Research On General Fast Electromagnetic Transient Simulation Of Converter For MMC-HVDC System

HVDC Flexible has been extensively studied thanks to its advantages in island power supply,offshore wind power transmission and asynchronous grid interconnection.This paper mainly studies general fast simulation model of MMC-HVDC converter and open-circuit fault diagnosis and location method of IGBT for sub-module.A fast simulation model is proposed to solve the problem of low simulation efficiency of detailed model of MMC-HVDC system,but most of the existing fast simulation models are applicable to merely one sort of sub-module topology of MMC,thus the versatility of these models are poor.In view of the problem of poor generality of existing fast simulation models,this paper presents a general fast simulation model applicable to multiple sub-module topologies of MMC.The model is not only applicable to multiple sub-module topologies,but also applicable to normal and blocking operation of the system.A simplified table of sub-modules is established,which is used to express the state information of the sub-modules into the bridge arm.Then self-defined program of the equivalent structure of the bridge arm is written by using the variables in the simplified table of sub-modules,and the equivalent structure of the bridge arm suitable for the normal operation of the system is established.In order to make the general fast simulation model applicable to both locking state and normal operation state of the system,three types of blocking structures are constructed on the basis of the equivalent structure of the bridge arm,so that MMC with the same sub-module characteristics can adopt the same type of locking structure,which simplifies the steps of building the blocking structure and enhances the generality of general fast simulation model.The feasibility and applicability of the proposed generalized fast simulation model are verified by comparison between the simulation results of the general fast simulation model with those of the detailed model.IGBT open-circuit fault in MMC system is a typical fault.The number of submodules in the project is usually up to several hundred.The method of locating the fault sub-module directly by information of sub-module capacitance voltage has a large computational burden.Based on the proposed general fast simulation model,this paper studies the open-circuit fault diagnosis and location method for high-level MMC sub-modules.This paper analyzes the influence of open-circuit fault of sub-module IGBT on output voltage and capacitor voltage increment of sub-module,and compares the change characteristics of capacitor voltage of fault sub-module after fault occurs at rectifier side and inverter side respectively.The strategy of combining typical diagnosis and location method of sub-module IGBT open-circuit fault is adopted so that computational burden of open-circuit fault diagnosis and location can be reduced for MMC with many sub-modules on bridge arm.This paper constructs simulation model of 2-terminal 81-level MMC-HVDC system,in which the fault sub-module adopts a detailed model,and the non-fault sub-module adopts a general fast simulation model.This paper verifies the feasibility and applicability of typical fault diagnosis and location methods for high-level MMC-HVDC system.