Introduction - Control of Power Inverters in Renewable Energy and Smart Grid Integration - page 44

measurement of the harmonic distortion of input and output signals up to the 500th-order
harmonic even at high fundamental frequencies, e.g. 400 Hz, and updated computer inter-
faces, e.g. two USB ports.

1.4 Wind Power Systems
During the last decade, more and more attention has been paid to utilising renewable energy
sources to tackle the energy and environmental issues being faced today worldwide. Wind
energy has been regarded as an environmentally friendly alternative energy source and has
attracted most of the attention. Many initiatives have been launched to increase the share of
wind power in electricity generation (Mathew 2006; Wagner and Mathur 2009).
In this section, wind power systems are briefly discussed. More details about wind power
systems can be found in many topics, e.g. (Ackerman 2005; Bianchi et al . 2007; Blaabjerg
and Chen 2006; Burton 2001; Heier 2006; Manwell et al . 2009; Mathew 2006; Mathew and
Philip 2011; Ragheb 2009; Spera 2009; Thongam and Ouhrouche 2011; Wagner and Mathur
2009).

1.4.1 Basics of Wind Power Generation
Assume that the wind speed is

v w m/s and the area swept by a wind turbine is A m 2 . Then
the volume of the air swept through in unit time is A

kg/m 3 , then the v w . If the air density is ρ

mass m of the air passing through the area in unit time is ρ A v w kg. The kinetic energy of this

mass of the air moving at velocity v w in unit time is

1
2 m

1
2 ρ

2 3

v

w =

A v

w .

This is actually the same as the power carried by the wind motion. For a wind turbine with
rotor blades of R m long, the area swept is A R 2 and hence the wind power available is = π

1
2 ρπ

R 2

3
w .

P w = v

In reality, it is impossible to convert all the energy into electricity. The actual power produced
by a wind turbine can be calculated as

1
2 ρπ

R 2

3
w

P m = v C p ( λ, β ) , (1.6)

where C p ( λ, β ) is the power coefficient that is dependent on the turbine design, the pitch angle

β and the tip-speed ratio λ defined as

λ = ω r R /v w , (1.7)

where ω r is the angular speed of the wind turbine. The tip-speed ratio plays a vital role in

extracting power from wind. If the rotor turns too slowly, most of the wind passes through