DC charging pile insulation detection circuit

Abstract

The utility model discloses a DC charging pile insulation detection circuit. The technical problem that an existing DC charging pile insulation detection circuit is large in detection error is mainly solved. The positive terminal and the negative terminal are used for being correspondingly and electrically connected with a positive electrode and a negative electrode of a direct-current charging gun respectively, and the first resistor, the second resistor, the third resistor and the fourth resistor are sequentially connected between the positive terminal and the negative terminal in series. The voltage source and the voltage detection circuit are respectively, correspondingly and electrically connected to a line between the second resistor and the third resistor, a second relay and a third relay are connected in parallel and then are connected in series with the first relay, and the single chip microcomputer is correspondingly and electrically connected with the voltage detection circuit. The DC charging pile insulation detection circuit can ensure the insulation detection accuracy and anti-interference capability when the insulation resistance is very large or the voltage is very low.

Description

Technical Field

[0001] The present application relates to the technical field of charging piles, and in particular to an insulation detection circuit for a DC charging pile. Background Art

[0002] With the increasing popularity of electric vehicles, DC charging piles, as the primary charging infrastructure, are attracting increasing attention for their safety and reliability. Testing the resistance between the positive and negative terminals of the charging gun output terminal and ground effectively assesses the insulation performance of the charging pile, ensuring compliance with safety standards and preventing safety incidents such as leakage and electric shock. Insulation resistance generally refers to the resistance exhibited by insulating materials in a circuit under a DC voltage. For DC charging piles, the higher the insulation resistance between the positive and negative terminals, the better the insulation performance and the lower the risk of leakage. Therefore, to ensure the safety and reliability of the equipment, DC charging piles should have a certain insulation resistance between the positive and negative terminals.

[0003] The existing technology known to the inventors usually uses the voltage balance method or the resistance voltage division method to realize the detection of insulation resistance. However, in the process of realizing the technical solution in the embodiment of the present application, the inventors of the present application found that the above-mentioned detection method has a large measurement error when the insulation resistance of the DC charging pile is small and the voltage on the DC charging gun is also very small. After research, the inventors found that the measurement error is due to the fact that the voltage measurement range of the insulation resistance detection circuit is large (that is, it needs to be able to detect 1000V voltage and also needs to be able to detect voltage below 10V), and the insulation resistance range is too large. When the voltage applied to the detection circuit is too low or the insulation resistance is small, the voltage that can be detected by the existing detection circuit will be very small. When encountering interference, the measurement error will increase, and the accuracy and reliability of the measurement cannot be guaranteed.

[0004] The information disclosed in this background technology section is only used to deepen the understanding of the background technology of the present disclosure and should not be regarded as an admission or any form of suggestion that the information constitutes the prior art known to those skilled in the art. Summary of the Invention

[0005] In view of at least one of the above technical problems, the present disclosure provides a DC charging pile insulation detection circuit, which mainly solves the technical problem of large detection error in existing DC charging pile insulation detection circuits.

[0006] According to one aspect of the present disclosure, a DC charging pile insulation detection circuit is provided, which includes a positive terminal and a negative terminal respectively used to be electrically connected to the positive and negative poles of a DC charging gun, a first resistor, a second resistor, a third resistor, and a fourth resistor sequentially connected in series between the positive terminal and the negative terminal, a voltage source and a voltage detection circuit respectively electrically connected to the line between the second resistor and the third resistor, a relay unit in which a second relay and a third relay are connected in parallel and then connected in series with the first relay, and a single-chip microcomputer electrically connected to the voltage detection circuit; the corresponding end of the first relay is grounded, the second relay is electrically connected to the line between the first resistor and the second resistor, the third relay is electrically connected to the line between the third resistor and the fourth resistor and is grounded; the voltage source is electrically connected to the line between the second resistor and the third resistor through a fifth resistor.

[0007] In some embodiments of the present disclosure, the voltage detection circuit includes a non-inverting amplification unit, an isolation unit, and an inverting amplification unit that are electrically connected in sequence.

[0008] In some embodiments of the present disclosure, the in-phase amplification unit includes a in-phase amplifier; the isolation unit includes a first optical coupler; and the inverting amplification unit includes an inverting amplifier.

[0009] In some embodiments of the present disclosure, the output terminal of the voltage detection circuit is electrically connected to an ADC pin of the microcontroller.

[0010] In some embodiments of the present disclosure, the voltage source includes a reference voltage chip.

[0011] In some embodiments of the present disclosure, the relay unit further includes a NAND gate that is communicatively connected to the single chip microcomputer and is used to control the conduction states of the first relay, the second relay, and the third relay.

[0012] In some embodiments of the present disclosure, the input terminals of the NAND gate are electrically connected to the single chip microcomputer via a transistor and a second optocoupler, respectively.

[0013] In some embodiments of the present disclosure, the first relay is connected to a high voltage ground, the line between the third resistor and the fourth resistor is connected to a low voltage ground, and a voltage isolation circuit is provided between the high voltage ground and the low voltage ground.

[0014] In some embodiments of the present disclosure, the voltage isolation circuit adopts a DC / DC isolation module.

[0015] One or more technical solutions provided in the embodiments of this application have at least any of the following technical effects or advantages:

[0016] 1. By setting up a high-precision voltage source, additional current can be injected into the corresponding detection resistor (third resistor). This ensures the lower limit of the voltage across the detection resistor when the insulation resistance of the charging pile is large or the voltage is very low, thereby effectively improving the detection accuracy and anti-interference ability of the detection circuit.

[0017] 2. The relay unit controlled by the single chip microcomputer can conveniently adjust the circuit structure of the detection circuit according to the measurement requirements, thereby achieving the purpose of rapid detection and improving the convenience of detection.

[0018] 3. The GND in the high-voltage area is isolated from the GND in the low-voltage area by a voltage isolation circuit, thus preventing the high-voltage ground from causing adverse interference to the low-voltage ground, which in turn causes large fluctuations in the microcontroller's collected data and affects the microcontroller's serial port communication. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a partial circuit schematic diagram of a DC charging pile insulation detection circuit in one embodiment of the present application.

[0020] Figure 2 FIG. 1 is a circuit schematic diagram of a voltage detection circuit in an embodiment of the present application.

[0021] Figure 3 1 is a circuit schematic diagram of a reference voltage circuit in an embodiment of the present application.

[0022] Figure 4 FIG. 1 is a circuit schematic diagram of a voltage isolation circuit in an embodiment of the present application.

[0023] Figure 5 This is a simplified diagram of the principle of an insulation detection circuit in one embodiment of the present application.

[0024] Figure 6 This is a simplified schematic diagram of another state of the insulation detection circuit in one embodiment of the present application.

[0025] Figure 7 This is a simplified schematic diagram of another state of the insulation detection circuit in one embodiment of the present application. DETAILED DESCRIPTION

[0026] The terms "first," "second," and so on used in this application are used to distinguish the objects being described and do not have any order or technical meaning. The terms "connection" and "coupling" used in this application, unless otherwise specified, include both direct and indirect connections (couplings). The procedures involved in or relied upon in the following embodiments are all conventional or simple procedures in the art, and those skilled in the art can make conventional choices or adaptive adjustments based on specific application scenarios. The devices and the like involved in the following embodiments, unless otherwise specified, are all conventional commercially available products.

[0027] In order to better understand the technical solution of the present application, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0028] In order to solve the technical problem of large detection error in the existing DC charging pile insulation detection method, this example discloses a DC charging pile insulation detection circuit. In order to realize the connection between the insulation detection circuit and the DC charging gun, see Figure 1 The insulation detection circuit includes a positive terminal U+ and a negative terminal U- for electrical connection to the positive and negative poles of the DC charging gun, respectively. A first resistor, a second resistor, a third resistor, and a fourth resistor are connected in series between the positive terminal U+ and the negative terminal U-. Figure 1 In this embodiment, the first resistor includes resistor R17 and resistor R18, the second resistor includes resistors R15 and R16, the third resistor is resistor R14, and the fourth resistor includes resistor R12 and resistor R13.

[0029] In addition, the DC charging pile insulation detection circuit also includes a relay unit, see Figure 1 In this embodiment, the relay unit includes a first relay K1, a second relay K2, and a third relay K3. The second relay K2 and the third relay K3 are connected in parallel. Specifically, the 5th pin of the second relay K2 is electrically connected to the 5th pin of the third relay K3, the 4th pin of the second relay K2 is connected to the line between resistors R17 and R16, and the 4th pin of the third relay K3 is connected to the line between resistors R13 and R14 and is grounded. In addition, one end of the first relay is grounded, and the other end is electrically connected to the 5th pin of the second relay K2 and the 5th pin of the third relay K3. This constitutes a relay unit structure in which the second relay K2 and the third relay K3 are connected in parallel and then in series with the first relay K1. By controlling the conduction state of each relay, the structure of the DC charging pile detection circuit is changed, and the insulation resistance of the positive terminal U+ and the negative terminal U- to ground is calculated based on the measured physical quantity.

[0030] In order to realize the control of the relay unit to control the on and off of different relays, and then obtain the corresponding detection circuit structure as needed, in this embodiment, see Figure 1A NAND gate U1 is provided, along with a single-chip microcomputer. The corresponding control signal is outputted from the I / O port of the single-chip microcomputer to achieve logical control of the NAND gate U1, thereby achieving the purpose of each relay performing a corresponding action. Specifically, in this embodiment, the NAND gate U1 uses a logic gate model SN74LVC1G38DBVR. Input ports A and B of the NAND gate U1 are respectively connected to the I / O port of the single-chip microcomputer via ports CON1 and CON2 to obtain the control level signal output by the single-chip microcomputer. The control ports of the second relay K2 and the third relay K3 are respectively electrically connected to input ports A and B of the NAND gate U1, and are directly controlled by the level signal outputted from the corresponding terminal of the single-chip microcomputer. Output port Y of the NAND gate U1 is electrically connected to the control terminal of the first relay K1. The control signal outputted by the single-chip microcomputer is logically operated by the NAND gate U1 to control the turning off of the first relay K1. In addition, in this embodiment, considering the difference between the working voltage of each relay and the voltage level of the single-chip microcomputer, in order to avoid adverse effects on the working stability of the single-chip microcomputer, an electrical isolation unit is set between the input ports A and B of the NAND gate U1 and the connection line of the single-chip microcomputer, see Figure 1 The electrical isolation unit includes a second optocoupler. In this example, the second optocoupler is specifically an optocoupler B1 or an optocoupler B2, and a transistor is set to drive each of them.

[0031] To avoid the problem of large insulation resistance detection errors caused by excessive voltage measurement range, see Figure 1 In this embodiment, a voltage source and a voltage detection circuit are provided between the second and third resistors. Specifically, the voltage source VB is connected to the circuit between resistors R14 and R15 via a fifth resistor, namely, resistor R9. The voltage detection circuit is connected to the circuit between resistors R14 and R15 via terminal V1 for voltage detection. Furthermore, in this embodiment, an RLC filter unit consisting of a resistor R11, an inductor L1, and a capacitor C7 is provided in the path between the voltage source and the voltage detection circuit and the circuit between resistors R14 and R15 to filter out noise. By providing a high-precision and stable voltage source VB, the lower limit of the voltage across the third resistor, namely, resistor R14, can be effectively increased, thereby improving the insulation resistance detection accuracy and anti-interference capability when the insulation resistance is high or the voltage is low.

[0032] See also Figure 2In this embodiment, the voltage detection circuit includes a non-inverting amplifier unit, an isolation unit, and an inverting amplifier unit connected in series. The non-inverting amplifier unit includes a non-inverting amplifier U3.1. The voltage detected at the V1 port is amplified by the non-inverting amplifier U3.1 and then connected to the input port of the first optocoupler B3 via an inverting amplifier U3.2. The first optocoupler serves as an isolation unit to achieve electrical isolation. The output port of the first optocoupler B3 is electrically connected to the ADC pin of the microcontroller via the inverting amplifier unit. In this example, the inverting amplifier unit includes an inverting amplifier U4.2.

[0033] In addition, in order to ensure that the voltage source can provide a high-precision and stable voltage and avoid measurement errors caused by voltage fluctuations, in this embodiment, see Figure 3 The voltage source includes a reference voltage circuit for generating a stable voltage. The circuit includes a reference voltage chip Q4. In this example, a reference voltage chip of model TL431 is selected.

[0034] In this embodiment, due to the presence of different voltage levels in the insulation resistance detection circuit, the corresponding first relay is connected to the high-voltage ground, and the line between the third resistor and the fourth resistor is connected to the low-voltage ground. When performing insulation resistance detection, the high-voltage ground corresponding to the high-voltage area will be connected to the earth. At this time, the high-voltage ground is very susceptible to interference, causing the voltage ripple to increase, thereby causing large fluctuations in the data collected by the single-chip microcomputer, and also affecting the serial port communication of the single-chip microcomputer. For this reason, in this embodiment, a voltage isolation circuit is set to isolate the high-voltage ground corresponding to the high-voltage area from the low-voltage ground corresponding to the low-voltage area. For details, see Figure 4 In this example, the voltage isolation circuit includes a DC / DC isolation module of model B0505S-1WR3, through which voltage isolation is achieved.

[0035] In actual testing, the insulation resistance detection circuit is simplified to Figure 5 As shown in the simplified principle diagram, R1 represents the first resistor, R2 represents the second resistor, R3 represents the third resistor, R4 represents the fourth resistor, K1 represents the first relay, K2 represents the second relay, K3 represents the third relay, R5 represents the fifth resistor, Vb is the voltage source, Rp represents the resistance of the positive pole of the DC power supply to ground, Rn represents the resistance of the negative pole of the AC power supply to ground, Up represents the voltage across Rp, and Un represents the voltage across Rn.

[0036] See here Figure 5 When K1, K2 and K3 are all open, the current I1 flows from the positive electrode U+ through the resistors R1, R2, R3, R4 in sequence to the negative electrode U-. According to Ohm's law, the voltage difference U between U+ and U- is:

[0037] U=I1×(R1+R2)+V adc1+I1×R4= I1×(R1+R2+R4)+V adc1 (1).

[0038] Since the current I adc1 The voltage flows from the reference voltage Vb through resistors R5 and R3 to the reference ground GND. According to Ohm's law, we can get:

[0039] (V b - V adc1 ) = I adc1 ×R5 (2).

[0040] Because the currents I1 and I adc1 The current flows through resistor R3, and according to Ohm's law:

[0041] V adc1 =(I adc1 + I1) × R3 (3).

[0042] Therefore, combining formula (2) and formula (3) we can get:

[0043] (4).

[0044] Furthermore, from formula (1) and formula (4), we can get:

[0045]

[0046] (5).

[0047] Then close K1 and K2 and keep K3 open. The simplified circuit schematic is shown in Figure 6 .

[0048] Since the current I adc2 The voltage flows from the reference voltage Vb through resistors R5 and R3 to the reference ground GND. According to Ohm's law, we can get:

[0049] (V b - V adc2 ) = I adc2 ×R5 (6).

[0050] Because the current I2, I adc2 The current flows through resistor R3, and according to Ohm's law and Kirchhoff's current law, we can get:

[0051] V adc2 =(I adc2 + I2) × R3 (7).

[0052] Therefore, combining equations (6) and (7), we can obtain:

[0053] (8).

[0054] Since the current I2 flows through R2, R3, R4 in sequence and reaches U-, Ohm's law shows that:

[0055] U n =I2×R2+V adc2 +I2×R4=I2×(R2+R4)+V adc2 (9).

[0056] Combining equations (8) and (9), we can obtain:

[0057]

[0058] (10).

[0059] And from Kirchhoff's current law we know:

[0060] I Rp +I1=I Rn +I2 (11).

[0061] Combining equations (8) to (11), we can obtain:

[0062]

[0063] (12).

[0064] Where, let k1= ,a= ;

[0065] Then formula (12) can be simplified as:

[0066] (13).

[0067] Then close K1, K3 and open K2, the simplified circuit schematic diagram is shown in Figure 7 .

[0068] Since the current I adc3 The voltage flows from the reference voltage Vb through resistors R5 and R3 to the reference ground GND. According to Ohm's law, we can get:

[0069] (V b - V adc3 ) = I adc3 ×R5 (14).

[0070] Because the currents I1 and I adc3 The current flows through resistor R3, and according to Ohm's law and Kirchhoff's current law, we can get:

[0071] V adc3=(I adc3 + I1) × R3 (15).

[0072] Therefore, combining equations (14) and (15), we can obtain:

[0073] (16).

[0074] Since the current I1 flows from U+ through R1, R2, R3 in sequence and reaches the reference ground GND, Ohm's law shows that:

[0075] U p =I1×(R1+R2)+V adc3 (17).

[0076] Combining equations (16) and (17), we can obtain:

[0077]

[0078] (18).

[0079] And from Kirchhoff's current law we know:

[0080] I Rn +I2=I Rp +I1+I adc3 (19).

[0081] Combining equations (15) to (19), we can obtain:

[0082]

[0083] (20).

[0084] Where, let k2= ,b= ;

[0085] Then formula (21) can be simplified as:

[0086] (twenty one).

[0087] Therefore, equations (13) and (14) form a set of two-variable linear equations. After solving the equations, we can obtain the values ​​of Rp and Rn, which are the insulation resistances of the positive and negative electrodes of the DC charging pile to the ground respectively:

[0088] ;

[0089] .

[0090] Although some preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0091] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of the inventive concept. Thus, if such changes and modifications fall within the scope of the claims of this application and their equivalents, this application is intended to include such changes and modifications.

Claims

1. A DC charging pile insulation detection circuit, characterized in that: It includes a positive terminal and a negative terminal for respectively electrically connecting to the positive and negative poles of the DC charging gun, a first resistor, a second resistor, a third resistor, and a fourth resistor connected in series between the positive terminal and the negative terminal, a voltage source and a voltage detection circuit respectively electrically connected to the line between the second resistor and the third resistor, a relay unit in which a second relay and a third relay are connected in parallel and then connected in series with the first relay, and a single-chip microcomputer electrically connected to the voltage detection circuit; The corresponding end of the first relay is grounded, the second relay is electrically connected to the line between the first resistor and the second resistor, the third relay is electrically connected to the line between the third resistor and the fourth resistor and is grounded; the voltage source is electrically connected to the line between the second resistor and the third resistor through the fifth resistor.

2. The DC charging pile insulation detection circuit according to claim 1, characterized in that: The voltage detection circuit includes a common-mode amplification unit, an isolation unit, and a reverse amplification unit that are electrically connected in sequence.

3. The DC charging pile insulation detection circuit according to claim 2, characterized in that: The in-phase amplification unit includes a in-phase amplifier; the isolation unit includes a first optical coupler; and the inverting amplification unit includes an inverting amplifier.

4. The DC charging pile insulation detection circuit according to claim 1 or 2, characterized in that: The output terminal of the voltage detection circuit is electrically connected to the ADC pin of the single chip microcomputer.

5. The DC charging pile insulation detection circuit according to claim 1, characterized in that: The voltage source includes a reference voltage chip.

6. The DC charging pile insulation detection circuit according to claim 1, characterized in that: The relay unit further includes a NAND gate which is in communication connection with the single chip microcomputer and is used to control the conduction states of the first relay, the second relay and the third relay.

7. The DC charging pile insulation detection circuit according to claim 6, characterized in that: The input terminals of the NAND gate are electrically connected to the single chip computer via a transistor and a second optical coupler respectively.

8. The DC charging pile insulation detection circuit according to claim 1, characterized in that: The first relay is connected to a high voltage ground, the line between the third resistor and the fourth resistor is connected to a low voltage ground, and a voltage isolation circuit is provided between the high voltage ground and the low voltage ground.

9. The DC charging pile insulation detection circuit according to claim 8, characterized in that: The voltage isolation circuit adopts a DC / DC isolation module.

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