Method and circuit for identifying a capacitive and resistive short circuit of an alternating current load

Abstract

The application relates to a method and circuit for identifying short circuit of capacitive and resistive loads in an alternating current load, the circuit comprising a current detection unit A, a MOS tube switching unit B, a residual current sampling unit E, a load short circuit detection unit C of a live wire / zero line, a test power supply control unit D, a live wire / live wire short circuit detection unit F, an MCU operation control unit G and a power supply unit H; the method can separately or simultaneously identify short circuit between the zero line and the live wire, the live wire and the ground wire and the live wire and the live wire; the method is a fast identification method considering both the capacitive load false short circuit and the resistive short circuit (true short circuit) current, the short circuit protection time is less than or equal to 150 microseconds, the identification cycle time is less than or equal to 10 milliseconds, and through the circuit technology, the identification error phenomenon caused by the capacitive load connected to the load output end of the MOS tube electronic switch protection can be reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of short circuit identification and protection, in particular to a method and circuit for identifying short circuit of capacitive and resistive loads in an AC load. BACKGROUND

[0002] With the rapid development of science and technology, high-power charging piles and AC power are being used more and more widely, and the requirements for electrical safety are becoming higher and higher. When AC power lines are short-circuited, the current in the line will increase sharply in an instant, possibly reaching several or even dozens of times the normal operating current. Such a powerful short-circuit current will generate heat and electric power far beyond the normal level in electrical equipment, which may cause serious consequences such as cable insulation breakdown, conductor melting, equipment component damage, etc., making the equipment unable to operate normally, and even causing permanent damage to the equipment, requiring high maintenance costs and replacement fees. AC short circuit can also cause voltage to drop suddenly, causing the voltage stability of the power system to be destroyed. Moreover, in an environment using high-power equipment, when AC power lines are short-circuited, dangerous arcs and flying high-temperature sparks will be generated, which can cause burns and the risk of fire (igniting surrounding flammable materials).

[0003] To this end, the applicant has developed a detection and protection circuit for high-power AC short circuit (patent number ZL202322634423.6), which proposes to compare the waveform peak value of the voltage at the AC input end with the waveform peak value of the short-circuit current. When the current waveform peak value voltage is greater than the voltage waveform peak value voltage, the system will quickly turn off the output of the MOS tube or IGBT tube at the zero crossing point of the AC power, accurately and quickly turning off the MOS tube or IGBT tube. The problem of high-temperature arcs and flying sparks generated by the zero line and live line, live line and ground line, and live line and live line due to line short circuit is solved, avoiding burns and fires. However, in the application process, it was found that, like the products on the market, there is a big shortcoming that capacitive loads (such as computers, variable frequency air conditioners, high-power LED lamps, and spliced display screens, etc.) in the line will be misjudged as short-circuited; that is, there is a false identification phenomenon caused by the output of the MOS tube electronic switch protector due to the connection of high-power capacitive loads. Therefore, further research and development are carried out to correctly and perfectly solve the identification of capacitive loads in the load line of the current limiting type protector, the zero line and live line, live line and ground line, and live line and live line due to capacitive loads in the line, and truly achieve short-circuit arc-free and no false action. SUMMARY

[0004] In view of the defects or deficiencies in the prior art, the technical problem to be solved by the present application is to provide a method and circuit for identifying short circuit of capacitive and resistive loads in an AC load.

[0005] In order to achieve the above object, the technical scheme adopted by the present application is to provide an AC load capacitive and resistive load short circuit identification circuit, which comprises current detection units A and A2, MOS tube switching unit B and B2, residual current sampling unit E, load short circuit detection unit C of live wire / zero line, test power supply control unit D and D2, live wire / live wire short circuit detection unit F, MCU operation control unit G and power supply unit H; the current detection units A and A2, the MOS tube switching units B and B2, the residual current sampling unit E, the load short circuit detection unit C of live wire / zero line, the test power supply control units D and D2, the live wire / live wire short circuit detection unit F and the power supply unit H are connected with the MCU operation control unit G; wherein the current detection unit A, the MOS tube switching unit B, the residual current sampling unit E, the load short circuit detection unit C of live wire / zero line and the test power supply control unit D, together with the MCU operation control unit G and the power supply unit H, form a live wire L1 phase line channel identification circuit; the current detection unit A2, the MOS tube switching unit B2, the test power supply control unit D2 and the live wire / live wire short circuit detection unit F, together with the MCU operation control unit G and the power supply unit H, form a live wire L2 phase line channel identification circuit.

[0006] The MCU operation control unit G comprises a chip U8.

[0007] The current detection unit A comprises a current transformer LH2, and the live wire L1 passes through the center hole of the current transformer LH2.

[0008] The residual current sampling unit E comprises a residual current transformer LH1, and three live wires and zero lines pass through the center hole of the residual current transformer LH1.

[0009] The MOS tube switching unit B comprises MOS switching tubes Q1 and Q2, the source electrodes of the MOS switching tubes Q1 and Q2 are connected, the drain electrode of the MOS switching tube Q1 is connected with the live wire L1 input end, and the drain electrode of the MOS switching tube Q2 is connected with the live wire L1 output end.

[0010] The load short circuit detection unit C of live wire / zero line comprises a first pin of a bidirectional optical coupler U2 input end connected with the zero line, a second pin of the bidirectional optical coupler U2 input end connected with one end of a resistor R2, and the other end of the resistor R2 connected with the live wire L1 output end.

[0011] The test power supply control unit D comprises a resistor R1, one end of the resistor R1 connected with one end of a resistor RT1 and the live wire L1 input end, the other end of the resistor R1 connected with a first pin of an optical coupler relay U1 input end, a second pin of the optical coupler relay U1 input end connected with the other end of the resistor RT1 and the live wire L1 output end.

[0012] The firewire / firewire short circuit detection unit F includes a resistor R26, one end of the resistor R26 is connected to the firewire L1 output end, the other end of the resistor R26 is connected to the first pin of the bidirectional optical coupler U9 input end, the second pin of the bidirectional optical coupler U9 input end is connected to the firewire L2 output end;

[0013] The circuit and working principle of the current detection unit A and the current detection unit A2 are consistent;

[0014] The circuit and working principle of the MOS tube switch unit B and the MOS tube switch unit B2 are consistent;

[0015] The circuit and working principle of the test power supply control unit D and the test power supply control unit D2 are consistent.

[0016] As a further improvement of the application, the second pin of the current transformer LH2 is connected to one end of resistors R14 and R15, respectively, and the resistor R15 is connected to the positive electrode of the amplifier U6 after passing through the resistor R15, the output end of the amplifier U6 is connected to one end of the resistor R18, the other end of the resistor R18 is connected to the 19th pin of the chip U8 in the MCU operation control unit G; the first pin of the current transformer LH2 is connected to one end of resistors R16 and R13, respectively, the other end of the resistor R16 is connected to the capacitor C7, the negative electrode of the amplifier U6, the capacitor C10 and one end of the resistor R17, respectively, the other end of the resistor R13 is connected to the other end of the capacitor C7, one end of the capacitor C8, one end of the capacitor C9 and the other end of the resistor R14, respectively, the other end of the capacitor C8 is grounded, and the other end of the capacitor C9 is connected to the other end of the resistor R15;

[0017] The positive power supply end of the amplifier U6 is connected to the 5V power supply and one end of the capacitor C6, respectively, the other end of the capacitor C6 is grounded, and the negative power supply end of the amplifier U6 is grounded, wherein the common point of R13, R14, C8, C9 and C7 is +2.5V reference voltage;

[0018] The model of the chip U8 is STC32G12K128;

[0019] The model of the operational amplifier U6 is TP10-2.

[0020] As a further improvement of the application, the first pin of the residual current transformer LH1 is connected to the resistor R19 and one end of the resistor R22; the other end of the resistor R19 is commonly connected to the +2.5V reference power supply with the capacitor C11, the capacitor C12, the capacitor C13 and one end of the resistor R20; the other end of the capacitor C11 is grounded; the other end of the resistor R22 is commonly connected to the negative electrode of the amplifier U7 with the other end of the capacitor C12, one end of the capacitor C14 and one end of the resistor R23;

[0021] The 2-pin of the other end of the residual current transformer LH1 is connected with the other end of the resistor R20 and the one end of the resistor R21, the other end of the resistor R21 and the other end of the capacitor C13 are commonly connected with the positive electrode of the amplifier U7; the output end of the amplifier U7 is connected with the one end of the resistor R24, the other end of the capacitor C14 and the other end of the resistor R23 respectively; the other end of the resistor R24 is connected with the 15th pin of the chip U8 in the MCU operation control unit G;

[0022] The model of the chip U8 is STC32G12K128.

[0023] As a further improvement of the application, the gate of the MOS switch tube Q1 is connected with the one end of the resistor R8, the gate of the MOS switch tube Q2 is connected with the one end of the resistor R9, the connection point of the other end of the resistor R8 and the other end of the resistor R9 is connected with the 6th pin and the 7th pin of the chip U3, the 5th pin of the chip U3 is connected with the source of the MOS switch tube Q1 and the MOS switch tube Q2, the 8th pin of the chip U3 is connected with the one end of the resistor R7, the other end of the resistor R7 and the one end of the capacitor EC3 are commonly connected with the 15V power supply, the other end of the capacitor EC3 is commonly grounded with the 3rd pin of the chip U4 and the 5th pin of the chip U3; the 2nd pin of the chip U3 is connected with the one end of the capacitor C5 and the 2nd pin of the chip U4 respectively, the 1st pin of the chip U4 is commonly grounded with the other end of the capacitor C5; the 3rd pin of the chip U3 is connected with the one end of the resistor R10, the other end of the resistor R10 is connected with the collector of the triode Q4, the emitter of the triode Q4 is commonly grounded with the one end of the resistor R12, the base of the triode Q4 is connected with the other end of the resistor R12 and the one end of the resistor R11 respectively, the other end of the resistor R11 is connected with the 18th pin of the chip U8 in the MCU operation control unit G;

[0024] The model of the chip U3 is TLP250:

[0025] The chip U4 is a DC / DC isolation switch power supply module;

[0026] The model of the chip U8 is STC32G12K128.

[0027] As a further improvement of the application, the 3rd pin of the emitter of the bidirectional optical coupling U2 is connected with the one end of the resistor R3 and the 20th pin of the chip U8 respectively; the other end of the resistor R3 is grounded; the 4th pin of the collector of the bidirectional optical coupling U2 and the one end of the capacitor C3 are commonly connected with the +5V power supply, the other end of the capacitor C3 is grounded.

[0028] As a further improvement of the application, the third pin of the output end of the optocoupler U1 is connected with the +5V power supply and one end of the capacitor C4, respectively, the fourth pin of the output end of the optocoupler U1 is connected with one end of the resistor R4, the other end of the resistor R4 is connected with the collector of the transistor Q3, the emitter of the transistor Q3 and the other end of the capacitor C4 are grounded, the other end of the resistor R6 is grounded, the base of the transistor Q3 is connected with one end of the resistor R6 and one end of the resistor R5, respectively, the other end of the resistor R5 is connected with the 17th pin of the chip U8 of the MCU operation control unit G.

[0029] The model of the chip U8 is STC32G12K128.

[0030] As a further improvement of the application, the third pin of the emitter of the bidirectional optocoupler U9 is connected with 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 collector of the bidirectional optocoupler U9 and one end of the capacitor C10 are commonly connected with the +5V power supply, and the other end of the capacitor C10 is grounded.

[0031] The model of the chip U8 is STC32G12K128.

[0032] Another object of the application is to provide a method for identifying the short circuit of capacitive load and resistive load in an AC load, which separately or simultaneously identifies the short circuit between the zero line and the live line, the live line and the ground line, and the live line and the live line,

[0033] Live line / zero line short circuit identification: when the current detection unit A detects that the live line current > threshold value, the MCU operation control unit G outputs a control signal to close the MOS switch tube of the MOS tube switching unit B, if the load short circuit detection unit C of the live line / zero line low level pulse time > threshold value, the MCU operation control unit G judges and confirms that it is a resistive short circuit, and outputs a control signal to simultaneously close the MOS tube switching unit B and the test power supply control unit D; if the load short circuit detection unit C of the live line / zero line low level pulse time < threshold value, the MCU operation control unit G judges and confirms that it is a capacitive short circuit.

[0034] Live line / ground line short circuit identification: when the current detection unit A detects that the live line current increases by a single time > threshold value, and the residual current sampling unit E detects that the residual current increases by a single time > threshold value, the MCU operation control unit detects these two voltage signals at the same time, then the MCU operation control unit G judges and confirms that it is a live ground short circuit, and outputs a signal to simultaneously close the MOS tube switching unit B and the test power supply control unit D.

[0035] Firewire / firewire short circuit identification: when the current detection unit A and A2 detect the current of two firewires simultaneously > threshold, the MCU operation control unit G outputs a control signal to simultaneously close the corresponding channel MOS tube switch unit B and B2; at this time, when the firewire / firewire short circuit detection unit F detects a low level pulse time > threshold, the MCU operation control unit G determines that it is a true firewire / firewire short circuit, and simultaneously outputs a closing signal to close the MOS tube switch unit B and B2 and the test power supply control unit D and D2; when the low level pulse time < threshold, it is judged that the load is normal.

[0036] As a further improvement of the application, firewire / zero line short circuit identification: when the current detection unit A detects that the firewire current > 80A, the MCU operation control unit G outputs a control signal to close the MOS switch tube of the MOS tube switch unit B, and if the low level pulse time of the load short circuit detection unit C of the firewire / zero line > 6ms, the MCU operation control unit G determines that it is a resistive short circuit, and outputs a control signal to simultaneously close the MOS tube switch unit B and the test power supply control unit D; when the output low level pulse time < 4ms, it is judged that it is a capacitive load short circuit.

[0037] Firewire / ground short circuit identification: when the current detection unit A detects that the firewire current increases by > 50A at a time, and the residual current sampling unit E increases by > 10A, the MCU operation control unit G detects these two voltage signals at the same time, and outputs a control voltage to close the MOS tube switch unit B and the test power supply control unit D.

[0038] Firewire / firewire short circuit identification: when the current detection unit A detects that the current of two firewires is simultaneously > 50A, the MCU operation control unit G outputs a control signal to simultaneously close the two corresponding channel MOS tube switch units B and B2; at this time, when the firewire / firewire short circuit detection unit F detects a low level pulse time > 6ms, the MCU operation control unit G determines that it is a true short circuit, and simultaneously outputs a closing signal to close the MOS tube switch unit B and B2 and the test power supply control unit D and D2; when the low level pulse time < 4ms, it is judged that the load is normal.

[0039] The beneficial effects of the application are:

[0040] (1) Detect short circuit before power-on and closing, the system will detect whether there is a short circuit phenomenon in the load circuit before closing, when detecting that there is a short circuit, the system will not supply power to the load, and the MOS is always in a closed state, avoiding damage to the cable by large current;

[0041] (2) The turn-off time is fast ≤ 150 microseconds, the detection period is short ≤ 10 milliseconds, the circuit is a single precise short circuit detection circuit, the maintenance time of the maximum short circuit current is ≤ 150 microseconds, avoiding damage to the cable by long time large current;

[0042] (3) Accurate identification of capacitive load (false short circuit) short circuit and resistive load (true short circuit) short circuit, when identified as resistive load (true short circuit) short circuit, cut off 220V power output, until the short circuit fault is eliminated, the system automatically identifies again, and the system will automatically recover (the system can be set to automatic / manual closing) when there is no short circuit; when identified as capacitive load (false short circuit) short circuit, the system will open the MOS tube switch within 10 milliseconds to supply power to the load;

[0043] (4) Suitable for large current starting: by adjusting the system current threshold parameter, the rated current 1.2~4 times starting current can be reached, which can adapt to the use of electric box total switch;

[0044] (5) Single switch, no oscillation with inductive load at the load end, (MOS tube) 220V multiple fast opening / closing, which will form a boost circuit with the inductive load in the load (such as: electric fan, air conditioner, refrigerator, transformer, industrial transformer), the voltage will be between 220V-1200V, which will damage the electronic equipment in the load circuit; Moreover, the MOS tube in this circuit only closes / open 1 time, even if there is inductive load in the load circuit (such as: transformer, motor, inductor) will not produce oscillation boost, and will not harm the electrical appliances in the load circuit;

[0045] (6) The device is self-generated and will not produce oscillation and damage the device, because the MOS tube of the detection circuit only acts once to close, it can achieve large current short circuit protection without damaging the device and the MOS tube, and the short circuit protection current value can be set to 1~3 times of the maximum working current of the MOS tube or IGBT tube;

[0046] (7) It has the functions of short circuit protection of fire wire and fire wire, fire wire and zero line, and fire wire and ground line. This circuit can be used in AC220 / AC380V electrical scenes, and has the functions of fire wire / zero line protection, fire wire / fire wire protection, and fire wire / ground line protection. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is the circuit principle diagram provided by the application;

[0048] Figure 2 is the partial circuit principle diagram (fire wire / zero line, fire wire / ground line short circuit detection circuit principle diagram) provided by the application;

[0049] Figure 3 is the current sampling circuit A provided by the application;

[0050] Figure 4 is the residual current sampling unit E provided by the application;

[0051] Figure 5MOS switch unit B provided by the present application;

[0052] Figure 6 Load short circuit detection unit C provided by the present application;

[0053] Figure 7 Zero point current waveform chart when capacitive short circuit (capacitive resistance) of the present application;

[0054] Figure 8 Zero point voltage waveform chart when capacitive short circuit (capacitive resistance) of the present application;

[0055] Figure 9 Zero point current waveform chart when resistive short circuit (resistive resistance) of the present application;

[0056] Figure 10 Zero point voltage waveform chart when resistive short circuit (resistive resistance) of the present application;

[0057] Figure 11 Non-zero point current waveform chart when capacitive short circuit (capacitive resistance) of the present application;

[0058] Figure 12 Non-zero point voltage waveform chart when capacitive short circuit (capacitive resistance) of the present application;

[0059] Figure 13 Non-zero point current waveform chart when resistive short circuit (resistive resistance) of the present application;

[0060] Figure 14 Non-zero point voltage waveform chart when resistive short circuit (resistive resistance) of the present application;

[0061] Figure 15 Test power supply control unit D provided by the present application;

[0062] Figure 16 L1 / L2 short circuit detection unit F provided by the present application;

[0063] Figure 17 MCU detection control unit G provided by the present application;

[0064] Figure 18 Power supply unit H provided by the present application;

[0065] Figure 19 Fire / zero short circuit detection control circuit block diagram provided by the present application;

[0066] Figure 20 Fire / ground short circuit detection control circuit block diagram provided by the present application;

[0067] Figure 21 L1 / L2 / L3 short circuit detection control block diagram provided by the present application. DETAILED DESCRIPTION

[0068] The application is further described in the following description with reference to the accompanying drawings, in which:

[0069] An AC load recognition circuit for capacitive and resistive load short circuit, as shown in Figure 1 、 Figure 2 , includes current detection units A and A2, MOS switch units B and B2, residual current sampling unit E, load short circuit detection unit C of live wire / zero line, test power control units D and D2, live wire / live wire short circuit detection unit F, MCU operation control unit G and power supply unit H; current detection units A and A2, MOS switch units B and B2, residual current sampling unit E, load short circuit detection unit C of live wire / zero line, test power control units D and D2, live wire / live wire short circuit detection unit F and power supply unit H are all connected with MCU operation control unit G. As shown in Figure 1 and Figure 2 , among them, current detection unit A, MOS switch unit B, residual current sampling unit E, load short circuit detection unit C of live wire / zero line and test power control unit D form the recognition circuit of live wire L1 phase line channel with MCU operation control unit G and power supply unit H; current detection unit A2, MOS switch unit B2, test power control unit D2 and live wire / live wire short circuit detection unit F form the recognition circuit of live wire L2 phase line channel with MCU operation control unit G and power supply unit H.

[0070] Current detection unit A, as shown in Figure 3 , is used to collect live wire current and convert the collected current peak waveform signal to obtain direct current pulsating voltage waveform signal. Current detection unit A includes current transformer LH2 for collecting current peak waveform signal, live wire passes through the center hole of current transformer, the 2nd pin of current transformer LH2 is connected to the positive electrode of amplifier U6 through resistor R15, the output end of amplifier U6 is connected with one end of resistor R18, the other end of resistor R18 is connected with MCU operation control unit G, and specifically the other end of resistor R18 is connected with the 19th pin of chip U8 in MCU operation control unit G. The model of operational amplifier U6 is preferably TP10-2;

[0071] The first pin of the current transformer LH2 is connected with one end of the resistors R16 and R13 respectively, the other end of the resistor R16 is connected with the capacitor C7, the negative pole of the amplifier U6, the capacitor C10 and one end of the resistor R17 respectively, the other end of the resistor R13 is connected with the other end of the capacitor C7, one end of the capacitor C8, one end of the capacitor C9 and the other end of the resistor R14 respectively, the other end of the capacitor C8 is grounded, the other end of the resistor R14 is connected with the second pin of the current transformer LH2 and one end of the resistor R15 respectively, the other end of the capacitor C9 is connected with the other end of the resistor R15.

[0072] The positive power supply end of the amplifier U6 is connected with the 5V power supply and one end of the capacitor C6 respectively, the negative power supply end of the amplifier U6 is grounded, the other end of the capacitor C6 is grounded.

[0073] In the current detection unit A, the current voltage signal collected by the current transformer LH2 is converted into a differential signal (including a positive differential signal + and a negative differential signal -) by the resistors R13, R14, R15, R61, R17, C7, C8, C9, C10, U6, etc., the sinusoidal differential signal is amplified by the U6 (TP10-2) and converted into a complete positive selected wave voltage waveform with +2.5V as the reference voltage, and the signal is sent to the MCU operation control unit G through the R18 for operation. Figure 1 The circuit and working principle of the current detection unit A2 are the same as those of the current detection unit A, except that the live wire L2 is connected. Since the electronic devices have bit number identification in the circuit diagram, in the schematic diagram, the same electronic devices of the current detection unit A2 as those of the current detection unit A are marked with "-1" to distinguish the device bit number identification, for example, the current transformer LH2 and the resistor R13 of the current detection unit A are marked as LH2-1 and R13-1 respectively in the circuit of the current detection unit A2. The other units (B2, D2, etc. below) are also marked according to the rule of adding "-1", which represents the electronic devices of the phase line channel circuit of the live wire L2.

[0074] The residual current sampling unit E, as shown in Figure 4 includes a residual current transformer LH1, the three-phase live wire and the zero line pass through the center hole of the residual current transformer LH1, the first pin of the residual current transformer LH1 is connected with the resistor R19 and one end of the resistor R22; the other end of the resistor R19 is connected with the capacitor C11, the capacitor C12, the capacitor C13 and one end of the resistor R20 respectively with the 2.5V power supply, the other end of the capacitor C11 is grounded; the other end of the resistor R22 is connected with the other end of the capacitor C12, one end of the capacitor C14 and one end of the resistor R23 to the negative pole of the amplifier U7;

[0075] Pin 2 of the other end of the residual current transformer LH1 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.

[0076] In the residual current sampling unit E, the current and voltage signals acquired by the residual current transformer LH1 are converted into differential signals by R19, R20, R21, R22, R23, R24, C11, C12, C13, C14, U7, etc. The sinusoidal differential signal is amplified by U6 (LM358) and transformed into a complete positive voltage waveform with +2.5V as the reference voltage. This signal is then sent to the MCU operation and control unit G for processing via R24.

[0077] 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 connection point of the other ends of resistors R8 and R9 is connected to pins 6 and 7 of chip U3. 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 other end of capacitor C3 is grounded via pins 3 and 5 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 via 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 via 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 (L1-MOS / OFF) of chip U8 in the MCU operation and control unit G. (Note: The last sentence appears to be incomplete and requires further context.) 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.

[0078] The following principles are involved in the MOSFET switching unit B:

[0079] (1) Isolation power supply: chip U4 is an isolation switch power module, the module 1 foot +12V, 2 foot signal ground, 3 foot switch tube Q1 / Q2 two MOS tube S pin, 4 foot output +15V output foot, MOS tube G (gate) level to provide a positive bias (the voltage according to the MOS tube specification book GS voltage for standard). Low voltage ground, R10, R11, R12, Q4 and U3 constitute a low voltage circuit drive circuit is always in the on state,

[0080] (2) low voltage drive: low voltage drive circuit by R10, R11, R12, Q4, U3, EC5 constitute, the drive off and on by MCU control.

[0081] (3) high voltage switch; high voltage switch circuit by U4, Q1, Q2, R7, R8, R9, EC3, U3 constitute, through the light coupling inside the photo sensor on and off, so that the output end of the chip U3 4, 5 and 7, 8 feet are on, 4, 5 feet of 5 feet of MOS tube S level, 7, 8 feet of internal for pull-up (8 feet of isolation power supply anode), through the MCU operation control unit G control output, can realize the closing and opening of MOS switch tube (normal output after opening, off after breaking 220V load output).

[0082] Fire line / zero line load short circuit detection unit C, as shown in Figure 5 , the first pin of the emitter of the bidirectional optocoupler U2 is connected with the zero line, the second pin of the bidirectional optocoupler U2 is connected with one end of the resistor R2, the other end of the resistor R2 is connected with the fire line output end; the third pin of the collector of the bidirectional optocoupler U2 is connected with one end of the resistor R3 and the twentieth pin of the chip U8 respectively; the other end of the resistor R3 is grounded; the fourth pin of the bidirectional optocoupler U2 and one end of the capacitor C3 are commonly connected with +5V power supply, and the other end of the capacitor C3 is grounded.

[0083] In the fire line / zero line load short circuit detection unit C, the working principle and process are as follows: when the current detected by the current detection unit A is greater than 80A (the threshold value can be changed, the same below), the current detection unit A will transmit the overcurrent signal to the MCU operation control unit G, and the MCU operation control unit G will transmit the tripping signal to the MOS switch unit B to trip. At this time, the test power supply control unit D (the circuit switch is in a normally closed state) starts to work, which will continuously provide a small current alternating current to the load end, and continuously supply power to the subsequent fire line / zero line load short circuit detection unit C. The circuit provides a small current alternating current to the load end, and continuously supplies power to the subsequent fire line / zero line load short circuit detection unit C. The circuit detects the voltage drop between the resistor R1 and the load, and the voltage drop is transmitted to the bidirectional optocoupler U2 through the resistor R2 to form a loop. The other end of the bidirectional optocoupler U2 will detect a direct current voltage of 0-5V, and then the voltage is transmitted to the MCU operation control unit G to obtain the resistance value of the load. It needs to be explained that Figure 21The C2 is the same as the circuit and working principle of the load short circuit detection unit C2, except that the live wire L2 is connected.

[0084] The load end short circuit detection circuit judgment process: when the MOS tube is closed, the AC voltage (220V / small current) of the resistance R1 and the photoelectric relay U1 passes through the load loop to form a voltage division, which is added to the double-direction photoelectric U2 to form a photoelectric loop. The secondary circuit of the photoelectric relay is composed of +5V, double-direction photoelectric U2 and resistance R3. The output low level pulse time of the circuit is detected to be 10 milliseconds. When the low level sampling signal is less than 4 milliseconds (the same as the following), it is normal (not short circuit / false short circuit). When the low level (L) signal is more than 6 milliseconds (the same as the following), it is determined as short circuit. Through this circuit, the resistance value of the load short circuit can also be detected, that is, the resistance value of the load loop can be obtained after the operation of the MCU.

[0085] In the live wire / zero line load short circuit detection unit C, the detection circuit continuously collects the high and low level time of 10 milliseconds to identify the resistance short circuit and capacity short circuit state (such as Figure 7 , Figure 8 , Figure 9 , Figure 10 , Figure 11 , Figure 12 , Figure 13 and Figure 14 ), specifically:

[0086] (1) When the low level (L) sampling signal of the output end of the detection circuit is more than 6 milliseconds (this predetermined value parameter can be modified according to the use scene), it is identified as resistance short circuit. The MCU will output control signal at the same time as the MOS tube and the detection voltage control circuit. At this time, the load end is cut off because the MOS tube is closed, and the 220V voltage output is cut off.

[0087] (2) When the output low level (L) sampling signal is less than 4 milliseconds (this predetermined value parameter can be modified according to the use scene), it is identified as capacity load short circuit (false short circuit). The MCU will open the MOS tube. At this time, the load output end has AC 220V voltage output because the MOS is opened.

[0088] In this process, the output low level pulse time of the circuit is detected (the high level detection sampling period is 10 milliseconds, the low level sampling signal is less than 4 milliseconds for normal load, and the low level sampling signal is more than 6 milliseconds for load short circuit). Moreover, by changing the resistance value of R2, the resistance value of the short circuit can be detected.

[0089] 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 live wire L1 input terminal. The other end of resistor R1 is connected to pin 1 of the output terminal of optocoupler relay U1. Pin 2 of the output terminal of optocoupler relay U1 is connected to the other end of resistor RT1 and the live wire L1 output terminal. 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 and the other end of capacitor C4 are 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 R6 is grounded. 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. Resistors RT1-1 and RT1 are both varistors, the difference being that they are connected to the live wire L2.

[0090] 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 will not be formed). This voltage divider and the load terminal short circuit detection circuit form a short circuit detection.

[0091] 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 the emitter 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 the collector of bidirectional optocoupler U9 and one end of capacitor C10 are connected to the +5V power supply, and the other end of capacitor C10 is grounded.

[0092] The working process and principle of the live wire / live wire short circuit detection unit F are as follows: when the currents of the live wire L1 and the live wire L2 reach the triggering condition at the same time, the MCU operation control unit G simultaneously turns off the two channel MOS tube switch unit B, at this time, the live wire / live wire short circuit detection unit F (phase line and phase line detection circuit) L1 / L2 / L3 detection circuit starts to work, because the detection voltage of the live wire / live wire short circuit detection unit F is connected to the L1-L2 / L2-L3 / L3-L1 phase line and phase line (AC380V), the added detection current passes through R1→U1→the load circuit→R1-1→U1-1 of the live wire L2 phase line channel to form the voltage division of the load circuit, the AC voltage division of the load circuit passes through the primary circuit of R26 and U9, and the DC output of the secondary circuit R25, U9 and EC10 is converted into a DC voltage output, and the low-level pulse time (the detection time is 10 milliseconds, when the low-level pulse time is less than 4 milliseconds, the load is normal, and when the low-level pulse time is greater than 6 milliseconds, it is a true short circuit) is detected.

[0093] The MCU operation control unit G, as shown in Figure 17 The 6th pin of the chip U8 is connected with one end of the capacitor C19, and the other end of the capacitor C19 is grounded; the 8th pin and the 9th pin of the chip U8 are connected with each other, and then connected with the +5V power supply, one end of the capacitor EC8 and one end of the capacitor C15, respectively; the other end of the capacitor EC8 and the other end of the capacitor C15 are commonly grounded with the 10th pin of the chip U8; the 11th pin of the chip U8 is connected with the +2.5V power supply as an AD value calibration value, and one end of the capacitors C16, C17 and C18 is commonly connected with the 1st pin of the amplifier U7; the other end of the capacitors C16, C17 and C18 is commonly grounded with the 3rd pin of the amplifier U7; the 2nd pin and the 2nd pin of the amplifier U7 are both connected with one end of the resistor R30, and the other end of the resistor R30 is connected with the +5V power supply.

[0094] In the MCU operation control unit G, the chip U8 is composed of an STC32G12K128 chip group, which 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-way MOS tube driving, three-way test power supply control, three-way AC220V load end short circuit detection circuit, three-way AC380V (live wire and live wire) load end short circuit detection circuit and other functional circuit composition.

[0095] The power supply unit H, as shown in Figure 18 is an active power supply circuit connected with an AC input end, which converts AC into DC for load use through a rectifier circuit.

[0096] It should be noted that the circuit for identifying the short circuit of the live wire L3 channel in the present application is the same as the circuit for identifying the short circuit of the live wire L2 channel, and the working principle is consistent, which will not be repeated here, and the figure is not shown.

[0097] The present application is a method for identifying the short circuit of capacitive and resistive loads in an AC load. The short circuit between the neutral wire and the live wire, the live wire and the ground wire, and the live wire and the live wire is identified separately or simultaneously. The identification method is as follows:

[0098] The live wire / neutral wire short circuit identification is shown in Figure 19

[0099] When the current detection unit A detects that the live wire current is greater than 80A (this threshold value can be modified according to the use scenario), the MCU operation control unit G outputs a control signal to close the MOS switch tube of the MOS switch unit B. If the load short circuit detection unit C of the live wire / neutral wire has a low-level pulse time greater than 6 milliseconds, the MOS switch unit B determines that it is short-circuited and outputs a control signal, and at the same time, the MOS switch unit B and the test power control unit D are closed, thereby completing the identification and protection. In this process, the test power control unit D is closed to prevent the MOS tube from being electrified at the load output end when it is closed, causing electric shock and electric arc.

[0100] The live wire / ground wire short circuit identification is shown in Figure 20

[0101] When the current detection unit A detects that the live wire current increases by more than the threshold value in a single time, for example, the threshold value is set to 50A, and at the same time, the residual current detection circuit E increases by 10A (this threshold value can be modified according to the use scenario), the MCU operation control unit G detects these two voltage signals at the same time, and the MOS switch unit B outputs a control voltage to close the MOS switch and the test power control unit D, thereby completing the identification and protection. The test power control unit D is closed to prevent the MOS tube from being electrified at the load output end when it is closed, causing electric shock and electric arc.

[0102] The live wire / live wire short circuit identification is shown in Figure 21

[0103] When the current detection unit A detects that the current of the two live wires is greater than the threshold value (for example, the threshold value is set to 80A) at the same time, the MCU operation control unit G outputs a control signal to close the two corresponding channel MOS switch units B at the same time. At this time, the live wire / live wire short circuit detection unit F detects that the low-level pulse time is greater than 6 milliseconds (this threshold value can be modified according to the use scenario), the MCU operation control unit G determines that it is short-circuited and outputs a closing signal, and at the same time, the two MOS switch units B and the two test power control units D are closed, thereby completing the identification and protection. The test power control unit D is closed to prevent the MOS tube from being electrified at the load output end when it is closed, causing electric shock and electric arc.​​​

[0104] The thresholds listed in the above various short circuit identification methods can be adjusted according to the use scenario and are not fixed.

[0105] In summary, the circuit and method of the application have the following advantages:

[0106] (1) Detect short circuit before power-on and closing

[0107] The system will detect whether there is a short circuit in the load circuit before closing, and when a short circuit is detected, the system will not power the load, and the MOS will always be in the off state to avoid damaging the cable by large current;

[0108] (2) Turn-off time is fast ≤ 150 microseconds, detection period is short ≤ 10 milliseconds

[0109] The circuit is a single-precision short circuit detection circuit, and the maximum current of the short circuit is maintained for ≤ 150 microseconds to avoid long-time large current damage to the cable;

[0110] (3) Accurately identify capacitive load (false short circuit) short circuit and resistive load (true short circuit) short circuit, when identifying resistive load (true short circuit) short circuit, cut off 220V power output until the short circuit fault is eliminated, the system automatically identifies again, and the system will automatically restore power supply when there is no short circuit;

[0111] When identifying capacitive load (false short circuit) short circuit, the system will open the MOS tube switch to power the load within 10 milliseconds;

[0112] (4) Suitable for large current starting: by adjusting the system current threshold parameter, the rated current 1.2~4 times starting current can be reached, which can adapt to the use of electric box total switch.

[0113] (5) Single switch, no oscillation with inductive load at the load end

[0114] (MOS tube) 220V multiple fast opening / closing, which will form a boost circuit with the inductive load (such as: electric fan, air conditioner, refrigerator, transformer, industrial transformer) in the load, the voltage will be between 220V-1200V, which will damage the electronic equipment of the load circuit;

[0115] Because the MOS tube in the circuit only closes / open 1 time, even if there is an inductive load (such as: transformer, motor, inductor) in the load circuit, it will not produce oscillation boost, and will not harm the electrical appliances in the load circuit;

[0116] (6) The device self-generation will not produce oscillation and damage the device

[0117] Because the MOS transistor of the detection circuit only acts once to shut down, large current short circuit protection can be achieved without damaging the equipment and the MOS transistor, and the short circuit protection current value can be set to 1-3 times the maximum working current of the MOS transistor or IGBT transistor;

[0118] (7) has the short circuit protection function of the fire line and the fire line, the fire line and the zero line and the fire line and the ground line;

[0119] The circuit can be used in the power consumption scene of AC220 / AC380V, has the fire line / zero line protection function, the fire line / fire line protection function and the fire line / ground line protection function.

[0120] The above is a further detailed description of the present application in combination with specific preferred embodiments, and the specific implementation of the present application cannot be limited to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, a number of simple deductions or substitutions can be made without departing from the concept of the present application, and all should be considered within the protection scope of the present application.

Claims

1. An identification circuit for short circuits of capacitive and resistive loads in an alternating current load, characterized in that It includes current detection unit A and A2, MOS switch unit B and B2, residual current sampling unit E, load short circuit detection unit C of firewire / zero line, test power control unit D and D2, firewire / firewire short circuit detection unit F, MCU operation control unit G and power supply unit H; current detection unit A and A2, MOS switch unit B and B2, residual current sampling unit E, load short circuit detection unit C of firewire / zero line, test power control unit D and D2, firewire / firewire short circuit detection unit F and power supply unit H are connected with MCU operation control unit G; wherein, current detection unit A, MOS switch unit B, residual current sampling unit E, load short circuit detection unit C of firewire / zero line and test power control unit D and MCU operation control unit G and power supply unit H form the identification circuit of firewire L1 phase line channel; current detection unit A2, MOS switch unit B2, test power control unit D2 and firewire / firewire short circuit detection unit F and MCU operation control unit G and power supply unit H are connected to form the identification circuit of firewire L2 phase line channel; The MCU operation control unit G comprises a chip U8; The current detection unit A comprises a current transformer LH2, and the firewire L1 passes through the center hole of the current transformer LH2. The residual current sampling unit E comprises a residual current transformer LH1, and three firewires and zero lines pass through the center hole of the residual current transformer LH1. The MOS switch unit B comprises MOS switch tubes Q1 and Q2, the source electrodes of the MOS switch tubes Q1 and Q2 are connected, the drain electrode of the MOS switch tube Q1 is connected with the firewire L1 input end, and the drain electrode of the MOS switch tube Q2 is connected with the fire L1 line output end. The load short circuit detection unit C of firewire / zero line comprises a first pin of a bidirectional optical coupler U2 input end connected with the zero line, a second pin of the bidirectional optical coupler U2 input end connected with one end of a resistor R2, and the other end of the resistor R2 connected with the firewire L1 output end. The test power control unit D comprises a resistor R1, one end of the resistor R1 connected with one end of a resistor RT1 and the firewire L1 input end, the other end of the resistor R1 connected with a first pin of an optical coupler relay U1 input end, a second pin of the optical coupler relay U1 input end connected with the other end of the resistor RT1 and the firewire L1 output end. The firewire / firewire short circuit detection unit F comprises a resistor R26, one end of the resistor R26 connected with the firewire L1 output end, the other end of the resistor R26 connected with a first pin of a bidirectional optical coupler U9 input end, and a second pin of the bidirectional optical coupler U9 input end connected with the firewire L2 output end. The circuit and working principle of the current detection unit A and the current detection unit A2 are consistent. The circuit and working principle of the MOS switch unit B and the MOS switch unit B2 are consistent. The circuit and working principle of the test power control unit D and the test power control unit D2 are consistent.

2. The circuit of claim 1, wherein, The second pin of the current transformer LH2 is connected with one end of resistors R14 and R15 respectively, and is connected with the positive electrode of an amplifier U6 after passing through the resistor R15. The output end of the amplifier U6 is connected with one end of a resistor R18, and the other end of the resistor R18 is connected with the 19th pin of a chip U8 in the MCU operation control unit G. The first pin of the current transformer LH2 is connected with one end of resistors R16 and R13 respectively. The other end of the resistor R16 is connected with a capacitor C7, the negative electrode of the amplifier U6, a capacitor C10 and one end of a resistor R17 respectively. The other end of the resistor R13 is connected with the other end of the capacitor C7, one end of a capacitor C8, one end of a capacitor C9 and the other end of the resistor R14 respectively. The other end of the capacitor C8 is grounded, and the other end of the capacitor C9 is connected with the other end of the resistor R15. The positive power supply end of the amplifier U6 is connected with a 5V power supply and one end of a capacitor C6 respectively, and the other end of the capacitor C6 is grounded. The negative power supply end of the amplifier U6 is grounded. The common point of R13, R14, C8, C9 and C7 is a +2.5V reference voltage. The model of the chip U8 is STC32G12K128. The model of the amplifier U6 is TP10-2.

3. The circuit of claim 1, wherein, The first pin of the residual current transformer LH1 is connected with one end of a resistor R19 and one end of a resistor R22. The other end of the resistor R19 is connected with a capacitor C11, a capacitor C12, a capacitor C13 and one end of a resistor R20 together to a +2.5V reference power supply. The other end of the capacitor C11 is grounded. The other end of the resistor R22 is connected with the other end of the capacitor C12, one end of a capacitor C14 and one end of a resistor R23 together to the negative electrode of an amplifier U7. The second pin of the other end of the residual current transformer LH1 is connected with the other end of the resistor R20 and one end of a resistor R21 respectively. The other end of the resistor R21 and the other end of the capacitor C13 are connected together to the positive electrode of the amplifier U7. The output end of the amplifier U7 is connected with one end of a resistor R24, the other end of the capacitor C14 and the other end of the resistor R23 respectively. The other end of the resistor R24 is connected with the 15th pin of the chip U8 in the MCU operation control unit G. The model of the chip U8 is STC32G12K128.

4. The circuit of claim 1, wherein, The gate of the MOS switch tube Q1 is connected with one end of the resistor R8, the gate of the MOS switch tube Q2 is connected with one end of the resistor R9, the connection point of the other end of the resistor R8 and the other end of the resistor R9 is connected with the 6th pin and the 7th pin of the chip U3, the 5th pin of the chip U3 is connected with the source of the MOS switch tube Q1 and the MOS switch tube Q2, the 8th pin of the chip U3 is connected with one end of the resistor R7, the other end of the resistor R7 and one end of the capacitor EC3 are commonly connected with a 15V power supply, the other end of the capacitor EC3 is commonly grounded with the 3rd pin of the chip U4 and the 5th pin of the chip U3; the 2nd pin of the chip U3 is connected with one end of the capacitor C5 and the 2nd pin of the chip U4 respectively, the 1st pin of the chip U4 is commonly grounded with the other end of the capacitor C5; the 3rd pin of the chip U3 is connected with one end of the resistor R10, the other end of the resistor R10 is connected with the collector of the triode Q4, the emitter of the triode Q4 is commonly grounded with one end of the resistor R12, the base of the triode Q4 is connected with the other end of the resistor R12 and one end of the resistor R11 respectively, the other end of the resistor R11 is connected with the 18th pin of the chip U8 in the MCU operation control unit G; The model of the chip U3 is TLP250: The chip U4 is a DC / DC isolation switch power supply module; The model of the chip U8 is STC32G12K128.

5. The circuit of claim 1, wherein, The 3rd pin of the emitter of the bidirectional optical coupler U2 is connected with one end of the resistor R3 and the 20th pin of the chip U8 respectively; the other end of the resistor R3 is grounded; the 4th pin of the collector of the bidirectional optical coupler U2 and one end of the capacitor C3 are commonly connected with a +5V power supply, and the other end of the capacitor C3 is grounded.

6. The circuit of claim 1, wherein, The 3rd pin of the output end of the optical coupler relay U1 is connected with a +5V power supply and one end of the capacitor C4 respectively, the 4th pin of the output end of the optical coupler relay U1 is connected with one end of the resistor R4, the other end of the resistor R4 is connected with the collector of the triode Q3, the emitter of the triode Q3 and the other end of the capacitor C4 are grounded, the other end of the resistor R6 is grounded, the base of the triode Q3 is connected with one end of the resistor R6 and one end of the resistor R5 respectively, the other end of the resistor R5 is connected with the 17th pin of the chip U8 in the MCU operation control unit G; The model of the chip U8 is STC32G12K128.

7. The circuit of claim 1, wherein, The 3rd pin of the emitter of the bidirectional optical coupler U9 is connected with 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 4th pin of the collector of the bidirectional optical coupler U9 and one end of the capacitor C10 are commonly connected with a +5V power supply, and the other end of the capacitor C10 is grounded; The model of the chip U8 is STC32G12K128.

8. A method for identifying short circuit of capacitive load and resistive load in an AC load applied to the circuit of any one of claims 1-7, which separately or simultaneously identifies short circuit between the zero line and the live line, the live line and the ground line, and the live line and the live line, characterized in that: Fire line / zero line short circuit identification: when the current detection unit A detects the fire line current > threshold value, the MCU operation control unit G outputs the control signal to close the MOS switch tube of the MOS switch unit B, and if the load short circuit detection unit C of the fire line / zero line low level pulse time > threshold value, the MCU operation control unit G judges and confirms the resistance short circuit, and outputs the control signal, closes the MOS switch unit B and the test power supply control unit D at the same time; if the load short circuit detection unit C of the fire line / zero line low level pulse time < threshold value, the MCU operation control unit G judges and confirms the capacitive short circuit; Fire line / ground line short circuit identification: when the current detection unit A detects the fire line current single increase > threshold value, and the residual current sampling unit E detects the single increase > threshold value, the MCU operation control unit detects the two voltage signals at the same time, and then the MCU operation control unit G judges and confirms the fire ground short circuit, and outputs the signal to close the MOS switch unit B and the test power supply control unit D at the same time; Fire line / fire line short circuit identification: when the current detection unit A and A2 detect the current of the two fire lines > threshold value at the same time, the MCU operation control unit G outputs the control signal to close the corresponding channel MOS switch unit B and B2 at the same time; at this time, when the fire line / fire line short circuit detection unit F detects the low level pulse time > threshold value, the MCU operation control unit G judges and confirms the fire line / fire line true short circuit, and outputs the closing signal to close the MOS switch unit B and B2 and the test power supply control unit D and D2 at the same time; when the low level pulse time < threshold value, it is judged that the load is normal.

9. The method for identifying capacitive load and resistance load short circuit in the alternating current load according to claim 8, characterized in that: Fire line / zero line short circuit identification: when the current detection unit A detects the fire line current > 80A, the MCU operation control unit G outputs the control signal to close the MOS switch tube of the MOS switch unit B, and if the load short circuit detection unit C of the fire line / zero line low level pulse time > 6ms, the MCU operation control unit G judges and confirms the resistance short circuit, and outputs the control signal to close the MOS switch unit B and the test power supply control unit D at the same time; when the output low level pulse time < 4ms, it is judged that the load is capacitive short circuit; Fire line / ground line short circuit identification: when the current detection unit A detects the fire line current single increase > 50A, and the residual current sampling unit E detects the increase > 10A, the MCU operation control unit G detects the two voltage signals at the same time, and then outputs the control voltage to close the MOS switch unit B and the test power supply control unit D. Firewire / firewire short circuit identification: when the current detection unit A detects the current of two firewire is > 50A at the same time, MCU operation control unit G output control signal at the same time close two corresponding channel MOS tube switch unit B and B2; At this time, the firewire / firewire short circuit detection unit F detects low level pulse time > 6ms, MCU operation control unit G determines to confirm true short circuit, at the same time output close signal, close MOS tube switch unit B and B2 and test power control unit D and D2; When the low level pulse time < 4ms, it is judged that the load is normal.

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