CN111812474A - Insulation detection circuit, system and method for DC charging pile - Google Patents

Insulation detection circuit, system and method for DC charging pile Download PDF

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Publication number
CN111812474A
CN111812474A CN202010807356.1A CN202010807356A CN111812474A CN 111812474 A CN111812474 A CN 111812474A CN 202010807356 A CN202010807356 A CN 202010807356A CN 111812474 A CN111812474 A CN 111812474A
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resistor
switch
voltage
resistance
insulation
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Inventor
胡敏康
夏显峰
周永志
王国玉
杨琦
肖杨
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NANJING NENGRUI AUTOMATION EQUIPMENT CO Ltd
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NANJING NENGRUI AUTOMATION EQUIPMENT CO Ltd
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Priority to CN202010807356.1A priority Critical patent/CN111812474A/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
    • G01R31/1227—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/025—Measuring very high resistances, e.g. isolation resistances, i.e. megohm-meters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/14—Measuring resistance by measuring current or voltage obtained from a reference source
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
    • G01R31/14—Circuits therefor, e.g. for generating test voltages, sensing circuits

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  • General Physics & Mathematics (AREA)
  • Electric Propulsion And Braking For Vehicles (AREA)
  • Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)

Abstract

The embodiment of the invention discloses a direct current charging pile insulation detection circuit, a system and a method, which comprises the following steps: the circuit comprises a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a first switch, a second switch, a third switch, a fourth switch and a fifth switch; the fourth switch, the first resistor, the second resistor, the third resistor, the fourth resistor and the fifth switch which are connected in series are connected in parallel with the fifth resistor, the first switch, the second switch and the sixth resistor which are connected in series, and the positive bus-to-ground insulation resistor and the negative bus-to-ground insulation resistor which are connected in series are connected in parallel; the first end of the fourth switch is electrically connected with the positive bus, and the first end of the fifth switch is electrically connected with the negative bus; the second end of the second resistor, the first end of the third switch, the first end of the third resistor, the second end of the first switch and the second end of the second switch are respectively grounded; the second end of the third switch is electrically connected with the first ends of the positive bus-to-ground insulation resistor and the negative bus-to-ground insulation resistor.

Description

Insulation detection circuit, system and method for DC charging pile
Technical Field
The embodiment of the invention relates to the technical field of new energy, in particular to a direct current charging pile insulation detection circuit, system and method.
Background
Electric automobile fills electric pile is new energy automobile's charging infrastructure. Direct current among the electric automobile fills electric pile, because of its characteristics that charge fast, is extensively laid. However, since the voltage of the dc charging post is large, a high requirement is placed on the insulating performance of the dc charging post in the design of the dc charging post.
As a high-voltage direct-current facility working outdoors for a long time, the high-voltage direct-current charging pile has a complex working environment, the insulating property of the high-voltage direct-current charging pile is influenced by factors such as liquid erosion, artificial damage, humidity change and the like, and the insulating property of the direct-current charging pile directly influences whether the charging safety of a user is ensured. Therefore, the insulation detection technology of the direct current charging pile is very important.
The direct current among the prior art fills electric pile insulation detection circuit and only chooses for use a control switch, and the insulation resistance value of positive, negative bus-bar terminal can receive the influence each other of both ends insulation value when calculating to influence the computational accuracy.
Disclosure of Invention
The embodiment of the invention provides a direct current charging pile insulation detection circuit, a system and a method, which are simple in structure and can realize efficient and accurate estimation of the insulation performance of a direct current charging pile.
In a first aspect, an embodiment of the present invention provides a dc charging pile insulation detection circuit, where the dc charging pile insulation detection circuit includes: the circuit comprises a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a first switch, a second switch, a third switch, a fourth switch and a fifth switch;
a first end of the fourth switch is electrically connected with the positive bus, and a second end of the fourth switch is respectively electrically connected with a first end of the first resistor and a first end of the positive bus to ground insulation resistor;
the second end of the first resistor is electrically connected with the first end of the second resistor;
the second end of the second resistor, the first end of the third switch and the first end of the third resistor are respectively grounded;
the second end of the third resistor is electrically connected with the first end of the fourth resistor;
a second end of the fourth resistor is electrically connected with a second end of the fifth switch and a second end of the negative bus-to-ground insulation resistor respectively;
the second end of the positive bus-to-ground insulation resistor and the first end of the negative bus-to-ground insulation resistor are respectively electrically connected with the second end of the third switch;
a first end of the fifth resistor is electrically connected with the positive electrode bus, and a second end of the fifth resistor is electrically connected with a first end of the first switch;
the second end of the first switch and the second end of the second switch are respectively grounded;
a first end of the second switch is electrically connected with a first end of the sixth resistor;
and the second end of the sixth resistor and the first end of the fifth switch are respectively electrically connected with the negative bus.
Optionally, the resistance value of the first resistor is equal to the resistance value of the fourth resistor;
the resistance value of the second resistor is equal to the resistance value of the third resistor;
the resistance value of the fifth resistor is equal to the resistance value of the sixth resistor.
Optionally, the resistance value of the first resistor is R1The resistance value of the second resistor is R2The resistance value of the third resistor is R3The resistance value of the fourth resistor is R4Wherein R is1＜＜R2，R3＜＜R4。
In a second aspect, an embodiment of the present invention further provides a system for detecting insulation of a dc charging pile, where the system for detecting insulation of a dc charging pile includes: the system comprises an analog-to-digital conversion module, a control module and the direct current charging pile insulation detection circuit of the first aspect;
the analog-to-digital conversion module is used for respectively acquiring the voltage at two ends of the second resistor and the voltage at two ends of the third resistor and respectively sending the voltage at two ends of the second resistor and the voltage at two ends of the third resistor to the control module;
the control module is used for determining the resistance value of the positive bus to ground insulation resistor and the resistance value of the negative bus to ground insulation resistor according to the voltage at the two ends of the second resistor and the voltage at the two ends of the third resistor.
In a third aspect, an embodiment of the present invention further provides a method for detecting insulation of a dc charging pile, where the detection is performed by using the dc charging pile insulation detection circuit of the first aspect, and the detection method includes:
closing the third switch, the fourth switch, and the fifth switch;
collecting a first voltage at two ends of the second resistor and a second voltage at two ends of the third resistor, and calculating a first ratio of the first voltage to the second voltage and a second ratio of the second voltage to the first voltage;
judging whether the first ratio or the second ratio is smaller than a preset ratio value or not;
if the first ratio or the second ratio is smaller than a preset ratio value, judging whether the first voltage or the second voltage is smaller than a preset voltage value;
and if the first voltage or the second voltage is smaller than a preset voltage value, determining that the positive bus-to-ground insulation resistance or the negative bus-to-ground insulation resistance is short-circuited.
Optionally, if the first voltage and the second voltage are greater than or equal to a preset voltage value, determining a resistance value of the positive bus to ground insulation resistor and a resistance value of the negative bus to ground insulation resistor based on a first relational expression, where the first relational expression is:
Figure BDA0002629631670000031
Figure BDA0002629631670000041
wherein R isPIs the insulation resistance, R, of the positive bus bar to groundnIs the insulation resistance, R, of the negative bus to ground1Is the first resistance, R2Is the second resistance, R3Is the third resistance, R4Is the fourth resistor, U2Is a first voltage, U, across the second resistor3Is a second voltage across the third resistor.
Optionally, if the first ratio and the second ratio are greater than or equal to a preset ratio, the first switch, the third switch, the fourth switch, and the fifth switch are closed, and the second switch is opened;
collecting a third voltage at two ends of the second resistor and a fourth voltage at two ends of the third resistor;
closing the second, third, fourth, and fifth switches and opening the first switch;
collecting a fifth voltage at two ends of the second resistor and a sixth voltage at two ends of the third resistor; determining the resistance value of the positive bus to ground insulation resistor and the resistance value of the negative bus to ground insulation resistor based on a second relational expression, wherein the second relational expression is as follows:
Figure BDA0002629631670000042
Figure BDA0002629631670000043
wherein R isPIs the insulation resistance, R, of the positive bus bar to groundnInsulating electricity to ground for the negative bus barR is1Is the first resistance, R2Is the second resistance, R3Is the third resistance, R4Is the fourth resistance, R5Is the fifth resistance, R6Is the sixth resistance, U'2Is a third voltage, U ', across the second resistor'3Is a fourth voltage, U ″, across the third resistor2Is a fifth voltage, U ″, across the second resistor3Is a sixth voltage across the third resistor.
Optionally, after determining the resistance value of the positive bus to ground insulation resistor and the resistance value of the negative bus to ground insulation resistor, the method further includes:
judging whether the resistance value of the positive bus to the ground insulation resistor is smaller than that of the negative bus to the ground insulation resistor;
if so, determining that the insulation performance of the direct current charging pile is qualified when the resistance value of the positive bus to ground insulation resistance is greater than or equal to a preset resistance value;
if not, when the resistance value of the insulation resistor of the negative bus to the ground is larger than or equal to the preset resistance value, the insulation performance of the direct current charging pile is determined to be qualified.
Optionally, before closing the third switch, the fourth switch, and the fifth switch, the method further includes:
turning off the first switch, the second switch, the third switch, the fourth switch, and the fifth switch;
collecting the voltage at two ends of the second resistor and the voltage of the third resistor;
judging whether the voltage at two ends of the second resistor and the voltage of the third resistor are both zero or not;
if so, determining that the first switch, the second switch, the third switch, the fourth switch and the fifth switch are disconnected;
otherwise, the first switch, the second switch, the third switch, the fourth switch and the fifth switch are detected until the voltage at the two ends of the second resistor and the voltage of the third resistor are both zero.
Optionally, closing the third switch, the fourth switch, and the fifth switch includes:
closing the fourth switch and the fifth switch;
collecting the voltage at two ends of the second resistor or the voltage of the third resistor;
determining a total voltage value of the system according to the voltage at two ends of the second resistor or the voltage of the third resistor;
and when the total pressure value of the system is determined to be within a preset total pressure range, closing the third switch, the fourth switch and the fifth switch.
According to the insulation detection circuit, the insulation detection system and the insulation detection method for the direct-current charging pile, provided by the embodiment of the invention, the insulation resistance of the positive bus to the ground and the insulation resistance of the negative bus to the ground can be determined by setting the first resistor, the second resistor, the third resistor, the fourth resistor, the fifth resistor, the sixth resistor, the first switch, the second switch, the third switch, the fourth switch and the fifth switch, so that the structure is simple; in addition, the mutual influence of the insulation resistance of the positive bus end and the negative bus end when the insulation resistance is calculated is eliminated by respectively controlling the on-off of the first switch and the second switch, the anti-interference capability of the system is improved, and the efficient and accurate estimation of the insulation performance of the direct current charging pile system can be realized; in addition, through the break-make of control third switch, fourth switch and fifth switch simultaneously, when needs carry out insulation detection to direct current charging pile, then close third switch, fourth switch and fifth switch, when need not carry out insulation detection to direct current charging pile, then break off third switch, fourth switch and fifth switch, the time that can nimble control detection insulating properties.
Drawings
Fig. 1 is a schematic structural diagram of a dc charging pile insulation detection circuit according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a dc charging pile insulation detection system according to a second embodiment of the present invention;
fig. 3 is a flowchart of a method for detecting insulation of a dc charging pile according to a third embodiment of the present invention;
fig. 4 is a flowchart of a method for detecting insulation of a dc charging pile according to a fourth embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
Example one
Fig. 1 is a schematic structural diagram of a dc charging pile insulation detection circuit according to an embodiment of the present invention, and as shown in fig. 1, the dc charging pile insulation detection circuit according to the embodiment of the present invention includes: a first resistor R1A second resistor R2A third resistor R3A fourth resistor R4A fifth resistor R5A sixth resistor R6A first switch S1A second switch S2And a third switch S3And a fourth switch S4And a fifth switch S5(ii) a Fourth switch S4Is electrically connected with the positive electrode bus U +, and a fourth switch S4Respectively with the first resistor R1First end, positive bus bar to ground insulation resistance RpIs electrically connected with the first end of the first terminal; a first resistor R1Second terminal and second resistor R2Is electrically connected with the first end of the first terminal; a second resistor R2Second terminal and third switch S3First terminal, third resistor R3The first ends of the first and second electrodes are respectively grounded; third resistor R3Second terminal and fourth resistor R4Is electrically connected with the first end of the first terminal; a fourth resistor R4Respectively with the fifth switch S5And the insulation resistance R of the negative bus to the groundnIs electrically connected with the second end of the first terminal; insulation resistance R of positive bus to groundpAnd the insulation resistance R of the negative bus to the groundnRespectively with the third switch S3Is electrically connected with the second end of the first terminal; fifth resistor R5The first end of the positive electrode is electrically connected with a positive electrode bus U +, and the fifth end is electrically connected with a negative electrode busResistance R5Second terminal and first switch S1Is electrically connected with the first end of the first terminal; first switch S1Second terminal and second switch S2The second ends of the first and second electrodes are respectively grounded; a second switch S2First terminal and sixth resistor R6Is electrically connected with the first end of the first terminal; a sixth resistor R6And a fifth switch S5Are respectively electrically connected with the negative bus bar U-.
The direct-current charging pile insulation detection circuit provided by the embodiment is directly electrically connected with a direct-current charging pile positive bus U + and a direct-current charging pile negative bus U-so as to realize an insulation detection function. It should be noted that, in order to clearly show the insulating performance of the dc charging pile positive bus U + to the ground and the insulating performance of the dc charging pile negative bus U-to-the-ground, in this embodiment, the insulating performance of the dc charging pile positive bus U + to the ground is equivalent to the insulating resistance R of the positive bus to the groundpAnd the U-to-ground insulation performance of the negative bus of the direct current charging pile is equivalent to the insulation resistance R of the negative bus to the groundn。
Illustratively, the positive bus bar ground insulation resistance R may be determined, for example, bypAnd insulation resistance R of negative bus to groundn: closing the fourth switch S4And a third switch S3The fifth switch S5And a first switch S1Opening the second switch S2For example, the second resistances R can be measured by the analog-to-digital conversion module respectively2Voltage across and third resistor R3The voltage across, illustratively, the second resistor R2A first voltage sampling point O is arranged at the second end of the first voltage sampling circuit1And at the third resistance R3Second terminal of the first voltage sampling point O2First voltage sampling point O1And a second voltage sampling point O2Connected with the analog-to-digital conversion module, and respectively measuring the second resistors R at the moment by the analog-to-digital conversion module2Voltage across and third resistor R3The voltage across; at this time, the second resistor R2The voltage across is, for example, U'2A third resistor R3The voltage across is, for example, U'3From kirchhoff's current law, the following equation can be obtained:
Figure BDA0002629631670000081
then the fourth switch S is closed and opened4And a third switch S3The fifth switch S5And a second switch S2Opening the first switch S1The second resistors R can then be detected separately, for example by means of an analog-to-digital converter2Voltage across and third resistor R3Voltage across, at this time, the second resistor R2The voltage across the terminals being, for example, U2A third resistor R3The voltage across the terminals being, for example, U3From kirchhoff's current law, the following equation can be obtained:
Figure BDA0002629631670000082
according to the two equations, the insulation resistance R of the positive bus of the direct current charging pile to the ground can be determinedpComprises the following steps:
Figure BDA0002629631670000083
insulation resistance R of negative bus to groundnComprises the following steps:
Figure BDA0002629631670000091
will measure the closing of the fourth switch S4And a third switch S3The fifth switch S5And a first switch S1Opening the second switch S2While the second resistor R2Voltage U 'at both ends'2A third resistor R3Voltage U 'at both ends'3And then closing and opening the fourth switch S4And a third switch S3The fifth switch S5And a second switch S2Opening the first switch S1While the second resistor R2Voltage U' at both ends2A third resistor R3Voltage U' at both ends3Substituting into the above equation, and thus,the insulation resistance R of the positive bus to the ground can be determinedpResistance value of (3) and insulation resistance R of negative bus to groundnBy controlling the first switches S separately1And a second switch S2The switching-on and switching-off of the system eliminates the mutual influence of the insulation resistance of the positive and negative bus ends when the insulation resistance is calculated, improves the anti-interference capability of the system, and improves the detection precision of the insulation performance of the direct current charging pile.
In addition, the embodiment of the invention sets the third switch S3And a fourth switch S4And a fifth switch S5. When the insulation detection of the direct current charging pile is needed, the third switch S is closed3And a fourth switch S4And a fifth switch S5When the insulation detection of the direct current charging pile is not needed, the third switch S is disconnected3And a fourth switch S4And a fifth switch S5The time for detecting the insulating property can be flexibly controlled.
Optionally, a first switch S1A second switch S2And a third switch S3And a fourth switch S4And a fifth switch S5For example, it may comprise an electronic switch or a relay used as a switch, for example, the first switch S may be controlled separately by an external control module1A second switch S2And a third switch S3And a fourth switch S4And a fifth switch S5Closed or open.
In summary, the insulation detection circuit for the dc charging pile provided by the embodiment of the present invention can determine the insulation resistance of the positive bus to the ground and the insulation resistance of the negative bus to the ground by setting the first resistor, the second resistor, the third resistor, the fourth resistor, the fifth resistor, the sixth resistor, the first switch, the second switch, the third switch, the fourth switch, and the fifth switch, and has a simple structure; in addition, the on-off of the first switch and the second switch is controlled respectively, so that the mutual influence of the insulation resistance of the positive bus end and the negative bus end when the insulation resistance is calculated is eliminated, the anti-interference capability of the system is improved, and the effect of efficiently and accurately estimating the insulation performance of the direct-current charging pile system can be realized; in addition, through the break-make of control third switch, fourth switch and fifth switch simultaneously, when needs carry out insulation detection to direct current charging pile, then close third switch, fourth switch and fifth switch, when need not carry out insulation detection to direct current charging pile, then break off third switch, fourth switch and fifth switch, the time that can nimble control detection insulating properties.
Optionally, with continued reference to FIG. 1, a first resistor R1Is equal to the fourth resistor R4The resistance value of (1); a second resistor R2Is equal to the third resistor R3The resistance value of (1); fifth resistor R5Is equal to the sixth resistor R6The resistance value of (c). The advantages of the arrangement are high detection precision, simple calculation and short data processing time.
Optionally, with continued reference to FIG. 1, a first resistor R1Has a resistance value of R1A second resistance R2Has a resistance value of R2Third resistor R3Has a resistance value of R3Fourth resistor R4Has a resistance value of R4Wherein R is1＜＜R2，R3＜＜R4。
The voltage of the dc charging post is considered to be very high, for example up to several hundred volts. Therefore, the present embodiment is implemented by setting the first resistor R1A fourth resistor R4A fifth resistor R5And a sixth resistor R6Wherein the first resistor R1A fourth resistor R4A fifth resistor R5And a sixth resistor R6Is relatively large, through the first resistor R1A fourth resistor R4A fifth resistor R5And a sixth resistor R6The voltage division is carried out, so that the current of the whole direct current charging pile insulation detection circuit is small, and in addition, the second resistor R2Is much smaller than the first resistor R1And a third resistor R3Is much smaller than the fourth resistor R4So that the second resistor R2Voltage across and third resistor R3The voltage at two ends is small, so that the external control module is favorable for the second resistor R2Voltage across and third resistor R3And collecting the voltage at two ends.
Illustratively, the first resistor R1Is 200k omega, and a second resistor R2Has a resistance value of 750 omega, and a third resistor R3Has a resistance value of 750 omega, and a fourth resistor R4Is 200k omega, and a fifth resistor R5Has a resistance value of 884k omega, and a sixth resistor R6Has a resistance value of 884k omega. The first resistor R is1A fourth resistor R4A fifth resistor R5And a sixth resistor R6The resistance value of (1) includes but is not limited to the above examples, and can be adjusted by those skilled in the art according to actual conditions.
Example two
Fig. 2 is a schematic structural diagram of a dc charging pile insulation detection system according to a second embodiment of the present invention, and as shown in fig. 2, the dc charging pile insulation detection system includes an analog-to-digital conversion module 10, a control module 20, and a dc charging pile insulation detection circuit 30 according to the first embodiment; the analog-to-digital conversion module 10 is used for respectively acquiring the second resistors R2Voltage across and third resistor R3Voltage across and second resistor R2Voltage across and third resistor R3The voltages at the two ends are respectively sent to the control module 20; the control module 20 is configured to control the second resistor R2Voltage across and third resistor R3Voltage at two ends determines insulation resistance R of positive bus to groundpResistance value of (3) and insulation resistance R of negative bus to groundnThe resistance value of (c).
In particular, the second resistor R2First terminal of (1), i.e. first voltage sampling point O1And a third resistor R3Second terminal of (1), i.e. second voltage sampling point O2Respectively electrically connected with the analog-to-digital conversion module 10 when the first switch S1A second switch S2And a third switch S3And a fourth switch S4And a fifth switch S5When the resistors are in different states, the analog-to-digital conversion module 10 respectively collects the second resistors R2Voltage across and third resistor R3The voltage at the two ends is sent to the control module 20, and the control module 20 is based on the second resistor R2Voltage across and third resistor R3Voltage determination positive bus pair at two endsGround insulation resistance RpResistance value of (3) and insulation resistance R of negative bus to groundnBased on the positive bus bar to ground insulation resistance RpResistance value of (3) and insulation resistance R of negative bus to groundnThe resistance value of the direct current charging pile determines whether the insulation performance of the direct current charging pile is qualified. Because the insulation detection system of the dc charging pile includes the insulation detection circuit 30 of the dc charging pile in the above embodiment, the insulation detection system of the dc charging pile provided in the embodiment of the present invention also has the beneficial effects described in the above embodiment, and details are not described here.
Alternatively, the analog-to-digital conversion module 10 may comprise, for example, an electronic circuit or an integrated IC that converts an analog signal into a digital signal.
Alternatively, the control module 20 may include a device having a control function, such as a Microcontroller Unit (MCU).
Optionally, with reference to fig. 2, the dc charging pile insulation detection system further includes a centralized control display screen 40, the centralized control display screen 40 is electrically connected to the control module 20, and the insulation fault is visually displayed through the centralized control display screen 40.
EXAMPLE III
Fig. 3 is a flowchart of a dc charging pile insulation detection method according to a third embodiment of the present invention, where the method uses the dc charging pile insulation detection circuit provided in any of the embodiments to perform detection. As shown in fig. 3, the method for detecting insulation of a dc charging pile according to the embodiment of the present invention may specifically include the following steps:
and S110, closing the third switch, the fourth switch and the fifth switch.
Wherein, with continued reference to fig. 1, the third switch S is closed3And a fourth switch S4And a fifth switch S5。
S120, collecting a first voltage at two ends of the second resistor and a second voltage at two ends of the third resistor, and calculating a first ratio of the first voltage to the second voltage and a second ratio of the second voltage to the first voltage.
S130, judging whether the first ratio or the second ratio is smaller than a preset ratio.
Therein, see furtherFIG. 1, collecting the second resistance R2First voltage U at both ends2And a third resistor R3Second voltage U across3. Because of the insulation resistance R of the positive bus to the groundpAnd insulation resistance R of negative bus to groundnThe difference between the two is very large, or the difference between the two is almost the same, so the situation is discussed separately, and the special situation is processed preferentially. If the insulation resistance R of the positive bus to the ground ispIs far less than the insulation resistance R of the cathode bus to the groundnOr insulation resistance R of negative bus to groundnIs far less than the insulation resistance R of the positive bus to the groundpAnd the situation that the positive pole and the negative pole of the direct current charging pile are short-circuited at one end can occur. And because of the first resistor R1And a second resistor R2Insulation resistance R to ground from positive buspIn parallel, a third resistor R3A fourth resistor R4Insulation resistance R to ground from cathode busnIn parallel connection, when the positive pole of the direct current charging pile is short-circuited, the direct current charging pile is characterized by a second resistor R2First voltage U at both ends2Much smaller than the third resistance R3Second voltage U across3(ii) a Or, the third resistor R3Second voltage U across3Much smaller than the second resistance R2First voltage U at both ends2. The embodiment calculates the first voltage U2And a second voltage U3First ratio and second voltage U3And a first voltage U2And comparing the first ratio or the second ratio with a preset ratio value to determine whether the insulation resistance of the positive and negative buses of the direct current charging pile to the ground is far greater at one end than at the other end.
S140, if the first ratio or the second ratio is smaller than the preset ratio, whether the first voltage or the second voltage is smaller than the preset voltage value is judged.
If the first ratio or the second ratio is smaller than the preset ratio, the insulation resistance R of the positive bus to the ground is indicatedpIs much smaller than the insulation resistance R of the cathode bus to the groundnOr insulation resistance R of negative bus to groundnMuch smaller than the positive bus to groundInsulation resistance RpHowever, it is not necessary that the positive and negative electrodes of the dc charging post have a short circuit at one end. Therefore, it is necessary to further determine the short circuit condition, specifically, the second resistor R2First voltage U at both ends2Or a third resistor R3Second voltage U across3Whether it is zero. However, considering the influence of the noise of the electronic circuit, the second resistor R is collected when one end of the positive and negative buses is short-circuited2First voltage U at both ends2Or a third resistor R3Second voltage U across3Not necessarily zero, so the present embodiment determines the first voltage U2Or a second voltage U3Whether the voltage value is smaller than the preset voltage value or not, wherein the preset voltage value is close to 0V but not equal to 0V, for example, 0.5V can be achieved, so that misjudgment caused by the influence of noise of the electronic circuit is avoided, and the detection precision is improved.
S150, if the first voltage or the second voltage is smaller than the preset voltage value, determining that the positive bus is short-circuited to the ground insulation resistor or the negative bus is short-circuited to the ground insulation resistor.
If the first voltage or the second voltage is smaller than the preset voltage value, for example, the first voltage or the second voltage is smaller than 0.5V, it is determined that the positive bus-to-ground insulation resistance or the negative bus-to-ground insulation resistance is short-circuited, that is, the insulation performance of the whole direct current charging pile is unqualified.
It should be noted that, a person skilled in the art may set the preset voltage value and the preset ratio value according to actual situations, and the embodiment is not particularly limited.
In this embodiment, when the third switch, the fourth switch, and the fifth switch are turned off, a first voltage at two ends of the second resistor and a second voltage at two ends of the third resistor are collected, a first ratio of the first voltage to the second voltage and a second ratio of the second voltage to the first voltage are calculated, and the first ratio or the second ratio is compared with a preset ratio value and the first voltage or the second voltage is compared with a preset voltage value to determine whether the ground insulation resistance of the positive bus to the ground insulation resistance or the ground insulation resistance of the negative bus to the ground insulation resistance is short-circuited, so that a problem that complicated operation is required when the ground insulation resistance of the positive bus to the ground insulation resistance or the ground insulation resistance of the negative bus to the ground insulation resistance is short-circuited is avoided, and operation steps are reduced and operation efficiency is improved.
Example four
Fig. 4 is a flowchart of a method for detecting insulation of a dc charging pile according to a fourth embodiment of the present invention. The present embodiment is optimized based on the above technical solutions. The same or corresponding terms as those in the above embodiments are not explained in detail herein.
Referring to fig. 4, the method for detecting insulation of the dc charging pile in this embodiment may specifically include the following steps:
and S210, collecting the voltage at two ends of the second resistor and the voltage of the third resistor.
Wherein, referring to fig. 1, the second resistance R is acquired2Voltage across and third resistor R3To determine the first switch S1A second switch S2And a third switch S3And a fourth switch S4And a fifth switch S5Whether it is in an open state, i.e., it is determined that the entire circuit is in an open state. Collecting the second resistance R by judging2Voltage across and third resistor R3Whether the voltages at the two ends are zero or not is judged, and then the first switch S is judged1A second switch S2And a third switch S3And a fourth switch S4And a fifth switch S5Is open.
S220, judging whether the voltage at the two ends of the second resistor and the voltage of the third resistor are both zero or not; if yes, go to S230; if not, the process proceeds to S240.
S230, determining that the first switch, the second switch, the third switch, the fourth switch and the fifth switch are normal; proceed to S250.
Wherein, if the voltage at the two ends of the second resistor and the voltage of the third resistor are both zero, the first switch S is determined1A second switch S2And a third switch S3And a fourth switch S4And a fifth switch S5In the off state, the next step, S250, is entered.
S240, the first switch, the second switch, the third switch, the fourth switch and the fifth switch are pairedDetecting until the second resistor R2Voltage across and third resistor R3All voltages of (1) are zero.
Wherein, if the voltage at the two ends of the second resistor and the voltage of the third resistor are both not zero, the first switch S cannot be determined1A second switch S2And a third switch S3And a fourth switch S4And a fifth switch S5Is off, it needs to be checked until the values of the first voltage and the second voltage are both zero, i.e. the first switch S1A second switch S2And a third switch S3And a fourth switch S4And a fifth switch S5The disconnection, i.e., the detection circuit is normal, proceeds to the next step, i.e., S250.
And S250, closing the fourth switch and the fifth switch.
Wherein, referring to fig. 1, the fourth switch S is closed4And a fifth switch S5The other switches remain open.
And S260, collecting the voltage at two ends of the second resistor or the voltage at two ends of the third resistor.
And S270, determining the total pressure value of the system according to the voltage at the two ends of the second resistor or the voltage at the two ends of the third resistor.
Wherein, referring to fig. 1, when the fourth switch S is closed4And a fifth switch S5While making the second resistance R collected2Voltage at both ends is UaA third resistor R3Voltage at both ends is UbThe total pressure value of the system is UDCThen U isDC＝[Ua*(R1+R2+R3+R4)]/R2。
And S280, when the total pressure value of the system is determined to be within the preset total pressure range, closing the third switch, the fourth switch and the fifth switch.
When the electric automobile is charged by the direct-current charging pile, information interaction can be carried out between the direct-current charging pile and a Battery Management System (BMS) on the electric automobile, and particularly, the BMS can provide requirements for the direct-current charging pile, namely, the working voltage required by the electric automobile. At the moment, the control module detects the direct current charging pile based on the detection result so as to ensureWhether the working voltage provided by the direct-current charging pile is within the working voltage requirement range provided by the BMS is determined, when the total pressure value of the system is within the preset total pressure range, the total pressure of the system is indicated to be within a normal working interval, the electric automobile can be charged, and the next step is carried out, namely the third switch S is closed3And a fourth switch S4And a fifth switch S5. Illustratively, the BMS can provide the DC charging pile with the operating voltage required by the electric vehicle as U0And the control module determines the total system pressure value provided by the direct current charging pile based on the total system pressure value, and if the total system pressure value is within a preset total pressure range, wherein the preset total pressure range is 96% U0～110％U0If the total pressure of the system is within the normal working interval, the electric automobile can be charged. Therefore, the damage to the insulation detection circuit of the direct current charging pile and other devices, such as an analog-to-digital conversion module, caused by higher system total voltage is avoided.
Optionally, before the third switch, the fourth switch and the fifth switch are closed, the first switch, the second switch, the third switch, the fourth switch and the fifth switch are firstly closed.
S290, collecting a first voltage at two ends of the second resistor and a second voltage at two ends of the third resistor, and calculating a first ratio of the first voltage to the second voltage and a second ratio of the second voltage to the first voltage.
Wherein the second resistance R can be detected, for example, by an analog-to-digital conversion module2First voltage U at both ends2And a third resistor R3Second voltage U across3Calculate U2/U3Is the first ratio, and calculating U3/U2I.e. the second ratio.
S300, judging whether the first ratio or the second ratio is smaller than a preset ratio; if yes, the process goes to S310; if not, the process proceeds to S340.
Wherein, if one of the first ratio or the second ratio is smaller than the preset ratio, the insulation resistance R of the positive bus to the ground is indicatedpIs far less than the insulation resistance R of the cathode bus to the groundnOr insulation resistance R of negative bus to groundnIs far less than the insulation resistance R of the positive bus to the groundpAt this time, there are two cases, the first case: one end of the positive electrode and the negative electrode of the direct current charging pile may be short-circuited; in the second case: although the positive bus bar is insulated from the ground by the resistor RpIs far less than the insulation resistance R of the cathode bus to the groundnOr insulation resistance R of negative bus to groundnIs far less than the insulation resistance R of the positive bus to the groundpHowever, the insulation resistance R of the positive bus bar to the groundpAnd insulation resistance R of negative bus to groundnNone are shorted. It is necessary to further determine whether it is the first case or the second case, i.e., to proceed to S310. If the first ratio and the second ratio are both larger than or equal to a preset ratio, the insulation resistance R of the positive bus to the ground is indicatedpAnd insulation resistance R of negative bus to groundnThe phase difference is almost zero, and at the moment, the insulation resistance R of the positive bus to the ground needs to be further determinedpAnd insulation resistance R of negative bus to groundnS340 is entered.
S310, judging whether the first voltage or the second voltage is smaller than a preset voltage value; if yes, go to S320; if not, the process proceeds to S330.
Wherein, if direct current fills electric pile positive and negative pole and has one end short circuit, then one in the first voltage or the second voltage of gathering is zero. However, considering the influence of the noise of the electronic circuit, the second resistor R is collected when one end of the positive and negative buses is short-circuited2First voltage U at both ends2Or a third resistor R3Second voltage U across3The first voltage or the second voltage is not necessarily zero, so the embodiment determines whether the first voltage or the second voltage is smaller than a preset voltage value, wherein the preset voltage value is close to 0V but not equal to 0V, for example, may be 0.5V, so as to avoid the erroneous determination caused by the noise of the electronic circuit itself, and improve the detection accuracy. If the first voltage U is2Or a second voltage U3If the voltage value is less than the preset voltage value, the insulation resistance R of the positive bus to the ground is indicatedpOr negative bus-to-ground insulation resistance RnShort-circuiting, i.e., entering S320. If the first voltage U is2And a second voltage U3Is greater than or equal to a preset voltage value,it indicates that the positive bus bar has insulation resistance to ground RpIs far less than the insulation resistance R of the cathode bus to the groundnOr insulation resistance R of negative bus to groundnIs far less than the insulation resistance R of the positive bus to the groundpHowever, the insulation resistance R of the positive bus bar to the groundpAnd insulation resistance R of negative bus to groundnAre not short-circuited, and at the moment, the insulation resistance R of the positive bus to the ground needs to be further determinedpAnd insulation resistance R of negative bus to groundnThe process proceeds to S330.
And S320, determining the insulation resistance of the positive bus to the ground or the insulation resistance of the negative bus to the ground is short-circuited.
Wherein, if the first voltage U is2Or a second voltage U3Is less than the preset voltage value, the insulation resistance R of the positive bus to the ground is determinedpOr negative bus-to-ground insulation resistance RnAnd (4) short-circuiting. At this moment, the insulating property of the whole direct current charging pile is judged to be unqualified.
Optionally, if the first voltage U is2The voltage value is smaller than the preset voltage value, for example, the insulation fault can be directly displayed on a centralized control display screen of the direct current charging pile; similarly, if the second voltage U is higher than the first voltage U3And if the voltage value is smaller than the preset voltage value, directly displaying the insulation fault on a centralized control display screen of the direct current charging pile.
S330, determining the resistance value of the positive bus to ground insulation resistor and the resistance value of the negative bus to ground insulation resistor based on the first relational expression; the first relation is:
Figure BDA0002629631670000181
Figure BDA0002629631670000182
wherein R isPInsulation resistance to ground for positive bus bar, RnIs the insulation resistance of the negative bus to ground, R1Is a first resistance, R2Is a second resistance, R3Is a third resistance, R4Is a fourth resistor, U2Is a second resistor R2At both ends of the firstA voltage, U3Is a third resistor R3A second voltage across; then, the process proceeds to S390.
If not, namely the first voltage and the second voltage are greater than or equal to the preset voltage value, the fact that the insulation resistance R of the positive bus to the ground is maintained is indicatedpIs far less than the insulation resistance R of the cathode bus to the groundnOr insulation resistance R of negative bus to groundnIs far less than the insulation resistance R of the positive bus to the groundpHowever, the insulation resistance R of the positive bus bar to the groundpAnd insulation resistance R of negative bus to groundnNone are shorted. At this time, the third switch S may be closed based on S2803And a fourth switch S4And a fifth switch S5According to kirchhoff's current law, the following equation is obtained:
Figure BDA0002629631670000191
or,
Figure BDA0002629631670000192
because of the insulation resistance R of the positive bus to the groundpIs far less than the insulation resistance R of the cathode bus to the groundnOr insulation resistance R of negative bus to groundnIs far less than the insulation resistance R of the positive bus to the groundpIf the positive bus bar is insulated from ground by the resistance RpIs far less than the insulation resistance R of the cathode bus to the groundnThen, the insulation resistance of whole direct current stake of charging does:
Figure BDA0002629631670000193
if the insulation resistance R of the negative bus to the groundnFar less than the insulation resistance R of the positive bus to the groundpThen, the insulation resistance of whole direct current stake of charging does:
Figure BDA0002629631670000194
it can be understood that if the insulation resistance R of the positive bus bar to ground is providedpIs much smaller than the insulation resistance R of the cathode bus to the groundnAt this time, only the minimum resistance, namely the insulation resistance R of the positive bus to the ground needs to be calculatedpI.e., if the minimum resistance, i.e., the insulation resistance R of the positive bus bar to groundpWithin the qualified range, the insulation resistance R of the negative bus to the groundnIs necessarily in an acceptable range, so the insulation resistance R of the current-pole bus to the groundpIs much smaller than the insulation resistance R of the cathode bus to the groundnOr insulation resistance R of negative bus to groundnFar less than the insulation resistance R of the positive bus to the groundpOnly the minimum resistance needs to be calculated, so that the operation steps are reduced, and the operation efficiency is improved. Specifically, the second resistance R acquired in S2902First voltage U at both ends2And a third resistor R3Second voltage U across3The minimum resistance can be determined by substituting the formula (3) or (4). The minimum resistance is determined and the process proceeds to S390.
S340, closing the first switch, the third switch, the fourth switch, and the fifth switch, and opening the second switch.
If the first ratio and the second ratio are larger than or equal to the preset voltage value, the first switch S is closed1And a third switch S3And a fourth switch S4And a fifth switch S5And opening the second switch S2。
And S350, collecting a third voltage at two ends of the second resistor and a fourth voltage at two ends of the third resistor.
Wherein, when the first switch S1And a third switch S3And a fourth switch S4And a fifth switch S5Closed and second switch S2When the circuit is disconnected, the second resistor R is collected2Third Voltage U 'at both ends'2And a third resistor R3Fourth voltage U 'at two ends'3. The following equation can be obtained from kirchhoff's current law:
Figure BDA0002629631670000201
wherein R isPInsulation resistance to ground for positive bus bar, RnIs the insulation resistance of the negative bus to ground, R1Is a first resistance, R2Is a second resistance, R3Is a third resistance, R4Is a fourth resistance, R5Is a fifth resistance, R6Is a sixth resistance, U'2Is a third voltage, U ', across the second resistor'3Is the fourth voltage across the third resistor.
And S360, closing the second switch, the third switch, the fourth switch and the fifth switch and opening the first switch.
Wherein the second switch S is closed2And a third switch S3And a fourth switch S4And a fifth switch S5And opening the first switch S1。
And S370, collecting a fifth voltage at two ends of the second resistor and a sixth voltage at two ends of the third resistor.
Wherein when the second switch S2And a third switch S3、S4And a fifth switch S5Closed and first switch S1When the circuit is disconnected, the second resistor R is collected2Fifth voltage U ″' at both ends2And a third resistor R3Sixth voltage U' at both ends3. The following equation can be obtained from kirchhoff's current law:
Figure BDA0002629631670000202
wherein, U ″)2Is the fifth voltage, U ″, across the second resistor3Is the sixth voltage across the third resistor. I.e. the first switch S1And a second switch S2The time-sharing closing eliminates the mutual influence of the insulation resistance values of the positive bus terminal and the negative bus terminal when the insulation resistance value is calculated, and improves the anti-interference capability of the system.
S380, determining the resistance value of the positive bus to the ground insulation resistor and the resistance value of the negative bus to the ground insulation resistor based on a second relational expression; the second relation is:
Figure BDA0002629631670000203
Figure BDA0002629631670000211
then, the process proceeds to S390.
Wherein, it is respectively for to try to find direct current according to equation (5) and equation (6) fills electric pile positive, negative bus insulation resistance:
Figure BDA0002629631670000212
Figure BDA0002629631670000213
then the first switch S will be closed1And a third switch S3And a fourth switch S4And a fifth switch S5And opening the second switch S2Second resistance R of time acquisition2Third Voltage U 'at both ends'2And a third resistor R3Fourth voltage U 'at two ends'3And when the second switch S is on2And a third switch S3、S4And a fifth switch S5Closed and first switch S1When the circuit is disconnected, the second resistor R is collected2Fifth voltage U ″' at both ends2And a third resistor R3Sixth voltage U' at both ends3The insulation resistance R of the positive bus to the ground can be determined by substituting the formulas (7) and (8)pAnd insulation resistance R of negative bus to groundn. Then, the process proceeds to S390.
S390, judging whether the resistance value of the positive bus to the ground insulation resistor is smaller than that of the negative bus to the ground insulation resistor; if yes, entering S400; if not, the process proceeds to S410.
According to the national standard, the minimum value of the resistance value of the positive bus to the ground insulation resistor and the resistance value of the negative bus to the ground insulation resistor is taken and used as the insulation resistor of the whole direct current charging pile. If the resistance value of the ground insulation resistor of the positive bus is smaller than that of the ground insulation resistor of the negative bus, the operation goes to S410; if the resistance value of the positive bus to ground insulation resistor is greater than or equal to the resistance value of the negative bus to ground insulation resistor, the process proceeds to S410.
And S400, when the resistance value of the positive bus to the ground insulation resistor is larger than or equal to a preset resistance value, determining that the insulation performance of the direct current charging pile is qualified.
And at the moment, the insulation resistance of the positive bus to the ground is used as the insulation resistance of the whole direct current charging pile. And when the resistance value of the positive bus to the ground insulation resistor is greater than or equal to the preset resistance value, determining that the insulation performance of the direct current charging pile is qualified.
And S410, when the resistance value of the insulation resistor of the negative bus to the ground is larger than or equal to the preset resistance value, determining that the insulation performance of the direct current charging pile is qualified.
And at the moment, the insulation resistance of the negative bus to the ground is used as the insulation resistance of the whole direct current charging pile. And when the resistance value of the negative bus to the ground insulation resistor is greater than or equal to the preset resistance value, determining that the insulation performance of the direct current charging pile is qualified.
Illustratively, take the positive bus bar to ground insulation resistance RpAnd insulation resistance R of negative bus to groundnThe smaller one of the two is the insulation resistance R of the whole direct current charging pileJ. Setting the positive and negative bus voltage of the DC charging pile to UDCWhen R isJ/UDCWhen the voltage is larger than or equal to 100 omega/V, judging that the insulation performance of the whole direct current charging pile is qualified; when R isJ/UDCAnd if the voltage is less than 100 omega/V, judging that the insulation performance of the whole direct current charging pile is unqualified.
According to the insulation detection method for the direct current charging pile, unnecessary operation steps are avoided, operation efficiency and operation precision are improved, meanwhile, the influence on detection precision when the states of the first switch, the second switch, the third switch, the fourth switch and the fifth switch are abnormal is avoided, and a high system total voltage is avoided for an insulation detection circuit of the direct current charging pile and other devices.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims (10)

1. The utility model provides a direct current fills electric pile insulation detection circuit which characterized in that includes: the circuit comprises a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a first switch, a second switch, a third switch, a fourth switch and a fifth switch;
a first end of the fourth switch is electrically connected with the positive bus, and a second end of the fourth switch is respectively electrically connected with a first end of the first resistor and a first end of the positive bus to ground insulation resistor;
the second end of the first resistor is electrically connected with the first end of the second resistor;
the second end of the second resistor, the first end of the third switch and the first end of the third resistor are respectively grounded;
the second end of the third resistor is electrically connected with the first end of the fourth resistor;
a second end of the fourth resistor is electrically connected with a second end of the fifth switch and a second end of the negative bus-to-ground insulation resistor respectively;
the second end of the positive bus-to-ground insulation resistor and the first end of the negative bus-to-ground insulation resistor are respectively electrically connected with the second end of the third switch;
a first end of the fifth resistor is electrically connected with the positive electrode bus, and a second end of the fifth resistor is electrically connected with a first end of the first switch;
the second end of the first switch and the second end of the second switch are respectively grounded;
a first end of the second switch is electrically connected with a first end of the sixth resistor;
and the second end of the sixth resistor and the first end of the fifth switch are respectively electrically connected with the negative bus.
2. The detection circuit according to claim 1, wherein the resistance value of the first resistor is equal to the resistance value of the fourth resistor;
the resistance value of the second resistor is equal to the resistance value of the third resistor;
the resistance value of the fifth resistor is equal to the resistance value of the sixth resistor.
3. The detection circuit of claim 1, wherein the first resistor has a resistance of R1The resistance value of the second resistor is R2The resistance value of the third resistor is R3The resistance value of the fourth resistor is R4Wherein R is1＜＜R2，R3＜＜R4。
4. A DC charging pile insulation detection system is characterized by comprising an analog-to-digital conversion module, a control module and the DC charging pile insulation detection circuit of any one of claims 1 to 3;
the analog-to-digital conversion module is used for respectively acquiring the voltage at two ends of the second resistor and the voltage at two ends of the third resistor and respectively sending the voltage at two ends of the second resistor and the voltage at two ends of the third resistor to the control module;
the control module is used for determining the resistance value of the positive bus to ground insulation resistor and the resistance value of the negative bus to ground insulation resistor according to the voltage at the two ends of the second resistor and the voltage at the two ends of the third resistor.
5. A direct current charging pile insulation detection method, characterized in that the direct current charging pile insulation detection circuit according to any one of claims 1-3 is adopted for detection, and the detection method comprises the following steps:
closing the third switch, the fourth switch, and the fifth switch;
collecting a first voltage at two ends of the second resistor and a second voltage at two ends of the third resistor, and calculating a first ratio of the first voltage to the second voltage and a second ratio of the second voltage to the first voltage;
judging whether the first ratio or the second ratio is smaller than a preset ratio value or not;
if the first ratio or the second ratio is smaller than a preset ratio value, judging whether the first voltage or the second voltage is smaller than a preset voltage value;
and if the first voltage or the second voltage is smaller than a preset voltage value, determining that the positive bus-to-ground insulation resistance or the negative bus-to-ground insulation resistance is short-circuited.
6. The detection method according to claim 5, wherein if the first voltage and the second voltage are equal to or greater than a preset voltage value, a resistance value of the positive bus bar to ground insulation resistance and a resistance value of the negative bus bar to ground insulation resistance are determined based on a first relational expression:
Figure FDA0002629631660000031
Figure FDA0002629631660000032
wherein R isPIs the insulation resistance, R, of the positive bus bar to groundnIs the insulation resistance, R, of the negative bus to ground1Is the first resistance, R2Is the second resistance, R3Is the third resistance, R4Is the fourth resistor, U2Is a first voltage, U, across the second resistor3Is a second voltage across the third resistor.
7. The detection method according to claim 5, wherein if the first ratio and the second ratio are greater than or equal to a preset ratio value, the first switch, the third switch, the fourth switch, and the fifth switch are closed and the second switch is opened;
collecting a third voltage at two ends of the second resistor and a fourth voltage at two ends of the third resistor;
closing the second, third, fourth, and fifth switches and opening the first switch;
collecting a fifth voltage at two ends of the second resistor and a sixth voltage at two ends of the third resistor; determining the resistance value of the positive bus to ground insulation resistor and the resistance value of the negative bus to ground insulation resistor based on a second relational expression, wherein the second relational expression is as follows:
Figure FDA0002629631660000033
Figure FDA0002629631660000034
wherein R isPIs the insulation resistance, R, of the positive bus bar to groundnIs the insulation resistance, R, of the negative bus to ground1Is the first resistance, R2Is the second resistance, R3Is the third resistance, R4Is the fourth resistance, R2Is the fifth resistance, R6Is the sixth resistance, U'2Is a third voltage, U ', across the second resistor'3Is a fourth voltage, U ″, across the third resistor2Is a fifth voltage, U ″, across the second resistor3Is a sixth voltage across the third resistor.
8. The detection method according to claim 6 or 7, wherein after determining the resistance value of the positive bus bar to ground insulation resistor and the resistance value of the negative bus bar to ground insulation resistor, the method further comprises:
judging whether the resistance value of the positive bus to the ground insulation resistor is smaller than that of the negative bus to the ground insulation resistor;
if so, determining that the insulation performance of the direct current charging pile is qualified when the resistance value of the positive bus to ground insulation resistance is greater than or equal to a preset resistance value;
if not, when the resistance value of the insulation resistor of the negative bus to the ground is larger than or equal to the preset resistance value, the insulation performance of the direct current charging pile is determined to be qualified.
9. The method of claim 5, wherein prior to closing the third switch, the fourth switch, and the fifth switch, further comprising:
turning off the first switch, the second switch, the third switch, the fourth switch, and the fifth switch;
collecting the voltage at two ends of the second resistor and the voltage of the third resistor;
judging whether the voltage at two ends of the second resistor and the voltage of the third resistor are both zero or not;
if so, determining that the first switch, the second switch, the third switch, the fourth switch and the fifth switch are disconnected;
otherwise, the first switch, the second switch, the third switch, the fourth switch and the fifth switch are detected until the voltage at the two ends of the second resistor and the voltage of the third resistor are both zero.
10. The detection method of claim 5, wherein closing the third switch, the fourth switch, and the fifth switch comprises:
closing the fourth switch and the fifth switch;
collecting the voltage at two ends of the second resistor or the voltage of the third resistor;
determining a total voltage value of the system according to the voltage at two ends of the second resistor or the voltage of the third resistor;
and when the total pressure value of the system is determined to be within a preset total pressure range, closing the third switch, the fourth switch and the fifth switch.
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