Three-phase alternating current input voltage detection circuit and electric welding machine

Abstract

The invention relates to the technical field of power electronic converters, and discloses a three-phase alternating current input voltage detection circuit and an electric welding machine. The primary side of a voltage transformer in the voltage detection circuit is connected with a three-phase alternating current power supply, the primary side of the voltage transformer adopts angle connection, and the secondary side of the voltage transformer is connected with the input side of a signal conditioning circuit; the secondary side of the voltage transformer is connected in a star shape, a neutral point is formed, and the neutral point is connected with the control ground; the output side of the signal conditioning circuit is connected with the input side of the controller, and the signal conditioning circuit and the controller are both connected with the control ground; the output side of the DC conversion device is connected with the signal conditioning circuit and the controller, and the input side ground of the DC conversion device is power ground. The secondary side of the voltage transformer adopts star connection to form a neutral point, so that the subsequent signal conditioning circuit processing process is simplified. Meanwhile, the control system is connected with the control ground, and the input side of the DC conversion device is connected with the power ground, thereby achieving the purpose of strong and weak current isolation.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic converters, and particularly to a three-phase AC input voltage detection circuit and a welding machine. Background Art

[0002] With the rapid development of the manufacturing industry, the welding machine, as the core equipment of the welding process, is widely used in many fields such as construction, bridges, automobiles, aerospace, shipbuilding, petrochemical industry, etc. With the continuous progress of technology and the continuous innovation of processes, higher requirements are put forward for the performance of the welding machine.

[0003] As an electrical equipment at the power grid terminal, the welding machine is powered by a three-phase three-wire system. In the case of three-phase AC power supply, only three-phase cables A, B, and C are provided, and the connection of the neutral line N is not provided. However, due to the use of the three-phase three-wire system for three-phase power supply without an N line, the three-phase input voltage detection can only detect the line voltage. Subsequently, the differential signal is processed in the signal conditioning circuit, resulting in a complex design of the signal conditioning circuit. In addition, the currently commonly used voltage detection method is resistance detection. The sampling resistor is directly connected to the A, B, and C high-voltage power lines. After the signal is divided by the resistor, it needs to be connected to the control system. The resistance detection method mixes the strong and weak power systems together, which is likely to cause safety accidents. Summary of the Invention

[0004] In view of this, the present invention provides a three-phase AC input voltage detection circuit and a welding machine to solve the problems of complex design of the signal conditioning circuit and non-isolation between the strong and weak power.

[0005] In a first aspect, the present invention provides a three-phase AC input voltage detection circuit, which includes: a voltage transformer, a signal conditioning circuit, a controller, and a DC conversion device. Among them,

[0006] The primary side of the voltage transformer is connected to a three-phase AC power supply. The primary side of the voltage transformer is connected in a delta configuration. The secondary side of the voltage transformer is connected to the input side of the signal conditioning circuit. The secondary side of the voltage transformer is connected in a star configuration and forms a neutral point, and the neutral point is connected to the control ground; the output side of the signal conditioning circuit is connected to the input side of the controller, and both the signal conditioning circuit and the controller are connected to the control ground; the input side of the DC conversion device is connected to the high-voltage DC bus, and the output side of the DC conversion device is respectively connected to the signal conditioning circuit and the controller. The ground of the input side of the DC conversion device is the power ground;

[0007] The primary side of the voltage transformer collects the three-phase AC input line voltage, and after magnetic isolation, star-delta transformation, and turns ratio voltage transformation processing, outputs three-phase AC phase voltage signals to the signal conditioning circuit; the signal conditioning circuit is used to condition the three-phase AC phase voltage signals; the DC conversion device is used to supply power to the signal conditioning circuit and the controller; the controller is used to analyze and process the conditioned three-phase AC phase voltage signals to determine whether there are problems such as single-phase cable disconnection or poor contact of wiring terminals in the three-phase AC power supply.

[0008] A three-phase AC input voltage detection circuit provided by the present invention forms a neutral point by adopting a star connection on the secondary side of the voltage transformer, artificially creates an N line, so that the three-phase line voltage can be converted into three-phase phase voltage through the voltage transformer, simplifies the subsequent signal conditioning circuit processing process, reduces the design complexity of the signal conditioning circuit, and can realize continuous linear measurement of the input voltage. At the same time, the control system composed of the secondary side of the voltage transformer, the signal conditioning circuit and the controller is connected to the control ground, and the input side of the DC conversion device is connected to the power ground, achieving the purpose of strong and weak electricity isolation and avoiding safety accidents caused by the mixing of strong and weak electricity systems.

[0009] In an optional implementation manner, the voltage transformer adopts 1 three-phase voltage transformer or 3 independent single-phase voltage transformers.

[0010] In an optional implementation manner, the signal conditioning circuit includes a first-stage operational amplifier circuit for phase A, a second-stage operational amplifier circuit for phase A, a first-stage operational amplifier circuit for phase B, a second-stage operational amplifier circuit for phase B, a first-stage operational amplifier circuit for phase C, a second-stage operational amplifier circuit for phase C, and a three-terminal voltage regulator. Among them,

[0011] The input end of each phase's first-stage operational amplifier circuit is connected to the corresponding phase's phase voltage, the output end of each phase's first-stage operational amplifier circuit is respectively connected to the input end of the corresponding phase's second-stage operational amplifier circuit and the output end of the three-terminal voltage regulator, and the output end of each phase's second-stage operational amplifier circuit is respectively connected to the output end of the three-terminal voltage regulator and the controller;

[0012] The power supply end of each phase's first-stage operational amplifier circuit, the power supply end of each phase's second-stage operational amplifier circuit, and the input end of the three-terminal voltage regulator are all connected to an external power supply, and the grounding end of each phase's first-stage operational amplifier circuit, the grounding end of each phase's second-stage operational amplifier circuit, and the grounding end of the three-terminal voltage regulator are all connected to the control ground.

[0013] In an optional implementation manner, each phase's first-stage operational amplifier circuit includes a first-stage operational amplifier, a first resistor, a second resistor, a third resistor, a fourth resistor, and a first capacitor. Among them,

[0014] The inverting input terminal of the first-stage operational amplifier is respectively connected to one end of the first resistor and one end of the second resistor. The other end of the first resistor is connected to the phase voltage of the corresponding phase, and the other end of the second resistor is connected to the control ground. The non-inverting input terminal of the first-stage operational amplifier is connected to its output terminal. The power supply terminal of the first-stage operational amplifier is connected to an external power supply. The output terminal of the first-stage operational amplifier is connected to one end of the third resistor. The other end of the third resistor is respectively connected to one end of the fourth resistor, one end of the first capacitor, and the input terminal of the second-stage operational amplifier circuit of the corresponding phase. The other end of the fourth resistor is connected to the output terminal of the three-terminal voltage regulator, and the other end of the first capacitor is connected to the control ground.

[0015] In an alternative embodiment, the second-stage operational amplifier circuit of each phase includes a second-stage operational amplifier. The non-inverting input terminal of the second-stage operational amplifier is respectively connected to the other end of the third resistor, one end of the fourth resistor, and one end of the first capacitor. The inverting input terminal of the second-stage operational amplifier is connected to its output terminal. The output terminal of the second-stage operational amplifier is respectively connected to the output terminal of the three-terminal voltage regulator and the controller. The power supply terminal of the second-stage operational amplifier is connected to an external power supply.

[0016] In an alternative embodiment, the controller includes: an analog-to-digital converter, which is used to convert the three-phase AC phase voltage signal from an analog signal to a digital signal.

[0017] In an alternative embodiment, the circuit further includes: a three-phase air switch, a rectifier circuit, and an energy storage device, where

[0018] The input side of the three-phase air switch is connected to a three-phase AC power supply. The output side of the three-phase air switch is respectively connected to the primary side of the voltage transformer and the input side of the rectifier circuit. The output side of the rectifier circuit is connected to the input side of the energy storage device, and the rectifier circuit is connected to the power ground;

[0019] The output side of the energy storage device is connected to the input side of the DC conversion device.

[0020] In an alternative embodiment, the DC conversion device includes a first DC / DC converter, a second DC / DC converter, and a third DC / DC converter, where

[0021] The input side of the first DC / DC converter is connected to the output side of the energy storage device. The output side of the first DC / DC converter is respectively connected to the input side of the second DC / DC converter and the input side of the third DC / DC converter;

[0022] The output side of the second DC / DC converter is connected to the signal conditioning circuit;

[0023] The output side of the third DC / DC converter is connected to the controller.

[0024] In an alternative embodiment, the DC conversion device further includes a fourth DC / DC converter, a fifth DC / DC converter, a sixth DC / DC converter, and a seventh DC / DC converter, wherein,

[0025] The input sides of the fourth DC / DC converter, the fifth DC / DC converter, the sixth DC / DC converter, and the seventh DC / DC converter are all connected to the output side of the first DC / DC converter, and the output sides of the fourth DC / DC converter, the fifth DC / DC converter, the sixth DC / DC converter, and the seventh DC / DC converter are respectively connected to the drive circuits corresponding to the switching tubes in the inverter circuit.

[0026] In a second aspect, the present invention provides a welding machine, including the three-phase AC input voltage detection circuit according to the first aspect or any corresponding embodiment thereof.

[0027] The welding machine provided by the present invention forms a neutral point by adopting a star connection on the secondary side of the voltage transformer, artificially creating an N line, so that the three-phase line voltage can be converted into three-phase phase voltage through the voltage transformer, simplifying the subsequent signal conditioning circuit processing process, reducing the design complexity of the signal conditioning circuit, and enabling continuous linear measurement of the input voltage. At the same time, the control system composed of the secondary side of the voltage transformer, the signal conditioning circuit, and the controller is connected to the control ground, and the input side of the DC conversion device is connected to the power ground, achieving the purpose of isolating strong and weak electricity and avoiding safety accidents caused by the mixing of strong and weak electricity systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0029] Figure 1 is a block diagram schematic of a three-phase AC input voltage detection circuit according to an embodiment of the present invention;

[0030] Figure 2 is a working principle block diagram of a signal conditioning circuit according to an embodiment of the present invention;

[0031] Figure 3 is the signal conditioning circuit diagram according to an embodiment of the present invention;

[0032] Figure 4 is the three-phase AC input voltage detection circuit diagram according to an embodiment of the present invention;

[0033] Figure 5 is another three-phase AC input voltage detection circuit diagram according to an embodiment of the present invention. Detailed implementation manners

[0034] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0035] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0036] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and can also be the internal connection of two elements. It can be a wireless connection or a wired connection. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0037] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0038] Such as Figure 1As shown in the figure, the present invention provides a three-phase AC input voltage detection circuit, including: a voltage transformer T11, a signal conditioning circuit U10, a controller U12 and a DC conversion device. Among them, the primary side of the voltage transformer T11 is connected to a three-phase AC power supply. The primary side of the voltage transformer T11 is connected in a delta connection. The secondary side of the voltage transformer T11 is connected to the input side of the signal conditioning circuit U10. The secondary side of the voltage transformer T11 is connected in a star connection and forms a neutral point, and the neutral point is connected to the control ground; the output side of the signal conditioning circuit U10 is connected to the input side of the controller U12. The signal conditioning circuit and the controller are both connected to the control ground; the input side of the DC conversion device is connected to the high-voltage DC bus, and the output side of the DC conversion device is respectively connected to the signal conditioning circuit U10 and the controller U12. The ground of the input side of the DC conversion device is the power ground.

[0039] Specifically, the voltage transformer T11 collects the three-phase AC input line voltage, and after magnetic isolation, star-delta transformation, and turns ratio voltage transformation processing, outputs three-phase AC phase voltage signals to the signal conditioning circuit U10. The signal conditioning circuit U10 is used to condition the three-phase AC phase voltage signals. The DC conversion device is used to supply power to the signal conditioning circuit U10 and the controller U12. The controller U12 is used to analyze and process the conditioned three-phase AC phase voltage signals to determine whether there is a problem of single-phase cable disconnection or poor contact of the wiring terminals in the three-phase AC power supply.

[0040] Further, the input side of the voltage transformer T11 is connected in a delta connection, and the input voltages are Uab, Ubc, and Uca; the output side is connected in a star connection, forming a neutral point, and the neutral point is connected to the control ground GND, and at the same time, three-phase phase voltage signals Ua, Ub, and Uc are formed. The three-phase phase voltage signals Ua, Ub, and Uc are sequentially connected to the signal conditioning circuit U10 and the controller U12. The signal conditioning circuit U10 inputs the conditioned three-phase AC phase voltage signals Ua1, Ub1, and Uc1 to the controller U12. When the controller U12 detects that a certain phase voltage is 0, it is determined that the input cable of that phase is disconnected; when the controller U12 detects that a certain phase voltage is significantly reduced, it is determined that the wiring terminal of that phase has poor contact.

[0041] In addition, the signal conditioning circuit U10 and the controller U12 at the rear stage of the output side of the voltage transformer T11 both use the control ground at GND. Power is taken from the high-voltage DC bus as the input of the DC conversion device. The output of the DC conversion device supplies power to the signal conditioning circuit U10 and the controller U12. The ground GND1 of the input side of the DC conversion device is the power ground, and the ground GND of the output side of the DC conversion device is the control ground.

[0042] A three-phase AC input voltage detection circuit provided by the present invention forms a neutral point by adopting a star connection on the secondary side of a voltage transformer, artificially creating an N wire, so that the three-phase line voltage can be converted into three-phase phase voltages through the voltage transformer, simplifying the subsequent signal conditioning circuit processing process, reducing the design complexity of the signal conditioning circuit, and enabling continuous linear measurement of the input voltage. At the same time, the control system composed of the secondary side of the voltage transformer, the signal conditioning circuit and the controller is connected to the control ground, and the input side of the DC conversion device is connected to the power ground, achieving the purpose of strong-weak electricity isolation and avoiding safety accidents caused by the mixed connection of the strong-weak electricity systems.

[0043] In an optional embodiment, as Figure 2 shown, the signal conditioning circuit includes a first-stage operational amplifier circuit for phase A, a second-stage operational amplifier circuit for phase A, a first-stage operational amplifier circuit for phase B, a second-stage operational amplifier circuit for phase B, a first-stage operational amplifier circuit for phase C, a second-stage operational amplifier circuit for phase C, and a three-terminal voltage regulator. Among them, the input end of each first-stage operational amplifier circuit is connected to the phase voltage of the corresponding phase, the output end of each first-stage operational amplifier circuit is respectively connected to the input end of the corresponding second-stage operational amplifier circuit and the output end of the three-terminal voltage regulator, and the output end of each second-stage operational amplifier circuit is respectively connected to the output end of the three-terminal voltage regulator and the controller. The power supply terminal of each first-stage operational amplifier circuit, the power supply terminal of each second-stage operational amplifier circuit, and the input terminal of the three-terminal voltage regulator are all connected to an external power supply, and the grounding terminal of each first-stage operational amplifier circuit, the grounding terminal of each second-stage operational amplifier circuit, and the grounding terminal of the three-terminal voltage regulator are all connected to the control ground.

[0044] Specifically, since each first-stage operational amplifier circuit for each phase is the same and each second-stage operational amplifier circuit for each phase is the same, therefore, the first-stage operational amplifier circuit for phase A and the second-stage operational amplifier circuit for phase A are taken as examples for illustration. As Figure 3As shown in the figure, the first-stage operational amplifier circuit of phase A includes a first-stage operational amplifier U17, a first resistor R4, a second resistor R6, a third resistor R10, a fourth resistor R9, and a first capacitor C6. Among them, the inverting input terminal of the first-stage operational amplifier U17 is respectively connected to one end of the first resistor R4 and one end of the second resistor R6. The other end of the first resistor R4 is connected to the phase voltage of phase A, and the other end of the second resistor R6 is connected to the control ground GND. The non-inverting input terminal of the first-stage operational amplifier U17 is connected to its output terminal. The power supply terminal of the first-stage operational amplifier U17 is connected to an external power supply. The output terminal of the first-stage operational amplifier U17 is connected to one end of the third resistor R10. The other end of the third resistor R10 is respectively connected to one end of the fourth resistor R9, one end of the first capacitor C6, and the input terminal of the second-stage operational amplifier circuit of phase A. The other end of the fourth resistor R9 is connected to the output terminal of the three-terminal voltage regulator U9, and the other end of the first capacitor C6 is connected to the control ground GND. The second-stage operational amplifier circuit of phase A includes a second-stage operational amplifier U18. The non-inverting input terminal of the second-stage operational amplifier U18 is respectively connected to the other end of the third resistor R10, one end of the fourth resistor R9, and one end of the first capacitor C6. The inverting input terminal of the second-stage operational amplifier U18 is connected to its output terminal. The output terminal of the second-stage operational amplifier U18 is respectively connected to the output terminal of the three-terminal voltage regulator U9 and the controller. The power supply terminal of the second-stage operational amplifier U18 is connected to an external power supply.

[0045] Further, each first-stage operational amplifier of each phase and each second-stage operational amplifier are powered by an external power supply of plus and minus 15V. The input terminal of the three-terminal voltage regulator U9 is connected to the external power supply of +15V. The signal conditioning circuit is provided with two-stage operational amplifiers for signal conditioning. The two-stage operational amplifiers are both powered by plus and minus 15V, and a three-terminal voltage regulator is provided to form a 3V reference voltage source. The input signal of the signal conditioning circuit is divided by the first resistor R4 and the second resistor R6 to form a signal with a positive peak value of 3V and a negative peak value of -3V, which is applied to the inverting input terminal of the first-stage operational amplifier U17. The signal output by the first-stage operational amplifier U17 forms a convergence point with the 3V reference voltage passing through the fourth resistor R9. If the resistance value of the third resistor R10 is set equal to the resistance value of the fourth resistor R9, the voltage at the convergence point is the signal output by the first-stage operational amplifier U17 plus 3V and then divided by 2, forming a signal with a signal reference line of 1.5V, a maximum peak voltage of 3V, and a minimum value of 0V. Then, this signal is applied to the non-inverting input terminal of the second-stage operational amplifier U18. Among them, the second-stage operational amplifier U18 is a voltage follower, and the output signal is the same as the signal at the non-inverting input terminal. The output signal directly enters the analog-to-digital sampling pin of the controller.

[0046] Taking the signal conditioning process of phase A as an example, its specific operation process is as follows:

[0047] The voltage of phase A on the secondary side of the voltage transformer T11 is

[0048]

[0049] where N1 is the number of turns of the primary side of the voltage transformer T11, and N2 is the number of turns of the secondary side of the voltage transformer T11.

[0050] The output voltage of the operational amplifier U17 is:

[0051] U17out = U17_

[0052] where the inverting terminal of the same name of the operational amplifier U17 The non-inverting terminal of the same name of the operational amplifier U17, U17+ = U17_.

[0053] The output voltage of the operational amplifier U18 is: U18+ = (R9 * U17out + 3R10) / (R9 + R10).

[0054] If R9 = R10 is set, then U18+ = (U17out + 3) / 2.

[0055] Furthermore,

[0056] U18+ = (U17_ + 3) / 2 = (Ua * R6 / (R4 + R6) + 3) / 2 =

[0057]

[0058] Finally, it is obtained that:

[0059] In an alternative embodiment, the controller includes: an analog-to-digital converter, which is used to convert the three-phase AC phase voltage signal from an analog signal to a digital signal.

[0060] Specifically, by arranging the analog-to-digital converter inside the controller, the circuit structure of the three-phase AC input voltage detection circuit is simplified.

[0061] In an alternative embodiment, as Figure 4 shown, the three-phase AC input voltage detection circuit further includes: a three-phase air switch, a rectification circuit and an energy storage device. Among them, the input side of the three-phase air switch U0 is connected to the three-phase AC power supply, the output side of the three-phase air switch U0 is respectively connected to the primary side of the voltage transformer T11 and the input side of the rectification circuit, the output side of the rectification circuit is connected to the input side of the energy storage device, and the rectification circuit is connected to the power ground GND1.

[0062] Specifically, the three-phase air switch U0 is a commonly used protection device in the power system. Its function is to cut off the circuit in a timely manner when faults such as overload and short circuit occur in the circuit, protecting electrical equipment and personal safety. The rectifier circuit is mainly composed of rectifier diodes, and its function is to convert three-phase alternating current into high-voltage direct current.

[0063] In an alternative embodiment, as Figure 4 shown, the DC conversion device includes a first DC / DC converter U1, a second DC / DC converter U2, and a third DC / DC converter U4. Among them, the input side of the first DC / DC converter U1 is connected to the output side of the energy storage device C1. The output side of the first DC / DC converter U1 is respectively connected to the input side of the second DC / DC converter U2 and the input side of the third DC / DC converter U4. The output side of the second DC / DC converter U2 is connected to the signal conditioning circuit U10, and the second DC / DC converter U2 is used to supply power to the signal conditioning circuit U10. The output side of the third DC / DC converter U4 is connected to the controller U12, and the third DC / DC converter U4 is used to supply power to the controller U12.

[0064] Specifically, the first DC / DC converter U1 takes power from the high-voltage DC bus. The first DC / DC converter U1 outputs power to the control system. The ground GND1 on the input side of the first DC / DC converter U1 is the power ground, and the ground GND on the output side of the first DC / DC converter U1 is the control ground. The output of the first DC / DC converter U1 is connected to the inputs of the DC / DC converters U2 and U4. The second DC / DC converter U2 outputs ±15V to supply power to the signal conditioning circuit U10; the third DC / DC converter U4 outputs +3.3V and +5V to supply power to the controller U12. Among them, the first DC / DC converter U1 is an isolated DC / DC converter. The second DC / DC converter U2 and the third DC / DC converter U4 are non-isolated DC / DC converters.

[0065] In an alternative embodiment, as Figure 4 shown, the three-phase AC input voltage detection circuit further includes: an inverter circuit and a transformer T0. Among them, the input side of the inverter circuit is connected to the output side of the energy storage device C1, the output side of the inverter circuit is connected to the primary side of the transformer T0, and the secondary side of the transformer T0 is respectively connected to two electrodes.

[0066] Specifically, in a welding machine, one electrode is connected to the power supply positive pole V0+, and the other electrode is connected to the power supply negative pole V0-. The current flows between the two electrodes, generating strong heat energy, melting the contacted metal materials and forming a weld.

[0067] In an alternative embodiment, as Figure 4As shown in the figure, the DC conversion device further includes a fourth DC / DC converter U5, a fifth DC / DC converter U6, a sixth DC / DC converter U7, and a seventh DC / DC converter U8. Among them, the input sides of the fourth DC / DC converter U5, the fifth DC / DC converter U6, the sixth DC / DC converter U7, and the seventh DC / DC converter U8 are all connected to the output side of the first DC / DC converter U1, and the output sides of the fourth DC / DC converter U5, the fifth DC / DC converter U6, the sixth DC / DC converter U7, and the seventh DC / DC converter U8 are respectively connected to the drive circuits corresponding to the switching tubes (Q1-Q4) in the inverter circuit.

[0068] Specifically, the output of the first DC / DC converter U1 is connected to the inputs of the DC / DC converters U5, U6, U7, and U8, and the outputs of U5, U6, U7, and U8 supply power to the drive circuits corresponding to the 4 switching tubes in the inverter bridge in sequence as +18V and -4V. The fourth DC / DC converter U5, the fifth DC / DC converter U6, the sixth DC / DC converter U7, and the seventh DC / DC converter U8 are isolated DC / DC converters.

[0069] In an alternative embodiment, the voltage transformer uses 1 three-phase voltage transformer or 3 independent single-phase voltage transformers.

[0070] Specifically, the voltage transformer can use Figure 4 the 1 three-phase voltage transformer shown in the figure, or it can also use Figure 5 the 3 independent single-phase voltage transformers shown in the figure.

[0071] The present invention provides a welding machine, including Figure 4 or Figure 5 the three-phase AC input voltage detection circuit shown in the figure.

[0072] A welding machine provided by the present invention forms a neutral point by using a star connection on the secondary side of the voltage transformer, artificially creates an N line, so that the three-phase line voltage can be converted into three-phase phase voltage through the voltage transformer, simplifies the subsequent signal conditioning circuit processing process, reduces the design complexity of the signal conditioning circuit, and can achieve continuous linear measurement of the input voltage. At the same time, the control system composed of the secondary side of the voltage transformer, the signal conditioning circuit, and the controller is connected to the control ground, and the input side of the DC conversion device is connected to the power ground, achieving the purpose of isolating strong and weak electricity and avoiding safety accidents caused by the mixing of strong and weak electricity systems.

[0073] Although embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations fall within the scope defined by the appended claims.

Claims

1. A three-phase AC input voltage detection circuit, characterized in that The circuit includes: a voltage transformer, a signal conditioning circuit, a controller, and a DC conversion device, where the primary side of the voltage transformer is connected to a three-phase AC power supply. The primary side of the voltage transformer is connected in a delta configuration. The secondary side of the voltage transformer is connected to the input side of the signal conditioning circuit. The secondary side of the voltage transformer is connected in a star configuration and forms a neutral point, and the neutral point is connected to the control ground; the output side of the signal conditioning circuit is connected to the input side of the controller, and both the signal conditioning circuit and the controller are connected to the control ground; the input side of the DC conversion device is connected to a high-voltage DC bus, the output side of the DC conversion device is respectively connected to the signal conditioning circuit and the controller, and the input side ground of the DC conversion device is the power ground; the primary side of the voltage transformer collects the three-phase AC input line voltage, and after magnetic isolation, star-delta transformation, and turns ratio voltage transformation processing, outputs a three-phase AC phase voltage signal to the signal conditioning circuit; the signal conditioning circuit is used to condition the three-phase AC phase voltage signal; the DC conversion device is used to supply power to the signal conditioning circuit and the controller; the controller is used to analyze and process the conditioned three-phase AC phase voltage signal to determine whether there is a problem of single-phase cable disconnection or poor contact of the wiring terminal in the three-phase AC power supply.

2. The three-phase AC input voltage detection circuit according to claim 1, wherein The voltage transformer uses 1 three-phase voltage transformer or 3 independent single-phase voltage transformers.

3. The three-phase AC input voltage detection circuit according to claim 1, wherein The signal conditioning circuit includes a first-stage operational amplifier circuit for phase A, a second-stage operational amplifier circuit for phase A, a first-stage operational amplifier circuit for phase B, a second-stage operational amplifier circuit for phase B, a first-stage operational amplifier circuit for phase C, a second-stage operational amplifier circuit for phase C, and a three-terminal voltage regulator, where the input end of each phase's first-stage operational amplifier circuit is connected to the phase voltage of the corresponding phase, the output end of each phase's first-stage operational amplifier circuit is respectively connected to the input end of the corresponding phase's second-stage operational amplifier circuit and the output end of the three-terminal voltage regulator, and the output end of each phase's second-stage operational amplifier circuit is respectively connected to the output end of the three-terminal voltage regulator and the controller; the power supply end of each phase's first-stage operational amplifier circuit, the power supply end of each phase's second-stage operational amplifier circuit, and the input end of the three-terminal voltage regulator are all connected to an external power supply, and the grounding end of each phase's first-stage operational amplifier circuit, the grounding end of each phase's second-stage operational amplifier circuit, and the grounding end of the three-terminal voltage regulator are all connected to the control ground.

4. The three-phase AC input voltage detection circuit according to claim 3, wherein Each phase's first-stage operational amplifier circuit includes a first-stage operational amplifier, a first resistor, a second resistor, a third resistor, a fourth resistor, and a first capacitor, where The inverting input terminal of the first-stage operational amplifier is respectively connected to one end of the first resistor and one end of the second resistor. The other end of the first resistor is connected to the phase voltage of the corresponding phase, and the other end of the second resistor is connected to the control ground. The non-inverting input terminal of the first-stage operational amplifier is connected to its output terminal. The power supply terminal of the first-stage operational amplifier is connected to an external power supply. The output terminal of the first-stage operational amplifier is connected to one end of the third resistor. The other end of the third resistor is respectively connected to one end of the fourth resistor, one end of the first capacitor, and the input terminal of the second-stage operational amplifier circuit of the corresponding phase. The other end of the fourth resistor is connected to the output terminal of the three-terminal voltage regulator, and the other end of the first capacitor is connected to the control ground.

5. The three-phase AC input voltage detection circuit according to claim 4, wherein, The second-stage operational amplifier circuit of each phase includes a second-stage operational amplifier. The non-inverting input terminal of the second-stage operational amplifier is respectively connected to the other end of the third resistor, one end of the fourth resistor, and one end of the first capacitor. The inverting input terminal of the second-stage operational amplifier is connected to its output terminal. The output terminal of the second-stage operational amplifier is respectively connected to the output terminal of the three-terminal voltage regulator and the controller. The power supply terminal of the second-stage operational amplifier is connected to an external power supply.

6. The three-phase AC input voltage detection circuit according to claim 1, wherein The controller includes: an analog-to-digital converter, which is used to convert the three-phase AC phase voltage signal from an analog signal to a digital signal.

7. The three-phase AC input voltage detection circuit according to claim 1, wherein The circuit further includes: a three-phase air switch, a rectifier circuit, and an energy storage device, where The input side of the three-phase air switch is connected to a three-phase AC power supply. The output side of the three-phase air switch is respectively connected to the primary side of the voltage transformer and the input side of the rectifier circuit. The output side of the rectifier circuit is connected to the input side of the energy storage device, and the rectifier circuit is connected to the power ground; The output side of the energy storage device is connected to the input side of the DC conversion device.

8. The three-phase AC input voltage detection circuit according to claim 7, wherein The DC conversion device includes a first DC / DC converter, a second DC / DC converter, and a third DC / DC converter, where The input side of the first DC / DC converter is connected to the output side of the energy storage device. The output side of the first DC / DC converter is respectively connected to the input side of the second DC / DC converter and the input side of the third DC / DC converter; The output side of the second DC / DC converter is connected to the signal conditioning circuit; The output side of the third DC / DC converter is connected to the controller.

9. The three-phase AC input voltage detection circuit according to claim 8, wherein, The DC conversion device further includes a fourth DC / DC converter, a fifth DC / DC converter, a sixth DC / DC converter, and a seventh DC / DC converter, where The input sides of the fourth DC / DC converter, the fifth DC / DC converter, the sixth DC / DC converter, and the seventh DC / DC converter are all connected to the output side of the first DC / DC converter, and the output sides of the fourth DC / DC converter, the fifth DC / DC converter, the sixth DC / DC converter, and the seventh DC / DC converter are respectively connected to the drive circuits corresponding to the switching tubes in the inverter circuit.

10. An electric welding machine, characterized in that, It includes the three-phase AC input voltage detection circuit according to any one of claims 1-9.

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