Abstract:

Wind turbines equipped with a doubly-fed induction generator have extra capability of power factor correction. Many control schemes have been proposed for how to govern the operation of DFIG. A test-bed to examine and evaluate these schemes is very valuable. This presentation is about a 2 kW test-bed that can be employed for both training and research. A variable speed motor serves as the prime mover for a generator, simulating the power captured by a wind turbine. The generator has wound-rotor, with a 1:1 ratio. Similar to industrial wind turbines equipped with DFIG, the rotor of the generator is connected to the grid by a back-to-back IGBT pair. When the motor speed is lowered below the synchronous speed, which represents a drop in wind power, the controller must adjusts the current injected to the generator rotor winding, so that the generator continues to deliver electricity at the same frequency and voltage level. This implies that the IGBT connected to the grid behaves as a rectifier and the IGBT connected to the rotor performs as an inverter. When the motor speed is raised above the generator synchronous speed, the controller must switch the functions of the two IGBT s. In this case the low frequency electricity from the rotor is converted to a higher frequency suitable to be injected to the grid. How much current is to be provided to the rotor or taken from it, is determined by the controller, through a computer program and based on a particular control scheme.