Intelligent control of static synchronous series compensator via an adaptive self-tuning PID controller for suppression of torsional oscillations

In this paper, an intelligent controller is proposed to control a static synchronous series compensator (SSSC) in order to mitigate subsynchronous resonance (SSR) oscillations in a power system. This intelligent controller is an adaptive self-tuning PID controller. To train the PID controller, the gradient descent method is employed where the learning rate is adapted in every iteration in order to accelerate the speed of convergence. This control scheme also requires a wavelet neural network (WNN) to identify the controlled system dynamic. To update the parameters of WNN, the gradient descent (GD) along with the adaptive learning rates derived by the Lyapunov method is used. The computer simulations are used to show the ability of the proposed controller. In addition, the performance of the proposed controller is compared with another self-tuning PID controller. The results demonstrate that the proposed controller has a successful performance in minimizing the SSR.     

Application of neural networks to predict the steady state performance of a Run-Around Membrane Energy Exchanger

Modeling the performance characteristics of thermal systems has been a research interest for many decades with moisture transfer systems experiencing a resurgence over the last decade, especially in heating, ventilating, and air conditioning (HVAC) applications. In this study, a neural network (NN) model is developed to predict the heat and moisture transfer performances (i.e., the sensible and latent effectivenesses) of a novel HVAC energy exchanger called the Run-Around Membrane Energy Exchanger (RAMEE) which is able to transfer both heat and moisture between exhaust and supply air streams. The training data set for the NN model covers a wide range of design and operating parameters and is produced using an experimentally validated finite difference (FD) model. Two separate NNs (one for sensible and one for latent energy transfer) each with five inputs and one output, are selected to represent the RAMEE. The results from NN models are numerically and experimentally validated. The root mean squared error (RMSE) between the FD and NN models are 0.05 °C and 2 × 10^?5 kg_v/kg_a, indicating satisfactory agreement for energy exchange calculations. The paper reports the weights and biases to make the results of this study reproducible. These NN models are very fast and easy to use therefore, they might be used for design and for estimating the annual energy savings in different buildings which use the RAMEE in their HVAC system. Additionally, the NN models can be used with optimization algorithms to maximize energy savings and minimize life-cycle costs for a given system.     

Microstructural, electrical, and mechanical characterization of Bi2Cu0.1V0.9O5.35 (BICUVOX) ceramics fabricated from co-precipitated precursor powders

Copper-doped bismuth vanadate (Bi₂Cu_0.1V_0.9O_5.35, BICUVOX) was synthesized by a co-precipitation process which resulted in a homogenous, fine-grained powder with an average particle size of ~0.45 μm. The consolidated BICUVOX powder was sintered at temperatures between 625 and 800 °C for 0–8 h in air. The correlation between the thermal processing schedule and the final microstructure were completed for all conditions through stereological analysis of the resultant cross-sectional scanning electron microscope images. From this work, the sintering schedule of 675 °C for 1 h resulted in acquiring a BICUVOX ceramic microstructure that displayed ~97 % relative density with an average grain size of ~1.29 μm. This processing condition was ~75–125 °C lower than typical sintering temperatures for the same density, and resulted in a final grain size that is ~5–10 μm smaller in size. The four-point conductivity testing of the BICUVOX ceramics in air showed values of ~0.003–0.007 and ~0.07–0.12 S/m at 300 °C and 500 °C, respectively, depending upon the thermal processing schedule. The average flexure strength of the same BICUVOX membrane was measured using a ring-on-ring configuration, and this measurement showed flexural strengths as high as 159.3 MPa. This strength is ~92 % greater than previously reported values for BICUVOX membranes.     

Prehydrolysis in softwood pulping produces a valuable biorefinery fraction for material utilization

A scaled-up prehydrolysis process was elaborated to demonstrate an industrially feasible operation step in a pulping process that generates a valuable side product in addition to the cellulose pulp. The valuable side product is aqueous process liquor, a softwood hydrolysate (SWH) herein produced in 60 L batches, and its components were recovered and utilized as materials. The process parameters were shown to influence the yield, composition, and quality of the obtained hydrolysates. Furthermore, the process conditions were shown to influence the ability of SWHs to form free-standing, foldable films in blends with either microfibrillated cellulose (MFC) or carboxymethyl cellulose (CMC). Films with oxygen permeabilities (OP) as low as 0.35 cm(3) μm day(-1) m(-2) kPa(-1) at 50% relative humidity, were produced from aqueous solutions providing a viable and green alternative to petroleum-based packaging barriers. The OPs were very low regardless of SWH film composition and upgrading conditions, whereas the films' tensile performance was directly controlled by the ratio of SWH to cocomponent.     

The birefringence and anisotropic planar shrinkage of polycarbonate/organoclay injection moldings

The main objective of the present work was the study of the effect of organoclay on planar shrinkage anisotropy of polymeric injection‐molded products by means of a rheological technique, in conjunction with birefringence measurements, performed on polycarbonate/organoclay samples. Polarized optical microscopy at elevated temperatures revealed that the birefringence due to the ordered‐silicate layers had a negative contribution to the overall birefringence of the samples. The maximum value of the calculated‐order parameter based on these results was found to be near unity, indicating an appreciable degree of flow alignment for the silicate layers. Different states of silicate layer orientation, with some layers aligned parallel to the in‐plane direction at the skin layer or partially tilted from the planar direction at the core region, were observed through the optical analysis along the thickness direction. The anisotropic shrinkage measurements showed that organoclay reduced both in‐flow and cross‐flow shrinkages, resulting in a low extent of planar shrinkage anisotropy. This can be attributed to the flow alignment of clay particles closely parallel to the in‐plane direction. Prolonged relaxation of the flow‐induced molecular orientation combined with faster solidification were also found to play an appreciable role in the decreased shrinkage anisotropy. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Miniaturized integrated antennas for far-field wireless powering

This paper describes a series of high-efficiency miniaturized antennas of different sizes that can be integrated with the same wireless-powered RFID chip. Since this RFID chip has power scavenging capability in different ISM bands, several integrated on-chip and off-chip antennas in the three ISM bands of 900 MHz, 2.4 GHz and 5.8 GHz are designed, including one antenna integrated on chip. All proposed antennas are derived from a new planar antenna structure which can be designed toward arbitrary input impedance within a given area constraint. The measurement results for the presented antennas show a different read range. The resulting read range versus antenna size diagram specifies the best operating frequency band for a given read range and occupied area. Though this diagram depends on the chip's specifications like the power-on sensitivity and input impedance, it can be generated for any chip. In addition, the measurement results concerning read range and radiation patterns for the proposed antennas are presented and compared with simulation results, showing very good agreement.     

Kinematics of a star-triangle planar parallel manipulator

This paper addresses kinematics of a 3 degree-of-freedom (DOF) planar parallel manipulator called Star-Triangle manipulator. The manipulator has good accuracy and a relatively large singularity-free workspace. First, position analysis of the manipulator is implemented indicating that both the inverse and forward position problems of the manipulator have only one solution. Then, velocity and singularity analyses of the manipulator are carried out and its isotropic configurations are identified using two Jacobian matrices. Based on the isotropic conditions, the workspace of manipulator is determined geometrically and it is shown that all points in the workspace are free of singularities. At last, kinematic accuracy of the manipulator is investigated on the workspace through a kinematic conditioning index (KCI).     

Application of homotopy analysis method to solve MHD Jeffery-Hamel flows in non-parallel walls

The MHD Jeffery-Hamel flows in non-parallel walls are investigated analytically for strongly nonlinear ordinary differential equations using homotopy analysis method (HAM). Results for velocity profiles in divergent and convergent channels are presented for various values of Hartmann and Reynolds numbers. The convergence of the obtained series solutions is explicitly studied and a proper discussion is given for the obtained results. Comparison between HAM and numerical solutions showed excellent agreement.     

Phase Stability in Mechanically Alloyed Mg–Ni System Studied by Experiments and Thermodynamic Calculations

In this study, microstructural evolution of Mg–Ni alloy during mechanical alloying(MA) was investigated.Also, a thermodynamic approach was utilized to predict the most stable phases formed in Mg–Ni alloy after MA. The phase composition and microstructural properties of Mg–Ni alloy were assessed by X-ray diffractometry, high-resolution field emission scanning electron microscopy and high-resolution transmission electron microscopy. The results showed that ball milling of magnesium and nickel powder mixture for 70 h yields nanostructural Mg2Ni compound with an average grain size of ~20 nm. Thermodynamic calculations revealed that in the composition ranges of 0.0 \ XMg\ 0.03(at.%)and 0.97 \ XMg\ 1, there is no driving force for amorphous phase formation. In the composition range of 0.07 \ XMg\ 0.93, the change of Gibbs free energy for amorphous phase formation was more negative than solid solution.While for XMg= 0.66(nominal composition of Mg2Ni intermetallic phase), the change of Gibbs free energy for intermetallic phase was found to be more negative than both amorphous and solid solution phases indicating that Mg2Ni intermetallic compound is the most stable phase, in agreement with the experimental observations.