فصلنامه روشهای هوشمند در صنعت برق
پیاپی 48 (زمستان 1400)

The production of clean electricity is one of the most basic human needs today. Therefore, the use of power plants that use renewable and environmentally friendly fuels (new energy) as their base fuel, has been highly appreciated. However, the output voltage level of local power plants based on new energies is as low as the input voltage of the next floors (inverters, etc.). Therefore, researchers have tried to solve this defect by using DC / DC boost converters. The structures related to these converters are different based on the designer's expectations such as voltage gain, output power, efficiency, input voltage specifications, etc. Boost converters are responsible for increasing the DC voltage by switching and storing energy in their inductor. But the same simple structure can be created with the help of new tricks such as using magnetic coupling, adding passive incremental circuits to the converter structure, creating more complete structures by using several active switches and even combining several structures together to the desired point in terms of voltage gain. On the other hand, with soft switching methods (resonance, snubber, etc.), the efficiency of boost converters is in the acceptable range. In this paper, the types of power plants based on new energy and then boost converters, which are the most basic elements of a power plant based on new energy, it is categorized in terms of incremental structures and applied methods for optimizing these converters, especially in terms of reducing losses and increasing efficiency.

The multilevel cascade inverter is one of the most widely used power-electronics based interfaces in electrical distribution systems. Due to high losses and harmonics, the switching frequency of the inverter should be low in medium and high power applications. For this reason, the conventional carrier wave-based sinusoidal pulse modulation (PWM) and space vector PWM that have high switching frequencies cannot be used in these applications. The optimal PWM methods for inverters with step modulation result in lower total harmonic distortion (THD) in output voltage than other common modulation methods. However, one of the major disadvantages of these methods is that the optimal switching angles should be determined using the switching table, limiting the application of the optimal PWM. This paper proposes a method for determination of switching angles by using the iterative quadratic programming method. In each iteration, the proposed method calculates the switching angles by solving the quadratic sub equations with equality constraints and linear equations. Also in the appropriate conditions, global and asymmetric convergences are faster, more accurate, and more efficient, and there is no need for much time and memory for switching angles determination. The optimum switching angles minimize the switching frequency, switching losses, and THD in voltage and current of a three-phase cascade multilevel inverter with step modulation. Also, the power circuit breakers are switched on and off only once in each period. The effectiveness of the proposed method is evaluated through simulation case studies in MATLAB environment.

Wind turbines and photovoltaic arrays are the most prominent and widely used intermittent Distributed Generations (DGs). Due to the right-of-way, environmental, economical and other restrictions, the connection of this type of DGs to the preferred point of the distribution network is very difficult or in some cases impossible. Therefore, because of non-optimal locations, they may cause a voltage rise at the Points of Common Coupling (PCCs). In this paper, a coordinated design of Switchable Capacitor Banks (SCBs) with dynamic reconfiguration of the distribution network is proposed to avoid low and high voltage violations. For this purpose, distribution network reconfiguration is implemented to mitigate voltage rise at PCCs and Capacitor Banks (CBs) to solve the low voltage problem. A novel method is presented for determining the optimal size of CBs. The proposed Capacitor Sizing Method (CSM) effectively determines the optimal values of reactive power for the given nodes. The optimal locations of SCB are determined using particle swarm optimization algorithm. The 24–hour reactive power curve optimized by the proposed method plays a pivotal role in designing SCBs. The simulation results show that the implementation of the dynamic network reconfiguration and SCBs placement is required to maintain a standard voltage profile for better employment of DG embedded distribution networks.

Hybrid Spread Spectrum (HSS) link is a suitable and robust physical layer structure for the tactical ad-hoc network. In this link, synchronization consists of two stages: Frequency hopping pattern synchronization and direct sequence code synchronization. In the presence of jamming, the use of the conventional fixed-threshold detection method increases the false alarm rate. Increasing the false alarm rate increases synchronization time in the HSS link. To solve this problem, the noise and jamming power estimator block is usually used at the receiver. Threshold value is adjusted instantaneously based on the estimated power in this method. This method has a high computational load and hardware complexity, and error in estimating noise and jamming power leads to an increase in the false alarm rate. In this paper, the proposed synchronization algorithm of the hybrid spread spectrum system is presented as an adaptive threshold, based on the statistical characteristics of the received signal. In the proposed algorithm, the threshold value is changed adaptively so that the false alarm rate remains constant at a minimum value. The theoretical analysis and simulation results show that the proposed algorithm can improve the detection probability and false alarm rate and reduce the synchronization time in the presence of a jamming compared to the conventional fixed threshold method.

Cadmium telluride (CdTe) solar cell is known for its high efficiency, low cost and high stability. In this paper, simulation of CdTe based solar cell (ZnO/ZnCdS/CdTe/NiO/Al) has been presented. ZnCdS, NiO and ZnO layers have been used as electron/hole transport layer (ETL/HTL) and transparent conductive oxide (TCO) layer, respectively. SCAPS-1D simulation software was used to evaluate the performance of the modelled multijunction CdTe solar cell. This software is capable of analyzing the efficiency with different parameters of cadmium telluride solar cell. The impact of thickness, carrier concentration, defect density of the CdTe, and ZnCdS/ CdTe interface defect density on the solar cell performance was also investigated. The optimized solar cell demonstrated a maximum power conversion efficiency (PCE) of 26.3 % with open circuit voltage (VOC) of 1.095 V, short circuit current density (JSC) of 27.22 mA/cm2 and FF of 88.14 % that shows huge promise in low-cost solar energy harvesting.

In this paper, a high step down converter with a synchronous rectifier is presented, so that both the main switch and the rectifier switch operate under soft switching condition. Since the proposed converter gain is much lower than the conventional buck converter, it does not have the problems of these converters such as narrow duty cycle, high voltage stress and high switch current, etc. In the proposed converter, the voltage stress on the switch is reduced, so a switch with lower drain-source resistance (RDS(ON)) can be used and the conduction losses are reduced. On the other hand, because the diodes of the circuit are switched off under zero current switching condition, do not have the problem of reverse recovery. Switching losses of the switches are also greatly reduced due to operating under zero voltage switching conditions. The proposed converter has been thoroughly analyzed and a practical 120 W prototype has been made to prove the correctness of the circuit analysis.