Parallel Hybrid Converter-Based STATCOM and Capacitor Voltage Control Technique

Abstract

The parallel-hybrid converter (PHC) is a promising high-power topology. Smaller capacitor size, lower capacitor and switch counts, and low-energy storage requirement are some of its important features. However, it requires a large dc-filter inductor to filter the dc-side harmonics. Moreover, since its dc and ac sides are strongly coupled, only a single stable operating point in terms of a fixed modulation-index (MI) value is possible. Even with an additional dedicated control effort, the obtained MI variation remains still limited. This article proposes the PHC-static compensator (STATCOM) configuration that eliminates the dc-filter inductor requirement and can also operate at any MI value without necessitating additional control efforts. A detailed power analysis of the PHC-STATCOM for balanced and unbalanced grid conditions (UGCs) is performed in this article. A new control technique for PHC-STATCOM is proposed, which effectively balances the capacitor voltages of its chain-links even during UGCs. The energy storage requirement of PHC-STATCOM is evaluated to obtain the capability curve and determine its capacitor size. The PHC-STATCOM is compared with the popular STATCOM configurations in terms of the capacitor and switch counts. The proposed principles of PHC-STATCOM for several three-phase balanced and UGCs are verified using simulation and experimental studies.