Optimal Voltage Regulation of Unbalanced Distribution Networks with Coordination of OLTC and PV Generation

Photovoltaic (PV) smart inverters can regulate voltage in distribution systems by modulating reactive power of PV systems. In this paper, an optimization framework for optimal coordination of reactive power injection of smart inverters and tap operations of voltage regulators for multi-phase unbalanced distribution systems is proposed. Optimization objectives are minimization of voltage deviations and tap operations. A novel linearization method convexifies the problem and speeds up the solution. The proposed method is validated against conventional rule-based autonomous voltage regulation (AVR) on the highly-unbalanced IEEE 37 bus test system. Simulation results show that the proposed method estimates feeder voltage accurately, voltage deviation reductions are significant, over-voltage problems are mitigated, and voltage imbalance is reduced.Comment: IEEE Power and Energy Society General Meeting 201

Smartphone photography as a teledentistry method to evaluate anterior composite restorations

Objective. Today, teledentistry have gain more attention than past due to the advances in technology. The aim of this study was to compare the use of smartphone photography as a method in teledentistry with the face-to-face examination in the evaluation of anterior composite restorations. Materials and Methods. In this study, photographs of 24 composite restorations in patients attended to the clinic of Ardabil Dental School were obtained using a smartphone without any additional equipment and sent by email to 10 remote observers. As a gold standard method, these restorations were evaluated by an experienced expert in restorative dentistry a face-to-face examination. In both methods FDI criteria were used to evaluate the restorations and classified them as acceptable or not. Sensitivity, specificity, positive and negative predictive values, and diagnostic accuracy of the photographic method relative to face-to-face method were calculated. Furthermore the Mann–Whitney U test was used to statistically compare the two methods in detail. Results. The sensitivity, specificity, positive predictive value, and negative predictive value of the smartphone photography method was 69.35%, 48.72%, 87.34%, and 23.75%, respectively. A diagnostic accuracy of 65.97% was obtained. Statistically, in overall the photographic method rated the restorations as better than they were in reality (face-to-face examination) ( p = 0.002 ). Conclusions. The diagnostic accuracy of the method of evaluating anterior composite restorations by smartphone photography was moderate and the use of this method in teledentistry, although was promising, needs to be improved

ResearchGate Social Network: Opportunities and Challenges

Introduction: ResearchGate, as one of the academic-social networks, has become a platform for scientific cooperation to promote scientific skills. A large number of researchers engage in scientific activities and share research results. This paper aims to study the ResearchGate related researches and examines its opportunities and challenges for the academic communities. Methods: The present research is a narrative-review. The study population includes English-language articles indexed in reputable databases such as Scopus and Web of Science and articles retrieved through Google Scholar published in reputable journals. Results: Activity in ResearchGate enhances citation indexes more than ever. According to some studies and due to the importance of citation in universities' ranking, the use of the ResearchGate professional network can lead to improving the ranking of universities in international ranking systems. However, according to former studies, there are drawbacks to this network, and it is necessary for the scientific communities to use the benefits of this network consciously. Conclusion: Familiarity with the opportunities and challenges of applying ResearchGate can provide relevant information to authorities to make informed decisions about using this social network in academic communities

Dynamic Weight-Based Collaborative Optimization for Power Grid Voltage Regulation

Power distribution grids with high PV generation are exposed to voltage disturbances due to the unpredictable nature of renewable resources. Smart PV inverters, if controlled in coordination with each other and continuously adapted to the real-time conditions of the generation and load, can effectively regulate nodal voltages across the feeder. This is a fairly new concept and requires communication and a distributed control logic to realize a fair utilization of reactive power across all PV systems. In this paper, a collaborative reactive power optimization is proposed to minimize voltage deviation under changing feeder conditions. The weight matrix of the collaborative optimization is updated based on the reactive power availability of each PV system, which changes over time depending on the cloud conditions and feeder loading. The proposed updates allow PV systems with higher reactive power availability to help other PV systems regulate their nodal voltage. Proof-of-concept simulations on a modified IEEE 123-node test feeder are performed to show the effectiveness of the proposed method in comparison with four common reactive power control methods

Coordination of OLTC and Smart Inverters for Optimal Voltage Regulation of Unbalanced Distribution Networks

Photovoltaic (PV) smart inverters can improve the voltage profile of distribution networks. A multi-objective optimization framework for coordination of reactive power injection of smart inverters and tap operations of on-load tap changers (OLTCs) for multi-phase unbalanced distribution systems is proposed. The optimization objective is to minimize voltage deviations and the number of tap operations simultaneously. A novel linearization method is proposed to linearize power flow equations and to convexify the problem, which guarantees convergence of the optimization and less computation costs. The optimization is modeled and solved using mixed-integer linear programming (MILP). The proposed method is validated against conventional rule-based autonomous voltage regulation (AVR) on the highly-unbalanced modified IEEE 37 bus test system and a large California utility feeder. Simulation results show that the proposed method accurately estimates feeder voltage, significantly reduces voltage deviations, mitigates over-voltage problems, and reduces voltage unbalance while eliminating unnecessary tap operations. The robustness of the method is validated against various levels of forecast error. The computational efficiency and scalability of the proposed approach are also demonstrated through the simulations on the large utility feeder.Comment: Accepted for Electric Power Systems Research. arXiv admin note: text overlap with arXiv:1901.0950

Service Quality Assessment of Hospital Libraries: a LibQUAL+ Survey

Objective: The purpose of this research is to evaluate the hospital libraries service quality of Shahid Beheshti University of Medical Sciences from the users’ perspectives based on the LibQUAL+ model. Furthermore, is to make a comparison between library services of general hospitals versus specialized one. Materials and methods: The survey used the LibQUAL+ model to evaluate service quality of libraries of general as well as specialized hospitals of Shahid Beheshti University of Medical Sciences (12 libraries) (Iran). The data were collected from library clients by administering the LibQUAL+ questionnaire in a printed format. Results: It has been revealed that hospital libraries have succeeded in satisfying the minimum expectations of its users but could not meet the customers’ desired expectations that make them delighted. Information Control is the least satisfying dimension, whereas the Library as a place is the most satisfying dimension. The users are more satisfied with general hospitals library services rather than specialized ones in all dimensions. Conclusion: The hospital libraries failed to meet the minimum expectations of users in two dimensions of information control and the library as a place. It is suggested to improve the quality and quantity of library facilities and to create a pleasant atmosphere for users by considering a proper space for the study of clients. This will lead to help hospital libraries to meet the desired level of requirements of users

Frequency Regulation with Heterogeneous Energy Resources: A Realization using Distributed Control

This paper presents one of the first real-life demonstrations of coordinated and distributed resource control for secondary frequency response in a power distribution grid. We conduct a series of tests with up to 69 heterogeneous active devices consisting of air handling units, unidirectional and bidirectional electric vehicle charging stations, a battery energy storage system, and 107 passive devices consisting of building loads and photovoltaic generators. Actuation commands for the test devices are obtained by solving an economic dispatch problem at every regulation instant using distributed ratio-consensus, primal-dual, and Newton-like algorithms. The distributed control setup consists of a set of Raspberry Pi end-points exchanging messages via an ethernet switch. The problem formulation minimizes the sum of device costs while tracking the setpoints provided by the system operator. We demonstrate accurate and fast real-time distributed computation of the optimization solution and effective tracking of the regulation signal by measuring physical device outputs over 40-minute time horizons. We also perform an economic benefit analysis which confirms eligibility to participate in an ancillary services market and demonstrates up to $53K of potential annual revenue for the selected population of devices

A Kernel-Based Predictive Model of EV Capacity for Distributed Voltage Control and Demand Response

Energy storage and reactive power supplied by electric vehicles (EVs) through vehicle-to-grid (V2G) operation can be coordinated to provide voltage support, thus reducing the need of grid reinforcement and active power curtailment. Optimization and control approaches for V2G-enabled reactive power control should be robust to variations and offer a certain level of optimality by combining real-time control with an hours-ahead scheduling scheme. This paper introduces an optimization and control framework that can be used for charging batteries and managing available storage while using the remaining capacity of the chargers to generate reactive power and cooperatively perform voltage control. Stochastic distributed optimization of reactive power is realized by integrating a robust distributed sub-gradient method with conditional ensemble predictions of V2G capacity. Hence, the proposed solutions can meet system operational requirements for the upcoming hours by enabling instantaneous cooperation among distributed EVs

A Kernel-Based Predictive Model Of Ev Capacity For Distributed Voltage Control And Demand Response

Energy storage and reactive power supplied by electric vehicles (EVs) through vehicle-to-grid (V2G) operation can be coordinated to provide voltage support, thus reducing the need of grid reinforcement and active power curtailment. Optimization and control approaches for V2G-enabled reactive power control should be robust to variations and offer a certain level of optimality by combining real-time control with an hours-ahead scheduling scheme. This paper introduces an optimization and control framework that can be used for charging batteries and managing available storage while using the remaining capacity of the chargers to generate reactive power and cooperatively perform voltage control. Stochastic distributed optimization of reactive power is realized by integrating a robust distributed sub-gradient method with conditional ensemble predictions of V2G capacity. Hence, the proposed solutions can meet system operational requirements for the upcoming hours by enabling instantaneous cooperation among distributed EVs