مجله مهندسی برق و الکترونیک ایران
سال نوزدهم شماره 4 (زمستان 1401)

From the point of view of network operation, the lack of proper management of electric vehicles in the network can change the load profile of the network and causes numerous peaks and valleys in it, which is not appropriate from the perspective of network operators. In this paper, an intelligent charging strategy in which according to the information recorded by drivers such as the length of the previous trip, the length of the next trip, arrival time and departure time of the car and with the aim of reducing daily costs and reducing network peak load for integration. The best electric vehicle is provided in the network. Highlights and key points of the article include examining the presence of charging parking lots in power supply instead of developing power transformers and examining the positive consequences of using discrete intelligent charging of electric vehicles to flatten network load profiles and reduce switching times, as well as considering electric vehicle charging schedules. There are various electric vehicles that have a normal distribution for cancellation situations or the presence of all subscribers in their satisfaction coefficient or cost coefficient. Also, two models of intelligent charging with the aim of minimizing the total daily cost and its peak-to-average load ratio have been presented to examine the effects of charging an electric vehicle from an economic and technical point of view. Also, fast and slow charging are two different charging methods that will be examined along with charging parking lots and the type of home charging for these case. In this study, a method for leveling the network load profile was introduced and the effect of the penetration level of electric vehicles on the network load profile was investigated and positive results were obtained. Charging in the early hours prevented the occurrence of peak load and also prevented damage to the network. A 37-bus distribution network has been used for the simulations, in which two technical and economic methods will be examined. In this research, YALMIP powerful toolboxes have been used. The results show that the proposed method will be effective in reducing the number of switching times and leveling the load profile.

In this paper, a mixed-integer linear programming (MILP) model is proposed to solve the charging problem of electric vehicles (EVs) using floating charge method meaning that the EV, could be supplied by each of the three phases connected to a special bus. In other words, unlike a usual household load which is only supplied by a particular phase, in the floating charge method it is assumed that each of the phases can supply the EV. Because of the importance of the loss reduction in the smart distribution networks, the active power loss is considered as the objective function of the proposed model. To evaluate the presented model, it is compared with two charging methods, namely uncoordinated and coordinated methods, using modified IEEE 31 bus distribution test system. The obtained results show that the proposed model, on one hand, decreases the total loss of the network and on the other hand, satisfies the voltage drop constraint in all of the considered cases adequately. Also, using the floating charge method, the system operator is able to improve the voltage magnitude of the neutral conductor.

Electric vehicle charging in the distribution network is one of the common techniques for technical and economic management of energy distribution, which, if implemented properly, will bring several benefits such as reducing network peak load, charging costs reduction, loss minimization, and etc. In most traditional charging methods, the constraints of fully charging electric vehicles at departure time from the parking lot have always been considered, while, in fact, it is not necessary to fully charge electric vehicles. Instead, it is better for each vehicle to be charged smartly based on its required energy for daily trips. In order to implement this smart method, electric vehicle owners provide information about the number of trips and the length of their route for the parking charge management unit. Then, the desired charge calculation is done according to the vehicle's specifications and their initial state of charge of the battery at arrival time to the parking lot. Finally, the charge manager will schedule charging based on the time of use tariff, the limitation of the distribution transformers, the charging level (normal or fast), etc. to so minimize the charging cost in compliance with the technical and economic constraints. The result of smart charging is compared in normal and fast charging mode and several limitations of the distribution network in the presence/absence of the demand response program. YALMIP and MOSEK software have been applied as solvers of the mixed-integer linear programming model.

Wireless power transfer (WPT) has been found to be a practical replacement for cable power transfer which provides a wide range of applications. This technology offers a remarkable solution for charging electric vehicles (EVs) due to more convenience and increased safety.  Moreover dynamic (in-motion) wireless charging offers the possibility of reducing the energy storage requirement on the vehicle battery. The high power requirement for short term charging in dynamic WPT may not be feasible using conventional two level inverters because of voltage and frequency limitations. So, the need of exploiting other topologies in this application that require high power, high frequency and high efficiency simultaneously is inevitable. In this paper a multilevel converter is proposed in order to improve efficiency and maximize the transferred power while decreasing higher order harmonics which reduce sensitivity to misalignment of coils. Simulation and experimental results on a designed 6 kW WPT system show high efficient power transfer with very low current distortion.

Nowadays high-voltage power sources is used in different areas such as generation of atmospheric-pressure plasma. Different voltage waveforms affect the plasma generation and its quality. In this paper a new high voltage square wave with DC-offset power source is presented to study the different parameters on plasma generation and propagation. The proposed converter which is based on power semiconductor devices is very simple and practical. The experimental prototype of the proposed converter can generate variable square wave AC voltage with 12 KV peak to peak and 15 KHz frequency, and variable DC-offset with 25 KV amplitude. The experimental power source is used for generation of the plasma and the effect of DC and AC components on generation and propagation of atmospheric plasma are investigated.

Multilevel inverters are a new generation of DC-AC converters at medium and high voltage and power levels. These converters have made great strides in the use of industrial applications compared to conventional two-level inverters due to lower harmonic distortion, filter size, EMI and dv/dt. Besides these merits, some disadvantages can be mentioned such as more power electronics devices and complex control structure. In order to resolve these disadvantages, this paper proposes a new switch-diode based multilevel inverter. This topology is presented with the aim of reducing the number of switches and drivers that are able to modularly increase the number of output levels. The proposed structure has been improved to achieve a higher number of output voltage levels relative to the number of switches, drivers and DC voltage source. To confirm the superiority of the proposed structure, a detailed comparison has been performed with other MLI topologies. In this paper, the nearest level modulation technique is used to generate the output voltage and is simulated in Matlab/Simulink environment. Finally, experimental results are presented to confirm the performance of the designed topology.

The unbalance currents injection by power electronic transformers in order to improve the unbalance voltage conditions of the network causes an imbalanced voltage in the DC link capacitors and creates an active powers inequality in the different phases. In this paper, the proposed control structure independently controls the active power of each phase by modifying the power angle between the voltages of the grid and transformer. Based on the presented analytical relations, the amplitude and phase of the desired zero component current can be calculated. The power angle variations in the different phases of the first stage create a zero-sequence current by the proposed control system which is equal to the result of analytical relations. The simulation results in two modes of the voltage imbalance and network fault show that by injecting the improvement negative currents, the active powers and the DC voltage of capacitors are significantly affected so these Divergences limit the transformer improvement capacity and create vulnerabilities for DC capacitors. After applying the proposed control method, proper convergence is created in the powers flow and DC capacitors voltage. Experimental results also show the convergence of these parameters after applying the proposed control method. Also, the conformity of the zero component by the proposed control structure with the calculated values from the presented analytical relations is clearly visible from the laboratory results.

The increase in the number of pulses in multipulse rectifiers leads to a reduction in harmonic current distortion. But this increase in the number of pulses leads to an increase in kVA, cost, and complexity of the multi-pulse rectifiers. As a result, in industrial applications, 12-pulse rectifiers are mainly used due to their lightweight, simple transformers, and low kVA rate, and low cost. The 12-pulse rectifiers cannot meet the standard limitations of IEEE Std. 519 means that the harmonic distortion of the input current is less than 5%, so they are usually used with the filter. In recent years, in order to increase the number of pulses and reduce the harmonic distortion of the input current without increasing cost and complexity in the 12-pulse rectifier, passive harmonic mitigation in the DC link has been introduced. In this paper, a pulse tripling circuit is proposed to upgrade the structure of a 12-pulse rectifier to 36 pulses with a very small kVA rate (kV equivalent to 1.34% of the rated load). Also, the 12-phase autotransformer used in the proposed structure is based on a polygon connection with a very low kVA rate compared to other autotransformer structures. As a result, the total kV rate of the proposed 36-pulse rectifier is about 24% kV of nominal load. Simulation results show that the harmonic distortion of the total input current in the proposed rectifier is less than 3%.

In this paper, a new open-switch fault diagnosis method is proposed for the six-phase AC-DC converter based on the difference between the phase current and the corresponding reference using an adaptive threshold. The open-switch faults are detected without any additional equipment and complicated calculations, since the proposed fault detection method is integrated with the controller required signals. The proposed fault-tolerant technique reduces the value of overcurrent and total harmonic distortion (THD) on the healthy and faulty phases, by considering the redundancy mode of space vectors in space vector pulse width modulation (SVPWM) and changing the switching signals in fault regions. This technique is performed without adding any legs, switches or triode for alternating currents (TRIAC) to the circuit. Finally, the proposed fault-tolerant technique is evaluated by MATLAB simulation and the results show its effectiveness.

Nowadays, permanent magnet synchronous motors have been widely used in industry due to the elimination of excitation losses, longer life and higher efficiency. Errors in engine and drive systems are unavoidable during operation. Therefore, a suitable scenario should be considered for when these systems fail. If the necessary predictions and control algorithms are not considered for the error conditions, heavy damages will be imposed on equipment and devices, especially at high power levels. One of the common control methods in inverters and synchronous motor drives is the proportional-integral control method. In most cases, simple proportional-integral control with fixed interest rates is used. In this paper, fuzzy logic with suitable membership functions is used to adaptively and intelligently determine the benefits of proportional-integral controller to control the speed of the permanent magnet synchronous motor in the event of an error. By combining fuzzy logic and gray wolf algorithm to achieve the optimal controller, a method is presented that takes advantage of the fuzzy controller along with the proportional-integral controller and using the gray wolf algorithm for optimization. Reconstruction results in optimal and stable control under various fault conditions. The proportional-integral controller interests used in conjunction with the gray wolf algorithm for speed control are determined using fuzzy logic for error conditions. In this paper, the proposed method in MATLAB software Simulink environment is simulated in two stages, once for step changes of reference speed and torque and once under three types of errors, and the results show improved reference speed tracking and reduction Distortion of three-phase currents and torque fluctuations.

Brushless DC motors called BLDC are used in many industrial and non-industrial applications today for reasons such as very high efficiency, easy control method and high reliability, and their use is increasingly used in mass production applications, especially home appliances. But these motors require the use of an electric drive, even in constant speed applications. Commercialization of these drives by reducing their price and increasing their reliability is one of the main goals of craftsmen and researchers. These goals have been achieved to some extent by using fewer power switches, reducing the number of current and voltage sensors, eliminating position sensors, and using sensorless control methods. But according to the electrolytic capacitors used to reduce DC voltage ripple are both significantly more expensive and, inherently, potentially cause the most damage to the drive. In this paper, with the aim of eliminating high-capacity electrolytic capacitor and using low capacity switched thin film capacitor in DC link, a new control method based on simultaneous control of speed and torque is presented, the use of which significantly causes torque ripple. Reduced voltage fluctuations in the DC link. The validity of the introduced method is checked using simulation in Simulink software and then a laboratory sample of the drive is tested and the results of theory and simulation are validated.

Among all the drive control methods of induction motors, the Direct Torque Control (DTC) method operates independently of the rotor parameters of the machine and, despite its simplicity, provides good torque control in both stable and transient modes. The use of residual comparators in these drives reduces the torque ripple and variable switching frequency. The most common solution is the use of spatial vector modulation (SVM), which depends on torque and reference flux. In this paper, two fuzzy controllers optimized by meta-heuristic algorithm, along with SVM technique for inverter, are used to control flux and torque. One of the objectives of this paper is to analyze and compare the performance of the fuzzy and proportional-integral controller in the presence of electrical errors and after its removal. Simulations are performed in MATLAB/Simulink software and the results and investigations are presented in shapes and tables. The results show that the proposed model improves the system response parameters such as settling time, maximum overshoot and stability of the system and shows that the fuzzy controller has a lower parting percentage and lower settling time for flux and torque than the proportional-integral controller.

In recent years, microturbines as one the distributed generation sources have widly used. This paper investigates the control structure of the microturbine and analyzes its performance in grid-connected mode. In this way, first, the mechanical model of the microturbine is presented. Then, the electrical structure of the microturbine, consisting  of permanent magnet synchronous generator (PMSG) and power electronics converters (PECs), is introduced. The PECs placed between the PMSG and DC-link are known as the generator-side converter and includes a three-phase diode rectifier and a buck converter. Also, a three-phase voltage source inverter (VSI) is employed between the DC-link and grid as the grid-side converter. As the paper novelty, two control approaches for the generator- and grid-side converters are defined, and then control structures of the converters are presented. Simulation results of the study system in the Simulink/MATLAB environment show that the in the first control approach the DC link voltage reaches a value 3.5 times the nominal value during the fault, while the peak value of the DC link voltage with the esecond control approach is 1.2 times the nominal value during the fault. Hence, the second control approach, in which the generator-side converter controls the DC bus voltage and the grid-side converter regulates the injected active and reactive powers, is better in terms of fault-ride-through performance.

In the event of voltage sag at the nearing of a wind park, severe currents may pass through the power electronic devices of the Doubly Fed Induction Generators (DFIGs). Hence, according to the Low Voltage Ride Through (LVRT) requirements, the wind parks are allowed to disconnect from the network after a certain time. Therefore, to avoid such actions, the LVRT requirement of wind parks is considered to be enhanced in this paper. This aim is achieved by offering a novel objective function in order to find the optimum impedance of Superconducting Fault Current Limiter (SFCL). To evaluate the effectiveness of the proposed method, it is verified in MATLAB/SIMULINK and its great performance to amend the LVRT of such wind parks is corroborated by the simulation results.

In this paper, a new magnetic structure for switched reluctance motors is presented. In this structure, both stator and rotor has a segmented topology and there is no magnetic flux path between two stator/rotor segments or any possible combination of them. The proposed segmental structure may be considered with different number of phases as well as different number of segments per phase for any of which the operation principle is the same. In this paper, three phases structure with four stator/rotor segments per phase is considered for examination. In this study, the magnetic structure is simulated using finite element method and the results are obtained accordingly. First, sensitivity analysis is carried out to analyze the most important geometrical parameters and their effects and then different characteristics of the motor are assessed. Next, the motor design aspects are presented. Considering torque per volume data values obtained for the proposed structure in comparison to the other similar topologies, the proposed motor structure has the highest torque among other switched reluctance motor topologies. Moreover, static and dynamic results in different load conditions confirm the proper performance of the proposed segmented motor. Besides, the proposed structure is a good candidate for high torque and low speed application because of high numbers of strokes per revolution.

In this paper, a novel structure of a axial flux switching machines for use in wind speed turbines at low speeds has been proposed, which in addition to the previous advantages, has a simple and economical design for the production of this type of machines. In this proposed machine, the magnets are placed on the surface of stator, and the three-phase winding is located in the space between the magnets. After designing according to the criteria like increasing electromotive force, reducing the cogging torque and reducing the total harmonic distortion, using the design of experiments and the surface response method combined with the finite element software, the appropriate dimensions are selected and the machine is optimized. To test the design accuracy, a prototype model is also made.

Linear induction motors have single and double-sided structures which are used in special applications, according to their advantages and disadvantages. Due to advantages such as lack of normal forces in double-sided type, these motors are more controllable and popular than the single-sided type, especially for transportation applications.  In literature, single-sided linear induction motors have gained more attentions; so, there are few work on double-sided type. In this paper, first, equations are proposed for calculation of the equivalent circuit parameters of these motors, considering end-effect. Then, a method is proposed to design the motor, employing the presented equivalent circuit. Using the proposed method, a double-sided linear induction motor is designed. Then, to minimize the primary weight and maximize the efficiency and the power factor, the designed motor is optimized by using Particle Swarm Optimization algorithm. One of the important factors in design that affects the construction cost is the weight of the machine. The optimization results show that the initial weight of the motor decreases from 44 kg in the non-optimal case to 18.31 kg in the optimal case. For validation, the optimization results are compared with finite element analysis results and a laboratory prototype test results. The comparison of the experimental and the finite element results with optimization results confirms the validity of the proposed method.

Due to the growing use of Plug-in Electric vehicles in transportation networks, scheduling the charge/discharge of electric vehicles in parking lots can have great impacts on the distribution network's resiliency. This paper presents a Bi-level optimization model to improve the resiliency of the distribution network that takes into account the interaction between the distribution network islanding problem and the charge/discharge scheduling of electric vehicles in available parking lots. In the upper-level problem, regarding the electrical loads and managing the charge/discharge of electric vehicles in electrified parking lots, the island boundaries are determined with the aim of maximize the load restoration. By knowing the islands' boundaries and restored parking lots from the upper-level problem, the changes in destination parking lots and travels characteristics are determined in lower-level problem to minimize the shortest path between the out-of-service destinations and in-service parking lots. The proposed model has been implemented and validated through applying several concurrent faults to the 118-bus active distribution network in presence of electric vehicles in the 25-node traffic network. A combination of mathematical programming and the evolutionary algorithm is applied to reach the final solution. The case studies' results confirm the efficiency of the proposed model for improving the resiliency of distribution networks with managing the charge/discharge of electric vehicle fleets in restored parking lots.

In recent years, climate change and increasing occurrence rate of high-impact rare (HR) natural events such as hurricanes have made it difficult to supply uninterrupted power to end-user customers. The extensive geographic area of electric distribution networks, as the last ring of the energy supply chain in power systems, has increased the vulnerability of these networks against natural events. Thus, distribution companies are inevitably inclined to implement some measures to improve the resilience of the associated network. Considering budget limitations, adopting optimal measures among a set of candidate solutions is a major challenge for distribution networks. A new method is presented in this paper to prioritize the resilience enhancement measures for distribution networks. In this regard, a set of candidate measures is first defined so as to improve the resilience of the distribution network against an HR event. Then, the candidate measures are ranked by the benefit to cost ratio (BCR) index which is calculated by dividing the relative resilience improvement to relative implementation cost for each measure. The proposed method was examined on the IEEE 33-bus test distribution network using MATLAB software. Numerical results verified the efficacy of the proposed method.

The change in the topology of active distribution networks (ADNs) is one of the essential challenges that might affect the protection schemes. The conventional protection schemes based on base topology result in some coordination constraint violations in other topologies due to the outage of upstream substations and distributed generation units. In this article, new combinational and adaptive protection schemes considering all ADNs’ topologies are proposed. In the proposed combinational protection scheme, one setting group is considered for all relays. The relays’ optimal settings are determined by solving one optimization problem, including all constraints corresponding to all topologies. Although the coordination constraint violations are reduced in the combinational protection scheme, the operating time of relays is increased due to the small feasible area of the optimization problem. Hence, proposing an adaptive protection scheme with different setting groups is useful. The number of coordination constraint violations is reduced in the proposed adaptive protection method, while the speed of the protection system is satisfying. Optimal selection of curves for the overcurrent relays is another contribution of this paper that has received less attention in the available research works. The proposed methods are applied to 8-bus and 30-bus IEEE test systems. Test results show that the proposed adaptive function is more appropriate than the combinational one.

After a permanent fault occurs if it is not possible to supply the load in the network, the optimal load restoration scheme allows the system to restoration the load with the lowest exit cost, the lowest load interruption, and in the shortest possible time. This article introduces a new design called Smart Load Shedding, abbreviated SLS. In the proposed SLS scheme, the types of devices in smart homes are divided into four categories: adjustable, interruptible, shiftable, and uncontrollable loads. In this design, a new two-layer algorithm is proposed to solve the service restoration problem. In the first layer, a heuristic method based on graph theory for optimal system configuration is presented. In the second layer, for optimal load restoration, tools such as rescheduling of distributed generation sources, load shedding, load curtailment, and sensitive load curtailment are used. This layer is a nonlinear mixed-integer nonlinear programming problem. To achieve the optimal global solution and less solution time, the model changes from nonlinear programming of non-convex mixed integer nonlinear programming to mixed-integer linear programming. A modified RBTS distribution system is used as a test system to demonstrate the effectiveness of the proposed method.

With the restructuring of power systems, increase of renewable energy sources, and as networks become smarter, power systems are facing new challenges such as uncertainty in available energy resources. An appropriate solution to address these challenges are to use energy storage systems. Therefore, sizing, location, and selection of energy storage systems are important to maximize their benefits. This paper is a review of research studies, examines the types of energy storage systems, their applications, methods of formulating objective functions and methods of solution. Another purpose of this paper is to investigate the issue of optimal Energy Storage System (ESS) planning in active distribution networks. It also provides a broad classification of the Storage Expansion Planning (SEP); and by reviewing several papers, it identifies trends and challenges, and suggestions for future work in this area.

Voltage flicker phenomenon is one of the main power quality problems in today's power networks. Before any compensation operation for this phenomenon, the location of each flicker sources must be identified and the effect of each of them on the network flicker value must be determined. Also, methods that require least number of monitoring points are more in demand due to the limitations of measuring voltage and current signals of the network, including cost and time consuming. In one of the latest studies in this regard, by introducing a method based on the wavelet transform and the approximate model of the transmission line between monitoring points, the location of all flicker sources are traced using minimum monitoring points. Moreover, the contribution of each flicker source is determined using of direct flicker voltage measurement. In this paper, an attempt has been made to improve the previous method, by modifying the approximate model intended for the transmission line, so that even if there is noise in the network, it can detect the exact location of flicker sources. Then, the effect of each flicker sources on the total amount of flicker of any network busbar is determined using the same monitoring points of the previous section and without the need for direct measurement.

Low-frequency oscillations (LFO) imperil the stability of the power system and reduce the Capacity of transmission lines. In the power systems, FACTS devices and Power System stabilizers are used to improve the stability. Static synchronous series compensators is one of the most important FACTS devices. This paper investigates the damping of LFO with static synchronous series compensator (SSSC) equipped with a complementary robust model predictive control in single machine infinite bus (SIMB) power system. The robust model predictive control uses the linear matrix inequality (LMI) to optimize the target function and ultimately obtain the control signal. In order to investigate the performance of the proposed controller, simulation has been carried out in a number of scenarios by considering the uncertainty of the parameters and load disturbances in the power system. In terms of robustness against changes of parameters and disturbances, response time, reduction of undershoot and overshoot, the SSSC equipped with the proposed controller (Robust model predictive controller) performs better than the SSSC equipped with fuzzy-PI controller, SSSC equipped PI controller whose parameters are optimized using genetic algorithm and SSSC equipped optimal fuzzy lead-lag controller. Simulation is carried out using MATLAB software.