Short circuit detection circuit and AC charging pile

Abstract

This invention proposes a short-circuit detection circuit for use in AC charging piles. The output terminal of the AC charging pile includes a neutral wire and three-phase live wires, comprising: a transformer auxiliary winding power supply connected to the neutral wire; an isolation detection circuit; and two isolating switch circuits. This application achieves a dual fault diagnosis mechanism for live-neutral short circuits and live-live short circuits by integrating the isolation detection and isolating switch circuits. Addressing the impedance coupling interference present in traditional solutions under multi-phase X-capacitor parallel scenarios, a time-division control strategy is adopted to alternately conduct the two isolating switches, avoiding coupling effects on the detection signal. Simultaneously, the electrical isolation characteristics between circuits are utilized to construct an independent detection loop, physically blocking the shunting effect of the equivalent branch of the X-capacitor, ensuring detection accuracy without the need for additional filtering modules.

Description

Technical Field

[0001] This utility model relates to the field of charging pile technology, and in particular to a short circuit detection circuit and an AC charging pile. Background Technology

[0002] Current AC charging pile output short-circuit detection technology is mainly based on capacitive voltage divider detection circuits. Its core principle is to monitor the voltage change between the phase line (L) and neutral line (N) at the charging pile output terminal in real time, and then collect the voltage signal using a capacitive voltage divider network. When the output terminal is normally open-circuited, the voltage divider circuit can measure a fixed high-level signal; when an output short circuit occurs, the voltage between the phase line and neutral line drops sharply, causing the voltage divider circuit to output a low-level signal. The system then determines the short-circuit fault and triggers the protection mechanism.

[0003] However, this solution has significant technical flaws in practical applications: when the charging gun is connected to an electric vehicle, the X-type safety capacitor configured at the input of the on-board charger forms an equivalent parallel capacitor. This capacitor, together with the voltage divider capacitor in the detection circuit, constitutes a new capacitive voltage divider network, leading to the following problems: 1) Under normal connection conditions, the introduction of the X capacitor significantly changes the voltage division ratio, causing an abnormal decrease in the voltage detection value and falsely triggering the short-circuit protection threshold; 2) The dispersion of X capacitor values ​​for different vehicle models results in poor adaptability of the traditional fixed threshold method; 3) The capacitive inrush current generated during the insertion and removal of the charging gun may cause misjudgment, seriously restricting the reliability of the charging equipment and the user experience. Utility Model Content

[0004] The main purpose of this invention is to propose a short-circuit detection circuit and an AC charging pile, aiming to solve the technical problem of false short-circuit detection caused by interference from the X capacitor at the vehicle end in traditional short-circuit detection circuits.

[0005] To achieve the above objectives, this application proposes a short-circuit detection circuit for use in AC charging piles, wherein the output terminal of the AC charging pile includes a neutral wire and three-phase live wires, comprising:

[0006] The transformer auxiliary winding power supply is connected to the neutral line;

[0007] An isolation detection circuit includes multiple input terminals, each of which is connected to each phase live wire, and is used to output a first fault signal when a short circuit is detected between the neutral wire and at least one phase live wire;

[0008] Two isolating switch circuits are provided, with the input end connected to the power supply of the transformer auxiliary winding, the controlled end connected to an external device, and the output end connected to one of the live phases. They are used to connect the power supply of the transformer auxiliary winding to one of the live phases when an external signal is received.

[0009] The isolation detection circuit is further configured to output a second fault signal when a short circuit is detected between the corresponding connected phase wire and any other phase wire, provided that one of the two isolation switch circuits is in operation.

[0010] In one embodiment, the isolation detection circuit includes:

[0011] Multiple detection optocouplers are provided, with the light-emitting end of each detection optocoupler connected to the live wire of each phase, and the receiving end of each detection optocoupler connected to an external device.

[0012] The detection optocoupler is used to activate the connection between the light-emitting end and the power supply of the transformer auxiliary winding when a short circuit occurs between the neutral wire and the corresponding live wire, and to emit light when the receiving end receives the light and outputs a first fault signal to an external device.

[0013] In one embodiment, the isolation detection circuit is further configured to drive the corresponding connected detection optocoupler to work when one of the isolation switch circuits is in working state, such that the corresponding connected phase wire and the detection optocoupler are in non-detection state, while the other detection optocouplers are in detection state.

[0014] When a short circuit occurs between a live wire in a non-detection state and another live wire, the light-emitting end of the corresponding detection optocoupler in the detection state is turned on and emits light. The corresponding receiving end receives the light and outputs a second fault signal to an external device.

[0015] In one embodiment, the isolation detection circuit further includes a first power supply, and the detection optocoupler light-emitting terminal includes a first resistor and a first light-emitting diode. The anode of the first light-emitting diode is connected to the corresponding live wire through the first resistor, and the cathode of the first light-emitting diode is grounded.

[0016] The receiving end of the detection optocoupler includes a second resistor and a first phototransistor. The emitter of the first phototransistor is connected to an external device and a first power supply through the second resistor, and the collector is grounded.

[0017] In one embodiment, the isolation switch circuit includes:

[0018] The optocoupler is controlled so that the light-emitting end is connected to an external device, one end of the receiving end is connected to a certain phase of the live wire, and the other end of the receiving end is connected to the power supply of the auxiliary winding of the transformer.

[0019] The control optocoupler is used to connect the transformer auxiliary winding power supply and the corresponding phase wire when the light-emitting end is turned on and emits light upon receiving an external signal, so as to control the corresponding connected phase wire and the detection optocoupler to be in a non-detection state.

[0020] In one embodiment, the isolating switch circuit further includes a second power supply, the light-emitting end of the control optocoupler includes a third resistor and a second light-emitting diode, the anode of the second light-emitting diode is connected to the second power supply through the third resistor, and the cathode of the second light-emitting diode is connected to an external device;

[0021] The receiving end of the control optocoupler includes a fourth resistor and a second phototransistor. The emitter of the second phototransistor is connected to a second power supply through the fourth resistor, and the collector is connected to a certain phase live wire.

[0022] In one embodiment, there are three detection optocouplers, including detection optocoupler U3, detection optocoupler U4 and detection optocoupler U5; there are two control optocouplers, including control optocoupler U1 and control optocoupler U2; the three-phase live wires include live wire L1, live wire L2 and live wire L3;

[0023] The receiving end of the control optocoupler U1 is connected to the power supply of the transformer auxiliary winding and the live wire L1, and the emitting end is connected to an external device; the receiving end of the control optocoupler U2 is connected to the power supply of the transformer auxiliary winding and the live wire L2, and the emitting end is connected to an external device.

[0024] The receiving end of the detection optocoupler U3 is connected to the first power supply, and the emitting end is connected to the live wire L3; the receiving end of the detection optocoupler U4 is connected to the first power supply, and the emitting end is connected to the live wire L2 and the receiving end of the control optocoupler U2; the receiving end of the detection optocoupler U5 is connected to the first power supply, and the emitting end is connected to the live wire L1 and the receiving end of the control optocoupler U2.

[0025] In one embodiment, the isolating switch circuit further includes:

[0026] Multiple relays, one of which is connected at one end to the neutral wire and at the other end to the power supply of the auxiliary winding of the transformer via a fifth resistor, and each of the other relays is connected at one end to one of the live phases and at the other end to one input terminal of the isolation detection circuit.

[0027] In addition, to achieve the above objectives, this application also proposes an AC charging pile, including a main charging circuit and a short-circuit detection circuit as described above.

[0028] In one embodiment of an AC charging pile, a main circuit switch is also included. The output terminal of the AC charging pile is connected to the main charging circuit and the short circuit detection circuit, and the main circuit switch is located at the output terminal of the AC charging pile.

[0029] This application proposes a short-circuit protection circuit for AC charging piles. It integrates isolation detection and disconnection switch circuits to achieve a dual fault diagnosis mechanism for live-to-neutral and live-to-live short circuits. Addressing the impedance coupling interference present in traditional solutions under multi-phase X-capacitor parallel scenarios, a time-division control strategy is employed to alternately conduct the two disconnection switches: short-circuit detection between live wires is performed the instant a single-phase live wire is energized. Timing isolation separates interference sources to different operating stages, avoiding coupling effects on the detection signal. Simultaneously, the electrical isolation characteristics between circuits are utilized to construct an independent detection loop, physically blocking the shunting effect of the equivalent branch of the X-capacitor, ensuring detection accuracy without the need for additional filtering modules. By optimizing circuit timing control and multiplexing isolation components, the reliability of live-to-neutral and live-to-live short-circuit detection is improved while reducing hardware complexity and production costs, providing a more efficient fault protection solution for charging equipment. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this utility model 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 only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0031] Figure 1 This is a structural diagram of a short-circuit detection circuit according to the present invention.

[0032] Figure 2 This is a circuit diagram of one embodiment of a short-circuit detection circuit according to the present invention;

[0033] Figure 3 This is a circuit diagram of an existing short-circuit detection circuit technology.

[0034] Reference numerals: Transformer auxiliary winding power supply 01, isolation detection circuit 02, isolation switch circuit 03, relay 04.

[0035] The realization of the purpose, functional features and advantages of this utility model will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0036] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0037] It should be noted that if the embodiments of this utility model involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0038] Furthermore, if the embodiments of this utility model involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, if the word "and / or" appears throughout the text, it means including three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution that simultaneously satisfies A and B. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this utility model.

[0039] This application proposes a short-circuit detection circuit for use in AC charging piles, wherein the output terminal of the AC charging pile includes a neutral wire and three-phase live wires, such as... Figure 1 As shown, it includes:

[0040] The transformer auxiliary winding power supply 01 is connected to the neutral wire; the isolation detection circuit 02 includes multiple input terminals, each of which is connected to each phase live wire, and is used to output a first fault signal when a short circuit is detected between the neutral wire and at least one phase live wire.

[0041] Two isolating switch circuits 03 have their input terminals connected to the transformer auxiliary winding power supply 01, their controlled terminals connected to external devices, and their output terminals connected to one of the live phase wires. These circuits are used to connect the transformer auxiliary winding power supply 01 to one of the live phase wires upon receiving an external signal. The isolation detection circuit 02 is also used to output a second fault signal when, while one of the isolating switch circuits 03 is in operation, a short circuit is detected between the corresponding connected live phase wire and any other live phase wire.

[0042] Specifically, the capacitor voltage divider short-circuit detection technology used in existing AC charging piles, while capable of fault diagnosis by monitoring voltage changes between the phase and neutral lines in its basic principle, exhibits significant limitations in handling complex application scenarios. When the charging gun is connected to the electric vehicle, the X-type safety capacitor inside the on-board charger forms a parallel loop with the pile-end detection circuit through the charging gun cable. This structural coupling alters the parameter characteristics of the original voltage divider network. Under normal operating conditions, the connection of the X capacitor significantly reduces the equivalent capacitive reactance between the phase and neutral lines, causing the actual voltage signal acquired by the voltage divider circuit to deviate from the preset reference value. Even without a real short circuit, the system may trigger a false alarm due to the voltage drop to the protection threshold. This false alarm phenomenon is particularly prominent in scenarios where the X capacitor parameters at the vehicle end are large, directly impacting the charging pile's startup success rate.

[0043] like Figure 3 As shown, another key shortcoming of traditional detection schemes lies in their fixed threshold judgment mechanism, which is difficult to adapt to the diverse needs of different vehicle models. Different electric vehicle manufacturers have varying EMC protection designs for on-board chargers, resulting in a wide dispersion in the actual capacitance value of the X capacitor across vehicles. When the detection system uses a fixed voltage threshold as the short-circuit criterion, it may cause continuous false triggering under normal connection conditions for high-capacitance models, while for low-capacitance models, the threshold setting may be too lenient, reducing the sensitivity to real short-circuit faults. This contradiction makes it difficult for the system to ensure the determinism of protection actions and to balance the compatibility requirements of different vehicle types, severely limiting the versatility of the charging equipment.

[0044] Furthermore, transient interference generated during the physical connection of the charging gun further exacerbates the risk of misjudgment by the detection system. At the moment of insertion and removal, the capacitive circuit formed between the X capacitor and the voltage divider capacitor at the charging terminal triggers a high-frequency charging and discharging process, generating a surge current with significant amplitude. This transient current couples into short-term voltage fluctuations in the detection circuit, and its amplitude characteristics are similar to the voltage drop in a real short-circuit fault. Especially in humid environments or under conditions of unstable contact impedance, the insertion and removal process may be accompanied by a step change in contact resistance, causing non-steady-state distortion in the output signal of the detection circuit. This further blurs the boundary between normal operation and real faults, making the system protection logic face more complex interference suppression challenges.

[0045] To address the aforementioned shortcomings, this application proposes a short-circuit detection circuit based on isolation detection and time-sharing control for detecting short circuits in AC charging piles. The short-circuit detection circuit includes a transformer auxiliary winding power supply 01, an isolation detection circuit 02, and two isolation switch circuits 03. The transformer auxiliary winding power supply 01 obtains energy from the main transformer via electromagnetic coupling, forming a low-voltage detection power supply independent of the charging circuit. Its output terminal is directly connected to the neutral line of the AC charging pile, constructing a detection potential platform based on the neutral line. The electrical isolation characteristics of the transformer auxiliary winding power supply 01, the isolation detection circuit 02, and the isolation switch circuits 03 achieve physical isolation between the detection circuit and the on-board charger, cutting off the parallel path between the on-board X capacitor and the pile-end detection circuit, fundamentally eliminating the influence of capacitive components at the vehicle end on the voltage divider network. Simultaneously, the low-voltage characteristics of the auxiliary winding power supply ensure the safety and reliability of the detection process, while providing a stable operating voltage for the subsequent isolation detection circuit 02.

[0046] The isolation detection circuit 02 has three independent input terminals, each connected to one of the three phase live wires, forming an insulation status monitoring channel between the neutral wire and each live wire. During the standby or initial connection phase of the charging pile, the circuit continuously monitors the voltage distribution between the neutral wire and each phase live wire. When any live wire short-circuits to the neutral wire due to insulation failure, the voltage balance of the corresponding channel is disrupted, and a first fault signal is output, achieving basic protection against live-neutral short circuits. At this time, the detection process is completely independent of the main charging circuit, avoiding the risk of misjudgment caused by the on-board X capacitor. Two isolating switch circuits 03 are connected to different phase live wires respectively. Their input terminals share the transformer auxiliary winding power supply 01, and the controlled terminals are connected in a time-sharing manner by an external controller. When an external device sends an activation signal, a designated isolating switch is turned on, connecting the auxiliary power supply to the live wire of that phase, forming a closed detection loop. At this time, if a live-wire short circuit occurs between the conducting phase and the auxiliary power supply and another non-conducting phase, the current will flow through the short circuit point to other phases, causing an abnormal voltage shift in the corresponding channel of the isolation detection circuit 02. The circuit identifies cross-phase short-circuit faults and outputs a second fault signal by comparing the potential difference between the conducting phase and other phases. This process involves time-division switching of the conducting phases to verify the inter-phase insulation status one phase at a time, thus avoiding signal crosstalk during multi-phase detection.

[0047] When the system is working, it first performs a basic screening for short circuits between the live and neutral wires through the isolation detection circuit 02. After confirming that there is no basic short circuit, the external controller activates the two isolating switch circuits 03 sequentially according to a preset timing sequence: when the first isolating switch is turned on, the system detects the insulation status between this phase and the other two phases; then it switches to the second isolating switch to verify the short circuits between the remaining phases. This time-division detection strategy decomposes the complex multiphase network into multiple independent detection stages, which not only avoids the capacitive reactance superposition effect caused by the parallel connection of multiphase X capacitors, but also isolates the transient interference caused by insertion and removal through the time dimension. Throughout the process, the first fault signal and the second fault signal form a hierarchical protection mechanism, respectively targeting the two fault modes of line-to-ground short circuit and line-to-line short circuit, to achieve accurate identification and rapid response to all types of short circuit faults.

[0048] This application proposes a short-circuit protection circuit for AC charging piles. It integrates isolation detection and disconnection switch circuit 03 to achieve a dual fault diagnosis mechanism for live-to-neutral and live-to-live short circuits. Addressing the impedance coupling interference present in traditional solutions under multi-phase X-capacitor parallel scenarios, a time-division control strategy is employed to alternately conduct the two disconnection switches: short-circuit detection between live wires is performed the instant a single-phase live wire is energized. Timing isolation separates interference sources to different operating stages, avoiding coupling effects on the detection signal. Simultaneously, the electrical isolation characteristics between circuits are utilized to construct an independent detection loop, physically blocking the shunting effect of the equivalent branch of the X-capacitor, ensuring detection accuracy without the need for additional filtering modules. By optimizing circuit timing control and multiplexing isolation components, the reliability of live-to-neutral and live-to-live short-circuit detection is improved while reducing hardware complexity and production costs, providing a more efficient fault protection solution for charging equipment.

[0049] In one embodiment, such as Figure 2 As shown, the isolation detection circuit 02 includes:

[0050] Multiple detection optocouplers are provided. The light-emitting end of each detection optocoupler is connected to the live wire of each phase, and the receiving end of each detection optocoupler is connected to an external device. The detection optocoupler is used to conduct and emit light when a short circuit occurs between the neutral wire and the corresponding live wire of the phase, and the receiving end receives the light and outputs a first fault signal to the external device.

[0051] Each optocoupler's light-emitting terminal is connected to the corresponding live wire via a current-limiting resistor, and its cathode side is connected to the negative terminal of the transformer auxiliary winding power supply 01, forming a voltage detection circuit with the neutral wire as the common reference point. Under normal operating conditions, a normal AC voltage exists between the live and neutral wires. At this time, the light-emitting terminal is subjected to a reverse bias voltage, the LED is in the off state, and the optocoupler receiver has no light signal input, maintaining a high impedance state. When a short circuit occurs between a live wire and the neutral wire, the live wire potential is forcibly pulled down to near the neutral wire potential, causing a significant increase in the forward voltage across the light-emitting terminal. When this voltage exceeds the LED's conduction threshold, current forms a path through the auxiliary winding power supply, the short circuit point, and the current-limiting resistor, driving the LED to emit light. The phototransistor at the receiver saturates and conducts under optical signal excitation, pulling the collector-emitter level down from high, outputting a clear first fault signal to the external controller. This process, through the electrical isolation characteristics of the optocoupler, converts the high-voltage side short-circuit state into a low-voltage side logic signal, achieving lossless transmission and safe isolation of fault information.

[0052] The three-phase live wires are connected to three independent detection optocouplers, forming parallel detection channels. When a live-to-neutral short circuit occurs in any phase, only the optocoupler in the corresponding channel is triggered, while the other channels remain silent. External equipment can accurately locate the faulty phase by identifying the level transition at the receiver of a specific optocoupler. Simultaneously, the output signals from the receivers of multiple optocouplers are integrated through a logic OR gate circuit, ensuring that a short circuit in any phase triggers system-level protection, balancing fault location accuracy and real-time response. The current-limiting resistor at the LED is matched to the voltage parameters of the auxiliary winding power supply, ensuring that only a sufficient driving current to light the LED is generated during a true short circuit, avoiding false triggering caused by line induced voltage or noise. The photoelectric conversion mechanism at the receiver relies entirely on the physical optical path, unaffected by electromagnetic interference, isolating common-mode noise from interfering with the fault judgment logic at the signal transmission level, thus improving the detection's anti-interference capability.

[0053] In one embodiment, the isolation detection circuit 02 is further configured to drive the corresponding connected detection optocoupler to work when one of the isolation switch circuits 03 is in working state, such that the corresponding connected phase wire and the detection optocoupler are in non-detection state, while the remaining detection optocouplers are in detection state; when a short circuit occurs between the non-detection wire and another phase wire, the light-emitting end of the corresponding detection optocoupler in detection state is turned on and emits light, and the corresponding receiving end receives the light and outputs a second fault signal to an external device.

[0054] When a disconnector circuit 03 is activated, the corresponding live wire controlled by it forms a closed loop with the transformer auxiliary winding power supply 01. At this time, the external controller synchronously sends a suppression signal (such as pulling down the control level) to the detection optocoupler connected to that phase, forcing its light-emitting terminal to be in a reverse bias state. Even if there is a live-to-neutral short circuit, the light-emitting diode cannot conduct. This operation puts the detection optocoupler of that phase into a non-detection state, temporarily removing it from live-to-neutral short circuit detection and avoiding false triggering caused by the activation of this phase. The detection optocouplers of the other unactivated phases remain in the detection state, continuously monitoring the insulation status between each phase and the neutral wire. When the activated phase (such as L1) experiences a live-to-live short circuit with any other phase (such as L2), the short-circuit current flows through the disconnector circuit 03 of L1 to L2, causing an abnormal rise in the potential of L2. Since the detection optocoupler of L2 is still in the detection state, its light-emitting terminal conducts and emits light because the voltage between L2 and the neutral wire exceeds the threshold, triggering the receiver to output a second fault signal. At this point, the L2 detection optocoupler essentially detects the cross-phase short circuit event indirectly by sensing the voltage shift of the neutral line to the short-circuited phase.

[0055] By switching on the disconnecting switch, a phase-to-phase short circuit is transformed into an abnormal voltage difference between a single phase and the neutral line. For example, when L1-L2 is short-circuited, L1 is pulled to the auxiliary power supply potential due to the disconnecting switch's operation, while L2 is at the same potential as L1 through the short-circuit point, resulting in a significant drop in L2's voltage relative to the neutral line. The L2 detection optocoupler is triggered when the forward voltage difference reaches a threshold, and the system can locate the short-circuited phase based on the triggered optocoupler channel. This mechanism simplifies complex phase-to-phase insulation detection to single-phase voltage monitoring, reducing detection complexity. By time-sharing the detection channel of the active phase, the system avoids signal conflicts caused by the same phase simultaneously participating in power supply and detection. The optocoupler in the non-detection state physically isolates the interference of the current phase's power supply circuit from the detection process, while the strong potential coupling characteristics of the active phase with other phases ensure that a phase-to-phase short circuit will inevitably cause a voltage anomaly in the non-active phase, achieving the inevitability of fault transmission and the determinism of detection.

[0056] In one embodiment, such as Figure 2 As shown, the isolation detection circuit 02 further includes a first power supply. The light-emitting end of the detection optocoupler includes a first resistor and a first light-emitting diode. The anode of the first light-emitting diode is connected to the corresponding live wire through the first resistor, and the cathode of the first light-emitting diode is grounded. The receiving end of the detection optocoupler includes a second resistor and a first phototransistor. The emitter of the first phototransistor is connected to an external device and to the first power supply through the second resistor, and the collector is grounded.

[0057] The light-emitting end of the optocoupler consists of a first resistor and a first light-emitting diode (LED) connected in series, forming a high-voltage side signal acquisition unit. The first resistor, connected in series between the live wire and the anode of the LED, performs both current limiting and voltage division functions, ensuring that the high voltage from the live wire is matched to the LED's withstand voltage and drive current range after voltage division. The LED cathode is directly grounded (neutral reference), forming a loop with the live-neutral voltage as the detection object. The phototransistor at the receiving end and a second resistor form a low-voltage side signal conversion unit. The second resistor acts as a pull-up resistor, connected between the first power supply and the phototransistor's emitter, defining the logic level reference for the signal output. When the insulation between the live wire and neutral wire is good, the live wire maintains a normal AC voltage to ground. Because the LED anode is connected to the live wire through the first resistor and the cathode is grounded, its terminals bear a reverse voltage (depending on the instantaneous polarity of the live wire). At this time, the LED is in a reverse cutoff state, no current flows through the light-emitting end, and the internal optical path of the optocoupler is broken. The phototransistor at the receiving end remains cut off due to the lack of light, and its emitter is pulled up to the first power supply voltage through the second resistor, outputting a high-level signal, indicating that the system is fault-free.

[0058] When a short circuit occurs between the live wire and the neutral wire, the live wire potential is forcibly pulled down to near the neutral wire potential. At this time, the anode of the LED forms a path with the short-circuit point through the first resistor, generating a forward voltage difference between the anode and the cathode. When this voltage difference exceeds the LED's conduction threshold, a forward current flows through the first resistor and the LED, driving it to emit light. After receiving the light signal, the phototransistor enters a saturated conduction state, and the impedance between the emitter and collector drops sharply, causing the emitter potential to be pulled down to near ground potential, outputting a low-level first fault signal. This signal triggers protection action through the external device interface. The first power supply provides independent power to the receiving circuit and achieves potential isolation from the high-voltage live wire system through an optocoupler. The light-emitting end and the receiving end of the optocoupler are coupled only through the optical path, completely blocking electrical interference from the high voltage of the live wire to the low-voltage control circuit. The combination of the second resistor and the phototransistor converts the light signal into a clear logic level (high / low), ensuring that external devices can accurately identify the fault state.

[0059] The design of the first resistor must meet two constraints: under normal live wire voltage, the resistance must be large enough to limit reverse leakage current and prevent false triggering; under short circuit, the resistance must be small enough to allow sufficient forward current to drive the LED. This dynamic impedance characteristic can effectively suppress malfunctions caused by transient surges or high-frequency noise in the line. Simultaneously, the optocoupler's photoelectric conversion mechanism has inherent filtering characteristics, responding only to continuous illumination signals, further filtering out transient interference pulses and improving system immunity.

[0060] In one embodiment, such as Figure 2 As shown, the isolating switch circuit 03 includes:

[0061] The control optocoupler has an emitting end connected to an external device, a receiving end connected to a certain phase live wire, and a receiving end connected to the transformer auxiliary winding power supply 01. The control optocoupler is used to connect the transformer auxiliary winding power supply 01 to the corresponding phase live wire when the emitting end is turned on by an external signal and emits light, so as to control the corresponding connected phase live wire and the detection optocoupler to be in a non-detection state.

[0062] The light-emitting end of the control optocoupler is directly controlled by an external device, forming a low-voltage side control signal input channel. When the external device sends an activation command, the light-emitting diode conducts and emits light, triggering the photosensitive device at the receiving end through the optical path. This process converts the low-voltage control signal into a high-voltage side electrical action, achieving complete electrical isolation between the high and low voltage systems and avoiding direct interference from high-voltage circuits to the control circuit. One end of the receiving end is connected to the transformer auxiliary winding power supply 01, and the other end is connected to the corresponding phase live wire. When the receiving end of the control optocoupler is turned on by light, a closed loop is formed between the auxiliary winding power supply and the live wire. At this time, the auxiliary winding power supply injects current into the live wire through the receiving end of the control optocoupler, forcing the live wire potential to be clamped to the potential of the auxiliary power supply. This active potential reconstruction forces the voltage difference between the live wire and the neutral wire to be adjusted, destroying the basic conditions for live-neutral voltage detection, thereby shielding the monitoring function of the phase detection optocoupler and setting it to a non-detection state.

[0063] When a live wire is not in detection mode, its voltage relative to the neutral wire is limited to an extremely low range due to the potential injection from the auxiliary power supply. In this state, even if a short circuit occurs between the live wire and the neutral wire, the voltage difference is insufficient to drive the LED of the detection optocoupler, thus avoiding false alarms. This design achieves dynamic shielding of the detection function by actively intervening in the live wire potential, rather than simply relying on the physical disconnection of an electrical switch. If a live wire in non-detection mode short-circuits with another live wire, the short-circuit current will cause an abnormal shift in the potential of the adjacent live wire. Since the detection optocoupler of the adjacent phase remains active, its light-emitting terminal can sense the shifted live-neutral voltage difference. When the voltage difference exceeds a threshold, the corresponding detection optocoupler is triggered, outputting a second fault signal. This mechanism transforms an interphase short circuit into a single-phase voltage anomaly in an adjacent phase through potential coupling, indirectly achieving the detection of cross-phase faults.

[0064] The coordination between control optocouplers and detection optocouplers forms a time-division detection architecture: only one phase is allowed to be in a non-detection state at any given time, while the remaining phases remain in the detection state. This dynamic switching strategy avoids conflicts caused by multiple phases being powered simultaneously, and ensures that if any phase experiences a short circuit to ground or between phases, at least one active detection channel can capture the fault. By cyclically switching the non-detection phases, the system can periodically complete a full-phase insulation status self-check, improving the completeness of fault coverage.

[0065] In one embodiment, the isolating switch circuit 03 further includes a second power supply. The light-emitting end of the control optocoupler includes a third resistor and a second light-emitting diode. The anode of the second light-emitting diode is connected to the second power supply through the third resistor, and the cathode of the second light-emitting diode is connected to an external device. The receiving end of the control optocoupler includes a fourth resistor and a second phototransistor. The emitter of the second phototransistor is connected to the second power supply through the fourth resistor, and the collector is connected to a certain phase live wire.

[0066] The light-emitting end of the control optocoupler consists of a third resistor connected in series with a second LED. The anode of the second LED is connected to the second power supply through the third resistor, while the cathode is connected to the control signal of the external device. The third resistor serves a dual purpose: limiting the current flowing through the LED to prevent damage from overcurrent; and ensuring compatibility between the low-voltage control signal output by the external device and the voltage system of the second power supply through resistance matching. The second power supply, as an independent power supply unit, is completely isolated from the high-voltage system of the main circuit, severing the direct electrical coupling between the control loop and the high-voltage loop at its source, ensuring operational safety and anti-interference capabilities. When the external device needs to activate the control optocoupler, it lowers the cathode potential of the second LED, creating a forward conduction condition between its anode and cathode. At this time, the voltage of the second power supply powers the LED through the third resistor, driving it to emit a light signal of a specific intensity. This design makes the transmission of control signals entirely dependent on optical coupling, completely eliminating the electrical connection risks between high and low voltage circuits. The external device only needs to provide a low-level logic signal to complete the operation control of the high-voltage side, significantly reducing system complexity.

[0067] The control optocoupler receiver employs a combination of a second phototransistor and a fourth resistor. The emitter of the second phototransistor is connected to the second power supply via the fourth resistor, while the collector is directly connected to a specific phase's live wire. When the light-emitting end is activated, the optical signal triggers the phototransistor to conduct, forming a current path from the second power supply to the live wire. The fourth resistor plays a dynamic impedance regulation role in this process: it prevents high-voltage reverse surges from the live wire from damaging the phototransistor and, together with the internal resistance of the conducting transistor, forms a voltage divider network, precisely clamping the live wire potential to the voltage level of the second power supply. This active potential intervention strategy forcibly eliminates the natural voltage difference between the controlled phase's live wire and neutral wire. After connecting the second power supply to the live wire through optocoupler conduction, the actual potential of the live wire is reconstructed to the reference voltage of the second power supply. At this time, the voltage difference between the live wire and neutral wire of that phase is compressed to near zero, causing the LED of the detection optocoupler for that phase to not receive sufficient forward bias voltage. Even if a live-neutral short circuit occurs, the detection circuit will not trigger an alarm. This unique design, which uses a potential shielding mechanism rather than physical disconnection, maintains the electrical continuity of the system while achieving selective failure of the detection function.

[0068] In one embodiment, such as Figure 2 As shown, there are three detection optocouplers, including detection optocoupler U3, detection optocoupler U4 and detection optocoupler U5; there are two control optocouplers, including control optocoupler U1 and control optocoupler U2; the three-phase live wires include live wire L1, live wire L2 and live wire L3; it is worth noting that in this embodiment, the first power supply and the above-mentioned second power supply are the same power supply.

[0069] The receiving end of the control optocoupler U1 is connected to the transformer auxiliary winding power supply O1 and the live wire L1, and the emitting end is connected to an external device; the receiving end of the control optocoupler U2 is connected to the transformer auxiliary winding power supply O1 and the live wire L2, and the emitting end is connected to an external device; the receiving end of the detection optocoupler U3 is connected to the first power supply, and the emitting end is connected to the live wire L3; the receiving end of the detection optocoupler U4 is connected to the first power supply, and the emitting end is connected to the live wire L2 and the receiving end of the control optocoupler U2; the receiving end of the detection optocoupler U5 is connected to the first power supply, and the emitting end is connected to the live wire L1 and the receiving end of the control optocoupler U2.

[0070] Optical couplers U1 and U2 control the isolation control functions of live wires L1 and L2, respectively. Their receiving ends are directly connected to the transformer auxiliary winding power supply O1 and the corresponding live wire, forming a high-voltage side potential adjustment channel. When an external device triggers the light-emitting end to conduct, the optical signal drives the photosensitive device at the receiving end to conduct, injecting the voltage of the auxiliary power supply into the corresponding live wire. This process actively clamps the live wire potential, disrupting the natural voltage difference between the live wire and the neutral wire, forcing it into a non-detection state. For example, when U1 is activated, the potential of L1 is reshaped by the auxiliary power supply, ensuring that the detection optical coupler U5 cannot be triggered when the insulation of that phase fails.

[0071] The detection optocoupler U3 is independently connected to the live wire L3. Its light-emitting end and L3 directly form a detection circuit, and the receiving end defines the logic output level through the first power supply. When L3 is not controlled by the optocoupler, its light-emitting end operates through the natural voltage difference between the live wire L3 and the neutral wire. If the insulation of L3 to the neutral wire fails, the light-emitting diode conducts, triggering the phototransistor and outputting a low-level fault signal. As the only detection unit in the three phases that is not dynamically controlled, U3 maintains continuous monitoring of L3, ensuring that at least one active fault detection channel exists in the system.

[0072] The light-emitting terminals of detection optocouplers U4 and U5 employ a composite connection design: the light-emitting terminal of U4 is simultaneously connected to the live wire L2 and the receiving terminal of the control optocoupler U2, while the light-emitting terminal of U5 is connected to the live wire L1 and the receiving terminal of U2. When the control optocoupler U2 is not activated, its receiving terminal is in the open state, and the light-emitting terminals of U4 and U5 form a detection circuit only through the corresponding live and neutral wires, performing conventional insulation monitoring. If U2 is activated, its receiving terminal conducts, introducing auxiliary power to L2. At this time, the light-emitting terminal of U4 cannot form an effective detection voltage because the potential of L2 is forcibly raised; simultaneously, the light-emitting terminal of U5 forms a bypass path because the receiving terminal of U2 is conducting, and its detection logic is affected by both the state of U2 and the potential of L1. This design achieves phase-to-phase state coupling, so that the control action of U2 not only acts on L2 but also indirectly affects the detection logic of L1.

[0073] When the control optocoupler U1 or U2 is activated, the corresponding live wire is placed in a non-detection state, but at least one of the remaining two detection optocouplers remains active. For example, when U1 activates and shields L1 detection, U3 still monitors L3, and U4 monitors L2; ​​when U2 activates and shields L2 detection, U3 monitors L3, and U5 continues to monitor L1 through dynamic path adjustment. This architecture ensures that at least two phases are in an effective monitoring state at any given time through time-division multiplexing and cross-detection. If a phase-to-phase short circuit occurs in the shielded phase (such as a short circuit between L1 and L2), its abnormal current will cause the potential of the adjacent phase to shift, triggering the output fault signal of the unshielded detection optocoupler, forming an indirect capture capability for cross-phase faults. The transformer auxiliary winding power supply 01 provides an independent potential reference for the control optocoupler, ensuring that the live wire potential adjustment process is isolated from the main power system. When the control optocoupler is turned on, the auxiliary power supply acts directly on the live wire through a low-impedance path, quickly completing the potential reconstruction. The first power supply of the detection optocoupler provides a stable logic level reference for its receiving end, avoiding interference from high-voltage side potential fluctuations on the signal output. The two power supply systems are physically isolated by optocouplers, which maintains detection accuracy while blocking potential interference paths between high and low voltage circuits.

[0074] In one embodiment, the isolation switch circuit 03 further includes:

[0075] Multiple relays 04, one end of which is connected to the neutral wire and the other end is connected to the transformer auxiliary winding power supply 01 through the fifth resistor, and one end of each of the other relays 04 is connected to one of the live phases and the other end is connected to one input terminal of the isolation detection circuit 02.

[0076] Relay 04, connected to the neutral wire, serves as the system's reference path switching node. One end of it is fixedly connected to the neutral wire, and the other end is connected to the transformer auxiliary winding power supply 01 via a fifth resistor. Relay 04 remains normally closed, ensuring a stable reference potential path between the neutral wire and the auxiliary winding power supply. When the system requires high-voltage side isolation or maintenance, relay 04 is controlled to open, physically disconnecting the neutral wire from the auxiliary power supply and eliminating interference from the neutral wire potential to the detection circuit. The fifth resistor in this path performs current limiting and buffering functions, limiting the current intensity injected by the auxiliary power supply into the neutral wire and suppressing voltage spikes caused by neutral wire potential fluctuations.

[0077] The remaining relays 04 correspond to the respective live wires of each phase. One end of each relay is fixedly connected to the corresponding live wire, and the other end is connected to the input terminal of the isolation detection circuit 02. Each live wire relay 04 independently controls the on / off state of the detection circuit for its corresponding phase: in normal operating mode, relay 04 remains in the conducting state, allowing the live wire signal to be transmitted to the isolation detection circuit 02 through the relay 04 contacts, realizing real-time monitoring of the insulation status of that phase. When a specific phase needs to be shielded or the system enters maintenance mode, an external control signal triggers the corresponding relay 04 to disconnect, completely cutting off the connection between that phase and the detection circuit, forming physical isolation, and preventing the faulty phase from interfering with other detection channels. The relay group 04 achieves dynamic reconstruction of the detection path through coordinated actions. For example, when a potential insulation fault is detected in a phase, the system can disconnect the relay 04 for that phase alone, while keeping the relays 04 for other phases conducting, thereby accurately pinpointing the faulty phase. If the neutral wire relay 04 disconnects synchronously, the system enters a fully isolated state, and the auxiliary power supply is completely disconnected from the main circuit, providing a safety guarantee for in-depth fault diagnosis. The relay group 04, together with the control optocoupler and the detection optocoupler, constitutes a multi-layer interlocking mechanism. For example, when the control optocoupler activates the potential clamping of a certain phase, the corresponding live wire relay 04 can be simultaneously disconnected, forming a dual protection of electrical isolation and potential shielding. At the same time, the state of the neutral wire relay 04 is linked with other relays 04 to ensure that any operation follows the timing logic of "disconnect before connect" or "connect before disconnect," preventing momentary short circuits caused by competition hazards.

[0078] Combining the above embodiments with the appendix Figure 2 , attached Figure 2This includes: VCC, the auxiliary winding power supply 01 for the transformer; 3.3V, the control terminal voltage (also the first and second power supplies mentioned in the above embodiments); U1 and U2, control optocouplers; U3-U5, detection optocouplers; and K2A, K2B, K3A, and K3B, relays. The receiving end of control optocoupler U1 is connected to VCC and the live wire L1, while the emitting end is connected to an external device. The receiving end of control optocoupler U2 is connected to VCC and the live wire L2, while the emitting end is connected to an external device. The receiving end of detection optocoupler U3 is connected to 3.3V, and the emitting end is connected to the live wire L3. The receiving end of detection optocoupler U4 is connected to 3.3V, and the emitting end is connected to the live wire L2 and the receiving end of control optocoupler U2. The receiving end of detection optocoupler U5 is connected to 3.3V, and the emitting end is connected to the live wire L1 and the receiving end of control optocoupler U2.

[0079] First, when the charging process of the charging pile enters the stage where short circuit detection is required, relays K2A, K2B, K3A, and K3B are closed, while optocouplers U1 and U2 are controlled to be de-conducted. If one or more optocouplers U3, U4, and U5 are detected to be conducting, a short circuit has occurred at the output, and the charging pile reports a fault. Otherwise, it is assumed that there is no short circuit between N and L1, N and L2, and N and L3, that is, there is no short circuit between the neutral wire and the live wire.

[0080] Next, control U1 to conduct while U2 does not conduct. If one of U3 or U4 is conducting at this time, a short circuit has occurred in the output, and the charging pile will report a fault. Otherwise, it is considered that there is no short circuit, that is, there is no short circuit between live wire L1 and live wire L2, or between live wire L1 and live wire L3.

[0081] Finally, control U2 to conduct while keeping U1 off. If either U3 or U5 is conducting at this point, a short circuit has occurred at the output, and the charging station will report a fault. Otherwise, it is assumed that no short circuit has occurred, meaning there is no short circuit between live wires L2 and L1, or between live wires L2 and L3. The charging station is functioning normally. Disconnect relays K2A, K2B, K3A, and K3B to continue the charging process.

[0082] Furthermore, to achieve the above objectives, this application also proposes an AC charging pile, including a main charging circuit and a short-circuit detection circuit as described above. The output terminal of the AC charging pile includes a neutral wire and three live wires. The short-circuit detection circuit includes: a transformer auxiliary winding power supply 01 connected to the neutral wire; an isolation detection circuit 02 including multiple input terminals, each input terminal connected to each of the live wires, used to output a first fault signal when a short circuit is detected between the neutral wire and at least one live wire; and two isolation switch circuits 03, with input terminals connected to the transformer auxiliary winding power supply 01, controlled terminals connected to external devices, and output terminals connected to one of the live wires, used to connect the transformer auxiliary winding power supply 01 to one of the live wires upon receiving an external signal. The isolation detection circuit 02 is also used to output a second fault signal when, while one of the two isolation switch circuits 03 is in operation, a short circuit is detected between the corresponding connected live wire and any other live wire.

[0083] When the system is working, it first performs a basic screening for short circuits between the live and neutral wires through the isolation detection circuit 02. After confirming that there is no basic short circuit, the external controller activates the two isolating switch circuits 03 sequentially according to a preset timing sequence: when the first isolating switch is turned on, the system detects the insulation status between this phase and the other two phases; then it switches to the second isolating switch to verify the short circuits between the remaining phases. This time-division detection strategy decomposes the complex multiphase network into multiple independent detection stages, which not only avoids the capacitive reactance superposition effect caused by the parallel connection of multiphase X capacitors, but also isolates the transient interference caused by insertion and removal through the time dimension. Throughout the process, the first fault signal and the second fault signal form a hierarchical protection mechanism, respectively targeting the two fault modes of line-to-ground short circuit and line-to-line short circuit, to achieve accurate identification and rapid response to all types of short circuit faults.

[0084] This application proposes a short-circuit protection circuit for AC charging piles. It integrates isolation detection and disconnection switch circuit 03 to achieve a dual fault diagnosis mechanism for live-to-neutral and live-to-live short circuits. Addressing the impedance coupling interference present in traditional solutions under multi-phase X-capacitor parallel scenarios, a time-division control strategy is employed to alternately conduct the two disconnection switches: short-circuit detection between live wires is performed the instant a single-phase live wire is energized. Timing isolation separates interference sources to different operating stages, avoiding coupling effects on the detection signal. Simultaneously, the electrical isolation characteristics between circuits are utilized to construct an independent detection loop, physically blocking the shunting effect of the equivalent branch of the X-capacitor, ensuring detection accuracy without the need for additional filtering modules. By optimizing circuit timing control and multiplexing isolation components, the reliability of live-to-neutral and live-to-live short-circuit detection is improved while reducing hardware complexity and production costs, providing a more efficient fault protection solution for charging equipment.

[0085] In one embodiment of an AC charging pile, a main circuit switch is also included. The output terminal of the AC charging pile is connected to the main charging circuit and the short-circuit detection circuit, and the main circuit switch is located at the output terminal of the AC charging pile. The core function and safety isolation mechanism of the main circuit switch are as follows:

[0086] The main circuit switch, as the core control node at the output end of the AC charging pile, plays a dual role as the main switch for power transmission and emergency fault isolation. Under normal operating conditions, its closed contacts ensure a complete path between the main charging circuit and the external vehicle battery system, allowing efficient power transfer from the grid to the battery. When overcurrent, short circuit, or system abnormality is detected, the main circuit switch forcibly disconnects the physical connection within milliseconds via an electromagnetic drive mechanism, completely blocking the energy transmission path. Internally, it employs an arc-resistant design and multiple arc-extinguishing structures to ensure reliability and safety during high-voltage, high-current interruption, while a dual mechanical and electrical interlocking mechanism prevents misoperation. The main charging circuit, as the backbone channel for power conversion and output, achieves stable AC power transmission and power matching through an optimized topology. Its core functions include voltage / current waveform shaping and dynamic load matching: suppressing harmonic interference through a power factor correction module and smoothing the output waveform using a filtering network to ensure compliance with the electrical quality standards of electric vehicle charging interfaces. During charging, the control module monitors the battery status (such as SOC and temperature) in real time and dynamically adjusts output parameters (such as pulse width modulation duty cycle) to achieve smooth switching between different charging stages, such as constant current and constant voltage. The circuit also integrates reverse current blocking to prevent battery energy from flowing back into the grid.

[0087] The short-circuit detection circuit employs multiple isolation devices and a tiered judgment strategy to construct a three-dimensional protection system. Current transformers and Hall effect sensors sample the output current signal in parallel, comparing it in real-time with a preset threshold using a high-speed comparator. When the instantaneous current exceeds the safety limit, the hardware trigger circuit sends a trip signal directly to the main circuit switch, prioritizing the software control system, ensuring protection action is initiated within microseconds. Simultaneously, the voltage differential detection module monitors abnormal line voltage drops, cross-validating this with temperature sensor data to effectively distinguish between a true short circuit and a transient surge. This circuit maintains real-time communication with the main charging control system's digital bus, enabling fault type identification and historical data recording.

[0088] The above embodiments are merely preferred embodiments of this utility model and do not limit the patent scope of this utility model. Any equivalent structural or procedural transformations made based on the content of this utility model specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this utility model.

Claims

1. A short-circuit detection circuit, applied to an AC charging pile, wherein the output terminal of the AC charging pile includes a neutral wire and three-phase live wires, characterized in that, include: The transformer auxiliary winding power supply is connected to the neutral line; An isolation detection circuit includes multiple input terminals, each of which is connected to each phase live wire, and is used to output a first fault signal when a short circuit is detected between the neutral wire and at least one phase live wire; Two isolating switch circuits are provided, with the input end connected to the power supply of the transformer auxiliary winding, the controlled end connected to an external device, and the output end connected to one of the live phases. They are used to connect the power supply of the transformer auxiliary winding to one of the live phases when an external signal is received. The isolation detection circuit is further configured to output a second fault signal when a short circuit is detected between the corresponding connected phase wire and any other phase wire, provided that one of the two isolation switch circuits is in operation.

2. The short-circuit detection circuit as described in claim 1, characterized in that, The isolation detection circuit includes: Multiple detection optocouplers are provided, with the light-emitting end of each detection optocoupler connected to the live wire of each phase, and the receiving end of each detection optocoupler connected to an external device. The detection optocoupler is used to activate the connection between the light-emitting end and the power supply of the transformer auxiliary winding when a short circuit occurs between the neutral wire and the corresponding live wire, and to emit light when the receiving end receives the light and outputs a first fault signal to an external device.

3. The short-circuit detection circuit as described in claim 2, characterized in that, The isolation detection circuit is also used to drive the corresponding connected detection optocoupler to work when a certain isolation switch circuit is in working state, so that the corresponding connected phase wire and the detection optocoupler are in non-detection state, and the other detection optocouplers are in detection state. When a short circuit occurs between a live wire in a non-detection state and another live wire, the light-emitting end of the corresponding detection optocoupler in the detection state is turned on and emits light. The corresponding receiving end receives the light and outputs a second fault signal to an external device.

4. The short-circuit detection circuit as described in claim 2, characterized in that, The isolation detection circuit also includes a first power supply, and the detection optocoupler light-emitting terminal includes a first resistor and a first light-emitting diode. The anode of the first light-emitting diode is connected to the corresponding live wire through the first resistor, and the cathode of the first light-emitting diode is grounded. The receiving end of the detection optocoupler includes a second resistor and a first phototransistor. The emitter of the first phototransistor is connected to an external device and a first power supply through the second resistor, and the collector is grounded.

5. The short-circuit detection circuit as described in claim 2, characterized in that, The isolating switch circuit includes: The optocoupler is controlled so that the light-emitting end is connected to an external device, one end of the receiving end is connected to a certain phase of the live wire, and the other end of the receiving end is connected to the power supply of the auxiliary winding of the transformer. The control optocoupler is used to connect the transformer auxiliary winding power supply and the corresponding phase wire when the light-emitting end is turned on and emits light upon receiving an external signal, so as to control the corresponding connected phase wire and the detection optocoupler to be in a non-detection state.

6. The short-circuit detection circuit as described in claim 5, characterized in that, The isolating switch circuit also includes a second power supply. The light-emitting end of the control optocoupler includes a third resistor and a second light-emitting diode. The anode of the second light-emitting diode is connected to the second power supply through the third resistor, and the cathode of the second light-emitting diode is connected to an external device. The receiving end of the control optocoupler includes a fourth resistor and a second phototransistor. The emitter of the second phototransistor is connected to a second power supply through the fourth resistor, and the collector is connected to a certain phase live wire.

7. The short-circuit detection circuit as described in claim 5, characterized in that, The detection optocouplers are three in number, including detection optocoupler U3, detection optocoupler U4 and detection optocoupler U5; the control optocouplers are two in number, including control optocoupler U1 and control optocoupler U2; the three-phase live wires are live wire L1, live wire L2 and live wire L3; The receiving end of the control optocoupler U1 is connected to the power supply of the transformer auxiliary winding and the live wire L1, and the emitting end is connected to an external device; the receiving end of the control optocoupler U2 is connected to the power supply of the transformer auxiliary winding and the live wire L2, and the emitting end is connected to an external device. The receiving end of the detection optocoupler U3 is connected to the first power supply, and the emitting end is connected to the live wire L3; the receiving end of the detection optocoupler U4 is connected to the first power supply, and the emitting end is connected to the live wire L2 and the receiving end of the control optocoupler U2; the receiving end of the detection optocoupler U5 is connected to the first power supply, and the emitting end is connected to the live wire L1 and the receiving end of the control optocoupler U2.

8. The short-circuit detection circuit as described in any one of claims 1-7, characterized in that, The isolating switch circuit also includes: Multiple relays, one of which is connected at one end to the neutral wire and at the other end to the power supply of the auxiliary winding of the transformer via a fifth resistor, and each of the other relays is connected at one end to one of the live phases and at the other end to one input terminal of the isolation detection circuit.

9. An AC charging pile, characterized in that, It includes a main charging circuit and a short-circuit detection circuit as described in any one of claims 1-8.

10. The AC charging pile as described in claim 9, characterized in that, It also includes a main circuit switch. The output terminal of the AC charging pile is connected to the main charging circuit and the short circuit detection circuit. The main circuit switch is located at the output terminal of the AC charging pile.

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