Analysis of SeaWiFS data off Northwest Borneo reveals coastal chlorophyll bloom extending more than 200km to deep South China Sea during winter. A combination of remote sensing products is used to ...untangle its statistical relation with various forcing factors. River discharge rate is estimated from satellite measurements of land rainfall, and surface chlorophyll over the middle shelf is shown to vary with river discharge and lag by one month. Strong (weak) chlorophyll blooms tend to occur in La Niña (El Niño) years. The study provides evidence that river runoff from maritime continent has major influence on equatorial ocean color.
•River discharge rate from Northwest Borneo is estimated by satellite measurements of land rainfall.•Surface chlorophyll blooms in winter extend over 200km to deep SCS and lag river discharge by 1–2 months.•Intensity of winter chlorophyll bloom is anti-correlated with ENSO index and monsoon strength.•River discharge provides nutrient to chlorophyll bloom and causes interannual variation of ocean color in the equatorial SCS.
Intrusion Detection for Cybersecurity of Smart Meters Sun, Chih-Che; Sebastian Cardenas, D. Jonathan; Hahn, Adam ...
IEEE transactions on smart grid,
2021-Jan., 2021-1-00, 20210101, 2021-01-01, Volume:
12, Issue:
1
Journal Article
Peer reviewed
Open access
The integration of Information and Communications Technology (ICT) enables real-time communication for smart meters to participate in power system operations. However, Advanced Metering ...Infrastructures (AMI) are vulnerable to cyber attacks. Both utilities and power consumers may become victims of cyber intrusions. In this paper, a two-stage cyber intrusion protection system is proposed. At the first stage of intrusion detection, a Support Vector Machine (SVM) is used as a detection algorithm to discover suspicious behaviors inside a smart meter. At the second stage, the Temporal Failure Propagation Graph (TFPG) technique is used to generate attack routes for identifying attack events. Finally, the proposed pattern recognition algorithm is used to calculate the similarity between a detected abnormal event and pre-defined cyber attacks. A higher similarity value implies a higher chance that a smart meter is under attack. An AMI security test platform has been developed to: (1) Collect training/testing data for SVM, (2) Simulate and analyze cyber attack events, and (3) Validate the proposed cyber attack protection system. The test platform consists of Network-Simulator 3 (NS-3) software to simulate an AMI network environment and single board computers (SBCs) to emulate the IEEE 802.15.4 communication between a grid router and a smart meter.
This article investigates the voltage monitoring and control feature for smart meters and identifies the impact of this feature on both power distribution and communication systems. Regarding the ...voltage monitoring, a cosimulation platform is developed using GridLAB-D and ns-3 to analyze the impact of adding voltage measurements to smart meter readings and assess the mitigation strategies for reducing timeout errors and packet drops of smart meter data. Regarding the voltage control, a new voltage stability control scheme is developed, which applies the voltage stability margin as the control objective, instead of the traditional voltage magnitude. The proposed control scheme makes use of existing advanced metering infrastructure and distributed energy resources (DERs), requiring small marginal costs. It is indicated that integrating the voltage monitoring and control feature, smart meters could enable the voltage stability issues being solved at end-user sides, i.e., the "last-mile" segment. It is also implied that the new feature could support the coordination of the local and system-level voltage controls using both customer-owned and utility-scale DERs.
Today's power distribution system is changing to a power-electronics-enabled distribution system, especially with the increasing penetration of distributed energy resources (DERs). To monitor and ...manage those electronic devices and DERs at the grid edge, the advanced metering infrastructure (AMI) with two-way communications presents great potential. At present, extensive research explores the upstream communication from smart meters to electric utilities (e.g., meter reading) but few examine the downstream communication from the utilities to smart meters (e.g., meter pinging). This paper discusses the AMI two-way communication and its recent industrial practice in the U.S., especially for applying the smart meter pinging functionality to monitor grid-edge devices and DERs. This paper then develops the two-way communication model and the network calculus method to quantify the impact of the two-way communication on the AMI network. In the end, the proposed method is validated with ns-3 simulation using the modified 13-node test feeder and real-world feeder systems.
Recent studies of pseudo-plane ideal flow (PIF) reveal a ubiquitous presence of vortex alignment in both homogeneous and stratified fluids, and in both inertial and rotating reference frames as well. ...The exact solutions of a steady-state PIF model suggest that stagnation points tend to be vertically aligned and the concentric structure represents a fixed-point phenomenon of the Euler equations. Exception occurs in the rotating frame when a flow holds inertial period and skew center becomes possible. Properties of stagnation points based on Morse theory are obtained, leading to a topological explanation of vertical alignment via pressure Hessian. The study thus uncovers a new aspect of vortex behavior in ideal fluid that requires vortex center to align with the direction of gravity when vortex evolution reaches a laminar end state characterized by steady pseudo-plane velocities. Though the phenomenon arises from the constraint of the Euler equations, under specific conditions the topological theory is applicable to viscous fluid and explains the curvilinear tilting of von Kármán swirling vortex.
Modeling of Wind Farm Participation in AGC Chang-Chien, Le-Ren; Sun, Chih-Che; Yeh, Yu-Ju
IEEE transactions on power systems,
05/2014, Volume:
29, Issue:
3
Journal Article
Peer reviewed
Wind power has become one of the most prominent renewable energy applications in the power industry. Its annual installation is continuously setting a record high. Due to the large portion of ...generation mix within the system, it is desirable to operate wind power under the automatic generation control (AGC). This issue also raises another concern on the modeling of wind farms under AGC. The traditional way of portraying wind farm production in simulation is to use an aggregated wind turbine model that is generally operated in maximum power point tracking (MPPT). This approach is not suitable for wind's participation in AGC. Therefore, more studies should be done to investigate how the individual wind turbines affect the wind farm performance under the set-point operation. This paper first illustrates the controllability of wind turbines under the set-point control. Following that, a comprehensive guidance of wind generator modeling is demonstrated to yield different approaches for developing the wind farm model. Two types of wind farm models are derived and demonstrated to portray the capability of set-point tracking under the intermittent wind condition. Associated simulations are presented and compared to show the different characteristics of these two wind farm models in depicting the set-point operation under AGC.
In this contribution, we provide a synthesis of results to date describing uptake and mass transport of water, vanadium species and protons in Nafion membranes for use as separators in VRFBs. ...Resistance issues as well as species cross-over are important contributors to performance loss in VRFBs. After a brief discussion of our state-of-the-art cell performance, we consider the uptake and transport of various species through a number of membrane materials. We draw together numerous previous studies and augment them with new data to provide a summary of our present state of understanding of the experimental facts regarding membrane behavior.
This work demonstrates a quantitative method to determine the hydrogen evolution rate occurring at the negative carbon electrode of the all vanadium redox flow battery (VRFB). Two carbon papers ...examined by buoyancy measurements yield distinct hydrogen formation rates (0.170 and 0.005 mu mol min-1 g-1). The carbon papers have been characterized using electron microscopy, nitrogen gas adsorption, capacitance measurement by electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). We find that the specific electrochemical surface area (ECSA) of the carbon material has a strong influence on the hydrogen generation rate. This is discussed in light of the use of high surface area material to obtain high reaction rates in the VRFB.
Quaternary ammonium functionalized Diels–Alder poly(phenylene)s (QDAPPs) with different ion exchange capacities (IECs) are examined as membranes in all-vanadium redox flow batteries. QDAPP membrane ...behavior is compared to a standard, Nafion 212, in measurements of cycling efficiencies, areal specific resistance (ASR), vanadium permeation and durability. The IEC of the QDAPPs clearly shows an impact on the cell ASR and vanadium crossover. The results imply a trade-off between performance, indicated by cell voltage loss at a given current density, and rate of cross-over driven capacity loss in the system. Among the membranes studied, QDAPP with moderate IEC represents the best trade-off of these factors and exhibits higher performance and lower capacity loss compared to Nafion 212. All QDAPP membranes are found to be more durable than the analogous cation exchange membrane, sulfonated DAPP (SDAPP), in V5+ solution.
•Quaternary ammonium functionalized poly(phenylene)s are studied for flow batteries•Membrane Ion Exchange Capacity controls conductivity, vanadium cross-over•Optimized QDAPP membrane exhibits high selectivity for use in VRFB•High energy efficiency and low capacity decay observed relative to Nafion
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