Iranian Journal of Electrical and Electronic Engineering
Volume:19 Issue: 2, Jun 2023

The quality of signal at a particular location is essential to determine the performance of mobile system. The problem of poor network in Lagos, Nigeria needs to be addressed especially now that the attention is toward online learning and meetings. Existing empirical Path Loss (PL) models designed elsewhere are not appropriate for predicting the 4G Long-Term Evolution (LTE) signal in Nigeria. This research developed a modified Okumura-Hata model in 4G network. The Okumura-Hata model being the closest to the measured values was modified using the PL exponent. The modified model was enhanced by Gravitational Search Algorithm (GSA). The measured data, modified and existing models were simulated using MATLAB R2018a software. Root Mean Square (RMSE) was used to evaluate the performance modified and existing and models. The result showed that Enhanced GSA model outperformed the existing models. The study successfully developed a modified PL model for LTE in Lagos, Nigeria. Therefore, modified model will be a good model in network planning for voice and fast online data connection in 4G LTE network.

One of the problems in digital control of power converters is calculation time in each sampling instant which effect on cost and complexity of digital controller. In this paper, a formula is introduced for calculating the number of clock cycles in each sample then interaction between sampling frequency and implementation cost (number of functional units and word length) of FPGA-based digital controller of DC-AC converter (three-phase four-legs inverter) is verified. The digital architecture is built on finite set model predictive control, and implemented on the FPGA board based on fixed-point calculations. We consider two digital architectures for design the controller in this study. One with four functional units and another with six functional units. This study aims to develop a mathematical equation for the number of clock cycles in each time instant to select the best switching state in the control algorithm, which affects the sampling frequency and clock frequency. Based on the obtained results, the number of functional units, word-length, and the number of switches determine the maximum clock cycles. By knowing maximum clock cycles the maximum sampling frequency is determined. In structure with four functional units, the maximum sampling frequency is 71 kHz for WL=8 bits and 17.7 kHz for WL=32 bits, and in structure, with six functional units, the maximum sampling frequencies are 97.6 and 24.4 kHz for WL=8 and WL=32 bits, respectively. In architecture with more functional units, we have greater sampling frequency with more accuracy and cost. The results obtained from this paper can be a reference for digital controller design.

This paper describes a spectrum observatory (SO) performed outdoor in two locations in Algeria and highlights the importance of the SO in the improvement of spectrum management in cognitive radio networks. These measurements were achieved in conjunction with the ANF (Agence Nationale des Fréquences), between January and February 2020. It surveys second, third, and fourth-generation mobile networks and DVB-T frequency bands. A comparative study of two measurement campaigns (in urban & rural) that were carried out via identical setup and equipment is presented. Some major short-duration measurement campaigns are cited and summarized for the state-of-the-art. Additionally, Different statistics are imputed and 3D graphics of the spectrum occupancy are plotted to highlight the spectrum opportunities in this region. This work aims to analyze the radio environment in Algeria and identify frequency bands that could be invested for the integration of new wireless systems and Cognitive Radio opportunistic networks. The evaluation of measurement results reveals low resource occupation, lower than 30.27%, for Constantine and 8.43% for Ouargla. The final part of the study inspects the effect of specific SO features upon the management strategy parameters’ selection. Via a meaningful SO, an efficient spectrum management strategy can achieve the safest users access to the idlest channels with the minimum costs and risks.

In this paper, a wind power system based on a doubly-fed induction generator (DFIG) is modeled and simulated. To guarantee high-performance control of the powers injected into the grid by the wind turbine, five intelligent super-twisting sliding mode controllers (STSMC) are used to eliminate the active power and current ripples of the DFIG. The STSMC controller is a high-order sliding mode controller which offers high robustness compared to the traditional sliding mode controller. In addition, it reduces the phenomenon of chattering due to the discontinuous component of the SMC technique. However, the simplicity, ease of execution, durability, and ease of adjusting response are among the most important features of this control compared to some other types. To increase the robustness and improve the response of STSMC, particle swarm optimization method is used for this purpose, where this algorithm is used for parameter calculation. The simulation results obtained using MATLAB software confirm the characteristics of the designed strategy in reducing chattering and ensuring good power control of the DFIG-based wind power.

This paper demonstrates an enhancement of power quality in grid integrated systems with the help of the proposed control strategy for voltage source converter based active power filters. The Shunt Active Power filters (SAPF) are extensively utilized in modern grid integrated systems to diminish the power quality concerns associated with it. The SAPF is one of the various power filters, which has better dynamic performance. The SAPF requires an accurate control strategy that provides robust performance under source and loads unbalance conditions. The proposed control scheme is responsible for generating the gate signals to activate the operation of Voltage Source Converter (VSC) based Active Power Filter. Thus, the performance of mitigation of harmonics of source current principally depends on the adopted algorithm. The present paper represents a performance study of a control scheme to mitigate power quality issues in the grid integrated system. The proposed system is modelled and simulated in MATLAB-Simulink in Simpower system block set.

The Direct power control and vector control of DFIG has known advantages, but certain disadvantages like steady state performance and transient performance of the system still persist. In order to overcome these, a novel technique based on Improved Sensorless Rotor Position Computational Algorithm with Integrated Direct Power and Vector Control (IDPVC) for S-VSC interfaced DFIG is proposed in this work. The advantages of both vector control and direct power control techniques are addressed in this method. This proposed IDPVC control minimizes the real and reactive power ripples at steady state and total harmonic distortion in stator current. In the proposed control, data acquired from sensorless rotor position computation makes the system more stable and avoids the sensor maintenance and feedback errors. The proposed system is tested for a 3.73 kW DFIG and compared with a benchmark DPC control of single VSC based DFIG. The results show the effectiveness of the approach under various wind speed conditions and found to be satisfactory.

This paper evaluates the wind potential of some specified locations in Nigeria, and then examines the response of wind energy conversion systems (WECSs) to this potential. The study employs eight probability distribution (PD) functions such as Weibull (Wbl), Rayleigh (Ryh), Lognormal (Lgl), Gamma (Gma), Inverse Gaussian (IG), Normal (Nl), Maxwell (Mwl) and Gumbel (Gbl) distributions to fit the wind data for nine locations in Nigeria viz. Kano, Maiduguri, Jos, Abuja, Akure, Abeokuta, Uyo, Warri and Ikeja. The paper then uses the maximum likelihood (ML) method to obtain the parameters of the distributions and then evaluates the goodness of fit for the PD models to characterize the locations’ wind speeds using the minimum Root Mean Square Error (RMSE). The paper analyses the techno-economic aspect of the WECSs based on the daily average wind speed; it evaluates the performance of ten 25 kW pitch-controlled wind turbines (WT1 – WT10) with dissimilar characteristics for each location, including the cost/kWh of energy (COE) and the sensitivity analyses of the WECSs. Results reveal that Ryh distribution shows the best fit for Kano, Jos, Abeokuta, Uyo, Warri and Ikeja, while the Lgl distribution shows the best fit for Maiduguri, Abuja and Akure due to their minimum RMSE. WT7 achieves the least COE ranging from $0.0328 in Jos to $4.4922 in Uyo and WT5 has the highest COE ranging from $0.1380 in Ikeja to $53.371 in Uyo. The paper also details the sensitivity analysis for the technical and economic aspects.

Due to the role of renewable energy sources in providing energy in future power systems, multi-terminal HVDC (MTDC) systems have attracted the attention of utilities and decision-makers. The reliability study of MTDC grids is critical for analyzing electrical power systems and providing a reliable power delivery system. Reliability modeling and study of six MTDC transmission networks containing hybrid DC circuit breakers for interrupting transmission line contingencies is presented in this paper. This study incorporates precise reliability models of MTDC grid configurations and describes a step-by-step grid expansion. Considering these reliability models, critical reliability indices of the demand bus of the grid have been obtained to calculate the amount of energy not supplied. Also, the influence of the tapping stations on the demand bus reliability features has been investigated. Since the components' characteristics significantly affect the system's reliability, the impact of the transformer and DC circuit breaker's failure rate and repair time on the reliability features of the demand bus of all MTDC grids have been assessed. The obtained results are employed to forecast the effect of simultaneous change of the repair time and failure rate of the transformer, the most influential component in determining the reliability indices, on the proposed configuration by incorporating multivariate linear regression.

Symmetrical nature of mean of electrical signals during normal operating conditions is used in the fault detection task for dependable, robust, and simple fault detector implementation is presented in this work. Every fourth cycle of the instantaneous current signal, the mean is computed and carried into the next cycle to discover nonlinearities in the signal. A fault detection task is completed using a comparison of two sub cycle means, and the same concept is extended to faulty phase classification. Under various fault and system operating situations, the suggested technique is assessed for regular faults, remote end faults, high resistive faults, and high impedance arcing faults. This paper's extensive case studies illustrate the suggested scheme's simplicity, computational flexibility, speed, and reliability. The suggested approach yields 100% consistent results in 4-8 msec detection time.

For reliable operation, distance relays have to be blocked in case of stable power swings (SPSs). Because these relays are prone to detect an SPS as a symmetrical 3-phase fault according to their symmetric nature. It should be noted that there are zero and negative sequence components during asymmetrical faults. However, these components do not exist during stable fluctuations or symmetrical faults. Consequently, according to the symmetric nature of the stable fluctuation, the distance relay may experience maloperation. This article proposes a new technique to discriminate a symmetrical 3-phase fault from an SPS. The proposed technique is based on the extraction of the exponentially decaying DC component in the 3-phase current by using the MIMIC impedance. This technique can detect the symmetrical fault in less than a quarter of one power cycle. The suitability of the technique is shown by simulating various symmetrical faults during fast and slow SPS conditions.

Today, it can be said that in every field in which timely information is needed, we can use the applications of time-series prediction. In this paper, among so many chaotic systems, the Mackey-Glass and Loranz are chosen. To predict them, Multi-Layer Perceptron Neural Network (MLP NN) trained by a variety of heuristic methods are utilized such as genetic, particle swarm, ant colony, evolutionary strategy algorithms, and population-based incremental learning. Also, in addition to expressed methods, we propose two algorithms of Bio-geography-Based Optimization (BBO) and fuzzy system to predict these chaotic systems. Simulation results show that if the MLP NN is trained based on the proposed meta-heuristic algorithm of BBO, training and testing accuracy will be improved by 28.5% and 51%, respectively. Also, if the presented fuzzy system is utilized to predict the chaotic systems, it outperforms approximately by 98.5% and 91.3% in training and testing accuracy, respectively.

Nowadays, magnetic gears (MGs) have become an alternative choice for mechanical gears because of their low maintenance, improved durability, indirect contact between inner and outer rotors, no lubrication, and high efficiency. Generally, although these advantages, MGs suffer from inherent issues, mainly the cogging torque. Therefore, cogging torque mitigation has become an active research area. This paper proposed a new cogging torque mitigation approach based on the radial slit of the ferromagnetic pole pieces of MGs. In this method, different numbers and positions of slits are applied. The best results are gained through an even number of slits which shows promising results of cogging torque mitigation on the inner rotor with a small mitigation in the mean torque on both rotors. This work is done by using Simcenter and MATLAB software packages. The inner rotor’s cogging torque has mitigated to 81.9 %, while the outer rotor’s cogging torque is increased only by 2.75 %.

By increasing the transceiver devices within the 3.1 to 10.6 GHz frequency band, the interferers and strong blockers from different equipment degraded the main received signals, so linearity performance becomes more notable. In this paper, a two-path low noise amplifier (LNA) is proposed for satisfying the overall efficiency of the Ultra-wideband (UWB) radar used in vital sign detection, precise indoor localization, and high data rate wireless communications. A novel high linear circuit is recommended based on Complementary Derivative Superposition (CDS) and Post Distortion (PD) techniques. High pass filter and inductive source degeneration structured input impedance matching. Post layout results of the designed UWB-LNA in 180-nm CMOS represented the average of third-order Intercept Point (IIP3) is 8.1 dBm, S21 is 11 dB and, S11 is below -10 dB. The minimum noise figure (NF) is 3.11 dB. The circuit draws 12.7 mA at 1.4-V. The chip area is 930 µm × 1090 µm. The proposed design in this work exhibits higher FOM compared to similar LNAs, It is clear, high-linearity performance in total bandwidth is an advantage compared to recent articles.