WINFIT - Superimposed Drive Train with Synchronous Generator for Wind Turbines
About three quarters of the installation investment of wind turbines contains the balance of plant, tower and rotor blades. The size of the tower and balance is directly depending on the weight of the nacelle. To reduce these costs, the weight needs to be decreased. Variable-speed drives give the best overall efficiency of the turbine, but a power converter with full power rating or a doubly-fed machine is required. In this project, a synchronous medium-voltage generator is directly connected to the grid and a superimposed gear with a small electrical drive is used for the speed variation of the turbine.
Currently a number of different concepts for variable-speed wind turbines are available on the market. The main concepts are doubly-fed induction generators and synchronous generators with full-power converters. The double-fed induction generator concept usually uses a converter that is designed to about 33% of the rated power. To be conforming to grid supply ordinances it must deliver the complete reactive power, so for wind turbines today it is designed for about 50% of the rated power, which makes it more cost intensive.
The drawbacks of the use of a low-speed synchronous generator exist mainly in the large overall volume of the full-scale converter and the maintenance of the system. The fulfillment of grid supply ordinances will need additional measures in this system to handle disturbances such as overvoltages and frequency swings. The proposed system has the advantage that the vast majority of the mechanical energy is passed to a standard synchronous generator, which is directly connected to the medium-voltage electric grid. To handle speed variability, e.g. in fluctuating wind conditions, the transmission is superimposed by a small electric drive system with about 10% of the rated power. A bi-directional converter topology ensures that the breaking energy of the electric drive can be fed into the supply grid.
Within the project a demonstrator will be constructed. The electric converter is built by PGS with standard industrial components with the focus on reliability. The design of the converter is completed and the components are being delivered to construct the demonstrator. Several safety functions are implemented and the design is made on modules that could be exchanged for maintenance or repair by a single person in the small area of a wind turbine.
The project is funded under the EFRE co-financed operational program for North Rhine-Westphalia under “Ziel 2 – Regionale Wettbewerbsfähigkeit und Beschäftigung 2007 - 2013".