A method for monitoring and forcibly warning the protection grounding state of an electric welding machine shell

Abstract

The application discloses a kind of electric welding machine shell protection ground state monitoring and forced warning method.The method contains magnetic balance hardware level passive electric leakage monitoring, active impedance high-frequency injection and quadrature demodulation quantitative measurement, adaptive filter bandwidth switching based on inverter working condition identification and software and hardware dual redundancy trigger action.System is locked optimal injection frequency by spectrum detection, uses quadrature demodulation to extract actual response current and analyzes equivalent impedance module value.By extracting inverter load transient step intensity, active low-pass filter cutoff frequency is dynamically adjusted to adapt to transient strong electromagnetic interference.Excluding extreme open circuit state, software level impedance exceeds standard trigger signal and hardware level electric leakage trigger signal are unified to silicon-controlled silicon gate by double trigger signal convergence circuit Output to controllable silicon gate, forced on-off attraction coil cut off main power supply.The application realizes active quantification and reliable lockout of ground state under strong interference.

Description

Technical Field

[0001] This invention relates to the field of electrical safety monitoring technology, specifically to a method for monitoring and mandating warning of the protective grounding status of a welding machine casing. Background Technology

[0002] Electric welding machines are common equipment in metal processing and engineering construction, and are widely used in many fields such as industrial manufacturing, building construction, and equipment maintenance. In actual operation, electric welding machines are usually in complex and harsh environments. They contain high-power transformer and inverter components, and operate with high working voltage and high current output.

[0003] To ensure operator safety and prevent equipment insulation aging or internal faults from causing the metal casing to become electrified, existing safety standards (such as GB 15579.1-2017 "Safety Requirements for Arc Welding Equipment") clearly require that the metal casing of welding machines must be reliably electrically connected to the ground. Conventional electrical protection schemes typically employ passive leakage current protection mechanisms. These mechanisms mainly utilize detection elements such as zero-sequence current transformers in the power supply circuit. When leakage occurs and some current flows to the ground through the casing, the detection element senses an imbalance between the input and return currents in the power supply line, generating an induced signal that triggers the subsequent protection circuit to trip and disconnect the power supply.

[0004] However, existing passive leakage protection mechanisms have limitations. This type of protection only triggers when a substantial leakage fault has occurred in the equipment, and cannot actively sense the integrity and true impedance of the casing grounding circuit under normal operating conditions. If the grounding wire is not installed correctly, accidentally falls off, or the grounding impedance exceeds the safety standard during operation, the passive detection element will not detect the abnormality at all since no leakage has occurred. If conventional active impedance measurement methods are used to investigate this hidden danger, the welding machine generates strong electromagnetic interference and load transients during arc initiation and welding inversion. Conventional measurement methods are difficult to accurately extract weak grounding impedance characteristic signals under strong background noise, and are prone to false tripping of the protection mechanism due to filtering hysteresis. At the same time, conventional single electrical triggering execution circuits lack multiple independent triggering mechanisms under complex and harsh operating conditions, and are at risk of failure under complex fault conditions. This means that existing technology cannot accurately and stably achieve online grounding status investigation and reliable interlocking when the welding machine is operating normally and there is no leakage. Once a sudden insulation breakdown leakage occurs, it will directly threaten the life safety of on-site workers. Summary of the Invention

[0005] The technical problem to be solved by this invention is that existing passive leakage protection mechanisms cannot actively detect potential grounding failures or impedance over-limits in the shell under normal operation and no leakage conditions; at the same time, it addresses the shortcomings of conventional active impedance measurement methods in accurately extracting weak signals under strong electromagnetic interference and transient load changes in welding machines, and the susceptibility to false tripping due to filtering hysteresis; and it also addresses the limitation of a single electrical triggering execution circuit in ensuring absolute reliability of the final forced power cut in harsh field environments. Therefore, this invention provides a method for monitoring and forcibly warning the protective grounding status of welding machine shells.

[0006] This invention provides a method for monitoring and mandating warning of the protective grounding status of a welding machine casing, comprising the following steps:

[0007] Step S100: The monitoring and forced warning system is powered on synchronously with the main power supply of the welding machine. The step-down transformer power supply unit outputs a 12V AC safety voltage. The buzzer alarm branch performs a brief power-on self-test sound to indicate that the microprocessor has started and completed the initialization of the internal registers and peripheral interfaces, and then actively shuts off the self-test sound.

[0008] In step S200, the magnetic balance physical actuator performs hardware-level passive monitoring. When leakage current occurs in the casing of the welding machine, causing a deviation in the instantaneous current phasor sum between the live wire and the neutral wire, the unbalanced magnetic field inside the magnetic ring coil is detected. An alternating induced electromotive force is generated at both ends of the magnetic ring coil. After rectification by the rectifier bridge, the alternating induced electromotive force is output as a DC trigger voltage. DC trigger voltage The signal is transmitted to the gate of the thyristor via the first isolation diode. The thyristor conducts, causing the trip coil to be energized and generating a magnetic attraction force, which pulls the trip linkage to forcibly disconnect the main power supply contactor of the welding machine.

[0009] In step S300, the microprocessor controls the active impedance monitoring module to perform active measurement of the grounding loop status. Based on the welding machine noise frequency band obtained by the carrier spectrum detection circuit, the microprocessor sends a frequency control word to the high-frequency characteristic signal generator and injects a characteristic AC voltage signal that avoids the noise frequency band. The broadband current transformer collects the return signal, and the quadrature demodulation hardware circuit performs analog mixing and low-pass filtering on the return signal to extract the DC level signal related to the grounding loop impedance and send it to the analog-to-digital conversion pin of the microprocessor.

[0010] Step S400: The microprocessor calculates the impedance magnitude. It also executes software-level forced interlocking actions, with a preset grounding safety threshold of [value missing]. When the calculation result meets the condition When the grounding loop exhibits open-circuit characteristics, the microprocessor outputs a high-level trigger pulse. High-level trigger pulse The high-level trigger pulse is transmitted to the gate of the thyristor via the second isolation diode. The thyristor is turned on, which drives the trip coil to operate, cuts off the power input to the welding machine, and maintains the operation of the buzzer alarm branch.

[0011] In the passive monitoring stage of magnetic balance at the hardware level, a toroidal magnetic core is used to detect the net alternating magnetic flux generated by the imbalance between the live and neutral currents in the main power supply circuit. The net alternating magnetic flux induces an alternating electromotive force on the secondary side, which is converted into a unidirectional pulsating DC trigger voltage by full-wave rectification. After amplitude attenuation by a current-limiting resistor, it is unidirectionally injected into the gate of the thyristor through the first isolation diode to complete the hardware-level tripping response under leakage fault conditions.

[0012] To achieve active quantization of grounding impedance in the absence of leakage current and to avoid strong electromagnetic interference generated by the inverter, the system performs carrier spectrum detection and adaptive frequency optimization. The frequency domain amplitude spectrum is obtained by acquiring the pulse width modulation signal of the inverter control and performing a discrete Fourier transform. The square of the frequency domain amplitude spectrum is calculated as the background noise energy density function. After removing the protection band of the inverter switching fundamental frequency and its integer multiples of harmonics, the global minimum point of this energy density function is found, and its corresponding frequency coordinates are determined as the optimal injection frequency. Subsequently, a discrete sine wave sequence is generated based on the optimal injection frequency and converted into an analog characteristic voltage signal. This characteristic signal is then non-contactly coupled and injected into the closed loop of the casing grounding through a high-frequency coupling transformer.

[0013] For the acquired total return current signal mixed with background noise, the system employs orthogonal demodulation technology for processing. The total return current signal is multiplied in the time domain by both a simulated in-phase reference voltage and a simulated quadrature reference voltage of the same frequency. The output mixed signal is then filtered by an active low-pass filter to remove high-frequency harmonic components and noise, extracting the in-phase DC characteristic level and the quadrature DC characteristic level. By calculating the square root of the sum of the squares of the in-phase and quadrature DC characteristic levels and multiplying it by 2, the amplitude of the actual response current in the grounding loop is obtained. Furthermore, the preset peak characteristic voltage amplitude is divided by the actual response current amplitude to obtain the equivalent impedance magnitude under the current environment, thus characterizing the physical grounding connection state.

[0014] To balance noise immunity accuracy and transient response speed in impedance measurement, the system incorporates an adaptive filter bandwidth switching mechanism based on inverter operating condition identification during quadrature demodulation. The real-time duty cycle is obtained by measuring the ratio of the high-level duration within a single switching cycle to the total cycle time. The discrete difference in duty cycles between adjacent discrete sampling cycles is calculated and divided by the sampling time interval to extract the absolute value of the time derivative, which characterizes the transient step intensity of the inverter load. When the absolute value of the time derivative exceeds the sudden change judgment threshold, the device is determined to be in an arcing or pulse step condition. The system controls a digital potentiometer to lower the input resistance in the active low-pass filter feedback network. Based on the reciprocal relationship between the input resistance and the feedback capacitance, the cutoff frequency is increased, widening the allowable signal bandwidth to accommodate transients caused by electromagnetic interference coupling. When the absolute value of the time derivative is less than or equal to the judgment threshold, the system is determined to be in a steady-state condition. The system controls the input resistance to increase, lowering the cutoff frequency to narrow the signal bandwidth and maintain quantization accuracy.

[0015] In the impedance comparison and alarm control stage, the system first compares the actual response current amplitude with the zero current dead zone threshold. When the current amplitude is lower than the dead zone threshold, it determines that the grounding conductor is physically disconnected and directly triggers an alarm to avoid software overflow errors caused by division by zero in subsequent impedance calculations. When the current amplitude is greater than or equal to the dead zone threshold and the calculated equivalent impedance modulus is greater than the set safety impedance threshold, it determines that there is a potential grounding resistance exceeding the standard, outputs a high-level trigger signal to the drive switch, and activates the audible and visual alarm by closing the closed loop.

[0016] In the final forced latch-up phase, the high-level trigger pulse output by the aforementioned software-level calculation and the hardware-level DC trigger voltage output by the aforementioned rectifier bridge are converged to the gate of the thyristor through independent isolation diodes, forming a dual trigger signal convergence circuit. Under individual or concurrent operating conditions of leakage faults or impedance exceeding limits, the maximum value obtained by subtracting the forward voltage drop of the corresponding diode from each of the two trigger signals is taken as the actual trigger voltage. The actual trigger voltage drives the generation of gate input current. When the gate input current reaches the trigger threshold, the thyristor is turned on, forcibly activating the trip coil. The alternating magnetic field generated by the coil produces an electromagnetic attraction force, overcoming the mechanical reaction force of the spring to pull the trip linkage, achieving physical disconnection and latch-up of the main power supply circuit.

[0017] The present invention, by adopting the above technical solution, can bring the following beneficial effects:

[0018] 1. This invention introduces a carrier spectrum detection circuit and a high-frequency characteristic signal injection mechanism into the main power supply circuit of the welding machine. By using orthogonal demodulation hardware circuits to perform real-time coherent extraction and impedance analysis of the grounding circuit return signal, it achieves accurate online monitoring of the protective grounding status of the welding machine casing in a strong electromagnetic interference environment. This completely solves the safety blind zone problem of grounding failure of the welding machine when no leakage occurs, caused by the inability to actively measure the grounding impedance in the existing passive leakage protection scheme, thus ensuring the personal safety of welding operators.

[0019] 2. This invention constructs an adaptive filter bandwidth switching architecture based on inverter operating condition identification. It extracts the transient rate of change of inverter control quantities in real time within the microprocessor and dynamically adjusts the cutoff frequency of the active low-pass filter accordingly. This enables the quadrature demodulation module to synchronously adjust the signal processing bandwidth according to the transient disturbance intensity of the welding condition during the arc ignition of the welding machine and under severe load disturbance conditions such as pulse welding. Through this logic with anti-interference adaptive adjustment capability, it avoids false triggering caused by filtering hysteresis in traditional monitoring methods and ensures the stability of system operation.

[0020] 3. This invention, by setting up a hardware-level dual trigger signal convergence circuit including a first isolation diode, a second isolation diode, and a thyristor, achieves conflict-free convergence of the software-level ground impedance over-limit trigger signal output by the microprocessor and the hardware-level leakage current trigger signal output by the magnetic balance detection mechanism at the physical level. This allows either trigger source to effectively conduct the thyristor and drive the trip coil to execute the mechanical trip of the circuit breaker. Through the dual redundancy trigger logic of software and hardware, reliable physical forced disconnection of the welding machine power supply is achieved under complex fault conditions, improving the overall reliability of electrical operations. Attached Figure Description

[0021] Figure 1 This is the main flowchart of the method for monitoring and mandating warning of the protective grounding status of the welding machine casing according to the present invention;

[0022] Figure 2 This is the overall hardware architecture diagram of the electric welding machine casing protective grounding status monitoring and forced warning system of the present invention;

[0023] Figure 3 This is a circuit topology diagram of the active impedance monitoring module and adaptive filter bandwidth switching of the present invention;

[0024] Figure 4 This is a schematic diagram of the hardware and software dual trigger signal convergence and physical forced locking circuit of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] See attached document Figure 1-2 This invention provides a method for monitoring and mandating warning of the protective grounding status of a welding machine casing, comprising the following steps:

[0028] Step S100: The monitoring and forced warning system is powered on synchronously with the main power supply of the welding machine. The step-down transformer power supply unit 10 outputs a 12V AC safety voltage. The buzzer alarm branch 40 performs a brief power-on self-test sound prompt. After the microprocessor 50 starts up and completes the initialization of the internal registers and peripheral interfaces, it actively shuts off the self-test sound.

[0029] In step S200, the magnetic balance physical actuator 20 performs hardware-level passive monitoring. When the welding machine experiences leakage current in its casing, causing a deviation in the instantaneous current phasor sum between the live wire and the neutral wire, the magnetic field imbalance inside the magnetic ring coil 21 is detected. An alternating induced electromotive force is generated at both ends of the magnetic ring coil 21. After rectification by the rectifier bridge 22, the alternating induced electromotive force outputs a DC trigger voltage. DC trigger voltage The signal is transmitted to the gate of the thyristor 23 via the first isolation diode 26. The thyristor 23 conducts, causing the trip coil 24 to be energized and generating a magnetic attraction force, which pulls the trip linkage to forcibly disconnect the main power supply contactor of the welding machine.

[0030] In step S300, the microprocessor 50 controls the active impedance monitoring module 30 to perform active measurement of the grounding loop status. Based on the welding machine noise frequency band obtained by the carrier spectrum detection circuit 31, the microprocessor 50 sends a frequency control word to the high-frequency characteristic signal generator 32 and injects a characteristic AC voltage signal that avoids the noise frequency band. The broadband current transformer 34 collects the return signal. The quadrature demodulation hardware circuit 33 performs analog mixing and low-pass filtering on the return signal, extracts the DC level signal related to the grounding loop impedance, and sends it to the analog-to-digital conversion pin of the microprocessor 50.

[0031] Step S400: Microprocessor 50 calculates the impedance magnitude. It also executes software-level forced interlocking actions, with a preset grounding safety threshold of [value missing]. When the calculation result meets the condition When the grounding loop exhibits open-circuit characteristics, the microprocessor 50 outputs a high-level trigger pulse. High-level trigger pulse The high-level trigger pulse is transmitted to the gate of the thyristor 23 via the second isolation diode 56. Turn on the thyristor 23 to drive the trip coil 24 to cut off the power input to the welding machine and maintain the operation of the buzzer alarm branch 40.

[0032] The above method is implemented through the monitoring and forced warning system. The system is connected in series with the main power supply circuit of the welding machine and connected to the grounding terminal of the welding machine's casing. The monitoring and forced warning system includes a step-down transformer power supply unit 10, a magnetic balance physical actuator 20, an active impedance monitoring module 30, a buzzer alarm branch 40, and a microprocessor 50. The active impedance monitoring module 30 further includes a carrier spectrum detection circuit 31, a high-frequency characteristic signal generator 32, an orthogonal demodulation hardware circuit 33, a broadband current transformer 34, and a high-frequency coupling transformer 35. The physical units work together to construct a dual safety redundancy trigger structure based on hardware leakage protection and high-frequency signal active impedance quantization.

[0033] The high-voltage input side of the step-down transformer power supply unit 10 is connected in parallel to the 380V or 220V primary AC power input terminal of the welding machine. The low-voltage output side of the step-down transformer power supply unit 10 outputs a 12V AC safety voltage. After rectification and voltage regulation, the 12V AC safety voltage outputs a DC working voltage, which provides working power to the buzzer alarm branch 40, the tripping execution circuit in the magnetic balance physical actuator 20, and the active impedance monitoring module 30, respectively. After the monitoring and forced warning system completes the power-on self-test, the buzzer alarm branch 40 is triggered to conduct power and perform the warning action only before a grounding abnormality is detected and the main power supply switch trips and cuts off the main power supply. When the main power supply switch trips and completely cuts off the main power supply, the buzzer alarm branch 40 stops sounding due to power loss.

[0034] The magnetic balance physical actuator 20 includes a detection magnetic ring coil 21, a rectifier bridge 22, a thyristor 23, and a trip coil 24. The live wire and neutral wire of the main power supply circuit of the welding machine pass through the inner hole of the detection magnetic ring coil 21 in the same direction. The induction output terminal of the detection magnetic ring coil 21 is electrically connected to the input AC terminal of the rectifier bridge 22. The positive output terminal of the rectifier bridge 22 is connected in series with a current limiting resistor 25 and a first isolation diode 26 and then connected to the gate of the thyristor 23. The negative output terminal of the rectifier bridge 22 is connected to the cathode of the thyristor 23. The trip coil 24 is connected in series between the anode of the thyristor 23 and the positive terminal of the independent DC control power supply. The cathode of the thyristor 23 is connected to the negative terminal of the DC control power supply. The mechanical actuation terminal of the trip coil 24 is physically linked with the trip linkage of the primary side main power supply contactor of the welding machine.

[0035] In the physical topology of the active impedance monitoring module 30, the signal output terminal of the high-frequency characteristic signal generator 32 is connected to the primary winding of the high-frequency coupling transformer 35. The secondary winding of the high-frequency coupling transformer 35 is connected in series in a closed physical loop consisting of the metal shell of the welding machine, the shell grounding wire, the earth, and the protective grounding wire of the power supply system. The broadband current transformer 34 is sleeved on the shell grounding wire. The signal output terminal of the broadband current transformer 34 is connected to the input terminal of the quadrature demodulation hardware circuit 33. The voltage acquisition terminal of the carrier spectrum detection circuit 31 is connected to the pulse width modulation port of the welding machine inverter power control board. The control bus and data interface of the carrier spectrum detection circuit 31, the high-frequency characteristic signal generator 32, and the quadrature demodulation hardware circuit 33 are all electrically connected to the corresponding pins of the microprocessor 50. The trigger signal output pin of the microprocessor 50 is connected in series with the second isolation diode 56 and then connected to the gate of the thyristor 23. The first isolation diode 26 and the second isolation diode 56 together constitute a hardware-level dual trigger signal convergence circuit to prevent current backflow.

[0036] The microprocessor 50 is specifically implemented as a digital signal processor or an embedded microcontroller with a hardware floating-point arithmetic unit. The high-frequency characteristic signal generator 32 is specifically implemented as a combination of a direct digital frequency synthesizer integrated chip and a power operational amplifier. The quadrature demodulation hardware circuit 33 is specifically implemented as a cascaded bipolar active low-pass filter circuit of a high-frequency analog multiplier chip.

[0037] Example 2

[0038] See attached document Figure 3-4 Based on Embodiment 1, in the overall system architecture described above, the magnetic balance physical actuator 20 serves as the first layer of underlying safety protection, operating independently of the software system to achieve ultra-fast pure hardware leakage protection. Specifically, this mechanism relies on the instantaneous sensing of the physical magnetic field;

[0039] The live wire and neutral wire of the main power supply circuit of the welding machine pass through the central hole of the detection magnetic ring coil 21 in the same direction. The specific lower-level feature of the detection magnetic ring coil 21 is realized as a zero-sequence current transformer. The detection magnetic ring coil 21 includes a ring magnetic core and a secondary side induction winding uniformly wound on the ring magnetic core. The material of the ring magnetic core is permalloy or nanocrystalline soft magnetic alloy to improve the leakage current detection sensitivity.

[0040] The two signal output pins of the secondary side induction winding are electrically connected to the two AC input terminals of the rectifier bridge 22, respectively. The specific lower-level feature of the rectifier bridge 22 is implemented as a full-wave bridge rectifier circuit composed of four rectifier diodes. The positive output terminal of the rectifier bridge 22 is connected to the gate of the thyristor 23 after being connected in series with the current limiting resistor 25 and the first isolation diode 26. The negative output terminal of the rectifier bridge 22 is connected to the cathode of the thyristor 23.

[0041] The detection magnetic ring coil 21 and rectifier bridge 22 are combined to perform physical-level leakage current monitoring of the main power supply circuit of the welding machine. The specific working process is carried out according to the following steps:

[0042] Step S201: Under the condition that the insulation of the welding machine is normal and there is no leakage, the input current flowing through the live wire. and the return current flowing through the neutral wire With equal amplitude and opposite direction, the alternating magnetic flux vectors generated by the two phase currents in the annular core of the detection magnetic ring coil 21 cancel each other out, the total magnetic flux inside the annular core is zero, the secondary side induction winding has no alternating induced electromotive force output, the rectifier bridge 22 has no DC trigger voltage generated, and the thyristor 23 maintains the blocking state.

[0043] Step S202: When the welding machine experiences a grounding leakage fault in its casing or when a shunt branch exists, part of the power supply current flows into the ground through the casing, and the live wire current... With neutral current It exhibits an unbalanced state, with leakage current. The amplitude satisfies the following formula:

[0044]

[0045] In the formula, This represents the instantaneous amplitude of the live wire current. The instantaneous amplitude of the neutral current, leakage current A periodically varying net alternating magnetic flux is excited inside the toroidal core. This net alternating magnetic flux links to the secondary induction winding, and according to the law of electromagnetic induction, an alternating induced electromotive force is generated at both ends of the secondary induction winding. ;

[0046] Step S203, Alternating induced electromotive force The AC input of the rectifier bridge 22 is transmitted to the rectifier bridge 22. The rectifier bridge 22 performs full-wave rectification, converting the alternating induced electromotive force into a unidirectional pulsating DC voltage. The unidirectional pulsating DC voltage is attenuated by the current-limiting resistor 25, and after being unidirectionally turned on by the first isolation diode 26, a DC trigger current is injected into the gate of the thyristor 23. When the instantaneous amplitude of the DC trigger current reaches the gate trigger current threshold of the thyristor 23... At this time, the anode and cathode of the thyristor 23 are connected, which closes and energizes the physical circuit containing the subsequent trip coil 24.

[0047] Preferably, after the magnetic balance physical actuator 20 completes the physical-level instantaneous sensing of the above-mentioned leakage state, its output DC trigger current needs to be directly applied to the end actuator to cut off the source of danger. The physical forced locking mechanism is connected in series between the system control circuit and the welding machine power supply circuit. It is mainly composed of a thyristor 23, a trip coil 24 and a mechanical trip linkage 28. The specific lower-level feature of the thyristor 23 is implemented as a unidirectional thyristor semiconductor device, and the specific lower-level feature of the trip coil 24 is implemented as an electromagnet coil assembly with an armature 241 and a reset spring 242 inside.

[0048] The anode of the thyristor 23 is electrically connected to one end of the trip coil 24, and the other end of the trip coil 24 is connected to the positive terminal of the internal control power supply of the welding machine. The cathode of the thyristor 23 is connected to the negative terminal of the control power supply, thereby forming a closed drive power circuit. One end of the armature 241 is physically hinged to the mechanical trip link 28, and the other end of the mechanical trip link 28 extends and is connected to the trip release execution end of the main power supply switch contactor 27 on the input side of the welding machine. The specific lower-level feature of the main power supply switch contactor 27 is realized as an air circuit breaker with a shunt trip mechanism.

[0049] The physical forced locking mechanism receives a trigger signal from the front end and executes a mechanical cutting action. The specific working process is as follows:

[0050] In step S204, under normal operating conditions where the welding machine does not leak current and the grounding impedance is within the safe threshold, neither the rectifier bridge 22 nor the microprocessor 50 outputs a trigger level. No current is injected into the gate of the thyristor 23, and the thyristor 23 maintains a high impedance open circuit state. The drive power circuit is in the off state, no current flows through the trip coil 24, the electromagnet coil assembly does not generate magnetic force, the armature 241 remains stationary under the action of the reset spring 242, the main power supply switch contactor 27 remains closed and conductive, and the welding machine normally obtains the working voltage.

[0051] Step S205: When a grounding leakage current or impedance exceeding the limit occurs, the leakage current trigger signal output by the rectifier bridge 22 or the impedance exceeding the limit trigger signal output by the microprocessor 50 is transmitted to the gate of the thyristor 23. When the instantaneous current at the input gate reaches the gate trigger current threshold... When the thyristor 23 is in a state of high impedance open circuit, a positive feedback conduction path is formed inside the thyristor 23, and the thyristor 23 changes from a high impedance open circuit state to a low impedance conduction state.

[0052] In step S206, the thyristor 23 is turned on, causing the drive power circuit to close, and the excitation current flows through the trip coil 24. Excitation current An alternating magnetic field is generated around the electromagnet coil assembly, and the alternating magnetic field exerts an electromagnetic attraction on the armature 241. Under ideal static conditions where the air gap magnetic flux is uniformly distributed and leakage flux is negligible, the electromagnetic attraction force... The calculation formula is as follows:

[0053]

[0054] In the formula, The permeability of free space, This refers to the number of turns in the winding of the trip coil 24. The effective cross-sectional area of ​​the electromagnet's magnetic circuit is... The length of the working air gap between armature 241 and the iron core;

[0055] Step S207, electromagnetic attraction Overcoming the mechanical reaction force of the reset spring 242, the armature 241 is attracted to the center position of the coil. The linear displacement of the armature 241 causes the mechanical tripping link 28 to undergo physical displacement. The displacement of the mechanical tripping link 28 triggers the shunt tripping mechanism inside the main power supply switch contactor 27 to act, forcing the main contacts of the main power supply switch contactor 27 to separate.

[0056] In step S208, after the main contacts of the main power supply switch contactor 27 are disconnected, the power supply of the main power supply circuit of the welding machine is forcibly cut off, the welding machine loses its welding arc ignition capability, and the step-down transformer power supply unit 10, being located on the downstream load side of the main power supply switch contactor 27, simultaneously loses its AC input power. The buzzer alarm branch 40 then loses power and stops sounding, completing the closed loop of the safety protection action.

[0057] Preferably, while basic physical leakage protection can handle serious leakage faults that have already occurred, it cannot proactively identify safety blind spots such as ungrounded casings or excessive impedance when no leakage occurs. Therefore, the active impedance monitoring module 30 serves as a second layer of intelligent safety protection, responsible for real-time quantification of the equivalent impedance of the grounding loop. Considering the strong electromagnetic interference generated during the welding machine's inverter process, the system must first dynamically optimize to avoid high-frequency interference bands before performing weak characteristic signal injection and impedance measurement.

[0058] The carrier spectrum detection loop 31 contains, in series, a voltage divider attenuation network 311, a high-speed opto-isolation circuit 312, and an anti-aliasing low-pass filter circuit 313. The input of the voltage divider attenuation network 311 is electrically connected to the pulse width modulation drive port of the welding machine inverter power control board. The microprocessor 50 integrates a direct memory access controller 54 and a fast Fourier transform hardware acceleration unit 55. The output of the anti-aliasing low-pass filter circuit 313 is connected to the analog-to-digital conversion pin of the microprocessor 50.

[0059] The specific lower-level feature of the voltage divider attenuation network 311 is implemented as a resistor-capacitor matching voltage divider circuit composed of non-inductive resistors. The specific lower-level feature of the high-speed opto-isolation circuit 312 is implemented as a high-speed digital optocoupler chip with push-pull output stage. The carrier spectrum detection circuit 31, combined with the microprocessor 50, performs background noise spectrum analysis and adaptive optimization calculation of injection frequency.

[0060] The inverter PWM carrier spectrum detection and adaptive optimization calculation of the injection frequency are performed according to the following steps:

[0061] In step S301, the voltage divider attenuation network 311 collects the pulse width modulation signal output from the inverter power control board of the welding machine, reduces the voltage amplitude of the pulse width modulation signal according to the attenuation ratio, and the reduced pulse width modulation signal is physically potential isolated between the high-voltage main circuit and the low-voltage control circuit by the high-speed opto-isolation circuit 312. The anti-aliasing low-pass filter circuit 313 filters out high-frequency components higher than the Nyquist frequency in the pulse width modulation signal and outputs the conditioned pulse width modulation signal. The microprocessor 50 accesses the controller 54 via direct memory access, controlling the analog-to-digital converter pin to sample the pulse-width modulated signal at a fixed sampling rate. Perform continuous-time sampling to generate a discrete-time data sequence in memory;

[0062] In step S302, the microprocessor 50 calls the Fast Fourier Transform hardware acceleration unit 55 to perform a Discrete Fourier Transform operation on the discrete time-domain data sequence in memory. The Fast Fourier Transform hardware acceleration unit 55 outputs the frequency domain discrete amplitude spectrum of the pulse width modulation signal under the current welding condition. Discrete amplitude spectrum in the frequency domain The switching base frequency of the inverter main circuit The frequency distribution coordinates of its higher-order harmonics;

[0063] In step S303, the microprocessor 50, within the set total measurement frequency band (the preset effective injection frequency band is 1kHz to 50kHz to ensure that the injected signal is effectively coupled in the high-frequency coupling transformer and the response signal strength is moderate), calculates the signal based on the frequency domain discrete amplitude spectrum. Calculate the corresponding background noise energy density function Background noise energy density function The calculation formula is as follows: Microprocessor 50 reads the preset safe frequency protection bandwidth from memory. Safe frequency protection bandwidth Used to define the frequency range affected by harmonic interference from welding machines;

[0064] In step S304, the microprocessor 50 executes a minimum value optimization algorithm, and the microprocessor 50 traverses discrete frequency variables within the total measurement frequency band. Search for noise energy density function The global minimum point is found by the microprocessor 50 during the traversal search, which eliminates the distance switch base frequency. The frequency difference of its integer multiples of harmonics is less than the safe frequency protection bandwidth. Frequency coordinates;

[0065] In step S305, the microprocessor 50 determines the frequency coordinate that satisfies the exclusive constraint condition and corresponds to the minimum noise energy density as the optimal injection frequency. Optimal injection frequency The decision logic satisfies the following formula: The frequency coordinate constraint is as follows: In the formula, A positive integer, representing the harmonic order. For the discrete frequency variables participating in the traversal operation, the microprocessor 50 will calculate the optimal injection frequency. The frequency control word is converted into the frequency control word required by the direct digital frequency synthesizer chip 322 and sent to the high-frequency characteristic signal generator 32 to complete the adaptive adaptation of the injected signal frequency to the electromagnetic environment.

[0066] Preferably, after completing the inverter PWM carrier spectrum detection and locking the optimal injection frequency... Afterwards, the system possesses extremely strong adaptability to electromagnetic interference environments. Subsequently, the system initiates the generation and physical injection process of impedance measurement characteristic signals. The high-frequency characteristic signal generator 32 internally includes a serial communication interface 321, a direct digital frequency synthesizer chip 322, a digital-to-analog converter 323, and a power operational amplifier circuit 324. The communication pin of the microprocessor 50 establishes a data connection with the serial communication interface 321 of the direct digital frequency synthesizer chip 322, and the output terminal of the high-frequency characteristic signal generator 32 establishes a physical electrical connection with the primary winding 352 of the high-frequency coupling transformer 35.

[0067] The high-frequency coupling transformer 35 includes a high-frequency ferrite core 351 and a primary winding 352. The output terminal of the high-frequency characteristic signal generator 32 is connected to the multi-turn primary winding 352. The grounding wire 36 of the welding machine's outer shell passes through the central hole of the high-frequency ferrite core 351 to form a single-turn secondary winding of the high-frequency coupling transformer 35. The high-frequency coupling transformer 35 provides electrical isolation between the high-voltage working circuit and the low-voltage measurement circuit while realizing signal injection.

[0068] The active generation and closed-loop injection process of high-frequency characteristic signals is performed according to the following steps:

[0069] In step S306, the microprocessor 50 calculates the corresponding frequency control word based on the optimal injection frequency determined by the carrier spectrum detection loop 31. The microprocessor 50 sends the frequency control word to the direct digital frequency synthesizer chip 322 inside the high-frequency characteristic signal generator 32 through the serial communication interface 321. The direct digital frequency synthesizer chip 322 outputs a discrete digital sine wave sequence of the corresponding frequency based on the frequency control word and the internal reference clock.

[0070] In step S307, the digital-to-analog converter 323 receives the discrete digital sine wave sequence and converts it into a stepped analog level signal. The power operational amplifier circuit 324 performs low-pass smoothing filtering and linear power amplification on the stepped analog level signal, and outputs an analog characteristic voltage signal with load driving capability. The peak amplitude of the open-circuit voltage at the output of the power operational amplifier circuit (primary winding side) is set between 10V and 24V. The actual response current injected into the closed loop is limited to a safe range in the milliampere level by the turns ratio of the high-frequency coupling transformer and the source impedance, ensuring sufficient injected power can still be provided on the primary side even with extremely low ground impedance. The time-domain expression is as follows:

[0071]

[0072] In the formula, To simulate the peak amplitude of the characteristic voltage signal, The optimal injection frequency is dynamically locked for the microprocessor 50. It is a time variable;

[0073] Step S308, simulate characteristic voltage signal The high-frequency alternating excitation current is directly applied to both ends of the primary winding 352 of the high-frequency coupling transformer 35. The high-frequency alternating excitation current excites high-frequency alternating magnetic flux inside the high-frequency ferrite core 351 of the high-frequency coupling transformer 35.

[0074] In step S309, the high-frequency alternating magnetic flux hinge passes through the outer shell grounding wire 36 of the central hole of the high-frequency ferrite core 351. According to Faraday's law of electromagnetic induction, the high-frequency alternating magnetic flux induces an injection test voltage of the same frequency on the outer shell grounding wire 36. The injection test voltage is directly connected in series and superimposed in the closed physical circuit composed of the metal shell of the welding machine, the outer shell grounding wire 36, the earth, and the protective grounding wire of the power supply system, thus completing the non-contact coupling injection action of the impedance measurement characteristic signal.

[0075] Preferably, after the characteristic signal is successfully injected into the closed physical circuit, the total return current signal collected by the broadband current transformer 34 inevitably contains extremely strong high-frequency background noise from the welding machine. In order to accurately extract the weak response current that reflects the true grounding impedance, the system uses an orthogonal demodulation algorithm to deeply condition and quantize the collected signal;

[0076] The quadrature demodulation hardware circuit 33 internally includes an in-phase analog multiplier 331, a quadrature analog multiplier 332, a first active low-pass filter 333, and a second active low-pass filter 334. The microprocessor 50 internally integrates a multi-channel analog-to-digital converter 51, a first digital-to-analog conversion channel 52, and a second digital-to-analog conversion channel 53. The signal output terminal of the broadband current transformer 34 is connected in parallel to the input terminals of the in-phase analog multiplier 331 and the quadrature analog multiplier 332. The analog output terminal of the first digital-to-analog conversion channel 52 is connected to the reference input terminal of the in-phase analog multiplier 331, and the analog output terminal of the second digital-to-analog conversion channel 53 is connected to the reference input terminal of the quadrature analog multiplier 332. The first active low-pass filter 333 is cascaded to the output terminal of the in-phase analog multiplier 331, and the second active low-pass filter 334 is cascaded to the output terminal of the quadrature analog multiplier 332.

[0077] The output terminals of the first active low-pass filter 333 and the second active low-pass filter 334 are respectively connected to different analog input channels of the multi-channel analog-to-digital converter 51. The specific lower-level features of the in-phase analog multiplier 331 and the quadrature analog multiplier 332 are implemented as a high-frequency four-quadrant analog multiplier integrated chip. The specific lower-level features are implemented as a second-order voltage-controlled voltage source (Sallen-Key) low-pass filter circuit based on a high-bandwidth operational amplifier. The two internal access resistors are synchronously adjusted by the digital potentiometer 336 to change the equivalent dominant pole.

[0078] The quadrature demodulation and impedance quantization of weak return current signals are performed according to the following steps:

[0079] Step S310: The broadband current transformer 34 acquires the total return current signal on the casing grounding conductor 36 in real time. Total return signal Including the response current excited by the injected characteristic voltage signal and the high-frequency background noise generated by the welding machine, the broadband current transformer 34 converts the total return current signal. It is converted into a corresponding proportional voltage signal and transmitted to the quadrature demodulation hardware circuit 33;

[0080] In step S311, the microprocessor 50 uses an internal timer and a digital discrete sine table to synchronously output and inject frequencies. The first digital-to-analog converter channel 52 converts the digital in-phase reference sequence into an analog in-phase reference voltage, using identical digital in-phase and digital quadrature reference sequences. The data is then transmitted to the in-phase analog multiplier 331, where the second digital-to-analog converter 53 converts the digital quadrature reference sequence into an analog quadrature reference voltage. And transmit it to the orthogonal analog multiplier 332;

[0081] Step S312, the in-phase analog multiplier 331 processes the total return signal. Analog in-phase reference voltage Perform time-domain multiplication and output in-phase mixer signal; quadrature analog multiplier 332 outputs total return signal. Orthogonal reference voltage Perform time-domain multiplication and output a quadrature mixing signal;

[0082] In step S313, the in-phase mixing signal is input to the first active low-pass filter 333, and the quadrature mixing signal is input to the second active low-pass filter 334. The first active low-pass filter 333 and the second active low-pass filter 334 filter out the high-frequency harmonic components generated by the mixing operation and the high-frequency background noise of the welding machine, retaining the injected frequencies. The relevant DC signal components, the first active low-pass filter 333 outputs in-phase DC characteristic level The second active low-pass filter 334 outputs an orthogonal DC characteristic level. ;

[0083] Step S314, the multi-channel analog-to-digital converter 51 pairs in-phase DC characteristic levels Orthogonal DC characteristic level Perform analog-to-digital conversion sampling to convert continuous analog voltage values ​​into discrete digital quantities and transmit them to the processing core of microprocessor 50;

[0084] In step S315, the microprocessor 50 performs impedance analysis based on the sampled digital quantity, and calculates the amplitude of the actual response current of the grounding loop. :

[0085]

[0086] In the formula, The digital quantization value of the in-phase DC characteristic level. The digital quantization value of the orthogonal DC characteristic level;

[0087] Step S316, the microprocessor 50 combines the preset peak amplitude of the analog characteristic voltage signal Calculate the equivalent impedance modulus of the enclosure grounding loop at the current injection frequency. :

[0088]

[0089] In the formula, The equivalent impedance magnitude is the quantized value. It directly represents the current physical connection and conduction status between the welding machine casing and the ground.

[0090] Preferably, the above-mentioned quadrature demodulation and impedance quantization process has extremely high measurement accuracy during the stable operation of the welding machine. However, under transient conditions such as arc ignition or pulse step, the drastic change in the main circuit load can cause a sharp change in the electromagnetic interference coupling strength. In order to balance the noise immunity accuracy and transient response speed of the measurement, and to prevent the forced locking mechanism from malfunctioning due to filtering hysteresis, the present invention further introduces an adaptive filter bandwidth switching mechanism based on inverter operating condition identification in the quadrature demodulation hardware circuit 33.

[0091] To achieve the dynamic adjustment function of the filtering bandwidth of the first active low-pass filter 333 and the second active low-pass filter 334, both the first active low-pass filter 333 and the second active low-pass filter 334 are internally configured with an RC feedback network 335. The RC feedback network 335 integrates a digital potentiometer 336. The specific lower-level feature of the digital potentiometer 336 is implemented as a dual-channel programmable variable resistor chip driven by a serial peripheral interface bus. The serial communication pin of the microprocessor 50 establishes a bus electrical connection with the control pin of the digital potentiometer 336. Through this serial peripheral interface bus, the microprocessor 50 uses the control quantity of the welding machine inverter control stage as a feedforward signal to adaptively adjust the signal processing bandwidth of the quadrature demodulation hardware circuit 33.

[0092] The adaptive filter bandwidth switching calculation based on inverter operating condition identification is performed according to the following steps:

[0093] In step S317, the microprocessor 50 continuously receives the pulse width modulation signal output by the carrier spectrum detection loop 31. The microprocessor 50 measures the pulse width modulation signal through its internal timer capture function. By dividing the high-level duration within a single switching cycle by the total cycle time, the microprocessor 50 calculates the real-time duty cycle of the welding machine inverter. ;

[0094] Step S318, microprocessor 50 sets the real-time duty cycle of adjacent sampling periods. Perform discrete difference operations to extract the absolute value of the time derivative of the duty cycle. The absolute value of the time derivative of the duty cycle The calculation formula is as follows:

[0095]

[0096] In the formula, This represents the real-time duty cycle for the current period. This represents the real-time duty cycle of the previous discrete cycle. For discrete sampling time intervals, the absolute value of the time derivative is given. Physically, the transient step intensity of the inverter load of the welding machine is characterized. This load step is accompanied by a sudden change in high di / dt in the main circuit, which is the main cause of enhanced electromagnetic interference coupling. Experimental results show that this sudden change in high di / dt will induce a high-amplitude, wide-frequency transient noise spike in the measurement circuit through the spatial magnetic field and parasitic capacitance. Therefore, it is used as the benchmark for adaptive identification of interference intensity.

[0097] Step S319: Microprocessor 50 reads the preset duty cycle change judgment threshold from memory. (A typical empirical setting is 5% / ms), the microprocessor 50 will calculate the absolute value of the time derivative of the duty cycle. Threshold for determining sudden changes in duty cycle Perform numerical comparison operations and switch the execution branch of the state machine according to the comparison results;

[0098] Step S320, when the comparison result satisfies At this time, the microprocessor 50 determines that the welding machine is currently in a transient state of arc ignition or pulse step. The microprocessor 50 sends a low-resistance control word to the digital potentiometer 336 through the serial peripheral interface bus, and the digital potentiometer 336 reduces its internal connection resistance. According to the cutoff frequency formula of a second-order Sallen-Key equivalent resistance active low-pass filter:

[0099]

[0100] In the formula, The cutoff frequency, As the fixed feedback capacitor of the RC feedback network 335, the first active low-pass filter 333 and the second active low-pass filter 334 are synchronously switched to the high cutoff frequency according to the above formula. State (typically set at 10kHz), high cutoff frequency The signal bandwidth allowed by orthogonal demodulation is widened to accommodate the signal transients caused by strong electromagnetic interference coupling at the moment of arc initiation, thus balancing noise reduction accuracy and response speed.

[0101] Step S321, when the comparison result satisfies At this time, the microprocessor 50 determines that the welding machine is currently in a steady-state condition of stable welding or no-load standby. The microprocessor 50 sends a high-resistance control word to the digital potentiometer 336 through the serial peripheral interface bus, and the digital potentiometer 336 increases the internal input resistor. The first active low-pass filter 333 and the second active low-pass filter 334 synchronously switch to the low cutoff frequency. State (typically set at 100Hz), low cutoff frequency It narrows the allowable bandwidth of the quadrature demodulation signal, blocks broadband noise interference from arc plasma radiation under stable welding conditions, and maintains the quantization accuracy of the equivalent impedance modulus.

[0102] Preferably, after undergoing closed-loop conditioning involving adaptive injection of high-frequency characteristic signals, orthogonal demodulation extraction, and feedforward dynamic filtering, the microprocessor 50 ultimately obtains a high-precision equivalent impedance modulus that is unaffected by transient interference. Based on this quantified impedance value, the system enters the core intelligent judgment and safety warning execution stage;

[0103] The buzzer alarm branch 40 includes a driver switch 41, an active buzzer 42, and an LED indicator network 43. The specific lower-level feature of the driver switch 41 is an N-channel metal-oxide-semiconductor field-effect transistor or an NPN bipolar transistor. The LED indicator network 43 is composed of a current-limiting resistor 431 and a red LED 432 connected in series. The general-purpose input / output pins of the microprocessor 50 are physically and electrically connected to the control terminal of the driver switch 41. The power output pins of the driver switch 41 are connected to the negative terminal of the active buzzer 42 and the negative terminal of the LED indicator network 43, respectively. The microprocessor 50 performs impedance value comparison and judgment and alarm control in combination with hardware parameters.

[0104] The intelligent assessment of grounding impedance and the audible and visual warning actions are performed according to the following steps:

[0105] In step S401, at the end of each impedance analysis operation cycle, the microprocessor 50 extracts the equivalent impedance magnitude stored in the internal register. With return current amplitude The microprocessor 50 reads the preset safety impedance threshold from memory. With zero current dead zone threshold According to the safety regulations for on-site operation of electric welding machines, the safety impedance threshold is... Set as ;

[0106] In step S402, the microprocessor 50 calls its internal arithmetic logic unit to first set the return current amplitude. With zero current dead zone threshold Perform the comparison when When the microprocessor 50 determines that the outer casing grounding wire 36 is in an extreme open circuit state of physical disconnection, the microprocessor 50 directly jumps to execute the alarm trigger command, avoiding the software overflow error of division by zero in the equivalent impedance modulus analysis calculation in step S316.

[0107] Step S403, when At that time, the microprocessor 50 will convert the equivalent impedance magnitude... With safety impedance threshold Execute the numerical comparison instruction; when the numerical comparison result satisfies When the microprocessor 50 determines that the current protective grounding status of the welding machine casing complies with the safety regulations, the general-purpose input / output pin of the microprocessor 50 continuously outputs a low-level control signal, driving the switch transistor 41 to maintain the open-circuit cutoff state, the active buzzer 42 and the LED indicator network 43 do not form a current loop, and the warning device does not activate.

[0108] Step S404, when the numerical comparison result satisfies When the microprocessor 50 determines that the welding machine has a safety hazard of excessive grounding resistance, the general-purpose input / output pin of the microprocessor 50 outputs a high-level trigger signal to the control electrode of the drive switch transistor 41.

[0109] In step S405, the high-level trigger signal causes the drive switch 41 to switch from the cut-off state to the saturated conduction state. The DC working voltage output by the step-down transformer power supply unit 10 after step-down and rectification and regulation flows to the system reference ground through the active buzzer 42, the LED indicator network 43 and the conduction drive switch 41, forming a closed conduction circuit. The active buzzer 42 is powered on to emit an audio alarm, and the red LED 432 lights up, completing the auditory and visual forced warning action.

[0110] Preferably, when the aforementioned intelligent judgment process determines that the grounding impedance exceeds the standard or presents a physical open circuit state, the software-level trigger pulse output by the microprocessor 50 needs to be combined with the underlying hardware response mechanism to ensure that the power-off command is forcibly and reliably executed. This software-level trigger pulse and the hardware-level leakage current trigger voltage output by the aforementioned rectifier bridge 22 are physically independent yet logically unified, converging together at the end of the physical forced locking mechanism to ultimately form a complete safety protection closed loop;

[0111] The impedance over-limit trigger signal output by the microprocessor 50 and the leakage trigger signal output by the rectifier bridge 22 work together on the gate of the thyristor 23 to construct a dual-redundant trigger circuit for hardware leakage protection and software impedance over-limit protection. The dual-redundant trigger circuit is composed of the first isolation diode 26 and the second isolation diode 56. The specific lower-level features of the first isolation diode 26 and the second isolation diode 56 are implemented as Schottky barrier diodes to reduce the forward conduction voltage drop.

[0112] The positive output terminal of the rectifier bridge 22 is connected to the anode of the first isolation diode 26 through the current limiting resistor 25. The trigger signal output pin of the microprocessor 50 (configured in push-pull output mode to provide sufficient trigger current drive capability) is connected to the anode of the second isolation diode 56. The cathodes of the first isolation diode 26 and the second isolation diode 56 establish a physical node in parallel and are connected together to the gate of the thyristor 23. The first isolation diode 26 and the second isolation diode 56 form a hardware-level dual trigger signal convergence circuit with the gate of the thyristor 23 as the only output terminal in terms of electrical characteristics.

[0113] The convergence and linkage execution process of intelligent signals and physical actuators proceeds according to the following steps:

[0114] In step S406, under normal operating conditions where the welding machine does not leak current and the grounding impedance is within a safe range, the rectifier bridge 22 outputs zero voltage, the microprocessor 50 outputs a low level, the first isolation diode 26 and the second isolation diode 56 are both in the open circuit cutoff state, there is no current injection at the gate of the thyristor 23, the thyristor 23 maintains a high impedance blocking state, the power supply circuit of the trip coil 24 is disconnected, and the main power supply switch contactor 27 closes to supply power.

[0115] Step S407: When a leakage fault occurs in the welding machine, the detection magnetic ring coil 21 generates an induced electromotive force, and the rectifier bridge 22 outputs a DC trigger voltage. DC trigger voltage The first isolation diode 26 is forward biased, and the trigger current is injected into the gate of the thyristor 23 through the first isolation diode 26. At the same time, the cathode potential of the second isolation diode 56 is raised, and the second isolation diode 56 is in reverse cutoff state. The reverse cutoff state blocks the current from flowing to the pin of the microprocessor 50, protecting the internal digital circuit of the microprocessor 50 from damage by reverse current.

[0116] Step S408: When the welding machine does not leak current but the microprocessor 50 calculates and confirms that the grounding loop impedance exceeds the safety threshold. At that time, the trigger signal output pin of the microprocessor 50 outputs a high-level trigger pulse. High-level trigger pulse The second isolation diode 56 is forward biased, and the trigger current is injected into the gate of the thyristor 23 through the second isolation diode 56. Similarly, the cathode potential of the first isolation diode 26 is raised, and the first isolation diode 26 is in reverse cutoff state, blocking the current from flowing back to the rectifier bridge 22.

[0117] In step S409, since the negative output terminal of the rectifier bridge 22 and the control ground of the microprocessor 50 are physically connected to the cathode of the thyristor 23, forming a unified reference zero potential, the actual trigger voltage reaching the gate of the thyristor 23 will be determined regardless of whether a trigger source is generated individually or simultaneously. Satisfy the following mathematical relationship:

[0118]

[0119] In the formula, The forward voltage drop of the first isolation diode 26 The forward voltage drop of the second isolation diode 56 is the actual trigger voltage reaching the gate. Generate gate input current The calculation formula is:

[0120]

[0121] In the formula, The equivalent gate input resistance of the thyristor 23 is given by the gate input current. Reaching the gate trigger current threshold When the thyristor 23 changes from a high-impedance blocking state to a low-impedance conducting state;

[0122] In step S410, the thyristor 23 is turned on, connecting the power supply circuit of the trip coil 24. The trip coil 24 is energized and generates electromagnetic attraction, which pulls the mechanical trip linkage 28 to move, forcibly disconnecting the main contact of the main power supply switch contactor 27. The power supply of the welding machine's main power supply circuit is cut off, completing the double redundancy trigger power-off action.

Claims

1. A method for monitoring and mandating warning of the protective grounding status of a welding machine casing, characterized in that, Includes the following steps: Step S100: The monitoring and forced warning system is powered on synchronously with the main power supply of the welding machine. The step-down transformer power supply unit (10) outputs a 12V AC safety voltage. The buzzer alarm branch (40) performs a brief power-on self-test sound prompt. The microprocessor (50) starts up and completes the initialization of the internal registers and peripheral interfaces before actively shutting off the self-test sound. In step S200, the magnetic balance physical actuator (20) performs hardware-level passive monitoring. When the welding machine experiences leakage current in the casing, causing a deviation in the instantaneous current phasor sum between the live wire and the neutral wire, the magnetic field inside the detection magnetic ring coil (21) becomes unbalanced, and an alternating induced electromotive force is generated at both ends of the detection magnetic ring coil (21). After rectification by the rectifier bridge (22), the alternating induced electromotive force outputs a DC trigger voltage. DC trigger voltage The signal is transmitted to the gate of the thyristor (23) via the first isolation diode (26). The thyristor (23) is turned on, causing the trip coil (24) to be energized and generating magnetic attraction, which pulls the trip linkage to forcibly disconnect the main power supply contactor of the welding machine. In step S300, the microprocessor (50) controls the active impedance monitoring module (30) to perform active measurement of the grounding loop status. The microprocessor (50) sends a frequency control word to the high-frequency characteristic signal generator (32) based on the welding machine noise frequency band obtained by the carrier spectrum detection circuit (31), injects a characteristic AC voltage signal that avoids the noise frequency band, the broadband current transformer (34) collects the return signal, and the quadrature demodulation hardware circuit (33) performs analog mixing and low-pass filtering on the return signal to extract the DC level signal related to the grounding loop impedance and send it to the analog-to-digital conversion pin of the microprocessor (50). Step S400, the microprocessor (50) calculates the impedance magnitude. It also executes software-level forced interlocking actions, with a preset grounding safety threshold of [value missing]. When the calculation result meets the condition When the grounding loop exhibits open-circuit characteristics, the microprocessor (50) outputs a high-level trigger pulse. High-level trigger pulse The high-level trigger pulse is transmitted to the gate of the thyristor (23) via the second isolation diode (56). Turn on the thyristor (23), drive the trip coil (24) to operate, cut off the power input to the welding machine, and maintain the operation of the buzzer alarm branch (40).

2. The method for monitoring and mandatory warning of the protective grounding status of a welding machine casing according to claim 1, characterized in that, In step S200, the specific process of the magnetic balance physical actuator (20) performing hardware-level leakage current status monitoring includes: When the welding machine is in a normal insulation state and there is no leakage, the input current flowing through the live wire and the return current flowing through the neutral wire have the same amplitude and opposite direction. The alternating magnetic flux vector generated by the two phase currents in the annular core of the detection magnetic ring coil (21) cancels each other out, and the total magnetic flux inside the annular core is zero. The thyristor (23) maintains the blocking state. When the welding machine experiences a grounding leakage fault in the casing or has a shunt branch, part of the power supply current flows into the ground through the casing. The resulting leakage current excites a periodically changing net alternating magnetic flux inside the toroidal core. The net alternating magnetic flux links to the secondary side induction winding and excites an alternating induced electromotive force at both ends of it. The alternating induced electromotive force is transmitted to the rectifier bridge (22) and converted into a unidirectional pulsating DC voltage. After the amplitude is attenuated by the current limiting resistor (25), and after being unidirectionally turned on by the first isolation diode (26), a DC trigger current is injected into the gate of the thyristor (23). When the instantaneous amplitude of the DC trigger current reaches the gate trigger current threshold of the thyristor (23), the anode and cathode of the thyristor (23) are connected.

3. The method for monitoring and mandatory warning of the protective grounding status of a welding machine casing according to claim 1, characterized in that, In step S300, the step of the microprocessor (50) acquiring the welding machine noise frequency band and determining the optimal injection frequency based on the carrier spectrum detection circuit (31) includes: The voltage divider attenuation network (311) collects the pulse width modulation signal output by the inverter power control board of the welding machine and reduces the voltage amplitude. After being isolated by the high-speed opto-isolation circuit (312) and filtered out by the anti-aliasing low-pass filter circuit (313), the high-frequency components are output. The microprocessor (50) performs continuous time sampling at a fixed sampling rate to generate discrete time domain data sequences. Call the Fast Fourier Transform hardware acceleration unit (55) to perform discrete Fourier transform operation on the discrete time domain data sequence, and output the frequency domain discrete amplitude spectrum containing the switching fundamental frequency of the inverter main circuit and the distribution coordinates of its higher harmonics. The microprocessor (50) calculates the corresponding background noise energy density function within the set total measurement frequency band. The preset effective injection frequency band is 1kHz to 50kHz to ensure that the injected signal is effectively coupled in the high-frequency coupling transformer and the response signal strength is moderate. The microprocessor executes a minimum value optimization algorithm to determine the frequency coordinate that satisfies the exclusive constraint condition and has the minimum corresponding noise energy density as the optimal injection frequency. Its decision logic satisfies the following formula: The frequency coordinate constraint is as follows: In the formula, The background noise energy density function, For positive integers representing harmonic orders, This is the switching base frequency of the inverter's main circuit. For discrete frequency variables participating in the traversal operation, The preset safe frequency protection bandwidth.

4. The method for monitoring and mandatory warning of the protective grounding status of a welding machine casing according to claim 3, characterized in that, The specific process of injecting a characteristic AC voltage signal that avoids the noise frequency band includes: The microprocessor (50) calculates the frequency control word corresponding to the optimal injection frequency and sends it to the direct digital frequency synthesizer chip (322) inside the high-frequency characteristic signal generator (32), and outputs a discrete digital sine wave sequence of the corresponding frequency. The digital-to-analog converter (323) converts the discrete digital sine wave sequence into a stepped analog level signal. The power operational amplifier circuit (324) performs low-pass smoothing filtering and linear power amplification, and outputs an analog characteristic voltage signal with load driving capability. The peak amplitude of the open-circuit voltage of the analog characteristic voltage signal at the output of the power operational amplifier circuit is set between 10V and 24V. The simulated characteristic voltage signal is applied to both ends of the primary winding (352) of the high-frequency coupling transformer (35) to generate a high-frequency alternating excitation current and a high-frequency alternating magnetic flux. The high-frequency alternating magnetic flux induces an injection test voltage of the same frequency on the outer casing grounding wire (36), which is directly connected in series and superimposed in the closed physical circuit to complete the non-contact coupling injection of the impedance measurement characteristic signal.

5. The method for monitoring and mandatory warning of the protective grounding status of a welding machine casing according to claim 1, characterized in that, In step S300, the quadrature demodulation hardware circuit (33) processes the return signal and extracts the DC level signal, including: The broadband current transformer (34) acquires the total return current signal containing the response current and high-frequency background noise in real time and converts it into a proportional voltage signal; the microprocessor (50) synchronously outputs a digital in-phase reference sequence and a digital quadrature reference sequence that are exactly the same as the optimal injection frequency, and converts them into two reference voltages respectively, namely the in-phase reference voltage and the analog quadrature reference voltage; The in-phase analog multiplier (331) and the quadrature analog multiplier (332) perform time-domain multiplication operations on the total return current signal and the two reference voltages, respectively, and output the in-phase mixer signal and the quadrature mixer signal; The first active low-pass filter (333) and the second active low-pass filter (334) respectively filter out the high-frequency harmonic components and background noise generated by the mixing operation, retain the DC signal components, and output the in-phase DC characteristic level and the quadrature DC characteristic level. After being sampled by analog-to-digital conversion, they are transmitted to the operation core of the microprocessor (50).

6. The method for monitoring and mandatory warning of the protective grounding status of a welding machine casing according to claim 5, characterized in that, The microprocessor (50) calculates the impedance magnitude based on the extracted DC level signal. The specific process includes: With the reference signal amplitude normalized and the multiplier gain set to 1, the microprocessor (50) calculates the amplitude of the actual response current of the grounding loop. : In the formula, The digital quantization value of the in-phase DC characteristic level. The digital quantization value of the orthogonal DC characteristic level; The microprocessor (50) combines the preset peak amplitude of the analog characteristic voltage signal Calculate the equivalent impedance modulus of the enclosure grounding loop at the current injection frequency. : Through the equivalent impedance magnitude It represents the current physical connection and conductivity between the welding machine casing and the ground.

7. The method for monitoring and mandatory warning of the protective grounding status of a welding machine casing according to claim 1, characterized in that, To balance noise immunity and transient response speed in measurement, the orthogonal demodulation hardware circuit (33) adopts an adaptive filter bandwidth switching mechanism based on inverter operating condition identification. The specific steps include: The microprocessor (50) measures the duration of the high level of the pulse width modulation signal in a single switching cycle and the total cycle time, calculates the real-time duty cycle of the welding machine inverter, and performs discrete difference operation on the real-time duty cycle of adjacent sampling cycles to extract the absolute value of the time differential that characterizes the transient step intensity of the welding machine inverter load. The absolute value of the time derivative is compared with a preset duty cycle abrupt change threshold. When the absolute value of the time derivative is greater than the duty cycle change judgment threshold, it is determined that it is in the transient working condition of arc initiation or pulse step. The microprocessor (50) controls the digital potentiometer (336) to reduce the internal access resistance, so that the first active low-pass filter (333) and the second active low-pass filter (334) are synchronously switched to the high cutoff frequency state, thus widening the allowable bandwidth of the quadrature demodulation signal. When the absolute value of the time derivative is less than or equal to the duty cycle change threshold, it is determined to be in steady state. The digital potentiometer (336) is controlled to increase the internal access resistance and synchronously switch to the low cutoff frequency state, thus narrowing the allowable bandwidth of the quadrature demodulation signal.

8. The method for monitoring and mandatory warning of the protective grounding status of a welding machine casing according to claim 1, characterized in that, In step S400, the specific steps of impedance value comparison and judgment and alarm control performed by the microprocessor (50) include: The microprocessor (50) extracts the equivalent impedance magnitude. First, the return current amplitude is compared with the preset zero current dead zone threshold. When the return current amplitude is less than the zero current dead zone threshold, it is determined that the shell grounding wire (36) is in an extreme open circuit state of physical disconnection. The alarm trigger command is executed directly to avoid the software overflow error of division by zero in the impedance analysis calculation. When the return current magnitude is greater than or equal to the zero current dead zone threshold, the equivalent impedance magnitude will be... With a safety impedance threshold set at 4Ω Execute the numerical comparison instruction; when At this time, the microprocessor (50) continuously outputs a low-level control signal to drive the switch (41) to maintain the open circuit cut-off state, and the warning device does not activate; when When the microprocessor (50) outputs a high-level trigger signal to the control electrode of the drive switch (41) to make it saturate and conduct. The DC working voltage output by the step-down transformer power supply unit (10) after step-down and rectification and regulation flows through the closed conduction circuit. The active buzzer (42) is powered on and emits an audio alarm and the red light-emitting diode (432) lights up, completing the forced warning action.

9. The method for monitoring and mandating warning of the protective grounding status of a welding machine casing according to claim 1, characterized in that, The software-level forced locking action in step S400 and the hardware-level passive monitoring action in step S200 are linked through a hardware-level dual trigger signal convergence circuit. The specific logic process includes: The DC trigger voltage output by the rectifier bridge (22) and the high-level trigger pulse output by the microprocessor (50) work together on the gate of the thyristor (23); wherein, the first isolation diode (26) and the second isolation diode (56) form a hardware-level dual trigger signal convergence circuit with the gate of the thyristor (23) as the only output terminal in terms of electrical characteristics; When the welding machine has a leakage fault, the DC trigger voltage output by the rectifier bridge (22) causes the first isolation diode (26) to be in a forward bias state to inject trigger current, while the second isolation diode (56) is in a reverse cutoff state to block the current from flowing to the pin of the microprocessor (50). When the microprocessor (50) calculates and confirms that the ground loop impedance exceeds the safety threshold At that time, the high-level trigger pulse output by the microprocessor (50) causes the second isolation diode (56) to be in a forward bias state to inject trigger current. Similarly, the first isolation diode (26) is in a reverse cutoff state, blocking the current from flowing back to the rectifier bridge (22). Whether the trigger source is generated individually or simultaneously, when the gate input current generated by the actual trigger voltage reaching the gate of the thyristor (23) reaches the gate trigger current threshold, the thyristor (23) changes from a high impedance blocking state to a low impedance conducting state.

10. A method for monitoring and mandating warning of the protective grounding status of a welding machine casing according to claim 2, characterized in that, The physical forced power cut-off process after the thyristor (23) is turned on includes: The trip coil (24) is connected in series between the anode of the thyristor (23) and the positive terminal of the independent DC control power supply. A positive feedback conduction path is formed inside the thyristor (23) and the power supply circuit of the trip coil (24) is connected. Excitation current flows through the trip coil (24). The excitation current generates an alternating magnetic field around the electromagnet coil assembly, which applies an electromagnetic attraction force to the armature (241). When the electromagnetic attraction force overcomes the mechanical reaction force of the return spring (242), it attracts the armature (241) to the center of the coil. The linear displacement of the armature (241) causes the mechanical trip link (28) to undergo physical displacement. The displacement of the mechanical trip link (28) triggers the shunt trip mechanism inside the main power supply switch contactor (27) to operate, forcing the main contacts of the main power supply switch contactor (27) to separate, and the power supply of the main power supply circuit of the welding machine is cut off, completing the double redundancy trigger power-off action.

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