Graphical models for optimal power flow

Optimal power flow (OPF) is the central optimization problem in electric power grids. Although solved routinely in the course of power grid operations, it is known to be strongly NP-hard in general, and weakly NP-hard over tree networks. In this paper, we formulate the optimal power flow problem over tree networks as an inference problem over a tree-structured graphical model where the nodal variables are low-dimensional vectors. We adapt the standard dynamic programming algorithm for inference over a tree-structured graphical model to the OPF problem. Combining this with an interval discretization of the nodal variables, we develop an approximation algorithm for the OPF problem. Further, we use techniques from constraint programming (CP) to perform interval computations and adaptive bound propagation to obtain practically efficient algorithms. Compared to previous algorithms that solve OPF with optimality guarantees using convex relaxations, our approach is able to work for arbitrary tree-structured distribution networks and handle mixed-integer optimization problems. Further, it can be implemented in a distributed message-passing fashion that is scalable and is suitable for “smart grid” applications like control of distributed energy resources. Numerical evaluations on several benchmark networks show that practical OPF problems can be solved effectively using this approach.     

PID-controller with predictor and auto-tuning algorithm: study of efficiency for thermal plants

The problem of efficiency estimation of an automatic control system (ACS) with a Smith predictor and PID-algorithm for thermal plants is considered. In order to use the predictor, it is proposed to include an auto-tuning module (ATC) into the controller; the module calculates parameters for a second-order plant module with a time delay. The study was conducted using programmable logical controllers (PLC), one of which performed control, ATC, and predictor functions. A simulation model was used as a control plant, and there were two variants of the model: one of them was built on the basis of a separate PLC, and the other was a physical model of a thermal plant in the form of an electrical heater. Analysis of the efficiency of the ACS with the predictor was carried out for several variants of the second order plant model with time delay, and the analysis was performed on the basis of the comparison of transient processes in the system when the set point was changed and when a disturbance influenced the control plant. The recommendations are given on correction of the PID-algorithm parameters when the predictor is used by means of using the correcting coefficient k for the PID parameters. It is shown that, when the set point is changed, the use of the predictor is effective taking into account the parameters correction with k = 2. When the disturbances influence the plant, the use of the predictor is doubtful, because the transient process is too long. The reason for this is that, in the neighborhood of the zero frequency, the amplitude-frequency characteristic (AFC) of the system with the predictor has an ascent in comparison with the AFC of the system without the predictor.     

A comparative analysis of three self-balancing wheelchair balancing mechanisms.

In the last 20 years, three different basic, dynamic balancing designs have been proposed for a self-balancing wheelchair (SBW) that allows the wheelchair user to transition from driving on all four wheels to driving while balanced on the two large rear wheels. The dynamic performance of these three SBW designs, the hanging pendulum counterweight (HPC), the single inverted pendulum (SIP), and the double inverted pendulum (DIP), are compared when controlled by a common state space controller. The four dynamic performance considerations of stability, driver dynamic stress, maneuverability and technical requirements were used to compare these designs while performing the following five tests: 1) transition from four-wheel to two-wheel, balancing mode; 2) stationary, self-balancing stability when subjected to an impact disturbance; 3) movement initiation, and stopping while balancing; 4) response to impact disturbances while moving; and 5) stability on low traction surfaces. In addition, the movement initiation and stopping test was repeated with increased chair mass and inertia to investigate the sensitivity of model performance to changes in model parameters. After comparing the three models it was determined that the HPC mechanism is the best choice for further development based on the criteria of stability, driver dynamic stress, maneuverability, and technical requirements. The HPC ranked equal or better compared to the SIP and DIP on 15 of 29 stability and performance factors. It was also the only design that was stable for all normally expected driving conditions.     

照明的明天：什么是热点

从社会、产品和应用的角度,举例说明未来数年照明的＂热点＂。从社会的角度,说明可持续发展以及相关节能产品和应用设计的持续重要性。要更加关注完全无废料的设计,即＂从摇篮到摇篮＂（from cradle to cradle）的设计。从产品的角度,说明固态将成为许多产品应用的标准。在固态照明方面,由于所提供的数据常常有误而令新用户不满,因此向固态照明转变的脚步会放缓。若有效控制固态照明中的眩光,须有新型的光学设计。目前的评价体系,是通过经验方法获得,完全不适用于固态照明环境,因此需要全新的眩光评价体系。普通室内照明的显色性和色表规格,过去以白炽灯为基准,现在须设定严格的新标准。在应用方面,若要达到非视觉生物效应,智能动态照明也要成为一种标准。我们将看到,为减少因生物钟失调而出现的问题,会广泛应用光学治疗。在固定路灯方面,随着汽车系统本身的发展,不会再优先考虑物体的能见度。我们需要的不再是路灯亮度概念,而是更加三维的概念。若综合考虑中间视觉的所有效果,路灯光源的最有效光谱应该偏暖白光。老年人会丧失短波长视觉能力,是其中的主要原因。     

The strengths of in vivo magnetic resonance imaging (MRI) to study environmental adaptational physiology in fish

Adaptational physiology studies how animals cope with their environment, even if this environment is subject to permanent fluctuations such as tidal or seasonal variations. Aquatic organisms are generally more prone to be exposed to osmotic, hypoxic and temperature challenges than terrestrial animals. Some of these challenges are more restraining in an aquatic environment. To date, very few studies have used in vivo magnetic resonance imaging (MRI) to uncover the physiological mechanisms that respond to or compensate for these challenges. This paper provides an overview of what has been accomplished thus far by using MRI to study the environmental physiology of fish. It introduces the reader to the use of small teleost fish such as carp (12 cm, 60 g) and eelpout (25 cm, 50 g) as models for such research and to provide new perceptions into the applicability of MRI tools based on new insights into the nature of MRI contrast. Representative MRI studies have made contributions to the identification of the lack of cell volume repair in stenohaline fish during osmotic stress. They have studied the underlying physiological mechanisms of brain anoxia tolerance in fish and have qualified the role of the cardio-circulatory system in setting thermal tolerance windows of fish.     

An improved Wigner Monte-Carlo technique for the self-consistent simulation of RTDs

We present an original approach to including quantum transport into classical Ensemble Monte Carlo (EMC) simulations. The method, based on the Wigner transport equation, is fully self-consistent, and includes impurity and phonon scattering according to the Fermi Golden rule. It is inspired by an approach suggested by Shifren et al. [IEEE Trans. Electron Dev. 50, 769 (2003)], with some major improvements that make possible successful comparison with other simulation techniques and experiments.     

Optical sensing of biomolecules using microring resonators

A biosensor application of vertically coupled glass microring resonators with Q/spl sim/12 000 is introduced. Using balanced photodetection, very high signal to noise ratios, and thus high sensitivity to refractive index changes (limit of detection of 1.8/spl times/10/sup -5/ refractive index units), are achieved. Ellipsometry and X-ray photoelectron spectroscopy results indicate successful modification of biosensor surfaces. Experimental data obtained separately for a bulk change of refractive index of the medium and for avidin-biotin binding on the ring surface are reported. Excellent repeatability and close-to-complete surface regeneration after binding are experimentally demonstrated.     

Risk-based resource optimization for transmission system maintenance

This paper describes a resource optimization approach for transmission system maintenance selection and scheduling that is based on the cumulative long-term risk caused by failure of each piece of equipment. This approach accounts for equipment failure probability, equipment damage, as well as outage consequence in terms of dispatch cost. A method of computing the change of equipment failure probabilities and expected time to failure when equipment condition data are available is described. The method is illustrated on a 566-bus model of a U.S. utility system.     

An optimal location of static VAr compensator based on Gramian critical energy for damping oscillations in power systems

The increase in the scale and complexity of interconnected power systems leads to multiple electromechanical oscillations. Therefore, the electric network needs to be made more stable. One type of Flexible alternating current transmission systems (FACTS) devices, namely the static VAr compensator (SVC), can be installed at buses to increase the stability margins and dampen the power system oscillations by exchanging capacitive and/or inductive load to maintain and/or control specific parameters of electrical power systems. The efficiency and performance of the SVC depend on its optimal location. Consequently, seeking the optimal placement for SVC has become a key issue. In this paper, we propose a novel method to find the optimal location for the SVC based on a two‐step approach. First, an energetic approach based on the combination of the controllability Gramian critical energy analysis with the balanced realization reduction technique is used to search for several feasible locations; then the transient stability is analyzed to compare and determine an optimal location through various test cases. The effectiveness of the proposed method has been demonstrated on the IEEE 39‐bus England power system and compared with the modal controllability index. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.