Self-excitation system for control of wind turbine driven induction generator using direct torque control

Abstract

This paper describes the direct torque and flux control (DTC) of a self-excited induction generator (SEIG) for wind energy conversion systems (WECS). The DTC-based WECS is more suitable for low power applications, owing to several advantages such as good torque control in steady-state and transient operating conditions, not requiring an accurate generator model, the absence of coordinate transforms and current controllers. The SEIG is excited by a voltage source converter (VSC) with a capacitor and start-up battery on the direct current (DC) side. The required reactive power for the SEIG is provided by the capacitor. The terminal voltage of the SEIG varies with wind speed and load conditions. The proposed DTC strategy is used to control the terminal voltage of the SEIG and DC voltage at a constant value when the load and wind speed are varied. The gate signals for the VSC are derived from an inverter switching table. The torque and stator flux of the induction generator are controlled through the voltage space vector selection. The proposed system gives good dynamic and steady-state performance. The effectiveness of the proposed control strategy is verified through simulations. Experimental results are presented to validate the simulation results.