Page 269 - Renewable Energy Devices and System with Simulations in MATLAB and ANSYS

256 Renewable Energy Devices and Systems with Simulations in MATLAB and ANSYS ®
®

1.4
1.2
Maximum power
tracking 13 m/s
1.0
Turbine output power 0.8 11 m/s

12 m/s
0.6

0.4
9 m/s 10 m/s
0.2 8 m/s
7 m/s
6 m/s
0.0
0.2 0.4 0.6 0.8 1.0 1.2 1.4
Turbine speed

FIGURE 10.4 Wind turbine characteristics at different wind speeds.

, (
i λ
.
.
.
.
.
C p λβ) = 073 151 − 058 β − 0 002 β 214 −13 2   e −18 4 . (10.5)

 i λ 
Using the wind turbine characteristics of Equations 10.1 through 10.5 and that power = torque ×
angular speed, a turbine output can be obtained at different wind speeds as shown in Figure 10.4.
This figure shows the turbine rotation family of curves in per-unit, assuming that the turbine can
have a margin for overpowering during high wind velocity, but typically 40% of the rated turbine
speed is the maximum safety range, which is why the curves range up to 1.4 pu. A similar family of
curves is plotted in Figure 7.12 for the discussion of maximum power tracking.
10.4 WIND ENERGY GENERATOR SYSTEMS
In order to select an electrical generator for small wind energy power application, it is necessary to
study and define a wide set of variables such as voltage, frequency, speed, output power, slip factor
(for induction machines), required source of reactive power, and field excitation along with other
parameters.
Usually, a DC link is used between the generator and the load or the network to which the power
has to be delivered, for example, an inverter or a rectifier on the generator side with an inverter
on the utility side. There are other factors to consider, such as the capacity of the system, type of
loads, availability of spare parts, voltage regulation, and cost. If loads are likely to be inductive
or maybe with a low-power factor (such as phase-controlled converters, motors, and fluorescent
lights), a synchronous generator could be a better choice than an IG (for larger power applica-
tions). On the other hand, for small power applications, an induction machine is easier to pur-
chase or maybe a permanent magnet brushless AC generator would be available when choosing for
inexpensive turbines. Selecting and sizing the generator is a very technical decision and viability
studies must be conducted, particularly using power systems or power electronics software simula-
tors. A gearbox will typically be used to convert the low-speed (typically 10–30 rpm) high-torque
turbine shaft power to the shaft of the electrical generator. A gearbox is often used in small wind
turbines, whereas multipole generator systems can be custom-made for multimegawatt systems.
The most typical machines to convert the turbine shaft mechanical power into electrical power are