Low-power-consumption welding machine power supply chopper circuit and chopper peak suppression method

Abstract

The invention discloses a low-power-consumption welding machine power supply chopper circuit and a chopper peak suppression method, the low-power-consumption welding machine power supply chopper circuit comprises a chopper module and an absorption circuit connected with the chopper module in parallel, the chopper module comprises a plurality of MOSFET switching devices connected in parallel, and the withstand voltage value of each MOSFET switching device is not greater than 200V; the capacitance value range of an absorption capacitor in the absorption circuit is [0, 30 uF]. According to the invention, an MOSFET switching device with a withstand voltage value not greater than 200V is adopted as a switching device in the chopper module, so that the conduction loss and the cost can be greatly reduced; while the withstand voltage value of the MOSFET switching device is reduced, the cost of increasing the capacitance value of the absorption capacitor is avoided, so that the low-spatter welding effect of the welding machine can be ensured.

Description

Technical Field

[0001] This invention relates to the field of inverter welding machine technology, and in particular to a low-power welding machine power supply chopper circuit and a chopper spike suppression method. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] The chopper circuit is a crucial component of the power supply circuit in an inverter welding machine. It controls the DC current through switching devices to achieve rapid changes in the output current, fulfilling the low-spatter requirement in the welding process. A chopper circuit typically consists of a chopper module and an absorption circuit connected in parallel across the chopper module. The chopper module includes switching devices, and the absorption circuit includes an absorption resistor and an absorption capacitor (RC absorption circuit) connected in parallel across the chopper module. Alternatively, the absorption circuit may include an absorption resistor and a diode series branch connected in parallel across the chopper module, with an absorption capacitor connected in parallel across the absorption resistor (RCD absorption circuit). The absorption resistor enables current freewheeling in the output reactor, while the absorption capacitor suppresses large voltage spikes, preventing damage to the switching devices.

[0004] Meanwhile, in order to avoid excessively high voltage spikes affecting the normal operation of the devices, the chopper module of the inverter welding machine chopper circuit usually uses switching devices with higher withstand voltage levels. Therefore, most inverter welding machines currently use medium and high voltage (600-1200V) Si-based IGBT modules.

[0005] While using medium-to-high voltage (600-1200V) Si-based IGBT modules can ensure welding stability and electrical reliability during chopping, it suffers from drawbacks such as high conduction losses, high heat generation, and high cost, which are detrimental to improving overall system efficiency. Taking the Infineon FZ600R12KE4, a widely used IGBT module in the industry, as an example, the conduction loss of a single module is calculated as 1.9V on-state voltage multiplied by 500A on-state current, resulting in a conduction loss of approximately 950W.

[0006] While existing technologies have disclosed the use of MOSFETs as switching devices in chopper circuits, when the withstand voltage of MOSFETs exceeds 300V, MOSFET devices offer no advantage over IGBT modules in terms of device stability and cost.

[0007] To reduce the voltage rating of switching devices, it is usually necessary to increase the capacitance of the absorption capacitor to suppress chopper voltage spikes. However, excessively large parallel capacitors can slow down the current drop during chopping, resulting in poor low-splash soldering. Furthermore, when the chopper is turned on again, the capacitor will generate extremely high surge pulse current through the MOSFET. The capacitance value is positively correlated with the pulse current duration, which may also damage the switching transistor.

[0008] Therefore, few inverter welding machines in the industry with secondary side chopper circuits can meet the first-level energy efficiency standard and have low-splash chopper technology, which poses a certain challenge to the energy saving and consumption reduction of inverter welding machines. Summary of the Invention

[0009] To address the aforementioned issues, this invention proposes a low-power welding machine power supply chopper circuit and a chopper spike suppression method. It employs MOSFET switching devices with a withstand voltage rating below 200V, making it applicable to MOSFET applications with withstand voltage ratings of 100V or even lower. This solves the problems of high conduction losses, large heat sink size, and high switching transistor cost associated with medium and high voltage IGBT devices. Simultaneously, by reducing the parasitic inductance of the absorption circuit, voltage spike suppression is achieved, requiring only a small absorption capacitor, or even eliminating the need for a parallel absorption capacitor, thus ensuring the welding machine exhibits excellent low-splash performance.

[0010] In some implementations, the following technical solutions are adopted: A low-power welding machine power supply chopper circuit includes a chopper module and an absorption circuit connected in parallel with the chopper module. The chopper switch module includes multiple MOSFET switching devices connected in parallel, and the withstand voltage of each MOSFET switching device is no greater than 200V. The capacitance value of the absorption capacitor in the absorption circuit is in the range of [0, 30uF].

[0011] As a further embodiment, the capacitance value of the absorption capacitor in the absorption circuit is in the range of [0, 20uF]; or, the capacitance value of the absorption capacitor in the absorption circuit is in the range of [0, 10uF].

[0012] As a further option, the withstand voltage of each MOSFET switching device is no greater than 100V.

[0013] As a further solution, when the capacitance of the absorption capacitor is zero, the maximum voltage spike during chopping is... The following relationship exists between the parasitic inductance L of the absorption circuit and the inductance L: ; Where K represents the rate of increase of the current flowing through the absorption circuit during the turn-off process of the chopper module; R represents the resistance value of the absorption resistor; | Represents the maximum output current value, which is dimensionless; Based on the value of the maximum voltage spike, determine the maximum value that the parasitic inductance L of the absorption circuit in the chopper circuit must satisfy.

[0014] As a further option, the parasitic inductance of the absorption circuit is no greater than 10uH.

[0015] As a further option, the resistance value of the absorption resistor in the absorption circuit is not greater than the ratio of the withstand voltage rating of the MOSFET switching device to the peak value of the chopping current.

[0016] As a further option, the absorption resistor can be a painted wire-wound resistor with two wires wound in parallel or two wires wound in reverse parallel, a plate resistor, a low-resistance busbar, a power chip resistor, or a through-hole wire-wound resistor.

[0017] As a further solution, the inverter circuit of the welding machine power supply includes two inverter modules connected in series or in parallel. Each inverter module is connected to the primary side of the corresponding main transformer, and the secondary sides of the two main transformers are connected to the two ends of the coupling reactor. The coupling reactor is a magnetic core, and the secondary sides of the two main transformers are respectively connected to one end of the two wire bundles of the coupling reactor, and the other ends of the two wire bundles are connected together. The wire bundles connected to the secondary sides of the two main transformers are wound in opposite directions on the magnetic core, that is, the same-name ends are reversed.

[0018] As a further option, multiple parallel-connected MOSFET switching devices are arranged in a ring on an aluminum substrate or PCB.

[0019] In other embodiments, the following technical solutions are adopted: A chopper spike suppression method is used to lay out the above-mentioned low-power welding machine power chopper circuit, including: multiple parallel-connected MOSFET switching devices are arranged in a ring on an aluminum substrate or PCB board, and the drain of each MOSFET switching device is directly electrically connected to the heat sink of the secondary side of the main transformer through an opening on the aluminum substrate or PCB board, so that the connection between the drain of each MOSFET switching device and the heat sink is as short as possible. The source of each MOSFET switching device is connected to the first copper plate, which is connected to the absorption resistor via the output copper busbar.

[0020] Compared with the prior art, the beneficial effects of the present invention are: (1) The lower the voltage rating of the MOSFET, the lower its conduction loss. This invention uses a MOSFET switching device with a voltage rating of no more than 200V as the switching device in the chopper module, which can greatly reduce conduction loss and cost.

[0021] Taking a standard 100V / 120A MOSFET as an example, its on-resistance is approximately 3-4mΩ. Due to heat dissipation issues, at least 20 MOSFETs need to be connected in parallel to carry a 500A current in engineering applications. This can result in I... 2 The R formula calculates the conduction loss to be 45W, which is significantly lower than the 950W conduction loss of a single medium-high voltage (600-1200V) IGBT module.

[0022] This invention replaces the commonly used medium and high voltage IGBT switching transistors with low voltage-rated MOSFET switching transistors, reducing the on-state heat loss from several kilowatts to tens of watts, greatly improving the efficiency of the welding machine power supply and achieving first-class energy efficiency. Taking the Aotai gas shielded welding machine as an example, the efficiency of the IGBT is 84.7%, and after using low voltage MOSFETs as chopper modules, the efficiency of the entire welding machine power supply is increased to 91.8%.

[0023] Furthermore, this invention can significantly reduce product costs. Infineon IGBTs cost 580 yuan, and industrial welding machines with a rated output current of 500A typically use two connected in parallel, costing 1160 yuan. In contrast, 100V / 120A MOSFETs cost 2.36 yuan, and 20 connected in parallel cost 47.2 yuan.

[0024] The above data shows that the low-power welding machine power supply chopper circuit and voltage spike suppression method proposed in this invention can achieve the industry's goal of low power consumption and low cost.

[0025] (2) While reducing the withstand voltage of the MOSFET switching device, the present invention does not increase the capacitance of the absorption capacitor, thus ensuring the low spatter welding effect of the welding machine. At the same time, since the maximum voltage spike during chopping is dominated by the parasitic inductance of the absorption circuit, the present invention reduces the parasitic inductance of the absorption circuit as much as possible through reasonable electrical layout and setting ultra-low inductance absorption resistors, thereby reducing the maximum voltage spike during chopping. Therefore, there is no need for an excessively large absorption capacitor, which ensures both the low spatter welding effect and the reduction of the maximum voltage spike during chopping, thus ensuring the reliable operation of the low withstand voltage MOSFET switching device.

[0026] Other features and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the existing inverter welding machine power supply circuit topology. Figure 2 The equivalent circuit diagram of the secondary side of the main transformer when the chopper module is turned off; Figure 3This is a schematic diagram of the circuit structure of two inverters connected in parallel in an embodiment of the present invention; Figure 4 This is a schematic diagram of the traditional secondary side wiring method for a main transformer; Figure 5 This is a schematic diagram of the voltage between the drain (D) and source (S) terminals of the chopper module. Figure 6 Equivalent circuit diagram of the secondary side of the main transformer considering parasitic parameters when the chopper module is turned off; Figure 7 This is a schematic diagram showing the rate of current rise in the absorption circuit when the chopper module is turned off. Figure 8 This is a schematic diagram of the secondary side wiring method of the main transformer in an embodiment of the present invention; Figure 9 This is a schematic diagram of the chopper voltage waveform of a MOSFET with a 100V withstand voltage specification in an embodiment of the present invention; Figures 10(a)-(c) show the low-splash effect of absorption capacitors with different capacitance values. Detailed Implementation

[0028] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0029] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0030] Example 1 As mentioned in the background section, existing technologies generally use Si-based IGBT modules with medium to high voltage (600-1200V) withstand voltage ratings, which have problems with high energy consumption and cost. If low voltage withstand voltage rating MOSFETs are used, new challenges will arise: how to ensure that the MOSFETs do not overvoltage when chopping under current conditions of 500A and above, and still meet the low spatter requirements of the soldering process. When using MOSFETs with low voltage ratings, the common practice is to increase the value of the snubber capacitor to suppress chopper voltage spikes and thus prevent the MOSFET from overvoltage. However, increasing the value of the snubber capacitor will reduce the rate of decrease of the chopper current, thereby affecting the low-splash soldering effect.

[0031] Meanwhile, during the second turn-on of the chopper, the absorption capacitor will generate an extremely high surge pulse current through the MOSFET. The capacitance value is positively correlated with the pulse current duration, which may also cause damage to the switching transistor.

[0032] Based on this, in one or more embodiments, a low-power welding machine power supply chopper circuit is disclosed, including a chopper module and an absorption circuit connected in parallel with the chopper module. The chopper module includes multiple MOSFET switching devices connected in parallel, and the withstand voltage of each MOSFET switching device is no greater than 200V. Furthermore, the capacitance of the absorption capacitor in the absorption circuit is no greater than 30uF. In some cases, the absorption capacitor can be zero, that is, no absorption capacitor is provided.

[0033] Compared to IGBT switching devices with medium to high voltage withstand ratings, this embodiment uses low-voltage MOSFETs in the chopper module, with withstand voltage values ​​not exceeding 200V, and even 100V and below. This significantly improves power efficiency, reduces the required heatsink volume, and greatly lowers costs. While using low-voltage MOSFETs, it also ensures low chopper voltage spikes, guaranteeing that MOSFETs with withstand voltage ratings of 200V and below, or even 100V and below, do not experience overvoltage under chopper current conditions of 500A and above. Furthermore, because the absorption capacitor has a small capacitance, it does not affect the low-splash soldering effect.

[0034] Figure 1 The most common power supply circuit topology for welding machines with low spatter function in the industry is given. After the three-phase power input, it is rectified by the rectifier module to the primary inverter side, then stepped down by the main transformer T and rectified by the diode, and then connected to the chopper module. The chopper module is connected in parallel with the absorption circuit. The absorption circuit is an RC absorption circuit, which includes the absorption resistor and absorption capacitor connected in parallel with the chopper module respectively; the output circuit has a series reactor L1.

[0035] Applying the low-power welding machine power supply chopper circuit from this embodiment to this topology and modeling the secondary side of the main transformer T, we can obtain the mathematical model when the chopper module is turned off, as follows: Figure 2 As shown.

[0036] The commonly used low-splash principle in the industry is as follows: when the current is output normally, by turning off the chopper module, the freewheeling current of the reactor L1 in the output circuit flows through the absorption circuit, and the voltage generated on the absorption resistor R is applied back to the two ends of the reactor L1, causing the freewheeling current to drop rapidly. The industry standard for a wide range of low splash is that the current drops from 200A to 50A within 100us, that is, the current drop rate is about 1.5A / us, when the low splash effect can be achieved.

[0037] Combination Figure 2 The expressions for the voltage and current Ia at the terminals D and S of the absorption circuit are as follows: ; in, L1 is the drain-source voltage across the MOSFET, and L2 is the output reactance. For the maximum output current, C is the absorption capacitor and R is the absorption resistor.

[0038] Damping coefficient α = 1 / 2RC, resonant frequency w0 = Obviously, the system needs to operate in a critically damped or overdamped state.

[0039] The critical damped state voltage is: ; The overdamped state voltage is: ; in, , ; The above analysis shows that when the value of the absorption capacitor C increases, the rate of decrease in the chopper current will decrease. Furthermore, the resistor R needs to satisfy... .

[0040] Therefore, the absorption capacitor value should be as small as possible while ensuring that the voltage at the C and E terminals does not exceed the MOSFET's withstand voltage, in order to ensure a low current drop rate during soldering spatter.

[0041] The following is an analysis of the value of the absorption capacitor: (1) When the capacitance of the absorption capacitor is 0, the current drop rate during chopping is determined by the expression Ia*R / L1. o This represents the maximum output current (i.e., peak current). Ia represents the time-domain output current in amperes.

[0042] Since the Ia*R of low-voltage MOSFETs does not exceed 200V (based on MOSFETs with a withstand voltage of 200V and below) compared to IGBTs with medium and high voltage withstand ratings, the value of the absorption resistor should not be greater than the ratio of the withstand voltage to the peak current.

[0043] Taking the operating conditions and parameters commonly used in low-spatter welding machines in the industry as an example, at 500A chopping, the inductance L1 of the welding machine output reactance is approximately 20uH. Using a 100V withstand voltage MOSFET as the chopping module, the maximum Ia*R does not exceed 100V, and the chopping current drop rate is 5A / us. Therefore, by fully utilizing the withstand voltage of the low-voltage MOSFET, a low-spatter welding effect can still be achieved.

[0044] Furthermore, as can be seen from the formula for the current drop rate, the output reactance of the welding power supply also determines the chopper current drop rate in the low-splash process; therefore, this embodiment proposes a method to improve the chopper current drop rate: When the inverter circuit of the welding machine power supply includes two inverter modules connected in series or parallel, each inverter module is connected to the primary side of the corresponding main transformer. One end of the secondary side of each main transformer is connected to one end of a coupling reactor, which is a magnetic core. The reactor wires connected to the secondary sides of the two main transformers are wound in opposite directions on the magnetic core, i.e., the same-named ends are reversed. After the two wire bundles of the coupling reactor are connected to the secondary sides of the two main transformers, their other ends are connected together.

[0045] Specifically, in combination Figure 3 The primary side of the main transformer uses a scheme of two inverters connected in parallel. On the secondary side of the main transformer, the two main transformers are rectified by diodes and then connected in parallel. Their two center taps are connected to... Figure 3 The two ends of the coupling reactor L1 are reversed, and the common terminal of the coupling reactor L1 is connected to the negative terminal of the output.

[0046] When current flows through the coupling reactor L1, it passes through both windings. Due to their opposite winding directions, they generate magnetic fields with the same flux but opposite directions, which cancel each other out in the core. Therefore, the coupling reactor L1 is essentially an air-core inductor, with a significantly lower inductance compared to the wire-wound inductors used in welding machines. Simultaneously, the coupling reactor also has a self-current sharing effect. When current I flows through branches 1 and 2 of the coupling reactor L1, if branch current I1 > branch current I2, the differential-mode current between branch currents I1 and I2 will generate a larger magnetic field in branch 1. This further increases the inductive reactance of branch 1, limiting the current growth in that branch. Furthermore, the direction of the magnetic field generated by branch 1 is consistent with the direction of branch current I2, causing branch current I2 to increase, ultimately achieving a near-equal current in both windings. Therefore, this solution can achieve self-current sharing without external interference through hardware.

[0047] (2) Taking the most common electrical structure in the industry as an example, we choose R=0.18Ω and follow the... Figure 4 The traditional wiring method is shown. The voltage across the D and S terminals of the chopper module is approximately 181V. Figure 5 A schematic diagram of the voltage between the drain (D) and source (S) terminals of the chopper module is provided. Figure 5In the diagram, the yellow line represents the output current, and the blue line represents the voltage across the MOSFET. The 90V obtained by multiplying the 0.18 ohms resistance by the 500A current is at point 1. If there were no parasitic inductance, the voltage would only reach point 1. However, due to the presence of the parasitic inductance, the voltage is further increased from 90V to point 2 (approximately 181V). The voltage spike at point 2 is mainly due to the parasitic inductance of the absorption circuit.

[0048] Considering parasitic parameters, the secondary-side chopper circuit is modeled as follows: Figure 6 As shown, consider the parasitic inductance Ls of resistor R and the parasitic inductance Lp on the electrical connection line between the absorption circuit and the chopper module. Establish a mathematical model of the voltage V and current Ia at the DS terminal of the chopper module when the switching transistor is turned off; obtain the complex frequency domain expression for the voltage across the DS terminals of the MOSFET. : ; in, The complex frequency domain expression of current. It is the complex frequency domain expression of the total impedance of the absorption circuit after considering parasitic inductance; The maximum output current is expressed in amperes (A). C is the absorption capacitor, and R is the absorption resistor.

[0049] In practical applications, since the current Ia is applied to the aforementioned absorption circuit system the instant the chopper module turns off, and since the chopper module requires time to turn off, the current Ia cannot be completely equivalent to a step signal. Instead, it is a ramp function that rises with a very high slope K. The voltage Ia reaches its peak value at time t1 when the chopper module is completely turned off, and then gradually decays. Since the model aims to find the peak voltage of the current Ia flowing through the absorption circuit, only the interval from time 0 (when the chopper module is turned off) to time t1 needs to be considered. Therefore, the expression for the current Ia is: ; The frequency domain expression of the above equation is: ; The maximum voltage spike during chopping is dominated by parasitic inductances Lp and Ls. Considering Lp and Ls together, it is equivalent to L = Ls + Lp. When considering the rate of current rise K at the moment the chopper module turns off, the maximum voltage spike... The following relationship exists between the inductance (in volts (V)) and the parasitic inductance L (in H) of the absorption circuit: ; in, This indicates the rate of increase of the current flowing through the absorption circuit during the turn-off process of the chopper module, measured in amperes per second (A / s). This indicates the resistance value of the absorption resistor; the unit is ohms (Ω). This represents the maximum output current value, without units, and is mentioned in the formula. It should be a physical quantity with a unit ampere (A), and its value is the value of the maximum output current.

[0050] Based on the maximum voltage spike By determining the value of L, the maximum value that the parasitic inductance L of the absorption circuit in the chopper circuit must satisfy can be determined.

[0051] Taking Aotai's gas shielded welding machine as an example, when the chopper module is turned off, the current rise rate of the current Ia flowing through the absorption circuit is approximately 4481 A / ms. Figure 7 As shown, with maximum output current For a 500A chopper current operating condition, the total parasitic inductance L, considering the parasitic inductance on the connection line between the absorption circuit and the MOSFET, as well as the parasitic inductance of the resistor itself in the absorption circuit, should be less than 2uH (at a 100K test frequency). Within this upper limit of parasitic inductance, the voltage spike generated by the current Ia through the chopper absorption circuit after the chopper module is turned off will basically satisfy Ohm's law (without capacitor), i.e., V max ≈ *R.

[0052] In engineering applications, when chopping with the |Io| value, the voltage across the DS terminals of the chopper module should be controlled to not exceed 80% of the device's nominal withstand voltage. In this embodiment, to fully utilize the device's withstand voltage characteristics, the resistor R is calculated as the device's withstand voltage V1 / |Io| - 0.1 (Ω). For example, if the MOSFET's withstand voltage is 100V and the maximum chopping current is 500A, then the absorption resistor R = 100 / 500 - 0.1 = 0.19Ω. If the MOSFET's withstand voltage is 200V, then the absorption resistor R = 200 / 500 - 0.1 = 0.39Ω. With this resistor value selection, the MOSFET's withstand voltage level can be applied close to its limit, fully utilizing the device's withstand voltage capability. When the inductance in the absorption circuit is extremely small, the resistance can be approximately equal to the ratio of the nominal withstand voltage to the maximum output current.

[0053] Therefore, substituting K=4481A / ms into the formula, we calculate that the value of |Io|LK / 1000 is 4.481V, and the peak value of the chopping voltage is approximately equal to Io*R.

[0054] It should be noted that there is no absorption capacitor at this time. The absorption circuit includes an absorption resistor connected in parallel across the chopper module, or the absorption circuit includes an absorption resistor connected in parallel across the chopper module and a diode series branch. In order to prevent voltage spike overvoltage, the parasitic inductance value of the absorption circuit is not greater than 2uH.

[0055] (3) Further consider the effect of adding an absorption capacitor C on smoothing the voltage spikes generated by parasitic inductances Lp and Ls. Analyzing the expressions for the voltage and current Ia at the terminals D and S of the initially established absorption circuit, the voltage expression under overdamped conditions is: ; As t approaches infinity, v = Io*R, the slope K is very large, and the voltage spike is: ; That is, absorption capacitor The parasitic inductance Ls is approximately of the same order as the inductance Ls, and the parasitic inductance Lp on the absorption circuit and MOSFET connection line also needs to be considered. Therefore, the capacitance C must be at least higher than [the parasitic inductance Ls]. .

[0056] In summary, when the chopper module is not connected in parallel with the absorption capacitor C, the total parasitic inductance, considering the parasitic inductance on the connection line between the absorption circuit and the MOSFET, as well as the parasitic inductance of the resistor itself in the absorption circuit, is less than 2uH. Within this upper limit of parasitic inductance, the voltage spike generated by the current Ia through the chopper absorption circuit after the chopper module is turned off will basically satisfy Ohm's law, i.e., V max ≈ *R.

[0057] When an absorption capacitor C is connected in parallel across the chopper module, the values ​​of parasitic inductances Lp and Ls can be higher than the aforementioned values. The voltage spikes during chopping can still be reduced by increasing the capacitor value. However, the capacitor value should not exceed 30uF; otherwise, the rate of decrease in the chopping current will decrease, severely affecting the low-splash effect in actual welding.

[0058] The mathematical model and relationship between capacitance, resistance, and parasitic inductance conform to the derivation of the above formula. The resistance value of the absorption resistor R is related to the peak value of the chopper current I. o and MOSFET withstand voltage rating V o The selection value is related to the value of the absorption resistor. The resistance value should not be greater than the ratio of the withstand voltage level of the MOSFET switching device to the peak value of the chopping current. After fixing the value of the absorption capacitor, the selection range of resistor R and parasitic inductance of the absorption circuit can be obtained.

[0059] It should be noted that the absorption circuit at this time has an absorption capacitor connected in parallel. The absorption circuit is a conventional RC absorption circuit or RCD absorption circuit, including an absorption resistor and an absorption capacitor connected in parallel across the chopper module. Alternatively, the absorption circuit includes an absorption resistor and a diode series branch connected in parallel across the chopper module; the absorption resistor has an absorption capacitor connected in parallel across its two ends.

[0060] The following are some typical parameter combinations: Taking a capacitor C of 1uF as an example, when a MOSFET with a withstand voltage of 100V is actually used and the peak chopping current is 500A, the absorption resistor R can be less than 0.2Ω. The sum of the parasitic inductance of the absorption resistor R and the parasitic inductance on the electrical traces of the absorption circuit and the chopper module is less than or equal to 2uH.

[0061] Taking a capacitor C of 1uF as an example, when a MOSFET with a withstand voltage of 200V is actually used and the peak chopping current is 500A, the absorption resistor R can be less than 0.4Ω. The sum of the parasitic inductance of the absorption resistor R and the parasitic inductance on the electrical traces of the absorption circuit and the chopper module is less than 2uH.

[0062] When the value of the absorption capacitor C is higher than 1uF, the allowable value of parasitic inductance can be increased. However, a higher capacitance value will lead to a worse welding effect in actual welding, and it will no longer be the optimal solution of the entire electrical parameter model.

[0063] Therefore, to maintain a low or even zero absorption capacitor value, it is necessary to minimize the parasitic inductance in the absorption circuit. This parasitic inductance mainly consists of the parasitic inductance Ls of the absorption resistor and the parasitic inductance Lp on the electrical connection line between the absorption circuit and the chopper module.

[0064] This embodiment provides a specific implementation method for reducing parasitic inductance in the absorption circuit.

[0065] Combination Figure 8 Specifically, the cathode of the full-wave rectifier diode on the secondary side of the main transformer is connected to the secondary heat sink A; multiple parallel-connected MOSFET switching devices are arranged in a ring on an aluminum substrate or PCB board, and the drain of each MOSFET switching device is directly electrically connected to the heat sink on the secondary side of the main transformer through an opening on the aluminum substrate or PCB board to achieve the shortest electrical connection path, thereby minimizing the parasitic inductance Lp on the electrical connection line between the absorption circuit and the chopper module.

[0066] The source of each MOSFET switching device is connected to the first copper plate B1, and the potential of the first copper plate B1 is led out through the output copper busbar B2; the output copper busbar B2 is connected to the output copper busbar B3, one end of the absorption resistor is electrically connected to the output copper busbar B3, and the other end is electrically connected to the heat sink of the secondary side of the main transformer.

[0067] In this embodiment, the first copper plate B1, the output copper busbar B2, and the output copper busbar B3 are all arranged parallel to the heat sink on the secondary side of the main transformer, and the current flow direction on the output copper busbar B3 is opposite to the current flow direction on the heat sink.

[0068] When the MOSFET is turned on, the current flows from the heat sink to the aluminum substrate or PCB of the MOSFET, and then to the output copper busbars B2 and B3. When turned on, it is in normal operation and there will be no overvoltage problem or voltage spikes caused by parasitic inductance.

[0069] When the MOSFET is turned off Figure 8 The black arrows indicate the direction of the current. The current starts from the heat sink, passes through a resistor connected to the two terminals of the heat sink, then flows to the third terminal of the resistor, exits from the copper busbar, and finally flows through the output copper busbar B3. When the MOSFET is turned off and chopped, since the heat sink A and the output copper busbar B3 are parallel and the current directions are opposite, the magnetic fields generated by the currents in the heat sink A and the output copper busbar B3 are in opposite directions, which can further reduce the parasitic inductance of the absorption circuit.

[0070] Furthermore, this embodiment reduces the parasitic inductance Ls of the absorption resistor by applying an ultra-low inductance scheme.

[0071] Specifically, the absorption resistor can be set up as multiple resistors connected in parallel. The resistor can be equivalent to a model of a resistor and a parasitic inductance connected in series. After multiple resistors are connected in parallel, the parasitic inductance on them is also connected in parallel, and the inductance becomes smaller and smaller as they are connected in parallel.

[0072] For parallel connection, resistors can be selected from painted wire-wound resistors with two wires wound in parallel or with two wires wound in reverse parallel, plate resistors, low-resistance busbars, power chip resistors, or through-hole wire-wound resistors.

[0073] Among them, the wire-wound resistor uses a double-wire parallel winding or a double-wire anti-parallel winding method for the internal resistance wire, so that the magnetic field generated by the current on the resistance wire is opposite in direction, thereby canceling the magnetic field and achieving ultra-low inductance; the busbar metal of the non-inductive low-resistance busbar can be selected as an alloy resistor with slightly higher resistivity; the power chip resistor can be a chip resistor with a TO-263 package, since the parasitic inductance of the chip resistor itself is extremely small, and its chopping voltage spike basically conforms to Ohm's law.

[0074] As a further step towards achieving ultra-low parasitic inductance, multiple through-hole wire-wound resistors and a single absorption capacitor are connected in parallel as a component. By connecting multiple such components in parallel, the parasitic inductance is reduced.

[0075] The low-power welding machine power supply chopper circuit uses 100V withstand voltage MOSFETs. Figure 8 The MOSFET and resistor layout shown are for reducing parasitic inductance. The snubber resistor has a resistance of 0.18Ω and the snubber capacitor has a capacitance of 0. When chopping at 500A, the voltage generated by this snubber resistor during chopping is approximately 90V. Figure 9The chopper voltage waveform is given. It can be seen from the waveform that there are basically no voltage spikes caused by parasitic inductance, and the voltage waveform basically satisfies Ohm's law.

[0076] The device layout is carried out using the method of reducing parasitic inductance in the absorption circuit in this embodiment; Figures 10(a)-(c) show the low splash effect corresponding to different absorption capacitors when using a MOSFET with a 100V withstand voltage rating, a chopping current peak of 500A, and an absorption resistor value of 0.19Ω; among them, Figure 10(a) shows the low splash effect corresponding to an absorption capacitor of 0uF, Figure 10(b) shows the low splash effect corresponding to an absorption capacitor of 10uF, and Figure 10(c) shows the low splash effect corresponding to an absorption capacitor of 35uF.

[0077] It can be seen that when the absorption capacitance is 0uF, the arc burns stably, with uniform brightness and concentrated shape, without obvious jumping or flickering, and there is basically no spatter; when the absorption capacitance is 10uF, there is a very small amount of spatter, but it basically meets the requirements for low spatter; while when the absorption capacitance is 35uF, the amount of spatter is large, the arc is unstable, and it is difficult to meet the welding requirements for low spatter.

[0078] This embodiment of the low-power welding machine power supply chopper circuit uses a low-voltage MOSFET as the secondary-side chopper module to solve the application problems of high conduction losses, large heat sink size, and high cost caused by medium and high voltage IGBTs. At the same time, the capacitance of the absorption capacitor is not too high, which ensures that the MOSFET with a withstand voltage of 100V or even lower is not over-voltage when the chopper current is 500A or higher, and has a low spatter welding effect, achieving low loss and first-class energy efficiency.

[0079] Example 2 In one or more embodiments, a chopper spike suppression method is disclosed for layouting the low-power welding machine power supply chopper circuit described in Embodiment 1, comprising: Multiple MOSFET switching devices connected in parallel are arranged in a ring on an aluminum substrate or PCB. The drain of each MOSFET switching device is directly electrically connected to the heat sink of the secondary side of the main transformer through an opening on the aluminum substrate or PCB, so that the connection between the drain of each MOSFET switching device and the heat sink is as short as possible. The source of each MOSFET switching device is connected to the first copper plate, and the potential of the first copper plate is led out through the output copper busbar; the current flow direction of the heat sink is opposite to the current flow direction of the output copper busbar; one end of the absorption resistor is electrically connected to the output copper busbar, and the other end is electrically connected to the heat sink of the secondary side of the main transformer.

[0080] The specific implementation of the above method is the same as in Embodiment 1, and will not be described in detail again.

[0081] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A low-power welding machine power supply chopper circuit, comprising a chopper module and an absorption circuit connected in parallel with the chopper module, characterized in that, The chopper switch module includes multiple MOSFET switching devices connected in parallel, each MOSFET switching device having a withstand voltage of no more than 200V; the absorption capacitor in the absorption circuit has a capacitance range of [0, 30uF].

2. The low-power welding machine power supply chopper circuit as described in claim 1, characterized in that, The capacitance value of the absorption capacitor in the absorption circuit is in the range of [0, 20uF]; or, the capacitance value of the absorption capacitor in the absorption circuit is in the range of [0, 10uF].

3. The low-power welding machine power supply chopper circuit as described in claim 2, characterized in that, Each MOSFET switching device has a withstand voltage of no more than 100V.

4. The low-power welding machine power supply chopper circuit as described in claim 1, characterized in that, When the capacitance of the absorption capacitor is zero, the maximum voltage spike occurs during chopping. The following relationship exists between the parasitic inductance L of the absorption circuit and the inductance L: ； Where K represents the rate of increase of the current flowing through the absorption circuit during the turn-off process of the chopper module; R represents the resistance value of the absorption resistor; | Represents the maximum output current value, which is dimensionless; Based on the value of the maximum voltage spike, determine the maximum value that the parasitic inductance L of the absorption circuit in the chopper circuit must satisfy.

5. The low-power welding machine power supply chopper circuit as described in claim 1, characterized in that, The parasitic inductance of the absorption circuit is no greater than 10uH.

6. The low-power welding machine power supply chopper circuit as described in claim 1, characterized in that, In the absorption circuit, the resistance value of the absorption resistor should not exceed the ratio of the withstand voltage rating of the MOSFET switching device to the peak value of the chopping current.

7. The low-power welding machine power supply chopper circuit as described in claim 1, characterized in that, The absorption resistor can be a painted wire-wound resistor with two wires wound in parallel or two wires wound in reverse parallel, a plate resistor, a low-resistance busbar, a power chip resistor, or a through-hole wire-wound resistor.

8. A low-power welding machine power supply chopper circuit as described in any one of claims 1-7, characterized in that, The inverter circuit of the welding machine power supply includes two inverter modules connected in series or in parallel. Each inverter module is connected to the primary side of the corresponding main transformer. The secondary sides of the two main transformers are connected to the two ends of the coupling reactor. The coupling reactor is a magnetic core. The secondary sides of the two main transformers are connected to one end of the two wire bundles of the coupling reactor, and the other ends of the two wire bundles are connected together. The wire bundles connected to the secondary sides of the two main transformers are wound in opposite directions on the magnetic core, that is, the same-name ends are reversed.

9. The low-power welding machine power supply chopper circuit as described in any one of claims 1-7, characterized in that, Multiple MOSFET switching devices connected in parallel are arranged in a ring on an aluminum substrate or PCB.

10. A chopper spike suppression method, used to lay out the low-power welding machine power supply chopper circuit according to any one of claims 1-7, characterized in that, include: Multiple MOSFET switching devices connected in parallel are arranged in a ring on an aluminum substrate or PCB. The drain of each MOSFET switching device is directly electrically connected to the heat sink of the secondary side of the main transformer through an opening on the aluminum substrate or PCB, so that the connection between the drain of each MOSFET switching device and the heat sink is as short as possible. The source of each MOSFET switching device is connected to the first copper plate, which is connected to the absorption resistor via the output copper busbar.

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