An innovative control strategy is proposed for enhancing the low voltage ride-through (LVRT) capability of a doubly fed induction generator based on wind energy conversion systems (DFIG-WECS). Within the proposed control method, the current control loops of the rotor side converter (RSC) are developed based on passivity theory. The control scheme for the grid side converter (GSC) is designed based on a two-term approach to keep the DC-link voltage close to a given value. The first term based on the maximal voltage of GSC is introduced in the GSC control loops as a reference reactive current. The second one reflecting the instantaneous unbalanced power flow between the RSC and GSC is also introduced in the GSC control loops as a disturbance considering the instantaneous power of the grid filter to compensate the instantaneous rotor power. The effectiveness of the proposed control strategy is verified via time domain simulation of a 2.0 MW-575 V DFIG-WECS using PSCAD/EMTP. Simulation results show that the control of the DFIG with the proposed approach can improve the LVRT capability better than with the conventional one.

SUMMARYThe increase of the scale and complexity of interconnected power systems leads to power system oscillations. Therefore, the electric network needs to be improved to be more stable. One type of flexible AC transmission system devices, namely, the thyristor-controlled series compensator (TCSC), can be placed in the transmission line to increase stability margins and dampen power oscillations by means of adjusting the impedance of the compensated line. The efficiency and robustness of TCSC controller depend on its optimal location in network. Hence, finding the optimal placement for TCSC has become a key issue. In this paper, a novel method based on a two-step approach is proposed to find the optimal location for TCSC. First, the energetic approach based on the combination of the controllability Gramian with the balanced realization reduction technique is applied to search feasible locations, and then the transient stability analysis is performed to compare and determine the optimal location through various test cases. The effectiveness of the proposed method has been demonstrated on the IEEE 39-bus England network.

Thyristor controlled series capacitors (TCSC)