New orientation technique of aligned D-Q reference frame for controlling doubly-fed induction generators

Doubly-Fed Induction Generators (DFIG) control requires orienting the d-q reference frame in a specific position. The d-axis is aligned with the grid voltage vector in grid voltage orientation. Conventionally, a Phase-Locked Loop (PLL) scheme is used to determine the position of the voltage vector. However, if there is a disturbance in the rotational speed of the voltage vector-due to frequency changes or phase angle disturbances-the PLL will produce an unstable output, disrupting the control performance particularly if the PLL gains are not accurately tuned. This paper proposes a new orientation method to demonstrate its effectiveness and reliability under frequency and phase angle disturbances. The proposed control is independent of the PLL scheme. To validate the proposed orientation scheme, a complete experimental test bench for a small-scale DFIG system was built, utilizing two Texas Instruments dSPACE boards DS1104 and DS1102 to control the Rotor-Side Converter (RSC) and Grid-Side Converter (GSC), respectively. The proposed orientation method and the comprehensive control of the DFIG are evaluated. The system's performance under different operating conditions is examined to guarantee independent active and reactive power control. The results prove that operating without a PLL, the proposed orientation technique ensures stable and effective performance under frequency and phase angle disturbances. A performance comparison of the proposed orientation technique and PLL technique is also provided to validate the efficacy of the proposed orientation approach.