Purpose and description
The electronic controller         The wind turbine controller consists of a number of computers which continuously monitor the condition of the wind turbine and collect statistics on its operation. As the name implies, the controller also controls a large number of switches, hydraulic pumps, valves and motors within the wind turbine. As wind turbine sizes increase to MW machines, it becomes even more important that they have a high availability rate, i.e. that they function reliably all the time.
        It is possible to monitor or set somewhere between 100 and 500 parameter values in a modern wind turbine. The controller may e.g. check the rotational speed of the rotor, the generator, its voltage and current. In addition, lightning strikes and their charge may be registered. Furthermore measurements may be made of of outside air temperature, temperature in the electronic cabinets, oil temperature in the gearbox, the temperature of the generator windings, the temperature in the gearbox bearings, hydraulic pressure, the pitch angle of each rotor blade (for pitch controlled or active stall controlled machines), the yaw angle (by counting the number of teeth on yaw wheel), the number of power cable twists, wind direction, wind speed from the anemometer, the size and frequency of vibrations in the nacelle and the rotor blades, the thickness of the brake linings, whether the tower door is open or closed (alarm system).
        Moreover, it should be noted that the controller also looks after the power quality of the current generated by the wind turbine.

Communicating with the outside world
        The controller communicates with the owner or operator of the wind turbine via a communications link, e.g. sending alarms or requests for service over the telephone or a radio link. It is also possible to call the wind turbine to collect statistics, and check its present status. In wind parks one of the turbines will usually be equipped with a PC from which it is possible to control and collect data from the rest of the wind turbines in the park. This PC can be called over a telephone line or a radio link.

Internal communications
Optical communications controller         There is usually a controller both at the bottom of the tower and in the nacelle. On recent wind turbine models, the communication between the controllers is usually done using fibre optics. The image to the right shows a fibre optics communications unit. On some recent models, there is a third controller placed in the hub of the rotor. That unit usually communicates with the nacelle unit using serial communications through a cable connected with slip rings and brushes on the main shaft.

Fail safe mechanisms and redundancy
        Computers and sensors are usually duplicated (redundant) in all safety or operation sensitive areas of newer, large machines. The controller continuously compares the readings from measurements throughout the wind turbine to ensure that both the sensors and the computers themselves are OK. The picture at the top of the page shows the controller of a megawatt machine, and has two central computers (we removed the cover on one of the two computers to show the electronics).

Control strategies
        Many of the business secrets of the wind turbine manufacturers are to be found in the way the controller interacts with the wind turbine components. Improved control strategies are responsible for an important part of the increase in wind turbine productivity in recent years.
        An interesting strategy pursued by some manufacturers is to adapt the operational strategy to the local wind climate. In this way it may e.g. be possible to minimise uneconomic tear and wear on the machine during (rare) periods of rough weather.

Electromagnetic Compatibility (EMC)
Radiation free room        There are very powerful electromagnetic fields around power cables and generators in a wind turbine. This means that the electronics in the controller system has to be insensitive to electromagnetic fields. Conversely, the electronics should not emit electromagnetic radiation which can inhibit the functioning of other electronic equipment.
         The image to the left shows a radiation free room with metal walls in the laboratory of one of the largest wind turbine controller manufacturers. The equipment in the room is used to measure electromagnetic emissions from the components of the controllers.