Improving the Reactive Current Compensation Capability of Cascaded H-Bridge Based STATCOM Under Unbalanced Grid Voltage

• Published in: IEEE journal of emerging and selected topics in power electronics Vol. 8; no. 2; pp. 1466 - 1476
• Main Authors: Neyshabouri, Yousef, Chaudhary, Sanjay K., Teodorescu, Remus, Sajadi, Rahman, Iman-Eini, Hossein
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 01.06.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Active control; Automatic voltage control; Capacitors; Cascaded H-bridge (CHB) converter; Converters; Electric potential; Flow equations; Legged locomotion; Load flow; low-voltage ride-through (LVRT); Mathematical model; Power electronics; Power flow; STATCOM; Static synchronous compensators; Unbalance; Voltage
• ISSN: 2168-6777; 2168-6785
• DOI: 10.1109/JESTPE.2019.2916571

This paper deals with the operation of a cascaded H-bridge (CHB) converter-based STATCOM under unbalanced grid conditions. Degrees of freedom and operational limitations of the CHB STATCOM during unbalanced grid condition are analyzed according to the converter power flow equations. Based on this analysis, an improved low-voltage ride-through (LVRT) strategy for the CHB STATCOM is proposed. In this strategy, the grid operator can control both the positive- and negative-sequence reactive currents independently within the operation range of the CHB STATCOM. In addition, to keep the submodules' capacitors voltages balanced, a zero-sequence voltage term is injected to the converter legs. The negative-sequence active current is also controlled to limit the injected zero-sequence voltage and keep the converter within the rated operation range. The performance and effectiveness of the proposed method are validated through PSCAD/EMTDC simulation of a 21-level CHB STATCOM. The results are experimentally demonstrated on a 9-level CHB STATCOM prototype.