نشریه مهندسی برق و مهندسی کامپیوتر ایران
سال نوزدهم شماره 4 (پیاپی 66، زمستان 1400)

This paper presents the findings of a practical study to detect the degradation factors of metal-oxide surge arresters in a distribution network in the mountainous region of Izeh, which experiences two warm and temperate climates annually. The surge arresters have defected in both periods when the network operating conditions and weather conditions are completely different. However, the appearance of the defected surge arresters in these periods is different. In this paper, by simulating the network, its permanent and transient state behaviors are analyzed. Based on the results and environmental conditions, the appropriate arresters' specifications for the network are obtained and compared with existing arresters. By considering different scenarios for ground resistance of arresters, the changes in energy absorbed by arresters are evaluated and the results are compared with those obtained in the practical reduction of ground resistance of some of arresters. By adding several arresters to the network, changes in the absorbed energy of arresters are investigated. Based on the research findings, the causes of arresters' failures in both warm and temperate periods are investigated. Finally, the findings of this research are validated by comparing the simulation results with field events, and some solutions are presented to overcome the problems.

Wireless power transmission technology with titles such as contactless power transmission, magnetic coupling power transfer, etc.are known and in fact, this method safely and reliably transmits power in such a way that does not require a mechanical connection between the source and the load. In this method, power transmission is done wirelessly using resonance induction coupling. By operating the transducer in the resonant mode, it will be possible to transfer a significant amount of power over an air distance of a few tens of centimeters, while the system efficiency is high and the voltage and current stress of the transducer are reasonable. In this paper, by presenting a method based on robust control and meta-heuristic algorithms, we improve the charging process of electric vehicles by considering uncertainty conditions. The simulation results show the better performance of the proposed controller compared to other controllers. Also, in this paper, the effect of connecting the charging station of electric vehicles to the distribution network is investigated by considering the optimal charging and discharging scheduling systems to maximize the economic profit of the vehicles and the charging station. In the proposed method, the best program for charging and discharging cars in order to maximize their profit is extracted based on genetic algorithm. According to the simulation results, optimal charging and discharging planning has reduced the value of losses to the total network energy to load the station in some trains, so that network targets such as losses and voltage deviation index are minimized and voltage stability index is maximized. In this study, minimization of losses, voltage deviation as well as maximization of voltage stability index have been investigated and the optimal location of the station has been obtained by considering these goals along with the profit of the station and vehicles. Finally, according to the results, with the planning of charging and discharging cars, in addition to providing the required charge, the profit of the station and cars has also increased.

In this paper, the sub-region method is used to analyze the outer-rotor permanent magnet synchronous machine. In this method, based on hypotheses such as geometry, electrical and magnetic characteristics, the machine is divided into four sub-regions of groove, groove opening, air gap and magnet. Based on Maxwell's equations and considered assumptions, the governing partial differential equations for each sub-region are presented and solved analytically. In this paper, after calculating the air-gap flux density caused by the armature winding current and magnets with three patterns of radial, parallel and Halbach magnetization, the other main quantities of the machine are calculated accordingly. To validate the analytical model, the results obtained from MATLAB software are compared with the values obtained from the finite element method.

In this paper, space-time codes for MIMO radar are used to achieve high resolution at target range and speed. The two-dimensional ambiguity function is known as a tool to compare radar performance in terms of resolution. A space-time code can be designed based on minimizing the distance between the actual target parameters in range, speed and angle. For this purpose, high resolution can be achieved by analyzing the ambiguity function and narrowing it down as much as possible. In this paper, the ambiguity function with two variables of amplitude and speed mismatch is considered and a new criterion to achieve high resolution performance in this field is proposed. In this case, by optimizing the proposed cost functions, the optimal space-time code is extracted. The proposed design can also be extended to phased-MIMO radar. The simulation results also show that our proposed scheme has a very narrow ambiguity function around the origin, while it has a performance very close to the optimal state in terms of target identification probability.

In this paper, a wideband printed antenna over an artificial magnetic conductor (AMC) surface is introduced which can be utilized for wireless applications such as WLAN, WiMAX, and multiple-input multiple-output (MIMO) systems. In the proposed structure, a planar AMC surface as the antenna ground plane is used to direct the radiation pattern of the antenna, and enhancing the impedance bandwidth. The proposed antenna design is composed of a pair of printed microstrip elements fed by an E-shape feed line for coupling the elements. The bandwidth of the designed antenna includes from 4.94 GHz to 6.9 GHz with a return loss of less than -10dBforlinear polarization in C-band. The rhombic-shape AMC unit cell indicates the bandwidth of 5.24-7.15 GHz for the ±90˚ reflection phase. By adding the AMC surface into the printed antenna, a wideband structure with acceptable miniaturization and gain enhancement to 7.25 dBi is achieved. The simulated results of the antenna’s impedance properties are performed by using full-wave simulators of HFSS and CST. Also, two-element array of the proposed design are investigated for different polarizations. Based on the obtained results, the operating bandwidth includes the frequency range from5.18GHz to 6.81 GHz and the isolation between the array elements is less than -22 dB. For this purpose, the antenna arrays can be applied for MIMO systems.

Slew rate and settling time are the important parameters in opamps with feedback. In this paper, the slew rate and settling time of the fully differential two stages folded cascade architecture amplifier with cascade compensation is analyzed. An important characteristic of the proposed analytical model is that the behavior of the transistors is examined in detail after applying the step in the input, and it is shown that the settling time as well as slew rate would depend on the size of the input step. The performed analysis can be beneficial for design and manual calculations in integrated circuits. Moreover, circuit level simulation is used to validate the analytical results with particular emphasis on slew rate and settling time. Simulations results show excellent conformance between the analytical equations and the simulation results.

In recent years, fractional order systems and fractional order control have increasingly attracted the attention of researchers in various fields of science and engineering. On the other hand, numerous control approaches have been extended in order to be utilized in fractional order systems. Despite this fact, few research studies have been devoted to generalizing integer order observers to fractional order ones. Since the applications of fractional order systems are increasing, developing fractional order observers seems to be essential. In this paper the problem of non-fragile adaptive sliding mode observer design for a class of fractional-order nonlinear systems with time delay is addressed. First, the states of the fractional-order pseudo-linear time-delay system with matched nonlinearity are estimated employing the sliding mode control method. Then the state estimation problem of fractional order systems with mismatched nonlinearity has been investigated. The asymptotic stability of the estimation error dynamics is proven by employing the Lyapunov stability analysis method for fractional order systems. The sufficient stability conditions are derived in the form of Linear Matrix Inequalities (LMIs). Eventually, the effective performance of the proposed approach in this paper has been corroborated through simulation of a numerical example and also a case study of a fractional order economic system.

A double recycling Op-Amp based on a simple recycling folded cascode Op-Amp is presented. The proposed Op-Amp has significantly improved performance compared to a recycling folded cascode. In the proposed Op-Amp, those cascode output current sources of recycling folded cascode that still have a constant value have been considered and have taken on a dynamic state through capacitive couplings in the path created between the input and output of the amplifier. DC gain, unity-gain bandwidth, and slew rate have been improved compared to the previous amplifier at the same power consumption. Simulation results using the 0.18μm CMOS technology show a DC gain enhancement of 6dB, 35% improvement in slew rate, and almost a 30% increase the bandwidth compared to the traditional recycling folded cascode Op-Amp. Also, smaller input-referred noise is achieved. Simulated results of proposed circuit show the values of SR, power consumption and DC gain are about 93.5 V/µs, 1.02mW and 68.3 dB respectively.