Abstract
Problems related to power quality, which in the last years were responsible only for small losses in low-voltage distribution systems, are now causing damage to power apparatuses and financial losses also in medium-voltage systems. The necessity of a better quality of power supply encourages the development of new specific custom power devices directly connected in medium-voltage distribution systems. It is well know that the multilevel converters are capable of being installed directly in the medium voltage, and presents several advantages when compared with conventional two-level converters. Some topologies, like the asymmetric cascaded multilevel converter, presents difficulties in regulating the voltages of all isolated dc-link capacitors. In this context, this article presents an asymmetric nineteen-level D–STATCOM (Distribution Static Synchronous Compensator) with a reactive power and dc-link regulation control loops for generic cascaded multilevel converters in order to improve the power quality in medium-voltage distribution systems. The performance of the proposed control method for a multilevel D–STATCOM is presented and evaluated in a downscaled prototype.
Highlights
The increasing energy demand and the industrial plants modernization brought together an increasing number of power-electronics devices directly connected to the medium-voltage distribution systems
The use of multilevel topologies combined with power quality conditioners, such as Static Synchronous
The nominal values of the dc voltages in each power module and the maximum level of total harmonic distortion (THD) required to the output voltage define the quantity of power modules that will compose the multilevel converter
Summary
The increasing energy demand and the industrial plants modernization brought together an increasing number of power-electronics devices directly connected to the medium-voltage distribution systems. All multilevel topologies have similar performance, only the Asymmetric CHB is capable of producing the same output-voltage level with a minimum number of power semiconductors [17,18,19]. The best modulation method is the hybrid modulation [23] that uses different frequencies for each power module This allows a reduction in switching frequency, which leads to a reduction in the converter losses [19,24]. Other strategies using the principle of commutation technique as in [27], or binary mode relation among dc-link voltage levels as in [28], or even a dedicated rectifier for each separated module have been proposed These solutions do not present a general control method for dc-link voltage regulation. The main contribution of this work is the development of an improved hybrid modulation and a new isolated and unequal dc-link voltage control strategy for the Asymmetric CHB topology
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