Large-scale use of wind power raises many questions in integration into the existing electric power grid. Wind power is an intermittent energy source which must be used when available. If a large fraction of a system's energy is to come from wind power, provisions must be made to supply load during days with low wind. These provisions might take the form of spinning reserve already allocated in the system, start-up of stand-by power plants, or interconnections to other areas that can take up the load.
Aim:
The purpose of this study is to further develop an understanding of wind power plant system by evaluating the performance, synchronization and interconnection to grid and problem occurring in this process.
The objectives for this report are to:
- Wind Forecasting
- Wind Plant Performance Characterization
- Grid Planning
- Grid Operational Impact Analysis
- Outreach and Education
- Integration of Wind Energy and Hydropower Technologies
Advantages of Indirect Grid Connection: Variable Speed
The advantage of indirect grid connection is that it is possible to run the wind turbine at variable speed.
The primary advantage is that gusts of wind can be allowed to make the rotor turn faster, thus storing part of the excess energy as rotational energy until the gust is over. Obviously, this requires an intelligent control strategy, since we have to be able to differentiate between gusts and higher wind speed in general. Thus it is possible to reduce the peak torque (reducing wear on the gearbox and generator), and we may also reduce the loadson the tower and rotor blades. The secondary advantage is that with power electronics one may control reactive power (i.e. the phase shifting of current relative to voltage in the AC grid), so as to improve the power quality in the electrical grid. This may be useful, particularly if a turbine is running on a weak electrical grid.
Theoretically, variable speed may also give a slight advantage in terms of annual production, since it is possible to run the machine at an optimal rotational speed, depending on the wind speed. From an economic point of view that advantage is so small, however, that it is hardly worth mentioning.
Disadvantages of Indirect Grid Connection
The basic disadvantage of indirect grid connection is cost. As we just learned, the turbine will need a rectifier and two inverters, one to control the stator current, and another to generate the output current. Presently, it seems that the cost of power electronics exceeds the gains to be made in building lighter turbines, but that may change as the cost of power electronics decreases. Looking at operating statistics from wind turbines using power electronics (published by the the German ISET Institute), it also seems that availability rates for these machines tend to be somewhat lower than conventional machines, due to failures in the power electronics.
Other disadvantages are the energy lost in the AC-DC-AC conversion process, and the fact that power electronics may introduce harmonic distortion of the alternating current in the electrical grid, thus reducing power quality. The problem of harmonic distortion arises because the filtering process mentioned above is not perfect, and it may leave some "overtones" (multiples of the grid frequency) in the output current.
1. What are battery bank storage systems?
2. How do battery banks work?
3. How are battery banks installed?
4. What variations are there in battery banks?
5. What are the main aims, objectives or key research questions of this proposed study?