AUT Journal of Electrical Engineering
Year:2020 | Volume:52 | Issue:2|Papers Count:12

The power-flow (PF) solution is a basic and powerful tool in power system analysis. Distribution networks (DNs), compared to transmission systems, have many fundamental distinctions that cause the conventional PF to be ineffective on these networks. This paper presents a new fast and efficient PF method which provides all different models of Distributed Generations (DGs) and their operational modes (P-V and P-Q nodes) in DNs. This study uses voltage-dependent load model instead of traditional load model (constant P-Q) which is modelled as the combination of a current source in parallel with a constant admittance. This kind of load model is closer to reality and makes the powerflow equations closer to linear conditions. To calculate the angles of the P-V buses, the numerical method (Newton-Raphson method) is applied by separating the PF equations for P-V and P-Q buses. Considering a series of approximations on the angles of these buses, the non-diagonal elements of the Jacobin matrix in Newton-Raphson method are fixed. Hence, the proposed numerical method converges toward an appropriate response in a very low number of iterations and high speed. The voltages of other buses (P-Q buses) are calculated linearly without needing any numerical methods. The presented method proves to be robust and reliable against reconfigured structures and meshed networks. Simulations have been carried out on 14-, 33-and 70-node IEEE test systems and large scale networks such as 6118-buses. The results show that the proposed method is at least 100 and 10 times faster than Gauss-Seidel and Newton-Raphson methods, respectively.

Decoupling the uplink and downlink user association improves the throughput of heterogeneous networks (HetNets) and balances the traffic load of macro-and small-base stations. Recently, fiber-wireless HetNets (FiWi-HetNets) have been considered as viable solutions for access networks. To improve the accuracy of user association and resource allocation algorithms in FiWi-HetNets, the capacity limitation of various backhaul technologies must be considered. In this paper, we investigate the backhaul-aware decoupled uplink/downlink (UL/DL) user association, subcarrier allocation, and power control optimization problem in FiWi-HetNets. In our system model, fiber and millimeter wave (mmWave) links are used as backhaul of base stations, and the backhaul capacity limitation and minimum required transmission rate (R_min) are modeled in the optimization problem. As the formulated optimization problem is non-convex, we present a heuristic algorithm to divide the main problem into two sub-problems that are solved iteratively. The proposed algorithms are evaluated through exhaustive simulations. The results indicate that decoupling UL/DL user association improves the sum rate of FiWi-HetNets. Besides, we evaluate the effect of backhaul capacity limitation and R_min on the sum rate of FiWi-HetNets. The effect of upgrading fiber backhaul technology is also investigated to evaluate the role of fiber backhaul on the sum rate of the radio access network.

Detecting ships in marine images is an essential problem in maritime surveillance systems. In recent years deep neural networks have been utilized as a tool having high potential to overcome the challenges of this application. Unfortunately the performance of such networks greatly drops when they are exposed to low size and low contrast optical images which have been captured by ground, aerial and satellite based systems. On the other hand, image clutters (e. g. sea waves, cloud and wave sequences caused by the floats) may exacerbate this problem. In this paper a new method is proposed to improve the performance of deep neural networks in detecting ships in low size and low contrast marine images which has been based on the concept of deep stacked extreme learning machines. In proposed method the extracted features have more generality in modeling of marine images based on superposition of dedicated mapping functions of extreme learning machines. Furthermore they have the minimal overlap thanks to performing decorrelation process on features which are propagated between network layers. The performance of the proposed method is evaluated on several marine images which have been captured in sunny, rainy and hazy conditions. The obtained results are compared with some other state-of-the-art detection methods by using standard parameters. Increased F-measure of the proposed method (i. e. 3. 5 percent compared to its closest alternative) in parallel with its better accuracy, recall and precision shows its effectiveness in detecting ships in low size and low contrast marine images.

A new fuzzy PI control algorithm for a novel yokeless and segmented armature axial flux-switching sandwiched permanent-magnet motor (YASA-AFFSSPM) is proposed in this paper. In the conventional fuzzy PI control of the permanent magnet synchronous motor the torque ripple is large and the control accuracy is not high precise. A new fuzzy PI control algorithm is proposed to solve this problem, and a prototype of the YASA-AFFSSPM motor is fabricated and the method is tested. The simulation and experimental results demonstrate that the new fuzzy PI controller can improve the robustness of the system and improve the precision. Further, the dynamic performance of the YASAAFFSSPM motor is excellent.

Typically, many of the modern buildings have concrete walls constructed from cinder block walls, that have periodic nature in their relative dielectric constant. This periodic nature excites higher-order Floquet harmonic modes at microwave frequencies, which leads to the propagation of scattered waves along with non-specular directions. Periodic structures exhibit different behaviors when illuminated by different types of incident polarizations. Previous studies mainly focus on the Transverse Electric (TE) incident wave, where the behavior of a periodic layer is characterized easily by only considering the function of the relative permittivity in the equations. But, for a Transverse Magnetic (TM) incident plane wave, the first-order derivative of the relative permittivity function must be taken into account in the formulations. Accordingly, in this paper, reflection and transmission coefficients from a typical concrete block wall are formulated for a TM polarized incident wave. Exact boundary equations are written, and the effect of oblique incidence is taken into account. Also, the periodic nature of the inhomogeneous layer is represented by the Fourier series. In addition, two types of numerical validation are provided to prove the accuracy of the given theory. The ability to calculate Fourier series coefficients by taking the Fast Fourier Transform (FFT) of the relative permittivity function enables the introduced method to treat any type of periodic inhomogeneities.

To calculate and evaluate wave scattering and penetration of electromagnetic waves in different biological tissues it is necessary to use a realistic model of the human body, with all tissues resolved and separately assigned with appropriate electric/magnetic properties. We report the development of a realistic 3D whole-body human model that has been adapted for simulation in CST software, containing 46 different resolved tissues with their relevant electrical properties over 1Hz-100 GHz, non-ionizing electromagnetic radiation. The model is based on whole-body magnetic resonance images (MRI) of Zubal-phantom data with voxel dimensions of 3. 6 mm. Wideband simulations are performed to show the successful application of the model in computational dosimetry. The results of the electric field calculation indicate that the peak of electric field in the body occurs at around 70 MHz, which is the same as the well-known resonant frequency of the body. Moreover, the difference between electric field intensity among tissues can be as high as 30 dB, and that tissues with lower water content (e. g. bones, knee) can generally have higher induced electric fields. High water content tissues such as the eye vitreous humor have generally lower induced electric fields. The model is available free of charge for research purposes at bioelectromag. ir.

This paper develops an improved robust multi-surface sliding mode controller for a complicated five degrees of freedom Underwater Vehicle-Manipulator System with floating base. The proposed method combines the robust controller with some corrective terms to decrease the tracking error in transient and steady state. This approach improves the performance of the nonlinear dynamic control scheme and makes the states stable even in presence of unknown effects of hydrodynamic disturbances and unmodelled dynamics. In this regard, the dynamic model of an UVMS is extracted using the Newton– Euler formulation which has been validated by using an ADAMS 3-D model. The control algorithm is based on Lyapunov technique and is able to provide the stability of the whole system during tracking of the desired trajectory with an acceptable precision. The controller parameters are also optimized utilizing the concept of Genetic Algorithm with the aim of increasing the speed of system while decreasing the tracking error which leads to bounded control inputs. Finally, the efficacy of the control scheme, is compared with other conventional methods and the simulation results show the short settling time, low and smooth control effort and asymptotic stability of the states as well as the sliding surfaces of the proposed controller.

Service level agreement (SLA) is a powerful tool to formalize the negotiation and agreement between the service provider and service seeker with the scope of service quality characteristics, compensations and tariffs. The service quality description is one the main parts of a SLA which can be characterized by the use of suitable and feasible quality of service (QoS) parameters. Determining suitable QoSparameters is the most important step in SLA codification. In this paper, we propose a novel method for determining the most related QoS parameters for characterizing the service quality in a SLA. The proposed method is a step-by-step algorithm which is based on selecting feasible parameters among a general initial list obtained from international references. The criteria for feasibility are perceivability and measurability from the end user’ s viewpoint. Our method is general and can be applied to each service. We also leverage on clustering algorithm to prioritize the feasible QoS parameters according to their popularity in international studies. Finally, we propose a statistical method to determine the threshold for the feasible parameters. We provide an interval for each threshold. We show the steps of our proposed methods via a case study as the final part of the paper.

A micro-fabricated metal-oxide based conductometric pH sensor is designed and fabricated in this manuscript. pH sensors have applications in various areas from farming to food processing, human health monitoring, industrial waste products investigation, etc. Accordingly, there is a relatively high demand for a reliable, rapid and precise pH sensor in the market. Relatively precise pH sensors have been already demonstrated for in-vitro analysis. Nevertheless, design and fabrication of pH sensors for in-vivo applications are still challenging. In this work, a relatively minute pH sensor is designed and fabricated for measuring the pH of the human stomach. Thanks to the relatively small footprint, it is possible to insert the sensor into the tip of a nasogastric (NG) tube to be inserted inside the stomach. A mixture of ZnO and SnO2 powders is used as the metal-oxide pH sensitive layer. Impedance spectroscopy is applied to investigate the frequency characteristics of the sensor. The layer behaves like a resistive load in relatively low frequencies and a capacitive load in relatively high frequencies, as investigated using Impedance spectrometer. Interdigitated microelectrodes coated by the pH sensitive layer is used to detect the variations of impedance when encountered to a pH sample. The sensor represents a relatively good sensitivity and short response time (less than 0. 5 s) for monitoring of pH in the range of 1 to 7.

Nowadays, because of the need to decrease fuel consumption and greenhouse gas emissions and also their capability of exchanging power with the grid and regulating the frequency and voltage of the grid at different times of the day, electric vehicles are used more than before all across the world. It is highly important to pay attention to the efficiency, and decrease in the weight and volume of these vehicles. The chargers of these vehicles can form a huge portion of the volume and weight of these vehicles. DC link capacitors are the large parts of these chargers. Based on the mathematical modeling and relationships of the system, this study focuses on the optimal capacitor value based on the required specifications. In the model presented in this article, the optimal value of DC link capacitor is estimated by taking into account instantaneous input power of the charger, the relationship of the energy balance between the grid and the DC link capacitor, and application of Taylor series to the output of the relationship. The optimal DC link capacitor value is estimated through calculating the DC link voltage, and measuring the exchanged energy and changes of DC Link Voltage during charging. The most considerable advantages of the proposed model are the simplicity of its design together with the minimum weight and volume of the charger due to its low capacitor value. SIMULINK environment of MATLAB software was used to evaluate the proposed model. The simulation results show that the model was successful.

This study aims to report on the application of Linear Quadratic Integral (LQI) based global maximum power point tracker (GMPPT) method for transferring the available maximum power from photovoltaic (PV) systems to load in unshaded and shaded conditions. For the maximum power transmission under varying the environmental conditions and partially shaded conditions, MPPT technologies are utilized in PV systems. For the improvement of functioning MPPT, a new two-level control structure which decreases difficulty in the control process and efficiently deals with the uncertainties in the PV systems is introduced. In the proposed approach, the reference voltage at the global maximum power point (GMPP) is estimated by a new scanning algorithm. The difference between the reference voltage and the voltage of the PV array is then used by LQI controller to generate the duty cycle for a boost converter. The design process of the proposed approach is explained as step by step. The benefits of the approach are quicker tracking capability, transferring maximum deliverable power and simple implementation. To verify the proposed method, several irradiation profiles that create several peaks in the P-V curve are used. The simulation results show that the proposed method causes PV systems to track the GMPP immediately so that no oscillation around the GMPP is observed. Therefore, maximum efficiency can be derived from the PV system.

In the present work, determining the optimal strategy of multi virtual power plants (VPPs) as well as the objective of maximizing profit through the multi-level control of VPPs are discussed by the micro-grid utilization center including virtual power plants. VPPs include renewable resources such as wind farms, photovoltaic, and conventional resources such as fuel cell, micro turbine, hybrid heat and power include gas and also waste heat boiler integrated with electrical resources and energy storage devices such as batteries. During the market competition process, the method of biding for each VPP is determined according to the optimal generation capacity of each VPP. In order to reduce the effects of uncertainty and unpredictability of the output power of wind farms, a more precise method for predicting using wavelet transform and artificial neural network as well as genetic algorithm method has been provided. Two operational models are described in this paper: 1) specify the optimal independent strategy of each VPP; and 2) The game theory model to specify the optimized strategy of 9-bus IEEE system including multiple virtual power plants as well as a model of load response according to pricing mechanism for time use and also removable electrical loads.