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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 fault current limiter (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.

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A single-switch ultra-high voltage DC-DC converter is proposed in this paper. In the introduced structure, a voltage multiplier cell (VMC) and three-winding coupled inductor (CL) are integrated to obtain an ultra-large voltage gain. The input current ripple of the presented configuration is very low due to utilizing an inductor in the input part of the converter which is a very important factor in clean energy applications. The CL leakage inductance energy is successfully recovered, and the main power switch voltage stress is clamped because of using a passive clamp circuit. Therefore, a switch with low os-state resistance can be applied, which declines the conduction losses as well as the cost of the suggested topology. Moreover, the common ground between the input and output of the proposed configuration makes it suitable for many applications such as photovoltaic systems. Some important merits include ultra-high voltage gain, operating in low duty cycles, reduced voltage stress of semiconductors, continuous input current, and high efficiency, which make the introduced converter very suitable for clean energy applications. The operation principle, steady-state analysis, design considerations, and theoretical efficiency analysis of the suggested converter are discussed completely in the paper. Also, the superiority of the proposed converter over recently suggested similar most important DC-DC converters is demonstrated in the comparison study. Finally, the performance and theoretical analysis of the converter are validated with the experimental results at an output voltage of 450 V and an output power of 250 W. K E Y W O R D S continuous input current, coupled inductor, DC-DC converter, high voltage gain, single switch, voltage multiplier cell 1 | INTRODUCTION In recent years, the generation of electricity power mostly belongs to fossil fuels. Nevertheless, searching for alternative clean energy resources like wind energies and solar is remarkably becoming a hot research topic among researchers. The consumption of fossil fuels has several disadvantages that can be overcome by the renewable energy sources

Ferroresonance or nonlinear resonance is a complex electrical phenomenon, which may cause over voltages and over currents in the electrical power system which endangers the system reliability and continuous safe operating. This paper studies the effect of circuit breaker shunt resistance on the control of chaotic ferroresonance in a voltage transformer. It is expected that this resistance generally can cause ferroresonance dropout. For confirmation this aspect Simulation has been done on a one phase voltage transformer rated 100VA, 275kV. The magnetization characteristic of the transformer is modeled by a single-value two-term polynomial with q=7. The simulation results reveal that considering the shunt resistance on the circuit breaker, exhibits a great mitigating effect on ferroresonance over voltages. Significant effect on the onset of chaos, the range of parameter values that may lead to chaos along with ferroresonance voltages has been obtained and presented

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This study presents a novel DC reactor-based ferroresonance and fault current limiter (DRFFCL) for stabilising ferroresonance oscillations of potential transformer (PT) in 33 kV distribution network and decreasing the amplitude of the fault current to an acceptable level. At first, the ferroresonance overvoltage is introduced and various types of overvoltage in the PT are studied. Then, the effects of the suggested DRFFCL on these oscillations are investigated. It is shown that the proposed DRFFCL not only can control the ferroresonance oscillations, but also can decrease the fault current amplitude in the case of short-circuit faults occurrence. The DRFFCL performance is simulated using MATLAB software and a scaled-down laboratory prototype is implemented and tested for the simulation results validation. The measured results are in agreement with the simulation results and clearly show the ability of the DRFFCL for controlling both the ferroresonance overvoltage and fault current.