Study On Unified Device Of Power Flow Control And Short Circuit Control For DC Power Grid

Multi-terminal DC transmission and DC power grid technology,which will play an important role in the future power system,possess unique advantages in embracing new energy and configuring energy resources efficiently.It is extremely important and necessary to solve problems about power flow control and short circuit in DC grid.When power flow is not regulated appropriately,excessive power in some lines may damage electrical equipment,which is harmful to power system.DC power flow controller can be employed to cope with it.Shrot circuit line must be removed in time,which can avoid sharp drop of bus voltage and system crash.DC circuit breaker is capable of interrupting fault current.This dissertation will carry out sutdy on topology and working mechanism of dc power flow controller,dc circuit breaker and power flow and unified device.The main patrs of this dissertation are as follows:1.The first part summarizes DC power flow controllers and DC circuit breakers in existing literatures.According to the controlled elements,the power flow controllers are divided into two types: voltage type and resistance type.Based on differences between main switches,the dc circuit breaker is divided into mechanical type,all-solid type and mixed type.The working principles,advantages and disadvantages of various schemes are analyzed in detail to pave the way for the research on the unified device of dc power flow control and short circuit control.2.Based on the defects of the existing dc circuit breakers,such as poor fault current suppression effect,damage to the power system and high equipment cost,the second presents a new single DC breaker and an assembly breaker.The topology,working principle,control strategy and parameter design requirements of the proposed two circuit breakers are described in detail,and the simulation model of the multi-terminal HVDC transmission system is built for simulation verification,and the economic and technical comparison with the existing scheme is made.3.In the third part,a unified device of dc power flow control and short circuit control is put forward to realize the integration of power flow control,short circuit current suppression and fault line removal.The specific working mode,control strategy and theoretical derivation are given,and a three-terminal dc loop network model is built for simulation verification.