Reliability evaluation method and system for flexible interconnected power distribution network containing three-terminal SOP

Abstract

The invention discloses a reliability evaluation method and system for a flexible interconnected power distribution network containing a three-terminal SOP, and the method comprises the steps: determining a topological structure of an MMC converter, constructing a sub-module reliability model based on the topological structure, and constructing a bridge arm reliability model considering the correlation between redundant configuration and sub-modules through the sub-module reliability model; constructing a reliability model of the MMC according to the topological structure of the MMC converter and the bridge arm reliability model; analyzing various running states of the three-terminal SOP, and constructing an SOP reliability model through the various running states and the reliability model of the MMC; and based on the SOP reliability model, through random simulation of an operation state and load transfer judgment, reliability evaluation of the flexible interconnected power distribution network is carried out, and the influence of SOP access on the reliability of the flexible interconnected power distribution network is analyzed. According to the method, the reliability change after the multi-terminal SOP is accessed to the power distribution network is quantitatively analyzed, events of different sequential relationships between fault occurrence, recovery and the like in the power distribution network system are considered, and the reliability evaluation level of the system can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of distribution network evaluation, and more specifically, relates to a reliability evaluation method and system for a flexible interconnected distribution network containing a three-terminal SOP. Background Art

[0002] With the continuous development of power electronics technology, various flexible and intelligent equipment have gradually penetrated into all levels of the distribution system, making the power grid operation more flexible and effectively realizing the flexible interconnection of the distribution network. The intelligent soft switch (Soft Open Point, SOP) is the core device of the Flexible Interconnected Distribution Network (FIDN). This device is usually used to replace the traditional normally open point (NOP) and serves as a connection hub to achieve "soft connection" between distribution network feeders and flexible closed-loop operation of the distribution network, thereby improving the flexibility of the distribution network, promoting the consumption of new energy, and improving load balancing.

[0003] Reliability is one of the core goals of distribution network planning and construction. In order to meet the strategic requirements of the State Grid to build a "strong and smart grid" and adapt to the needs of high-quality development of distribution networks under the new situation, it is urgent to carry out reliability quantitative evaluation research on flexible interconnected distribution networks.

[0004] Due to the different number of converter ports, SOP can be divided into two-terminal SOP and multi-terminal SOP. Two-terminal SOP is suitable for interconnection wiring with a relatively simple structure. In urban distribution networks, due to the widespread existence of complex wiring such as double-ring networks, multi-terminal SOP including three-terminal SOP and four-terminal SOP also has research value. At present, the research scenario for reliability modeling of SOP devices is concentrated on two-terminal flexible switches, and the research focus is on modular multi-level converter ports (MMC) that constitute flexible multi-state switches.

[0005] CN109149982A proposes a reliability assessment method for a modular level converter power module. The method calculates the junction temperature of the IGBT and diode in a steady state according to the model data of the IGBT module, the model data of the capacitor, and the MMC task profile; uses the rain flow counting method to count the junction temperatures of the IGBT and diode throughout the year to obtain a low-frequency thermal cycle list throughout the year; uses a preset life model to calculate the life values ​​of the IGBT, diode, and capacitor based on the low-frequency thermal cycle list throughout the year and the hot spot temperature of the capacitor; simulates the above steps to repeatedly calculate multiple groups of life values ​​to obtain a Weibull life distribution, and uses the Weibull life distribution to evaluate the reliability of the power module in the MMC.

[0006] CN110739679A discloses a reliability analysis method for a flexible multi-state switch based on a Bayesian network method; according to the similarity between the Bayesian network and the fault tree, a fault tree of the MMC in the flexible multi-state switch is first established, and the fault tree is hierarchically converted into a Bayesian network using the fault probability table corresponding to the logical relationship in the fault tree, and a reliability model of a three-terminal flexible multi-state switch based on the MMC topology is established to represent multiple operating states.

[0007] However, the above studies did not fully consider the redundant configuration of sub-modules, the correlation between sub-modules and the overall topological structure of MMC in the reliability modeling of MMC, and did not involve the overall reliability quantitative evaluation of the actual example of flexible interconnected distribution network containing SOP. Summary of the invention

[0008] In order to solve the deficiencies in the prior art, the present invention provides a reliability assessment method and system for a flexible interconnected distribution network containing a three-terminal SOP.

[0009] The present invention adopts the following technical solution.

[0010] The first aspect of the present invention proposes a reliability assessment method for a flexible interconnected distribution network containing a three-terminal SOP, characterized in that it includes the following contents: Determine the topology of the MMC converter, and build a submodule reliability model based on the topology, and build a bridge arm reliability model that takes into account the redundancy configuration and the correlation between the submodules through the submodule reliability model; And build the reliability model of MMC according to the topological structure of MMC converter and the reliability model of bridge arm; Analyze various operating states of the three-terminal SOP operation, and build the SOP reliability model through various operating states and the MMC reliability model; Based on the SOP reliability model, the reliability of the flexible interconnected distribution network is evaluated through random simulation of operating status and load transfer judgment, and the impact of SOP access on the reliability of the flexible interconnected distribution network is analyzed.

[0011] Preferably, the topological structure of the MMC converter is as follows: each phase of the MMC converter is composed of two upper and lower bridge arms, a converter valve base controller is connected to the connection between the upper and lower bridge arms of each phase, and each bridge arm is composed of several submodules and a bridge arm reactor. The submodule is composed of a half-bridge submodule.

[0012] Preferably, the submodule reliability model is specifically: According to the structure of the half-bridge submodule, when calculating the reliability of the submodule, the reliability of the energy storage capacitor C, the bypass switch K1, and the press-fit packaged thyristor K2 in the submodule are multiplied, and then multiplied by the square of the reliability of the IGBT in the submodule, and the result is the reliability of the submodule.

[0013] Preferably, the bridge arm reliability model taking into account the redundancy configuration and the correlation between the submodules is specifically: When calculating the bridge arm reliability model, the reliability of the bridge arm with only normal submodules and the bridge arm with only redundant submodules are calculated respectively; The reliability of the bridge arm with only normal submodules is the joint distribution probability that the reliability of all normal submodules is greater than the set life threshold; The reliability of the bridge arm with only redundant submodules is 1 minus the joint distribution probability that the reliability of all normal submodules is less than or equal to the set life threshold; The reliabilities of the bridge arms with only normal submodules and only redundant submodules are converted into the form of Copula functions, and the reliabilities of the bridge arms with only normal submodules and only redundant submodules in the form of Copula functions are merged, and the merged reliability is the complete reliability of the bridge arm.

[0014] Preferably, the reliability of the bridge arms having only normal submodules and only redundant submodules in the form of Copula functions are respectively:

[0015]

[0016] in, and They are t The reliability of the bridge arms with only normal submodules and only redundant submodules at the time; for t The reliability of the bridge arm reactor at the time for t The reliability of the submodule at the moment, , are the number of normal and redundant submodules respectively, Indicates k A normal working submodule, For N Select one of the submodules k The number of combinations; is the correlation coefficient; is the failure rate of the submodule; The complete reliability of a single bridge arm for:

[0017] in, is the Gumbel Archimedean Copula function; For N+N Select one of the 0 submodules j The number of combinations; For k Select one of the submodules j The number of combinations.

[0018] Preferably, the reliability model of the MMC is constructed according to the topological structure of the MMC converter and the bridge arm reliability model, specifically: Calculate the cube of the product of the square of the complete reliability of a single bridge arm and the reliability of the converter valve base controller, and then multiply the cube result with the reliability of the external cooling system, internal cooling system, monitoring system in the valve cooling system, and the reliability of the station control system and pole control system in the converter station control and protection system. The result is the reliability of the MMC.

[0019] Preferably, the analysis of various operating states of the three-terminal SOP operation and the construction of the SOP reliability model through various operating states and the reliability model of the MMC are specifically as follows: The various operating states of the three-terminal SOP operation include a normal state and a fault state, and the fault state includes a single MMC port fault, a two MMC port fault, and a three MMC port fault; The sequence numbers of the normal state, the single MMC port failure, the two MMC ports failure, and the three MMC ports failure are set to 0, 1, 2, and 3 respectively; The SOP reliability model is: the probability of occurrence of various operating states is the product of the number of combinations of corresponding numbers extracted from the three fault states, the cube of the reliability of the MMC, and the corresponding number power of the difference between 1 and the reliability of the MMC.

[0020] Preferably, based on the SOP reliability model, the reliability assessment of the flexible interconnected distribution network is performed by randomly simulating the operating status and load transfer judgment, and the impact of the access of SOP on the reliability of the flexible interconnected distribution network is analyzed, specifically: Set the simulation years, set the simulation time limit based on the set simulation years, and initialize the simulation time; Generate a random number between 0 and 1, and calculate the fault-free working time and fault recovery time of each component in the flexible interconnected distribution network according to the random number. The fault-free working time is the natural logarithm of the random number divided by the inverse of the fault rate of the component; the fault recovery time is the natural logarithm of the random number divided by the inverse of the repair rate of the component; The component with the shortest fault-free working time is regarded as the current fault component; the component is a component or device on the feeder of the distribution network, and when the component fails, the feeder where the component is located fails; Randomly generate SOP fault status according to the probability of occurrence of various SOP operating states; According to the SOP fault status, determine whether the load can be successfully transferred within the power outage range. If it can be transferred, the simulation time is updated to be the sum of the current simulation time and the fault-free working time, fault recovery time and switching operation time of the current faulty component; if it cannot be transferred, the power outage number, power outage time and power shortage information of the affected load points within the power outage range are recorded, and the simulation time is updated to be the sum of the current simulation time and the fault-free working time and fault recovery time of the current faulty component; Determine whether the simulation time reaches the upper limit of the simulation time. If not, repeat the above contents starting from generating random numbers. If reached, calculate the system reliability index and obtain the system reliability index without SOP for comparison.

[0021] Preferably, judging whether the load can be successfully transferred within the power outage range according to the SOP fault state is specifically as follows: The power outage range refers to the range from the upstream of the power supply path to the downstream of the current fault component; When the SOP fault state is that a single MMC port fails, and the failed MMC port is not connected to the feeder where the current failed component is located, the SOP can effectively transfer power, otherwise it cannot effectively transfer power.

[0022] Preferably, the system reliability index includes the expected value of the average power outage frequency of the system 、Expected value of average power outage time of the system And the expected annual power shortage of the system .

[0023] The second aspect of the present invention proposes a flexible interconnected distribution network reliability assessment system containing a three-terminal SOP according to the method described in the first aspect of the present invention, comprising: a submodule reliability model construction module, a bridge arm reliability model construction module, an MMC reliability model construction module, an SOP reliability model construction module, and a reliability assessment module, characterized in that: Submodule reliability model building module: used to determine the topology of the MMC converter and build a submodule reliability model based on the topology; Bridge arm reliability model construction module: used to construct a bridge arm reliability model taking into account the redundancy configuration and the correlation between sub-modules through sub-module reliability models; MMC reliability model building module: used to build the MMC reliability model according to the topological structure of the MMC converter and the bridge arm reliability model; SOP reliability model building module: Analyzes the various operating states of the three-terminal SOP operation, and builds the SOP reliability model through various operating states and the MMC reliability model; Reliability assessment module: Based on the SOP reliability model, the reliability of the flexible interconnected distribution network is assessed through random simulation of operating status and load transfer judgment, and the impact of SOP access on the reliability of the flexible interconnected distribution network is analyzed.

[0024] The beneficial effects of the present invention are that, compared with the prior art, the present invention establishes a multi-terminal SOP component reliability model according to the correlation between sub-modules SM, the physical topology of MMC, and the operation mode of SOP. Compared with the prior art, the sub-module redundant configuration, the correlation between sub-modules and the overall topology of MMC are fully considered, and the established reliability model is more accurate and comprehensive; the present invention studies, analyzes and integrates various failure modes of the operation of the flexible interconnected distribution network FIDN; the failure of the flexible interconnected distribution network is sampled and simulated by random numbers, and the failure state obtained by sampling is matched with the above-mentioned failure mode to obtain the outage information of each load of the system, and the reliability change of the multi-terminal SOP after accessing the distribution network is quantitatively analyzed, which is suitable for large-scale systems, takes into account the timing relationship between different events (such as failure occurrence, recovery, etc.) in the distribution network system, and can significantly improve the system reliability assessment level. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of MMC topology and its submodule structure; Figure 2 It is a schematic diagram of the component combination relationship on a single bridge arm; Figure 3 This is a schematic diagram of the combination relationship of the internal components of the MMC; Figure 4 This is a topological diagram of the example of this embodiment; Figure 5 is the graph of the bridge arm reliability changing with the operation time; Figure 6 For different System reliability indicators; Figure 7 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only embodiments of a part of the present invention, rather than all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0027] like Figure 7 As shown, embodiment 1 of the present invention proposes a reliability assessment method for a flexible interconnected distribution network containing a three-terminal SOP, which is characterized by comprising the following contents: Determine the topology of the MMC converter, and build a submodule reliability model based on the topology, and build a bridge arm reliability model that takes into account the redundancy configuration and the correlation between the submodules through the submodule reliability model; The reliability model of MMC is constructed according to the topological structure of MMC converter and the reliability model of bridge arm; It should be noted that most electronic component failures follow "random failures", and this failure mode can be well modeled using exponential distribution. Exponential distribution provides a simple model that conforms to common failure modes, especially for situations where the failure rate is relatively low and stable at the beginning of equipment and system operation. Assuming that each component in the MMC system is in the early stage of the life curve, the failure rate is relatively low and remains stable, so its reliability function can be approximated by exponential distribution. Then at time t, the reliability of each component is:

[0028] Where: is the failure rate of the component.

[0029] Analyze various operating states of the three-terminal SOP operation, and build the SOP reliability model through various operating states and the MMC reliability model; Based on the SOP reliability model, the reliability of the flexible interconnected distribution network is evaluated through random simulation of operating status and load transfer judgment, and the impact of SOP access on the reliability of the flexible interconnected distribution network is analyzed.

[0030] Preferably, the topology of the MMC converter is as follows: Figure 1 As shown in the figure, each phase of the MMC consists of two bridge arms, the upper and lower arms. Each bridge arm has several sub-modules (SM) and a bridge arm reactor. Composition: Sub-modules can be divided into: Half-Bridge Sub-Module (HBSM) and Full-Bridge Sub-Module (FBSM) according to their specific structures. Although the full-bridge sub-module has the DC fault ride-through capability that the half-bridge sub-module does not have, due to its large investment and operating losses, most of the current projects use MMCs in the form of half-bridge sub-modules. Specifically, this embodiment uses MMCs in the form of half-bridge sub-modules. As the basic component unit of MMC, each SM is composed of a storage capacitor C, two insulated gate bipolar transistors (IGBT) and a protection switch composed of a bypass switch K1 and a crimped package thyristor K2. In actual application engineering, K1 and K2 improve the safety and reliability of MMC during operation.

[0031] The submodule SM is usually configured with a redundant design. This redundancy enables the system to quickly switch to the backup module when a single point failure occurs in the submodule, ensuring that the MMC continues to operate normally, thereby avoiding the system from completely failing due to a single failure. In this way, the redundant design significantly improves the overall reliability and fault tolerance of the equipment. When the submodule failure does not exceed the allowed number, the system can still operate normally, and the faulty submodule can be replaced during the next maintenance; when the number of faulty submodules exceeds a certain number, the MMC will exit operation.

[0032] Hot standby and cold standby are two commonly used backup methods in redundant design to improve system reliability and availability. The main difference between them is whether the standby devices are activated during normal operation and their switching speed in the event of a failure. Hot standby devices are always activated under normal circumstances and are ready to take over the work of the main system or equipment at any time. Once the main system fails, the standby system can take over immediately and continue to provide services with almost no downtime. The cold standby system is normally in a "closed" state. When a failure occurs, the standby system takes a certain amount of time to start and configure before it can take over the work, and there is a certain amount of downtime. It can be seen that hot standby is more suitable for scenarios with strict requirements for high availability and rapid recovery than cold standby. Therefore, most power projects currently adopt hot standby strategies.

[0033] according to Figure 1 It can be seen that all the normally working submodules on the bridge arm are combined in series, and there are several redundant submodules in parallel with each normally working submodule, which can quickly take over in case of failure to ensure the normal operation of the MMC. After all the submodules are connected in the above form, they are connected in series with the bridge arm reactor to form a bridge arm. The three phases of the MMC are completely symmetrical, and when a single half-bridge submodule is used, the upper and lower bridge arms have exactly the same structure.

[0034] In addition to the six bridge arms consisting of submodules, bridge arm reactors and other equipment, the MMC also has a converter station control and protection system and a valve cooling system. The converter station control and protection system is mainly responsible for fault monitoring, protection actions and data communication, ensuring that it can respond quickly and execute protection measures when a fault occurs, thereby ensuring the safety and reliable operation of the system. The valve cooling system controls the temperature by cooling the semiconductor valve to prevent failures caused by overheating, extend the life of the equipment and ensure the stable operation of the MMC system. Both are core parts to ensure equipment reliability. In order to further prevent the failure of these two protection systems from threatening the normal operation of the equipment, in actual projects, the converter station control and protection system and the valve cooling system are equipped with hot standby redundancy.

[0035] Preferably, the submodule reliability model is specifically: According to the structure of the half-bridge submodule, when calculating the reliability of the submodule, the reliability of the energy storage capacitor C, the bypass switch K1, and the press-fit packaged thyristor K2 in the submodule are multiplied, and then multiplied by the square of the reliability of the IGBT in the submodule, and the result is the reliability of the submodule.

[0036] Reliability of submodules The formula is as follows:

[0037] Where: , , , They are the reliability of energy storage capacitor C, IGBT, bypass switch K1, and press-fit package thyristor K2 respectively.

[0038] Since the reliability of the above components is assumed to obey the exponential distribution, the failure rate of the submodule can be further obtained. for:

[0039] Where: , , , They are the failure rates of energy storage capacitor C, IGBT, bypass switch K1, and press-fit packaged thyristor K2 respectively.

[0040] Preferably, the bridge arm reliability model taking into account the redundancy configuration and the correlation between the submodules is specifically: Reliability of bridge arm reactor The relationship between the failure rate and

[0041] Where: is the failure rate of the bridge arm reactor.

[0042] The present invention uses the k / n(G) model to study the reliability of equipment under redundant configuration conditions. submodules are working and are set up with According to the MMC topology, the following can be obtained: Figure 2 The combination relationship of the bridge arm components is shown.

[0043] When calculating the bridge arm reliability model, the reliability of the bridge arm with only normal submodules and the bridge arm with only redundant submodules are calculated respectively; Reliability of the bridge arm with only normal submodules is the joint distribution probability that the reliability of all normal submodules is greater than the set life threshold;

[0044] in, For the 1st, 2nd, ..., N The reliability of a normal submodule, is the set lifespan threshold, is the joint distribution probability; Reliability of bridge arms with only redundant submodules It is 1 minus the joint distribution probability that the reliability of all normal submodules is less than or equal to the set life threshold, and the formula is expressed as:

[0045] in, For the 1st, 2nd, ..., N Reliability of 0 redundant submodules; The reliabilities of the bridge arms with only normal submodules and only redundant submodules are converted into the form of Copula functions, and the reliabilities of the bridge arms with only normal submodules and only redundant submodules in the form of Copula functions are merged, and the merged reliability is the complete reliability of the bridge arm.

[0046] It should be noted that most previous studies on the establishment of MMC reliability models assume that the submodules are completely independent of each other. However, since the input or removal of a submodule will actually affect the switching frequency of the entire bridge arm submodule, the submodules are not strictly independent. The Copula theory is often used to describe the correlation between multiple random variables.

[0047] Copula function is a mathematical tool used to describe the dependency relationship or dependency structure between multiple random variables. It can model the dependency relationship and their marginal distribution separately without involving the specific form of the marginal distribution. It has been studied and applied in the power field such as joint scheduling optimization, load forecasting and power generation scheduling.

[0048] According to Sklar's theorem, for dimensional random variables, with marginal distributions , the joint distribution is , then there exists a Copula function , so that:

[0049] Common Copula functions include Gaussian Copula, t-Copula, Archimedean Copula, etc. Among them, Archimedean Copula with one parameter is the most widely used. This type of Copula uses a monotonically decreasing function to describe the dependencies between random variables. Common ones include: Clayton Copula, Gumbel Copula, Frank Copula. Since the present invention assumes that each MMC component is in the early stage of the life curve, t-Copula and Gumbel Archimedean Copula that focus on high-tail dependencies (i.e., the common failure of multiple devices when their life is close to the limit) are more appropriate, and the latter is finally selected considering the calculation indirectness.

[0050] The generators of the Gumbel Archimedean Copula are:

[0051] Where: is the correlation coefficient, .

[0052] The two-dimensional Gumbel Archimedean Copula has the form:

[0053] Where: When , the function corresponds to an independent Copula, that is, there is no correlation; hour, The smaller the value, the stronger the correlation. When , it approaches perfect correlation; and is the cumulative distribution function value of the marginal distribution.

[0054] Preferably, the reliability of the bridge arms having only normal submodules and only redundant submodules in the form of Copula functions are respectively:

[0055]

[0056] in, and They are t The reliability of the bridge arms with only normal submodules and only redundant submodules at the time; for t The reliability of the bridge arm reactor at the time for t The reliability of the submodule at the moment, , are the number of normal and redundant submodules respectively, Indicates k A normal working submodule, For N Select one of the submodules k The number of combinations; is the correlation coefficient; is the failure rate of the submodule; Using the k / n(G) model and Sklar theory, combined with the two-dimensional Gumbel Archimedean Copula function, the complete reliability of a single bridge arm is obtained. for:

[0057] in, is the Gumbel Archimedean Copula function; For N+N Select one of the 0 submodules j The number of combinations; For k Select one of the submodules j The number of combinations.

[0058] There is also a converter valve-based controller at the connection between the upper and lower bridge arms of each phase, which will be taken into consideration in the subsequent calculation of MMC reliability.

[0059] Preferably, the reliability model of the MMC is constructed according to the topological structure of the MMC converter and the bridge arm reliability model, specifically: like Figure 3 As shown, the valve cooling system and the converter station control and protection system form a parallel system with the three-phase bridge arms a, b, and c, and such a whole is an MMC port. Each MMC port is connected to a distribution network feeder.

[0060] The valve cooling system is composed of an internal cooling system, an external cooling system and a monitoring system in parallel, while the converter station control and protection system is composed of a station control system and a pole control system in parallel.

[0061] Therefore, the square of the complete reliability of a single bridge arm is calculated and multiplied by the cube of the reliability of the converter valve base controller. The cube result is then multiplied by the reliability of the external cooling system, internal cooling system, monitoring system in the valve cooling system, and the reliability of the station control system and pole control system in the converter station control and protection system. The result is the reliability of the MMC, which is expressed as follows:

[0062] Where: is the reliability of the converter valve based controller; , , They are the reliability of the external cooling system, internal cooling system, and monitoring system in the valve cooling system; , They are the reliability of the station control system and the pole control system in the converter station control and protection system respectively.

[0063] Preferably, the analysis of various operating states of the three-terminal SOP operation and the construction of the SOP reliability model through various operating states and the reliability model of the MMC are specifically as follows: The various operating states of the three-terminal SOP operation include a normal state and a fault state, and the fault state includes a single MMC port fault, a two MMC port fault, and a three MMC port fault; The sequence numbers of the normal state, the single MMC port failure, the two MMC ports failure, and the three MMC ports failure are set to 0, 1, 2, and 3 respectively; Based on the state space analysis method, the SOP reliability model is established as follows: the probability of occurrence of various operating states is the product of the number of combinations of corresponding serial numbers extracted from the three fault states, the cube of the reliability of the MMC, and the corresponding serial number power of the difference between 1 and the reliability of the MMC.

[0064] The reliability model of the three-terminal SOP is expressed as follows:

[0065] Where: , , , They are the probabilities of three-port SOP being normal, a single MMC port failing, two MMC ports failing, and three MMC ports failing.

[0066] Preferably, based on the SOP reliability model, the reliability assessment of the flexible interconnected distribution network is performed by randomly simulating the operating status and load transfer judgment, and the impact of the access of SOP on the reliability of the flexible interconnected distribution network is analyzed, specifically: Set the number of simulation years, and set the upper limit of simulation time based on the set number of simulation years. The upper limit of simulation time set in this embodiment is 8760 times of simulated reading, and the initial simulation time is 0; Generate a random number between 0 and 1, and calculate the fault-free working time and fault recovery time of each component in the flexible interconnected distribution network based on the random number. The fault-free working time is the natural logarithm of the random number divided by the inverse of the fault rate of the component; the fault recovery time is the natural logarithm of the random number divided by the inverse of the repair rate of the component. The formula is expressed as:

[0067] in, Trouble-free working time; is the fault recovery time; For the i The failure rate of each component; For the i The repair rate of each component; is a random number; The component with the shortest fault-free working time is regarded as the current fault component; the component is a component or device on the feeder of the distribution network, and when the component fails, the feeder where the component is located fails; Randomly generate SOP fault status according to the probability of occurrence of various SOP operating states; According to the SOP fault status, determine whether the load can be successfully transferred within the power outage range. If it can be transferred, the simulation time is updated to be the sum of the current simulation time and the fault-free working time, fault recovery time and switching operation time of the current faulty component; if it cannot be transferred, the power outage number, power outage time and power shortage information of the affected load points within the power outage range are recorded, and the simulation time is updated to be the sum of the current simulation time and the fault-free working time and fault recovery time of the current faulty component; Determine whether the simulation time reaches the upper limit of the simulation time. If not, repeat the above contents starting from generating random numbers. If reached, calculate the system reliability index and obtain the system reliability index without SOP for comparison.

[0068] Preferably, judging whether the load can be successfully transferred within the power outage range according to the SOP fault state is specifically as follows: The power outage range refers to the range from the upstream of the power supply path to the downstream of the current fault component; When the SOP fault state is that a single MMC port fails, and the failed MMC port is not connected to the feeder where the current failed component is located, the SOP can effectively transfer power, otherwise it cannot effectively transfer power.

[0069] It should be noted that the analysis process for determining whether the load can be successfully transferred within the power outage range is as follows: the MMC capacity and structure of each port of the SOP of this embodiment are consistent, and the capacity is large enough to achieve full transfer of the power outage load when a feeder failure occurs. The engineering example power distribution system used in this embodiment only considers a single fault.

[0070] 1) A single MMC port fails.

[0071] If the faulty feeder in the system is connected to the faulty MMC port, the disconnected load on the faulty feeder cannot be transferred, and the reliability index is calculated by cutting off the affected load. If the faulty feeder does not correspond to the faulty MMC port, the disconnected load on the faulty feeder can be transferred by another feeder, and continue to operate normally after the switching operation.

[0072] 2) Both MMC ports failed.

[0073] No matter which two ports fail, the three-terminal SOP cannot realize power transfer, and the reliability index is calculated by cutting off the affected load.

[0074] 3) Three MMC ports failed.

[0075] The three-terminal SOP will be completely out of operation. In this case, its power transfer capacity cannot be exerted, and the faulty feeder can only supply power to the affected loads through other means.

[0076] In summary, when a system failure occurs, the SOP can only effectively transfer load when a single port failure occurs in the three-terminal SOP and the failed MMC port is not connected to the failed feeder.

[0077] Preferably, the system reliability index includes the expected value of the average power outage frequency of the system 、Expected value of average power outage time of the system And the expected annual power shortage of the system .

[0078] Specifically, this embodiment uses a flexible interconnection project in a certain area of ​​East my country as the background to conduct reliability calculation analysis. The calculation example after adding the three-terminal SOP is shown in the figure below. Figure 4 As shown in the figure, the blue part is a three-terminal SOP device. Assuming that the capacity and structure of each port MMC are consistent and the capacity is large enough, when a feeder fails, all the disconnected loads can be transferred. This example includes three feeders, three substations and 26 load nodes. The converter MMC of this project adopts a half-bridge topology with a DC voltage of 50kV and a single submodule capacitor voltage of 1kV, that is, 50 submodules are configured for each bridge arm without redundancy. Since in actual projects, MMC often has 6%~8% redundant submodules, this project sets 4 redundant submodules for each bridge arm.

[0079] This example analyzes different correlation coefficients The reliability of the MMC bridge arm varies with the operating time. The reliability of the three-terminal SOP flexible interconnected distribution network is analyzed quantitatively to determine the impact of the three-terminal SOP access on the reliability of the distribution network.

[0080] The failure rate of the submodule SM obtained in this embodiment is shown in Table 1. It should be noted that the reliability and the failure rate are in an exponential relationship, so the failure rate can also represent the correlation and variation of the reliability.

[0081] Table 1 Failure rate of submodule components

[0082] From the data in Table 2, it can be concluded that the reliability of the MMC in this embodiment takes into account the correlation between the sub-modules, so the reliability of the MMC will change with time and the value of the correlation coefficient.

[0083] Table 2 Failure rate of other components of SOP

[0084] Depend on Figure 5 As shown, when When redundancy is not set, the reliability of the bridge arm of the MMC gradually decreases with the running time, so the SOP equipment should be repaired and replaced in time after long-term use. And as the correlation coefficient is smaller and the sub-module correlation is stronger, the bridge arm reliability is higher, and the MMC is higher, so the reliability of the SOP equipment is also higher.

[0085] A reliability assessment is carried out, and the calculation results of the reliability assessment index of the flexible interconnected distribution network are shown in Table 3.

[0086] Table 3 Comparison of reliability index calculation results

[0087] Analysis of the data in Table 3 shows that the access of SOP can significantly improve the system reliability for the distribution network feeder system, and with the improvement of correlation, the system reliability index is further improved. Comparing the indicators of the flexible interconnected distribution network with SOP and the ordinary distribution network without SOP access, After the SOP devices with values ​​of 0.8, 0.6 and 0.4 were connected to the distribution network, SAIFI increased by approximately 0.863%, 0.884% and 1.048% respectively, SAIDI increased by approximately 0.968%, 0.856% and 1.092% respectively, and EASAI increased by approximately 0.160%, 0.237% and 0.255%.

[0088] Further visualization of the reliability indicators of the distribution system Figure 6 As shown. It can be seen that with the correlation coefficient When it drops below 0.6, the reliability is greatly improved. Therefore, the access of SOP can not only effectively improve the reliability of the distribution network, but also further improve the reliability of the distribution network with the improvement of the correlation of sub-modules.

[0089] Embodiment 2 of the present invention proposes a flexible interconnected distribution network reliability assessment system containing a three-terminal SOP according to the method described in Embodiment 1 of the present invention, comprising: a submodule reliability model construction module, a bridge arm reliability model construction module, an MMC reliability model construction module, an SOP reliability model construction module, and a reliability assessment module, characterized in that: Submodule reliability model building module: used to determine the topology of the MMC converter and build a submodule reliability model based on the topology; Bridge arm reliability model construction module: used to construct a bridge arm reliability model taking into account the redundancy configuration and the correlation between sub-modules through sub-module reliability models; MMC reliability model building module: used to build the MMC reliability model according to the topological structure of the MMC converter and the bridge arm reliability model; SOP reliability model building module: Analyzes the various operating states of the three-terminal SOP operation, and builds the SOP reliability model through various operating states and the MMC reliability model; Reliability assessment module: Based on the SOP reliability model, the reliability of the flexible interconnected distribution network is assessed through random simulation of operating status and load transfer judgment, and the impact of SOP access on the reliability of the flexible interconnected distribution network is analyzed.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A reliability assessment method for a flexible interconnected distribution network containing a three-terminal SOP, characterized in that: Includes the following: Determine the topology of the MMC converter, and build a submodule reliability model based on the topology, and build a bridge arm reliability model that takes into account the redundancy configuration and the correlation between the submodules through the submodule reliability model; and build an MMC reliability model based on the topology of the MMC converter and the bridge arm reliability model; Analyze various operating states of the three-terminal SOP operation, and build the SOP reliability model through various operating states and the MMC reliability model; Based on the SOP reliability model, the reliability of the flexible interconnected distribution network is evaluated through random simulation of operating status and load transfer judgment, and the impact of SOP access on the reliability of the flexible interconnected distribution network is analyzed.

2. A reliability assessment method for a flexible interconnected distribution network containing a three-terminal SOP according to claim 1, characterized in that: The topological structure of the MMC converter is as follows: each phase of the MMC converter consists of two upper and lower bridge arms, a converter valve base controller is connected to the connection between the upper and lower bridge arms of each phase, and each bridge arm consists of several submodules and a bridge arm reactor. The submodule is composed of a half-bridge submodule.

3. A reliability assessment method for a flexible interconnected distribution network containing a three-terminal SOP according to claim 2, characterized in that: The submodule reliability model is specifically: According to the structure of the half-bridge submodule, when calculating the reliability of the submodule, the reliability of the energy storage capacitor C, the bypass switch K1, and the press-fit packaged thyristor K2 in the submodule are multiplied, and then multiplied by the square of the reliability of the IGBT in the submodule, and the result is the reliability of the submodule.

4. A reliability assessment method for a flexible interconnected distribution network containing a three-terminal SOP according to claim 3, characterized in that: The bridge arm reliability model taking into account the redundancy configuration and the correlation between the submodules is specifically: When calculating the bridge arm reliability model, the reliability of the bridge arm with only normal submodules and the bridge arm with only redundant submodules are calculated respectively; The reliability of the bridge arm with only normal submodules is the joint distribution probability that the reliability of all normal submodules is greater than the set life threshold; The reliability of the bridge arm with only redundant submodules is 1 minus the joint distribution probability that the reliability of all normal submodules is less than or equal to the set life threshold; The reliabilities of the bridge arms with only normal submodules and only redundant submodules are converted into the form of Copula functions, and the reliabilities of the bridge arms with only normal submodules and only redundant submodules in the form of Copula functions are merged, and the merged reliability is the complete reliability of the bridge arm.

5. A reliability assessment method for a flexible interconnected distribution network containing a three-terminal SOP according to claim 4, characterized in that: The reliability of the bridge arms with only normal submodules and only redundant submodules in the form of Copula functions are: in, and They are t The reliability of the bridge arms with only normal submodules and only redundant submodules at the time; for t The reliability of the bridge arm reactor at the time for t The reliability of the submodule at the moment, , are the number of normal and redundant submodules respectively, Indicates k A normal working submodule, For N Select one of the submodules k The number of combinations; is the correlation coefficient; is the failure rate of the submodule; The complete reliability of a single bridge arm for: in, is the Gumbel Archimedean Copula function; For N+N Select one of the 0 submodules j The number of combinations; For k Select one of the submodules j The number of combinations.

6. A reliability assessment method for a flexible interconnected distribution network containing a three-terminal SOP according to claim 5, characterized in that: The reliability model of the MMC is constructed according to the topological structure of the MMC converter and the bridge arm reliability model, specifically: Calculate the cube of the product of the square of the complete reliability of a single bridge arm and the reliability of the converter valve base controller, and then multiply the cube result with the reliability of the external cooling system, internal cooling system, monitoring system in the valve cooling system, and the reliability of the station control system and pole control system in the converter station control and protection system. The result is the reliability of the MMC.

7. A reliability assessment method for a flexible interconnected distribution network containing a three-terminal SOP according to claim 6, characterized in that: The analysis of various operating states of the three-terminal SOP operation and the construction of the SOP reliability model through various operating states and the MMC reliability model are as follows: The various operating states of the three-terminal SOP operation include a normal state and a fault state, and the fault state includes a single MMC port fault, a two MMC port fault, and a three MMC port fault; The sequence numbers of the normal state, the single MMC port failure, the two MMC ports failure, and the three MMC ports failure are set to 0, 1, 2, and 3 respectively; The SOP reliability model is: the probability of occurrence of various operating states is the product of the number of combinations of corresponding numbers extracted from the three fault states, the cube of the reliability of the MMC, and the corresponding number power of the difference between 1 and the reliability of the MMC.

8. A reliability assessment method for a flexible interconnected distribution network containing a three-terminal SOP according to claim 7, characterized in that: Based on the SOP reliability model, the reliability of the flexible interconnected distribution network is evaluated by randomly simulating the operating status and load transfer judgment, and the impact of SOP access on the reliability of the flexible interconnected distribution network is analyzed, specifically: Set the simulation years, set the simulation time limit based on the set simulation years, and initialize the simulation time; Generate a random number between 0 and 1, and calculate the fault-free working time and fault recovery time of each component in the flexible interconnected distribution network according to the random number. The fault-free working time is the natural logarithm of the random number divided by the inverse of the fault rate of the component; the fault recovery time is the natural logarithm of the random number divided by the inverse of the repair rate of the component; The component with the shortest trouble-free working time is regarded as the current fault component; The component is a component or device on a distribution network feeder, and when the component fails, the feeder where the component is located fails; Randomly generate SOP fault status according to the probability of occurrence of various SOP operating states; According to the SOP fault status, determine whether the load can be successfully transferred within the power outage range. If it can be transferred, the simulation time is updated to be the sum of the current simulation time and the fault-free working time, fault recovery time and switching operation time of the current faulty component; if it cannot be transferred, the power outage number, power outage time and power shortage information of the affected load points within the power outage range are recorded, and the simulation time is updated to be the sum of the current simulation time and the fault-free working time and fault recovery time of the current faulty component; Determine whether the simulation time reaches the upper limit of the simulation time. If not, repeat the above contents starting from generating random numbers. If reached, calculate the system reliability index and obtain the system reliability index without SOP for comparison.

9. A reliability assessment method for a flexible interconnected distribution network containing a three-terminal SOP according to claim 8, characterized in that: According to the SOP fault status, it is determined whether the load can be successfully transferred within the power outage range, specifically: The power outage range refers to the range from the upstream of the power supply path to the downstream of the current fault component; When the SOP fault state is that a single MMC port fails, and the failed MMC port is not connected to the feeder where the current failed component is located, the SOP can effectively transfer power, otherwise it cannot effectively transfer power.

10. The reliability assessment method of a flexible interconnected distribution network containing a three-terminal SOP according to claim 8, characterized in that: The system reliability index includes the expected value of the average power outage frequency of the system , Expected value of average power outage time of the system And the expected annual power shortage of the system .

11. A reliability assessment system for a flexible interconnected distribution network containing a three-terminal SOP using the method according to any one of claims 1 to 10, comprising: Submodules include reliability model building module, bridge arm reliability model building module, MMC reliability model building module, SOP reliability model building module, and reliability evaluation module, which are characterized by: Submodule reliability model building module: used to determine the topology of the MMC converter and build a submodule reliability model based on the topology; Bridge arm reliability model construction module: used to construct a bridge arm reliability model taking into account the redundancy configuration and the correlation between sub-modules through sub-module reliability models; MMC reliability model building module: used to build the MMC reliability model according to the topological structure of the MMC converter and the bridge arm reliability model; SOP reliability model building module: Analyzes the various operating states of the three-terminal SOP operation, and builds the SOP reliability model through various operating states and the MMC reliability model; Reliability assessment module: Based on the SOP reliability model, the reliability of the flexible interconnected distribution network is assessed through random simulation of operating status and load transfer judgment, and the impact of SOP access on the reliability of the flexible interconnected distribution network is analyzed.

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