Current injection type DC circuit breaker and current injection method

Abstract

The present invention provides a current injection type DC circuit breaker and a current injection method. The current injection type DC circuit breaker includes: a mechanical switch, a power switch module, a resonant inductor, a pre-charge power module, an energy consumption module and a control unit; the mechanical switch is arranged in a flow branch, the power switch module, the resonant inductor and the pre-charge power module are connected in series to form an adjustable resonant current injection branch, the adjustable resonant current injection branch and the energy consumption module are connected in parallel with the flow branch, the control unit is connected with the flow branch, the power switch module and the mechanical switch, and the control unit controls the mechanical switch and the power switch module according to the current amplitude and change rate of the flow branch. The present invention improves the reliability of the DC circuit breaker in shutting down under complex working conditions, reduces the voltage and current tolerance pressure of the device, reduces the change rate of the voltage and current of the zero-crossing attachment of the flow branch, improves the breaking speed of the DC circuit breaker, and enhances the reliability of the equipment.

Description

Technical Field

[0001] The invention relates to electric power technology, in particular to a current injection type DC circuit breaker and a current injection method. Background Art

[0002] With the increasing demand for renewable energy such as wind power and photovoltaics, and the rapid development of power electronics technology, high-voltage direct current transmission systems are attracting more and more attention from countries around the world. However, since the DC side impedance of the DC grid is very small, when a short circuit occurs, the current rises rapidly. If the fault current cannot be removed in time, all converters will be locked and the system will stop operating. Therefore, the DC circuit breaker is one of the key devices to ensure the reliable operation of the DC transmission system.

[0003] The difficulty in the development of DC circuit breakers is that there is no natural zero-crossing point for current, and the mature arc-extinguishing technology in AC circuit breakers cannot be applied. In order to complete the interruption of DC, it is necessary to create an "artificial current zero-crossing point". Commonly used methods are passive resonance type and current injection type. The passive resonance type has the advantages of simple structure, easy control, and low cost, but the breaking time is related to the loop parameters, generally more than tens of milliseconds, and poor rapid responsiveness. The current injection type DC circuit breaker reversely superimposes the high-frequency oscillating current generated by the current injection branch on the flow branch, thereby constructing an artificial zero-crossing point in the flow branch to achieve effective interruption of the fault current. This type of DC circuit breaker has the advantages of low loss and high reliability. It is suitable for high-voltage and high-current occasions and has received widespread attention in the industry.

[0004] However, conventional current injection DC circuit breakers are only suitable for high current fault conditions. In other fault conditions, the peak value of the current injection is much higher than the fault current, causing the mechanical break to be subjected to a large current and voltage change rate near the current zero point, which can easily cause problems such as arc failure or arc reignition, making the DC circuit breaker at risk of breaking failure. Summary of the invention

[0005] In view of the defects of the DC circuit breaker in the prior art, the object of the present invention is to provide a current injection type DC circuit breaker, comprising: a mechanical switch, a power switch module, a resonant inductor, a pre-charge power module, an energy consumption module and a control unit; wherein,

[0006] The mechanical switch is arranged in the flow branch, the power switch module, the resonant inductor and the pre-charging power module are connected in series to form an adjustable resonant current injection branch, the adjustable resonant current injection branch and the energy consumption module are connected in parallel with the flow branch, the control unit is connected with the flow branch, the power switch module and the mechanical switch, and the control unit controls the mechanical switch and the power switch module according to the current amplitude and change rate of the flow branch to realize the switching of the current injection type DC circuit breaker.

[0007] In an embodiment of the present invention, the pre-charging power module includes: a resonant capacitor.

[0008] In an embodiment of the present invention, the power switch module comprises: two power semiconductor switch devices and a capacitor;

[0009] The two power semiconductor switch devices are connected in forward direction and in parallel with the capacitor.

[0010] In an embodiment of the present invention, the power switch module comprises: four power semiconductor switch devices and a capacitor;

[0011] The four power semiconductor switch devices are connected in forward direction and in parallel with the capacitor.

[0012] In the embodiment of the present invention, the current injection type DC circuit breaker comprises: at least two power switch modules, and the power switch modules are electrically connected to each other.

[0013] In the embodiment of the present invention, the energy consumption module includes: a lightning arrester.

[0014] At the same time, the present invention also provides a current injection method for a DC circuit breaker, which uses the above-mentioned current injection type DC circuit breaker to perform fault current injection; wherein,

[0015] The control unit controls the mechanical switch and the power switch module according to the current amplitude and the change rate of the current-carrying branch to realize the switching of the current injection type DC circuit breaker.

[0016] The present invention provides a current injection type DC circuit breaker topology structure and method, which improves the reliability of the DC circuit breaker in shutting down under complex working conditions, and can automatically adjust the number of switched capacitors according to the magnitude of the fault current in the pulse current injection stage, control the peak value of the injected current, and adapt to different breaking currents. At the same time, it reduces the voltage and current withstand pressure of the device, reduces the change rate of the voltage and current of the zero-crossing attachment of the current-carrying branch, thereby improving the breaking speed of the DC circuit breaker, enhancing the reliability of the equipment, and meeting the safety, reliability, and economy requirements of the high-voltage DC transmission system.

[0017] In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are specifically cited below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 A principle block diagram of a specific example of a DC circuit breaker provided in an embodiment of the present invention;

[0020] Figure 2(a) is a half-bridge structure submodule;

[0021] Figure 2(b) shows the full-bridge structure submodule;

[0022] Figure 3 A current flow diagram for normal operation provided by an embodiment of the present invention;

[0023] FIG4( a ) is a current flow diagram of a half-bridge submodule topology structure during a pulse current injection phase provided by an embodiment of the present invention;

[0024] FIG4( b ) is a current flow diagram of a half-bridge submodule topology structure during a pulse current injection phase provided by an embodiment of the present invention;

[0025] FIG5(a) is a current flow diagram of a full-bridge submodule topology structure provided by an embodiment of the present invention when the current is in the positive direction during the pulse current injection phase;

[0026] FIG5( b ) is a current flow diagram of a full-bridge submodule topology structure provided by an embodiment of the present invention when the current is in the positive direction during the pulse current injection phase;

[0027] FIG6( a ) is a current flow diagram of a full-bridge submodule topology structure provided by an embodiment of the present invention when the current is reversed during the pulse current injection phase;

[0028] FIG6( b ) is a current flow diagram of a full-bridge submodule topology structure provided by an embodiment of the present invention when the current is reversed during the pulse current injection phase;

[0029] Figure 7 A current flow diagram of the energy consumption stage provided by an embodiment of the present invention;

[0030] Figure 8 A flowchart of a control unit provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] 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.

[0032] The current injection type DC circuit breaker of the prior art is only suitable for large current fault conditions. In other fault conditions, the peak value of the current injection is much higher than the fault current, so that the mechanical break is subjected to a large current and voltage change rate near the current zero point, which may easily cause problems such as arc failure to extinguish or arc reignition, making the DC circuit breaker at risk of breaking failure. Based on this, the present invention proposes a current adaptive injection type DC circuit breaker topology structure.

[0033] The present invention provides a current injection type DC circuit breaker topology structure, comprising: a mechanical switch, a power switch module, a resonant inductor, a resonant capacitor, a lightning arrester and a control unit.

[0034] The mechanical switch constitutes a current-carrying branch, the power switch module, the resonant inductor, and the resonant capacitor constitute a current injection branch, which is connected in parallel with the current-carrying branch, and the lightning arrester constitutes an energy consumption branch; the control unit is connected to the detected power line, the mechanical switch, and the power switch module, and determines the occurrence of a fault by measuring the current amplitude and change rate of the current-carrying branch, and controls the mechanical switch and the power switch module in an orderly manner to achieve reliable opening and closing of the DC circuit breaker.

[0035] The power switch module in the injection branch can adopt a half-bridge structure or a full-bridge structure, wherein the half-bridge structure includes two switch tubes and a capacitor, and the full-bridge structure includes four switch tubes and a capacitor; and multiple groups of power switch modules can be used in the injection branch, which can be connected in series, in parallel, or in a combination of series and parallel to meet the application requirements of different transmission voltages and power levels.

[0036] An embodiment of the present invention further provides a control method for a current injection type DC circuit breaker. Based on the above-mentioned current injection type DC circuit breaker topology structure, the control method includes:

[0037] In the normal current-carrying state, the mechanical switch is turned on, carrying the main current, and the power switch module injected into the branch is not triggered;

[0038] When the control unit detects a fault current, it sends a trip command to the mechanical switch, triggers the power switch, and injects a pulse current into the branch circuit that is equal in amplitude to the fault current and opposite in direction, generating an "artificial current zero crossing point" to achieve reliable shutdown of the mechanical switch.

[0039] The energy consumption branch formed by the lightning arrester consumes the remaining energy in the inductor after the circuit breaker cuts off the fault current. During the pulse current injection stage, the control unit switches the capacitor by controlling the on and off states of the power electronic devices in the power switch module;

[0040] The injection branch includes multiple groups of power switch modules, which can dynamically adjust the number of capacitor switching, change the impedance of the injection loop, effectively control the waveform of the injected current pulse, and realize adaptive current injection under different fault currents.

[0041] Figure 1 FIG. 1 is a schematic diagram of the structure of an embodiment of the present invention. Figure 1 As shown, it includes a mechanical switch K, N power switch modules, and a resonant inductor L r , resonant capacitor C r and lightning arrester, in which the mechanical switch K is connected in series with the power line to form a current branch, and the current injection branch includes N power switch modules, resonant inductor L r and resonant capacitor C r , connected in parallel with the current branch; the arrester is connected in parallel with the resonant capacitor Cr to absorb excess energy under fault conditions. The control unit detects the magnitude of the fault current in the power line, dynamically controls the on and off of the power electronic devices in the power switch module in the current injection branch, switches the capacitor, and controls the waveform of the injected current pulse to achieve adaptive current injection under different fault currents.

[0042] FIG. 2( a ) and FIG. 2( b ) show two power switch modules provided by an embodiment of the present invention; wherein,

[0043] FIG2(a) is a circuit connection diagram of a half-bridge submodule, in which the power semiconductor switch device IGBT1 and the power semiconductor switch device IGBT2 are connected in forward direction and connected in parallel with the capacitor C;

[0044] FIG2( b ) is a circuit connection diagram of a full-bridge submodule, in which power semiconductor switching devices IGBT1 , power semiconductor switching devices IGBT2 , power semiconductor switching devices IGBT3 , and power semiconductor switching devices IGBT4 are respectively connected in forward direction and connected in parallel with a capacitor C.

[0045] In addition, for the half-bridge submodule, the switching direction of the capacitor is fixed, while the full-bridge submodule can achieve bidirectional switching of the capacitor, which has a more flexible control method.

[0046] Figure 3 The figure shows the current flow diagram when there is no fault in the DC system. The mechanical switch K in the rated current branch remains in the on state, and all switches in the injection branch remain in the closed state.

[0047] When the control unit detects a fault signal, the DC circuit breaker operates as follows:

[0048] (1) When the mechanical switch is opened under current-carrying conditions, an arc is generated, further increasing the fault current;

[0049] (2) In the pulse current injection stage, before the mechanical switch is fully opened, the control unit determines the number of capacitors to be switched in the first stage by looking up the table based on the detected fault current to achieve the fastest pulse current rise. In the second stage, near the zero point of the mechanical switch current, the number of capacitors to be switched is adjusted again to reduce the current change rate and improve the arc extinguishing success rate.

[0050] (3) Energy consumption stage, when the resonant capacitor C r When the voltage is high enough, the arrester will operate and transfer the fault current to the arrester. The current flow is shown in the figure. Figure 7 shown.

[0051] FIG4(a) and FIG4(b) are current flow diagrams of a half-bridge submodule topology during the pulse current injection stage.

[0052] When IGBT1 is turned off and IGBT2 is turned on, capacitor C is bypassed, as shown in Figure 4(a);

[0053] When IGBT1 in the switch module is turned on and IGBT2 is turned off, capacitor C is connected to the injection branch, as shown in FIG4( b ), thereby realizing the capacitor switching function.

[0054] FIG. 5( a ) and FIG. 5( b ) are current flow diagrams of a full-bridge submodule topology structure provided in an embodiment of the present invention when the current is in the positive direction during the pulse current injection phase.

[0055] When IGBT1 and IGBT3 are turned off, and IGBT2 and IGBT4 are turned on, as shown in FIG5( a ); or, when IGBT1 and IGBT3 are turned on, and IGBT2 and IGBT4 are turned off, capacitor C is bypassed and is not connected to the injection branch;

[0056] When IGBT2 and IGBT3 are turned off and IGBT1 and IGBT4 are turned on, as shown in FIG5(b), capacitor C is connected to the injection branch in the forward direction.

[0057] FIG. 6( a ) and FIG. 6( b ) are current flow diagrams when the current is reversed during the pulse current injection phase in a full-bridge structure submodule topology structure provided by an embodiment of the present invention.

[0058] When IGBT1 and IGBT3 are turned on and IGBT2 and IGBT4 are turned off, as shown in FIG6( a ), or when IGBT1 and IGBT3 are turned off and IGBT2 and IGBT4 are turned on, capacitor C is bypassed and is not connected to the injection branch;

[0059] When IGBT2 and IGBT3 are turned on and IGBT1 and IGBT4 are turned off, as shown in FIG6( b ), capacitor C is reversely connected to the injection branch.

[0060] Figure 8 Shown is a flowchart of the control unit in an embodiment of the present invention.

[0061] When a fault signal is detected, the DC circuit breaker starts the shut-off action and the mechanical switch opens;

[0062] After that, the current injection branch starts working. First, the control unit detects the current fault current signal and determines the number and time of connecting the power switch modules by looking up the table to achieve the set current rise rate. When the injected current rises to a certain value, the current of the mechanical switch is close to the zero point. At this time, the control unit adjusts the number of connected power switch modules again to reduce the current rise rate and improve the success rate of arc extinguishing. In the pulse current injection stage, the control unit can detect the injected current I p,meas (t) and ideal current I p,ideal The difference in size is used to dynamically adjust the number of branch power switch modules connected in real time to make the injected current close to the ideal current.

[0063] From the above description, it can be seen that the current adaptive injection type DC circuit breaker topology structure proposed in the present invention has the following advantages: in the pulse current injection stage, the number of switching power switch modules is automatically adjusted to control the peak value of the injected current, and it can adapt to different breaking currents. At the same time, the voltage and current withstand pressure of the device is reduced, and the change rate of the voltage and current of the zero-crossing accessory of the current branch is reduced, thereby improving the breaking speed of the DC circuit breaker, enhancing the reliability of the equipment, and meeting the safety, reliability and economy requirements of the high-voltage DC transmission system.

[0064] Obviously, the above embodiments are merely examples for clear explanation and cannot be used to limit the scope of rights of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

[0065] The preferred embodiments of the present invention have been described above with reference to the accompanying drawings. Many features and advantages of these embodiments are clear from this detailed description, and therefore the appended claims are intended to cover all such features and advantages of these embodiments that fall within their true spirit and scope. In addition, since many modifications and changes are readily apparent to those skilled in the art, the embodiments of the present invention are not intended to be limited to the precise structure and operation illustrated and described, but all suitable modifications and equivalents that fall within their scope may be included.

[0066] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0067] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks 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 processes in the flowchart and / or block diagram. 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.

[0068] These computer program instructions may also be stored in a computer readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture including an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0069] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0070] The present invention uses specific embodiments to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A current injection type DC circuit breaker, characterized in that: The current injection type DC circuit breaker comprises: a mechanical switch, a power switch module, a resonant inductor, a pre-charge power module, an energy consumption module and a control unit; wherein, The mechanical switch is arranged in the flow branch, the power switch module, the resonant inductor and the pre-charging power module are connected in series to form an adjustable resonant current injection branch, the adjustable resonant current injection branch and the energy consumption module are connected in parallel with the flow branch, the control unit is connected with the flow branch, the power switch module and the mechanical switch, and the control unit controls the mechanical switch and the power switch module according to the current amplitude and change rate of the flow branch to realize the switching of the current injection type DC circuit breaker; The power switch module in the adjustable resonant current injection branch adopts a half-bridge structure and / or a full-bridge structure, wherein the half-bridge structure includes two power semiconductor switch devices and a capacitor, wherein the two power semiconductor switch devices are connected in forward direction and in parallel with the capacitor; the full-bridge structure includes four power semiconductor switch devices and a capacitor; wherein the four power semiconductor switch devices are connected in forward direction and in parallel with the capacitor; and the power switch modules are electrically connected to each other; When the control unit detects a fault current, it determines the number and time of connected power switch modules by looking up a table to achieve the set current rise rate; when the injected current rises to a preset value, the control unit adjusts the number of connected power switch modules again to reduce the current rise rate and improve the arc extinguishing success rate; in the pulse current injection stage, the control unit dynamically adjusts the number of connected branch power switch modules in real time by detecting the difference between the injected current and the ideal current.

2. The current injection type DC circuit breaker according to claim 1, characterized in that: The pre-charging power module includes: a resonant capacitor.

3. The current injection type DC circuit breaker according to claim 1, characterized in that: The energy consumption module includes: a lightning arrester.

4. A current injection method for a DC circuit breaker, characterized in that: The method uses the current injection type DC circuit breaker according to any one of claims 1 to 3 to perform fault current injection; wherein, The control unit controls the mechanical switch and the power switch module according to the current amplitude and the change rate of the current-carrying branch to realize the switching of the current injection type DC circuit breaker.

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