An identification circuit for capacitive and resistive short circuits in ac loads

Abstract

The utility model relates to an identification circuit of capacitive and resistive load short circuit in alternating current load, and the circuit includes current detection unit A, MOS tube switch unit B, residual current sampling unit E, live wire / zero line's load short circuit detection unit C, test power control unit D, live wire / live wire short circuit detection unit F, MCU operation control unit G and power supply unit H, the utility model can be alone or simultaneously identified between zero line and live wire, live wire and ground wire, live wire and live wire short circuit, is the rapid identification of the current of the capacitive load false short circuit and resistive short circuit (true short circuit) in addition, and can reduce the identification error phenomenon of MOS tube electronic switch protection load output end because of the capacitive load.

Description

Technical Field

[0001] This utility model relates to the field of short circuit identification and protection technology, and in particular to an identification circuit for short circuits in capacitive and resistive loads in AC loads. Background Technology

[0002] With the rapid development of technology, the use of high-power charging piles and AC power is becoming increasingly widespread, leading to higher and higher requirements for electrical safety. When an AC power line short-circuits, the current in the line increases dramatically and instantaneously, potentially reaching several times or even tens of times the normal operating current. Such a powerful short-circuit current generates heat and electrodynamic forces far exceeding normal levels in electrical equipment, potentially causing serious consequences such as cable insulation breakdown, conductor melting, and damage to equipment components. This can render the equipment unable to operate normally or even cause permanent damage, requiring high repair and replacement costs. AC short circuits can also cause voltage drops, disrupting the voltage stability of the power system. Furthermore, in environments using high-power equipment, a short circuit in an AC power line can generate dangerous electric arcs and splashing high-temperature sparks, posing a risk of burns and fires (igniting nearby flammable materials).

[0003] To address this issue, the applicant developed a detection and protection circuit for high-power AC short circuits (patent number ZL202322634423.6). This circuit compares the peak voltage waveform at the AC input terminal with the peak short-circuit current waveform. When the peak voltage of the current waveform is greater than the peak voltage of the voltage waveform, the system quickly shuts off the output of the MOSFET or IGBT. It can also accurately and quickly shut off the MOSFET or IGBT when the AC current crosses zero. This solves the problem of high-temperature arcs and splashing sparks generated when short circuits occur between the neutral and live wires, between the live and ground wires, and between live wires, thus preventing burns and fires. Later, during application, it was discovered that, like other products on the market, there was a significant drawback: capacitive loads in the circuit (such as computers, inverter air conditioners, high-power LED lights, video walls, etc.) would be misjudged as short circuits. This meant that the output of the MOSFET electronic switch protector would be incorrectly identified due to the connection of high-power capacitive loads. Further research and development were conducted to find a correct and perfect solution for the current-limiting protector's identification of capacitive loads in the circuit, and for correcting short circuits between AC neutral and live wires, live and ground wires, and live and live wires due to capacitive loads in the circuit. The goal was to achieve true arc-free short circuits and prevent malfunctions. Utility Model Content

[0004] In view of the defects or deficiencies in the existing technology, the technical problem to be solved by this utility model is to provide an identification circuit for short circuits of capacitive and resistive loads in AC loads.

[0005] To achieve the above objectives, the technical solution adopted by this utility model is to provide an identification circuit for capacitive and resistive load short circuits in AC loads, including a current detection unit A, a MOSFET switching unit B, a residual current sampling unit E, a live / neutral load short circuit detection unit C, a test power supply control unit D, a live / live short circuit detection unit F, an MCU operation control unit G, and a power supply unit H; characterized in that, The current detection unit A, the MOSFET switching unit B, the residual current sampling unit E, the live / neutral load short circuit detection unit C, the test power control unit D, the live / live short circuit detection unit F, and the power supply unit H are all connected to the MCU operation and control unit G.

[0006] As a further improvement of this utility model, the current detection unit A includes a current transformer L2. The live wire passes through the center hole of the current transformer L2. The second pin of the current transformer L2 is connected to one end of resistors R14 and R15 respectively, and then connected to the input terminal of amplifier U6 through resistor R15. The output terminal of amplifier U6 is connected to one end of resistor R18, and the other end of resistor R18 is connected to the 19th pin of chip U8 in MCU operation and control unit G. The first pin of the current transformer L2 is connected to resistor R16. One end of R13 is connected to the following: the other end of resistor R16 is connected to capacitor C7, amplifier U6, capacitor C10, and one end of resistor R17; the other end of R13 is connected to the other end of capacitor C7, capacitor C8, capacitor C9, and one end of resistor R14, which is a +2.5V reference voltage; the other end of capacitor C8 is grounded; the other end of resistor R14 is connected to pin 2 of current transformer L12 and one end of resistor R15; and the other end of capacitor C9 is connected to the other end of resistor R15. The power input terminal of the detection circuit of the current transformer L2 is connected to a 5V power supply and one end of capacitor C6, with the other end of capacitor C6 grounded. The common point of R13, R14, C8, C9, and C7 is a +2.5V reference voltage.

[0007] As a further improvement of this utility model, the residual current sampling unit E includes a residual current transformer L1. The three live wires and the neutral wire pass through the center hole of the residual current transformer L1. Pin 1 of the residual current transformer L1 is connected to one end of resistors R19 and R22. The other end of resistor R19 is connected to a +2.5V reference power supply, along with one end of capacitors C11, C12, C13, and R20. The other end of capacitor C11 is grounded. The other end of resistor R22, along with the other end of capacitor C12, one end of capacitor C14, and one end of resistor R23, are connected to the negative terminal of amplifier U7. Pin 2 of the other end of the residual current transformer L1 is connected to the other end of resistor R20 and one end of resistor R21 respectively. The other end of resistor R21 and the other end of capacitor C13 are connected to the positive terminal of amplifier U7. The output terminal of amplifier U7 is connected to one end of resistor R24, the other end of capacitor C14 and the other end of resistor R23 respectively. The other end of resistor R24 ​​is connected to pin 15 (leakage AD pin) of chip U8 in MCU operation and control unit G.

[0008] As a further improvement of this utility model, the MOS transistor switching unit B includes a MOS transistor Q1. The sources of MOS transistors Q1 and Q2 are connected together. The drain of MOS transistor Q1 is connected to the live wire input terminal, and the drain of MOS transistor Q2 is connected to the live wire output terminal. The gate of MOS transistor Q1 is connected to one end of resistor R8, and the gate of MOS transistor Q2 is connected to one end of resistor R9. The other ends of resistors R8 and R9 are connected to pins 6 and 7 of chip U3, pin 5 of chip U3 is connected to the sources of MOS transistors Q1 and Q2, and pin 8 of chip U3 is connected to one end of resistor R7. The other end of resistor R7... One end of capacitor EC3 is connected to a 15V power supply, and the other end of capacitor EC3 is grounded together with pin 3 of chip U4; pin 2 of chip U3 is connected to one end of capacitor C5 and pin 2 of chip U4 respectively, and pin 1 of chip U4 is grounded together with the other end of capacitor C5; pin 3 of chip U3 is connected to one end of resistor R10, and the other end of resistor R10 is connected to the collector of transistor Q4; the emitter of transistor Q4 is grounded together with one end of resistor R12; the base of transistor Q4 is connected to the other end of resistor R12 and one end of resistor R11 respectively, and the other end of resistor R11 is connected to pin 18 (L1-MOS / OFF) of chip U8 in MCU operation and control unit G.

[0009] As a further improvement of this utility model, the load short-circuit detection unit C for the live / neutral wire includes a bidirectional optocoupler U2 whose first pin is connected to the neutral wire, a bidirectional optocoupler U2 whose second pin is connected to one end of a resistor R2, and the other end of a resistor R2 connected to the live wire (load output terminal); a bidirectional optocoupler U2 whose third pin is connected to one end of a resistor R3 and the 20th pin of a chip U8; the other end of a resistor R3 is grounded; and a bidirectional optocoupler U2 whose fourth pin and one end of a capacitor C3 are connected to a +5V power supply, and the other end of a capacitor C3 is grounded.

[0010] As a further improvement of this utility model, the test power supply control unit D includes a resistor R1. One end of the resistor R1 is connected to one end of the resistor RT1 and the input terminal of the live wire L1. The other end of the resistor R1 is connected to the first pin of the optocoupler relay U1. The second pin of the optocoupler relay U1 is connected to the other end of the resistor RT1 and the output terminal of the live wire L1. The third pin of the optocoupler relay U1 is connected to the +5V power supply and one end of the capacitor C4, respectively. The fourth pin of the optocoupler relay U1 is connected to one end of the resistor R4. The other end of the resistor R4 is connected to the collector of the transistor Q3. The emitter of the transistor Q3 is grounded. The base of the transistor Q3 is connected to one end of the resistor R6 and one end of the resistor R5, respectively. The other end of the resistor R5 is connected to the 17th pin (L1-AC / OFF) of the chip U8 of the MCU operation control unit G.

[0011] As a further improvement of this utility model, the live wire / live wire short circuit detection unit F includes a resistor R26. One end of the resistor R26 is connected to the output terminal of the live wire L1, and the other end of the resistor R26 is connected to the first pin of the bidirectional optocoupler U9. The second pin of the bidirectional optocoupler U9 is connected to the output terminal of the live wire L2. The third pin of the bidirectional optocoupler U9 is connected to one end of the resistor R25 and the 16th pin of the chip U8, respectively. The other end of the resistor R25 is grounded. The fourth pin of the bidirectional optocoupler U9 and one end of the capacitor C10 are connected to a +5V power supply, and the other end of the capacitor C10 is grounded.

[0012] The beneficial effects of this utility model are: (1) Detect short circuit before powering on and closing the circuit. Before closing the circuit, the system will detect whether there is a short circuit in the load circuit. When a short circuit is detected, the system will not supply power to the load and the MOS will always be in the off state to avoid large current damage to the cable. (2) Fast turn-off time ≤150 microseconds, short detection cycle ≤10 milliseconds. This circuit is a single accurate short circuit detection circuit. The duration of the maximum short circuit current is ≤150 microseconds, avoiding long-term damage to the cable by large current. (3) Accurately identify short circuits in capacitive loads (false short circuits) and resistive loads (true short circuits). When a short circuit in a resistive load (true short circuit) is identified, the 220V power supply output is cut off until the short circuit fault is cleared. The system will automatically re-identify the short circuit. When there is no short circuit, the system will automatically recover (the system can be set to automatically / manually close the switch). When a short circuit in a capacitive load (false short circuit) is identified, the system will turn on the MOSFET switch to supply power to the load within 10 milliseconds. (4) Suitable for high current starting: By adjusting the system current threshold parameters, the starting current can be 1.2 to 4 times the rated current, which can be used for the main switch of the electrical box; (5) Single switching will not cause oscillation with the inductive load at the load end. The multiple rapid switching on / off of the 220V MOSFET will form a boost circuit with the inductive load (such as: electric fan, air conditioner, refrigerator, transformer, industrial transformer). The voltage will be between 220V and 1200V, which will damage the electrical appliances and electronic equipment in the load circuit. Moreover, since the MOSFET in this circuit is only switched on / off once, even if there is an inductive load in the load circuit (such as: transformer, motor, inductor), there will be no oscillation boost, and it will not harm the electrical appliances in the load circuit. (6) The equipment will not generate vibration and damage the equipment. Since the MOS transistor of the detection circuit only operates once to turn off, it can achieve high current short circuit protection without damaging the equipment and the MOS transistor. The short circuit protection current value can be set to 1 to 3 times the maximum operating current of the MOS transistor or IGBT transistor. (7) It has short circuit protection functions for live wire to live wire, live wire to neutral wire and live wire to ground wire. This circuit can be used in AC220 / AC380V power supply scenarios and has live wire / neutral wire protection function, live wire / live wire protection function and live wire / ground wire protection function. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the circuit principle provided by this utility model; Figure 2 This is a partial circuit schematic diagram (live wire / neutral wire, live wire / ground wire short circuit detection circuit schematic diagram) provided by this utility model. Figure 3 This utility model provides a current sampling circuit A; Figure 4 This utility model provides a residual current sampling unit E; Figure 5 This utility model provides a MOS switching unit B; Figure 6 This utility model provides a load short-circuit detection unit C; Figure 7 This is a waveform diagram of the zero-point current during a capacitive short circuit (capacitive resistance) of this utility model; Figure 8 This is a waveform diagram of the zero-point voltage of the capacitive short circuit (capacitive resistor) of this utility model; Figure 9 This is a waveform diagram of the zero-point current during a resistive short circuit (resistive resistor) of this utility model; Figure 10 This is a waveform diagram of the zero-point voltage of the resistive short circuit (resistive resistor) of this utility model; Figure 11 This is a waveform diagram of the non-zero current (capacitive resistor) during a capacitive short circuit of this utility model; Figure 12 This is a waveform diagram of the non-zero voltage at the capacitive short circuit (capacitive resistance) of this utility model; Figure 13 This is a waveform diagram of the non-zero current during a resistive short circuit (resistive resistor) of this utility model; Figure 14 This is a waveform diagram of the non-zero voltage at the resistive short circuit (resistive resistor) of this utility model; Figure 15 This utility model provides a test power supply control unit D; Figure 16 This utility model provides the L1 / L2 short-circuit detection unit F; Figure 17 This utility model provides an MCU detection and control unit G; Figure 18 The power supply unit H provided by this utility model; Figure 19 This is a block diagram of the live / neutral short circuit detection and control circuit provided by this utility model; Figure 20 This is a block diagram of the fire / ground short circuit detection and control circuit provided by this utility model; Figure 21 This is a block diagram of the L1 / L2 / L3 short circuit detection and control provided by this utility model. Detailed Implementation

[0014] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0015] A circuit for short-circuiting capacitive and resistive loads in an AC load, such as... Figure 1 , Figure 2 As shown, the system includes current detection units A and A2, MOSFET switching units B and B2, residual current sampling unit E, live / neutral load short circuit detection unit C, test power control units D and D2, live / live short circuit detection unit F, MCU operation and control unit G, and power supply unit H; all of these components are connected to the MCU operation and control unit G.

[0016] Current detection unit A, such as Figure 3As shown, this is used to acquire the live wire current and convert the acquired current peak waveform signal into a DC pulsating voltage waveform signal. The current detection unit A includes a current transformer L2 for transmitting the acquired current peak waveform signal. The live wire passes through the center hole of the current transformer. Pin 2 of the current transformer L2 is connected to the input terminal of amplifier U6 via resistor R15. The output terminal of amplifier U6 is connected to one end of resistor R18, and the other end of resistor R18 is connected to the MCU operation control unit G. Specifically, the other end of resistor R18 is connected to pin 19 of chip U8 in the MCU operation control unit G. The preferred model of operational amplifier U6 is TP10-2. The first pin of current transformer L2 is connected to one end of resistors R16 and R13 respectively. The other end of resistor R16 is connected to capacitor C7, amplifier U6, capacitor C10 and one end of resistor R17 respectively. The other end of R13 is connected to the other end of capacitor C7, capacitor C8, capacitor C9 and one end of resistor R14 respectively. The other end of capacitor C8 is grounded. The other end of resistor R14 is connected to the second pin of current transformer L2 and one end of resistor R15 respectively. The other end of capacitor C9 is connected to the other end of resistor R15. The power input terminal of current transformer L2 is connected to a 5V power supply and one end of capacitor C6, while the other end of capacitor C6 is grounded.

[0017] In the current detection unit A, the current and voltage signals acquired by the current transformer 12 are converted into differential +1 signals by resistors R13, R14, R15, R61, R17, C7, C8, C9, C10, and U6. These sinusoidal differential signals are amplified by U6 (TP10-2) and transformed into a complete positive voltage waveform with a reference voltage of +2.5V. This signal is then sent to the MCU (MCU) operation and control unit G for processing via resistor R18. It should be noted that... Figure 1 The circuit and working principle of A2 are the same as those of the current detection unit A, the difference being that A2 is connected to the live wire L2.

[0018] Residual current sampling unit E, such as Figure 4 As shown, the circuit includes a residual current transformer L1. The three-phase live wire and neutral wire pass through the center hole of the residual current transformer L1. Pin 1 of the residual current transformer L1 is connected to one end of resistors R19 and R22. The other end of resistor R19 is connected to one end of capacitors C11, C12, C13, and R20 respectively to a 2.5V power supply. The other end of capacitor C11 is grounded. The other end of resistor R22, the other end of capacitor C12, one end of capacitor C14, and one end of resistor R23 are all connected to the negative terminal of amplifier U7. Pin 2 of the other end of the leakage inductor L1 is connected to the other end of resistor R20 and one end of resistor R21 respectively. The other end of resistor R21 and the other end of capacitor C13 are connected to the positive terminal of amplifier U7. The output terminal of amplifier U7 is connected to one end of resistor R24, the other end of capacitor C14 and the other end of resistor R23 respectively. The other end of resistor R24 ​​is connected to pin 15 (leakage AD pin) of chip U8 in MCU operation and control unit G.

[0019] In the residual current sampling unit E, the current and voltage signals acquired by the voltage transformer L1 are converted into differential signals by R19, R20, R21, R22, R23, R24, C11, C12, C13, C14, U7, etc., and then amplified by a signal amplifier. The sinusoidal differential signal is amplified by U6 (LM358) and converted into a complete positive voltage waveform with a reference voltage of +2.5V. This signal is then sent to the MCU operation and control unit G for processing via R24. MOSFET switching unit B, such as Figure 5 As shown, the circuit includes MOS switches Q1 and Q2. The sources of MOS switches Q1 and Q2 are connected together. The drain of MOS switch Q1 is connected to the live wire input terminal, and the drain of MOS switch Q2 is connected to the live wire output terminal. The gate of MOS switch Q1 is connected to one end of resistor R8, and the gate of MOS switch Q2 is connected to one end of resistor R9. The other ends of resistors R8 and R9 are connected to pins 6 and 7 of chip U3, respectively. Pin 5 of chip U3 is connected to the sources of MOS switches Q1 and Q2. Pin 8 of chip U3 is connected to one end of resistor R7. The other end of resistor R7 and one end of capacitor C3 are connected to a 15V power supply. The connections are as follows: the other end of capacitor C3 is grounded together with pin 3 of chip U4; pin 2 of chip U3 is connected to one end of capacitor C5 and pin 2 of chip U4 respectively; pin 1 of chip U4 is grounded together with the other end of capacitor C5; pin 3 of chip U3 is connected to one end of resistor R10; the other end of resistor R10 is connected to the collector of transistor Q4; the emitter of transistor Q4 is grounded together with one end of resistor R12; the base of transistor Q4 is connected to the other end of resistor R12 and one end of resistor R11 respectively; the other end of resistor R11 is connected to pin 18 of chip U8 in the MCU operation and control unit G (L1-MOS / OFF). Further explanation is needed. Figure 1 The circuit and working principle of B2 are the same as those of the MOSFET switching unit B, the difference being that it is connected to the live wire L2.

[0020] The following principles are involved in the MOSFET switching unit B: (1) Isolated power supply: Chip U4 is an isolated switching power supply module (pin 1 of this module is connected to +12V, pin 2 is connected to signal ground, pin 3 is connected to the source pin of the two MOSFETs Q1 / Q2, and pin 4 is the +15V output pin, which provides a forward bias voltage to the gate (G) stage of the MOSFETs (this voltage is based on the GS voltage in the MOSFET datasheet). The low-voltage ground line, R10, R11, R12, Q4 and U3 constitute the driving circuit of the low-voltage circuit, which is always in the on state. (2) Low-voltage side drive: The low-voltage side drive circuit consists of R10, R11, R12, Q4, U3, and EC5. The turn-off and turn-on of this drive are controlled by the MCU.

[0021] (3) High-voltage switch; The high-voltage switch circuit consists of U4 (isolation power supply), Q1, Q2, R7, R8, R9, EC3, and U3. By turning on and off the photoelectric sensor inside the optocoupler, pins 4 and 5 and pins 7 and 8 of the output terminal of chip U3 are turned on respectively. Pin 5 of pins 4 and 5 is connected to the source of the MOS transistor, and pins 7 and 8 are internal pull-up (pin 8 is connected to the positive terminal of the isolation power supply). By controlling the output of the MCU operation control unit G, the MOS switch can be turned on and off (the output is normal after turning on, and the 220V load output is disconnected after turning off).

[0022] Live / neutral wire load short circuit detection unit C, such as Figure 5 As shown, pin 1 of bidirectional optocoupler U2 is connected to the neutral wire; pin 2 of bidirectional optocoupler U2 is connected to one end of resistor R2, and the other end of resistor R2 is connected to the live wire output terminal; pin 3 of bidirectional optocoupler U2 is connected to one end of resistor R3 and pin 20 of chip U8 respectively; the other end of resistor R3 is grounded; pin 4 of bidirectional optocoupler U2 and one end of capacitor C3 are connected to the +5V power supply, and the other end of capacitor C3 is grounded.

[0023] In the load short-circuit detection unit C for the live / neutral wire, the working principle and process are as follows: When the current detected by the current detection unit A is >80A (the set threshold can be changed, the same applies below), the current detection unit A will transmit the overcurrent signal to the MCU operation and control unit G. The MCU operation and control unit G will transmit the trip signal to the MOS switch unit B for tripping. At this time, the test power control unit D (the circuit switch is normally closed) starts to work. This circuit will continuously provide a small current of AC power to the load terminal, continuously powering the subsequent load short-circuit detection unit C for the live / neutral wire. This circuit detects the voltage division between the detection resistor R1 and the load. This voltage division forms a loop through the resistor R2 to the bidirectional optocoupler U2. The other end of the bidirectional optocoupler U2 will detect a DC voltage of 0-5V, and then use this voltage to obtain the resistance value of the load through the MCU operation and control unit G. It should be noted that... Figure 21The circuit and working principle of C2 are the same as those of the load short circuit detection unit C2, the difference being that it is connected to the live wire L2.

[0024] The short-circuit detection circuit at the load end determines the following process: When the MOSFET is off, the AC voltage (220V / small current) from resistor R1 and chip U1 is divided by the load circuit. This divided voltage is then applied to the bidirectional optocoupler U2 through resistor R2 to form a photoelectric circuit. The secondary circuit of the optocoupler consists of +5V, bidirectional optocoupler U2, and resistor R3. The sampling period for detecting the low-level pulse output of this circuit is 10ms. When the low-level sampling signal is <4ms (a predetermined value, the same below), the load is normal (no short circuit / false short circuit). When the low-level (L) signal is >6ms (a predetermined value, the same below), it is confirmed as a short circuit. This circuit can also detect the resistance value of the load short circuit, that is, the resistive load resistance of the load circuit can be obtained after calculation by the MCU.

[0025] In the load short-circuit detection unit C for the live / neutral wires, the detection circuit continuously samples the high and low level times for 10 milliseconds to identify resistive and capacitive short-circuit states (e.g., Figure 7 , Figure 8 , Figure 9 , Figure 10 , Figure 11 , Figure 12 , Figure 13 and Figure 14 Specifically: (1) When the low-level (L) sampling signal at the output of the detection circuit is greater than 6ms (this predetermined parameter can be modified according to the application scenario), it is identified as a resistive short circuit. The MCU will output a control signal and simultaneously control the MOS transistor and the detection voltage circuit. At this time, the 220V voltage output is cut off at the load end because the MOS transistor is turned off. (2) When the output low level (L) sampling signal is <4ms (this predetermined parameter can be modified according to the usage scenario), the capacitive load short circuit (false short circuit) is identified; the MCU will turn on the MOS transistor, and at this time the load output terminal will have AC220V voltage output due to the turn on of the MOS transistor.

[0026] During this process, the low-level pulse time of the circuit output is detected (the high-level detection sampling period is 10ms, the low-level sampling signal <4ms indicates normal load, and the low-level sampling signal >6ms indicates a short circuit in the load); and by changing the resistance value of R2, the detailed parameters of the resistance value during a short circuit can be detected.

[0027] Test power control unit D, such as Figure 15As shown, the circuit includes resistor R1. One end of resistor R1 is connected to one end of resistor RT1 and the input terminal of live wire L1. The other end of resistor R1 is connected to pin 1 of optocoupler relay U1. Pin 2 of optocoupler relay U1 is connected to the other end of resistor RT1 and the output terminal of live wire L1. Pin 3 of optocoupler relay U1 is connected to the +5V power supply and one end of capacitor C4. Pin 4 of optocoupler relay U1 is connected to one end of resistor R4. The other end of resistor R4 is connected to the collector of transistor Q3. The emitter of transistor Q3 is grounded. The base of transistor Q3 is connected to one end of resistor R6 and one end of resistor R5. The other end of resistor R5 is connected to pin 17 (L1-AC / OFF) of chip U8 of MCU operation and control unit G. Further explanation is needed. Figure 1 The circuit and working principle of D2 are the same as those of the test power control unit D, the difference being that it is connected to the live wire L2.

[0028] The working process and principle of the test power control unit D are as follows: The drive circuit composed of electronic components R4, R5, R6, Q3, EC4, and U1 is always in the conducting state. The AC circuit runs from the input terminal of the live wire-L1 to R1, the optocoupler relay U1 (conducting in standby state), and then to the output terminal of the live wire-L1. The output terminal of the live wire forms a circuit through the load to the neutral wire. When the MOSFET is turned off, this circuit and the load circuit form a voltage divider mode (when the MOSFET is turned on, a voltage divider mode is not formed). This voltage divider and the load terminal short circuit detection circuit form a short circuit detection.

[0029] Live wire / live wire short circuit detection unit F, such as Figure 16 As shown, the system includes resistor R26, one end of which is connected to the L1 live wire output terminal, and the other end of which is connected to pin 1 of bidirectional optocoupler U9. Pin 2 of bidirectional optocoupler U9 is connected to the L2 live wire output terminal. Pin 3 of bidirectional optocoupler U9 is connected to one end of resistor R25 and pin 16 of chip U8, respectively. The other end of resistor R25 is grounded. Pin 4 of bidirectional optocoupler U2 and one end of capacitor C10 are connected to the +5V power supply, and the other end of capacitor C10 is grounded.

[0030] The working process and principle of the live wire / live wire short circuit detection unit F are as follows: When the currents of live wires L1 and L2 simultaneously reach the trigger condition, the MCU operation control unit G simultaneously turns off the two channel MOS transistor switching units B. At this time, the live wire / live wire short circuit detection unit F (phase line to phase line detection circuit) L1 / L2 / L3 detection circuit starts to work. Since the detection voltage of the live wire / live wire short circuit detection unit F is connected to the phase lines (AC380V) of L1-L2 / L2-L3 / L3-L1, the measured current passes through R1→U1→load circuit of L1 channel to R1-1→U1-2 of L2 channel to form a voltage divider in the load circuit. The AC voltage divider of the load circuit passes through R26, U9 primary, and the DC output of the secondary circuit R25, U9, EC10 will return to the DC voltage output. By detecting the low level pulse time (detection time 10ms, when the low level duration <4ms, the load is normal), the detection is performed. A low-level duration greater than 6ms constitutes a true short circuit.

[0031] MCU computing control unit G, such as Figure 17 As shown, it includes chip U8. Pin 6 of chip U8 is connected to one end of capacitor C19, and the other end of capacitor C19 is grounded. Pins 8 and 9 of chip U8 are connected in parallel and then connected to a +5V power supply, one end of capacitor EC8, and one end of capacitor C15. The other ends of capacitor EC8 and capacitor C15 are grounded together with pin 10 of chip U8. Pin 11 of chip U8 is connected to a +2.5V power supply as the AD calibration value. One end of capacitors C16, C17, and C18 is connected to pin 1 of chip U7. The other ends of capacitors C16, C17, and C18 are grounded together with pin 3 of chip U7. Pins 2 and 3 of chip U7 are both connected to one end of resistor R30, and the other end of resistor R30 is connected to a +5V power supply.

[0032] In the MCU operation and control unit G, chip U8 is composed of STC32G12K128 chip. This chip is a 32-bit industrial-grade chip with stable performance and strong anti-interference ability. The circuit includes L1 current AD sampling, L2 current AD sampling, L3 current AD sampling, residual current AD sampling, three-channel MOSFET drive, three-channel test power supply control, three-channel AC220V load terminal short circuit detection circuit, three-channel AC380V (live wire to live wire) load terminal short circuit detection circuit, and other functional circuits.

[0033] Power supply unit H, such as Figure 18 As shown, the active power supply circuit is connected to the AC input terminal, and the AC power is converted into DC power by the rectifier circuit to supply the load.

[0034] It should be noted that the circuit for short circuit identification of the L3 channel of the live wire in this utility model is the same as the circuit for short circuit of the L2 channel of the live wire, and the working principle is also the same. It will not be described again here, and it is not shown in the attached drawings.

[0035] This utility model discloses a method for identifying short circuits in capacitive and resistive loads in AC loads. The method identifies short circuits individually or simultaneously based on short circuits between the neutral and live wires, between the live wire and ground wire, and between live wires. The identification method is as follows: Live / neutral short circuit identification, such as Figure 19 As shown: When current detection unit A detects a live wire current > 80A (this threshold can be modified according to the application scenario), the MCU operation and control unit G outputs a control signal to turn off the MOSFET of the MOSFET switching unit B. If the low-level pulse time of the live / neutral wire load short circuit detection unit C is > 6 milliseconds, the MOSFET switching unit B determines that a short circuit has occurred and outputs a control signal, simultaneously turning off the MOSFET switching unit B and the test power control unit D, thus completing the identification and protection process. During this process, turning off the test power control unit D is to prevent leakage current injury and arcing caused by the load output terminal being energized when the MOSFET is turned off.

[0036] Live / ground short circuit identification, such as Figure 20 As shown: When current detection unit A detects a single increase in live wire current exceeding a threshold (e.g., a threshold set to 50A), and simultaneously detects an increase of 10A in residual current detection circuit E (this threshold can be modified according to the application scenario), and the MCU operation and control unit G detects both voltage signals at the same time, the MOSFET switching unit B outputs a control voltage to shut down the MOSFET switch and the test power supply control unit D, thus completing the identification and protection process. Shutting down the test power supply control unit D prevents leakage current injury and arcing caused by the load output terminal remaining energized when the MOSFET is off.

[0037] Live wire / live wire short circuit identification, such as Figure 21 As shown: When the current detection unit A detects that the current in both live wires simultaneously exceeds a threshold (e.g., the threshold is set to 80A), the MCU operation and control circuit G outputs a control signal to simultaneously shut down the two corresponding channel MOSFET switching units B. At this time, the live wire / live wire load terminal short circuit detection F detects a low-level pulse time greater than 6 milliseconds (this threshold can be modified according to the application scenario). The MCU operation and control unit G determines that a short circuit has occurred and simultaneously outputs a shutdown signal, shutting down the two MOSFET switching units B and the two test power control units D, thus completing the identification and protection. Shutting down the test power control unit D is to prevent leakage current injury and arcing caused by the load output terminal being energized when the MOSFETs are turned off.

[0038] The thresholds listed in the various short-circuit identification methods above can be adjusted according to the usage scenario and are not fixed.

[0039] In summary, the circuit and method of this utility model have the following advantages: (1) Detect short circuits before powering on and closing the circuit. Before closing the circuit, the system will check for short circuits in the load circuit. If a short circuit is detected, the system will not supply power to the load, and the MOS will always be in the off state to avoid large current damage to the cable. (2) Fast shutdown time ≤150 microseconds, short detection cycle ≤10 milliseconds This circuit is a single-time accurate short-circuit detection circuit, and the duration of the maximum short-circuit current is ≤150 microseconds, avoiding damage to the cable from prolonged high current. (3) Accurately identify short circuits in capacitive loads (false short circuits) and resistive loads (true short circuits). When a short circuit in a resistive load (true short circuit) is identified, the 220V power supply output is cut off until the short circuit fault is cleared. The system will automatically identify it again. When there is no short circuit, the system will automatically restore power supply. When a short circuit is detected in a capacitive load (false short circuit), the system will turn on the MOSFET switch to supply power to the load within 10 milliseconds; (4) Suitable for high current start-up: By adjusting the system current threshold parameters, the starting current can be 1.2 to 4 times the rated current, which can be used for the main switch of the electrical box.

[0040] (5) Single switching, will not cause oscillation with the inductive load at the load end. Repeated rapid switching on and off of a 220V MOSFET will form a boost circuit with inductive loads (such as electric fans, air conditioners, refrigerators, transformers, and industrial transformers). This voltage will be between 220V and 1200V, which will damage the electrical and electronic equipment in the load circuit. Since the MOSFET in this circuit is only turned on / off once, even if there is an inductive load in the load circuit (such as a transformer, motor, or inductor), it will not cause oscillation and voltage boost, nor will it harm the electrical appliances in the load circuit. (6) The equipment itself will not generate vibrations that could damage it. Since the MOSFET of this detection circuit only operates once to turn off, it can provide high-current short-circuit protection without damaging the equipment or the MOSFET. The short-circuit protection current value can be set to 1 to 3 times the maximum operating current of the MOSFET or IGBT. (7) It has short-circuit protection functions for live wire to live wire, live wire to neutral wire and live wire to ground wire; This circuit can be used in AC220 / AC380V power supply scenarios and has live wire / neutral wire protection, live wire / live wire protection, and live wire / ground wire protection functions.

[0041] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the protection scope of the present invention.

Claims

1. A short-circuit identification circuit for capacitive and resistive loads in AC loads, characterized in that, It includes a current detection unit A, a MOSFET switching unit B, a residual current sampling unit E, a live / neutral load short-circuit detection unit C, a test power control unit D, a live / live short-circuit detection unit F, an MCU operation and control unit G, and a power supply unit H; characterized in that, The current detection unit A, the MOSFET switching unit B, the residual current sampling unit E, the live wire / neutral wire load short circuit detection unit C, the test power control unit D, the live wire / live wire short circuit detection unit F, and the power supply unit H are all connected to the MCU operation and control unit G. The load short-circuit detection unit C for the live / neutral wire includes a bidirectional optocoupler U2 whose first pin is connected to the neutral wire, a bidirectional optocoupler U2 whose second pin is connected to one end of a resistor R2, and the other end of a resistor R2 connected to the output terminal of the live wire L1; a bidirectional optocoupler U2 whose third pin is connected to one end of a resistor R3 and the 20th pin of a chip U8; the other end of a resistor R3 is grounded; and a bidirectional optocoupler U2 whose fourth pin and one end of a capacitor C3 are connected to a +5V power supply, with the other end of a capacitor C3 grounded.

2. The circuit according to claim 1, characterized in that, The current detection unit A includes a current transformer L2. The live wire passes through the center hole of the current transformer L2. The second pin of the current transformer L2 is connected to one end of resistors R14 and R15 respectively. After passing through resistor R15, it is connected to the input terminal of amplifier U6. The output terminal of amplifier U6 is connected to one end of resistor R18. The other end of resistor R18 is connected to the 19th pin of chip U8 in MCU operation and control unit G. The first pin of the current transformer L2 is connected to one end of resistors R16 and R13 respectively. The other end of resistor R16 is connected to capacitor C7, amplifier U6, capacitor C10, and one end of resistor R17 respectively. The other end of R13 is connected to the other end of capacitor C7, capacitor C8, capacitor C9, and one end of resistor R14. This point is a +2.5V reference voltage. The other end of capacitor C8 is grounded. The other end of resistor R14 is connected to the second pin of current transformer L12 and one end of resistor R15 respectively. The other end of capacitor C9 is connected to the other end of resistor R15. The power input terminal of the detection circuit of the current transformer L2 is connected to a 5V power supply and one end of capacitor C6, respectively. The other end of capacitor C6 is grounded. The common point of R13, R14, C8, C9, and C7 is a +2.5V reference voltage.

3. The circuit according to claim 1, characterized in that, The residual current sampling unit E includes a residual current transformer L1. Three live wires and a neutral wire pass through the center hole of the residual current transformer L1. Pin 1 of the residual current transformer L1 is connected to one end of resistors R19 and R22. The other end of resistor R19 is connected to one end of capacitors C11, C12, C13, and R20, respectively, to a +2.5V reference power supply. The other end of capacitor C11 is grounded. The other end of resistor R22, along with the other end of capacitor C12, one end of capacitor C14, and one end of resistor R23, are connected to the negative terminal of amplifier U7. Pin 2 of the other end of the residual current transformer L1 is connected to the other end of resistor R20 and one end of resistor R21 respectively. The other end of resistor R21 and the other end of capacitor C13 are connected to the positive terminal of amplifier U7. The output terminal of amplifier U7 is connected to one end of resistor R24, the other end of capacitor C14 and the other end of resistor R23 respectively. The other end of resistor R24 ​​is connected to pin 15 of chip U8 in MCU operation and control unit G.

4. The circuit according to claim 1, characterized in that, The MOS transistor switching unit B includes a MOS transistor Q1. The sources of MOS transistors Q1 and Q2 are connected together. The drain of MOS transistor Q1 is connected to the live wire input terminal, and the drain of MOS transistor Q2 is connected to the live wire output terminal. The gate of MOS transistor Q1 is connected to one end of resistor R8, and the gate of MOS transistor Q2 is connected to one end of resistor R9. The other ends of resistors R8 and R9 are connected to pins 6 and 7 of chip U3, respectively. Pin 5 of chip U3 is connected to the sources of MOS transistors Q1 and Q2. Pin 8 of chip U3 is connected to one end of resistor R7, and the other end of resistor R7... One end of capacitor EC3 is connected to a 15V power supply, and the other end of capacitor EC3 is grounded together with pin 3 of chip U4; pin 2 of chip U3 is connected to one end of capacitor C5 and pin 2 of chip U4 respectively, and pin 1 of chip U4 is grounded together with the other end of capacitor C5; pin 3 of chip U3 is connected to one end of resistor R10, and the other end of resistor R10 is connected to the collector of transistor Q4; the emitter of transistor Q4 is grounded together with one end of resistor R12; the base of transistor Q4 is connected to the other end of resistor R12 and one end of resistor R11 respectively, and the other end of resistor R11 is connected to pin 18 of chip U8 in MCU operation and control unit G.

5. The circuit according to claim 1, characterized in that, The test power supply control unit D includes a resistor R1. One end of resistor R1 is connected to one end of resistor RT1 and the input terminal of live wire L1. The other end of resistor R1 is connected to pin 1 of optocoupler relay U1. Pin 2 of optocoupler relay U1 is connected to the other end of resistor RT1 and the output terminal of live wire L1. Pin 3 of optocoupler relay U1 is connected to a +5V power supply and one end of capacitor C4, respectively. Pin 4 of optocoupler relay U1 is connected to one end of resistor R4. The other end of resistor R4 is connected to the collector of transistor Q3. The emitter of transistor Q3 is grounded. The base of transistor Q3 is connected to one end of resistor R6 and one end of resistor R5, respectively. The other end of resistor R5 is connected to pin 17 of chip U8 of MCU operation control unit G.

6. The circuit according to claim 1, characterized in that, The live wire / live wire short circuit detection unit F includes a resistor R26. One end of the resistor R26 is connected to the output terminal of the live wire L1, and the other end of the resistor R26 is connected to the first pin of the bidirectional optocoupler U9. The second pin of the bidirectional optocoupler U9 is connected to the output terminal of the live wire L2. The third pin of the bidirectional optocoupler U9 is connected to one end of the resistor R25 and the 16th pin of the chip U8, respectively. The other end of the resistor R25 is grounded. The fourth pin of the bidirectional optocoupler U9 and one end of the capacitor C10 are connected to the +5V power supply, and the other end of the capacitor C10 is grounded.

Images