Emergency Control Strategy for Power Systems with Renewables Considering a Utility-scale Energy Storage Transient

Integration of renewable energy generators has greatly altered both static and dynamic characteristics of the system.Combined with the uncertainties it introduced,the risk of a system being transient instable is significantly alleviated.This paper proposes a multi-objective coordinated post-contingency control method.It aims to increase post-contingency system security with emergence control(EC)while minimizing the total control cost.Two ECs are adopted in this paper:energy storage systems(ESSs)and emergency load shedding(ELS).ESSs are immediately connected to the network after contingency occurrence to provide both active and reactive power support.ELS will be triggered when the support from ESSs is insufficient to stabilize the system to prevent further deterioration of system security.Performance of the proposed method was evaluated on a modified New England 39-bus benchmark system.The results indicate that the proposed method can find solutions to stabilize the system against credible contingencies and optimally balance between system stability and economy.

Comparison of three flocculants for heavy cyanobacterial bloom mitigation and subsequent environmental impact

Cyanobacteria can accumulate as a heavy biomass on the leeward side of large eutrophic lakes,posing a potential threat to public health.The mitigating capacity of three flocculants and their potential impacts on the major environmental features of water and sediments was evaluated.Results indicate that polyaluminum chloride(PAC)and ferric chloride(FeCl)are efficient flocculants that can rapidly mitigate cyanobacterial blooms with chlorophyll-a concentrations higher tnan 1500 ug/L within 15 min.In comparison,cationic starch with chitosan could only treat cyanobacterial blooms in chlorophyll-a concentrations of less than 200μg/L.The addition of FeClcaused a decline in the pH value,while dissolved oxygen in the water column dropped to 2 mg/L during cationic starch with chitosan treatment for a high cyanobacterial biomass group.Thus,a combination of flocculants and oxygenators should be considered when treating high-concentration cyanobacterial blooms for emergency purposes.Additionally,the cell lysis of cyanobacteria caused by cationic starch with chitosan can result in an increase in total dissolved phosphorus and total dissolved nitrogen.Furthermore,the high accumlation of nutrients in sediments after the settling of cyanobacteria can cause high internal phosphorus pollution.The increase in the total organic carbon of the sediments can threaten lake restoration achieved by planting submerged macrophytes.

Online Decision-Making and Control of Power System Stability Based on Super-Real-Time Simulation

During power grid cascading failure,the operating point changes frequently,resulting in a mismatch or inaccuracy of online pre-decision making emergency control strategy.To solve this problem,an online power system stability decisionmaking and control method based on super-real-time simulation is presented in this paper.A decision-making and control system is developed in which the three main operation modes,offline pre-decision-making,online pre-decision-making,and real-time control,are all coordinated.To verify the method,ADPSS(advanced digital power system simulator)is used to simulate a digital power grid with about 20,000 buses.The closed-loop operation of the digital power grid and the online decisionmaking and control system are implemented.Test results show that when online pre-decision making control strategies are mismatched,aided real-time control works well and can prevent power grid stability loss.

Decentralized Voltage Control of Power Systems Using Multi-agent Systems

systems.In our proposed smart self-healing method,two types of control agents are defined,namely master and local,which are applied in two steps.In the first step,the power system returns to the normal state after fault occurrence.Immediately after a fault detection in a power system,the system is divided into three subsystems using spectral graph partitioning.Partitioning is conducted based on reactive power flow in transmission lines.For each subsystem,a local control agent and a performance index(PI)are defined.Whenever the PI of a subsystem exceeds its threshold limit,the local control agent uses the Sugeno fuzzy system to intelligently select and apply control actions.In the second step as performed by the master control agent,the power system is transformed to an optimal state by solving the optimization problem.Simulations on a 39-bus New England reveal the effective performance of the proposed method.

Swarm controlled emergence for ant clustering

Purpose–Swarm controlled emergence is proposed as an approach to control emergent effects in(artificial)swarms.The method involves the introduction of specific control agents into the swarm systems.Control agents behave similar to the normal agents and do not directly influence the behavior of the normal agents.The specific design of the control agents depends on the particular swarm system considered.The aim of this paper is to apply the method to ant clustering.Ant clustering,as an emergent effect,can be observed in nature and has inspired the design of several technical systems,e.g.moving robots,and clustering algorithms.Design/methodology/approach–Different types of control agents for that ant clustering model are designed by introducing slight changes to the behavioural rules of the normal agents.The clustering behaviour of the resulting swarms is investigated by extensive simulation studies.Findings–It is shown that complex behavior can emerge in systems with two types of agents(normal agents and control agents).For a particular behavior of the control agents,an interesting swarm size dependent effect was found.The behaviour prevents clustering when the number of control agents is large,but leads to stronger clustering when the number of control agents is relatively small.Research limitations/implications–Although swarm controlled emergence is a general approach,in the experiments of this paper the authors concentrate mainly on ant clustering.It remains for future research to investigate the application of the method in other swarm systems.Swarm controlled emergence might be applied to control emergent effects in computing systems that consist of many autonomous components which make decentralized decisions based on local information.Practical implications–The particular finding,that certain behaviours of control agents can lead to stronger clustering,can help to design improved clustering algorithms by using heterogeneous swarms of agents.Originality/value–In general,the control of(unwanted)emergent effects in artificial systems is an important problem.However,to date not much research has been done on this topic.This paper proposes a new approach and opens a different research direction towards future control principles for self-organized systems that consist of a large number of autonomous components.

Probabilistic Energy and Reserve Co-dispatch for High-renewable Power Systems and Its Convex Reformulation

This paper proposes a probabilistic energy and reserve co-dispatch(PERD) model to address the strong uncertainties in high-renewable power systems. The expected costs of potential renewable energy curtailment/load shedding are fully considered in this model, which avoids insufficient or excessive emergency control capacity to produce more economical reserve decisions than conventional chance-constrained dispatch methods. Furthermore, an analytical reformulation approach of PERD is proposed to make it tractable. We firstly develop an approximation technique with high precision to convert the integral terms in objective functions into analytical ones. Then, the calculation of probabilistic constraints is equivalently transformed into an unconstrained optimization problem by introducing value-at-risk(Va R) representation. Specifically, the Va R formulas can be computed by a computationally-cheap dichotomy search algorithm. Finally, the PERD model is transformed into a convex problem, which can be solved reliably and efficiently using off-the-shelf solvers. Case studies are performed on IEEE test systems and real provincial power grids in China to illustrate the scalability and efficiency of the proposed method.

Frequency Stability of Power System with Large Share of Wind Power Under Storm Conditions

The operation of transmission systems with large share of wind power is specially challenging under storm conditions.Under the stormy wind speed conditions,wind turbine protection system is designed to shut down the turbine to avoid excessive mechanical load.The sudden loss of wind power from large offshore plants is difficult to forecast accurately,which results in a large amount of power imbalance.The severity of such a wind power imbalance towards frequency stability needs to be studied for the future power systems.In addition,the overhead transmission lines can also be affected during storms,thereby increasing their probability of failure in the operation of power system under the islanded conditions.This paper investigates how the stormy weather can threaten the frequency stability of future Danish power system with large share of wind power and how to avoid the frequency instability through proper control and defence strategies such as high-voltage direct current(HVDC)control and load shedding.Sensitivity studies are performed for ramp rates of HVDC control,load shedding strategies,inertia of the system with different volumes of disturbances to understand their impact on frequency stability.

An enhanced cascading failure model integrating data mining technique

An enhanced cascading failure model integrating data mining technique is proposed in this paper.In order to better simulate the process of cascading failure propagation and further analyze the relationship between failure chains,in view of a basic framework of cascading failure described in this paper,some significant improvements in emerging prevention and control measures,the subsequent failure search strategy as well as the statistical analysis for the failure chains are made elaborately.Especially,a sequential pattern mining model is employed to find out the association pertinent to the obtained failure chains.In addition,a cluster analysis model is applied to evaluate the relationship between the intermediate data and the consequence of obtained failure chain,which can provide the prediction in potential propagation path of cascading failure to reduce the risk of catastrophic events.Finally,the case studies are conducted on the IEEE 10-machine-39-bus test system as benchmark to demonstrate the validity and effectiveness of the proposed enhanced cascading failure model.Some preliminary concluding remarks and comments are drawn.

Traumatic Diaphragmatic Hernia Associated with Pelvic Ring Fracture

Traumatic diaphragmatic hernia （TDH） is an uncommon injury and a marker of severe trauma.This injury is rarely associated with pelvic ring fracture,although TDH is one of the most dangerous comorbidities of such fractures.Since this condition is easily misdiagnosed in emergency cases,we reported two cases and analyzed the clinical symptoms,diagnosis,treatment,and outcome of this comorbidity.Based on these results,we recommended an appropriate method for diagnosis and treatment and proposed a contraindication in treating TDH associated with pelvic fracture.