مجله مهندسی برق و الکترونیک ایران
سال بیستم شماره 4 (زمستان 1402)

In this paper, an improved structure for two-stage inverters is proposed, which profits from high voltage boosting ability without using a transformer. The proposed structure consists of two main stages, including an improved dc-dc converter and an H-bridge. Using only one switch in the input section (the proposed dc-dc converter), not only reduces the cost and dimensions of the converter, but also minimizes the number of working modes (only two modes) and, as a result, simplifies its control. The presence of a common ground point in the input section is a feature that can eliminate the leakage current caused by solar cells in photovoltaic applications. Due to the continuity of the input current and the ability to increase the voltage in the proposed structure, it will be possible to track the maximum power point in the application of solar cells. It will be possible to control the effective value of the output voltage of the proposed structure by controlling the duty cycle of the switch of the input section. In this article, the proposed structure is introduced and additional explanations about its different operational modes are provided along with calculations related to loss and efficiency analysis. Also, a comparison between the proposed structure and a number of existing structures is presented. To prove the correct operation of the proposed converter as well as the correctness of theoretical calculations, simulation results extracted from PSCAD/EMTDC software are presented.

In this paper, the operation of hybrid grid-connected inverter has been improved by changing the control scheme. Hybrid grid-connected inverter -HGCI-, which injects active power and compensates power quality problems, needs low DC link voltage because of thyristor-controlled LC filter in the output branch. This structure uses instantaneous reactive power theory which doesn’t perform well in distorted grid voltage condition. Hence, in these conditions, HGCI can’t inject active power and improve power quality. In this paper, Recursive digital filter method is used to improve HGCI in a way that operates in weak grid voltage. Instantaneous reactive power theory and recursive digital filter are both simulated in MATLAB/SIMULINK and the results are presented. Simulation results prove the satisfactory operation of HGCI in weak grid conditions.

The modular multilevel converter (MMC) is a common choice for high power applications due to its expandable structure. However, the use of a large number of capacitors in the MMC structure has caused the primary technical challenge in reducing its reliability. In power electronics applications, capacitors are one of the components with the highest probability of failure. As well, the MMC structure requires many voltage sensors to maintain the capacitor voltage balance, which raises the converter's cost. Furthermore, the use of a large number of voltage sensors increases the amount of information exchanged between the power system and the central processor, limiting its performance. Therefore, capacitance health monitoring (CHM) of capacitors is necessary by reducing the number of voltage sensors. The paper presents a CHM method using fewer sensors. In the proposed method, one voltage sensor is used for both half-bridge sub-modules, and the voltage of the capacitors is obtained using a capacitor voltage estimation method with low computational burden. In addition, a straightforward CHM method is presented using the ratio of estimated to measured capacitor voltage rise during positive arm current. Simulation and experimental results show the efficiency of CHM methods and proposed sensor reduction in different conditions.

In this paper, a generalized discontinuous modulation strategy based on circuit-level decoupling concept (GCLD-DPWM) is presented for Vienna rectifier under unbalanced grid condition. The purpose of the proposed control scheme, is not only to sustain the advantages of the conventional method such as switching loss mitigation, reducing the complexity of the modulation strategy and fast processing, but also to ensure a reliable and near unity power factor operation of the rectifier under mains unbalance circumstances. To serve this purpose, a new control parameter has been introduced through which the modulation reference signals are modified according to the grid unbalance percentage. In this way, the flexibility of the system will significantly increase, while the desired control objectives are achieved. The software implementation of the control technique has been carried out on Vienna rectifier under the voltage drops of 20% and 30% in the grid. The dynamic response of unbalanced input is also presented. Simulation results demonstrate the validity of the proposed control scheme in terms of aforementioned advantages.

today , due to various reasons such as increasing the prices of energy carriers , increasing the amount of pollutants in the environment , the use of renewable energy sources in the production of electrical energy is growing .among the renewable energy systems , photovoltaic systems are hugely popular because of their stability , high lifetime and low cost of service and maintenance .therefore , evaluation of their performance in order to understand the different aspects of their performance is necessary because the lack of attention to this critical issue in the use of these resources will not only be useful but also it may incur the cost of irreversible economic costs .in order to avoid this problem , various software tools have been proposed to simulate and evaluate the pre-construction of electrical power generation units .in this paper , with the help of accurate meteorological data including annual radiation and ambient temperature , the feasibility of installing a 30 kW PV grid-connected to the grid in a training center has been investigated by using PVsyst software . the simulation results showed that using solar resources for generating electrical energy in this location would be appropriate.

Various methods have been proposed to control the speed of induction motors. Among these methods, the direct torque control (DTC) method contains the desired dynamic response. One of the main problems of DTC is the expensive hardware of this type of drivers, especially the current sensors cost. In practice, at least three current sensors are required, two of which are located on the output phases of the inverter and one sensor on the inverter’s DC link for protection purposes. The aim of this paper is to present a new and inexpensive method for direct torque control of induction motor using only one DC link current sensor. In this method, the zero vector is removed and each of the real vectors 1 to 6 is replaced by two proposed virtual vectors. As a result, it is possible to estimate the phase currents of the motor utilizing only one current sensor in the DC link for a wide range of speeds, even low speeds and close to zero speeds. Another advantage of the proposed method is its constant switching frequency. The proposed idea is simulated using Matlab/Simulink environment and the dynamic response of the system is improved. Also, the ripple reduction in the flux as well as the torque of motor is obtained compared to the conventional DTC method.

Security of power supply is the energetic driver in advent and so, advance of the smart distribution networks (SDNs). The main goal of the conventional SDN expansion planning (SDNEP) is to eco-reliability supply the incremental annual demand by providing an optimal timetable for the sites and sizes of either pre-existed equipment to be expanded or new ones to be installed. Also, it gives a solution to well-operate the expanded network. SDN expansion planning (SDNEP) is to identify a cost-effective timetable for the sites and sizes of either pre-existed equipment to be replaced/reinforced or new ones to be installed in order to supply the increasing electricity load while responding to all the technical and operational constraints and requirements. In SDNs, despite the communication system plays a vital role, but, cyber-physical security of these systems exceedingly vulnerable to cyber-attacks (CAs), especially in the consumer's section. So, this paper suggests an approach for designing cyber-secure SDN (CSDN) by posing the problem as a dynamic modeling of tri-level cyber-secure SDNEP (CSDNEP) program. To evaluate the effectiveness of CSDNEP, computer simulation is done on a large scale SDN and the results are discussed.

Simultaneous consumption of electrical and thermal energy, together with economic and technical advantages of close-to-consumption feeding of consumers, has demonstrated the importance of multi-carrier energy systems planning in recent years. Therefore, in this paper, the planning of an islanded hybrid system (IHS) with renewable energy sources (RESs), combined heat and power system (CHP), boiler, electric and thermal energy storage systems (ESSs) to provide clean energy for electric and thermal consumers is presented. The proposed design is responsible for minimizing the total weighted annual operating costs and pollution consumption of the system. The problem is then subjected to the planning-operation constraints and modeling the RESs and ESSs. The proposed problem is in the form of mixed-integer nonlinear programming. Therefore, in order to obtain the optimal solution with a low standard deviation error, the Grey Wolf Optimizer (GWO) is developed in this paper. The novelties of this paper include the extraction of the IHS with electric and thermal sources and ESSs, and provision of clean energy to the electrical and thermal consumers. Finally, by implementing the proposed design on the actual data of Rafsanjan city in Iran and investigating the numerical results, the ability of design to obtain the optimal hybrid combination of RESs and ESSs to supply electric and thermal consumers from an economic and environmental point of view is confirmed.

This study detects the activity of disabled people living in smart homes based on monitoring their behavior and desires to achieve the final model and store it in the database of the building management system for decision making and automatic operation of equipment used to meet the needs of residents. First, a suitable set of sensors are installed to record and process data correctly in different parts of the building and some to control vital signs depending on the type of disability are installed on the body. . First: selecting sensors and implementing recording techniques, and focusing on the major activities of people with disabilities in smart homes, second: classifying and processing the data collected using the support vector machine (svm) algorithm; svm was performed using the optimal data congestion algorithm (pso) and finally the final pattern for storage in the building management system database.

In this paper, operation of smart distribution network in the presence of the multi-microgrid considering microgrids (MGs) participating in the energy and ancillary services (reactive power and reserve regulation markets) markets is presented. The proposed scheme minimizes difference between MGs cost and their revenue in these markets. Problem constraints include AC optimal power flow equations in the smart distribution networks and multi-microgrid, operation model of sources, storages and demand response. In this problem, there is uncertainty in load, market price, renewable power, and mobile storage. Hence, the stochastic optimization based on unscented transformation method is used to model of these uncertainties. Moreover, this problem is as non-linear. In the following, Ant-lion optimizer uses to achieve optimal solution. Finally, by implement the proposed scheme on the standard networks, the simulation results obtaining from different case studies confirm the capability of the scheme in the improving of networks operation situation with respected to load flow analysis, while it obtains a suitable economic situation for MGs.

This paper proposes a proper hierarchical control strategy composed of a modified droop controller in primary level and a distributed finite-time average controller in secondary layer. The aim of this paper is to achieve precise active and reactive power sharing and frequency and voltage alignment in an islanded AC microgrid (MG). To do so, a typical AC MG is simulated in MATLAB/SIMULINK software, and the proposed method is modeled and implemented. In the simulated AC MG, the distributed generation (DG) units are photovoltaic (PV) systems. The obtained results illustrate that the proposed method appropriately shares active and reactive powers among presented DGs in various operational modes such as load change, increase or decrease in DGs’ output power as well as connection and disconnection of communication links. It also accurately  restores the frequency and voltages of DGs to their nominal values.

With deregulation of modern power systems, electricity market price forecasting become more and more important in managing electricity market which plays a key role in practical operation of electricity market and smart grids. In this paper, a hybrid approach is proposed for probabilistic mid-term electricity price forecasting. In proposed method, feature matrix is extracted using neighborhood component analysis while the seasonality of observed electricity prices is decomposed. After preparation of training dataset, each subset divided to training and validation subsets. Afterwards, using each training data subset and by utilizing a long short-term memory network configuration with three hidden layers, a prediction model will be trained and will be tested with training and validation data sets. The simulation results show that proposed hybrid method caused a decrease in the point forecasting error. Error reduction results to a decrease in final error of combined model and the best MAPE is related to Winsorized model with value of 9.2009 which shows a reduction in MAPE equal to 9.633 percent compared with the method presented for comparison. The results show that the proposed method for electricity price forecasting is an efficient method and can be used for mid-term probabilistic electricity price forecasting.

Individual and public awareness of global warming and pollution has required the different sectors of industry to pay more attention to this issue and take some action in this regard. The electrical industry as the backbone of most other industries should devote more effort for pollution reduction. Unit commitment is the process of determining the state of the units for the day-ahead market. Therefore, managing unit commitment is the best option for contamination reduction. However, in the smart grid, customers can be part of the market via demand response programs. On the other hand, congestion is one of the main problems of the transmission network. Demand response programs could have a positive effect on congestion alleviation as they reduce the total power transmitted via the transmission system. In this paper, the effect of aggregated demand response programs as virtual power plants on operation cost, congestion and emission of network-constrained unit commitment is investigated. Moreover, the best rate of the incentive paid to the demand response programs participants is determined. In this study, according to the simultaneous implementation of the unit commitment problem and the demand response program, which is a complex nonlinear problem with continuous and discrete variables, the MILP method has been applied. Moreover, the transmission system is also considered to fully analyze the impact of demand response programs in the electricity market and its impact on reducing congestion. The recommended strategy is carried out on the IEEE 24 bus reliability test system to prove the effectiveness of demand response programs integration for cost and emission reduction.

Using security-constrained unit commitment as a preventative method of supplying power system frequency response can increase the penetration of renewable energy sources while maintaining frequency response parameters within their allowable range. Moreover, it can reduce the need for corrective actions such as under-frequency load shedding and can prevent power blackouts. So far, there have been two views about the virtual inertia of grid-connected energy storage units, pessimistic (lack of virtual inertia) and optimistic (failure-free frequency response). However, in reality, the frequency response supply system may experience malfunction and incorrect operation, which is modeled and analyzed in this paper from a techno-economic standpoint. False sensor detection, control system malfunction, wrong power injection of energy storage, inverter failure, improper parameter setting, etc., can all be considered disruptive factors. However, in order to have a more general model, the article avoids dealing with the reason behind the poor performance of the storage system and focuses only on its effects, i.e., the possibility of the storage system not participating correctly. The proposed model takes into account the system's frequency stability by linearly integrating the nadir frequency and the rate of change of frequency limits to the robust mixed-integer linear programming model with YALMIP and MOSEK solvers. The results of implementing this model in the IEEE-RTS96 network show that neglecting energy storage system malfunctions can lead to violations of frequency constraints that must be compensated by increasing costs and keeping more online units with more free headroom.

Frequency is one of the important components of the power system, which must be within the allowable range. With the occurrence of a severe disturbance, the governor system and rotating storage of power plants do not have the necessary ability to prevent a rapid drop in frequency. Under frequency load, shedding plans are one of the most important protection plans that are responsible for keeping the frequency within the permissible range in the event of severe disturbances. In this paper, while accurately calculating the active power required to keep the frequency constant, by affecting the spinning reverse energy of power systems in the load shedding stages, the minimum load is calculated to recover the frequency of the power system and the load is cut off. Designed for 4 stages of load shedding operations, in each stage, the amount of power deficit compensated by the rotating storage energy is checked and then the load is cut off. As an example, for a disturbance of 0.8 per unit, the amount of 0.3 per unit is compensated by the stored energy and only 0.5 per unit of load is disconnected from the network. In order to show the effectiveness of the proposed plan, the simulation results of using this plan for an island system have been compared with the simulation results of two common offloading plans. The results show that the proposed design shows more reliable and appropriate performance than the other two common designs. In this paper, while accurately calculating the active power required to keep the frequency constant, by affecting the spinning reverse energy of power systems in the load shedding stages, the minimum load is calculated to recover the frequency of the power system and the load is cut off. Designed for 4 stages of load shedding operations, in each stage, the amount of power deficit compensated by the rotating storage energy is checked and then the load is cut off. As an example, for a disturbance of 0.8 per unit, the amount of 0.3 per unit is compensated by the stored energy and only 0.5 per unit of load is disconnected from the network. In order to show the effectiveness of the proposed plan, the simulation results of using this plan for an island system have been compared with the simulation results of two common offloading plans. The results show that the proposed design is more reliable and appropriate performance than the other two common designs.

In this paper, the capacity of power line communication (PLC) system in the applications of distribution networks is investigated. Unlike the conventional application of PLC in high-voltage networks, using relays in distribution networks is necessary considering their longer channel lengths and meshed structure. Then, determination of the average maximum capacity of communication system, so-called Ergodic capacity, is necessary demand for selection of appropriate PLC system in distribution network. The capacity of a communication system depends on various factors such as the channel characteristics, the system bandwidth and the noises in the network. In comparison with the studies in the field of PLC system, the PLC system with amplify- and- forward relaying considering the impulsive noises has not been analyzed. In this paper, using the practical models of channel and noise, the ergodic capacity of channel is calculated a function of input signal' signal to noise ratio. In this proposed scheme, the affecting parameters including statistical channel distribution, distance between source and relay nodes, distance between relay and destination nodes, the transmitted signal power and signal to impulsive noise ratio are considered. To do so, the signal to noise ratio in destination node is formulated with mathematical expressions, and then, the ergodic capacity is obtained using the Shannon theorem. Furthermore, the impact of assigned power to the source and relay on the capacity is investigated. Finally, by simulating a sample channel, the ergodic capacity is obtained for the different values of transmitted signal power, impulsive signal to noise ratio and channel length. The simulation results show that the average capacity changes linearly in terms of path losses; such that for SNR=20 dB and in the presence of the relay, by reducing the length of the line from 200 m to 10 m, the capacity increases by approximately 3.5 bits/s/Hz.