Tidal generation takes place in locations where the boundary conditions for electrical power transmission are challenging: In most cases, there is no surface-breaking structure permitted, all equipment has to be located on the seabed; the distance from turbine to shore is in the range of 1 to 5 km. For a single turbine, there has to be a submarine cable over the full distance. For an array of tidal turbines, there is the option to have one or more connection points near or at the turbines and thereby to reduce the length of installed submarine cables. In order to use the turbine with good hydraulic efficiency, the turbine speed has to be adjusted to the changing tidal flow. Therefore, a converter is needed between generator and grid connection to provide the generator with the frequency appropriate for the turbine speed. A converter usually consists of two inverters and a DC link in between. In reference to the converter, the connection for the tidal array can be placed either between converter and turbine or between converter and grid or on the DC link. Additionally, the generator can be designed as induction generator or as permanent magnet generator, the latter allowing the use of diode rectifier or thyristor rectifier as turbine inverter. Combining all the options for the generator, for the position of the connection point and for the converter design, there are many possible array setups, which have to be evaluated using the following criteria: control performance, stability in respect to turbulent flow, availability of components, estimation of risks and costs. The array setup resulting out of the evaluation is a system with a diode rectifier on each turbine generator, a DC connection point, a DC cable to shore and an inverter on shore. The race for the best tidal turbine design is open and ongoing, but not decided yet. The race for the best tidal array design is about to start. The road which is taken by many competitors for the turbine design is changing to a poorly paved path or even a dead end, when it comes to interconnected arrays. The choice is either to stay on the nice road without moving on to interconnected arrays by multiplying single turbine setups, accepting the cost of a long sub-sea cable connected to each turbine.
Connecting an array of tidal turbines to the grid
2012
10 Seiten, 6 Bilder, 5 Quellen
Conference paper
English
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