Microwave power source, microwave plasma system, ignition method and self-tuning method

Abstract

The present invention discloses a microwave power source, a microwave plasma system, an ignition method and a self-tuning method. The microwave power source includes a microwave signal generator for generating microwave signals; a signal adjustment unit for adjusting the amplitude and phase of the microwave signal and for loading pulse signals of different frequencies and duty cycles; a semiconductor amplification unit; a signal transmission and load detection unit for sending the microwave signal amplified by the semiconductor amplification unit to the load, and detecting the sent microwave signal and the microwave reflection signal generated by the load to obtain a detection sampling signal; and a control unit for receiving and analyzing the detection sampling signal to control the signal transmission frequency of the microwave signal generator and / or the control signal adjustment unit adjustment method according to the analysis result. The present invention realizes automatic ignition frequency search, automatic ignition process and self-tuning process, and solves the problem that the current traditional microwave plasma equipment is difficult to automatically ignite and difficult to work stably.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 2020101914439 filed with the China Patent Office on March 18, 2020, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present invention relates to the field of plasma physics technology, and in particular to a microwave power source, a microwave plasma system, an ignition method and a self-tuning method. Background Art

[0004] Microwave plasma refers to the process of transmitting energy through electromagnetic waves to excite gas to produce ionized plasma. Compared with other methods of exciting plasma, microwave plasma has the following advantages: 1. Higher degree of ionization and decomposition, 2. Higher electron temperature, thus achieving lower plasma temperature, 3. No electrodes, no pollution caused by electrode loss, 4. Wide working pressure range, can be applied to a variety of gases; therefore, microwave plasma technology is widely used in many industrial fields such as material synthesis, material analysis, surface treatment, medical cosmetology, semiconductor material preparation, etc., and has achieved good application results.

[0005] However, conventional microwave plasma torches have at least the following disadvantages:

[0006] 1) It is difficult to achieve automatic ignition: According to the principle of microwave plasma torch, the output frequency of microwave power source must be in the optimal excitation response frequency band of the torch. The traditional microwave plasma torch uses magnetron as microwave power source. The frequency of magnetron is unstable and uncontrollable, which makes it difficult to excite the torch for automatic ignition.

[0007] 2) Unable to unify automatic ignition and automatic maintenance states: The load matching states of the plasma torch tube before plasma generation and after successful plasma excitation are quite different. Once automatic ignition is successful, the microwave power source needs to be able to quickly track and adapt to the load changes. The microwave power source of the traditional plasma torch cannot automatically optimize the matching, resulting in low microwave energy coupling efficiency after ignition, and manual adjustment of transmission matching is required;

[0008] 3) Poor time-varying adjustability: During the entire operation of the microwave plasma torch, as the temperature, airflow, and gas change, it is necessary to adjust the transmission matching from the microwave power source to the torch tube in real time to achieve a better energy coupling effect. Traditional microwave plasma torches are more difficult to achieve this, and interruptions will occur when the working state changes.

[0009] The above defects are also the fundamental reason why traditional microwave plasma torches are difficult to achieve large-scale industrialization in practical applications. Summary of the invention

[0010] In order to solve the problems in the prior art, the present invention provides a microwave power source, a microwave plasma system, an ignition method and a self-tuning method, which can realize automatic ignition, automatic tracking of the torch tube load state and real-time optimization of load matching, and can be applied to a brand-new semiconductor microwave power source and a corresponding plasma torch for various applications. The technical solution is as follows:

[0011] In one aspect, the present invention provides a microwave power source, comprising:

[0012] A microwave signal generator, used for generating a microwave signal of a corresponding transmission frequency according to instructions;

[0013] A signal adjustment unit, used to adjust the amplitude and phase of the microwave signal generated by the microwave signal generator, and to load pulse signals with different frequencies and duty cycles;

[0014] a semiconductor amplifying unit, used for amplifying the microwave signal conditioned by the signal conditioning unit;

[0015] A signal transmission and load detection unit, used for sending the microwave signal amplified by the semiconductor amplification unit to the load, and detecting the microwave signal sent to the load and the microwave reflection signal generated by the load mismatch to obtain a detection sampling signal;

[0016] A control unit is used to receive and analyze the detection sampling signal of the signal transmission and load detection unit to generate a first control instruction and / or a second control instruction according to the analysis result, wherein the first control instruction is used to control the signal transmission frequency of the microwave signal generator, and the second control instruction is used to control the signal adjustment unit to adjust the amplitude, phase and / or pulse modulation mode of the microwave signal.

[0017] Furthermore, the signal conditioning unit includes a controllable attenuator, a controllable phase shifter, and a controllable high-speed RF switch, wherein the controllable attenuator is used to receive control instructions from the control unit and attenuate the microwave signal according to the control instructions; the controllable phase shifter is used to receive control instructions from the control unit and adjust the phase of the microwave signal according to the control instructions; the controllable high-speed RF switch is used to receive control instructions from the control unit and pulse modulate the microwave signal according to the control instructions.

[0018] Furthermore, the signal transmission and load detection unit includes a transmission directional coupler, a circulator, a reflection directional coupler, a transmission power detection module and a reflection power detection module, wherein the transmission directional coupler, the circulator and the reflection directional coupler are used to transmit the amplified microwave signal to the load, the transmission power detection module is used to couple and sample the microwave signal transmitted to the load and send the obtained first detection voltage signal to the control unit, and the reflection power detection module is used to couple and sample the microwave reflection signal generated by load mismatch and send the obtained second detection voltage signal to the control unit.

[0019] Furthermore, the microwave signal generator includes a voltage-controlled oscillator and a phase-locked loop that are discretely or integratedly arranged, so as to achieve that the generated microwave signal is adjustable in the frequency range of 25-3000 MHz.

[0020] Furthermore, the load is a plasma generating device.

[0021] On the other hand, the present invention provides a microwave plasma system, comprising a plasma generating device and a microwave power source as described above, wherein the plasma generating device receives a signal transmission from the microwave power source and a microwave signal transmitted by a load detection unit to generate an electric field at a pipe mouth of the plasma generating device that can break through gas to generate plasma.

[0022] On the one hand, the present invention provides an automatic ignition method for a microwave plasma system, comprising: presetting a transmission frequency range of a microwave signal generator, scanning within the transmission frequency range to find a minimum return loss, and using the transmission frequency corresponding to the minimum return loss as an ignition frequency.

[0023] Further, the microwave plasma system is the above-mentioned microwave plasma system, and the ignition frequency is determined in advance by the following steps:

[0024] S101, a microwave signal generator of a microwave power source generates a microwave signal according to an initial transmission frequency instruction;

[0025] S102, the signal transmission and load detection unit of the microwave power source transmits the amplified microwave signal to the plasma generator, performs coupled sampling detection on the microwave signal transmitted to the plasma generator to obtain a first detection voltage signal, and performs coupled sampling detection on the microwave reflection signal generated by the mismatch of the plasma generator to obtain a second detection voltage signal;

[0026] S103, sampling the voltage of the current first detection voltage signal and the second detection voltage signal, and calculating the return loss value corresponding to the microwave power source;

[0027] S104, adjusting the transmission frequency instruction issued to the microwave signal generator, and repeatedly executing S01 and S103 until the transmission frequency range of the microwave signal generator is scanned;

[0028] S105 , searching for a minimum return loss from a plurality of return loss values ​​in the scanning process, determining a transmission frequency corresponding to the minimum return loss, and using the transmission frequency as an ignition frequency.

[0029] Furthermore, the method for calculating the return loss value corresponding to the microwave power source in step S103 is as follows:

[0030] According to the first detection voltage signal and the transmission signal sampling voltage, the control unit of the microwave power source calculates the forward power; according to the second detection voltage signal and the reflection signal sampling voltage, the control unit calculates the reverse power; the return loss value is calculated by the following formula:

[0031] RL=P_r-P_f, where RL is the return loss, P_r is the reverse power, and P_f is the forward power.

[0032] The present invention also provides two self-tuning methods for microwave plasma systems, so as to tune the microwave plasma system to a stable working state after ignition. The first self-tuning method comprises the following steps:

[0033] S201, calculating an initial return loss value of a microwave power source corresponding to an initial transmitting frequency of a microwave signal generator of a microwave power source;

[0034] S202, respectively reducing and increasing the transmission frequency of the microwave signal generator, and respectively calculating a first return loss value in a state of reducing the transmission frequency and a second return loss value in a state of increasing the transmission frequency;

[0035] S203, comparing the initial return loss value, the first return loss value, and the second return loss value to determine the frequency convergence trend. If the frequency convergence trend is a downward frequency convergence trend, execute S204; if the frequency convergence trend is an upward frequency convergence trend, execute S205;

[0036] S204, gradually reducing the transmission frequency of the microwave signal generator until a minimum return loss value is found, and using the transmission frequency corresponding to the minimum return loss value as the tuning frequency of the microwave signal generator;

[0037] S205 , gradually increasing the transmission frequency of the microwave signal generator until a minimum return loss value is found, and using the transmission frequency corresponding to the minimum return loss value as the tuning frequency of the microwave signal generator.

[0038] Further, step S203 includes:

[0039] If the first return loss value is smaller than the initial return loss value and smaller than the second return loss value, it is determined that the frequency convergence trend is a frequency downward convergence trend;

[0040] If the second return loss value is smaller than the initial return loss value and smaller than the first return loss value, it is determined that the frequency convergence trend is a frequency upward convergence trend;

[0041] If the initial return loss value is smaller than the first return loss value and smaller than the second return loss value, the adjustment amplitude of the transmission frequency in step S202 is reduced, and the process returns to execute steps S202 and S203.

[0042] The second self-tuning method includes the following steps:

[0043] S301, calculating an initial return loss value of a microwave power source corresponding to an initial transmitting frequency of a microwave signal generator of a microwave power source;

[0044] S302, adjusting the transmission frequency of the microwave signal generator in a first direction, and calculating a first return loss value after the transmission frequency is adjusted;

[0045] S303, comparing the initial return loss value and the first return loss value, if the first return loss value is smaller than the initial return loss value, executing S304, otherwise executing S305-S306;

[0046] S304, continue to adjust the transmission frequency of the microwave signal generator along the first direction until the minimum return loss value is found, and use the transmission frequency corresponding to the minimum return loss value as the tuning frequency of the microwave signal generator;

[0047] S305, adjusting the transmission frequency of the microwave signal generator along a second direction opposite to the first direction, and calculating a second return loss value after the transmission frequency is adjusted;

[0048] S306, comparing the initial return loss value and the second return loss value, if the second return loss value is smaller than the initial return loss value, executing S307, otherwise executing S308;

[0049] S307, continue to adjust the transmission frequency of the microwave signal generator along the second direction until the minimum return loss value is found, and use the corresponding transmission frequency as the tuning frequency of the microwave signal generator;

[0050] S308. Reduce the adjustment amplitude of the transmission frequency, and return to execute S302-S306.

[0051] Furthermore, the microwave plasma system is the above-mentioned microwave plasma system, and the method for obtaining the return loss value of the corresponding microwave power source according to the transmission frequency is as follows:

[0052] The microwave signal generator of the microwave power source generates a microwave signal according to the initial transmission frequency instruction;

[0053] The signal transmission and load detection unit of the microwave power source transmits the amplified microwave signal to the plasma generator, performs coupled sampling detection on the microwave signal transmitted to the plasma generator to obtain a first detection voltage signal, and performs coupled sampling detection on the microwave reflection signal generated by the mismatch of the plasma generator to obtain a second detection voltage signal;

[0054] The voltage of the current first detection voltage signal and the second detection voltage signal is sampled. According to the first detection voltage signal and the sampling voltage of the transmission signal, the control unit of the microwave power source calculates the forward power; according to the second detection voltage signal and the sampling voltage of the reflection signal, the control unit calculates the reverse power; the return loss value is calculated by the following formula:

[0055] RL=P_r-P_f, where RL is the return loss, P_r is the reverse power, and P_f is the forward power.

[0056] In addition, the present invention also provides a working method of a microwave plasma system, comprising the following steps:

[0057] S401, starting a microwave power source of a microwave plasma system;

[0058] S402, start the ignition frequency optimization program, find the microwave generator transmission frequency corresponding to the minimum return loss, and use the transmission frequency as the ignition frequency point;

[0059] S403, starting the plasma ignition process, including adjusting the transmission power of the microwave generator at the ignition frequency point until the return loss change value reaches a preset return loss mutation threshold, and then determining that the ignition is successful;

[0060] S404, starting a self-tuning process, scanning and searching for a tuning frequency of the microwave generator;

[0061] S405, performing mismatch monitoring on the microwave plasma system, and if it is monitored that the real-time return loss value of the microwave power source is greater than a preset alarm loss threshold, issuing a prompt message and / or returning to execute steps S402-S405.

[0062] The present invention has the following technical effects:

[0063] a. Before igniting the plasma torch, find the best ignition frequency through load detection;

[0064] b. Use load tracking algorithm to achieve the best coupling state of the plasma torch to maintain microwave power, so that the plasma torch tube can always work stably;

[0065] c. All-semiconductor technology can accurately control the frequency, power and phase of microwave signals;

[0066] d. High reliability and stable operation reduce frequent ignition operations and extend service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. 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 creative work.

[0068] Figure 1 is a schematic structural diagram of a microwave plasma system provided by an embodiment of the present invention;

[0069] Figure 2 is a schematic diagram of the structure of a signal conditioning unit provided by an embodiment of the present invention;

[0070] Figure 3 is a structural schematic diagram of a signal transmission and load detection unit provided in an embodiment of the present invention;

[0071] Figure 4 is a schematic diagram of the working process of a microwave plasma system provided by an embodiment of the present invention;

[0072] Figure 5 It is a flow chart of an ignition frequency optimization program provided by an embodiment of the present invention;

[0073] Figure 6 is a schematic diagram of a plasma ignition process provided by an embodiment of the present invention;

[0074] Figure 7 is a schematic diagram of a first self-coordination process provided by an embodiment of the present invention;

[0075] Figure 8 It is a schematic diagram of the second self-coordination process provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0076] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings 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 should fall within the scope of protection of the present invention.

[0077] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, device, product or equipment that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0078] In one embodiment of the present invention, a microwave power source is provided. Figure 1 , the microwave power source comprises:

[0079] A microwave signal generator, used for generating a microwave signal of a corresponding transmission frequency according to instructions;

[0080] A signal adjustment unit, used to adjust the amplitude and phase of the microwave signal generated by the microwave signal generator, and to load pulse signals with different frequencies and duty cycles;

[0081] a semiconductor amplifying unit, used for amplifying the microwave signal conditioned by the signal conditioning unit;

[0082] A signal transmission and load detection unit, used for sending the microwave signal amplified by the semiconductor amplification unit to a load, and detecting the microwave signal sent to the load and the microwave reflection signal generated by the load mismatch to obtain a detection sampling signal. Specifically, the load is a plasma generating device (hereinafter referred to as a plasma torch);

[0083] A control unit is used to receive and analyze the detection sampling signal of the signal transmission and load detection unit to generate a first control instruction and / or a second control instruction according to the analysis result, wherein the first control instruction is used to control the signal transmission frequency of the microwave signal generator, and the second control instruction is used to control the signal adjustment unit to adjust the amplitude, phase and / or pulse modulation mode of the microwave signal.

[0084] Figure 1 A microwave plasma system is also provided, comprising a plasma generating device (plasma torch) and the microwave power source as described above, wherein the microwave power source is responsible for generating microwave signals of appropriate frequency and power and transmitting them to the plasma torch to stimulate plasma production and maintain plasma stability; the plasma generating device receives the signal transmission of the microwave power source and the microwave signal transmitted by the load detection unit to generate an electric field at the tube mouth of the plasma generating device that can break through the gas to generate plasma.

[0085] In summary, the microwave signal generator generates a microwave signal of a specified frequency f according to the control unit instruction and transmits it to the signal control unit. The signal adjustment unit can adjust the amplitude and phase of the signal, and can load pulse signals of different frequencies and duty cycles; the microwave signal adjusted by the signal control unit is transmitted to the semiconductor amplification unit for amplification, and then transmitted to the signal transmission and load detection unit. The signal transmission and load detection unit sends the amplified microwave signal to the plasma torch tube, and can detect the microwave emission signal and the microwave reflection signal generated by the torch tube load mismatch, and transmit the detection sampling signal to the control unit. The control unit calculates and analyzes the emission signal sampling voltage and the reflection signal sampling voltage, and controls the signal emission frequency of the microwave signal emission unit according to the analysis results. At the same time, the signal control unit controls the amplitude, phase, and pulse modulation mode of the signal to realize the self-ignition, self-maintenance, and automatic optimization of the microwave plasma torch tube for different ionized gases. The following is a detailed description of each unit:

[0086] The microwave signal generator is a controllable frequency generator, which can generate a microwave signal with a set flat path according to the setting of the system control unit. The microwave signal generator can be implemented with a discrete voltage-controlled oscillator and a phase-locked loop, or can be designed with an integrated IC. In this embodiment, an integrated chip HMC832 is used for design. The chip integrates a voltage-controlled oscillator and a phase-locked loop, which can cover a frequency range of 25MHz to 3000MHz and can achieve the frequency band required for plasma excitation. During the operation of the system, the microwave signal generator can adjust the signal frequency in real time according to the instructions of the system control unit.

[0087] See also Figure 2The signal conditioning unit is composed of a controllable attenuator, a controllable phase shifter, and a controllable high-speed radio frequency switch, wherein the controllable attenuator can accept the setting instructions of the system control unit to attenuate the microwave signal generated by the microwave signal generator, and the controllable phase shifter can accept the setting instructions of the system control unit to adjust the phase of the microwave signal generated by the microwave signal generator by 0 to 360 degrees; the controllable high-speed radio frequency switch can accept the setting instructions of the system control unit to pulse modulate the microwave signal generated by the microwave signal generator; in general, the signal conditioning unit can adjust the amplitude, phase, and pulse modulation of the microwave signal generated by the microwave signal generator through the instructions of the system control unit, and transmit the adjusted microwave signal to the semiconductor amplification unit.

[0088] The semiconductor amplification unit is composed of a multi-stage semiconductor amplifier, which can be used to amplify the microwave signal after signal conditioning and then output it.

[0089] See also Figure 3 The signal transmission and load detection unit is composed of a transmission directional coupler, a circulator, a reflection directional coupler, a transmission power detection module, and a reflection power detection module. The transmission directional coupler, the circulator, and the reflection directional coupler can transmit the amplified microwave signal to the transmitting end, and can also couple and sample the transmitted microwave signal and the reflected signal generated by the output load mismatch, and transmit the detection voltage to the system control unit for analysis and calculation. The power coupled from the forward power coupler can be detected by the power detector to obtain the forward power detection voltage V DF , the reverse power coupled by the circulator can be detected by the power detector to obtain the reverse power detection voltage V DR , V DF and V DR It will be transmitted to the system monitoring unit. After voltage sampling and calculation, the forward power P_f and reverse power P_r can be obtained in dBm. Then the output return loss RL=P_r-P_f in the working state of the power amplifier can also be calculated in dB. The smaller the RL, the smaller the microwave energy reflected by the power amplifier output, and the higher the load absorption energy. The higher the RL, the greater the reflected microwave energy and the lower the load absorption energy.

[0090] The system control unit is implemented by a microprocessor. The system control unit can control the microwave signal generator, signal conditioning unit, semiconductor power amplifier unit, and microwave transmission and load detection unit, and can adjust the frequency and power of the output microwave signal; extract various parameters, including module temperature monitoring, forward power extraction, and reverse power extraction; calculate return loss and establish an alarm mechanism, including over-temperature alarm, forward power alarm, reverse power alarm, load standing wave ratio alarm, etc.

[0091] The plasma torch is a component that generates plasma. When the microwave power source transmits microwave energy to the plasma torch, an electric field of a certain field strength is generated at the opening of the torch, which can break through the gas ejected from the inner tube of the torch and generate plasma. The frequency response of the input end of the plasma torch is quite different before and after successful ignition. This is the pain point that makes it difficult to stimulate the automatic ignition of the torch and to automatically adjust the transmission matching, resulting in interruptions during the operation of the plasma torch.

[0092] The present invention can realize that before the plasma torch is ignited, the optimal ignition frequency point is found through load detection, microwave energy is emitted to generate plasma, and after the plasma is generated, after the matching frequency of the torch changes significantly, the matching frequency is automatically tracked, the microwave signal emission frequency is optimized, and the best ignition maintenance effect is achieved. At the same time, when the working conditions of the torch change, the automatic optimization state is maintained, the optimal coupling state of the microwave power is maintained, and the operation of the plasma torch is always kept stable. The specific implementation methods are as follows:

[0093] The working process of the microwave plasma system in the embodiment of the present invention is as follows, see Figure 4 :

[0094] S401, starting a microwave power source of a microwave plasma system;

[0095] S402, start the ignition frequency optimization program, find the microwave generator transmission frequency corresponding to the minimum return loss, and use the transmission frequency as the ignition frequency point;

[0096] S403, starting the plasma ignition process, including adjusting the transmission power of the microwave generator at the ignition frequency point until the return loss change value reaches a preset return loss mutation threshold, and then determining that the ignition is successful;

[0097] S404, starting a self-tuning process, scanning and searching for a tuning frequency of the microwave generator;

[0098] S405, performing mismatch monitoring on the microwave plasma system, and if it is monitored that the real-time return loss value of the microwave power source is greater than a preset alarm loss threshold, issuing a prompt message and / or returning to execute steps S402-S405.

[0099] The ignition frequency optimization procedure in step S402 is as follows: Figure 5 As shown: First, pre-set a scanning frequency range (the frequency range can be determined based on the input echo of the static torch tube), as well as a frequency step and scanning power. The scanning frequency range can be scanned in full frequency band according to the frequency step at low power, and the return loss RL = P_r-P_f at each frequency point can be calculated and recorded, and the frequency point with the lowest RL is selected and recorded as the ignition frequency point. The specific steps are as follows:

[0100] S101, a microwave signal generator of a microwave power source generates a microwave signal according to an initial transmission frequency instruction;

[0101] S102, the signal transmission and load detection unit of the microwave power source transmits the amplified microwave signal to the plasma generator, performs coupled sampling detection on the microwave signal transmitted to the plasma generator to obtain a first detection voltage signal, and performs coupled sampling detection on the microwave reflection signal generated by the mismatch of the plasma generator to obtain a second detection voltage signal;

[0102] S103, sampling the voltage of the current first detection voltage signal and the second detection voltage signal, and calculating the return loss value corresponding to the microwave power source;

[0103] S104, adjusting the transmission frequency instruction issued to the microwave signal generator, and repeatedly executing S01 and S103 until the transmission frequency range of the microwave signal generator is scanned;

[0104] S105 , searching for a minimum return loss from a plurality of return loss values ​​in the scanning process, determining a transmission frequency corresponding to the minimum return loss, and using the transmission frequency as an ignition frequency.

[0105] Furthermore, the method for calculating the return loss value corresponding to the microwave power source in step S103 is as follows:

[0106] According to the first detection voltage signal and the transmission signal sampling voltage, the control unit of the microwave power source calculates the forward power; according to the second detection voltage signal and the reflection signal sampling voltage, the control unit calculates the reverse power; the return loss value is calculated by the following formula:

[0107] RL=P_r-P_f, where RL is the return loss, P_r is the reverse power, and P_f is the forward power.

[0108] The plasma ignition process in S403 is as follows: Figure 6 As shown in the figure: after searching for the plasma torch ignition frequency, the microwave power source transmits a signal. Plasma excitation requires sufficient electric field strength to generate plasma. When the electric field is sufficient to ionize the gas to generate plasma, the plasma will form a load at the torch mouth, changing the output matching of the torch tube. The specific manifestation is that before ignition, the output return loss of the microwave power source is good, and after the ignition is successful, the output load changes and the matching frequency changes, resulting in an instantaneous deterioration of the output return loss at the ignition frequency. By judging this instantaneous change state, it is determined whether the ignition is successful. The plasma automatic ignition process is as follows Figure 6, you can set a power increase step and a reflection loss mutation threshold. The difference between the reflection loss RL' after each power increase and the reflection loss before the power increase exceeds the threshold, and it is judged that the reflection loss has a mutation, and the ignition is successful. The specific steps are as follows:

[0109] S501, the microwave signal generator generates a microwave signal according to the current transmission power instruction;

[0110] S502, the control unit calculates the return loss and the return loss change value of the microwave power source corresponding to the current transmission power of the microwave signal generator;

[0111] S503, comparing the return loss change value with a preset return loss mutation threshold value, if the return loss change value is less than the return loss mutation threshold value, increasing the power value in the transmission power instruction issued to the microwave signal generator, and repeatedly executing S501-S503, otherwise executing S504;

[0112] S504: Determine whether the ignition is successful, and record the current transmission power of the microwave signal generator as the ignition power.

[0113] After successful ignition, the output frequency of the microwave power source does not match the optimal power frequency of the plasma torch in the working state, and needs to be self-tuned to the optimal frequency point. The embodiment of the present invention designs a self-tuning process so that the microwave power source can self-tune to the optimal working state of the microwave plasma torch, that is, the output optimal matching state of the microwave power source, and maintain the stable operation of the plasma torch. The present invention also provides two self-tuning methods for microwave plasma systems, so that the microwave plasma system can be tuned to a stable working state after ignition.

[0114] The first self-tuning method is shown in Figure 7 , the specific steps are as follows:

[0115] S201, calculating an initial return loss value of a microwave power source corresponding to an initial transmitting frequency of a microwave signal generator of a microwave power source;

[0116] S202, respectively reducing and increasing the transmission frequency of the microwave signal generator, and respectively calculating a first return loss value in a state of reducing the transmission frequency and a second return loss value in a state of increasing the transmission frequency;

[0117] S203, comparing the initial return loss value, the first return loss value, and the second return loss value to determine the frequency convergence trend. If the frequency convergence trend is a downward frequency convergence trend, execute S204; if the frequency convergence trend is an upward frequency convergence trend, execute S205;

[0118] S204, gradually reducing the transmission frequency of the microwave signal generator until a minimum return loss value is found, and using the transmission frequency corresponding to the minimum return loss value as the tuning frequency of the microwave signal generator;

[0119] S205 , gradually increasing the transmission frequency of the microwave signal generator until a minimum return loss value is found, and using the transmission frequency corresponding to the minimum return loss value as the tuning frequency of the microwave signal generator.

[0120] Further, step S203 includes:

[0121] If the first return loss value is smaller than the initial return loss value and smaller than the second return loss value, it is determined that the frequency convergence trend is a frequency downward convergence trend;

[0122] If the second return loss value is smaller than the initial return loss value and smaller than the first return loss value, it is determined that the frequency convergence trend is a frequency upward convergence trend;

[0123] If the initial return loss value is smaller than the first return loss value and smaller than the second return loss value, the adjustment amplitude of the transmission frequency in step S202 is reduced, and the process returns to execute steps S202 and S203.

[0124] The second self-tuning method is shown in Figure 8 , the specific steps are as follows:

[0125] S301, calculating an initial return loss value of a microwave power source corresponding to an initial transmitting frequency of a microwave signal generator of a microwave power source;

[0126] S302, adjusting (for example, decreasing) the transmission frequency of the microwave signal generator in a first direction, and calculating a first return loss value after the transmission frequency is adjusted;

[0127] S303, comparing the initial return loss value and the first return loss value, if the first return loss value is smaller than the initial return loss value, executing S304, otherwise executing S305-S306;

[0128] S304, continue to adjust the transmission frequency of the microwave signal generator along the first direction until the minimum return loss value is found, and use the transmission frequency corresponding to the minimum return loss value as the tuning frequency of the microwave signal generator;

[0129] S305, adjusting (corresponding to increasing) the transmission frequency of the microwave signal generator along a second direction opposite to the first direction, and calculating a second return loss value after the transmission frequency is adjusted;

[0130] S306, comparing the initial return loss value and the second return loss value, if the second return loss value is smaller than the initial return loss value, executing S307, otherwise executing S308;

[0131] S307, continue to adjust the transmission frequency of the microwave signal generator along the second direction until the minimum return loss value is found, and use the corresponding transmission frequency as the tuning frequency of the microwave signal generator;

[0132] S308. Reduce the adjustment amplitude of the transmission frequency, and return to execute S302-S306.

[0133] It should be noted that when S308 needs to be executed, it means that the return loss values ​​after adjusting the transmission frequency in the first direction and the second direction are both greater than the initial return loss value, which means that the convergence trend of the return loss cannot be determined. At this time, the adjustment amplitude (adjustment step) of the transmission frequency needs to be reduced. Obviously, the adjustment amplitude of the transmission frequency here needs to be set to a minimum value to avoid wireless looping of the self-coordination process; if after several cycles, the adjustment amplitude reaches the set minimum value, and the convergence trend of the return loss still cannot be determined, the initial return loss value is used as the tuning frequency of the microwave signal generator.

[0134] The idea of ​​the above two self-tuning methods is the same, that is, taking the initial frequency as the reference, the tuning frequency of the microwave signal generator is tested to find the minimum return loss. It should be noted that the first direction in step S302 can also be adjusted up first, and the second direction in step S305 corresponds to adjusting down. The amplitude of each adjustment is called the adjustment step. The smaller the adjustment step, the higher the accuracy of finding the minimum return loss. The adjustment step can be set manually.

[0135] As described above, the method for obtaining the return loss value of the corresponding microwave power source according to the transmitting frequency is as follows:

[0136] The microwave signal generator of the microwave power source generates a microwave signal according to the initial transmission frequency instruction;

[0137] The signal transmission and load detection unit of the microwave power source transmits the amplified microwave signal to the plasma generator, and performs coupled sampling detection on the microwave signal transmitted to the plasma generator to obtain a first detection voltage signal (i.e., a forward power detection voltage V DF ), and coupled sampling detection is performed on the microwave reflection signal generated by the mismatch of the plasma generating device to obtain a second detection voltage signal (i.e., the reverse power detection voltage V DR );

[0138] V DF and V DRIt will be transmitted to the system monitoring unit, and the voltage of the current first detection voltage signal and the second detection voltage signal is sampled. According to the first detection voltage signal and the sampling voltage of the transmission signal, the control unit of the microwave power source calculates the forward power P_f; according to the second detection voltage signal and the sampling voltage of the reflection signal, the control unit calculates the reverse power P_r. The forward power / reverse power is calculated according to the sampled amplitude voltage as a conventional method; the return loss value is calculated by the following formula:

[0139] RL=P_r-P_f, where RL is the return loss, P_r is the reverse power, and P_f is the forward power.

[0140] In addition, when the working state of the plasma torch changes, such as gas changes, flow changes, and temperature changes, the plasma torch may interrupt ignition. At this time, the plasma torch will be in a mismatch state, that is, the output return loss of the microwave power source suddenly changes to a higher value. In the embodiment of the present invention, an alarm threshold RL=A is set in step S105. When the real-time RL' of the microwave power source is greater than A, it is judged as an ignition interruption alarm, and the working process of the plasma torch will return to the automatic ignition frequency search process, and restart the automatic ignition and self-tuning program.

[0141] The sequence of the above embodiments of the present invention is only for description and does not represent the advantages or disadvantages of the embodiments.

[0142] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A microwave power source, characterized in that: include: A microwave signal generator, used for generating a microwave signal of a corresponding transmission frequency according to instructions; A signal adjustment unit, used to adjust the amplitude and phase of the microwave signal generated by the microwave signal generator, and to load pulse signals with different frequencies and duty cycles; a semiconductor amplifying unit, used for amplifying the microwave signal conditioned by the signal conditioning unit; A signal transmission and load detection unit, used for sending the microwave signal amplified by the semiconductor amplification unit to the load, and detecting the microwave signal sent to the load and the microwave reflection signal generated by the load mismatch to obtain a detection sampling signal; A control unit is used to receive and analyze the detection sampling signal of the signal transmission and load detection unit to generate a first control instruction and / or a second control instruction according to the analysis result, wherein the first control instruction is used to control the signal transmission frequency of the microwave signal generator, and the second control instruction is used to control the signal adjustment unit to adjust the amplitude, phase and / or pulse modulation mode of the microwave signal.

2. The microwave power source according to claim 1, characterized in that: The signal conditioning unit includes a controllable attenuator, a controllable phase shifter, and a controllable high-speed RF switch, wherein the controllable attenuator is used to receive the control instruction of the control unit and attenuate the microwave signal according to the control instruction; the controllable phase shifter is used to receive the control instruction of the control unit and adjust the phase of the microwave signal according to the control instruction; the controllable high-speed RF switch is used to receive the control instruction of the control unit and pulse modulate the microwave signal according to the control instruction.

3. The microwave power source according to claim 1, characterized in that: The signal transmission and load detection unit includes a transmission directional coupler, a circulator, a reflection directional coupler, a transmission power detection module and a reflection power detection module, wherein the transmission directional coupler, the circulator and the reflection directional coupler are used to transmit the amplified microwave signal to the load, the transmission power detection module is used to couple and sample the microwave signal transmitted to the load and send the obtained first detection voltage signal to the control unit, and the reflection power detection module is used to couple and sample the microwave reflection signal generated by load mismatch and send the obtained second detection voltage signal to the control unit.

4. The microwave power source according to claim 1, characterized in that: The microwave signal generator comprises a voltage-controlled oscillator and a phase-locked loop which are arranged discretely or integratedly, so as to realize that the generated microwave signal is adjustable in the frequency range of 25-3000 MHz.

5. The microwave power source according to any one of claims 1 to 4, characterized in that: The load is a plasma generating device.

6. A microwave plasma system, characterized in that: The invention comprises a plasma generating device and a microwave power source as claimed in any one of claims 1 to 5, wherein the plasma generating device receives a microwave signal transmitted by a signal transmission of the microwave power source and a load detection unit to generate an electric field at a pipe mouth of the plasma generating device that can break through gas to generate plasma.

7. An automatic ignition method for a microwave plasma system according to claim 6, characterized in that: include: The transmitting frequency range of the microwave signal generator is preset, and the minimum return loss is found by scanning within the transmitting frequency range, and the transmitting frequency corresponding to the minimum return loss is used as the ignition frequency point.

8. The automatic ignition method of a microwave plasma system according to claim 7, characterized in that: The microwave plasma system is the microwave plasma system according to claim 6, and the ignition frequency is determined in advance by the following steps: S101, a microwave signal generator of a microwave power source generates a microwave signal according to an initial transmission frequency instruction; S102, the signal transmission and load detection unit of the microwave power source transmits the amplified microwave signal to the plasma generator, performs coupled sampling detection on the microwave signal transmitted to the plasma generator to obtain a first detection voltage signal, and performs coupled sampling detection on the microwave reflection signal generated by the mismatch of the plasma generator to obtain a second detection voltage signal; S103, sampling the voltage of the current first detection voltage signal and the second detection voltage signal, and calculating the return loss value corresponding to the microwave power source; S104, adjusting the transmission frequency instruction issued to the microwave signal generator, and repeatedly executing S01 and S103 until the transmission frequency range of the microwave signal generator is scanned; S105 , searching for a minimum return loss from a plurality of return loss values ​​in the scanning process, determining a transmission frequency corresponding to the minimum return loss, and using the transmission frequency as an ignition frequency.

9. The automatic ignition method of a microwave plasma system according to claim 8, characterized in that: The method for calculating the return loss value corresponding to the microwave power source in step S103 is as follows: According to the first detection voltage signal and the transmission signal sampling voltage, the control unit of the microwave power source calculates the forward power; according to the second detection voltage signal and the reflection signal sampling voltage, the control unit calculates the reverse power; the return loss value is calculated by the following formula: RL=P_r-P_f, where RL is the return loss, P_r is the reverse power, and P_f is the forward power.

10. A self-tuning method for a microwave plasma system according to claim 6, characterized in that: After the microwave plasma system is ignited, tune it to a stable working state by following the steps below: S201, calculating an initial return loss value of a microwave power source corresponding to an initial transmitting frequency of a microwave signal generator of a microwave power source; S202, respectively reducing and increasing the transmission frequency of the microwave signal generator, and respectively calculating a first return loss value in a state of reducing the transmission frequency and a second return loss value in a state of increasing the transmission frequency; S203, comparing the initial return loss value, the first return loss value, and the second return loss value to determine the frequency convergence trend. If the frequency convergence trend is a downward frequency convergence trend, execute S204; if the frequency convergence trend is an upward frequency convergence trend, execute S205; S204, gradually reducing the transmission frequency of the microwave signal generator until a minimum return loss value is found, and using the transmission frequency corresponding to the minimum return loss value as the tuning frequency of the microwave signal generator; S205 , gradually increasing the transmission frequency of the microwave signal generator until a minimum return loss value is found, and using the transmission frequency corresponding to the minimum return loss value as the tuning frequency of the microwave signal generator.

11. The self-tuning method of a microwave plasma system according to claim 10, characterized in that: Step S203 includes: If the first return loss value is smaller than the initial return loss value and smaller than the second return loss value, it is determined that the frequency convergence trend is a frequency downward convergence trend; If the second return loss value is smaller than the initial return loss value and smaller than the first return loss value, it is determined that the frequency convergence trend is a frequency upward convergence trend; If the initial return loss value is smaller than the first return loss value and smaller than the second return loss value, the adjustment amplitude of the transmission frequency in step S202 is reduced, and the process returns to execute steps S202 and S203.

12. A self-tuning method for a microwave plasma system according to claim 6, characterized in that: After the microwave plasma system is ignited, tune it to a stable working state by following the steps below: S301, calculating an initial return loss value of a microwave power source corresponding to an initial transmitting frequency of a microwave signal generator of a microwave power source; S302, adjusting the transmission frequency of the microwave signal generator in a first direction, and calculating a first return loss value after the transmission frequency is adjusted; S303, comparing the initial return loss value and the first return loss value, if the first return loss value is smaller than the initial return loss value, executing S304, otherwise executing S305-S306; S304, continue to adjust the transmission frequency of the microwave signal generator along the first direction until the minimum return loss value is found, and use the transmission frequency corresponding to the minimum return loss value as the tuning frequency of the microwave signal generator; S305, adjusting the transmission frequency of the microwave signal generator along a second direction opposite to the first direction, and calculating a second return loss value after the transmission frequency is adjusted; S306, comparing the initial return loss value and the second return loss value, if the second return loss value is smaller than the initial return loss value, executing S307, otherwise executing S308; S307, continue to adjust the transmission frequency of the microwave signal generator along the second direction until the minimum return loss value is found, and use the corresponding transmission frequency as the tuning frequency of the microwave signal generator; S308. Reduce the adjustment amplitude of the transmission frequency, and return to execute S302-S306.

13. The self-tuning method of a microwave plasma system according to claim 10 or 12, characterized in that: The microwave plasma system is the microwave plasma system according to claim 6, and the method for obtaining the return loss value of the corresponding microwave power source according to the transmission frequency is as follows: The microwave signal generator of the microwave power source generates a microwave signal according to the initial transmission frequency instruction; The signal transmission and load detection unit of the microwave power source transmits the amplified microwave signal to the plasma generator, performs coupled sampling detection on the microwave signal transmitted to the plasma generator to obtain a first detection voltage signal, and performs coupled sampling detection on the microwave reflection signal generated by the mismatch of the plasma generator to obtain a second detection voltage signal; The voltage of the current first detection voltage signal and the second detection voltage signal is sampled. According to the first detection voltage signal and the sampling voltage of the transmission signal, the control unit of the microwave power source calculates the forward power; according to the second detection voltage signal and the sampling voltage of the reflection signal, the control unit calculates the reverse power; the return loss value is calculated by the following formula: RL=P_r-P_f, where RL is the return loss, P_r is the reverse power, and P_f is the forward power.

14. A working method of the microwave plasma system according to claim 6, characterized in that: The following steps are involved: S401, starting a microwave power source of a microwave plasma system; S402, start the ignition frequency optimization program, find the microwave generator transmission frequency corresponding to the minimum return loss, and use the transmission frequency as the ignition frequency point; S403, starting the plasma ignition process, including adjusting the transmission power of the microwave generator at the ignition frequency point until the return loss change value reaches a preset return loss mutation threshold, and then determining that the ignition is successful; S404, starting a self-tuning process, scanning and searching for a tuning frequency of the microwave generator; S405, performing mismatch monitoring on the microwave plasma system, and if it is monitored that the real-time return loss value of the microwave power source is greater than a preset alarm loss threshold, issuing a prompt message and / or returning to execute steps S402-S405.

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