Showing 11 results for Mid
A. Hajiaboli, Hodjat-Kashani, M. Omidi,
Volume 3, Issue 3 (October 2007)
Abstract
This paper presents a novel implementation of an electromagnetically coupled
patch antenna using air gap filled substrates to achieve the maximum bandwidth. We also
propose an efficient modeling technique using the FDTD method which can substantially
reduce the simulation cost for modeling the structure. The simulated results have been
compared with measurement to show the broadband behavior of the antenna and the
accuracy of the proposed modeling technique. The measured results show a 16% of
VSWR<2 bandwidth which is considerable considering the inherent bandwidth limitations
in microstrip antenna technology.
A. Hamidi, A. Ahmadi, S. Karimi,
Volume 14, Issue 1 (March 2018)
Abstract
In AC-DC power conversion, active front end rectifiers offer several advantages over diode rectifiers such as bidirectional power flow capability, sinusoidal input currents and controllable power factor. A digital finite control set model predictive controller based on fixed-point computations of an active front end rectifier with unity displacement of input voltage and current to improve dynamic response has been presented in this paper. Here by using a predictive cost function and fixed-point computations, the optimal switching state to be applied in the next sampling is selected. The low-cost architecture is implemented on a FPGA platform. Designed architecture is constructed based on fixed-point arithmetic with minimal functional units. The control algorithm, which is used in this architecture, is Finite-Set Model Predictive Control (FS-MPC). Compared with other controllers, this controller provides a much better dynamic performance. Finally, in order to evaluate the accuracy of the fixed-point computations several cases for various loading conditions and word lengths are verified.
Hamid Salarvand, Meysam Doostizadeh, Farhad Namdari,
Volume 18, Issue 4 (December 2022)
Abstract
Owing to the portability and flexibility of mobile energy storage systems (MESSs), they seem to be a promising solution to improve the resilience of the distribution system (DS). So, this paper presents a rolling optimization mechanism for dispatching MESSs and other resources in microgrids in case of a natural disaster occurrence. The proposed mechanism aims to minimize the total system cost based on the updated information of the status of the DS and transportation network (TN). In addition, the characteristics of the protection system in DS (i.e., relays with fixed protection settings), the constraints related to the protection coordination are examined under pre- and post-event conditions. The coordinated scheduling at each time step is formulated as a two-stage stochastic mixed-integer linear program (MILP) with temporal-spatial and operation constraints. The proposed model is carried out on the Sioux Falls TN and the IEEE 33-bus test system. The results demonstrate the effectiveness of MESS mobility in enhancing DS resilience due to the coordination of mobile and stationary resources.
A. Hamidi, S. Karimi, A. Ahmadi,
Volume 19, Issue 2 (June 2023)
Abstract
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.
O. Mahmoudi Mehr, M. R. Mohammadi, M. Soryani,
Volume 19, Issue 3 (September 2023)
Abstract
Speckle noise is an inherent artifact appearing in medical images that significantly lowers the quality and accuracy of diagnosis and treatment. Therefore, speckle reduction is considered as an essential step before processing and analyzing the ultrasound images. In this paper, we propose an ultrasound speckle reduction method based on speckle noise model estimation using a deep learning architecture called “speckle noise-based inception convolutional denoising neural network" (SNICDNN). Regarding the complicated nature of speckle noise, an inception module is added to the first layer to boost the power of feature extraction. Reconstruction of the despeckled image is performed by introducing a mathematical method based on solving a quadratic equation and applying an image-based inception convolutional denoising autoencoder (IICDAE). The results of various quantitative and qualitative evaluations on real ultrasound images demonstrate that SNICDNN outperforms the state-of-the-art methods for ultrasound despeckling. SNICDNN achieves 0.4579 dB and 0.0100 additional gains on average for PSNR and SSIM, respectively, compared to other methods. Denoising ultrasound based on its noise model estimation is not only a novel approach in comparison to traditional denoising autoencoder models but also due to the fact that it uses mathematical solutions to recover denoised images, SNICDNN shows a greater power in ultrasound despeckling.
Atefeh Sohrabi, Hamideh Dashti, Javad Ahmadi-Shokouh,
Volume 19, Issue 4 (December 2023)
Abstract
In this article, an active electrically small Horn antenna for very high frequency (VHF) and ultra-high frequency (UHF) frequencies is presented. The proposed horn antenna has a height of 5 cm and a diameter of 4.28 cm which can cover 6-12 GHz without a special active circuit with the VSWR of less than 2. A Non-foster Active Adaptation Circuit is used to reduce the antenna input frequency from 164 MHz to 880 MHz. Good matching is visible between the simulation results and the measurement of the antenna reflection coefficient with the active matching circuit. The proposed structure has more than 137 % bandwidth. With the proposed active antenna, the problem of non-portability of VHF and UHF Horn antenna antennas has been solved. Finally, by analyzing the time domain, the stability of the circuit is examined, and the results of the stability test show that the system, including the antenna and the circuit, is stable. The antenna and the matching circuits are simulated by CST microwave studio and advanced design system, respectively.
Hamid Karimi,
Volume 20, Issue 1 (March 2024)
Abstract
This paper proposes a stochastic optimization problem for local integrated hydrogen-power energy systems. In the proposed model, the integrated system tries to reduce the day-ahead operation costs using dispatchable resources, renewable energy resources, battery energy storage systems, demand response programs, and energy trading with the upstream network. Also, the integrated system is able to transact electricity with the upstream network to get more benefits. When the generation of renewable resources is high, the integrated system can convert the surplus electricity to hydrogen by power-to-gas units. The generated hydrogen can be sold to different industries or stored in the hydrogen tank storage. During peak hours, the stored hydrogen can be imported into the gas-to-power unit to generate the required electricity. The sector coupling between electricity and hydrogen provides more flexibility for integrated systems and is an effective solution to control the uncertainty of renewable energy resources in order to increase the power and energy flexibilities. The simulation results show that the proposed sector coupling provides the opportunity for electricity and hydrogen trading for integrated system. The benefit of the integrated system by electricity and hydrogen trading with the upstream network and different industries are $ 88.39, and $ 6846, respectively.
Neda Gorji Kandi, Hamid Behnam, Ali Hosseinsabet,
Volume 20, Issue 2 (June 2024)
Abstract
Ayoub Hamidi, Ahmad Cheldavi, Asghar Habibnejad Korayem,
Volume 20, Issue 3 (September 2024)
Abstract
This paper proposes a structure for concrete composite materials that effectively attenuates transmitted power through the composite slab across a wide frequency range. The proposed structure is practical for electromagnetic interference shielding applications. To assess its effectiveness, the proposed structure has been compared with two other structures: a traditional wire mesh used in reinforced composites and an array of helices, a cutting-edge technique for manufacturing lightweight concretes with significant improvements in shielding properties. The comparison among full-wave simulation results indicates that the proposed method leverages the benefits of both techniques. It achieves a shielding effectiveness exceeding 30 dB from low frequencies up to 8.5 GHz and beyond 55 dB from low frequencies up to 4 GHz. Furthermore, an experimental measurement was conducted to validate the full-wave simulation results. An experimental sample was fabricated according to the simulated proposed structure, and the measured shielding effectiveness confirmed the composite's capability in wideband electromagnetic shielding. Theoretically, the proposed structure can enhance the concrete's mechanical characteristics while improving its shielding effectiveness, making it suitable for designing ultra-high-performance concretes.
Noor Fazliana Fadzail, Samila Mat Zali, Ernie Che Mid,
Volume 21, Issue 2 (Special Issue on the 1st International Conference on ELECRiS 2024 Malaysia - June 2025)
Abstract
The activation function has gained popularity in the research community since it is the most crucial component of the artificial neural network (ANN) algorithm. However, the existing activation function is unable to accurately capture the value of several parameters that are affected by the fault, especially in wind turbines (WT). Therefore, a new activation function is suggested in this paper, which is called the double sigmoid activation function to capture the value of certain parameters that are affected by the fault. The fault detection in WT with a doubly fed induction generator (DFIG) is the basis for the ANN algorithm model that is presented in this study. The ANN model was developed in different activation functions, namely linear and double sigmoid activation functions to evaluate the effectiveness of the proposed activation function. The findings indicate that the model with a double sigmoid activation function has greater accuracy than the model with a linear activation function. Moreover, the double sigmoid activation function provides an accuracy of more than 82% in the ANN algorithm. In conclusion, the simulated response demonstrates that the proposed double sigmoid activation function in the ANN model can effectively be applied in fault detection for DFIG based WT model.
Murni Nabila Mohd Zawawi, Zainuddin Mat Isa, Baharuddin Ismail, Mohd Hafiz Arshad, Ernie Che Mid, Md Hairul Nizam Talib, Muhammad Fitra Zambak,
Volume 21, Issue 2 (Special Issue on the 1st International Conference on ELECRiS 2024 Malaysia - June 2025)
Abstract
This study introduces a pioneering method to enhance the efficiency and effectiveness of three-phase five-level reduced switch cascaded H-bridge multilevel inverters (CHB MLI) by employing the Henry Gas Solubility Optimization (HGSO) algorithm. Targeting the selective harmonic elimination (SHE) technique, the research emphasizes the optimization of switching angles to significantly reduce total harmonic distortion (THD) and align the fundamental output voltage closely with the reference voltage. Central to this exploration are three distinct objective functions (OFs), meticulously designed to assess the HGSO algorithm’s performance across various modulation indices. Simulation results, facilitated by PSIM software, illustrate the impactful role these objective functions play in the optimization process. OF1 demonstrated a superior ability in generating low OF values and maintaining a consistent match between reference and fundamental voltages across the modulation index spectrum. Regarding the reduction of THD, it is crucial to emphasize that all OFs can identify the most effective switching angle to minimize THD and eliminate the fifth harmonic to a level below 0.1%. The findings highlight the potential of HGSO in solving complex optimization challenges within power electronics, offering a novel pathway for advancing modulation strategies in CHB MLIs and contributing to the development of more efficient, reliable, and compact power conversion systems.
