Rapid protection of modern electric networks using fault current limiters (FCLs) is often delayed and limited by the inherent controller, sensor, and power electronic unit delays. This article proposes a novel self-activated FCL (SAFCL), comprising a dc saturation winding, series ac limiter windings, and ac parallel reactor, which limits the fault current in less than 0.4 ms. Furthermore, the advantage of this SAFCL, when compared to a traditional saturated core FCL (SCFCL), is that it does not rely on any external controller, sensor, controllable solid-state switch, and battery. In the normal state, the SAFCL behaves like a saturated reactor with a very low impedance and in the fault state, cores are entered to the unsaturation region without relying on an external controller which imposes a high impedance to limit the fault, rapidly. The performance of the SAFCL is evaluated through off-line MATLAB and Maxwell ANSYS FEM simulations, and is also validated by experimental studies conducted on a scaled-down prototype.

Wind energy has always been developed as one of the vital parts of modern power systems. However, by integration of wind-based generation, the level of fault current is likely to be increased which can damage the wind generators, microgrid components, and upstream grids. Consequently, utilizing viable protecting structures might preserve wind generator structures and other sections of the electric system as well. In this paper, first, the issue of the fault current of wind generators is discussed, and then well-known solution for protecting wind generators against fault current will be classified based on the comprehensive review. Next, various power electronic-based structures which are proper for protection of systems against the fault current, will be debated and ultimately the features of reviewed structures will be compared and summarized in a table for the case of wind energy generator protection.

Ferroresonance occurrence is a source of damage, causing overvoltage on voltage transformer (VT) and isolators of the grid equipment. Some solutions are available to protect VTs from the ferroresonance overvoltage. However, they just act after the ferroresonance occurrence. In this letter, to prevent the occurrence of ferroresonance, a dc reactor-based protection device is introduced. Analytical studies and simulations by MATLAB/Simulink and Maxwell ANSYS demonstrate the capability of the proposed protection device as a VT ferroresonance inhibitor. Experimental results from a scaled-down laboratory prototype are also provided to verify the proposed solution.

A fault current limiter (FCL) is an effective means of limiting fault currents that is a promising power system protection solution. This paper presents a comparative survey of research activities and emerging technologies of FCL and discusses in detail the features of an inductive FCL. Inductive FCLs possess superior performance and higher speed of operation in comparison with other FCLs. The magnetic structure of an inductive FCL is instrumental to superior performance. The review study discusses the feasibility and effectiveness of the magnetic flux based FCLs. In addition, the magnetic behavior of FCLs is discussed considering the analytical study of their equivalent circuits. Moreover, a comprehensive comparative study of inductive FCLs is presented based on their technical operational characteristics.

This article presents a novel high-temperature superconductive (HTS) power flow controller and current limiter (PFCCL), which limits fault currents and manages power flow in the intended transmission line. The proposed device includes series HTS reactors, HTS controlling dc coil, recovery resistive coil, and power electronic switches, which protects the microgrid from the upstream ac grid, short-circuit faults, and it controls the power flow between a microgrid and the upstream grid. Performance of the proposed PFCCL is mathematically analyzed, utilizing MATLAB and Maxwell software, and then validated by laboratory scaled-down experimental setup. It is shown that the simulation results are in fair agreement with the developed experimental laboratory setup results.

The protection of distribution networks is one of the most substantial issues, which needs special attention. Using appropriate protective equipment enhances the safety of the power distribution network during the fault conditions. Fault current limiter (FCL) is a kind of modern preserving system being used for protecting power networks and equipment. One of the main concerns of power networks is the voltage restoration of buses during faulty conditions. In this study, a group of coordinated DC reactor type faults current limiters are designed and tested to protect the network and restore its buses voltage within the fault period. To coordinate FCLs and measurement devices during the fault sequences, a wireless communication system and decision-making computer are used. The proposed FCLs coordination strategy is modelled and simulated in MATLAB platform and the results are validated by the developed laboratory test setup.

Power systems are subjected to various types of faults as well as ferroresonance overvoltages. These results in the interruption of the normal operation of the power grid, failure of equipment, electrical fires, etc. To tackle these issues, this study proposes a dual function limiter to control the fault current and ferroresonance phenomenon in power systems. This compound device is a solid-state series transformer-based limiter that includes IGBT switches, capacitors, rectifiers, and a DC reactor. During the grid normal operation, the proposed limiter is not active and therefore is invisible and it operates in the instant of fault inception or ferroresonance overvoltage occurrences. Analytical studies in all operation modes are presented and assessments on the performance of the proposed ferroresonance and fault current limiter (FFCL) are conducted in Matlab. Simulation results confirm the reported analytical studies and FFCL's performance.

In this paper, a new control approach using an optimal linear control with prescribed degree of stability for modular multi-level converters (MMC) is presented and analyzed. The proposed controller relies on a linear quadratic regulator with integral action which brings the ability of state variable reference tracking for modular multi-level converters. Since MMC is a complex system with several state variables, a unified control system design for this system is vital. The proposed controller of this study is designed to obtain wider stability margin thanks to the implementation of prescribed degree of stability concept to minimize the quadratic performance index of the control structure. By means of this method, the poles of the closed-loop system will be shifted to the desired places in the left half side of the S-plane. The main advantages of this control strategy compared to previous methods are that it will be possible to control the state of energy for each phase separately, while there will be superior tolerance to nonlinearities and the enhanced stability margin with less sensitivity to plant-parameter variations. The performance of the designed controller is verified through MATLAB^TM simulations (The MathWorks, Natick, MA, USA) with the nonlinear model of MMC.

This paper develops a model to study the inertial dynamics of single Type 4 Wind Turbine Generator (WTG)s that emulate the response of grid-friendly Virtual Synchronous Generator (VSG)s. In this vein, a simplified linearized model is developed for the WTG in the electromechanical time scale considering complete WTG dynamics to obtain/investigate the power System Frequency Response (SFR) characteristics. The objectives are to obtain virtual frequency motion equation, present the mechanism of inertia provision clearly, and feature physical interpretations of inertial frequency response. Accordingly, the available inertia constant and damping coefficient are estimated/expressed analytically in frequency-domain that synthetically embed the impacts of key control parameters as well as the initial operating points. It is realized that the available inertia constant and damping coefficient are adjustable and frequency dependent in contrast to that's manifested by a conventional synchronous generator. The developed virtual frequency motion equation is used in turn to establish/investigate the complete SFR model of a generic test power grid which features enormous wind power generation capacity factor. The theoretical analysis shows that the SFR attributes could get adjusted/enhanced by proper tuning of the WTG control parameters. Comprehensive and comparative time domain simulations are also performed in the MATLAB/Simulink platform. It is to verify the accuracy of the proposed models in the evaluation of SFR characteristics and authenticate the theoretical analysis.

This paper presents a dynamic model of modular multilevel converters (MMCs), which are considered as an effective interface between energy sources and the power grid. By improving the converter performance, appropriate reactive power compensation is guaranteed. Modulation indices are calculated based on detailed harmonic evaluations of both dynamic and steady-state operation modes, which is considered as the main contribution of this paper in comparison with other methods. As another novelty of this paper, circulating current control is accomplished by embedding an additional second harmonic component in the modulation process. The proposed control method leads to an effective reduction in capacitor voltage fluctuation and losses. Finally, converter’s maximum stable operation range is modified, which provides efficiency enhancements and also stability assurance. The proficiency and functionality of the proposed controller are demonstrated through detailed theoretical analysis and simulations with MATLAB/Simulink.

Expansion of high-voltage dc (HVdc) systems to multi-terminal HVdc (MT-HVdc) systems/grids considerably increases the short-circuit levels. In order to protect the emerging MT-HVdc systems/grids against fault currents, proper dc fault current limiters (FCLs) must be developed. This paper proposes an innovative high inductance solid-state dc-reactor-based FCL (HISS-DCRFCL) to be used in HVdc applications. In fact, during the HISS-DCRFCL normal operation, its inductance value is extremely low, and its value becomes considerably high during the fault period, which decreases the fault current amplitude. The proposed HISS-DCRFCL performance is analyzed by MATLAB/Simulink and the simulation results are verified and confirmed by laboratory experimental results using a scaled-down laboratory prototype setup.

This paper presents a type of solar thermal power plant and also studies the efficiency of the common type of this distributed generation resource. In order to improve the efficiency of the power station, several techniques are studied such as the combined cycle plant, the thermoelectric generator and the intelligent control application. The thermodynamic analysis of the power plant and the performance of the equipment with an intelligent control system are validated by the developed experimental prototype.

This article presents a multi-objective-based imperialist competitive algorithm (ICA) for optimal tuning of voltage source converter (VSC) stations control parameters in multi-terminal high-voltage direct current (MT-HVDC) grid. The key objective here is to enhance the control performance of the MT-HVDC grid VSC-HVDC stations under dynamic situations. As VSC-HVDC stations are non-linear apparatuses of the MT-HVDC grids, conventional methods for the tuning of the control parameters which are commonly based on approximated linear plant models do not reach to optimal results. Therefore, as the main contribution of this research, an effective ICA-based multi-objective optimization technique is adopted for optimal tuning of the VSC-HVDC stations control parameters. The proposed composite objective function in this algorithm consists of both inner and outer loop parameter optimization characteristics. A fuzzification technique is used in this study to normalize all objective functions and to find the optimal solution. To confirm the merits of the presented optimization method, a detailed model of a four-terminal MT-HVDC grid is developed and its transient and steady-state performance in case of classically and ICA tuned have been studied and compared.

This paper develops a data-driven strategy for identification and voltage control for DC-DC power converters. The proposed strategy does not require a pre-defined standard model of the power converters and only relies on power converter measurement data, including sampled output voltage and the duty ratio to identify a valid dynamic model for them over their operating regime. To derive the power converter model from the measurements, a local model network (LMN) is used, which is able to describe converter dynamics through some locally active linear sub-models, individually responsible for representing a particular operating regime of the power converters. Later, a local linear controller is established considering the identified LMN to generate the control signal (i.e., duty ratio) for the power converters. Simulation results for a stand-alone boost converter as well as a bidirectional converter in a test DC microgrid demonstrate merit and satisfactory performance of the proposed data-driven identification and control strategy. Moreover, comparisons to a conventional proportional-integral (PI) controllers demonstrate the merits of the proposed approach.

This paper reports a general overview of current research on analysis and control of the power grid with grid scale PV-based power generations as well as of various consequences of grid scale integration of PV generation units into the power systems. Moreover, the history of PV renewable growth, deregulation of power system and issues related to grid-connected PV systems considering its contribution to various responsibilities like frequency control, virtual inertia capabilities and voltage regulation are discussed. Moreover, various outcomes of the high-penetrated grid with PV power plants such as power quality, active and reactive power control, protection, balancing and reliability under various loading conditions are reviewed and discussed.

The protection of sensitive loads against voltage drop is a concern for the power system. A fast fault current limiter and circuit breaker can be a solution for rapid voltage recovery of sensitive loads. This paper proposes a compound type of current limiter and circuit breaker (CLCB) which can limit fault current and fast break to adjust voltage sags at the protected buses. In addition, it can act as a circuit breaker to open the faulty line. The proposed CLCB is based on a series L-C resonance, which contains a resonant transformer and a series capacitor bank. Moreover, the CLCB includes two anti-parallel power electronic switches (a diode and an IGBT) connected in series with bus couplers. In order to perform an analysis of CLCB performance, the proposed structure was simulated using MATLAB. In addition, an experimental prototype was built, tested, and the experimental results were reported. Comparisons show that experimental results were in fair agreement with the simulation results and confirm CLCB’s ability to act as a fault current limiter and a circuit breaker.

This paper presents a transformerless step-upmultilevel inverter based on a switched-capacitor structure. One of the main contributions of the proposed topology is replacing the separated DC voltage sourcewith capacitorswhich are charged at predetermined time intervals. Therefore, a high-level staircase voltage waveform can be achieved by discharging some of these capacitors on the load. The other contribution of the proposed structure is to eliminate themagnetic elements which traditionally boost the input DC voltage. In addition, asymmetrical or unequal amounts of capacitor voltages create more voltage levels, which enable voltage level increments without increasing the number of semiconductor devices. This paper introduces a self-balanced boost Switched-CapacitorsMultilevel Inverter (SCMLI) which is able to create a nearly sinusoidal voltage waveform with a maximum voltage of up to 45 times that of the input voltage DC source. Higher level output voltage levels are also achievable by extending the circuit topology. After determination of the switching angles and selecting the proper switching states for each level, an offline NLC method is used for modulation, which eases the control implementation. Analysis, simulation and experiments are carried out for a 91-level inverter (45 levels for positive and negative voltages and one for zero voltage) are presented.

This paper presents a novel approach on analysis and evaluation of required energy for emulating virtual inertia of HVDC interconnected system for stabilizing the frequency deviations. Presented study is in the scheme of Automatic Generation Control (AGC) task with the HVDC links for inertia emulation. This issue became more important, considering the fact that renewable based generation with the lack of inertia can affect the task of frequency regulation. Therefore, in this paper the sizing issue of an aggregated storage system located in HVDC links of interconnected system is addressed and analyzed. Proposed model is validated using Matlab software for a two area interconnected system.