Trends in Wind Turbine Generator Systems

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.

I. Introduction

The objective of this paper is to review the trends in wind turbine generator systems and to describe a number of possible future generator systems. Although there are also smaller wind turbines, this paper focuses on large wind turbines. Fig. 1 shows how the wind turbine size has grown over the past decades [1]. Also the wind turbine market has grown significantly over the past decades [1]. Fig. 1.

Development of power and size of wind turbines. Source: Bundesverband WindEnergie e.V.