Short circuit detection circuit for an alternating current charging device

Abstract

The application discloses a short circuit detection circuit of an alternating current charging device and relates to the technical field of new energy vehicles.The circuit comprises a transistor driving unit, a relay unit and a voltage division detection unit; the input end of the transistor driving unit is used for being connected with the short circuit detection enable pin of a master control micro control unit, and the output end is connected with the control end of the relay unit; the signal end of the relay unit is used for being connected with the alternating current zero line output end and the alternating current live wire output end of an alternating current charging loop respectively, and the output end is connected with the input end of the voltage division detection unit; and the output end of the voltage division detection unit is used for being connected with the short circuit detection collection pin of the master control micro control unit. By adopting the application, active short circuit detection is realized, the detection response speed and accuracy are improved, the charging short circuit hidden danger is avoided, and the high reliability requirement of the alternating current charging device on the short circuit detection is met.

Description

Technical Field

[0001] This application relates to the field of new energy vehicle technology, specifically to a short-circuit detection circuit for an AC charging device. Background Technology

[0002] With the increasing number of electric vehicles on the road, AC charging plays a crucial role in electric vehicle refueling. Charging scenarios are diverse and environments are complex, making it essential to monitor the insulation status of the charging link during charging. Short-circuit detection, as a vital safety protection measure, can effectively prevent safety hazards during charging and ensure the safety of users and equipment. Currently, short-circuit detection technology for electric vehicle charging equipment has become a focus of industry attention, and related technologies are constantly developing, but problems such as low detection accuracy and slow response speed still exist.

[0003] In existing technologies, conventional short-circuit detection methods mainly include the following: First, using simple fuses or circuit breakers for overcurrent protection, but their response speed is slow and they cannot detect short-circuit faults in a timely manner; second, using voltage comparators to detect abnormal circuit voltage, but they are susceptible to interference and have a high false alarm rate; third, monitoring circuit current through current sensors, but this is costly and complex to install. Each of these methods has its advantages and disadvantages. For example, fuses are inexpensive but cannot be reused, voltage comparators have a fast response but poor anti-interference ability, and current sensors have high accuracy but high system complexity.

[0004] The shortcomings of conventional methods in existing technologies mainly include insufficient detection accuracy, slow response speed, poor anti-interference ability, high system complexity, and high cost, making it difficult to meet the high reliability requirements of electric vehicle charging equipment for short circuit detection. Utility Model Content

[0005] This application provides a short-circuit detection circuit for AC charging equipment to solve the problem of low reliability of short-circuit detection in existing electric vehicle charging equipment.

[0006] In a first aspect, this application provides a short-circuit detection circuit for an AC charging device, the circuit comprising: Transistor drive unit, relay unit, and voltage divider detection unit; The input terminal of the transistor drive unit is used to connect to the short-circuit detection enable pin of the main control microcontroller unit, and the output terminal is connected to the control terminal of the relay unit. The signal terminals of the relay unit are used to connect to the AC neutral wire output terminal and the AC live wire output terminal of the AC charging circuit, respectively, and the output terminals are connected to the input terminals of the voltage divider detection unit. The output of the voltage divider detection unit is used to connect to the short-circuit detection acquisition pin of the main microcontroller unit.

[0007] By adopting the above technical solutions, active short circuit detection is achieved, improving detection response speed and accuracy, avoiding potential short circuit hazards during charging, and meeting the high reliability requirements of AC charging equipment for short circuit detection.

[0008] In one specific implementation, the voltage divider detection unit includes: Current-limiting resistor R1, voltage-dividing resistor R2, and voltage-dividing resistor R3; The first end of the voltage divider resistor R2 is connected to the relay unit, the second end is connected to the first end of the voltage divider resistor R3, and the second end of the voltage divider resistor R3 is grounded. The first end of the current-limiting resistor R1 is connected to the short-circuit detection acquisition pin, and the second end is connected between the second end of the voltage divider resistor R2 and the first end of the voltage divider resistor R3.

[0009] By adopting the above technical solution, accurate voltage division of the detection voltage can be achieved, protecting the pins of the main control microcontroller unit and improving the accuracy of short circuit detection and component safety.

[0010] In one specific implementation, the transistor driving unit includes: Transistor Q1 has its base connected to the short-circuit detection enable pin, its collector connected to the relay unit, and its emitter grounded. Transistor Q1 includes a base current limiting resistor and a base resistor.

[0011] By adopting the above technical solution, the relay unit is stably driven, the transistor and MCU pins are protected, and the reliability of the drive circuit is improved.

[0012] In one specific implementation scheme, the relay unit includes: Relay K1 has one end of its coil connected to the collector of transistor Q1, and the other end connected to the power supply. The first normally open contact is connected to the voltage divider detection unit, the second normally open contact is connected to the power supply, the first common terminal is connected to the AC live wire output terminal, and the second common terminal is connected to the AC neutral wire output terminal.

[0013] By adopting the above technical solution, accurate injection of detection voltage and signal transmission can be achieved, and the charging circuit can be isolated during non-detection stages, thereby improving the targeting of detection and charging safety.

[0014] In one specific implementation scheme, the relay unit further includes: First current limiting unit and second current limiting unit; The first end of the first current limiting unit is connected to the AC live wire output terminal, and the second end is connected to relay K1; The first end of the second current limiting unit is connected to the AC neutral output terminal, and the second end is connected to relay K1.

[0015] By adopting the above technical solutions, surge current is suppressed, relays and voltage divider units are protected, and the circuit's anti-interference capability and service life are improved.

[0016] In one specific implementation, the first current limiting unit includes resistors R4, R5, R6 and R7 connected in series, and the second current limiting unit includes resistors R8, R9, R10 and R11 connected in series.

[0017] By adopting the above technical solutions, surge energy is dispersed, detection voltage loss is reduced, and surge suppression capability and circuit redundancy are improved.

[0018] In one specific implementation scheme, when there is a short circuit between the AC live wire output terminal and the AC neutral wire output terminal, the detection voltage is divided by the voltage divider resistors R2 and R3, so that the short circuit detection acquisition pin can obtain the first voltage signal. When there is no short circuit between the AC live wire output terminal and the AC neutral wire output terminal, the short circuit detection acquisition pin acquires the second voltage signal.

[0019] By adopting the above technical solutions, clear judgment criteria are provided for the main control microcontroller unit, reducing false alarm and missed alarm rates and improving detection accuracy and response timeliness.

[0020] In one specific implementation, the resistance ratio of voltage divider resistor R2 to voltage divider resistor R3 is configured as follows: When the relay unit is energized and there is a short circuit between the AC live wire output terminal and the AC neutral wire output terminal, the first voltage signal generated on the short circuit detection and acquisition pin is within the voltage range that the main control microcontroller unit recognizes as high level.

[0021] By adopting the above technical solution, the first voltage signal is accurately identified, adapted to different MCUs, and the omission of judgment or component damage is avoided, thereby improving circuit compatibility.

[0022] In one specific implementation scheme, both the AC live wire output terminal and the AC neutral wire output terminal are used to connect to the AC charging interface of the electric vehicle.

[0023] By adopting the above technical solutions, a complete charging path is covered, external short circuits are avoided from being missed, and product versatility and charging safety are improved.

[0024] In one specific implementation, the relay unit, when energized, is used to inject a DC detection voltage signal into the AC neutral output terminal; The voltage divider detection unit is used to sample the DC detection voltage signal at the AC live wire output terminal; The main control microcontroller unit determines whether there is a short circuit between the AC live wire output terminal and the AC neutral wire output terminal of the AC charging circuit by judging the DC voltage signal level on the short circuit detection acquisition pin.

[0025] By adopting the above technical solutions, the anti-interference capability is enhanced, the detection response speed and accuracy are improved, and normal charging is not interfered with.

[0026] In summary, one or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages: 1. This application can quickly and accurately detect whether there is a short circuit in the AC charging circuit, effectively improve the accuracy and response speed of short circuit detection, solve the problems of insufficient short circuit detection accuracy and slow response speed, ensure that electric vehicle charging equipment can promptly identify potential short circuit hazards, and ensure charging safety. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a short-circuit detection circuit for an AC charging device provided in an embodiment of this application; Figure 2 This is another schematic diagram of a short-circuit detection circuit for an AC charging device provided in an embodiment of this application.

[0028] Reference numerals: 100, transistor driving unit; 200, relay unit; 201, first current limiting unit; 202, second current limiting unit; 300, voltage divider detection unit. Detailed Implementation

[0029] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0030] In the description of the embodiments of this application, the words "for example" or "for instance" are used to indicate examples, illustrations, or explanations. Any embodiment or design that is described as "for example" or "for instance" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design options. Rather, the use of the words "for example" or "for instance" is intended to present the relevant concepts in a specific manner.

[0031] In the description of the embodiments of this application, the term "multiple" means two or more. For example, multiple systems means two or more systems, and multiple screen terminals means two or more screen terminals. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. The terms "comprising," "including," "having," and variations thereof all mean "including but not limited to," unless otherwise specifically emphasized.

[0032] The following is in conjunction with the appendix Figure 1 and attached Figure 2 This application will be described in further detail.

[0033] This application discloses a short-circuit detection circuit for an AC charging device, such as... Figure 1 and Figure 2 As shown, the circuit includes: Transistor driving unit 100, relay unit 200 and voltage divider detection unit 300; The input terminal of the transistor driving unit 100 is used to connect to the short circuit test enable pin (EN) of the main control microcontroller unit, and the output terminal is connected to the control terminal of the relay unit 200. The signal terminals of the relay unit 200 are used to connect to the AC neutral wire output (NOUT) and AC live wire output (LOUT) of the AC charging circuit respectively, and the output terminals are connected to the input terminals of the voltage divider detection unit 300. The output of the voltage divider detection unit 300 is used to connect to the short circuit detection acquisition pin (DET) of the main microcontroller unit.

[0034] In this embodiment of the application, the main control microcontroller unit refers to a microcontroller unit (MCU) used to control the overall operation of the AC charging equipment, initiate the short circuit detection process, process the detection signal and output the judgment result.

[0035] In this embodiment, the short-circuit detection enable pin EN is a pin on the main microcontroller unit used to output a control signal to initiate the short-circuit detection process.

[0036] In this embodiment, the short-circuit detection acquisition pin DET is a pin on the main control microcontroller unit used to acquire the voltage signal output by the voltage divider detection unit 300 to determine whether there is a short circuit in the AC charging circuit.

[0037] In this embodiment of the application, the AC charging circuit refers to the circuit path in the AC charging device used to transmit AC mains power to the electric vehicle. The circuit includes at least an AC live wire output terminal LOUT for transmitting AC live wire power and an AC neutral wire output terminal NOUT for transmitting AC neutral wire power.

[0038] In some embodiments, when the charging gun of the AC charging device is inserted into the electric vehicle, the main control microcontroller detects the insertion signal through the charging request control circuit and then outputs a high-level control signal to the short-circuit detection enable pin EN. This signal is transmitted to the input terminal of the transistor driving unit 100, causing the transistor driving unit 100 to enter the working state. When the transistor driving unit 100 receives the high-level control signal, it outputs a driving current to the control terminal of the relay unit 200, driving the coil inside the relay unit 200 to be energized.

[0039] The signal terminals of the relay unit 200 are used to connect to the AC neutral output terminal NOUT and the AC live output terminal LOUT of the AC charging circuit respectively, so as to realize the signal interaction with the charging circuit. When the coil of the relay unit 200 is energized, its internal contacts will switch from the open state to the closed state. At this time, the relay unit 200 will transmit the voltage signal of the AC charging circuit to the input terminal of the voltage divider detection unit 300, and at the same time, it can inject the external detection voltage into the AC neutral output terminal NOUT.

[0040] When the voltage divider detection unit 300 receives the voltage signal transmitted by the relay unit 200, it will divide the voltage signal through the internal resistor element to convert the high voltage signal into a low voltage signal that conforms to the acquisition range of the main control microcontroller unit. The low voltage signal after voltage division is transmitted to the short circuit detection acquisition pin DET through the output terminal of the voltage divider detection unit 300. The main control microcontroller unit can determine whether there is a short circuit in the AC charging circuit by analyzing the magnitude of the low voltage signal.

[0041] Based on the above embodiments, as another optional embodiment, the voltage divider detection unit 300 includes: Current-limiting resistor R1, voltage-dividing resistor R2, and voltage-dividing resistor R3; The first end of the voltage divider resistor R2 is connected to the relay unit 200, the second end is connected to the first end of the voltage divider resistor R3, and the second end of the voltage divider resistor R3 is grounded. The first end of the current-limiting resistor R1 is connected to the short-circuit detection acquisition pin DET, and the second end is connected between the second end of the voltage divider resistor R2 and the first end of the voltage divider resistor R3.

[0042] In some embodiments, when the contacts of the relay unit 200 are engaged, the detection voltage transmitted by the relay unit 200 is input to the voltage divider resistor R2 through this terminal; the second terminal of the voltage divider resistor R2 is used to connect to the first terminal of the voltage divider resistor R3, so that the voltage divider resistor R2 and the voltage divider resistor R3 form a series connection relationship. The series structure can ensure that the detection voltage is divided between the two resistors according to the resistance ratio; the second terminal of the voltage divider resistor R3 is used to connect to the system ground, providing a grounding path for the series circuit composed of the voltage divider resistor R2 and the voltage divider resistor R3, ensuring that the voltage division process can be carried out stably.

[0043] When a low voltage signal is generated at the common connection point after voltage division, the signal will be transmitted to the short circuit detection acquisition pin DET through the current limiting resistor R1. The current limiting resistor R1 will limit the current during the transmission process to a safe range, preventing excessive current from flowing into the pin of the main control microcontroller unit, thereby protecting the main control microcontroller unit from damage.

[0044] When a short circuit exists between the AC live wire output terminal LOUT and the AC neutral wire output terminal NOUT of the AC charging circuit, the detection voltage injected by the relay unit 200 will be transmitted to the AC live wire output terminal LOUT through the short circuit path, and then to the first end of the voltage divider resistor R2. After the detection voltage is divided by the voltage divider resistors R2 and R3, a low voltage signal is formed at the common connection point. After the current is limited by the current limiting resistor R1, the low voltage signal is transmitted to the short circuit detection acquisition pin DET of the main control microcontroller unit for the main control microcontroller unit to identify the short circuit state. When there is no short circuit in the AC charging circuit, there is no detection voltage at the AC live wire output terminal LOUT, and there is no effective voltage signal at the common connection point. The short circuit detection acquisition pin DET can only acquire a voltage close to the system ground.

[0045] Based on the above embodiments, as another optional embodiment, the transistor driving unit 100 includes: Transistor Q1, the base of transistor Q1 is connected to the short-circuit detection enable pin EN, the collector is connected to the relay unit 200, and the emitter is grounded; Transistor Q1 includes a base current limiting resistor and a base resistor.

[0046] In some embodiments, transistor Q1 adopts an NPN structure; the base of transistor Q1 is the control terminal of transistor Q1, the collector of transistor Q1 is the output terminal of transistor Q1, and the emitter of transistor Q1 is the ground terminal of transistor Q1; the base current limiting resistor is a resistor connected in series between the base of transistor Q1 and the short-circuit detection enable pin EN, used to limit the current flowing into the base and prevent excessive current from damaging the resistive element of transistor Q1; the base resistor is a resistor connected in parallel between the base and emitter of transistor Q1, used to stabilize the base bias voltage of transistor Q1 and ensure the stable operation of transistor Q1.

[0047] In some embodiments, the base limiting current resistor is connected in series between the base of transistor Q1 and the short-circuit detection enable pin EN. When the short-circuit detection enable pin EN outputs a high-level control signal, the signal flows into the base of transistor Q1 through the base limiting current resistor. The base limiting current resistor limits the current flowing into the base within a safe range, preventing excessive current from causing the base of transistor Q1 to break down. The base resistor is connected in parallel between the base and emitter of transistor Q1, which can stabilize the voltage between the base and emitter of transistor Q1, prevent transistor Q1 from being mistakenly turned on or off due to voltage fluctuations, and ensure the stability of the operating state of transistor Q1.

[0048] In some embodiments, when the base of transistor Q1 receives sufficient on-state current, the collector and emitter of transistor Q1 will switch from a cutoff state to a conduction state. At this time, the control terminal of relay unit 200 will obtain a grounding path through transistor Q1, a voltage difference will be formed across the coil of relay unit 200, and current will be generated in the coil, thereby driving the contacts of relay unit 200 to operate. The emitter of transistor Q1 is used to connect to system ground, providing a return path for the current between the collector and emitter of transistor Q1, ensuring that transistor Q1 can conduct normally and transmit drive current.

[0049] When the short-circuit detection enable pin EN of the main control microcontroller unit outputs a low level, the current flowing into the base of transistor Q1 disappears, the collector and emitter of transistor Q1 return to the cut-off state, the control terminal of relay unit 200 loses the grounding path, no current is generated in the coil, the contacts of relay unit 200 remain open, and the transmission of signals to voltage divider detection unit 300 stops.

[0050] In some embodiments, transistor Q1 may be of model DTC143ZCA, which features low on-state voltage and high switching speed, and can meet the response speed requirements of short-circuit detection; the base current limiting resistor may be 10kΩ, and the base resistor may be 10kΩ. The combination of the two can ensure that the base current of transistor Q1 is stable within a safe range of 0.1mA to 0.5mA.

[0051] Based on the above embodiments, as another optional embodiment, the relay unit 200 includes: Relay K1 has one end of its coil connected to the collector of transistor Q1, and the other end connected to the power supply. Its first normally open contact is connected to the voltage divider detection unit 300, and its second normally open contact is connected to the power supply. Its first common terminal is connected to the AC live wire output terminal LOUT, and its second common terminal is connected to the AC neutral wire output terminal NOUT.

[0052] In some embodiments, the first common terminal of relay K1 is pin 3, which is connected to the AC live wire output terminal LOUT, and the second common terminal is pin 6, which is connected to the AC neutral wire output terminal NOUT; the normally closed contacts of relay K1 are pins 2 and 7; the first normally open contact of relay K1 is pin 4, which is connected to the voltage divider detection unit 300, and the second normally open contact is pin 5, which is connected to the power supply; wherein, pins 2, 3, and 4 form one set of contacts, and pins 5, 6, and 7 form another set of contacts.

[0053] When the main control microcontroller outputs a high-level signal through the short-circuit detection enable pin EN, this signal flows into the base of transistor Q1, causing the collector and emitter of transistor Q1 to conduct. The coil of relay K1 forms a complete current loop through the power supply, the coil, and transistor Q1. The coil is energized and generates electromagnetic attraction, driving the first normally open contact to close with the first common terminal and the second normally open contact to close with the second common terminal. At this time, the DC detection voltage of the power supply is transmitted to the second common terminal through the second normally open contact, and then injected into the AC neutral output terminal NOUT of the AC charging circuit from the second common terminal. If there is a short circuit between the AC live output terminal LOUT and the AC neutral output terminal NOUT, the injected DC detection voltage will be transmitted to the AC live output terminal LOUT through the short-circuit path, and then transmitted to the input terminal of the voltage divider detection unit 300 through the first common terminal and the first normally open contact. After the voltage divider detection unit 300 divides the DC detection voltage, it transmits the low voltage signal to the short-circuit detection acquisition pin DET of the main control microcontroller for the main control microcontroller to determine the short-circuit state.

[0054] If there is no short circuit between the AC live wire output terminal LOUT and the AC neutral wire output terminal NOUT, there is no DC detection voltage at the AC live wire output terminal LOUT. The first common terminal can only obtain a voltage close to the system ground through a weak leakage current in the line. This voltage is transmitted to the voltage divider detection unit 300 through the first normally open contact, and the output low voltage signal is close to 0V. Based on this, the main control microcontroller unit determines that the charging circuit is normal. When the main control microcontroller unit stops outputting a high-level signal, transistor Q1 is turned off, the coil of relay K1 is de-energized, the electromagnetic attraction disappears, and the first normally open contact and the first common terminal, as well as the second normally open contact and the second common terminal, are both returned to the open state, stopping the injection of DC detection voltage and signal transmission, and the short circuit detection process terminates.

[0055] In some embodiments, the model of relay K1 may be G6K-2F-Y-TRDC5, and the power supply voltage for powering the coil of relay K1 and providing DC detection voltage may be 12V.

[0056] Based on the above embodiments, as another optional embodiment, the relay unit 200 further includes: First current limiting unit 201 and second current limiting unit 202; The first terminal of the first current limiting unit 201 is connected to the AC live wire output terminal LOUT, and the second terminal is connected to the relay K1. The first terminal of the second current limiting unit 202 is connected to the AC neutral output terminal NOUT, and the second terminal is connected to the relay K1.

[0057] In some embodiments, when a surge current is generated between the AC live wire output terminal LOUT and the relay K1, the first current limiting unit 201 will quickly suppress the surge current to prevent it from impacting the relay K1 and to prevent the surge current from being transmitted to the voltage divider detection unit 300 through the relay K1, thus affecting the normal operation of the voltage divider detection unit 300. When a surge current is generated between the AC neutral wire output terminal NOUT and the relay K1 due to mains power fluctuations or the plugging and unplugging of the charging plug, the second current limiting unit 202 will impede the surge current through its own resistive element, limiting the surge current to a safe range and preventing the surge current from flowing into the relay K1 and causing contact erosion or coil damage.

[0058] Based on the above embodiments, as another optional embodiment, the first current limiting unit 201 includes resistors R4, R5, R6 and R7 connected in series, and the second current limiting unit 202 includes resistors R8, R9, R10 and R11 connected in series.

[0059] In some embodiments, resistors R4 to R7 are four fixed-value resistors constituting the first current limiting unit 201. The four resistors are connected in series to jointly bear the voltage division of surge voltage and the limitation of surge current. Resistors R8 to R11 are four fixed-value resistors constituting the second current limiting unit 202. The four resistors are also connected in series and have the same function as resistors R4 to R7.

[0060] The first current limiting unit 201 includes resistors R4, R5, R6 and R7 connected in series. One end of resistor R7 serves as the first end of the first current limiting unit 201 and is used to connect to the AC live wire output terminal LOUT of the AC charging circuit. One end of resistor R4 serves as the second end of the first current limiting unit 201 and is used to connect to the first common terminal of relay K1.

[0061] The second current limiting unit 202 includes resistors R8, R9, R10 and R11 connected in series. One end of resistor R8 serves as the first end of the second current limiting unit 202 and is used to connect to the AC neutral output terminal NOUT of the AC charging circuit. One end of resistor R11 serves as the second end of the second current limiting unit 202 and is used to connect to the second common terminal of relay K1.

[0062] In some embodiments, the resistance values ​​of resistors R4 to R11 are all 270Ω; this resistance configuration can ensure surge suppression while keeping the voltage loss during normal detection within 0.5V, thus avoiding inaccurate detection results due to excessive voltage loss.

[0063] In some embodiments, the number of resistors used in the first current limiting unit 201 and the second current limiting unit 202 can be adjusted according to the actual surge protection requirements of the AC charging device, and is not limited to four resistors. Specifically, the first current limiting unit 201 may use only one resistor, with its first end connected to the AC live wire output terminal LOUT and its second end connected to the relay K1. A single resistor can achieve basic surge current suppression through its own impedance characteristics. Alternatively, two resistors may be used, connected in series. The first end of the series connection is connected to the AC live wire output terminal LOUT, and the second end is connected to the relay K1. The two resistors share the surge voltage and current. Three, five, six, or seven resistors may also be used, all connected in series. The two ends of the series connection correspond to the first and second ends of the first current limiting unit 201, respectively. The multi-resistor series structure can further disperse surge energy and improve surge suppression capability.

[0064] The method for adjusting the number of resistors in the second current limiting unit 202 is exactly the same as that in the first current limiting unit 201. Depending on the surge risk level of the AC neutral output terminal NOUT, one, two, three, five, six, or seven resistors can be selected. After all the resistors are connected in series, their two ends are connected to the AC neutral output terminal NOUT and the relay K1 respectively, ensuring that the surge current between the AC neutral output terminal NOUT and the relay K1 can be effectively suppressed.

[0065] In some embodiments, the resistance values ​​of the resistors used in the first current limiting unit 201 and the second current limiting unit 202 can be adjusted according to actual needs and are not limited to 270Ω. For example, the resistance value can be selected as 150Ω, which can provide a larger impedance for surge current and is suitable for scenarios with frequent mains power fluctuations and high surge current peaks; it can also be selected as 200Ω, which balances the surge suppression effect with the voltage loss during normal detection and is suitable for most conventional AC charging scenarios; it can also be selected as 300Ω, 330Ω, or 180Ω, etc. Resistors with different resistance values ​​can limit the surge current between the AC neutral output terminal NOUT, the AC live output terminal LOUT and the relay K1 within a safe range through their own current limiting characteristics, while ensuring that the detection voltage can be transmitted smoothly through the current limiting unit during normal short circuit detection, and will not cause detection signal attenuation or distortion due to excessive resistance value, thus affecting the accuracy of short circuit detection.

[0066] Regardless of the number of resistors used in the first current limiting unit 201 and the second current limiting unit 202, or the resistance value of the resistors selected, their core function is to suppress the surge current between the AC neutral output terminal NOUT, the AC live output terminal LOUT and the relay K1, protect the relay K1 and the subsequent voltage divider detection unit 300 from surge impact, and at the same time not affect the signal and voltage transmission in the normal short circuit detection process, ensuring the stability and reliability of the entire short circuit detection circuit.

[0067] Based on the above embodiments, as another optional embodiment, when there is a short circuit between the AC live wire output terminal LOUT and the AC neutral wire output terminal NOUT, the detection voltage is divided by the voltage divider resistors R2 and R3, so that the short circuit detection acquisition pin DET can acquire the first voltage signal. When there is no short circuit between the AC live wire output terminal LOUT and the AC neutral wire output terminal NOUT, the short circuit detection acquisition pin DET acquires the second voltage signal.

[0068] In this embodiment, the first voltage signal refers to the voltage signal generated at the common connection point of the AC live wire output terminal LOUT and the AC neutral wire output terminal NOUT when there is a short circuit between them. The voltage is divided by voltage divider resistors R2 and R3 and transmitted to the short circuit detection acquisition pin DET via current limiting resistor R1. The second voltage signal refers to the voltage signal acquired by the short circuit detection acquisition pin DET when there is no short circuit between the AC live wire output terminal LOUT and the AC neutral wire output terminal NOUT. This signal is usually close to the system ground voltage. The voltage generated by the weak leakage current in the line is usually less than 0.1V and will not affect the status judgment of the main control microcontroller unit.

[0069] In some embodiments, when a short circuit exists between the AC live wire output terminal LOUT and the AC neutral wire output terminal NOUT, the contacts of the relay unit 200 close, and the detection voltage provided by the power supply is injected into the AC neutral wire output terminal NOUT. Since there is a short circuit between the AC live wire output terminal LOUT and the AC neutral wire output terminal NOUT, the detection voltage is directly transmitted to the AC live wire output terminal LOUT through the short circuit path. The detection voltage of the AC live wire output terminal LOUT is transmitted to the first end of the voltage divider resistor R2. After the detection voltage is divided by the voltage divider resistors R2 and R3, a first voltage signal is formed at their common connection point. After the first voltage signal is current-limited by the current-limiting resistor R1, it is transmitted to the short circuit detection acquisition pin DET of the main control microcontroller unit. After receiving the first voltage signal, the main control microcontroller unit will identify that there is a short circuit fault in the AC charging circuit and execute subsequent actions such as prohibiting charging and alarm.

[0070] When there is no short circuit between the AC live wire output terminal LOUT and the AC neutral wire output terminal NOUT, the detection voltage cannot be transmitted to the AC live wire output terminal LOUT through the short circuit path; there is no detection voltage at the AC live wire output terminal LOUT, and there is also no detection voltage input at the first end of the voltage divider resistor R2; no current is generated in the series circuit formed by the voltage divider resistors R2 and R3, and the voltage at their common connection point is close to the system ground voltage. This voltage is transmitted to the short circuit detection acquisition pin DET through the current limiting resistor R1, which is the second voltage signal; after receiving the second voltage signal, the main control microcontroller unit will recognize that the AC charging circuit is in a normal state and there is no short circuit fault, and then allow the AC charging device to start the charging program.

[0071] In some embodiments, when the detection voltage injected by the relay unit 200 is 12V, the resistance of the voltage divider resistor R2 is 30kΩ, and the resistance of the voltage divider resistor R3 is 10kΩ, the voltage value of the first voltage signal is approximately 3V, and the voltage value of the second voltage signal is approximately 0V; this voltage difference can be clearly identified by the main control microcontroller unit, ensuring the accuracy of short circuit judgment.

[0072] Based on the above embodiments, as another optional embodiment, the resistance ratio of voltage divider resistor R2 to voltage divider resistor R3 is configured as follows: When the relay unit 200 is activated and there is a short circuit between the AC live wire output terminal LOUT and the AC neutral wire output terminal NOUT, the first voltage signal generated on the short circuit detection and acquisition pin DET is within the voltage range that the main control microcontroller unit recognizes as high level.

[0073] In this embodiment, the voltage range that the main microcontroller unit identifies as high level refers to the voltage range that the short-circuit detection acquisition pin DET of the main microcontroller unit can effectively identify as a high-level signal. This range is determined by the hardware characteristics of the main microcontroller unit, and this range may vary between different models of main microcontroller units. However, the industry standard high-level recognition range is usually 2V to 5V. If the voltage signal is lower than the lower limit of this range, the main microcontroller unit will identify it as low level. If the voltage signal is higher than the upper limit of this range, it may exceed the withstand voltage range of the acquisition pin of the main microcontroller unit, resulting in damage to the acquisition pin or the main microcontroller unit.

[0074] In some embodiments, when the relay unit 200 is energized and there is a short circuit between the AC live wire output terminal LOUT and the AC neutral wire output terminal NOUT of the AC charging circuit, the first voltage signal generated after the detection voltage is divided by the voltage divider resistors R2 and R3 must be within the voltage range that the main control microcontroller unit recognizes as high level.

[0075] Specifically, determine the high-level voltage range corresponding to the short-circuit detection acquisition pin DET of the selected main microcontroller unit, and record the lower limit and upper limit of this range, denoted as U. 下限 U 上限 Determine the detection voltage value injected into relay unit 200, denoted as U. 检测 This value is determined by the DC power supply that powers the coil of relay K1, typically 12V; calculate the resistance ratio range of voltage divider resistors R2 and R3 to ensure the first voltage signal, denoted as U1, falls within [U... 下限 U 上限 Within the range.

[0076] The voltage divider formulas for voltage divider circuits include: U1=U 检测 ×(R3 / (R2+R3)).

[0077] Where U1 is the voltage value of the first voltage signal, U 检测 The detection voltage value injected into the relay unit 200, R2 is the resistance value of the voltage divider resistor R2, and R3 is the resistance value of the voltage divider resistor R3.

[0078] When U 检测 When the value of U1 is fixed, its magnitude is determined by the ratio of the voltage divider resistor R3 to (R2+R3), that is, by the resistance ratio of the voltage divider resistors R2 and R3. If the resistance ratio of the two is too large, the value of U1 will be too small, possibly lower than the high-level recognition range of the main microcontroller unit. 下限 This can cause the main control microcontroller to mistakenly identify the first voltage signal as low, making it unable to accurately determine the short-circuit state of the AC charging circuit. If the resistance ratio between the two is too small, it can lead to an excessively large value for U1, potentially exceeding the high-level recognition range of the main control microcontroller. 上限 This can damage the short-circuit detection and acquisition pin DET of the main control microcontroller unit, and even cause the main control microcontroller unit to malfunction.

[0079] In some embodiments, if the main control microcontroller unit identifies a high-level voltage range of 2V to 5V, and the detection voltage injected by the relay unit 200 is 12V, it is deduced that the resistance ratio of the voltage divider resistor R2 to the voltage divider resistor R3 should be between 1.4 and 5. In this case, the resistance value of the voltage divider resistor R2 can be 30kΩ, the resistance value of the voltage divider resistor R3 can be 10kΩ, and the voltage value of the first voltage signal is approximately 3V.

[0080] Based on the above embodiments, as another optional embodiment, both the AC live wire output terminal LOUT and the AC neutral wire output terminal NOUT are used to connect to the AC charging interface of the electric vehicle.

[0081] When a user needs to charge an electric vehicle, they insert the charging gun into the vehicle's AC charging port. At this time, the AC live wire output (LOUT) and AC neutral wire output (NOUT) form a complete circuit with the charging circuit inside the electric vehicle through the charging gun cable. After the main control microcontroller detects the charging gun insertion signal through the charging request control circuit, it immediately initiates a short-circuit detection process to check the short circuit between the AC live wire output (LOUT), AC neutral wire output (NOUT), and the electric vehicle's charging port. If the detection result is no short circuit, the AC charging device will send a charging permission signal to the electric vehicle and then start the charging program, transmitting AC power to the electric vehicle through the AC live wire output (LOUT) and AC neutral wire output (NOUT). If the detection result is a short circuit, the AC charging device will prevent charging from starting and prompt the user to troubleshoot the fault through an alarm circuit.

[0082] Based on the above embodiments, as another optional embodiment, when the relay unit 200 is energized, it is used to inject a DC detection voltage signal into the AC neutral output terminal NOUT; The voltage divider detection unit 300 is used to sample the DC detection voltage signal at the AC live wire output terminal LOUT; The main control microcontroller unit determines whether there is a short circuit between the AC live wire output terminal LOUT and the AC neutral wire output terminal NOUT of the AC charging circuit by judging the DC voltage signal level on the short circuit detection acquisition pin DET.

[0083] In this embodiment, the DC detection voltage signal refers to a stable voltage signal provided by the DC power supply that powers the coil of relay K1, free from AC harmonic interference. This signal differs from the AC mains voltage transmitted during normal operation of the AC charging circuit. Its voltage value can be set according to the short-circuit detection requirements, typically 12V. This ensures that the first voltage signal formed after voltage division is within the high-level recognition range of the main control microcontroller unit, while also preventing damage to components in the AC charging circuit due to excessive voltage. The DC voltage signal level refers to the high or low voltage state formed after the DC detection voltage signal is processed by the voltage divider detection unit 300. It is typically divided into a high-level state and a low-level state, corresponding to the short-circuit state and normal state of the AC charging circuit, respectively.

[0084] In some embodiments, when the relay unit 200 is energized, it is used to inject a DC detection voltage signal into the AC neutral output terminal NOUT of the AC charging circuit. The energizing action of the relay unit 200 is controlled by the transistor driving unit 100. When the transistor Q1 is turned on, the coil of the relay K1 is energized, and the contacts switch to connect with the normally open contacts. At this time, the DC power supply that powers the coil of the relay K1 will transmit the DC detection voltage signal to the second current limiting unit 202 through one of the normally open contacts. After the DC detection voltage signal is current-limited by the second current limiting unit 202, it is injected into the AC neutral output terminal NOUT. Since the DC detection voltage signal has the characteristics of voltage stability and no zero-crossing, it can provide a more reliable signal source for short circuit detection and avoid detection errors caused by AC voltage fluctuations or zero crossings.

[0085] The voltage divider detection unit 300 is used to sample the DC detection voltage signal at the AC live wire output terminal LOUT of the AC charging circuit. When there is a short circuit between the AC live wire output terminal LOUT and the AC neutral wire output terminal NOUT of the AC charging circuit, the DC detection voltage signal injected into the AC neutral wire output terminal NOUT will be transmitted to the AC live wire output terminal LOUT through the short circuit path. The DC detection voltage signal at the AC live wire output terminal LOUT will be transmitted to the voltage divider resistor R2 of the voltage divider detection unit 300 through the first current limiting unit 201. The voltage divider detection unit 300 performs voltage division processing on the DC detection voltage signal through the voltage divider resistors R2 and R3 to form a low DC voltage signal. After the current is limited by the current limiting resistor R1, the low DC voltage signal is transmitted to the short circuit detection acquisition pin DET of the main control microcontroller unit. When there is no short circuit between the AC live wire output terminal LOUT and the AC neutral wire output terminal NOUT, there is no DC detection voltage signal at the AC live wire output terminal LOUT, and the signal sampled by the voltage divider detection unit 300 is close to the system ground voltage, which is also a DC signal.

[0086] The main control microcontroller determines whether a short circuit exists between the AC live wire output (LOUT) and the AC neutral wire output (NOUT) of the AC charging circuit by judging the DC voltage signal level on the short circuit detection acquisition pin (DET). The main control microcontroller internally presets high-level and low-level judgment thresholds. The high-level judgment threshold is typically set to the middle value of the high-level recognition range, and the low-level judgment threshold is typically set close to the system ground voltage. If the main control microcontroller detects a DC voltage signal level on the short circuit detection acquisition pin (DET) higher than the high-level judgment threshold, it determines that a short circuit exists between the AC live wire output (LOUT) and the AC neutral wire output (NOUT) of the AC charging circuit. If the detected DC voltage signal level is lower than the low-level judgment threshold, the AC charging circuit is considered normal. Because the DC voltage signal does not have the zero-crossing characteristic of the AC signal, the main control microcontroller can make a judgment without waiting for the signal to cross zero, which significantly improves the response speed of short circuit detection.

[0087] This implementation uses a DC detection voltage signal for short-circuit detection, which, compared to the existing technology that uses an AC voltage signal, has advantages such as strong anti-interference capability, fast detection response speed, and high detection accuracy. The DC voltage signal is not affected by mains harmonics, voltage spikes and drops, etc., ensuring that the signal sampled by the voltage divider detection unit 300 is stable and reliable, reducing the false judgment rate. At the same time, the main control microcontroller unit has a simple logic for judging the DC voltage signal level, without the need for complex signal filtering and rectification processing, further simplifying the short-circuit detection program design and reducing the computational burden of the main control microcontroller unit. In addition, the injection of the DC detection voltage signal only occurs during the short-circuit detection stage and stops after the detection is completed, so it will not cause any interference to the normal charging process of the AC charging equipment.

[0088] In some embodiments, the voltage value of the DC detection voltage signal injected by the relay unit 200 is 12V; the main control microcontroller sets the high-level judgment threshold of the DC voltage signal to 1.5V and the low-level judgment threshold to 0.5V, that is, when the collected DC voltage signal is greater than or equal to 1.5V, it is judged as high level, and when the collected DC voltage signal is less than or equal to 0.5V, it is judged as low level.

Claims

1. A short-circuit detection circuit for an AC charging device, characterized in that, include: Transistor drive unit, relay unit, and voltage divider detection unit; The input terminal of the transistor driving unit is used to connect to the short-circuit detection enable pin of the main control microcontroller unit, and the output terminal is connected to the control terminal of the relay unit. The signal terminal of the relay unit is used to connect to the AC neutral wire output terminal and the AC live wire output terminal of the AC charging circuit respectively, and the output terminal is connected to the input terminal of the voltage divider detection unit. The output of the voltage divider detection unit is used to connect to the short-circuit detection acquisition pin of the main control microcontroller unit.

2. The short-circuit detection circuit for AC charging equipment according to claim 1, characterized in that, The voltage divider detection unit includes: Current-limiting resistor R1, voltage-dividing resistor R2, and voltage-dividing resistor R3; The first end of the voltage divider resistor R2 is connected to the relay unit, the second end is connected to the first end of the voltage divider resistor R3, and the second end of the voltage divider resistor R3 is grounded. The first end of the current-limiting resistor R1 is connected to the short-circuit detection and acquisition pin, and the second end is connected between the second end of the voltage divider resistor R2 and the first end of the voltage divider resistor R3.

3. The short-circuit detection circuit for AC charging equipment according to claim 1, characterized in that, The transistor driving unit includes: Transistor Q1, wherein the base of transistor Q1 is connected to the short-circuit detection enable pin, the collector is connected to the relay unit, and the emitter is grounded; The transistor Q1 includes a base current limiting resistor and a base resistor.

4. The short-circuit detection circuit for AC charging equipment according to claim 3, characterized in that, The relay unit includes: Relay K1, one end of the coil of relay K1 is connected to the collector of transistor Q1, the other end of the coil is connected to the power supply, the first normally open contact is connected to the voltage divider detection unit, the second normally open contact is connected to the power supply, the first common terminal is connected to the AC live wire output terminal, and the second common terminal is connected to the AC neutral wire output terminal.

5. The short-circuit detection circuit for AC charging equipment according to claim 4, characterized in that, The relay unit also includes: First current limiting unit and second current limiting unit; The first end of the first current limiting unit is connected to the AC live wire output terminal, and the second end is connected to the relay K1; The first end of the second current limiting unit is connected to the AC neutral output terminal, and the second end is connected to the relay K1.

6. The short-circuit detection circuit for AC charging equipment according to claim 5, characterized in that, The first current limiting unit includes resistors R4, R5, R6 and R7 connected in series, and the second current limiting unit includes resistors R8, R9, R10 and R11 connected in series.

7. The short-circuit detection circuit for AC charging equipment according to claim 2, characterized in that, When there is a short circuit between the AC live wire output terminal and the AC neutral wire output terminal, the detection voltage is divided by the voltage divider resistors R2 and R3, so that the short circuit detection acquisition pin can acquire the first voltage signal. When there is no short circuit between the AC live wire output terminal and the AC neutral wire output terminal, the short circuit detection acquisition pin acquires the second voltage signal.

8. The short-circuit detection circuit for AC charging equipment according to claim 7, characterized in that, The resistance ratio of the voltage divider resistors R2 and R3 is configured as follows: When the relay unit is energized and there is a short circuit between the AC live wire output terminal and the AC neutral wire output terminal, the first voltage signal generated on the short circuit detection and acquisition pin is within the voltage range that the main control microcontroller unit recognizes as high level.

9. The short-circuit detection circuit for AC charging equipment according to claim 1, characterized in that, Both the AC live wire output terminal and the AC neutral wire output terminal are used to connect to the AC charging interface of the electric vehicle.

10. The short-circuit detection circuit for the AC charging device according to claim 1, characterized in that, When the relay unit is engaged, it is used to inject a DC detection voltage signal into the AC neutral output terminal. The voltage divider detection unit is used to sample the DC detection voltage signal at the AC live wire output terminal; The main control microcontroller unit determines whether there is a short circuit between the AC live wire output terminal and the AC neutral wire output terminal of the AC charging circuit by judging the DC voltage signal level on the short circuit detection acquisition pin.

Images