A method for rapid fault isolation of a common DC bus system

Abstract

The invention discloses a method for rapid isolation of faults in a common DC bus system, which is characterized by comprising the following steps: S1, partitioning the source, network and load of the common DC bus system into protection zones; S2, dividing the protection actions after a fault occurs in each zone according to the structure of the common DC bus system; S3, reliably distinguishing the fault in the AC protection zone from the fault in the remaining protection zones according to whether the AC side of each zone is energized after the action; S4, when a single zone is acted upon and the remaining two zones are not acted upon, the fault zone is determined according to the action result of the single zone; S5, if the remaining protection zones are all acted upon, the fault is determined according to the DC bus protection zone; S6, forming a partition protection reliability weight according to whether each zone is equipped with a fuse, a circuit breaker and a device lockout, comparing the protection reliability weights of each zone, and determining the fault zone according to the zone with the largest weight; and the weight can be set according to the protection means, thereby determining the fault zone.

Description

Technical Field

[0001] The present invention relates to the field of power distribution and utilization, and in particular to a method for quickly isolating faults in a common direct current bus system. Background Art

[0002] The protection configuration scheme of the multi-terminal DC system needs to take into account the transient characteristics of the DC system fault, ensure that the faulty power supply can be quickly cut off when a fault occurs in the multi-terminal DC system, ensure the safe operation of the multi-terminal DC system equipment, and achieve the reliability and rapidity of the protection configuration scheme. However, in terms of action speed, since the multi-terminal DC system uses a large number of power electronic equipment, the power electronic equipment has weak short-circuit current tolerance and fast action rate, which is difficult to coordinate well with the circuit breaker action time, and it is easy for the protection to fail to act accurately. Therefore, how to effectively coordinate the action time of the power electronic equipment and the circuit breaker action time is a difficulty in designing the protection scheme of the multi-terminal DC system.

[0003] The available protection measures for multi-terminal DC systems include power electronic interlocks, circuit breakers, fuses, etc. However, the instantaneous short-circuit current of a multi-terminal DC system fault is large, the duration is short, and it is difficult to distinguish between upper and lower levels of protection. It is difficult to form an effective protection system relying solely on a single protection measure.

[0004] For example, a "fault zoning method for DC power distribution system" disclosed in Chinese patent literature, with publication number: CN2019107867212, discloses a method of zoning a DC bus system to confirm the fault location, but it is unable to determine the regional reliability based on the protection measures. Summary of the invention

[0005] To this end, the present invention provides a method for quickly isolating faults in a common DC bus system, which can quickly and reliably determine the fault area when a fault occurs in the common DC bus system, isolate the fault area, and achieve rapid fault judgment of the DC system.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for quickly isolating a fault in a common DC bus system comprises the following steps:

[0008] S1. Divide the source, grid and load of the common DC bus system into protection zones;

[0009] S2. According to the common DC bus system structure, the protection actions after a fault occurs in each area are divided;

[0010] S3. According to whether the AC side is energized after each area is operated, the fault in the AC protection area can be reliably distinguished from the fault in other protection areas;

[0011] S4: When a single area is activated and the remaining two areas are not activated, the fault area is determined according to the single area activation result;

[0012] S5. If all other protection zones are activated, the fault is determined as that of the DC bus protection zone;

[0013] S6. Based on whether each area is equipped with fuses, circuit breakers, and device lockouts, a partition protection reliability weight can be formed. The protection reliability weights of each area can be compared, and the fault area can be determined based on the area with the largest weight. The system can be partitioned to quickly determine the fault location, and the problem of being unable to determine the fault point that may occur in actual operation can be solved by dividing the reliability weights of each area.

[0014] Preferably, the DC bus system includes an AC / DC converter, a DC bus, an AC converter and a load.

[0015] Preferably, the protection partition in S1 includes:

[0016] Electronic power valve protection zone, protection means include power electronic device lockout, fast fuse, AC circuit breaker;

[0017] Load protection area, protection means include power electronic device lockout and fast fuse;

[0018] DC bus protection zone, protection means include fast fuses and DC circuit breakers;

[0019] AC protection zone, protection means include inverse time AC circuit breaker. It is convenient to isolate the fault area and realize fast fault judgment of DC system.

[0020] Preferably, the protection actions for the faults in each area in S2 include:

[0021] When the electronic power valve protection zone fails, the power electronic device is locked, the connection between itself and the AC side and the DC side is cut off, the short-circuit current is reduced, and the DC area stops supplying power;

[0022] When a fault occurs in the load protection zone, the power electronic devices are locked, the power supply point is cut off, the load is disconnected from the network, and the DC zone stops supplying power.

[0023] When a fault occurs in the DC bus protection zone, the power supply and load are disconnected from the DC network, the DC circuit breaker in the DC bus protection zone is activated, and the DC zone stops supplying power.

[0024] When a fault occurs in the AC protection zone, the power electronic devices are locked, the connection between the DC side and the AC side is cut off, the fault current is disconnected, and both the DC area and the AC area stop supplying power. Simple logic judgment facilitates engineering implementation, avoids the problem of being unable to determine the fault point in the actual operation of a complex protection system, and improves the reliability of the protection system.

[0025] Preferably, in the protection action, the fast fuse acts as a backup protection action for locking the power electronic device and the DC circuit breaker in the DC bus protection zone.

[0026] Preferably, the reliability weight in S6 includes:

[0027] The reliability of fuse, circuit breaker and device locking action is set to a, b and c respectively. It is generally believed that a>b>c. If multiple protection means are configured in a single area, the protection reliability weight is accumulated according to the configuration means.

[0028] Preferably, S6 further includes: when two-area actions occur, determining the faulty area according to the protection actions of each area.

[0029] The embodiments of the present invention have the following advantages:

[0030] (1) When a common DC bus system fails, the fault area can be quickly and reliably determined, the fault area can be isolated, and the DC system fault can be quickly determined. (2) Simpler logical judgment is used to facilitate engineering implementation, avoiding the problem of complex protection systems being unable to determine the fault point during actual operation, thereby improving the reliability of the protection system. (3) Weights can be set according to the protection means to determine the fault area, providing a method for quickly determining faults when there is no precise fault location. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the prior art description are briefly introduced below. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0032] The structures, proportions, sizes, etc. illustrated in this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with the technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantial technical significance. Any structural modification, change in proportion or adjustment of size shall still fall within the scope of the technical contents disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0033] Figure 1 This is a schematic diagram of a typical common DC bus system.

[0034] Figure 2 This is a schematic diagram of the protection zones of a typical common DC bus system.

[0035] Figure 3It is a flow chart of the determination method of the present invention.

[0036] Figure 4 It is a flow chart of the steps of the present invention.

[0037] In the figure:

[0038] 1-AC side; 2-converter; 3-load; 4-AC protection zone; 5-electronic valve protection zone; 6-busbar protection zone; 7-load protection zone. DETAILED DESCRIPTION

[0039] The following is a description of the implementation of the present invention by specific embodiments. People familiar with the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] like Figure 1-4 As shown, in a preferred embodiment, the present invention discloses a method for quickly isolating faults in a common DC bus system.

[0041] Among them, the typical common DC bus system structure is as follows: Figure 1 The common DC bus includes several AC / DC converters, DC bus, DC feeder and DC load. The protection partitions of the typical common DC bus system are shown in Figure 1. Figure 2 As shown, the zones include: power electronic valve protection zone, load protection zone, DC bus protection zone and AC protection zone.

[0042] A method for quickly isolating faults in a common DC bus system Figure 3 As shown, the following steps are included:

[0043] Step 1: divide the common DC bus system source, grid, and load into protection zones, which can generally be divided into four fault zones. Common protection methods, action time limits, and protection requirements for each zone include:

[0044] (1) Power electronic valve protection zone

[0045] Protection means: power electronic device lockout, fast fuse, AC circuit breaker;

[0046] Protection time limit: The blocking action time of power electronic devices is about 100us, the action time of fast fuse is 1~10ms, and the AC circuit breaker is more than 100ms;

[0047] Protection requirements: The power electronic valve protection zone mainly includes rectifiers, inverters and DC converters. The power electronic valve protection zone is mainly used to protect its own component failures.

[0048] (2) Load protection area

[0049] Protection means: power electronic device lockout, fast fuse;

[0050] Protection time limit: The locking action time of power electronic devices is about 100us, and the action time of fast fuse is 1~10ms;

[0051] Protection requirements: The load protection area mainly includes DC loads and AC loads, among which the loads are mainly electric vehicle charging piles. Therefore, the load protection is also mainly to protect the components of the charging piles themselves.

[0052] (3) DC bus protection zone

[0053] Protection means: fast fuse, DC circuit breaker;

[0054] Protection time limit: fast fuse action time 1~10ms, DC circuit breaker action time more than 10ms;

[0055] Protection requirements: The DC bus protection zone mainly includes the DC bus and DC feeder. DC cable faults are generally permanent faults, which can be divided into single-pole grounding faults, inter-pole short circuit faults and line break faults.

[0056] (4) AC protection zone: (more than 10ms)

[0057] Protection means: inverse time AC circuit breaker;

[0058] Protection time limit: The action time of the inverse time AC circuit breaker is more than 100ms;

[0059] Protection requirements: The AC protection zone mainly includes AC power supply and AC transformer. AC system faults are mainly AC line short circuit faults, including single-phase short circuit, two-phase grounding / ungrounding short circuit and three-phase symmetrical short circuit.

[0060] The protection of each partition is in the following order from fast to slow according to the action rate: valve area protection = load protection < DC network protection < AC protection.

[0061] Step 2: According to the common DC bus system structure, the protection actions after a fault occurs in each area are divided:

[0062] (1) AC protection zone fault

[0063] When a fault occurs in the AC protection zone, first the valve zone protection power electronic devices are locked (with fast fuses as backup), cutting off the connection between the DC side and the AC side to prevent the DC side from outputting short-circuit current in the opposite direction to the AC side. The DC bus protection zone and the load protection zone do not operate, and finally the AC protection zone operates to disconnect the fault current; power supply to both the DC zone and the AC zone stops.

[0064] (2) Fault in the power electronic valve protection zone

[0065] When a fault occurs in the power electronic valve protection zone, the power electronic devices in the power electronic valve protection zone are first locked (with fast fuses as backup), cutting off the connection between itself and the AC and DC sides. After the power electronic valve protection zone is activated, the fault point disappears, the short-circuit current decreases, and the DC bus protection zone, load protection zone, and AC protection zone do not activate; the DC area stops supplying power, and the AC area is not affected.

[0066] (3) Load protection zone fault

[0067] When a fault occurs in the load protection zone, first the power electronic valve protection zone device is locked (with a fast fuse as a backup) to cut off the power supply point. Then the load protection zone is activated to disconnect the load from the network. Neither the AC protection zone nor the DC bus protection zone is activated. The DC zone stops supplying power, and the AC zone is not affected.

[0068] (4) DC bus protection zone fault

[0069] When a fault occurs in the DC bus protection zone, first the power electronic valve protection zone and the load protection zone are activated to disconnect the power supply and load from the DC network. Secondly, the DC circuit breaker in the DC bus protection zone is activated (with a fast fuse as a backup), and the AC protection zone is not activated; the DC area stops supplying power, and the AC area is not affected.

[0070] The protection action results are shown in Table 1, where 1 indicates action and 0 indicates no action.

[0071] Table 1 Correspondence between protection actions and fault areas

[0072]

[0073] Step 3: Due to the transient nature of the DC side fault, the protection of the DC part may malfunction after the fault occurs, but the possibility of malfunction of the AC protection zone is low. According to whether the AC side is energized after the action in Table 1, the fault in the AC protection zone can be reliably distinguished from the fault in other protection zones.

[0074] Step 4: When a single area is activated and the remaining two areas are not activated, the fault area is determined according to the single area activation result.

[0075] Step 5: If the other protection zones are all activated, the fault is determined as that of the DC bus protection zone.

[0076] Step 6, when two-area action occurs, determine the fault area according to the protection action correspondence table in Table 1; if the action results of the two areas exceed the protection action correspondence table, the partition protection reliability weight can be formed according to whether each area is equipped with fuses, circuit breakers, and device lockouts. The fuse, circuit breaker, and device lockout action reliability are set to a, b, and c respectively. It is generally believed that a>b>c. If a single area is equipped with multiple protection means, the protection reliability weight is accumulated according to the configuration means, and the protection reliability weights of each area are compared. The fault area is determined according to the area with the largest weight.

[0077] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A method for rapid isolation of faults in a common DC bus system, characterized in that: The steps include: S1. Divide the source, grid and load of the common DC bus system into protection zones; S2. According to the common DC bus system structure, the protection actions after a fault occurs in each area are divided; S3. Distinguish the faults in the AC protection zone from those in other protection zones according to whether the AC side is energized after each zone is activated; S4: When a single area is activated and the remaining two areas are not activated, the fault area is determined according to the single area activation result; S5. If all other protection zones are activated, the fault is determined as that of the DC bus protection zone; S6. When two-area actions occur, the fault area is determined according to the protection action correspondence table; if the action results of the two areas exceed the protection action correspondence table, the partition protection reliability weight is formed according to whether each area is equipped with fuses, circuit breakers, and device lockouts, and the fuse, circuit breaker, and device lockout action reliability is set. If a single area is equipped with multiple protection means, the protection reliability weight is accumulated according to the configuration means, and the protection reliability weights of each area are compared. The fault area is determined according to the area with the heavier weight.

2. A method for rapid isolation of faults in a common DC bus system according to claim 1, characterized in that: The DC bus system includes an AC / DC converter, a DC bus, an AC device and a load.

3. A method for rapid isolation of faults in a common DC bus system according to claim 1 or 2, characterized in that: The protection partition in S1 includes: Electronic power valve protection zone, protection means include power electronic device lockout, fast fuse, AC circuit breaker; Load protection area, protection means include power electronic device lockout and fast fuse; DC bus protection zone, protection means include fast fuses and DC circuit breakers; AC protection zone, protection means include inverse time AC circuit breaker.

4. A method for rapid isolation of faults in a common DC bus system according to claim 1, characterized in that: The protection actions for each area fault in S2 include: When the electronic power valve protection zone fails, the power electronic device is locked, the connection between itself and the AC side and the DC side is cut off, the short-circuit current is reduced, and the DC area stops supplying power; When a fault occurs in the load protection zone, the power electronic devices are locked, the power supply point is cut off, the load is disconnected from the network, and the DC zone stops supplying power. When a fault occurs in the DC bus protection zone, the power supply and load are disconnected from the DC network, the DC circuit breaker in the DC bus protection zone is activated, and the DC zone stops supplying power. When a fault occurs in the AC protection zone, the power electronic devices are locked, the connection between the DC side and the AC side is cut off, the fault current is disconnected, and power supply to both the DC area and the AC area is stopped.

5. A method for rapid isolation of faults in a common DC bus system according to claim 4, characterized in that: In the protection action, the fast fuse acts as a backup protection action for locking the power electronic device and the DC circuit breaker in the DC bus protection zone.

6. A method for rapid isolation of faults in a common DC bus system according to claim 1, characterized in that: The reliability weights in S6 include: The reliability of fuse, circuit breaker and device locking action is set to a, b and c respectively, where a>b>c. If multiple protection means are configured in a single area, the protection reliability weight is accumulated according to the configured means.

7. A method for rapid isolation of faults in a common DC bus system according to claim 1 or 6, characterized in that: The step S6 further includes: when two-area actions occur, determining the fault area according to the protection actions of each area.

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