Estratégia de controle de margem de tensão aprimorada para sistemas HVDC multiterminal com base no conversor modular multinível para robustez frente a perturbações

Abstract

In modern systems, multi-terminal high-voltage direct current (MTDC) transmission technology has been considered the key technology for long-distant bulk electric power transmission, asynchronous grid interconnections, and offshore wind energy converter systems (WECS). The main purpose of an MTDC grid is to share power among the AC grids. However, this technology presents challenges in its operation and control. Therefore, for its control it is necessary to use appropriate control system strategies, such as master-slave, voltage margin, voltage droop, and their combinations. In this work, it is proposed a modification in the DC voltage control loop of the voltage margin control strategy aiming to avoid degradation of current control and to increase the supportability to disturbances in the power grid. This modification is based on closed-loop control of the power and feed-forward compensation of the DC grid power. The performance of the proposed method was assessed in a four-terminal meshed MTDC system topology based on the multilevel modular converter (MMC) under abnormal operating conditions and a comparison with the voltage margin and voltage droop control strategies was accomplished. The operation scenarios consider challenging and common failures for MTDC network control systems such as power flow variation in a converter station, open-circuit of a DC transmission line, and failure of a converter station. The proposed control presented the best performance, obtaining a new balance of power flow with less power and voltage oscillations.