Opportunities for enhancing the security and reliability of power supply as well as the utilization of renewable and efficient energy sources have generated major interest in Microgrids. A microgrid typically consists of interconnected loads, distributed generators (DG) and energy storages, and should be able to operate in parallel with the utility grid or as a power-island. The main focus of this thesis is on the transition between parallel and islanded operation of a microgrid. A literature review on existing microgrids was carried out. Based on the survey, a microgrid test system was implemented on PSCAD/EMTDC simulation program. The microgrid controls essential for the study and a load shedding scheme were designed and implemented. When the microgrid changes from parallel to islanded operation, its controls need to be changed. It was found that delays in microgrid control mode transition can impact the amount of load need to be shed to preserve the frequency stability and the power quality of the islanded microgrid. The importance of fast detection of islanding was therefore highlighted. The IEEE standard 1547.4-2011 recommends application of the existing DG synchronization criteria for microgrid synchronization. The adequacy of these criteria for synchronization of a microgrid with highly unbalanced loading was investigated. It was found that the required criteria can be met with the support of switched capacitors for voltage balancing, and a circuit breaker supervised by a synchro-check relay is sufficient to successfully reconnect an islanded microgrid back to the utility. In order to meet the requirement for fast detection of islanding of microgrids, new islanding detection technique was proposed. In the proposed scheme, Discrete Wavelet Transform was used to extract features from transient current and voltage signals, and then a Decision Tree classifier was employed to distinguish islanding events from other transients. Simulation based tests asserted that the proposed technique has a high reliability and fast response compared to most existing islanding detection methods. Also, the detection time of the proposed method was invariant with the power imbalance in the microgrid, and gave a zero non-detection-zone with any type of generator.

Using a unique panel data set for German grocery prices we find significant price synchronization within food retail chains as well as within individual food stores (between products). Price synchronization between chains appears to be less pronounced. Common shocks can only explain some synchronization, indicating that strategic motives as well as menu costs are of significant importance. (author's abstract) / Series: Working Papers Series "Growth and Employment in Europe: Sustainability and Competitiveness"

This Master of Applied Science thesis presents a single phase grid connected DC/AC inverter with reactive power (VAR) control for residential photovoltaic (PV) applications. The inverter, utilizing the voltage sourced inverter (VSI) configuration, allows the local residential PV generation to actively supply reactive power to the utility grid. A low complexity grid synchronization method was introduced to generate the parallel and orthogonal components of the grid voltage in a highly computationally efficient manner in order to create a synchronized current reference to the current control loop. In addition, the inverter is able to use a small long life film type capacitor on the DC-link by utilizing a notch filter on the voltage control loop. Simulations were performed on PSCAD/EMTDC platform and a prototype was also developed in the lab to prove the effectiveness of the controllers and the grid synchronization method.

This Master of Applied Science thesis presents a single phase grid connected DC/AC inverter with reactive power (VAR) control for residential photovoltaic (PV) applications. The inverter, utilizing the voltage sourced inverter (VSI) configuration, allows the local residential PV generation to actively supply reactive power to the utility grid. A low complexity grid synchronization method was introduced to generate the parallel and orthogonal components of the grid voltage in a highly computationally efficient manner in order to create a synchronized current reference to the current control loop. In addition, the inverter is able to use a small long life film type capacitor on the DC-link by utilizing a notch filter on the voltage control loop. Simulations were performed on PSCAD/EMTDC platform and a prototype was also developed in the lab to prove the effectiveness of the controllers and the grid synchronization method.

Molecular, cellular, and physiological processes within an organism are set to occur at specific times throughout the day. The timing of these processes is under control of a biological clock. Nearly all organisms on Earth have biological clocks, ranging from unicellular bacteria and fungi to multicellular plants, insects, reptiles, fish, birds, and mammals. The biological clock is an endogenous time-keeping mechanism that generates the onset of many processes and coordinates the phases of processes over 24 hours. While the biological clock allows these organisms to maintain roughly 24-hour, or circadian, timing in daily processes, many organisms have the ability to set their clocks, or entrain them, to changes in light. In mammals, the suprachiasmatic nucleus (SCN) is the master biological clock that entrains daily physiological and behavioral rhythms to the appropriate times of day and night. The SCN is located in the hypothalamus and contains thousands of neurons and glia that function in coordinating system-level physiological rhythms that are entrained to environmental light cues. Many of these neurons and glia are individual circadian oscillators, and the cellular mechanisms that couple them into ensemble oscillations are emerging. Adenosine triphosphate (ATP) is a transmitter involved in local communication among astrocytes and between astrocytes and neurons. ATP released from astrocytes may play a role in SCN cellular communication and synchrony. Extracellular ATP accumulated rhythmically in the rat SCN in vivo, and ATP released from rat SCN astrocytes in vitro was rhythmic, with a periodicity near 24 hours. ATP released from mouse SCN astrocytes was circadian, and disruption of the molecular clock abolished rhythmic extracellular ATP accumulation. SCN astrocyte cultures with disrupted molecular clocks also had marked reductions in total ATP accumulation compared to SCN astrocyte cultures with functional biological clocks. Furthermore, ATP-induced calcium transients were rhythmic, and this rhythmic purinergic sensitivity was abolished in clock mutant astrocytes. Pharmacological blockade of purinergic signaling, with antagonists of both the P2X7 and P2Y1 receptors, led to a gradual reduction in the amplitude of coordinated ATP accumulation over three days. These purinergic receptor antagonists, as expected, led to a reduction in calcium responses of SCN astrocytes to ATP and led to a dampening of clock gene expression rhythms as determined by PER2::LUC bioluminescence reporting in SCN astrocytes. These data demonstrate that astrocytes of the mammalian SCN rhythmically release ATP and are rhythmically sensitive to ATP in a manner dependent on their intrinsic molecular clock. Ensemble rhythmicity of SCN astrocytes is, in turn, dependent on that rhythmic purinergic signaling via both P2X and P2Y classes of ATP receptors. These results are indicative of a functional role for ATP accumulation within the SCN, with astrocytes releasing ATP every 24 hours for continual signaling onto astrocytes and neurons to maintain daily coordinated synchrony of the clocks in these cells.

Thesis (PhD)--University of South Australia, 1993.

The rapid evolution of current and upcoming high speed and complex communications networks often necessitates flawless time synchronization among the network nodes in order to guarantee performance. GPS based synchronizers have long been used for synchronizing telecommunications equipment, currently providing an accuracy of up to 10ns. Such high accuracy demands excellent operation from GPS timing receivers. Interference is an important threat to GPS performance. Any degradation in performance, due to the introduction of interference, can cause these receivers to provide a low quality timing solution, or to lose lock with incoming GPS signals altogether. This consideration motivates the study of the performance of GPS timing receivers in the presence of harmful interference. This work is devoted to the theoretical and practical investigations of the effects of RF interference on GPS-based synchronizers and their impacts on communications networks. Contributions made during this work include: a) Identification of the processes and the parameters involved in producing a timing solution which are vulnerable to interference; b) experimentbased confirmation of a hypothesis about the effects of interference on GPS timing receivers; c) identification of the effects of degraded synchronization on the performance of communications networks, especially CDMA and GSM cellular networks, which rely upon GPS based synchronizers; and d) proposal of a method to predict and avoid communications network performance degradation.

Report (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Abstract. Includes bibliographical references (leaf 32). Also available via the Internet.

Thesis (Ph.D.)--University of Delaware, 2008. / Principal faculty advisor: Guang R. Gao, Dept. of Electrical & Computer Engineering. Includes bibliographical references.

Thesis (Ph. D.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains x, 139 p. : ill. Includes abstract. Includes bibliographical references (p. 132-139).