Series compensator based on cascaded transformers coupled with three-phase bridge converters

This paper proposes a multilevel series compensator (MSC) to deal with: (i) voltage sags/swells, (ii) harmonic compensation or (iii) reactive power compensation. Such a device can be considered as a dynamic voltage restorer (DVR) or a series active power filter (Series-APF). The MSC can improve the power-quality of loads located in stiff systems. The configuration is based on three-phase bridge (TPB) converters connected by means of cascaded single-phase transformers. This arrangement permits to use a single dc-link. A generalization for K-stages in which K-transformers are coupled with K-TPB converters, is presented. The topology permits to generate a high number of levels in the voltage waveforms with a low number of power switches. The multilevel waveforms are generated by the converters through a suitable PWM strategy that takes into consideration the transformer turns ratios. Modularity and simple maintenance makes proposed MSC an attractive solution compared to some conventional configurations. Model, PWM strategy and overall control are discussed in this paper. Simulation and experimental results are presented.