Direct-coupled multilevel cascaded series var compensators

Series var compensators based on force-commutated static power converters are proving to be a viable alternative to shunt compensators as a means of enhancing power transmission and distribution capability. This paper proposes a converter structure, based on a multilevel cascade of single-phase converters, which can be coupled to the transmission system without transformers. The individual converters are switching at very low frequencies, resulting in high efficiency, and are fed from independent self-controlled dc capacitor buses, Advantages of the proposed series compensator include low injected voltage harmonic distortion and fast response to changes in the compensation level. Pattern generation options are presented. Gating and control schemes are discussed. Simulation results are verified experimentally.