AC output short circuit detection device

Abstract

An embodiment of the present invention provides an AC output short-circuit detection device. The device includes: a first DC power supply connected to a unidirectional output current-limiting circuit; a unidirectional output current-limiting circuit connected to the first DC power supply and a switching circuit; a switching circuit connected to the unidirectional output current-limiting circuit, a current-limiting and detection circuit, and an MCU; a current-limiting and detection circuit connected to the switching circuit, the AC power live wire, and the MCU; and a residual voltage detection circuit connected to the AC power live wire, the AC power neutral wire, and the MCU. This embodiment of the present invention enables short-circuit detection at the AC output.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit detection, and in particular to an AC output terminal short-circuit detection device. Background Art

[0002] Most existing AC charging piles do not have an output short-circuit detection function before AC output power is supplied. If the output end of the AC charging pile is not short-circuited before power is supplied, a short circuit at the output end may cause the output current to be too large at the moment the charging pile output is closed, causing the internal components of the charging pile to burn out and the charging pile to be damaged. Summary of the Invention

[0003] An embodiment of the present invention provides an AC output terminal short-circuit detection device to implement short-circuit detection of the AC output terminal.

[0004] The technical solution of the embodiment of the present invention is achieved as follows:

[0005] An AC output short-circuit detection device, wherein the AC output is the output of an AC charging pile, comprises: a first DC power supply, a unidirectional output current limiting circuit, a switching circuit, a current limiting and detection circuit, a residual voltage detection circuit, and a microcontroller unit, and a live wire switch and a neutral wire switch are provided between the AC input and the AC output, wherein:

[0006] A first DC power supply is connected to the unidirectional output current limiting circuit and is used to: output a DC current;

[0007] a unidirectional output current limiting circuit, one end of which is connected to the first DC power supply and the other end of which is connected to the switching circuit, for blocking the current from the switching circuit to the first DC power supply and transmitting the DC current output by the first DC power supply to the switching circuit;

[0008] A switch circuit, one end of which is connected to the unidirectional output current limiting circuit, one end of which is connected to the current limiting and detection circuit, one end of which is connected to the AC power supply neutral line and the connection point is located between the neutral line switch and the AC output terminal, and another end of which is connected to the MCU, and is used to: open or close under the control of the MCU;

[0009] A current limiting and detection circuit, one end of which is connected to the switch circuit, one end of which is connected to the live wire of the AC power supply and the connection point is located between the live wire switch and the AC output terminal, and another end of which is connected to the MCU, and is used to: output a short-circuit detection voltage of the AC output terminal to the MCU;

[0010] A residual voltage detection circuit, one end of which is connected to the live wire of the AC power supply and the connection point is located between the live wire switch and the AC output terminal, one end of which is connected to the neutral wire of the AC power supply and the connection point is located between the neutral wire switch and the AC output terminal, and another end of which is connected to the MCU, and is used to: output the residual voltage detection voltage of the AC output terminal to the MCU;

[0011] The MCU is connected to the switch circuit, the current limiting and detection circuit, and the residual voltage detection circuit, respectively, and is used to control the opening and closing of the switch circuit and determine whether there is a short circuit at the AC output end according to the voltage output by the current limiting and detection circuit and the voltage output by the residual voltage detection circuit.

[0012] The first DC power supply includes a DC power supply and a first capacitor; wherein one end of the first capacitor is connected to the DC power supply, and the other end is grounded.

[0013] The unidirectional output current limiting circuit includes a first diode and a first resistor; wherein, the positive electrode of the first diode is connected to the first DC power supply, and the negative electrode of the first diode is connected to the switching circuit; one end of the first resistor is grounded and shares a ground terminal with the first DC power supply, and the other end is connected to the switching circuit.

[0014] The unidirectional output current limiting circuit further includes a second diode and a fuse;

[0015] One end of the second diode is connected to the cathode of the first diode, and the other end is connected between the first resistor and the switch circuit; the fuse is connected between the first resistor and the switch circuit.

[0016] The switch circuit includes a first switch and a second switch;

[0017] Among them, the first switch is connected between the unidirectional output current limiting circuit and the current limiting and detection circuit; the second switch is connected between the unidirectional output current limiting circuit and the AC power supply neutral line, and the connection point with the AC power supply neutral line is located between the neutral line switch and the AC output end.

[0018] The current limiting and detection circuit includes a second resistor, a unidirectional optocoupler and a third resistor, wherein:

[0019] The second resistor is connected between the switch circuit and the positive electrode of the primary side of the unidirectional optocoupler;

[0020] The positive electrode of the primary side of the unidirectional optocoupler is connected to the second resistor, and the negative electrode is connected to the AC power live wire, and the connection point is located between the live wire switch and the AC output terminal;

[0021] One end of the third resistor is connected to the second DC power supply, and the other end is connected to the positive electrode of the secondary side of the unidirectional optocoupler and the second IO port of the MCU;

[0022] The negative pole of the secondary side of the unidirectional optocoupler is grounded.

[0023] The current limiting and detection circuit further includes a sixth resistor, a voltage clamping device, a seventh resistor and a second capacitor;

[0024] Among them, the sixth resistor is connected between the second resistor and the positive pole of the primary side of the unidirectional optocoupler; the voltage clamping device is connected between the second resistor and the negative pole of the primary side of the unidirectional optocoupler; the seventh resistor is connected in parallel with the primary side of the unidirectional optocoupler; one end of the second capacitor is connected to the second IO port of the MCU, and the other end is grounded.

[0025] The residual voltage detection circuit includes: a fourth resistor, a bidirectional optocoupler and a fifth resistor, wherein:

[0026] The fourth resistor is connected between the AC power supply live wire and one end of the primary side of the bidirectional optocoupler, and the connection point between the fourth resistor and the AC power supply live wire is located between the live wire switch and the AC output terminal;

[0027] The other end of the primary side of the bidirectional optocoupler is connected to the AC power supply neutral line and the connection point is located between the neutral line switch and the AC output terminal;

[0028] One end of the fifth resistor is connected to the third DC power supply, and the other end is connected to the positive electrode of the secondary side of the bidirectional optocoupler and the first IO port of the MCU;

[0029] The negative pole of the secondary side of the bidirectional optocoupler is grounded.

[0030] The residual voltage detection circuit further includes a third capacitor;

[0031] One end of the third capacitor is connected to the first IO port of the MCU, and the other end is grounded.

[0032] The MCU is used to: when an external load is connected to the AC output end, output a disconnect signal to the live wire switch and the neutral wire switch; when it is detected that the residual voltage detection voltage output by the residual voltage detection circuit meets the set first voltage range, send a closing signal to the switch circuit; and after waiting for a preset time, if it is detected that the short-circuit detection voltage output by the current limiting and detection circuit meets the set second voltage range, it is determined that there is a short circuit at the AC output end.

[0033] In the above embodiment, by adding a switching circuit, the circuit between the first DC power supply and the AC output end can be disconnected, thereby improving the reliability of the circuit; by adding a residual voltage detection circuit, positive and negative residual voltage detection of the AC output end is realized. At the same time, this circuit is also a residual voltage discharge circuit of the AC output end, and together with the current limiting and detection circuit, short-circuit detection of the AC output end is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0035] Figure 1 A schematic structural diagram of an AC output short-circuit detection device provided in one embodiment of the present invention;

[0036] Figure 2 A schematic structural diagram of an AC output short-circuit detection device provided by another embodiment of the present invention;

[0037] Figure 3 This is a structural diagram of an AC output short-circuit detection device provided by yet another embodiment of the present invention. DETAILED DESCRIPTION

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0039] The terms "first," "second," "third," "fourth," and so on (if any) in the description and claims of the present invention and in the drawings described above are used to distinguish similar objects and are not necessarily used to describe a particular order or precedence. It should be understood that the terms used in this way are interchangeable where appropriate, so that the embodiments of the present invention described herein can, for example, be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having," as well as any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to these processes, methods, products, or apparatus.

[0040] Figure 1 This is a schematic diagram of the structure of an AC output short circuit detection device provided by an embodiment of the present invention, wherein the AC output terminal is the output terminal of an AC charging pile. Figure 1 As shown, the device mainly includes: a first DC power supply, a unidirectional output current limiting circuit, a switching circuit, a current limiting and detection circuit, a residual voltage detection circuit and an MCU (Micro Controller Unit). In addition, a live wire switch and a neutral wire switch are provided between the AC input terminal and the AC output terminal. The live wire switch is located on the AC power supply live wire between the AC input and output terminals, and the neutral wire switch is located on the AC power supply neutral wire between the AC input and output terminals.

[0041] 1) A first DC power supply connected to the unidirectional output current limiting circuit, configured to output a DC current.

[0042] In practical applications, if the AC output terminal is the output terminal of an AC charging pile, the first DC power supply can share the power generated by the flyback power supply circuit on the AC charging pile's power board. Alternatively, the flyback power supply can be supplemented with an independent winding to generate an additional power supply, or a separate power supply module can be used. The first DC power supply is typically designed for 12V (volts).

[0043] 2) A unidirectional output current limiting circuit, one end of which is connected to the first DC power supply and the other end of which is connected to the switching circuit, for blocking the current from the switching circuit to the first DC power supply and for transmitting the DC current output by the first DC power supply to the switching circuit.

[0044] 3) The switch circuit has one end connected to the unidirectional output current limiting circuit, one end connected to the current limiting and detection circuit, one end connected to the AC power supply neutral line and the connection point is located between the neutral line switch and the AC output terminal, and another end connected to the MCU, and is used to: open or close under the control of the MCU.

[0045] In actual application, the switch circuit is disconnected by default.

[0046] 4) A current limiting and detection circuit, one end of which is connected to the switching circuit, one end of which is connected to the live wire of the AC power supply and the connection point is located between the live wire switch and the AC output terminal, and one end of which is connected to the MCU. It is used to output a short-circuit detection voltage at the AC output terminal to the MCU.

[0047] 5) A residual voltage detection circuit, one end of which is connected to the live wire of the AC power supply and the connection point is located between the live wire switch and the AC output terminal; one end of which is connected to the neutral wire of the AC power supply and the connection point is located between the neutral wire switch and the AC output terminal; and another end of which is connected to the MCU, and is used to: output the residual voltage detection voltage at the AC output terminal to the MCU.

[0048] 6) MCU, which is respectively connected to the switching circuit, the current limiting and detection circuit, and the residual voltage detection circuit, and is used to: control the opening and closing of the switching circuit, and determine whether there is a short circuit at the AC output end based on the residual voltage detection voltage output by the residual voltage detection circuit and the short-circuit detection voltage output by the current limiting and detection circuit.

[0049] The MCU is also connected to the live wire switch and the neutral wire switch to control the opening and closing of the live wire switch and the neutral wire switch.

[0050] Figure 1 L in in AC input live wire port, N in For AC input neutral terminal, L out For AC output live wire port, N out It is the AC output neutral port, and the external load is connected through L out With N outWhen the AC output terminal is the output terminal of an AC charging station, the external load is typically an onboard charger for an electric vehicle. Relays can be used for the live and neutral switches.

[0051] like Figure 1 As shown, when the external load is connected to the AC output end, the MCU will output a disconnect signal to the live wire switch on the AC power supply live wire and the neutral wire switch on the AC power supply neutral wire; after that, the MCU detects whether the residual voltage detection voltage output by the residual voltage detection circuit meets the set first voltage range. If so, a closing signal is sent to the switch circuit, and after waiting for a preset time, the MCU detects whether the short-circuit detection voltage output by the current limiting and detection circuit meets the set second voltage range. If so, it is determined that there is a short circuit at the AC output end.

[0052] Specifically, when an external load is connected to the AC output terminal, there are two situations at the AC output terminal: Situation 1: There is a short circuit at the AC output terminal; Situation 2: There is no short circuit at the AC output terminal, and since there are usually safety capacitors on the external load, there is usually positive residual voltage or negative residual voltage on the safety capacitor. The residual voltage of the safety capacitor is the residual voltage at the AC output terminal, that is, there are two situations for Situation 2, one is that there is a positive residual voltage at the AC output terminal, and the other is that there is a negative residual voltage at the AC output terminal. The following is a description of these three situations respectively. Figure 1 The working process of the device shown is described below:

[0053] Case 1: There is a short circuit at the AC output terminal, that is, the impedance of the AC output terminal is 0Ω (ohm)

[0054] In this case, when an external load is connected to the AC output terminal, the MCU outputs a disconnect signal to the live wire switch on the AC power supply live wire and the neutral wire switch on the AC power supply neutral wire;

[0055] Since the residual voltage at the AC output end is almost 0V, almost no current flows through the residual voltage detection circuit. The MCU detects that the residual voltage detection voltage output by the residual voltage detection circuit meets the set first voltage range and sends a closing signal to the switch circuit.

[0056] After the switching circuit is closed, the DC current output by the first DC power supply forms a current loop through the switching circuit, the current limiting and detection circuit, and the external load. The MCU detects that the short-circuit detection voltage output by the current limiting and detection circuit meets the set second voltage range, and determines that there is a short circuit at the AC output end.

[0057] Case 2: There is no short circuit at the AC output terminal (i.e. there is a certain impedance at the AC output terminal), and there is a positive residual voltage at the AC output terminal

[0058] In this case, when an external load is connected to the AC output terminal, the MCU outputs a disconnect signal to the live wire switch on the AC power supply live wire and the neutral wire switch on the AC power supply neutral wire;

[0059] Since there is a positive residual voltage at the AC output end, the positive residual voltage at the AC output end will be discharged through the residual voltage detection circuit. When the MCU detects that the residual voltage detection voltage output by the residual voltage detection circuit meets the set first voltage range, it sends a closing signal to the switch circuit;

[0060] After the switching circuit is closed, the DC current output by the first DC power supply forms a current loop through the switching circuit, the current limiting and detection circuit, and the external load, thereby charging the safety capacitor on the external load. When the voltage on the safety capacitor is close to the voltage of the first DC power supply, the MCU detects that the short-circuit detection voltage output by the current limiting and detection circuit does not meet the set second voltage range, and determines that there is no short circuit at the AC output end.

[0061] Case 3: There is no short circuit at the AC output terminal (i.e. there is a certain impedance at the AC output terminal), and there is a negative residual voltage at the AC output terminal

[0062] In this case, when an external load is connected to the AC output terminal, the MCU outputs a disconnect signal to the live wire switch on the AC power supply live wire and the neutral wire switch on the AC power supply neutral wire;

[0063] Since there is a negative residual voltage at the AC output end, the negative residual voltage at the AC output end will be discharged through the residual voltage detection circuit. When the MCU detects that the residual voltage detection voltage output by the residual voltage detection circuit meets the set first voltage range, it sends a closing signal to the switch circuit;

[0064] After the switching circuit is closed, the DC current output by the first DC power supply forms a current loop through the switching circuit, the current limiting and detection circuit, and the external load to charge the safety capacitor on the external load. When the voltage on the safety capacitor is close to the voltage of the first DC power supply, the MCU detects that the short-circuit detection voltage output by the current limiting and detection circuit does not meet the set second voltage range, and determines that there is no short circuit at the AC output end.

[0065] Through the above analysis, we can see that there are three situations at the AC output terminal: there is a short circuit at the AC output terminal, there is no short circuit at the AC output terminal and there is a positive residual voltage at the AC output terminal, and there is no short circuit at the AC output terminal and there is a negative residual voltage at the AC output terminal. Figure 1 The devices shown can all be detected correctly.

[0066] Figure 1 The device shown can disconnect the circuit between the first DC power supply and the AC output terminal by adding a switching circuit, thereby improving the reliability of the circuit; and by adding a residual voltage detection circuit, it can realize positive and negative residual voltage detection of the AC output terminal. At the same time, this circuit also serves as a residual voltage discharge circuit for the AC output terminal, and together with the current limiting and detection circuit, it can realize short-circuit detection of the AC output terminal.

[0067] Figure 2 This is a structural diagram of an AC output short-circuit detection device provided by another embodiment of the present invention. Figure 2 As shown:

[0068] 1) The first DC power supply includes a DC power supply V CC1 and a first capacitor C1.

[0069] Among them, one end of C1 is connected to V CC1 , the other end is grounded. C1 is V CC1 Energy storage and filtering capacitors.

[0070] 2) The unidirectional output current limiting circuit includes a first diode D1 and a first resistor R1.

[0071] Among them, the positive terminal of D1 is connected to V CC1 , the negative pole is connected to the switch circuit; one end of R1 is grounded and shares the ground terminal with the first DC power supply, and the other end is connected to the switch circuit. Figure 2 It can be seen that the other end of R1 is actually connected to K2 in the switch circuit.

[0072] D1 is a unidirectional conducting diode to ensure that V CC1 Normal output, no reverse current flows into V CC1 R1 is V CC1 The output current limiting resistor R1 can be a common resistor or a PPTC (Polymeric Positive Temperature Coefficient) resistor.

[0073] 3) The switch circuit includes: a first switch K1 and a second switch K2.

[0074] Among them, K1 is connected between the unidirectional output current limiting circuit and the current limiting and detection circuit; K2 is connected between R1 in the unidirectional output current limiting circuit and the AC power supply neutral line, and the connection point with the AC power supply neutral line is located between the neutral line switch and the AC output end.

[0075] K1 and K2 are disconnected by default.

[0076] K1 and K2 are generally relays, but can also be switching devices such as optocouplers.

[0077] 4) The current limiting and detection circuit includes: a second resistor R2, a unidirectional optocoupler OP1 and a third resistor R3, wherein:

[0078] 1) R2 is connected between the switch circuit and the positive electrode of the primary side of OP1;

[0079] like Figure 2As shown, in fact, R2 is connected between K1 in the switch circuit and the positive electrode of the primary side of OP1; at the same time, Figure 2 It can be seen that D1 is connected to V CC1 Between K1.

[0080] like Figure 2 As shown, the primary side of OP1 is a unidirectional diode.

[0081] 2) The positive electrode of the primary side of OP1 is connected to the second resistor R2, and the negative electrode is connected to the live wire of the AC power supply, and the connection point is located between the live wire switch and the AC output terminal;

[0082] 3) One end of R3 is connected to the second DC power supply V CC2 , the other end is connected to the positive pole of the secondary side of OP1 and the second IO port of MCU;

[0083] The negative terminal of the secondary side of OP1 is grounded. Figure 2 As shown, the secondary side of OP1 is an NPN transistor, wherein the collector of the NPN transistor is the positive electrode of the secondary side, and the emitter is the negative electrode of the secondary side.

[0084] V CC2 It is the power supply voltage of the secondary side of OP1, generally 3.3V is selected; R3 is the pull-up resistor.

[0085] 5) The residual voltage detection circuit includes: a fourth resistor R4, a bidirectional optocoupler OP2, and a fifth resistor R5, wherein:

[0086] R4 is connected between the live wire of the AC power supply and one end of the primary side of OP2, and the connection point between R4 and the live wire of the AC power supply is between the live wire switch and the AC output terminal;

[0087] The other end of the primary side of OP2 is connected to the AC power supply neutral line and the connection point is between the neutral line switch and the AC output terminal;

[0088] One end of R5 is connected to the third DC power supply VCC3, and the other end is connected to the positive electrode of the secondary side of OP2 and the first IO port of MCU;

[0089] The negative electrode of the secondary side of OP2 is grounded.

[0090] like Figure 2 As shown, the primary side of OP2 is a bidirectional diode, the secondary side of OP2 is an NPN transistor, the collector of the NPN transistor is the positive electrode of the secondary side, and the emitter is the negative electrode of the secondary side.

[0091] R4 and OP2 form the forward and reverse discharge paths of the AC output terminal; V CC3 It is the power supply voltage of the secondary side of OP2, generally 3.3V is selected; R5 is the pull-up resistor.

[0092] The following three situations exist at the AC output end, respectively Figure 2 The working process of the device shown is described below:

[0093] Case 1: There is a short circuit at the AC output terminal, that is, the impedance of the AC output terminal is 0Ω

[0094] In this case, when an external load is connected to the AC output terminal, the MCU outputs a disconnect signal to the live wire switch on the AC power supply live wire and the neutral wire switch on the AC power supply neutral wire;

[0095] Since the residual voltage at the AC output is almost 0V, almost no current flows through the primary side of R4 and OP2, and no current flows through the secondary side of OP2, that is, the secondary side of OP2 is disconnected, and the level V on the first IO port of MCU is RES is high level (such as: V RES greater than a set first voltage threshold);

[0096] MCU detects V RES If it is high, it can be known that the secondary side of OP2 is disconnected, and it can be inferred that no current flows through the primary side of OP2. It can also be inferred that the residual voltage at the AC output end is less than the preset safety residual voltage threshold (such as 50V), thus sending a closing signal to K1 and K2 in the switch circuit;

[0097] After K1 and K2 are closed, V CC1 The output DC current forms a current loop through D1, K1, R2, the primary side of OP1, the external load, K2, R1, and C1. Since the impedance of the AC output terminal is very low, generally 0Ω, the DC current continues to flow through the primary side of OP1, and the secondary side of OP1 is turned on. The voltage level V DECT is low level (such as: V DECT is less than the set second voltage threshold), the MCU determines that there is a short circuit at the AC output terminal.

[0098] Case 2: There is no short circuit at the AC output terminal (i.e. there is a certain impedance at the AC output terminal), and there is a positive residual voltage at the AC output terminal

[0099] In this case, when an external load is connected to the AC output terminal, the MCU outputs a disconnect signal to the live wire switch on the AC power supply live wire and the neutral wire switch on the AC power supply neutral wire;

[0100] Since there is a positive residual voltage at the AC output end, the positive residual voltage at the AC output end will discharge through R4 and the primary side of OP2 in the residual voltage detection circuit, and the secondary side of OP2 will be turned on, V RES Gradually decreases, when V RES When the voltage drops to a set value, the secondary side of OP2 is disconnected, so that V RES Increases, MCU detects VRES is high level (such as: V RES is greater than the set first voltage threshold), a closing signal is sent to K1 and K2 in the switch circuit; wherein, the MCU detects that V RES If it is high, it can be known that the secondary side of OP2 is disconnected, and it can be inferred that no current flows through the primary side of OP2. It can also be inferred that the residual voltage at the AC output end is less than the preset safety residual voltage threshold (such as 50V), thus sending a closing signal to K1 and K2 in the switch circuit;

[0101] After K1 and K2 are closed, V CC1 The output DC current forms a current loop through D1, K1, R2, the primary side of OP1, the external load, K2, R1, and C1. CC1 Charge the safety capacitor of the external load;

[0102] After K1 and K2 are closed for a period of time, the voltage on the safety capacitor of the external load is close to V CC1 If the voltage is 0, no current flows through the primary side of OP1, and the secondary side of OP1 is disconnected, so V DECT is high level (such as: V DECT is greater than or equal to a set second voltage threshold), the MCU determines that the AC output terminal is in a non-short-circuit state.

[0103] Case 3: There is no short circuit at the AC output terminal (i.e. there is a certain impedance at the AC output terminal), and there is a negative residual voltage at the AC output terminal

[0104] In this case, when an external load is connected to the AC output terminal, the MCU outputs a disconnect signal to the live wire switch on the AC power supply live wire and the neutral wire switch on the AC power supply neutral wire;

[0105] Since there is a negative residual voltage at the AC output end, the negative residual voltage at the AC output end will discharge through R4 in the residual voltage detection circuit and the primary side of OP2, and then the secondary side of OP2 will be turned on, V RES Gradually decreases, when V RES When the voltage drops to a set value, the secondary side of OP2 is disconnected, so that V RES Increases, MCU detects V RES is high level (such as: V RES is greater than the set first voltage threshold), a closing signal is sent to K1 and K2 in the switch circuit; wherein, the MCU detects that V RES If it is high, it can be known that the secondary side of OP2 is disconnected, and it can be inferred that no current flows through the primary side of OP2. It can also be inferred that the residual voltage at the AC output end is less than the preset safety residual voltage threshold (such as 50V), thus sending a closing signal to K1 and K2 in the switch circuit;

[0106] After K1 and K2 are closed, VCC1 The output DC current forms a current loop through D1, K1, R2, the primary side of OP1, the external load, K2, R1, and C1. CC1 Charge the safety capacitor of the external load; at the same time, the negative residual voltage passes through N out , K2, R1, C1, D1, K1, R2, the primary side of OP1, L out Rapid discharge;

[0107] After K1 and K2 are closed for a period of time, the voltage on the safety capacitor of the external load is close to V CC1 If the voltage is 0, no current flows through the primary side of OP1, and the secondary side of OP1 is disconnected, so V DECT is high level (such as: V DECT is greater than or equal to a set second voltage threshold), the MCU determines that the AC output terminal is in a non-short-circuit state.

[0108] Through the above analysis, we can see that there are three situations at the AC output terminal: there is a short circuit at the AC output terminal, there is no short circuit at the AC output terminal and there is a positive residual voltage at the AC output terminal, and there is no short circuit at the AC output terminal and there is a negative residual voltage at the AC output terminal. Figure 2 The devices shown can all be detected correctly.

[0109] Figure 2 In the device shown, K1 and K2 are disconnected by default, thereby disconnecting the circuit between the first DC power supply and the AC output end by default, thereby improving the reliability of the circuit; and the residual voltage detection circuit realizes the detection of positive and negative residual voltages at the AC output end. The circuit is also the residual voltage discharge circuit of the AC output end. When the MCU detects that the residual voltage detection voltage output by the residual voltage detection circuit is high, it can be determined that the residual voltage at the AC output end is less than the set safety residual voltage threshold, and a short-circuit detection action is performed before AC output, which can avoid the risk of large impact current at the moment of current limiting and detection circuit opening, and greatly reduces the withstand power of the resistor in the device, so that the device can use ordinary resistors, reducing the size and cost of the device and improving the reliability of the device.

[0110] Figure 3 This is a structural diagram of an AC output short-circuit detection device provided by another embodiment of the present invention. Figure 3 As shown, the device Figure 2 The device shown is compared to:

[0111] a) The unidirectional output current limiting circuit further includes a second diode D2.

[0112] One end of D2 is connected to the negative electrode of D1, and the other end is connected between R1 and the switch circuit.

[0113] like Figure 3As shown, the other end of D2 is actually connected between R1 and K2 in the switch circuit.

[0114] D2 can provide a discharge circuit for the negative residual voltage on the external load to reduce the negative residual voltage of the external load on V CC1 impact.

[0115] b) The unidirectional output current limiting circuit further includes a fuse F1.

[0116] Among them, F1 is connected between R1 and the switching circuit.

[0117] like Figure 3 As shown, F1 is actually connected between R1 and K2 in the switching circuit.

[0118] F1 can be a protective resistor. If an unexpected overcurrent occurs, F1 will be disconnected to protect other devices.

[0119] 3) The current limiting and detection circuit further includes a sixth resistor R6 and a voltage clamping device D3.

[0120] Among them, R6 is connected between R2 and the positive electrode of the primary side of OP1; D3 is connected between R2 and the negative electrode of the primary side of OP1.

[0121] D3 can be a voltage regulator or other voltage clamping device. Figure 3 As shown, D3 uses a voltage-stabilizing diode. At this time, the cathode of D3 is connected to R2, and the anode is connected to the cathode of the primary side of OP1.

[0122] 4) The current limiting and detection circuit further includes a seventh resistor R7.

[0123] Among them, R7 is connected in parallel with the primary side of OP1.

[0124] e) The current limiting and detection circuit further includes a second capacitor C2.

[0125] One end of C2 is connected to the second IO port of the MCU, and the other end is grounded. C2 is a high-frequency filter capacitor.

[0126] 6) The residual voltage detection circuit further includes a third capacitor C3.

[0127] One end of C3 is connected to the first IO port of the MCU, and the other end is grounded. C3 is a high-frequency filter capacitor.

[0128] The following three situations exist at the AC output end, respectively Figure 3 The working process of the device shown is described below:

[0129] Case 1: There is a short circuit at the AC output terminal, that is, the impedance of the AC output terminal is 0Ω

[0130] In this case, when an external load is connected to the AC output terminal, the MCU outputs a disconnect signal to the live wire switch on the AC power supply live wire and the neutral wire switch on the AC power supply neutral wire;

[0131] Since the residual voltage at the AC output is almost 0V, almost no current flows through the primary side of R4 and OP2, and no current flows through the secondary side of OP2, that is, the secondary side of OP2 is disconnected, and the level V on the first IO port of MCU is RES is high level (such as: V RES greater than a set first voltage threshold);

[0132] MCU detects V RES If it is high, it can be known that the secondary side of OP2 is disconnected, and it can be inferred that no current flows through the primary side of OP2. It can also be inferred that the residual voltage at the AC output end is less than the preset safety residual voltage threshold (such as 50V), thus sending a closing signal to K1 and K2 in the switch circuit;

[0133] After K1 and K2 are closed, V CC1 The output DC current forms a current loop through D1, K1, R2, R6, R7, D3, the primary side of OP1, the external load, K2, F1, R1, and C1. Since the impedance of the AC output terminal is very low, generally 0Ω, the DC current continues to flow through the primary side of OP1, and the secondary side of OP1 is turned on. The voltage level V DECT is low level (such as: V DECT is less than the set second voltage threshold), the MCU determines that there is a short circuit at the AC output terminal.

[0134] R2 and D3 form a voltage clamping circuit, clamping the voltage of the circuit consisting of R6, R7, and the primary side of OP1 to a low voltage. R6 is the current-limiting resistor for the combined current of the primary side of OP1 and R7. Because the forward voltage of the primary side of OP1 is maintained at a fixed voltage (e.g., 1.4V), the resistance of R6 determines the maximum combined current of the primary side of OP1 and R7. R7 is connected in parallel with the primary side of OP1, bypassing some of the current flowing through R6. The current flowing through R7 is generally 3 to 15 mA.

[0135] Case 2: There is no short circuit at the AC output terminal (i.e. there is a certain impedance at the AC output terminal), and there is a positive residual voltage at the AC output terminal

[0136] Among them, when the AC output end is the output end of an AC charging pile, the impedance range of the AC output end is generally 100Ω~10MΩ (megaohm).

[0137] In this case, when an external load is connected to the AC output terminal, the MCU outputs a disconnect signal to the live wire switch on the AC power supply live wire and the neutral wire switch on the AC power supply neutral wire;

[0138] Since there is a positive residual voltage at the AC output end, the positive residual voltage at the AC output end will discharge through R4 and the primary side of OP2 in the residual voltage detection circuit, and the secondary side of OP2 will be turned on, V RES Gradually decreases, when V RES When the voltage drops to a set value, the secondary side of OP2 is disconnected, so that V RES Increases, MCU detects V RES is high level (such as: V RES is greater than the set first voltage threshold), a closing signal is sent to K1 and K2 in the switch circuit; wherein, the MCU detects that V RES If it is high, it can be known that the secondary side of OP2 is disconnected, and it can be inferred that no current flows through the primary side of OP2. It can also be inferred that the residual voltage at the AC output end is less than the preset safety residual voltage threshold (such as 50V), thus sending a closing signal to K1 and K2 in the switch circuit;

[0139] After K1 and K2 are closed, the DC current output by VCC1 forms a current loop through D1, K1, R2, R6, R7, D3, the primary side of OP1, the external load, K2, F1, R1, and C1. VCC1 charges the safety capacitor of the external load. R2 and D3 form a voltage clamp circuit, clamping the voltage of the circuit consisting of R6, R7, and the primary side of OP1 to a lower voltage value. R6 is the current-limiting resistor for the total current of the primary side of OP1 and R7. Because the forward voltage of the primary side of OP1 is maintained at a fixed voltage (e.g., 1.4V), the resistance value of R6 determines the maximum total current of the primary side of OP1 and R7. R7 is connected in parallel with the primary side of OP1, bypassing some of the current flowing through R6. The current flowing through R7 is generally 3-15mA.

[0140] After K1 and K2 are closed for a period of time (usually 2 to 5 seconds), the voltage on the safety capacitor of the external load is close to V CC1 The voltage and current basically flow through R7. No current flows through the primary side of OP1, and the secondary side of OP1 is disconnected, so V DECT is high level (such as: V DECT The MCU determines that the AC output terminal is in a non-short-circuit state. The larger the current flowing through R7 is within a certain range, the less the current flowing through the primary side of OP1 will be, thereby shortening V RES The time it takes to change from low level to high level reduces the detection time of the MCU.

[0141] Case 3: There is no short circuit at the AC output terminal (i.e. there is a certain impedance at the AC output terminal), and there is a negative residual voltage at the AC output terminal

[0142] In this case, when an external load is connected to the AC output terminal, the MCU outputs a disconnect signal to the live wire switch on the AC power supply live wire and the neutral wire switch on the AC power supply neutral wire;

[0143] Since there is a negative residual voltage at the AC output end, the negative residual voltage at the AC output end will discharge through R4 in the residual voltage detection circuit and the primary side of OP2, and then the secondary side of OP2 will be turned on, V RES Gradually decreases, when V RES When the voltage drops to a set value, the secondary side of OP2 is disconnected, so that V RES Increases, MCU detects V RES is high level (such as: V RES is greater than the set first voltage threshold), a closing signal is sent to K1 and K2 in the switch circuit; wherein, the MCU detects that V RES If it is high, it can be known that the secondary side of OP2 is disconnected, and it can be inferred that no current flows through the primary side of OP2. It can also be inferred that the residual voltage at the AC output end is less than the preset safety residual voltage threshold (such as 50V), thus sending a closing signal to K1 and K2 in the switch circuit;

[0144] After K1 and K2 are closed, V CC1 The output DC current forms a current loop through D1, K1, R2, R6, R7, D3, the primary side of OP1, the external load, K2, F1, R1, and C1. CC1 Charge the safety capacitor of the external load; at the same time, the negative residual voltage passes through N out , K2, F1, D2, K1, R2, R6, R7, D3, the primary side of OP1, and Lout are quickly discharged. Among them, R2 and D3 form a voltage clamping circuit, clamping the voltage of the circuit composed of R6, R7, and the primary side of OP1 to a lower voltage value. R6 is the current-limiting resistor for the total current of the primary side of OP1 and R7. Because the forward voltage of the primary side of OP1 is maintained at a fixed voltage (such as 1.4V), the resistance value of R6 will determine the maximum total current of the primary side of OP1 and R7. R7 is connected in parallel with the primary side of OP1, and R7 will bypass part of the current flowing through R6. Generally, the current flowing through R7 is 3~15mA.

[0145] After K1 and K2 are closed for a period of time (usually 2 to 5 seconds), the voltage on the safety capacitor of the external load is close to V CC1 The voltage, current basically all flows through R7, no current flows through the primary side of OP1, then the secondary side of OP1 is disconnected, so V DECT is high level (such as: V DECTThe MCU determines that the AC output terminal is in a non-short-circuit state. The larger the current flowing through R7 is within a certain range, the less the current flowing through the primary side of OP1 will be, thereby shortening V RES The time it takes to change from low level to high level reduces the detection time of the MCU.

[0146] Through the above analysis, we can see that there are three situations at the AC output terminal: there is a short circuit at the AC output terminal, there is no short circuit at the AC output terminal and there is a positive residual voltage at the AC output terminal, and there is no short circuit at the AC output terminal and there is a negative residual voltage at the AC output terminal. Figure 3 The devices shown can all be detected correctly.

[0147] Figure 3 In the device shown, K1 and K2 are disconnected by default, thereby disconnecting the circuit between the first DC power supply and the AC output end by default, thereby improving the reliability of the circuit; and the residual voltage detection circuit realizes the detection of positive and negative residual voltages at the AC output end. The circuit is also the residual voltage discharge circuit of the AC output end. When the MCU detects that the residual voltage detection voltage output by the residual voltage detection circuit is high, it can be determined that the residual voltage at the AC output end is less than the set safety residual voltage threshold, and a short-circuit detection action is performed before AC output, which can avoid the risk of large impact current at the moment of current limiting and detection circuit opening, and greatly reduces the withstand power of the resistors in the device and the withstand power of the voltage stabilizing device, so that the device can use ordinary resistors and voltage stabilizing devices, reducing the size and cost of the device and improving the reliability of the device.

[0148] Those skilled in the art will appreciate that the features described in the various embodiments and / or claims of this disclosure may be combined and / or coupled in various ways, even if such combinations and / or couplings are not explicitly described in this application. In particular, without departing from the spirit and teachings of this application, the features described in the various embodiments and / or claims of this application may be combined and / or coupled in various ways, and all such combinations and / or couplings fall within the scope of this application.

[0149] The principles and implementation methods of the present invention are described herein using specific embodiments. The description of the above embodiments is only used to help understand the core ideas of the present invention and is not intended to limit this application. For those skilled in the art, changes can be made in the specific implementation methods and application scope based on the ideas, spirit and principles of the present invention. Any modifications, equivalent replacements, improvements, etc. made therein should be included within the scope of protection of this application.

Claims

1. An AC output short circuit detection device, characterized in that: The AC output terminal is the output terminal of the AC charging pile. The device includes: a first DC power supply, a unidirectional output current limiting circuit, a switching circuit, a current limiting and detection circuit, a residual voltage detection circuit and a microcontroller unit, and a live wire switch and a neutral wire switch are provided between the AC input terminal and the AC output terminal, wherein: A first DC power supply is connected to the unidirectional output current limiting circuit and is used to: output a DC current; a unidirectional output current limiting circuit, one end of which is connected to the first DC power supply and the other end of which is connected to the switching circuit, for blocking the current from the switching circuit to the first DC power supply and transmitting the DC current output by the first DC power supply to the switching circuit; A switch circuit, one end of which is connected to the unidirectional output current limiting circuit, one end of which is connected to the current limiting and detection circuit, one end of which is connected to the AC power supply neutral line and the connection point is located between the neutral line switch and the AC output terminal, and another end of which is connected to the MCU, and is used to: open or close under the control of the MCU; A current limiting and detection circuit, one end of which is connected to the switch circuit, one end of which is connected to the live wire of the AC power supply and the connection point is located between the live wire switch and the AC output terminal, and another end of which is connected to the MCU, and is used to: output a short-circuit detection voltage of the AC output terminal to the MCU; A residual voltage detection circuit, one end of which is connected to the live wire of the AC power supply and the connection point is located between the live wire switch and the AC output terminal, one end of which is connected to the neutral wire of the AC power supply and the connection point is located between the neutral wire switch and the AC output terminal, and another end of which is connected to the MCU, and is used to: output the residual voltage detection voltage of the AC output terminal to the MCU; The MCU is connected to the switch circuit, the current limiting and detection circuit, and the residual voltage detection circuit, respectively, and is used to control the opening and closing of the switch circuit and determine whether there is a short circuit at the AC output terminal based on the voltage output by the current limiting and detection circuit and the voltage output by the residual voltage detection circuit; The residual voltage detection circuit includes: a fourth resistor, a bidirectional optocoupler and a fifth resistor, wherein: The fourth resistor is connected between the AC power supply live wire and one end of the primary side of the bidirectional optocoupler, and the connection point between the fourth resistor and the AC power supply live wire is located between the live wire switch and the AC output terminal; The other end of the primary side of the bidirectional optocoupler is connected to the AC power supply neutral line and the connection point is located between the neutral line switch and the AC output terminal; One end of the fifth resistor is connected to the third DC power supply, and the other end is connected to the positive electrode of the secondary side of the bidirectional optocoupler and the first IO port of the MCU; The negative pole of the secondary side of the bidirectional optocoupler is grounded.

2. The device according to claim 1, characterized in that The first DC power supply includes a DC power supply and a first capacitor; wherein one end of the first capacitor is connected to the DC power supply, and the other end is grounded.

3. The device according to claim 1, characterized in that The unidirectional output current limiting circuit includes a first diode and a first resistor; wherein, the positive electrode of the first diode is connected to the first DC power supply, and the negative electrode of the first diode is connected to the switching circuit; one end of the first resistor is grounded and shares a ground terminal with the first DC power supply, and the other end is connected to the switching circuit.

4. The device according to claim 3, characterized in that The unidirectional output current limiting circuit further includes a second diode and a fuse; One end of the second diode is connected to the cathode of the first diode, and the other end is connected between the first resistor and the switch circuit; the fuse is connected between the first resistor and the switch circuit.

5. The device according to claim 1, characterized in that The switch circuit includes a first switch and a second switch; Among them, the first switch is connected between the unidirectional output current limiting circuit and the current limiting and detection circuit; the second switch is connected between the unidirectional output current limiting circuit and the AC power supply neutral line, and the connection point with the AC power supply neutral line is located between the neutral line switch and the AC output end.

6. The device according to claim 1, characterized in that The current limiting and detection circuit includes a second resistor, a unidirectional optocoupler and a third resistor, wherein: The second resistor is connected between the switch circuit and the positive electrode of the primary side of the unidirectional optocoupler; The positive electrode of the primary side of the unidirectional optocoupler is connected to the second resistor, and the negative electrode is connected to the AC power live wire, and the connection point is located between the live wire switch and the AC output terminal; One end of the third resistor is connected to the second DC power supply, and the other end is connected to the positive electrode of the secondary side of the unidirectional optocoupler and the second IO port of the MCU; The negative pole of the secondary side of the unidirectional optocoupler is grounded.

7. The device according to claim 6, characterized in that The current limiting and detection circuit further includes a sixth resistor, a voltage clamping device, a seventh resistor and a second capacitor; Among them, the sixth resistor is connected between the second resistor and the positive pole of the primary side of the unidirectional optocoupler; the voltage clamping device is connected between the second resistor and the negative pole of the primary side of the unidirectional optocoupler; the seventh resistor is connected in parallel with the primary side of the unidirectional optocoupler; one end of the second capacitor is connected to the second IO port of the MCU, and the other end is grounded.

8. The device according to claim 1, characterized in that The residual voltage detection circuit further includes a third capacitor; One end of the third capacitor is connected to the first IO port of the MCU, and the other end is grounded.

9. The device according to claim 1, characterized in that The MCU is used to: when an external load is connected to the AC output end, output a disconnect signal to the live wire switch and the neutral wire switch; when it is detected that the residual voltage detection voltage output by the residual voltage detection circuit meets the set first voltage range, send a closing signal to the switch circuit; and after waiting for a preset time, if it is detected that the short-circuit detection voltage output by the current limiting and detection circuit meets the set second voltage range, it is determined that there is a short circuit at the AC output end.

Images