Steady state short-circuit model of HVDC converter for fault analysis in the AC/DC hybrid systems

The conventional fault analysis algorithms and fault analytical models may not be suitable for the ac/dc hybrid systems because of the highly nonlinear converters. To alleviate the problem, the paper presents a steady state short-circuit converter model based on the switching function theory for analyzing faults in the ac system, including asymmetric faults. In order to regard the effect of the short-circuit power provided by the HVDC system on the fault features of the ac system accurately, the converter is treated as voltage dependent injection current sources. Expressions for the amplitude and phase of the fundamental current feeding the converter are given. Like other power system components, the model is also developed in terms of sequence components. A simple test system is used as an example. The effectiveness of the proposed model is verified by the calculation results comparing with PSCAD/EMTDC simulation results.