STATCOM Control for Integration of Wind Farm to the Weak Grid

This paper focuses on the STATCOM modeling and nonlinear controller design for fast voltage regulation during the grid disturbance when the wind farm is integrated to a weak grid. A sliding mode inverse controller for the STATCOM connected at the PCC of the wind farm is proposed. It utilizes the inverse system theory to form a pseudo-linear system of the STATCOM. Then the variable structure sliding mode control, with the feature of insensitivity to parameters variation, could be implemented to enhance the system robustness. The comprehensive control scheme could maintain the dc-link voltage of STATCOM and rapidly regulate the ac voltage at PCC to its reference by injecting the reactive current, so as to enhance the voltage stability of wind farm during the transient response. Simulation in PSCAD/EMTDC verified that the STATCOM with the controller proposed can reduce the voltage drop experienced by the wind farm by providing dynamic reactive power support, thus improving the fault ride-through capability of the wind farm.published_or_final_versio

Necessary and sufficient conditions for local creation of quantum discord

We show that a local channel cannot create quantum discord (QD) for zero QD states of size $d\geq3$ if and only if either it is a completely decohering channel or it is a nontrivial isotropic channel. For the qubit case this propertiy is additionally characteristic to the completely decohering channel or the commutativity-preserving unital channel. In particular, the exact forms of the completely decohering channel and the commutativity-preserving unital qubit channel are proposed. Consequently, our results confirm and improve the conjecture proposed by X. Hu et al. for the case of $d\geq3$ and improve the result proposed by A. Streltsov et al. for the qubit case. Furthermore, it is shown that a local channel nullifies QD in any state if and only if it is a completely decohering channel. Based on our results, some protocols of quantum information processing issues associated with QD, especially for the qubit case, would be experimentally accessible.Comment: 8 page