Vol. 18, No. 1, February 2021


Nikola Knežević, Branko Lukić, Kosta Jovanović, Leon Žlajpah, Tadej Petrič
End-Effector Cartesian Stiffness Shaping – Sequential Least Squares Programming Approach
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Abstract: Control of robot end-effector (EE) Cartesian stiffness matrix (or the whole mechanical impedance) is still a challenging open issue in physical human-robot interaction (pHRI). This paper presents an optimization approach for shaping the robot EE Cartesian stiffness. This research targets collaborative robots with intrinsic compliance - serial elastic actuators (SEAs). Although robots with SEAs have constant joint stiffness, task redundancy (null-space) for a specific task could be used for robot reconfiguration and shaping the stiffness matrix while still keeping the EE position unchanged. The method proposed in this paper to investigate null-space reconfiguration's influence on Cartesian robot stiffness is based on the Sequential Least Squares Programming (SLSQP) algorithm, which presents an expansion of the quadratic programming algorithm for nonlinear functions with constraints. The method is tested in simulations for 4 DOF planar robot. Results are presented for control of the EE Cartesian stiffness initially along one axis, and then control of stiffness along both planar axis - shaping the main diagonal of the EE stiffness matrix.
Keywords: Cartesian Stiffness Control, Robot Redundancy, Physical Human-Robot Interaction, Sequential Last Squares Programming.

Dejan N. Milić, Daniela M. Milović, Jelena A. Anastasov
Experimental Indoor Validation of Weak Intensity Fluctuations over Free-space Optical Communication Link
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Abstract: In this paper, we present experimental results for characterizing turbulence phenomena in free-space optical (FSO) communication under laboratory controlled conditions. Collected data is used for statistical determination of the probability density function (PDF) of irradiance signal fluctuations. In literature, there are a number of empirical models for variety of turbulence regimes. Thus, obtained PDF is compared with selected models from the bibliography in order to describe properly statistical properties of real turbulent channel and help improving of FSO system performance calculation. In overall, analysis has shown that the results obtained under given constraints fit well with the exponentiated Weibull turbulence model.
Keywords: Free space optics, Probability Density Function (PDF), Scintillation, Turbulence.

Evgeniia A. Bulycheva, Sergey A.Yanchenko
Real-Time Harmonic Identification Under Varying Grid Conditions
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Abstract: One of the challenges of the power quality management is a need for reliable harmonic identification in grids with multiple non-linear loads. This paper proposes a novel method to accurately determine time-varying harmonic contributions of non-linear loads to the total grid voltage distortion. The use of the invasive measurement approach and ternary pulse sequence as a stimuli guarantees an accurate assessment of harmonic contribution with the account for time-variating harmonic impacts. The application of proposed approach is demonstrated by means of time-domain grid simulation with implemented white-box model of a pulse sequence generator. Statistical estimation of the accuracy of the proposed approach as well as comparison with typical harmonic identification methods justify its effectiveness under non-stationary network conditions.
Keywords: Harmonic identification, Harmonic contribution, Impedance measure¬ment, Non-linear load, Power quality.

Bhagya Rajesh Navada, Santhosh Krishan Venkata
Filter Design Using Data Fusion for a Pneumatic Control Valve
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Abstract: This paper presents a filter design technique for a pneumatic valve using data fusion techniques. The objective of this paper is to examine the suppression of the effect of parameters causing deviation from normal system performance using the technique of data fusion over time. The output of a system affected by inherited noise is processed by applying operations such as finding the statistical variance, time warping, interpolation, and extrapolation. These techniques are used to compute the transfer function of the filter, which when cascaded with the system will suppress the effect of noise on the process. The operation of the control valve is affected by characteristics such as stiction, structural deformation, etc. The characteristics of the system are studied and data for multiple time instances are extracted to carry out fusion across time by dynamic time warping. Tests show that the filter presented here can suppress the effects of stiction and mechanical deformation on the output signal.
Keywords: Control valve, Data fusion, Dynamic time warping, Filter, Spline interpolation.

Atul Kumar Pandey, Nisha Gupta
An Energy Efficient Hybrid MAC Protocol for Smart Home Networks
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Abstract: In this paper cluster-based hybrid MAC (CB-HMAC) protocol, based on IEEE 802.15.4 MAC is proposed for smart home networks. The CB-HMAC is specially designed for short packet transmission in a dense home network environment. Simulation results show that the proposed CB-HMAC is more energy-efficient than other medium access control (MAC) protocols without sacrificing much delay and throughput.
Keywords: Energy management, Medium access control (MAC), Smart Home networks, Wireless personal area network.

Robert Agyare Ofosu, Benjamin Odoi, Mercy Asamoah
Electricity Consumption Forecast for Tarkwa Using Autoregressive Integrated Moving Average and Adaptive Neuro Fuzzy Inference System
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Abstract: Electricity has become one of the inelastic goods in our world today. The proper functioning of most equipment today relies on electricity. Taking Tarkwa which is a mining community into consideration, the various mines, schools, shops, banks and other companies in the municipality massively rely on electricity for their day to day running. Therefore, knowing the exact amount of electricity to produce and distribute for the smooth running of businesses and basic living is of great necessity. This study compared and formulated a model to forecast and predict the daily electrical energy consumption in Tarkwa for the year 2019. The data used was a monthly dataset for the year 2018 and it comprised of the temperature, wind speed, population and electricity consumption for Tarkwa. The methods used were Artificial Neuro-Fuzzy Inference System (ANFIS) and Autoregressive Integrated Moving Average (ARIMA). The ANFIS was used as a predictor to predict the electricity consumption based on the training and testing of the dependent and independent variables. The ARIMA was used to forecast the dependent and independent variables for 2019. These simulations were done using MATLAB and Minitab. The results of the analysis revealed that the training and testing dataset allowed ANFIS to learn and understand the system but the ANFIS could only forecast the 2019 electricity consumption after the input data to the system was changed to the ARIMA forecasted 2019 independent variables. It was observed that the amount of electricity consumed in 2019 increased by 14%.
Keywords: Electricity consumption, Error metrics, ARIMA, ANFIS, Forecast.

Ana Radojević, Danijela Nikolić, Jasna Radulović, Jasmina Skerlić
Energy Benchmarking in Educational Buildings in the City of Kragujevac – Possibilities for Energy Efficiency Improvement
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Abstract: The implementation of energy efficiency measures and use of renewable energy sources in educational buildings can significantly contribute to reducing energy consumption, but also to CO2 emissions in the entire public sector. The paper shows the comparison of energy consumption indicators for 61 elementary school buildings which have previously been divided in 12 groups, according to the period of construction and size, based on the national typology called TABULA, as the first step of further study on how to use the renewable energy sources.
The aim of this paper is to use the energy benchmarking process to select representative facilities which are suitable for applying renewable energy sources, for their further energy efficiency improvement.
Indicators of annual specific electricity consumption and CO2 emissions per unit area [kWh/m2] and per user [kWh/user] were calculated. After that, from two groups (in which the highest electricity consumption and CO2 emissions are 68.37% and 74.53% of the total consumption/ emissions), one representative facility was selected.
Keywords: Energy benchmarking, Educational buildings, Electrical energy consumption, CO2 emission.

Miloš Milovanović, Jordan Radosavljević, Bojan Perović
Optimal Placement and Sizing of Shunt Capacitors in Distorted Distribution Systems Using a Hybrid Algorithm
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Abstract: In this paper, a novel hybrid phasor particle swarm optimization and gravitational search algorithm, namely the hybrid PPSOGSA algorithm, is proposed to find the optimal size and location of shunt capacitors in distribution systems with non-linear loads. The performance of PPSOGSA are studied and evaluated using the IEEE 9- and 85-bus test systems with the objective of minimizing the total annual cost of the system. The procedure is conducted taking into account effects of harmonic distortion and discrete size of capacitors available in the market. Simulation results are compared with those obtained by other optimization techniques, and verified using the Electrical Transient Analysis Program (ETAP). It was established that that the hybrid PPSOGSA algorithm provides better solutions in terms of convergence and accuracy.
Keywords: Capacitor placement, Distribution system, Harmonic distortion, Hybrid algorithm.

Milić Djekić
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