CN114498564B - Protection circuit and method for vehicle-mounted inverter - Google Patents

Protection circuit and method for vehicle-mounted inverter Download PDF

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Publication number
CN114498564B
CN114498564B CN202210090054.6A CN202210090054A CN114498564B CN 114498564 B CN114498564 B CN 114498564B CN 202210090054 A CN202210090054 A CN 202210090054A CN 114498564 B CN114498564 B CN 114498564B
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resistor
inverter
potential
voltage dividing
limit
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CN114498564A (en
Inventor
赵武
严达
孟雅纯
谭川
冯薇丽
刘洪浩
谢肇柏
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Dongfeng Trucks Co ltd
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Dongfeng Trucks Co ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
    • H02H7/12—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
    • H02H7/122—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for inverters, i.e. dc/ac converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H1/00—Details of emergency protective circuit arrangements
    • H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/26—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents
    • H02H3/32—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
    • H02H7/12—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
    • H02H7/122—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for inverters, i.e. dc/ac converters
    • H02H7/1225—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for inverters, i.e. dc/ac converters responsive to internal faults, e.g. shoot-through

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Protection Of Static Devices (AREA)
  • Inverter Devices (AREA)
  • Emergency Protection Circuit Devices (AREA)

Abstract

The application discloses a protection circuit and method of a vehicle-mounted inverter, and relates to the technical field of automobile electricity. A protection circuit for an on-board inverter, comprising: the two voltage dividing branches are connected in series, one end of each voltage dividing branch is configured to be connected with the inverter, the other end of each voltage dividing branch is configured to be grounded, and one voltage dividing branch is adjustable; a controller connected to a connection point a of the two voltage dividing branches to detect a potential of the connection point a and determine whether to limit an output of the inverter according to the detected potential; at the same time, the controller is further configured to control the adjustable voltage dividing branch. According to the method, output cutting is conducted from the inverter through comparison of the connection point potential, external leakage protection can be achieved, failure protection of internal insulation can also be achieved, reaction is rapid, and safety and reliability are guaranteed through real-time monitoring; meanwhile, the output protection of the inverter can be realized under the condition that the user does not have physiological perception, and the user experience is greatly improved.

Description

Protection circuit and method for vehicle-mounted inverter
Technical Field
The application relates to the technical field of automobile electricity, in particular to a protection circuit and method of a vehicle-mounted inverter.
Background
With the improvement of the quality of life level, trucks also have comfort requirements like caravans, and further, there is a need for use of household appliances on trucks, which require the trucks to provide a domestic mains supply.
In order for trucks to be able to provide utility power, an inverter is required to convert the on-board dc 24V power supply to ac 220V at the civil frequency. However, the 220V ac power at power frequency presents a fatal safety hazard if it is in direct contact with a person. Research shows that the human body can generate slight cramp when being subjected to more than 3mA of current, the reflective finger muscle contracts, and the human body can die when exceeding 10mA of current.
At present, protection measures of the vehicle-mounted inverter on the output 220V circuit are mainly to add a fuse on the output line, and when the output is short-circuited, the fuse is fused through local large heat generated by short-circuit current, and the output line is cut off to protect electric appliances and user safety.
Although the output alternating current safety used for the vehicle-mounted inverter can cut off the circuit, the fusing of the fuse needs to depend on energy generated by short-circuit current, which results in long reaction time and insufficient safety; secondly, high leakage voltage is generated, short-time impact can damage the vehicle-mounted electric appliance, and the human body is uncomfortable.
Disclosure of Invention
The embodiment of the application provides a protection circuit and a protection method for an on-vehicle inverter, which are used for solving the technical problem that the safety and reliability of the on-vehicle inverter are poor in the related technology.
In a first aspect, there is provided a protection circuit of an on-vehicle inverter, including:
the two voltage dividing branches are connected in series, one end of each voltage dividing branch is configured to be connected with the inverter, the other end of each voltage dividing branch is configured to be grounded, and one voltage dividing branch is adjustable;
a controller connected to a connection point a of the two voltage dividing branches to detect a potential of the connection point a and determine whether to limit an output of the inverter according to the detected potential; at the same time, the controller is further configured to control the adjustable voltage dividing branch.
Before the potential of the connection point A is detected, calculating to obtain the maximum potential limit and the minimum potential limit of the connection point A, namely the potential upper limit and the potential lower limit according to the voltage distribution condition of the two voltage division branches; then, the controller continuously detects the potential of the connection point A, judges whether the output abnormality of the inverter occurs according to the detected potential and the upper and lower lines of the potential, and limits the output of the inverter when the output abnormality of the inverter occurs.
During the detection of connection a, the controller can also simultaneously control an adjustable voltage dividing branch, by means of which the potential of connection a is changed.
In some embodiments, the adjustable voltage dividing branch comprises a resistor R2, a resistor R3 and a switching device, wherein the resistor R2 and the resistor R3 are connected in series, and the switching device is controlled by the controller and is connected in parallel with the resistor R2 or the resistor R3; and/or
The other of said voltage dividing branches comprises a resistor R1.
In the embodiment of the application, the switch of the switching device can be controlled and controlled by the controller, and the connection and short circuit cutting of the resistors connected in parallel with the switching device are realized under the control of the controller, so that the voltage division regulation of the voltage division branch is realized.
In some embodiments, if the switching device is a field effect transistor, the field effect transistor is connected in parallel with the resistor R3, and a control electrode of the field effect transistor is connected to the controller.
In this embodiment, taking a field effect transistor Q as an NMOS transistor, a drain of the field effect transistor Q is connected to one end of the resistor R3 near the inverter, a source is connected to the other end of the resistor R3, and a gate receives the high and low levels output by the controller. If the controller outputs a low-level signal, the field effect transistor Q is cut off, the resistor R3 is connected into a voltage dividing branch, and the impedance of the voltage dividing branch is increased; if the controller outputs a high-level signal, the field effect transistor Q is turned on, the resistor R3 is short-circuited, and the impedance on the voltage dividing branch is reduced.
In some embodiments, the controller is connected to the connection point a by a sampling branch.
In some embodiments, the resistor R1 or the resistor R2 or the resistor R3 is formed by a plurality of resistor units connected in series.
In some embodiments, the adjustable voltage dividing leg is located remotely from the inverter.
The protection circuit is applied to a development product 2kW inverter for verification, and a sample is tested, so that leakage protection can be performed after the leakage current is larger than 0.68mA, the protection judgment time is 72ms, and the protection judgment time is far higher than the 3.5mA/250ms leakage standard specified in QC/T1036-2016 automobile power inverter, so that personal safety can be reliably protected. According to the embodiment of the application, the protection can be performed under the condition that a human body does not feel, and the electric leakage level is far beyond that of similar products, so that the user experience is improved.
Comparatively, an inverter with prior art leakage protection was measured, in which the protection circuit cuts off the output of the high-voltage power supply when the leakage current reached 2.1mA, and the protection operation time was 2920ms. According to physiological reaction of human body, the 0.9mA-3.5mA human body can produce numbness but not pathological phenomenon.
In a second aspect, a protection method for a vehicle-mounted inverter is provided, including the following steps:
providing a protection circuit of the vehicle-mounted inverter;
pre-adjusting the voltage dividing branch and determining the upper potential limit and the lower potential limit of the connecting point A;
and continuously detecting the potential of the connection point A, and judging whether to limit the output of the inverter according to the upper potential limit, the lower potential limit and the detected potential.
Before the potential of the connection point A is detected, calculating to obtain the maximum potential limit and the minimum potential limit of the connection point A, namely the potential upper limit and the potential lower limit according to the voltage distribution condition of the two voltage division branches; then, the controller continuously detects the potential of the connection point A, judges whether the output abnormality of the inverter occurs according to the detected potential and the upper and lower lines of the potential, and limits the output of the inverter when the output abnormality of the inverter occurs. Meanwhile, in the process of detecting the connection point A, the controller can also control the adjustable voltage dividing branch at the same time, and the potential of the connection point A is changed through the adjustable voltage dividing branch.
In some embodiments, the output of the inverter is limited if the detected potential exceeds the upper potential limit or is below the lower potential limit.
In some embodiments, if the detected potential exceeds the upper potential limit, determining that the inverter is out of order; and/or
And if the detected potential is lower than the potential lower limit, judging that the internal insulation failure fault of the inverter exists.
If the output of the inverter has reduced insulation resistance, human body contact leakage (the resistance is kiloohm level) and even direct grounding, the potential detected at the connection point A exceeds the upper potential limit and is detected by the controller DSP, the controller immediately controls the inverter to close the output so as to play a role in protecting the external leakage of the inverter.
Assuming that there is a leakage outside, which is equivalent to connecting an impedance R4 in parallel to two ends of a resistor R1, the equivalent schematic diagram is shown in fig. 2, and the first potential range of the connection point a is:
V·R 2 /(R 1 ∥R 4 +R 3 )＜V A ＜V·(R 2 +R 3 )/(R 1 ∥R 4 +R 2 +R 3 )，
wherein R is 1 、R 2 、R 3 、R 4 The values of the resistor R1, the resistor R2, the resistor R3 and the resistor R4 are the output voltage of the inverter.
If the insulation resistance of the internal circuit of the inverter is reduced, the potential of the connection point A is reduced, and the potential detected at the connection point A is lower than the potential lower limit and is detected by the controller DSP, the controller immediately controls the inverter to close the output so as to realize the protection of the internal insulation failure fault of the inverter.
Assuming that there is an insulation failure in the interior, which is equivalent to connecting an impedance R5 in parallel to two ends of the resistor R2 and the resistor R3, the equivalent schematic diagram is as shown in fig. 3, and the second potential range of the connection point a is:
V·R 2 ∥R 5 /(R 1 +R 2 ∥R 5 )＜V A ＜V·(R 2 +R 3 )∥R 5 /[R 1 +(R 2 +R 3 )∥R 5 ]，
wherein R is 1 、R 2 、R 3 、R 5 Is a resistor R1, a resistor R2, a resistor R3 and an impedance R 5 V is the output voltage of the inverter.
In some embodiments, if the adjustable voltage dividing branch includes a resistor R2, a resistor R3, and a switching device, the switching device is connected in parallel with the resistor R3; the other voltage dividing branch comprises a resistor R1; the calculation formula for determining the upper potential limit of the connection point a is:
Rmax＝V·(R 2 +R 3 )/(R 1 +R 2 +R 3 )，
the calculation formula for determining the potential lower limit of the connection point (A) is as follows:
Rmin＝V·(R 2 )/(R 1 +R 2 )，
wherein R is 1 、R 2 、R 3 The values of the resistor R1, the resistor R2 and the resistor R3 are the output voltage of the inverter.
If external leakage occurs, V in the first potential range A ＞V·(R 2 +R 3 )/(R 1 +R 2 +R 3 ) The method comprises the steps of carrying out a first treatment on the surface of the If external insulation failure occurs, V in the second potential range A ＜V·(R 2 )/(R 1 +R 2 )。
The beneficial effects that technical scheme that this application provided brought include:
output cut-off is carried out from the inverter through the comparison of the connection point potential, so that external leakage protection and failure protection of internal insulation can be realized, the reaction is rapid, and the safety and the reliability are ensured through real-time monitoring; meanwhile, the output protection of the inverter can be realized under the condition that the user does not have physiological perception, and the user experience is greatly improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic structural diagram of a protection circuit of an on-vehicle inverter according to an embodiment of the present application;
fig. 2 is an equivalent schematic diagram of a protection circuit of an on-vehicle inverter according to an embodiment of the present application when external leakage occurs;
fig. 3 is an equivalent schematic diagram of a protection circuit of an on-vehicle inverter according to an embodiment of the present application when an internal insulation failure occurs.
The realization, functional characteristics and advantages of the present application will be further described with reference to the embodiments, referring to the attached drawings.
Detailed Description
For the purposes of making the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present application based on the embodiments herein.
The flow diagrams depicted in the figures are merely illustrative and not necessarily all of the elements and operations/steps are included or performed in the order described. For example, some operations/steps may be further divided, combined, or partially combined, so that the order of actual execution may be changed according to actual situations.
The embodiment of the application provides a protection circuit of an on-vehicle inverter, which is used for cutting off output from the inverter through comparison of connection point potentials, so that external leakage protection and failure protection of internal insulation can be realized, the reaction is rapid, and the safety and the reliability are ensured through real-time monitoring; meanwhile, the output protection of the inverter can be realized under the condition that the user does not have physiological perception, and the user experience is greatly improved.
Some embodiments of the present application are described in detail below with reference to the accompanying drawings. The following embodiments and features of the embodiments may be combined with each other without conflict.
Referring to fig. 1, an embodiment of the present application provides a protection circuit of an on-vehicle inverter, including:
the two voltage dividing branches are connected in series, one end of each voltage dividing branch is configured to be connected with the inverter, the other end of each voltage dividing branch is configured to be grounded, and one voltage dividing branch is adjustable;
a controller connected to a connection point a of the two voltage dividing branches to detect a potential of the connection point a and determine whether to limit an output of the inverter according to the detected potential; at the same time, the controller is further configured to control the adjustable voltage dividing branch.
The working principle of the protection circuit of the vehicle-mounted inverter in the embodiment of the application is as follows:
before the potential of the connection point A is detected, calculating to obtain the maximum potential limit and the minimum potential limit of the connection point A, namely the potential upper limit and the potential lower limit according to the voltage distribution condition of the two voltage division branches; then, the controller continuously detects the potential of the connection point A, judges whether the output abnormality of the inverter occurs according to the detected potential and the upper and lower lines of the potential, and limits the output of the inverter when the output abnormality of the inverter occurs.
Further, during the detection of the connection a, the controller may also control the adjustable voltage dividing branch, by which the potential of the connection a is changed, the minimum impedance of the adjustable voltage dividing branch is also greater than zero, irrespective of the change in impedance of the adjustable voltage dividing branch, and the potential measured at the connection a is also compared with the upper and lower potential limits.
Specifically, one end of each of the two connected voltage dividing branches is an inverter, the other end of each of the two connected voltage dividing branches is grounded, and then the voltage from the connection point A to the ground is the measured potential.
As a preferred scheme of the embodiment of the application, the adjustable voltage dividing branch comprises a resistor R2, a resistor R3 and a switching device, wherein the resistor R2 and the resistor R3 are connected in series, and the switching device is controlled by the controller and is connected in parallel with the resistor R2 or the resistor R3; and/or
The other of said voltage dividing branches comprises a resistor R1.
In the embodiment of the application, the switch of the switching device can be controlled and controlled by the controller, and the connection and short circuit cutting of the resistors connected in parallel with the switching device are realized under the control of the controller, so that the voltage division regulation of the voltage division branch is realized.
Further, if the switching device is a field effect transistor, the field effect transistor is connected in parallel with the resistor R3, and a control electrode of the field effect transistor is connected with the controller.
Preferably, the adjustable voltage dividing branch is arranged remotely from the inverter. If the resistor R3 is far away from the inverter, the resistor R1, the resistor R2, and the resistor R3 are sequentially connected in series, and then the other end of the resistor R3 is grounded.
In this embodiment, taking a field effect transistor Q as an NMOS transistor, a drain of the field effect transistor Q is connected to one end of the resistor R3 near the inverter, a source is connected to the other end of the resistor R3, and a gate receives the high and low levels output by the controller. If the controller outputs a low-level signal, the field effect transistor Q is cut off, the resistor R3 is connected into a voltage dividing branch, and the impedance of the voltage dividing branch is increased; if the controller outputs a high-level signal, the field effect transistor Q is turned on, the resistor R3 is short-circuited, and the impedance on the voltage dividing branch is reduced.
Further, the controller is connected to the connection point a through a sampling branch. The sampling branch comprises a resistor R, and in practice, the resistor R is formed by connecting a plurality of small resistors with smaller resistance values in series.
Further, the resistor R1 or the resistor R2 or the resistor R3 is formed by a plurality of resistor units connected in series. The impedance of each branch is of the megaohm level, a plurality of megaohm resistors are connected in series, and the problem that overvoltage or overcurrent occurs during normal operation does not cause damage to electronic devices on the branch or harm to human bodies.
In this embodiment, the controller limits the output of the inverter if the detected potential exceeds the upper potential limit or falls below the lower potential limit.
Further, if the detected potential exceeds the upper potential limit, it is determined that the inverter is out of leakage. The inverter outputs alternating current, the adjustable voltage dividing branch circuit enables the connecting point A to have an upper potential limit relative to the ground, and the situation that when the external leakage exists, the output voltage is divided by the set leakage current threshold value 5mA to obtain external insulation impedance, and the external impedance is infinite when the electric leakage does not exist normally can be understood, and then the potential of the connecting point A is the upper potential limit; as shown in fig. 2, a resistor R4 is connected in parallel to the voltage dividing branch near the inverter. When abnormal leakage occurs, the leakage current exceeds 5mA, that is, the potential of the corresponding connection point A exceeds the upper potential limit.
If the output of the inverter has reduced insulation resistance, human body contact leakage (the resistance is kiloohm level) and even direct grounding, the potential detected at the connection point A exceeds the upper potential limit and is detected by the controller DSP, the controller immediately controls the inverter to close the output so as to play a role in protecting the external leakage of the inverter.
Assuming that there is a leakage outside, which is equivalent to connecting an impedance R4 in parallel to two ends of a resistor R1, the equivalent schematic diagram is shown in fig. 2, and the first potential range of the connection point a is:
V·R 2 /(R 1 ∥R 4 +R 3 )＜V A ＜V·(R 2 +R 3 )/(R 1 ∥R 4 +R 2 +R 3 )，
wherein R is 1 、R 2 、R 3 、R 4 The values of the resistor R1, the resistor R2, the resistor R3 and the resistor R4 are the output voltage of the inverter.
On the other hand, if the detected potential is lower than the potential lower limit, it is determined that the internal insulation failure of the inverter has occurred. The controller controls the adjustable voltage dividing branch to change the impedance on the voltage dividing branch, and the potential lower limit of the connecting point A can also be obtained; as shown in fig. 3, a resistor R5 is connected in parallel to the voltage dividing branch which is located away from the inverter.
If the insulation resistance of the internal circuit of the inverter is reduced, the potential of the connection point A is reduced, and the potential detected at the connection point A is lower than the potential lower limit and is detected by the controller DSP, the controller immediately controls the inverter to close the output so as to realize the protection of the internal insulation failure fault of the inverter.
Assuming that there is an insulation failure in the interior, which is equivalent to connecting an impedance R5 in parallel to two ends of the resistor R2 and the resistor R3, the equivalent schematic diagram is as shown in fig. 3, and the second potential range of the connection point a is:
V·R 2 ∥R 5 /(R 1 +R 2 ∥R 5 )＜V A ＜V·(R 2 +R 3 )∥R 5 /[R 1 +(R 2 +R 3 )∥R 5 ]，
wherein R is 1 、R 2 、R 3 、R 5 Is a resistor R1, a resistor R2, a resistor R3 and an impedance R 5 V is the output voltage of the inverter.
If external leakage occurs, V in the first potential range A ＞V·(R 2 +R 3 )/(R 1 +R 2 +R 3 ) The method comprises the steps of carrying out a first treatment on the surface of the If external insulation failure occurs, V in the second potential range A ＜V·(R 2 )/(R 1 +R 2 )。
Therefore, the potential upper limit and the potential lower limit of the connecting point A are determined by selecting a proper connecting point A to distinguish internal and external insulation failure and electric leakage and protect the internal and external insulation failure and the electric leakage, so that potential safety hazards such as electric leakage and the like to equipment and user personnel are avoided.
The protection circuit is applied to a development product 2kW inverter for verification, and a sample is tested, so that leakage protection can be performed after the leakage current is larger than 0.68mA, the protection judgment time is 72ms, and the protection judgment time is far higher than the 3.5mA/250ms leakage standard specified in QC/T1036-2016 automobile power inverter, so that personal safety can be reliably protected.
Comparatively, an inverter with prior art leakage protection was measured, in which the protection circuit cuts off the output of the high-voltage power supply when the leakage current reached 2.1mA, and the protection operation time was 2920ms. According to physiological reaction of human body, the 0.9mA-3.5mA human body can produce numbness but not pathological phenomenon.
Therefore, the embodiment of the application can protect the human body without feeling, and the electric leakage level is far higher than that of similar products, so that the user experience is improved.
The embodiment of the application also provides a protection method of the vehicle-mounted inverter, which comprises the following steps:
providing a protection circuit of the vehicle-mounted inverter;
pre-adjusting the voltage dividing branch and determining the upper potential limit and the lower potential limit of the connecting point A;
and continuously detecting the potential of the connection point A, and judging whether to limit the output of the inverter according to the upper potential limit, the lower potential limit and the detected potential.
Before the potential of the connection point A is detected, calculating to obtain the maximum potential limit and the minimum potential limit of the connection point A, namely the potential upper limit and the potential lower limit according to the voltage distribution condition of the two voltage division branches; then, the controller continuously detects the potential of the connection point A, judges whether the output abnormality of the inverter occurs according to the detected potential and the upper and lower lines of the potential, and limits the output of the inverter when the output abnormality of the inverter occurs.
Further, during the detection of the connection a, the controller may also control the adjustable voltage dividing branch, by which the potential of the connection a is changed, the minimum impedance of the adjustable voltage dividing branch is also greater than zero, irrespective of the change in impedance of the adjustable voltage dividing branch, and the potential measured at the connection a is also compared with the upper and lower potential limits.
As a preferred scheme of the embodiment of the application, the adjustable voltage dividing branch comprises a resistor R2, a resistor R3 and a switching device, wherein the resistor R2 and the resistor R3 are connected in series, and the switching device is controlled by the controller and is connected in parallel with the resistor R2 or the resistor R3; and/or the other of said voltage dividing branches comprises a resistor R1.
In the embodiment of the application, the switch of the switching device can be controlled and controlled by the controller, and the connection and short circuit cutting of the resistors connected in parallel with the switching device are realized under the control of the controller, so that the voltage division regulation of the voltage division branch is realized.
Further, if the switching device is a field effect transistor, the field effect transistor is connected in parallel with the resistor R3, and a control electrode of the field effect transistor is connected with the controller.
Preferably, the adjustable voltage dividing branch is arranged remotely from the inverter. If the resistor R3 is far away from the inverter, the resistor R1, the resistor R2, and the resistor R3 are sequentially connected in series, and then the other end of the resistor R3 is grounded.
Further, the controller is connected to the connection point a through a sampling branch. The sampling branch comprises a resistor R, and in practice, the resistor R is formed by connecting a plurality of small resistors with smaller resistance values in series. The resistor R1 or the resistor R2 or the resistor R3 is formed by a plurality of resistor units connected in series. The impedance of each branch is of the megaohm level, a plurality of megaohm resistors are connected in series, and the problem that overvoltage or overcurrent occurs during normal operation does not cause damage to electronic devices on the branch or harm to human bodies.
In this embodiment, taking a field effect transistor Q as an NMOS transistor, a drain of the field effect transistor Q is connected to one end of the resistor R3 near the inverter, a source is connected to the other end of the resistor R3, and a gate receives the high and low levels output by the controller. If the controller outputs a low-level signal, the field effect transistor Q is cut off, the resistor R3 is connected into a voltage dividing branch, and the impedance of the voltage dividing branch is increased; if the controller outputs a high-level signal, the field effect transistor Q is turned on, the resistor R3 is short-circuited, and the impedance on the voltage dividing branch is reduced.
In this embodiment, the controller limits the output of the inverter if the detected potential exceeds the upper potential limit or falls below the lower potential limit.
Further, if the detected potential exceeds the upper potential limit, it is determined that the inverter is out of leakage. The inverter outputs alternating current, the adjustable voltage dividing branch circuit enables the connecting point A to have an upper potential limit relative to the ground, and the situation that when the external leakage exists, the output voltage is divided by the set leakage current threshold value 5mA to obtain external insulation impedance, and the external impedance is infinite when the electric leakage does not exist normally can be understood, and then the potential of the connecting point A is the upper potential limit; as shown in fig. 2, a resistor R4 is connected in parallel to the voltage dividing branch near the inverter. When abnormal leakage occurs, the leakage current exceeds 5mA, that is, the potential of the corresponding connection point A exceeds the upper potential limit.
If the output of the inverter has reduced insulation resistance, human body contact leakage (the resistance is kiloohm level) and even direct grounding, the potential detected at the connection point A exceeds the upper potential limit and is detected by the controller DSP, the controller immediately controls the inverter to close the output so as to play a role in protecting the external leakage of the inverter.
Specifically, if the adjustable voltage dividing branch includes a resistor R2, a resistor R3, and a switching device, the switching device is connected in parallel with the resistor R3; the other voltage dividing branch comprises a resistor R1, and the calculation formula for determining the potential upper limit of the connecting point (A) is as follows:
Rmax＝V·(R 2 +R 3 )/(R 1 +R 2 +R 3 )，
wherein R is 1 、R 2 、R 3 The values of the resistor R1, the resistor R2 and the resistor R3 are the output voltage of the inverter.
Assuming that there is a leakage outside, which is equivalent to connecting an impedance R4 in parallel to two ends of a resistor R1, the equivalent schematic diagram is shown in fig. 2, and the first potential range of the connection point a is:
V·R 2 /(R 1 ∥R 4 +R 3 )＜V A ＜V·(R 2 +R 3 )/(R 1 ∥R 4 +R 2 +R 3 )，
wherein R is 1 、R 2 、R 3 、R 4 The values of the resistor R1, the resistor R2, the resistor R3 and the resistor R4 are the output voltage of the inverter.
If external leakage occurs, V in the first potential range A ＞V·(R 2 +R 3 )/(R 1 +R 2 +R 3 )。
On the other hand, if the detected potential is lower than the potential lower limit, it is determined that the internal insulation failure of the inverter has occurred. The controller controls the adjustable voltage dividing branch to change the impedance on the voltage dividing branch, and the potential lower limit of the connecting point A can also be obtained; as shown in fig. 3, a resistor R5 is connected in parallel to the voltage dividing branch which is located away from the inverter.
If the insulation resistance of the internal circuit of the inverter is reduced, the potential of the connection point A is reduced, and the potential detected at the connection point A is lower than the potential lower limit and is detected by the controller DSP, the controller immediately controls the inverter to close the output so as to realize the protection of the internal insulation failure fault of the inverter.
Specifically, if the adjustable voltage dividing branch includes a resistor R2, a resistor R3, and a switching device, the switching device is connected in parallel with the resistor R3; the other voltage dividing branch comprises a resistor R1, and the calculation formula for determining the potential lower limit of the connecting point (A) is as follows:
Rmin＝V·(R 2 )/(R 1 +R 2 )，
wherein R is 1 、R 2 The values of the resistor R1 and the resistor R2 are the output voltage of the inverter.
Assuming that there is an insulation failure in the interior, which is equivalent to connecting an impedance R5 in parallel to two ends of the resistor R2 and the resistor R3, the equivalent schematic diagram is as shown in fig. 3, and the second potential range of the connection point a is:
V·R 2 ∥R 5 /(R 1 +R 2 ∥R 5 )＜V A ＜V·(R 2 +R 3 )∥R 5 /[R 1 +(R 2 +R 3 )∥R 5 ]，
wherein R is 1 、R 2 、R 3 、R 5 Is a resistor R1, a resistor R2, a resistor R3 and an impedance R 5 V is the output voltage of the inverter.
If external insulation failure occurs, V in the second potential range A ＜V·(R 2 )/(R 1 +R 2 )。
Therefore, the potential upper limit and the potential lower limit of the connecting point A are determined by selecting a proper connecting point A to distinguish internal and external insulation failure and electric leakage and protect the internal and external insulation failure and the electric leakage, so that potential safety hazards such as electric leakage and the like to equipment and user personnel are avoided.
The protection circuit is applied to a development product 2kW inverter for verification, and a sample is tested, so that leakage protection can be performed after the leakage current is larger than 0.68mA, the protection judgment time is 72ms, and the protection judgment time is far higher than the 3.5mA/250ms leakage standard specified in QC/T1036-2016 automobile power inverter, so that personal safety can be reliably protected.
Comparatively, an inverter with prior art leakage protection was measured, in which the protection circuit cuts off the output of the high-voltage power supply when the leakage current reached 2.1mA, and the protection operation time was 2920ms. According to physiological reaction of human body, the 0.9mA-3.5mA human body can produce numbness but not pathological phenomenon.
Therefore, the embodiment of the application can protect the human body without feeling, and the electric leakage level is far higher than that of similar products, so that the user experience is improved.
In the description of the present application, it should be noted that the azimuth or positional relationship indicated by the terms "upper", "lower", etc. are based on the azimuth or positional relationship shown in the drawings, and are merely for convenience of description of the present application and simplification of the description, and are not indicative or implying that the apparatus or element in question must have a specific azimuth, be configured and operated in a specific azimuth, and thus should not be construed as limiting the present application. Unless specifically stated or limited otherwise, the terms "mounted," "connected," and "coupled" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the terms in this application will be understood by those of ordinary skill in the art as the case may be.
It should be noted that in this application, relational terms such as "first" and "second" and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The foregoing is merely a specific embodiment of the application to enable one skilled in the art to understand or practice the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (4)

1. A protection method of a protection circuit based on an on-board inverter is characterized in that,
the protection circuit includes:
the two voltage dividing branches are connected in series, one end of each voltage dividing branch is configured to be connected with the inverter, the other end of each voltage dividing branch is configured to be grounded, and one voltage dividing branch is adjustable;
a controller connected to a connection point a of the two voltage dividing branches to detect a potential of the connection point a and determine whether to limit an output of the inverter according to the detected potential; at the same time, the controller is further configured to control the adjustable voltage dividing branch;
the adjustable voltage dividing branch comprises a resistor R2, a resistor R3 and a switching device, wherein the resistor R2 and the resistor R3 are connected in series, and the switching device is controlled by the controller and is connected with the resistor R2 or the resistor R3 in parallel; and/or
The other of the voltage dividing branches comprises a resistor R1;
if the switching device is a field effect tube, the field effect tube is connected with the resistor R3 in parallel, and the control electrode of the field effect tube is connected with the controller;
the protection method comprises the following steps:
pre-adjusting the voltage dividing branch and determining the upper potential limit and the lower potential limit of the connecting point A;
continuously detecting the potential of the connection point A, and judging whether to limit the output of the inverter according to the upper potential limit, the lower potential limit and the detected potential;
limiting the output of the inverter if the detected potential exceeds the upper potential limit or is below the lower potential limit;
if the detected potential exceeds the upper potential limit, judging that the external electric leakage of the inverter is faulty; and/or
If the detected potential is lower than the potential lower limit, judging that the internal insulation failure fault of the inverter exists;
if the adjustable voltage division branch circuit comprises a resistor R2, a resistor R3 and a switching device, the switching device is connected with the resistor R3 in parallel; the other voltage dividing branch comprises a resistor R1; the calculation formula for determining the upper potential limit of the connection point a is:
Rmax＝V·(R2+R3)/(R1+R2+R3)，
the calculation formula for determining the potential lower limit of the connection point (A) is as follows:
Rmin＝V·(R2)/(R1+R2)，
wherein R1, R2 and R3 are the resistance values of the resistor R1, the resistor R2 and the resistor R3, and V is the output voltage of the inverter.
2. The protection method of a vehicle-mounted inverter-based protection circuit according to claim 1, wherein the controller is connected to the connection point a through a sampling branch.
3. The protection method of a vehicle-mounted inverter-based protection circuit according to claim 1, wherein the resistor R1 or the resistor R2 or the resistor R3 is formed of a plurality of resistor units connected in series.
4. The method of protecting an on-board inverter-based protection circuit of claim 1, wherein the adjustable voltage dividing branch is located remotely from the inverter.
CN202210090054.6A 2022-01-25 2022-01-25 Protection circuit and method for vehicle-mounted inverter Active CN114498564B (en)

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Publication number Priority date Publication date Assignee Title
JP2012173053A (en) * 2011-02-18 2012-09-10 Mitsubishi Heavy Ind Ltd Electric leak detecting device and method for the same
CN105527535A (en) * 2016-01-05 2016-04-27 惠州市蓝微新源技术有限公司 DC leakage insulation detection system and method based on variable-resistor network
CN110927457A (en) * 2019-11-08 2020-03-27 华为技术有限公司 Inverter and insulation detection circuit
CN113922652A (en) * 2021-11-17 2022-01-11 阳光电源股份有限公司 Inverter, inverter system, lightning protection circuit and control method of lightning protection circuit

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2012173053A (en) * 2011-02-18 2012-09-10 Mitsubishi Heavy Ind Ltd Electric leak detecting device and method for the same
CN105527535A (en) * 2016-01-05 2016-04-27 惠州市蓝微新源技术有限公司 DC leakage insulation detection system and method based on variable-resistor network
CN110927457A (en) * 2019-11-08 2020-03-27 华为技术有限公司 Inverter and insulation detection circuit
CN113922652A (en) * 2021-11-17 2022-01-11 阳光电源股份有限公司 Inverter, inverter system, lightning protection circuit and control method of lightning protection circuit

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