Direct power control of doubly fed induction generator based on extended power theory under unbalanced grid condition

Abstract

Conventional table-based direct power control (DPC) achieves quick dynamic response with very simple structure, which has been widely studied for power control of doubly fed induction generator (DFIG) system. However, DPC presents high steady power ripples and rich current harmonics with variable switching frequency. Furthermore, it would produce highly distorted stator current and power oscillations under unbalanced grid voltage conditions if no special measure is taken. This paper proposes a novel DPC method to solve the problems above. On one hand, it uses space vector modulation (SVM) to synthesis the rotor voltage reference, which is obtained based on the principle of deadbeat power control. As a result, the switching frequency is constant and the power ripples as well as current harmonics are significantly reduced. On the other hand, it uses extended power theory to replace the conventional instantaneous power theory, which can achieve autonomous active power ripple elimination in the stator side with sinusoidal stator currents even under unbalanced grid voltage condition. The positive/negative sequence extraction of stator voltages and currents are not required, which further simplifies the structure of system. The effectiveness of the proposed method is validated by the presented simulation results from a 15 kW DFIG system.