Reliability Modeling Of Flexible Multi-State Switch Considering The Uncertainty Of Loading

With the development of smart distribution networks and the customization and diversification of customers’ demand,distribution networks are gradually shifting from traditional form to providing reliable,efficient and high-quality power supply services.Flexible multi-state switch is a type of key distribution equipment for improving the flexibility and reliability power supply in distribution network.The reliability of component itself is critical in distribution network planning and reliability assessment.The reliability of flexible multi-state switch is affected by many factors such as internal structure,working mode and uncertainty of system operating state.However,traditional power system component reliability modeling is mostly based on the steady-state statistical parameters of components,which can only reflect the reliability level of components.under certain fixed working conditions,while ignoring the influence of the actual operating conditions and the uncertainty of the component state on its reliability.This fixed component reliability calculation result cannot be designed and trouble-shooted for equipment reliability.And provide a scientific basis for reliability assessment of power system distribution network.Therefore,in this paper,considering the influence of the uncertainty of flexible multi-state switch in the actual operation and the diversity of the working mode on its reliability,the reliability modeling of the flexible multi-state switch is studied,and the reliability model of flexible multi-state switch considering the uncertainty of the loading state is established.The main work of this paper is as follows:Firstly,the function of flexible multi-state switch based on MMC topology as well as the integration mode in distribution network is introduced.The MMC topology,control and protection system and fault causes are analyzed and introduced in detail.The fault tree analysis model of MMC is constructed.On this basis,the physical structure reliability model of MMC is established.Secondly,considering the influence of source-load uncertainty on the reliability of IGBT module,in order to accurately evaluate the reliability of IGBT module under the influence of random current loading,Monte Carlo simulation and optimal power flow method are used to solve the current loading expectation of IGBT module.Thus,the equivalent reliability model of IGBT module considering the influence of random current loading is established.At the same time,the relationship between sub-module failure rate and voltage loading is analyzed.Considering the arm pressure equalization strategy,the mathematical induction method is used for the sub-module successive faults.The arm reliability calculation formula is improved and deduced.And the bridge arm dynamic reliability model considering the voltage load sharing mechanism is established.Then,the relationship between the topology and operating characteristics of the flexible multi-state switch is analyzed,and the device is divided into several subsystem.Considering the difference between reliability indices of three-terminal MMC in the flexible multi-state switch,an eight-state transition model is established.And Markov method is used to solve the state transition model,obtaining the reliability indices such as state probability and average duration.Finally,the simulation and analysis are carried out,which verifies the proposed model and method.With the improved three IEEE33 node feeder groups as the test system,the reliability calculation results of IGBT module,three-terminal MMC converter and the eight-state probability and average duration of the flexible multi-state switch are given.And the impact of different redundancy on the reliability of flexible multi-state switches are discussed.