C1 as a dynamic capacitor, L1 as a dynamic inductor,

[0025] 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;

[0026] The transducer load circuit is connected in parallel with the inductor L0 in the matching network circuit.

[0027] Further preferably, the phase-locked loop includes a zero-crossing comparator, an XOR gate, a digital filter and a PI controller;

[0028] The front-end power input of the parallel inductor and the rear-end transducer output of the parallel inductor are input as two input signals into the zero-crossing comparison circuit, and then through the XOR gate, the output end of the XOR gate is connected to the digital filter, and the output end of the digital filter is connected to the PI controller.

[0029] Preferably, the phase angle calculation of the resonance point frequency is realized, specifically comprising the following steps:

[0030] 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 power input of the front end of the parallel inductor and the output of the transducer end of the rear end of the parallel inductor according to the system impedance;

[0031] Step B, input specific circuit parameters to calculate the phase angle 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, and compare to obtain the phase angle that can put the transducer in a parallel resonant working state.

[0032] Further preferably, the calculation of the system impedance is specifically as follows:

[0033]

[0034] 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 inductance, and L1 is the dynamic inductance;

[0035] The power input at the front end of the parallel inductor is recorded as I2, and the output at the rear end of the parallel inductor is recorded as I1. The transfer functions of I1 and I2 are obtained according to the calculated system impedance, which are as follows:

[0036]

[0037] Wherein: I2 is the power input of the front end of the parallel inductor, I1 is the output of the transducer end of the rear end of the parallel inductor, R is the resistance, S is the Laplace operator, C0 is the static capacitance, C0 is the dynamic capacitance, L0 is the inductance, and L1 is the dynamic inductance;

[0038] 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.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The present invention provides an ultrasonic power supply load parallel resonance point frequency phase-locked adjustment device and method. By analyzing the characteristic relationship between the ultrasonic power supply and the transducer load and matching the parallel inductance parameters, a method is proposed to detect the phase relationship between the front-end power supply current of the parallel matching inductance node and the final output current output to the transducer at the back end, and the transducer load parallel resonance frequency point tracking is achieved by adjusting the phase difference between the two groups of currents. Because the transducer works at the parallel resonance point, its current is small, and there is a problem of detecting the zero-crossing point. Through the design of the phase-locked loop, the interference effect of the zero-point square wave comparison of the final output current output from the back end to the transducer can be filtered out, so that the system can quickly respond to the frequency change of the load and accurately work at the parallel resonance point. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 4 is a schematic diagram of a phase-locked loop in an embodiment of the present invention.

[0042] Figure 2 It is a schematic diagram of the ultrasonic power supply and transducer load system in an embodiment of the present invention.

[0043] Figure 3 1 is an equivalent circuit diagram of a parallel matching inductor and a transducer in an embodiment of the present invention.

[0044] Figure 4 The current zero-crossing square wave comparison in the embodiment of the present invention is sampled via XOR to obtain a phase difference diagram. DETAILED DESCRIPTION

[0045] 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.

[0046] Example 1

[0047] 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 frequency phase-locked adjustment device and method for a load parallel resonance point of an ultrasonic power supply.

[0048] A method for phase-locked regulation of the frequency of an ultrasonic power supply load parallel resonance point comprises the following steps:

[0049] S1, the equivalent circuit of the matching network circuit and the transducer load circuit is calculated to obtain the system impedance, and the transfer function of the power input of the front end of the parallel inductor and the output of the transducer end of the rear end of the parallel inductor is calculated according to the system impedance;

[0050] S2, bring in specific parameters to calculate the phase angle between the power input at the front end of the parallel inductor and the output at the transducer end at the rear end of the parallel inductor, and compare to obtain the phase angle that can make the transducer work in parallel resonance;

[0051] S3, using zero-crossing comparison to convert the power input at the front end of the parallel inductor and the output at the rear end of the parallel inductor into a zero-crossing square wave signal;

[0052] S4, performing XOR operation on the zero-crossing square wave signal inputted by the front-end power supply of the parallel inductor and the outputted by the rear-end transducer of the parallel inductor to generate an XOR signal;

[0053] S5. Filter the XOR signal to obtain the phase difference between the power input at the front end of the parallel inductor and the output at the transducer end at the rear end of the parallel inductor, and perform closed-loop control on the phase difference and a reference set value to achieve phase locking.

[0054] Among them, filtering can effectively filter out the interference effect of the zero-point square wave comparison of the final output current output from the back end to the transducer. Combined with the set phase-locked loop, the phase difference between the currents I1 and I2 in the circuit can be maintained at the required 90°, ensuring that the circuit is always at the resonance point when working.

[0055] This embodiment proposes an ultrasonic power supply load parallel resonance point frequency phase-locked adjustment device, such as Figure 2 As shown, it includes an ultrasonic power converter, a matching network circuit, a transducer load circuit, and a phase-locked loop;

[0056] 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;

[0057] The phase-locked loop tracks and adjusts the frequency of the power input at the front end of the parallel inductor and the output at the transducer end at the rear end of the parallel inductor;

[0058] 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;

[0059] 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;

[0060] The transducer load circuit can be equivalent to an equivalent circuit composed of resistance, inductance and capacitance.

[0061] 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. The L0 and C0 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.

[0062] 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;

[0063] The transducer load circuit is connected in parallel with the inductor L0 in the matching network circuit, such as Figure 3 shown.

[0064] Analyze the entire circuit, detect the I2 and I1 currents, and perform transfer function analysis on them:

[0065] Depend on Figure 3 The impedance of the entire system is obtained from the circuit in:

[0066]

[0067] 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:

[0068]

[0069] Simplifying gives the general transfer function form:

[0070]

[0071] 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:

[0072] L1=2730.94uH; R=30.1614Ω; C1=0.02336nF; C0=19.6417nF;

[0073] The matching inductor parameters are as follows:

[0074] L0=3.4mH;

[0075] According to the selected transducer parameters and matching inductor parameters, the transducer parallel resonant frequency is calculated as follows:

[0076]

[0077] 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:

[0078] θ=89.8°

[0079] 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:

[0080] θ=90.7°

[0081] Assuming that the matching inductance parameter L0 increases by a certain amount, becoming L0 = 3.4*120% = 4.08mH, the phase angle is:

[0082] θ=88.9°

[0083] 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.

[0084] The calculation results show that 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.

[0085] Based on the above analysis, a frequency tracking scheme is designed. The ultrasonic power supply detects I1 and I2, and uses a hardware comparison circuit to convert the zero-crossing comparison into a square wave signal. The zero-crossing square waves of I1 and I2 are XORed to generate an XOR signal. The XOR signal is filtered to obtain the phase difference, and the closed-loop control is performed with the reference 0.5 for phase locking. Its internal structure and workflow are shown below. Figure 1 shown.

[0086] Due to the characteristics of the system, the current zero crossing has certain noise glitches, and these noise glitches are symmetrically distributed on the transition edge of the square wave under the action of the zero crossing comparator. By integrating and filtering the phase detection signal, such symmetrically distributed noise glitches can be filtered out in a targeted manner, such as Figure 4 shown.

[0087] 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.

[0088] 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 phase-locking frequency regulation of an ultrasonic power supply load parallel resonance point, 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 I1 at one end of the inductor L0 and the current I2 output from the end to the ultrasonic transducer, and calculate the zero-crossing square wave comparison signal of the currents I1 and I2; S2. performing an XOR operation on the zero-crossing square wave comparison signal, and obtaining the phase difference between the currents I1 and I2 after filtering; S3. Use a reference value to perform closed-loop control on the phase difference between I1 and I2 to achieve phase locking, so that the phase difference is maintained at 90°.

2. The method for phase-locked frequency regulation of an ultrasonic power supply load parallel resonance point according to claim 1, characterized in that: In the step S2, the zero-crossing square wave signals of the currents I1 and I2 are filtered, specifically, noise glitches distributed on the transition edges of the zero-crossing square wave comparison signals are eliminated by integral filtering.

3. The method for phase-locked frequency regulation of an ultrasonic power supply load parallel resonance point according to claim 1, characterized in that: The reference value for maintaining the phase difference at 90° in step S3 is specifically 0.5; When the offset is added, the reference value becomes an arbitrary value.

4. An ultrasonic power supply load parallel resonance point frequency phase-locked adjustment device, comprising an ultrasonic power supply converter, a matching network circuit, and a transducer load circuit, characterized in that: It also includes a phase-locked loop for closed-loop control; 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 an inverter power module, and the output frequency of the power converter is changed by adjusting the PWM frequency; The matching network circuit 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 phase-locked loop performs frequency tracking and adjustment on 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, and performs phase locking.

5. The ultrasonic power supply load parallel resonance point frequency phase-locked adjustment device according to claim 4, characterized in that: The equivalent circuit of the transducer load circuit specifically includes a resistor R, a capacitor C0, a dynamic capacitor C1, a dynamic inductor L1, 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 transducer load circuit is connected in parallel with the inductor L0 in the matching network circuit.

6. The ultrasonic power supply load parallel resonance point frequency phase-locked adjustment device according to claim 4, characterized in that: The phase-locked loop includes a zero-crossing comparator, an XOR gate, a digital filter and a PI controller; The front-end power input of the parallel inductor and the rear-end transducer output of the parallel inductor are input as two input signals to the zero-crossing comparator, and then through the XOR gate, the output end of the XOR gate is connected to the digital filter, and the output end of the digital filter is connected to the PI controller.

7. The ultrasonic power supply load parallel resonance point frequency phase-locked 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 power input of the front end of the parallel inductor and the output of the transducer end of the rear end of the parallel inductor 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 parallel inductor and the output current at the transducer end at the rear end of the parallel inductor, and compare to obtain the phase angle that can put the transducer in a parallel resonant working state.

8. The ultrasonic power supply load parallel resonance point frequency phase-locked 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 inductance, and L1 is the dynamic inductance; The power input at the front end of the parallel inductor is recorded as I2, and the output at the rear end of the parallel inductor 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 at the front end of the parallel inductor, I1 is the output at the transducer end at the rear end of the parallel inductor, R is the resistance, s is the Laplace operator, C0 is the static capacitance, C1 is the dynamic capacitance, L0 is the inductance, and L1 is the dynamic inductance.

9. The device for phase-locked frequency regulation of an ultrasonic power supply load parallel resonance point 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 the parallel resonance point working state.

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