A novel hybrid gravitational search and pattern search algorithm for load frequency control of nonlinear power system

In this paper, a hybrid gravitational search algorithm (GSA) and pattern search (PS) technique is proposed for load frequency control (LFC) of multi-area power system. Initially, various conventional error criterions are considered, the PI controller parameters for a two-area power system are optimized employing GSA and the effect of objective function on system performance is analyzed. Then GSA control parameters are tuned by carrying out multiple runs of algorithm for each control parameter variation. After that PS is employed to fine tune the best solution provided by GSA. Further, modifications in the objective function and controller structure are introduced and the controller parameters are optimized employing the proposed hybrid GSA and PS (hGSA-PS) approach. The superiority of the proposed approach is demonstrated by comparing the results with some recently published modern heuristic optimization techniques such as firefly algorithm (FA), differential evolution (DE), bacteria foraging optimization algorithm (BFOA), particle swarm optimization (PSO), hybrid BFOA-PSO, NSGA-II and genetic algorithm (GA) for the same interconnected power system. Additionally, sensitivity analysis is performed by varying the system parameters and operating load conditions from their nominal values. Also, the proposed approach is extended to two-area reheat thermal power system by considering the physical constraints such as reheat turbine, generation rate constraint (GRC) and governor dead band (GDB) nonlinearity. Finally, to demonstrate the ability of the proposed algorithm to cope with nonlinear and unequal interconnected areas with different controller coefficients, the study is extended to a nonlinear three unequal area power system and the controller parameters of each area are optimized using proposed hGSA-PS technique.     

复杂曲面零件消失模发泡模具设计与制造

分析了不同类零件在消失模发泡模具开发过程中的关键技术,重点针对具有复杂曲面的管接头和阀体类零件,结合UG Modeling & Manufacturing软件平台,论述了三维造型、模具设计和数控编程在整个工艺路线中的使用要点,总结了行之有效的方法和经验。     

A Method for Presuming Total Output Fluctuation of Highly Penetrated Photovoltaic Generation Considering Mutual Smoothing Effect

Mutual smoothing effect of renewable energy (RE) is quite important because the amount and cost of countermeasures for maintaining soundness of power systems highly depend on evaluation of the effect. In spite of its importance, there is as yet no established method to evaluate the effect. The authors present a method for presuming the total output fluctuations of highly penetrated RE from a few measured data considering the effect. By analyzing the measured data, existing photovoltaic (PV) output fluctuations are revealed to be coherent at slower swing periods and random at faster swing periods. To represent the PV’s output fluctuation tendencies, a “Transfer Hypothesis” is introduced. A “Constant Transfer Swing Period Hypothesis” and “–20 dB/dec Slope Hypothesis” are also introduced. These hypotheses are verified by direct and indirect methods using the measured data. Only 3 sites’ data are able to presume total fluctuation of 15 sites successfully. The relationship between distance and the transfer swing period for every 2 sites out of the 15 sites agrees with these hypotheses. Finally, the authors show the total fluctuation presumption of highly penetrated PV deployment in the Hokuriku region using the proposed methods. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(3): 31–42, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22327     

Current state of neural networks applications in power system monitoring and control

For over two decades Neural Network (NN) has been applied to power system monitoring and control. Conventional controllers suffer from certain limitations which NN as an Artificial Intelligence (AI) technique is able to overcome. Therefore, many researchers prefer to use NN technique in the monitoring and control of power systems. This paper reviews published recently schemes for control and monitoring based on NN. The performance of various NN controllers is compared with one another as well as to the performance of other types of controllers. This review further reveals that the design of a proper NN control can maintain first-swing stability, damp oscillation, ensure voltage stability and the reliable supply of electric power.     

浇注温度对球墨铸铁消失模铸造组织及性能的影响

在不同浇注温度下制备了消失模铸造球墨铸铁Y型试块,对比分析了球墨铸铁的石墨形态、基体组织及力学性能的区别.结果表明:当浇注温度较高时(约1 510℃),由于碳、硅烧损严重,在球墨铸铁的基体组织中生成大量的碳化物;浇注温度较低时(约1 410℃)不利于球墨铸铁的球化,降低了球墨铸铁的球化率及球化级别,由于球墨铸铁的球化效果不良,导致球墨铸铁的抗拉强度及伸长率降低;而1 460℃的浇注温度对于消失模铸造球墨铸铁比较适宜.     

消失模铝铸件针孔形成机理研究

探讨了铝液变质、晶粒细化、浇注温度及聚苯乙烯模样等对消失模铝铸件针孔的影响 .研究结果表明 ,干砂消失模铸造工艺冷却速度比树脂砂工艺和粘土砂工艺慢 ,更易产生针孔 ;若用0 .2 %Ti对消失模铸造铝液进行细化处理 ,则可以大大减少冷却速度慢对其针孔形成的不利影响 ,使铝件密度接近或达到树脂砂工艺的水平 .为减少针孔 ,应尽量采用低密度的聚苯乙烯模样 ,并应有一个适当高的浇注温度     

基于无模型算法和电动汽车辅助调节的新能源电力系统频率协调控制

为解决风电并网导致电力系统频率偏差过大的问题,设计了一种基于无模型负荷频率控制和电动汽车辅助调节的频率协调控制策略,能够在系统受到风电和负荷扰动时对其频率偏差进行快速调节。利用新能源电力系统的频率偏差设计了无模型自适应滑模负荷频率控制器,对传统机组进行二次频率调节。同时为充分利用电动汽车的快速响应能力,采用分频技术将区域控制高频偏差信号接入集群电动汽车控制中心作为调频参考指令,使得电动汽车参与辅助系统调频。最后通过Matlab/Simulink软件在不同的工况下进行对比分析,仿真结果验证了所提出策略的有效性。     

长条对称型消失模铸件的收缩不均性分析

通过对“特殊横壁”铸件的试验测试发现，长条对称型消失模铸件，如采用不同的浇注方案，其铸件的收缩率相差较大，采用水平卧式浇注，铸件对称的两边收缩率基本相同，而采用垂直立式浇注，铸件对称的上下收缩率相差较大，分析了长条对称型消失模铸件收缩不均性的原因，对此类铸件的工艺设计原则及浇注方案的确定进行了初步探讨。     

镁合金消失模铸造的研究现状及发展

针对镁合金消失模铸造的特点综述了镁合金消失模铸造用泡沫材料、消失模制备方法、消失模铸造镁合金充型特性、消失模铸造镁合金铸件的热处理及抗腐蚀性能等研究概况,分析了镁合金消失模铸造有待于进一步解决的问题,提出消失模铸造下一步的研究方向。     

Decentralized Resilient H∞ Load Frequency Control for Cyber-Physical Power Systems Under DoS Attacks

This paper designs a decentralized resilient H_∞ load frequency control (LFC) scheme for multi-area cyber-physical power systems (CPPSs). Under the network-based control framework, the sampled measurements are transmitted through the communication networks, which may be attacked by energy-limited denial-of-service (DoS) attacks with a characterization of the maximum count of continuous data losses (resilience index). Each area is controlled in a decentralized mode, and the impacts on one area from other areas via their interconnections are regarded as the additional load disturbance of this area. Then, the closed-loop LFC system of each area under DoS attacks is modeled as an aperiodic sampled-data control system with external disturbances. Under this modeling, a decentralized resilient H_∞ scheme is presented to design the state-feedback controllers with guaranteed H_∞ performance and resilience index based on a novel transmission interval-dependent loop functional method. When given the controllers, the proposed scheme can obtain a less conservative H_∞ performance and resilience index that the LFC system can tolerate. The effectiveness of the proposed LFC scheme is evaluated on a one-area CPPS and two three-area CPPSs under DoS attacks.