Electrical - Wind Energy: Renewable Energy and the Environment - page 144

Control of the turbine for furling units is accomplished mechanically. If the unit is connected
to the grid through an inverter, then the power output of the wind turbine is converted to DC and a
disconnect switch is mandatory. Southwest Wind Power has a unique wind turbine where the DC
rectifier, controller, and inverter are all inside the nacelle (for photo of unit, see Figure 6.17 ). The
controller regulates an electromagnetic brake for shutdown and to limit rotor rpm in high winds.
The connections are the disconnect switch to the grid and a wireless two-way remote to turn the unit
on and off. Options are a wireless remote display to observe the performance in real time and collect
kilowatt-hour data for day, month, and year. The remote may be connected to a personal computer
(PC) for monitoring turbine performance, and software allows the user to obtain a power curve for
the wind turbine.
For wind turbines with induction generators connected to the grid, the controller (Figures 7.15
and 7.16) has more sensors and functions, for example, measurement of wind speed and rpm
to determine switches for start-up (motor) if needed, connection of the generator, and control
for shutdown and overspeed. The controller will also have sensors for faults, any of which will
shut down the wind turbine. The controller may provide communication to an external personal
computer on site or far away. Additionally, the PC may be able to change the parameters of the
controller.
For large wind turbines there are between 100 and 500 parameters to monitor, and there may
be two controllers, one in the nacelle and one at the bottom of the tower, which is done with
fiber optics on new wind turbines. On some models there is a third controller in the hub for pitch
control. CPUs and sensors for safety or operation-sensitive areas are duplicated for redundancy.
The controller communicates status and operating conditions of the turbine and provides fault
alarms and service requests to the outside world, the owner or operator. Statistics are collected
at the computer to provide a baseline for that wind turbine. Finally, for wind farms, supervisory
control and data acquisition (SCADA) are part of the control system [12]. Several companies
have SCADA systems for wind farms, which can even have different wind turbines. Operational
information on each wind turbine is compared to the baseline database to alert wind farm opera-
tors of potential problems. At the control room, which could be on site or located at a city or even
the headquarters, operators monitor each wind turbine in the wind farm and can turn them on
and off. There have been instances of high winds and the transmission lines are full, so output
from wind farms had to be curtailed, and wind turbines were shut down within a short period.
FIGURE 7.15 Disconnects and controller for a 50 kW wind turbine.