Multi-port adaptive DC fault current limiter

Abstract

The invention discloses a multi-port adaptive DC fault current limiter, the multi-port adaptive DC fault current limiter comprises a plurality of magnetic core units and a circuit unit, one end of each magnetic core unit is connected with a corresponding DC port through a corresponding DC circuit breaker, and the other end of each magnetic core unit is connected to a high-voltage DC bus; the circuit unit comprises a diode bridge circuit and an external follow current branch, the midpoint of each bridge arm of the diode bridge circuit is correspondingly connected with one end of each magnetic core unit, and the common cathode end and the common anode end of the diode bridge circuit are connected with the external follow current branch to form an energy consumption loop. According to the invention, bidirectional, rapid and adaptive limitation of the short-circuit fault current of the multi-port flexible DC system can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of high-voltage electrical equipment, and in particular to a multi-port adaptive DC fault current limiter. Background Art

[0002] With the transformation of the global energy structure and the rapid development of new energy, flexible direct current transmission systems have attracted widespread attention due to their ability to achieve high-power, long-distance, and cross-regional power transmission. However, when a bipolar short-circuit fault occurs in a flexible direct current transmission system, the fault current rises rapidly, which poses a severe challenge to the stability and reliability of the system. To address this problem, existing DC current limiters (FCLs) are designed to limit the fault current, but they have some significant shortcomings.

[0003] First, many existing magnetic saturation DC current limiters only have unidirectional current limiting characteristics due to the unidirectionality of the magnetic flux loop, and have no bidirectional fault limiting effect. For short-circuit faults that may occur on any side of any port in a multi-port DC system, unidirectional current limiters cannot provide comprehensive protection; secondly, some current limiters do not react quickly enough when a fault occurs and cannot effectively limit the current before the fault current reaches its peak, which may cause damage to power electronic devices and power equipment; finally, general current limiting reactors will introduce a large inductance of a fixed value, thereby increasing the time required for the system to recover from dynamic to steady state, reducing the dynamic response capability of the system.

[0004] Therefore, in response to the above three problems, a multi-port bidirectional, fast-response, and adaptive fault current limiting solution is urgently needed. Summary of the invention

[0005] The present invention aims to solve the technical problems in the related art at least to a certain extent. To this end, the purpose of the present invention is to provide a multi-port adaptive DC fault current limiter, which has a multi-port bidirectional current limiting characteristic, can effectively deal with bipolar short circuit faults that may be caused by faults occurring at different ports in the flexible DC transmission system, and can quickly and effectively limit the fault current regardless of which side of the current limiter the fault occurs on; in addition, it utilizes the iron core desaturation principle to quickly introduce a large inductance at the beginning of the fault current rise to achieve rapid limitation of the fault current; the device can also automatically adjust its inductance value according to the magnitude and direction of the fault current to achieve adaptive current limiting, which helps to improve the arc extinguishing efficiency of the DC circuit breaker, reduce the risk of damage to the circuit breaker when breaking the fault current, and improve the flexibility and reliability of the system.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A multi-port adaptive DC fault current limiter, comprising:

[0008] A plurality of magnetic core units, one end of each of the plurality of magnetic core units is connected to a corresponding DC port through a corresponding DC circuit breaker, and the other end of each of the plurality of magnetic core units is connected to a high-voltage DC bus;

[0009] The circuit unit includes a diode bridge circuit and an external freewheeling branch, wherein the midpoints of each bridge arm of the diode bridge circuit are respectively connected to one end of each magnetic core unit, and the common cathode terminal and the common anode terminal of the diode bridge circuit are respectively connected to the external freewheeling branch to form an energy consumption loop.

[0010] Preferably, each of the magnetic core units has the same structure, and each of the magnetic core units includes two two-column iron cores, wherein permanent magnets are disposed on the upper and lower transverse yokes of each iron core.

[0011] Preferably, the left and right core columns of the first iron core are wound with a first coil and a second coil; the left and right core columns of the second iron core are wound with a third coil and a fourth coil; wherein the second coil and the third coil are connected end to end, and the output ends of the first coil and the fourth coil are respectively connected to the DC circuit breaker and the high-voltage DC bus.

[0012] Preferably, the first coil and the second coil are wound in opposite directions, and the third coil and the fourth coil are wound in opposite directions.

[0013] Preferably, the excitation directions of all permanent magnets are the same.

[0014] Preferably, the permanent magnets are made of rare earth permanent magnet material, and all permanent magnets have the same thickness.

[0015] Preferably, the cross-sectional area of ​​all permanent magnets is equal to the cross-sectional area of ​​the transverse yoke in which they are located.

[0016] Preferably, the external freewheeling branch comprises a resistor and a thyristor connected in series with the resistor.

[0017] The present invention has at least the following technical effects:

[0018] (1) The present invention provides a multi-port adaptive DC fault current limiter, which can realize bidirectional, fast, and adaptive limitation of short-circuit fault current in a multi-port flexible DC system. When a short-circuit fault occurs on either side, the iron core on the current inlet side of the magnetic core part of the device will desaturate, and the inductance value will increase accordingly, limiting the peak value and rising speed of the fault current; when the circuit returns to normal, the iron core of the magnetic core part will re-enter the saturation state, so it has a good adaptive current limiting effect.

[0019] (2) The present invention can also effectively reduce the short-circuit current of the flexible DC system during a short-circuit fault, which is beneficial to reducing the cutting capacity of the DC circuit breaker, improving its service environment, reducing the cost of maintaining the DC circuit breaker, and has good economic efficiency.

[0020] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the structure of a multi-port adaptive DC fault current limiter according to an embodiment of the present invention.

[0022] Figure 2 Schematic diagram of the structure of a magnetic core unit according to an embodiment of the present invention.

[0023] Figure 3 The figure is a schematic diagram of the function of the multi-port adaptive DC fault current limiter in the current limiting stage according to an embodiment of the present invention.

[0024] Figure 4 The figure is a schematic diagram of the function of the multi-port adaptive DC fault current limiter in the fault clearing stage according to an embodiment of the present invention.

[0025] Figure 5 The figure is a schematic diagram of the function of the multi-port adaptive DC fault current limiter in the recovery stage according to an embodiment of the present invention.

[0026] Figure 6 Schematic diagram of a magnetic circuit simulation model of a core portion of an embodiment of the present invention.

[0027] Figure 7(a)-7(c) 1 is a distribution diagram of the core magnetic induction intensity of the magnetic core part of the multi-port adaptive DC fault current limiter in various states according to an embodiment of the present invention.

[0028] Figure 8(a)-8(d) Schematic diagram of fault current variation curve before and after a short circuit fault occurs in branch 1 under different conditions in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The present embodiment is described in detail below, and examples of the embodiment are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0030] A multi-port adaptive DC fault current limiter according to the present embodiment will be described below with reference to the accompanying drawings.

[0031] Figure 1FIG. 1 is a schematic diagram of the structure of a multi-port adaptive DC fault current limiter according to an embodiment of the present invention. Figure 1 As shown, the multi-port adaptive DC fault current limiter includes a plurality of magnetic core units 10 and a circuit unit 20 connected thereto. One end of the plurality of magnetic core units 10 is connected to the corresponding DC port through the corresponding DC circuit breaker, and the other end of the plurality of magnetic core units is connected to the high-voltage DC bus, such as one end of the first magnetic core unit 10 is connected to the corresponding DC port P1 through the DC circuit breaker CB1. The circuit unit 20 includes a diode bridge circuit 21 and an external freewheeling branch 22, wherein the midpoints of each bridge arm of the diode bridge circuit 21 are respectively connected to one end of each magnetic core unit 10, and the common cathode terminal and the common anode terminal of the diode bridge circuit 21 are respectively connected to the external freewheeling branch 22 to form an energy consumption loop.

[0032] The multi-port adaptive DC fault current limiter of this embodiment can quickly and flexibly limit short-circuit currents in different directions generated when a fault occurs at any port in the multi-port flexible DC system, and has good response speed and adaptability.

[0033] Figure 2 Schematic diagram of the structure of the magnetic core unit of the embodiment of the present invention. The structure of each magnetic core unit is the same, such as Figure 2 As shown, each magnetic core unit includes two two-column iron cores, wherein the iron cores are made of silicon steel sheets, and the two iron cores are exactly the same, and permanent magnets are arranged on the upper and lower transverse yokes of each iron core. In addition, the first coil and the second coil are wound on the left and right core columns of the first iron core; the third coil and the fourth coil are wound on the left and right core columns of the second iron core, the second coil and the third coil are connected end to end, and the outlet ends of the first coil and the fourth coil are respectively connected to the DC circuit breaker and the high-voltage DC bus.

[0034] It should be noted that the winding directions of the first coil and the second coil are opposite, and the winding directions of the third coil and the fourth coil are opposite. All permanent magnets are made of rare earth permanent magnet materials, and the excitation directions and thicknesses of all permanent magnets are the same. In addition, the cross-sectional areas of all permanent magnets are equal to the cross-sectional areas of the yokes in which they are located.

[0035] In one embodiment of the present invention, the external freewheeling branch 22 includes a resistor R and a thyristor G connected in series with the resistor. The external freewheeling branch 22 is used to consume the energy stored in the magnetic core unit 10 .

[0036] The working principle of the multi-port adaptive DC fault current limiter of this embodiment is as follows:

[0037] (1) Under normal circumstances, the current of the DC system flows from the A end to the Y end. The current of the DC system is small, and the magnetomotive force generated by the permanent magnet is much larger than the magnetomotive force generated by the DC system. The iron core of the device magnetic core unit 10 is in a magnetic saturation state. At this time, the inductance value is small and does not affect the normal operation of the system.

[0038] (2) Current limiting stage: When a short circuit occurs, the current increases rapidly and the magnetic motive force generated by the DC system increases. Figure 3 As shown, in the fault branch such as the branch where the P1 port is located, the current flows from the Y end to the A end. In the iron core on the current inlet side, that is, near the Y end, that is, the second iron core, the magnetomotive force is opposite to the magnetomotive force generated by the permanent magnet, so that the iron core on the inlet side, that is, the second iron core, is desaturated, that is, in a non-saturated state, and the equivalent inductance value increases. In the iron core on the current outlet side, the magnetomotive force generated by the DC system is in the same direction as the magnetomotive force generated by the permanent magnet, so the iron core on the outlet side is still in a magnetic saturation state, and the equivalent inductance value is small, but the overall inductance value of the magnetic core unit 10 in the fault branch is still increased, thereby playing a role in suppressing the fault current.

[0039] (3) Fault clearing stage: The DC circuit breaker receives the trip signal and starts to operate, isolating the faulty part from the system. At this time, the DC circuit breaker switches to the energy consumption branch, which is mainly composed of metal oxide lightning arresters. Figure 4 As shown, since the potential of the fault branch is higher than that of the non-fault branch, the diode is turned on, and the current passes through the diode bridge circuit 21 and flows through the external freewheeling branch 22 composed of the resistor R and the thyristor G for freewheeling. At this time, the thyristor G is turned on, and the energy stored in the magnetic core unit 10 is consumed through the resistor R in the branch, which effectively reduces the dissipated energy and dissipation time of the metal oxide arrester, which is beneficial to the DC circuit breaker to cut off the fault part.

[0040] (4) Recovery stage: After the resistance is consumed, the energy stored in the magnetic core unit 10 gradually decreases, and the corresponding current flowing through the thyristor G decreases. When the current is less than the maintenance current required for the thyristor G to turn on, it can also be understood that when the energy in the magnetic core unit 10 of all ports is completely dissipated, the thyristor G is turned off, the external freewheeling branch 22 is disconnected, and the multi-port current limiting action process ends. At this time, since the current flowing through the coil is also reduced, the reverse magnetomotive force generated by the DC system is also reduced, such as Figure 5 As shown, the core on the current inlet side returns to a saturated state, and the inductance value is low, which does not affect the normal working performance of the circuit.

[0041] In order to verify the advantages of the multi-port adaptive DC fault current limiter in terms of bidirectional, fast and adaptive compared with the ordinary current limiting reactor, a magnetic circuit simulation model of the core part of the device was built in the finite element simulation. Figure 6As shown, the magnetic circuit simulation parameters are shown in Table 1. In addition, PSCAD (electromagnetic transient simulation software) is used to establish a simplified model of the flexible DC power grid, and the circuit simulation parameters are shown in Table 2. At t=3s, a bipolar short circuit fault occurs in the circuit, and the fault current flowing through each branch is compared and analyzed. In addition, during the simulation process, ordinary current limiter reactors and multi-port current limiters are used to limit the fault current. By comparing the current limiting effects of ordinary fault current limiters and multi-port current limiters, the advantages of the present invention can be seen.

[0042] Table 1 Magnetic circuit simulation parameters

[0043] Structural parameters Numeric <![CDATA[L1]]> 550cm <![CDATA[L2]]> 350cm <![CDATA[L3]]> 350cm <![CDATA[L4]]> 600cm <![CDATA[L5]]> 350cm Coil turns 44

[0044] Table 2 Circuit simulation parameters

[0045]

[0046] The distribution diagram of the magnetic induction intensity of the core when the device is in normal state, when the left core fails, and when the right core fails is as follows: Figure 7(a)-7(c) As shown, it can be seen that under the finite element simulation parameters: in the normal state, the side columns of the two cores are in a saturated state, and the saturation degree of the core on the current outlet side (the right side in the figure) is higher than that on the inlet side. In the event of a short circuit fault, the core on the current inlet side is desaturated, and the saturation degree of the core on the current outlet side is slightly deepened, which is in line with the current limiting principle of the magnetic core part when a fault occurs as described above.

[0047] The fault current variation curves before and after a short circuit fault occurs in branch 1 under different conditions are as follows: Figure 8(a)-8(d) As shown, FIG8(a) is the fault current variation curve when the current limiter is not used, FIG8(b) is the fault current variation curve when the fixed reactor is used, FIG8(c) is the fault current variation curve when the multi-port current limiter is used, and FIG8(d) is the fault current variation curve flowing through branch one under different conditions. When the ordinary current limiter is used, the fault current of each branch decreases to a certain extent, and the fault current in branch one decreases most significantly, from about 45kA to about 28kA, as shown in FIG8(b); when the multi-port adaptive DC fault current limiter is used, the limiting effect on the fault current is more obvious than that of the ordinary current limiter. Taking branch one as an example, the fault current further decreases from about 28kA to about 13kA, as shown in FIG8(c); In addition, it can be clearly seen from FIG8(d) that the multi-port current limiter has advantages over the ordinary current limiter. On the one hand, it has a better peak limiting effect on the fault current, which reduces the fault current by about 33%; on the other hand, it has a better limiting effect on the rising speed of the fault current.

[0048] In summary, the present invention provides a multi-port adaptive DC fault current limiter, which can realize bidirectional, fast, and adaptive limitation of short-circuit fault current of a multi-port flexible DC system. When a short-circuit fault occurs on either side, the iron core on the current inlet side of the magnetic core part of the device will desaturate, and the inductance value will increase accordingly, limiting the peak value and rising speed of the fault current; when the circuit returns to normal, the iron core of the magnetic core part will re-enter the saturation state, so it has a good adaptive current limiting effect; the present invention can also effectively reduce the short-circuit current of the flexible DC system during a short-circuit fault, which is beneficial to reducing the cutting capacity of the DC circuit breaker, improving its service environment, reducing the cost of maintaining the DC circuit breaker, and has good economy.

[0049] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0050] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A multi-port adaptive DC fault current limiter, characterized in that: include: A plurality of magnetic core units, one end of each of the plurality of magnetic core units is connected to a corresponding DC port through a corresponding DC circuit breaker, and the other end of each of the plurality of magnetic core units is connected to a high-voltage DC bus; The circuit unit includes a diode bridge circuit and an external freewheeling branch, wherein the midpoints of each bridge arm of the diode bridge circuit are respectively connected to one end of each magnetic core unit, and the common cathode terminal and the common anode terminal of the diode bridge circuit are respectively connected to the external freewheeling branch to form an energy consumption loop.

2. The multi-port adaptive DC fault current limiter according to claim 1, characterized in that: Each of the magnetic core units has the same structure, and each of the magnetic core units includes two two-column iron cores, wherein permanent magnets are arranged on the upper and lower transverse yokes of each iron core.

3. The multi-port adaptive DC fault current limiter according to claim 2, characterized in that: The first coil and the second coil are wound on the left and right core columns of the first iron core; the third coil and the fourth coil are wound on the left and right core columns of the second iron core; wherein the second coil and the third coil are connected end to end, and the outlet ends of the first coil and the fourth coil are respectively connected to the DC circuit breaker and the high-voltage DC bus.

4. The multi-port adaptive DC fault current limiter according to claim 3, characterized in that: The first coil and the second coil are wound in opposite directions, and the third coil and the fourth coil are wound in opposite directions.

5. The multi-port adaptive DC fault current limiter according to claim 2, characterized in that: All permanent magnets are excited in the same direction.

6. The multi-port adaptive DC fault current limiter according to claim 5, characterized in that: The permanent magnets are made of rare earth permanent magnet material, and all the permanent magnets have the same thickness.

7. The multi-port adaptive DC fault current limiter according to claim 5, characterized in that: The cross-sectional area of ​​all permanent magnets is equal to the cross-sectional area of ​​the transverse yoke in which they are located.

8. The multi-port adaptive DC fault current limiter according to any one of claims 1 to 7, characterized in that: The external freewheeling branch includes a resistor and a thyristor connected in series with the resistor.

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