Thyristor ring-based mixed-bridge MMC valve side AC grounding fault protection circuit and method
By adding thyristor branches in hybrid bridge MMC converters and triggering them to clear fault currents, the problems of high cost and long fault current clearance in traditional technologies are solved, and rapid fault handling and cost reduction are achieved.
Patent Information
- Application Number
- CN202411233581.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-04
- Publication Date
- 2025-01-10
AI Technical Summary
Traditional valve-side AC single-phase grounding fault protection technology based on mixed bridge MMC converters requires the addition of a large number of thyristor devices, resulting in high construction costs and long clearance of AC fault current, which may cause damage to the transformer and affect the normal operation of the power grid.
Add three thyristor branches connected to the head and tail on the basis of the mixed bridge MMC converter, and trigger these branches in the event of a failure, close the converter submodule, turn on the fast mechanical switch, and remove the trigger signal to quickly clear the AC Fault current.
It realizes rapid clearance of AC fault current, reduces the capacitance overvoltage of the submodule, reduces the cost of infrastructure, and avoids the overcurrent of the bridge arm, ensuring the protection of the converter and the normal operation of the power grid.
Smart Images
Figure CN119297928A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of multi-level power electronic converters, and in particular to a thyristor ring-based mixed bridge MMC valve-side AC grounding fault protection circuit and method. Background Art
[0002] MMC (Modular Multilevel Converter) is increasingly widely used in the fields of long-distance and large-capacity HVDC (High Voltage Direct Current) transmission, due to its high modularity, low output AC voltage harmonics, high operating efficiency, and easy expansion of DC voltage. Hybrid bridge MMC converters have gradually been put into practical projects due to their excellent DC fault ride-through and protection capabilities.
[0003] Problems such as insulation damage of wall bushings can cause valve-side AC single-phase grounding faults in converters. For traditional asymmetric unipolar HVDC systems based on mixed-bridge MMC converters, valve-side AC single-phase grounding faults can cause overvoltages in the capacitors of the three-phase upper arm half-bridge and full-bridge sub-modules of the converter, and overvoltages in the capacitors of the three-phase lower arm full-bridge sub-modules, which may damage the capacitor components and power electronic components in the sub-modules.
[0004] In recent years, the valve-side AC single-phase ground fault protection technology for hybrid bridge MMCs mostly requires the addition of a large number of thyristor devices, such as connecting bidirectional thyristors in parallel on the AC output side of each submodule, which increases the cost of converter construction. In addition, an AC circuit breaker is required to clear the fault current. Due to the long action time of the AC circuit breaker, the AC fault current lasts for a long time, causing damage to the transformer and threatening the normal operation of the AC power grid. Summary of the invention
[0005] In view of the deficiencies mentioned in the above technical background, the present invention provides a mixed bridge MMC valve-side AC grounding fault protection circuit and method based on a thyristor ring, which reduces the overvoltage of the submodule capacitor and realizes the rapid clearing of the AC fault current.
[0006] To achieve the above-mentioned purpose, the present invention provides the following technical solution: a mixed bridge MMC valve-side AC grounding fault protection circuit based on a thyristor ring, which adds three thyristor branches connected end to end on the basis of a traditional mixed bridge MMC converter, namely a first thyristor branch T1, a second thyristor branch T2 and a third thyristor branch T3.
[0007] The DC side of the mixed bridge MMC converter is connected to the first fast mechanical switch and the second fast mechanical switch.
[0008] When a single-phase grounding fault occurs on the valve side, fault protection is implemented. First, the three thyristor branches are triggered and all sub-modules in the converter are locked to quickly eliminate the DC line current. Then the first and second fast mechanical switches on the DC side are opened, and finally the trigger signals of the three thyristor branches are removed to quickly clear the AC fault current.
[0009] Furthermore, the thyristor branches are connected as follows: the anode of the first thyristor branch T1 is connected to the upper end of the upper bridge arm inductor of phase A, and the cathode is connected to the upper end of the upper bridge arm inductor of phase B; the anode of the second thyristor branch T2 is connected to the upper end of the upper bridge arm inductor of phase B, and the cathode is connected to the upper end of the upper bridge arm inductor of phase C; the anode of the third thyristor branch T3 is connected to the upper end of the upper bridge arm inductor of phase C, and the cathode is connected to the upper end of the upper bridge arm inductor of phase A.
[0010] Furthermore, the three thyristor branches are each formed by M thyristors connected in series, and M = kU T / V T ,
[0011] Where, k is the voltage safety margin, U T V is the voltage across the thyristor branch when the converter is running at rated speed. T It is the voltage that a single thyristor can withstand across its two ends.
[0012] The technical solution of the present invention also provides: a mixed bridge MMC valve side AC grounding fault protection method based on a thyristor ring, comprising the following steps:
[0013] S1, collect the three-phase AC current i of the converter a 、i b 、i c , if i a +i b +i c If it is greater than the set fault threshold, it is determined that a valve-side AC single-phase grounding fault has occurred, and a fault blocking signal is sent to the remote healthy converter;
[0014] Among them, the fault threshold can be set to 0.1 times the rated AC current amplitude;
[0015] S2, after detecting a fault, triggers three thyristor branches, connects the three-phase upper bridge arm reactors, and simultaneously locks all submodules of the converter to quickly clear the DC current;
[0016] S3, opening the first and second fast mechanical switches on the DC side to isolate the faulty converter;
[0017] S4, remove the trigger signals of the three thyristor branches and quickly cut off the AC fault current.
[0018] The technical solution of the present invention also provides: an electronic device, comprising:
[0019] one or more processors;
[0020] a storage device having one or more programs stored thereon;
[0021] When the one or more programs are executed by the one or more processors, the one or more processors implement any of the above-mentioned thyristor ring-based mixed bridge MMC valve-side AC grounding fault protection methods.
[0022] The technical solution of the present invention also provides: a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any of the above-mentioned thyristor ring-based mixed bridge MMC valve-side AC grounding fault protection methods.
[0023] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:
[0024] 1. The fault protection method of the present invention can quickly disconnect the AC fault current and quickly clear the AC fault within 20ms without damaging the valve-side transformer or affecting the normal operation of the AC power grid.
[0025] 2. The fault protection method of the present invention realizes semi-decoupling of the converter AC / DC circuits by triggering three thyristor branches, effectively reducing the overvoltage of the capacitors of the three-phase upper and lower bridge arm submodules. In addition, the AC fault current only flows through the three thyristor branches, avoiding overcurrent in the bridge arm and effectively protecting the MMC converter.
[0026] 3. The infrastructure cost of the present invention is low. Only three thyristor branches are added. There is no need to connect bidirectional thyristors in parallel on the AC output side of each submodule, which greatly reduces the infrastructure cost of the converter. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Figure 1 It is a circuit structure diagram of the AC grounding fault protection circuit on the mixed bridge MMC valve side based on the thyristor ring of the present invention;
[0028] Figure 2 It is a control flow chart of the mixed bridge MMC valve side AC grounding fault protection method based on thyristor ring of the present invention.
[0029] In the figure: 1. upper bridge arm; 2. lower bridge arm; 3. full bridge submodule; 4. half bridge submodule; 5. bridge arm reactor; 6. thyristor ring; 7. first fast mechanical switch; 8. second fast mechanical switch. DETAILED DESCRIPTION
[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.
[0031] The following will be combined with the drawings in the embodiments of the present disclosure to clearly and completely describe the technical solutions in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.
[0032] In one embodiment of the present invention, Figure 1 As shown, the conventional mixed-bridge MMC converter is a three-phase structure of A, B, and C, and each phase includes an upper bridge arm 1, a lower bridge arm 2, and two bridge arm reactors 5, which are an upper bridge arm reactor and a lower bridge arm reactor respectively; each bridge arm includes N mutually cascaded sub-modules, and the sub-modules in each bridge arm are in the form of a mixed full-bridge sub-module 3 and a half-bridge sub-module 4.
[0033] The DC side of the mixed bridge MMC converter is connected to the first fast mechanical switch 7 and the second fast mechanical switch 8. Figure 1 S1 is the first fast mechanical switch, S2 is the second fast mechanical switch, and the converter is isolated when the fast mechanical switch is turned on.
[0034] The present invention is based on a thyristor ring-based mixed bridge MMC valve-side AC grounding fault protection circuit structure, which adds three end-to-end connected thyristor branches 6 on the basis of a traditional mixed bridge MMC converter, namely a first thyristor branch T1, a second thyristor branch T2 and a third thyristor branch T3.
[0035] Among them, the anode of the first thyristor branch T1 is connected to the upper end P1 of the upper arm inductor of phase A, and the cathode is connected to the upper end P2 of the upper arm inductor of phase B; the anode of the second thyristor branch T2 is connected to the upper end P2 of the upper arm inductor of phase B, and the cathode is connected to the upper end P3 of the upper arm inductor of phase C; the anode of the third thyristor branch T3 is connected to the upper end P3 of the upper arm inductor of phase C, and the cathode is connected to the upper end P1 of the upper arm inductor of phase A.
[0036] The three thyristor branches are each composed of M thyristors connected in series, and M = kU T / V T .
[0037] Where, k is the voltage safety margin, U TV is the voltage across the thyristor branch when the converter is running at rated speed. T It is the voltage that a single thyristor can withstand across its two ends.
[0038] Based on the mixed bridge MMC valve side AC grounding fault protection circuit of the thyristor ring, the mixed bridge MMC valve side AC grounding fault protection method of this embodiment is as follows: Figure 2 As shown, the following controls are included:
[0039] S1, collect the three-phase AC current i of the mixed bridge MMC converter a 、i b and i c :
[0040] If i a +i b +i c If it is less than the set fault threshold, it is determined that no single-phase AC grounding fault on the valve side occurs, and the mixed bridge MMC converter maintains normal operation;
[0041] If i a +i b +i c If it is greater than the set fault threshold, it is determined that a valve-side AC single-phase grounding fault has occurred, and a fault lockout signal is sent to the remote healthy converter through the communication optical fiber.
[0042] In particular, in this embodiment, the fault threshold is set to 0.1 times the rated AC current amplitude.
[0043] S2, after detecting a fault, triggers the three thyristor branches T1, T2 and T3, connects the three-phase upper bridge arm reactors, and locks all full-bridge sub-modules 3 and half-bridge sub-modules 4 of the converter at the same time:
[0044] That is, the four IGBT switches T in the full-bridge submodule F1 , T F2 , T F3 and T F4 Both IGBT switches T H1 and T H2 All turned off.
[0045] S3, collect the DC side current i of the converter dc , after detecting that the DC current is zero, the DC side fast mechanical switches S1 and S2 of the converter are disconnected to isolate the faulty converter;
[0046] S4, remove the trigger signals of the three thyristor branches:
[0047] When the AC current flowing through the thyristor branch is less than the holding current of the thyristor device, the thyristor is naturally turned off, thereby quickly cutting off the AC fault current within 20ms.
[0048] In summary, the technical solution of the present invention can achieve the same output characteristics as the traditional mixed bridge MMC converter. At the same time, for the single-phase grounding fault on the valve side, it can effectively reduce the overvoltage of the sub-module capacitor with fewer protection circuits and realize the rapid removal of the AC fault current.
[0049] This embodiment also proposes an electronic device for a mixed bridge MMC valve side AC grounding fault protection method based on a thyristor ring, the device includes a processor and a memory, the processor and the memory are coupled, the memory stores program instructions, and the above-mentioned task management method is implemented when the program instructions stored in the memory are executed by the processor.
[0050] Among them, the processor can be a general-purpose processor, including a CPU (central processing unit), NP (network processor), etc.; it can also be a DSP (digital signal processor), ASIC (application-specific integrated circuit), FPGA (field programmable gate array), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components.
[0051] The memory may include RAM (Random Access Memory) and may also include Non-Volatile Memory (Non-volatile Memory), such as at least one disk storage. The memory may be an internal RAM type memory, and the processor and memory may be integrated into one or more independent circuits or hardware, such as ASIC.
[0052] It should be noted that the computer program in the above-mentioned memory can be implemented in the form of a software functional unit and sold or used as an independent product, and can be stored in a computer-readable storage medium. The technical solution of the present invention, in essence, or the part that contributes to the prior art or the part of the technical solution can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device, which can be a personal computer, an electronic device, or a network device, etc., to perform all or part of the steps of the methods of various embodiments of the present invention.
[0053] This embodiment further proposes a computer-readable storage medium, which stores computer instructions, and the computer instructions are used to enable a computer to execute the above-mentioned thyristor ring-based mixed bridge MMC valve-side AC grounding fault protection method.
[0054] The storage medium may be an electronic medium, a magnetic medium, an optical medium, an electromagnetic medium, an infrared medium, or a semiconductor system or a propagation medium. The storage medium may also include semiconductor or solid-state memory, magnetic tape, a removable computer disk, RAM (random access memory), ROM (read-only memory), a hard disk, and an optical disk. Optical disks may include CD-ROM (compact disk - read-only memory), CD-RW (compact disk - read / write), and DVD.
[0055] 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.
[0056] For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances. When an element is referred to as being "assembled on", "installed on", "fixed on" or "set on" another element, it can be directly on the other element or there can also be a centered element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be a centered element at the same time. The terms "vertical", "horizontal", "up", "down", "left", "right" and similar expressions used herein are only for illustrative purposes and are not intended to be the only implementation method.
[0057] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.
[0058] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.
Claims
1. A thyristor ring-based mixed bridge MMC valve-side AC ground fault protection circuit, comprising a mixed bridge MMC converter, the mixed bridge MMC converter having a three-phase structure of A, B, and C, each phase comprising an upper bridge arm module (1), a lower bridge arm module (2), and two bridge arm reactors (5), which are an upper bridge arm reactor and a lower bridge arm reactor respectively; the upper and lower bridge arm modules of each phase each comprise N cascaded submodules, the submodules comprising a full-bridge submodule (3) and a half-bridge submodule (4), characterized in that: On the basis of the mixed bridge type MMC converter, a first thyristor branch T1, a second thyristor branch T2, and a third thyristor branch T3 are added, the three thyristor branches are connected end to end, and each thyristor branch is connected to one end of the upper bridge arm reactor of any two phases, and one end of the upper bridge arm reactor is connected to the AC side of the upper bridge arm module; the DC side of the mixed bridge type MMC converter is connected to the first fast mechanical switch (7) and the second fast mechanical switch (8), and the converter is isolated when the fast mechanical switch is turned on.
2. The thyristor ring-based mixed bridge MMC valve-side AC grounding fault protection circuit according to claim 1, characterized in that: The anode of the first thyristor branch T1 is connected to the upper end of the upper bridge arm inductor of phase A, and the cathode is connected to the upper end of the upper bridge arm inductor of phase B; the anode of the second thyristor branch T2 is connected to the upper end of the upper bridge arm inductor of phase B, and the cathode is connected to the upper end of the upper bridge arm inductor of phase C; the anode of the third thyristor branch T3 is connected to the upper end of the upper bridge arm inductor of phase C, and the cathode is connected to the upper end of the upper bridge arm inductor of phase A.
3. The thyristor ring-based mixed bridge MMC valve-side AC grounding fault protection circuit according to claim 1, characterized in that: In the mixed bridge MMC converter, the three thyristor branches are respectively formed by connecting M thyristors in series, and the calculation is as follows: M=kU T / V T Where, k is the voltage safety margin, U T V is the voltage across the thyristor branch when the converter is running at rated speed. T It is the voltage that a single thyristor can withstand across its two ends.
4. A thyristor ring mixed bridge MMC valve side AC grounding fault protection method, characterized in that: The following steps are involved: S1, collecting the three-phase AC current of the mixed bridge MMC converter. If the sum of the three-phase AC current is greater than the preset fault threshold, it is determined that the converter has a valve-side AC single-phase grounding fault, and a fault locking signal is sent to the remote healthy converter through the communication optical fiber; S2, after detecting a fault, triggering three thyristor branches, connecting the three-phase bridge arm reactors of the mixed bridge type MMC converter, and locking all submodules in the mixed bridge type MMC converter to eliminate the DC line current; S3, opening the first fast mechanical switch and the second fast mechanical switch on the DC side to isolate the faulty converter; S4. Remove the trigger signals of the three thyristor branches to cut off the AC fault current.
5. The thyristor ring-based mixed bridge MMC valve-side AC grounding fault protection method according to claim 4 is characterized in that: The fault threshold is set to 0.1 times the AC rated current amplitude.
6. An electronic device, characterized in that: include: one or more processors; a storage device having one or more programs stored thereon; When the one or more programs are executed by the one or more processors, the one or more processors implement the method as claimed in any one of claims 4 to 5.
7. A computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the program is executed by a processor, the steps in the thyristor ring-based mixed bridge MMC valve-side AC grounding fault protection method described in any one of claims 4 to 5 are implemented.