A three-phase mains voltage detection circuit

Abstract

This utility model discloses a three-phase grid voltage detection circuit, comprising: a switching module, a control module, three phase voltage sampling modules, and two comparison modules. The phase voltage sampling modules sample the phase voltages of the three-phase AC power of the tested grid and convert them into DC voltages. The comparison modules output a first-level signal through their comparison output terminals when the DC voltage is greater than a first voltage, and output a second-level signal through their comparison output terminals when the DC voltage is less than the first voltage. The switching modules turn off in response to the first-level signal to input the DC voltage to the control module, and turn on in response to the second-level signal to input the ground voltage to the control module. The control modules determine whether the three-phase AC power of the tested grid is under-voltage or over-voltage based on the DC voltage, and determine whether a phase is missing in the three-phase AC power of the tested grid based on the ground voltage. This utility model's three-phase grid voltage detection circuit has a simple structure and low cost.

Description

Technical Field

[0001] This utility model relates to the field of inverter welding technology, and in particular to a three-phase mains voltage detection circuit. Background Technology

[0002] In complex power grid systems, grid voltage in different regions may fluctuate between excessively high and low levels at different times. When the grid voltage exceeds the normal operating voltage range of the inverter welding machine, excessively high voltage can damage power devices due to overvoltage; excessively low voltage will result in insufficient input power, leading to unstable output current and voltage, affecting welding performance, and potentially causing device overheating or overcurrent damage due to excessive input current. For three-phase inverter welding machines, a single input phase loss can also cause insufficient input power, resulting in unstable output current and voltage, affecting welding performance, and potentially causing device overheating or overcurrent damage due to excessive input current. Therefore, inverter welding machines need to have input grid voltage detection and judgment functions. They must be able to promptly identify abnormal grid voltage inputs and trigger protection and alarm functions to remind users to troubleshoot, ensuring the stable and reliable operation of the welding machine. Existing grid voltage detection circuits suffer from problems such as circuit complexity, high cost, and low reliability. Utility Model Content

[0003] This invention provides a three-phase grid voltage detection circuit, which has a simple circuit structure, low cost, and high reliability.

[0004] This invention provides a three-phase grid voltage detection circuit, comprising: a switching module, a control module, three phase voltage sampling modules, and two comparison modules; the input terminal of each phase voltage sampling module is connected to one phase AC input terminal of the three-phase AC power of the grid under test, the output terminal of one phase voltage sampling module is connected to the first terminal of the switching module and the control module, and the output terminals of the other two phase voltage sampling modules are connected to the first input terminal of the comparison modules. The phase voltage sampling modules are used to sample the phase voltage of the three-phase AC power of the grid under test and convert the phase voltage into DC voltage; the second input terminal of the comparison modules is connected to a first voltage, and the comparison modules are used to output a first level signal through the comparison output terminal when the DC voltage is greater than the first voltage; and to output a second level signal through the comparison output terminal when the second output voltage is less than the first voltage; the control terminal of the switching module is connected to the comparison output terminal, and the second terminal of the switching module is grounded, used to turn off in response to the first level signal to input the DC voltage to the control module; and to turn on in response to the second level signal to input the ground voltage to the control module; the control module is used to determine whether the three-phase AC power of the grid under test is under-voltage or over-voltage based on the DC voltage, and to determine whether the three-phase AC power of the grid under test is missing a phase based on the ground voltage.

[0005] Optionally, the phase voltage sampling module includes a step-down unit, a first filter unit, an amplification unit, a second filter unit, and a rectification unit. The input terminal of the step-down unit serves as the input terminal of the phase voltage sampling module, used to convert the phase voltage into a first AC voltage. The input terminal of the first filter unit is connected to the output terminal of the step-down unit, and the first filter unit is used to filter out high-frequency noise on the first AC voltage. The input terminal of the amplification unit is connected to the output terminal of the first filter unit, and the amplification unit is used to amplify the first AC voltage into a second AC voltage. The input terminal of the second filter unit is connected to the output terminal of the amplification unit, and the second filter unit is used to filter out high-frequency noise on the second AC voltage. The input terminal of the rectification unit is connected to the output terminal of the second filter unit, and the output terminal of the rectification unit serves as the output terminal of the phase voltage sampling module, used to convert the second AC voltage into a DC voltage.

[0006] Optionally, the step-down unit includes a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, and a first capacitor; the first resistor, the second resistor, the third resistor, the fourth resistor, and the first capacitor are connected in series, the first end of the first resistor serves as the input end of the step-down unit, and the second end of the first capacitor serves as the output end of the step-down unit; the first end of the fifth resistor is connected to the second end of the first capacitor, and the second end of the fifth resistor is grounded.

[0007] Optionally, the first filter unit includes a sixth resistor and a second capacitor; the first end of the sixth resistor serves as the input terminal of the first filter unit, and the second end of the sixth resistor is connected to the first end of the second capacitor and serves as the output terminal of the first filter unit; the second end of the second capacitor is grounded.

[0008] Optionally, the amplification unit includes a first operational amplifier, a seventh resistor, an eighth resistor, a first filter capacitor, and a second filter capacitor; the non-inverting input terminal of the first operational amplifier serves as the input terminal of the amplification unit, the first power supply terminal of the first operational amplifier is connected to a first voltage, the second power supply terminal of the first operational amplifier is connected to a second voltage, and the output terminal of the first operational amplifier serves as the output terminal of the amplification unit; the first terminal of the seventh resistor is grounded, the second terminal of the seventh resistor is connected to the inverting input terminal of the first operational amplifier and the first terminal of the eighth resistor, and the second terminal of the eighth resistor is connected to the output terminal of the first operational amplifier; the first terminal of the first filter capacitor is connected to the first power supply terminal of the first operational amplifier, and the second terminal of the first filter capacitor is grounded; the first terminal of the second filter capacitor is connected to the second power supply terminal of the second operational amplifier, and the second terminal of the second filter capacitor is grounded.

[0009] Optionally, the second filter unit includes a ninth resistor and a third capacitor; the first end of the ninth resistor serves as the input terminal of the second filter unit, the second end of the ninth resistor is connected to the first end of the third capacitor and serves as the output terminal of the second filter unit; the second end of the third capacitor is grounded.

[0010] Optionally, the rectifier unit includes a first diode, a tenth resistor, and a fourth capacitor; the anode of the first diode serves as the input terminal of the rectifier unit, and the cathode of the first diode is connected to the first terminal of the tenth resistor and the first terminal of the fourth capacitor; the second terminal of the tenth resistor and the second terminal of the fourth capacitor are grounded.

[0011] Optionally, the comparator module includes an eleventh resistor, a twelfth resistor, a thirteenth resistor, a fourteenth resistor, a fifteenth resistor, a comparator, a fifth capacitor, a second diode, and a third diode; the first end of the eleventh resistor serves as the first input terminal of the comparator module, and the second end of the eleventh resistor is connected to the inverting input terminal of the comparator; the first end of the twelfth resistor serves as the second input terminal of the comparator module, and the second end of the twelfth resistor is connected to the non-inverting input terminal of the comparator, the first end of the thirteenth resistor, the fifth capacitor, and the cathode of the second diode; the second end of the thirteenth resistor is grounded, and the second end of the fifth capacitor is grounded; the first end of the fourteenth resistor is connected to the anode of the second diode, and the second end of the fourteenth resistor is connected to the output terminal of the comparator, the first end of the fifteenth resistor, and the anode of the third diode; the second end of the fifteenth resistor is connected to a first voltage, and the cathode of the third diode serves as the comparator output terminal of the comparator module.

[0012] Optionally, the switching module includes a first transistor; the first electrode of the first transistor serves as the first terminal of the switching module, the second electrode of the first transistor serves as the second terminal of the switching module, and the gate of the first transistor serves as the control terminal of the switching module; the three-phase grid voltage detection circuit further includes a current-limiting resistor, which is connected between the output terminal of the phase voltage sampling module and the first terminal of the switching module.

[0013] Optionally, the three-phase mains voltage detection circuit also includes a second operational amplifier; the non-inverting input of the second operational amplifier is connected to the first terminal of the switching module, and the output of the second operational amplifier is connected to the inverting input of the second operational amplifier and the control module.

[0014] The three-phase grid voltage detection circuit provided in this embodiment includes a switching module, a control module, three phase voltage sampling modules, and two comparison modules. The phase voltage sampling modules accurately acquire and convert the phase voltages of the three-phase AC power, providing accurate and reliable voltage signals for the entire three-phase grid voltage detection circuit. The comparison modules output the comparison result of the DC voltage and the first voltage as a level signal, providing a certain degree of isolation. This prevents the DC voltage signal output by the phase voltage sampling modules from directly affecting the control module, preventing misjudgments by the control module due to abnormal fluctuations or interference in the DC voltage signal, thus improving the reliability of the detection results. Through the switching function of the switching module, the control module can receive different signals (DC voltage from phase voltage sampling and ground voltage) using a single input channel, thereby realizing the detection of multiple states of the three-phase power grid (undervoltage, overvoltage, and phase loss). This avoids setting up a separate input channel for each detection state, simplifying the overall circuit structure and reducing hardware costs.

[0015] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this utility model, nor is it intended to limit the scope of this utility model. Other features of this utility model will become readily apparent from the following description. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of a three-phase mains voltage detection circuit provided in an embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram of another three-phase mains voltage detection circuit provided in this embodiment of the utility model;

[0019] Figure 3 This is a schematic diagram of another three-phase mains voltage detection circuit provided in this embodiment of the utility model;

[0020] Figure 4 This is a schematic diagram of another three-phase mains voltage detection circuit provided in this embodiment of the utility model;

[0021] Figure 5 This is a schematic diagram of another three-phase mains voltage detection circuit provided in this embodiment of the utility model;

[0022] Figure 6This is a schematic diagram of another three-phase mains voltage detection circuit provided in this embodiment of the utility model;

[0023] Figure 7 This is a schematic diagram of another three-phase grid voltage detection circuit provided in this embodiment of the utility model. Detailed Implementation

[0024] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0025] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this utility model are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this utility model described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0026] As described in the background section, existing grid voltage detection circuits suffer from circuit complexity and high cost. Research by the inventors has revealed that the reason for these problems is that existing grid voltage detection circuits, in order to simultaneously detect multiple states of a three-phase power grid (undervoltage, overvoltage, and phase loss), require a separate input channel for each detection state, resulting in overall circuit complexity and increased hardware costs.

[0027] To solve the above-mentioned technical problems, this utility model provides a three-phase grid voltage detection circuit. Figure 1 This is a schematic diagram of a three-phase mains voltage detection circuit provided in an embodiment of this utility model. (Reference) Figure 1 The three-phase grid voltage detection circuit includes: a switching module 11, a control module 12, three phase voltage sampling modules 13, and two comparison modules 14.

[0028] The input terminal of each phase voltage sampling module 13 is connected to one phase AC input terminal of the three-phase AC power of the power grid under test. The output terminal of one phase voltage sampling module 13 is connected to the first terminal of the switch module 11 and the control module 12. The output terminals of the other two phase voltage sampling modules 13 are connected to the first input terminal of the comparison module 14. The phase voltage sampling module 13 is used to sample the phase voltage of the three-phase AC power of the power grid under test and convert the phase voltage into DC voltage.

[0029] The second input terminal of the comparison module 14 is connected to the first voltage VCC. The comparison module 14 is used to output a first level signal through the comparison output terminal when the DC voltage is greater than the first voltage VCC; and to output a second level signal through the comparison output terminal when the second output voltage is less than the first voltage VCC.

[0030] The control terminal of the switch module 11 is connected to the comparison output terminal, and the second terminal of the switch module 11 is grounded. It is used to turn off in response to the first level signal to input DC voltage to the control module 12; and to turn on in response to the second level signal to input ground voltage to the control module 12.

[0031] The control module 12 is used to determine whether the three-phase AC power of the tested power grid is under-voltage or over-voltage based on the DC voltage, and to determine whether the three-phase AC power of the tested power grid is missing a phase based on the grounding voltage.

[0032] Specifically, the switch module 11 isolates the signals for undervoltage, overvoltage, and phase loss detection through two states: on and off. During undervoltage and overvoltage detection, the switch module is off, ensuring the accurate input of the sampled DC voltage of the phase voltage to the control module. During phase loss detection, the switch module 11 is on, allowing the ground voltage to be input to the control module 12. This avoids signal interference between different detection states, ensuring the control module 12 can accurately determine different grid states. Through the switching function of the switch module 11, the control module 12 can receive different signals (sampled DC voltage of the phase voltage and ground voltage) using a single input channel, thereby enabling the detection of multiple states (undervoltage, overvoltage, and phase loss) of the three-phase grid. This avoids the need for separate input channels for each detection state, simplifying the overall circuit structure and reducing hardware costs.

[0033] The tested three-phase AC power grid includes phase A, phase B, and phase C. The input terminals of the phase voltage sampling modules 13 are connected to the AC input terminals of each phase of the three-phase AC power grid, i.e., to phase A, phase B, and phase C respectively. The phase voltage sampling module 13 connected to the AC input terminal of phase A is called the phase A phase voltage sampling module 13, the phase voltage sampling module 13 connected to the AC input terminal of phase B is called the phase B phase voltage sampling module 13, and the phase voltage sampling module 13 connected to the AC input terminal of phase C is called the phase C phase voltage sampling module 13.

[0034] This utility model embodiment schematically shows the situation where the output terminal of the A-phase voltage sampling module 13 is connected to the first terminal of the switch module 11 and the control module 12, and the output terminals of the B-phase voltage sampling module 13 and the C-phase voltage sampling module 13 are connected to the first input terminal of the comparison module 14.

[0035] When the DC voltage output by phase B voltage sampling module 13 or phase C voltage sampling module 13 is greater than the first voltage VCC, the corresponding comparison module 14 outputs a first level signal (e.g., a low level signal), causing the switch module 11 to turn off. The DC voltage output by phase A voltage sampling module 13 is then input to the control module 12. The control module 12 determines whether the power grid is undervoltage or overvoltage based on this DC voltage. For example, the control module 12 compares the received DC voltage with set undervoltage and overvoltage thresholds. If the DC voltage is lower than the undervoltage threshold, the phase voltage is determined to be undervoltage; if the DC voltage is higher than the overvoltage threshold, the phase voltage is determined to be overvoltage; if the DC voltage is between the undervoltage and overvoltage thresholds, the phase voltage is considered to be within the normal range. When the control module 12 determines that a phase voltage is undervoltage, it sends control commands to other relevant devices or modules to protect and regulate the power grid. For example, it controls the alarm module to issue an alarm signal to remind maintenance personnel to conduct an inspection. If an overvoltage is detected in a certain phase, the control module 12 can control the relay to operate, cut off the circuit of the overvoltage phase, and protect the equipment and load from the effects of overvoltage.

[0036] When the DC voltage output by phase B voltage sampling module 13 or phase C voltage sampling module 13 is less than the first voltage VCC, the corresponding comparison module 14 outputs a second-level signal (e.g., a high-level signal), the switch module 11 is turned on, and the ground voltage (e.g., 0V) is input to the control module 12. The control module 12 determines that the measured power grid is missing a phase based on the ground voltage. This is because the comparison module 14 will only output a second-level signal when the DC voltage output by the corresponding phase voltage sampling module 13 is lower than the first voltage VCC, thereby turning on the switch module 11 and inputting the ground voltage to the control module 12. The first-level signal and the second-level signal are high and low level signals, respectively. For example, the first-level signal is a low-level signal, and the second-level signal is a high-level signal.

[0037] The comparison module 14 outputs the voltage comparison result as a level signal, which provides a certain degree of isolation. This prevents the DC voltage signal output by the phase voltage sampling module 13 from directly affecting the control module, thus preventing misjudgments by the control module 12 due to abnormal fluctuations or interference in the DC voltage signal. Simultaneously, by outputting a clear level signal, it also better protects the control module 12, ensuring it operates in a relatively stable and reliable signal environment.

[0038] Continue to refer to Figure 1 The working principle of this three-phase mains voltage detection circuit is as follows:

[0039] Assuming the three-phase power grid is operating normally, the DC voltage output by phase B voltage sampling module 13 and phase C voltage sampling module 13 is greater than the first voltage VCC. Comparison module 14 outputs the first level signal, switch module 11 is turned off, and the DC voltage output by phase A voltage sampling module 13 is input to control module 12. Control module 12 compares this DC voltage with the undervoltage threshold and overvoltage threshold to determine whether the phase A voltage is normal.

[0040] If a phase (such as phase B) experiences a phase loss fault, the DC voltage output by phase B voltage sampling module 13 will be less than the first voltage VCC. The corresponding comparison module 14 will output a second level signal, the switch module 11 will be turned on, and the ground voltage will be input to the control module 12. The control module 12 will determine that there is a phase loss in the power grid based on the ground voltage.

[0041] The three-phase grid voltage detection circuit provided in this embodiment includes a switching module, a control module, three phase voltage sampling modules, and two comparison modules. The phase voltage sampling modules accurately acquire and convert the phase voltages of the three-phase AC power, providing accurate and reliable voltage signals for the entire three-phase grid voltage detection circuit. The comparison modules output the comparison result of the DC voltage and the first voltage as a level signal, providing a certain degree of isolation. This prevents the DC voltage signal output by the phase voltage sampling modules from directly affecting the control module, preventing misjudgments by the control module due to abnormal fluctuations or interference in the DC voltage signal, thus improving the reliability of the detection results. Through the switching function of the switching module, the control module can receive different signals (DC voltage from phase voltage sampling and ground voltage) using a single input channel, thereby realizing the detection of multiple states of the three-phase power grid (undervoltage, overvoltage, and phase loss). This avoids setting up a separate input channel for each detection state, simplifying the overall circuit structure and reducing hardware costs.

[0042] Figure 2 This is a schematic diagram of another three-phase mains voltage detection circuit provided in this embodiment of the utility model, as shown below. Figure 2 As shown, optionally, the phase voltage sampling module 13 includes a step-down unit 131, a first filter unit 132, an amplification unit 133, a second filter unit 134, and a rectification unit 135.

[0043] The input terminal of the step-down unit 131 serves as the input terminal of the phase voltage sampling module 13, and is used to convert the phase voltage into a first AC voltage.

[0044] The input terminal of the first filter unit 132 is connected to the output terminal of the step-down unit 131. The first filter unit 132 is used to filter out high-frequency noise on the first AC voltage.

[0045] The input terminal of the amplification unit 133 is connected to the output terminal of the first filter unit 132. The amplification unit 133 is used to amplify the first AC voltage into a second AC voltage.

[0046] The input terminal of the second filter unit 134 is connected to the output terminal of the amplifier unit 133. The second filter unit 134 is used to filter out high-frequency noise on the second AC voltage.

[0047] The input terminal of the rectifier unit 135 is connected to the output terminal of the second filter unit 134. The output terminal of the rectifier unit 135 serves as the output terminal of the phase voltage sampling module 13. The rectifier unit 135 is used to convert the second AC voltage into DC voltage.

[0048] Specifically, step-down unit 131 proportionally reduces the phase voltage of the power grid (e.g., 380VAC) to a first AC voltage (e.g., 10VAC) suitable for subsequent processing. In some embodiments, voltage level matching can be achieved through a transformer or resistor divider circuit to prevent high voltage from directly entering the subsequent circuit and causing damage.

[0049] The first filtering unit 132 filters out high-frequency noise (such as harmonics and electromagnetic interference) in the first AC voltage after step-down. In some embodiments, an RC filter circuit or an LC filter can be used to suppress noise above the target frequency and retain the fundamental signal.

[0050] Amplification unit 133 amplifies the filtered first AC signal (e.g., 10VAC) into a second AC voltage (e.g., ±15VAC). In some embodiments, an operational amplifier (e.g., an instrumentation amplifier) ​​can be used to boost the signal amplitude to ensure that the subsequent rectified DC voltage reaches the threshold range required by the control module.

[0051] The second filtering unit 134 filters out high-frequency noise that may be introduced during amplification. In some embodiments, the second filtering unit 134 is similar to the first filtering unit, but with more stringent design parameters to further improve signal purity and prevent amplification noise from affecting detection accuracy.

[0052] The rectifier unit 135 converts the filtered second AC voltage into a smooth DC voltage. In some embodiments, a bridge rectifier circuit (such as a rectifier bridge composed of four diodes) and capacitor filtering can be used to convert the sine wave into pulsating DC, and then a stable DC signal (such as 0-10VDC) can be output after energy storage by a capacitor for comparison and judgment by the control module 12.

[0053] Figure 3 This is a schematic diagram of another three-phase mains voltage detection circuit provided in this embodiment of the utility model, as shown below. Figure 3As shown, optionally, the step-down unit 131 includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, and a first capacitor C1.

[0054] The first resistor R1, the second resistor R2, the third resistor R3, the fourth resistor R4, and the first capacitor C1 are connected in series. The first terminal of the first resistor R1 serves as the input terminal of the step-down unit 131, and the second terminal of the first capacitor C1 serves as the output terminal of the step-down unit 131. The first terminal of the fifth resistor R5 is connected to the second terminal of the first capacitor C1, and the second terminal of the fifth resistor R5 is grounded.

[0055] In the AC circuit, the first resistor R1, the second resistor R2, the third resistor R3, and the fourth resistor R4 constitute a voltage divider circuit. According to the voltage divider principle of series circuits, the total voltage is distributed across each resistor according to their resistance values. When the phase voltage of the measured power grid is input to the step-down unit 131, most of the voltage drops across these series resistors, thereby reducing the voltage at the output terminal (the second terminal of the first capacitor C1), thus realizing the function of converting the phase voltage into the first AC voltage.

[0056] The first capacitor, C1, functions as a filter and blocks DC in the circuit. For AC signals, the capacitor has a certain capacitive reactance, and together with the series resistor, it forms an RC circuit. The capacitor can filter high-frequency noise, making the output AC voltage smoother and reducing the impact of high-frequency interference on subsequent circuits. Simultaneously, the capacitor also blocks DC components, ensuring that the output is a pure AC signal.

[0057] The main function of the fifth resistor R5 is to provide a stable reference ground for the circuit, and it also limits and buffers the output signal to protect subsequent circuits from excessive current. Furthermore, in some cases, it can work with the first capacitor C1 to form a low-pass filter, further filtering out high-frequency noise in the output signal. The first capacitor C1 acts as an isolation device between the power grid and the control system; therefore, a Y1-grade safety capacitor is required.

[0058] Continue to refer to Figure 3 Optionally, the first filter unit 132 includes a sixth resistor R6 and a second capacitor C2. The first end of the sixth resistor R6 serves as the input terminal of the first filter unit 132, and the second end of the sixth resistor R6 is connected to the first end of the second capacitor C2 and serves as the output terminal of the first filter unit 132; the second end of the second capacitor C2 is grounded.

[0059] The input AC voltage signal contains a fundamental frequency signal (the desired useful signal) and high-frequency noise (unwanted interference signal). The high-frequency noise has a higher frequency and a lower capacitive reactance when passing through the capacitor; most of the high-frequency noise flows to ground through the second capacitor C2. Conversely, the fundamental frequency is relatively low, and the capacitor has a higher capacitive reactance, allowing the fundamental signal to be successfully transmitted to the output terminal through the sixth resistor R6. This achieves the function of filtering out the high-frequency noise on the first AC voltage.

[0060] Continue to refer to Figure 3 Optionally, the amplification unit 133 includes a first operational amplifier U1, a seventh resistor R7, an eighth resistor R8, a first filter capacitor FC1, and a second filter capacitor FC2.

[0061] The non-inverting input terminal of the first operational amplifier U1 serves as the input terminal of the amplification unit 133. The first power supply terminal of the first operational amplifier U1 is connected to the first voltage VCC, the second power supply terminal of the first operational amplifier U1 is connected to the second voltage -VEE, and the output terminal of the first operational amplifier U1 serves as the output terminal of the amplification unit 133.

[0062] The first end of the seventh resistor R7 is grounded, the second end of the seventh resistor R7 is connected to the inverting input of the first operational amplifier U1 and the first end of the eighth resistor R8, and the second end of the eighth resistor R8 is connected to the output of the first operational amplifier U1.

[0063] The first terminal of the first filter capacitor FC1 is connected to the first power supply terminal of the first operational amplifier U1, and the second terminal of the first filter capacitor FC1 is grounded. The first terminal of the second filter capacitor FC2 is connected to the second power supply terminal of the first operational amplifier U1, and the second terminal of the second filter capacitor is grounded.

[0064] Specifically, the eighth resistor R8 and the seventh resistor R7 together form the feedback loop of the first operational amplifier U1, used to determine the amplification factor. The first filter capacitor FC1 is used to filter the positive power supply, removing high-frequency noise and ripple to provide a stable positive power supply for the operational amplifier. The second filter capacitor FC2 is used to filter the negative power supply, removing high-frequency noise and ripple to provide a stable negative power supply for the operational amplifier.

[0065] Optionally, the amplification unit 133 further includes a first clamping diode CD1 and a second clamping diode CD2. The first terminal of the first clamping diode CD1 is connected to the non-inverting input terminal of the first operational amplifier U1, and the second terminal of the first clamping diode CD1 is connected to a second voltage -VEE. The first terminal of the second clamping diode CD2 is connected to the non-inverting input terminal of the first operational amplifier U1, and the second terminal of the second clamping diode CD2 is connected to a first voltage VCC.

[0066] Continue to refer to Figure 3 Optionally, the second filter unit 134 includes a ninth resistor R9 and a third capacitor C3. The first end of the ninth resistor R9 serves as the input terminal of the second filter unit 134, and the second end of the ninth resistor R9 is connected to the first end of the third capacitor C3 and serves as the output terminal of the second filter unit 134; the second end of the third capacitor C3 is grounded.

[0067] When the second AC voltage signal containing high-frequency noise enters the filtering unit, most of the high-frequency noise is bypassed to ground through the third capacitor C3 due to its low capacitive reactance. The desired low-frequency signal (such as the fundamental signal), however, can smoothly reach the output terminal through the ninth resistor R9 because of the larger capacitive reactance of the third capacitor C3. This achieves the filtering out of high-frequency noise in the second AC voltage signal.

[0068] Continue to refer to Figure 3 Optionally, the rectifier unit 135 includes a first diode D1, a tenth resistor R10, and a fourth capacitor C4. The anode of the first diode D1 serves as the input terminal of the rectifier unit 135, and the cathode of the first diode D1 is connected to the first terminal of the tenth resistor R10 and the first terminal of the fourth capacitor C4. The second terminal of the tenth resistor R10 and the second terminal of the fourth capacitor C4 are grounded.

[0069] Specifically, the first diode D1 utilizes its unidirectional conductivity for rectification. When the input second AC voltage signal is in the positive half-cycle, the first diode D1 conducts, allowing current to flow through it to subsequent circuit components; conversely, when the input signal is in the negative half-cycle, the first diode D1 is cut off, preventing current flow. Thus, after passing through the first diode D1, the AC signal is converted into a unidirectional pulsating DC signal.

[0070] The tenth resistor R10 and the fourth capacitor C4 form an RC filter circuit. The fourth capacitor C4 has the characteristic of storing and releasing charge. During the conduction period of the first diode D1, the fourth capacitor C4 charges. During the cutoff period of the first diode D1, the fourth capacitor C4 discharges through the tenth resistor R10. Through this charging and discharging process, the fourth capacitor C4 can smooth the fluctuations of the pulsating DC signal, making the output DC voltage more stable. The function of the tenth resistor R10 is to limit the discharge rate of the fourth capacitor C4, preventing excessively rapid discharge from causing excessive fluctuations in the output voltage.

[0071] Figure 4 This is a schematic diagram of another three-phase mains voltage detection circuit provided in this embodiment of the utility model, as shown below. Figure 4As shown, optionally, the comparison module 14 includes an eleventh resistor R11, a twelfth resistor R12, a thirteenth resistor R13, a fourteenth resistor R14, a fifteenth resistor R15, a comparator U2, a fifth capacitor C5, a second diode D2, and a third diode D3.

[0072] The first terminal of the eleventh resistor R11 serves as the first input terminal of the comparator module 14, and the second terminal of the eleventh resistor R11 is connected to the inverting input terminal of comparator U2. The first terminal of the twelfth resistor R12 serves as the second input terminal of the comparator module 14, and the second terminal of the twelfth resistor R12 is connected to the non-inverting input terminal of comparator U2, the first terminal of the thirteenth resistor R13, the fifth capacitor C5, and the cathode of the second diode D2. The second terminal of the thirteenth resistor R13 is grounded, and the second terminal of the fifth capacitor C5 is grounded. The first terminal of the fourteenth resistor R14 is connected to the anode of the second diode D2, and the second terminal of the fourteenth resistor R14 is connected to the output terminal of comparator U2, the first terminal of the fifteenth resistor R15, and the anode of the third diode D3. The second terminal of the fifteenth resistor R15 is connected to the first voltage VCC, and the cathode of the third diode D3 serves as the comparator output terminal of the comparator module U2.

[0073] Optionally, the first power supply terminal of comparator U2 is connected to the first voltage VCC, and the second power supply terminal of comparator U2 is grounded.

[0074] The comparison module 14 also includes a third filter capacitor FC3. The first end of the third filter capacitor FC3 is connected to the first power supply terminal of the comparator U2, and the second end of the third filter capacitor FC3 is grounded.

[0075] Specifically, the eleventh resistor R11 serves as a current limiter and impedance matcher, preventing excessive current from damaging the inverting input of the comparator. It also adjusts the amplitude of the input signal. The second terminal of the thirteenth resistor R13 is grounded; together with the twelfth resistor R12, it forms a voltage divider circuit, dividing the input voltage to provide a suitable reference voltage for the non-inverting input of comparator U2. The second terminal of the fifth capacitor C5 is grounded; it acts as a filter, smoothing the reference voltage, reducing voltage fluctuations and noise interference, making the reference voltage more stable, and improving the comparator's comparison accuracy.

[0076] The fourteenth resistor, R14, is used to adjust the strength of the feedback signal and also serves as a current limiter. When the comparator outputs a high level, current is drawn from the first voltage VCC through the fifteenth resistor, R15, to ensure the amplitude and driving capability of the output signal. The cathode of the third diode, D3, serves as the comparator output terminal of comparator module 14. Its function is to limit and isolate the output signal, preventing abnormally high voltage from damaging subsequent connected circuits, and also avoiding signal interference between different modules.

[0077] Comparator U2 compares the voltages at its inverting and non-inverting inputs: when the voltage at the inverting input (i.e., the DC voltage output by the phase voltage sampling module) is less than the reference voltage at the non-inverting input, comparator U2 outputs a high level. At this time, due to the pull-up effect of the fifteenth resistor R15, the output will show a high-level signal close to the first voltage VCC. When the voltage at the inverting input is greater than the reference voltage at the non-inverting input, comparator U2 outputs a low level. At this time, the voltage at the output of comparator U2 is close to ground potential.

[0078] Figure 5 This is a schematic diagram of another three-phase mains voltage detection circuit provided in this embodiment of the utility model, as shown below. Figure 5 As shown, optionally, the switching module 11 includes a first transistor T1. The first electrode of the first transistor T1 serves as the first terminal of the switching module 11, the second electrode of the first transistor T1 serves as the second terminal of the switching module 11, and the gate of the first transistor T1 serves as the control terminal of the switching module 11.

[0079] The three-phase grid voltage detection circuit also includes a current-limiting resistor LR1, which is connected between the output terminal of the phase voltage sampling module 13 and the first terminal of the switching module 11.

[0080] Specifically, the first transistor T1 can be a field-effect transistor (such as a MOSFET) or a transistor, or other devices with switching characteristics. For example, the first transistor T1 is an N-channel MOSFET. By applying a suitable voltage signal to the gate of the first transistor T1, the on and off states of the first transistor T1 can be controlled. When the gate voltage meets the on-condition, the first transistor T1 is turned on, forming a path between the first and second terminals of the switching module 11; when the gate voltage does not meet the on-condition, the first transistor T1 is turned off, disconnecting the first and second terminals of the switching module 11.

[0081] A current-limiting resistor LR1 is connected between the output terminal of the phase voltage sampling module 13 and the first terminal of the switching module 11. The signal output by the phase voltage sampling module 13 may experience voltage fluctuations or excessive current. Directly connecting it to the switching module 11 could damage the first transistor T1 in the switching module. The current-limiting resistor LR1 limits the current flowing through the circuit, ensuring it does not exceed the maximum current that the first transistor T1 can withstand, thus protecting the first transistor T1.

[0082] Figure 6 This is a schematic diagram of another three-phase mains voltage detection circuit provided in this embodiment of the utility model, as shown below. Figure 6 As shown, optionally, the three-phase grid voltage detection circuit also includes a second operational amplifier U3.

[0083] The non-inverting input of the second operational amplifier U3 is connected to the first terminal of the switching module 11, and the output of the second operational amplifier U3 is connected to the inverting input of the second operational amplifier U3 and the control module 12.

[0084] The output of the second operational amplifier U3 is connected to its own inverting input, forming a voltage follower (also known as a buffer) circuit structure. In a voltage follower, the output voltage changes with the input voltage and features high input impedance and low output impedance. The high input impedance means it draws very little current from the preceding circuit (switching module 11), having almost no impact on its operation; the low output impedance allows it to provide a large driving capability to the subsequent circuit (control module 12), ensuring a stable output voltage even with changes in the load of the subsequent circuit.

[0085] In the three-phase mains voltage detection circuit, the switching module 11 and the control module 12 have different electrical characteristics and operating requirements. The second operational amplifier U3, acting as a voltage follower, provides signal isolation, preventing the load characteristics of the control module 12 from affecting the output signal of the switching module 11 and ensuring stable operation of the switching module 11. Secondly, since the control module 12 may require a certain driving capability to correctly process the input signal, while the output signal of the switching module 11 may have limited driving capability, the low output impedance of the second operational amplifier U3 can provide sufficient drive current to the control module 12, ensuring that the signal can be accurately transmitted to the control module 12 for processing.

[0086] Figure 7 This is a schematic diagram of another three-phase mains voltage detection circuit provided in this embodiment of the utility model, as shown below. Figure 7 As shown, optionally, there are switch module 11, control module 12, three phase voltage sampling modules 13 and two comparison modules 14.

[0087] Optionally, the phase voltage sampling module 13 includes a step-down unit 131, a first filter unit 132, an amplification unit 133, a second filter unit 134, and a rectification unit 135.

[0088] Optionally, the step-down unit 131 includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, and a first capacitor C1.

[0089] Optionally, the amplification unit 133 includes a first operational amplifier U1, a seventh resistor R7, an eighth resistor R8, a first filter capacitor FC1, and a second filter capacitor FC2. Optionally, the amplification unit 133 also includes a first clamping diode CD1 and a second clamping diode CD2.

[0090] Optionally, the second filter unit 134 includes a ninth resistor R9 and a third capacitor C3. Optionally, the rectifier unit 135 includes a first diode D1, a tenth resistor R10, and a fourth capacitor C4.

[0091] Optionally, the rectifier unit 135 includes a first diode D1, a tenth resistor R10, and a fourth capacitor C4. Optionally, the comparator module 14 includes an eleventh resistor R11, a twelfth resistor R12, a thirteenth resistor R13, a fourteenth resistor R14, a fifteenth resistor R15, a comparator U2, a fifth capacitor C5, a second diode D2, and a third diode D3. Optionally, the switch module 11 includes a first transistor T1. The three-phase mains voltage detection circuit also includes a current-limiting resistor LR1. Optionally, the three-phase mains voltage detection circuit also includes a second operational amplifier U3.

[0092] refer to Figure 7 The working principle of this three-phase mains voltage detection circuit is as follows:

[0093] Using the control line reference ground as the neutral point of the three-phase power supply A / B / C, a phase voltage sampling module 13 is added to each phase, and the phase voltage sampling module 13 of each phase is the same; the signal sampled by the phase voltage sampling module 13 of phase A is used for high and low grid voltage detection and phase loss detection of phase A, and the signals sampled by the phase voltage sampling modules 13 of phases B and C are used for phase loss detection processing of phases B and C.

[0094] A series resistors R1, R2, R3, R4, and C1 are introduced between phase A and the control line reference ground for isolation and voltage reduction (the first capacitor C1 acts as an isolation device between the power grid and control module 12, therefore a Y1-grade safety capacitor is required). The first AC voltage across the fourth resistor R4 is passed through a low-pass filter composed of the sixth resistor R6 and the second capacitor C2 to remove high-frequency noise. The filtered first AC signal is amplified into a second AC voltage by an amplifier circuit composed of the first operational amplifier U1, the seventh resistor R7, and the eighth resistor R8. The amplified first AC voltage (i.e., the second AC voltage) is then passed through a low-pass filter composed of the ninth resistor R9 and the third capacitor C3 to remove high-frequency noise. The filtered second AC voltage is then passed through a peak sampling circuit composed of the first diode D1 and the fourth capacitor C4 to obtain a stable DC voltage signal, the DC voltage value of which is close to the peak value of the first AC voltage signal (the tenth resistor R10 is the discharge resistor of the peak sampling circuit).

[0095] The B-phase voltage sampling module 13 and the C-phase voltage sampling module 13 operate on the same principle as the A-phase voltage sampling module 13. After processing, the DC voltage signal passes through the comparison module 14. If there is voltage input in phase B, the comparator U2 outputs a low level; if there is no voltage in phase B, the comparator U2 outputs a high level.

[0096] The signal output from comparator U2 controls the first transistor T1 via the third diode D3. When there is voltage in phase B, the first transistor T1 is turned off, and the output voltage Vo is the DC voltage output by the phase A voltage sampling module 13. The control module 12 determines whether there is undervoltage or overvoltage based on the magnitude of this DC voltage. When there is no voltage in phase B, the first transistor T1 is turned on, and the output voltage Vo is 0V. The control module 12 determines that a phase is missing. The processing logic of the output of the phase C comparator module 14 on the first transistor T1 is the same as that of phase B. When the control module 12 determines that there is undervoltage, overvoltage, or phase loss, it will shut down the inverter drive, shut down the welding machine output, and display an alarm on the display panel.

[0097] The relationship between the effective value of the input line voltage and the output voltage is: Vo = K * Vin - V D1 ;

[0098] Where K is the conversion coefficient, V D1 This is the voltage drop across the first diode, D1.

[0099]

[0100] Where ω represents the angular frequency of the AC signal, r1 represents the resistance of the first resistor R1, r2 represents the resistance of the second resistor R2, r3 represents the resistance of the third resistor R3, r4 represents the resistance of the fourth resistor R4, r5 represents the resistance of the fifth resistor R5, r7 represents the resistance of the seventh resistor R7, r8 represents the resistance of the eighth resistor R8, and XC1 represents the capacitance of the first capacitor C1.

[0101] Set the normal input line voltage range Vin min <Vin<Vin max The corresponding output voltage range is K*Vin min <Vo<K*Vin max Among them, Vin min Vin represents the minimum line voltage. max This represents the maximum value of the line voltage.

[0102] When the output voltage Vo <K*Vin min The timing control module 12 determines that there is an undervoltage condition; when the output voltage Vo > K*Vin max When the output voltage Vo = 0V, the control module 12 determines that the voltage is overvoltage; when the output voltage Vo = 0V, the control module 12 determines that the voltage is missing a phase.

[0103] Based on the same inventive concept, this utility model also provides a welding machine, including the three-phase grid voltage detection circuit provided in any embodiment of this utility model, which has the corresponding functional modules and beneficial effects of the three-phase grid voltage detection circuit, and will not be described again in this embodiment.

[0104] The specific embodiments described above do not constitute a limitation on the scope of protection of this utility model. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this utility model should be included within the scope of protection of this utility model.

Claims

1. A three-phase mains voltage detection circuit, characterized in that, include: The system includes a switching module, a control module, a three-phase voltage sampling module, and two comparison modules. The input terminal of each phase voltage sampling module is connected to one phase AC input terminal of the three-phase AC power of the power grid under test. The output terminal of one phase voltage sampling module is connected to the first terminal of the switch module and the control module. The output terminals of the other two phase voltage sampling modules are connected to the first input terminal of the comparison module. The phase voltage sampling module is used to sample the phase voltage of the three-phase AC power of the power grid under test and convert the phase voltage into DC voltage. The second input terminal of the comparison module is connected to a first voltage, and the comparison module is used to output a first level signal through the comparison output terminal when the DC voltage is greater than the first voltage. And when the DC voltage is less than the first voltage, a second level signal is output through the comparison output terminal; The control terminal of the switch module is connected to the comparison output terminal, and the second terminal of the switch module is grounded to turn off in response to the first level signal, so as to input the DC voltage to the control module; And to conduct in response to the second level signal to input the ground voltage to the control module; The control module is used to determine whether the three-phase AC power of the tested power grid is under-voltage or over-voltage based on the DC voltage, and to determine whether the three-phase AC power of the tested power grid is missing a phase based on the grounding voltage.

2. The three-phase mains voltage detection circuit according to claim 1, characterized in that, The phase voltage sampling module includes a step-down unit, a first filter unit, an amplification unit, a second filter unit, and a rectification unit; The input terminal of the step-down unit serves as the input terminal of the phase voltage sampling module, used to convert the phase voltage into a first AC voltage; The input terminal of the first filtering unit is connected to the output terminal of the step-down unit, and the first filtering unit is used to filter out high-frequency noise on the first AC voltage. The input terminal of the amplification unit is connected to the output terminal of the first filtering unit, and the amplification unit is used to amplify the first AC voltage into a second AC voltage. The input terminal of the second filtering unit is connected to the output terminal of the amplification unit, and the second filtering unit is used to filter out high-frequency noise on the second AC voltage; The input terminal of the rectifier unit is connected to the output terminal of the second filter unit, and the output terminal of the rectifier unit serves as the output terminal of the phase voltage sampling module. The rectifier unit is used to convert the second AC voltage into the DC voltage.

3. The three-phase mains voltage detection circuit according to claim 2, characterized in that, The step-down unit includes a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, and a first capacitor; The first resistor, the second resistor, the third resistor, the fourth resistor, and the first capacitor are connected in series. The first end of the first resistor serves as the input terminal of the step-down unit, and the second end of the first capacitor serves as the output terminal of the step-down unit. The first end of the fifth resistor is connected to the second end of the first capacitor, and the second end of the fifth resistor is grounded.

4. The three-phase mains voltage detection circuit according to claim 2, characterized in that, The first filter unit includes a sixth resistor and a second capacitor; The first end of the sixth resistor serves as the input end of the first filter unit, and the second end of the sixth resistor is connected to the first end of the second capacitor and serves as the output end of the first filter unit. The second terminal of the second capacitor is grounded.

5. The three-phase mains voltage detection circuit according to claim 2, characterized in that, The amplification unit includes a first operational amplifier, a seventh resistor, an eighth resistor, a first filter capacitor, and a second filter capacitor; The non-inverting input terminal of the first operational amplifier serves as the input terminal of the amplification unit. The first power supply terminal of the first operational amplifier is connected to the first voltage, the second power supply terminal of the first operational amplifier is connected to the second voltage, and the output terminal of the first operational amplifier serves as the output terminal of the amplification unit. The first terminal of the seventh resistor is grounded, the second terminal of the seventh resistor is connected to the inverting input terminal of the first operational amplifier and the first terminal of the eighth resistor, and the second terminal of the eighth resistor is connected to the output terminal of the first operational amplifier. The first end of the first filter capacitor is connected to the first power supply terminal of the first operational amplifier, and the second end of the first filter capacitor is grounded. The first end of the second filter capacitor is connected to the second power supply terminal of the first operational amplifier, and the second end of the second filter capacitor is grounded.

6. The three-phase mains voltage detection circuit according to claim 2, characterized in that, The second filter unit includes a ninth resistor and a third capacitor; The first end of the ninth resistor serves as the input end of the second filter unit, and the second end of the ninth resistor is connected to the first end of the third capacitor and serves as the output end of the second filter unit. The second terminal of the third capacitor is grounded.

7. The three-phase mains voltage detection circuit according to claim 2, characterized in that, The rectifier unit includes a first diode, a tenth resistor, and a fourth capacitor; The anode of the first diode serves as the input terminal of the rectifier unit, and the cathode of the first diode is connected to the first terminal of the tenth resistor and the first terminal of the fourth capacitor. The second terminal of the tenth resistor and the second terminal of the fourth capacitor are grounded.

8. The three-phase mains voltage detection circuit according to claim 1, characterized in that, The comparison module includes an eleventh resistor, a twelfth resistor, a thirteenth resistor, a fourteenth resistor, a fifteenth resistor, a comparator, a fifth capacitor, a second diode, and a third diode; The first end of the eleventh resistor serves as the first input terminal of the comparison module, and the second end of the eleventh resistor is connected to the inverting input terminal of the comparator. The first end of the twelfth resistor serves as the second input terminal of the comparator module, and the second end of the twelfth resistor is connected to the non-inverting input terminal of the comparator, the first end of the thirteenth resistor, the fifth capacitor, and the cathode of the second diode. The second terminal of the thirteenth resistor is grounded, and the second terminal of the fifth capacitor is grounded. The first end of the fourteenth resistor is connected to the anode of the second diode, and the second end of the fourteenth resistor is connected to the output terminal of the comparator, the first end of the fifteenth resistor, and the anode of the third diode. The second terminal of the fifteenth resistor is connected to the first voltage, and the cathode of the third diode serves as the comparison output terminal of the comparison module.

9. The three-phase mains voltage detection circuit according to claim 1, characterized in that, The switching module includes a first transistor; The first electrode of the first transistor serves as the first terminal of the switching module, the second electrode of the first transistor serves as the second terminal of the switching module, and the gate of the first transistor serves as the control terminal of the switching module. The three-phase grid voltage detection circuit also includes a current-limiting resistor, which is connected between the output terminal of the phase voltage sampling module and the first terminal of the switching module.

10. The three-phase mains voltage detection circuit according to claim 1, characterized in that, It also includes a second operational amplifier; The non-inverting input of the second operational amplifier is connected to the first terminal of the switching module, and the output of the second operational amplifier is connected to the inverting input of the second operational amplifier and the control module.

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