Converter and Output Filter Topologies for STATCOMs

This chapter reviews different converter topologies and output filter configurations used in STATCOM applications. The output voltage and harmonic control of a STATCOM is obtained by individual control of each switch in the STATCOM. Several converter topologies can be considered for STATCOMs. The multi-pulse converters are developed using the most widely known 6-pulse configurations. The variations of multi-pulse converters such as 12-pulse, 24-pulse and 48-pulse that are built by combining 6-pulse converters via phase-shifting isolation transformers are introduced in terms of control methods and structures in this chapter. On the other hand, the multilevel converters are considered to be used in recent STATCOM topologies as an alternative to the multi-pulse configurations, owing to their multi MVA switching capability that is inherited from series or parallel connection of converter cells. The diode clamped, flying capacitor, and cascaded H-bridge configurations of multilevel converters, that are the most widely known topologies, are comprehensively introduced in this chapter. The multilevel converter topologies provide several advantages such as harmonic elimination, lower electromagnetic interference, better output waveforms, and increased power factor correction (PFC) capabilities together. Furthermore, each switch can be controlled individually to robustly tackle the unbalanced load operations even in higher switching frequencies relatively to the multi-pulse configuration. The related subsections propose control and operation properties of converters besides introducing the main topological issues. The filtering requirements of STATCOM are particularly considered in this chapter where the passive and active filters are introduced in detail. The passive filters designed with reactive components such as individual L and C or their combinations as LC or LCL are surveyed according to design and analytical criteria. Besides, active power filters (APFs) that provide several feedback control methods increasing the efficiency and controllability are discussed in the following part. The control methods of STATCOM converters are introduced in a separate section where the recent control approaches and analytical calculations required are presented in detail. The block diagrams of the industrial STATCOM applications are also discussed