Simulation Modeling and Analysis of UHVDC with Split Connection to 500 kV/1000 kV AC System

Abstract

The structure and function scheme of UHVDC with split connection are analyzed. The key aspects of the control system, such as voltage balance between high voltage converter and low voltage converter, transformer tap-changer (TCC) control and reactive power control, are analyzed and modeled. When an alternate current (AC) grid has a fault, the converter connects to the other normal AC grid in the inverter, which is controlled by the traditional commutation failure prediction (CFPRED) control strategy, will fail to commutate. In this paper, an improved CFPRED control strategy is proposed. The control strategy takes the CFPRED angle of the converter which connected to the fault AC network as the CFPRED angle of the converter which connected to the normal AC network. The electromagnetic transient simulation model of actual control system was established on the PSCAD/EMTDC, and the simulation results show that the improved CFPRED control strategy can ensure the converter commutate successfully which connected to the normal AC grid during the fault of another AC gird.