Two Types of UHVDC Control System Suitable for Hierarchical Connection to AC Power Grid

As a new type of power grid mode, hierarchical connection mode makes UHVDC (Ultra High Voltage Direct Current) links connect to different voltage-level AC power system, and its control system is needed to be redegined. Combining with the control system in traditional UHVDC system, the control system of UHVDC in the forms of hierarchical connection is analyzed, two kinds of technical ways are introduced, and two different control system of UHVDC with hierarchical connection are designed. Based on PSCAD\EMTDC simulation platform, detail simulation model is built as to two kinds of control systems, and the differences between control systems are analyzed. The results show that the control system at the inverter side under hierarchical connection mode is greatly different to traditional UHVDC control system. The control system designed in this paper can meet the controlling requirement of UHVDC system under hierarchical connection mode.