Design and real-time implementation of data-driven adaptive wide-area damping controller for back-to-back VSC-HVDC

This paper proposes a data-driven adaptive wide-area damping controller (D-WADC) for back-to-back VSC-HVDC to suppress the low frequency oscillation in a large-scale interconnected power system. The proposed D-WADC adopts a dual-loop control structure to make full use of the active and reactive power control of VSC-HVDC to improve the damping of the power system. A data-driven algorithm named the goal representation heuristic dynamic programming is employed to design the proposed D-WADC, which means the design procedure only requires the input and output data rather than the mathematic model of the concerned power system. Thus, the D-WADC can adapt to the change of operating condition through online weight modification. Besides, the adaptive delay compensator (ADC) is added to effectively compensate the stochastic delay involved in the wide-area feedback signal. Case studies are conducted based on the simplified model of a practical power system and the 16-machine system with a back-to-back VSC-HVDC. Both the simulation and hardware-in-loop experiment results verify that the proposed D-WADC can effectively suppress the low-frequency oscillation under a wide range of operating conditions, disturbances, and stochastic communication delays

Genes related to apoptosis predict necrosis of the liver as a phenotype observed in rats exposed to a compendium of hepatotoxicants

<p>Abstract</p> <p>Background</p> <p>Some of the biochemical events that lead to necrosis of the liver are well-known. However, the pathogenesis of necrosis of the liver from exposure to hepatotoxicants is a complex biological response to the injury. We hypothesize that gene expression profiles can serve as a signature to predict the level of necrosis elicited by acute exposure of rats to a variety of hepatotoxicants and postulate that the expression profiles of the predictor genes in the signature can provide insight to some of the biological processes and molecular pathways that may be involved in the manifestation of necrosis of the rat liver.</p> <p>Results</p> <p>Rats were treated individually with one of seven known hepatotoxicants and were analyzed for gene expression by microarray. Liver samples were grouped by the level of necrosis exhibited in the tissue. Analysis of significantly differentially expressed genes between adjacent necrosis levels revealed that inflammation follows programmed cell death in response to the agents. Using a Random Forest classifier with feature selection, 21 informative genes were identified which achieved 90%, 80% and 60% prediction accuracies of necrosis against independent test data derived from the livers of rats exposed to acetaminophen, carbon tetrachloride, and allyl alcohol, respectively. Pathway and gene network analyses of the genes in the signature revealed several gene interactions suggestive of apoptosis as a process possibly involved in the manifestation of necrosis of the liver from exposure to the hepatotoxicants. Cytotoxic effects of TNF-α, as well as transcriptional regulation by JUN and TP53, and apoptosis-related genes possibly lead to necrosis.</p> <p>Conclusion</p> <p>The data analysis, gene selection and prediction approaches permitted grouping of the classes of rat liver samples exhibiting necrosis to improve the accuracy of predicting the level of necrosis as a phenotypic end-point observed from the exposure. The strategy, along with pathway analysis and gene network reconstruction, led to the identification of 1) expression profiles of genes as a signature of necrosis and 2) perturbed regulatory processes that exhibited biological relevance to the manifestation of necrosis from exposure of rat livers to the compendium of hepatotoxicants.</p

Resilience assessment for power systems under sequential attacks using double DQN with improved prioritized experience replay

The information and communication technology enhances the performance and efficiency of cyber-physical power systems (CPPSs). However, it makes the topology of CPPSs more exposed to malicious cyber attacks in the meantime. This article proposes a double deep-Q-network (DDQN)-based resilience assessment method for power systems under sequential attacks. The DDQN agent is devoted to identifying the least sequential attacks to the ultimate collapse of the power system under different operating conditions. A cascading failure simulator considering the characteristics of generators is developed to avoid a relatively optimistic assessment result. In addition, a novel resilience index is proposed to reflect the capability of the power system to deliver power under sequential attacks. Then, an improved prioritized experience replay technique is developed to accelerate the convergence rate of the training process for DDQN agent. Simulation results on the IEEE 39-bus, 118-bus, and 300-bus power systems demonstrate the effectiveness of the proposed DDQN-based resilience assessment method

Dual-loop SFC scheme for BTB-VSC-HVDC interconnecting asynchronous AC grids

This study proposes a dual-loop supplementary frequency control (SFC) scheme for back-to-back voltage source converter high-voltage DC (BTB-VSC-HVDC) interconnecting asynchronous AC grids, to provide frequency support for each other after a large disturbance. The proposed dual-loop SFC consists of the frequency-active power (f–P) loop and the frequency-reactive power (f–Q) loop. The former deployed on the P-loop of VSC-HVDC can provide frequency support for the disturbed grid during the primary frequency regulation and improve the steady-state characteristics of the frequency response, while the latter attached to the Q-loop of VSC-HVDC supports virtual inertia to ameliorate the transient characteristics of the frequency response. Simulation studies are conducted based on the equivalently simplified model of Southwest Power Grid and Hubei Power Grid interconnected by Chongqing-Hubei BTB-VSC-HVDC. Simulation results show that the proposed SFC scheme can effectively improve the transient and steady-state characteristics of the system frequency response under a wide range of operating condition

Damping control design for pulse width modulation series compensator using GrHDP

This paper presents an adaptive damping controller for the pulse width modulation series compensator (PWMSC) to suppress the low frequency oscillation. The adaptive damping controller is designed by using goal representation heuristic dynamic programming (GrHDP), which can facilitate the mapping relationship between input and output signals and improve the control characteristics significantly compared with the conventional heuristic dynamic programming (HDP). Moreover, the adaptive damping controller does not need the system model and has strong learning ability. Simulations results of IEEE 16-machine 68-bus power system show that the proposed GrHDP damping controller can suppress oscillation quickly and has better damping performance than the conventional lead-lag damping controller and HDP based damping controller under different operating conditions and disturbances

A Data Driven-based Adaptive Wide-area Damping Control for back to back VSC-HVDC

This paper proposed a data driven-based adaptive wide-area damping controller (A-WADC) for back-to-back VSC-HVDC to suppress the low frequency oscillation in the large interconnected power system. The proposed A-WADC employs the wide-area measurement signals as input and adjust the active and reactive power control reference of VSC-HVDC simultaneously. The data driven-based goal representation heuristic dynamic programming was used to designed A-WADC to adapt to the change of operation conditions, which only requires the input and output data rather than the mathematic model of the controlled system. In addition, the adaptive delay compensator (ADC) was added for the A-WADC to effectively compensate the time-varying delays involved in wide area signal. Case studies were conducted under the equivalent simplified model of a practical power system with back-to-back voltage source converter based high voltage direct current transmission (VSC-HVDC). Simulation results verify that the proposed A-WADC can effectively suppress the low-frequency oscillation and improve the transient stability of the system under different operating conditions and communication delays

The 187 possible edges present in at least one of 500 networks are plotted

The 107 out of 187 edges are presented less than 25 times in 500 networks. The x-axis is the number of occurrences of the edges and the y-axis is the frequency.<p><b>Copyright information:</b></p><p>Taken from "Genes related to apoptosis predict necrosis of the liver as a phenotype observed in rats exposed to a compendium of hepatotoxicants"</p><p>http://www.biomedcentral.com/1471-2164/9/288</p><p>BMC Genomics 2008;9():288-288.</p><p>Published online 16 Jun 2008</p><p>PMCID:PMC2478688.</p><p></p