Arc voltage sampling circuit and sampling method suitable for welding power source

Abstract

The invention provides an arc voltage sampling circuit and method suitable for a welding power source. The arc voltage sampling circuit comprises an anti-interference absorption unit, a sampling conditioning unit and an isolation conversion unit. The anti-interference absorption unit is electrically connected to the output end of the welding power source so as to collect arc voltage signals. The anti-interference absorption unit comprises two common-mode absorption capacitor banks connected between a positive bus and a negative bus in series, and the middle point of the two common-mode absorption capacitor banks is electrically connected to the ground. The sampling conditioning unit comprises a sampling network and a filter capacitor, the sampling network comprises a plurality of divider resistors connected in series between positive and negative buses, the filter capacitor is connected in parallel with the output of the sampling network, and at least one stage of RC filter is formed between the filter capacitor and the divider resistors in the sampling network. The isolation conversion unit comprises an optical coupling isolator and a conversion circuit. The optical coupling isolator isolates the arc voltage sampling signal and converts the arc voltage sampling signal into a switching value signal or an analog quantity signal with various output amplitudes based on the conversion circuit.

Description

Technical Field

[0001] The invention relates to the field of welding, and in particular to an arc voltage sampling circuit and a sampling method suitable for a welding power source. Background Art

[0002] The thrust function is usually required in the welding process of welding power supplies. The thrust function refers to the specific function of the welding power supply that can automatically increase the output current when the arc is short-circuited or the molten droplet is transferred to the workpiece. This function is mainly achieved by increasing the arc current during the molten droplet transfer and accelerating the arc short-circuit time, thereby improving the weld formation effect and reducing the possibility of electrode adhesion. The arc state recognition is the basis for the realization of this thrust function, and the arc state can be judged by collecting the arc voltage of the welding output circuit.

[0003] There are three main traditional arc voltage collection methods: the first is to directly collect the welding circuit voltage, and the collected signal is directly sent to the control chip for short circuit judgment. This collection method has a simple circuit and high signal accuracy, but because the signal ground is shared with the welding circuit, the signal is easily interfered with, which is not conducive to the stability of the system. The second method also directly collects the welding circuit voltage, but the collected signal is first linearly isolated before being sent to the control chip for short circuit judgment. The signal obtained by this collection method is not easily interfered with, and the collected signal is highly accurate and stable, but the linear isolation circuit is more complex and requires additional auxiliary power isolation, which not only has high design costs but also large circuit volume. The third method is based on the PWM square wave analog output voltage output by the pulse width control chip. This collection method has a simple circuit and strong anti-interference; but the collected signal cannot accurately feedback the actual arc voltage state and has poor accuracy, and the analog collected signal value has a large distortion with the fluctuation of the grid voltage.

[0004] Furthermore, the current arc voltage sampling can only simply identify and judge the two states of short circuit and droplet separation, but cannot identify and judge the droplet transition process, so there are problems such as rough control and low control accuracy. Summary of the invention

[0005] In order to overcome the deficiencies of the prior art, the present invention provides an arc voltage sampling circuit and a sampling method suitable for a welding power source, which have high signal acquisition accuracy and simple circuit structure.

[0006] In order to achieve the above-mentioned purpose, the present invention provides an arc voltage sampling circuit, which includes an anti-interference absorption unit, a sampling conditioning unit and an isolation conversion unit. The anti-interference absorption unit is electrically connected to the output end of the welding power supply to collect the arc voltage signal. The anti-interference absorption unit includes two common-mode absorption capacitor groups connected in series between the positive and negative busbars, and the midpoints of the two common-mode absorption capacitor groups are electrically connected to the ground. The sampling conditioning unit is arranged at the output end of the anti-interference absorption unit and includes a sampling network and a filter capacitor. The sampling network includes a plurality of voltage-dividing resistors connected in series between the positive and negative busbars, and the filter capacitor is connected in parallel to the output of the sampling network. At least one RC filter is formed between the filter capacitor and the voltage-dividing resistor in the sampling network. The isolation conversion unit includes an optocoupler isolator and a conversion circuit electrically connected to the output end of the sampling network. The optocoupler isolator isolates the arc voltage sampling signal and converts the arc voltage sampling signal into a switch signal or an analog signal with multiple output amplitudes based on the conversion circuit.

[0007] According to one embodiment of the present invention, the anti-interference receiving unit also includes an impedance load and a backfeed absorption element connected between the positive and negative bus bars and in parallel with each other, the impedance load provides impedance for the welding power supply on the input side, and the backfeed absorption element absorbs the impact signal fed back from the output side of the arc voltage sampling circuit.

[0008] According to one embodiment of the present invention, the sampling network includes voltage-dividing resistors R1 and R2 connected in series on the positive bus and a voltage-dividing resistor R3 connected between the positive and negative bus bars, a filter capacitor C2 connected to the output side of the voltage-dividing resistor R1 and forming a first-stage RC filter with the voltage-dividing resistor R1, and a filter capacitor C3 connected to the output side of the voltage-dividing resistor R2 and forming a second-stage RC filter together with the voltage-dividing resistors R2 and R3.

[0009] According to an embodiment of the present invention, the sampling and conditioning unit further includes a voltage-stabilizing diode ZD1 disposed at the output side of the voltage-dividing resistor R1 and reversely connected between the positive and negative busbars. When the voltage-stabilizing diode ZD1 is broken down, the output side potential of the voltage-dividing resistor R1 is stabilized.

[0010] According to one embodiment of the present invention, the sampling and conditioning unit further includes a voltage regulator diode ZD2 reversely connected between the output end of the sampling network and the optocoupler isolator. The arc voltage signal output by the sampling network drives the rear-end optocoupler isolator after breaking down the voltage regulator diode ZD2.

[0011] According to one embodiment of the present invention, the conversion circuit includes a pull-up resistor R4, a current limiting resistor R5 and a ground filter capacitor C1, the pull-up resistor R4 is electrically connected between the collector of the photocoupler and the power supply voltage, the input end of the current limiting resistor R5 is connected to the common end of the pull-up resistor R4 and the collector of the photocoupler, and its output end serves as the output of the conversion circuit and is connected to the ground potential via the ground filter capacitor C1, and a low-pass filter is formed between the current limiting resistor R5 and the ground filter capacitor C1.

[0012] According to an embodiment of the present invention, based on the arc voltage sampling signal output by the sampling and conditioning unit, the optocoupler isolator has three working states: saturation conduction, saturation shutdown and impedance;

[0013] When the optocoupler is in an impedance state, a voltage divider network is formed between the optocoupler and the conversion circuit so that the output of the conversion circuit changes linearly with the arc voltage sampling signal, and the conversion circuit outputs analog signals with multiple output amplitudes corresponding to the arc state.

[0014] According to one embodiment of the present invention, an arc voltage sampling circuit suitable for a welding power supply also includes an analog quantity identification unit, which includes an amplifier U2, an output resistor R6, and an output filter capacitor C1. The in-phase input terminal of the amplifier U2 is connected to the conversion circuit to receive the output signal of the conversion unit, and the output terminal of the amplifier U2 is connected to its inverting input terminal to form a signal follower. One end of the output resistor R6 is connected to the output of the amplifier U2, and the other end thereof serves as the output of the analog quantity identification unit and is connected to the ground potential via the output filter capacitor C7.

[0015] According to one embodiment of the present invention, the arc voltage sampling circuit suitable for the welding power supply also includes a high and low level identification interface, which outputs the switching signal formed by the optocoupler isolator in saturation conduction and saturation shutdown to the switching input receiving end of the welding power supply controller.

[0016] On the other hand, the present invention also provides an arc voltage sampling method applicable to a welding power source, comprising:

[0017] Collect arc voltage signal output by welding power supply and perform common mode noise absorption;

[0018] Sampling and filtering the arc voltage signal to form an arc voltage sampling signal;

[0019] The arc voltage sampling signal is output to the isolation conversion unit. Based on the driving of the arc voltage sampling signal, the optocoupler isolator in the isolation conversion unit works in any one of the three working states of saturation off, saturation on and impedance;

[0020] When the optocoupler isolator works in an impedance state: the output of the conversion circuit changes linearly with the arc voltage sampling signal, and the analog signal output by the conversion circuit in this state is obtained;

[0021] Based on at least one preset standard arc voltage signal characterizing the transition state of the molten droplet, the acquired analog signal is judged to identify the transition state of the molten droplet.

[0022] In summary, in the arc voltage sampling circuit and sampling method suitable for welding power supply provided by the invention, the anti-interference absorption unit uses two common-mode capacitor groups with their midpoints connected to the ground potential to absorb and release the common-mode noise from the output circuit of the welding power supply, thereby improving the anti-interference ability of the sampling circuit and improving the acquisition accuracy of the arc voltage signal. The sampling and conditioning circuit collects the arc voltage signal through a sampling network composed of voltage-dividing resistors; at the same time, a filter capacitor is set in parallel with the output of the sampling network, and the voltage-dividing resistors and filter capacitors in the network are used to form at least one RC filter, and the collected signal is filtered and conditioned while sampling the arc voltage signal, thereby further improving the accuracy of the arc voltage signal after sampling. The sampled arc voltage signal is sent to the photoelectric coupler in the isolation conversion unit, and the front-end sampling and the back-end control signal (switch quantity signal or analog quantity signal) are isolated based on the photoelectric coupler to greatly improve the anti-interference strength of the back-end control signal.

[0023] Furthermore, while using a photocoupler to isolate the front and rear ends, the photocoupler isolator is set to have three working states: saturated conduction, saturated shutdown, and impedance. In the impedance state, a voltage divider network is formed between the photocoupler isolator and the conversion circuit so that the output of the conversion circuit changes linearly with the arc voltage sampling signal. Based on the output of the conversion circuit in the impedance state, the refined identification of the droplet transition state during the welding process can be accurately judged, thereby achieving precise control of the thrust function during the welding process.

[0024] In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Shown is a schematic diagram of an arc voltage sampling circuit applicable to a welding power source provided by an embodiment of the present invention.

[0026] Figure 2 Shown Figure 1 The arc voltage sampling circuit shown in the figure is working as a timing diagram.

[0027] Figure 3 It is a schematic flow chart of an arc voltage sampling method applicable to a welding power source provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0028] Arc state recognition based on arc voltage sampling is the basis for welding power supply to realize thrust function. The three commonly used arc voltage sampling methods are not only difficult to be compatible between circuit volume, cost and sampling accuracy, but the existing sampling methods can usually only identify the two states of arc short circuit and arc disconnection, and there is a problem of low thrust control accuracy.

[0029] In view of this, the present invention provides an arc voltage sampling circuit suitable for welding power supply with strong anti-interference ability and simple circuit structure. Figure 1 As shown, the arc voltage sampling circuit suitable for welding power supply provided in this embodiment includes an anti-interference absorption unit 10, a sampling conditioning unit 20 and an isolation conversion unit 30. The anti-interference absorption unit 10 is electrically connected to the output end of the welding power supply to collect arc voltage signals. The anti-interference absorption unit 10 includes two common-mode absorption capacitor groups connected in series between the positive and negative busbars, and the midpoint K of the two common-mode absorption capacitor groups is electrically connected to the ground. The sampling conditioning unit 20 is arranged at the output end of the anti-interference absorption unit 10 and includes a sampling network 21 and a filter capacitor. The sampling network 21 includes a plurality of voltage-dividing resistors connected in series between the positive and negative busbars. The filter capacitor is connected in parallel to the output of the sampling network. At least one RC filter is formed between the filter capacitor and the voltage-dividing resistor in the sampling network 21. The isolation conversion unit 30 includes an optocoupler isolator U1 and a conversion circuit 31 electrically connected to the output end of the sampling network. The optocoupler isolator U1 isolates the arc voltage sampling signal and converts the arc voltage sampling signal into a switch signal or an analog signal with multiple output amplitudes based on the conversion circuit 31.

[0030] like Figure 1 As shown, the positive bus terminal OUT+ and the negative bus terminal OUT- of the arc voltage sampling circuit suitable for the welding power supply are respectively connected to the output terminal of the welding power supply to collect arc voltage signals in real time. In this embodiment, capacitor C4 and capacitor C6 are respectively used as two common-mode absorption capacitor groups in the anti-interference absorption unit 10, and capacitor C4 and capacitor C6 are connected in series between the positive bus terminal OUT+ and the negative bus terminal OUT-, and the midpoint K of the two capacitors is connected to the ground, releasing the common-mode noise input by the front-end welding power supply to improve the anti-interference ability of the arc voltage sampling circuit. Although this embodiment is described by taking each common-mode absorption capacitor group as an example including only one capacitor. However, the present invention does not make any limitation to this. In other embodiments, each common-mode absorption capacitor group can include a plurality of capacitors connected in series in sequence, but the capacitance in the two mode absorption capacitor groups is substantially the same to achieve the absorption and release of common-mode noise.

[0031] Further, such as Figure 1As shown, the anti-interference absorption unit 10 also includes an impedance load and a backfeed absorption element connected between the positive and negative busbars and in parallel with each other. The impedance load provides high impedance for the welding power supply on the input side to reduce the influence of the arc voltage sampling circuit on the front-end welding power supply, and ensures the control accuracy of the front-end welding power supply to maintain the stable output of the arc voltage at each stage. The backfeed absorption element can absorb and release a small amount of high-frequency and high-voltage impact signals backfed from the output side of the arc voltage sampling circuit to further improve the stability and sampling accuracy of the sampling circuit. Specifically, in this embodiment, the impedance load is a resistor R7, and the backfeed absorption element is a capacitor C5. However. The present invention does not make any limitation to this. In other implementations, the impedance load can also be an impedance unit composed of a resistor and a capacitor, and the backfeed absorption element can also be an inductor.

[0032] The arc voltage signal collected from the output end of the welding power supply enters the sampling network 21 composed of the voltage-dividing resistor after being absorbed by the anti-interference absorption unit 1 for common-mode noise absorption at the input end and the reverse impact signal absorption at the output end. In this embodiment, the sampling network 21 includes voltage-dividing resistors R1 and R2 connected in series on the positive bus and a voltage-dividing resistor R3 connected between the positive and negative busbars. Different arc voltage signals loaded into the sampling network 21 will generate loop currents of corresponding sizes to drive the optocoupler isolator U1 in the rear-end isolation conversion unit 3, so that the optocoupler isolator U1 is in different working states. In the sampling network 21, the two ends of the voltage-dividing resistor R3 serve as the output of the sampling network 21, and the sampling conditioning unit 2 includes two filter capacitors C2 and C3 connected in parallel to the two ends of the voltage-dividing resistor R3. Among them, the voltage-dividing resistor R1 and the filter capacitor C2 constitute a primary RC filter, while the voltage-dividing resistors R2, R3 and the filter capacitor C3 together form a secondary RC filter.

[0033] In the sampling and conditioning unit 2 provided in the present embodiment, the voltage-dividing resistors R1, R2, and R3 divide the voltage and power of the collected arc voltage signal, and also form a multi-stage RC filter together with the two filter capacitors C2 and C3 to make the sampled arc voltage signal more stable. Since the filter coefficient of the RC filter will affect the response speed of signal transmission, the voltage-dividing resistor value and the filter capacitor value need to be adjusted according to the use environment and welding process requirements during design. Preferably, the set value voltage-dividing resistors R1 and R2 are variable resistors with adjustable resistance values, and the filter capacitors C2 and C3 can also be variable capacitors.

[0034] In this embodiment, if Figure 1As shown, the sampling and conditioning unit 2 also includes a voltage-stabilizing diode ZD1 which is arranged at the output side of the voltage-dividing resistor R1 and is reversely connected between the positive and negative busbars. When the collected arc voltage signal is very high and is still greater than the breakdown voltage Vzd1 of the voltage-stabilizing diode ZD1 after being divided by the voltage-dividing resistor R1, the voltage-stabilizing diode ZD1 is broken down and the potential of the point V1 on the output side of the voltage-dividing resistor R1 is stabilized at Vzd1. When the arc voltage signal after being divided by the voltage-dividing resistor R1 is less than Vzd1, the voltage-stabilizing diode ZD1 does not work. On the one hand, the setting of the voltage-stabilizing diode ZD1 can protect the rear-end arc voltage sampling circuit to avoid damage to the rear-end arc voltage sampling circuit due to the impact of the excessively high arc voltage signal; on the other hand, the high arc voltage signal clamping based on Vzd1 also makes the maximum driving current of the rear-end optical coupler isolator U1 a stable value (i.e., Vzd1 / (R2+R3), thereby greatly reducing the influence of the unstable arc voltage signal on the optical coupler isolator U1 and improving the anti-interference ability of the arc voltage sampling circuit.

[0035] Further, such as Figure 1 As shown, the sampling and conditioning unit 2 also includes a voltage regulator diode ZD2 reversely connected between the output end of the sampling network 21 and the optocoupler isolator U1. The arc voltage signal output by the sampling network 21 drives the rear optocoupler isolator U1 after breaking down the voltage regulator diode ZD2. The voltage regulator diode ZD2 mainly realizes the role of breakdown and shutdown in this circuit. Specifically, when the arc voltage signal is high, the arc voltage sampling signal is still greater than the breakdown voltage Vzd2 of the voltage regulator diode ZD2 when it is transmitted to the voltage regulator diode ZD2; the voltage regulator diode ZD2 is turned on, and the arc voltage sampling signal transmitted to the voltage regulator diode ZD2 continues to drive the rear optocoupler isolator U1 after being consumed by Vzd2. On the contrary, if the arc voltage sampling signal is less than the breakdown voltage Vzd2 of the voltage regulator diode ZD2 when it is transmitted to the voltage regulator diode ZD2, the voltage regulator diode ZD2 remains in the off state, and the optocoupler isolator U1 cannot receive the driving signal, so that the conversion circuit 31 outputs a high level.

[0036] The voltage stabilizing diodes ZD1 and ZD2 clamp the arc voltage signal responded by the optocoupler isolator U1 to the upper and lower limits, respectively, to avoid interference from too low arc voltage signals or too high arc voltages, and to improve the output accuracy of the back-end analog quantity or switch quantity. At the same time, the stable breakdown voltages Vzd1 and Vzd2 also make it easier to design the resistance and capacitance values ​​of the sampling network 21 when performing voltage division and power division. However, the present invention does not make any limitation to this. In other embodiments, the voltage stabilizing diodes ZD1 and ZD2 may not be provided.

[0037] In the arc voltage sampling circuit suitable for welding power supply provided in this example, the photocoupler U1 realizes the isolation of the front and rear stage signals. The conversion circuit 31 includes a pull-up resistor R4, a current limiting resistor R5 and a ground filter capacitor C1, the pull-up resistor R4 is electrically connected between the collector of the photocoupler U1 and the power supply voltage VCC, the input end of the current limiting resistor R5 is connected to the common end of the pull-up resistor R4 and the collector of the photocoupler U1, the output end of the current limiting resistor R5 is used as the output Vin of the conversion circuit 31 and is connected to the ground potential GND through the ground filter capacitor C1, and a low-pass filter is formed between the current limiting resistor R5 and the ground filter capacitor C1.

[0038] In this embodiment, based on the arc voltage sampling signal output by the sampling and conditioning unit 2, the optical coupler isolator U1 has three working states: saturation conduction, saturation off, and impedance. Figure 2 As shown, during welding, when the welding wire abuts against the workpiece and is in a short-circuit state or the welding wire has just separated from the base material and entered the arc-starting state, the arc voltage signal output by the welding power supply is zero or very low. The voltage regulator diode ZD2 remains in the off state, and the arc voltage sampling signal cannot drive the rear-end optocoupler isolator U1, and the optocoupler isolator U1 is in a saturated cut-off state. The output Vin of the conversion circuit 31 (i.e., the input of the next-level circuit) is connected to the power supply voltage VCC through the pull-up resistor R4, i.e., Vin=VCC. The rear-end analog quantity recognition unit or the high and low level recognition unit can judge whether the current arc is in a short-circuit state or an arc-starting state based on this.

[0039] As the welding wire and the base material are continuously separated, the arc voltage signal gradually increases. The arc voltage signal sampled by the sampling network 21 breaks down the voltage stabilizing diode ZD2 and drives the optocoupler isolator U1 to enter an impedance state. Figure 2 As shown, in the impedance state, the pull-up resistor R4 in the conversion circuit 31 and the output end of the optocoupler isolator U1 are connected in series to form a voltage divider network, and the output Vin of the conversion circuit 31 is at a value between VCC and GND and the value changes linearly with the arc voltage sampling signal. At this time, the analog signal output by the conversion circuit 31 in this state can be obtained. Based on at least one preset standard arc voltage signal characterizing the transition state of the droplet, the obtained analog signal is judged to identify the transition state of the droplet.

[0040] As the arc length continues to increase, the arc voltage also continues to increase, and the rear-end photocoupler U1 enters a saturated conduction state. The output end of the photocoupler U1 is fully turned on, and the output Vin of the conversion circuit 31 is connected to GND through the current limiting resistor R5, that is, Vin = GND. Based on this, the rear-end analog quantity recognition unit or the high and low level recognition unit can judge that the current arc gradually enters the necking state before the arc is disconnected. Further, in the process of the arc voltage signal increasing continuously, if the potential of the point V1 on the output side of the voltage-dividing resistor R1 is greater than the breakdown voltage Vzd1 of the voltage-stabilizing diode ZD1, the voltage-stabilizing diode ZD1 is broken down, and the potential of the point V1 is stabilized at Vzd1, so that the rear-end photocoupler U1 is in a saturated conduction state. In this embodiment, the potential of the point V1 when the photocoupler U1 initially enters the saturated conduction state will be less than Vzd1, that is, the photocoupler U1 has entered a saturated conduction state when the voltage-stabilizing diode ZD1 is not broken down. This setting enables the photocoupler U1 to isolate and convert the arc voltage signal within the entire impedance range to increase the recognition range of the arc voltage state. However, the present invention is not limited to this.

[0041] In this embodiment, the output Vin of the conversion circuit 31 is directly transmitted as an analog quantity, which can be directly connected to the high and low level identification interface 4 (such as the GPIO interface of the controller MCU) at the back end to identify the high and low levels. Specifically, the high and low level identification interface 4 identifies the switch signal (i.e., GND and VCC) formed when the optocoupler isolator U1 is in saturation conduction and saturation shutdown, thereby realizing the judgment of the two states of arc short circuit and arc disconnection.

[0042] Further, the arc voltage sampling circuit suitable for welding power supply provided in this embodiment also includes an analog quantity identification unit 5, which includes an amplifier U2, an output resistor R6 and an output filter capacitor C7. The in-phase input end of the amplifier U2 is connected to the conversion circuit 31 to receive the output signal Vin of the conversion unit 31, and the output end of the amplifier U2 is connected to its reverse input end to form a signal follower. One end of the output resistor R6 is connected to the output of the amplifier U2, and the other end thereof is used as the output of the analog quantity identification unit 5 and is connected to the ground potential through the output filter capacitor C7. In the analog quantity identification unit 5 provided in this embodiment, the amplifier U2 is used for signal following and front and rear signal blocking, and the output resistor R6 and the output filter capacitor C7 implement low-pass filtering. The filtered signal is directly transmitted to the ADC sampling pin of the back-end controller (such as MCU or DSP) for real-time data acquisition. The controller judges the signal input by the ADC sampling pin based on one or more standard arc voltage signals that characterize the droplet transition state, and then accurately identifies multiple states of the arc during the droplet transition. Specifically, when the signal input by the controller ADC sampling pin is close to the standard arc voltage signal during droplet transition, it indicates that the current arc voltage is in the droplet transition state; and when the signal input by the ADC sampling pin is close to the standard arc voltage signal during droplet ejection, it indicates that the front arc voltage is in the ejection transition state. If the ACD sampling pin input is VCC, it indicates that the current arc voltage is in a short circuit or arcing state. If the ACD sampling pin input is GND, it indicates that the current arc voltage is in a necking or disconnection state before disconnection.

[0043] However, the present invention does not make any limitation to this. In other embodiments, the corresponding welding process processing function and control strategy can also be called to process and convert the signal input by the ADC sampling pin, so as to realize high-precision subdivision control of the molten droplet at each stage in the non-short-circuit state during welding. In other implementations, the combination of an analog quantity sampling circuit and a comparator can also be used to replace the analog quantity identification unit provided in this embodiment, so as to realize the judgment of the arc state. Specifically, the analog quantity sampling circuit can regularly collect the output signal Vin of the conversion circuit 31, and compare the collected output signal Vin with at least one preset standard arc voltage signal, so as to realize the identification of each stage of the molten droplet in the non-short-circuit state.

[0044] Corresponding to the arc voltage sampling circuit applicable to the welding power supply, this embodiment provides an arc voltage sampling method applicable to the welding power supply, such as Figure 3 As shown, it includes:

[0045] Step S10, collecting the arc voltage signal output by the welding power supply and performing common mode noise absorption. Specifically, this embodiment uses the anti-interference absorption unit 1 to absorb the common mode noise input by the front-end welding power supply to improve the sampling accuracy and stability of the arc voltage signal.

[0046] Step S20: Utilize the sampling and conditioning unit 2 to sample and filter the arc voltage signal to form an arc voltage sampling signal.

[0047] Step S30, output the arc voltage sampling signal to the isolation conversion unit 3, the optocoupler isolator U1 in the isolation conversion unit 3 isolates the arc voltage sampling signal and converts the arc voltage sampling signal into a switch signal or an analog signal with multiple output amplitudes based on the conversion circuit 31.

[0048] Step S40: When the optocoupler isolator operates in an impedance state, the output of the conversion circuit changes linearly with the arc voltage sampling signal, and the analog signal output by the conversion circuit in this state is obtained.

[0049] Step S50: Based on at least one preset standard arc voltage signal characterizing the transition state of the droplet, the analog signal obtained is judged to identify the transition state of the droplet. Specifically, the analog identification unit 5 is used to identify the analog signal of VCC, GND output by the conversion circuit 31 and the optical coupler isolator U1 in the impedance state, thereby realizing the accurate identification and control of multiple states such as the short circuit of the arc, multiple droplet states in the non-short circuit state, and the arc disconnection.

[0050] In summary, in the arc voltage sampling circuit and sampling method suitable for welding power supply provided by the invention, the anti-interference absorption unit uses two common-mode capacitor groups with their midpoints connected to the ground potential to absorb and release the common-mode noise from the output circuit of the welding power supply, thereby improving the anti-interference ability of the sampling circuit and improving the acquisition accuracy of the arc voltage signal. The sampling and conditioning circuit collects the arc voltage signal through a sampling network composed of voltage-dividing resistors; at the same time, a filter capacitor is set in parallel with the output of the sampling network, and the voltage-dividing resistors and filter capacitors in the network are used to form at least one RC filter, and the collected signal is filtered and conditioned while sampling the arc voltage signal, thereby further improving the accuracy of the arc voltage signal after sampling. The sampled arc voltage signal is sent to the photoelectric coupler in the isolation conversion unit, and the front-end sampling and the back-end control signal (switch quantity signal or analog quantity signal) are isolated based on the photoelectric coupler to greatly improve the anti-interference strength of the back-end control signal.

[0051] Furthermore, while using a photocoupler to isolate the front and rear ends, the photocoupler isolator is set to have three working states: saturated conduction, saturated shutdown, and impedance. In the impedance state, a voltage divider network is formed between the photocoupler isolator and the conversion circuit so that the output of the conversion circuit changes linearly with the arc voltage sampling signal. Based on the output of the conversion circuit in the impedance state, the refined identification of the droplet transition state during the welding process can be accurately judged, thereby achieving precise control of the thrust function during the welding process.

[0052] Although the present invention has been disclosed as above by the preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make slight changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope of protection required by the claims.

Claims

1. An arc voltage sampling circuit suitable for a welding power supply, characterized in that: include: An anti-interference absorption unit is electrically connected to the output end of the welding power supply to collect arc voltage signals, wherein the anti-interference absorption unit comprises two common-mode absorption capacitor groups connected in series between the positive and negative busbars, and the midpoints of the two common-mode absorption capacitor groups are electrically connected to the ground; A sampling conditioning unit is arranged at the output end of the anti-interference absorption unit and includes a sampling network and a filter capacitor. The sampling network includes a plurality of voltage-dividing resistors connected in series between the positive and negative busbars. The filter capacitor is connected in parallel to the output of the sampling network. At least one RC filter is formed between the filter capacitor and the voltage-dividing resistors in the sampling network. The isolation conversion unit includes an optocoupler isolator and a conversion circuit electrically connected to the output end of the sampling network. The optocoupler isolator isolates the arc voltage sampling signal and converts the arc voltage sampling signal into a switch signal or an analog signal with multiple output amplitudes based on the conversion circuit.

2. The arc voltage sampling circuit suitable for welding power supply according to claim 1, characterized in that: The anti-interference receiving unit also includes an impedance load and a backfeed absorption element connected between the positive and negative busbars and in parallel with each other. The impedance load provides impedance for the welding power supply on the input side, and the backfeed absorption element absorbs the impact signal backfeeded from the output side of the arc voltage sampling circuit.

3. The arc voltage sampling circuit suitable for welding power supply according to claim 1, characterized in that: The sampling network includes voltage-dividing resistors R1 and R2 connected in series on the positive busbar and a voltage-dividing resistor R3 connected between the positive and negative busbars, a filter capacitor C2 connected to the output side of the voltage-dividing resistor R1 and forming a primary RC filter with the voltage-dividing resistor R1, and a filter capacitor C3 connected to the output side of the voltage-dividing resistor R2 and forming a secondary RC filter together with the voltage-dividing resistors R2 and R3.

4. The arc voltage sampling circuit suitable for welding power supply according to claim 3, characterized in that: The sampling and conditioning unit further includes a voltage-stabilizing diode ZD1 disposed at the output side of the voltage-dividing resistor R1 and reversely connected between the positive and negative busbars. When the voltage-stabilizing diode ZD1 is broken down, it stabilizes the potential at the output side of the voltage-dividing resistor R1.

5. The arc voltage sampling circuit suitable for welding power supply according to claim 1 or 4, characterized in that: The sampling and conditioning unit further includes a voltage stabilizing diode ZD2 reversely connected between the output end of the sampling network and the optocoupler isolator. The arc voltage signal output by the sampling network drives the rear optocoupler isolator after breaking down the voltage stabilizing diode ZD2.

6. The arc voltage sampling circuit suitable for welding power supply according to claim 1, characterized in that: The conversion circuit includes a pull-up resistor R4, a current limiting resistor R5 and a ground filter capacitor C1. The pull-up resistor R4 is electrically connected between the collector of the photocoupler and the power supply voltage. The input end of the current limiting resistor R5 is connected to the common end of the pull-up resistor R4 and the collector of the photocoupler. The output end serves as the output of the conversion circuit and is connected to the ground potential via the ground filter capacitor C1. A low-pass filter is formed between the current limiting resistor R5 and the ground filter capacitor C1.

7. The arc voltage sampling circuit suitable for welding power supply according to claim 1, characterized in that: Based on the arc voltage sampling signal output by the sampling and conditioning unit, the optical coupler isolator has three working states: saturation conduction, saturation shutdown and impedance; When the optocoupler is in an impedance state, a voltage divider network is formed between the optocoupler and the conversion circuit so that the output of the conversion circuit changes linearly with the arc voltage sampling signal, and the conversion circuit outputs analog signals with multiple output amplitudes corresponding to the arc state.

8. The arc voltage sampling circuit suitable for welding power supply according to claim 6, characterized in that: The arc voltage sampling circuit suitable for welding power supply also includes an analog quantity identification unit, which includes an amplifier U2, an output resistor R6 and an output filter capacitor C1. The in-phase input terminal of the amplifier U2 is connected to the conversion circuit to receive the output signal of the conversion unit, and the output terminal of the amplifier U2 is connected to its inverting input terminal to form a signal follower. One end of the output resistor R6 is connected to the output of the amplifier U2, and the other end thereof serves as the output of the analog quantity identification unit and is connected to the ground potential via the output filter capacitor C7.

9. The arc voltage sampling circuit suitable for welding power supply according to claim 1 or 7, characterized in that: The arc voltage sampling circuit suitable for welding power supply also includes a high and low level identification interface, which outputs the switching signal formed by the optocoupler isolator in saturation conduction and saturation shutdown to the switching input receiving end of the welding power supply controller.

10. A method for sampling arc voltage of a welding power source, characterized in that: include: Collect arc voltage signal output by welding power supply and perform common mode noise absorption; Sampling and filtering the arc voltage signal to form an arc voltage sampling signal; The arc voltage sampling signal is output to the isolation conversion unit. Based on the driving of the arc voltage sampling signal, the optocoupler isolator in the isolation conversion unit works in any one of the three working states of saturation off, saturation on and impedance; When the optocoupler isolator works in an impedance state: the output of the conversion circuit changes linearly with the arc voltage sampling signal, and the analog signal output by the conversion circuit in this state is obtained; Based on at least one preset standard arc voltage signal characterizing the transition state of the molten droplet, the acquired analog signal is judged to identify the transition state of the molten droplet.

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