Multi-level energy storage power supply system for argon arc welding and control method thereof

Abstract

The application relates to the technical field of welding power sources, and provides a multi-level energy storage power supply system for argon arc welding and a control method thereof. The system comprises an input rectification and filtration unit, an energy storage unit, a direct-current level multiplication module, an inverter unit, an output rectification unit, a control chip and a harmonic detection circuit. The direct-current level multiplication module is connected between the energy storage unit and the inverter unit, comprises a plurality of capacitor bootstrap units, and is used for multiplying n+1 direct-current levels into 2n direct-current levels. The inverter unit is used for inverting the 2n direct-current levels into 4n+1-level alternating currents. The harmonic detection circuit is arranged at an alternating current input side of the input rectification and filtration unit, a data output end is connected with a data input end of the control chip, and a control signal output end of the control chip is connected with the input rectification and filtration unit, the energy storage unit, the direct-current level multiplication module and the inverter unit. The system greatly reduces the harmonic distortion rate of the output voltage, and fundamentally improves the stability of a welding arc.

Description

Technical Field

[0001] This application relates to the field of welding power supply technology, specifically to a multi-level energy storage power supply system and its control method for argon arc welding. Background Technology

[0002] Argon arc welding (ATW) is a high-quality arc welding method widely used in demanding applications such as long-distance pipelines and pressure vessels. The welding power source, as the core of the ATW equipment, directly affects arc stability and weld quality through its output characteristics.

[0003] Currently, there are three main types of welding power supplies: tapped rectifier power supplies achieve stepped voltage regulation by changing the number of coil turns through physical taps, but the output current changes in a step manner, resulting in insufficient regulation precision; diesel or gasoline generator sets are convenient to use as independent power sources, but the output waveform quality is poor, and there are problems such as high energy consumption, high noise, and emission pollution; grid power supplies provide stable power, but may face limitations such as insufficient coverage and poor power supply reliability in the field, and the harmonics generated by welding loads will pollute the power grid.

[0004] To address harmonic issues during welding, existing technologies typically employ increasing generator capacity or adding passive filtering equipment such as voltage stabilizers. However, these solutions suffer from low resource utilization efficiency, increased equipment size and cost, and an inability to fundamentally resolve the source of harmonic generation. Furthermore, the demands for high instantaneous power during the arc initiation phase, the requirement for current stability during the stabilization phase, and the expectation of energy recovery during the arc termination phase make it difficult for a single power supply configuration to achieve optimal power supply for all operating conditions.

[0005] Therefore, there is an urgent need for a new type of energy storage power system that can output high-quality waveforms, has harmonic suppression capabilities, and can adapt to different welding conditions. Summary of the Invention

[0006] In view of this, embodiments of this application provide a multi-level energy storage power supply system and its control method for argon arc welding, which solves the problems of high harmonic content in the output waveform, insufficient arc stability, low energy utilization efficiency, and inability to meet the needs of different welding conditions in existing welding power supplies.

[0007] The first aspect of this application provides a multi-level energy storage power supply system for argon arc welding, comprising an input rectifier filter unit, an energy storage unit, a DC level multiplier module, an inverter unit, an output rectifier unit, a control chip, and a harmonic detection circuit; The input rectifier and filter unit is connected to the mains power supply and is used to rectify and filter the AC power from the mains power supply and output DC power. The energy storage unit includes n energy storage modules connected in series, which are used to store electrical energy and provide n+1 DC levels; The DC level multiplier module is connected between the energy storage unit and the inverter unit, and includes multiple capacitor bootstrap units for multiplying the n+1 DC levels into 2n DC levels; The inverter unit adopts an H-bridge topology to convert the 2n DC levels into 4n+1 AC levels, and achieves welding output and harmonic compensation under the drive of the control chip. The output rectifier unit is used to rectify the AC power output from the inverter unit and supply it to the welding torch. The harmonic detection circuit is located on the AC input side of the input rectifier filter unit. The data output terminal of the harmonic detection circuit is connected to the data input terminal of the control chip. The control signal output terminal of the control chip is connected to the control signal input terminals of the input rectifier filter unit, the energy storage unit, the DC level multiplier module, and the inverter unit, respectively.

[0008] A second aspect of this application provides a control method for a multi-level energy storage power supply system for argon arc welding as described in the first aspect, comprising: Acquire the grid current signal and separate the harmonic current component from the grid current signal; Obtain the status parameters of each energy storage module, and calculate the PWM duty cycle of each energy storage module based on the status parameters; The current modulation mode is determined based on the welding conditions, and the mode is switched between SVPWM modulation mode and SHEPWM modulation mode. Based on the welding output command, harmonic compensation command, and duty cycle of each energy storage module, PWM drive signals for the DC level multiplier module and inverter unit are generated. The DC level multiplier module multiplies n+1 DC levels into 2n DC levels, and the inverter unit inverts the 2n DC levels into an AC output waveform of 4n+1 levels.

[0009] The first aspect of this application provides a multi-level energy storage power supply system for argon arc welding. Through the cooperation of a DC level multiplier module and an H-bridge inverter structure, the n+1 DC levels provided by n energy storage modules are multiplied into 2n DC levels, thereby outputting an AC waveform with 4n+1 levels. This significantly reduces the harmonic distortion rate of the output voltage and fundamentally improves the stability of the welding arc.

[0010] By employing two complementary modulation strategies, SVPWM and SHEPWM, and dynamically switching according to the welding conditions, specific low-order harmonics are eliminated while ensuring dynamic response speed, thus balancing rapid response during the arc initiation and termination phases with waveform quality during the stable welding phase.

[0011] By using harmonic detection and compensation functions, the inverter unit generates a compensation current that is out of phase with the grid harmonics, thereby reducing the system's harmonic pollution to the grid and improving energy utilization efficiency.

[0012] By adopting a power supply architecture that integrates the power grid and energy storage units, the power ratio is dynamically allocated according to different welding conditions, which effectively improves the overall efficiency and power supply reliability of the system.

[0013] It is understandable that the beneficial effects of the second aspect mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a connection diagram of a multilevel energy storage power supply system for argon arc welding provided in an embodiment of this application; Figure 2 This is a circuit diagram of a capacitor bootstrap unit provided in an embodiment of this application; Figure 3 This is a flowchart of a control method for a multi-level energy storage power supply system for argon arc welding, provided in an embodiment of this application.

[0016] In the picture: 11-Input Rectifier Filter Unit 12-Energy Storage Unit 13-DC Level Multiplier Module 14-Inverter Unit 15-Output Rectifier Unit 16-Control Chip 17-Harmonic Detection Circuit Cs-energy storage capacitor Cb - Bootstrap capacitor S1~S4: Controllable switches Q1~Q4: H-bridge switching transistors Detailed Implementation

[0017] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0018] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0019] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0020] As used in this application specification and the appended claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if detected [the described condition or event]" may be interpreted, depending on the context, as meaning "once determined," "in response to determination," "once detected [the described condition or event]," or "in response to detection [the described condition or event]."

[0021] Furthermore, in the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0022] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0023] The multi-level energy storage power supply system for argon arc welding provided in this application includes: an input rectifier and filter unit, an energy storage unit, a DC level multiplier module, an inverter unit, an output rectifier unit, a control chip, and a harmonic detection circuit; The input rectifier and filter unit is connected to the mains power supply and is used to rectify and filter the AC power from the mains power supply and output DC power. The energy storage unit includes n energy storage modules connected in series, which are used to store electrical energy and provide n+1 DC levels; The DC level multiplier module is connected between the energy storage unit and the inverter unit, and includes multiple capacitor bootstrap units for multiplying the n+1 DC levels into 2n DC levels; The inverter unit adopts an H-bridge topology to convert the 2n DC levels into 4n+1 AC levels, and achieves welding output and harmonic compensation under the drive of the control chip. The output rectifier unit is used to rectify the AC power output from the inverter unit and supply it to the welding torch. The harmonic detection circuit is located on the AC input side of the input rectifier filter unit. The data output terminal of the harmonic detection circuit is connected to the data input terminal of the control chip. The control signal output terminal of the control chip is connected to the control signal input terminals of the input rectifier filter unit, the energy storage unit, the DC level multiplier module, and the inverter unit, respectively.

[0024] In applications, such as Figure 1 As shown, the system includes an input rectifier and filter unit 11, an energy storage unit 12, a DC level multiplier module 13, an inverter unit 14, an output rectifier unit 15, a control chip 16, and a harmonic detection circuit 17.

[0025] In applications, the input rectifier and filter unit 11 serves as the interface circuit between the system and the mains power supply. Rectification refers to using the unidirectional conductivity of devices such as diodes or thyristors to convert alternating current (AC) into unidirectional pulsating direct current (DC); filtering, on the other hand, uses the energy storage characteristics of capacitors to smooth the ripple components in the pulsating DC. The purpose of this unit is to provide a stable DC power input for the subsequent energy storage unit and inverter unit. Its input terminal receives mains frequency AC power, and its output terminal provides a rectified and filtered DC voltage.

[0026] In the application, energy storage unit 12 serves as the system's energy buffer, consisting of n energy storage modules connected in series. Each energy storage module can employ energy storage elements such as supercapacitors or batteries, its function being to store electrical energy and release it rapidly when needed. The n+1 DC levels refer to the fact that when n energy storage modules are connected in series, by selecting different numbers of modules, a total of n+1 different voltage levels—0, V, 2V up to nV—can be obtained at the output terminal, where V is the nominal voltage of a single energy storage module.

[0027] In the application, the DC level multiplier module 13 is used to multiply the n+1 DC levels provided by the energy storage unit 12 into 2n DC levels. Level multiplication refers to using the series-parallel switching characteristics of capacitors to obtain more voltage levels without increasing the number of energy storage modules. This module consists of multiple capacitor bootstrap units, which realize the series-parallel recombination of capacitors by controlling the on-off timing of the switches, thereby obtaining a denser level distribution.

[0028] In the application, inverter unit 14 adopts an H-bridge topology, which is the power conversion stage for DC-to-AC conversion. An H-bridge is a bridge circuit composed of four power switches, named for its H-shaped topology. The core function of the H-bridge is to map DC voltage to the positive and negative half-cycles of AC voltage. Due to its symmetrical positive and negative output characteristics, 2n positive DC input levels can be inverted by the H-bridge to obtain 4n+1 AC levels, including zero level.

[0029] In applications, the output rectifier unit 15 is a conversion stage that converts the alternating current output from the inverter unit 14 into a direct current suitable for welding. This unit typically consists of two parts: a high-frequency transformer and an output rectifier. The high-frequency transformer uses the principle of electromagnetic induction to achieve voltage transformation and electrical isolation, while the output rectifier rectifies the alternating current from the transformer's secondary winding into direct current and, after filtering, outputs a stable welding current to supply the welding torch.

[0030] In the application, the control chip 16 is responsible for coordinating the collaborative work of various functional units. The control chip 16 typically employs a DSP or MCU with high-performance digital signal processing capabilities. Its main functions include: acquiring the grid voltage and current signals of the input rectifier filter unit 11, the voltage, current, and temperature signals of each module of the energy storage unit 12, and the voltage and current signals at the output terminal; executing control algorithms such as harmonic separation algorithm, modulation mode switching algorithm, and energy storage equalization algorithm based on the acquired signals; and outputting PWM drive signals to control the switching actions of the DC level multiplier module 13 and the inverter unit 14.

[0031] Specifically, the complete working process of the system is as follows: The AC power from the grid is first converted to DC power by the input rectifier and filter unit 11. This DC power is then connected in parallel with the output of the energy storage unit 12 and fed into the DC level multiplier module 13. The energy storage unit 12 consists of n energy storage modules connected in series, providing n+1 different DC levels. The capacitor bootstrap unit in the DC level multiplier module 13 uses a switch to reassemble the series and parallel capacitors, multiplying the n+1 input levels into 2n levels. The inverter unit 14 receives the multiplied multi-level DC power and, under the PWM drive of the control chip 16, inverts it into an AC output of 4n+1 levels. The output rectifier unit 15 steps down and rectifies the high-frequency AC power, ultimately outputting a stable DC welding current to supply the welding torch. Throughout the process, the control chip 16 monitors the status of each component in real time and performs coordinated control, achieving functions such as multi-level output, harmonic compensation, and energy storage balancing.

[0032] The input rectifier and filter unit 11 can employ a passive rectification and filter scheme using an uncontrolled rectifier bridge and a large-capacity electrolytic capacitor, or it can use an active power factor correction circuit to achieve unity power factor rectification. The energy storage unit 12 can use a supercapacitor module as the energy storage element to obtain high power density and long cycle life, or it can use a lithium battery module to obtain high energy density.

[0033] This embodiment, through the combination of a DC level multiplier module and an H-bridge inverter structure, significantly increases the number of output levels without increasing system complexity, making the output waveform closer to an ideal sine wave and fundamentally reducing the harmonic content of the output voltage and current. The high-quality output waveform directly improves the stability of the welding arc, reduces arc drift and arc interruption, thereby improving weld formation quality and welding efficiency.

[0034] In one embodiment, such as Figure 2 As shown, the capacitor bootstrap unit includes an energy storage capacitor Cs, a bootstrap capacitor Cb, and multiple controllable switches; the energy storage capacitor Cs is used to store electrical energy from the energy storage module; the bootstrap capacitor Cb is used to achieve voltage superposition by switching between series and parallel connections with the energy storage capacitor Cs; the controllable switches are used to switch the connection state of the energy storage capacitor Cs and the bootstrap capacitor Cb under the drive of the PWM signal of the control chip 16, so that a single capacitor bootstrap unit outputs multiple levels including zero level, single level, and double level.

[0035] In applications, the energy storage capacitor Cs is the main energy storage element of the capacitor bootstrap unit. Its primary function is to receive and store electrical energy from the upstream energy storage module, while also serving as an energy source for external output. Energy storage refers to the process by which a capacitor accumulates charge in the electric field between its two plates; the voltage across the capacitor is proportional to the amount of charge stored. The energy storage capacitor Cs needs to have a low equivalent series resistance to reduce energy loss, while also requiring sufficient voltage rating and capacitance to meet power transmission requirements.

[0036] In applications, the bootstrap capacitor Cb is a key component for achieving voltage multiplication. Its core function is to achieve voltage superposition by switching between series and parallel connections with the energy storage capacitor Cs. Bootstrapping utilizes the characteristic that the voltage across a capacitor cannot change abruptly. The bootstrap capacitor is first charged to a certain voltage, and then connected in series with another voltage source, thus obtaining the sum of the two voltages at the output. During the parallel charging phase, the bootstrap capacitor Cb is charged to the same voltage V as the energy storage capacitor Cs. During the series discharging phase, it is connected in series with the energy storage capacitor Cs, at which point the output voltage is 2V, achieving voltage multiplication.

[0037] In this application, the controllable switch is the actuator that switches the capacitor connection state. Driven by the PWM signal of the control chip 16, it is switched on and off according to a set timing sequence. In this scheme, each capacitor bootstrap unit contains four controllable switches S1, S2, S3, and S4, which control the charging and discharging paths of the energy storage capacitor Cs and the bootstrap capacitor Cb, respectively. By coordinating the on and off states of the four switches, the capacitor bootstrap unit can output three different voltage levels: zero level, single level V, and double level 2V.

[0038] Specifically, the capacitor bootstrap unit outputs different voltage levels by coordinating the on / off states of four switches. When a zero-level output is required, switches S1 and S2 are both off, isolating the output from the energy storage module, and the output voltage is 0V. When a single-level V is required, switches S1 and S2 are on while S3 and S4 are off. In this case, only the energy storage capacitor Cs is connected to the output circuit, and the output voltage is equal to the energy storage capacitor voltage V. When a double-level 2V is required, switches S1 is on, S2 is off, S3 is off, and S4 is on. In this case, the bootstrap capacitor Cb, which has been pre-charged to voltage V, forms a series connection with the energy storage capacitor Cs, and the output voltage is the sum of their voltages, 2V. Through this switching timing control, a single capacitor bootstrap unit can output three voltage levels, and multiple units cascaded together can produce a richer combination of voltage levels.

[0039] Among them, the energy storage capacitor Cs can be made of aluminum electrolytic capacitors to obtain a larger capacitance and lower cost, or film capacitors can be used to obtain a lower equivalent series resistance and a longer service life. The controllable switch can be made of MOSFET to adapt to medium and low voltage high current applications and obtain a faster switching speed, or IGBT to adapt to high voltage high power applications.

[0040] This embodiment achieves a multiplication of voltage levels through a capacitor bootstrap structure. Compared to directly increasing the number of energy storage modules, it offers advantages such as simpler structure, lower cost, and higher reliability. The bootstrap capacitor automatically maintains its voltage equal to that of the energy storage capacitor during normal system operation, eliminating the need for additional voltage equalization circuits and reducing system complexity.

[0041] In one embodiment, the harmonic detection circuit 17 includes a current sensor and a signal conditioning circuit, used to detect the grid current and send the detection signal to the control chip 16; the control chip 16 is used to separate the harmonic current component according to the detection signal, generate a compensation current command with the same amplitude and opposite phase as the harmonic current component, and convert the compensation current command into a PWM drive signal of the inverter unit 14 so that the inverter unit 14 outputs the compensation current.

[0042] In this application, the harmonic detection circuit 17 is located on the AC input side of the input rectifier filter unit 11, specifically between the grid connection point and the rectifier bridge. This location allows for the detection of all current drawn from the grid by the system, including the fundamental current and all harmonic currents. Harmonics refer to sinusoidal wave components whose frequencies are integer multiples of the fundamental frequency. Nonlinear loads such as welding power supplies generate a large number of odd harmonics during operation, and these harmonics fed back to the grid cause a deterioration in power quality.

[0043] In the application, the current sensor and the signal conditioning circuit together constitute the hardware part of the harmonic detection circuit 17. The function of the current sensor is to convert the grid current signal into a voltage signal suitable for processing by the control chip, typically using the Hall effect principle to achieve non-contact measurement and electrical isolation. The function of the signal conditioning circuit is to filter, amplify, and adjust the sensor output signal to the standard range of the control chip's ADC input.

[0044] In the application, after receiving the harmonic detection signal, the control chip 16 executes a harmonic separation algorithm to separate the harmonic components from the grid current. It then generates a compensation current command with the same amplitude but opposite phase to the harmonic current. The opposite phase means that the compensation current and the harmonic current differ by half a cycle in time, and their superposition cancels each other out. The control chip 16 converts the compensation current command into a PWM drive signal adjustment for the inverter unit 14, enabling the inverter unit 14 to generate the compensation current simultaneously with the output welding current, thus achieving active suppression of grid harmonics.

[0045] Specifically, the harmonic compensation process is as follows: The control chip 16 first generates a compensation current command with equal amplitude but opposite phase to the separated harmonic current components. Then, the compensation current command is superimposed on the modulation signal of the welding output to form a composite modulation signal. This composite modulation signal controls the operation of the inverter unit 14, causing it to generate the compensation current simultaneously with the output welding current. Because the compensation current and the grid harmonic current are out of phase, they cancel each other out after being superimposed at the grid connection point, thereby reducing the harmonic current injected into the grid and improving the power quality of the grid.

[0046] Among these methods, Hall effect closed-loop current sensors can be used to achieve high measurement accuracy and good linearity, while Rogowski coils can be used to achieve non-contact measurement of large currents. Harmonic separation algorithms can employ the dq transform method based on synchronous rotating coordinate transformation, or frequency domain analysis methods based on fast Fourier transform.

[0047] This embodiment achieves active suppression of power grid harmonic pollution through harmonic detection and compensation. Compared with traditional passive filtering schemes, the active compensation scheme has a faster response speed and better compensation effect. This scheme reuses inverter unit 14 as the source of compensation current, eliminating the need for additional power conversion circuits, simplifying the system structure and reducing costs.

[0048] In one embodiment, the control chip 16 is configured with an SVPWM modulation module and a SHEPWM modulation module, and switches between the two modulation modes according to the welding conditions; when the load current change rate or power change rate is detected to exceed a preset threshold, the control chip 16 switches to the SVPWM modulation module to provide a fast dynamic response; when the load state stability duration is detected to exceed a preset duration, the control chip 16 switches to the SHEPWM modulation module to eliminate low-order harmonics of a specific number.

[0049] In applications, SVPWM, or Space Vector Pulse Width Modulation, is a high-performance PWM modulation technique. Its core idea is to synthesize the desired reference voltage vector by selecting an appropriate combination of voltage vectors within each switching cycle. SVPWM offers advantages such as high DC voltage utilization and fast dynamic response, making it particularly suitable for transient conditions with rapidly changing loads, such as the arc initiation and termination stages of welding. When the control chip 16 detects that the load current change rate or power change rate exceeds a preset threshold, it indicates that the load is in a rapidly changing state. Switching to SVPWM mode at this time ensures that the output quickly tracks load changes and maintains arc stability.

[0050] In applications, SHEPWM (Specific Harmonic Elimination Pulse Width Modulation) is a modulation technique that eliminates specific harmonics based on pre-calculated switching angles. Its basic principle is to represent the output waveform as a Fourier series, set the amplitude of the specific harmonic to zero, establish a system of nonlinear equations, and solve for the switching angle that satisfies the condition. SHEPWM has the advantages of good harmonic elimination and low switching frequency, making it suitable for use under steady-state conditions with stable load operation. When the control chip 16 detects that the stable load state lasts for a longer than a preset duration, switching to SHEPWM mode can reduce switching losses while maintaining output quality.

[0051] Specifically, the complete process of modulation mode switching is as follows: In each control cycle, the control chip 16 acquires the load current and voltage signals, calculates the current value, power value, and their rate of change. The calculated rate of change is compared with a preset threshold to determine whether to switch the modulation mode. If the current mode is SHEPWM and the rate of change exceeds the threshold, it switches to SVPWM mode; if the current mode is SVPWM and the rate of change remains below the threshold for a preset duration, it switches to SHEPWM mode. The switching action is performed near the zero-crossing point of the output voltage to avoid current spikes. After the switching is completed, a lockout time is set to prevent frequent switching.

[0052] The SVPWM modulation module can be implemented using a traditional algorithm combining sector determination and time calculation, or a fast algorithm based on lookup tables can be used to reduce the computational burden. The switching angle of the SHEPWM modulation module can be calculated offline using the Newton-Raphson method and stored in a lookup table, or an optimized algorithm can be used to solve it online to adapt to varying operating conditions.

[0053] This embodiment dynamically switches between two complementary modulation strategies, SVPWM and SHEPWM, to accommodate the differentiated needs of various working conditions during welding. SVPWM is used during transient processes such as arc initiation and arc termination to ensure rapid response and maintain arc stability; while SHEPWM is used during the stable welding stage to eliminate specific low-order harmonics and obtain optimal output waveform quality.

[0054] According to the above-mentioned multi-level energy storage power system, the control chip 16 is also used to perform energy storage unit equalization control; the control chip 16 collects the terminal voltage, output current and temperature signals of each energy storage module in real time. When the state parameters of any energy storage module exceed the preset range, the PWM duty cycle of the corresponding switch of the energy storage module is reduced to limit its output power, while the output duty cycle of other energy storage modules in normal state is increased to compensate for the total output power.

[0055] In applications, balanced control of energy storage units is a key technology to ensure the safe and reliable operation of multi-module energy storage systems. Due to differences in manufacturing processes and usage environments, the energy storage modules connected in series inevitably differ in capacity, internal resistance, and aging degree. These differences lead to inconsistencies in voltage, current, and temperature among the modules during charging and discharging. The control chip 16 monitors the operating status of each energy storage module by acquiring its terminal voltage, output current, and temperature signals in real time. These three parameters reflect the state of charge, output load, and thermal safety status of the energy storage module, respectively.

[0056] In applications, when the state parameters of any energy storage module exceed the preset range, the control chip 16 redistributes power by adjusting the PWM duty cycle. The PWM duty cycle is the ratio of the on-time to the total time of a switching cycle; a larger duty cycle results in a higher output power for the module. For modules with out-of-limit state parameters, reducing their duty cycle limits their output power, preventing further degradation due to overuse. Simultaneously, increasing the duty cycle of other normal modules compensates for the power shortfall, ensuring the total output power meets the welding load requirements.

[0057] Specifically, the energy storage unit equalization control process is as follows: The control chip 16 periodically collects voltage, current, and temperature data from all energy storage modules. It checks whether each parameter is within the normal range and marks the module status. For normal modules, the duty cycle is set as the baseline value; for abnormal modules, a derating factor is calculated proportionally based on the degree of exceedance, and their duty cycle is reduced. The power deficit caused by derating is calculated and proportionally allocated to normal modules, increasing their duty cycle to compensate. The adjusted duty cycle is output to the corresponding switch drive circuit of each module.

[0058] The terminal voltage detection circuit can employ a resistor divider network with operational amplifier buffer to achieve high measurement accuracy, or it can use an isolation amplifier to achieve electrical isolation between the high and low voltage sides. The temperature detection circuit can use an NTC thermistor with voltage divider measurement to achieve lower cost, or it can use a digital temperature sensor to simplify the signal conditioning circuit.

[0059] This embodiment achieves balanced management of a multi-module energy storage system through PWM duty cycle adjustment. This strategy does not simply cut off modules with limited capacity from the system, but rather adjusts the duty cycle to allow them to continue operating at lower power, thus protecting the limited modules while maximizing the utilization of the overall system capacity. The dynamic power redistribution mechanism ensures the stability of the welding output power, avoiding power fluctuations caused by the partial withdrawal of some modules.

[0060] In one embodiment, the input rectifier and filter unit 11 and the energy storage unit 12 are connected in parallel to supply power to the inverter unit 14. The control chip 16 dynamically adjusts the power distribution ratio between the grid power supply and the energy storage unit 12 according to the welding condition stage. During the arc ignition stage, the energy storage unit 12 undertakes the main power supply task. During the stable welding stage, the grid power supply undertakes the main power supply task, and the energy storage unit 12 is used to smooth power fluctuations. During the arc termination stage, the grid power supply provides feedback charging to the energy storage unit 12.

[0061] In applications, the arc initiation stage is the initial stage of the welding process, requiring instantaneous high power to establish an arc between the welding torch electrode and the workpiece. At this time, the workpiece surface has not yet been preheated, resulting in high contact resistance. Therefore, a high open-circuit voltage and a large short-circuit current are needed to break down the gap and establish a stable arc. After detecting the arc initiation signal, the control chip 16 adjusts the power allocation so that the energy storage unit 12 undertakes the main power supply task. This fully utilizes the high power density characteristics of the energy storage unit 12 to quickly respond to the high power demand during the arc initiation stage, avoiding the impact of grid power supply lag on arc initiation stability.

[0062] In application, the stable welding stage is the main operating stage where the arc has been established and maintains stable combustion. At this time, the welding current and voltage are relatively stable, and the power demand fluctuates little. After the control chip 16 detects that the load has entered a steady state, it adjusts the power distribution so that the grid undertakes the main power supply task. The energy storage unit 12 is mainly used to smooth power fluctuations and compensate for harmonics. The grid power supply provides a stable basic power output, and the energy storage unit 12 absorbs the instantaneous power fluctuations of the load with its fast response capability. The two work together to ensure the stability of the welding current.

[0063] In application, the arc-extinguishing phase is the final stage of the welding process, during which the welding current gradually decreases until the arc is extinguished. During this phase, power demand gradually decreases, and excess energy can be fed back and stored. Upon detecting the arc-extinguishing signal, the control chip 16 activates the feedback charging function of the energy storage unit 12, storing excess electrical energy from the grid in the energy storage unit 12 to prepare for the next arc ignition. This energy feedback mechanism improves the overall energy utilization efficiency of the system.

[0064] Specifically, the power distribution ratio is controlled by adjusting the limiting values ​​of the two current commands. The control chip 16 sets the upper limit of the grid current and the upper limit of the energy storage current according to the current welding conditions. The sum of the two should be greater than or equal to the current value corresponding to the total power demand to ensure the power supply to the load. During the arc initiation stage, the upper limit of the energy storage current is set larger and the upper limit of the grid current is set smaller; during the steady-state stage, the ratio of the two is reversed; during the arc termination stage, the upper limit of the grid current is greater than the load demand, and the excess current is used to charge the energy storage unit.

[0065] The power allocation strategy can employ a rule-based static allocation scheme for simplified implementation, or a dynamic allocation scheme based on optimization algorithms to achieve the optimal energy efficiency ratio. The operating condition identification algorithm can use a simple threshold-based method, or an intelligent method based on pattern recognition to improve identification accuracy.

[0066] This embodiment achieves optimal power supply configuration for various welding conditions through a coordinated power supply strategy involving the power grid and energy storage units, along with dynamic power allocation. During the arc-starting phase, the high-power characteristics of the energy storage unit ensure rapid response; during the stabilization phase, the continuous power supply capability of the power grid reduces energy storage losses; and during the arc-ending phase, excess energy is used to recharge the energy storage unit, improving energy efficiency. This strategy fully leverages the advantages of both power sources while avoiding the limitations of a single power source.

[0067] like Figure 3 As shown in the embodiments of this application, a control method for a multi-level energy storage power supply for argon arc welding is also provided, including the following steps: S1. Acquire the grid current signal and separate the harmonic current component from the grid current signal; S2. Obtain the status parameters of each energy storage module, and calculate the PWM duty cycle of each energy storage module based on the status parameters; S3. Determine the current modulation mode based on the welding conditions and switch between SVPWM modulation mode and SHEPWM modulation mode; S4. Generate PWM drive signals for the DC level multiplier module and inverter unit based on the welding output command, harmonic compensation command and duty cycle of each energy storage module; S5. The DC level multiplier module multiplies n+1 DC levels into 2n DC levels, and the inverter unit inverts the 2n DC levels into an AC output waveform of 4n+1 levels.

[0068] In the application, step S1 acquires the grid current signal and separates the harmonic current components to provide raw data for subsequent harmonic compensation control. The grid current signal is obtained by a current sensor installed at the input terminal. The signal output by the sensor is processed by a signal conditioning circuit and then sent to the control chip for analog-to-digital conversion. The control chip uses a harmonic separation algorithm to extract the harmonic components from the sampled grid current. Commonly used methods include time-domain methods based on coordinate transformation and frequency-domain methods based on Fourier transform.

[0069] In the application, step S2, acquiring the status parameters of each energy storage module and calculating the PWM duty cycle, is the core step in achieving balanced energy storage management. The control chip synchronously acquires the terminal voltage, output current, and temperature signals of each energy storage module through multiple sampling channels. Based on the acquired parameters, it determines whether each module is in normal working condition. For normal modules, a baseline duty cycle is set; for abnormal modules, the duty cycle is reduced according to the degree of exceeding limits, and the power deficit is allocated to normal modules for compensation.

[0070] In application, step S3, determining the current modulation mode based on the welding conditions, is a crucial step in dynamically optimizing the output waveform. The control chip detects the load current and power in each control cycle and calculates their rate of change, comparing the rate of change with a preset threshold to determine the load state. When the rate of change exceeds the threshold, indicating a transient load, it switches to SVPWM mode; when the rate of change remains below the threshold, indicating a steady-state load, it switches to SHEPWM mode.

[0071] In application, step S4, generating the PWM drive signal, is the execution step that transforms the control algorithm output into the action of the power devices. The control chip determines the fundamental modulation signal based on the welding output command, superimposes the harmonic compensation command to form a composite modulation signal, and then combines it with the duty cycle coefficient of each energy storage module to generate the PWM drive signals for each switch of the DC level multiplier module and each switch of the inverter unit.

[0072] In the application, step S5, level multiplication and inverter output, is the final stage of power conversion. The DC level multiplication module receives n+1 DC levels from the energy storage unit and, under PWM signal control, multiplies them to 2n DC levels through capacitor bootstrapping. The inverter unit adopts an H-bridge topology and, under PWM signal control, maps the 2n DC levels to the positive and negative half-cycles of the AC voltage, generating an AC output waveform with 4n+1 levels, including zero level.

[0073] Specifically, the complete execution flow of the control method is as follows: The control chip executes the control algorithm in a fixed-cycle loop. At the beginning of each cycle, signals such as grid current, state parameters of each energy storage module, and output voltage and current are collected. The harmonic separation algorithm is executed to extract harmonic components from the grid current and generate compensation current commands. The equalization algorithm is executed to calculate the duty cycle of each energy storage module. The load state is determined and the modulation mode is selected. The welding command, compensation command, and duty cycle parameters are input into the PWM generation module to calculate the action time of each switch. The PWM signal is output to the drive circuit to control the power devices, completing one control cycle.

[0074] In this process, grid current acquisition can employ a single-sampling method to simplify control, or an oversampling filtering method to improve the signal-to-noise ratio. Harmonic separation algorithms can utilize dq transform-based methods or FFT-based frequency domain analysis methods. PWM signal generation can be achieved through software calculations for flexibility, or a hardware PWM module can be used to reduce the processor load.

[0075] The control method provided in this embodiment achieves comprehensive optimized control of a multi-level energy storage power system through the coordinated operation of harmonic detection and compensation, energy storage balance management, modulation mode switching, and multi-level PWM generation. This method ensures high-quality waveform output during welding while effectively suppressing grid harmonics and ensuring safe and balanced use of energy storage units.

[0076] In one embodiment, the step of separating the harmonic current component from the grid current signal includes: S11. Obtain the phase angle of the grid voltage through a phase-locked loop; S12. The sampled grid current is transformed into a rotating coordinate system synchronized with the grid voltage through coordinate transformation to obtain the d-axis current component and the q-axis current component. S13. Perform low-pass filtering on the d-axis current component and the q-axis current component to extract the fundamental DC component. S14. Subtract the fundamental DC component from the original dq current component to obtain the harmonic current component, and transform it back to the stationary coordinate system through inverse coordinate transformation as the reference value of the compensation current.

[0077] In application, obtaining the phase angle of the grid voltage through a phase-locked loop (PLL) in step S11 is a prerequisite for harmonic separation. A PLL is a phase-tracking control system used to extract phase angle information synchronized with the grid voltage signal. The basic structure of a PLL includes three components: a phase detector, a loop filter, and a voltage-controlled oscillator (VCO). The input is the sampled grid voltage value, and the output is the phase angle synchronized with the grid voltage fundamental wave. This phase angle serves as the rotation angle for subsequent coordinate transformations, ensuring that the transformed coordinate system remains synchronized with the grid voltage fundamental wave.

[0078] In application, step S12, coordinate transformation, is a mathematical transformation process that converts the current components in the three-phase stationary coordinate system to a rotating coordinate system synchronized with the grid voltage. For a three-phase system, the abc three-phase currents are first converted into components in the αβ two-phase stationary coordinate system using the Clarke transformation, and then the αβ components are transformed into the dq rotating coordinate system using the Park transformation. The significance of this transformation is that in the dq coordinate system, which rotates synchronously with the grid, the fundamental current component is represented as a DC quantity, while the harmonic components are represented as AC quantities, which provides convenient conditions for subsequent filtering and separation.

[0079] In application, step S13, low-pass filtering, is a crucial step in extracting the fundamental component from the current in the dq coordinate system. In the dq rotating coordinate system synchronized with the grid voltage, the fundamental component of the grid current is a DC quantity, while the harmonic components are AC quantities of different frequencies. Therefore, low-pass filtering of the d-axis and q-axis currents separately can extract the fundamental DC component. The cutoff frequency setting of the filter needs to balance the filtering effect and the dynamic response speed.

[0080] In application, step S14, calculating and inverse transforming the harmonic current components, is the final step in generating the compensation current reference value. Subtracting the low-pass filtered fundamental DC component from the original dq current component yields the dq harmonic current component containing only harmonic elements. Then, the harmonic current component is transformed back to the stationary coordinate system using inverse Park and inverse Clarke transforms, serving as the reference value for the compensation current. The polarity of the compensation current reference value is set to the negative value of the harmonic current, ensuring that the compensation current and harmonic current are out of phase and thus cancel each other out.

[0081] The phase-locked loop (PLL) can be implemented using a simple method based on zero-crossing detection, or a synchronous reference coordinate system PLL based on the Park transform can be used to obtain better dynamic performance. The low-pass filter can be implemented using a first-order RC filter for simplification, or a Butterworth or Chebyshev second-order filter can be used to obtain better frequency selectivity.

[0082] The harmonic separation method based on dq transform provided in this embodiment has the advantages of clear principle, simple implementation, and moderate computational load. Compared with the frequency domain analysis method based on FFT, the dq transform method does not require the accumulation of data for multiple cycles, has a faster response speed, and is more suitable for real-time control applications. This method has been widely verified in fields such as active power filters and has a mature and reliable engineering practice foundation.

[0083] In one embodiment, the step of determining the current modulation mode based on the welding conditions includes: S31. Detect the load current and load power in each control cycle and calculate their rate of change; S32. When the load current change rate or load power change rate exceeds the first preset threshold, or when an arc initiation characteristic signal or an arc termination characteristic signal is detected, switch to SVPWM modulation mode. S33. When the load current change rate is lower than the second preset threshold for more than a preset time, switch to SHEPWM modulation mode. S34. After switching modulation modes, set a lock time and keep the current modulation mode unchanged during the lock time.

[0084] In applications, step S31, which involves detecting the load current and power and calculating the rate of change in each control cycle, is fundamental to determining the operating condition. The control chip acquires the output current and voltage signals and calculates the instantaneous power. The current rate of change is calculated by dividing the difference between the current value and the value of the previous cycle by the cycle time; the power rate of change is calculated similarly. To suppress the influence of sampling noise, the rate of change calculation typically employs multi-point differential or sliding window averaging methods for smoothing.

[0085] In application, there are multiple conditions for switching to SVPWM modulation mode in step S32, and the switch is triggered when any one of them is met. The first condition is that the absolute value of the load current change rate exceeds a first preset threshold, indicating that the load is undergoing rapid changes. The second condition is that the absolute value of the load power change rate exceeds a preset threshold, which complements the current change rate condition. The third condition is the detection of an arc initiation characteristic signal, manifested as a sudden drop in voltage and a sudden increase in current. The fourth condition is the detection of an arc termination characteristic signal, manifested as a decrease in current according to a set pattern.

[0086] In application, the condition for switching to SHEPWM modulation mode in step S33 is that the load enters steady-state operation. Specifically, the criterion is that the absolute value of the load current change rate remains below a second preset threshold for a preset duration. When the control chip continuously detects a consistently low change rate, it determines that the load has entered steady-state and can switch to SHEPWM mode to optimize the output waveform quality. The second preset threshold should be lower than the first preset threshold to avoid misjudgment when the load fluctuates slightly.

[0087] In applications, setting a lockout time after the modulation mode switch in step S34 is an important measure to prevent system oscillation. The lockout time refers to a period of time after the switch is completed during which the current modulation mode remains unchanged regardless of changes in load conditions. The selection of the lockout time requires balancing two factors: too short a time may lead to frequent switching and system instability, while too long a time may result in slow system response when load conditions have changed. The lockout time is implemented using a software timer, which starts timing at the moment of switching and resumes normal mode judgment after the timing ends.

[0088] Specifically, the complete process of modulation mode judgment and switching is as follows: At the beginning of each control cycle, it is first checked whether it is within the lockout time. If so, the judgment logic is skipped and the PWM calculation of the current mode is executed directly. If it is not within the lockout time, the load current and voltage are collected, and the rate of change is calculated. The rate of change is compared with a threshold: if the current mode is SHEPWM and the rate of change exceeds the first threshold or an arc initiation / outgoing signal is detected, it is switched to SVPWM mode and the lockout timer is started; if the current mode is SVPWM and the rate of change remains below the second threshold for a preset duration, it is switched to SHEPWM mode and the lockout timer is started.

[0089] The rate of change can be calculated using a simple first-order difference method, or advanced filtering algorithms such as Kalman filtering can be used to improve estimation accuracy and noise resistance. Arc initiation and termination feature detection can employ a simple threshold-based judgment method, or a waveform matching-based detection method can be used to improve recognition accuracy.

[0090] The modulation mode switching strategy provided in this embodiment achieves the complementary advantages of SVPWM and SHEPWM modulation methods. By monitoring the load status in real time and intelligently switching modes, the system utilizes the fast response characteristics of SVPWM to maintain arc stability during transient processes, and utilizes the harmonic cancellation characteristics of SHEPWM to obtain optimal waveform quality during steady-state processes. The time-locking mechanism effectively avoids system oscillations caused by frequent switching.

[0091] In one embodiment, the step of calculating the PWM duty cycle of each energy storage module based on state parameters includes: S21. Determine whether the terminal voltage, output current and temperature of each energy storage module are within the preset normal range; S22. For energy storage modules whose status parameters are within the normal range, set their PWM duty cycle as the reference duty cycle. S23. For energy storage modules whose terminal voltage is lower than the lower threshold, output current exceeds the upper threshold, or temperature exceeds the safety threshold, reduce the PWM duty cycle of the energy storage module proportionally according to the degree of exceeding the limit. S24. Calculate the power deficit caused by the reduced duty cycle, and allocate the power deficit to the energy storage module in normal condition, and correspondingly increase its PWM duty cycle to compensate.

[0092] In application, step S21, determining whether the status parameters of each energy storage module are within the normal range, is the first step in equalization control. The preset normal ranges are determined based on the technical specifications of the energy storage components: the normal range for terminal voltage is between the lower and upper limits of the nominal voltage; the normal range for output current is from zero to a certain multiple of the rated current, allowing for a certain overload margin; the normal range for temperature is determined based on the allowable operating temperature range of the energy storage components. The control chip compares the parameters collected in each control cycle with the above ranges and marks the status of each module.

[0093] In application, step S22 sets the PWM duty cycle of the energy storage module whose status parameters are within the normal range as the reference duty cycle. The reference duty cycle is calculated based on the total power demand and the number of modules. The setting principle is that each normal module equally shares the load power to achieve uniform discharge and extend the service life of each module.

[0094] In application, step S23 requires reducing the PWM duty cycle of energy storage modules whose state parameters exceed the normal range to limit output power, based on the degree of exceedance. The derating factor is calculated using a piecewise method: when the parameters are within the normal range, the derating factor is 1, meaning no derating; when the parameters exceed the normal range, the derating factor is reduced linearly or non-linearly according to the degree of exceedance. The final duty cycle is equal to the base duty cycle multiplied by the minimum value of each derating factor, ensuring the duty cycle is constrained by the most severely exceeded parameter.

[0095] In application, step S24, calculating the power deficit and allocating it to normal modules, is a crucial step in ensuring stable total output power. The power deficit is equal to the sum of the power differences before and after derating in each restricted module. The power deficit is allocated according to the proportion of the remaining capacity of each normal module, and their duty cycles are increased accordingly. After adjustment, the duty cycle of each normal module should not exceed the upper limit. If it does, it needs to be limited and recalculated and allocated. If necessary, the total output power should be reduced to ensure system safety.

[0096] Specifically, the complete process for calculating the PWM duty cycle is as follows: Periodically collect voltage, current, and temperature data from all modules. Determine if each parameter is within the normal range and mark the module status. For normal modules, calculate the reference duty cycle. For abnormal modules, calculate the voltage derating factor, current derating factor, and temperature derating factor, take the minimum value as the comprehensive derating factor, and multiply it by the reference duty cycle to obtain the actual duty cycle of the module. Calculate the power deficit and allocate it proportionally to normal modules, adjusting their duty cycles for compensation. Output the final duty cycle to the switching drive circuit of each module.

[0097] The normal range threshold for the state parameters can be a fixed value for simplified implementation, or an adaptive threshold based on historical data can be used. The derating factor can be calculated using a piecewise linear function for ease of understanding and debugging, or a smooth exponential function can be used to avoid abrupt changes in output power.

[0098] The PWM duty cycle calculation method provided in this embodiment enables refined management of multi-module energy storage systems. By dynamically adjusting the output power ratio of each module based on status parameters, it protects modules in poor condition from damage caused by overuse while fully utilizing the capabilities of normal modules to compensate for power deficits, ensuring the stability of the total output power. Through balanced control, the usage intensity of each energy storage module is more uniform, effectively extending the overall service life of the energy storage system.

[0099] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A multi-level energy storage power supply system for argon arc welding, characterized in that, include: Input rectifier and filter unit, energy storage unit, DC level multiplier module, inverter unit, output rectifier unit, control chip, and harmonic detection circuit; The input rectifier and filter unit is connected to the mains power supply and is used to rectify and filter the AC power from the mains power supply and output DC power. The energy storage unit includes n energy storage modules connected in series, which are used to store electrical energy and provide n+1 DC levels; The DC level multiplier module is connected between the energy storage unit and the inverter unit, and includes multiple capacitor bootstrap units for multiplying the n+1 DC levels into 2n DC levels; The inverter unit adopts an H-bridge topology to convert the 2n DC levels into 4n+1 AC levels, and achieves welding output and harmonic compensation under the drive of the control chip. The output rectifier unit is used to rectify the AC power output from the inverter unit and supply it to the welding torch. The harmonic detection circuit is located on the AC input side of the input rectifier filter unit. The data output terminal of the harmonic detection circuit is connected to the data input terminal of the control chip. The control signal output terminal of the control chip is connected to the control signal input terminals of the input rectifier filter unit, the energy storage unit, the DC level multiplier module, and the inverter unit, respectively.

2. The multi-level energy storage power supply system for argon arc welding according to claim 1, characterized in that, The capacitor bootstrap unit includes an energy storage capacitor, a bootstrap capacitor, and multiple controllable switches. The energy storage capacitor is used to store electrical energy from the energy storage module; The bootstrap capacitor is used to achieve voltage superposition by switching between series and parallel connection with the energy storage capacitor; The controllable switch is used to switch the connection state of the energy storage capacitor and the bootstrap capacitor under the PWM signal drive of the control chip, so that the single capacitor bootstrap unit outputs multiple levels including zero level, single level and double level.

3. The multi-level energy storage power supply system for argon arc welding according to claim 1, characterized in that, The harmonic detection circuit includes a current sensor and a signal conditioning circuit, used to detect the grid current and send the detection signal to the control chip. The control chip is used to separate the harmonic current component according to the detection signal, generate a compensation current command with the same amplitude and opposite phase as the harmonic current component, and convert the compensation current command into a PWM drive signal for the inverter unit so that the inverter unit outputs the compensation current.

4. The multi-level energy storage power supply system for argon arc welding according to claim 1, characterized in that, The control chip is equipped with an SVPWM modulation module and a SHEPWM modulation module, and switches between the two modulation modes according to the welding conditions. When the load current change rate or power change rate is detected to exceed a preset threshold, the control chip switches to the SVPWM modulation module to provide a fast dynamic response; When the load condition is detected to be stable for a duration exceeding a preset time, the control chip switches to the SHEPWM modulation module to eliminate low-order harmonics of a specific number.

5. The multi-level energy storage power supply system for argon arc welding according to claim 1, characterized in that, The control chip is also used to perform energy storage unit equalization control, including: The terminal voltage, output current, and temperature signals of each energy storage module are collected in real time. When the state parameters of any energy storage module exceed the preset range, the PWM duty cycle of the corresponding switch of the energy storage module is reduced to limit its output power, while the output duty cycle of other energy storage modules in normal state is increased to compensate for the total output power.

6. The multi-level energy storage power supply system for argon arc welding according to claim 1, characterized in that, The input rectifier and filter unit is connected in parallel with the energy storage unit to supply power to the inverter unit. The control chip dynamically adjusts the power distribution ratio between the grid power supply and the energy storage unit according to the welding process stage. During the arc initiation phase, the energy storage unit undertakes the main power supply task; During the stable welding phase, the grid power supply undertakes the main power supply task, and the energy storage unit is used to smooth power fluctuations; during the arc termination phase, the grid power supply provides feedback charging to the energy storage unit.

7. A control method for a multi-level energy storage power supply system for argon arc welding as described in any one of claims 1 to 6, characterized in that, include: Acquire the grid current signal and separate the harmonic current component from the grid current signal; Obtain the status parameters of each energy storage module, and calculate the PWM duty cycle of each energy storage module based on the status parameters; The current modulation mode is determined based on the welding conditions, and the mode is switched between SVPWM modulation mode and SHEPWM modulation mode. Based on the welding output command, harmonic compensation command, and duty cycle of each energy storage module, PWM drive signals for the DC level multiplier module and inverter unit are generated. The DC level multiplier module multiplies n+1 DC levels into 2n DC levels, and the inverter unit inverts the 2n DC levels into an AC output waveform of 4n+1 levels.

8. The control method according to claim 7, characterized in that, The separation of harmonic current components from the power grid current signal includes: The phase angle of the grid voltage is obtained through a phase-locked loop; The sampled grid current is transformed into a rotating coordinate system synchronized with the grid voltage through coordinate transformation to obtain the d-axis current component and the q-axis current component; The d-axis current component and q-axis current component are low-pass filtered to extract the fundamental DC component; The harmonic current component is obtained by subtracting the fundamental DC component from the original dq current component, and then transformed back to the stationary coordinate system through inverse coordinate transformation as the reference value of the compensation current.

9. The control method according to claim 7, characterized in that, The step of determining the current modulation mode based on the welding conditions includes: In each control cycle, the load current and load power are detected and their rate of change is calculated. When the load current change rate or load power change rate exceeds the first preset threshold, or when an arc initiation characteristic signal or an arc termination characteristic signal is detected, the mode is switched to SVPWM modulation mode. When the load current change rate is below the second preset threshold for a continuous period of time, switch to SHEPWM modulation mode. After switching modulation modes, a lock time is set to keep the current modulation mode unchanged during the lock time.

10. The control method according to claim 7, characterized in that, The calculation of the PWM duty cycle of each energy storage module based on the state parameters includes: Determine whether the terminal voltage, output current, and temperature of each energy storage module are within the preset normal range; For energy storage modules whose status parameters are within the normal range, set their PWM duty cycle as the reference duty cycle; For energy storage modules whose terminal voltage is below the lower threshold, output current exceeds the upper threshold, or temperature exceeds the safety threshold, the PWM duty cycle of the energy storage module is reduced proportionally according to the degree of exceeding the limit. Calculate the power deficit caused by the reduced duty cycle, and allocate the power deficit to the energy storage modules in normal condition, thereby increasing their PWM duty cycle accordingly to compensate.

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