Study on dynamic characteristics of UHVDC system under hierarchical infeed mode with STATCOM

This paper focuses on the investigation of the dynamic characteristics of Ultra High Voltage Direct Current (UHVDC) system Under Hierarchical Infeed Mode (UHVDC-HIM) with Static Synchronous Compensator (STATCOM). The STATCOM at the inverter side of UHVDC-HIM is developed in PSCAD/EMTDC, and their power flow equations are derived. Based on these equations, the control schemes for rectifier and inverter side of UHVDC-HIM and STATCOM are properly designed. Several dynamic characteristics indices such as Commutation Failure Immunity Index (CFII), Commutation Failure Probability Index (CFPI), fault recovery time and Temporary Overvoltage (TOV) are evaluated in detail. The impact of different sizes of STATCOM and Short Circuit Ratio (SCR) of AC sources on dynamic characteristics of UHVDC-HIM system during single-phase and three-phase faults are examined. The analysis shows that higher SCR values and greater capacity of STATCOM can make the UHVDC-HIM system less vulnerable to Commutation Failure (CF), considerably enhance the fault recovery time and effectively reduce the TOV.