A leakage current detection circuit

Abstract

The present invention relates to a leakage current detection circuit, which includes a CT current transformer with a hollow structure, a sampling module for sampling the secondary current of the CT current transformer, a control module connected to the sampling module, and an action module connected to the control module and acting when the sampled current is greater than a set value. The live wire and the neutral wire simultaneously penetrate from one side of the hollow structure of the CT current transformer to the other side and are connected to a load. The leakage current detection circuit further includes an no-load self-detection module. The no-load self-detection module includes a branch connected to the live wire, a current-limiting module arranged on the branch, and a switch module arranged on the branch and controlled by the control module to be turned on and off. The branch penetrates through the hollow structure of the CT current transformer in the same direction as the live wire. The switch module is disconnected when the load is connected and is connected when there is no load. This circuit has good reliability, high precision, and good flexibility for leakage current detection, and has a simple circuit structure, which is beneficial to cost savings.

Description

Technical Field

[0001] The present invention relates to the technical field of charging piles, and particularly to a leakage current detection circuit. Background Art

[0002] Before the AC charging pile product starts charging, in order to protect the personal safety of the operator, the AC charging pile system needs to detect the leakage current between the live wire (UL) and the neutral wire (UN) on the line. The common practice in the prior art is to connect a residual current protection switch (RCD) in the circuit. When the leakage current is greater than a certain value, the residual current protection switch (RCD) will automatically disconnect the connected load, such as Figure 1 As shown, for example, when a type B residual current protection switch is connected, when the leakage current is greater than 30 mA, the residual current protection switch will automatically disconnect the connected load, thereby protecting the safety of the operator. However, using this method for leakage current detection has low accuracy, and the operating current of the residual current protection cannot be adjusted, resulting in insufficient flexibility in its use. Summary of the Invention

[0003] In view of the above problems, the purpose of the present invention is to provide a leakage current detection circuit with high accuracy and good flexibility in use.

[0004] To achieve the above purpose, the technical solution of the present invention is: a leakage current detection circuit, characterized in that: it includes a CT transformer with a hollow structure, a sampling module for sampling the secondary current of the CT transformer, a control module connected to the sampling module, and an action module connected to the control module and operating when the sampled current is greater than a set value. The CT transformer allows the live wire and the neutral wire to pass through from one side of its hollow structure to the other side and be connected to the load.

[0005] Further, the leakage current detection circuit further includes an no-load self-detection module. The no-load self-detection module includes a branch connected to the live wire, a current-limiting module provided on the branch, and a switch module provided on the branch and controlled by the control module for on-off. The branch passes through the hollow structure of the CT transformer in the same direction as the live wire. The switch module is disconnected when the load is connected and connected when there is no load.

[0006] Further, the switch module includes a first relay, an NPN-type triode, and a DC power supply. The armature part of the first relay is connected to the branch, one end of the coil part is connected to the DC power supply, and the other end is connected to the collector of the NPN-type triode. The base of the NPN-type triode is connected to the control module and the emitter is grounded.

[0007] Further, a diode is connected in parallel at both ends of the coil part of the first relay, and the negative pole of the diode is connected to the end of the coil part of the first relay connected to the DC power supply.

[0008] Further, the base of the NPN transistor is connected to the control module through a first resistor, and the base of the NPN transistor is also grounded through a second resistor.

[0009] Further, the set value is 30 mA.

[0010] Further, the current limiting module includes a plurality of third resistors connected in series on the branch.

[0011] Further, the action module is an alarm connected to the control module or a second relay connected in the load loop and controlled by the control module for on-off.

[0012] Further, the sampling module includes an RN8209 type metering chip and a fourth resistor connected in parallel with the metering chip.

[0013] Further, the control module is an MCU.

[0014] Compared with the prior art, the advantages of the present invention are as follows: The leakage current detection circuit can not only detect the leakage current when the load is carried, but also perform self-detection on the leakage current when the load is unloaded. It has diverse functions, improves the reliability of detection, and makes the charging pile safer and more reliable to use; With this circuit, leakage currents of different magnitudes can be detected as needed, making the leakage current detection controllable, with good flexibility in use and more intelligent. At the same time, sampling is performed using a metering chip, with high accuracy, which is beneficial to improving the accuracy of leakage current detection; In addition, the circuit structure is simple, the materials have strong versatility, and there are fewer wiring connections, which is convenient for improving production efficiency and thus saving costs. Description of the Drawings

[0015] Figure 1 It is the circuit diagram of leakage current detection in the prior art.

[0016] Figure 2 It is the circuit diagram of leakage current detection of this application. Detailed Embodiment

[0017] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0018] Such as Figure 2The following is the leakage current detection circuit diagram in this application. As shown in the figure, the leakage current detection circuit includes a CT current transformer 1 with a hollow structure, a sampling module 2 for sampling the secondary current of the CT current transformer 1, a control module 3 connected to the sampling module 2, and an action module connected to the control module 3 and operating when the sampled current is greater than a set value. The live wire UL and the neutral wire UN simultaneously penetrate from one side of the hollow structure of the CT current transformer 1 to the other side and are connected to the load RL1. With this leakage current detection circuit, according to the working characteristics of the current transformer, when the currents in the live wire UL and the neutral wire UN are equal, since the currents in the live wire UL and the neutral wire UL enter and exit, the current on the secondary side of the CT current transformer 1 is zero. When there is a leakage current, the currents in the live wire UL and the neutral wire UN are not equal, and a current will be generated on the secondary side of the CT current transformer 1. Therefore, by sampling and judging the secondary current of the CT current transformer 1 through the sampling module 2, it can be determined whether there is a leakage current. When the leakage current is greater than a certain value, that is, when the secondary current of the CT current transformer 1 is greater than the set value, the action module performs corresponding actions. This set value can be adjusted according to the usage environment. In this embodiment, this set value is taken as 30 mA. That is, when the secondary side current of the CT current transformer 1 is greater than 30 mA, the action module operates. When selecting the CT current transformer 1, the maximum current of the CT current transformer 1 should be greater than twice the actual current to prevent damage after the wiring is reversed.

[0019] In order to enable this leakage current detection circuit to perform self-detection of leakage current when the load is disconnected, that is, when it is no-load, the leakage current detection circuit further includes a no-load self-detection module 5. The no-load self-detection module 5 includes a branch UL1 connected to the live wire UL, a current-limiting module 51 provided on the branch UL1, and a switch module 52 provided on the branch UL1 and controlled by the control module 3 for on / off. The branch UL1 penetrates the hollow structure of the CT current transformer 1 in the same direction as the live wire UL. The switch module 52 is disconnected when the load is connected and is connected when it is no-load. That is, when the load RL1 is connected to the circuit, the no-load self-detection module 5 does not work, and when the load RL1 is disconnected, the leakage current detection during no-load is performed. When it is no-load, the switch module 52 is closed and connected. Due to the current-limiting module 51 provided on the branch UL1, there will be a stable current on the branch UL1, and there will also be a stable secondary side current on the secondary side of the CT current transformer 1. When there is a leakage current, the secondary side current of the CT current transformer 1 will change, and thus the self-detection of leakage current during no-load is performed.

[0020] Specifically, the switch module 52 includes a first relay K1, an NPN-type triode V8, and a DC power supply VCC. The armature part of the first relay K1 is connected to the branch UL1, and one end of the coil part of the first relay K1 is connected to the DC power supply VCC, and the other end is connected to the collector of the NPN-type triode V8. The base of the NPN-type triode V8 is connected to the control module 3 and the emitter is grounded. In this embodiment, the DC power supply VCC is a 5V DC power supply, the first relay K1 is of the HF46F-5-HS1 type, and the NPN-type triode V8 is of the 2SC2412 type. To prevent current backflow, a diode VD1 is connected in parallel at both ends of the coil part of the first relay K1, and the negative pole of the diode VD1 is connected to the end of the coil part of the first relay K1 connected to the DC power supply VCC. In this embodiment, the diode VD1 is of the 1N4148 type. At the same time, to prevent the NPN-type triode V8 from being damaged by overcurrent, the base of the NPN-type triode V8 is connected to the control module 3 through a first resistor R144, and the base of the NPN-type triode V8 is also grounded through a second resistor R147. When the load RL1 is disconnected and the control signal M_PE3-LEAK_YK_K of the control module 3 is at a high level, the NPN-type triode V8 conducts, and there is current flowing through the coil part of the first relay K1. The armature part of the first relay K1 closes, and there is current flowing through the branch UL1, so that the leakage current self-detection during no-load can be carried out. When the load RL1 is connected to the circuit and the control signal M_PE3-LEAK_YK_K of the control module 3 is at a low level, the NPN-type triode V8 cuts off and disconnects, and there is no current flowing through the coil part of the first relay K1. The armature part of the first relay K1 opens, and there is no current flowing through the branch UL1, and the no-load self-detection module does not work.

[0021] In this embodiment, the current-limiting module 51 includes five third resistors R1, R2, R3, R4, and R5 connected in series on the branch UL1, and their resistance values are 2MΩ, 2MΩ, 1.2MΩ, 1MΩ, and 1MΩ respectively, and the total resistance value is 7.2MΩ. After the branch UL1 conducts, there will be a current of about 30mA on the branch UL1. This current will cause a corresponding secondary-side current to be generated on the secondary side of the CT transformer 1. If the secondary-side current detected by the sampling module 2 is consistent with this, it means that there is no leakage current during no-load. If not, it can be determined that there is a leakage current. Of course, the number of resistors and the resistance value distribution set in the current-limiting module 51 can be adjusted according to actual needs.

[0022] As a preferred embodiment, the above-mentioned action module is an alarm 4 connected to the control module 3. When the current on the secondary side of the CT transformer 1 detected by the sampling module 2 is greater than the set value, that is, when the leakage current is greater than a certain value, the alarm 4 will emit an alarm signal to remind the operator to pay attention and disconnect the power supply or perform corresponding operations. Of course, the above-mentioned action module can also be a second relay arranged on the load circuit (only the case where the action module is an alarm is shown in the figure, and the case where it is a second relay is not shown). When the load RL1 is connected, when the leakage current is greater than a certain value, the control module 3 sends an action signal to the second relay to disconnect the load circuit, thus ensuring operation safety.

[0023] In this embodiment, the sampling module 2 includes an RN8209 type metering chip, and a fourth resistor R6 is also connected in parallel across the two ends of the metering chip. The control module 3 in this embodiment is an MCU.

[0024] When the leakage current detection circuit of the present application is working with the load RL1 connected, it is possible to set in the MCU to detect the current on the secondary side of the CT transformer 1 cyclically every certain time (such as 2S). When the detected current is greater than the preset set value, the MCU can send an instruction to the alarm 4 to give an alarm or send an instruction to the second relay to disconnect the load circuit.

[0025] Although the embodiments of the present invention have been shown and described, those skilled in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A leakage current detection circuit, characterized in that: It includes a CT transformer (1) with a hollow structure, a sampling module (2) for sampling the secondary current of the CT transformer (1), a control module (3) connected to the sampling module (2), and an action module connected to the control module (3) and acting when the sampled current is greater than a set value. The CT transformer (1) allows the live wire and the neutral wire to penetrate from one side of its hollow structure to the other side and be connected to the load at the same time; The control module (3) is an MCU; The leakage current detection circuit further includes an no-load self-detection module (5). The no-load self-detection module (5) includes a branch connected to the live wire, a current-limiting module (51) arranged on the branch, and a switch module (52) arranged on the branch and controlled by the control module (3) for on / off. The branch passes through the hollow structure of the CT transformer (1) in the same direction as the live wire. The switch module (52) is disconnected when the load is connected and connected when there is no load; When there is no load, the switch module (52) is closed and connected. Due to the current-limiting module (51) arranged on the branch, there will be a stable current on the branch, and there will also be a stable secondary-side current on the secondary side of the CT transformer (1). When there is a leakage current, the secondary-side current of the CT transformer (1) will change, so as to perform self-detection of leakage current during no-load.

2. The leakage current detection circuit according to claim 1, characterized in that: The switch module (52) includes a first relay, an NPN-type triode, and a DC power supply. The armature part of the first relay is connected to the branch, one end of the coil part is connected to the DC power supply, and the other end is connected to the collector of the NPN-type triode. The base of the NPN-type triode is connected to the control module (3), and the emitter is grounded.

3. The leakage current detection circuit according to claim 2, characterized in that: Both ends of the coil part of the first relay are connected in parallel with a diode, and the negative pole of the diode is connected to the end of the coil part of the first relay connected to the DC power supply.

4. The leakage current detection circuit according to claim 2, characterized in that: The base of the NPN-type triode is connected to the control module (3) through a first resistor, and the base of the NPN-type triode is also grounded through a second resistor.

5. The leakage current detection circuit according to claim 1, characterized in that: The set value is 30 mA.

6. The leakage current detection circuit according to claim 1, characterized in that: The current-limiting module (51) includes a plurality of third resistors connected in series on the branch.

7. The leakage current detection circuit according to claim 1, characterized in that: The action module is an alarm (4) connected to the control module (3) or a second relay connected in the load loop and controlled by the control module (3) for on / off.

8. The leakage current detection circuit according to claim 1, characterized in that: The sampling module (2) includes an RN8209 type metering chip and a fourth resistor connected in parallel with the metering chip.

Images