The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

Although conventional electromechanical circuit breakers have a proven record as effective and reliable devices for circuit protection, emerging power distribution technologies and architectures, such as dc microgrids, require improved interruption performance characteristics (eg, faster switching speed) The need for faster switching operation, in combination with the latest developments of advanced power semiconductor technologies, has spurred an increase in the research and development in the area of solid-state circuit breakers This article provides a comprehensive review of various solid-state circuit breaker technologies that have been reported in the literature during recent years First, we categorize solid-state circuit breakers based on key features and subsystems, including power semiconductor devices, main circuit topologies, voltage clamping methods, gate drivers, fault detection methods, and commutation methods for power semiconductor devices Second, we discuss the various challenges associated with the design of solid-state circuit breakers from the perspective of generic applications and provide a comparison of several solid-state breaker technologies based on key metrics Finally, we provide a useful framework and point of reference for future development of solid-state circuit breakers for many emerging power distribution applications

A Review of Solid-State Circuit Breakers

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.

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DC Microgrid Protection: A Comprehensive Review

The present work aims to explore the performance of fuzzy system-based medical image processing for brain disease prediction. The imaging mechanism of NMR (Nuclear Magnetic Resonance) and the complexity of human brain tissues cause the brain MRI (Magnetic Resonance Imaging) images to present varying degrees of noise, weak boundaries, and artifacts. Hence, improvements are made over the fuzzy clustering algorithm. While ensuring the model safety performance, a brain image processing and brain disease diagnosis prediction model is designed based on improved fuzzy clustering and HPU-Net (Hybrid Pyramid U-Net Model for Brain Tumor Segmentation). Brain MRI images collected from the Department of Brain Oncology, XX Hospital, are employed in simulation experiments to validate the performance of the proposed algorithm. Moreover, CNN (Convolutional Neural Network), RNN (Recurrent Neural Network), FCM (Fuzzy C-Means), LDCFCM (Local Density Clustering Fuzzy C-Means), and AFCM (Adaptive Fuzzy C-Means) are included in simulation experiments for performance comparison. Results demonstrated that the proposed algorithm has more nodes, lower energy consumption, and more stable changes than other models under the same conditions. Regarding the overall network performance, the proposed algorithm can complete the data transmission tasks the fastest, basically maintaining at about 4.5 seconds on average, which performs remarkably better than other models. A further prediction performance analysis reveals that the proposed algorithm provides the highest prediction accuracy for the Whole Tumor under the DSC coefficient, reaching 0.936. Besides, its Jaccard coefficient is 0.845, proving its superior segmentation accuracy over other models. To sum up, the proposed algorithm can provide higher accuracy while ensuring energy consumption, a more apparent denoising effect, and the best segmentation and recognition effect than other models, which can provide an experimental basis for the feature recognition and predictive diagnosis of brain images.

/pdf/fuzzy-system-based-medical-image-processing-for-brain-3f8ta08jgz.pdf

Fuzzy System Based Medical Image Processing for Brain Disease Prediction

The proliferation of distributed energy resources is setting the stage for modern distribution systems to operate as microgrids, which can avoid power disruptions and serve as resources for fast recovery during macrogrid disturbances. Microgrids are, therefore, major assets to improve the grid resilience. However, the offered resilience is seriously undermined if microgrids are not properly protected in the event of faults within their own boundaries. Distribution protective devices cannot reliably protect microgrids due to the variable and often limited short-circuit capacities of microgrids. Moreover, the research on microgrid protection has not led to a commercially available microgrid relay to date and has little prospect of reaching that level in the near future. As a result, the existing options for reliable microgrid protection remain effectively the subtransmission and transmission system protective devices, e.g., directional overcurrent, distance, and differential relays. Although years of operation in macrogrids support these relays, their performance for microgrids is yet to be analyzed. This paper presents such analysis for different relay types by considering various fault and generation conditions in a microgrid. Time-domain simulations are used to identify the scenarios where the relays function correctly as well as the problematic conditions, on which future research should focus. This paper also presents a short review on direct current (dc) microgrids and their protection requirements.

Microgrid Protection

The Z-source dc circuit breaker has been introduced as a new circuit for quickly and automatically switching off in response to faults. A modified Z-source breaker design is introduced for the operation at medium-voltage dc with future applications in naval ship power systems. Compared to existing designs, the respective design will allow for greater control of step changes in load. This new design also limits capacitor current in the circuit and can be easily modified for fault detection. Analysis of the breaker operation is presented during both the fault and step changes in load. Low-voltage laboratory validation of the breaker was carried out on two different versions of the proposed circuit.

Modified Z-Source DC Circuit Breaker Topologies

Current trends in Naval shipboard power system architecture indicate that the electrification of future warships is inevitable, and it will be equipped with loads that draw periodic pulsed currents from the dc microgrid or have large transients while switching state. In order to monitor the operation of those loads, solely time-based features are not enough as they do not provide sufficiently unique information to differentiate various transient stages of the load profile. The focus of more recent research has been on extracting time–frequency features. However, no comprehensive solution exists that could work for any general load profile. The proposed load monitoring and fault detection method presented in this article outlines a data clustering-based approach to extract unique feature vectors from short-time Fourier transform analysis for any pulsed load. These features can then be used to identify various events in the load transient as well as shunt faults and series arcing faults. Implementation and performance of the scheme for several load profiles and fault scenarios are included.

STFT Cluster Analysis for DC Pulsed Load Monitoring and Fault Detection on Naval Shipboard Power Systems

The z-source breaker has been introduced as a new circuit for quickly and automatically switching off in response to faults. A modified z-source breaker design is introduced for operation at medium-voltage dc with future applications in naval ship power systems. Compared to existing designs the respective design will allow for step changes in load. This new design also limits capacitor current in the circuit and can be easily modified for fault detection. Analysis of the breaker operation is presented during both fault and step changes in load. Low voltage laboratory validation of the breaker was carried out on two different versions of the proposed circuit.

Modified z-source DC circuit breaker topologies

Since the great debate between Thomas Edison and Nikola Tesla, our nation's power system has operated on alternating current (ac). This was chosen over direct current (dc) because of the need to increase voltage with ac transformers to a high value using transformers for long-distance power transmission. The system has served its purpose well, but now, many energy sources, such as solar panels, fuel cells, and batteries, supply dc voltage. Also, dc/dc power converters are commonly used to transform voltage and to interface these dc sources with a larger system. Because of this, local dc power systems (or microgrids) have become popular topics in research literature. It also turns out that interfacing a wind power generator to a dc system is simpler than interfacing it to an ac system because ac/dc conversion is needed for the former and ac/dc/ac conversion is needed for the latter. Although energy sources and power conversion are readily available for dc power systems, some highperformance applications require fast-acting dc circuit breakers, which are currently in the experimental phase. This article discusses options for high-performance dc circuit breakers and specifically details the coupled-inductor dc breaker. This breaker is demonstrated for fault protection in a notional dc microgrid.

DC Microgrid Protection: Using the Coupled-Inductor Solid-State Circuit Breaker

This paper considers design details of the z-source breaker. Specifically, the effect of coupled inductors on the z-source breaker is studied. It is shown that the inductor weight can be reduced by 30% and the inductor volume can be reduced by about 25% when coupled inductors are used. Furthermore, the coupling plays a part in the commutation process meaning that the breaker can operate with one capacitor instead of two. These results mean that the major components of the z-source breaker can be greatly reduced. Simulations are carried out to verify the results.

Atif Maqsood

Papers

Modified Z-Source DC Circuit Breaker Topologies

STFT Cluster Analysis for DC Pulsed Load Monitoring and Fault Detection on Naval Shipboard Power Systems

Modified z-source DC circuit breaker topologies

DC Microgrid Protection: Using the Coupled-Inductor Solid-State Circuit Breaker

Z-source Dc circuit breakers with coupled inductors