The management aim for a wind power system is to ensure that the system achieves the best energy yield from the prevailing wind conditions at the respective location. This requires that the wind power system (WPS) is operated by the control system at the highest possible level of efficiency in every operating condition without leaving the specified operating range of the WPS. In addition to these commercial requirements, the operation of the WPS must also ensure that dangerous operating conditions are recognised early enough and that the WPS control system acts appropriately to avoid dangers to the environment and the system that could arise from malfunctions.
If necessary, the system behaviour can be continuously monitored via remote data and on-site monitoring and interventions implemented in the WPS control system.
However, the control system must implement the control parameters of the system fully automatically during normal system operation in order to dispense with operating personnel as much as possible.
The specifications for the system control result from the wind behaviour and these specifications must also be noted by the operator. To do this e.g. requirements are determined via the network.
As the wind levels can to some extent fluctuate widely, the requirements for the control system are correspondingly high. It must be ensured that the system components are not subject to impermissible loads from wind gusts, wind turbulence or influences from the grid network as these can lead to early wear or even the failure of components.
A wind power system with blade adjustment can, in normal cases, react better to such fluctuations than a system with fixed blade angles; this however means that the control system requirements are correspondingly higher due to the complexity of the various influences.
The monitoring and automatic control of rotor speed and the power output are significant for the secure control of the system.
The speed and output control in wind power systems with blade adjustment (pitch systems) is generally implemented with the blade angle used as the main control parameter. The blade angle in these systems controls how the wind energy is transferred to the rotor.
Systems without blade adjustment (stall systems) do not have active speed and power control. The flow separation at the rotor blade in these kinds of systems creates a passive, aerodynamic output limitation. Speed regulation is then implemented via the network.
Numerous parameters must be recorded and processed by the WPS control system in order to securely control the WPS: These include, amongst others:
Modern wind power systems mainly use drag devices, so-called "cup anemometers" to determine the wind speed, while the wind direction is detected with a wind vane. These parameters can also be recorded with ultrasonic sensors. The wind speed measured in this way is mainly significant in the start-up phase for the control of large wind power systems. Today, the rotor is used by the control system as a wind measuring system during output operation because the anemometer is subject to too many interference factors during system operation. The rotor, gear and generator speeds are recorded by appropriate sensors and transmitted to the control system.
The following control variables (amongst others) of the system are controlled by the control system when a pitch system is operated:
Based on the position of the measured blade angle, the blade adjustment system (pitch drive) or the control system of the system orientation (azimuth drive) obtains data from the control system to operate the system within the specified working range.
The problem with pitch drive is that the three blades have the same blade angle and the blade adjustment is implemented at the same rate.
If this cannot be ensured, the aerodynamic imbalance can lead to loading of the components in the drive train. These components are the rotor hub, main shaft, main bearing, gears, coupling and generator, all of which react with increased wear to such loads.
The problem with azimuth drives is to ensure that the control system is, on the one hand, sufficiently slow and maintains the system in position, but on the other hand to ensure that the system is positioned precisely in the wind to achieve the correct air flow over the rotor blades.
The control system must therefore differentiate between various operating conditions when operating the wind power systems in order to correctly process the recorded measurement parameters.
In a pitch-controlled system, the following operating conditions can be differentiated (amongst others):
During the above operating conditions, the system control records all parameters and compares them with the specifications. If there are any deviations, interventions are implemented according to the algorithms stored in the control system. If the WPS control system cannot correct the deviation, the control system generates an error message to inform the operator about the deviation. The WPS is stopped by the control system if there are any safety-relevant deviations from the standard conditions. The error messages are recorded by the system software and can be automatically sent to the operator in various formats, read out from the remote system monitor or directly analysed by the system processor.
The operator can then monitor and analyse the operation of the system without having to be constantly present at the system. The operator has the ability to intervene directly in the system control in order to optimise system operation and change settings.
The ability to read out and analyse the recorded system variables also means that the system operation can be improved, error sources minimised and special local conditions taken into account so that the availability and economic efficiency of the system can be improved.
It is necessary that the systems are regularly checked during maintenance for the economic operation of the system. The individual system components are checked at regular intervals in order to record and maintain the condition of the components and replace worn or defective components where necessary. The aim is to avoid unplanned malfunctions and related servicing requirements and profit losses as far as possible to maintain the technical availability of the wind power system at the highest levels.
The recorded system parameters from the control system are also useful here as e.g. worn assemblies can be detected through their increasing appearances in the error statistics and so be replaced during maintenance activities.
The early detection of damage is further increased by the additional use of systems for monitoring wear conditions. These systems mean that the system maintenance can then be based on replacing the components dependent on their condition and not simply for preventative purposes. This enables more effective planning with shorter standstill times for e.g. replacement of larger components thereby helping to improve the commercial results.