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Reliable and economic protection of DC grids against fault currents is the main challenge for the development of voltage source converter-based DC grids. Application of fault current limiters (FCLs) can limit the rapid increase of fault current and reduce the DC circuit breaker (DCCB) requirements to isolate the fault. This article reports a bidirectional solid-state FCL (BSSFCL) to protect the DC lines against DC short circuit fault. In addition, it can limit fault current in both directions. The circuit and principle operating of the proposed BSSFCL are presented. Then, the current limiting performance of the proposed BSSFCL is analyzed and its parameter design requirements are presented. Finally, the performance of the proposed BSFFCL is compared with that of the RL-current limiting circuit (RL-CLC), mutual inductance-type FCL (MIFCL), and restive mutual-inductance solid-state FCL (RMI-SSFCL). The numerical analysis and simulations were done using the PSCAD/EMTDC software. It was found that, the BSSFCL could effectively enhance the breaking capability of DCCBs. Moreover, it outperforms the RL-CLC, MIFCL, RMI-SSFCL in terms of the fault current limiting, the fault clearing time and metal oxide arrester (MOA) energy absorption of DCCBs. [ABSTRACT FROM AUTHOR]

This paper presents an intelligent method for online voltage stability margin (VSM) assessment using optimized adaptive ANFIS. Harris Hawks Optimization Algorithm (HHOA) is used to train the ANFIS and conventional wavelet transform (WT) is also applied as a feature extraction technique on the network voltage profile. The network voltage profile is used as the main data to estimate VSM because it contains the necessary information about the network structure, load levels, production pattern, and control system performance in the network. Using wavelet transform technique with high resolution, the necessary features for entering the ANFIS block are extracted, but due to the variety and multiplicity of these features, especially for large networks, the Principal Component Analysis (PCA) method is used to select the appropriate features and remove additional data. The characteristic of this hybrid algorithm is that it can be used both in dynamic and static conditions of the network. Finally, the proposed VSM estimation algorithm is applied to the 39-bus and 118-bus IEEE test systems, and its results are evaluated. The comparison of the results with other VSM methods shows that the proposed algorithm is effective for large power grids. [ABSTRACT FROM AUTHOR]

Summary: This paper concentrates on the issues with the aim of providing a constant dc‐link voltage and desired power sharing for a distributed energy storage system (DESS)‐based hybrid microgrid under load variations. The hybrid microgrid which is consisted of PV system, lithium battery‐based storage system and a grid‐connected dc/ac converter are controlled by designing a controller based on the zero dynamics‐based mathematical equations of all used converters. Two buck and bidirectional buck‐boost dc/dc converters employed in PV and DESS systems, respectively, are responsible for damping the dc‐link voltage fluctuations, and also the grid‐connected converter is set to enhance the grid power quality and supply continuously the grid‐connected loads. The main contributions of the proposed control technique are simplicity and providing the simultaneous stable performance for both DC and AC sides under both DC and grid‐connected loads variations. Moreover, another contribution of the proposed control technique is providing accurate coordination in both steady‐state and dynamic conditions. To analyze the proposed controller, the dynamic operations of the converters in various operating conditions are evaluated. In this evaluation, several curves based on their zero dynamics are achieved, and their desired operations are completely investigated in different operating conditions. Simulation results in MATLAB/SIMULINK verify the proposed controller ability at reaching the desired zero dynamics and the stable performance of the proposed hybrid microgrid. [ABSTRACT FROM AUTHOR]

Integration of large-scale wind power plants (WPPs) in power systems faces high short circuit current and low-voltage ridethrough (LVRT) challenges under fault condition. The use of superconducting fault current limiters (SFCLs) was found to be a promising and cost effective solution to solve these problems. This paper presents a theoretical analysis of Bridge-type SFCL (BTSFCL) performance supported by PSCAD/EMTDC based simulation to enhance the LVRT capability of doubly-fed induction generator (DFIG)-based WPPs. It suppresses the transient fault current without any delay time and prevents from instantaneous voltage sag in the connecting point at fault inception time. The main advantages of BTSFCL are: simplicity, high reliability and automatic operation under fault condition for enhancing the LVRT performance. The studied WPP is modeled based on an aggregated doubly-fed induction-generator (DFIG) wind turbine. Simulation results reveal that BTSFCL limits the transient short circuit current contribution of WPP and enhances the LVRT capability of the DFIG-based WPP. Also, the performance of BTSFCL is compared with the static synchronous compensator (STATCOM) for enhancing the LVRT capability. [ABSTRACT FROM AUTHOR]