Abstract
Voltage source converters (VSCs) are able to provide both positive- and negative-sequence short circuit currents under unbalanced faults. Their short circuit responses can be significantly different from those of conventional synchronous generators. This paper developed a static fault analysis method by considering dual-sequence current control of VSCs under unbalanced faults where VSCs are treated as voltage-dependent current sources in both positive- and negative-sequence networks. Since the control strategy of VSCs varies, flexible parameters are included in the model to reflect their diverse short circuit behaviours. The proposed method is verified through a modified IEEE 9-bus system and a simplified western Danish power system with real time simulations. This analytical method can be used to help understand and evaluate the impact of dual-sequence current control of VSCs on future converter-dominated power systems.
Highlights
With proliferated renewable energy integration and the gradual retirement of conventional generation units, power systems are undergoing significant changes in regard to their generation mixes
This paper developed a static fault analysis method that considers the dual-sequence current control of Voltage source converters (VSCs) under grid unbalanced faults
The VSCs are treated as voltage-dependent current sources with flexible parameters that represent different control strategies
Summary
With proliferated renewable energy integration and the gradual retirement of conventional generation units, power systems are undergoing significant changes in regard to their generation mixes. If VSCs are controlled to provide a negative-sequence short circuit current, the negative-sequence network will not be passive anymore and power-flow-based methods become insufficient. This paper develops a static fault analysis method that considers dual-sequence current control of VSCs under unbalanced faults It treats VSCs as voltage-dependent current sources in both positiveand negative-sequence networks. The method is used to help explain a phenomenon that the system does not have a stable fault response when the share of negative-sequence reactive power from VSCs is high or when the system has a low short-circuit power. This phenomenon has not been revealed by previous studies. The proposed method can be utilized to help understand and evaluate the impact of dual-sequence current control of VSCs on the system
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