Auxiliary circuit and operation method

Abstract

The invention discloses an auxiliary circuit and an operation method. The operation method comprises the following steps: establishing an auxiliary circuit based on a to-be-protected circuit, wherein the auxiliary circuit comprises a plurality of auxiliary modules; establishing auxiliary operation strategies based on an auxiliary module, wherein the auxiliary operation strategies comprise a first auxiliary operation strategy, a second auxiliary operation strategy and a third auxiliary operation strategy; under the applied auxiliary operation strategy, when a short-circuit fault occurs on the alternating current side, the fault impulse voltage can be effectively reduced, the influence of the fault is reduced, and meanwhile, the economic cost can be effectively saved by utilizing the original elements of the bridge arm change-over switch.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic inverters, and in particular to an auxiliary circuit and an operating method. Background Art

[0002] With the large-scale application of new energy technologies in power systems, traditional AC transmission systems have been unable to meet current transmission needs due to their lack of flexibility and poor economy. MMC is based on fully controlled semiconductor devices. It not only inherits the self-commutation capability of traditional VSC, but also avoids direct series connection of semiconductor devices through modular design, thus making it very convenient to realize high-voltage and large-capacity converter design.

[0003] However, conventional MMCs require a large number of capacitors, switching semiconductors, and heat sinks, which makes the MMC project occupy a large area. If used in offshore wind power, the construction cost is very high. To address this problem, a bridge arm reuse modular multi-level converter has emerged. This converter divides each phase bridge arm into three bridge arms: upper, middle, and lower. By reusing the middle bridge arm, the utilization rate of the submodule is greatly improved. While ensuring the output voltage quality, it also reduces the number of submodules required for the converter, effectively reducing the investment cost and volume of the converter.

[0004] Because AM-MMC needs to repeatedly switch and reuse the bridge arm during operation, the bridge arm switching switch needs to be used frequently. Therefore, the reliable on and off of the bridge arm switching switch is the key to ensuring the normal operation of AM-MMC. However, when a short circuit fault occurs on the AC side, a large fault voltage will be generated, and the bridge arm switching switch may be damaged. Therefore, it is necessary to design an auxiliary circuit to reduce the fault voltage, thereby protecting the bridge arm switching switch. Summary of the invention

[0005] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0006] In view of the above existing problems, the present invention is proposed.

[0007] Therefore, the present invention provides an auxiliary circuit and an operating method, which can solve the problems mentioned in the background technology.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0009] In a first aspect, the present invention provides an auxiliary circuit, comprising:

[0010] The auxiliary circuit includes a plurality of auxiliary modules;

[0011] The auxiliary module includes a flow branch, an energy absorption branch and a buffer branch;

[0012] Different auxiliary modules are connected in series or in parallel, and the outputs of the series auxiliary modules are connected to the modular multilevel converter submodules, and the inputs are connected to the AC end.

[0013] As a preferred solution of the auxiliary circuit described in the present invention, it also includes:

[0014] The flow branch, energy absorption branch and buffer branch in the auxiliary module are connected in parallel with each other;

[0015] The conduction of different branches in the auxiliary module corresponds to different auxiliary operation strategies.

[0016] As a preferred solution of the auxiliary circuit of the present invention, the auxiliary circuit further comprises:

[0017] The current-carrying branch is any circuit used to conduct the current of the power system;

[0018] The energy absorbing branch is any circuit used to absorb excess energy in the power system;

[0019] The buffer branch is any circuit used to reduce the shutdown voltage during a fault.

[0020] As a preferred solution of the auxiliary circuit of the present invention, wherein: the auxiliary operation strategy includes: a first auxiliary operation strategy, a second auxiliary operation strategy and a third auxiliary operation strategy;

[0021] When the first auxiliary operation strategy is implemented, the flow branch is turned on;

[0022] When the second auxiliary operation strategy is implemented, the buffer branch is turned on;

[0023] When the third auxiliary operation strategy is implemented, the energy absorption branch is turned on.

[0024] As a preferred solution of the auxiliary circuit of the present invention, the buffer branch comprises: a first buffer metal oxide arrester and a buffer capacitor;

[0025] When the current branch is disconnected, the first buffer metal oxide arrester is used to block AC harmonics and suppress the discharge current during reclosing;

[0026] When the current-passing branch is turned on again, the snubber capacitor will discharge through the first buffer metal oxide arrester and the thyristor inside the current-passing branch;

[0027] To ensure that the current-carrying branch is normally turned off, the discharge current is not greater than the maximum turn-off current of the thyristor inside the current-carrying branch.

[0028] As a preferred solution of the auxiliary circuit described in the present invention, the energy absorption branch includes a second buffer metal oxide arrester.

[0029] As a preferred solution of the auxiliary circuit described in the present invention, wherein: the residual value of the first buffer metal oxide arrester is not greater than half of the residual value of the second buffer metal oxide arrester.

[0030] In a second aspect, the present invention provides an operating method of an auxiliary circuit, comprising:

[0031] Establishing an auxiliary circuit based on the circuit to be protected, wherein the auxiliary circuit includes a plurality of auxiliary modules;

[0032] Establishing an auxiliary operation strategy based on the auxiliary module, the auxiliary operation strategy comprising: a first auxiliary operation strategy, a second auxiliary operation strategy and a third auxiliary operation strategy;

[0033] When the protection circuit is powered on, the auxiliary circuit operation is controlled by the auxiliary operation strategy.

[0034] In a third aspect, the present invention provides a computer device, comprising a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of the above-mentioned method when executing the computer program.

[0035] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program implements the steps of the method described above when executed by a processor.

[0036] Compared with the prior art, the invention has the following beneficial effects: the invention proposes an auxiliary circuit and an operation method, establishes an auxiliary circuit based on the circuit to be protected, and the auxiliary circuit includes several auxiliary modules; establishes an auxiliary operation strategy based on the auxiliary module, and the auxiliary operation strategy includes: a first auxiliary operation strategy, a second auxiliary operation strategy and a third auxiliary operation strategy; when the circuit with protection is powered on, the auxiliary circuit operation is controlled by the auxiliary operation strategy. After the circuit with protection is powered on, the first auxiliary operation strategy is first executed, at which time the flow branch is turned on to ensure that the current of the power system can flow normally. Subsequently, according to the actual operation of the power system, it is switched to the second auxiliary operation strategy in a timely manner, at which time the buffer branch is turned on to reduce the shutdown voltage during a fault and protect the power system from damage by overvoltage. When the power system needs to absorb excess energy, the third auxiliary operation strategy is executed, the energy absorption branch is turned on, and the excess energy is absorbed, thereby maintaining the stable operation of the system. Through this flexible switching of operation strategies, the auxiliary circuit of the present application can effectively protect the power system and improve the reliability and safety of its operation. Under the auxiliary operation strategy of the invention, when a short circuit fault occurs on the AC side, the fault impulse voltage can be effectively reduced, the impact of the fault can be reduced, and at the same time, by utilizing the original components of the bridge arm switching switch, economic costs can be effectively saved. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. 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 creative labor. Among them:

[0038] Figure 1 An auxiliary circuit topology diagram of an auxiliary circuit and operating method of a bridge arm switching switch provided by an embodiment of the present invention;

[0039] Figure 2 A schematic diagram of an AM-MMC single-phase structure of an auxiliary circuit and an operation method provided by an embodiment of the present invention;

[0040] Figure 3 A schematic diagram of current paths at different times of an auxiliary circuit and an operating method provided by an embodiment of the present invention;

[0041] Figure 4 A DC side voltage waveform diagram of an auxiliary circuit and an operating method provided by an embodiment of the present invention;

[0042] Figure 5 A bridge arm switch voltage waveform diagram of an auxiliary circuit and an operating method provided by an embodiment of the present invention;

[0043] Figure 6 A bridge arm submodule capacitance waveform diagram of an auxiliary circuit and operation method provided by one embodiment of the present invention;

[0044] Figure 7 An internal structural diagram of a computer device providing an auxiliary circuit and operating method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0045] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0046] Example 1

[0047] Reference Figure 1-Figure 7 , is the first embodiment of the present invention, which provides an auxiliary circuit and an operating method, including:

[0048] There are some problems in the existing related technologies. For example, in the power system, when a fault occurs, the traditional protection device may not respond in time, resulting in system damage or fault expansion.

[0049] The present application provides an auxiliary circuit and an operating method thereof that can effectively solve the above-mentioned problems. Next, multiple embodiments will be combined to explain in detail how to implement the auxiliary circuit design of the bridge arm switching switch;

[0050] Figure 1 An auxiliary circuit topology diagram of an auxiliary circuit and an operating method of a bridge arm switching switch is shown, including:

[0051] In the embodiment of the present application, the auxiliary circuit includes several auxiliary modules;

[0052] The auxiliary module includes a flow branch, an energy absorption branch and a buffer branch;

[0053] Different auxiliary modules are connected in series or in parallel, and the outputs of the series auxiliary modules are connected to the modular multilevel converter submodules, and the inputs are connected to the AC end.

[0054] In an optional embodiment, the auxiliary module may also include a control unit for dynamically adjusting the working mode of each auxiliary module according to the operating state and fault condition of the power system. The control unit may be a microprocessor or a dedicated integrated circuit, which can monitor the voltage and current parameters of the power system in real time, and judge whether it is necessary to switch to different auxiliary operation strategies according to the preset logic. For example, during normal operation, the control unit will maintain the first auxiliary operation strategy to ensure that the flow branch is turned on, and when a short circuit fault is detected, the control unit will quickly switch to the second auxiliary operation strategy to reduce the voltage at the fault point and protect the power system. In addition, the control unit can also activate the third auxiliary operation strategy according to the energy absorption demand of the power system, so that the energy absorption branch is turned on, absorb excess energy, and maintain the stability of the system. Through this intelligent control, the auxiliary circuit can respond to various operating conditions more flexibly and effectively, ensuring the safe and stable operation of the power system.

[0055] In an optional embodiment, the auxiliary module may also include a detection unit for real-time monitoring of the voltage and current parameters of the power system. The detection unit may be a current transformer or a voltage sensor, which can provide accurate power system operation data to the control unit. When the power system is operating normally, the detection unit will continuously monitor the voltage and current to ensure that the power system operates within a safe range. When an abnormal situation is detected, such as when the voltage or current exceeds a preset threshold, the detection unit will immediately notify the control unit and trigger the corresponding auxiliary operation strategy to switch to protect the power system from damage. This real-time monitoring and rapid response mechanism is one of the key factors that enable the auxiliary circuit of the present invention to effectively protect the power system.

[0056] In an optional embodiment, the auxiliary module may also include different protection elements, such as fuses or circuit breakers, to provide an additional layer of protection. These protection elements can be designed to act quickly when an overcurrent or short circuit is detected, thereby cutting off the faulty circuit and preventing the fault from spreading to the entire power system. In addition, the auxiliary module may also be equipped with a temperature sensor to monitor the operating temperature of the module to ensure that it operates within a safe temperature range and avoid damage caused by overheating. Through these multi-level protection measures, the auxiliary circuit can provide more comprehensive and reliable protection to ensure the stability and safety of the power system.

[0057] In the embodiment of the present application, considering the introduction of the auxiliary circuit, only three branches, namely the current-passing branch, the energy-absorbing branch and the buffer branch, are used to realize the final auxiliary circuit function. However, the present application does not impose any restrictions, and this part can add or delete different branches according to the actual situation encountered by relevant technical personnel.

[0058] In the embodiment of the present application, the flow branch, the energy absorption branch and the buffer branch in the auxiliary module are connected in parallel with each other;

[0059] The conduction of different branches in the auxiliary module corresponds to different auxiliary operation strategies.

[0060] In an optional embodiment, when different branches or units are selected, different auxiliary operation strategies can be designed according to the actual branch or unit conditions. For example, when the current branch is turned on, the circuit can maintain the flow of normal current to ensure the continuity of the power system; the energy absorption branch is activated when abnormal current or voltage is detected to absorb excess electric energy to prevent system overload; the buffer branch intervenes when the system needs additional stability and protection to provide additional electric energy buffering. The flexible use of these branches enables the auxiliary circuit to dynamically adjust its working mode according to the real-time status of the power system, thereby achieving effective protection and stable operation of the power system.

[0061] In an optional embodiment, in actual application, the operation method of the auxiliary circuit may further include optimizing the control strategy of each branch to adapt to different power system operation conditions. For example, when the load of the power system is light, the flow branch may be used preferentially to reduce energy loss; when the load is heavy or a fault occurs, the energy absorption branch or buffer branch may be switched to protect the power system from damage. The control unit dynamically adjusts the working state of each branch according to the real-time data provided by the detection unit to ensure the safety and efficiency of the power system.

[0062] In an optional embodiment, the design of the auxiliary circuit can also take into account modularity and scalability, so that in different power systems, the number of auxiliary modules can be increased or decreased as needed to adapt to different power system scales and protection requirements. This design not only improves the applicability of the auxiliary circuit, but also reduces the cost of maintenance and upgrades. Through modular design, the auxiliary circuit can more flexibly adapt to various complex power system environments, providing a strong guarantee for the stable operation of the power system.

[0063] It should be noted that no matter which branches and units are selected when designing the auxiliary circuit, all branches or units should be mobilized in the auxiliary operation strategy, otherwise the design of the auxiliary circuit will be redundant and cannot fully play its due role.

[0064] In the embodiment of the present application, the auxiliary operation strategy includes: a first auxiliary operation strategy, a second auxiliary operation strategy and a third auxiliary operation strategy;

[0065] When the first auxiliary operation strategy is implemented, the flow branch is turned on;

[0066] When the second auxiliary operation strategy is implemented, the buffer branch is turned on;

[0067] When the third auxiliary operation strategy is implemented, the energy absorption branch is turned on.

[0068] In an optional embodiment, the auxiliary operation strategy is designed for different branches and units. The relevant technical personnel here can make relevant designs according to actual needs, but the purpose of the auxiliary operation strategy finally designed is to achieve switching between flow, buffering and energy absorption. All auxiliary operation strategies whose purpose is to achieve switching between flow, buffering and energy absorption should be within the scope of protection of this application.

[0069] In the embodiment of the present application, the control strategy under the fault condition is carefully explained below in combination with the single-phase ground short circuit condition occurring on the AC side.

[0070] As attached Figure 3 As shown in (a), under normal system operation, the upper and lower bridge arm switches are turned on in turn, and the system current flows through the bridge arm switches, i.e., the current-carrying branches.

[0071] As attached Figure 3 As shown in (b), when a single-phase ground fault occurs on the AC side, the system detects the fault and sends a shutdown command to the power electronic switch. At this stage, the fault current rises rapidly. When the IGCT of the current-carrying branch receives the shutdown command, it immediately acts and turns off the upper and lower switches at the same time. At this time, the current begins to commutate from the current-carrying branch to the buffer branch.

[0072] As attached Figure 3 As shown in (c), as the voltage of the buffer capacitor continues to increase, the voltage of the buffer branch also increases. When the voltage reaches the operating voltage of the energy-absorbing MOV, the fault current is commutated from the buffer branch to the energy-absorbing branch. After the current is completely transferred to the energy-absorbing branch, the MOV absorbs the remaining energy in the system, the energy absorption process is completed, and the voltage across the bridge arm switching switch drops back to the voltage during normal operation, and the entire shutdown process is completed. After the disconnection process is completed, the IGCT element of the current-carrying branch receives the reclosing command and turns on again, completing the closing. If the system is still in a fault state at this time, the disconnection is completed again according to the above disconnection process. If the ground short circuit fault is over, the upper and lower bridge arms remain turned on alternately, and the system resumes normal operation.

[0073] It should be noted that establishing an auxiliary operation strategy can ensure that when a fault occurs in the power system, each branch can be quickly and accurately switched to the corresponding operating state, thereby minimizing the impact of the fault on the power system.

[0074] In the embodiment of the present application, the auxiliary circuit further includes:

[0075] A current-carrying branch is any circuit used to conduct current in a power system;

[0076] An energy absorbing branch is any circuit used to absorb excess energy in a power system;

[0077] A snubber is any circuit used to reduce the turn-off voltage during a fault.

[0078] In an optional embodiment, there may be many types of circuits for conducting the current of the power system, for example, basic circuit elements such as resistors, capacitors or inductors. These elements can be configured into different circuit topologies to meet specific current conduction requirements. For example, resistors can be used to limit the magnitude of the current, capacitors can be used to smooth voltage fluctuations, and inductors can be used to suppress sudden changes in current. By reasonably selecting and combining these basic elements, a current-passing branch suitable for different power system requirements can be constructed.

[0079] In an optional embodiment, there may be many types of circuits for absorbing excess energy in the power system, and the design of the energy absorption branch needs to consider how to effectively absorb and process the excess energy in the power system. This usually involves the application of energy conversion and storage technology. For example, supercapacitors or flywheel energy storage systems can be used to absorb and store energy, or energy can be converted into heat energy for release through resistors. When designing the energy absorption branch, it is necessary to ensure that it can respond quickly to energy fluctuations in the power system and has sufficient capacity to handle the energy.

[0080] In an optional embodiment, there are many ways to achieve the reduction of the shutdown voltage during a fault. The design goal of the buffer branch is to quickly intervene and reduce the shutdown voltage when a fault occurs in the power system to protect the power equipment from damage. This usually requires the use of fast-response switching elements, such as semiconductor switches, and buffer elements that can withstand high voltages and large currents. The design of the buffer branch should ensure that the fault current can be quickly cut off when a fault occurs, and the impact on the power system is minimized during the cutting process.

[0081] In the embodiment of the present application, the buffer branch includes: a first buffer metal oxide arrester and a buffer capacitor;

[0082] When the current branch is disconnected, the first buffer metal oxide arrester is used to block AC harmonics and suppress the discharge current during reclosing;

[0083] When the current-passing branch is turned on again, the snubber capacitor will discharge through the first buffer metal oxide arrester and the thyristor inside the current-passing branch;

[0084] To ensure that the current-carrying branch is normally turned off, the discharge current is not greater than the maximum turn-off current of the thyristor inside the current-carrying branch.

[0085] In the embodiment of the present application, the energy absorption branch includes: a second buffer metal oxide arrester.

[0086] In the embodiment of the present application, the residual value of the first buffer metal oxide arrester is not greater than half of the residual value of the second buffer metal oxide arrester.

[0087] It should be noted that the buffer branch of the present application includes a first buffer metal oxide arrester and a buffer capacitor, the energy absorption branch includes a second buffer metal oxide arrester, and the current branch is composed of the components of the bridge arm switch itself, that is, the IGCT with the characteristics of high voltage resistance, large current capacity, low cost, and low operating loss. It is to simplify the design of the auxiliary circuit and ensure that it can respond quickly and execute corresponding protection measures when the power system fails.

[0088] In the embodiment of the present application, a topological structure of an auxiliary circuit that can be implemented is as shown in the attached figure. Figure 1 As shown in the figure, the topology consists of three branches in parallel, namely the flow branch, the buffer branch and the energy absorption branch. This topology utilizes the components of the bridge arm switching switch. The flow branch is composed of the components of the bridge arm switch itself, that is, the IGCT with the characteristics of high withstand voltage, large flow capacity, low cost, and low operating loss. The buffer branch is composed of MOV and capacitor in series, and the energy absorption branch is composed of MOV. Due to the steep wave effect of the metal oxide lightning arrester, when the voltage rise rate is too high, the residual voltage of the MOV on the energy absorption branch may be higher than the design value, and the power electronic device will be damaged by overvoltage. The buffer capacitor in the buffer branch can reduce the voltage rise rate and play a role in reducing the overvoltage during the shutdown process, thereby reducing the residual voltage of the line and protecting the safety of the device. The buffer MOV can suppress the discharge current of the capacitor during reclosing. When the bridge arm switching switch is turned on again, the energy of the buffer capacitor is discharged through the buffer MOV to ensure that the discharge current is lower than the maximum shutdown current of the bridge arm switching switch.

[0089] In the embodiment of the present application, the buffer branch can effectively reduce the impulse voltage so that the bridge arm switching switch can be smoothly turned off. Therefore, it is necessary to perform parameter design on the buffer capacitor and buffer MOV on the buffer branch. The parameter design basis of the buffer MOV and buffer capacitor will be elaborated in detail below.

[0090] In the embodiment of the present application, the parameters of the buffer MOV are designed so that when the bridge arm switching switch is in the off state, the buffer MOV can block the AC harmonics and suppress the discharge current during reclosing. When the bridge arm switching switch is turned on again, the buffer capacitor will discharge through the buffer MOV and IGCT. To ensure that the IGCT of the current-carrying branch can be turned off normally, the discharge current cannot be greater than the maximum turn-off current of the IGCT, that is:

[0091]

[0092] Among them, I main is the maximum off current of IGCT, R mov1 is the equivalent resistance of the buffer MOV,

[0093] In the embodiment of the present application, the parameters of the buffer capacitor are designed. Due to the steep wave effect of the metal oxide surge arrester, when the voltage rise rate is too high, the residual voltage of the MOV on the energy absorption branch may be higher than the design value, and the power electronic device may be damaged by overvoltage. The buffer capacitor in the buffer branch can reduce the voltage rise rate and play a role in reducing the overvoltage during the shutdown process, thereby reducing the line residual voltage and protecting the safe operation of the components.

[0094] During the IGCT shutdown process, the sum of the voltages of the buffer MOV and the capacitor should be equal to the voltage of the buffer MOV on the energy absorption branch, that is:

[0095] U mov1 +U c =U mov2

[0096] Among them, U mov1 is the voltage of the buffer MOV on the buffer branch; U c is the maximum voltage on the capacitor; U mov2 is the voltage of the MOV on the energy absorption branch

[0097] In the embodiment of the present application, during the shutdown process, if the wavefront time of the current is greater than the time for the energy-absorbing MOV to reach the standard residual voltage, it can be ensured that the overvoltage at both ends of the device will not exceed the designed residual voltage value of the buffer MOV, thereby avoiding overvoltage damage. In summary, the following formula can be obtained:

[0098]

[0099] Thus, the minimum value of capacitance can be obtained. If the capacitance is too large, the economic cost and volume will increase. Therefore, the buffer capacitance should not be too large, so the residual voltage of the buffer MOV should not be too high. Generally, the residual voltage of the buffer MOV should not exceed half of the residual voltage of the energy-absorbing MOV.

[0100] In the embodiment of the present application, conventional MMC needs to be equipped with a large number of capacitors, switching semiconductors and heat sinks, which makes the MMC project occupy a large area. If it is used in offshore wind power, the construction cost is very high. To address this problem, a bridge arm multiplexing modular multi-level converter has emerged. The converter divides each phase bridge arm into three bridge arms: upper, middle and lower. Figure 2 As shown, the utilization rate of the submodules is greatly improved by reusing the middle bridge arms, which reduces the number of submodules required for the converter while ensuring the output voltage quality, and effectively reduces the investment cost and volume of the converter.

[0101] In summary, the present invention proposes an auxiliary circuit and an operation method, establishing an auxiliary circuit based on a circuit to be protected, the auxiliary circuit includes several auxiliary modules; establishing an auxiliary operation strategy based on the auxiliary module, the auxiliary operation strategy includes: a first auxiliary operation strategy, a second auxiliary operation strategy and a third auxiliary operation strategy; when the protected circuit is powered on, the auxiliary circuit operation is controlled by the auxiliary operation strategy. After the circuit with the protection circuit is powered on, the first auxiliary operation strategy is first executed, at which time the flow branch is turned on to ensure that the current of the power system can flow normally. Subsequently, according to the actual operation of the power system, it is switched to the second auxiliary operation strategy in a timely manner, at which time the buffer branch is turned on to reduce the shutdown voltage during a fault and protect the power system from overvoltage damage. When the power system needs to absorb excess energy, the third auxiliary operation strategy is executed, the energy absorption branch is turned on, and the excess energy is absorbed, thereby maintaining the stable operation of the system. Through this flexible switching of operation strategies, the auxiliary circuit of the present application can effectively protect the power system and improve the reliability and safety of its operation. Under the auxiliary operation strategy of the invention, when a short circuit fault occurs on the AC side, the fault impulse voltage can be effectively reduced, the impact of the fault can be reduced, and at the same time, by utilizing the original components of the bridge arm switching switch, economic costs can be effectively saved.

[0102] This embodiment also provides an auxiliary circuit operation method, including:

[0103] Establishing an auxiliary circuit based on the circuit to be protected, the auxiliary circuit including several auxiliary modules;

[0104] Establishing an auxiliary operation strategy based on the auxiliary module, the auxiliary operation strategy includes: a first auxiliary operation strategy, a second auxiliary operation strategy and a third auxiliary operation strategy;

[0105] When the protection circuit is powered on, the operation of the auxiliary circuit is controlled by the auxiliary operation strategy.

[0106] The above-mentioned unit modules may be embedded in or independent of a processor in a computer device in the form of hardware, or may be stored in a memory in a computer device in the form of software, so that the processor can call and execute operations corresponding to the above-mentioned modules.

[0107] This embodiment also provides a computer device, which may be a terminal, and its internal structure diagram may be as shown in FIG. Figure 7As shown. The computer device includes a processor, a memory, a communication interface, a display screen and an input device connected through a system bus. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The communication interface of the computer device is used to communicate with an external terminal in a wired or wireless manner, and the wireless manner can be achieved through WIFI, an operator network, NFC (near field communication) or other technologies. When the computer program is executed by the processor, an operation method of an auxiliary circuit is implemented. The display screen of the computer device can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer device can be a touch layer covered on the display screen, or a key, trackball or touchpad set on the computer device housing, or an external keyboard, touchpad or mouse, etc.

[0108] This embodiment further provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the following steps are implemented:

[0109] Establishing an auxiliary circuit based on the circuit to be protected, the auxiliary circuit including several auxiliary modules;

[0110] Establishing an auxiliary operation strategy based on the auxiliary module, the auxiliary operation strategy includes: a first auxiliary operation strategy, a second auxiliary operation strategy and a third auxiliary operation strategy;

[0111] When the protection circuit is powered on, the operation of the auxiliary circuit is controlled by the auxiliary operation strategy.

[0112] Example 2

[0113] Reference Figure 4-Figure 6 , which is an embodiment of the present invention, provides an auxiliary circuit and an operating method. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through experiments.

[0114] In order to verify the effectiveness and reliability of the proposed auxiliary circuit and strategy for switching bridge arms, the performance of the auxiliary circuit was verified based on a simulation example on the Matlab / Simulink platform. The DC side voltage of the simulation is 20KV, the number of sub-modules of the upper, middle and lower bridge arms is 12 each, the rated voltage of a single sub-module is 833.3V, the capacitance value on the buffer branch is 20μF, the residual voltage of the buffer MOV is 1500V, and the residual voltage of the energy-absorbing MOV is 3000V.

[0115] In order to verify the effect of the buffer branch, a simulation model with and without a buffer branch was set up for comparison. At 0.5s, a single-phase short-circuit grounding fault occurred in phase A, and the current path gradually shifted to the buffer branch. At 0.6s, the current path switched from the buffer branch to the energy absorption branch. At 0.8s, the single-phase grounding fault ended, and the system resumed normal operation after 1s. Figure 4 As shown in (a), when no buffer branch is set, a large surge voltage will be generated on the DC side, rising from 20KV in normal operation to 27KV. Figure 4 As shown in (b), when the buffer branch is set, the impulse voltage on the DC side increases from 20KV in normal operation to 22KV, and the increase rate decreases from 35% to 10%, indicating that the buffer branch has a good inhibitory effect on the impulse voltage. Figure 5 and Figure 6 is the switching switch voltage and the submodule capacitor voltage, Figure 5 (a) is the bridge arm switching switch voltage when no buffer circuit is set. At this time, the impact voltage of the bridge arm switching switch exceeds 30KV. Figure 5 (b) is the bridge arm switching switch voltage when the buffer circuit is set. At this time, the impact voltage of the bridge arm switching switch is less than 10KV, indicating that the buffer circuit can effectively protect the bridge arm switching switch. Figure 6 It can be seen that when the fault occurs, the impulse voltage of the capacitor voltage of the lower bridge arm is 980V, which is 17% higher than 833.3V during normal operation. The capacitor voltage fluctuates greatly in the buffer branch. When the path is transferred to the energy absorption branch, the fluctuation of the capacitor voltage gradually decreases and tends to be stable. The rated voltage is restored after the fault is removed after 0.8s, and normal operation is restored after 1s, which is in line with the rated setting and consistent with the operating conditions before the fault.

[0116] After applying this auxiliary circuit, AM-MMC can avoid generating excessive impact voltage when a ground short circuit fault occurs on the AC side, ensure stable operation of the submodule capacitor voltage, smoothly complete AC / DC conversion, and ensure reliable switching of each phase current and stable power output.

[0117] 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. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

[0118] 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 complete hardware embodiments, complete software embodiments, or embodiments 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 disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code. The scheme in the embodiments of the present application can be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0119] 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 generate 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.

[0120] 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 comprising 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.

[0121] 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. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0122] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0123] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. An auxiliary circuit, characterized in that: include: The auxiliary circuit includes a plurality of auxiliary modules; The auxiliary module includes a flow branch, an energy absorption branch and a buffer branch; Different auxiliary modules are connected in series or in parallel, and the outputs of the series auxiliary modules are connected to the modular multilevel converter submodules, and the inputs are connected to the AC end.

2. The auxiliary circuit according to claim 1, characterized in that Also includes: The flow branch, energy absorption branch and buffer branch in the auxiliary module are connected in parallel with each other; The conduction of different branches in the auxiliary module corresponds to different auxiliary operation strategies.

3. The auxiliary circuit according to claim 2, characterized in that: The auxiliary circuit further comprises: The current-carrying branch is any circuit used to conduct the current of the power system; The energy absorbing branch is any circuit used to absorb excess energy in the power system; The buffer branch is any circuit used to reduce the shutdown voltage during a fault.

4. The auxiliary circuit according to claim 3, characterized in that: The auxiliary operation strategy includes: a first auxiliary operation strategy, a second auxiliary operation strategy and a third auxiliary operation strategy; When the first auxiliary operation strategy is implemented, the flow branch is turned on; When the second auxiliary operation strategy is implemented, the buffer branch is turned on; When the third auxiliary operation strategy is implemented, the energy absorption branch is turned on.

5. The auxiliary circuit according to claim 4, characterized in that The buffer branch includes: a first buffer metal oxide arrester and a buffer capacitor; When the current branch is disconnected, the first buffer metal oxide arrester is used to block AC harmonics and suppress the discharge current during reclosing; When the current-passing branch is turned on again, the snubber capacitor will discharge through the first buffer metal oxide arrester and the thyristor inside the current-passing branch; To ensure that the current-carrying branch is normally turned off, the discharge current is not greater than the maximum turn-off current of the thyristor inside the current-carrying branch.

6. The auxiliary circuit according to claim 5, characterized in that The energy absorbing branch includes: a second buffer metal oxide arrester.

7. The auxiliary circuit method according to claim 6, characterized in that: The residual value of the first buffer metal oxide arrester is not greater than half of that of the second buffer metal oxide arrester.

8. A method for operating an auxiliary circuit, characterized in that: include: Establishing an auxiliary circuit based on the circuit to be protected, wherein the auxiliary circuit includes a plurality of auxiliary modules; Establishing an auxiliary operation strategy based on the auxiliary module, the auxiliary operation strategy comprising: a first auxiliary operation strategy, a second auxiliary operation strategy and a third auxiliary operation strategy; When the protection circuit is powered on, the auxiliary circuit operation is controlled by the auxiliary operation strategy.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to claim 8 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to claim 8 are implemented.

Images