Three-phase four-wire null line detection circuit, method, power supply, electric energy meter and acquisition terminal

Abstract

The application provides a three-phase four-wire zero-line detection circuit, method, power supply, electric energy meter and acquisition terminal, and relates to the field of circuit electron technology.The circuit comprises three-way AC input ends of a three-phase bridge rectifier circuit connected with A phase, B phase and C phase of a three-phase AC power supply, a first filter capacitor connected in parallel between a DC positive output end and a DC negative output end of the three-phase bridge rectifier circuit, a first input end of a half-voltage power supply unit connected with the DC positive output end of the three-phase bridge rectifier circuit, a second input end of the half-voltage power supply unit connected with the DC negative output end of the three-phase bridge rectifier circuit, an anode of a first rectifier diode connected with an output end of the half-voltage power supply unit, a cathode of the first rectifier diode connected to a common power supply node, a positive pole of an input buffer capacitor connected with the common power supply node, a negative pole of the input buffer capacitor connected with the DC negative output end of the three-phase bridge rectifier circuit, and a DC-DC isolation power supply connected in parallel between the positive and negative poles of the input buffer capacitor.The application realizes simple three-phase four-wire zero-line detection.

Description

Technical Field

[0001] This invention relates to the field of circuit electronics technology, and in particular to a three-phase four-wire neutral wire missing detection circuit, method, power supply, energy meter, and data acquisition terminal. Background Technology

[0002] In a three-phase four-wire power supply system, the neutral wire is crucial. A disconnected neutral wire can lead to equipment damage or even a safety accident. Therefore, reliable neutral wire detection in a three-phase four-wire power supply system is of paramount importance.

[0003] In a three-phase four-wire system with a missing neutral wire, the varistor and voltage sampling circuit in the metering circuit will generate a small leakage current. Although this leakage current may not be noticeable under normal operating conditions, it can interfere with the detection circuit when a neutral wire missing fault occurs, leading to misjudgment or inaccurate detection results. To cope with this interference and achieve reliable detection, existing three-phase four-wire neutral wire missing detection schemes are often quite complex. Summary of the Invention

[0004] This invention provides a three-phase four-wire neutral wire missing detection circuit, method, power supply, energy meter, and data acquisition terminal to solve the shortcomings of the existing three-phase four-wire neutral wire missing detection scheme, and to realize a simple three-phase four-wire neutral wire missing detection.

[0005] This invention provides a three-phase four-wire neutral wire missing detection circuit, comprising: 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.

[0006] In some embodiments, the missing zero-line 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.

[0007] In some embodiments, 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.

[0008] In some embodiments, 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.

[0009] In some embodiments, it 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.

[0010] In some embodiments, it 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.

[0011] The present invention also provides a three-phase four-wire neutral wire missing method based on the three-phase four-wire neutral wire missing detection circuit described in any one of the above claims, comprising: 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.

[0012] The present invention also provides a power supply, including the three-phase four-wire neutral wire missing detection circuit described in any of the above claims.

[0013] The present invention also provides an energy meter, including the three-phase four-wire neutral wire missing detection circuit described in any of the above claims.

[0014] The present invention also provides a data acquisition terminal, including the three-phase four-wire missing neutral wire detection circuit described in any of the above claims.

[0015] The three-phase four-wire neutral wire missing detection circuit, method, power supply, energy meter, and data acquisition terminal provided by this invention utilize a neutral wire path diode that conducts when the neutral wire is normal and cuts off when the neutral wire is missing. Therefore, the neutral wire connection status can be directly determined simply by detecting the voltage across the neutral wire path diode, thus achieving a simple three-phase four-wire neutral wire missing detection. Attached Figure Description

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

[0017] Figure 1 This is one of the structural schematic diagrams of the three-phase four-wire missing neutral wire detection circuit provided in the embodiments of the present invention.

[0018] Figure 2 This is the second schematic diagram of the three-phase four-wire missing neutral wire detection circuit provided in the embodiment of the present invention.

[0019] Figure 3 This is a schematic diagram of the missing zero-line detection circuit provided in an embodiment of the present invention.

[0020] Figure 4 This is a schematic diagram of the structure of the half-voltage power supply unit provided in an embodiment of the present invention.

[0021] Figure 5 This is a flowchart illustrating the three-phase four-wire missing neutral wire detection method provided in this embodiment of the invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0023] Figure 1 This is one of the structural schematic diagrams of the three-phase four-wire neutral wire missing detection circuit provided in the embodiments of the present invention, such as... Figure 1 As shown, this embodiment of the invention provides a three-phase four-wire neutral wire missing detection circuit, which includes: 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 neutral wire power supply unit, and a neutral wire missing detection circuit.

[0024] The three-phase bridge rectifier circuit has three AC input terminals, a positive DC output terminal, and a negative DC output terminal. The three AC input terminals are connected to phases A, B, and C of the three-phase AC power supply, respectively. The first filter capacitor C1 is connected in parallel between the positive DC output terminal and the negative DC output terminal of the three-phase bridge rectifier circuit.

[0025] 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 is connected to the negative DC output terminal of the three-phase bridge rectifier circuit. The anode of the first rectifier diode D5 is connected to the output terminal 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 terminal of the input buffer capacitor C2 is connected to the common power supply node, and the negative terminal of the input buffer capacitor C2 is connected to the negative DC output terminal of the three-phase bridge rectifier circuit. A DC-DC isolation power supply is connected in parallel across the positive and negative terminals of the input buffer capacitor C2.

[0026] The neutral wire power supply unit includes a neutral wire current-limiting resistor R1, neutral wire path diodes (i.e., diodes D1, D2, and D3), and a second rectifier diode D4 connected in series. One end of the neutral wire current-limiting resistor R1 is connected to the neutral wire, and the cathode of the second rectifier diode D4 is connected to the common power supply node. A neutral wire missing detection circuit is connected in parallel across the neutral wire path diodes D1, D2, and D3 to detect the connection status of the neutral wire.

[0027] Specifically, this invention provides a three-phase four-wire neutral wire missing detection circuit. Its overall architecture is designed to obtain energy from a three-phase AC power supply and provide a stable isolated DC power supply, while also possessing real-time monitoring capabilities for the neutral wire connection status. The circuit mainly includes a three-phase AC input and rectification / filtering section, a common power supply node formation section, a DC-DC isolated power supply, and a neutral wire missing detection section.

[0028] The three-phase AC input and rectification / filtering section converts external three-phase AC power into pulsating DC voltage and performs preliminary filtering. This section receives the A-phase, B-phase, and C-phase inputs from the external three-phase AC power supply. The three-phase inputs are connected to the three AC input terminals of a three-phase bridge rectifier circuit. The three-phase bridge rectifier circuit rectifies the three-phase AC power into pulsating DC voltage.

[0029] Figure 2 This is a second schematic diagram of the three-phase four-wire neutral wire missing detection circuit provided in this embodiment of the invention, as shown below. Figure 2 As shown, the three-phase bridge rectifier circuit consists of 12 diodes. It is composed of two independent, standard three-phase full-wave bridge rectifiers, each of which contains 6 diodes.

[0030] Each rectifier circuit is a standard three-phase full-wave bridge rectifier consisting of six diodes. The first bridge rectifier is connected to the first set of three-phase voltages output from the phase-shifting transformer. The second bridge rectifier is connected to the second set of three-phase voltages output from 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 positive and negative DC output terminals of the three-phase bridge rectifier circuit. The main function of the first filter capacitor C1 is to filter and smooth the pulsating DC voltage after rectification, forming a relatively stable DC bus voltage as the energy source for subsequent circuits.

[0032] To ensure the stability and redundancy of the DC-DC isolated power supply, this invention uses two independent power supply circuits to jointly supply power to the DC-DC isolated power supply. These two circuits are the neutral power supply path and the half-voltage power supply path, respectively. They 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 the higher voltage to supply power to the DC-DC isolated power supply.

[0033] The neutral wire power supply unit is used to obtain energy from an external neutral wire. The neutral wire power supply unit includes a neutral wire current-limiting resistor R1, neutral wire path diodes D1, D2, and D3, and a second rectifier diode D4. One end of the neutral wire current-limiting resistor R1 is connected to the external neutral wire to limit the current in the neutral wire path. The neutral wire current-limiting resistor R1, neutral wire path diodes D1, D2, and D3, and the second rectifier diode D4 are connected in series. The cathode of the second rectifier diode D4 is connected to the common power supply node (i.e., the positive terminal of the input buffer capacitor C2), merging with the cathode of the first rectifier diode D5.

[0034] It should be noted that the number of diodes in the neutral path can be determined based on the actual required forward voltage drop. Figure 1 The neutral-path diodes D1, D2, and D3 are just examples. When the forward voltage drop of a single neutral-path diode is sufficient to meet the actual required forward voltage drop, only one neutral-path diode is needed. When the forward voltage drop of a single neutral-path diode is insufficient to meet the actual required forward voltage drop, multiple neutral-path diodes can be used, connected in series.

[0035] When the external neutral wire connection is normal, the neutral wire power supply unit, through the corresponding diodes in the three-phase bridge rectifier circuit, forms a rectifier circuit with phases A, B, and C of the three-phase AC power supply. In this case, one end of the neutral wire current-limiting resistor R1 is connected to the external neutral wire. After rectification, the voltage at the common power supply node is approximately... The phase voltage is times that of 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 terminal of the half-voltage power supply unit is connected to the positive DC output terminal of the three-phase bridge rectifier circuit (i.e., the positive terminal of the first filter capacitor C1), and the second input terminal is connected to the negative DC output terminal of the three-phase bridge rectifier circuit (i.e., the negative terminal of the first filter capacitor C1). The output terminal 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 phases A, B, and C of a three-phase AC power supply are connected to form a rectifier circuit via a three-phase bridge rectifier circuit, then after rectification by the three-phase bridge rectifier circuit, the voltage across the first filter capacitor C1 will be approximately... The phase voltage is reduced by half. The half-voltage supply unit reduces this voltage by half, and after processing, the anode of the first rectifier diode D5 will receive approximately [amount missing]. The phase voltage is times that of the phase voltage.

[0038] Due to the neutral power supply path provided The phase double voltage is significantly higher than that provided by the half-voltage power supply path. Because of the phase voltage multiplication, under normal neutral wire connection conditions, the system will preferentially select the energy provided by the rectifier circuit formed by the neutral wire and phases A, B, and C, 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 conducting, while the first rectifier diode D5 is in a reverse biased or non-conducting state.

[0039] The positive terminal of input buffer capacitor C2 is connected to the common power supply node, and the negative terminal of input buffer capacitor C2 is connected to the DC negative output terminal (i.e., GND) of the three-phase bridge rectifier circuit. Input buffer capacitor C2 plays a further filtering and smoothing role here, ensuring that a stable DC input voltage with low ripple is provided for the subsequent DC-DC isolated power supply, and can provide the large current required for instantaneous operation 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 to the required stable DC output voltage and providing electrical isolation. Electrical isolation is crucial for improving system safety, suppressing common-mode noise, and protecting operators.

[0041] The neutral wire missing detection circuit can monitor the connection status of the external neutral wire in real time. The circuit is connected in parallel across the neutral wire path diodes D1, D2, and D3. When a neutral wire is present, the neutral wire power supply path prioritizes supplying power to the common power supply node. In this case, the neutral wire path diodes D1, D2, and D3, as part of the neutral wire power supply unit, will have current flowing through them and will conduct normally. When the neutral wire path diodes D1, D2, and D3 are conducting, a forward voltage drop will be generated across them. The neutral wire missing detection circuit detects the voltage across the neutral wire path diodes D1, D2, and D3; if a voltage is detected, the neutral wire connection is confirmed to be normal.

[0042] In the event of a missing neutral wire, the neutral power supply path is interrupted, and no current flows. The energy required by the DC-DC isolated power supply will only be provided through the half-voltage power supply path, i.e., the rectifier circuit consisting of phases A, B, and C is powered by the half-voltage power supply unit and the first rectifier diode D5. Since there is no current in the neutral wire loop, the neutral wire path diodes D1, D2, and D3 will be in the off state, and there will be almost no voltage (close to 0V) across them. The neutral wire missing detection circuit detects the voltage across the neutral wire path diodes; if no voltage is detected, it can be determined that the neutral wire is missing or the connection is abnormal.

[0043] The three-phase four-wire neutral wire missing detection circuit provided in this embodiment of the invention conducts the neutral wire path diode when the neutral wire is normal and cuts off when the neutral wire is missing. Therefore, the neutral wire connection status can be directly determined simply by detecting the voltage across the neutral wire path diode, thus achieving a simple three-phase four-wire neutral wire missing detection.

[0044] Furthermore, the voltage across the diode in the neutral wire path differs significantly between the two states: a normal neutral wire and a missing neutral wire. This substantial voltage difference provides an extremely high signal-to-noise ratio and a clear judgment threshold, enabling the circuit to accurately distinguish between the two operating conditions. This effectively avoids misjudgments caused by voltage fluctuations or critical states, thus ensuring the high reliability of the detection results.

[0045] The detection principle of this invention does not rely on direct sampling of the three-phase AC voltage. Traditional voltage sampling-based algorithms are easily affected by the leakage current of the varistor connected in parallel at the AC input terminal, or the voltage division effect of other parallel voltage sampling circuits. However, this invention fundamentally avoids these interference sources by monitoring an independent, low-power DC signal path, ensuring the purity and accuracy of the detection and exhibiting outstanding anti-interference capabilities.

[0046] The entire detection process is completed automatically by hardware circuitry, without relying on software algorithms. This not only ensures extremely fast real-time response speed but also frees the main processor from complex real-time sampling and algorithm calculations, greatly reducing the performance requirements for the processor and the complexity of software development. More importantly, the detection function is independent of the software's running state, improving the stability and robustness of the entire system.

[0047] In some embodiments, such as Figure 2 As shown, the three-phase four-wire neutral wire missing detection circuit provided in this embodiment of the invention further includes three current-limiting resistors R2, R3, and R4. The three current-limiting resistors R2, R3, and R4 are respectively connected to phase A, phase B, and phase C of the three-phase AC power supply to their respective AC input terminals of the three-phase bridge rectifier circuit.

[0048] Specifically, the three-phase AC power supply (phases A, B, and C) first passes through their respective current-limiting resistors R2, R3, and R4. These resistors limit the current input to the three-phase bridge rectifier circuit, especially during power connection or short-circuit faults, protecting the diodes and other downstream components of the three-phase bridge rectifier circuit. The three-phase AC power, 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 three-phase AC power into pulsating DC power. Then, the first filter capacitor C1, which is connected in parallel between the DC positive output terminal and the DC negative output terminal, filters and smooths the DC voltage to form a relatively stable main DC bus voltage.

[0050] The three-phase four-wire missing neutral wire detection circuit provided in this embodiment of the invention protects the diodes and other downstream components of the three-phase bridge rectifier circuit through three current-limiting resistors R2, R3 and R4.

[0051] In some embodiments, such as Figure 2 As shown, the three-phase four-wire neutral wire missing detection circuit provided in this embodiment of the invention further includes three thermistors RT1, RT2, and RT3. The three thermistors RT1, RT2, and RT3 are connected in parallel between phase A, phase B, and phase C of the three-phase AC power supply and the neutral wire, respectively.

[0052] Specifically, three thermistors RT1, RT2, and RT3 are connected in parallel between phases A, B, and C of the three-phase AC power supply and the neutral line, respectively. These thermistors are typically used here to provide overcurrent or overheat protection. For example, when the thermistor has a positive temperature coefficient, its resistance increases sharply when an overload or short circuit causes excessive current and self-heating, thus limiting the current and providing protection. Alternatively, the thermistors can act as temperature sensors, monitoring the temperature at the connection point between the phase and neutral lines to prevent localized overheating caused by poor connections or abnormal loads. Together, they improve the safety and reliability of the input power supply line.

[0053] The three-phase four-wire missing neutral wire detection circuit provided in this embodiment of the invention provides overcurrent protection or overheat protection through three thermistors RT1, RT2 and RT3.

[0054] In some embodiments, Figure 3 This is a schematic diagram of the structure of the missing neutral wire detection circuit provided in an embodiment of the present invention, as shown below. Figure 3 As shown, the missing neutral wire detection circuit includes: a first current-limiting resistor R5, a protection diode D6, an optocoupler 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 neutral-line diode D1, and the cathode of the protection diode D6 is connected to the cathode of the neutral-line diode D3. The anode of the light-emitting diode of the optocoupler 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 phototransistor of the optocoupler OP1 is connected to the power supply voltage terminal, and the first bias resistor R6 is connected between the emitter of the phototransistor and the reference potential terminal.

[0056] The signal shaping unit is used to shape the output signal of the phototransistor into high and low level digital signals. 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 the 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.

[0057] Specifically, one end of the first current-limiting resistor R5 is connected to the anode of the neutral path diode D1, and the cathode of the protection diode D6 is connected to the cathode of the neutral path diode D3. The anode of the light-emitting diode in the optocoupler OP1 is connected to the other end of the first current-limiting resistor R5, and the cathode of the light-emitting diode is connected to the anode of the protection diode D6. Thus, the neutral-line missing detection circuit, formed by the first current-limiting resistor R5, the light-emitting diode of the optocoupler OP1, and the protection diode D6 connected in series, is connected in parallel across the neutral path diodes D1, D2, and D3 to monitor voltage changes across the neutral path diodes. The conduction threshold of the neutral-line missing detection circuit 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] In optocoupler OP1, the collector of the phototransistor 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 LED of optocoupler OP1 emits light, the phototransistor is turned on, and its emitter potential rises; when it does not emit light, the phototransistor is turned off, and the emitter potential is pulled low by the first bias resistor R6.

[0059] The core of the missing neutral wire detection circuit lies in accurately detecting the voltage change across the diodes in the neutral wire path and using an optocoupler to achieve reliable signal isolation and output. Its detection logic is based on the principle that the conduction threshold of the missing neutral wire detection circuit is less than the forward conduction voltage drop of the diodes D1, D2, and D3 in the neutral wire path.

[0060] When the neutral wire is properly connected, current flows to the common power supply node through the neutral wire current-limiting resistor R1, neutral wire path diodes D1, D2, and D3, and the second rectifier diode D4. Therefore, neutral wire path diodes D1, D2, and D3 are in the forward conducting state. The conduction threshold of the neutral wire missing detection circuit is less than the forward voltage drop of neutral wire path diode D1. For example, the forward voltage drop of neutral wire path diodes D1, D2, and D3 is 2V, while the conduction threshold of the neutral wire missing detection circuit is 1V.

[0061] Therefore, when the neutral wire is normal, the sum of the forward voltage drops of diodes D1, D2, and D3 in the neutral wire path is sufficient to turn on the LED inside optocoupler OP1, causing it to emit light. This allows the phototransistor inside optocoupler OP1 to receive the light signal and quickly turn on (saturate). When the phototransistor is on, its emitter potential will rise significantly (pulled up, approaching the power supply voltage VCC). The signal shaping unit receives a high-level signal, indicating "neutral wire normal".

[0062] When the neutral wire is missing, no current flows through the neutral wire pass diodes D1, D2, and D3, and they are no longer in the forward conducting state. This causes the LED inside the optocoupler OP1 to be in the off state. The emitter of the phototransistor is pulled low through the bias resistor R6, approaching the reference potential. The signal shaping unit receives a low-level signal, indicating "neutral wire missing".

[0063] The three-phase four-wire missing neutral wire detection circuit provided in this embodiment of the invention achieves complete electrical isolation between the high-voltage main circuit and the low-voltage control circuit through an optocoupler, thereby greatly improving the safety and anti-interference capability of the entire system while ensuring high reliability of detection.

[0064] In some embodiments, such as Figure 3 As shown, 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.

[0065] A delay capacitor C3 is connected in parallel between the input terminal and the reference potential terminal of the signal shaping unit; one end of the second current-limiting resistor R7 is connected to the input terminal 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 terminal; one end of the second bias resistor R8 is connected to the power supply voltage terminal, and the other end of the second bias resistor R8 is connected to the collector of the first transistor Q1; a second filter capacitor C4 is connected in parallel between the collector of the first transistor Q1 and the reference potential terminal; and the detection output terminal is connected to the collector of the first transistor Q1.

[0066] Specifically, the input terminal of the signal shaping unit is connected to the emitter of the phototransistor of optocoupler OP1. Depending on the conduction state of optocoupler OP1, this input terminal will present a high or low level.

[0067] The delay capacitor C3 is connected in parallel between the input terminal of the signal shaping unit and the reference potential terminal GND-MCU. When the emitter potential of the phototransistor changes, the charging and discharging process of the delay capacitor C3 introduces a certain delay. This delay is crucial for anti-interference and preventing false triggering during signal transients (such as switching moments or noise spikes), ensuring that the signal input to subsequent transistors stabilizes after a certain period of time. Simultaneously, the delay capacitor C3 also acts as a filter, smoothing high-frequency noise in the input signal.

[0068] The 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, further smoothing and delaying the signal. More importantly, the second current-limiting resistor R7 also limits the current flowing into the base of the first transistor Q1, protecting it from overcurrent damage and providing suitable bias conditions for the first transistor Q1.

[0069] The first transistor Q1 is typically an NPN transistor configured as a common-emitter amplifier. When the phototransistor output of the optocoupler OP1 is low, indicating a missing neutral line, the input of the signal shaping unit receives a low-level signal. The base current of the first transistor Q1 is insufficient to turn it on, and the first transistor Q1 is in the off state.

[0070] When the phototransistor of optocoupler OP1 outputs a high level, indicating that the neutral line is normal, 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 conduct and enter the saturation state.

[0071] Because the first transistor Q1 uses a common-emitter configuration, the signal level at its output (collector) is out of phase with 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 the off state, its collector is pulled high by R8 to a potential close to the power supply voltage terminal VCC, forming a definite 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 definite low-level output. The second bias resistor R8 ensures a stable high level at the output when the first transistor Q1 is 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 out 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 and low level signal.

[0074] The detection output is directly connected to the collector of the first transistor Q1. After the above-mentioned delay, filtering, inversion, and shaping processes, the detection output will provide a clear and stable digital signal with high and low levels, which can be directly used to determine the neutral wire connection status. For example, a low level is output when the neutral wire is normal, and a high level is output when the neutral wire is missing.

[0075] The three-phase four-wire neutral wire missing detection circuit provided in this invention transforms the easily interfered original signal from optocoupler OP1 into a jitter-resistant, level-standard, and waveform-clean "logically perfect" signal through a three-step process of delay filtering, level shaping, and output smoothing. This plays a decisive role in ensuring that the final decision of the entire neutral wire missing detection system is not interfered with, does not produce false judgments, and is perfectly compatible with digital systems.

[0076] In some embodiments, Figure 4 This is a schematic diagram of the structure of the half-voltage power supply unit provided in an embodiment of the present invention, as shown below. Figure 4 As shown, the half-voltage power supply unit includes: a first voltage divider resistor R9, a second voltage divider resistor R10, a second transistor Q2, and a feedback resistor R11.

[0077] One end of the first voltage divider resistor R9 serves as the first input terminal of the half-voltage power supply unit, and the other end of the first voltage divider resistor R9 is connected to the voltage divider node; one end of the second voltage divider resistor R10 is connected to the voltage divider node, and the other end of the second voltage divider resistor R10 serves as the second input terminal of the half-voltage power supply unit; the source of the second transistor Q2 is connected to the first input terminal of the half-voltage power supply unit, the gate of the second transistor Q2 is connected to the voltage divider node, and the drain of the second transistor Q2 serves as the output terminal 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 divider node.

[0078] Specifically, the first input terminal of the half-voltage power supply unit is connected to the positive terminal of the main DC bus voltage, while the second input terminal is connected to the negative terminal of the main DC bus voltage, providing input voltage for the entire unit.

[0079] The first voltage divider resistor R9 and the second voltage divider resistor R10 are connected in series between the first input terminal and the second input terminal. The first voltage divider resistor R9 and the second voltage divider resistor R10 constitute a standard resistor divider, used to generate a reference voltage at the voltage divider node that is approximately half the input voltage. If the resistance values ​​of the first voltage divider resistor R9 and the second voltage divider resistor R10 are equal, the voltage at the voltage divider node will be half the input voltage. This voltage at the voltage divider node serves as the reference input for subsequent voltage regulation components. It should be noted that the first voltage divider resistor R9 and the second voltage divider resistor R10 can be composed of a single resistor, or they can each be composed of multiple resistors connected in series and parallel.

[0080] The second transistor Q2 and the feedback resistor R11 together form an active voltage regulator and current amplifier circuit. Its core function is to replicate and amplify the driving capability of the voltage signal provided by the voltage divider node in order to output a stable half-value voltage.

[0081] The second transistor, Q2, is a depletion-type N-channel field-effect transistor. This type of transistor is in the on-state when the gate-source voltage (Vgs) is zero. The source of the second transistor Q2 is connected to the first input terminal (high potential), and its gate is connected to the voltage divider node (intermediate potential) formed by the first voltage divider resistor R9 and the second voltage divider resistor R10. Since the gate potential is always lower than the source potential, its gate-source voltage Vgs is always negative. For a depletion-type N-channel MOSFET, the negative gate-source voltage Vgs keeps it in a controllable on-state, and its on-resistance (or drain current) changes with the negative value of Vgs, providing the physical basis for the circuit's voltage regulation function.

[0082] The feedback resistor R11 is connected between the drain and gate of the second transistor Q2, forming a negative feedback loop. This negative feedback mechanism ensures that the output voltage closely follows and stabilizes near the reference voltage point set by the voltage divider network.

[0083] When the output voltage (drain voltage) attempts to rise, the gate voltage of the second transistor Q2 is also pulled up accordingly through the feedback effect of the feedback resistor R11. This causes the negative value of the gate-source voltage Vgs to become smaller (closer to zero), thus enhancing the conduction capability of the second transistor Q2 (reducing the equivalent resistance). The enhanced conduction capability suppresses the rise in output voltage, thereby pulling it back to the stable point.

[0084] When the output voltage (drain voltage) attempts to decrease, the gate voltage of the second transistor Q2 is pulled down accordingly through the feedback effect of the feedback resistor R11. This results in a larger negative value for the gate-source voltage Vgs, weakening the conduction capability of the second transistor Q2 (increasing its equivalent resistance). The weakened conduction capability raises the output voltage, thus counteracting its decreasing trend.

[0085] Meanwhile, due to the extremely high input impedance and relatively low output impedance of the field-effect transistor, the half-voltage supply unit can control a large output current with almost zero input current. This means that it can obtain a voltage signal from the high-resistance voltage divider node and utilize the power supply energy from the source to reproduce a stable voltage at the drain that is strongly load-driving and related to the gate reference voltage. This process essentially achieves current amplification or power buffering, providing sufficient drive current for subsequent loads (such as DC-DC isolated power supplies).

[0086] The three-phase four-wire neutral wire missing detection circuit provided in this invention solves the two major pain points of traditional resistor voltage divider schemes—instability and inability to drive the load—through two core mechanisms: active negative feedback voltage regulation and current amplification. It not only generates a half-voltage value, but also creates a stable, reliable, and powerful half-voltage "power supply," providing a high-quality operating voltage for subsequent DC-DC isolated power supply modules, which is a key prerequisite for ensuring the stable operation of the entire system.

[0087] The present invention also provides a method for detecting a three-phase four-wire missing neutral wire using the above-described three-phase four-wire neutral wire detection circuit. Figure 5 This is a flowchart illustrating the three-phase four-wire missing neutral wire detection method provided in this embodiment of the invention, as shown below. Figure 5 As shown, the method provided by the present invention includes: Step 510: Obtain the level signal output by the three-phase four-wire neutral wire missing detection circuit.

[0088] Specifically, the main control unit (e.g., microcontroller (MCU), digital signal processor (DSP), or dedicated logic circuit) acquires and reads the level signal of the detection output terminal of the three-phase four-wire neutral wire detection circuit in real time or periodically through its input / output (I / O) ports. This detection output terminal is connected to the output of the signal shaping unit in the neutral wire detection circuit, providing a stable digital logic signal with clearly defined high and low levels.

[0089] Step 520: Determine the connection status of the neutral wire based on the level signal.

[0090] Specifically, after acquiring the level signal, the main control unit will judge the signal according to the preset logic rules to determine the connection status of the external neutral wire.

[0091] Based on the working principle of the aforementioned three-phase four-wire neutral wire missing detection circuit, when the main control unit receives a low level, it determines that the current neutral wire connection is normal. The main control unit can record the normal state or continue to perform other routine operations. When the main control unit receives a high level, it determines that the current neutral wire is missing or the connection is abnormal. The main control unit can trigger corresponding protection measures or alarm operations, such as: illuminating the alarm indicator light, emitting a buzzer, reporting fault information through the communication interface, or controlling the system to enter a safety protection mode, etc.

[0092] The three-phase four-wire neutral wire missing detection method provided in this invention can quickly and reliably determine the connection status of the neutral wire in a three-phase four-wire system by simply monitoring a digital logic level. This method has clear logic, is easy to implement using digital circuits such as microcontrollers, and has high real-time performance and practicality, effectively improving the safety and reliability of electrical equipment.

[0093] The present invention also provides a power supply, including the above-described three-phase four-wire neutral wire missing detection circuit.

[0094] Specifically, the power supply provided by this invention, through its internally integrated three-phase four-wire neutral wire missing detection circuit, upgrades from a simple power conversion device into an intelligent power supply unit with input status perception and active protection capabilities, representing a significant advancement in the field of three-phase power supply design in terms of safety, reliability, and integration.

[0095] The present invention also provides an energy meter, including the above-described three-phase four-wire neutral wire missing detection circuit.

[0096] Specifically, the electricity meter provided by this invention, through its internally integrated three-phase four-wire neutral wire missing detection circuit, transforms from a passive metering device into an intelligent terminal capable of proactively sensing grid faults, achieving self-protection, recording critical events, and reporting alarms. This not only greatly improves the reliability and lifespan of the electricity meter itself but also provides strong technical support for achieving safer and smarter power distribution network management.

[0097] The present invention also provides a data acquisition terminal, including the above-mentioned three-phase four-wire missing neutral wire detection circuit.

[0098] Specifically, the data acquisition terminal provided by this invention, through its internally integrated three-phase four-wire neutral wire missing detection circuit, upgrades it from a simple data acquisition and forwarding device into an intelligent Internet of Things terminal with self-protection capabilities and advanced power grid fault diagnosis capabilities. This is of great significance for building a more resilient, transparent, and easier-to-maintain modern intelligent power distribution network.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

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 missing 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. 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.

2. The three-phase four-wire neutral wire missing detection circuit according to claim 1, 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.

3. 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.

4. 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.

5. The three-phase four-wire neutral wire missing detection circuit according to claim 1 or 4, 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.

6. 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 1-5, 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.

7. A power supply, characterized in that, Includes the three-phase four-wire missing neutral wire detection circuit as described in any one of claims 1-5.

8. An electricity meter, characterized in that, Includes the three-phase four-wire missing neutral wire detection circuit as described in any one of claims 1-5.

9. 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 1-5.

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