Plasma power supply control method and system based on power tracking variable frequency output

Abstract

The present invention provides a plasma power supply control method and system based on power tracking variable frequency output, belonging to the field of automatic control technology. The method adopts a pure software algorithm to control the piezoelectric ceramic transformer to work at the optimal working point. The dual closed-loop control consisting of a frequency closed loop and a power closed loop can adjust the frequency and PWM duty cycle in real time according to the working conditions, so that the plasma power supply maintains the maximum power and continuously and stably outputs, thereby enhancing the system stability, and does not require hardware phase-locked control, thereby reducing the circuit complexity and reducing the product cost.

Description

Technical Field

[0001] The present invention relates to the field of automatic control technology, and in particular to a plasma power supply control method and system based on power tracking variable frequency output. Background Art

[0002] Plasma is called the fourth state of matter and can be obtained by controlling the high voltage ionization of air by piezoelectric ceramic transformers. Its technology is widely used in the fields of energy, new materials and processing, and environment. Plasma can efficiently process and activate the surface of materials, and can also sterilize, disinfect and remove odors. The main plasma power supply control methods include frequency regulation control, pulse density regulation control, etc.

[0003] For handheld plasma power supplies used for surface treatment of various materials, an increase in operating frequency can reduce the dissipation of surface charges, extend the life of the piezoelectric ceramic transformer, and further improve the treatment effect. However, due to the material characteristics of the piezoelectric ceramic transformer, an increase in operating frequency also reduces the output step-up ratio, thereby deteriorating the treatment effect. Therefore, the piezoelectric ceramic transformer needs to operate at the anti-resonance frequency point, which is the optimal operating point. At this time, the input voltage and current impedance angle is 0°, but different working conditions and loads will affect the impedance angle. Keeping the plasma power supply working continuously at the optimal operating point is the key control technology. At present, the voltage and current impedance angle can be controlled to 0° through hardware phase locking, but its cost is high, the circuit design is complex, and the design of phase-locking parameters for different types of piezoelectric ceramic transformers is relatively cumbersome.

[0004] Based on this, there is an urgent need for a plasma power control method with low cost and simple circuit design. Summary of the invention

[0005] The purpose of the present invention is to provide a plasma power supply control method and system based on power tracking variable frequency output, aiming to solve the problem of complex and high cost of hardware phase-locked control circuit.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] The present invention provides a plasma power supply control method based on power tracking variable frequency output, the plasma power supply control method comprising:

[0008] Collecting output voltage values ​​and output current values ​​of the piezoelectric ceramic transformer at different times of multiple sampling points, determining output voltage amplitudes and output current amplitudes of the piezoelectric ceramic transformer at different times of multiple sampling points according to the output voltage values ​​and output current values ​​at different times of multiple sampling points, and calculating the current impedance value of the piezoelectric ceramic transformer according to the output voltage amplitudes and output current amplitudes at different times of multiple sampling points; different times are different time points within the same switching cycle;

[0009] Determine whether the current scanning frequency of the piezoelectric ceramic transformer is less than the set frequency threshold. If so, increase the current scanning frequency by the set value, use the increased scanning frequency as the scanning frequency of the next switching cycle of the piezoelectric ceramic transformer, and recalculate the current impedance value of the piezoelectric ceramic transformer until the current scanning frequency of the piezoelectric ceramic transformer is greater than or equal to the set frequency threshold.

[0010] Selecting the maximum value of the current impedance value of the piezoelectric ceramic transformer, determining the frequency point corresponding to the maximum value of the current impedance value, and making the PWM module work at the frequency point; the frequency corresponding to the maximum value of the current impedance value is the anti-resonance frequency point;

[0011] After the PWM module is made to work at the frequency point, an output voltage value and an output current value of the piezoelectric ceramic transformer in the current switching cycle are obtained, and a true value of the impedance angle is determined according to the output voltage value and the output current value in the current switching cycle;

[0012] Subtracting the impedance angle actual value from the impedance angle rated value to obtain an impedance angle difference value, and determining the adjustment frequency according to the impedance angle difference value;

[0013] Acquire an input voltage value of the piezoelectric ceramic transformer, and determine a duty cycle corresponding to the input voltage value according to the input voltage value;

[0014] A PWM regulation signal is obtained according to the regulation frequency and the duty cycle corresponding to the input voltage value; the PWM regulation signal includes a first regulation signal and a second regulation signal; the first regulation signal is used to realize frequency closed-loop regulation of the plasma power supply, and the second regulation signal is used to realize power closed-loop regulation of the plasma power supply.

[0015] Optionally, before the step of “increasing the current scanning frequency by a set value”, the step further includes:

[0016] Setting a frequency increment count variable, and determining whether the frequency increment count variable is less than a set count threshold;

[0017] If yes, the frequency increment count variable is incremented by 1 until the frequency increment count variable is greater than or equal to the set count threshold;

[0018] If not, the frequency increment count variable is cleared and the current scanning frequency is incremented by the set value.

[0019] Optionally, determining the real value of the impedance angle according to the output voltage value and the output current value in the current switching cycle specifically includes:

[0020] Obtain a voltage and current array according to the output voltage value and the output current value in the current switching cycle;

[0021] Determine the corresponding positions of the voltage zero-crossing point and the current zero-crossing point in the voltage and current array;

[0022] Calculate the array position difference according to the corresponding position of the voltage zero-crossing point in the voltage and current array and the corresponding position of the current zero-crossing point in the voltage and current array; the array position difference represents the time difference between the voltage zero-crossing point and the current zero-crossing point;

[0023] Obtaining a phase difference between voltage and current according to the array position difference;

[0024] The real value of the impedance angle is obtained according to the phase difference between the voltage and the current.

[0025] Optionally, the specific formula for obtaining the phase difference between voltage and current according to the array position difference is:

[0026]

[0027] in, It represents the phase difference between voltage and current, A represents the dimension of the voltage and current array within one switching cycle, and Δx represents the position difference of the array.

[0028] Optionally, the acquiring an input voltage value of the piezoelectric ceramic transformer and determining a duty cycle corresponding to the input voltage value according to the input voltage value specifically includes:

[0029] Determine whether the input voltage value obtained at the current moment is less than the input voltage value at the previous moment;

[0030] If yes, the number of times the input voltage value obtained at the current moment is less than the input voltage value at the previous moment is accumulated until the accumulated number is greater than the set threshold, and the input voltage value at the current moment is recorded at the same time;

[0031] An input voltage level corresponding to the input voltage value at the current moment is determined, and a duty cycle corresponding to the input voltage value is determined according to the rated working voltage of the piezoelectric ceramic transformer, the voltage level corresponding to the rated working voltage, and the input voltage level.

[0032] To achieve the above object, the present invention also provides a plasma power supply control system based on power tracking variable frequency output, the system comprising:

[0033] A voltage and current acquisition and impedance value calculation unit, used to acquire output voltage values ​​and output current values ​​of the piezoelectric ceramic transformer at different times of multiple sampling points, determine output voltage amplitudes and output current amplitudes of the piezoelectric ceramic transformer at different times of multiple sampling points according to the output voltage values ​​and output current values ​​at different times of multiple sampling points, and calculate the current impedance value of the piezoelectric ceramic transformer according to the output voltage amplitudes and output current amplitudes at different times of multiple sampling points; different times are different time points within the same switching cycle;

[0034] The anti-resonance frequency point scanning and calculation unit is used to determine whether the current scanning frequency of the piezoelectric ceramic transformer is less than the set frequency threshold. If so, the current scanning frequency is incremented by the set value, and the incremented scanning frequency is used as the scanning frequency of the next switching cycle of the piezoelectric ceramic transformer, and the voltage and current acquisition and impedance value calculation unit is returned to recalculate the current impedance value of the piezoelectric ceramic transformer until the current scanning frequency of the piezoelectric ceramic transformer is greater than or equal to the set frequency threshold; it is also used to select the maximum value of the current impedance value of the piezoelectric ceramic transformer, determine the frequency point corresponding to the maximum value of the current impedance value, and make the PWM module work at the frequency point; the frequency corresponding to the maximum value of the current impedance value is the anti-resonance frequency point;

[0035] An impedance angle true value determination unit, used to obtain an output voltage value and an output current value of the piezoelectric ceramic transformer in a current switching cycle after the PWM module is made to operate at the frequency point, and determine the impedance angle true value according to the output voltage value and the output current value in the current switching cycle;

[0036] A frequency determination unit is used to obtain an impedance angle difference by subtracting the impedance angle real value from the impedance angle rated value, and determine the adjustment frequency according to the impedance angle difference.

[0037] A duty cycle determining unit, used to obtain an input voltage value of the piezoelectric ceramic transformer, and determine a duty cycle corresponding to the input voltage value according to the input voltage value;

[0038] The regulating unit is used to obtain a PWM regulating signal according to the regulating frequency and the duty cycle corresponding to the input voltage value; the PWM regulating signal includes a first regulating signal and a second regulating signal; the first regulating signal is used to realize frequency closed-loop regulation of the plasma power supply, and the second regulating signal is used to realize power closed-loop regulation of the plasma power supply.

[0039] Optionally, the impedance angle true value determination unit specifically includes:

[0040] Obtain a voltage and current array according to the output voltage value and the output current value in the current switching cycle;

[0041] Determine the corresponding positions of the voltage zero-crossing point and the current zero-crossing point in the voltage and current array;

[0042] Calculate the array position difference according to the corresponding position of the voltage zero-crossing point in the voltage and current array and the corresponding position of the current zero-crossing point in the voltage and current array; the array position difference represents the time difference between the voltage zero-crossing point and the current zero-crossing point;

[0043] Obtaining a phase difference between voltage and current according to the array position difference;

[0044] The real value of the impedance angle is obtained according to the phase difference between the voltage and the current.

[0045] Optionally, the duty cycle determining unit specifically includes:

[0046] Determine whether the input voltage value obtained at the current moment is less than the input voltage value at the previous moment;

[0047] If yes, the number of times the input voltage value obtained at the current moment is less than the input voltage value at the previous moment is accumulated until the accumulated number is greater than the set threshold, and the input voltage value at the current moment is recorded at the same time;

[0048] An input voltage level corresponding to the input voltage value at the current moment is determined, and a duty cycle corresponding to the input voltage value is determined according to the rated working voltage of the piezoelectric ceramic transformer, the voltage level corresponding to the rated working voltage, and the input voltage level.

[0049] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0050] The present invention provides a plasma power supply control method and system based on power tracking variable frequency output, which adopts a pure software algorithm to control the piezoelectric ceramic transformer to work at the optimal working point. The dual closed-loop control consisting of a frequency closed loop and a power closed loop can adjust the frequency and PWM duty cycle in real time according to the working conditions, so that the plasma power supply maintains the maximum power and continuously and stably outputs, thereby enhancing the system stability, and does not require hardware phase-locked control, thereby reducing the circuit complexity and reducing the product cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0052] Figure 1 It is a flow chart of the plasma power supply control method based on power tracking variable frequency output of the present invention;

[0053] Figure 2 It is a module structure diagram of the plasma power supply control system based on power tracking variable frequency output of the present invention;

[0054] Figure 3 A schematic diagram of a working process in a specific application of the present invention;

[0055] Figure 4 The working flow chart of the unit for determining the true value of the impedance angle;

[0056] Figure 5 It is a schematic diagram of the working process of the frequency closed-loop regulation subunit;

[0057] Figure 6 This is the working flow chart of the power closed-loop regulation subunit.

[0058] Explanation of symbols:

[0059] Voltage and current acquisition and impedance value calculation unit-1, anti-resonance frequency point scanning and calculation unit-2, impedance angle true value determination unit-3, frequency determination unit-4, duty cycle determination unit-5, adjustment unit-6. DETAILED DESCRIPTION

[0060] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0061] The purpose of the present invention is to provide a plasma power supply control method and system based on power tracking variable frequency output, aiming to solve the problem of complex and high cost of hardware phase-locked control circuit.

[0062] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0063] like Figure 1 As shown, the present invention provides a plasma power supply control method based on power tracking variable frequency output, and the plasma power supply control method comprises the following steps:

[0064] S1: collecting output voltage values ​​and output current values ​​of the piezoelectric ceramic transformer at different moments of multiple sampling points, determining the output voltage amplitude and output current amplitude of the piezoelectric ceramic transformer at different moments of multiple sampling points according to the output voltage values ​​and the output current values ​​at different moments of multiple sampling points, and calculating the current impedance value of the piezoelectric ceramic transformer according to the output voltage amplitude and the output current amplitude at different moments of multiple sampling points; different moments are different time points within the same switching cycle.

[0065] Preferably, the output voltage values ​​and output current values ​​of the piezoelectric ceramic transformer at different times at multiple sampling points are collected and transferred to an array using a continuous sampling mode and DMA; the maximum value is obtained using a traversal method.

[0066] S2: Determine whether the current scanning frequency of the piezoelectric ceramic transformer is less than the set frequency threshold. If so, increase the current scanning frequency by the set value, use the increased scanning frequency as the scanning frequency of the next switching cycle of the piezoelectric ceramic transformer, and return to execute step S1, recalculate the current impedance value of the piezoelectric ceramic transformer, until the current scanning frequency of the piezoelectric ceramic transformer is greater than or equal to the set frequency threshold, and execute step S3.

[0067] Preferably, in step S2, before the step of "increasing the current scanning frequency by a set value", the step further includes:

[0068] A frequency increment count variable is set to determine whether the frequency increment count variable is less than a set count threshold.

[0069] If so, the frequency increment count variable is incremented by 1 until the frequency increment count variable is greater than or equal to the set count threshold.

[0070] If not, the frequency increment count variable is cleared, and the current scanning frequency is incremented by the set value. Since the maximum voltage and current values ​​obtained by sampling are required in the calculation process, in order to prevent the scanning frequency from increasing too quickly and causing inaccurate maximum voltage and current values, a frequency increment count variable is set. This variable is usually accumulated in the PWM interrupt, and the counting threshold is selected according to the PWM switching frequency.

[0071] S3: Select the maximum value of the current impedance value of the piezoelectric ceramic transformer, determine the frequency point corresponding to the maximum value of the current impedance value, and make the PWM module work at the frequency point; the frequency corresponding to the maximum value of the current impedance value is the anti-resonance frequency point.

[0072] S4: After the PWM module is operated at the frequency point, the output voltage value and the output current value of the piezoelectric ceramic transformer in the current switching cycle are obtained, and the real value of the impedance angle is determined according to the output voltage value and the output current value in the current switching cycle.

[0073] Further, determining the real value of the impedance angle according to the output voltage value and the output current value in the current switching cycle specifically includes:

[0074] S41: Obtain a voltage and current array according to the output voltage value and the output current value in the current switching cycle.

[0075] S42: Determine corresponding positions of the voltage zero-crossing point and the current zero-crossing point in the voltage and current array.

[0076] S43: Calculate the array position difference according to the corresponding position of the voltage zero crossing point in the voltage and current array and the corresponding position of the current zero crossing point in the voltage and current array; the array position difference represents the time difference between the voltage zero crossing point and the current zero crossing point.

[0077] S44: Obtaining a phase difference between voltage and current according to the array position difference.

[0078] S45: Obtain the true value of the impedance angle according to the phase difference between the voltage and the current. The accuracy of the impedance angle is positively correlated with the dimension of the single-cycle voltage and current array, and the impedance angle result is within ±90°.

[0079] Specifically, the specific formula for obtaining the phase difference between voltage and current according to the array position difference is:

[0080]

[0081] in, It represents the phase difference between voltage and current, A represents the dimension of the voltage and current array within one switching cycle, and Δx represents the position difference of the array.

[0082] S5: Subtract the actual value of the impedance angle from the rated value of the impedance angle to obtain an impedance angle difference, and determine the adjustment frequency according to the impedance angle difference.

[0083] S6: Acquire an input voltage value of the piezoelectric ceramic transformer, and determine a duty cycle corresponding to the input voltage value according to the input voltage value.

[0084] Further, the step of obtaining an input voltage value of the piezoelectric ceramic transformer and determining a duty cycle corresponding to the input voltage value according to the input voltage value specifically includes:

[0085] S61: Determine whether the input voltage value obtained at the current moment is less than the input voltage value at the previous moment.

[0086] S62: If yes, the number of times the input voltage value obtained at the current moment is less than the input voltage value at the previous moment is accumulated until the accumulated number is greater than a set threshold, and the input voltage value at the current moment is recorded at the same time.

[0087] S63: Determine the input voltage level corresponding to the input voltage value at the current moment, and determine the duty cycle corresponding to the input voltage value according to the rated working voltage of the piezoelectric ceramic transformer, the voltage level corresponding to the rated working voltage, and the input voltage level.

[0088] S7: According to the duty cycle corresponding to the adjustment frequency and the input voltage value, a PWM adjustment signal is obtained; the PWM adjustment signal includes a first adjustment signal and a second adjustment signal; the first adjustment signal is used to implement frequency closed-loop adjustment of the plasma power supply, and the second adjustment signal is used to implement power closed-loop adjustment of the plasma power supply. Specifically, the value of the PWM period register at the frequency point is calculated by the relationship between the frequency point and the PWM clock frequency (PWM clock frequency / frequency point value), and a PWM upper and lower drive tubes are configured in the PWM action register as symmetrical outputs, and the duty cycle is obtained by combining the value of the given fixed comparison register, so that the PWM works at the frequency point. Automatic power regulation is actually to adjust the duty cycle, that is, to calculate the values ​​of different PWM comparison registers.

[0089] To achieve the above purpose, Figure 2 As shown, the present invention also provides a plasma power control system based on power tracking variable frequency output, the system comprising: a voltage and current acquisition and impedance value calculation unit 1, an anti-resonance frequency point scanning and calculation unit 2, an impedance angle true value determination unit 3, a frequency determination unit 4, a duty cycle determination unit 5 and an adjustment unit 6.

[0090] The voltage and current acquisition and impedance value calculation unit 1 is used to acquire the output voltage value and output current value of the piezoelectric ceramic transformer at different times of multiple sampling points, determine the output voltage amplitude and output current amplitude of the piezoelectric ceramic transformer at different times of multiple sampling points according to the output voltage value and the output current value at different times of multiple sampling points, and calculate the current impedance value of the piezoelectric ceramic transformer according to the output voltage amplitude and the output current amplitude at different times of multiple sampling points; different times are different time points within the same switching cycle.

[0091] The anti-resonance frequency point scanning and calculation unit 2 is used to determine whether the current scanning frequency of the piezoelectric ceramic transformer is less than the set frequency threshold. If so, the current scanning frequency is incremented by the set value, and the incremented scanning frequency is used as the scanning frequency of the next switching cycle of the piezoelectric ceramic transformer, and the voltage and current acquisition and impedance value calculation unit is returned to recalculate the current impedance value of the piezoelectric ceramic transformer until the current scanning frequency of the piezoelectric ceramic transformer is greater than or equal to the set frequency threshold; it is also used to select the maximum value of the current impedance value of the piezoelectric ceramic transformer, determine the frequency point corresponding to the maximum value of the current impedance value, and make the PWM module work at the frequency point; the frequency corresponding to the maximum value of the current impedance value is the anti-resonance frequency point.

[0092] The impedance angle true value determination unit 3 is used to obtain the output voltage value and output current value of the piezoelectric ceramic transformer in the current switching cycle after the PWM module is operated at the frequency point, and determine the impedance angle true value according to the output voltage value and the output current value in the current switching cycle.

[0093] The frequency determination unit 4 is used to obtain an impedance angle difference by subtracting the impedance angle real value from the impedance angle rated value, and determine the adjustment frequency according to the impedance angle difference.

[0094] The duty cycle determining unit 5 is used to obtain an input voltage value of the piezoelectric ceramic transformer, and determine a duty cycle corresponding to the input voltage value according to the input voltage value.

[0095] The regulating unit 6 is used to obtain a PWM regulating signal according to the regulating frequency and the duty cycle corresponding to the input voltage value; the PWM regulating signal includes a first regulating signal and a second regulating signal; the first regulating signal is used to realize frequency closed-loop regulation of the plasma power supply, and the second regulating signal is used to realize power closed-loop regulation of the plasma power supply.

[0096] Specifically, the impedance angle true value determination unit 3 specifically includes:

[0097] A voltage and current array is obtained according to the output voltage value and the output current value in the current switching cycle.

[0098] The corresponding positions of the voltage zero-crossing point and the current zero-crossing point in the voltage and current array are determined.

[0099] The array position difference is calculated according to the corresponding position of the voltage zero crossing point in the voltage and current array and the corresponding position of the current zero crossing point in the voltage and current array; the array position difference represents the time difference between the voltage zero crossing point and the current zero crossing point.

[0100] The phase difference between the voltage and the current is obtained according to the array position difference.

[0101] The real value of the impedance angle is obtained according to the phase difference between the voltage and the current.

[0102] Furthermore, the duty cycle determining unit 5 specifically comprises:

[0103] It is determined whether the input voltage value obtained at the current moment is less than the input voltage value at the previous moment.

[0104] If so, the number of times the input voltage value obtained at the current moment is less than the input voltage value at the previous moment is accumulated until the accumulated number is greater than the set threshold, and the input voltage value at the current moment is recorded at the same time.

[0105] An input voltage level corresponding to the input voltage value at the current moment is determined, and a duty cycle corresponding to the input voltage value is determined according to the rated working voltage of the piezoelectric ceramic transformer, the voltage level corresponding to the rated working voltage, and the input voltage level.

[0106] A specific application of the present invention is as follows:

[0107] like Figure 3 As shown, the control system of the present invention is mainly divided into two parts: power-on frequency sweep and frequency closed loop. The power-on frequency sweep is to scan the anti-resonance frequency point through the set frequency range, and the impedance value is calculated every 50 Hz. Since the impedance value at the anti-resonance point is relatively large, the frequency of the maximum impedance point is found and sent to the frequency closed loop for adjustment. The frequency closed loop PI input is the rated value of the impedance angle and the actual value of the impedance angle, and the output is the adjustment frequency. The impedance angle is adjusted to 0°, that is, the piezoelectric ceramic transformer works near the anti-resonance frequency point, and the power is automatically adjusted according to the actual bus voltage change. The bus voltage is the input voltage of the piezoelectric ceramic transformer. The magnetic rod is connected to the piezoelectric ceramic transformer, and the duty cycle adjustment signal acts on the piezoelectric ceramic transformer through the magnetic rod.

[0108] The working process of the anti-resonance frequency point scanning and calculation unit includes the following steps:

[0109] 101: First determine whether the scan stop flag is 0, if it is 0, proceed to the next step, otherwise it means that the scan has ended or has not started.

[0110] 102: Setting the frequency increment count variable and the count threshold. In a specific embodiment of the present invention, the count threshold is 2000, that is, the scanning frequency is incremented by 50 Hz every 2000 beats. The increment frequency value can be adjusted according to the main frequency of the selected control chip. The impedance value is calculated once for each frequency increment.

[0111] 103: Compare the current impedance value calculated with the previous one, and record the larger value and its corresponding frequency point.

[0112] 104: After determining that the scanning frequency exceeds the set frequency range, the scanning is stopped to obtain the frequency corresponding to the maximum impedance value point. The selection of the frequency range set here is determined according to the material of the piezoelectric ceramic transformer.

[0113] 105: Scan the stop flag position 1, calculate the PWM period and comparison register value at this time and output them.

[0114] The working process of the impedance angle true value determination unit 3 is as follows: Figure 4 As shown, due to the sinusoidal distortion of the voltage and current sampled by the hardware under harsh working conditions, the phase difference calculated using the voltage and current maximum position difference fails, and the voltage and current waveforms are distorted near the 0 point, affecting the calculation. The present invention designs a true zero-crossing point detection algorithm to obtain the voltage and current phase difference. The voltage and current sampling in the present invention only includes the positive half cycle of the waveform, and the negative half cycle sampling value is 0, including the following steps:

[0115] 201: Determine whether the voltage and current zero point detection completion flag is equal to 0. If it is equal to 0, proceed to the next step, otherwise it indicates that the detection is completed.

[0116] 202: Starting from the first bit of the voltage and current array, find the first zero value point and assign its position in the array to the UzeroIndex and IzeroIndex variables.

[0117] 203: backward detect the values ​​of a positions in the array, determine whether the voltage and current are both greater than 0, if so, it means that the 0 value point is a real zero-crossing point; if not, continue to backward detect the values ​​of a positions in the array until a 0 value point is detected and the voltage and current of a values ​​are greater than 0. The selection of a value is related to the dimension occupied by a cycle of voltage and current in the array. In the present invention, the dimension of a cycle in the array is 100, and the value of a is selected as 20. If there is a point equal to 0 in the voltage or current array in a position, record the position of the point in the array and assign it to select, and re-backward detect the values ​​of a position until the real zero-crossing point position is detected and assigned to the UzeroIndex and IzeroIndex variables.

[0118] 204: Subtracting UzeroIndex from IzeroIndex yields the array position difference of the actual zero-crossing point of the voltage and current. Subtracting the array position difference from a periodic array dimension and multiplying by 360° yields the voltage and current phase difference angle value, that is, the actual impedance angle value.

[0119] The regulation unit includes a frequency closed-loop regulation subunit and a power closed-loop regulation subunit, wherein the frequency closed-loop regulation subunit is the outer loop part of the overall closed-loop system. Figure 5As shown, after the impedance angle difference is obtained, the impedance angle difference is sent to the frequency closed-loop PI, the rated impedance angle is 0°, the frequency closed-loop PI outputs the adjustment frequency, the period register value and the comparison register value are calculated, and sent to the PWM module to achieve frequency closed-loop adjustment. High-precision PWM is required here, otherwise the impedance angle adjustment accuracy is low. The present invention can control the impedance angle adjustment accuracy within ±4°.

[0120] The working process of the power closed-loop regulation subunit is as follows: Figure 6 As shown, since the present invention is used in a handheld plasma power supply, when a battery is used, the bus voltage will decrease as the power decreases, so it is necessary to adjust the PWM duty cycle in real time to maintain full power operation, and according to the external power gear selection, the PWM duty cycle needs to be adjusted at the same time. The automatic power adjustment first needs to calculate the duty cycle and voltage level corresponding to different power levels under the rated working voltage, which are used to convert and increase the duty cycle when the voltage decreases. The automatic power adjustment includes the following steps:

[0121] 301: Determine whether the input voltage value of the piezoelectric ceramic transformer is lower than the rated working voltage value. Here, the value of the rated working voltage is determined according to different control board designs. If the voltage value of this beat is less than the previous beat, proceed to the next step.

[0122] 302: In order to eliminate the misjudgment caused by voltage fluctuation, the number of voltage reductions needs to be accumulated and assigned to the dif_U variable. When the number of reductions exceeds the set threshold, it is determined to be a real voltage reduction. The threshold selection here is determined based on engineering experience. If it is determined to be a real voltage reduction, proceed to the next step.

[0123] 303: Record the current input voltage value and the corresponding input voltage level, and calculate the duty cycle value of the rated working voltage corresponding to the voltage level. The calculation formula is that the rated working voltage multiplied by the duty cycle value is equal to the input voltage level corresponding to the current input voltage value multiplied by the adjusted duty cycle value (the duty cycle corresponding to the input voltage value). After obtaining the adjusted duty cycle value, update the corresponding PWM duty cycle register to achieve automatic power adjustment.

[0124] Based on the above, the present invention controls the piezoelectric ceramic transformer to operate at the optimal working point through a pure software algorithm, and the online calculation accuracy of the impedance angle reaches within ±4°. The dual closed-loop control can adjust the frequency and PWM duty cycle in real time according to the working conditions, so that the plasma power supply maintains the maximum power and continuously and stably outputs, thereby enhancing the system stability. At the same time, the product cost is greatly reduced without the need for hardware phase-locked control.

[0125] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0126] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A plasma power supply control method based on power tracking variable frequency output, characterized in that: The plasma power supply control method comprises: Collecting output voltage values ​​and output current values ​​of the piezoelectric ceramic transformer at different times of multiple sampling points, determining output voltage amplitudes and output current amplitudes of the piezoelectric ceramic transformer at different times of multiple sampling points according to the output voltage values ​​and output current values ​​at different times of multiple sampling points, and calculating the current impedance value of the piezoelectric ceramic transformer according to the output voltage amplitudes and output current amplitudes at different times of multiple sampling points; different times are different time points within the same switching cycle; Determine whether the current scanning frequency of the piezoelectric ceramic transformer is less than the set frequency threshold. If so, increase the current scanning frequency by the set value, use the increased scanning frequency as the scanning frequency of the next switching cycle of the piezoelectric ceramic transformer, and recalculate the current impedance value of the piezoelectric ceramic transformer until the current scanning frequency of the piezoelectric ceramic transformer is greater than or equal to the set frequency threshold. Selecting the maximum value of the current impedance value of the piezoelectric ceramic transformer, determining the frequency point corresponding to the maximum value of the current impedance value, and making the PWM module work at the frequency point; the frequency corresponding to the maximum value of the current impedance value is the anti-resonance frequency point; After the PWM module is made to work at the frequency point, an output voltage value and an output current value of the piezoelectric ceramic transformer in the current switching cycle are obtained, and a true value of the impedance angle is determined according to the output voltage value and the output current value in the current switching cycle; Subtracting the impedance angle actual value from the impedance angle rated value to obtain an impedance angle difference value, and determining the adjustment frequency according to the impedance angle difference value; Acquire an input voltage value of the piezoelectric ceramic transformer, and determine a duty cycle corresponding to the input voltage value according to the input voltage value; A PWM regulation signal is obtained according to the regulation frequency and the duty cycle corresponding to the input voltage value; the PWM regulation signal includes a first regulation signal and a second regulation signal; the first regulation signal is used to realize frequency closed-loop regulation of the plasma power supply, and the second regulation signal is used to realize power closed-loop regulation of the plasma power supply.

2. The plasma power supply control method based on power tracking variable frequency output according to claim 1, characterized in that: Before the step of "increasing the current scanning frequency by a set value", it also includes: Setting a frequency increment count variable, and determining whether the frequency increment count variable is less than a set count threshold; If yes, then the frequency increment count variable is incremented by 1 until the frequency increment count variable is greater than or equal to the set count threshold; If not, the frequency increment count variable is cleared and the current scanning frequency is incremented by the set value.

3. The plasma power supply control method based on power tracking variable frequency output according to claim 1, characterized in that: Determining the true value of the impedance angle according to the output voltage value and the output current value in the current switching cycle specifically includes: Obtain a voltage and current array according to the output voltage value and the output current value in the current switching cycle; Determine the corresponding positions of the voltage zero-crossing point and the current zero-crossing point in the voltage and current array; Calculate the array position difference according to the corresponding position of the voltage zero-crossing point in the voltage and current array and the corresponding position of the current zero-crossing point in the voltage and current array; the array position difference represents the time difference between the voltage zero-crossing point and the current zero-crossing point; Obtaining a phase difference between voltage and current according to the array position difference; The real value of the impedance angle is obtained according to the phase difference between the voltage and the current.

4. The plasma power supply control method based on power tracking variable frequency output according to claim 3 is characterized in that: The specific formula for obtaining the phase difference between voltage and current according to the array position difference is: in, It represents the phase difference between voltage and current, A represents the dimension of the voltage and current array within one switching cycle, and Δx represents the position difference of the array.

5. The plasma power supply control method based on power tracking variable frequency output according to claim 1, characterized in that: The step of obtaining an input voltage value of the piezoelectric ceramic transformer and determining a duty cycle corresponding to the input voltage value according to the input voltage value specifically includes: Determine whether the input voltage value obtained at the current moment is less than the input voltage value at the previous moment; If yes, the number of times the input voltage value obtained at the current moment is less than the input voltage value at the previous moment is accumulated until the accumulated number is greater than the set threshold, and the input voltage value at the current moment is recorded at the same time; An input voltage level corresponding to the input voltage value at the current moment is determined, and a duty cycle corresponding to the input voltage value is determined according to the rated working voltage of the piezoelectric ceramic transformer, the voltage level corresponding to the rated working voltage, and the input voltage level.

6. A plasma power control system based on power tracking variable frequency output, characterized in that: The system comprises: A voltage and current acquisition and impedance value calculation unit, used to acquire output voltage values ​​and output current values ​​of the piezoelectric ceramic transformer at different times of multiple sampling points, determine output voltage amplitudes and output current amplitudes of the piezoelectric ceramic transformer at different times of multiple sampling points according to the output voltage values ​​and output current values ​​at different times of multiple sampling points, and calculate the current impedance value of the piezoelectric ceramic transformer according to the output voltage amplitudes and output current amplitudes at different times of multiple sampling points; different times are different time points within the same switching cycle; The anti-resonance frequency point scanning and calculation unit is used to determine whether the current scanning frequency of the piezoelectric ceramic transformer is less than the set frequency threshold. If so, the current scanning frequency is incremented by the set value, and the incremented scanning frequency is used as the scanning frequency of the next switching cycle of the piezoelectric ceramic transformer, and the voltage and current acquisition and impedance value calculation unit is returned to recalculate the current impedance value of the piezoelectric ceramic transformer until the current scanning frequency of the piezoelectric ceramic transformer is greater than or equal to the set frequency threshold; it is also used to select the maximum value of the current impedance value of the piezoelectric ceramic transformer, determine the frequency point corresponding to the maximum value of the current impedance value, and make the PWM module work at the frequency point; the frequency corresponding to the maximum value of the current impedance value is the anti-resonance frequency point; An impedance angle true value determination unit, used to obtain an output voltage value and an output current value of the piezoelectric ceramic transformer in a current switching cycle after the PWM module is made to operate at the frequency point, and determine the impedance angle true value according to the output voltage value and the output current value in the current switching cycle; A frequency determination unit is used to obtain an impedance angle difference by subtracting the impedance angle real value from the impedance angle rated value, and determine the adjustment frequency according to the impedance angle difference. A duty cycle determining unit, used to obtain an input voltage value of the piezoelectric ceramic transformer, and determine a duty cycle corresponding to the input voltage value according to the input voltage value; The regulating unit is used to obtain a PWM regulating signal according to the regulating frequency and the duty cycle corresponding to the input voltage value; the PWM regulating signal includes a first regulating signal and a second regulating signal; the first regulating signal is used to realize frequency closed-loop regulation of the plasma power supply, and the second regulating signal is used to realize power closed-loop regulation of the plasma power supply.

7. The plasma power supply control system based on power tracking variable frequency output according to claim 6, characterized in that: The impedance angle true value determination unit specifically includes: Obtain a voltage and current array according to the output voltage value and the output current value in the current switching cycle; Determine the corresponding positions of the voltage zero-crossing point and the current zero-crossing point in the voltage and current array; Calculate the array position difference according to the corresponding position of the voltage zero-crossing point in the voltage and current array and the corresponding position of the current zero-crossing point in the voltage and current array; the array position difference represents the time difference between the voltage zero-crossing point and the current zero-crossing point; Obtaining a phase difference between voltage and current according to the array position difference; The real value of the impedance angle is obtained according to the phase difference between the voltage and the current.

8. The plasma power supply control system based on power tracking variable frequency output according to claim 7, characterized in that: The duty cycle determining unit specifically includes: Determine whether the input voltage value obtained at the current moment is less than the input voltage value at the previous moment; If yes, the number of times the input voltage value obtained at the current moment is less than the input voltage value at the previous moment is accumulated until the accumulated number is greater than the set threshold, and the input voltage value at the current moment is recorded at the same time; An input voltage level corresponding to the input voltage value at the current moment is determined, and a duty cycle corresponding to the input voltage value is determined according to the rated working voltage of the piezoelectric ceramic transformer, the voltage level corresponding to the rated working voltage, and the input voltage level.

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