A full-operating-condition insulation monitoring method for multi-voltage-level on-board microgrids

Abstract

The present invention proposes a full-operating-condition insulation monitoring device applied to a multi-voltage-level on-board microgrid, wherein the full-operating-condition insulation monitoring device comprises: a power battery bus circuit, a DC load bus circuit, an insulation monitor and a bidirectional DC / DC converter, wherein the power battery bus circuit and the DC load bus circuit are connected via the bidirectional DC / DC converter to achieve a bidirectional flow of energy between the power battery and the DC load bus; wherein the insulation monitor comprises a unique insulation monitoring circuit, wherein the insulation monitoring circuit achieves the insulation monitoring requirements of the multi-voltage-level on-board microgrid through the coupling relationship between the insulation resistance of the power battery positive bus and the DC load positive bus, and through conversion. The present invention also designs a corresponding full-operating-condition insulation monitoring method for the insulation monitoring device of the present invention.

Description

Technical Field

[0001] The present invention relates to the field of vehicle safety detection technology, and in particular to a full-operating-condition insulation monitoring method and monitoring equipment thereof applied to a multi-voltage-level on-board microgrid. Background Art

[0002] With the continuous development of motor and power conversion technology, electric drive has become the mainstream development direction of driving modes for various types of transport platforms such as electric vehicles, high-speed railways, and military special vehicles. Compared with electric vehicles, high-speed railways, etc., the grid voltage of the on-board power system of special vehicles is high. If the insulation link between the high-voltage system and the vehicle body is damaged and destroyed, the insulation performance will be reduced, which will seriously endanger the personal safety of the occupants and passengers. At present, insulation monitoring technology in the field of civil electrical systems has been widely used. For example, there are relatively mature products in the fields of electric vehicles, medical equipment, industrial production, etc. However, there are significant differences between on-board microgrid systems and civil electrical systems. Mature insulation monitoring products in the civil field cannot meet the requirements of insulation monitoring of on-board integrated power systems, mainly manifested in:

[0003] 1. The vehicle-mounted microgrid system contains multiple voltage levels and complex working conditions. The system includes multiple energy sources such as engine-generator sets, batteries, and supercapacitors, and their voltage levels are also different. The connection relationship between the energy sources will also change under different working conditions. The civil electrical system generally contains only one power supply and only one voltage level.

[0004] 2. The on-board microgrid system has many branches and a complex structure. The system includes multiple energy sources, DC / DC converters, drive motors, water pumps, fan motors, and various controllers. It contains many electrical branches, and the characteristics of each load device are different, making the characteristics of the power grid extremely complex. In addition, the large number of load devices also leads to a large distributed capacitance of the system, which has a greater impact on the insulation resistance test. The general civil electrical system has fewer branches and a relatively simple electrical structure.

[0005] 3. Harsh working environment and high requirements for real-time detection. The working environment of special vehicles is very harsh, with severe impact and vibration, and many sudden failures. The real-time requirements for insulation detection are high, otherwise serious consequences may occur. Since there are many load devices and they are all densely packed in a small space, it is more difficult to locate the fault.

[0006] In summary, the mature insulation monitoring products in the existing civilian field cannot meet the insulation monitoring requirements of the on-board power system of special vehicles. Therefore, the present invention aims to solve the above problems and design a full-operating insulation monitoring method for multi-voltage level on-board microgrids, which is of great significance for real-time and accurate monitoring of the insulation performance between the high-voltage system and the vehicle body, ensuring the personal safety of passengers and passengers, the normal operation of electrical equipment and the safe operation of the vehicle. Summary of the invention

[0007] In order to solve the problems existing in the prior art, one aspect of the present invention proposes a full-operating-condition insulation monitoring device applied to a multi-voltage-level on-board microgrid, wherein the full-operating-condition insulation monitoring device comprises: a power battery bus circuit, a DC load bus circuit, an insulation monitor and a bidirectional DC / DC converter, wherein the power battery bus circuit and the DC load bus circuit are connected through the bidirectional DC / DC converter to realize a bidirectional flow of energy between the power battery and the DC load bus; the power battery bus circuit comprises: a power battery negative bus, a power battery positive bus, a resistor R1, and a resistor R3, wherein the power battery negative bus is connected to one end of the resistor R3, and the resistor R4 is connected to the power battery positive bus. The other end of the resistor R3 is connected to the resistor R1, the other end of the resistor R1 is connected to the positive bus of the power battery, and the connection between the resistor R3 and the resistor R1 is commonly connected to the ground terminal; the DC load bus circuit includes: a DC load positive bus, a DC load negative bus, and a resistor R2; one end of the resistor R2 is connected to the DC load positive bus, and the other end is connected to the ground terminal GND; wherein the insulation monitor includes only one insulation monitoring circuit, and the insulation monitoring circuit realizes the insulation monitoring requirements of the multi-voltage level on-board microgrid through the coupling relationship between the insulation resistance of the power battery positive bus and the DC load positive bus, and through conversion.

[0008] Preferably, the insulation monitoring circuit includes a first switch S1, a built-in power supply Ui, a second switch S2, a first resistor, a second resistor, a third switch S3 and a fourth switch S4; the switches S1, S2 and S3 are double-contact point type switching switches of the same type, each having a first contact and a second contact; one end of the first switch S1 is connected between the resistors R1 and R3, and is also connected to the ground terminal, and the other end is connected to the built-in power supply Ui through a contact; the built-in power supply Ui is placed between the first switch S1 and the second switch S2, the negative end of the built-in power supply Ui is connected to the first contact of the first switch S1, and the positive end of the built-in power supply Ui is connected to the first contact of the second switch S2; one end of the second switch S2 is connected between the first resistor and the second resistor, and the first resistor is connected to the negative bus of the power battery through the fourth switch S4; the second resistor is connected to the positive bus of the DC load through the third switch S3.

[0009] Preferably, the bidirectional DC / DC converter comprises: a plurality of reverse-conducting insulated gate bipolar transistors, a plurality of inductors and a capacitor C; the number of the reverse-conducting insulated gate bipolar transistors is four, namely T1, T2, T3, and T4, each of which comprises an insulated gate bipolar transistor IGBT and a reverse-parallel connected diode D; wherein T1 is connected in series with T3, T2 is connected in series with T4, the emitters of the insulated gate bipolar transistors IGBT in T3 and T4 are connected to the negative bus of the DC load; the collector of the insulated gate bipolar transistor IGBT of T1 is connected to the positive bus 201 of the DC load, and the insulated gate bipolar transistor D of T1 is connected to the positive bus 202 of the DC load. The emitter of the insulated gate bipolar transistor IGBT is connected to T3 and is also connected to the second inductor L2; the collector of the insulated gate bipolar transistor IGBT of T2 is connected to the DC load positive bus 201, the emitter of the insulated gate bipolar transistor IGBT of T2 is connected to T4 and is also connected to the first inductor L1, the emitter of the insulated gate bipolar transistor IGBT of T4 is connected to the DC load negative bus 100, L1 is connected in parallel with L2 and then connected in series with one end of the third inductor L3, and the other end of L3 is connected to the power battery positive bus 101; the positive and negative electrodes of the capacitor C are respectively connected to the DC load positive bus and the DC load negative bus.

[0010] Preferably, the insulation monitoring circuit includes three working modes: a power-on inspection working mode, a passive switching bridge method insulation monitoring mode under normal power supply conditions, and a timed forced active working mode under normal power supply conditions.

[0011] Preferably, the insulation monitoring requirements include: negative bus insulation monitoring, positive bus insulation monitoring; the coupling relationship is: the DC load bus increases the insulation resistance R 2 When the power battery bus is connected in parallel with the resistor R U =(U 1 -U x )R 2 / (U 2 -U 1 ) has the same effect, the converted insulation resistance R' 2 =R 2 / / R U ; The power battery busbar insulation resistance R 2 The DC load bus should be connected in parallel with the resistor R' U =-(U 2 -U x )R 1 / (U 2 -U 1 ), the converted insulation resistance R' 1 =R 1 / / R' U .

[0012] According to another aspect of the present invention, the present invention provides a full-operating-condition insulation monitoring method for a multi-voltage-level on-board microgrid, the method comprising: reading the bus voltage U1, U2 of the multi-voltage-level on-board microgrid system; judging whether the bus voltage U1, U2 is zero; if so, the multi-voltage-level on-board microgrid system is not powered on, and the insulation monitoring circuit enters a power-on inspection working mode based on active monitoring; in this mode, a built-in power supply Ui is connected to actively measure the insulation resistance of the positive and negative busbars of the multi-voltage-level on-board microgrid system; if not, it indicates that the multi-voltage-level on-board microgrid system is powered on, and at this time, the bus nominal voltage U1, U2 and the lower bridge voltage U of the power battery bus circuit are recorded. x ;

[0013] According to the lower bridge voltage U x and the busbar nominal voltage U1, to determine whether an insulation fault occurs in the multi-voltage level on-board microgrid system;

[0014] if:

[0015]

[0016] Then it enters the timed forced active working mode under normal high voltage power supply;

[0017] if:

[0018]

[0019] Then it enters the passive switching bridge insulation monitoring mode under normal power supply conditions.

[0020] Preferably, the power-on inspection working mode includes:

[0021] (1) Measurement of insulation resistance of power battery positive busbar

[0022] The first switch S 1 Contact 2 is closed, the second switch S 2 Contact 2 is closed, the third switch S 3 Contact 1 is closed, the fourth switch S 4 Disconnect; at this time, the voltage across the upper bridge arm resistor is U y According to Kirchhoff's current law, we can get

[0023]

[0024] It can be solved

[0025]

[0026] (2) Measurement of insulation resistance of DC load positive bus

[0027] The first switch S 1 Contact 2 is closed, the second switch S 2 Contact 2 is closed, the third switch S 3 Contact 2 is closed, the fourth switch S 4 Disconnect; at this time, the voltage across the upper bridge arm resistor is measured to be U' y According to Kirchhoff's current law, we can get

[0028]

[0029] Solved

[0030]

[0031] (3) Measurement of negative busbar insulation resistance

[0032] The first switch S 1 Contact 1 is closed, the second switch S 2 Contact 1 is closed, the third switch S 3 Disconnect, the fourth switch S 4 When the voltage across the lower bridge arm resistor is U x According to Kirchhoff's current law, we can get

[0033]

[0034] Solved

[0035]

[0036] Preferably, the passive bridge method insulation monitoring mode under normal high voltage power supply condition includes:

[0037] The first switch S 1 Contact 1 is closed, the second switch S 2 Close contact 2, or S 1 Close contact 2, S 2 Contact 1 is closed, the third switch S 3 Contact 1 is closed, the fourth switch S 4 Connect:

[0038] (1) Under normal circumstances, R 1 =R 2 =R 3 =∞,

[0039] (2) When According to the principle of balanced bridge method, R 1 or R 2 A drop occurred, or R 1 , R2 At the same time, a decrease occurred, R 3 Much larger than R 1 , R 2 The smaller of

[0040]

[0041] At this time, the third switch S 3 When contact 2 is connected, the voltage measured by the insulation monitoring circuit is assumed to be U' x , which can be calculated

[0042]

[0043] Combining the above two equations, we can get

[0044]

[0045]

[0046] (3) When When R 3 A decrease occurred, R 1 , R 2 Much larger than R 3 , which can be regarded as R 1 =R 2 =∞, we can calculate

[0047]

[0048] Thus, we can solve

[0049]

[0050] Preferably, the passive bridge insulation monitoring mode under normal high voltage power supply condition further includes:

[0051] Considering the U measured under normal circumstances x It won't be exactly In order to extend the service life of the switch, the threshold Δ is set according to the insulation resistance requirement. When the switch S 3 Action, measurement R 1 , R 2 The exact value of Only measure R 1 and converted R' 2 The parallel value of .

[0052] Preferably, the timed forced active working mode under normal high voltage power supply condition includes:

[0053] (1) Measurement of positive busbar insulation resistance

[0054] The first switch S 1 Contact 1 is closed, the second switch S 2 Contact 1 is closed, the third switch S 3 Contact 1 is closed, the fourth switch S 4 Disconnect, the voltage across the upper bridge arm resistor is U y According to Kirchhoff's current law, we can get

[0055]

[0056] Then, the first switch S 1 Contact 2 is closed, the second switch S 2 Contact 2 is closed, the third switch S 3 Contact 2 is closed, the fourth switch S 4 Disconnect, and measure the voltage across the upper bridge arm resistor to be U' y According to Kirchhoff's current law, we can get

[0057]

[0058] The combined solution is

[0059]

[0060]

[0061] (2) Measurement of negative busbar insulation resistance

[0062] The first switch S 1 Contact 1 is closed, the second switch S 2 Contact 1 is closed, the third switch S 3 Disconnect, the fourth switch S 4 The voltage across the lower bridge arm resistor is U' x , can be obtained

[0063]

[0064] Solved

[0065]

[0066] The following beneficial technical effects can be obtained by using the insulation monitoring method and monitoring device of the present invention:

[0067] 1. The equivalent conversion method is adopted to solve the insulation detection problem of high-voltage DC busbars of two voltage levels, and the precise positioning of faults is achieved through switching design.

[0068] 2. The power-on inspection, passive switching bridge insulation monitoring under normal power supply conditions, and timed forced active operation are integrated into one insulation monitoring circuit, realizing full-time and full-condition monitoring, with a simple system structure and high working reliability.

[0069] 3. The online monitoring method combining active monitoring and passive monitoring is adopted to solve the monitoring and detection problem when insulation faults occur simultaneously on the positive and negative busbars. At the same time, the switching operation is minimized, which effectively improves the service life of the monitoring device. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Various embodiments or examples ("examples") of the present disclosure are disclosed in the following detailed description and accompanying drawings. The drawings are not necessarily drawn to scale. In general, unless otherwise specified in the claims, the operations of the disclosed methods of the present disclosure may be performed in any order. In the drawings:

[0071] Figure 1 A circuit diagram of a full-operating-condition insulation monitoring method applied to a multi-voltage-level vehicle-mounted microgrid according to the present invention is shown;

[0072] Figure 2 The equivalent circuit after conversion according to the present invention is shown;

[0073] Figure 3 The figure is a working flow chart of the composite insulation monitoring scheme according to the present invention. DETAILED DESCRIPTION

[0074] Before explaining one or more embodiments of the present disclosure in detail, it should be understood that the embodiments are not limited to the construction details in their specific applications, and the steps or methods proposed in the following embodiments or drawings. The system and method of the present invention will be described in detail below with reference to the drawings.

[0075] Figure 1 The circuit diagram of the full-operating-condition insulation monitoring method for multi-voltage-level vehicle-mounted microgrids according to the present invention is shown. As shown in the figure, the circuit includes: two high-voltage DC circuits, an insulation monitor and a bidirectional DC / DC; the two high-voltage DC circuits, one of which is a nominal voltage of U 1 The power battery bus circuit has a nominal voltage of U 2 The two high-voltage DC circuits are connected via a bidirectional DC / DC phase, enabling bidirectional energy flow between the power battery and the DC load bus. Figure 1As shown, the negative bus 100 of the power battery and the negative bus 100 of the DC load are actually the same bus. In the power battery bus loop, the negative bus 100 of the power battery is connected to one end of the resistor R3, the other end of the resistor R3 is connected to another resistor R1, the other end of the resistor R1 is connected to the positive bus 101 of the power battery, and the connection between the resistor R3 and the resistor R1 is connected to the ground terminal. The insulation monitor of the present invention includes only one insulation monitoring circuit, which includes: a first switch S1, a built-in power supply Ui, a second switch S2, a first resistor 103, a second resistor 104, a third switch S3 and a fourth switch S4. Switches S1, S2, and S3 are double-contact switches of the same type, which have a first contact 1 and a second contact 2. One end (normally closed end) of the first switch S1 is connected between the resistors R1 and R3, and is also connected to the grounding section, and the other end thereof is connected to the built-in power supply Ui through contact 1 or 2. The built-in power supply Ui is placed between the first switch S1 and the second switch S2, the negative terminal of the built-in power supply Ui is connected to the first contact 1 of the first switch S1, and the positive terminal of the built-in power supply Ui is connected to the first contact 1 of the second switch S2. One end (normally closed end) of the second switch S2 is connected between the first resistor 103 and the second resistor 104, and the first resistor 103 is connected to the negative bus of the power battery through the fourth switch S4. The DC load bus circuit includes a DC load positive bus 201, a DC load negative bus 200, and a resistor R2. The second resistor R104 is connected to the DC load positive bus 201 through the third switch S3. The voltage between the insulation monitor and the first resistor 103 is recorded as U x (the voltage across the lower bridge arm resistor), the voltage between the second resistor 104 of the insulation monitor is recorded as U y (Voltage across the upper bridge arm resistor).

[0076] The bidirectional DC / DC includes a plurality of reverse-conducting insulated gate bipolar transistors, a plurality of inductors and a capacitor C. Figure 1As shown, there are four reverse-conducting insulated gate bipolar transistors, namely T1, T2, T3, and T4, each of which includes an insulated gate bipolar transistor IGBT and a reverse-parallel connected diode D. T1 is connected in series with T3, T2 is connected in series with T4, and the emitters of the insulated gate bipolar transistors IGBT in T3 and T4 are connected to the negative bus 100 of the DC load. The collector of the insulated gate bipolar transistor IGBT of T1 is connected to the DC load positive bus 201, the emitter of the insulated gate bipolar transistor IGBT of T1 is connected to T3, and is also connected to the second inductor L2; the collector of the insulated gate bipolar transistor IGBT of T2 is connected to the DC load positive bus 201, the emitter of the insulated gate bipolar transistor IGBT of T2 is connected to T4, and is also connected to the first inductor L1, the emitter of the insulated gate bipolar transistor IGBT of T4 is connected to the DC load negative bus 100, L1 is connected in parallel with L2 and then connected in series with one end of the third inductor L3, and the other end of L3 is connected to the power battery positive bus 101. Capacitor C is connected to the DC load negative bus 100 and the DC load positive bus 201. The nominal voltage is U 2 The DC load bus circuit includes a resistor R2, one end of which is connected to the DC load positive bus 201, and the other end of which is connected to the ground terminal GND.

[0077] When in use, an EMC filter circuit may be used in series with the above-mentioned dual-circuit insulation monitoring circuit.

[0078] According to the general design idea, two sets of insulation monitoring circuits are required to monitor the insulation of two high-voltage DC buses. However, the structure of using two or more sets of insulation monitoring circuits for distributed insulation monitoring in a system is complicated, and each insulation monitoring circuit needs to be corrected accordingly in order to eliminate the influence of other monitoring circuits other than itself, which leads to poor design flexibility.

[0079] To this end, the present invention designs a method to obtain the insulation resistance coupling relationship of two high-voltage DC busbars and realizes an insulation monitoring circuit to meet the insulation monitoring requirements of multiple voltage levels through conversion. The specific steps are as follows:

[0080] (1) Negative bus insulation monitoring: The power battery negative bus and the DC load negative bus are actually the same bus. Their measured insulation resistances must be equal. Therefore, only one of them needs to be measured, which is called the negative bus insulation resistance. Figure 1 R 3 shown.

[0081] (2) Positive bus insulation monitoring: Through theoretical calculation, it can be found that Figure 1 The insulation resistance R of the power battery busbar 1 Insulation resistance R between DC load and bus2 There is a coupling relationship between them, and the DC load bus increases the insulation resistance R 2 When connected in parallel with the power battery busbar, the resistor R U =(U 1 -U x )R 2 / (U 2 -U 1 ) has the same effect, that is, the converted insulation resistance R' 2 =R 2 / / R U ;Power battery busbar insulation resistance R 2 Converted to DC load bus, parallel resistor R' U =-(U 2 -U x )R 1 / (U 2 -U 1 )(Connecting a resistor with a negative resistance in parallel is equivalent to removing a parallel branch), that is, the converted insulation resistance R' 1 =R 1 / / R' U ,like Figure 2 shown.

[0082] Based on the above analysis, due to the insulation resistance R 1 Insulation resistance R between DC load and bus 2 There is a coupling relationship between the positive busbars on both sides, so a set of insulation monitoring circuits can be used to simultaneously monitor the insulation resistance of the positive busbars on both sides through the conversion method. Of course, it is precisely because of this coupling relationship that the insulation resistance of the positive busbars on both sides measured by the traditional insulation monitoring scheme is not the real resistance value, but the insulation resistance of one side and the insulation resistance of the other side after conversion in parallel. It is impossible to accurately know the insulation status of each side. Therefore, further monitoring and analysis are required to accurately locate the fault. To this end, the present invention is designed based on Figure 3 The working process of the insulation monitoring system is shown.

[0083] like Figure 3 As shown, the insulation monitoring system of the present invention mainly includes the following three working modes:

[0084] (1) Power-on inspection working mode:

[0085] After starting, first read the bus voltage U1, U2 of the power grid system, enter step ST1, and determine whether the high-voltage system is powered on. If the bus voltage is zero, it means that the high-voltage system is not powered on. At this time, enter step ST3 and enter the power-on inspection working mode based on active monitoring, that is, connect to the built-in power supply Ui, and actively measure the positive and negative bus insulation resistance of the system to ensure that the insulation state of the vehicle power system grid is good and the safe operation of the system is guaranteed.

[0086] (2) Passive switching bridge insulation monitoring mode under normal power supply conditions:

[0087] If the bus voltage is not zero, it means that the high voltage system is powered on. At this time, the bus nominal voltage U1, U2 and the lower bridge voltage U2 of the power battery bus circuit are recorded. x After power on, the process goes to step ST2 to determine whether an insulation fault occurs in the vehicle-mounted microgrid system. In step ST2, the lower bridge voltage U x And the power battery bus circuit nominal voltage U 1 half of the relationship; if:

[0088]

[0089] Then the process goes to step ST5 to determine that an insulation fault occurs in the negative bus, and then the process goes to step ST6 to measure the insulation resistance of the negative bus.

[0090] if:

[0091]

[0092] Then, the process goes to step ST7 to determine whether the positive busbar has insulation fault. In order to extend the service life of the switch and take into account the real-time performance of insulation monitoring, in step ST, the present invention sets a threshold value Δ according to the insulation resistance requirement. If yes, then go to step ST10 to measure the insulation resistance of the positive busbars on both sides. If no, then go to step ST9 to measure the parallel value of the insulation resistance on both sides.

[0093] It can be seen that in the passive switching bridge insulation monitoring mode under normal power supply conditions, in order to achieve the decoupling of the insulation resistance of the power battery bus positive bus and the DC load positive bus, the insulation fault must be carried out in two steps. The first step is mainly to realize the discovery of insulation faults, that is, to use the balanced bridge method to monitor the insulation status of the system in real time and discover insulation faults in time; the second stage is mainly to realize the measurement of insulation resistance, that is, to use a switching switch to switch the position of the bridge in the system, and calculate the insulation resistance value through the voltage values ​​measured twice, so as to realize the decoupling of the insulation resistance of the two buses, the power battery bus positive bus and the DC load positive bus.

[0094] (3) Timed forced active working mode under normal power supply conditions:

[0095] In step ST2, if there is

[0096]

[0097] Then enter the timed forced active working mode under normal high voltage power supply, and enter step ST4. Since the passive switching bridge method insulation monitoring mode uses the balanced bridge principle, it is difficult for the system to make a quick judgment when insulation faults occur in both the positive and negative busbars. Therefore, the forced insulation monitoring circuit enters the active working mode at regular intervals to monitor whether a bipolar insulation fault has occurred in the system, and promptly discover the insulation fault in the system. In step ST4, set the cycle time T. The cycle time T of the present invention is set to 1 minute. If it is greater than 1 minute, enter step ST11 to measure the bipolar insulation indicators of the two loops.

[0098] Combination Figure 1 The insulation monitoring circuit diagram shown in the figure details the operation process of the above three modes:

[0099] 1. High voltage inspection working mode before power-on

[0100] (1) Measurement of insulation resistance of power battery positive busbar

[0101] The first switch S 1 Contact 2 is closed, the second switch S 2 Contact 2 is closed, the third switch S 3 Contact 1 is closed, the fourth switch S 4 Disconnect. At this time, the voltage across the upper bridge arm resistor is U y According to Kirchhoff's current law, we can get

[0102]

[0103] It can be solved

[0104]

[0105] (2) Measurement of insulation resistance of DC load positive bus

[0106] The first switch S 1 Contact 2 is closed, the second switch S 2 Contact 2 is closed, the third switch S 3 Contact 2 is closed, the fourth switch S 4 Disconnect. At this time, the voltage across the upper bridge arm resistor is measured as U' y According to Kirchhoff's current law, we can get

[0107]

[0108] Solved

[0109]

[0110] (3) Measurement of negative busbar insulation resistance

[0111] The first switch S 1 Contact 1 is closed, the second switch S 2 Contact 1 is closed, the third switch S 3 Disconnect, the fourth switch S 4 When the voltage across the lower bridge arm resistor is U x According to Kirchhoff's current law, we can get

[0112]

[0113] Solved

[0114]

[0115] 2. Passive bridge insulation monitoring mode under normal high voltage power supply

[0116] The first switch S 1 Contact 1 is closed, the second switch S 2 Close contact 2 (or: S 1 Close contact 2, S 2 Close contact 1), third switch S 3 Contact 1 is closed, the fourth switch S 4 Connected.

[0117] (1) Under normal circumstances, R 1 =R 2 =R 3 =∞,

[0118] (2) When According to the principle of balanced bridge method, R 1 or R 2 A drop occurred, or R 1 , R 2 At the same time, a decrease occurred, R 3 Much larger than R 1 , R 2 The smaller of 3 =∞). We can get

[0119]

[0120] At this time, the third switch S 3 When contact 2 is connected, the voltage measured by the insulation monitoring circuit is assumed to be U' x , similarly we can calculate

[0121]

[0122] Combining equations (7) and (8), we can get

[0123]

[0124]

[0125] (3) When When R 3 A decrease occurred, R 1 , R 2 Much larger than R 3 (Can be regarded as R 1 =R 2 =∞).

[0126] It can be calculated

[0127]

[0128] Thus, we can solve

[0129]

[0130] In the above calculation, the larger insulation resistance is regarded as infinite. In fact, the insulation resistance cannot be infinite. Under normal circumstances, the measured U x It won't be exactly In order to extend the service life of the switch and take into account the real-time performance of insulation monitoring, the threshold Δ is set according to the insulation resistance requirement. When the switch S 3 Action, measurement R 1 , R 2 The exact value of Only measure R 1 and converted R' 2 The parallel value of .

[0131] 3. Timed forced active working mode under normal high voltage power supply

[0132] (1) Measurement of positive busbar insulation resistance

[0133] First, the first switch S 1 Contact 1 is closed, the second switch S 2 Contact 1 is closed, the third switch S 3 Contact 1 is closed, the fourth switch S 4 Disconnect. At this time, the voltage across the upper bridge arm resistor is U y According to Kirchhoff's current law, we can get

[0134]

[0135] Then, the first switch S 1 Contact 2 is closed, the second switch S 2 Contact 2 is closed, the third switch S 3 Contact 2 is closed, the fourth switch S 4 Disconnect. The voltage across the upper bridge arm resistor is measured as U' y According to Kirchhoff's current law, we can get

[0136]

[0137] Combining equations (13) and (14), we can obtain

[0138]

[0139]

[0140] (2) Measurement of negative busbar insulation resistance

[0141] The first switch S 1 Contact 1 is closed, the second switch S 2 Contact 1 is closed, the third switch S 3 Disconnect, the fourth switch S 4 The voltage across the lower bridge arm resistor is measured to be U' x , can be obtained

[0142]

[0143] Solved

[0144]

[0145] Although the present invention has been described with reference to the embodiments shown in the accompanying drawings, equivalent or alternative means may be used without departing from the scope of the claims. The components described and illustrated in the present invention are merely examples of systems / devices and methods that can be used to implement the embodiments of the present disclosure, and may be replaced with other devices and components without departing from the scope of the claims.

Claims

1. A full-operating-condition insulation monitoring system for multi-voltage-level on-board microgrids, comprising: A power battery bus circuit, a DC load bus circuit, an insulation monitor and a bidirectional DC / DC converter, wherein the power battery bus circuit and the DC load bus circuit are connected through the bidirectional DC / DC converter to achieve a bidirectional flow of energy between the power battery and the DC load bus; The power battery bus circuit includes: a power battery negative bus, a power battery positive bus, a resistor R1, and a resistor R3, wherein the power battery negative bus is connected to one end of the resistor R3, the other end of the resistor R3 is connected to the resistor R1, the other end of the resistor R1 is connected to the power battery positive bus, and the connection between the resistor R3 and the resistor R1 is commonly connected to the ground terminal; The DC load bus circuit includes: a DC load positive bus, a DC load negative bus, and a resistor R2; one end of the resistor R2 is connected to the DC load positive bus, and the other end is connected to the ground terminal GND; the characteristics are: The insulation monitor includes a single insulation monitoring circuit, which realizes the insulation monitoring requirements of the multi-voltage level vehicle-mounted microgrid by conversion through the coupling relationship between the insulation resistance of the power battery positive bus and the DC load positive bus; The insulation monitoring requirements include: negative bus insulation monitoring, positive bus insulation monitoring; the coupling relationship is: when the DC load bus increases the insulation resistance R2, the resistance R2 is connected in parallel with the power battery bus. U =(U1-U x )R2 / (U2-U1) has the same effect, the converted insulation resistance R'2=R2 / / R U The power battery bus insulation resistance R2 is converted to the DC load bus parallel resistance R' U =-(U2-U x )R1 / (U2-U1), the converted insulation resistance R'1=R1 / / R' U ; Among them, U1 is the power battery bus voltage, and U2 is the DC load bus voltage.

2. The full-condition insulation monitoring system according to claim 1 is characterized in that: The insulation monitoring circuit includes a first switch S1, a built-in power supply Ui, a second switch S2, a first resistor, a second resistor, a third switch S3 and a fourth switch S4; the switches S1, S2 and S3 are double-contact point type switching switches of the same type, each having a first contact and a second contact; one end of the first switch S1 is connected between the resistors R1 and R3, and is also connected to the ground terminal, and the other end is connected to the built-in power supply Ui through a contact; the built-in power supply Ui is placed between the first switch S1 and the second switch S2, the negative end of the built-in power supply Ui is connected to the first contact of the first switch S1, and the positive end of the built-in power supply Ui is connected to the first contact of the second switch S2; one end of the second switch S2 is connected between the first resistor and the second resistor, and the first resistor is connected to the negative bus of the power battery through the fourth switch S4; the second resistor is connected to the positive bus of the DC load through the third switch S3.

3. The full-condition insulation monitoring system according to claim 1 is characterized in that: The bidirectional DC / DC converter comprises: a plurality of reverse-conducting insulated gate bipolar transistors, a plurality of inductors and a capacitor C; the number of the reverse-conducting insulated gate bipolar transistors is four, namely T1, T2, T3 and T4, each of which comprises an insulated gate bipolar transistor IGBT and a reverse-parallel connected diode D; wherein T1 is connected in series with T3, T2 is connected in series with T4, the emitters of the insulated gate bipolar transistors IGBT in T3 and T4 are connected to the negative bus of the DC load; the collector of the insulated gate bipolar transistor IGBT of T1 is connected to the positive bus 201 of the DC load, and the insulated gate bipolar transistor IGBT of T1 is connected to the positive bus 202 of the DC load. The emitter of the bipolar transistor IGBT is connected to T3 and is also connected to the second inductor L2; the collector of the insulated gate bipolar transistor IGBT of T2 is connected to the DC load positive bus 201, the emitter of the insulated gate bipolar transistor IGBT of T2 is connected to T4 and is also connected to the first inductor L1, the emitter of the insulated gate bipolar transistor IGBT of T4 is connected to the DC load negative bus 100, L1 is connected in parallel with L2 and then connected in series with one end of the third inductor L3, and the other end of L3 is connected to the power battery positive bus 101; the positive and negative electrodes of the capacitor C are respectively connected to the DC load positive bus and the DC load negative bus.

4. The full-condition insulation monitoring system according to claim 1 is characterized in that: The insulation monitoring circuit includes three working modes: a power-on inspection working mode, a passive switching bridge method insulation monitoring mode under normal power supply conditions, and a timed forced active working mode under normal power supply conditions.

5. The full-operating-condition insulation monitoring method performed by the full-operating-condition insulation monitoring system according to any one of claims 1 to 4, characterized in that: The method comprises: Read the power battery bus voltage U1 and DC load bus voltage U2 of the multi-voltage level vehicle microgrid system; Determine whether U1 and U2 are zero; If yes, the multi-voltage level vehicle-mounted microgrid system is not powered on, the insulation monitoring circuit enters a power-on inspection working mode based on active monitoring; in this mode, the built-in power supply Ui is connected to actively measure the insulation resistance of the positive and negative busbars of the multi-voltage level vehicle-mounted microgrid system; If not, it means that the multi-voltage level vehicle-mounted microgrid system is powered on. At this time, U1, U2, and the lower bridge voltage U of the power battery bus circuit are recorded. x ; According to the lower bridge voltage U x and U1, to determine whether an insulation fault occurs in the multi-voltage level on-board microgrid system; if: Then it enters the timed forced active working mode under normal high voltage power supply; if: Then it enters the passive switching bridge insulation monitoring mode under normal power supply conditions.

6. The full-condition insulation monitoring method according to claim 5, characterized in that: The power-on inspection working mode includes: (1) Measurement of insulation resistance of power battery positive busbar The first switch S1 connects contact 2, the second switch S2 connects contact 2, the third switch S3 connects contact 1, and the fourth switch S4 is disconnected; at this time, the voltage across the upper bridge arm resistor is measured to be U y According to Kirchhoff's current law, we can get It can be solved (2) Measurement of insulation resistance of DC load positive bus The first switch S1 connects to contact 2, the second switch S2 connects to contact 2, the third switch S3 connects to contact 2, and the fourth switch S4 is disconnected; at this time, the voltage across the upper bridge arm resistor is measured to be U y ′, according to Kirchhoff’s current law, we can get Solved (3) Measurement of negative busbar insulation resistance The first switch S1 connects contact 1, the second switch S2 connects contact 1, the third switch S3 is disconnected, and the fourth switch S4 is connected. At this time, the voltage across the lower bridge arm resistor is measured to be U x According to Kirchhoff's current law, we can get Solved 7. The full-condition insulation monitoring method according to claim 6 is characterized in that: The passive bridge insulation monitoring mode under normal high voltage power supply condition includes: The first switch S1 connects to contact 1, the second switch S2 connects to contact 2, or S1 connects to contact 2, S2 connects to contact 1, the third switch S3 connects to contact 1, and the fourth switch S4 connects to: (1) Under normal circumstances, (2) When According to the principle of the balanced bridge method, it means that R1 or R2 has decreased, or R1 and R2 have decreased at the same time, and R3 is much larger than the smaller one of R1 and R2, so formula 1 can be obtained: At this time, the third switch S3 connects the contact 2, and the voltage measured by the insulation monitoring circuit is U' x , we can calculate formula 2: Combining equation 1 and equation 2, we can get (3) When When , it means that R3 has decreased, R1 and R2 are much larger than R3, which can be regarded as R1=R2=∞, and it can be calculated that Thus, we can solve 8. The full-condition insulation monitoring method according to claim 7, characterized in that: The passive bridge insulation monitoring mode under the normal high voltage power supply condition also includes: Considering the U measured under normal circumstances x It won't be exactly In order to extend the service life of the switch, the threshold Δ is set according to the insulation resistance requirement. When , the switch S3 is activated to measure the accurate values ​​of R1 and R2; when Only measure the parallel value of R1 and the reduced R'2.

9. The full-condition insulation monitoring method according to claim 5, characterized in that: The timed forced active working mode under the normal high voltage power supply condition includes: (1) Measurement of positive busbar insulation resistance The first switch S1 connects contact 1, the second switch S2 connects contact 1, the third switch S3 connects contact 1, and the fourth switch S4 is disconnected. At this time, the voltage across the upper bridge arm resistor is measured to be U y According to Kirchhoff's current law, we can get Then, the first switch S1 connects the contact 2, the second switch S2 connects the contact 2, the third switch S3 connects the contact 2, and the fourth switch S4 is disconnected. The voltage across the upper bridge arm resistor is measured to be U' y According to Kirchhoff's current law, we can get The combined solution is (2) Measurement of negative busbar insulation resistance The first switch S1 connects contact 1, the second switch S2 connects contact 1, the third switch S3 is disconnected, and the fourth switch S4 is connected. The voltage across the lower bridge arm resistor is measured to be U' x , can be obtained Solved

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