Design and Implementation of High-Efficiency, Lightweight, System-Friendly Solid-State Circuit Breaker

Direct current (DC) distribution system has shown potential over the alternative current (AC) distribution system in some application scenarios, e.g., electrified transportation, renewable energy, data center, etc. Because of the fast response speed, DC solid-state circuit breaker (SSCB) becomes a promising technology for the future power electronics intensive DC energy system with fault-tolerant capability. First, a thorough literature survey is performed to review the DC-SSCB technology. The key components for DC-SSCB, including power semiconductors, topologies, energy absorption units, and fault detection circuits, are studied. It is observed that the prior studies mainly focus on the basic interruption capability of the DC-SSCB. There are not so many studies on SSCB’s size optimization or system-friendly functions. Second, an insulated gate bipolar transistor (IGBT) based lightweight SSCB is proposed. With the reduced gate voltage, the proposed SSCB can limit the peak fault current without the bulky and heavy fault current limiting the inductor, which exists in the conventional SSCB circuit. Thus, the specific power density of the SSCB is substantially improved compared with the conventional design. Meanwhile, to understand the impact of different design parameters on the performance of SSCB, an analytical model is built to establish the relationship between SSCB dynamic performance and operating conditions considering the key components and circuit parasitics. Simulation and test results demonstrate the accuracy of the proposed model. To limit the fault current with the proposed SSCB without a current limiting inductor, power semiconductors need to operate in the active region temporarily. During this interval, a severe voltage oscillation has been observed experimentally, leading to the DC-SSCB overstress and eventually the failure. A detailed MATLAB/Simulink model is built to understand the mechanism causing the voltage oscillation. Three suppression methods using enhanced gate drive circuitry are proposed and compared. Test results based on a 2kV/1kA SSCB prototype demonstrate the effectiveness of the proposed oscillation mitigation method and the accuracy of the derived model. Meanwhile, when the system fault impedance is close to zero (e.g., high di/dt), the influence of the parasitic inductance contributed by interconnection (e.g., bus bar, module package, etc.) cannot be neglected. To study the influence of the bus bar connections on SSCB with high di/dt, a Q3D extractor is adopted to extract the parasitic parameters of the SSCB and understand the influence of different bus bar connections. A vertical bus bar is proposed to suppress the side effect and verified by the Q3D extractor and experimental results. Finally, a system-friendly SSCB is demonstrated. The proposed gate drive enables the SSCB to operate in the current limitation mode for the overcurrent limitation. The current limitation level and limitation time can be tuned by the gate drive. Then, this dissertation provides an all-in-one solution with integrated circuitries as the fault detector, actuator for the semiconductor’s operating status regulation, and coordinated control. This allows the developed SSCB to limit system fault current not exceeding short-circuit current rating (SCCR) and also take different responses under different fault cases. The feasibility and the effectiveness of the proposed system-friendly SSCB are validated with experimental results based on a 200V/10A SSCB demonstrator

Power distribution investigation of a hexagonal diffused cellular indoor visible light communications system

This paper presents a three dimensions (3D) model of optical power distribution in a diffused cellular indoor visible light communication (VLC) system. To achieve an ideal system which has a maximum coverage area with a minimum power consumption, both hexagon geometric structure and holographic light shaping diffuser (LSD) are employed. We analysed the mathematical models for both square and hexagonal structures with and without using LSD. In addition, the practical system consisting of a (Luxeon Star/O) royal blue LED as a transmitter is used to verify and evaluate the system performance. The system operates at a date rate of 5 Mb/s using the on-off keying non-return-to-zero (OOK-NRZ) modulation format. The simulation results show that using hexagon geometry and a 30o holographic LSD diffuser, the received optical power distribution becomes uniform. The coverage area of the cellular link is therefore significantly extended by 343%. In addition the experimental results for a single cell system are also presented

Power distribution and Q-factor analysis of diffuse cellular indoor visible light communication systems

Comparing with the existing incandescent, light-emitting diodes (LEDs) offer higher power efficiency, higher brightness, longer lifetime, and have a fast dynamic response in the order of a few megahertz. LEDs are recently expected to be utilised for the next generation indoor optical wireless communication (OWC) system. In this paper, we present a mathematical design model as well as a practical measurement for an indoor diffuse cellular visible light communication (VLC) system. It operates at a date rate of 5 Mb/s using the on-off keying non-return-to-zero (OOK-NRZ) modulation format. Using commercially available luminit holographic light shaping diffusers (LSD), we show that the achieved distributions of received power and the Q-factor are more uniform. The range and coverage area of the cellular link are therefore significantly extended

Optimisation of transmission bandwidth for indoor cellular OWC system using a dynamic handover decision-making algorithm

In this paper, we propose a novel cellular optical wireless communications (COWC) system with four diffused cells. A dynamic handover scheme is proposed to make the link more flexible by the way of adaptive channel allocation in different environments. The simulation results show that the proposed algorithm offers almost five times of the maximum dynamic transmission bandwidth and energy efficiency compared to the worst scenarios when all base stations (BS)s are active

A Wearable Robotic Hand for Hand-over-Hand Imitation Learning

Dexterous manipulation through imitation learning has gained significant attention in robotics research. The collection of high-quality expert data holds paramount importance when using imitation learning. The existing approaches for acquiring expert data commonly involve utilizing a data glove to capture hand motion information. However, this method suffers from limitations as the collected information cannot be directly mapped to the robotic hand due to discrepancies in their degrees of freedom or structures. Furthermore,it fails to accurately capture force feedback information between the hand and objects during the demonstration process. To overcome these challenges, this paper presents a novel solution in the form of a wearable dexterous hand, namely Hand-over-hand Imitation learning wearable RObotic Hand (HIRO Hand),which integrates expert data collection and enables the implementation of dexterous operations. This HIRO Hand empowers the operator to utilize their own tactile feedback to determine appropriate force, position, and actions, resulting in more accurate imitation of the expert's actions. We develop both non-learning and visual behavior cloning based controllers allowing HIRO Hand successfully achieves grasping and in-hand manipulation ability.Comment: 7 page

Parity violating scalar-tensor model in teleparallel gravity and its cosmological application

The parity violating model based on teleparallel gravity is a competitive scheme for parity violating gravity, which has been preliminary studied in the literature. To further investigate the parity violating model in teleparallel gravity, in this paper, we construct all independent parity-odd terms that are quadratic in torsion tensor and coupled to a scalar field in a way without higher-order derivatives. Using these parity-odd terms, we formulate a general parity violating scalar-tensor model in teleparallel gravity and obtain its equations of motion. To explore potentially viable models within the general model, we investigate the cosmological application of a submodel of the general model in which terms above the second power of torsion are eliminated. We focus on analyzing cosmological perturbations and identify the conditions that preserve the parity violating signal of gravitational waves at linear order while avoiding the ghost instability.Comment: 17 pages. arXiv admin note: text overlap with arXiv:2201.02357, arXiv:2301.0284

Flagship Report: Mission-Aligned Investing - The Future of Foundations: Impact at Scale?

The purpose of this report is to aid and inform the movement towards mission-aligned investment and heightened transparency, Cornerstone Capital Group and the Massachusetts Institute of Technology's Sustainability Lab (S-Lab) have developed a set of observations on the relative transparency and mission alignment of a set of large foundations. Our goal is not to single out particular foundations but rather to increase broader understanding of mission-aligned investing and transparency