Aplicações de conversores multiníveis modulares no processamento e condicionamento da energia elétrica

Abstract

This document investigates the use of modular multilevel converters (MMC) for harmonics mitigation in high voltage, as well as for medium voltage applications. Due to the fully modular topology of the converter it is possible to synthesize voltages and currents with a number of levels directly proportional to the number of modules con-nected in series. For this reason, the MMC can be connected to the high voltage side of distribution network with no need of magnetic transformers. To achieve the objec-tives, the converter is analyzed according to simplified mathematical models in which the modules are treated as controlled voltage sources. Based on these mathematical models, the DC bus controller, the AC currents controller and circulating currents controller are designed. The reference signals for the controllers are obtained from the instantaneous power theory, while the design of the controllers is performed in the orthogonal axis system (α,β). Despite the use of dedicated controller for the DC bus, this does not guarantee the capacitors voltages equalization of the MMC modules. For this purpose, it is designed an algorithm capable to ordering in an ordinary way the modules according to their capacitors voltages. For each new time step the modules that be active are selected while the other ones remain in the inactive state. Thus, the capacitors charge and discharge process remains balanced during normal operation of the MMC as reactive power compensator and as shunt active power filter. Simulation results are presented to validate the mathematical models and control strategies. In addition, hardware-in-the-loop simulation results contribute to the analysis of closed-loop controls and sorting algorithms. Experimental results obtained in a three-phase prototype show the system operation. Finally, the complementary proposals for the development of this study are presented.