A method for controlling and protecting the closing and opening of a marine hybrid medium-voltage DC circuit breaker.

Abstract

This invention discloses a control and protection method for the closing and opening of a marine hybrid medium-voltage DC circuit breaker. Based on the topology of a marine hybrid medium-voltage DC circuit breaker consisting of a fast mechanical switch in the main current-carrying branch, a power electronic switch in the transfer branch, and a surge arrester in the energy-dissipating branch, the circuit breaker operation process is divided into four states: closing action, closing hold, opening action, and opening hold. This includes control and protection strategies. During the dynamic processes of circuit breaker opening and closing, the operating states of the fast mechanical switch in the main current-carrying branch and the power electronic switch in the transfer branch switch are switched, controlled by the control and protection system according to a specific logical timing sequence. The control and protection strategy for the marine hybrid DC circuit breaker proposed in this invention mainly targets the operating states of each branch under different circuit breaker states. Combining the technical performance of the mechanical switch and the power electronic switch, the topology, and the DC system state, it controls and protects the circuit breaker's opening and closing processes, ensuring the safe and reliable operation and operation of the circuit breaker.

Description

Technical Field

[0001] This invention relates to the field of integrated marine power systems and DC circuit breaker control and protection technology, specifically to a hybrid DC circuit breaker opening and closing control and protection method applicable to marine medium-voltage DC power distribution systems. Background Technology

[0002] A hybrid DC circuit breaker consists of a main mechanical branch that carries the load current, a power electronic transfer branch that interrupts the short-circuit current, and an energy-dissipating branch that suppresses interruption overvoltage and absorbs energy stored in the system inductor. Its topology is as follows: Figure 1 As shown.

[0003] The main challenges in the closing and opening control and protection of hybrid DC circuit breakers are as follows: First, short-circuit faults in DC systems develop extremely rapidly, requiring DC circuit breakers to quickly interrupt them; second, DC system circuits store a large amount of energy, which needs to be dissipated in a timely manner; and third, DC systems generate very high overvoltages when the circuit breaker is turned off, seriously affecting the safety of components in the system. Therefore, during the dynamic processes of circuit breaker opening and closing, the switching of the operating states of the fast mechanical switches in the main current-carrying branches and the power electronic switches in the transfer branches of the circuit breaker needs to be controlled by the control and protection system according to a certain logical sequence to ensure rapid fault clearing, timely dissipation of excess energy, and guarantee of the safety of system components.

[0004] Existing related patent technologies, such as patent document (CN110932245B), disclose a control and protection device and method for a hybrid DC circuit breaker. This device uses three independent merging units for sampling, a 3-out-of-2 logic to determine overcurrent, and calculates the preset waiting time t1 in real time based on the equivalent circuit parameters of the main branch and the transfer branch. However, this solution has the following technical problems in practical engineering applications: First, the algorithm for real-time calculation of equivalent circuit parameters (t0, tz) is highly complex and sensitive to parameter drift in the complex electromagnetic environment of ships, easily leading to increased control delay. This makes it difficult to meet the stringent requirements of extremely fast fault current rise rate (up to 20kA / ms) and a total breaking time of less than 5ms for marine medium-voltage DC systems. Second, it lacks clear identification logic for the fault current wavefront and waveback. Forced tripping during the rapid rise of the fault current can easily exceed the breaking capacity of the transfer branch semiconductor devices. Third, it lacks a dedicated mechanical switch after-arc reignition protection and backoff mechanism. If commutation fails or a re-breakdown occurs, it will directly damage the arc-extinguishing chamber.

[0005] For example, patent document (CN110391646A) discloses a hybrid DC circuit breaker closing and opening control system, proposing an architecture of circuit breaker monitoring equipment, control and protection equipment, and valve interface equipment, and briefly describing the basic closing and opening sequence and the cooling self-locking function of the reclosing arrester. The technical problems of this solution are: the control logic is too simplified, and a systematic state machine model (closing action / holding, opening action / holding) is not established. It lacks hard mechanical and software interlock protection for the isolating switch and grounding switch of the marine switchgear, and cannot effectively prevent maloperation such as closing with grounding or opening and closing of the isolating switch under load. At the same time, its opening process only relies on the current zero-crossing judgment, and does not combine the rapid fault development characteristics unique to marine DC systems to carry out wavefront refusal protection and precise control of post-arc insulation recovery time, resulting in insufficient pertinence and reliability of the protection strategy.

[0006] Therefore, to ensure the safe and reliable operation and action of the hybrid DC circuit breaker, this invention formulates circuit breaker closing and opening control and protection strategies based on the operating status of each branch under different circuit breaker conditions, combined with the technical performance of mechanical switches and power electronic switches, topology, and DC system status. This serves as the theoretical and technical support for the development of the hybrid circuit breaker control and protection system and as a reference for the development of the controller. Summary of the Invention

[0007] This invention proposes a method for controlling and protecting the opening and closing of a large-capacity, fast-opening, marine hybrid medium-voltage DC circuit breaker. The method mainly includes control and protection strategies to ensure the normal operation of the circuit breaker under different operating conditions and the safety of the equipment itself and the system.

[0008] (1) For the four operating states of the hybrid circuit breaker in the actual system operation process, namely closing and holding, closing action, opening and holding and opening action, formulate the closing and opening control strategy of the circuit breaker to achieve fast closing and opening.

[0009] (2) Based on the hybrid DC circuit breaker topology and system fault current characteristics, and combined with the circuit breaker breaking capacity, formulate protection strategies for the circuit breaker under different transient stable operating conditions to ensure operational safety.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A method for controlling and protecting the closing and opening of a marine hybrid medium-voltage DC circuit breaker is disclosed. This method is based on a marine hybrid medium-voltage DC circuit breaker topology comprising a main current-carrying branch fast mechanical switch, a transfer branch power electronic switch, and a power-dissipating branch surge arrester. The method divides the circuit breaker operation into four states: closing action, closing hold, opening action, and opening hold. It includes a control strategy and a protection strategy. The control strategy addresses the four different operating states of the hybrid circuit breaker during actual system operation, including the operating status of relevant branches and the overall control strategy during different operating states and actions. The protection strategy is determined based on the analysis of the circuit breaker under different operating conditions to ensure the safety of the equipment itself and the system operation under different operating states. (1) The control and protection system monitors the status of the circuit breaker disconnector and grounding switch and the current parameters of each branch in real time, and switches between four states according to system instructions and real-time status; (2) In the closing operation state, perform isolation and grounding switch status inspection and logic interlock judgment. After passing, unlock the transfer branch power electronic switch, monitor the main circuit current and judge whether it is lower than the safety threshold. If it is lower, close the fast mechanical switch and lock the transfer branch power electronic switch. If it is higher, directly lock the transfer branch and terminate the closing. (3) In the tripping operation state, the characteristic parameters of the main circuit current and the rate of change of the current are analyzed in real time, and the wave front refusal protection judgment is executed. After the tripping condition is met, the fast mechanical switch tripping command and the transfer branch power electronic switch unlocking command are issued simultaneously. After the main current-carrying branch current reaches zero, the preset arc recovery time is delayed, and the transfer branch power electronic switch is locked. Then the main current-carrying branch current and the total system current are monitored. If both are greater than zero and show an upward trend, it is determined that the mechanical switch is reignited, the fast mechanical switch closing command is executed, and the tripping failure is reported. (4) When the circuit is closed and open, maintain the corresponding branch conduction or hot standby blocking state, and continuously perform overcurrent and overvoltage monitoring and background status reporting.

[0012] Furthermore, the safety threshold under the closing action state is set to be greater than the rated operating current of the DC system and less than the maximum withstand current of the power electronic switch of the transfer branch; in the step of monitoring the main circuit current and determining whether it is lower than the safety threshold, if the determination is false, the power electronic switch of the transfer branch is blocked, the closing procedure is terminated and a "refused to close" or "closing failure" message is reported.

[0013] Furthermore, the control strategy under the closed-hold state includes: the control system maintains the output of the closing command for the fast mechanical switch of the main branch of the hybrid circuit breaker, and maintains the blocking hot standby state for the power electronic switch of the transfer branch; the control system maintains the reporting of the "closed" status to the background and real-time monitoring of the main circuit current of the circuit breaker.

[0014] Furthermore, the tripping and holding state is divided into an out-of-operation state and a hot standby state. In the out-of-operation state, the disconnecting switch is tripped and the grounding switch is closed. The control system maintains the fast mechanical switch tripping command and the transfer branch interlocking command, and reports the "out of operation" state. In the hot standby state, the disconnecting switch is closed and the grounding switch is tripped. The control system maintains the fast mechanical switch tripping command and the transfer branch high-resistance state command, and reports the "awaiting closing" state.

[0015] Furthermore, the control strategy under the tripping operation state includes: the control system trips the hybrid circuit breaker. According to the topology and tripping principle, it first trips the fast mechanical switch of the main current-carrying branch and simultaneously unlocks the solid-state switch of the transfer branch. When the mechanical switch contacts separate and arcing begins, the current begins to transfer from the mechanical switch to the transfer branch. After the current has been completely transferred to the transfer branch and the mechanical switch ports have the capacity to withstand a certain transient voltage stress, the solid-state switch of the transfer branch is locked. The current then transfers from the transfer branch to the energy-dissipating branch. The surge arrester in the energy-dissipating branch dissipates the system energy, and the system current begins to decrease. After the energy is dissipated, the system current drops to zero.

[0016] Furthermore, the specific judgment of the wavefront refusal protection under the tripping action state is as follows: real-time acquisition of the main circuit current value and its rate of change di / dt, and AND logic judgment between the two; if the current is at the fault rising wavefront and the expected tripping current will exceed the circuit breaker's tripping capacity, the tripping procedure will not be executed temporarily or will wait until the tripping capacity is within the range after the wavefront before execution; if the current is within the tripping capacity range, the synchronous tripping command will be triggered immediately.

[0017] Furthermore, the preset post-arc recovery time t AR The minimum time interval between contacts of a fast mechanical switch that allows it to withstand transient voltage stress without breakdown and reignition, when the arc-extinguishing current between the contacts is zero, is determined based on this.

[0018] Furthermore, the method applies a full breaking time constraint to the entire tripping operation. The full breaking time, from receiving the breaking command and meeting the breaking conditions, to the system circuit current dropping to zero and being cut off, has a total duration of no more than 5ms. The full breaking time is determined by the maximum breaking time t of the fast mechanical switch. Rmax Minimum break time t ARmin and the energy dissipation time t of the energy-consuming branch. ED Cooperative allocation is determined.

[0019] Furthermore, the protection strategy includes: protection during the closing operation state, protection during the closing action process, and protection during the opening action process.

[0020] Furthermore, the protection strategy under the closing operation state includes: overvoltage protection between the primary system and ground and cabinet, with ground protection surge arresters configured between the circuit breaker incoming and outgoing busbars and ground and cabinet. When the primary system of the circuit breaker suffers overvoltage, the surge arresters limit the overvoltage to a certain range and simultaneously discharge transient overvoltage energy; operating current overcurrent protection, where the control protection system monitors the current of the main circuit optical CT1 or the fast mechanical switch branch optical CT2 of the circuit breaker. When the monitored current exceeds a set value of 1, an "overload warning" message is sent to the superior system; when the monitored current exceeds a set value of 2, an "application for tripping" message is sent to the superior system; the protection strategy for the closing operation process includes: operational interlock protection between the disconnecting switch and the grounding switch, with a mechanical interlock device set between the disconnecting switch and the grounding switch to ensure that the grounding switch is in the open state before the disconnecting switch is closed, and the disconnecting switch is in the open state before the grounding switch is closed; software interlock protection between the disconnecting switch, the grounding switch and the circuit breaker body, through control protection The system monitors the status of disconnecting switches and grounding switches, performs AND logic judgment on the status of disconnecting switches and grounding switches, and then executes the circuit breaker closing procedure. The circuit breaker short-circuit closing protection strategy includes: when the circuit breaker closes, first unlock the solid-state switch of the transfer branch, monitor and judge the total current CT1 of the circuit breaker. When the current is greater than the set value, it is judged as a short-circuit fault, the solid-state switch of the transfer branch is locked, and the fault current is interrupted in time. If the current is less than the set threshold, the mechanical switch is closed and then the power electronic switch of the transfer branch is locked. The protection strategy for the opening operation process includes: wavefront opening protection. After the hybrid circuit breaker receives the opening command, it monitors the CT1 current and analyzes the current value and current di / dt in real time, and performs AND logic judgment on the two to analyze whether it is at the wavefront or waveback of the fault point to determine whether to execute the circuit breaker opening procedure; mechanical switch arc re-ignition protection. During the opening process, by monitoring the current of the fast mechanical switch, it is determined that the commutation is completed when the current is zero, and a delay of a period of time t is performed. AR To ensure the post-arc insulation between the contacts of the fast mechanical switch is restored and has the ability to withstand a certain transient voltage, the power electronic switch of the transfer branch is then locked. After the power electronic switch of the transfer branch is locked, the current of the fast mechanical switch branch is monitored in real time until the total current is zero. If the current of the fast mechanical switch is greater than zero and both the current and the total current show an upward trend, it is determined that the mechanical switch has reignited and the interruption has failed. At this time, a closing command for the fast mechanical switch is issued to protect the contacts of the fast mechanical switch from damage due to prolonged arcing.

[0021] Compared with the prior art, the present invention has the following significant advantages: Based on the hybrid DC circuit breaker topology and system fault current characteristics, and combined with the circuit breaker's breaking capacity, this invention proposes a method for controlling and protecting the closing and opening of a hybrid circuit breaker under different transient stable operating conditions.

[0022] (1) The tripping control strategy proposed in this invention takes into account the tripping time requirements, the characteristics of the fault current and the tripping capacity of the circuit breaker. The control strategy of quickly switching the main current branch mechanical switch while tripping ensures the smooth operation of the tripping action. The closing control strategy takes into account the system status before closing and the status of the DC circuit breaker disconnector and grounding switch. The strategy of first switching the transfer branch power electronic switch and then closing the main current branch mechanical switch prevents damage to the system equipment.

[0023] (2) The tripping protection strategy proposed in this invention is based on the system short-circuit current characteristics and combined with the circuit breaker's breaking capacity. It formulates fault current wavefront refusal protection and fast mechanical switch arc reignition protection strategies to prevent the breaking current from exceeding the circuit breaker's breaking capacity during the circuit breaker tripping process, which would lead to the failure of the power electronic switching devices to turn off and the fast mechanical switch reigniting. The closing protection strategy includes protection strategies such as mechanical interlocking and software interlocking of the circuit breaker cabinet during the closing operation to ensure the safety of equipment and personnel during the circuit breaker closing process; as well as overvoltage and overcurrent protection in the closing state to prevent damage to system equipment. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a hybrid circuit breaker topology. Figure 2 A schematic diagram of the hybrid circuit breaker control and protection system. Figure 3 Flowchart of the hybrid circuit breaker closing control strategy; Figure 4 A schematic diagram of the tripping control timing of a hybrid circuit breaker; Figure 5 This is a schematic diagram of the tripping control process for a hybrid circuit breaker.

[0025] In the diagram: K hav For fast mechanical switching, K s To transfer the branch circuit power electronic switch, K dis For disconnecting switches, K Es For grounding switches, CT1 is the main circuit optical CT, and CT2 is the main current-carrying branch optical CT. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0027] The present invention discloses a marine hybrid medium-voltage DC circuit breaker closing and opening control and protection method, which is based on the marine hybrid medium-voltage DC circuit breaker topology including a main current-carrying branch fast mechanical switch, a transfer branch power electronic switch and an energy-consuming branch surge arrester. The circuit breaker operation process is divided into four states: closing action, closing holding, opening action and opening holding.

[0028] During the dynamic processes of opening and closing of a hybrid DC circuit breaker, the switching of operating states between the fast mechanical switch of the main current-carrying branch and the power electronic switch of the transfer branch requires control and protection system intervention according to a specific logical sequence. This invention primarily addresses the operating states of each branch under different conditions of a hybrid circuit breaker. By combining the technical performance, topology, and system characteristics of the mechanical and power electronic switches, it determines the circuit breaker control and protection strategies to ensure the safe and reliable operation and operation of the circuit breaker.

[0029] In addition to the main current-carrying branch fast mechanical switch, transfer branch power electronic switch, and energy-consuming branch lightning protection connected in parallel with the circuit breaker body, the primary system configuration of the hybrid circuit breaker includes isolating switches and grounding switches at both ends of the circuit breaker body to meet power outage maintenance requirements. Considering circuit breaker protection requirements, current sensors (optical CTs) are installed in both the main circuit and the main current-carrying fast mechanical switch branch. A schematic diagram of the connection between the control system and the primary system is shown below. Figure 2 As shown.

[0030] Figure 2 The control and protection system and the primary system of the circuit breaker mainly consist of three parts: 1) Control system, which controls the fast mechanical switch K hav Solid-state switch K for operation of opening, closing and transfer branches s 1) Opening and closing; 2) Data monitoring, monitoring the current parameters of the main circuit CT1 and the main current-carrying branch CT2 of the circuit breaker; 3) Status monitoring, monitoring the disconnecting switch K of the circuit breaker. dis1 and K dis2 Grounding switch K Es1 and K Es2 Main current branch fast mechanical switch K hav and transfer branch solid-state switch K s The opening and closing status of the circuit breaker.

[0031] 1. Control Strategy In actual system operation, hybrid circuit breakers have four different operating states: closing action, closing hold, opening action, and opening hold. The operating states of the relevant branches and the overall control strategy of the circuit breaker are as follows during different operating states and actions.

[0032] (1) Control strategy for closing process The closing operation of a hybrid circuit breaker requires consideration of the system status before closing, as well as the status of the DC circuit breaker's isolating and grounding switches, to avoid safety threats to related equipment and personnel due to misoperation. Additionally, extreme operating conditions must be considered, such as closing the circuit breaker under short-circuit conditions on the load side (line side), ensuring the circuit breaker has the ability to promptly trip and interrupt fault current. Therefore, this invention determines the following closing action strategy: 1) Determine the status of the isolating and grounding switches on both sides of the circuit breaker; 2) Unlock the solid-state switch of the transfer branch; 3) Determine the current characteristics of the optical CT1; 4) Close the fast mechanical switch of the main current-carrying branch; 5) Lock the solid-state switch of the transfer branch; 6) Closing complete. A schematic diagram of the closing action flow is shown below. Figure 3 As shown.

[0033] like Figure 3 As shown, when the circuit breaker receives a closing command from the backend (upper-level) control system, it first initiates a patrol inspection program on the primary switch status of the circuit breaker and performs an AND logic judgment on the status of the grounding switch and disconnecting switch. If the output is false, the closing program terminates and reports a "reject closing" message to the backend; if the output is true, the solid-state switch K of the transfer branch is unlocked. s Then, it monitors and determines whether the current of the optical CT1 is less than the set threshold. If the output is false, the solid-state switch K is locked. s The closing procedure terminates and reports a "refused to close" or "closing failed" message to the backend. If the output is true, the main branch fast mechanical switch K is closed. hav After the contacts are closed, the solid-state switch K of the transfer branch is then locked. s Once the circuit breaker is closed, a "successful circuit breaker" message is sent to the backend.

[0034] (2) Closed-holding state control strategy In the closed operation state, the fast mechanical switch of the main branch of the hybrid circuit breaker is in the closed state; the power electronic switch of the transfer branch is in the hot standby blocking state, that is, the control system and secondary power supply system are working normally, and the IGBT device is in the locked state; the voltage between the terminals of the energy-consuming branch is the on-state voltage drop of the fast mechanical switch, which can be ignored, and the surge arrester is in a high impedance state.

[0035] In this state, the control strategy is as follows: the control system maintains a closed state for the control command of the fast mechanical switch of the main current-carrying branch; and maintains a blocked state for the IGBT devices of the power electronic switch in the transfer branch. In this state, the control system should continue to report the "closed" status to the backend and monitor the current of the circuit breaker's optical CT1 in real time.

[0036] (3) Control strategy for tripping process In the hybrid circuit breaker tripping operation, based on the topology and tripping principle, the main current-carrying branch fast mechanical switch is tripped first, while the transfer branch solid-state switch is unlocked simultaneously. When the mechanical switch contacts separate and arcing begins, the current starts to transfer from the mechanical switch to the transfer branch. After the current has completely transferred to the transfer branch and the mechanical switch ports can withstand a certain transient voltage stress, the transfer branch solid-state switch is locked, and the current is transferred from the transfer branch to the energy-dissipating branch. The energy-dissipating branch surge arrester dissipates the system energy, and the system current begins to decrease. After the energy is dissipated, the system current drops to zero.

[0037] This invention proposes the following requirements for hybrid circuit breaker breaking technology: 1) Breaking time requirements In this invention, the breaking time of the hybrid circuit breaker is required to be less than 5ms, meaning the time from when the circuit breaker receives the breaking command and meets the breaking conditions to when the system circuit current drops to zero (provisionally less than 150A) is no more than 5ms. When determining the control strategy, the blocking time of the solid-state switch in the transfer branch is particularly important. A reasonable blocking time needs to be determined. If blocking is premature, it may lead to insufficient post-arc recovery time of the fast mechanical switch, resulting in reignition; if blocking is delayed, the transient junction temperature of the solid-state switch in the transfer branch will be too high, causing semiconductor device failure, and the total blocking time will exceed 5ms. Therefore, the following key factors need to be comprehensively considered and determined: a. Maximum breaking time t of the fast mechanical switch in the main current branch Rmax This refers to the maximum time interval between the issuance of the disconnection command by the circuit breaker control and protection system and the activation of the arc by the moving contact of the fast mechanical switch; b. Minimum post-arc recovery time t of the fast mechanical switch in the main current-carrying branch ARmin This refers to the minimum time interval between the contacts of a fast-acting mechanical switch, where the arc-extinguishing current is zero and the switch can withstand the transient voltage stress after the circuit breaker trips without breakdown and reignition. c. Energy dissipation time t of the surge arrester in the energy-consuming branch. ED If we ignore the transfer time from the transfer branch to the energy dissipation branch, the energy dissipation time can be understood as the time interval from the lockout of the solid-state switch of the transfer branch to the drop of the loop current to zero.

[0038] 2) Operating system and fault current characteristics The system fault current rises significantly (di / dt), reaching a maximum of approximately 20 kA / ms, with peak values ​​exceeding 100 kA. If the circuit breaker trips before the fault current peak, the tripping current will exceed the circuit breaker's breaking capacity. Therefore, it is necessary to trip after the fault current peak and determine whether the system current is within the circuit breaker's breaking capacity range.

[0039] In summary, the control strategy for determining the circuit breaker's tripping action is as follows: 1) Determine whether the system current is within the circuit breaker's tripping capacity; 2) Trip the main current-carrying branch's fast mechanical switch and simultaneously turn on the transfer branch's solid-state switch; 3) After the system current has been transferred from the main current-carrying branch to the transfer branch and after a certain delay, lock the transfer branch's solid-state switch; 4) Trip complete.

[0040] Based on the system fault current, the timing sequence of the hybrid circuit breaker tripping logic control is as follows: Figure 4 As shown.

[0041] like Figure 4 The control timing sequence shows that after the circuit breaker receives the disconnection command from the upper level, it first determines whether the system current characteristics are within the circuit breaker's disconnection capacity range; then it issues the disconnection command, that is, it simultaneously issues the disconnection command for the main current-carrying branch's fast mechanical switch and the unlocking command for the transfer branch's solid-state switch; after monitoring that the current in the main current-carrying branch is zero, it delays for t... AR Then, the solid-state switch of the transfer branch is locked; finally, the total current of the circuit breaker and the current of the main current-carrying branch are monitored. If the current of the main current-carrying branch is zero, the tripping is successful and the tripping procedure is completed. If both the current of the main current-carrying branch and the total current are greater than zero, it is determined that the mechanical switch has experienced a re-breakdown and re-ignition. A closing command for the mechanical switch of the main current-carrying branch is then issued, and a "tripping failure" message is reported to the system. A detailed flowchart of the tripping control strategy is shown below. Figure 5 As shown.

[0042] like Figure 5 In the circuit breaker tripping control flow diagram shown, after the circuit breaker displays a successful tripping indication, the disconnecting switch K can then be activated. ds Opening operation and grounding switch K Es Closing operation.

[0043] (4) Tripping and holding state control strategy The tripping operation status includes two states: circuit breaker out of operation and hot standby.

[0044] 1) Control strategy for exiting the running state The circuit breaker is out of service, the disconnecting switch is open, and the grounding switch is closed. The main branch fast mechanical switch is open; the transfer branch power electronic switch is in hot standby or out of service; the voltage between the circuit breaker terminals is zero, and the surge arrester is in a high impedance state.

[0045] In this state, the control strategy is as follows: the control system maintains the open state for the control command of the main current-carrying branch's fast mechanical switch; the IGBT devices of the transfer branch's power electronic switch remain in a locked state. In this state, the control system should continuously report "out of operation" status to the backend.

[0046] 2) Control strategy under hot-spreading conditions In hot standby mode, the circuit breaker disconnector is closed and the grounding switch is open. The main branch fast mechanical switch is open; the transfer branch power electronic switch is in hot standby blocking mode, meaning the control system and secondary power supply system are operating normally, and the IGBT devices are in a locked state; the voltage between the terminals of the energy-consuming branch is the system DC voltage, and the surge arrester is in a high-impedance state.

[0047] In this state, the control strategy is as follows: the control system's control command for the main current-carrying branch's fast mechanical switch is in a tripped and held state; the IGBT devices in the transfer branch's power electronic switch remain in a high-impedance, off state. In this state, the control system should continuously report a "waiting to close" status to the backend.

[0048] 2. Protection Strategy The hybrid circuit breaker protection strategy is determined based on the analysis of the circuit breaker under different operating conditions, ensuring the safety of the equipment itself and the system operation under different operating conditions.

[0049] (1) Protection under closed operation state When a hybrid circuit breaker is in closed operation, the voltage between the primary circuit terminals can be approximately zero, the voltage to ground and between the circuit breaker and the cabinet is the system's rated DC voltage, and the operating current is the system's DC current. Therefore, the protection strategy under this condition is as follows: 1) Overvoltage protection between the primary system and ground and cabinet Purpose of protection: Overvoltage protection between the primary system and ground and cabinet is mainly to protect the primary system from damage caused by system overvoltage.

[0050] Protection measures: Grounding surge arresters are installed between the incoming and outgoing busbars of the circuit breaker and the ground and cabinet. When the primary system of the circuit breaker is subjected to overvoltage, the surge arresters limit the overvoltage to a certain range and discharge transient overvoltage energy.

[0051] 2) Overcurrent protection during operation Purpose of protection: To protect the safe operation of the fast-acting mechanical switch contacts and the arc-extinguishing chamber, and to ensure that the operating temperature of the circuit breaker's arc-extinguishing chamber is within a safe range.

[0052] Protection measures: The control and protection system monitors the current of the main circuit optical CT1 or the branch optical CT2 of the fast mechanical switch. When the current is detected to be greater than the set value 1, it sends an "overload warning" message to the superior system. When the current is detected to be greater than the set value 2, it sends a "trip request" message to the superior system.

[0053] (2) Protection during closing operation The closing operation process includes the closing of the circuit breaker itself and the closing of the disconnecting switch and grounding switch. The main protection measures are as follows: 1) Operational interlock protection between disconnecting switches and grounding switches Purpose of protection: To prevent misoperation that could cause a short circuit between the busbar and ground. Before closing the isolating switch, the grounding switch should be in the closed state.

[0054] Protection measures: A mechanical interlocking device is installed between the disconnecting switch and the grounding switch to ensure that the grounding switch is in the open state before the disconnecting switch is closed, and the disconnecting switch is in the open state before the grounding switch is closed.

[0055] 2) Software interlock protection between disconnecting switches, grounding switches, and the circuit breaker body Purpose of protection: To prevent misoperation, such as closing the isolating switch before the circuit breaker body is closed, or closing the isolating switch after the circuit breaker's fast mechanical switch is closed, resulting in the isolating switch being closed under load.

[0056] Protection measures: By controlling the protection system, the status of the disconnecting switch and the grounding switch is monitored. After performing a logical judgment on the status of the disconnecting switch and the grounding switch, the circuit breaker closing procedure is executed.

[0057] 3) Circuit breaker short-circuit closing protection Protection objective: Considering the relatively long closing and opening times of fast mechanical switches and the system's judgment time, this protection aims to prevent situations where the circuit breaker cannot be opened in time when the load side is under short-circuit conditions.

[0058] Protection measures: When the circuit breaker is closed, first unlock the solid-state switch of the transfer branch, monitor and judge the total current CT1 of the circuit breaker. If the current detected is greater than the set value, it is judged as a short circuit fault, the solid-state switch of the transfer branch is locked, and the fault current is interrupted in time. If the current detected is less than the set threshold, the mechanical switch is closed and then the power electronic switch of the transfer branch is locked. For detailed strategies, see Figure 2 As shown.

[0059] (3) Protection during tripping operation During the tripping process, the main considerations are the circuit breaker's breaking capacity, avoiding situations such as restarting of the fast mechanical switch leading to tripping failure, and the breaking current exceeding the breaking capacity of the power electronic switch, causing device failure. Detailed protection strategies are as follows: 1) Wavefront interruption protection Purpose of protection: To prevent the circuit breaker from failing to trip when the fault current is still rising after receiving the tripping command, which could result in the actual tripping current exceeding the circuit breaker's tripping current and causing damage to the fast mechanical switch arc-extinguishing chamber or the power electronic switching devices.

[0060] Protection measures: After receiving the tripping command, the hybrid circuit breaker monitors the CT1 current and analyzes the current value and current di / dt in real time. It then performs an AND logic judgment on the two to analyze whether it is at the wavefront or waveback of the fault point and determines whether to execute the circuit breaker tripping procedure.

[0061] 2) Mechanical switch after-arc reignition protection Purpose of protection: To prevent the mechanical switch from reigniting during the breaking process of a hybrid circuit breaker, which could lead to circuit breaker failure or damage due to prolonged arcing in the mechanical switch's arc extinguishing chamber.

[0062] Protective measures: a) During the disconnection process, the commutation is considered complete once the current reaches zero by monitoring the fast mechanical switch, and a delay of t is applied. AR Ensure that the post-arc insulation between the contacts of the fast mechanical switch is restored and that it has the ability to withstand a certain transient voltage before locking the power electronic switch of the transfer branch. b) After the power electronic switch of the transfer branch is locked, the current of the fast mechanical switch branch is monitored in real time until the total current is zero. If the current of the fast mechanical switch is greater than zero and both the current and the total current show an upward trend, it is determined that the mechanical switch reignites and the interruption fails. At this time, a closing command for the fast mechanical switch is issued to protect the fast mechanical switch contacts from prolonged arcing and damage.

Claims

1. A method for controlling and protecting the closing and opening of a marine hybrid medium-voltage DC circuit breaker, characterized in that, The method is based on a marine hybrid medium-voltage DC circuit breaker topology that includes a fast mechanical switch in the main current-carrying branch, a power electronic switch in the transfer branch, and a surge arrester in the energy-consuming branch. It divides the circuit breaker operation into four states: closing action, closing hold, opening action, and opening hold. The method includes control and protection strategies. The control strategy addresses the four different operating states of the hybrid circuit breaker during actual system operation, including the operating status of relevant branches and the overall control strategy during different operating states and actions. The protection strategy is determined based on the analysis of the circuit breaker under different operating conditions to ensure the safety of the equipment itself and the system operation under different operating states. (1) The control and protection system monitors the status of the circuit breaker disconnector and grounding switch and the current parameters of each branch in real time, and switches between four states according to system instructions and real-time status; (2) In the closing operation state, perform isolation and grounding switch status inspection and logic interlock judgment. After passing, unlock the transfer branch power electronic switch, monitor the main circuit current and judge whether it is lower than the safety threshold. If it is lower, close the fast mechanical switch and lock the transfer branch power electronic switch. If it is higher, directly lock the transfer branch and terminate the closing. (3) In the tripping operation state, the characteristic parameters of the main circuit current and the rate of change of the current are analyzed in real time, and the wave front refusal protection judgment is executed. After the tripping condition is met, the fast mechanical switch tripping command and the transfer branch power electronic switch unlocking command are issued simultaneously. After the main current-carrying branch current reaches zero, the preset arc recovery time is delayed, and the transfer branch power electronic switch is locked. Then the main current-carrying branch current and the total system current are monitored. If both are greater than zero and show an upward trend, it is determined that the mechanical switch is reignited, the fast mechanical switch closing command is executed, and the tripping failure is reported. (4) When the circuit is closed and open, maintain the corresponding branch conduction or hot standby blocking state, and continuously perform overcurrent and overvoltage monitoring and background status reporting.

2. The method for controlling and protecting the closing and opening of a marine hybrid medium-voltage DC circuit breaker according to claim 1, characterized in that, The safety threshold under the closing action state is set to be greater than the rated operating current of the DC system and less than the maximum withstand current of the power electronic switch of the transfer branch; in the step of monitoring the main circuit current and judging whether it is lower than the safety threshold, if the judgment is false, the power electronic switch of the transfer branch is blocked, the closing procedure is terminated and a "refused to close" or "closing failure" message is reported.

3. The method for controlling and protecting the closing and opening of a marine hybrid medium-voltage DC circuit breaker according to claim 1, characterized in that, The control strategy under the closed-hold state includes: the control system maintains the closed command output for the fast mechanical switch of the main branch of the hybrid circuit breaker, and maintains the locked-out hot standby state for the power electronic switch of the transfer branch. The control system continuously reports the "closed" status to the backend and monitors the main circuit current of the circuit breaker in real time.

4. The method for controlling and protecting the closing and opening of a marine hybrid medium-voltage DC circuit breaker according to claim 1, characterized in that, The tripping and holding state is divided into out-of-operation state and hot standby state; in the out-of-operation state, the disconnecting switch is tripped, the grounding switch is closed, the control system holds the fast mechanical switch tripping command and the transfer branch interlocking command, and reports the "out of operation" state; In hot standby mode, when the disconnecting switch is closed and the grounding switch is opened, the control system maintains the rapid mechanical switch opening command and the high-resistance state command of the transfer branch, and reports the "waiting to close" status.

5. The method for controlling and protecting the closing and opening of a marine hybrid medium-voltage DC circuit breaker according to claim 1, characterized in that, The control strategy under the tripping operation state includes: the control system trips the hybrid circuit breaker. According to the topology and tripping principle, the main current-carrying branch fast mechanical switch is first tripped, and the transfer branch solid-state switch is unlocked at the same time. When the mechanical switch contacts separate and arcing begins, the current begins to transfer from the mechanical switch to the transfer branch. After the current is completely transferred to the transfer branch and the mechanical switch ports can withstand a certain transient voltage stress, the transfer branch solid-state switch is locked. The current is transferred from the transfer branch to the energy-dissipating branch. The energy-dissipating branch surge arrester dissipates the system energy, and the system current begins to decrease. After the energy is dissipated, the system current drops to zero.

6. The method for controlling and protecting the closing and opening of a marine hybrid medium-voltage DC circuit breaker according to claim 1, characterized in that, The specific judgment of the wavefront refusal protection under the tripping action state is as follows: real-time acquisition of the main circuit current value and its rate of change di / dt, and AND logic judgment between the two; if the current is at the fault rising wavefront and the expected tripping current will exceed the tripping capacity of the circuit breaker, the tripping procedure will not be executed temporarily or will be executed after the wavefront tripping capacity is reached. If the current is within the breaking capacity range, a synchronous tripping command will be triggered immediately.

7. The method for controlling and protecting the closing and opening of a marine hybrid medium-voltage DC circuit breaker according to claim 1, characterized in that, The preset post-arc recovery time t AR The minimum time interval between contacts of a fast mechanical switch that allows it to withstand transient voltage stress without breakdown and reignition, when the arc-extinguishing current between the contacts is zero, is determined based on this.

8. The method for controlling and protecting the closing and opening of a marine hybrid medium-voltage DC circuit breaker according to claim 1, characterized in that, The method applies a full breaking time constraint to the entire tripping operation. The full breaking time, from receiving the breaking command and meeting the breaking conditions, to the system circuit current dropping to zero and being cut off, has a total duration of no more than 5ms. The full breaking time is determined by the maximum breaking time t of the fast mechanical switch. Rmax Minimum break time t ARmin and the energy dissipation time t of the energy-consuming branch. ED Cooperative allocation is determined.

9. The method for controlling and protecting the closing and opening of a marine hybrid medium-voltage DC circuit breaker according to claim 1, characterized in that, The protection strategy includes: protection during the closing operation state, protection during the closing action process, and protection during the opening action process.

10. The method for controlling and protecting the closing and opening of a marine hybrid medium-voltage DC circuit breaker according to claim 9, characterized in that, The protection strategies under the closed operation state include: overvoltage protection between the primary system and ground and cabinet, with ground protection surge arresters configured between the circuit breaker incoming and outgoing busbars and ground and cabinet. When the primary system of the circuit breaker suffers overvoltage, the surge arresters limit the overvoltage to a certain range and simultaneously discharge transient overvoltage energy; operating current overcurrent protection, where the control protection system monitors the current of the main circuit optical CT1 or the fast mechanical switch branch optical CT2 of the circuit breaker. When the monitored current exceeds the set value 1, an "overload warning" message is sent to the superior system; when the monitored current exceeds the set value 2, an "application for tripping" message is sent to the superior system; the protection strategies for the closing operation process include: operational interlock protection between the disconnecting switch and the grounding switch, with a mechanical interlock device between the disconnecting switch and the grounding switch to ensure that the grounding switch is in the open state before the disconnecting switch is closed, and the disconnecting switch is in the open state before the grounding switch is closed; and software interlock protection between the disconnecting switch, the grounding switch, and the circuit breaker body, through the control protection system. The circuit breaker's short-circuit closing protection strategy includes: When the circuit breaker closes, first unlock the transfer branch solid-state switch, monitor and judge the total circuit breaker current CT1. If the current is greater than a set value, it is judged as a short-circuit fault, the transfer branch solid-state switch is locked, and the fault current is promptly interrupted. If the current is less than a set threshold, the mechanical switch is closed, and then the transfer branch power electronic switch is locked. The tripping operation protection strategy includes: wavefront tripping protection; after receiving the tripping command, the hybrid circuit breaker monitors the CT1 current and analyzes the current value and current di / dt in real time, and performs an AND logic judgment on both to analyze whether it is at the wavefront or waveback of the fault point, and determines whether to execute the circuit breaker tripping procedure; mechanical switch arc re-ignition protection; during the tripping process, by monitoring the current of the fast mechanical switch, it is determined that the commutation is complete when the current is zero, and a delay of a period of time t is performed. AR To ensure the post-arc insulation between the contacts of the fast mechanical switch is restored and has the ability to withstand a certain transient voltage, the power electronic switch of the transfer branch is then locked. After the power electronic switch of the transfer branch is locked, the current of the fast mechanical switch branch is monitored in real time until the total current is zero. If the current of the fast mechanical switch is greater than zero and both the current and the total current show an upward trend, it is determined that the mechanical switch has reignited and the interruption has failed. At this time, a closing command for the fast mechanical switch is issued to protect the contacts of the fast mechanical switch from damage due to prolonged arcing.

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