Vol. 15, No. 2, June 2018


Dejan B. Popović, Aleksandar Veg
Active Hip Orthosis for Assisting the Training of the Gait in Hemiplegics
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Abstract: The gait restoration is a significant component of the rehabilitation of patients with hemiplegia after central nervous system lesion. The typical symptom of the disability is the lack of hip extension during the stance phase and hip flexion during the swing phase of the affected leg; therefore, asymmetry and perturbed balance while walking. We developed a new modular orthosis for assisting hip flexion and extension during the therapeutic sessions of the gait in hemiplegic individuals based on thorough analysis of the gait characteristics of normal gait. The system is designed to fit into the powered postural controller Walkaround®. The system is developed based on the estimation of torque and power requirement for the gait at speeds up to 1.1 m/s. The model used for the simulation is a known double pendulum in the sagittal plane. The kinematics and dynamics used as the input for the simulation have been recorded in the gait laboratory with eight cameras and force platforms. The system needs to be clinically evaluated before it possibly can be turned into innovation.
Keywords: Hip orthosis, Modular orthosis, Walkaround®, Gait modeling, Hemiplegia.

Amin Safari, Hossein Shahsavari, Farshad Babaei
Optimal Design of Controllers for Power Network Connected SOFC Using of Multi-objective PSO
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Abstract: In this paper, we study the concept and forming manner of Solid Oxide Fuel Cell (SOFC) into the electrical system and then, its effect on small signal stability is investigated. The paper illustrates the essential module, mathematical analysis and small signal modeling of the SOFC joined to single machine system. The aim of this study is to reduce power oscillations in the presence of the SOFC with optimal stabilizer. The multi-objective Particle Swarm Optimization (MOPSO) technique has been used for designing a Power System Stabilizer (PSS) in order to improve the performance of the system. Two objective functions are regarded for the design of PSS parameters in order to maximize the damping factor and the damping ratio of the system. To evaluate the efficiency of the proposed optimal stabilizers, four scenarios are considered and then, its results have been analyzed. The proposed PSS tuning technique can be applied to a multi-machine system connected to the SOFC. The efficiency of MOPSO based proposed PSS on the oscillations the system related to SOFC is illustrated by time-domain simulation and also, the comparison of the MOPSO based proposed PSS with the PSS based-single objective method has been prepared.
Keywords: Solid Oxide Fuel Cell, Multi-objective PSO, Small Signal Model, Multi-machine System.

Megavath Venkatesh Naik, Paulson Samuel
A High Efficiency Non-Inverting Multi Device Buck-Boost DC-DC Converter with Reduced Ripple Current and Wide Bandwidth for Fuel Cell Low Voltage Applications
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Abstract: The voltage produced by the fuel cell (FC) device is unregulated and varies from 0.4 V to 0.8 V on full load to no-load respectively. When these devices are used in low voltage applications and output voltage lies between higher and lower values of input voltage range, it is required to connect a DC-DC buck-boost converter to get a fixed output voltage. In this paper, a new non-inverting multi device buck boost converter (MDBBC) is proposed, in which the multi device buck and boost converters are connected in cascade and operate individually either in buck or boost operating modes. The paper also includes the steady state analysis of MDDBC based on the state space averaging technique. A prototype model of proposed converter compatible with FCS-1000 Horizon FC model with rating of 270 W, 36 V is designed and developed. The proposed converter is experimentally validated with the results obtained from the prototype model, and results show the superiority of the converter with higher efficiency and lesser ripple current observed under steady state operation of the converter.
Keywords: Buck-Boost Converter, Multi Device Operation, Ripple Current Reduction, Buck-Boost Converters for Portable Applications.

Jelena M. Purenović, Nedeljko Dučić, Branko Matović, Milovan Purenović
The Influence of Multifunctional Microalloyed Ceramics Microstructure on Its Capacity Propertie
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Abstract: Modified porous alumo-silicate ceramics, alloyed with magnesium and microalloyed with aluminum, belongs to modern multifunctional ceramic materials. Microalloying has led to important changes in dielectric and electrical properties of ceramics, such as dielectric constant and electrical resistance. These changes are conditioned by the microstructural properties of modified porous ceramics. The obtained results have shown the unity of the influence of composition, structure, morphology and application of microalloyed multifunctional alumo-silicate ceramics on electrophysical properties. Microstructural investigations have shown that this type of ceramics has an amorphous-crystal structure, which causes important changes in its electrical properties and affects its activity. Therefore the ceramics can be considered as an active dielectric. A correlation between microstructural properties and structurally sensitive, i.e. electrophysical properties of microalloyed multifunctional alumo-silicate ceramics, was confirmed.
Keywords: Microalloying, Microstructure, Multifunctional Ceramics, Electrical Properties.

Vesna Javor, Leonid Stoimenov, Nikola Džaković, Nikola Dinkić, Dario Javor, Hans-Dieter Betz
LINETGIS Analysis of Lightning Flash Density in Serbia Based on Ten Years Data
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Abstract: Lightning detection networks installed throughout the world provide data for obtaining flash density maps and information about lightning discharges characteristics. According to the IEC 62858 Standard, lightning data for at least ten years is required to ensure that short time scale variations in lightning parameters are accounted for. LINET (European Lightning Detection Network) was installed in Serbia in 2008, so its data for the last ten years period are used for the analysis in this paper. LINETGIS is a new software application based on geographical information system (GIS) technology in order to obtain regional flash density maps of Serbia. LINETGIS application may be used for up-to-date regional flash density maps of Serbia, but also for any other GIS covered area.
Keywords: Lightning flash density map, GIS technology, Lightning current, Lightning detection system.

Aleksandra Panajotović, Nikola Sekulović, Aleksandra Cvetković, Daniela Milović
Performance of Cooperative Multi-hop Multiuser Relaying Networks
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Abstract: This paper presents both capacity and error performances of cooperative multi-hop multiuser relay system. All multi-hop cooperative relays in the system apply maximal-ratio combining (MRC) scheme, while signal transmission to end users is carried out using opportunistic scheduling algorithm. Numerical results for spectral efficiency and average symbol error probability (ASEP) for considered system are presented and discussed.
Keywords: Amplify-and-forward relay, Average symbol error probability, Multi-hop, Multiuser, Rayleigh fading, System capacity.

Uglješa Jovanović, Igor Jovanović, Marjan Blagojević, Dejan Krstić, Dragan Mančić
Low-cost Teslameter based on Hall Effect Sensor MLX90242
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Abstract: A low-cost teslameter based on a Hall effect sensor MLX90242 is proposed in this paper. The proposed teslameter is built around a PIC18F4550 microcontroller and it can measure magnetic flux density in the range between –55 mT and 55 mT. Temperature stability of measurements originates from the MLX90242 sensor itself. In order for the proposed transducer to be accurate, it has undergone a calibration procedure using a highly accurate teslameter employed as reference instruments and high-quality variable-field electromagnet. The proposed teslameter can store measurements on a PC via built-in USB communication.
Keywords: Calibration, Hall effect sensor, Microcontroller, Teslameter, Variable-field electromagnet.

Oleg V. Dvornikov, Vladimir А. Tchekhovski, Valentin L. Dziatlau, Nikolay N. Prokopenko, Nikolay V. Butyrlagin
Design of Low-Temperature DDOAs on the Elements of BiJFet Array Chip MH2XA030
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Abstract: Brief information about the new BiJFet array chip (AC) MH2XA030 intended for accelerated creation of analog integrated circuits (IC), which retain their performance under the influence of penetrating radiation and extremely low temperatures (up to minus 197С) is presented. The features of schematic design of two types of DDOAs (OAmp3, OAmp4) are considered. The recommendations on the schematic design of the DDOA are developed taking into account the static characteristics of the field effect and bipolar transistors of the AC under the influence of low temperatures. The amplitude-frequency response of the DDOA and the dependence of the noise voltage on the frequency of Fourier density are given. At a temperature of 197 С cryogenic amplifiers OAmp3 (OAmp4) are characterized by the following parameters: the current consumption is less than 500 μA, the input current is less than 1 fA, the voltage gain is more than 50.000 (200.000), the offset voltage is less than 200 (60) μV. The results of the circuit simulation of the instrumentation amplifier based on DDOA OAmp3 are presented.
Keywords: Analog integrated circuits, Array chip, Radiation hardness, Cryogenic electronics, Differential difference operational amplifier.

©2018 Serbian Journal of Electrical Engineering