Three-phase four-wire zero line missing detection circuit and method, power supply, electric energy meter and acquisition terminal
By designing a three-phase four-wire neutral wire missing detection circuit and monitoring the conduction status of the neutral wire path diode, the problems of complexity and susceptibility to interference in existing detection schemes are solved, realizing simple and reliable neutral wire missing detection and improving the system's stability and anti-interference capability.
Patent Information
- Application Number
- CN202511646002.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-11
- Publication Date
- 2026-02-27
AI Technical Summary
The existing neutral wire missing detection scheme in a three-phase four-wire power supply system is complex and easily affected by leakage current interference, leading to misjudgment or inaccurate detection results.
Design a three-phase four-wire neutral wire missing detection circuit, including a three-phase bridge rectifier circuit, a filter capacitor, a half-voltage power supply unit, a neutral wire power supply unit, and a neutral wire missing detection circuit. The circuit achieves simple detection by monitoring the conduction state of the neutral wire path diode, avoiding direct sampling of the three-phase AC voltage.
It achieves simple and reliable zero-line detection, improves the signal-to-noise ratio and anti-interference capability of detection, reduces the performance requirements of the processor, and enhances the stability and robustness of the system.
Smart Images
Figure CN121577983A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of circuit electronics, and in particular to a three-phase four-wire zero-line detection circuit, method, power supply, electric energy meter and acquisition terminal. BACKGROUND
[0002] The zero line in a three-phase four-wire power supply system is crucial, and once the zero line is disconnected, it can cause damage to equipment and even safety accidents. Therefore, it is of great significance to reliably detect the missing zero line in a three-phase four-wire power supply system.
[0003] In the case of a three-phase four-wire missing zero line, the internal voltage sampling circuit of the voltage-dependent resistor and the measurement circuit will generate a weak leakage current. Although these leakage currents may not be easily detected under normal operating conditions, they can cause interference to the detection circuit when a zero-line fault occurs, resulting in misjudgment or inaccuracy of the detection results. In order to cope with such interference and achieve reliable detection, existing three-phase four-wire zero-line detection schemes are often complex. SUMMARY
[0004] The present application provides a three-phase four-wire zero-line detection circuit, method, power supply, electric energy meter and acquisition terminal to solve the defect that the existing three-phase four-wire zero-line detection scheme is complex, and to achieve simple three-phase four-wire zero-line detection.
[0005] The present application provides a three-phase four-wire zero-line detection circuit, comprising: a three-phase bridge rectifier circuit having three AC input terminals, a DC positive output terminal and a DC negative output terminal, the three AC input terminals being connected to the A, B and C phases of a three-phase AC power supply, respectively; a first filter capacitor connected in parallel between the DC positive output terminal and the DC negative output terminal of the three-phase bridge rectifier circuit; a half-voltage power supply unit, the first input terminal of the half-voltage power supply unit being connected to the DC positive output terminal of the three-phase bridge rectifier circuit, and the second input terminal of the half-voltage power supply unit being connected to the DC negative output terminal of the three-phase bridge rectifier circuit; a first rectifier diode, the anode of the first rectifier diode being connected to the output terminal of the half-voltage power supply unit, and the cathode of the first rectifier diode being connected to a common power supply node; an input buffer capacitor, the positive electrode of the input buffer capacitor being connected to the common power supply node, and the negative electrode of the input buffer capacitor being connected to the DC negative output terminal of the three-phase bridge rectifier circuit; a DC-DC isolation power supply connected in parallel across the input buffer capacitor; The zero line power supply unit comprises a zero line current limiting resistor, a zero line passage diode and a second rectifier diode connected in series, one end of the zero line current limiting resistor is connected to a zero line, and a cathode of the second rectifier diode is connected to the common power supply node; The zero line detection circuit is connected in parallel between two ends of the zero line passage diode, and is used for detecting a connection state of the zero line.
[0006] In some embodiments, the zero line detection circuit comprises: A first current limiting resistor, one end of the first current limiting resistor is connected to an anode of the zero line passage diode; A protection diode, a cathode of the protection diode is connected to a cathode of the zero line passage diode; An optoelectronic coupler, an anode of a light emitting diode of the optoelectronic coupler is connected to the other end of the first current limiting resistor, a cathode of the light emitting diode is connected to an anode of the protection diode, and a collector of a light sensitive transistor of the optoelectronic coupler is connected to a power supply voltage end; A first bias resistor connected between an emitter of the light sensitive transistor and a reference potential end; A signal shaping unit, used for shaping an output signal of the light sensitive transistor into a digital signal with high and low levels, an input end of the signal shaping unit is connected to the emitter of the light sensitive transistor, an output end of the signal shaping unit is a detection output end, used for outputting a zero line detection result, a power supply voltage connection end of the signal shaping unit is connected to the power supply voltage end, and a reference potential connection end of the signal shaping unit is connected to the reference potential end.
[0007] In some embodiments, the signal shaping unit comprises: A delay capacitor connected in parallel between the input end of the signal shaping unit and the reference potential end; A second current limiting resistor, one end of the second current limiting resistor is connected to the input end of the signal shaping unit; A first transistor, a base of the first transistor is connected to the other end of the second current limiting resistor, and an emitter of the first transistor is connected to the reference potential end; A second bias resistor, one end of the second bias resistor is connected to the power supply voltage end, and the other end of the second bias resistor is connected to a collector of the first transistor; A second filter capacitor connected in parallel between the collector of the first transistor and the reference potential end; The detection output end is connected to the collector of the first transistor.
[0008] In some embodiments, the half voltage power supply unit comprises: A first voltage dividing resistor, one end of the first voltage dividing resistor serving as a first input end of the half voltage supply unit, the other end of the first voltage dividing resistor being connected to a voltage dividing node; A second voltage dividing resistor, one end of the second voltage dividing resistor being connected to the voltage dividing node, the other end of the second voltage dividing resistor serving as a second input end of the half voltage supply unit; A second transistor, a source of the second transistor being connected to the first input end of the half voltage supply unit, a gate of the second transistor being connected to the voltage dividing node, a drain of the second transistor serving as an output end of the half voltage supply unit; A feedback resistor, one end of the feedback resistor being connected to the drain of the second transistor, the other end of the feedback resistor being connected to the voltage dividing node.
[0009] In some embodiments, further comprising: Three current limiting resistors, respectively connecting A phase, B phase and C phase of the three-phase alternating current power supply to respective alternating current input ends of the three-phase bridge rectifier circuit.
[0010] In some embodiments, further comprising: Three thermistors, respectively connected in parallel between A phase, B phase and C phase of the three-phase alternating current power supply and the neutral line.
[0011] The present application also provides a three-phase four-wire zero-line detection method based on the three-phase four-wire zero-line detection circuit according to any one of the above, comprising: Obtaining a level signal output by the three-phase four-wire zero-line detection circuit; According to the level signal, determining the connection state of the zero line.
[0012] The present application also provides a power supply comprising the three-phase four-wire zero-line detection circuit according to any one of the above.
[0013] The present application also provides an electric energy meter comprising the three-phase four-wire zero-line detection circuit according to any one of the above.
[0014] The present application also provides a collection terminal comprising the three-phase four-wire zero-line detection circuit according to any one of the above.
[0015] The three-phase four-wire zero-line detection circuit, method, power supply, electric energy meter and collection terminal provided by the present application can directly determine the connection state of the zero line by detecting the voltage across the zero-line path diode when the zero line is normal, and by detecting the voltage across the zero-line path diode when the zero line is missing, thereby achieving simple three-phase four-wire zero-line detection. BRIEF DESCRIPTION OF DRAWINGS
[0016] In order to make the technical solutions in the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and based on these drawings, the ordinary skilled in the art can obtain other drawings without creative effort.
[0017] Figure 1 is one of the structural schematic diagrams of the three-phase four-wire zero-line missing detection circuit provided by the embodiments of the present application.
[0018] Figure 2 is another structural schematic diagram of the three-phase four-wire zero-line missing detection circuit provided by the embodiments of the present application.
[0019] Figure 3 is a structural schematic diagram of the zero-line missing detection circuit provided by the embodiments of the present application.
[0020] Figure 4 is a structural schematic diagram of the half-voltage power supply unit provided by the embodiments of the present application.
[0021] Figure 5 is a flow schematic diagram of the three-phase four-wire zero-line missing detection method provided by the embodiments of the present application. DETAILED DESCRIPTION
[0022] In order to make the technical solutions in the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and based on these drawings, the ordinary skilled in the art can obtain other drawings without creative effort.
[0023] Figure 1 is one of the structural schematic diagrams of the three-phase four-wire zero-line missing detection circuit provided by the embodiments of the present application, as Figure 1 indicated, the embodiments of the present application provide a three-phase four-wire zero-line missing detection circuit, which comprises a three-phase bridge rectifier circuit, a first filter capacitor C1, a half-voltage power supply unit, a first rectifier diode D5, an input buffer capacitor C2, a DC-DC isolation power supply, a zero-line power supply unit, and a zero-line missing detection circuit.
[0024] The three-phase bridge rectifier circuit has three-way AC input terminals, a DC positive output terminal, and a DC negative output terminal. The three-way AC input terminals are connected to phase A, phase B, and phase C of a three-phase AC power supply, respectively. The first filter capacitor C1 is connected in parallel between the DC positive output terminal and the DC negative output terminal of the three-phase bridge rectifier circuit.
[0025] The first input end of the half-voltage power supply unit is connected to the direct current positive output end of the three-phase bridge rectifier circuit, and the second input end of the half-voltage power supply unit is connected to the direct current negative output end of the three-phase bridge rectifier circuit. The anode of the first rectifier diode D5 is connected to the output end of the half-voltage power supply unit, and the cathode of the first rectifier diode D5 is connected to a common power supply node. The positive pole of the input buffer capacitor C2 is connected to the common power supply node, and the negative pole of the input buffer capacitor C2 is connected to the direct current negative output end of the three-phase bridge rectifier circuit. The DC-DC isolation power supply is connected in parallel between the positive and negative poles of the input buffer capacitor C2.
[0026] The zero line power supply unit comprises a zero line current limiting resistor R1, zero line pass diodes (i.e. diodes D1, D2 and D3) and a second rectifier diode D4 connected in series, one end of the zero line current limiting resistor R1 is connected to a zero line, and the cathode of the second rectifier diode D4 is connected to a common power supply node. The lack of zero line detection circuit is connected in parallel between the two ends of the zero line pass diodes D1, D2 and D3, and is used for detecting the connection state of the zero line.
[0027] Specifically, the present application provides a three-phase four-wire zero line detection circuit, which is designed to obtain energy from a three-phase alternating current power supply and provide a stable isolated direct current power supply, while having the ability to monitor the connection state of the zero line in real time. The circuit mainly comprises a three-phase alternating current input and rectification filtering part, a common power supply node forming part, a DC-DC isolation power supply and a zero line detection part.
[0028] The three-phase alternating current input and rectification filtering part is used for converting an external three-phase alternating current power supply into a pulsating direct current voltage and performing preliminary filtering. The part receives A-phase, B-phase and C-phase inputs from an external three-phase alternating current power supply. The three-phase inputs are respectively connected to the three-way alternating current input ends of the three-phase bridge rectifier circuit. The three-phase bridge rectifier circuit rectifies the three-phase alternating current into a pulsating direct current voltage.
[0029] Figure 2 is a structural schematic diagram of the three-phase four-wire zero line detection circuit provided by the embodiment of the present application, as Figure 2 shown, the three-phase bridge rectifier circuit composed of 12 diodes is composed of two independent, standard three-phase full-wave bridge rectifiers, and each three-phase full-wave bridge rectifier contains 6 diodes.
[0030] Each rectifier circuit is a standard three-phase full-wave bridge rectifier composed of 6 diodes. The first bridge rectifier is connected to the first set of three-phase voltages output by the phase-shifting transformer. The second bridge rectifier is connected to the second set of three-phase voltages output by the phase-shifting transformer (with a 30-degree phase difference from the first set).
[0031] The first filter capacitor C1 is connected in parallel between the DC positive output end and the DC negative output end of the three-phase bridge rectifier circuit. The main function of the first filter capacitor C1 is to filter and smooth the pulsed DC voltage after rectification, so as to form a relatively stable DC bus voltage as the energy source for the subsequent circuit.
[0032] In order to ensure the stability and redundancy of the DC-DC isolated power supply, the present application supplies power to the DC-DC isolated power supply through two independent power supply circuits. The two circuits are zero line power supply path and half voltage power supply path, which form an "or" gate structure through the second rectifier diode D4 and the first rectifier diode D5. The system will preferentially select the circuit with higher voltage to supply power to the DC-DC isolated power supply.
[0033] The zero line power supply unit is used to obtain energy from the external zero line. The zero line power supply unit includes a zero line current limiting resistor R1, zero line path diodes D1, D2, D3 and a second rectifier diode D4. One end of the zero line current limiting resistor R1 is connected to the external zero line for limiting the current in the zero line path. The zero line current limiting resistor R1, the zero line path diodes D1, D2, D3 and the second rectifier diode D4 are connected in series, and the cathode of the second rectifier diode D4 is connected to the common power supply node (i.e. the positive side of the input buffer capacitor C2), which is combined with the cathode of the first rectifier diode D5.
[0034] It should be noted that the number of zero line path diodes can be determined according to the actual required conduction voltage drop, Figure 1 The zero line path diodes D1, D2 and D3 are only an example. When the conduction voltage drop of a zero line path diode can meet the actual required conduction voltage drop, the number of zero line path diodes can be one. When the conduction voltage drop of a zero line path diode cannot meet the actual required conduction voltage drop, the number of zero line path diodes can be multiple, and the multiple zero line path diodes are connected in series.
[0035] When the external zero line is connected normally, the zero line power supply unit forms a rectifier circuit with the A phase, B phase and C phase of the three-phase alternating current power supply through the corresponding diodes in the three-phase bridge rectifier circuit. In this case, one end of the zero line current limiting resistor R1 is connected to the external zero line. After rectification, the voltage at the common power supply node is about times the phase voltage.
[0036] The half voltage power supply unit obtains energy from the full DC bus voltage generated by the three-phase bridge rectifier circuit. The first input end of the half voltage power supply unit is connected to the DC positive output end of the three-phase bridge rectifier circuit (i.e. the positive end of the first filter capacitor C1), and the second input end of the half voltage power supply unit is connected to the DC negative output end of the three-phase bridge rectifier circuit (i.e. the negative end of the first filter capacitor C1). The output end of the half voltage power supply unit is connected to the anode of the first rectifier diode D5, and the cathode of the first rectifier diode D5 is connected to the common power supply node.
[0037] If the A phase, B phase and C phase of the three-phase AC power supply pass through the three-phase bridge rectifier circuit to form a rectifier circuit. In this case, after rectification by the three-phase bridge rectifier circuit, the voltage across the first filter capacitor C1 is about times the phase voltage. The half voltage power supply unit reduces this voltage by half, and after processing, the anode of the first rectifier diode D5 will obtain a voltage of about times the phase voltage.
[0038] Since the times phase voltage provided by the zero line power supply path is significantly higher than the times phase voltage provided by the half voltage power supply path, in the case of normal connection of the zero line, the system will preferentially select the energy provided by the rectifier circuit composed of the zero line and the A phase, B phase and C phase, and supply power to the DC-DC isolated power supply through the second rectifier diode D4. At this time, the second rectifier diode D4 is turned on, and the first rectifier diode D5 is in reverse bias or non-conducting state.
[0039] The positive electrode of the input buffer capacitor C2 is connected to the common power supply node, and the negative electrode of the input buffer capacitor C2 is connected to the DC negative output end of the three-phase bridge rectifier circuit (i.e. GND). The input buffer capacitor C2 plays a further filtering and smoothing role here, ensuring a stable, low ripple DC input voltage for the subsequent DC-DC isolated power supply, and being able to provide a large current required at the moment to prevent input voltage drop.
[0040] The DC-DC isolated power supply is connected in parallel across the positive and negative terminals of the input buffer capacitor C2. The DC-DC isolated power supply is responsible for converting the input DC voltage into the required stable DC output voltage, and providing electrical isolation. Electrical isolation is crucial for improving the safety of the system, suppressing common mode noise and protecting operating personnel.
[0041] The zero-line missing detection circuit can monitor the connection state of the external zero line in real time. The zero-line missing detection circuit is connected in parallel between the two ends of the zero-line passage diodes D1, D2 and D3. In the case that the zero line exists, the zero-line power supply passage preferentially supplies power to the common power supply node. At this time, the zero-line passage diodes D1, D2 and D3, as part of the zero-line power supply unit, have current flowing therethrough and are normally turned on. When the zero-line passage diodes D1, D2 and D3 are turned on, a forward conduction voltage drop is generated between the two ends thereof. The zero-line missing detection circuit detects the voltage between the two ends of the zero-line passage diodes D1, D2 and D3, and if the voltage is detected, it is confirmed that the zero line is normally connected.
[0042] In the case that the zero line is missing, the zero-line power supply passage is interrupted, and no current flows therethrough. The energy required by the DC-DC isolated power supply can only be provided through the half-voltage power supply passage, that is, the rectifier circuit composed of the A phase, the B phase and the C phase is supplied with power through the half-voltage power supply unit and the first rectifier diode D5. Since no current exists in the zero-line circuit, the zero-line passage diodes D1, D2 and D3 are in the off state, and there is almost no voltage (close to 0V) between the two ends thereof. The zero-line missing detection circuit detects the voltage between the two ends of the zero-line passage diodes, and if the voltage is not detected, it is determined that the zero line is missing or abnormally connected.
[0043] The three-phase four-wire zero-line missing detection circuit provided by the embodiment of the present application has the zero-line passage diodes turned on when the zero line is normal, and the zero-line passage diodes turned off when the zero line is missing. Therefore, by detecting the voltage between the two ends of the zero-line passage diodes, the connection state of the zero line can be directly determined, thereby achieving simple three-phase four-wire zero-line missing detection.
[0044] In addition, there is a great difference in the voltage between the two ends of the zero-line passage diodes in the case that the zero line is normal and the case that the zero line is missing. This significant voltage difference provides a very high signal-to-noise ratio and a clear judgment threshold for detection, so that the circuit can accurately distinguish between the two working conditions, effectively avoids misjudgment caused by voltage fluctuation or critical state, and thus ensures the high reliability of the detection result.
[0045] The detection principle of the present application does not depend on direct sampling of the three-phase alternating voltage. The accuracy of the traditional voltage sampling algorithm is easily affected by the leakage current of the voltage-sensitive resistor connected in parallel at the alternating current input end or the voltage division effect of other parallel voltage sampling circuits. The present application monitors an independent, low-power direct current signal passage, fundamentally avoids these interference sources, and ensures the purity and accuracy of the detection and outstanding anti-interference ability.
[0046] The whole detection process is automatically completed by the hardware circuit, and does not need to rely on the software algorithm. This not only guarantees the extremely fast real-time response speed, but also releases the main processor from the complex real-time sampling and algorithm operation, greatly reduces the requirement for the processor performance and the complexity of software development. More importantly, the detection function is independent of the software running state, and the stability and robustness of the whole system are improved.
[0047] In some embodiments, as shown in Figure 2 The three-phase four-wire zero-line missing detection circuit provided by the embodiment of the present application further includes three current limiting resistors R2, R3 and R4. The three current limiting resistors R2, R3 and R4 are respectively connected to the A phase, B phase and C phase of the three-phase alternating current power supply to the respective alternating current input end of the three-phase bridge rectifier circuit.
[0048] Specifically, the A phase, B phase and C phase of the three-phase alternating current power supply first pass through the respective current limiting resistors R2, R3 and R4. The role of these resistors is to limit the current input to the three-phase bridge rectifier circuit, especially at the moment of power connection or when a short circuit fault occurs, to protect the diodes and other downstream elements of the three-phase bridge rectifier circuit. The three-phase alternating current after passing through the current limiting resistors R2, R3 and R4 is then input to the three-phase bridge rectifier circuit.
[0049] The three-phase bridge rectifier circuit converts the three-phase alternating current into pulsating direct current, and then the direct current voltage is filtered and smoothed by the first filter capacitor C1 connected in parallel between the direct current positive output end and the direct current negative output end, to form a relatively stable main direct current bus voltage.
[0050] The three-phase four-wire zero-line missing detection circuit provided by the embodiment of the present application realizes the protection of the diodes and other downstream elements of the three-phase bridge rectifier circuit through the three current limiting resistors R2, R3 and R4.
[0051] In some embodiments, as shown in Figure 2 The three-phase four-wire zero-line missing detection circuit provided by the embodiment of the present application further includes three current limiting resistors R2, R3 and R4. The three current limiting resistors R2, R3 and R4 are respectively connected to the A phase, B phase and C phase of the three-phase alternating current power supply to the respective alternating current input end of the three-phase bridge rectifier circuit.
[0052] Specifically, the three-way thermistor RT1, RT2 and RT3 are connected in parallel between the A phase, B phase and C phase of the three-phase alternating current power supply and the zero line respectively. These thermistors are usually used to provide overcurrent protection or overheat protection here. For example, when the thermistor is a positive temperature coefficient thermistor, the resistance value of the thermistor will increase sharply when the circuit is overloaded or short-circuited, causing excessive current and self-heating, thereby limiting the current and playing a protective role; or the thermistor acts as a temperature sensor to monitor the temperature at the connection point of the phase line and the zero line, preventing local overheating caused by poor connection or abnormal load. They together improve the safety and reliability of the input power line.
[0053] The three-phase four-wire zero-line detection circuit provided by the embodiment of the present application provides overcurrent protection or overheat protection through the three-way thermistor RT1, RT2 and RT3.
[0054] In some embodiments, Figure 3 is a structural schematic diagram of the zero-line detection circuit provided by the embodiment of the present application, as Figure 3 shown, the zero-line detection circuit includes a first current-limiting resistor R5, a protection diode D6, an optoelectronic coupler OP1, a first bias resistor R6 and a signal shaping unit.
[0055] One end of the first current-limiting resistor R5 is connected to the anode of the zero-line passage diode D1, and the cathode of the protection diode D6 is connected to the cathode of the zero-line passage diode D3 The anode of the light-emitting diode of the optoelectronic coupler OP1 is connected to the other end of the first current-limiting resistor R5, the cathode of the light-emitting diode is connected to the anode of the protection diode D6, the collector of the light-sensitive transistor of the optoelectronic coupler OP1 is connected to the power supply voltage end, and the first bias resistor R6 is connected between the emitter of the light-sensitive transistor and the reference potential end.
[0056] The signal shaping unit is used to shape the output signal of the light-sensitive transistor into a digital signal with high and low levels. The input end of the signal shaping unit is connected to the emitter of the light-sensitive transistor; the output end of the signal shaping unit is a detection output end for outputting the zero-line detection result; the power supply voltage connection end of the signal shaping unit is connected to the power supply voltage end; and the reference potential connection end of the signal shaping unit is connected to the reference potential end.
[0057] Specifically, one end of the first current-limiting resistor R5 is connected to the anode of the neutral line pass diode D1, the cathode of the protection diode D6 is connected to the cathode of the neutral line pass diode D3, the other end of the first current-limiting resistor R5 is connected to the anode of the light-emitting diode in the optocoupler OP1, and the cathode of the light-emitting diode is connected to the anode of the protection diode D6. At this point, the missing neutral line detection loop formed by the first current-limiting resistor R5, the light-emitting diode in the optocoupler OP1, and the protection diode D6 is connected in parallel across the neutral line pass diodes D1, D2, and D3, and is used to monitor the voltage change across the neutral line pass diodes. The turn-on threshold of the missing neutral line detection loop is the sum of the voltage drop across the first current-limiting resistor R5, the forward voltage drop of the light-emitting diode in the optocoupler OP1, and the forward voltage drop of the protection diode D6.
[0058] The collector of the phototransistor in the optocoupler OP1 is connected to the power supply voltage terminal VCC of the isolation power supply, and the first bias resistor R6 is connected between the emitter of the phototransistor and the reference potential terminal GND-MCU. When the light-emitting diode in the optocoupler OP1 emits light, the phototransistor turns on and the potential at its emitter rises; when it does not emit light, the phototransistor is cut off and the potential at its emitter is pulled low by the first bias resistor R6.
[0059] The core of the missing neutral line detection circuit is to accurately detect the voltage change across the neutral line pass diodes, and to use the optocoupler to achieve reliable signal isolation and output. The detection logic is based on the principle that the turn-on threshold of the missing neutral line detection loop is less than the forward conduction voltage drop of the neutral line pass diodes D1, D2, and D3.
[0060] When the neutral line is normally connected, the current flows through the neutral line current-limiting resistor R1, the neutral line pass diodes D1, D2, and D3, and the second rectifier diode D4 to the common power supply node. Therefore, the neutral line pass diodes D1, D2, and D3 are in a forward conduction state. The turn-on threshold of the missing neutral line detection loop is less than the forward conduction voltage drop of the neutral line pass diode D1. For example, the forward conduction voltage drop of the neutral line pass diodes D1, D2, and D3 is 2V, and the turn-on threshold of the missing neutral line detection loop is 1V.
[0061] Therefore, when the neutral line is normal, the sum of the forward conduction voltage drops of the neutral line pass diodes D1, D2, and D3 is sufficient to turn on the light-emitting diode inside the optocoupler OP1 to emit light, so that the phototransistor inside the optocoupler OP1 receives the light signal and quickly turns on (saturates). When the phototransistor turns on, the potential at its emitter will rise significantly (be pulled high, close to the power supply voltage terminal VCC). The signal shaping unit receives a high-level signal, indicating that the "neutral line is normal".
[0062] When the zero line is missing, the zero line pass diodes D1, D2, D3 no longer have current passing through, and the zero line pass diodes D1, D2, D3 are no longer in a forward conducting state. Thus, the light emitting diode inside the optocoupler OP1 is in a cut-off state. The emitter of the phototransistor is pulled low through the bias resistor R6, close to the reference potential end. The signal shaping unit receives a low level signal, indicating "zero line missing".
[0063] The three-phase four-wire zero line missing detection circuit provided by the embodiment of the present application realizes complete electrical isolation between the high-voltage main circuit and the low-voltage control circuit through the optocoupler, thereby greatly improving the safety and anti-interference ability of the entire system while ensuring high reliability of detection.
[0064] In some embodiments, as shown in FIG. 1, the signal shaping unit includes a delay capacitor C3, a second current limiting resistor R7, a first transistor Q1, a second bias resistor R8, and a second filter capacitor C4. Figure 3
[0065] The delay capacitor C3 is connected in parallel between the input end and the reference potential end of the signal shaping unit; one end of the second current limiting resistor R7 is connected to the input end of the signal shaping unit; the base of the first transistor Q1 is connected to the other end of the second current limiting resistor R7, and the emitter of the first transistor Q1 is connected to the reference potential end; one end of the second bias resistor R8 is connected to the power supply voltage end, and the other end of the second bias resistor R8 is connected to the collector of the first transistor Q1; the second filter capacitor C4 is connected in parallel between the collector of the first transistor Q1 and the reference potential end; and the detection output end is connected to the collector of the first transistor Q1.
[0066] Specifically, the input end of the signal shaping unit is connected to the emitter of the phototransistor of the optocoupler OP1. According to the conducting state of the optocoupler OP1, the input end will present a high level or a low level.
[0067] The delay capacitor C3 is connected in parallel between the input end and the reference potential end GND-MCU of the signal shaping unit. When the emitter potential of the phototransistor changes, the charging and discharging process of the delay capacitor C3 will introduce a certain delay, which is crucial for anti-interference and preventing false triggering during signal transients (such as switch transients or noise spikes), ensuring that the signal input to the subsequent transistor is stable for a certain time. At the same time, the delay capacitor C3 also plays a filtering role, smoothing the high-frequency noise in the input signal.
[0068] A second current-limiting resistor R7 is connected in series between the input terminal of the signal shaping unit and the base of the first transistor Q1. The second current-limiting resistor R7, together with the delay capacitor C3, forms an RC low-pass filter network to further smooth and delay the signal. More importantly, the second current-limiting resistor R7 also limits the current flowing into the base of the first transistor Q1, protecting the first transistor Q1 from overcurrent damage and providing a suitable bias condition for the first transistor Q1.
[0069] The first transistor Q1 is typically an NPN transistor configured as a common-emitter amplifier. When the opto-coupler OP1's photo transistor outputs a low level, indicating the absence of the neutral line, the input terminal of the signal shaping unit receives a low level signal, and the base current of the first transistor Q1 is insufficient to turn it on, leaving the first transistor Q1 in a cut-off state.
[0070] When the opto-coupler OP1's photo transistor outputs a high level, indicating the presence of the neutral line, the input terminal of the signal shaping unit (i.e., the base of the first transistor Q1 via the second current-limiting resistor R7) receives a high level signal. Through the current-limiting effect of the second current-limiting resistor R7, sufficient current flows into the base of the first transistor Q1, causing the first transistor Q1 to turn on and enter a saturated state.
[0071] Since the first transistor Q1 is configured as a common-emitter, the signal level at its output (collector) is inversely proportional to the signal level at its input (base). That is, a high input level results in a low output level, and a low input level results in a high output level.
[0072] The second bias resistor R8 is connected between the power supply voltage terminal VCC and the collector of the first transistor Q1, acting as a pull-up resistor. When the first transistor Q1 is in a cut-off state, its collector is pulled high by R8 to a potential close to the power supply voltage terminal VCC, forming a clear high level output. When the first transistor Q1 is turned on and saturated, its collector potential is pulled low to a potential close to the reference potential terminal GND-MCU, forming a clear low level output. The second bias resistor R8 ensures a stable high level at the output terminal when the first transistor Q1 is cut off.
[0073] The second filter capacitor C4 is connected in parallel between the collector of the first transistor Q1 and the reference potential terminal. The second filter capacitor C4 is used to filter out high-frequency noise and glitches in the output signal, smooth the transient voltage fluctuations that may occur during the switching process of the first transistor Q1, and ensure that the detection output terminal provides a pure and stable digital high-low level signal.
[0074] The detection output end is directly connected to the collector of the first transistor Q1. After the delay, filtering, inversion and shaping processing, the detection output end will provide a digital signal with clear and stable high and low levels, which can be directly used for judging the connection state of the zero line. For example, a low level is output when the zero line is normal, and a high level is output when the zero line is missing.
[0075] The three-phase four-wire zero-line detection circuit provided by the embodiment of the present application converts the original signal from the photoelectric coupler OP1, which is easy to be disturbed, into a logic perfect signal with anti-jitter, standard level and clean waveform through three steps of delay filtering, level shaping and output smoothing. This plays a decisive role in ensuring that the final decision of the entire zero-line detection system is not disturbed and misjudged, and is perfectly compatible with the digital system.
[0076] In some embodiments, Figure 4 is a structural schematic diagram of the half-voltage power supply unit provided by the embodiment of the present application, as Figure 4 shown, the half-voltage power supply unit comprises a first voltage dividing resistor R9, a second voltage dividing resistor R10, a second transistor Q2 and a feedback resistor R11.
[0077] One end of the first voltage dividing resistor R9 serves as a first input end of the half-voltage power supply unit, and the other end of the first voltage dividing resistor R9 is connected to a voltage dividing node; one end of the second voltage dividing resistor R10 is connected to the voltage dividing node, and the other end of the second voltage dividing resistor R10 serves as a second input end of the half-voltage power supply unit; the source of the second transistor Q2 is connected to the first input end of the half-voltage power supply unit, the gate of the second transistor Q2 is connected to the voltage dividing node, and the drain of the second transistor Q2 serves as an output end of the half-voltage power supply unit; one end of the feedback resistor R11 is connected to the drain of the second transistor Q2, and the other end of the feedback resistor R11 is connected to the voltage dividing node.
[0078] Specifically, the first input end of the half-voltage power supply unit is connected to the positive pole of the main DC bus voltage, and the second input end is connected to the negative pole of the main DC bus voltage, thereby providing an input voltage for the entire unit.
[0079] The first voltage dividing resistor R9 and the second voltage dividing resistor R10 are connected in series between the first input end and the second input end. The first voltage dividing resistor R9 and the second voltage dividing resistor R10 constitute a standard resistance voltage divider for generating a reference voltage at the voltage dividing node, which is approximately equal to half of the input voltage. If the resistance values of the first voltage dividing resistor R9 and the second voltage dividing resistor R10 are equal, the voltage at the voltage dividing node will be half of the input voltage. The voltage at this voltage dividing node serves as the reference input of the subsequent voltage stabilizing element. It should be noted that the first voltage dividing resistor R9 and the second voltage dividing resistor R10 can be composed of one resistor, or can be composed of multiple resistors in series or parallel.
[0080] The second transistor Q2 and the feedback resistor R11 together form an active voltage stabilizing and current amplifying circuit. The core function of this circuit is to replicate and amplify the driving capability of the voltage signal provided by the voltage dividing node, so as to output a stable half voltage.
[0081] The second transistor Q2 is a depletion mode N-channel field effect transistor. This type of transistor is in an on state when the gate-source voltage Vgs is zero. The source of the second transistor Q2 is connected to the first input (high potential), and the gate is connected to the voltage dividing node (intermediate potential) formed by the first voltage dividing resistor R9 and the second voltage dividing resistor R10. Since the gate potential is always lower than the source potential, the gate-source voltage Vgs is always negative. For a depletion mode N-channel MOSFET, a negative gate-source voltage Vgs puts it in a controllable on state, and its on resistance (or drain current) changes with the negative value of Vgs, which provides the physical basis for the voltage stabilizing function of the circuit.
[0082] The feedback resistor R11 is connected between the drain of the second transistor Q2 and the gate of the second transistor Q2, forming a negative feedback loop. This negative feedback mechanism ensures that the output voltage closely follows and stabilizes around the reference voltage point set by the voltage dividing network.
[0083] When the output voltage (drain voltage) tries to rise, the gate voltage of the second transistor Q2 will also be pulled up accordingly through the feedback effect of the feedback resistor R11. This will cause the negative value of the gate-source voltage Vgs to decrease (closer to zero), causing the on capability of the second transistor Q2 to increase (equivalent resistance decreases). The increased on capability will suppress the rise of the output voltage, thus pulling it back to the stable point.
[0084] When the output voltage (drain voltage) tries to decrease, the gate voltage of the second transistor Q2 will be pulled down accordingly through the feedback effect of the feedback resistor R11. This will cause the negative value of the gate-source voltage Vgs to increase, causing the on capability of the second transistor Q2 to weaken (equivalent resistance increases). The weakened on capability will raise the output voltage, thus resisting its downward trend.
[0085] At the same time, since field effect transistors have extremely high input impedance and relatively low output impedance, the half voltage supply unit can control a larger output current with almost zero input current. This means that it can obtain a voltage signal from a high-impedance voltage dividing node, and use the power energy from the source to reproduce a stable voltage with strong load driving capability at the drain, which is related to the reference voltage at the gate. This process essentially realizes the function of current amplification or power buffering, and can provide sufficient driving current for subsequent loads such as DC-DC isolated power supplies.
[0086] The three-phase four-wire zero-line detection circuit provided by the embodiment of the present application solves the two pain points of the traditional resistance voltage division scheme, i.e., instability and incapability of supporting a load, through two core mechanisms of active negative feedback voltage stabilization and current amplification. The three-phase four-wire zero-line detection circuit not only generates a half voltage value, but also creates a stable, reliable and strong half voltage "power supply", which provides a high-quality working voltage for subsequent DC-DC isolation power supply modules, and is a key prerequisite for ensuring stable operation of the entire system.
[0087] The present application also provides a three-phase four-wire zero-line detection method using the three-phase four-wire zero-line detection circuit, Figure 5 The present application provides a three-phase four-wire zero-line detection method, and Figure 5 The method provided by the present application includes the following steps: Step 510: Obtain a level signal output by the three-phase four-wire zero-line detection circuit.
[0088] Specifically, the master control unit (for example, a microcontroller MCU, a digital signal processor DSP or a special logic circuit) collects and reads the level signal of the detection output end of the three-phase four-wire zero-line detection circuit in real time or periodically through its input / output (I / O) port. The detection output end is connected to the output of the signal shaping unit in the zero-line detection circuit and can provide a stable digital logic signal with clear high and low levels.
[0089] Step 520: Determine the connection state of the zero line according to the level signal.
[0090] Specifically, after obtaining the level signal, the master control unit determines the connection state of the external zero line according to the preset logic rule.
[0091] Based on the working principle of the three-phase four-wire zero-line detection circuit, when the master control unit obtains a low level, it is determined that the current zero line is connected normally. The master control unit can record the normal state or continue other normal operations. When the master control unit obtains a high level, it is determined that the current zero line is missing or connected abnormally. The master control unit can trigger corresponding protection measures or alarm operations, such as lighting an alarm indicator, emitting a buzzing sound, reporting fault information through a communication interface, or controlling the system to enter a safety protection mode, etc.
[0092] The three-phase four-wire zero-line detection method provided by the embodiment of the present application can quickly and reliably determine the connection state of the zero line in the three-phase four-wire system by simply monitoring a digital logic level. The method has clear logic and is easy to implement through a microcontroller or other digital circuit, has high real-time performance and practicability, and can effectively improve the safety and reliability of the electrical equipment.
[0093] The application further provides a power supply comprising the three-phase four-wire zero-line missing detection circuit.
[0094] Specifically, the power supply provided by the application is upgraded from a simple electric energy conversion device to an intelligent power supply unit with input state sensing and active protection capability through the internally integrated three-phase four-wire zero-line missing detection circuit, which represents an important progress in the field of three-phase power supply design in terms of safety, reliability and integration.
[0095] The application further provides an electric energy meter comprising the three-phase four-wire zero-line missing detection circuit.
[0096] Specifically, the electric energy meter provided by the application is transformed from a passive metering device to an intelligent terminal capable of actively sensing power grid faults, implementing self-protection, recording key events and reporting alarms through the internally integrated three-phase four-wire zero-line missing detection circuit, which not only greatly improves the reliability and service life of the electric energy meter itself, but also provides strong technical support for realizing safer and more intelligent power distribution network management.
[0097] The application further provides a collection terminal comprising the three-phase four-wire zero-line missing detection circuit.
[0098] Specifically, the collection terminal provided by the application is upgraded from a simple data collection and forwarding device to an intelligent Internet of Things terminal with self-protection capability and advanced power grid fault diagnosis capability through the internally integrated three-phase four-wire zero-line missing detection circuit, which is of great significance for building a more resilient, more transparent and easier-to-maintain modern intelligent power distribution network.
[0099] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the application, and not to limit them; although the application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the application.
Claims
1. A three-phase four-wire neutral wire missing detection circuit, characterized in that, include: A three-phase bridge rectifier circuit has three AC input terminals, a DC positive output terminal, and a DC negative output terminal. The three AC input terminals are respectively connected to phase A, phase B, and phase C of a three-phase AC power supply. The first filter capacitor is connected in parallel between the positive DC output terminal and the negative DC output terminal of the three-phase bridge rectifier circuit. A half-voltage power supply unit, wherein the first input terminal of the half-voltage power supply unit is connected to the positive DC output terminal of the three-phase bridge rectifier circuit, and the second input terminal of the half-voltage power supply unit is connected to the negative DC output terminal of the three-phase bridge rectifier circuit; The first rectifier diode has its anode connected to the output terminal of the half-voltage power supply unit and its cathode connected to a common power supply node. An input buffer capacitor is provided, with its positive terminal connected to the common power supply node and its negative terminal connected to the DC negative output terminal of the three-phase bridge rectifier circuit. A DC-DC isolated power supply is connected in parallel across the positive and negative terminals of the input buffer capacitor; The neutral power supply unit includes a neutral current limiting resistor, a neutral path diode, and a second rectifier diode connected in series. One end of the neutral current limiting resistor is connected to the neutral line, and the cathode of the second rectifier diode is connected to the common power supply node. A neutral wire detection circuit is connected in parallel across the two ends of the neutral wire path diode to detect the connection status of the neutral wire.
2. The three-phase four-wire neutral wire missing detection circuit according to claim 1, characterized in that, The missing zero-wire detection circuit includes: A first current-limiting resistor, one end of which is connected to the anode of the neutral wire diode; A protection diode, wherein the cathode of the protection diode is connected to the cathode of the neutral wire diode; An optocoupler, wherein the anode of the light-emitting diode of the optocoupler is connected to the other end of the first current-limiting resistor, and the cathode of the light-emitting diode is connected to the anode of the protection diode; the collector of the phototransistor of the optocoupler is connected to the power supply voltage terminal; A first bias resistor is connected between the emitter of the phototransistor and the reference potential terminal. A signal shaping unit is used to shape the output signal of the phototransistor into a high- or low-level digital signal; the input terminal of the signal shaping unit is connected to the emitter of the phototransistor; the output terminal of the signal shaping unit is a detection output terminal used to output the neutral line detection result; the power supply voltage connection terminal of the signal shaping unit is connected to the power supply voltage terminal; the reference potential connection terminal of the signal shaping unit is connected to the reference potential terminal.
3. The three-phase four-wire neutral wire missing detection circuit according to claim 2, characterized in that, The signal shaping unit includes: A delay capacitor is connected in parallel between the input terminal of the signal shaping unit and the reference potential terminal; The second current-limiting resistor has one end connected to the input terminal of the signal shaping unit; A first transistor, the base of which is connected to the other end of the second current-limiting resistor, and the emitter of which is connected to the reference potential terminal; A second bias resistor, one end of which is connected to the power supply voltage terminal, and the other end of which is connected to the collector of the first transistor; The second filter capacitor is connected in parallel between the collector of the first transistor and the reference potential terminal; The detection output terminal is connected to the collector of the first transistor.
4. The three-phase four-wire neutral wire missing detection circuit according to claim 1, characterized in that, The half-voltage power supply unit includes: The first voltage divider resistor has one end serving as the first input terminal of the half-voltage power supply unit, and the other end of the first voltage divider resistor is connected to the voltage divider node. The second voltage divider resistor has one end connected to the voltage divider node and the other end serving as the second input terminal of the half-voltage power supply unit. The second transistor has its source connected to the first input terminal of the half-voltage power supply unit, its gate connected to the voltage divider node, and its drain serving as the output terminal of the half-voltage power supply unit. A feedback resistor, one end of which is connected to the drain of the second transistor, and the other end of which is connected to the voltage divider node.
5. The three-phase four-wire neutral wire missing detection circuit according to claim 1, characterized in that, Also includes: Three current-limiting resistors are respectively connected to phases A, B, and C of the three-phase AC power supply to their respective AC input terminals of the three-phase bridge rectifier circuit.
6. The three-phase four-wire neutral wire missing detection circuit according to claim 1 or 5, characterized in that, Also includes: Three thermistors are connected in parallel between phase A, phase B, and phase C of the three-phase AC power supply and the neutral wire, respectively.
7. A method for detecting a missing neutral wire in a three-phase four-wire system based on the three-phase four-wire neutral wire detection circuit according to any one of claims 1-6, characterized in that, include: Obtain the level signal output by the three-phase four-wire neutral wire missing detection circuit; The connection status of the neutral wire is determined based on the level signal.
8. A power supply, characterized in that, Includes the three-phase four-wire missing neutral wire detection circuit as described in any one of claims 1-6.
9. An electricity meter, characterized in that, Includes the three-phase four-wire missing neutral wire detection circuit as described in any one of claims 1-6.
10. A data acquisition terminal, characterized in that, Includes the three-phase four-wire missing neutral wire detection circuit as described in any one of claims 1-6.