Commutation failure is a common fault for HVDC transmission systems. The DC overcurrent induced during commutation failure not only endangers equipment safety but also threatens the system stability. ...In this paper, a reduced-order system model that can accurately describe the overcurrent dynamics during commutation failure in AC-DC system is first established using a singular perturbation method. Then a regular perturbation method is suggested to obtain the time-domain analytical solution for overcurrent estimation based on the reduced-order weak nonlinear system. A parametric study is further provided with phase portrait, showing how the equivalent reactance of AC system and relevant parameters of HVDC itself can affect the overcurrent caused by commutation failure, and how voltage stability is affected. The proposed overcurrent estimation method and qualitative analysis results are verified using several AC-DC test systems including an actual 177-machine provincial power system in China.
A simple yet effective semi-supervised method is proposed in this paper based on consistency regularization for crowd counting, and a hybrid perturbation strategy is used to generate strong, diverse ...perturbations, and enhance unlabeled images information mining. The conventional CNN-based counting methods are sensitive to texture perturbation and imperceptible noises raised by adversarial attack, therefore, the hybrid strategy is proposed to combine a spatial texture transformation and an adversarial perturbation module to perturb the unlabeled data in the semantic and non-semantic spaces, respectively. Moreover, a cross-distribution normalization technique is introduced to address the model optimization failure caused by BN layer in the strong perturbation, and to stabilize the optimization of the learning model. Extensive experiments have been conducted on the datasets of ShanghaiTech, UCF-QNRF, NWPU-Crowd, and JHU-Crowd++. The results demonstrate that the proposed semi-supervised counting method performs better over the state-of-the-art methods, and it shows better robustness to various perturbations.
Although the flight control of quadrotor unmanned aerial vehicles have been widely studied, it is still very challenging to suppress multiple disturbances and efficiently utilize the inherent multi ...time-scale characteristics. As a well-known antidisturbance strategy, composite hierarchical antidisturbance control (CHADC) can compensate and attenuate disturbances simultaneously, thus enhancing the control performance of complex systems significantly. In the meantime, the singular perturbation theory (SPT) is employed to analyze the multi time-scale properties, and the original system is decomposed into the slow and fast subsystems. In this article, we present an antidisturbance control scheme based on the SPT and CHADC to enhance the capability of antidisturbance. A novel composite hierarchical antidisturbance (CHAD) predictor-corrector is proposed for the slow subsystem to integratively handle the disturbances from guidance and control perspective, and a CHAD <inline-formula><tex-math notation="LaTeX">{{H}_{\infty }}</tex-math></inline-formula> controller is employed for the fast subsystem subject to external disturbances and inertial uncertainties. Meanwhile, the compensability of disturbance is explicitly analyzed. Finally, experiments are carried out to validate the effectiveness of the proposed scheme.
Symmetry‐adapted perturbation theory (SAPT) is a well‐established method to compute accurate intermolecular interaction energies in terms of physical effects such as electrostatics, induction ...(polarization), dispersion, and exchange. With many theory levels and variants, and several computer implementations available, closed‐shell SAPT has been applied to produce numerous intermolecular potential energy surfaces for complexes of experimental interest, and to elucidate the interactions in various complexes relevant to catalysis, organic synthesis, and biochemistry. In contrast, the development of SAPT for general open‐shell complexes is still a work in progress. In the last decade, new developments from several research groups, including the author's, have greatly enhanced the capabilities of SAPT. The new and emerging approaches are designed to make SAPT more widely applicable (including interactions involving multireference systems, complexes in arbitrary spin states, and intramolecular noncovalent interactions), more accurate (enhanced description of intramolecular correlation, a better account of exchange effects, relativistic SAPT, and explicitly correlated SAPT), and more efficient (enhanced density‐fitted implementations, linear‐scaling variants, empirical dispersion, and an implementation on graphics processing units). The new developments open up avenues for SAPT applications to an unprecedented variety of weakly interacting complexes.
This article is categorized under:
Electronic Structure Theory > Ab Initio Electronic Structure Methods
Electronic Structure Theory > Density Functional Theory
Molecular and Statistical Mechanics > Molecular Interactions
Most important concepts reviewed in this work, shaped into a noncovalently interacting complex.
A multiplicative perturbation M of a matrix T has the form
, where E and F are square matrices. It is proved that every acute perturbation is essentially a strong perturbation, which is a type of ...multiplicative perturbation. It is also proved that for every multiplicative perturbation
is a strong perturbation if and only if it is a weak perturbation and is rank-preserving. Some norm equations for the Moore-Penrose inverse are derived in the framework of the weak perturbation, through which some norm upper bounds for
are obtained. As an application, the perturbation estimation for the solution to the least squares problems is provided. The sharpness of the newly obtained upper bounds are illustrated by several numerical examples.
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