Novel VSC-Based STATCOM Model Based on Dynamic Phasors for Unbalanced Distribution Networks

Abstract

This paper presents the dynamic phasor-based modeling of three-phase voltage-source converters (VSC) operating as static var compensators (STATCOM). The generalized averaging theory is used to represent the DC, 1st, and 2nd harmonics of the converter fundamental response. The VSC model is characterized by the use of basic power system elements. On the AC side, it consists of three wye-connected, single-phase complex transformers whose taps replicate the AC-to-DC energy conversion of the converter commanded by the modulating variables. On the DC side, a capacitor is connected in parallel with a current source to reproduce the $2{\omega }$ effects of the network unbalances. Dynamic controllers based on symmetrical components were developed for the VSC to operate as STATCOM. All these aspects distinguish the proposed VSC model from the switching-based model (SBM) and averaged-value model (AVM). The model’s dynamic behavior was validated by comparing it to the SBM and AVM, using a five-bus, three-phase network taken from Simulink/Simscape Electrical. Root mean square errors were smaller than 5.56% and 5.53%, with the new model being 43 and 17 times more computationally efficient than the SBM and AVM, respectively. The IEEE 34-bus test system with two STATCOM was also studied to verify the model practicality. Short-circuit faults were assessed to prove that both STATCOM suitably perform under unbalanced operating conditions.

Keywords

• Dynamic phasors
• unbalanced three-phase power networks
• VSC modeling
• VSC-based STATCOM