Sistema HVDC multiterminal com conversores comutados pela linha e conversores multinível modulares

Abstract

Hybrid High voltage dc transmission systems (HVDC) are compound by line com- mutated converters (LCC) and voltage source converters (VSC). In the transmission of bulk power flow, the VSC are modular multilevel converters. Hybrid HVDC systems have huge potential for application at continental countries such as Brazil, China and Australia, for example. The use of MMC in HVDC improves the ac power quality and overall system stability, while the main LCC advantage is the higher power transmission capability at a relatively lower cost. Accordingly, instead of substituting all LCCs for MMCs, the current tendency is to take advantage of each one of them on hybrid systems. The operating modes and controls for the MMC based on full bridge submodules – the FBMMC - are presented. It is tested, through simulation of electromagnet transients, the main contributions, which are listed on following. A voltage balancing algorithm for the FBMMC is proposed, as well as a strategy to control the capacitors voltages, which was found to be fundamental during the operation in Statcom mode. The use of FBMMC in hybrid multiterminal HVDC is discussed later. In case of a system with one LCC and two FBMMC, it is proposed a set of control techniques in order to enable the elimination of the dc short-circuit current without blocking the converters. It is shown that the dc short-circuit current can be controlled in all cases keeping full ac voltage control. In order to promote the black start of an LCC connected to an entirely passive network, a hybrid configuration with one FBMMC in parallel is proposed (both dc terminals and the point of coupling with the ac system are in common) with the inverter end of an HVDC-LCC. The presented start-up strategy showed stability during load insertion and rejection.