A Fault Isolation Method for a Three-Level DC / DC Parallel System

Abstract

The present application discloses a fault isolation method for a three-level DC / DC parallel system, which includes a plurality of isolation units and an energy supply unit; the isolation units are installed on the input side or the output side of the corresponding group of DC / DC units, and the energy supply unit is connected to the output end of the three-level DC / DC parallel system; the fault isolation includes the following processes: S100: When any DC / DC unit has a short-circuit fault, all DC / DC units are driven to block; S200: The isolation unit of the faulty group disconnects the faulty DC / DC unit from the three-level DC / DC parallel system; during this process, the energy supply unit supplies energy to the load; S300: After the faulty DC / DC unit is isolated, the remaining DC / DC units are restarted and resume supplying energy to the load. The beneficial effects of the present application: When a fault occurs, by blocking the drive of all DC / DC units, the spread of the fault can be avoided. Subsequently, the faulty DC / DC unit is disconnected through the isolation unit, which can ensure the operation safety of the subsequent three-level DC / DC parallel system after restarting.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and particularly relates to a fault isolation method for a three-level DC / DC parallel system. Background Art

[0002] The parallel technology of power electronic converters can effectively improve the reliability of the system. For example, three-level DC / DC is widely used in fields such as photovoltaic, UPS, and fuel cells. When a unit fails, if the system isolation is not timely, the fault will not only affect the faulty module, but also cause the fault to spread, making other modules unable to work properly, resulting in the output voltage being unable to be maintained and the entire system crashing. Therefore, fault isolation is a very important link in system fault tolerance. Summary of the Invention

[0003] One of the purposes of the present application is to provide a method capable of isolating a fault point when a three-level DC / DC parallel system fails.

[0004] To achieve at least one of the above purposes, the technical solution adopted by the present application is: a fault isolation method for a three-level DC / DC parallel system, including a plurality of isolation units and an energy supply unit; the isolation units are installed on the input side or the output side of the corresponding group of DC / DC units, and the energy supply unit is connected to the output end of the three-level DC / DC parallel system; the specific fault isolation includes the following process:

[0005] S100: When any of the DC / DC units has a short-circuit fault, all the DC / DC units are driven to be blocked.

[0006] S200: The isolation unit in the faulty group disconnects the faulty DC / DC unit from the three-level DC / DC parallel system; during this process, the energy supply unit supplies energy to the load.

[0007] S300: After the faulty DC / DC unit is isolated, the remaining DC / DC units are unblocked and resume supplying energy to the load.

[0008] Preferably, the short-circuit fault of the DC / DC unit includes the short-circuit fault of the IGBT unit; for the short-circuit fault of the IGBT unit, any one of a fuse, a contactor, and an electronic switch is adopted by the isolation unit.

[0009] Preferably, the short-circuit fault of the DC / DC unit includes the short-circuit fault of the diode; for the short-circuit fault of the diode, any one of a fuse, a contactor, an electronic switch, and a diode is adopted by the isolation unit.

[0010] Preferably, the three-level DC / DC parallel system is an N + n redundant system; where N represents the number of the DC / DC units operating normally, and n represents the number of the standby DC / DC units; when the isolation unit uses a fuse, the value of N is greater than 6.

[0011] Preferably, for the short-circuit fault of the IGBT unit, when the isolation unit is installed on the input side of the DC / DC unit, the number of the isolation units is two and they are respectively connected to the positive and negative buses; when the isolation unit is installed on the output side of the DC / DC unit, the number of the isolation units is one and it is connected to the neutral line.

[0012] Preferably, for the short-circuit fault of the diode, when the isolation unit does not use a diode, the isolation unit is only installed on the input side of the DC / DC unit; the number of the isolation units is two and they are respectively connected to the positive and negative buses.

[0013] Preferably, for the short-circuit fault of the diode, when the isolation unit uses a diode, when the isolation unit is installed on the input side or the output side of the DC / DC unit; the number of the isolation units is two and they are respectively connected to the positive and negative buses.

[0014] Preferably, when the three-level DC / DC parallel system operates normally, the energy supply unit is adapted to store energy through the output end of the three-level DC / DC parallel system.

[0015] Preferably, the energy supply unit includes a battery pack or a supercapacitor bank; the battery pack or the supercapacitor bank is adapted to be directly connected to the output end of the three-level DC / DC parallel system.

[0016] Preferably, the energy supply unit includes a bidirectional DC / DC unit and a battery pack or a supercapacitor bank; the battery pack or the supercapacitor bank is adapted to be connected to the output end of the three-level DC / DC parallel system through the bidirectional DC / DC unit.

[0017] Compared with the prior art, the beneficial effects of the present application are as follows:

[0018] (1) By installing an isolation unit on each DC / DC unit, the present application can drive and block all the DC / DC units when a fault occurs in the DC / DC unit, so as to avoid the spread of the fault. Subsequently, the faulty DC / DC unit is disconnected from the three-level DC / DC parallel system through the corresponding isolation unit, thereby ensuring the operation safety of the subsequent three-level DC / DC parallel system after restart.

[0019] (2) Meanwhile, in this application, by connecting an energy supply unit to the output end of the three-level DC / DC parallel system, when all the DC / DC units are driven and blocked, the load can continue to be powered by the energy supply unit to ensure the normal operation of the load. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of circuit analysis when an IGBT unit fails in an existing three-level DC / DC Figure 1 .

[0021] Figure 2 Schematic diagram of circuit analysis when an IGBT unit fails in an existing three-level DC / DC Figure 2 .

[0022] Figure 3 Schematic diagram of circuit analysis when a diode fails in an existing three-level DC / DC Figure 1 .

[0023] Figure 4 Schematic diagram of circuit analysis when a diode fails in an existing three-level DC / DC Figure 2 .

[0024] Figure 5 Schematic diagram of the circuit installation structure of one embodiment of the present invention Figure 1 .

[0025] Figure 6 Schematic diagram of the circuit installation structure of one embodiment of the present invention Figure 2 .

[0026] Figure 7 Schematic diagram of the circuit installation structure of another embodiment of the present invention Figure 1 .

[0027] Figure 8 Schematic diagram of the circuit installation structure of another embodiment of the present invention Figure 2 .

[0028] Figure 9 Schematic diagram of the circuit installation structure of still another embodiment of the present invention Figure 1 .

[0029] Figure 10 Schematic diagram of the circuit installation structure of still another embodiment of the present invention Figure 2 .

[0030] Figure 11 Schematic diagram of the structure of one embodiment of the energy supply unit in the present invention.

[0031] Figure 12 Schematic diagram of the structure of another embodiment of the energy supply unit in the present invention.

[0032] In the figure: DC / DC unit 100, first converter 110, second converter 120, load 200, isolation unit 310, energy supply unit 320. Specific implementation manners

[0033] Next, in combination with specific implementation manners, the present application will be further described. It should be noted that on the premise of no conflict, the following-described embodiments or technical features can be arbitrarily combined to form new embodiments.

[0034] In the description of the present application, it should be noted that for orientation terms, if there are terms such as "center", "transverse", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicating the orientation and position relationship is based on the orientation or position relationship shown in the drawings. This is only for facilitating the description of the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and should not be construed as limiting the specific protection scope of the present application.

[0035] It should be noted that the terms "first", "second", etc. in the description and claims of the present application are used to distinguish similar objects and do not necessarily need to describe a specific order or sequence.

[0036] One preferred embodiment of the present application is as Figures 5 to 12 shown. A fault isolation method for a three-level DC / DC parallel system includes a plurality of isolation units 310 and an energy supply unit 320. The isolation unit 310 is installed on the input side or the output side of the corresponding group of DC / DC units 100, and the energy supply unit 320 is connected to the output end of the three-level DC / DC parallel system; the specific fault isolation includes the following process:

[0037] S100: When any DC / DC unit 100 has a short-circuit fault, all DC / DC units 100 perform drive blocking.

[0038] S200: The isolation unit 310 in the faulty group disconnects the faulty DC / DC unit 100 from the three-level DC / DC parallel system; during this process, the energy supply unit 320 supplies energy to the load 200.

[0039] S300: After the faulty DC / DC unit 100 is isolated, the remaining DC / DC units 100 restart and resume power supply to the load 200; at the same time, the three-level DC / DC parallel system without the faulty DC / DC unit 100 after restart can also charge the energy supply unit 320.

[0040] It can be understood that the three-level DC / DC parallel system of the present application includes multiple groups of DC / DC units 100, and the multiple groups of DC / DC units 100 are connected in parallel with each other. Thus, when any one or more groups of DC / DC units 100 have a short-circuit fault, forced series connection may occur between the multiple groups of DC / DC units 100 connected in parallel, which may in turn cause abnormal operation of other DC / DC units 100.

[0041] It can also be understood that as Figures 1 to 10 shown, the DC / DC unit 100 includes a first converter 110, an IGBT unit group, a diode group, and a second converter 120. Common short-circuit faults of the DC / DC unit 100 include IGBT unit short-circuit faults and diode short-circuit faults.

[0042] In this embodiment, as Figures 5 to 10 shown, when the DC / DC unit 100 has a short-circuit fault, it will cause the output voltage of the three-level DC / DC parallel system to become abnormal. Therefore, to implement the circuit transformation of the traditional three-level DC / DC parallel system, it is first necessary to stabilize its output voltage; that is, connect the energy supply unit 320 to the output end of the traditional three-level DC / DC parallel system. When the three-level DC / DC parallel system is working normally, the energy supply unit 320 can store energy through the three-level DC / DC parallel system; when the DC / DC unit 100 has a short-circuit fault, the energy supply unit 320 can maintain the voltage stability of the output end of the three-level DC / DC parallel system to the load 200. And, during the subsequent driving block of the DC / DC unit 100, the energy supply unit 320 can continue to supply power to the load 200 to ensure that the load 200 continues to operate normally during the driving block of the DC / DC unit 100.

[0043] In one embodiment of the present application, as Figure 11 shown, the energy supply unit 320 includes a battery pack or a supercapacitor pack; the battery pack or the supercapacitor pack can be directly connected to the output end of the three-level DC / DC parallel system. Thus, when the three-level DC / DC parallel system is working normally, the battery pack or the supercapacitor pack can be charged and stored with energy. When there is a short-circuit fault in the DC / DC unit 100, the battery pack or the supercapacitor pack can release the electric energy stored in itself and supply it to the load 200.

[0044] Of course, in order to further improve the voltage stability of the power supply unit 320 during the power supply process and the voltage stability of the three-level DC / DC parallel system for charging the power supply unit 320. Another embodiment of the present application is as follows Figure 12 As shown, the power supply unit 320 includes a bidirectional DC / DC unit and a battery pack or a supercapacitor bank; the battery pack or the supercapacitor bank can be connected to the output end of the three-level DC / DC parallel system through the bidirectional DC / DC unit.

[0045] For the convenience of understanding the subsequent content, the fault analysis of the traditional three-level DC / DC parallel system can be carried out first.

[0046] For the sake of simplifying the narrative content, as Figures 1 to 4 shown, two sets of DC / DC units 100 can be taken and marked as #1 and #2 respectively; and it is assumed that the DC / DC unit 100 of the #1 group fails.

[0047] (1) IGBT fault analysis.

[0048] The IGBT unit group includes two IGBT units. The two IGBT units of the DC / DC unit 100 of the #1 group can be marked as S1 and S2 respectively. The two IGBT units of the DC / DC unit 100 of the #2 group are marked as S3 and S4 respectively.

[0049] As Figure 1 and Figure 2 shown, when the IGBT unit marked as S1 has a short-circuit fault, the first converter 110 and the second converter 120 of the DC / DC unit 100 of the #1 group are forcibly connected together. Due to the non-isolation of the system, the first converter 110 and the second converter 120 of the DC / DC unit 100 of the #2 group are also forcibly connected together, thereby causing the abnormal operation of the DC / DC unit 100 of the #2 group.

[0050] Specifically, as Figure 1 and Figure 2 shown, whether the IGBT unit marked as S3 in the DC / DC unit 100 of the #2 group is turned off and the IGBT unit marked as S4 is turned on; or the IGBT unit marked as S3 is turned on and the IGBT unit marked as S4 is turned off. Abnormal currents can be formed between the two sets of DC / DC units 100 as Figure 1 and Figure 2The circuit indicated by the bold line; meanwhile, the direction indicated by the dashed arrow in the figure is the current direction of the circuit. Thus, the short-circuit current of the fault group #1 will be introduced into the normal group #2, resulting in the continuous charging of the inductor L4, and the current will increase more and more with the accumulation of time. When the accumulated current exceeds the set upper threshold, all the IGBT unit drives have to be blocked. At this time, the upper bus voltage of the two DC / DC units 100 gradually drops to zero, and the lower bus voltage is equal to the input voltage, and the entire three-level DC / DC parallel system shuts down.

[0051] (2) Diode fault analysis.

[0052] The diode group includes two diodes. The two diodes of the DC / DC unit 100 marked as #1 can be respectively marked as D1 and D2. The two diodes of the DC / DC unit 100 marked as #2 can be respectively marked as D3 and D4.

[0053] As Figure 3 and Figure 4 shown, when the diode marked as D1 has a short-circuit fault, the first converter 110 and the second converter 120 of the DC / DC unit 100 in group #1 are forcibly connected together. Due to the non-isolation of the system, the first converter 110 and the second converter 120 of the DC / DC unit 100 in group #2 are also forcibly connected together, resulting in the abnormal operation of the DC / DC unit 100 marked as #2.

[0054] Specifically, as Figure 3 shown, when the IGBT unit marked as S3 in the DC / DC unit 100 of group #2 is turned on and the IGBT unit marked as S4 is turned off, a short-circuit loop as indicated by the bold line in Figure 3 can be formed between the two DC / DC units 100. Meanwhile, the direction indicated by the dashed arrow in the figure is the current direction of the short-circuit loop. The inductor L1 can directly span between the input side and the output side of the DC / DC unit 100, resulting in the reverse flow of the short-circuit current, and causing the upper bus capacitor to rapidly charge the inductors L1 and L3.

[0055] Similarly, as Figure 4 shown, when the IGBT unit marked as S3 in the DC / DC unit 100 of group #2 is turned off and the IGBT unit marked as S4 is turned on, a short-circuit loop as indicated by the bold line in Figure 4 can be formed between the two DC / DC units 100; meanwhile, the direction indicated by the dashed arrow in the figure is the current direction of the loop. The current of the inductor L1 continues to flow through the diode D3.

[0056] Therefore, after the diode fails, it needs to be immediately isolated to prevent affecting the normal operation of other units.

[0057] The following will elaborate on the specific isolation methods when short - circuit faults occur in the IGBT unit and the diode short - circuit fault respectively in the three - level DC / DC parallel system. To simplify the elaboration content, only two DC / DC units 100 of the three - level DC / DC parallel system are selected and marked as #1 and #2 respectively.

[0058] (1) The isolation methods for IGBT unit short - circuit faults include but are not limited to the following two embodiments.

[0059] Embodiment 1: As Figure 5 and Figure 6 shown, the isolation unit 310 uses fuses to isolate the faulty IGBT unit. From Figure 1 and Figure 2 it can be known that when a short - circuit fault occurs in the IGBT unit, the positive input terminal of the DC / DC unit 100 in the faulty group is forcibly connected to the output mid - point to form a short - circuit loop. Thus, the fuse can be connected to the formed short - circuit loop, and then the fuse is blown by the short - circuit current to disconnect the connection between the positive input terminal and the output mid - point of the DC / DC unit 100 in the faulty group.

[0060] In this embodiment, as Figure 5 and Figure 6 shown, the fuse can be set on the input side of the DC / DC unit 100 or on the output side of the DC / DC unit 100. When the fuse is set on the input side of the DC / DC unit 100, the number of fuses is two, and the two fuses are respectively connected to the positive and negative busbars of the DC / DC unit 100. When the fuse is set on the output side of the DC / DC unit 100, the number of fuses is one, and the fuse can be connected to the output terminal mid - line of the DC / DC unit 100. Thus, the number of fuses can be saved.

[0061] Specifically, as Figure 5As shown, take the example where the fuse is installed on the input side of the DC / DC unit 100. The two fuses on the input side of the DC / DC unit 100 in Group #1 are respectively marked as F1 and F2; the two fuses on the input side of the DC / DC unit 100 in Group #2 are respectively marked as F3 and F4. Assume that the IGBT unit marked as S1 in Group #1 has a short-circuit fault; after the fault is successfully detected, the drive of all IGBT units included in the DC / DC units 100 of all groups is blocked. Thus, a short-circuit loop including fuse F1 and fuse F3 can be formed; at this time, the voltage of the input-side power supply is greater than the half-bus voltage, so a short-circuit current is formed in the short-circuit loop; because there are two diode loops for current shunting at the negative end, the fuse F1 at the positive end melts first, and then disconnects the faulty Group #1 and the entire three-level DC / DC parallel system. During this process, the energy supply unit 320 and the load 200 are temporarily connected and the energy supply is maintained; at the same time, the energy supply unit 320 can also be connected to the short-circuit loop to absorb the short-circuit current flowing into the bus, and thus can support the bus. Subsequently, the drive block of all IGBT units is released, but the DC / DC unit 100 of the faulty group is disconnected from the DC / DC units 100 of the remaining normal groups due to the open circuit of the positive bus on the input side. Furthermore, the restarted three-level DC / DC parallel system can resume power supply to the load 200 through the DC / DC units 100 of the normal groups; at the same time, the restarted three-level DC / DC parallel system can also charge and store energy in the energy supply unit 320.

[0062] It can be understood that in order to meet the above isolation requirements, the input-side power supply of the three-level DC / DC parallel system has the ability to draw out the short-circuit current; at the same time, the energy supply unit 320 has the ability to absorb the short-circuit current, and the diode has the ability to withstand the short-circuit current shunting.

[0063] In this embodiment, the three-level DC / DC parallel system is an N + n redundant system; where N represents the number of normally operating DC / DC units 100, and n represents the number of standby DC / DC units 100; when the isolation unit 310 uses a fuse, the value of N needs to be greater than 6; at the same time, the value of n is generally greater than or equal to 1.

[0064] It can be understood that when the DC / DC unit 100 of the faulty group is isolated and disconnected, restarting the three-level DC / DC parallel system will cause the load current borne by each DC / DC unit 100 to increase under the condition that the input-side voltage remains unchanged. If the number of remaining DC / DC units 100 in the three-level DC / DC parallel system is too small, the increased load current borne by each DC / DC unit 100 will be overloaded, which will further cause the fuse of the DC / DC unit 100 in the normal group to melt, resulting in the shutdown of the entire three-level DC / DC parallel system again. Therefore, when the isolation unit 310 uses a fuse, it is necessary to ensure that the three-level DC / DC parallel system includes a sufficient number of DC / DC units 100, so that after some DC / DC units 100 fail and are isolated, the load current borne by the remaining DC / DC units 100 will not be overloaded.

[0065] Embodiment 2: As Figure 7 and Figure 8 shown, the isolation unit 310 uses a contactor or an electronic switch to isolate the faulty IGBT unit. From Figure 1 and Figure 2 it can be known that when a short-circuit fault occurs in an IGBT unit, the input positive terminal of the DC / DC unit 100 of the faulty group is forcibly connected to the output midpoint. Thus, the contactor or the electronic switch can be connected in the formed short-circuit loop, and then the connection between the input positive terminal and the output midpoint of the DC / DC unit 100 of the faulty group can be disconnected by opening and closing the contactor or the electronic switch.

[0066] In this embodiment, as Figure 7 and Figure 8 shown, the contactor or the electronic switch can be arranged on the input side of the DC / DC unit 100 or on the output side of the DC / DC unit 100. When the contactor or the electronic switch is arranged on the input side of the DC / DC unit 100, the number of contactors or electronic switches is two, and the two contactors or electronic switches are respectively connected to the positive and negative busbars of the DC / DC unit 100. When the contactor or the electronic switch is arranged on the output side of the DC / DC unit 100, the number of contactors or electronic switches is one, and the contactor or the electronic switch can be connected to the output midpoint line of the DC / DC unit 100; since the current in the midpoint line is relatively small, the conduction loss of the device can be reduced to a certain extent.

[0067] Specifically, as Figure 7 shown, taking the contactor or the electronic switch installed on the input side of the DC / DC unit 100 as an example. The two contactors or electronic switches on the input side of the DC / DC unit 100 of the #1 group are respectively marked as S11 and S12; the two contactors or electronic switches on the input side of the DC / DC unit 100 of the #2 group are respectively marked as S21 and S22.

[0068] Initially, all four contactors or electronic switches are in the normally closed state. Assume that the IGBT unit marked as S1 in Group #1 has a short - circuit fault; after successful fault detection, drive blocking is performed on all IGBT units included in the DC / DC units 100 of all groups; at the same time, the contactor or electronic switch marked as S11 connected to the faulty group is opened; during this process, the power supply unit 320 and the load 200 are temporarily connected and the power supply is maintained. Subsequently, the drive blocking of all IGBT units is released. Since the contactor or electronic switch of the DC / DC unit 100 of the faulty group is in the open state, the DC / DC unit 100 of the faulty group is disconnected from the DC / DC units 100 of the remaining normal groups. Thus, the restarted three - level DC / DC parallel system can supply power to the load 200 normally again; at the same time, the restarted three - level DC / DC parallel system can also charge and store energy in the power supply unit 320.

[0069] It can be understood that, compared with Embodiment 1, Embodiment 2 has no requirement for the number of DC / DC units 100 included in the three - level DC / DC parallel system. And during the isolation process of the DC / DC unit 100 of the faulty group, by opening the contactor or electronic switch and performing drive blocking on the IGBT unit simultaneously, a short - circuit loop cannot be formed, thereby avoiding the device from bearing the short - circuit current. However, Embodiment 2 will cause an increase in the conduction loss of the three - level DC / DC parallel system. Therefore, for Embodiment 1 and Embodiment 2, those skilled in the art can make a choice according to actual needs.

[0070] (2) The isolation methods for diode short - circuit faults include but are not limited to the following three embodiments.

[0071] Embodiment 1: As Figure 5 shown, the isolation unit 310 uses fuses to isolate the faulty diode. As Figure 3 and Figure 4 known, when there is a diode with a short - circuit fault, the input positive terminal of the DC / DC unit 100 of the faulty group is forced to be connected to the output positive terminal to form a reverse short - circuit loop. Thus, the fuse can be connected to the formed short - circuit loop, and then the fuse is blown by the short - circuit current to disconnect the connection between the input positive terminal and the output positive terminal of the DC / DC unit 100 of the faulty group.

[0072] In this embodiment, as Figure 5 shown, the fuses are only set on the input side of the DC / DC unit 100, and the number of fuses is two. The two fuses are respectively connected to the positive and negative busbars of the DC / DC unit 100.

[0073] It can be understood that if the fuses are set on the output side of the DC / DC unit 100, asFigure 3 and Figure 4 As shown, when a short - circuit fault occurs in the diode, the short - circuit loop does not pass through the neutral line of the DC / DC unit 100. Therefore, if the fuse wants to isolate the faulty diode, it can only be set on the positive and negative busbars on the output side of the DC / DC unit 100. When one of the diodes fails and the corresponding fuse blows, the drive block of all IGBT units is released. The remaining normal diodes in the DC / DC unit 100 of the faulty group can still conduct, making the DC / DC unit 100 of the faulty group prone to overload and thus triggering a fault again.

[0074] Specifically, as Figure 5 shown, the two fuses on the input side of the DC / DC unit 100 of group #1 are respectively marked as F1 and F2; the two fuses on the input side of the DC / DC unit 100 of group #2 are respectively marked as F3 and F4. Assume that the diode marked as D1 in group #1 has a short - circuit fault. After successful fault detection, the drive block of all IGBT units included in the DC / DC unit 100 of all groups is performed. Subsequently, the IGBT unit marked as S3 in group #2 is turned on, creating a short - circuit loop between the entire faulty group #1 and the normal group #2, and then the fuse F1 is blown. During this process, the energy supply unit 320 and the load 200 are temporarily connected and the energy supply is maintained; at the same time, the energy supply unit 320 can also be connected to the short - circuit loop to absorb the short - circuit current flowing into the busbar, and thus can support the busbar. Subsequently, the drive block of all IGBT units is released, but due to the open circuit of the positive busbar on the input side of the DC / DC unit 100 of the faulty group, the entire DC / DC unit 100 of the faulty group is disconnected from the DC / DC units 100 of the other normal groups. Then the restarted three - level DC / DC parallel system can resume power supply to the load 200 through the DC / DC units 100 of the normal groups; at the same time, the restarted three - level DC / DC parallel system can also charge and store energy in the energy supply unit 320.

[0075] It can be understood that in order to avoid overload, the number of DC / DC units 100 included in the three - level DC / DC parallel system in this embodiment needs to meet the above - mentioned redundancy system N + n value requirements.

[0076] It can also be understood that when all IGBT units are driven and blocked, no short - circuit loop will be generated between Group #1 and Group #2. Therefore, in order to ensure that the fuse connected to the faulty diode can be blown, a short - circuit loop needs to be constructed; that is, the IGBT unit marked as S3 in the normal Group #2 is turned on, so that a short - circuit loop including the faulty diode and the fuse connected thereto can be formed between Group #1 and Group #2. Since the conduction direction of diode D4 is opposite to the current direction of the required short - circuit loop, turning on the IGBT unit marked as S4 in Group #2 cannot form the required short - circuit loop either.

[0077] Embodiment 2: As Figure 7 shown, the isolation unit 310 adopts a contactor or an electronic switch to isolate the faulty diode. From Figure 3 and Figure 4 it can be known that when a short - circuit fault occurs in a diode, the input positive terminal of the DC / DC unit 100 of the faulty group is forcibly connected to the output positive terminal to form a reverse short - circuit loop. Thus, a contactor or an electronic switch can be connected to the formed short - circuit loop, and then the connection between the input positive terminal and the output positive terminal of the DC / DC unit 100 of the faulty group can be disconnected by opening and closing the contactor or the electronic switch.

[0078] In this embodiment, as Figure 7 shown, the contactor or the electronic switch is only arranged on the input side of the DC / DC unit 100; the number of contactors or electronic switches is two, and the two contactors or electronic switches are respectively connected to the positive and negative busbars of the DC / DC unit 100.

[0079] Specifically, as Figure 7 shown, the two contactors or electronic switches on the input side of the DC / DC unit 100 of Group #1 are respectively marked as S11 and S12; the two contactors or electronic switches on the input side of the DC / DC unit 100 of Group #2 are respectively marked as S21 and S22.

[0080] Initially, all four contactors or electronic switches are in the normally closed state. Assume that the diode marked as D1 in Group #1 has a short - circuit fault; after successful fault detection, all IGBT units included in the DC / DC units 100 of all groups are drive - blocked; at the same time, the contactor or electronic switch marked as S11 connected to the faulty group is opened; during this process, the power supply unit 320 and the load 200 are temporarily connected and power supply is maintained. Subsequently, the drive - blocking of all IGBT units is released. Since the contactor or electronic switch of the DC / DC unit 100 of the faulty group is in the open state, the DC / DC unit 100 of the faulty group is disconnected from the DC / DC units 100 of the remaining normal groups. Thus, the restarted three - level DC / DC parallel system can supply power to the load 200 normally again; at the same time, the restarted three - level DC / DC parallel system can also charge and store energy in the power supply unit 320.

[0081] Embodiment 3: As Figure 9 and Figure 10 shown, the isolation unit 310 uses diodes to isolate the faulty diode. From Figure 3 and Figure 4 it can be known that when there is a short - circuit fault in a diode, the input positive terminal of the DC / DC unit 100 of the faulty group is forcibly connected to the output positive terminal to form a reverse short - circuit loop. Thus, the diode used for isolation can be placed in the formed short - circuit loop, and then the connection between the input positive terminal and the output positive terminal of the DC / DC unit 100 of the faulty group is disconnected through the diode.

[0082] In this embodiment, as Figure 9 and Figure 10 shown, the diodes used for isolation can be set on the input side of the DC / DC unit 100 or on the output side of the DC / DC unit 100. Whether the diodes used for isolation are set on the input side or the output side of the DC / DC unit 100, the number of diodes used for isolation is two, and the two diodes are respectively connected to the positive and negative busbars of the DC / DC unit 100. When the diodes used for isolation are set on the output side of the DC / DC unit 100, the conduction loss of the device can be reduced to a certain extent.

[0083] Specifically, taking the case where the diodes used for isolation are set on the input side of the DC / DC unit 100 as an example. As Figure 9 shown, the two diodes used for isolation in Group #1 are respectively marked as D11 and D12, and the two diodes used for isolation in Group #2 are respectively marked as D21 and D22.

[0084] Initially, the conduction directions of diode D11 and diode D1 are the same, the conduction directions of diode D12 and diode D2 are the same, the conduction directions of diode D21 and diode D3 are the same, and the conduction directions of diode D22 and diode D4 are the same; thus, the normal operation of the DC / DC unit 100 can be ensured.

[0085] Suppose that diode D1 in the #1 group has a short-circuit fault, and the IGBT units of all DC / DC units 100 are blocked; Figure 4 It can be seen that a reverse short-circuit loop can theoretically be formed between the #1 group and the #2 group. And the isolation diodes D11 and D21 are both located in the above short-circuit loop. Since the conduction direction of diode D11 is opposite to the current direction of the short-circuit loop, the short-circuit loop cannot conduct. That is, through the reverse cut-off of diode D11, when diode D1 has a short-circuit fault, a short-circuit loop cannot be formed, and thus the fault group #1 is disconnected from the three-level DC / DC parallel system. During this process, the energy supply unit 320 and the load 200 are temporarily connected and the energy supply is maintained. Subsequently, the drive block of all IGBT units is released. Since the DC / DC unit 100 of the fault group is cut off by diode D11, the DC / DC unit 100 of the fault group is disconnected from the DC / DC units 100 of the other normal groups. Furthermore, the restarted three-level DC / DC parallel system can supply energy to the load 200 normally again; at the same time, the restarted three-level DC / DC parallel system can also charge and store energy for the energy supply unit 320.

[0086] The above describes the basic principle, main features, and advantages of the present application. Those skilled in the art of this industry should understand that the present application is not limited by the above embodiments. What is described in the above embodiments and the specification is only the principle of the present application. Without departing from the spirit and scope of the present application, the present application will have various changes and improvements, and these changes and improvements all fall within the scope of the present application claimed. The scope of protection claimed by the present application is defined by the appended claims and their equivalents.

Claims

1. A fault isolation method for a three-level DC / DC parallel system, the three-level DC / DC parallel system comprising multiple groups of DC / DC units, and the multiple groups of DC / DC units being connected in parallel with each other; characterized in that, It further includes a plurality of isolation units and power supply units; the isolation units are installed on the input side or the output side of the corresponding group of DC / DC units, and the power supply units are connected to the output end of the three-level DC / DC parallel system; the specific fault isolation includes the following process: S100: When any of the DC / DC units has a short-circuit fault, all the DC / DC units are driven to block, so that the input positive terminal of the DC / DC units in the fault group is forced to be connected to the output midpoint or the output positive terminal to form a short-circuit loop; S200: The isolation units in the fault group are connected to the short-circuit loop, thereby disconnecting the faulty DC / DC unit from the three-level DC / DC parallel system; during this process, the power supply unit supplies power to the load and absorbs the short-circuit current flowing into the bus by connecting to the short-circuit loop; S300: After the faulty DC / DC unit is disconnected, the remaining DC / DC units are released from the block and resume power supply to the load.

2. The fault isolation method of the three-level DC / DC parallel system according to claim 1, characterized in that: The short-circuit fault of the DC / DC unit includes the short-circuit fault of the IGBT unit; for the short-circuit fault of the IGBT unit, any one of a fuse, a contactor, and an electronic switch is adopted for the isolation unit.

3. The fault isolation method of the three-level DC / DC parallel system according to claim 1, characterized in that: The short-circuit fault of the DC / DC unit includes the short-circuit fault of the diode; for the short-circuit fault of the diode, any one of a fuse, a contactor, an electronic switch, and a diode is adopted for the isolation unit.

4. The fault isolation method for the three-level DC / DC parallel system according to claim 2 or 3, characterized in that: The three-level DC / DC parallel system is an N + n redundant system; where N represents the number of normally operating DC / DC units, and n represents the number of standby DC / DC units; then when the isolation unit adopts a fuse, the value of N is greater than 6.

5. The fault isolation method of the three-level DC / DC parallel system according to claim 2, characterized in that: When the isolation unit is installed on the input side of the DC / DC unit, the number of the isolation units is two and they are respectively connected to the positive and negative buses; when the isolation unit is installed on the output side of the DC / DC unit, the number of the isolation units is one and it is connected to the neutral line.

6. The fault isolation method of the three-level DC / DC parallel system according to claim 3, characterized in that: When the isolation unit does not adopt a diode, the isolation unit is only installed on the input side of the DC / DC unit; the number of the isolation units is two and they are respectively connected to the positive and negative buses.

7. The fault isolation method of the three-level DC / DC parallel system according to claim 3, characterized in that: When the isolation unit adopts a diode, the isolation unit is installed on the input side or the output side of the DC / DC unit; the number of the isolation units is two and they are respectively connected to the positive and negative buses.

8. The fault isolation method of the three-level DC / DC parallel system according to claim 1, characterized in that: When the three-level DC / DC parallel system is working normally, the power supply unit is adapted to store energy through the output end of the three-level DC / DC parallel system.

9. The fault isolation method of the three-level DC / DC parallel system according to claim 8, characterized in that: The power supply unit includes a battery pack or a supercapacitor pack; the battery pack or the supercapacitor pack is adapted to be directly connected to the output end of the three-level DC / DC parallel system.

10. The fault isolation method of the three-level DC / DC parallel system according to claim 8, characterized in that: The power supply unit includes a bidirectional DC / DC unit and a battery pack or a supercapacitor pack; the battery pack or the supercapacitor pack is adapted to be connected to the output end of the three-level DC / DC parallel system through the bidirectional DC / DC unit.

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