Introduction - Control of Power Inverters in Renewable Energy and Smart Grid Integration - page 46

0.5

v w1

0.4

v w2

0.3

v w3

v w4

0.2

0.1

v w6 v w5

0

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Turbine speed (pu)

(a) C p as a function of the turbine speed normalised to the rated speed

1.6

1.4

v w1

1.2

1

v w2

0.8

0.6

v w3

0.4

v w4

v w5

0.2

v w6

0

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Turbine speed (pu)

(b) Power P m

Figure 1.40 Power coefficient C p and mechanical power P m at different wind speeds

wind turbine is shown in Figure 1.42, with major components including blades, a rotor hub,
drivetrain (bearing and gears, etc.), a generator and the associated control system.
Wind turbines can be used for stand-alone applications, connected to a utility power grid or
even combined with photovoltaic systems, batteries and diesel generators, etc. to form hybrid
systems. Small-scale wind turbines are often used in stand-alone applications, e.g. for water
pumping, communication stations, and supply of electricity to farms and light towers, etc. that
are far from the utility grid. For utility-scale applications of wind power, a large number of
turbines are usually built together to form wind farms to fully utilise the available wind power
and to reduce the investment cost on infrastructure.
A wind turbine can be designed for fixed-speed or variable-speed operation. Variable-speed
wind turbines can produce more energy than fixed-speed ones but power electronic converters
are needed to provide a voltage at a fixed frequency and a fixed amplitude.
Most turbine manufacturers have opted for a direct drive configuration to remove the
gears between the low speed turbine rotor and the high speed three-phase generator. This