ABB's new Converter Generation for Megawatt Size Windturbines

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Increasing power of wind turbines, Multi Megawatt wind farms, Windpower replacing conventional power generation and thus consequently resulting in demanding requirements for installation and operation of wind turbines pose a new challenge to the energy conversion system associated with wind turbines. ABB's substantial market share in generators, combined with thorough expertise in power electronics systems led to the decision of entering this renewable energy segment, namely through providing whole drive trains consisting of generator and frequency converter set out of a single hand. This new focus is almost obvious, since ABB is already a well established supplier of industrial drives systems, which share close commonality with wind turbine generation.

The increasing demand for converters in wind turbines originates in the focus on variable speed systems. Variable speed is achieved through small converters, which compensate the slip of a double fed induction machine thus protecting the expensive gear box against the dynamics of gusty winds. A gearless direct drive system with low speed synchronous machines requires a converter rated for full power. Essential advantages of those systems directs ABB's focus on wind turbines with full-size converters based on IGCT (Integrated Gate Commutated Thyristor) technology, which are available on platforms from 1000 kW up to 5000 kW. The rather sturdy IGCTs are the better choice over IGBTs (Insulated Gate Bipolar Transistor) in terms of required number of components. For converters in the Megawatt range a medium voltage system is clearly preferable, and IGCTs are available in voltage ratings eliminating the need for series connection of semiconductors. The overall lowered parts count not only delivers a better efficiency, but also reduces operational costs such as maintenance and spare parts stocking.

ABB has devised a very cost aggressive concept to establish a very competitive position against turbine systems without converters. Both the life cycle cost and the cost and size of ancillary equipment have been accounted for. While some advantages, such as lower protection level, are favoring the common low voltage, mostly 690V, the resulting large currents for Megawatt ratings cause higher expenditures for bus work and installation. Medium voltage systems (ABB uses 3000 to 5000 Volts) substantially reduce cabling, the size of converters, the number of paralleled semiconductors, and finally requires less cooling because of lowered ohmic losses.

The major topic for the grid connection of windpower drives is Power Quality. ABB's R&D Centers are among the leaders when it comes to reduction of harmonics and high speed control of power flow from generator to grid, which has been demonstrated only recently. The converters are able to control speed and torque without speed sensors, and are capable of buffering power shocks through both the prop's inertia and the intermediate dc circuit. Operational comfort is even significantly enhanced through the ability of the converter to store energy during a short time grid loss.

The modularity of the converter systems allows different applications for both single turbine sets and combination in wind farms. The converter fits either into the nacelle or in the bottom of the tower, the latter for direct drive systems where nacelles are missing. In wind farms, several turbines share a single, common converter set in a dedicated housing. It is essential that only a medium voltage system that allows for this physical separation of generators and converters.

With advanced technology, brain power and long term market reputation, ABB is determined to become a leading supplier of State-of-the-Art converter systems at a very competitive price level. The first orders are approving a challenging strategy in the segment of Distributed Power Generation and Windpower.

Dipl.- Ing.(TH) Detlev Hillmann
Business Development Distributed Power
ABB Industrie AG
5300 Turgi/Switzerland

 

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