Simulation of a Hybrid System Wind Turbine-Battery-Ultracapacitor.

Abstract

In order to improve the predictability of power generation from wind, short term energy storage in batteries combined with ultra capacitors (UCaps) is proposed. The system is simulated with SIMULINK and contains detailed models of a lead acid battery pack and a simple model of the UCap bank. The wind energy conversion system (WECS) is simulated by measured time series with a time resolution of one second.

The objective of the simulation is to determinate the system configuration that is able to guarantee a predictable energy output to the grid during a given time interval. Within this time, the storage system should be able to compensate all type of rapid changes originated by wind speed fluctuations. Another important issue is the integration of an ultra capacitor bank. It is investigated its influence on the charge and discharge stress of the battery.

It is demonstrated that quick changes in wind power generation can be covered by a reasonable size of battery capacity for a prediction time interval of 10 min. Very short transients in energy flow (1-10 s) are absorbed by the UCap bank which minimizes the deterioration of the battery because important current peaks do not reach the battery.

The final system design is based on measurements at a 600 kW constant speed WECS. Its typical, very sharp changes in power output (more than 200 kW/s possible) are smoothed by a 500 Ah lead acid battery with 300 cells in series (voltage range: 480 – 720 V). In parallel to the battery a 10 F UCap bank is connected. To hold 720 V, the bank consists of 240 UCaps connected in series (3 V / 2400 F each).