Control strategy of doubly fed induction generators for a wind diesel energy system

This paper presents a new control structure for a variable speed wind diesel energy system based on doubly-fed induction generators to provide energy to an isolated load. Both generator rotor currents are controlled using an indirect vector scheme approach using a d-q reference frame with the d-axis aligned with the stator flux. The scheme uses a common DC bus for the rotor side inverters and a stator side inverter to enable sub and super synchronous speed operation for both machines. The generator driven by the diesel engine regulates the stator flux magnitude and controls the q-axis rotor current in order to assure the orientation of the reference frame. The speed of the diesel engine is changed depending on the load in order to reduce the fuel consumption. The electrical torque of the generator driven by the wind turbine is controlled to track an optimum speed where maximum energy is extracted from the wind. Results are presented for load impacts and the tracking of the optimum speed both for the diesel and the wind energy system.