Emergency Control Strategy Research Articles

An emergency control strategy considering variable frequency air conditioning load

As a high-quality flexible load, variable frequency air conditioning load has the potential to respond quickly to emergency control without significantly negative impact on users. This paper presents an emergency control strategy considering aggregated variable frequency air conditioning load. First, the operation principle of air conditioning is introduced, and a single air conditioning model is established. On this basis, the two control methods are compared and analyzed, and the impact of location on emergency control strategy is considered. The effectiveness of the emergency control strategy is verified by an example simulation.

Catastrophic mass mortalities caused by Photobacterium damselae affecting farmed marine fish from Deeba Triangle, Egypt

Farmed marine fish constitute 20% of the total farmed fish production in Egypt, and the Deeba Triangle produces a relatively large portion of this percentage. Last year, several private fish farms in the Deeba Triangle have suffered severe economic losses due to acute fish mass kills. This study aimed to investigate the hidden aetiologies behind these colossal mass fish kills and to propose an emergency control strategy. Several tons of dead farmed fish were remarkably scattered throughout affected ponds and at the vicinity of impacted fish farms. Moribund farmed European seabass (Dicentrarchus labrax), thin-lipped grey mullet (Liza ramada) and gilthead seabream (Sparus aurata) have exhibited skin darkness, emaciation, congested gills and fins, ascites, skin erosions and ulcerations. Internally, moribund fish emitted unpleasant odour upon opening the abdomen together with severe congestion and haemorrhages in kidneys and brain. Mottled atrophied spleens were the most prominent findings, while the gastrointestinal tracts were filled with whitish caseous material. The liver was pale with multiple whitish nodules. Photobacterium damselae was the most retrievable bacterial pathogen from most infected fish and trash fish. Photobacterium damselae subspecies piscicida and Photobacterium damselae subspecies damselae were definitively identified from examined moribund fish using both conventional morpho-chemical and molecular assays. Data analysis has revealed that the poor water quality was profoundly incriminated in triggering the bacterial infections with a fate of mass mortalities. Conclusively, adopting various strict biosecurity strategies will be the key factors in prevention of future episodes of mass kills.

Emergency control strategy for eliminating over-voltage of weak sending-end power grid under HVDC block fault

Emergency control strategy for eliminating over-voltage of weak sending-end power grid under HVDC block fault

Impact of cascading failure based on line vulnerability index on power grids

This paper proposes a new method to identify the vulnerable lines in power grids and predicts the cascading failure path by constructing a cascading failure model of power grids. The line vulnerability index (LVI) of power grids based on line degree and line overload risk is firstly proposed. Then, a cascading failure model of power grids based on LVI is presented while overload emergency control strategy is employed to reduce generation and load powers. Roulette algorithm is used to select sub-fault lines. Finally, the model is applied to the IEEE 39-bus system for simulation. Based on LVI with different weights, simulation results analyze the impact of cascading failure on power grids structure and power balance. It shows that the grid cascading failure model based on the proposed line vulnerability index can simulate the process of cascading failure, comprehensively identify the vulnerable lines of power grid and accurately predict the path of cascading failure.

Comparative study of chemical characterization and source apportionment of PM2.5 in South China by filter-based and single particle analysis

Single particle aerosol mass spectrometers (SPAMS) have created significant interest among atmospheric scientists by virtue of their ability to provide real-time size-resolved information on the chemical composition of aerosols. The objective of this study is to evaluate the newly developed single particle analysis technique in terms of chemical characterization and source apportionment of ambient aerosols by comparing it with traditional filter-based methods. In this study, an air quality monitoring campaign was conducted over a period of 25 days at an urban area in Yulin city, southern China, by employing both SPAMS and traditional filter-based measurements to establish the performance of SPAMS. It was observed that the chemical characterization of particles based on SPAMS did not agree well with the filter-based analysis. Based on the filter analysis, sulfate was the most abundant component in PM2.5 (23.5%), followed by OC (18.1%), while for single particle analysis (number concentration), EC-containing particles showed the largest contribution to PM2.5 (>40%), followed by OC (15.7%). In terms of source apportionment via positive matrix factorization, six sources were identified by each of the two approaches. Both the approaches showed relatively good agreements for secondary species, traffic, and dust sources; however, discrepancies were noted for industry, fossil fuel, and biomass burning sources. Finally, investigation of diurnal profiles and two specific emission episodes monitored during the Chinese New Year and traffic activities demonstrated the relative advantage of single particle analysis over filter-based methods. Overall, single particle analysis can provide source apportionment with a high time resolution, which is helpful for policy makers to analyze and implement emergency control strategies during air pollution episodes. However, SPAMS performs quantification of number concentration rather than mass concentration and is limited to particles larger than 200 nm, which leads to discrepancies between the two methods. SPAMS measurements can therefore not simply replace traditional filter-based analyses, which needs to be carefully considered in the selection of the monitoring implementation.

VSC-HVDC Interties for Urban Power Grid Enhancement

Urban power grids are facing many operational and expansion challenges to meet further demand growth and increased reliability requirements. Advanced transmission technologies have been considered by the electric utilities to effectively increase the utilization of existing infrastructure and operational flexibility. The focus of this paper is on VSC-HVDC technologies for urban power grid enhancement and modernization. First, a potential technical scheme is proposed for converting an existing AC circuit to DC operation, which could boost the power transfer capability of the critical transmission corridor and increase network operational flexibility. Second, this paper proposes three operation modes for the VSC-HVDC interties in urban power grids corresponding to normal, emergency and island operating conditions, respectively. An integrated, adaptive emergency control strategy (AEC) is proposed that can enable adaptive power flow responses of the VSC-HVDC intertie under varying system operating conditions and critical contingencies. The flexibility and effectiveness of the proposed operational principles of urban VSC-HVDC intertie and the corresponding control strategies are verified in PSCAD/EMTDC using a realistic urban power grid in China.

Biogenic amines in fresh fish and fishery products and emerging control

Occurrence of biogenic amines in fresh fish and fishery products constitute a significant safety concern. Ingestion of histamine is identified as the causative agent of several food poisoning incidences on an annual basis. In addition, cadaverine, putrescine and tyramine have been recognized as potentiators of histamine poisoning. Accumulation of biogenic amines in fresh fish and fishery products has been mainly attributed to growth of bacteria possessing amino acid decarboxylase activity, which is facilitated by lack of hygienic conditions and strict temperature control during their storage. To this end, the effectiveness of traditional and modern approaches to control biogenic amine accumulation has been in the epicenter of intensive study. The aim of the present review article is to update and integrate current knowledge regarding the biogenic amine content of fresh fish and fishery products as well as the capacity of traditional and emerging control strategies.

Emergency Control Strategy for Line Overload Considering Power Source and Load Fluctuation

Uncertain factors such as the integration of renewable energy into the grid and load fluctuations have brought more risks to the safe dispatch of the grid. The random power flow is used to calculate the impact of distributed power sources and load fluctuations on the grid, and to quantify the probability distribution of line power, which can avoid the drawbacks of deterministic power flow that cannot fully reflect the line overload risk. Combining the line overload level with the traditional load shedding method can effectively prevent the system from cascading failures caused by the risk of line overload, improve the optimistic calculation results caused by the load shedding strategy in emergency situations that cannot consider source load fluctuations, and make the grid control more safe and reliable.

Step Coordination Control Strategy Based on WAMS for AC/DC Hybrid System

The power system’s stability is judged through the processing and analysis of wide-area information, and matching and executing the corresponding control measures based on data can be used as an effective backup and supplement to the security and stability control devices. This paper proposes an online additional emergency control strategy based on energy function for the situation that the security and stability control strategy formulated offline may have mode mismatch. This strategy relies on the energy function index that describes the unstable situation of the power system. Based on the real-time data from SCADA and PMU, it combines the energy function method and the trajectory prediction to achieve the function of additional control of the power grid in an emergency. The cases are analyzed to verify the effectiveness of the proposed method. The simulation results demonstrate that the step coordination control strategy could be realized, and the practicality is improved.

Optimal Emergency Frequency Control Based on Coordinated Droop in Multi-Infeed Hybrid AC-DC System

In multi-infeed hybrid AC-DC (MIDC) systems, the asynchronous interconnection between regional grids, complicated system dynamics and possible emergency faults have enormous effects on the frequency stability. To address the frequency instability problems in emergency situations, this paper proposes a decentralized emergency frequency control (EFC) strategy based on coordinated droop for the MIDC system. First, a P-f droop control for LCC-HVDC systems is introduced, and the coordinated droop mechanism among LCC-HVDC systems and generators is designed. Then, to appropriately allocate the power imbalance among the LCC-HVDC systems and generators, an optimal emergency frequency control (OEFC) problem is formulated, and the optimal droop coefficients are selected in a decentralized way, which can deal with various control objectives. A Lyapunov stability analysis shows that the closed-loop equilibrium is locally asymptotically stable considering the LCC-HVDC dynamics. The effectiveness of the proposed emergency control strategy is verified through simulations.

An Real-Time Emergency Control Method Based On Unbalanced Transient Energy Function

In this paper, an emergency control strategy by combining generator tripping and load shedding is presented. Firstly, the unbalanced transient energy function of power system is defined, and its key features are analysed. Then, by combining the unbalanced power characteristics for power system in steady state operation condition, the method for calculating the control quantities of generator tripping and load shedding is proposed. Furthermore, a realtime closed-loop emergency control strategy is proposed. Since the proposed method by only using measurement data is based on the essential of transient instability, the accurate control quantities can be obtained. Compared with single generator tripping control, the low frequency and low voltage problem of system can be improved effectively with the combined emergency control strategy. Simulation results of New England 39-bus system validate the effectiveness of the proposed control strategy.

Emergency control strategy of power system transient instability based on DBN

In order to satisfy the real-time emergency control decision-making after power system transient instability, an emergency control strategy based on deep belief network is proposed in this paper. Firstly, the DBN instability degree prediction model is established to fit the mapping relationship between generator power angle characteristics and transient stability coefficient; secondly, according to the fitting instability degree index, the sensitivity of generator tripping is solved to determine the generator tripping control action bus; finally, according to the emergency control optimization model and transient stability constraints, the optimal generator tripping strategy is solved and verified in New England 10-machine and 39-node system. The results show that the proposed method has high prediction accuracy andefficiency, which can make the unstable system quickly resume stable operation.

Dengue Virus is Hyperendemic in Nigeria from 2009 to 2020: A Contemporary Systematic Review.

BackroundData on Dengue virus (DENV) infection prevalence, geographic distribution and risk factors are necessary to direct appropriate utilization of existing and emerging control strategies. This study aimed to determine the pooled prevalence, risk factors of DENV infection and the circulating serotypes within Nigeria from January 1, 2009 to December 31, 2020.Materials and methodsTwenty-one studies out of 2,215 available articles were eligible and included for this systematic review. Relevant articles were searched, screened and included in this study according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) criteria. The risk of bias in primary studies was assessed by Cochrane's method. Heterogeneity of pooled prevalence was calculated using the chi-square test on Cochrane's Q statistic, which was quantified by I-square values. The random-effects analyses of proportions were used to determine the pooled prevalence of DENV antibodies, antigen and RNA from eligible studies.ResultsOf these, 3 studies reported co-circulation of all the 4 serotypes, while 2 separately reported co-circulation of DENV-1 &2 and DENV-1 to -3. All the antibody-based studies had significantly high heterogeneity (I2 >90%, P <0.05), while the NS1 and PCR-based studies had low heterogeneity (I2 <25%, P >0.05). The pooled prevalence of DENV IgM, IgG, RNA, NS1 and neutralizing antibodies were 16.8%, 34.7%, 7.7%, 7.7% and 0.7%, respectively. South-east Nigeria had the highest pooled DENV-IgG seropositivity, 77.1%. Marital status, gender, educational level and occupation status, the proximity of residence to refuse dumpsite, frequent use of trousers and long sleeve shirts were significantly associated with DENV IgG seropositivity (P <0.05).ConclusionBased on these findings, it can be inferred that Nigeria is hyperendemic for Dengue fever and needs concerted efforts to control its spread within and outside the country.

Advanced automated emergency control strategy for embedded VSC-HVDC links

This paper proposes an advanced emergency control strategy for embedded VSC-HVDC links after AC disturbances, such as line tripping and generation loss. The control goals are to minimize the impact of the disturbance on the AC-network, which includes improving the long-term voltage stability with utilizing possible unloading capacity of parallel AC elements. The proposed algorithm is evaluated against other control strategies for embedded VSC-HVDC links by applying it to a simple demonstration network. The test system includes all necessary VSC converter dynamics, the VSC-HVDC link current and voltage limits and simple load recovery characteristics for an evaluation of the long term voltage stability. The simulation results are explained and the advantages of the proposed emergency control strategy are discussed.

Emergency Support of Transmission Voltages by Active Distribution Networks: A Non-Intrusive Scheme

Non-negligible amounts of Distributed Generating Units (DGUs) are already connected to power systems, predominantly to medium- and low-voltage networks. The interaction between distribution and transmission systems is gaining the attention of system operators. Given the high controlability of DGUs, the active distribution networks can potentially support the transmission system during emergency situations. Previously proposed voltage emergency controls involving distribution network assets focused on preserving the transmission system integrity, even if it implies affecting the distribution system operation (intrusive schemes). More attention needs to be devoted to supporting transmission voltages, while preserving the distribution network operation (non-intrusive schemes). This paper introduces a new adaptive and non-intrusive voltage emergency control scheme based on the synchronization of DGUs and the load tap changer of the corresponding distribution transformer. The conclusions are derived from time-domain simulations using an extended version of the IEEE Nordic test system for voltage stability assessment.

Real-Time LCC-HVDC Maximum Emergency Power Capacity Estimation Based on Local PMUs

The maximum active power that a Line-Commutated-Converter High Voltage Direct Current (LCC-HVDC) can provide instantly, called LCC-HVDC-MC Maximum Emergency Power Capacity, is an important information for determining the emergency control strategy of a power system subject to a large disturbance. However, it is a challenging task to calculate this capacity accurately due to system model uncertainties and contingencies. To address this problem, we propose to estimate this capacity by real-time tracking the Thevenin equivalent (TE) parameters of the AC system based on local PMUs. This new TE estimation method can handle the large disturbances and yield an accurate HVDC-MC while considering various constraints. Specifically, we first investigate the impacts of the TE potential changes on the TE impedance estimation under a large disturbance. To reduce the estimation error caused by the TE potential change, we develop an adaptive current screening process of the current measurements. Moreover, we use the total least square estimation method to further filter out the PMU errors. Finally, we calculate LCC-HVDC maximum emergency power capacity while accounting for the limitations of the control performance, voltage dependent current order limit, the converter capacity, and the AC voltage. The simulations show that the proposed method can accurately track the TE parameters and the real-time LCC-HVDC maximum emergency power capacity following a large disturbance.

Decomposition-Based Stability Analysis for Isolated Power Systems With Reduced Conservativeness

An isolated power system (IPS) usually operates in an islanded mode. Because of the lack of support from an external power grid, stability is a prominent issue for IPSs. This article proposes a novel stability analysis approach for IPSs based on the input-to-state stability (ISS) theory. Compared with existing stability analyses that use simulations and direct methods, the proposed method decomposes the stability analysis process by considering the ISS properties of subsystems and a network equation that reflects their connections. Thus, it has good adaptability for the stability analysis of systems with flexible operating conditions. Algorithms are presented for estimating the ISS properties of subsystems, and asymptotic gains in a piecewise linear form are adopted. The small gain theorem is used for the decomposed stability analysis, and a practical algorithm to numerically check the small gain condition is presented. Time-domain simulations were performed with a test system to verify the effectiveness of the proposed decomposition-based stability analysis approach. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —Power systems used in shipboards, airplanes, remote areas, and so on are usually classified as isolated power systems (IPSs). The continuity of power supply in IPSs is the prerequisite of fulfilling certain tasks. Due to the lack of support from the bulk power grid, the normal operation of IPSs can be threatened by various external disturbances, such as disasters, battle damages, device failures, and so on. To maintain the survivability and reliability of IPSs under extreme conditions, fast reconfiguration and emergency control approaches are often performed, which lead to system topology changes and frequent connection/disconnection operation of devices in IPSs. Because of the limited generation capacity of an IPS, a stability analysis after an emergency is important for ensuring that the IPS can perform tasks normally, and can provide guidance for designing fast reconfiguration and emergency control strategies. However, current stability analysis approaches have limited applicability or are overly conservative for analyzing the stability of IPSs. To address the challenge of changeable topologies for the stability analysis of an IPS, this article proposes a decomposition-based analysis approach using input-to-state stability (ISS) theory. By decomposing the entire system into several subsystems, the system’s stability can be checked through the ISS properties of subsystems and their connections. The ISS properties of subsystems can be estimated offline, which saves time for online calculation. To reduce the conservativeness of stability analysis, the asymptotic gains in piecewise linear form are adopted in this article. Practical algorithms are designed for efficiently checking the proposed decomposition-based stability conditions. The research outcome provides a fast and flexible stability analysis approach that can adapt to the frequent changes in the operating conditions of IPSs.

Security Assessment and Coordinated Emergency Control Strategy for Power Systems with Multi-Infeed HVDCs

Short-circuit faults in a receiving-end power system can lead to blocking events of the feed-in high-voltage direct-current (HVDC) systems, which may further result in system instability. However, security assessment methods based on the transient stability (TS) simulation can hardly catch the fault propagation phenomena between AC and DC subsystems. Moreover, effective emergency control strategies are needed to prevent such undesired cascading events. This paper focuses on power systems with multi-infeed HVDCs. An on-line security assessment method based on the electromagnetic transient (EMT)-TS hybrid simulation is proposed. DC and AC subsystems are modeled in EMTDC/PSCAD and PSS/E, respectively. In this way, interactions between AC and DC subsystems can be well reflected. Meanwhile, high computational efficiency is maintained for the on-line application. In addition, an emergency control strategy is developed, which coordinates multiple control resources, including HVDCs, pumped storages, and interruptible loads, to maintain the security and stability of the receiving-end system. The effectiveness of the proposed methods is verified by numerical simulations on two actual power systems in China. The simulation results indicate that the EMT-TS hybrid simulation can accurately reflect the fault propagation phenomena between AC and DC subsystems, and the coordinated emergency control strategy can work effectively to maintain the security and stability of systems.

Model-Free Emergency Frequency Control Based on Reinforcement Learning

Unexpected large power surges will cause instantaneous grid shock and, thus, emergency control plans must be implemented to prevent the system from collapsing. In this article, with the aid of reinforcement learning, novel model-free control (MFC)-based emergency control schemes are presented. First, multi-Q-learning-based emergency plans are designed for limited emergency scenarios by using offline-training-online-approximation methods. To solve the more general multiscenario emergency control problem, a deep deterministic policy gradient (DDPG) algorithm is adopted to learn near-optimal solutions. With the aid of deep Q network, DDPG-based strategies have better generalization abilities for unknown and untrained emergency scenarios, and thus are suitable for multiscenario learning. Through simulations using benchmark systems, the proposed schemes are proven to achieve satisfactory performances.

A novel approach to emergency risk assessment using FMEA with extended MULTIMOORA method under interval-valued Pythagorean fuzzy environment

PurposeThe application of the traditional failure mode and effects analysis (FMEA) technique has been widely questioned in evaluation information, risk factor weights and robustness of results. This paper develops a novel FMEA framework with extended MULTIMOORA method under interval-valued Pythagorean fuzzy environment to solve these problems.Design/methodology/approachThis paper introduces innovatively interval-value Pythagorean fuzzy weighted averaging (IVPFWA) operator, Tchebycheff metric distance and interval-value Pythagorean fuzzy weighted geometric (IVPFWG) operator into the MULTIMOORA submethods to obtain the risk ranking order for emergencies. Finally, an illustrative case is provided to demonstrate the practicality and feasibility of the novel fuzzy FMEA framework.FindingsThe feasibility and validity of the proposed method are verified by comparing with the existing methods. The calculation results indicate that the proposed method is more consistent with the actual situation of project and has more reference value.Practical implicationsThe research results can provide supporting information for risk management decisions and offer decision-making basis for formulation of the follow-up emergency control and disposal scheme, which has certain guiding significance for the practical popularization and application of risk management strategies in the infrastructure projects.Originality/valueA novel approach using FMEA with extended MULTIMOORA method is developed under IVPF environment, which considers weights of risk factors and experts. The method proposed has significantly improved the integrity of information in expert evaluation and the robustness of results.