A new hybrid control technique for operation of DC microgrid under islanded operating mode

This study proposes a novel combined primary and secondary control approach for direct current microgrids, specifically in islanded mode. In primary control, this approach establishes an appropriate load power sharing between the distributed energy resources based on their rated power. Simultaneously, it considers the load voltage deviation and provides satisfactory voltage regulation in the secondary control loop. The proposed primary control is based on an efficient droop mechanism that only deploys the local variable measurements, so as to overcome the side effects caused by communication delays. In the case of secondary control, two different methods are devised. In the first, low bandwidth communication links are used to establish the minimum required data transfer between the converters. The effect of communication delay is further explored. The second method excludes any communication link and only uses local variables. Accordingly, a self-sufficient control loop is devised without any communication requirement. The proposed control notions are investigated in MATLAB/Simulink platform to highlight system performance. The results demonstrate that both proposed approaches can effectively compensate for the voltage deviation due to the primary control task. Detailed comparisons of the two methods are also provided.     

Fabrication and characterization of bioactive glass/hydroxyapatite nanocomposite foam by gelcasting method

Bioceramic foams have been applied for drug releasing agents, cell loading, and widely for hard tissue scaffold. The aim of this study was fabrication and characterization of nanostructure bioceramic composite foam (BCF) consisting of hydroxyapatite (HA) and bioactive glass (BG) via gelcasting method for applications in tissue engineering. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analysis techniques were utilized in order to evaluate respectively, phase composition, dimension, morphology, and interconnectivity of pores, and particle size of synthesized HA, BG, and BCF. The results showed that fabrication of the BCF with a particle size in the range 20-42 nm and pore size in the range 100-250 μm was successfully performed. The maximum values of compressive strength and elastic modulus of the BCF were found to be about 1.95 MPa and 204 MPa, respectively, related to a sample sintered at 900 °C for 4 h. The mean values of the true (total) and apparent (interconnected) porosity were calculated in the range 86-91% and 60-71%, respectively. It seems that the measured properties make the BCF a good candidate for tissue engineering applications, preferentially in drug delivery, cell loading, and other nonloading applications.     

Evaluation of Cascade-Multilevel-Converter-Based STATCOM for Arc Furnace Flicker Mitigation

As an industry customer of electric power, an electrical arc furnace (EAF) is a major flicker source that causes major power quality problems. For a 40-MVA EAF in Tennessee, USA, a cascade-multilevel converter (CMC)-based STATic synchronous COMpensator (STATCOM) with high bandwidth is proposed for EAF flicker mitigation. In this paper, flicker mitigation techniques by using a CMC-based STATCOM are presented and verified through a transient network analyzer (TNA) system. The required STATCOM capacity is first studied through a generalized steady-state analysis. Second, the STATCOM control strategy for flicker mitigation is introduced, and simulation results are given. Finally, a TNA system of the STATCOM and an EAF system are designed and implemented. Experimental results from the TNA test show that the proposed CMC-based STATCOM and its controller can efficiently and rapidly mitigate the EAF flicker     

A multi-objective control strategy for grid connection of DG (distributed generation) resources

This paper presents a flexible control technique for connection of DG (distributed generation) resources to distribution networks, especially during ride-through on faulty grid. This strategy is derived from the abc/αβ and αβ/dq transformations of the ac system variables. The active and reactive currents injected by the DG source are controlled in the synchronously rotating orthogonal dq reference frame. The transformed variables are used to control the VSI (voltage source inverter) which connects the DG to the distribution network. Using a P.L.L. (phase locked loop) in circuit of proposed control technique, the angle of positive sequence has been detected, in order to synchronize the currents to the distribution network. The proposed control technique has the capability of providing active and reactive powers and harmonic currents to nonlinear loads with a fast dynamic response. Simulation results and mathematical analysis have been completed in order to achieve a reduced THD (total harmonic distortion), increased power factor and compensated load’s active and reactive powers. The analyses show the high performance of this control strategy in DG applications in comparison with other existing strategies.     

Application of headspace-solid-phase microextraction and HPLC for the analysis of the aroma volatile components of treacle and determination of its content of 5-hydroxymethylfurfural (HMF)

In this investigation, the headspace volatiles of treacle samples from three different producers were subjected to GC-MS and HPLC analysis in order to assess the variation in their aroma volatile composition and their content of 5-hydroxymethylfurfural (HMF). The volatile constituents were rich in aliphatic short chain acids, specially acetic acid, alcohols, aldehydes, ketones, and furan derivatives. The HMF content varied according to the producer from 66 mg/kg to 179 mg/kg. The present investigation is considered to be the first, which determine the volatile aroma profile and HMF content for treacle.     

An adaptive out-of-step relay [for power system protection]

The paper describes the development of an adaptive out-of-step relay, from the formulation of its concept to its field implementation at the Florida-Georgia interface. Adaptive relaying seeks to make adjustments to the relay characteristics as power system conditions change, thereby making the relay more attuned to the prevailing power system conditions. The work described here began as a theoretical examination of the out-of-step relaying application, its possible shortcomings, and the opportunities to make adaptive improvements. It is shown that for a system that behaves primarily as a two-machine power system, the out-of-step relay could be made more secure by applying the principle of equal area criterion. The paper describes the theory of such a relay, its hardware configuration, and the system as it is installed in the field. The newly developed technology of synchronized phasor measurements plays an important role in the realization of this relay. The paper includes a summary of the field experience gathered over a period of one year     

Putative mechanism for anticancer properties of Ag–PP (NPs) extract

One of the most important challenges in treating cancer is the invasion and the angiogenesis of cancer cells. The synthesis of green nanoparticles (NPs) and their use in therapeutic fields is one of the most effective methods with minimal side effects in cancer treatment. In this study, cytotoxic and anti‐angiogenic effects of silver NPs (AgNPs) coated with palm pollen extract [Ag–PP(NPs)] were evaluated. For this purpose, the cells were treated with NPs and then were subjected to trypan blue testing (48 h). Then, the cancer invasion was evaluated by the scratch procedure and the expressions of the vascular endothelial growth factor (VEGF) and its receptor (VEGF‐R) genes were estimated using real‐time PCR assay. Also, the angiogenesis effect of the NPs was investigated with chick chorioallantoic membrane (CAM) assay. The Ag–PP(NPs) induced cytotoxicity on MCF7 cells. The findings also showed that Ag–PP(NPs) inhibit invasive cancer cells and reduce the expression of VEGF and VEGF‐R and significantly reduced the number and vessels lengths and the lengths and weights of the embryos in CAM assay. Ag–PP(NPs) with the induction of cytotoxic effects, metastatic inhibition and anti‐angiogenesis properties should be considered as an appropriate option for treatment of cancerInspec keywords: nanomedicine, genetics, cellular biophysics, toxicology, patient treatment, silver, cancer, biochemistry, biomedical materials, nanoparticles, nanofabrication, membranesOther keywords: minimal side effects, cancer treatment, silver NPs, cancer invasion, vascular endothelial growth factor, receptor genes, VEGF‐R, real‐time polymerase chain reaction assay, angiogenesis effect, chick chorioallantoic membrane assay, MCF7 cells, invasive cancer cells, cytotoxic effects, putative mechanism, anticancer properties, antiangiogenic effects, antiangiogenesis properties, Ag–PP‐induced cytotoxicity, metastatic inhibition, palm pollen extraction, trypan blue testing, time 48.0 hour, Ag     

Digital Control of a Power Conditioner for Fuel Cell/Super-capacitor Hybrid System

This article proposes a digital control scheme to operate a proton exchange membrane fuel cell module of 1.2 kW and a super-capacitor through a DC/DC hybrid converter. A fuel cell has been proposed as a primary source of energy, and a super-capacitor has been proposed as an auxiliary source of energy. Experimental validation of the system implemented in the laboratory is provided. Several tests have been performed to verify that the system achieves excellent output voltage (V₀) regulation and super-capacitor voltage (V_SC) control under disturbances from fuel cell power (P_FC) and output power (P₀) as well as other perturbations described in analysis results.     

Subsynchronous resonance countermeasure using phase imbalance

Since the discovery in 1970 that subsynchronous resonance (SSR) was the main cause of the shaft failures at the Mohave plant in Southern Nevada, extensive research and development efforts have been devoted to the development of effective SSR mitigation measures. This paper presents a contribution to these efforts by providing a new concept for simple and reliable SSR mitigation. The basic idea is to reduce the energy exchange between the two sides of turbine-generator sets at subsynchronous oscillations by weakening the electromechanical coupling. This is attained by creating phase imbalance at subsynchronous oscillations. The imbalance diminishes the capability of the three phase currents to develop interacting electromagnetic torques and, therefore, suppresses energy exchange between the electrical and mechanical sides of turbine-generator sets. The objective of this paper is to study the influence of having the phase imbalance associated with the generator to be protected from potential torsional interaction problems     

Design issues for a single core transformer thyristor controlledphase-angle regulator

Power electronics have become increasingly reliable and cost effective at the transmission voltage level. New applications of FACTS devices are just emerging, the thyristor controlled phase-angle regulator (TCPAR) being one of them. This paper identifies and discusses several gate control and system issues for application of a single core transformer thyristor controlled phase-angle regulator. Alternative TCPAR designs are proposed