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PID-Type Fuzzy Controller for Grid-Supporting Inverter of Battery in Embedded Small Variable Speed Wind Turbine  [PDF]
Ferdian Ronilaya, Hajime Miyauchi, Adi Kurniawan
Journal of Power and Energy Engineering (JPEE) , 2014, DOI: 10.4236/jpee.2014.24022
Abstract: Frequency and voltage of embedded variable speed wind turbine (VSWT) driving a permanent magnet synchronous generator (PMSG) is strongly affected by wind speed fluctuations. In practice, power imbalance between supply and demand is also common, especially when VSWT-PMSG is connected to a weak micro grid (MG). If load demand fluctuations become high, isolated MG may be unable to stabilize the frequency and voltage so that battery storage needs to be installed into the MG to adjust energy supply and demand. To allow flexible control of active and reactive power flow from/to battery storage, grid-supporting inverters are used. For a system that contains highly nonlinear components, the use of conventional linear proportional-integral-derivative (PID) controllers may cause system performance deterioration. Additionally, these controllers show slow, oscillating responses, and complex equations are required to obtain optimum responses in other controllers. To cope with these limitations, this paper proposes PID-type fuzzy controller (PIDfc) design to control grid-supporting inverter of battery. To ensure safe battery operating limits, we also propose a new controller scheme called intelligent battery protection (IBP). This IBP is integrated into PIDfc. Several simulation tests are performed to verify the scheme’s effectiveness. The results show that the proposed PIDfc controller exhibits improved performance and acceptable responses, and can be used instead of conventional controllers.
Better Than Their Reputation? On the Reliability of Relevance Assessments with Students  [PDF]
Philipp Schaer
Computer Science , 2012,
Abstract: During the last three years we conducted several information retrieval evaluation series with more than 180 LIS students who made relevance assessments on the outcomes of three specific retrieval services. In this study we do not focus on the retrieval performance of our system but on the relevance assessments and the inter-assessor reliability. To quantify the agreement we apply Fleiss' Kappa and Krippendorff's Alpha. When we compare these two statistical measures on average Kappa values were 0.37 and Alpha values 0.15. We use the two agreement measures to drop too unreliable assessments from our data set. When computing the differences between the unfiltered and the filtered data set we see a root mean square error between 0.02 and 0.12. We see this as a clear indicator that disagreement affects the reliability of retrieval evaluations. We suggest not to work with unfiltered results or to clearly document the disagreement rates.
Maintenance Scheduling of Distribution System with Optimal Economy and Reliability  [PDF]
Siyuan Hong, Haifeng Li, Fengjiao Wang
Engineering (ENG) , 2013, DOI: 10.4236/eng.2013.59B003
Abstract: With the continuous expansion of power distribution grid, the number of distribution equipments has become larger and larger. In order to make sure that all the equipments can operate reliably, a large amount of maintenance tasks should be conducted. Therefore, maintenance scheduling of distribution network is an important content, which has significant influence on reliability and economy of distribution network operation. This paper proposes a new model for maintenance scheduling which considers load loss, grid active power loss and system risk as objective functions. On this basis, Differential Evolution algorithm is adopted to optimize equipment maintenance time and load transfer path. Finally, the general distribution network of 33 nodes is taken for example which shows the maintenance scheduling model’s effectiveness and validity.
Using Atmospheric Pressure Tendency to Optimise Battery Charging in Off-Grid Hybrid Wind-Diesel Systems for Telecoms  [PDF]
Shane Phelan,Paula Meehan,Stephen Daniels
Energies , 2013, DOI: 10.3390/en6063052
Abstract: Off grid telecom base stations in developing nations are powered by diesel generators. They are typically oversized and run at a fraction of their rated load for most of their operating lifetime. Running generators at partial load is inefficient and, over time, physically damages the engine. A hybrid configuration uses a battery bank, which powers the telecoms’ load for a portion of the time. The generator only operates when the battery bank needs to be charged. Adding a wind turbine further reduces the generator run hours and saves fuel. The generator is oblivious to the current wind conditions, which leads to simultaneous generator-wind power production. As the batteries become charged by the generator, the wind turbine controller is forced to dump surplus power as heat through a resistive load. This paper details how the relationship between barometric pressure and wind speed can be used to add intelligence to the battery charger. A Simulink model of the system is developed to test the different battery charging configurations. This paper demonstrates that if the battery charger is aware of upcoming wind conditions, it will provide modest fuel savings and reduce generator run hours in small-scale hybrid energy systems.
Reliability, compliance, and security in web-based course assessments
Scott Bonham
Physical Review Special Topics. Physics Education Research , 2008,
Abstract: Pre- and postcourse assessment has become a very important tool for education research in physics and other areas. The web offers an attractive alternative to in-class paper administration, but concerns about web-based administration include reliability due to changes in medium, student compliance rates, and test security, both question leakage and utilization of web resources. An investigation was carried out in introductory astronomy courses comparing pre- and postcourse administration of assessments using the web and on paper. Overall no difference was seen in performance due to the medium. Compliance rates fluctuated greatly, and factors that seemed to produce higher rates are identified. Notably, email reminders increased compliance by 20%. Most of the 559 students complied with requests to not copy, print, or save questions nor use web resources; about 1% did copy some question text and around 2% frequently used other windows or applications while completing the assessment.
Micro-Grid Smooth Switchover Method Based on Controller State Following  [PDF]
Yang Fu, Lisha Huang, Jingjing Zhao
Journal of Power and Energy Engineering (JPEE) , 2015, DOI: 10.4236/jpee.2015.34019
Abstract:

Micro-grid smooth switchover between different operation modes is important for steady operation and reliable power supply of micro-grid. In order to reduce the transient fluctuation of voltage and frequency during switchover, this paper proposed a new switchover method based on controller state following. When transferring to island mode, the control method for inverter of storage device changed from PQ control to V/f control. Before switchover, the output of V/f controller is always following the output of PQ controller. So that the sudden change of output is avoided at the moment of switchover. A micro-grid model with photovoltaic and battery is built on DIgSILENT Power Factory simulation software, to simulate micro-grid switchover from grid-connected mode to island mode. Results show this method can effectively suppress the transient fluctuation of voltage and frequency, and reduce the influence of transient process on power grid. This conclusion has important practical significance on micro-grid smooth switchover from grid-con- nected mode to island mode.

Reliability and Validity of the CogState Battery Chinese Language Version in Schizophrenia  [PDF]
Na Zhong, Haifeng Jiang, Jin Wu, Hong Chen, Shuxing Lin, Yan Zhao, Jiang Du, Xiancang Ma, Ce Chen, Chengge Gao, Kenji Hashimoto, Min Zhao
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0074258
Abstract: Background Cognitive impairment in patients with schizophrenia is a core symptom of this disease. The computerized CogState Battery (CSB) has been used to detect seven of the most common cognitive domains in schizophrenia. The aim of this study was to examine the reliability and validity of the Chinese version of the CSB (CSB-C), in Chinese patients with schizophrenia. Methodology/Principal Findings Sixty Chinese patients with schizophrenia and 58 age, sex, and education matched healthy controls were enrolled. All subjects completed the CSB-C and the Repeated Battery for the Assessment of Neuropsychological Status (RBANS). To examine the test-retest reliability of CSB-C, we tested 33 healthy controls twice, at a one month interval. The Cronbach α value of CSB-C in patients was 0.81. The test-retest correlation coefficients of the Two Back Task, Gronton Maze Learning Task, Social Emotional Cognition Task, and Continuous Paired Association Learning Task were between 0.39 and 0.62 (p<0.01) in healthy controls. The composite scores and all subscores for the CSB-C in patients were significantly (p<0.01) lower than those of healthy controls. Furthermore, composite scores for patients on the RBANS were also significantly lower than those of healthy controls. Interestingly, there was a positive correlation (r = 0.544, p<0.001) between the composite scores on CSB-C and RBANS for patients. Additionally, in the attention and memory cognitive domains, corresponding subsets from the two batteries correlated significantly (p<0.05). Moreover, factor analysis showed a two-factor model, consisting of speed, memory and reasoning. Conclusions/Significance The CSB-C shows good reliability and validity in measuring the broad cognitive domains of schizophrenia in affected Chinese patients. Therefore, the CSB-C can be used as a cognitive battery, to assess the therapeutic effects of potential cognitive-enhancing agents in this cohort.
含柴油发电机和蓄电池储能的独立微电网频率分层控制
Frequency hierarchical control for islanded micro-grid consisting of diesel generator and battery energy storage system
 [PDF]

马艺玮,杨苹,陈思哲,赵卓立,王月武
控制理论与应用 , 2015, DOI: 10.7641/CTA.2015.41155
Abstract: 针对由间歇性可再生能源、柴油发电机组和蓄电池储能系统构成的独立微电网, 提出一种新型的频率分层控制方案, 建立适合蓄电池储能系统和柴油发电机组不同控制特性的分层控制结构及其协调控制策略, 提高了独立微电网频率控制的稳定性和灵活性. 在一级控制中, 采用改进型下垂控制的蓄电池储能系统, 来处理较小变化幅度和较短变化周期的随机净负荷波动, 提高独立微电网系统的瞬态频率响应特性和频率质量. 在二级控制中, 采用改进的柴油发电机PID调速控制, 应对较大变化幅度和较长变化周期的系统净负荷波动, 实现系统频率的无差控制. 最后, 通过对东澳岛风柴蓄混合能源独立微电网系统在不同运行条件下的频率控制仿真结果, 验证了所提方法的可行性和有效性.
For islanded micro-grid consisting of the intermittent renewable energy sources with Diesel generator (DE) and battery energy storage system (BS), a novel frequency hierarchical control scheme is presented with the frequency hierarchical control structure and the coordinated control strategy, which are suitable for different characteristics of DE and BS for improving the frequency stability and flexibility of islanded micro-grid. In the frequency primary control, a modified droop frequency control of BS is given to improve the transient frequency response and reduce frequency deviation by rejecting the fast, small and random net-load fluctuations. In the frequency secondary control, a modified PID control of DE governor is proposed to deal with the slow and big net-load fluctuations to achieve the zero steady-state error frequency control of islanded micro-grid. Finally, the performance of the proposed method is validated in the practical application to Dong’ao islanded wind-diesel-battery hybrid energy micro-grid operated under various conditions.
Distribution System Reliability Analysis for Smart Grid Applications  [PDF]
Tawfiq M. Aljohani, Mohammed J. Beshir
Smart Grid and Renewable Energy (SGRE) , 2017, DOI: 10.4236/sgre.2017.87016
Abstract: Reliability of power systems is a key aspect in modern power system planning, design, and operation. The ascendance of the smart grid concept has provided high hopes of developing an intelligent network that is capable of being a self-healing grid, offering the ability to overcome the interruption problems that face the utility and cost it tens of millions in repair and loss. In this work, we will examine the effect of the smart grid applications in improving the reliability of the power distribution networks. The test system used in this paper is the IEEE 34 node test feeder, released in 2003 by the Distribution System Analysis Subcommittee of the IEEE Power Engineering Society. The objective is to analyze the feeder for the optimal placement of the automatic switching devices and quantify their proper installation based on the performance of the distribution system. The measures will be the changes in the reliability system indices including SAIDI, SAIFI, and EUE. In addition, the goal is to design and simulate the effect of the installation of the Distributed Generators (DGs) on the utility’s distribution system and measure the potential improvement of its reliability.
Secure Operation and Optimal Generation Scheduling Considering Battery Life for an Isolated Northwest Grid of Saudi Arabia  [PDF]
Hani Albalawi, Karthikeyan Balasubramaniam, Elham Makram
Journal of Power and Energy Engineering (JPEE) , 2017, DOI: 10.4236/jpee.2017.51004
Abstract: Maintenance schedule of generators in an interconnected power system presents multifaceted challenges, two important ones being optimal operation cost and secure operation. When a generator is scheduled for maintenance, achieving optimal generation scheduling for the committed generators is necessary but it is not sufficient for secure operation of power systems. This problem is decomposed into two subproblems: i) Finding the optimal set points for the generators; ii) Validating secure operation with those set points from i). Both these subproblems [i) and ii)] have been studied extensively in the literatures. However, the research here focuses on incorporating battery energy storage systems (BESS) in power operation, a renewable generation that can provide smooth and flexible reserves of power, an area that has not yet been fully explored. In addition, incorporating BESS while considering both the cost implications and addressing secure operation has not yet been addressed in previous literatures. The purpose of this paper is to present both secure and optimal operation besides improving the longevity of the BESS. Feasibility of the proposed approach is demonstrated on Tabuk region—an isolated northwest grid of Saudi Arabia.
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