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An E-STATCOM (energy storage + STATCOM) can be considered as a viable option to improve voltage and frequency stability of a renewable energy dominated grid due to its ability to provide active and reactive power support together with other services related to power quality. The E-STATCOM can be formed by integrating an energy storage system with a STATCOM, which provides both active and reactive power support simultaneously or whichever is needed. A power electronic converter is the heart of this kind of support system, which is mostly decided by the voltage and power rating for which it is intended to be designed. In this work, two different power converter topologies, e.g., two-level converter and modular multilevel converter, have been considered where the former is generally used at comparatively lower power levels, and the latter is quite appropriate at high power levels. The nature of the load (e.g., high power density, high energy density, or a combination of both) plays a decisive role in choosing the appropriate type of energy storage system. In this chapter, a hybrid storage system is introduced, which is formed with a battery and ultracapacitors aimed at utilizing the merits of both types of storage technologies. The challenges related to the integration of the hybrid storage system with the aforementioned converters are first addressed, and then suitable control techniques are developed for satisfactory operation. In addition, an algorithm is proposed to balance the state of charge (SoC) among the distributed storage modules, which is necessary to keep some key parameters within their specified limits. Performance of the complete system, including the aforesaid controllers, has been verified through PSCAD/EMTDC simulation for a grid-connected large-scale wind farm. The results show that various grid codes can be possible to maintain the point of common coupling of a large wind farm with the help of an E-STATCOM. Fault tolerant operation and other power quality issues along with their mitigation are also discussed in this chapter. |
