A digital variable polarity gas metal arc welding power source for thin plates

Abstract

The present invention discloses a digital variable polarity gas metal arc welding power source for thin plates. The power source includes a main arc main circuit, an auxiliary arc stabilizing circuit, a control circuit, a control circuit power supply module, and a human-machine interaction system; among them, the main arc main circuit includes a three-phase rectifier filter circuit, an IGBT primary inverter circuit, a high-frequency transformer, a fast rectifier filter circuit, and a secondary inverter circuit connected in sequence; the three-phase rectifier filter circuit is connected to a three-phase AC power supply, and the secondary inverter circuit is connected to the auxiliary arc stabilizing circuit; the inverter of the present invention has a high frequency and good dynamic performance, and can flexibly adjust the welding current waveform through a digital control method, realizing precise control of the heat output during thin plate welding, and having good adaptability in the application of thin plate welding.

Description

Technical Field

[0001] The present invention relates to the technical field of welding power sources, and more specifically, to a digital variable polarity welding power source for thin plates. Technical Background

[0002] Thin plates are lightweight, high-strength, low-cost, and have excellent comprehensive performance. In the field of automobile manufacturing, thin plates have been widely used. They can not only effectively reduce the body weight and fuel consumption of vehicles, but also reduce inertia and improve vehicle performance. However, during the welding process of thin plates, due to factors such as the poor stiffness and anti-deformation ability of thin plates themselves and their sensitivity to heat input, problems such as welding deformation, burn-through, and molten pool collapse are likely to occur. The variable polarity MAG welding method, as a low heat input welding method, has better comprehensive performance compared with methods such as cold metal transfer (CMT), laser welding, and friction stir welding. It not only has a lower manufacturing cost but also can flexibly control the output waveform, improve the welding quality, and reduce the heat input to the workpiece.

[0003] In recent years, variable polarity welding equipment has become the research focus in the field of thin plate welding at home and abroad. In a digital variable polarity MAG welding system for thin steel plates, the variable polarity power source is the core of the entire system. Its dynamic performance, response speed, and operating stability directly determine the control accuracy of energy during the welding process and affect the welding quality. Since welding is a non-linear time-varying process and is affected by uncertain factors, it will lead to poor quality of the entire welding formation. Currently, domestic variable polarity welding power sources have the following problems:

[0004] 1. Poor system stability, slow response speed, and low waveform control accuracy.

[0005] 2. During the welding process, arc extinction problems are likely to occur during the switching of the positive and negative polarities of the welding current, affecting the welding quality.

[0006] 3. Due to the existence of multiple adjustable parameters such as the peak welding current, base welding current, short-circuit current, and EN / EP ratio, it is difficult to match the parameters.

[0007] 4. The main circuit and the auxiliary circuit contain multiple active power devices, and the complexity of the control circuit of the power source is relatively high.

[0008] The above-mentioned factors have restricted the popularization and application of variable polarity MAG welding technology in China. Feng Ruijie et al. developed a full digital variable polarity MIG welding system for welding magnesium alloys (Feng Ruijie. Research on the full digital variable polarity MIG welding system for magnesium alloys and its process optimization [D]. South China University of Technology, 2016.), which obtained good welding results in the welding of magnesium alloy thin plates. However, the auxiliary arc stabilizing circuit it adopted can only output constant high-voltage pulses, resulting in low control accuracy of energy during the welding process and narrowing the range of its welding process parameters. Summary of the Invention

[0009] The object of the present invention is to overcome the disadvantages in the prior art and provide a variable polarity MAG digital welding power source, so as to solve problems such as instantaneous arc extinction during variable polarity change, low energy control accuracy, and poor working reliability of traditional variable polarity power sources.

[0010] In the primary IGBT inverter circuit of the present invention, an asymmetric IGBT full-bridge inverter circuit is introduced, realizing ZVS in a wider range, improving the energy utilization rate of the welding system, and reducing the energy consumption of the equipment. In addition, a three-phase fully controlled rectifier circuit is introduced in the auxiliary arc stabilizing circuit, which can flexibly adjust the amplitude of the high-voltage pulse, has higher energy control accuracy, a wider range of welding process parameters, and better welding adaptability during thin plate welding.

[0011] The object of the present invention is achieved by at least one of the following technical solutions.

[0012] A digital variable polarity gas metal arc welding power source for thin plates includes a main arc main circuit, an auxiliary arc stabilizing circuit, a control circuit, a control circuit power supply module, and a human-machine interaction system;

[0013] Among them, the main arc main circuit includes a three-phase rectifier filter circuit, an IGBT primary inverter circuit, a high-frequency transformer, a fast rectifier filter circuit, and a secondary inverter circuit connected in sequence; the three-phase rectifier filter circuit is connected to a three-phase AC power supply, and the secondary inverter circuit is connected to the auxiliary arc stabilizing circuit;

[0014] The three-phase rectifier filter circuit converts the 380V three-phase alternating current input from the three-phase AC power supply into a smooth direct current of 535V - 540V; the IGBT primary inverter circuit and the high-frequency transformer convert the smooth direct current into a high-frequency alternating current; the high-frequency alternating current is converted into an adjustable direct current of 0 - 400A after passing through the fast rectifier filter circuit; the secondary inverter circuit is used to change the polarity of the direct current obtained by the fast rectifier filter circuit to form a variable polarity welding current required for welding; the auxiliary arc stabilizing circuit is connected to the three-phase AC power supply to provide an adjustable pulsed high voltage for the welding arc when the welding current changes polarity, ensuring reliable re-ignition of the welding arc after it extinguishes at the moment when the welding current passes through zero.

[0015] The control circuit is respectively connected to the IGBT primary inverter circuit, the secondary inverter circuit, the auxiliary arc stabilizing circuit, the control circuit power supply module, and the human-machine interaction system.

[0016] Furthermore, the three-phase rectifier filter circuit includes a three-phase rectifier module and an LC filter module connected in series; the three-phase rectifier module is connected to the three-phase AC power supply;

[0017] The IGBT primary inverter circuit includes a first IGBT switch, a second IGBT switch, a third IGBT switch, a fourth IGBT switch, and a first RC absorption protection circuit;

[0018] Among them, the first IGBT switch, the second IGBT switch, and the third IGBT switch are connected in series and then connected in parallel with the LC filter module. The auxiliary capacitor and the fourth IGBT switch are connected in series and then connected in parallel with the series-connected second IGBT switch and third IGBT switch. One end of the primary of the high-frequency transformer is connected between the series-connected second IGBT switch and third IGBT switch, and the other end is connected between the series-connected auxiliary capacitor and fourth IGBT switch;

[0019] In the first RC absorption protection circuit, the first resistor and the third capacitor are connected in series and then connected in parallel with the first IGBT switch; the second resistor and the fourth capacitor are connected in series and then connected in parallel with the second IGBT switch; the third resistor and the fifth capacitor are connected in series and then connected in parallel with the third IGBT switch; the fourth resistor and the sixth capacitor are connected in series and then connected in parallel with the fourth IGBT switch.

[0020] Furthermore, the secondary inverter circuit is a half-bridge structure, including a fifth IGBT switch and a sixth IGBT switch, and the polarity of the current is changed by controlling the conduction time of the upper and lower bridge arms;

[0021] The auxiliary arc stabilization circuit includes an input fully controlled rectifier filter circuit and a full-bridge IGBT inverter circuit;

[0022] The input fully controlled rectifier filter circuit is connected to a three-phase AC power supply, the full-bridge IGBT inverter circuit is connected to the input fully controlled rectifier filter circuit, and the load of the arc generated between the positive and negative poles of the welding power supply is connected to the full-bridge IGBT inverter circuit.

[0023] The input fully controlled rectifier filter circuit is used to convert three-phase alternating current into direct current with adjustable input voltage. The full-bridge IGBT circuit is used to change the polarity of the input voltage and adjust the duration of the high-voltage pulse; the full-bridge IGBT inverter circuit can generate a positive high-voltage pulse by controlling the turn-on of the seventh IGBT switch and the tenth IGBT switch, and the pulse width can be adjusted by adjusting the turn-on time; by controlling the turn-on of the eighth IGBT switch and the ninth IGBT switch, a negative high-voltage pulse can be generated, and the pulse width can be adjusted by adjusting the turn-on time; the auxiliary arc stabilization circuit provides a stable and adjustable high-voltage pulse during the commutation of the welding current, ensuring the reliable reignition of the welding arc.

[0024] Furthermore, the control circuit includes an ARM controller, a primary inverter drive module, a secondary inverter drive module, a main arc current sampling circuit, a voltage sampling circuit, an auxiliary arc stabilization drive circuit, and a fault detection module;

[0025] Among them, the ARM controller is respectively connected to the IGBT primary inverter circuit, the secondary inverter circuit and the auxiliary arc stabilizing circuit through a primary inverter drive module, a secondary inverter drive module and an auxiliary arc stabilizing drive circuit for driving;

[0026] The primary inverter drive module is used to drive the on and off of the IGBT switch tube in the IGBT primary inverter circuit to realize two control modes of constant voltage and constant current; the secondary inverter drive module is used to drive the on and off of the IGBT switch tube in the secondary inverter circuit to control the change of the polarity of the welding current; the auxiliary arc stabilizing drive circuit is used to drive the on and off of the IGBT switch tube in the auxiliary arc stabilizing circuit;

[0027] The auxiliary arc stabilizing circuit is respectively connected to the ARM controller to input current and voltage sampling signals through the main arc current sampling circuit and the voltage sampling circuit;

[0028] The ARM controller is respectively connected to the human-machine interaction system, the fault detection module and the control power supply module.

[0029] Further, the ARM controller includes an ARM Cortex-M4 core microprocessor or an STM32F407 microprocessor.

[0030] Further, the human-machine interaction system is based on the Modbus communication protocol and is connected to the ARM controller by using the RS485 communication method to realize the setting and real-time display of welding parameters.

[0031] Further, the control power supply module includes a step-down transformer, a first voltage stabilizing circuit with an output of +3.3V, a second voltage stabilizing circuit with an output of +5V, a third voltage stabilizing circuit with an output of +10V, a fourth voltage stabilizing circuit with an output of +15V, a fourth voltage stabilizing circuit with an output of -15V, and a sixth voltage stabilizing circuit with an output of +24V;

[0032] The step-down transformer is respectively connected to the 220V alternating current output by the power grid and the input ends of the first voltage stabilizing circuit, the second voltage stabilizing circuit, the third voltage stabilizing circuit and the fourth voltage stabilizing circuit; the first voltage stabilizing circuit, the second voltage stabilizing circuit and the third voltage stabilizing circuit are respectively connected to the ARM controller; the fourth voltage stabilizing circuit is respectively connected to the primary inverter drive module and the voltage sampling circuit; the fifth voltage stabilizing circuit and the sixth voltage stabilizing circuit are connected to the main arc main circuit voltage sampling circuit.

[0033] Further, by controlling the duty cycle of the IGBT switch tube on the IGBT primary inverter circuit, the output current and voltage of the voltage and current sampling circuits are adjusted to follow the reference current and reference voltage set by the ARM controller;

[0034] During the welding process, if the constant current mode is selected, the ARM controller samples the current signal output by the main arc main circuit in real time through the current sampling circuit, compares the sampled current signal with the reference current, and adjusts the duty cycle through the digital PI controller to achieve the constant current closed-loop control of the welding current; if the constant voltage mode is selected, the ARM controller samples the voltage signal output by the main arc main circuit in real time through the voltage sampling circuit, compares the sampled voltage signal with the reference voltage, and adjusts the duty cycle through the digital PI controller to achieve the closed-loop control of the arc voltage;

[0035] The voltage sampling circuit samples the voltage signal output by the main arc main circuit in real time to determine the arc ignition state or short-circuit state, and displays it on the display screen of the human-machine interaction system.

[0036] Furthermore, the ARM controller, the primary inverter drive module, the voltage sampling circuit, the current sampling circuit, and the IGBT primary inverter circuit constitute a primary inverter drive control system;

[0037] The ARM controller of the primary inverter control system controls the primary inverter drive module to send PWM drive signals to the IGBT primary inverter circuit according to the reference current and reference voltage signals set by the human-machine interaction system, and adjusts the duty cycle of the IGBT switch tube in the IGBT primary inverter circuit through the voltage and current signals of the main arc main circuit sampled in real time by the voltage sampling circuit and the current sampling circuit, so as to achieve the double closed-loop control of voltage and current;

[0038] To ensure the stability and reliability of the welding power supply, the control circuit is provided with overvoltage and undervoltage protection at the input end, and overheat protection, overcurrent protection, and overcurrent protection of the primary side of the transformer are provided on the primary inverter circuit module; when a fault occurs in the welding power supply, the control circuit immediately shuts off the output of the primary inverter circuit drive signal, and at the same time displays the fault type code on the display screen of the human-machine interaction system and issues an alarm.

[0039] Furthermore, the ARM controller, the secondary inverter drive module, the secondary inverter circuit, and the voltage sampling circuit constitute a secondary inverter control system;

[0040] Among them, the ARM controller determines whether the welding process is in a short-circuit state or an arc ignition state by sampling the arc voltage in real time through the voltage sampling circuit, and indirectly determines the necking state of the molten droplet liquid bridge of the arc load by sampling the change rate of the arc voltage through the arc sampling circuit;

[0041] Then, combined with the time when the welding current set by the ARM controller is negative polarity, the switching states of the fifth switch tube and the sixth switch tube in the secondary inverter circuit are controlled;

[0042] The ARM controller of the secondary inverter control system uses a human-computer interaction system to set the short-circuit voltage, compares the set short-circuit voltage with the arc voltage sampled in real time by the voltage sampling circuit to determine the switching time of the welding current polarity, and controls the secondary inverter drive module to send a PWM drive signal to drive the on and off of the IGBT switch tube of the secondary inverter circuit, thereby realizing rapid switching of the welding current polarity.

[0043] Compared with the prior art, the present invention has the following advantages:

[0044] 1) The variable polarity MAG welding power supply of the present invention adopts an auxiliary arc stabilization circuit with controllable arc stabilization pulse voltage. The appropriate arc stabilization pulse voltage is matched according to different application scenarios to ensure the reliable reignition of the arc during the current polarity switching process. At the same time, since the pulse voltage peak is adjustable, the adjustment range of the welding process parameters is improved and the process window is expanded.

[0045] 2) The present invention introduces an asymmetric IGBT full-bridge inverter circuit into the primary IGBT inverter circuit, thereby achieving a wider range of ZVS, improving the energy utilization rate of the welding system, and reducing the energy consumption of the equipment.

[0046] 3) The controller of the variable polarity MAG welding power supply of the present invention adopts a high-performance microprocessor based on ARM Cortex-M4. The system has fast data processing speed and excellent dynamic performance. It realizes the fine design and real-time control of the segmented and graded welding arc current, effectively improving the control accuracy of the welding energy, and is suitable for thin plate welding occasions with high heat input requirements.

[0047] 4) The human-computer interaction system of the variable polarity MAG welding power supply of the present invention adopts RS485 communication mode. Compared with the traditional digital tube screen, the human-computer interaction system is more user-friendly, convenient in setting and displaying process parameters, occupies less chip resources, and has strong anti-interference ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a schematic diagram of the structure of a thin plate digital variable polarity metal active gas shielded welding power supply according to an embodiment of the present invention;

[0049] Figure 2 This is a main circuit topology diagram of a thin plate digital variable polarity metal active gas shielded welding power supply according to an embodiment of the present invention;

[0050] Figure 3 This is a schematic diagram of the structure of the control circuit power supply module in an embodiment of the present invention;

[0051] Figure 4 This is a block diagram of a primary inverter control system in an embodiment of the present invention;

[0052] Figure 5It is the block diagram of the secondary inversion control system in the embodiment of the present invention;

[0053] Figure 6 It is the primary inversion drive circuit diagram in the embodiment of the present invention;

[0054] Figure 7 It is the secondary inversion drive circuit diagram in the embodiment of the present invention;

[0055] Figure 8 It is the main arc main circuit current sampling circuit diagram in the embodiment of the present invention;

[0056] Figure 9 It is the main arc main circuit voltage sampling circuit diagram in the embodiment of the present invention. Specific embodiments

[0057] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0058] Embodiment 1:

[0059] A thin - plate digital variable - polarity gas - shielded metal arc welding power source, as Figure 1 shown, includes a main arc main circuit, an auxiliary arc - stabilizing circuit, a control circuit, a control circuit power supply module, and a human - machine interaction system;

[0060] Among them, the main arc main circuit includes a three - phase rectification and filtering circuit, an IGBT primary inversion circuit, a high - frequency transformer, a fast rectification and filtering circuit, and a secondary inversion circuit connected in sequence; the three - phase rectification and filtering circuit is connected to a three - phase AC power supply, and the secondary inversion circuit is connected to the auxiliary arc - stabilizing circuit;

[0061] The three - phase rectification and filtering circuit converts the 380V three - phase alternating current input from the three - phase AC power supply into a smooth direct current of 535V - 540V; the IGBT primary inversion circuit and the high - frequency transformer convert the smooth direct current into a high - frequency alternating current; the high - frequency alternating current is converted into an adjustable direct current of 0 - 400A after passing through the fast rectification and filtering circuit; the secondary inversion circuit is used to change the polarity of the direct current obtained by the fast rectification and filtering circuit to form the variable - polarity welding current required for welding; the auxiliary arc - stabilizing circuit is connected to the three - phase AC power supply to provide an adjustable pulsed high voltage for the welding arc when the welding current changes polarity, ensuring reliable reignition of the welding arc after it extinguishes at the moment when the welding current passes through zero;

[0062] The control circuit is respectively connected to the IGBT primary inversion circuit, the secondary inversion circuit, the auxiliary arc - stabilizing circuit, the control circuit power supply module, and the human - machine interaction system.

[0063] In this embodiment, the three - phase rectification and filtering circuit includes a three - phase rectification module MDS100 and an LC filtering module connected in series; the three - phase rectification module MDS100 is connected to the three - phase AC power supply;

[0064] In this embodiment, as Figure 2 shown, the IGBT primary inverter circuit uses an asymmetric full-bridge structure, with a working frequency of 20 kHz. The IGBT primary inverter circuit includes a first IGBT switch Q1, a second IGBT switch Q2, a third IGBT switch Q3, a fourth IGBT switch Q4, and a first RC snubber protection circuit;

[0065] Among them, the first IGBT switch Q1, the second IGBT switch Q2, and the third IGBT switch Q3 are connected in series and then connected in parallel with the LC filter module. The auxiliary capacitor C7 and the fourth IGBT switch Q4 are connected in series and then connected in parallel with the series-connected second IGBT switch Q2 and third IGBT switch Q3. One end of the primary of the high-frequency transformer is connected between the series-connected second IGBT switch Q2 and third IGBT switch Q3, and the other end is connected between the series-connected auxiliary capacitor C7 and fourth IGBT switch Q4;

[0066] In the first RC snubber protection circuit, the first resistor R1 and the third capacitor C are connected in series and then connected in parallel with the first IGBT switch Q1; the second resistor R2 and the fourth capacitor C4 are connected in series and then connected in parallel with the second IGBT switch Q2; the third resistor R3 and the fifth capacitor C5 are connected in series and then connected in parallel with the third IGBT switch Q3; the fourth resistor R4 and the sixth capacitor C6 are connected in series and then connected in parallel with the fourth IGBT switch Q4.

[0067] In this embodiment, the first IGBT switch Q1, the second IGBT switch Q2, the third IGBT switch Q3, and the fourth IGBT switch Q4 are all IGBT single tubes FF100R12RT4.

[0068] The working process of the IGBT primary inverter circuit is as follows: The fourth IGBT switch Q4 conducts, and the fifth capacitor C5, the third resistor R3, the primary inductor of the transformer, and the auxiliary capacitor C7 form a loop. The fourth capacitor C4, the second resistor R2, the primary inductor of the transformer, and the fourth IGBT switch Q4 form a loop. During this period, the fifth capacitor C5 and the primary inductor of the transformer release energy, and the fourth capacitor C4 stores energy. When the energy of the fifth capacitor C5 is released to 0, the third IGBT switch Q3 conducts with zero voltage switching (ZVS). The third IGBT switch Q3, the primary inductor of the transformer, and the auxiliary capacitor C7 form a loop. During this period, the auxiliary capacitor and the primary inductor of the transformer release energy. After that, under the energy cycle of the auxiliary capacitor C7 and the primary inductor of the transformer, the second IGBT switch Q2 and the third IGBT switch Q3 commutate, the second IGBT switch Q2 conducts with ZVS, and the third IGBT switch Q4 turns off. The first IGBT switch Q1 conducts, and the first IGBT switch Q1, the auxiliary capacitor C7, the sixth capacitor C6, and the LC filter circuit form a loop. During this period, the auxiliary capacitor C7 stores energy for the next cycle.

[0069] The fast rectifier filter circuit includes a rectifier diode module FRS300BA50 and a second RC absorption protection circuit.

[0070] The first secondary output terminal 1 of the high-frequency transformer is connected to the connection point of the first rectifier diode D1 and the second rectifier diode D2 of the diode module FRS300BA50. The second secondary output terminal 2 of the high-frequency transformer is connected to the arc load. The third secondary output terminal 3 of the high-frequency transformer is connected to the connection point of the third rectifier diode D3 and the fourth rectifier diode D4 of the diode module FRS300BA50. In the second RC absorption protection circuit, the fifth resistor R5 and the eighth capacitor C8 are connected in series and then connected to the first rectifier diode D1 of the rectifier diode module FRS300BA50. The sixth resistor R6 and the ninth capacitor C9 are connected in series and then connected to the second rectifier diode D2 of the rectifier diode module FRS300BA50. The seventh resistor R7 and the tenth capacitor C10 are connected in series and then connected to the third rectifier diode D3 of the rectifier diode module FRS300BA50. The eighth resistor R8 and the eleventh capacitor C11 are connected in series and then connected to the fourth rectifier diode D4 of the rectifier diode module FRS300BA50.

[0071] The secondary inverter circuit includes an IGBT module GPK600SG120D2 and a third RC absorption protection circuit.

[0072] The fifth IGBT switch Q5 and the sixth IGBT switch Q6 of the IGBT module GPK600SG120D2 are connected in series and then connected to the first rectifier diode D1, the second rectifier diode D2, the third rectifier diode D3, and the fourth rectifier diode D4 of two diode modules FRS300BA50. The arc load is connected to the connection point between the fifth IGBT switch Q5 and the sixth IGBT switch Q6 of the IGBT module GPK600SG120D2. In the third RC absorption protection circuit, the ninth resistor R9 and the twelfth capacitor C12 are connected in series and then connected to the fifth switch Q5 of the IGBT module GPK600SG120D2, and the tenth resistor R10 and the thirteenth capacitor C13 are connected in series and then connected to the sixth switch Q6 of the IGBT module GPK600SG120D2.

[0073] In this embodiment, as Figure 2 shown, the secondary inverter circuit is a half-bridge structure, including a fifth IGBT switch Q5 and a sixth IGBT switch Q6, and the polarity of the current is changed by controlling the conduction time of the upper and lower bridge arms;

[0074] In this embodiment, as Figure 2 shown, the auxiliary arc stabilizing circuit includes an input fully controlled rectifier filter circuit and a full-bridge IGBT inverter circuit;

[0075] The first thyristor VT1 and the fourth thyristor VT4 of the input fully controlled rectifier filter circuit are connected in series and then connected in parallel with the series-connected second thyristor VT2 and fifth thyristor VT5, and the series-connected third thyristor VT3 and sixth thyristor VT6. The series-connected third thyristor VT3 and sixth thyristor VT6 are connected to a filter circuit composed of a fifth inductor L5, a fourteenth capacitor C14, and a fifteenth capacitor C15;

[0076] The full-bridge IGBT inverter circuit mentioned above includes IGBT single tubes of the IKW40N120H3 model and a third RC absorption protection circuit.

[0077] The seventh IGBT switch tube Q7 and the eighth IGBT switch tube Q8 of the full-bridge IGBT inverter circuit IKW40N120H3 are connected in series and then connected in parallel with the ninth IGBT switch tube Q9 and the tenth IGBT switch tube Q10 after being connected in series; in the third RC absorption protection circuit, the eleventh resistor R11 and the sixteenth capacitor C16 are connected in series and then connected to the seventh IGBT switch tube Q7 of the IGBT single tube of the IKW40N120H3 model; the twelfth resistor R12 and the seventeenth capacitor C17 are connected in series and then connected to the eighth IGBT switch tube Q8 of the IGBT single tube of the IKW40N120H3 model; the thirteenth resistor R13 and the eighteenth capacitor C18 are connected in series and then connected to the ninth IGBT switch tube Q9 of the IGBT single tube of the IKW40N120H3 model; the fourteenth resistor R14 and the nineteenth capacitor C19 are connected in series and then connected to the tenth IGBT switch tube Q10 of the IGBT single tube of the IKW40N120H3 model;

[0078] The input fully-controlled rectifier and filter circuit is connected to a three-phase AC power supply, the full-bridge IGBT inverter circuit is connected to the input fully-controlled rectifier and filter circuit, and the load of the arc generated between the positive and negative poles of the welding power supply is connected to the full-bridge IGBT inverter circuit.

[0079] The input fully-controlled rectifier and filter circuit is used to convert three-phase alternating current into direct current with an adjustable input voltage, and the full-bridge IGBT circuit is used to change the polarity of the input voltage and adjust the duration of the high-voltage pulse;

[0080] The input fully-controlled rectifier and filter circuit includes the first thyristor VT1, the second thyristor VT2, the third thyristor VT3, the fourth thyristor VT4, the fifth thyristor VT5 and the sixth thyristor VT6. The auxiliary arc stabilizing drive circuit applies trigger pulses to a single thyristor every 60° in the order of VT1-VT2-VT3-VT4-VT5-VT6, and the full-bridge adjusts the rectified input voltage by changing the phase shift angle; the full-bridge IGBT inverter circuit can generate a positive high-voltage pulse by controlling the conduction of the seventh IGBT switch tube Q7 and the tenth IGBT switch tube Q10, and the pulse width can be adjusted by adjusting the conduction time; by controlling the conduction of the eighth IGBT switch tube Q8 and the ninth IGBT switch tube Q9, a negative high-voltage pulse can be generated, and the pulse width can be adjusted by adjusting the conduction time; the auxiliary arc stabilizing circuit provides a stable and adjustable high-voltage pulse during the commutation of the welding current, ensuring the reliable reignition of the welding arc.

[0081] In this embodiment, the voltage sampling circuit is as Figure 9 shown. The voltage sampling circuit first rectifies and divides the input voltage, converts it into a DC signal within the range of 6V, then uses a linear optocoupler for isolation to avoid interference from the main circuit, and finally performs isolation voltage division to convert it into a voltage feedback signal of 0 to 3.3V.

[0082] The control circuit includes an ARM controller, a primary inverter drive module, a secondary inverter drive module, a main arc current sampling circuit, a voltage sampling circuit, an auxiliary arc stabilizing drive circuit, and a fault detection module;

[0083] Among them, the ARM controller is respectively connected to the IGBT primary inverter circuit, the secondary inverter circuit, and the auxiliary arc stabilizing circuit through the primary inverter drive module, the secondary inverter drive module, and the auxiliary arc stabilizing drive circuit for driving;

[0084] The primary inverter drive module is used to drive the turn-on and turn-off of the IGBT switch tubes in the IGBT primary inverter circuit to achieve two control modes of constant voltage and constant current; the secondary inverter drive module is used to drive the turn-on and turn-off of the IGBT switch tubes in the secondary inverter circuit to control the change of the polarity of the welding current; the auxiliary arc stabilizing drive circuit is used to drive the turn-on and turn-off of the IGBT switch tubes in the auxiliary arc stabilizing circuit;

[0085] The auxiliary arc stabilizing circuit is respectively connected to the ARM controller through the main arc current sampling circuit and the voltage sampling circuit to input current and voltage sampling signals;

[0086] The ARM controller is respectively connected to the human-machine interaction system, the fault detection module, and the control power supply module.

[0087] In this embodiment, the primary inverter drive module adopts a high-frequency pulse transformer isolation type topology structure, as Figure 6 shown; the primary inverter drive module uses a P-channel field effect transistor IRF9Z24 and an N-channel field effect transistor IRFZ24 to form a push-pull circuit, amplifies the input PWM signal, and then generates four drive signals through isolation by a high-frequency pulse transformer to drive the corresponding IGBT switch tubes in the primary high-frequency inverter drive circuit to conduct or turn off.

[0088] In this embodiment, the secondary inverter drive circuit is designed based on the KA962 drive chip, as Figure 7 shown. In the figure, C, G, and E are respectively connected to the collector, gate, and emitter of the fifth switch tube Q5 and the sixth switch tube Q6 in the secondary inverter circuit. The PWM signal is input from the first pin 1 of the KA962 drive chip, amplified and then output from the tenth pin 10 of the KA962 drive chip, and then amplified through the Q15 and Q16 IGBT power amplification circuits to drive the fifth switch tube Q5 and the sixth switch tube Q6. Different gate resistors are used for the turn-on and turn-off of the IGBT to accelerate the turn-off speed to solve the trailing effect during the turn-off of the IGBT. The KA962 drive chip has a built-in overcurrent detection terminal. When a fault is detected, the KA962 drive chip will output a negative voltage by itself to turn off the IGBT output and pull down the level of the seventh pin 7 of the KA962 drive chip to send out a fault signal.

[0089] In this embodiment, the ARM controller uses an ARM Cortex-M4 core microprocessor.

[0090] In this embodiment, a HAS500-S Hall current sensor is used to sample the output current signal. The current sampling circuit is as Figure 8 shown. The Hall current sensor utilizes the Hall effect to indirectly obtain the magnitude of the conductor current by measuring the magnetic field around the conductor, avoiding loop interference. The output voltage of this Hall sensor is 4V, and the voltage needs to be divided to reduce it to within the range of 3.3V before it can be received by the single-chip microcomputer.

[0091] The human-machine interaction system uses a SMART 600IE V3 model Siemens touch screen. Based on the Modbus communication protocol, it is connected to the ARM chip of the control circuit by using the RS485 communication method to realize the setting and real-time display of welding parameters.

[0092] As Figure 3 shown, the control power supply module includes a step-down transformer, a first voltage stabilization circuit with an output of +3.3V, a second voltage stabilization circuit with an output of +5V, a third voltage stabilization circuit with an output of +10V, a fourth voltage stabilization circuit with an output of +15V, a fourth voltage stabilization circuit with an output of -15V, and a sixth voltage stabilization circuit with an output of +24V;

[0093] The step-down transformer is respectively connected to the 220V alternating current output from the power grid and the input ends of the first voltage stabilization circuit, the second voltage stabilization circuit, the third voltage stabilization circuit, and the fourth voltage stabilization circuit; the first voltage stabilization circuit, the second voltage stabilization circuit, and the third voltage stabilization circuit are respectively connected to the ARM controller; the fourth voltage stabilization circuit is respectively connected to the primary inverter drive module and the voltage sampling circuit; the fifth voltage stabilization circuit and the sixth voltage stabilization circuit are connected to the main arc main circuit voltage sampling circuit.

[0094] By controlling the duty cycle of the IGBT switch tube on the IGBT primary inverter circuit, the output current and voltage of the voltage and current sampling circuit are adjusted to follow the reference current and reference voltage set by the ARM controller;

[0095] During the welding process, if the constant current mode is selected, the ARM controller samples the current signal output from the main arc main circuit in real time through the current sampling circuit, compares the sampled current signal with the reference current, and adjusts the duty cycle through the digital PI controller to achieve the constant current closed-loop control of the welding current; if the constant voltage mode is selected, the ARM controller samples the voltage signal output from the main arc main circuit in real time through the voltage sampling circuit, compares the sampled voltage signal with the reference voltage, and adjusts the duty cycle through the digital PI controller to achieve the closed-loop control of the arc voltage;

[0096] The voltage sampling circuit samples the voltage signal output by the main arc main circuit in real time to determine the arc ignition state or short - circuit state, and display it on the display screen of the man - machine interaction system.

[0097] As Figure 4 shown, the ARM controller, the primary inverter drive module, the voltage sampling circuit, the current sampling circuit, and the IGBT primary inverter circuit constitute the primary inverter drive control system;

[0098] The ARM controller of the primary inverter control system controls the primary inverter drive module to send PWM drive signals to the IGBT primary inverter circuit according to the reference current and reference voltage signals set by the man - machine interaction system, and adjusts the duty cycle of the IGBT switching tubes in the IGBT primary inverter circuit through the voltage and current signals of the main arc main circuit sampled in real time by the voltage sampling circuit and the current sampling circuit, after digital PID operation, to achieve double - closed - loop control of voltage and current;

[0099] To ensure the stability and reliability of the welding power source, the control circuit is equipped with over - voltage and under - voltage protection at the input end, and over - heat protection, over - current protection, and over - current protection of the primary side of the transformer on the primary inverter circuit module; when a fault occurs in the welding power source, the control circuit immediately shuts off the output of the primary inverter circuit drive signal, and at the same time displays the fault type code on the display screen of the man - machine interaction system and issues an alarm.

[0100] As Figure 5 shown, the ARM controller, the secondary inverter drive module, the secondary inverter circuit, and the voltage sampling circuit constitute the secondary inverter control system;

[0101] Among them, the ARM controller of the secondary inverter control system determines whether the welding process is in a short - circuit state or an arc - ignition state by sampling the arc voltage in real time through the voltage sampling circuit, and indirectly determines the necking state of the droplet liquid bridge of the arc load by the change rate of the arc voltage sampled by the arc sampling circuit;

[0102] Then, combined with the time when the welding current set by the ARM controller is negative - polarity, it controls the switching states of the fifth switching tube Q5 and the sixth switching tube Q6 in the secondary inverter circuit;

[0103] The ARM controller of the secondary inverter control system sets the short - circuit voltage by the man - machine interaction system, compares the set short - circuit voltage with the arc voltage sampled in real time by the voltage sampling circuit to judge the switching time of the welding current polarity, and controls the secondary inverter drive module to send PWM drive signals to drive the conduction and cut - off of the IGBT switching tubes in the secondary inverter circuit, to achieve rapid switching of the welding current polarity.

[0104] The working principle of the present invention is as follows: 380V three-phase alternating current is converted into direct current of 535V - 540V through a three-phase rectifier filter circuit. The duty cycle of the IGBT in the primary inverter full-bridge circuit is adjusted to output high-frequency alternating current. The high-frequency transformer then converts the energy of the primary into alternating current with low voltage and high current, which is then converted into adjustable direct current of 0 - 400A through a fast rectifier filter module. Finally, it is converted into welding current with variable polarity through a secondary inverter half-bridge circuit, and the set welding current waveform is output; the current sampling circuit and voltage sampling circuit detect the voltage and current values output by the welding power supply in real time and send them to the controller for data processing; the human-machine interaction system mainly realizes functions such as presetting process parameters and displaying various states; the auxiliary arc stabilizing drive circuit drives the on and off of the IGBT switching tube in the auxiliary arc stabilizing circuit to provide an accurately adjustable pulsed high voltage at the current commutation device, playing an arc stabilizing role; through the above operations, the variable polarity MAG welding power supply of the present invention can accurately control the heat input of the welding arc, is particularly suitable for thin plate welding occasions, and can achieve high-quality weld seams.

[0105] Embodiment 2:

[0106] The difference between this embodiment and Embodiment 1 is that the controller uses an STM32F407 microprocessor.

[0107] Embodiment 3:

[0108] The difference between this embodiment and Embodiment 1 is that the human-machine interaction system uses the S7-1200KTP model.

[0109] The preferred embodiments of the present application disclosed above are only used to help understand the present invention and its core idea. For those of ordinary skill in the art, according to the idea of the present invention, there will be changes in specific application scenarios and implementation operations. This specification should not be construed as a limitation to the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A digital variable polarity gas metal arc welding power source for thin plates, characterized in that, It includes a main arc main circuit, an auxiliary arc stabilizing circuit, a control circuit, a control circuit power supply module, and a human-machine interaction system; Among them, the main arc main circuit includes a three-phase rectifier filter circuit, an IGBT primary inverter circuit, a high-frequency transformer, a fast rectifier filter circuit, and a secondary inverter circuit connected in sequence; the three-phase rectifier filter circuit is connected to a three-phase AC power supply, and the secondary inverter circuit is connected to the auxiliary arc stabilizing circuit; The three-phase rectifier filter circuit converts the 380V three-phase alternating current input from the three-phase AC power supply into a smooth direct current of 535V - 540V; the IGBT primary inverter circuit and the high-frequency transformer convert the smooth direct current into a high-frequency alternating current; the high-frequency alternating current is converted into an adjustable direct current of 0 - 400A after passing through the fast rectifier filter circuit; the secondary inverter circuit is used to change the polarity of the direct current obtained by the fast rectifier filter circuit to form a variable-polarity welding current required for welding; the auxiliary arc stabilizing circuit is connected to the three-phase AC power supply and is used to provide an adjustable pulse high voltage for the welding arc when the welding current changes polarity, ensuring reliable re-ignition of the welding arc after it extinguishes at the moment when the welding current passes through zero; The control circuit is respectively connected to the IGBT primary inverter circuit, the secondary inverter circuit, the auxiliary arc stabilizing circuit, the control circuit power supply module, and the human-machine interaction system; The secondary inverter circuit is a half-bridge structure, including a fifth IGBT switch tube (Q5) and a sixth IGBT switch tube (Q6), and changes the current polarity by controlling the conduction time of the upper and lower bridge arms; The auxiliary arc stabilizing circuit includes an input fully controlled rectifier filter circuit and a full-bridge IGBT inverter circuit; The input fully controlled rectifier filter circuit is connected to the three-phase AC power supply, the full-bridge IGBT inverter circuit is connected to the input fully controlled rectifier filter circuit, and the load of the arc generated between the positive and negative poles of the welding power supply is connected to the full-bridge IGBT inverter circuit; The input fully controlled rectifier filter circuit is used to convert three-phase alternating current into a direct current with adjustable input voltage, and the full-bridge IGBT circuit is used to change the input voltage polarity and adjust the duration of the high-voltage pulse; the full-bridge IGBT inverter circuit generates a positive high-voltage pulse by controlling the turn-on of the seventh IGBT switch tube (Q7) and the tenth IGBT switch tube (Q10), and the turn-on time can be adjusted to adjust the width of the positive high-voltage pulse; by controlling the turn-on of the eighth IGBT switch tube (Q8) and the ninth IGBT switch tube (Q9), a negative high-voltage pulse is generated, and the turn-on time can be adjusted to adjust the width of the negative high-voltage pulse; the auxiliary arc stabilizing circuit provides a stable and adjustable high-voltage pulse during the commutation period of the welding current, ensuring reliable re-ignition of the welding arc; The control circuit includes an ARM controller, a primary inverter drive module, a secondary inverter drive module, a main arc current sampling circuit, a voltage sampling circuit, an auxiliary arc stabilizing drive circuit, and a fault detection module; Among them, the ARM controller is respectively connected to the IGBT primary inverter circuit, the secondary inverter circuit, and the auxiliary arc stabilizing circuit through the primary inverter drive module, the secondary inverter drive module, and the auxiliary arc stabilizing drive circuit for driving; The primary inverter drive module is used to drive the on and off of the IGBT switch tubes in the IGBT primary inverter circuit, realizing two control modes of constant voltage and constant current; the secondary inverter drive module is used to drive the on and off of the IGBT switch tubes in the secondary inverter circuit, controlling the change of the polarity of the welding current; the auxiliary arc stabilizing drive circuit is used to drive the on and off of the IGBT switch tubes in the auxiliary arc stabilizing circuit; The auxiliary arc stabilizing circuit is respectively connected to the ARM controller input current and voltage sampling signals through the main arc current sampling circuit and the voltage sampling circuit; The ARM controller is respectively connected to the human-machine interaction system, the fault detection module, and the control power supply module.

2. The digital variable polarity gas metal arc welding power source for thin plates according to claim 1, characterized in that, The three-phase rectifier filter circuit includes a three-phase rectifier module and an LC filter module connected in series; the three-phase rectifier module is connected to the three-phase AC power supply; The IGBT primary inverter circuit includes a first IGBT switch tube (Q1), a second IGBT switch tube (Q2), a third IGBT switch tube (Q3), a fourth IGBT switch tube (Q4), and a first RC absorption protection circuit; Among them, the first IGBT switch tube (Q1), the second IGBT switch tube (Q2), and the third IGBT switch tube (Q3) are connected in series and then connected in parallel with the LC filter module. The auxiliary capacitor (C7) and the fourth IGBT switch tube (Q4) are connected in series and then connected in parallel with the series-connected second IGBT switch tube (Q2) and third IGBT switch tube (Q3). One end of the primary of the high-frequency transformer is connected between the series-connected second IGBT switch tube (Q2) and third IGBT switch tube (Q3), and the other end is connected between the series-connected auxiliary capacitor (C7) and fourth IGBT switch tube (Q4); In the first RC absorption protection circuit, the first resistor (R1) and the third capacitor (C3) are connected in series and then connected in parallel with the first IGBT switch tube (Q1); the second resistor (R2) and the fourth capacitor (C4) are connected in series and then connected in parallel with the second IGBT switch tube (Q2); the third resistor (R3) and the fifth capacitor (C5) are connected in series and then connected in parallel with the third IGBT switch tube (Q3); the fourth resistor (R4) and the sixth capacitor (C6) are connected in series and then connected in parallel with the fourth IGBT switch tube (Q4).

3. The digital variable polarity gas metal arc welding power source for thin plates according to claim 1, characterized in that, By controlling the duty cycle of the IGBT switch tubes on the IGBT primary inverter circuit, the output current and voltage of the voltage and current sampling circuits are adjusted to follow the reference current and reference voltage set by the ARM controller; During the welding process, if the constant current mode is selected, the ARM controller samples the current signal output by the main arc main circuit in real time through the current sampling circuit, compares the sampled current signal with the reference current, and adjusts the duty cycle through the digital PI controller to realize the constant current closed-loop control of the welding current; If the constant voltage mode is selected, the ARM controller samples the voltage signal output by the main arc main circuit in real time through the voltage sampling circuit, compares the sampled voltage signal with the reference voltage, and adjusts the duty cycle through the digital PI controller to achieve the closed-loop control of the arc voltage; The voltage sampling circuit samples the voltage signal output by the main arc main circuit in real time to determine the arc ignition state or short circuit state, and displays it on the display screen of the human-machine interaction system.

4. A digital variable polarity gas metal arc welding power source for thin plates according to claim 1, characterized in that, The ARM controller includes an ARM Cortex-M4 core microprocessor or an STM32F407 microprocessor.

5. A digital variable polarity gas metal arc welding power source for thin plates according to claim 1, characterized in that, The human-machine interaction system is based on the Modbus communication protocol, and is connected to the ARM controller by using the RS485 communication method to achieve the setting and real-time display of welding parameters.

6. A thin-plate digitalized variable polarity gas metal arc welding power source according to claim 1, characterized in that The control power supply module includes a step-down transformer, a first voltage stabilizing circuit with an output of +3.3V, a second voltage stabilizing circuit with an output of +5V, a third voltage stabilizing circuit with an output of +10V, a fourth voltage stabilizing circuit with an output of +15V, a fourth voltage stabilizing circuit with an output of -15V, and a sixth voltage stabilizing circuit with an output of +24V; The step-down transformer is respectively connected to the 220V alternating current output by the power grid and the input ends of the first voltage stabilizing circuit, the second voltage stabilizing circuit, the third voltage stabilizing circuit, and the fourth voltage stabilizing circuit; the first voltage stabilizing circuit, the second voltage stabilizing circuit, and the third voltage stabilizing circuit are respectively connected to the ARM controller; the fourth voltage stabilizing circuit is respectively connected to the primary inverter drive module and the voltage sampling circuit; the fifth voltage stabilizing circuit and the sixth voltage stabilizing circuit are connected to the main arc main circuit voltage sampling circuit.

7. A digital variable polarity gas metal arc welding power source for thin plates according to claim 1, characterized in that, The ARM controller, the primary inverter drive module, the voltage sampling circuit, the current sampling circuit, and the IGBT primary inverter circuit constitute a primary inverter drive control system; The ARM controller of the primary inverter drive control system controls the primary inverter drive module to send a PWM drive signal to the IGBT primary inverter circuit according to the reference current and reference voltage signals set by the human-machine interaction system, and adjusts the duty cycle of the IGBT switch tube in the IGBT primary inverter circuit through the voltage and current signals of the main arc main circuit sampled in real time by the voltage sampling circuit and the current sampling circuit, so as to achieve the double closed-loop control of voltage and current; The control circuit is provided with overvoltage and undervoltage protection at the input end, and overheat protection, overcurrent protection, and primary side overcurrent protection of the transformer are provided on the primary inverter circuit module; when a fault occurs in the welding power supply, the control circuit immediately closes the output of the primary inverter circuit drive signal, and at the same time displays the fault type code on the display screen of the human-machine interaction system and issues an alarm.

8. A digital variable polarity gas metal arc welding power source for thin plates according to claim 1, characterized in that, The ARM controller, the secondary inverter drive module, the secondary inverter circuit, and the voltage sampling circuit constitute a secondary inverter control system; Among them, the ARM controller determines whether the welding process is in a short circuit state or an arc ignition state by sampling the arc voltage in real time through the voltage sampling circuit, and indirectly determines the necking state of the molten droplet liquid bridge of the arc load by the change rate of the arc voltage sampled by the arc sampling circuit; Then, combined with the time when the welding current set by the ARM controller is negative polarity, the switching states of the fifth IGBT switch tube (Q5) and the sixth IGBT switch tube (Q6) in the secondary inverter circuit are controlled; The ARM controller of the secondary inverter control system uses a human-machine interaction system to set the short-circuit voltage, compares the set short-circuit voltage with the arc voltage sampled in real time by the voltage sampling circuit to determine the switching time of the welding current polarity, and controls the secondary inverter drive module to send PWM drive signals to drive the conduction and cutoff of the IGBT switch tubes in the secondary inverter circuit, so as to realize the rapid switching of the welding current polarity.

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