Researches On Commutation Characteristics And Interruption Performance Of The Hybrid HVDC Circuit Breaker

HVDC grid has high voltage level and small line impedance.When a short circuit fault occurs in the HVDC grids,the fault current of the line rapidly rises.In order to ensure the safety and stability of the system,the DC circuit breakers should cut off the faulty line in a short time and have enough breaking capacity to isolate the fault from the DC system.Hybrid DC circuit breaker,which offer the combination of low losses of mechanical switches and fast switching actions of power electronic switches,its fast operating performance and high breaking capacity provide an important guarantee for the safe and stable of the HVDC grids.At the same time,the current commutation is the key to successfully interrupt the fault current of the Hybrid DC circuit breaker,and the change of various electrical parameters of the circuit breakers has a greater impact on its interruption performance,volume and cost.Therefore,the influencing factors and the influencing rule of the commutation characteristics and interruption performance of the hybrid DC circuit breakers are studied,which is of great significance to the development of hybrid DC circuit breaker.In this paper,the full controlled DC circuit breaker of ABB and the cascaded full-bridge DC circuit breaker of global energy interconnection research institute are used as research objects,and their topological construction and working principles are analyzed theoretically.In order to facilitate the analysis of the internal action process when the circuit breaker cuts the fault,it is divided into four stages according to the internal action sequence of the circuit breaker.Based on the simplified model of the DC network,the current path and the commutation process of the circuit breaker are studied in detail.The equivalent commutation model of FCCB and CFCB and the absorption current model of MOV are presented respectively.On the basis of the proposed equivalent mathematical model,the main influencing parameters of the current commutation and interruption performance of the two kinds of circuit breakers and its influencing rule are given respectively.Secondly,the simulation models of FCCB and CFCB are built in PSCAD/EMTDC,which using power electronic switches,mechanical switches,buffer circuit,and MOV.The simulation of the circuit breaker is performed separately,and the simulation waveforms verify the accuracy of the model.On the basis of the simulation models of the two kinds of circuit breakers,the main influencing factors such as MOV reference voltage,mechanical switch actuation time and stray inductance are changed respectively with other parameters constant.And using the simulation waveforms to verify the correctness of the influence of the each influence parameters on the current commutation of the circuit breaker,MOV current duration time,the voltage of the circuit breaker and MOV absorption energy.Finally,compare the effects of influence parameters of MOV reference voltage,mechanical switch actuation time,stray inductance and other factors on the commutation process and interruption performance of FCCB and CFCB.And the conclusion of the current commutation characteristics and the interruption characteristics of hybrid HVDC circuit breaker are obtained,which make a reference to develop hybrid HVDC circuit breakers with much shorter switching times and a higher breaking capacity.