Ripple

About: Ripple is a research topic. Over the lifetime, 14761 publications have been published within this topic receiving 159908 citations.

Design and control of an LCL-filter-based three-phase active rectifier

Abstract: This paper proposes a step-by-step procedure for designing the LCL filter of a front-end three-phase active rectifier. The primary goal is to reduce the switching frequency ripple at a reasonable cost, while at the same time achieving a high-performance front-end rectifier (as characterized by a rapid dynamic response and good stability margin). An example LCL filter design is reported and a filter has been built and tested using the values obtained from this design. The experimental results demonstrate the performance of the design procedure both for the LCL filter and for the rectifier controller. The system is stable and the grid current harmonic content is low both in the lowand high-frequency ranges. Moreover, the good agreement that was obtained between simulation and experimental results validates the proposed approach. Hence, the design procedure and the simulation model provide a powerful tool to design an LCL-filter-based active rectifier while avoiding trial-and-error procedures that can result in having to build several filter prototypes.

Controlled ripple texturing of suspended graphene and ultrathin graphite membranes

Abstract: Graphene is nature's thinnest elastic material and displays exceptional mechanical and electronic properties Ripples are an intrinsic feature of graphene sheets and are expected to strongly influence electronic properties by inducing effective magnetic fields and changing local potentials The ability to control ripple structure in graphene could allow device design based on local strain and selective bandgap engineering Here, we report the first direct observation and controlled creation of one- and two-dimensional periodic ripples in suspended graphene sheets, using both spontaneously and thermally generated strains We are able to control ripple orientation, wavelength and amplitude by controlling boundary conditions and making use of graphene's negative thermal expansion coefficient (TEC), which we measure to be much larger than that of graphite These results elucidate the ripple formation process, which can be understood in terms of classical thin-film elasticity theory This should lead to an improved understanding of suspended graphene devices, a controlled engineering of thermal stress in large-scale graphene electronics, and a systematic investigation of the effect of ripples on the electronic properties of graphene

Theory of ripple topography induced by ion bombardment

Abstract: When an amorphous solid is etched by an off‐normal incidence ion beam, a ripple topography often results. A theory explaining the origin of these waves is presented. For incidence angles close to the normal, we find that the ripple wave vector is parallel to the surface component of the beam direction, provided that longitudinal straggling of the beam is not too large. The ripple orientation is rotated by 90° when the beam is close to grazing incidence. The wavelength given by the theory varies as λ∼( f T)−1/2 exp(−ΔE/2kBT) for high temperatures T and low fluxes f, where ΔE is the activation energy for surface self‐diffusion. The predicted magnitude of the wavelength is in reasonable accord with experiments in this regime.

A filter family designed for use in quadrature mirror filter banks

Abstract: This paper discusses a family of filters that have been designed for Quadrature Mirror Filter (QMF) Banks. These filters provide a significant improvement over conventional optimal equiripple and window designs when used in QMF banks. The performance criterion for these filters differ from those usually used for filter design in a way which makes the usual filter design techniques difficult to apply. Two filters are actually designed simultaneously, with constraints on the stop band rejection, transition band width, and pass and transition band performance of the QMF filter structure made from those filters. Unlike most filter design problems, the behavior of the transition band is constrained, which places unusual requirements on the design algorithm. The requirement that the overall passband behavior of the QMF bank be constrained (which is a function of the passband and stop band behavior of the filter) also places very unusual requirements on the filter design. The filters were designed using a Hooke and Jeaves optimization routine with a Hanning window prototype. Theoretical results suggest that exactly flat frequency designs cannot be created for filter lengths greater than 2, however, using the discussed procedure, one can obtain QMF banks with as little as ±.0015dB ripple in their frequency response. Due to the nature of QMF filter applications, a small set of filters can be derived which will fit most applications.

Constant boost control of the Z-source inverter to minimize current ripple and voltage stress

Abstract: This paper proposes two constant boost-control methods for the Z-source inverter, which can obtain maximum voltage gain at any given modulation index without producing any low-frequency ripple that is related to the output frequency and minimize the voltage stress at the same time. Thus, the Z-network requirement will be independent of the output frequency and determined only by the switching frequency. The relationship of voltage gain to modulation index is analyzed in detail and verified by simulation and experiments.