Insulation detection circuit for charging pile

Abstract

The application relates to the technical field of electric vehicles, and particularly discloses an insulation detection circuit for a charging pile, which comprises a power supply, an MCU, a triode Q1, an operational amplifier U1, a resistor R1 and a resistor R2; the emitter and the base of the triode Q1 are short-circuited; the emitter of the triode Q1 is further connected with a measured object and the positive input end of the operational amplifier U1; the collector of the triode Q1 is grounded; one end of the resistor R1 is grounded, the other end of the resistor R1 is connected with one end of the resistor R2, and the other end of the resistor R2 is connected with the output end of the operational amplifier U1; the negative input end of the operational amplifier U1 is further connected with the other end of the resistor R1; the output end of the operational amplifier U1 is further connected with the first sampling port of the MCU; the power supply is connected with the measured object, and the voltage range of the power supply is 9-12V. The technical scheme of the application makes the insulation detection of the charging pile free from electric shock risk and meets the precision requirement.

Description

Technical Field

[0001] This invention relates to the field of electric vehicle technology, and in particular to an insulation detection circuit for charging piles. Background Technology

[0002] Electric vehicles (BEVs) are vehicles powered by an onboard power source, using an electric motor to drive the wheels. Because the output voltage of an electric vehicle's charging and discharging system ranges from 200V to 950V, leakage or contact with the human body could pose a significant safety hazard and threaten lives. Therefore, insulation testing of both the charging station and the electric vehicle is necessary during the charging process.

[0003] To avoid interference caused by insulation testing, only one of the charging pile or the electric vehicle can be tested at a time. Therefore, the method adopted is to perform insulation testing on the charging pile before charging and on the electric vehicle during charging. Currently, the insulation testing circuit of the charging pile uses a high voltage of 500V to measure the current across the insulation resistance to obtain the insulation resistance. Using high voltage for testing poses certain safety hazards.

[0004] Therefore, an insulation detection circuit for charging piles that eliminates the risk of electric shock and meets accuracy requirements is needed. Summary of the Invention

[0005] This invention provides an insulation detection circuit for charging piles, which enables insulation detection of charging piles to be performed without the risk of electric shock and meets accuracy requirements.

[0006] To solve the above-mentioned technical problems, this application provides the following technical solution:

[0007] The insulation detection circuit for charging piles includes: power supply, MCU, transistor Q1, operational amplifier U1, resistor R1, and resistor R2;

[0008] The emitter and base of transistor Q1 are shorted, and the emitter of transistor Q1 is also connected to the object under test and the positive input terminal of operational amplifier U1, respectively; the collector of transistor Q1 is grounded.

[0009] One end of resistor R1 is grounded, the other end of resistor R1 is connected to one end of resistor R2, and the other end of resistor R2 is connected to the output terminal of operational amplifier U1.

[0010] The negative input terminal of operational amplifier U1 is also connected to the other end of resistor R1; the output terminal of operational amplifier U1 is also connected to the first sampling port of MCU.

[0011] The power supply is connected to the object under test, and the voltage range of the power supply is 9-12V.

[0012] The basic principles and beneficial effects of the scheme are as follows:

[0013] This solution uses transistor Q1 to measure the voltage corresponding to the object under test, which is then amplified by operational amplifier U1 by 3.01 times and input to the analog-to-digital converter ADC1 of the MCU for sampling. The insulation resistance value is then directly calculated using the formula mentioned above.

[0014] The transistor Q2 circuit serves as a temperature calibration circuit. The measured voltage is amplified 3.01 times by an operational amplifier U2 through a 100K resistor R5 connected in series. This voltage is used for temperature compensation calibration and is input to the analog-to-digital converter ADC2 of the MCU for sampling to correct the measured resistance value of the device under test.

[0015] In summary, this solution, due to its use of low voltage and the absence of risk of electric shock, achieves 10% accuracy, meets accuracy requirements, and is more versatile and applicable to a wider range of situations.

[0016] Furthermore, it also includes transistor Q2, operational amplifier U2, resistor R3, resistor R4, and reference resistor R5;

[0017] One end of the reference resistor R5 is connected to the power supply, and the other end of the reference resistor R5 is connected to the emitter of the transistor Q2; the other end of the reference resistor R5 is also connected to the positive input terminal of the operational amplifier U2.

[0018] The emitter of transistor Q2 is shorted to the base, and the collector of transistor Q2 is grounded.

[0019] One end of resistor R3 is grounded, the other end of resistor R3 is connected to one end of resistor R4, and the other end of resistor R4 is connected to the output of operational amplifier U2.

[0020] The negative input terminal of operational amplifier U2 is also connected to the other end of resistor R3; the output terminal of operational amplifier U2 is also connected to the second sampling port of MCU.

[0021] Furthermore, the MCU includes an analog-to-digital converter (ADC1) and an analog-to-digital converter (ADC2), wherein the ADC1 acquires a sampling signal from a first sampling port, and the ADC2 acquires a sampling signal from a second sampling port.

[0022] Furthermore, both transistors Q1 and Q2 are NPN transistors.

[0023] Furthermore, the operational amplifiers U1 and U2 are low quiescent current operational amplifiers.

[0024] Furthermore, the MUC calculates the resistance Riso of the tested object according to the following formula:

[0025] Riso=VCC / (Is*e^(UD / UT))

[0026] Where VCC is the supply voltage, Is is the reverse saturation current, UD is the voltage applied across transistor Q1, and UT is the temperature voltage equivalent. Attached Figure Description

[0027] Figure 1 This is a circuit topology diagram of an insulation detection circuit used in a charging pile, as shown in the embodiment. Detailed Implementation

[0028] The following detailed description illustrates the specific implementation method:

[0029] Example

[0030] like Figure 1 As shown, the insulation detection circuit for charging piles in this embodiment includes the device under test, a power supply, an MCU, a transistor Q1, an operational amplifier U1, resistors R1 and R2; it also includes a transistor Q2, an operational amplifier U2, resistors R3 and R4, and a reference resistor R5. In this embodiment, the resistance of resistor R1 is 20kΩ, the resistance of resistor R2 is 40.2kΩ, the resistance of resistor R3 is 20kΩ, the resistance of resistor R4 is 40.2kΩ, and the resistance of reference resistor R5 is 100kΩ.

[0031] The power supply is connected to the device under test. In this embodiment, the power supply voltage range is 9-12V, and 9V is used in this embodiment. This is because the voltage needs to be at least 10 times greater than the diode voltage (0.9V) to negligible the diode voltage (i.e., 9V), and the maximum voltage must not exceed the operating voltage range of the low quiescent current operational amplifier; therefore, the commonly used 12V is selected.

[0032] The power supply is 9V, and the insulation resistance of the tested object ranges from 100K to 1G.

[0033] The emitter and base of transistor Q1 are shorted, and the emitter of transistor Q1 is also connected to the object under test and the positive input terminal of operational amplifier U1, respectively; the collector of transistor Q1 is grounded.

[0034] One end of resistor R1 is grounded, the other end of resistor R1 is connected to one end of resistor R2, and the other end of resistor R2 is connected to the output terminal of operational amplifier U1.

[0035] The negative input terminal of operational amplifier U1 is also connected to the other end of resistor R1; the output terminal of operational amplifier U1 is also connected to the first sampling port of MCU.

[0036] One end of the reference resistor R5 is connected to the power supply, and the other end of the reference resistor R5 is connected to the emitter of the transistor Q2; the other end of the reference resistor R5 is also connected to the positive input terminal of the operational amplifier U2.

[0037] The emitter of transistor Q2 is shorted to the base, and the collector of transistor Q2 is grounded.

[0038] One end of resistor R3 is grounded, the other end of resistor R3 is connected to one end of resistor R4, and the other end of resistor R4 is connected to the output of operational amplifier U2.

[0039] The negative input terminal of operational amplifier U2 is also connected to the other end of resistor R3; the output terminal of operational amplifier U2 is also connected to the second sampling port of MCU.

[0040] In this embodiment, the MCU includes an analog-to-digital converter (ADC1) and an analog-to-digital converter (ADC2), wherein the ADC1 acquires a sampling signal from a first sampling port, and the ADC2 acquires a sampling signal from a second sampling port.

[0041] Both transistors Q1 and Q2 are NPN transistors. The emitter and base of transistors Q1 and Q2 are shorted to act as the anode of the PN junction, and the collector acts as the cathode of the PN junction. They are used as diodes as a whole. The reason for not using diodes is that the temperature drift consistency of the PN junction of transistors is better and the compensation is more accurate.

[0042] Operational amplifiers U1 and U2 are low quiescent current operational amplifiers because the insulation resistance of the tested object is above MΩ and the current flowing through the transistor is in the nA to uA range. Therefore, the quiescent current of the operational amplifier is required to be in the fA range.

[0043] In this embodiment, the object under test is connected in series with transistor Q1 and powered by a 9V battery. Since transistor Q1 is used as a diode, according to the voltage-current formula of a diode, the current equation of the diode is:

[0044] I = Is * [e^(UD / UT) - 1]

[0045] Where Is is the reverse saturation current, which is a fixed value for a given diode, i.e., a constant; UD is the voltage applied across the diode; and UT is the temperature voltage equivalent (26mV at room temperature).

[0046] Since the calculated forward voltage UD is 700mV, which is much greater than UT's 26mV, -1 can be omitted, and the formula is modified as follows:

[0047] I = Is * e^(UD / UT) (1)

[0048] In addition, the diode current I = (VCC - UD) / Riso, since VCC (9000mV) is much larger than UD (700mV), the formula is modified as follows:

[0049] I = VCC / Riso (2)

[0050] Combining formulas (1) and (2), we obtain:

[0051] Riso=VCC / (Is*e^(UD / UT)) (3)

[0052] By measuring the value of UD, the resistance Riso of the object under test can be directly calculated according to formula (3).

[0053] In this embodiment, the voltage corresponding to different test objects (i.e., insulation resistance) measured by transistor Q1 is amplified by operational amplifier U1 by 3.01 times and then input to the analog-to-digital converter ADC1 of the MCU for sampling. The insulation resistance value is then directly calculated using formula 3.

[0054] The transistor Q2 circuit serves as a temperature calibration step. The measured voltage, pre-connected to a 100K resistor R5, is amplified 3.01 times by operational amplifier U2 to obtain the measured voltage corresponding to the 100K insulation resistance. This voltage is used for temperature compensation calibration and is input to the MCU's analog-to-digital converter ADC2 for sampling, correcting the insulation resistance value measured in step 3. Specifically:

[0055] First, calculate the theoretical voltage at 100K:

[0056] U100K=(ln(VCC / (100000*Is)))*UT

[0057] Then calculate the temperature compensation coefficient:

[0058] K=U100K / (Uadc2 / 3.01)=((ln(VCC / (100000*Is)))*UT)*3.01 / Uadc2

[0059] Resistance of the object being measured:

[0060] Riso=VCC / (Is*e^(Uadc1 / 3.01*K / UT))

[0061] =VCC / (Is*e^(Uadc1*(((ln(VCC / (100000*Is))))*UT) / Uadc2) / UT))

[0062] To verify the accuracy of this solution, as shown in Table 1, the measured voltages of the test objects with resistances of 1K, 10K, 100K, 1M, 10M, and 100M were compared with the measured voltages of the test objects with resistance values ​​10% higher. The voltage deviation was greater than 2.4mV. The analog-to-digital converter of the MCU can accurately distinguish this voltage, which meets the detection requirements. Therefore, this solution can achieve an accuracy of 10%.

[0063] Table 1

[0064]

[0065] The above are merely embodiments of the present invention. The invention is not limited to the fields covered by these embodiments. Commonly known structures and characteristics in the solutions are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are able to access all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, under the guidance of this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. An insulation detection circuit for a charging station, characterized in that, The application relates to a voltage measurement circuit. The emitter and the base of the triode Q1 are short-circuited, and the emitter of the triode Q1 is connected with a measured object and the positive input end of the operational amplifier U1 respectively; the collector of the triode Q1 is grounded. One end of the resistor R1 is grounded, the other end of the resistor R1 is connected with one end of the resistor R2, and the other end of the resistor R2 is connected with the output end of the operational amplifier U1. The negative input end of the operational amplifier U1 is also connected with the other end of the resistor R1; the output end of the operational amplifier U1 is also connected with the first sampling port of the MCU. The power supply is connected with the measured object, and the voltage range of the power supply is 9-12V. The application further comprises a triode Q2, an operational amplifier U2, a resistor R3, a resistor R4 and a reference resistor R5.

2. The insulation detection circuit for a charging station according to claim 1, characterized in that: One end of the reference resistor R5 is connected with the power supply, and the other end of the reference resistor R5 is connected with the emitter of the triode Q2; the other end of the reference resistor R5 is also connected with the positive input end of the operational amplifier U2. The emitter of the triode Q2 is also short-circuited with the base, and the collector of the triode Q2 is grounded. One end of the resistor R3 is grounded, the other end of the resistor R3 is connected with one end of the resistor R4, and the other end of the resistor R4 is connected with the output end of the operational amplifier U2. The negative input end of the operational amplifier U2 is also connected with the other end of the resistor R3; the output end of the operational amplifier U2 is also connected with the second sampling port of the MCU. The MCU comprises an analog-to-digital converter ADC1 and an analog-to-digital converter ADC2, wherein the analog-to-digital converter ADC1 obtains a sampling signal from the first sampling port; the analog-to-digital converter ADC2 obtains a sampling signal from the second sampling port.

3. The insulation detection circuit for a charging station according to claim 2, characterized in that: The triode Q1 and the triode Q2 are both NPN triodes.

4. The insulation detection circuit for a charging station according to claim 3, characterized in that: The operational amplifier U1 and the operational amplifier U2 are low static current operational amplifiers.

5. The insulation detection circuit for a charging station according to claim 4, characterized in that: The MCU calculates the resistance Riso of the measured object according to the following formula:

6. The insulation detection circuit for a charging station according to claim 5, characterized in that: Riso = VCC / (Is*e^(UD / UT)) wherein VCC is the power supply voltage, Is is the reverse saturation current of the triode Q1 used as a diode, UD is the voltage applied to the triode Q1, and UT is the temperature voltage equivalent. ​

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