混合级联直流输电系统逆变侧LCC换流变故障性涌流影响分析及抑制方案OA

The inverter side of a hybrid cascaded HVDC system adopts a cascade structure of a line-commutated converter(LCC)and a modular multilevel converter(MMC).To address the difficulty in identifying the faulted phase when an external fault occurs on the valve side of the LCC converter transformer,an extended differential protection scheme for the converter transformer is proposed.First,the fault-induced inrush current(FIIC)caused by a valve-side single-phase-to-ground(SPG)fault on the LCC converter transformer is analyzed.It is clearly demonstrated that activating the bypass pair of the faulted phase can suppress FIIC,whereas triggering the bypass pair of non-faulted phases will aggravate its development.Second,considering the complex coupling between the LCC and MMC inverters,the adverse effects of FIIC on both LCC and MMC converter transformers are analyzed.To overcome the difficulty in accurately identifying the faulted phase during a valve-side external SPG fault of the LCC converter transformer under existing protection configurations,an extended differential protection scheme is proposed,enabling faulted phase identification and FIIC suppression.Finally,simulations conducted on the PSCAD/EMTDC platform verify the effectiveness of the proposed protection scheme in both faulted phase identification and FIIC suppression.