Controllable zero-crossing direct-current circuit breaker and control method thereof

Abstract

The invention provides a controllable zero-crossing direct-current circuit breaker and a control method thereof, and belongs to the technical field of power electronics. The controllable zero-crossing direct-current circuit breaker comprises a through-flow branch, a current transfer branch and an energy dissipation branch, adopts semi-control and full-control devices, and is simple in logic, economical and reliable. According to the circuit breaker, the thyristors and the IGBTs are matched to input the pre-charging capacitors, the bidirectional breaking capacity is achieved, and the short-circuit current of a direct-current power grid can be effectively broken; meanwhile, the number of current zero crossing points of a mechanical switch branch during a fault is greatly increased, and the reliability of the direct-current circuit breaker is enhanced. The invention provides a control method of a controllable zero-crossing direct-current circuit breaker. The controllable zero-crossing type direct-current circuit breaker is controlled under the two conditions that the direct-current line where the circuit breaker is located operates normally or before the fault of the direct-current line where the circuit breaker is located is detected and after the fault of the direct-current line where the controllable zero-crossing type direct-current circuit breaker is detected.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a controllable zero-crossing DC circuit breaker and a control method thereof. Background Art

[0002] In recent years, flexible DC transmission technology has demonstrated its advantages in long-distance, high-capacity transmission applications. Multi-terminal modular circuits (MMCs) have become the preferred topology for DC grids and multi-terminal DC transmission. A typical example is the half-bridge MMC used in the Zhangbei DC grid. However, because half-bridge submodules lack the ability to clear DC-side faults, DC circuit breakers are required to interrupt the fault current.

[0003] Currently used DC circuit breakers mainly include forced overcurrent type DC circuit breakers and self-oscillation type DC circuit breakers. Forced overcurrent type DC circuit breakers (such as the classic ABB hybrid DC circuit breaker) force the current to be transferred to the power electronic branch through the current commutation switch of the mechanical branch. This type of circuit breaker has a fast fault clearing speed, but the current commutation switch of the mechanical branch generates a large amount of conduction loss in steady state, resulting in poor economic efficiency. Self-oscillation type DC circuit breakers can be further divided into active and passive types. Passive oscillation type DC circuit breakers use the LC oscillation of the transfer branch to generate a resonant current with a gradually increasing oscillation amplitude, which can cause the mechanical branch current to have more current zero crossings. However, this method takes a long time to generate current zero crossings and has low fault clearing efficiency. Active oscillation type DC circuit breakers use the resonant current with a gradually decreasing oscillation amplitude generated by pre-charged capacitors and inductors to cause the mechanical branch current to quickly cross zero. However, this method generates a small number of current zero crossings and has poor fault clearing stability.

[0004] In order to solve the above problems, the present invention proposes a controllable zero-crossing DC circuit breaker and a control method thereof. Summary of the Invention

[0005] The purpose of the present invention is to propose a controllable zero-crossing DC circuit breaker and a control method thereof to solve the problems of large conduction loss of hybrid DC circuit breakers, slow current zero-crossing speed of passive oscillation DC circuit breakers, and small number of current zero-crossing points of active oscillation DC circuit breakers in the above-mentioned prior art. The present invention provides a controllable zero-crossing DC circuit breaker and a control method thereof. The controllable zero-crossing DC circuit breaker includes a flow branch, a current transfer branch, and an energy dissipation branch. The flow branch is used to realize the conduction of the steady-state current of the DC line when the DC line is operating normally; the current transfer branch is used to transfer the fault current to the current transfer branch after detecting a fault in the DC line, and carry the fault current transferred by the flow branch, and control the current of the flow branch to repeatedly cross zero through the pre-charge capacitor in the transfer branch; the energy dissipation branch is used to absorb the residual energy in the line after the fault occurs, so that the current in each branch is zero. Control of the zero-crossing DC circuit breaker is implemented in two scenarios: before the DC line where the circuit breaker is located is operating normally or a fault is detected, and after a fault is detected on the DC line where the zero-crossing DC circuit breaker is located. The zero-crossing DC circuit breaker uses semi-controlled and fully controlled devices, offering simple logic, high cost-effectiveness, and strong control capabilities.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0007] In one aspect, the present invention provides a controllable zero-crossing DC circuit breaker, comprising:

[0008] The current-carrying branch is used to conduct the steady-state current of the DC line when the DC line is operating normally;

[0009] The current transfer branch is used to transfer the fault current to the current transfer branch after detecting a fault in the DC line, and carry the fault current transferred by the through-current branch. The pre-charged capacitor in the transfer branch controls the through-current branch current to repeatedly cross zero.

[0010] The energy dissipation branch is used to absorb the residual energy in the line after a fault occurs, so that the current in each branch is zero.

[0011] Preferably, the through-current branch comprises a mechanical switch MS.

[0012] Preferably, the current transfer branch comprises a series combination of N current-driven switches and N main circuit breakers;

[0013] The current driven switch comprises a thyristor unit, an IGBT unit, a diode unit and a pre-charge capacitor unit, and each unit is combined in series and parallel;

[0014] The current-driven switch includes two operating modes during operation: negative input and bypass. The operating mode is dynamically controlled by the current of the flow branch during fault.

[0015] The main circuit breaker is composed of N IGBTs connected in anti-series.

[0016] Preferably, the current-passing branch and the current-transferring branch are connected in parallel to form a common point A and a common point B.

[0017] Preferably, the current transfer branch is composed of a half-controlled thyristor and a fully-controlled IGBT connected in series and in parallel.

[0018] Preferably, the energy dissipation branch is connected in parallel with the current flow branch and the current transfer branch, and the connection points are also the common point A and the common point B;

[0019] The energy dissipation branch is a lightning arrester MOV, which is used to dissipate DC fault energy.

[0020] On the other hand, before the DC line where the controllable zero-crossing DC circuit breaker is located operates normally or a fault in the DC line where the controllable zero-crossing DC circuit breaker is located is detected, the present invention provides a control method for the controllable zero-crossing DC circuit breaker, comprising:

[0021] All IGBTs and thyristors in the current transfer branch are turned off, and the steady-state current or fault current flows through the current-passing branch.

[0022] On the other hand, after detecting a fault in a DC line where a controllable zero-crossing DC circuit breaker is located, the present invention also provides another control method for the controllable zero-crossing DC circuit breaker, comprising:

[0023] At time t1, the protection device sends a trip command to the mechanical switch MS of the on-state low-loss branch, triggering T1 and T4, turning on the main circuit breaker. Current flows through the current transfer branch. The current-driven switch determines the number of submodules put into operation by identifying the current size of the on-state branch, forcing the on-state branch current to repeatedly cross zero.

[0024] At time t2, the mechanical switch completes the disconnection, opening the main circuit breaker, and the current-driven switch enters the locking mode. The current flows from the current transfer branch through the energy dissipation branch;

[0025] At time t3, the energy dissipation branch consumes the residual fault energy and the fault current drops to 0.

[0026] Compared with the closest existing technology, the technical solution provided by the present invention has the following beneficial effects:

[0027] (1) The control method of the controllable zero-crossing DC circuit breaker provided by the present invention is divided into two situations: the DC line where the controllable zero-crossing DC circuit breaker is located is operating normally or before a fault occurs in the DC line where the controllable zero-crossing DC circuit breaker is located, and after a fault occurs in the DC line where the controllable zero-crossing DC circuit breaker is located. The control method is simple and has strong controllability.

[0028] (2) The through-current branch of the present invention plays the role of conducting the steady-state current of the DC line, reducing the loss of the DC line and saving costs. The current transfer branch promptly forces the current to transfer after the fault current occurs, so that the current of the through-current branch repeatedly passes through zero.

[0029] (3) The technical solution provided by the present invention fully utilizes the comprehensive fault clearing method using diodes, thyristors and IGBTs, which can achieve bidirectional fault clearing and has a good fault clearing effect;

[0030] (4) The technical solution provided by the present invention allows current to flow through the flow branch before the DC line where the controllable zero-crossing DC circuit breaker is operating normally or a fault in the DC line where the controllable zero-crossing DC circuit breaker is detected. The flow branch has a small loss resistance and is more economical in steady state.

[0031] (5) The technical solution provided by the present invention detects a fault in the DC line where the controllable zero-crossing DC circuit breaker is located, and as the pre-charged capacitor in the current transfer branch is discharged, the fault current can be forced to flow through the current transfer branch;

[0032] (6) The technical solution provided by the present invention uses low-cost semi-controlled and fully controlled devices, which can effectively save investment. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a structural diagram of a controllable zero-crossing DC circuit breaker in Example 1 of the present invention;

[0034] Figure 2 is a schematic diagram of a steady-state current path in Example 2 of the present invention;

[0035] Figure 3 Schematic diagram of the flow path of the DC line fault current before the fault is detected in Example 3 of the present invention;

[0036] Figure 4 Schematic diagram of the flow path of the fault current in the DC line in S101 after a fault is detected in Embodiment 4 of the present invention.

[0037] Figure 5 Schematic diagram of the flow path of the fault current in the DC line in S102 after a fault is detected in Example 4 of the present invention.

[0038] Figure 6 Schematic diagram of the flow path of the DC line fault current in S103 after a fault is detected in Embodiment 4 of the present invention. DETAILED DESCRIPTION

[0039] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0040] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0041] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0042] The present invention will be described in further detail below with reference to the accompanying drawings.

[0043] Example 1:

[0044] Embodiment 1 of the present invention provides a controllable zero-crossing DC circuit breaker, which specifically includes a current-carrying branch, a current transfer path, and an energy dissipation branch. The functions of each branch are as follows:

[0045] The current-passing branch is used to conduct the steady-state current of the DC line when the DC line is operating normally;

[0046] The current transfer branch is used to transfer the fault current to the current transfer branch after detecting a fault in the DC line, and carry the fault current transferred by the through-current branch. The pre-charged capacitor in the transfer branch controls the through-current branch current to repeatedly cross zero.

[0047] The energy dissipation branch is used to absorb the residual energy in the line after a fault occurs, so that the current in each branch is zero.

[0048] The schematic diagram of the structure of the controllable zero-crossing DC circuit breaker provided in Example 1 of the present invention is as follows: Figure 1 As shown, Figure 1 In the figure, the current-carrying branch, the current-transfer branch, and the energy-dissipating branch are connected in parallel, and A and B represent common points.

[0049] The above-mentioned through-current branch includes a mechanical switch MS.

[0050] The above-mentioned current transfer branch is composed of N current drive switches and N main circuit breakers connected in series.

[0051] The above-mentioned current driven switch is composed of a pre-charge capacitor, a diode, a thyristor and an IGBT connected in series and parallel.

[0052] The main circuit breaker is composed of N IGBTs and IGBTs connected in anti-series.

[0053] The above-mentioned current-driven switch includes two operating modes during operation: negative input and bypass. The operating mode is dynamically controlled by the current of the flow branch during fault.

[0054] The energy dissipation branch is a lightning arrester MOV, the purpose of which is to dissipate DC fault energy.

[0055] The circuit diagram of the controllable zero-crossing DC circuit breaker provided in Example 1 of the present invention connected to the DC circuit is as follows: Figure 2 shown.

[0056] Example 2:

[0057] Embodiment 2 of the present invention provides a control method for a controllable zero-crossing DC circuit breaker, and the specific process is as follows:

[0058] When the DC line where the controllable zero-crossing DC circuit breaker is located is operating normally, the thyristors in the current transfer branch are all turned off, the energy dissipation branch is out of operation, the MS in the current-passing branch is turned on, and the steady-state current flows through the current-passing branch. The flow path of the steady-state current when the DC line is operating normally is shown in the figure below. Figure 2 shown.

[0059] Example 3:

[0060] The control method of the controllable zero-crossing DC circuit breaker provided in Example 3 of the present invention has the following specific process:

[0061] Before detecting a fault in the DC line where the controllable zero-crossing DC circuit breaker is located, the MS in the through-current branch is turned on, and the fault current flows through the through-current branch. The flow path of the DC line fault current before the fault is detected is shown in the figure below. Figure 3 shown.

[0062] Example 4:

[0063] The control method for a controllable zero-crossing DC circuit breaker provided in Example 4 of the present invention is applicable to detecting a fault in a DC line where the controllable zero-crossing DC circuit breaker is located. The specific process is as follows:

[0064] S101: At time t1, the protection device sends a trip command to the mechanical switch MS of the low-loss branch in the on-state, triggering T1 and T4, turning on the main circuit breaker, and the current flows through the current transfer branch. The current-driven switch obtains the number of sub-modules put into operation by identifying the current size of the flow branch, forcing the flow branch current to repeatedly cross zero. The flow path of the fault current is shown in the figure below. Figure 4 As shown;

[0065] S102: At t2, the mechanical switch completes the disconnection, opens the main circuit breaker, and the current-driven switch enters the locking mode. The current flows from the current transfer branch through the energy dissipation branch. The flow path of the fault current is shown in the following diagram: Figure 5 As shown;

[0066] S103: At time t3, the energy dissipation branch consumes the residual fault energy, the fault current drops to 0, and the DC circuit breaker operation process is completed. The flow path diagram of the fault current is as follows: Figure 6 shown.

[0067] For the convenience of description, the various parts of the above-mentioned device are divided into various modules or units according to their functions and described separately. Of course, when implementing this application, the functions of each module or unit can be implemented in the same or multiple software or hardware.

[0068] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0069] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0070] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0071] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Ordinary technicians in the relevant field can still modify or replace the specific implementation methods of the present invention with equivalents by referring to the above embodiments. Any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention are within the scope of protection of the claims of the present invention to be approved.

Claims

1. A controllable zero-crossing DC circuit breaker, characterized in that: include: The current-carrying branch is used to conduct the steady-state current of the DC line when the DC line is operating normally; The current transfer branch is used to transfer the fault current to the current transfer branch after detecting a fault in the DC line, and carry the fault current transferred by the through-current branch. The pre-charged capacitor in the transfer branch controls the through-current branch current to repeatedly cross zero. The energy dissipation branch is used to absorb the residual energy in the line after a fault occurs, so that the current in each branch is zero.

2. A control method for a controllable zero-crossing DC circuit breaker according to claim 1, characterized in that: include: After detecting a fault in the DC line where the controllable zero-crossing DC circuit breaker is located, At time t1, the protection device sends a trip command to the mechanical switch MS of the flow branch, triggering T1 and T4, turning on the main circuit breaker, and the current flows through the current transfer branch. The current-driven switch determines the number of submodules put into operation by identifying the current size of the flow branch, forcing the flow branch current to repeatedly cross zero. At t2, the mechanical switch completes disconnection, disconnecting the main circuit breaker, and the current drives the switch into the locking mode; Current flows from the current transfer branch through the energy dissipation branch. At time t3, the energy dissipation branch consumes the residual fault energy and the fault current drops to 0.

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