Application Of Ultra-high Voltage Multi-terminal Direct Current Engineering In Large-scale Power Systems

In order to study the applications of multi-terminal direct current transmission in multi-AC power grids, this paper have done several researches.MTDC has a great of application requirements and prospects. The general situations of practical engineering and the operating theories including converter technique, connection strategy and control logic have been overviewed in this paper. The advantages of low line loss, convenient power control, flexible expansion and stable operating performance have made parallel MTDC widespread used in almost practical projects.This paper has studied the steady state power calculation and dynamic models in power system simulation software PSS/E. The control strategies of normal operating mode and block-restarting logic in fault have been focused on. The Constant Current Control, Constant Voltage Control and Voltage Dependent Current Order Limit Loop were particularly expounded. This paper also showed the significances and key points of MTDC steady data cards and dynamic model cards.Two testing power systems have been simulated with AC/DC power system faults which illustrate the dynamic responds of power angle of generators, power flow in transmission line, main bus voltage and DC system. The former was composed of two four-machine grids with a bipolar four-terminal DC transmission which separated the two grids with no AC connection and the latter was based on Ningxia to Zhejiang HVDC project. The results validated the features and effectiveness of MTDC models in PSS/E which showed that these models can reach the demands of multi-AC power grids that can be applied in the dynamic response researches of large-scale power systems.