Fault Modeling and Analysis of Grid-connected Inverters with Decoupled Sequence Control

With an increasing number of inverter-interfaced generators (IIGs), the power system is undergoing massive shifts towards the power electronic dominated power system. Such paradigm change would pose significant challenges to existing fault analysis theory and the protection system, as a result of the disparate short-circuit response. Given this, the fault analysis theory needs to be further investigated and expanded to address issues arising from the new grid paradigm. Under this context, this paper proposes an analytic model for short-circuit analysis of IIGs with decoupled sequence control (DSC) based on the Laplace transform. With the proposed model, the full time-scale fault current expression can be obtained and the fault characteristic can be analyzed. Compared with existing studies, the proposed model distinguishes itself by three key merits. First, the proposed model takes into account the delay feature of controller, which enables to conduct analysis in transient. Second, the model covers the impact of controller parameters and low voltage ride through (LVRT) strategy in detail which usually is missing in most existing literature. Third, the proposed model provides theoretical foundation of IIGs with DSC in the fault analysis, which makes it more applicable for the protection setup issues in reality.