Initial study of using rechargeable batteries in wind power generation with variable speed induction generators

There is a possibility of having a small rechargeable battery bank consisting of one or two groups of batteries inside a wind turbine tower. This paper investigates such a possibility for wind turbines using double fed induction generators (DFIGs). Two schemes are proposed. The first scheme, BS1, uses rechargeable batteries as an energy source/sink for the control of generator rotor currents. The second scheme, BS2, in addition to the batteries under BS1, has another group of batteries to smooth wind turbine power output and to provide power balancing and emergency support to the grid. A case study is used to evaluate these two schemes. The study is based on the statistics of the wind speeds measured at Dunstaffnage, Scotland, and the manufacturer´s data for the turbine generator. It shows that if the proposed BS2 scheme is adopted and some mild assumptions are used in simulation: (1) variation of the turbine power output to the grid is reduced ´ the variation of the output of a wind farm is within 13´ of the combined ratings of all turbines in the farm; (2) less variation in power also means smoother currents and reduced I ² R loss - for some cables in the wind farm plant this is a reduction of more than 53-; (3) requirements or ratings of some equipment can be reduced - the capacitor and filtering circuits for the DC bus are no longer required and the ratings of some transformers can be reduced; (4) some complicated control can be simplified - the control for the grid-side converter under the current -DFIG scheme- is replaced by a simple battery charging/discharging algorithm; (5) the wind turbine plant will be more supportive to the grid; and from the grid point of view, the performance of the wind farms adopting the proposed BS2 scheme will be similar to and in certain aspects even better than that of power plants using fossil fuels; and (6) all the above will bring some economic benefits at the expense of some additional costs associ- - ated with using batteries. Some practical issues, including available space in a typical turbine tower, are also discussed. The simulation results presented, however, are limited to steady-state models. Further research will include the type of batteries to be used, more detailed dynamic studies and quantified analysis of economic benefits and costs.