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In this study, a power converter topology and control schemes for the power converter stages are proposed for a DC extreme fast charger. The proposed system is composed of a cascaded H-bridge (CHB) converter as the active front end (AFE), and an input series output parallel (ISOP), which includes three parallel connected dual active bridge (DAB) cells. A modified Lyapunov Function (LF) based control strategy is applied to obtain high current control response for the AFE. An additional controller to remove the voltage unbalances among the H-bridges is also presented. Additionally, the triple phase-shift (TPS) control method is applied for the ISOP DAB converter. A Lagrange Multiplier (LM) based optimization study is performed to minimize the RMS current of the transformer. The performance of the proposed converter topology and control strategies is validated with MATLAB/Simulink simulations. 

The increasing demand for electric vehicles, due to advantages such as higher energy efficiency, lower fuel costs, and less vehicle maintenance, is expected to drive the need for electric vehicle charging infrastructure. Due to their reduced size and weight, high power and scalable compact solid state transformers (SST) are growing in popularity. This study presents the total loss analysis and control design for a direct grid connected single-phase SST for a fast charging station. A control strategy to achieve robust current control, DC voltage and power balancing, and power loss minimization (PLM) is implemented for this system. Detailed analyses and simulation results obtained from MATLAB/Simulink are given to prove the effectiveness of the proposed control techniques. 

In this paper, a 10 kV SiC MOSFET-based solid-state transformer (SST) operating at 13 kV to 7.2 kV, 667 kW, and 20 kHz is modeled and optimized to reach maximum power density and efficiency. In order to reach optimum configuration, different core material/type/size, primary/secondary turns, insulation type/thickness, and cooling systems are considered; then based on a systematic approach the best solution is obtained. To reach this goal, the magnetic part of SST forced air-cooling, and the water-cooling system is modeled in ANSYS MAXWELL/Simplorer, ANSYS-ICEPAK, and ANSYS-FLUENT, respectively. The simulation results show a high efficient SST with an effectiveness of the cooling system. 

Due to dc microgrid nature, dc fault current has no zero-crossing current and could increase up to a thousand amps. Because of that, a dc circuit breaker (DCCB) with the ultra-fast response and high efficiency is required. Regarding this issue, this paper presents a novel thyristor-based DCCB. Then the optimal values of the proposed DCCB components are obtained by cost-power loss multi-objective optimization method. Finally, to keep the maximum temperature of the thyristor below the maximum allowed value, an optimum forced-air microchannel that has high reliability, low cost, and high efficiency is proposed for the proposed thyristor-based DCCB. 

DC microgrids have attracted significant attention over the last decade in both academia and industry. DC microgrids have demonstrated superiority over AC microgrids with respect to reliability, efficiency, control simplicity, integration of renewable energy sources, and connection of dc loads. Despite these numerous advantages, designing and implementing an appropriate protection system for dc microgrids remains a significant challenge. The challenge stems from the rapid rise of dc fault current which must be extinguished in the absence of naturally occurring zero crossings, potentially leading to sustained arcs. In this paper, the challenges of DC microgrid protection are investigated from various aspects including, dc fault current characteristics, ground systems, fault detection methods, protective devices, and fault location methods. In each part, a comprehensive review has been carried out. Finally, future trends in the protection of DC microgrids are briefly discussed. 

This paper presents a novel harmonic-based overcurrent relay which detects and isolates three-phase faults in a meshed microgrid. The harmonic signals are generated by two Distributed Generators (DGs) which each of them communicate with its adjacent DG. In the first step, a set of features are extracted from DG output signal and then fed to a Support Vector Machine (SVM) to detect occurrence of fault. Once the fault is detected, based on minimum voltage measured by DG, two closest DGs will recognize and these two DGs inject two distinct harmonics to activate harmonic-based relays. As each set of relays located at either beginning or end of each section is activated by current with specific frequency, these relays behave like directional relays without using voltage transformers. As a result, the proposed method is cost-effective solution. The optimum Time Dial Settings (TDSs) of these relays are obtained by solving a coordination problem with Particle Swarm Optimization (PSO) algorithm. Real-time results are taken by OPAL-RT to show the effectiveness of the proposed method for two different locations of fault in a meshed microgrid. 

This paper presents a novel noncommunication protection architecture based on utilizing the selected Distributed Generators (DGs) which provide high-frequency harmonics for harmonic-based overcurrent relays to detect and isolate three-phase faults in meshed microgrids. The most prominent features of this structure include limited number of DGs required to inject harmonics, no need for using centralized communication system, and the fault can be detected and located in all conditions such as load disconnection/connection and DG disconnection/connection. The optimum Time Dial Settings (TDSs) of these relays are obtained by solving a coordination problem with Particle Swarm Optimization (PSO) algorithm. Real-time results are produced using OPAL-RT to show the effectiveness of the proposed method for two different locations of faults in a meshed microgrid. 

Fault Current Limiters (FCLs) are one of the main solutions to upcoming challenges in microgrid protection. Regarding the high penetration of distributed generations (DGs) in future power system, designing cheap and effective FCL is a necessity. The present study addresses this issue by proposing an embedded FCL operating based on modifying the secondary control of four-wire DG. As this method is presented for a four-wire system, besides very low implementing cost, it has independency and flexibility to only limit the current of DG faulted phase. This study also provides real-time simulation results by OPAL-RT to compare the proposed method with a virtual-impedance-based FCL to validate its effectiveness. Finally, experimental results are presented to validate the effectiveness of the proposed FCL.