A stratified method to transient stability assessment in large-scale power systems based on mutual information theory and artificial intelligence algorithm is proposed in this paper. A set of inter-complementary dynamic stability features are picked up one by one through the maximum-relevance minimum-redundancy (MRMR) algorithm. Besides, multiple extreme learning machines (ELMs) are trained based on the generated feature datasets. Because of the high requirement of evaluation speed in practical application, in order to balance the contradiction between assessment speed and accuracy, a hierarchical assessment structure is adopted in the final assessment process. Different ensemble classifiers with different response times are trained to construct different layers. The performance of the proposed technique is tested in the IEEE-39 bus system and a practical 1648 bus system provided by PSS/E. The experimental results indicate that, compared to other traditional methods, the proposed hierarchical method can give a more accurate result in a shorter period of time. As an efficient method, it is suitable for on-line transient stability assessment.

Millimeter-wave (mmWave) networking represents a core technology to meet the demanding bandwidth requirements of emerging connected vehicles. However, the feasibility of mmWave vehicleto-everything (V2X) connectivity has long been questioned. One major doubt lies in how the highly directional mmWave links can sustain under high mobility. In this paper, we present the first comprehensive reality check of mmWave V2X networks. We deploy an experimental testbed to mimic a typical mmWave V2X scenario, and customize a COTS mmWave radio to enable microscopic investigation of the channel and the link. We further construct a high-fidelity 3D ray-tracer to reproduce the mmWave characteristics at scale. With this toolset, we study the mmWave V2X coverage, mobility and blockage, codebook/beam management, and spatial multiplexing. Our measurement debunks some common misperceptions of mmWave V2X networks. In particular, due to the constrained roadway network structures, we find the beam management can be handled easily by the often-denounced beam scanning schemes, as long as the codebook is properly designed. Blockage can be almost eliminated through proper basestation deployment and cooperation. Highly effective spatial multiplexing can be realized even without sophisticated MIMO radios. Our work points to possible ways to realize efficient and reliable mmWave networks under high mobility, while maintaining the simplicity of standard network protocols.

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