23-01-2013, 11:38 AM
Wind Energy Conversion Systems (WECS)-Technological Issues from Electrical Perspective
Wind Energy Conversion.ppt (Size: 894.5 KB / Downloads: 81)
Abstract
This paper reviews Wind Energy Conversion System in the three
main electrical aspects
Wind Turbine Generator
Power Electronic Converters
Grid Connection issues.
A current state of Wind Generators are discussed and compared in some criteria along with trends in WECS market.
Power Electronic Converter topologies are discussed which are available in WECS along with its control strategies.
Moreover the grid connection issues such as Fault Ride through Capability, Harmonics emission and Flicker etc. are discussed.
Introduction
The electrical energy consumption continues to grow and there is a steady
increase of the demand on the power capacity, efficient production, distribution and
utilization of energy.
The traditional power systems are changing globally, a large number of dispersed generation (DG) units, including both renewable and Nonrenewable energy sources
wind turbines
photovoltaic (PV) generators
fuel cells
small hydro
wave generators
and gas/steam powered combined heat and power stations
are being integrated into power systems at distribution.
Wind energy has assumed leading place in the race of the renewable sources for various reasons.
In the last decade most prominent increasing power source is Wind. World Wind Energy Association (WWEA) figures shows that over the past five years the average growth in worldwide new installations has been 30.9 % .
Wind Turbine Generators
WTGs can be classified into three types according to its operation speed and the size of
the associated converters as below:
1.FSWT (Fixed Speed Wind Turbine)
using a multi-stage gearbox and a standard squirrel-cage induction generator (SCIG), directly connected to the grid led the market until 2003.
2.VSWT (Variable Speed Wind Turbine) with PSFC (Partial scale Frequency Converter)
using a multi-stage gearbox and a doubly fed induction generator (DFIG) with PSFC.The power electronic converter feeding the rotor winding has a power rating of approximately 30% of the rated power; the stator winding of the DFIG is directly connected to the grid. DFIG with PSFC overtook and has been the leading WTG concept with 85% of the market share reported in 2008 [4].
3.VSWT (Variable Speed Wind Turbine) with FSFC (Full Scale Frequency converter)
WRSG (Wound Rotor Synchronous Generator) has been the main concept; however PMSG (Permanent Magnet Synchronous Generator) has been drawing more attention and increasing its market share in the past recent years due to the benefits of PMSG and drawbacks of WRSG [5].
Power Converters for WECS
Currently, VSWT (Variable Speed Wind Turbine) with PSFC (Partial Scale Frequency Converter) and FSFC (full scale frequency converter) are dominant in the wind market.
The performance of power converters plays a key role in these two wind power generation systems. Some promising and actual converter in market are shown as follow[3],[10],[14-21].
Power Converters for WECS/Two-level Power Converter
However, as fast increasing in power and voltage range of the wind turbines, 2L-BTB converter may suffer from larger switching losses and lower efficiency at Mega-Watts (MW) and Medium-Voltage (MV) power level.
Available switching devices could probably need to be paralleled or series in order to obtain the required power and voltage of wind turbines, - this will lead to reduced simplicity and reliability of the power converter.
Another problem in 2L-BTB solution is the two-level output voltage. The only two voltage stages introduce relative higher dv/dt stresses to the generator and transformer. Bulky output filters may be needed to limit voltage gradient and reduce the THD.
This topology is state-of-the-art in DFIG based wind turbines and several manufacturers also are using this topology for full-rating power converter wind turbines with squirrel-cage induction generator (e.g. Siemens Wind Power).