Investigation of Modular Multilevel Converters for E-STATCOM Applications

The power quality in electrical grids can be improved by static synchronous compensators (STATCOM), classically realized by low voltage inverters and conventional transformers. One of the main challenges for current and future STATCOM solution is the increase of flexibility for optimized power quality management by not only exchanging reactive power but also active power. For active power supply energy storage systems need to be integrated, classically at the dc link of the low voltage inverter. However, by the usage of classical low-voltage inverters, the power is quite limited even by parallel connection and bulky transformers are needed. Instead this paper suggests an E-STATCOM based on the modular multilevel converter (MMC) with integration of batteries at the dc link by isolated dc-dc conversion state. In this way, very high energy capacities can be installed and very high active and reactive power can be provided at very high efficiencies for safe and reliable grid operation.