A multi-port adaptive dc fault current limiter
By designing a multi-port adaptive DC fault current limiter, and utilizing a combination of magnetic core units and circuit units, bidirectional fast current limiting of flexible DC systems is achieved. This solves the problems of unidirectionality and insufficient response speed of current limiters in existing technologies, and improves the system's protection capability and economy.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- WUHAN UNIV
- Filing Date
- 2024-10-24
- Publication Date
- 2026-05-29
AI Technical Summary
Existing DC current limiters have problems such as unidirectional current limiting characteristics, slow response, and insufficient dynamic response capability, and cannot effectively protect multi-port flexible DC systems from bipolar short-circuit faults at any port.
Design a multi-port adaptive DC fault current limiter, which combines magnetic core unit and circuit unit, and uses the core desaturation principle to achieve bidirectional current limiting. It can quickly respond and adjust the inductance value according to the magnitude and direction of the fault current. It combines diode bridge circuit and external freewheeling branch to consume energy.
It achieves bidirectional, fast, and adaptive current limiting for flexible DC systems, reduces the peak value and rise rate of fault current, reduces the risk of damage to DC circuit breakers, and improves the flexibility and reliability of the system.
Smart Images
Figure CN119448160B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of high-voltage electrical equipment technology, and in particular to a multi-port adaptive DC fault current limiter. Background Technology
[0002] With the transformation of the global energy structure and the rapid development of new energy sources, flexible direct current (DC) transmission systems have attracted widespread attention due to their ability to achieve high-power, long-distance, and cross-regional power transmission. However, in the event of a bipolar short-circuit fault, the fault current in a flexible DC transmission system rises rapidly, posing a severe challenge to the system's stability and reliability. To address this issue, existing DC current limiters (FCLs) are designed to limit the fault current, but they have some significant shortcomings.
[0003] First, many existing magnetically saturated DC current limiters, due to the unidirectional nature of the magnetic flux loop, only have unidirectional current limiting characteristics and lack bidirectional fault limiting effects. For multi-port DC systems, short-circuit faults that may occur on either side of any port cannot be fully protected by unidirectional current limiters. Second, some current limiters do not react quickly enough when a fault occurs, failing to effectively limit the current before the fault current reaches its peak value, which may damage power electronic devices and electrical equipment. Finally, current-limiting reactors generally introduce a large inductance of a fixed value, thereby increasing the time required for the system to recover from dynamic to steady state and reducing the system's dynamic response capability.
[0004] Therefore, a multi-port, bidirectional, fast-response, and adaptive fault rate limiting solution is urgently needed to address the above three issues. Summary of the Invention
[0005] This invention aims to at least partially solve the technical problems in related technologies. Therefore, the purpose of this invention is to provide a multi-port adaptive DC fault current limiter, which possesses multi-port bidirectional current limiting characteristics. It can effectively address bipolar short-circuit faults that may occur in flexible DC transmission systems due to faults occurring at different ports. Regardless of which side of the current limiter the fault occurs on, it can quickly and effectively limit the fault current. Furthermore, utilizing the core desaturation principle, it can rapidly introduce a large inductance in the early stages of fault current rise, achieving rapid limitation of the fault current. This device can also automatically adjust its inductance value according to the magnitude and direction of the fault current, achieving adaptive current limiting. This helps improve the arc-extinguishing efficiency of DC circuit breakers, reduces the risk of damage to circuit breakers when interrupting fault currents, and improves the flexibility and reliability of the system.
[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:
[0007] A multi-port adaptive DC fault current limiter, comprising:
[0008] Multiple magnetic core units, one end of which is connected to a corresponding DC port via a corresponding DC circuit breaker, and the other end of which is connected to a high-voltage DC bus.
[0009] The circuit unit includes a diode bridge circuit and an external freewheeling branch. The midpoint of each arm of the diode bridge circuit is connected to one end of each magnetic core unit. The common cathode and common anode terminals of the diode bridge circuit are connected to the external freewheeling branch to form a power dissipation loop.
[0010] Preferably, each of the magnetic core units has the same structure, and each magnetic core unit includes two two-column iron cores, wherein permanent magnets are provided on the upper and lower transverse yokes of each iron core.
[0011] Preferably, a first coil and a second coil are wound on the left and right core columns of the first iron core; a third coil and a 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 output terminals 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, all permanent magnets are excitationd in the same direction.
[0014] Preferably, the permanent magnets are made of rare earth permanent magnet materials, 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 they belong to.
[0016] Preferably, the external freewheeling branch includes a resistor and a thyristor connected in series with the resistor.
[0017] This invention has at least the following technical effects:
[0018] (1) This invention provides a multi-port adaptive DC fault current limiter, which can achieve bidirectional, fast, and adaptive limiting 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 input side of the magnetic core part of the device will desaturate, and the inductance value will increase accordingly, limiting the peak value and rise rate of the fault current; when the circuit returns to normal, the iron core of the magnetic core part re-enters the saturation state, thus having a good adaptive current limiting effect.
[0019] (2) The present invention can also effectively reduce the short-circuit current during short-circuit faults in flexible DC systems, which is conducive to reducing the cutting capacity of DC circuit breakers, improving their service environment, reducing the cost of maintaining DC circuit breakers, and has good economic benefits.
[0020] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description
[0021] Figure 1 This is a 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 This is a schematic diagram of the magnetic core unit according to an embodiment of the present invention.
[0023] Figure 3 This is a schematic diagram illustrating the function of the multi-port adaptive DC fault current limiter during the current limiting stage in an embodiment of the present invention.
[0024] Figure 4 This is a schematic diagram illustrating 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 This is a schematic diagram illustrating the function of the multi-port adaptive DC fault current limiter during the recovery phase in an embodiment of the present invention.
[0026] Figure 6 This is a schematic diagram of the magnetic circuit simulation model of the magnetic core part in an embodiment of the present invention.
[0027] Figures 7(a)-7(c) This is a diagram showing the distribution of magnetic induction intensity of the core portion of the multi-port adaptive DC fault current limiter in various states according to an embodiment of the present invention.
[0028] Figures 8(a)-8(d) This is a schematic diagram of the fault current change curves before and after a short-circuit fault occurs in branch 1 under different conditions according to an embodiment of the present invention. Detailed Implementation
[0029] The following describes this embodiment in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.
[0030] A multi-port adaptive DC fault current limiter according to this embodiment is described below with reference to the accompanying drawings.
[0031] Figure 1This 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 multiple magnetic core units 10 and circuit units 20 connected to them. One end of each magnetic core unit 10 is connected to a corresponding DC port via a corresponding DC circuit breaker, and the other end of each magnetic core unit is connected to a high-voltage DC bus. For example, one end of the first magnetic core unit 10 is connected to the corresponding DC port P1 via a DC circuit breaker CB1. The circuit unit 20 includes a diode bridge circuit 21 and an external freewheeling branch 22. The midpoint of each arm of the diode bridge circuit 21 is connected to one end of each magnetic core unit 10, and the common cathode and common anode terminals of the diode bridge circuit 21 are connected to the external freewheeling branch 22 to form an energy dissipation loop.
[0032] The multi-port adaptive DC fault current limiter of this embodiment can quickly and flexibly limit the short-circuit current in different directions generated when any port in a multi-port flexible DC system fails, and has good response speed and adaptability.
[0033] Figure 2 This is a schematic diagram of the structure of a magnetic core unit according to an embodiment of the present invention. Each magnetic core unit has the same structure, as shown below. Figure 2 As shown, each magnetic core unit includes two two-column iron cores, which are made of silicon steel sheets and are identical. Permanent magnets are mounted on the upper and lower transverse yokes of each core. Furthermore, a first coil and a second coil are wound on the left and right core columns of the first core; a third coil and a fourth coil are wound on the left and right core columns of the second core. The second and third coils are connected end-to-end, and the output terminals of the first and fourth coils are connected to a DC circuit breaker and a high-voltage DC bus, respectively.
[0034] It should be noted that the first and second coils are wound in opposite directions, as are the third and fourth coils. All permanent magnets are made of rare-earth permanent magnet materials, and all permanent magnets have the same excitation direction and thickness. Furthermore, the cross-sectional area of all permanent magnets is equal to the cross-sectional area of the transverse yoke they belong to.
[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 in this embodiment is as follows:
[0037] (1) Under normal circumstances, the current of the DC system flows from end A to end Y. The current of the DC system is small, and the magnetomotive force generated by the permanent magnet is much greater than that generated by the DC system. The iron core of the magnetic core unit 10 of the device is in a state of magnetic saturation. 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 fault occurs, the current increases rapidly, and the magnetomotive force generated by the DC system increases. For example... Figure 3 As shown, in the faulty branch, such as the branch containing port P1, the current flows from end Y to end A. In the core near the current inlet (i.e., the second core), the magnetomotive force (MOF) is opposite in direction to the MOF generated by the permanent magnet, causing the second core to desaturate, resulting in an increased equivalent inductance. However, in the core at the current outlet, the MOF generated by the DC system is in the same direction as the MOF generated by the permanent magnet. Therefore, the core at the outlet remains magnetically saturated, resulting in a smaller equivalent inductance. Nevertheless, the overall inductance of the core unit 10 in the faulty branch still increases, thus suppressing the fault current.
[0039] (3) Fault Clearing Stage: Upon receiving the trip signal, the DC circuit breaker begins to operate, isolating the faulty section from the system. At this time, the DC circuit breaker switches to a power-dissipating branch, mainly composed of metal oxide surge arresters. At this point, if... Figure 4 As shown, since the potential of the faulty branch is higher than that of the non-faulty branch, the diode conducts, and the current flows through the diode bridge circuit 21 and then through the external freewheeling branch 22 composed of resistor R and thyristor G. At this time, thyristor G conducts, and the energy stored in the magnetic core unit 10 is consumed through resistor R in the branch, effectively reducing the energy dissipation and dissipation time of the metal oxide surge arrester, which is beneficial for the DC circuit breaker to disconnect the faulty part.
[0040] (4) Recovery Phase: After the energy is consumed by the resistor, the energy stored in the core unit 10 gradually decreases, corresponding to a decrease in the current flowing through the thyristor G. When the current is less than the holding current required for the thyristor G to turn on, which can also be understood as when the energy in the core unit 10 at all ports is dissipated, the thyristor G is turned off, the external freewheeling branch 22 is disconnected, and the multi-port current limiting process ends. At this time, since the current flowing through the coil also decreases, the reverse magnetomotive force generated by the DC system also decreases, such as... Figure 5 As shown, the iron core on the current inlet side returns to saturation, and the inductance value is low, which does not affect the normal operating performance of the circuit.
[0041] To verify the advantages of the multi-port adaptive DC fault current limiter compared to ordinary current-limiting reactors, such as bidirectional operation, speed, and adaptability, a magnetic circuit simulation model of the device's core was built in finite element simulation, as shown below. Figure 6As shown in Table 1, the magnetic circuit simulation parameters are as follows. In addition, a simplified model of the flexible DC power grid was established using PSCAD (electromagnetic transient simulation software), and the circuit simulation parameters are shown in Table 2. A bipolar short-circuit fault was induced in the circuit at t=3s, and the fault current flowing through each branch was compared and analyzed. Furthermore, during the simulation, both a conventional current limiter reactor and a multi-port current limiter were used to limit the fault current. By comparing the current limiting effects of the conventional fault current limiter and the multi-port current limiter, the advantages of this invention can be seen.
[0042] Table 1 Magnetic Circuit Simulation Parameters
[0043] Structural parameters numerical values <![CDATA[L1]]> 550cm <![CDATA[L2]]> 350cm <![CDATA[L3]]> 350cm <![CDATA[L4]]> 600cm <![CDATA[L5]]> 350cm Number of coil turns 44
[0044] Table 2 Circuit Simulation Parameters
[0045]
[0046] The magnetic induction intensity distribution of the core is shown in the diagrams when the device is in normal condition, when the left core fails, and when the right core fails. Figures 7(a)-7(c) As shown, under the finite element simulation parameters, both cores are in a saturated state under normal conditions, and the saturation level of the core on the current outlet side (right side in the figure) is higher than that on the inlet side. However, during a short circuit fault, the core on the current inlet side desaturates, while the saturation level of the core on the current outlet side slightly increases, which is consistent with the current limiting principle of the magnetic core when a fault occurs, as described above.
[0047] The fault current change curves before and after a short-circuit fault in branch 1 under different conditions are shown in the figure. Figures 8(a)-8(d) As shown in Figure 8(a), the fault current variation curve is shown without a current limiter; Figure 8(b) shows the fault current variation curve with a fixed reactor; Figure 8(c) shows the fault current variation curve with a multi-port current limiter; and Figure 8(d) shows the fault current variation curve flowing through branch 1 under different conditions. When using a conventional current limiter, the fault current in each branch decreases to a certain extent, with the most significant decrease in branch 1, from approximately 45kA to about 28kA, as shown in Figure 8(b). When using a multi-port adaptive DC fault current limiter, the limiting effect on the fault current is more significant compared to using a conventional current limiter. Taking branch 1 as an example, the fault current further decreases from approximately 28kA to about 13kA, as shown in Figure 8(c). In addition, Figure 8(d) clearly shows the advantages of the multi-port current limiter compared to the conventional current limiter. On the one hand, it has a better peak current limiting effect, resulting in a decrease in the fault current of about 33%; on the other hand, it has a better limiting effect on the rise rate of the fault current.
[0048] In summary, this invention provides a multi-port adaptive DC fault current limiter that can achieve bidirectional, rapid, and adaptive limiting of short-circuit fault current in multi-port flexible DC systems. When a short-circuit fault occurs on either side, the iron core on the current input side of the device's magnetic core will desaturate, correspondingly increasing the inductance value and limiting the peak value and rise rate of the fault current. When the circuit returns to normal, the iron core re-enters saturation, thus exhibiting excellent adaptive current limiting effect. This invention can also effectively reduce the short-circuit current during short-circuit faults in flexible DC systems, which is beneficial for reducing the breaking capacity of DC circuit breakers, improving their service environment, and reducing the costs associated with maintaining DC circuit breakers, thus demonstrating good economic efficiency.
[0049] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.
[0050] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.
Claims
1. A multi-port adaptive DC fault current limiter, characterized in that, include: Multiple magnetic core units, one end of the multiple magnetic core units, i.e., end A, is connected to the corresponding DC port through the corresponding DC circuit breaker, and the other end of the multiple magnetic core units, i.e., end Y, is connected to the high-voltage DC bus. The circuit unit includes a diode bridge circuit and an external freewheeling branch. The midpoint of each arm of the diode bridge circuit is connected to one end of each magnetic core unit. The common cathode and common anode terminals of the diode bridge circuit are connected to the external freewheeling branch to form an energy dissipation loop. Each of the magnetic core units has the same structure, and each magnetic core unit includes two two-column iron cores, wherein permanent magnets are provided on the upper and lower transverse yokes of each iron core; The first iron core has a first coil and a second coil wound on its left and right core columns; the second iron core has a third coil and a fourth coil wound on its left and right core columns; wherein the first coil, the second coil, the third coil and the fourth coil are connected end to end in sequence, and the output terminals of the first coil and the fourth coil are respectively connected to the DC circuit breaker and the high voltage DC bus. The first coil and the second coil are wound in opposite directions, the third coil and the fourth coil are wound in opposite directions, and the second coil and the third coil are wound in the same direction; The external freewheeling branch includes a resistor and a thyristor connected in series with the resistor; The working principle of the multi-port adaptive DC fault current limiter is as follows: (1) Under normal circumstances, the current of the DC system flows from end A to end Y. The current of the DC system is small, and the magnetomotive force generated by the permanent magnet is much greater than that generated by the DC system. The iron core of the magnetic core unit is in a state of magnetic saturation, and the inductance value is small at this time. (2) Current limiting stage: When a short circuit fault occurs, the current increases rapidly, and the magnetomotive force generated by the DC system increases. In the fault branch, the current flows from the Y end to the A end. In the iron core near the Y end on the current inlet side, the magnetomotive force is opposite in direction to the magnetomotive force generated by the permanent magnet, causing the iron core on the inlet side, i.e., the second iron core, to desaturate 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 state of magnetic saturation. (3) Fault clearing stage: The DC circuit breaker starts to operate after receiving the trip signal, and isolates the faulty part from the DC system. Since the potential of the faulty branch is higher than that of the non-faulty branch, the diode corresponding to the faulty branch is turned on. The current flowing through the magnetic core unit of the faulty branch passes through the diode corresponding to the faulty branch, the resistor in the external freewheeling branch and the thyristor in sequence, and then returns to the magnetic core unit of the faulty branch through the diode corresponding to the non-faulty branch, the magnetic core unit and the high-voltage DC bus. At this time, the thyristor is turned on, and the energy stored in the magnetic core unit is consumed through the resistor in the external freewheeling branch, effectively reducing the energy dissipation and dissipation time of the metal oxide surge arrester. (4) Recovery phase: After the resistor is consumed, the energy stored in the magnetic core unit gradually decreases, and the current flowing through the thyristor decreases accordingly. When the current is less than the holding current required for the thyristor to turn on, the thyristor is turned off, the external freewheeling branch is disconnected, and the multi-port current limiting operation process ends.
2. The multi-port adaptive DC fault current limiter as described in claim 1, characterized in that, All permanent magnets are excited in the same direction.
3. The multi-port adaptive DC fault current limiter as described in claim 2, characterized in that, The permanent magnets are made of rare earth permanent magnet materials, and all permanent magnets have the same thickness.
4. The multi-port adaptive DC fault current limiter as described in claim 2, characterized in that, The cross-sectional area of all permanent magnets is equal to the cross-sectional area of the transverse yoke they belong to.