可关断电流源换流器谐波解析分析与影响评估OA

In conventional high voltage direct current(HVDC)transmission,line commutated converters(LCCs)are employed at the receiving end.During AC voltage dips,the extinction angle margin decreases,which can easily trigger commutation failures.The switchable current source converter effectively avoids commutation failure risks by virtue of its active switchable capability.However,in transient conditions,after the fully controlled devices of the switchable current source converter are switched off,the surge arrester needs to be conducted to assist the commutation process.Nevertheless,the conduction of the surge arrester introduces additional forced commutation stages,which affects the harmonic characteristics of the system.In view of the current insufficiency in theoretical analytical research on this type of converter,this paper conducts an analytical analysis on the harmonic characteristics of the switchable current source converter and an assessment study on the filter stress.Firstly,the differences in the switching sequence of the controllable line commutated converter(CLCC)under steady-state and transient conditions and their impacts on the commutation characteristics are analyzed.Secondly,the analytical expressions of the voltage and current at each stage of the converter considering the influence of the forced commutation angle are derived.Thirdly,based on the fast Fourier transform(FFT)theory,the harmonic components on both AC and DC sides are accurately analyzed.Finally,a simulation model is built in PSCAD/EMTDC to verify the correctness and effectiveness of the proposed harmonic analysis method,and the current stress of the filter under various working modes is verified through simulation.