Trends in Wind Turbine Generator Systems

TLDR

Wind turbine generator systems are evolving toward lighter, more efficient designs, with hydraulic transmissions offering variable speed but lower efficiency, brushless DFIGs improving low‑voltage ride‑through, magnetic pseudo‑direct‑drive units and superconducting generators promising size and weight reductions, and power electronics moving toward modular multilevel topologies. This paper reviews the trends in wind turbine generator systems. The review surveys current generator configurations—constant‑speed squirrel‑cage induction, variable‑speed DFIG with gearbox and converter, and direct‑drive systems—and examines prospective future generator designs.

Abstract

This paper reviews the trends in wind turbine generator systems. After discussing some important requirements and basic relations, it describes the currently used systems: the constant speed system with squirrel-cage induction generator, and the three variable speed systems with doubly fed induction generator (DFIG), with gearbox and fully rated converter, and direct drive (DD). Then, possible future generator systems are reviewed. Hydraulic transmissions are significantly lighter than gearboxes and enable continuously variable transmission, but their efficiency is lower. A brushless DFIG is a medium speed generator without brushes and with improved low-voltage ride-through characteristics compared with the DFIG. Magnetic pseudo DDs are smaller and lighter than DD generators, but need a sufficiently low and stable magnet price to be successful. In addition, superconducting generators can be smaller and lighter than normal DD generators, but both cost and reliability need experimental demonstration. In power electronics, there is a trend toward reliable modular multilevel topologies.