Disk-and-washer cavities for an accelerator

Studied is the behavior of disk-and-washer accelerator cavities, in which the single radial stem support is adopted. The support leads about 70% larger and 20% smaller rf power loss than that of the calculated value in the normal cell and in the end cell, respectively. The distortion of the field is limited in the region of the so-called coupling cells. The properties of the coupled cavities, as the dispersion curve or the effect of tuners on the relative axial field is measured and well explained by the biperiodic coupled resonator model. The manufacturing of the actual cavity is also described, in which electroplating and welding methods are developed. The transverse coupling impedance calculated for a multiple-cell cavity are comparable with the instability experiments made in the TRISTAN accumulation ring.     

Reflections on China–US energy cooperation: Overcoming differences to advance collaboration

This article discusses the developments achieved during the 2012–2013 working group sessions on the China–US Energy Cooperation Program held in Shanghai, China and New York, United States. A panel of experts and scholars from both countries discussed the progress made in advancing the cooperation, the opportunities that the collaboration will create, and the challenges that hinder definitive collaboration. The current issues that confront the initiative indicate that the major obstacle to cooperation between China and the US is a matter of different viewpoints. For the two countries to move forward in their intention to establish a joint undertaking, they should come to a compromise on policy issues, perceptions on energy security, and market intervention.     

Optimization approach to unified AC/DC power flow applied to traction systems with catenary voltage constraints

This paper presents two innovative contributions related to the combined AC/DC power flow in railway power supply systems (RPSSs). First, most of the power flow equations (the linear ones) are expressed in a compact matrix form by using graph theory based protocol. Such approach simplifies the statement of the unified power flow problem and allows the train motion to be modeled without varying the system topology. Second, the problem is formulated as an Optimization Problem (OP) instead of using the non-constrained power flow approach. This technique allows the authors to simulate the effect of trains regenerative braking, considering system constraints such as the catenary voltage limit, which determines the amount of available regenerated energy injected to the network, and burned through the resistors.     

基于储能优化及荷电状态均衡的直流微电网控制研究

为了实现直流微电网中储能设备的优化控制以及荷电状态均衡控制,提出了一种基于储能优化及荷电状态均衡的直流微电网控制策略。分析了直流微电网结构和储能模型,利用模拟电机特性结合电压电流双闭环PI控制方法优化储能设备控制,通过模拟电机特性结合下垂系数控制法达到荷电状态均衡控制,并搭建Simulink仿真模型进行验证。由仿真结果可知:在风力输出功率和光伏输出功率波动时,在模拟直流电机特性的储能装置控制优化策略下,蓄电池能够有效抑制母线电压波动,维持系统各部分功率平衡;在蓄电池充电、放电及充放电过程中,在模拟电机特性与下垂系数控制下,让荷电状态高的蓄电池输出较多功率,而荷电状态低的蓄电池则吸收较多功率,最终实现并联蓄电池荷电状态的平衡。研究结果表明,该方法能有效抑制母线电压跌落,增强直流母线的稳定性。     

Off-grid solar photovoltaic-alkaline electrolysis-metal hydrogen storage-fuel cell system: An investigation for application in eco-neighborhood in Ningbo,China

This study proposes a combined hydrogen, heating and power system based on solar energy for the off-grid application of distributed renewable energy. With hydrogen as the energy carrier, the stable consumption of renewable energy can be achieved by integrating alkaline water electrolysis (AWE), metal hydride (MH) hydrogen storage, and proton exchange membrane fuel cells (PEMFCs). An energy management strategy is proposed based on the coordinated control of mass, energy, and information flow. Fluctuations in multi-source heat flow during solar photovoltaic (PV) power generation, hydrogen production, hydrogen-storage, and PEMFC power generation were studied based on electric and heating loads of typical winter and summer days in an eco-neighborhood in Ningbo, China. Owing to differences in solar radiation between summer and winter, the total electric energy generated by PV panels was 6179 kWh and 3667 kWh for summer and winter, respectively. The start-up times for AWE and MHs were 0.92 h and 0.32 h in summer and 1.70 h and 0.55 h in winter, respectively. After one day of operation, the hydrogen and heat surpluses were 57.17 kg and 5735.83 MJ in summer, while in winter the hydrogen surplus and heat deficit were 30.87 kg and 226.41 MJ, respectively.     

Determination of the combined vibrational and acoustic emission signature of a wind turbine gearbox and generator shaft in service as a pre-requisite for effective condition monitoring

A review of current progress in Condition Monitoring (CM) of wind turbine gearboxes and generators is presented, as an input to the design of a new continuous CM system with automated warnings based on a combination of vibrational and Acoustic Emission (AE) analysis. For wind turbines, existing reportage on vibrational monitoring is restricted to a few case histories whilst data on AE is even scarcer. In contrast, this paper presents combined vibration and AE monitoring performed over a continuous period of 5 days on a wind turbine. The vibrational and AE signatures for a healthy wind turbine gearbox and generator were obtained as a function of wind speed and turbine power, for the full normal range of these operational variables. i.e. 5–25 m/s and 0–300 kW respectively. The signatures have been determined as a vital pre-requisite for the identification of abnormal signatures attributable to shaft and gearbox defects. Worst-case standard deviations have been calculated for the sensor data. These standard deviations determine the minimum defect signal that could be detected within the defined time interval without false alarms in an automated warning system.     

Optimal microgrid programming based on an energy storage system,price-based demand response,and distributed renewable energy resources

Microgrids (MGs) in distribution systems can be operated in far regions at lower investment costs using renewable distributed energy resources (DERs). The present paper introduces a stochastic model for optimal energy-heat programming and the daily storage of an MG. Bi-level stochastic programming is presented for integrated energy-heat scheduling and storage in the presence of an energy storage system (ESS) and demand response (DR) based on social welfare maximization. Out of the incentive-based DR programs, the tender and redemption and the ancillary services market programs were selected and applied to the given model. Besides, the time of use (TOU) -based DR and real-time pricing (RTP) were considered as the price-based demand response (PBDR) programs in optimal programming. The PBDR programs have been included in the objective function using a linear function based on consumer benefits. The proposed bi-level stochastic model was solved using a developed metaheuristic optimization algorithm called the lightning search algorithm (LSA) in the present work. The Latin hypercube sampling (LHS) and KMEANS methods were used to produce and reduce the scenario. The proposed framework was investigated in a 33-bus test model. The obtained simulation results were evaluated from different aspects. The TOU and RTP effects and ESS are shown in obtained numerical analysis by considering the operating cost, total social welfare, and the client's utility function.     

冷热电联供型孤岛微电网环保经济调度模型

分布式风光伏及冷热电负荷具有较强的不确定性,增加了孤岛微电网的调度运行难度。研究冷热电联供型孤岛微电网的环保经济调度问题,通过在孤岛微电网中融入可中断负荷,将可中断负荷视为虚拟发电资源参与微电网调度运行,同时考虑微电网运行方案的经济性和环保性。采用基于可信性测度的模糊机会约束规划处理分布式风光及冷热电负荷的不确定性,进而转化为确定性等价类。采用基于满意度指标的多目标处理方法兼顾经济目标和环保目标。算例分析验证了模型的有效性。     

Optimal power flow of a distribution system based on increasingly tight cutting planes added to a second order cone relaxation

Convex relaxations of the optimal power flow (OPF) problem have received a lot of attention in the recent past. In this work, we focus on a second-order cone (SOC) relaxation applied to an OPF based on a branch flow model of a radial and balanced distribution system. We start by examining various sets of conditions ensuring the exactitude of such a relaxation, which is the main focus of the existing literature. In particular, we observe that these sets always include a requirement on the objective to be a minimization of a function increasing with the branch flow apparent powers. We consider this hypothesis to be at odds with what is to be expected of an active distribution system and demonstrate in specific case studies its counterproductive impact. We continue by introducing an objective function allowing distributed generations and storages (DGS) to take advantage of the benefits they bring to the power system as a whole. As this entails the possibility for the relaxation not to be exact, we describe and prove the theoretical convergence to optimality of an algorithm consisting in adding an increasingly tight linear cut to the SOC relaxation. In order to allow the attainment of a solution satisfying the network constraints in a finite number of steps, we continue by introducing a tailored termination criterion. Afterwards, we investigate the ability of our algorithm to obtain a satisfactory solution on several case studies, spanning various network sizes, number of nodes equipped with DGs and their level of penetration. We then conclude on the benefits brought about by this approach and reflect on its limits and the opportunities for further improvements.