Browsing by Author "Ren, Hui"

Now showing 1 - 11 of 11
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    Classification and discussion on methods for cascading failure Analysis in Transmission System
    (IEEE, 2008) Watts Casimis, David; Ren, Hui
    Given the incidence of blackouts during recent years, there has been an increased interest in understanding them to increase system reliability in the future. Multiple research efforts have been devoted to cascading models, and there is a need for the comparison and discussion of the different modeling theories and focuses of these models. This paper reviews models proposed these years for the analysis of cascading blackouts, proposing a classification based on their assumptions, system representation and underlying modeling theories. A further discussion of the underlying reason of cascading blackouts and modeling focuses is made, concluding that modeling focusing on how the system is driven to present critical condition can give more practical advices on how to relieve the system stress and mitigate the risk of cascading failures.
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    Critical transitions analysis in self-organized power systems by OPA
    (IEEE, 2016) Ren, Hui; Chen, Qunjie; Wang, Fei; Watts Casimis, David Eduardo; Sun, Chenjung
    Understanding the mechanism of large scale outages is the precondition for designing of an effective prevention scheme. Complex system study shows that sudden transitions of the system from one regime to another may happen due to the nonlinear interaction among consisting components. Power systems are good examples of complex systems, and previous research shows that their critical transitions can be observed and predicted by statistical measures. These critical transitions include voltage collapse and system's entering a higher stress level from a long-term evolutional perspective. This paper continues the analysis of critical transitions in self-organized power system by Oak-PSERC-Alaska (OPA) model, a well-accepted model for the study of cascading blackouts from long-term perspective. Based on the self-organization mechanism designed in OPA, the mechanism of critical transition of power system entering a critical state is explained. The effects of local reliability on the transition is analyzed by comparing different cases. Time series of fractional load-shedding and fractional line loading are constructed and the performance of early warning of these two time series are discussed. The proposed research provide more insights on the mechanism of large blackouts, and easily available early warning signals, which are possible to implement as early warning of large catastrophic power system outage. Moreover, the fact that our research is conducted from a long-term point of view enables it to serve as a planning-assistant tool for a future power system with higher resilience.
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    Early warning mechanism for power system large cascading failures
    (IEEE, 2012) Ren, Hui; Fan, Xiaozhou; Watts Casimis, David; Lv, Xingchen
    As the interconnection of power grids, failure of single component could propagate out, and because of the scale of the power system, it is almost impossible to analysis all failure patterns. Traditional methods for online cascading analysis could face almost unsolvable obstacles on computational burden and accuracy. This paper discusses the mechanisms of early warning of cascading blackouts. Researches have shown, from the complex system point of view, the existence of early-warning signals to indicate for a wide class of systems whether a critical threshold is approaching. Instead of focusing on identifying the possible failure patterns that could lead to cascading blackouts, from the complex system point of view, early warning of cascading blackouts could be realized by identifying how far the system is to the critical state by simulation using fast computational techniques and a group of system indices, providing helpful aid for the operator.
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    Early warning signals for critical transitions in power systems
    (2015) Ren, Hui; Watts Casimis, David
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    Flexible transmission planning considering growing uncertainties from Renewable energy integration
    (IEEE, 2012) Ren, Hui; Fan, Xiaozhou; Watts Casimis, David; Lv, Xingchen
    Power systems are set to undergo dramatic changes driven by several factors ranging from climate change to technological developments. It is expected that networks will become more flexible to deal with increasing uncertainties, in those coming from future generation technologies and their locations as well as those from system operation practices. These developments will require fundamental changes in the way power systems are planned. This paper introduces a method of flexible transmission network planning with the traditional corrective control action assumed in the course of network planning. A two-stage solution algorithm is proposed combing Genetic Algorithm and Monte Carlo simulation. Candidate planning schemes are decided by Genetic Algorithm. Monte Carlo simulation and sensitivity method are used to find the most vulnerable part of the network, and then decides the amended control devices needed to be installed to achieve the optimum objective function and satisfy operational constraints (for each tested planning scheme). Discrete constraints associated with voltage control devices are included to make the simulation more realistic. The most flexible planning scheme is then defined as the one which needs the least investment on extra control devices. The proposed approach is implemented on an 18- bus test system and its feasibility is demonstrated.
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    MicroGrid Operation and Design Optimization With Synthetic Wins and Solar Resources
    (IEEE, 2012) Bustos, Cristián; Watts Casimis, David; Ren, Hui
    Microgrids have been significantly developed, enhanced by concerns about climate change and energy security, their decreasing costs and the development of renewable energy sources. However, an important concern is the limited information available to estimate these renewable resources. We develop an optimization model with cost and reliability objective functions for the design and operation of micro-networks using a nested strategy and limited resource information. Design optimization utilizes Genetic Algorithms and 2 objective functions: Expected Energy Not Supplied EENS and Levelized Cost of Energy. In addition, Green House Gas (GHG) emissions are estimated. Operational optimization utilizes Generating Sets Search Algorithm. We include models for wind turbines, solar panels, fuel cells, diesel generators, gas turbines, and battery banks. We address the limited data available for these applications by synthesizing series of wind and solar radiation with basic statistical parameters. Pareto-Optimal trade-off curves between cost and reliability are presented here for an example network.
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    Network motif as an indicator for cascading outages due to the decrease of connectivity
    (IEEE, 2017) Chen, Qunjie; Ren, Hui; Sun, Chenjung; Mi, Zengqiang; Watts Casimis, David Eduardo
    Complex network study pointed out that, between the macro level and the micro level, there still exist abundant various dimensions addressed as subgraph, including motifs, cliques, cores... The structural property of these subgraphs plays an import role for the robustness in the function of the system. In this paper, the network motif existing in different IEEE test systems and real power grids are identified, and the consistency between the structural feature of motif and power system design for reliable power supply is revealed. By incorporating the transmission line margin into the procedure of finding significant motifs, the risk of cascading overloads due to insufficient transmission capacity and the decrease of connectivity of the power network is reflected by the occurrence of certain motifs in the power network. Through the simulation of cascading failures along the continuous increase of load demand and random line failures, different phases in the evolution of cascading failures are defined, and the patterns in the occurrence of motifs corresponded to different phases are identified. The performance of network motifs as a warning signal for higher risk of large outages is also tested under continuous line/node removal scenario. Test results show that the occurrence of motifs can be a good supplement to the EENS to describe the risk of outages.
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    Reliability enhancement of the system with large amount of wind power integration
    (IEEE, 2011) Ren, Hui; Chen, Y.; Teng, Weijun; Watts Casimis, David
    The power output from wind farms is highly volatile, uncertain and hard to be predicted accurately. Then sometimes positive short-run correlation between variations of wind power output and load could bring more and larger disturbances in the system operation, bringing reliability and economic concerns. The integration of wind power generators in power systems poses some challenges, and besides installing extra reserve capacities, transmission reinforcement or other advanced controls may be required to avoid transmission overloads or voltage problem induced by wind power variation. Moreover, a well-developed transmission network may need less reserve capacity for a given reliability level, providing incentives for the research of this paper. In this paper, an optimization & sensitivity method is proposed to identify the vulnerable area of the transmission system with large amount of wind integration. IEEE-57 bus system is used as the test system. Test cases with various objective functions and allocation of reserve capacity are designed and therefore different upgrade schemes are obtained by the method. Monte Carlo simulation is used for the reliability & economic evaluation of the test system with a group of indices, including a new index - entropy. Test results and comparison show the effective of the method, and also the potential of entropy for assessing the robust of the transmission network.
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    Review Of Operating Reserves And Day-Ahead Unit Commitment Considering Variable Renewable Energies: International Experience
    (IEEE, 2017) Ren, Hui; Ortega Soto, Javiera Constanza; Watts Casimis, David
    The steady growth of wind power generation has produced that the system operators have to face more challenges to keep their operations safe all the time. The quantification of operational reserves takes a very important role because this type of reserves corresponds to the generation capacity, and other resources, that are ready to respond in case of contingency. This paper presents a review of operating reserves used in electric systems to compensate the fluctuations in load and generation, and maintain the equilibrium between supply and demand. The present study includes a review of: (1) the concept of operating reserves, (2) the methods used by markets around the world to include the assessment of operating reserves in the Day-Ahead Unit Commitment process. The purpose of this study is to compare the different methodologies used in electricity markets around the world to model the quantification of operating reserves requirements. The main conclusion found is that deterministic quantification of the operating reserves evaluated on many stochastic scenarios is the most common approach because it increases the accuracy of the solutions found when compare to the use of the central forecast. Moreover, the markets are expanding the type of resources than can provide operating reserves including demand side response.
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    The Spatial Statistics of Self-organized in Power System
    (IEEE, 2018) Jiang, Nannan; Ren, Hui; Watts Casimis, David Eduardo; Liu, Ying; Lu, Haitao; Tian, Jiefu
    Self-organized criticality (SOC) is one of explanation accepted so far on the mechanism of large blackouts. Based on the previous study on the temporal statistics of self-organized power system, the spatial statistics of the power system along its evolution is analyzed for better understanding of the mechanism of large blackouts. The conventional sensitivity method, Power Transfer Distribution Factor (PTDF), is used as the spatial weight matrix for the calculation of spatial auto correlation by Moran's I. An equivalent transmission capacity is defined as the observation. Besides Moran's I, mean, standard deviation and Entropy of equivalent transmission capacity are also provided for a better understanding of the effect of the evolution of transmission capacity on the system entering SOC, when large blackouts are of bigger possibility. IEEE -118 system is taken as a test system for the analysis. The analysis shows that spatial auto correlation by Moran's I is better for describing the heterogeneity of the power system and is a prospective candidate for the early warning of power system entering SOC.
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    The temporal-spatial stochastic model of plug-in hybrid electric vehicles
    (IEEE, 2017) Jiang, He; Ren, Hui; Sun, Chenjun; Watts Casimis, David Eduardo
    Plug-in hybrid electric vehicles (PHEVs) are considered as one of the most complicated loads/power sources because of the temporal and spatial stochastic features compared to other controllable loads. Most of the studies on the modelling of PHEVs are based on the travel survey or only considers their temporal stochastics. However, with the development of charging stations and commercial passenger cars, or for specific study, such as voltage quality, the spatial stochastics cannot be neglected. A comprehensive simulation model considering the temporal and spatial stochastics is then needed. In this paper, we build a stochastic model of PHEV, considering PHEV's temporal in arrival time, departure time and driving time and spatial randomness in the charging and discharging locations. IEEE-13 is taken as a test system and the effect of PHEVs on the daily load curve is investigated. The model is going to be a good compliment for the travel survey bases study.