Journal of Operation and Automation in Power Engineering
Volume:9 Issue: 3, Autumn 2021

In the last years, microgrids have been introduced for better managing the overall power network. The two-way communication between supplier and consumer sides of a smart microgrid causes to better apply the demand side management methods to this type of system. For this reason, the multi-objective demand side management of a smart microgrid is investigated in this study. The economic and environmental indices of the microgrid are considered as the primary objective functions of the proposed demand side management method. The load variations of the microgrid are improved based on the applied demand response program. The operator of the microgrid can provide the demand of the system using a wind turbine, photovoltaic panel, diesel generator, micro turbine, fuel cell, energy storage system and the upstream network. The stochastic behavior of renewable units is also considered to evaluate the proposed method in a more realistic condition. The combination of the multi-objective ant lion optimization algorithm and the analytical hierarchy process method is utilized to solve the demand side management problem. Numerical results, which are obtained from evaluating the proposed method in a sample microgrid, demonstrate the high efficiency of the proposed demand side management method in improving the economic and environmental indices of the microgrid.

High power permanent magnet synchronous generators (PMSGs) are suitable for wind power applications because of their high efficiency. According to the electromagnetic machine design principles, the main disadvantages of low-speed and high-power generators are large size, heavy weight and high manufacturing cost. The main objective of this paper is to optimize the exterior-rotor PMSG for direct-drive wind turbine applications in order to reduce the generator system cost under design constraints. At first, a multidisciplinary and accurate model is proposed for optimal designing of exterior-rotor permanent magnet wind generator system. Next, the design variables that affect the generator system cost are investigated and specified. Furthermore, the impact of these variables on generator efficiency as one of the main design constraints, are investigated. At last, the unified particle swarm optimization (UPSO) technique is used to optimize the design variables based on the presented analytical model. By comparison the optimal design results of this study with two 500-kW inner-rotor PMSGs and one 15-kW prototype exterior-rotor PM wind generator, it is shown that the proposed method yields an optimal design with lower total volume, lower generator system cost and higher efficiency. Moreover, 3-D finite element analysis is employed to verify the obtained results of the proposed optimal design of 500-kW exterior-rotor PMSG.

Mitigating the cogging torque is an important issue in designing the YASA machines. The main aim of the paper is to optimize an efficient technique to mitigate the cogging torque of YASA machines. In the suggested technique, the permanent magnets (PMs) are segmented into several segments in the radial direction, and then these PM segments are shifted at appropriate angles in the peripheral direction. The proposed PM segmentation method is compared with the conventional PM segmentation as well as the conventional PM skewing approaches in terms of the amount of cogging torque reduction and the amount of negative impact on the generator load-ability. It is shown that compared to the other two studied approaches, the proposed method is more effective in reducing cogging torque and at the same time, has a less negative impact on the generator output power. Using the suggested technique and via several finite elements based simulations, it is shown that without causing a significant negative impact on the generator load-ability, the generator cogging torque can be reduced considerably (about 90%). By implementing the RSM (Response Surface Methodology), optimal shift angles of the PM segments (factors) are determined to mitigate the cogging torque and maintain the generator load-ability. The experiments are carried out based on the RSM, as an important topic in the statistical DOE (Design of Experiments) approach, to study the impacts of PM segments shift angles on the output power and cogging torque of the YASA-AFPM generator. All of the experimental samples are extracted via the FEA simulations. Also, some of the simulation results are verified using the experimental tests.

Fault location in transmission lines compensated by flexible alternating current transmission system (FACTS) devices and series capacitor (SC) compensators is much more complicated than simple lines due to the presence of time-variant voltage and current sources in the topology of transmission lines. In recent years, due to the increasing presence of reactive power compensators in power systems and the researchers’ desire to study the presence of such equipment in the network, many articles have been published in the field of fault location in transmission lines equipped with reactive power compensators. Thus, the fault location problem in electrical power transmission lines equipped with reactive power compensators, including FACTS and SC devices, is comprehensively discussed and analyzed in this paper. For the first time, all the basic indices and factors that have always been very effective in analyzing the fault location problem in transmission lines equipped with reactive power compensators in various papers are classified thoroughly. Then, based on the types of reactive power compensators, all the literature published in the field of fault location in compensated transmission lines are categorized. Finally, a comparison table is presented to examine the fundamental indices of the literature in this field.

optimal and economic operation is one of the main topics in power systems. In this paper, a stochastic single objective framework for GenCoʼs optimal self-scheduling unit commitment under the uncertain condition and in the presence of SH units is proposed. In order to solve this problem, a new meta-heuristic optimization technique named antlion optimizer (ALO) has been used. Some of the capabilities of the ALO algorithm for solving the optimization problems included : (1) the exploration and utilization, (2) abiding convergence, (3) capable of maintaining population variety, (4) lack of regulation parameters, (5) solving problems with acceptable quality. To approximate the simulation conditions to the actual operating conditions, the uncertainties of the energy price, spinning and non-spinning reserve (operating services) prices, as well as the renewable energy resources uncertainty, are considered in the proposed model. The objective function of the problem is profit maximization and modeled as a mixed-integer programming (MIP) problem. The proposed model is implemented on an IEEE 118-bus test system and is solved in the form of six case studies. Finally, the simulation results substantiate the strength and accuracy of the proposed model.

Grid-connected inverter-based photovoltaic (PV) systems play an important role in Distributed Power Generation (DPG). For this application, quasi impedance source inverter is very suitable due to its ability to increase or decrease the output voltage of the inverter in a single-stage and high reliable condition. Conventionally, to remove the harmonics, which are yielded by switching the grid-connected inverter, LCL filters are utilized at the inverter output. These filters can cause some problems at the Point of Common Coupling (PCC). The aim of this paper is to improve the quality of the injected power of the photovoltaic array, which is connected to the low voltage grid by quasi-Z-source inverter (QZSI). For this purpose, a two-stage control procedure containing DC and AC stages is performed. In the DC stage, the dynamic characteristics of the quasi-Z-source network are investigated by small-signal analysis. Using the transfer functions obtained from the dynamic model, the capacitor voltage of the quasi-Z-source network is suitably controlled to generate the appropriate voltage to the grid interface inverter. In the AC stage, in order to inject high-quality current into the grid as well as eliminating the resonance peak caused by the LCL filter, a systematic procedure is used to design the PR controller parameters and active damping coefficient. Simulation of the overall system includes solar panels, maximum power point tracking algorithm, quasi-Z-source inverter, and LCL filter to model the grid-tied PV system with the possible details. Simulations are carried out in MATLAB/Simulink environment, and results depict suitable performance of the studied power conditioning system with designed parameters.

Hybrid 2/3 level inverter is a combination of three-level diode clamped inverter and conventional two-level inverter. This structure has the advantages of both two-level and three-level structures. Also, the number of switches is less than three level diode clamped inverter. In this paper, a modified structure for a hybrid 2/3 level inverter, which is based on quasi-Z-source network, is investigated. This structure improves the performance of the 2/3 level inverter and develops the voltage boost capability of the structure. Increasing the output voltage can be achieved by selecting the appropriate short-circuit interval in quasi-Z-source network. In addition, short-circuit intervals in quasi-Z-source networks allow the inverter to operate without any dead time, which results in higher quality for output AC voltage. A modified switching method is presented for the proposed inverter and the related calculations are performed. Also, a simple control scheme is proposed to balance the neutral-point of the structure and to compensate the voltage imbalance of the Quasi network’s capacitors. The proposed structure can be used to connect different distributed generation sources to an islanded load or to a low voltage grid. Simulations are carried out in MATLAB/Simulink environment and results depict suitable performance of proposed inverter.

Power quality, reliability, loss reduction, and fault clearing times are essential factors in distribution networks. Radial distribution networks often face two problems, line losses and voltage drop at the end of the grid. Connecting distributed generation (DG) can resolve these problems, but it can also cause miscoordination. Protection coordination in the presence of DGs is a major challenge of radial networks. Herein, the optimal location and size of DGs in a radial distribution network protected by fuse and recloser were determined to modify bus voltage profile and reduce active-reactive lines' losses. Since the protection coordinate was eliminated by connecting DGs to the network, by using the SFCL in the output of DGs and minimizing its size, it attempted to restore the protection coordination between the fuse and the recloser. In this method, a nonlinear multi-objective function was introduced to be optimized by genetic and PSO algorithms. The simulation was performed in DIgSILENT software. The effectiveness of the proposed method was verified via IEEE 33-bus test systems.