Current Limiting High-Voltage DC Circuit Breaker With Reclosing Function

At present,the flexible DC power grid transmission technology with modular multi-level converters has gradually developed into an important choice in the field of new energy generation due to its advantages of high stability and cost-effectiveness.Overhead line transmission is the main transmission method for DC power grids.In recent years,new energy power generation technology has steadily developed,and its green power generation method has led to an increasing proportion of renewable new energy power generation applications.Compared with AC transmission,high-voltage DC transmission can more effectively improve the efficiency of new energy utilization,thus the scale of DC transmission system continues to expand.Compared with AC power,which has a natural zero crossing point and uses AC arc extinguishing methods,DC power uses high-power power electronic switches to turn off fault currents.However,due to the increasing application and capacity of DC transmission systems,their structures become more complex,which poses great risks to the safe and stable operation of DC transmission systems and converter stations.The impedance of the DC power grid is very low,and once a fault occurs,the current will rapidly rise within a few milliseconds,seriously threatening the safety of the power grid.Therefore,it is necessary to quickly and effectively remove the fault.Firstly,this thesis provides a detailed discussion on the research background of DC circuit breakers,and then introduces the current research status of circuit breakers at home and abroad.The development history of circuit breakers was elaborated,and the background,improvement plans,and working principles of three classic DC circuit breakers,mechanical,solid-state,and hybrid,were analyzed.The advantages and disadvantages of various DC circuit breakers were pointed out one by one.It was pointed out that hybrid DC circuit breakers,as the main DC breaking equipment,were applied in practical engineering to meet the current demand for high capacity and high voltage circuit breakers in DC transmission systems.Secondly,the key technologies in the development process of DC circuit breakers were introduced separately.Firstly,the arcing problem that the circuit breaker needs to solve and the solutions were summarized and described;Explained the principles and characteristics of commonly used ultra fast mechanical switches at present;Explain the working process and interruption principle of the lightning arrester,which is mainly used for energy absorption,in the circuit breaker;By explaining the reclosing process and its importance in the working process of the circuit breaker,theoretical foundation and technical support will be laid for subsequent analysis and design.Then,taking into account the advantages of existing traditional hybrid DC circuit breaker topologies,this thesis proposes a current limiting hybrid high voltage DC circuit breaker with reclosing function(RFL-HDCCB)topology.This topology utilizes capacitors to store energy;Using inductance to reduce the rate of current rise;The use of bypass branches reduces the energy absorbed by lightning arresters;The symmetrical structure is adopted in the current limiting branch,which not only ensures the bidirectional breaking fault current function of the circuit breaker,but also realizes the reclosing function of the circuit breaker.This circuit breaker can ensure that whether there is an instantaneous fault or a permanent fault on the transmission line,it can complete the reclosing function and restore normal power supply to the system.Firstly,the paper conducts a theoretical analysis of the working principle of RFL-HDCCB,and selects the optimal device parameters of RFL-HDCCB through comparative analysis;Finally,a system simulation model was built using PSCAD simulation software and the feasibility of the proposed topology was verified.The verification results indicate that the RFL-HDCCB topology can reduce the peak and rise rate of short-circuit current,thereby reducing the energy consumption demand of the lightning arrester in the circuit breaker,and thus reducing the performance demand for the lightning arrester.Moreover,the current limiting ability of the circuit breaker is significant,and the superposition of reclosing functions enhances the rationality of the proposed scheme.Finally,the topology of RFL-HDCCB is improved,and a capacitor commutation DC circuit breaker with current limiting function(CC-HDCCB)with reclosing function is proposed,This topology has low cost and has current limiting and reclosing functions.It uses capacitors to replace IGBTs to achieve circuit state switching,resulting in a sharp reduction in the number of IGBTs used.Moreover,through the use of current limiting branches,the peak and rate of current are suppressed,the requirements for lightning arrester energy absorption capacity are reduced,and the time for fault interruption is shortened.Compared with the RFL-HDCCB topology mentioned earlier,it greatly reduces cost and technical difficulty.By studying and analyzing the working principle of the proposed topology,parameter design was carried out,and finally,a system simulation model was built using PSCAD software to verify the simulation model.By comparing and analyzing with typical circuit breaker design schemes,the rationality and superiority of the proposed scheme have been proven.