Operation of Grid-Connected DFIG Under Unbalanced Grid Voltage Condition

Towards a time-domain modeling framework for small-signal analysis of unbalanced microgrids

“…First, the waveforms x abc,i (t) and x abc,i (t−τ ) are transformed into αβγ-coordinates via the Clarke transformation. Second, in αβγ-coordinates the positive and negative sequences are extracted via the "signal delay cancellation" approach as employed in [23]- [25]. The third and final transformation step consists of transforming the obtained positive and negative sequences into dq0 coordinates via the standard dq0-transformation.…”

“…To overcome this problem and inspired by [23]- [25], we employ a 3-step coordinate transformation based on the "signal delay cancellation" approach to represent the electrical waveforms in their respective positive and negative synchronous reference frames. To the best of our knowledge, this transformation has thus far only been used for control design under unbalanced conditions, see [23]- [25], but not-as in the present casefor the derivation of microgrid models suitable for smallsignal analysis. We remark that, in addition to microgrids, the approach can equivalently be applied to other types of unbalanced nonlinear power networks on both the distribution and the transmission level.…”

Control& Implementation of Fuzzy Based DFIG Wind Power Generators in Unbalanced Microgrids

“…The existing unbalanced vector control schemes for DGs conventionally use two pairs of individual controllers for the positive and negative sequence components of unbalanced currents [12]- [15]. Tuning of these controllers due to the delays of the decomposing positive/negative sequences filters often requires complex algorithms in unbalanced vector control schemes [14], [15].…”

“…However, under unbalanced voltage condition, auxiliary control loops using negative sequences quantities must be added to the conventional vector speed controllers which form an extended unbalanced vector control scheme [7], [17]. Figure 2 shows details of the unbalanced vector control scheme for the rotor-side converter [12], [13]. This control strategy mitigates the torque pulsations and the grid unbalanced effects on the generator via independent control of the stator real/reactive power components, p * s and q * s. The sequential…”

Simplified Modeling of a DFIG for Transient Studies in Wind Power Applications

“…The fifth-order model of DFIG-based WTs has extensively been used to study its behavior under generic conditions, as demonstrated in [27]- [30]. However, this kind of model gives rise to a complicated system that does not enable carrying out a simple analytical study of the DFIG under transient conditions.…”