Multi-terminal MMC-HVDC Transmission Network Connected DFIG Based Wind Energy

Abstract

Modular multilevel converter (MMC) plays the dominant role in integrating renewable energy from a remote location via a high-voltage DC transmission line. This work develops the MMC-based multi-terminal HVDC network, where the wind energy is integrated through the doubly fed induction generator (DFIG). The MMC’s arm circulating current and submodule capacitor voltage balancing controls are taken into account to present the actual dynamics of MMC. Instead of using an equivalent current source for the representation of renewable energy, this article considers the full dynamics of the DFIG and associated converters. It then scales one entire unit’s dynamics to form the wind farm. It optimally tracks the maximum wind energy during the wind speed variation via field-oriented control. The high voltage AC side is established for wind energy integration by employing feed-forward control. The controller for MMC supports reactive power during symmetrical and unsymmetrical low voltage faults at the point of common coupling (PCC) of the AC grid in line with the grid code. The proposed strategy is simulated in a real-time digital simulator (RTDS) machine. The results verify the fault ride-through (FRT) capability improvement of the MMC-HVDC network during the low voltage faults at the PCC of the AC grid. Moreover, the control proposed strategy successfully extracted the optimum wind energy under wind speed variation.