Analysis and Implementation of a 5-Level Hybrid Inverter with Reduced Switching Devices Using Phase-Shifted PWM

The demand for high reliability and the performance-to-size ratio of multilevel inverters (MLIs) have triggered rapid growth in MLIs with the reduced number of controlled-switching devices, isolated dc sources, gate driver circuits, and voltage stress across the switching devices. However, the development of alternative MLIs away from traditional MLI mostly comes at the trade-offs amongst structural and control complexity, power loss, and industrial practicality as the number of voltage levels increase. Thus, this paper presents and analyzes a modest two-stage single-phase hybrid MLI with a high performance-to-size ratio, which generates a five-level voltage waveform across the load with a unity voltage gain, and reduced switches. In the first stage of inverter topology, the controlled-switching devices and gate drivers have been reduced by half as compared to its counterparts. Moreover, the inverter topology’s advantages have been demonstrated on an experimental setup using a recently developed phase-shifted PWM strategy.journal articl

An Investigation of a Power Module for Multiple Series-Connected Si-MOSFETs Realizing Voltage Balance by a Fully Digital Active Gate Control

This paper presents a concept of a power module with multiple series-connected power devices controlled by fully digital active gate drivers. The performance of series-connected power devices with lower voltage ratings is expected to be higher than the case of using only one device with higher voltage ratings. The required voltage balance of each power device to prevent an overvoltage issue can be achieved by a fine adjustment of the switching speed using the active gate control. As a first design example, a prototype module configured mainly by two series Si-MOSFETs, active gate drive circuits, and a fully digital controller was designed and developed. It was experimentally verified that suitable active gate control can realize the voltage balance in two series-connected MOSFETs under continuous operation.journal articl

A Coherent Random Number Utilization Scheme for a Fault-tolerant Parallel Execution Model Based on Hierarchical Omission

High productivity, scalability, load balancing, and fault tolerance are all important issues of massively parallel computing. A parallel execution model called HOPE, which we are proposing, addresses these issues by “hierarchical omission of redundant computations”. Every HOPE worker performs the entire divide-and-conquer computation with its own planned order, whereas it can omit subcomputations whose results are obtained from other workers at runtime, achieving fault tolerance and parallel efficiency as a team of workers. In most random number generation algorithms, a random number is generated on the basis of the internal state after the previous random number generation. Therefore, simple reordering does not preserve coherent results/conditions among workers based on the properties of utilized random numbers. In order to always use the same sequence for each hierarchical subcomputation, this study explores coherent random number utilization schemes, using Sobol' sequences or the PCG random number generator, which allow generation starting from the latter part by skipping the first part. In addition, the Monte Carlo method is an important application of random numbers. In this study, we examine a HOPE application that computes highly dimensional numerical integrals for pricing securities known as MBS (mortgage-backed securities) using the Monte Carlo method, where the convergence speed of integration errors is independent of dimensionalityjournal articl

Volunteer Support Network for Elderly Foreigners : A New Movement of Korean Residents in Kyoto

departmental bulletin pape

Observation of B+ → χc0K+

journal articl

Dead time compensation for three-level flying capacitor inverter with phase shift PWM

Multilevel inverter can obtain low distortion output voltage and current wave. However, dead time causes an output voltage error in the phase of inverter. Dead time error causes nonlinearity of output voltage and phase currents ripples with 5th and 7th order ripples of fundamental frequency. Current ripple decreases motor control performance. This paper presents dead time compensation for three-level flying capacitor inverter which is operated by phase shift pulse width modulation. This method is focused on the fact that power switching devices, which cause voltage error by dead time, depend on current polarities. The algorithm is simple, and the dead time is inserted at the instant of turning-on and turning-off of switching devices so as not to affect output voltage. The simulation result shows that high order harmonics which caused by dead time effect are eliminated using this method.journal articl

Temporal average of the spiral occupancy (disregarding handedness) for a pair of 3×3 pacemaker clusters (red +) in varying distances.

<p>Averages are over 500 minutes and 400 runs for each configuration. The cell positions on the developmental path were randomized in each run, except for the manually placed pacemaker clusters. The pattern revealed in these pictures cannot be extrapolated from single-run information as in <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1000422#pcbi-1000422-g004" target="_blank">Figures 4</a> and <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1000422#pcbi-1000422-g005" target="_blank">5</a> (although the latter hints at it); it fully emerges only after an ensemble average is considered.</p

Detected target wave events (red +) over density plot of ‘pacemaker’ cells that are in the oscillatory regime when signaling begins at .

<p>The tree-like structure of fracturing target wave emitters is clearly visible. The shown density of pacemaker cells is a Gaussian smoothing (width 2.0 grid points) of the binary distribution, color runs from white (0.0) to black (1.0).</p

Regulation of Spatiotemporal Patterns by Biological Variability: General Principles and Applications to <i>Dictyostelium discoideum</i>

<div><p>Spatiotemporal patterns often emerge from local interactions in a self-organizing fashion. In biology, the resulting patterns are also subject to the influence of the systematic differences between the system’s constituents (biological variability). This regulation of spatiotemporal patterns by biological variability is the topic of our review. We discuss several examples of correlations between cell properties and the self-organized spatiotemporal patterns, together with their relevance for biology. Our guiding, illustrative example will be spiral waves of cAMP in a colony of <i>Dictyostelium discoideum</i> cells. Analogous processes take place in diverse situations (such as cardiac tissue, where spiral waves occur in potentially fatal ventricular fibrillation) so a deeper understanding of this additional layer of self-organized pattern formation would be beneficial to a wide range of applications. One of the most striking differences between pattern-forming systems in physics or chemistry and those in biology is the potential importance of variability. In the former, system components are essentially identical with random fluctuations determining the details of the self-organization process and the resulting patterns. In biology, due to variability, the properties of potentially very few cells can have a driving influence on the resulting asymptotic collective state of the colony. Variability is one means of implementing a few-element control on the collective mode. Regulatory architectures, parameters of signaling cascades, and properties of structure formation processes can be "reverse-engineered" from observed spatiotemporal patterns, as different types of regulation and forms of interactions between the constituents can lead to markedly different correlations. The power of this biology-inspired view of pattern formation lies in building a bridge between two scales: the patterns as a collective state of a very large number of cells on the one hand, and the internal parameters of the single cells on the other.</p></div

Space-time plot of the chain of events shown in Figure 3.

<p>This 3D representation reduces spiral waves tips and target wave origins to points, allowing one to see the whole temporal evolution at a glance. As before, target wave events are shown as red +, spirals as green (light gray)×(right handed) and blue (dark gray) * (left handed). Note that this picture represents only a single (but representative) realization of the system dynamics.</p