Introduction of Wind Turbine Generator System

Introduction of Wind Turbine Generator System

Yingzhao Lin

Abstract

In this article two types of Wind Turbine Generator Systems are introduced. Their advantages and disadvantages are presented and compared. At the end of this article, we conclude which type of Wind Turbine Generator System will be the most advanced.

Key Words

Wind Turbine Generator System, Fixed Blade Stall Induction WTGS, Pitch Variable Speed Constant Frequency WTGS, Doubly Fed Induction WTGS, Permanent Magnet Direct Drive WTGS

Introduction

Wind Turbine Generator System is a device which absorbs the energy from wind and changes it into electrical energy. A WTGS includes tower, nacelle, hub and 3 blades. An area where WTGSs are built in is called wind field. There are two types of WTGSs running in wind fields, one is Fixed Blade Stall Induction WTGS, and another is Pitch Variable Speed Constant Frequency WTGS. FBSI-WTGS can’t change the angle of its blades, and the rotor speed is almost fixed when wind speed is higher than rated value.

I, Fixed Blade Stall Induction Wind Turbine Generator System

The blades of FBSI-WTGS are fixed on its hub directly, so once they are fixed they can’t be turned. Therefore, there is not a pitch control system inside its hub. Because of the stall characteristic of the blades, the rotor speed can’t increase when wind speed is higher than rated value. They mean that it is not necessary for main control system to control pitch and rotor speed, so the main control system for wind turbine is simple, and the software is easy to design. However, because of these advantages, the rated wind speed for FBSI-WTGS is higher, and the output power decreases when the wind speed is higher than rated value. Therefore, pitch and converting technology is applied.

II, Pitch Variable Speed Constant Frequency Wind Turbine Generator System

The blades of PVSCF-WTGS are driven by pitch control system which is fixed inside the hub, so the angle of blades can be adjusted when wind speed is higher than rated value. Because applies a converter, the request of rotor speed is not strict. Therefore, the rated wind speed is reduced, the range of wind speed for rated power is wider, and more power is generated. Comparison for the power curve of the two types of WTGS is as follow. Therefore, PVSCF-WTGS is more advanced.

Generally, PVSCF-WTGS can be divided into Doubly Fed Induction WTGS and Permanent Magnet Direct Drive WTGS according to the different generators. In order to work with a variable speed, this type of wind turbine has a converter.

Doubly fed induction generator is a high speed generator, but the rotor speed is low, so a

Perfect FBSI-WTGS

PVSCF-WTGS

Power Curves

transfer case is necessary. The converter is connected with the generator’s rotor, so the rated power of the converter is about 1/3 of the wind turbine’s rated power. As the name suggests, the generator of Permanent Magnet Direct Drive WTGS is driven by the rotor of wind turbine in a low speed directly, so there is not a transfer case inside the wind turbine. The converter is connected between the generator stator and grid. It is a full power converter.

Doubly Fed Induction WTGS has a cheap converter. However, its transfer case is easily broken, and the maintenance costs are very expensive. Permanent Magnet Direct Drive WTGS has an expensive converter, but as the converter technology development, the converter will become cheaper, so Permanent Magnet Direct Drive WTGS will be more advanced than Doubly Fed Induction WTGS.

Conclusions

The structure and control system of FBSI-WTGS are simple, but the energy conversion efficiency is low. As the computer control technology development, controlling a PVSCF-WTGS becomes easier and easier, although the structure of PVSCF-WTGS is complex. PVSCF-WTGS will be widely applied, especial Permanent Magnet Direct Drive WTGS.

Reference

[1] Hangye Ye, “Control T echnology for Wind Turbine Generator System”, Beijing: China Machine Press, 2002.