Direct Power Control Techniques for Doubly-Fed Induction Generator Driven by Small Hydro Turbine

Abstract

This thesis presents a direct power control techniques for the doubly-fed induction generator driven by small hydro turbine. The doubly-fed induction generator system uses the back-to-back three-level neutral point clamped voltage source converter, which is controlled by the voltage vector control. The objective of the proposed control scheme is to control the active and reactive power delivered to the utility grid. The rotor-side converter is controlled for the independent rotor current control of the stator active and reactive power of generator. The control scheme for the grid-side converter is to keep the dc-link voltage constant and makes available active and reactive power to the utility grid. In addition, a novel modified carrier-based pulsedwidth modulation strategy for the proposed converter has been proposed. This technique uses only single triangular carrier wave, which is employed for generating the gating pulses in the proposed converter. This significantly simplifies the modulation strategy. The simulation results for 1 kW generator system validate the proposed topology and control scheme. The performance simulations show that this control strategy yields a good dynamic responses and high accuracy to the active and reactive power control for both sub-synchronous and super-synchronous speed operations.