Ripple Amplitude Research Articles

New AC–AC Modular Multilevel Converter Solution for Medium-Voltage Machine-Drive Applications: Modular Multilevel Series Converter

Due to its scalability, reliability, high power quality and flexibility, the modular multilevel converter is the standard solution for high-power high-voltage applications in which an AC–DC–AC connection is required such as high-voltage direct-current transmission systems. However, this converter presents some undesired features from both structural and operational perspectives. For example, it presents a high number of components, which results in high costs, size, weight and conduction losses. Moreover, the modular multilevel converter presents problems dealing with DC-side faults, with unbalanced grid conditions, and many internal control loops are required for its proper operation. In variable-frequency operation, the modular multilevel converter presents some serious limitations. The most critical are the high-voltage ripples, in the submodule capacitors, at low frequencies. Thus, many different AC–AC converter solutions, with modular multilevel structure, have been proposed as alternatives for high-power machine-drive applications such as offshore wind turbines, pumped-hydro-storage systems and industrial motor drives. These converters present their own drawbacks mostly related to control complexity, operational limitations, size and weight. This paper introduces an entirely new medium-voltage AC–AC modular multilevel converter solution with many operational and structural advantages in comparison to the modular multilevel converter and other alternative topologies. The proposed converter presents high performance at low frequencies, regarding the amplitude of the voltage ripples in the submodule capacitors, which could make it very suitable for machine-drive applications. In this paper, an analytical description of the voltage ripples in the submodule capacitors is proposed, which proves the high performance of the converter under low-frequency operation. Moreover, the proposed converter presents high performance under unbalanced grid conditions. This important feature is demonstrated through simulation results. The converter solution introduced in this paper has a simple structure, with decoupled phases, which leads to the absence of undesired circulating currents and to a straightforward control, with very few internal control loops for its proper operation, and with simple modulation. Since the converter phases are decoupled, no arm inductors are required, which contributes to the weight and size reduction of the topology. In this paper, a detailed comparison analysis with the modular multilevel converter is presented based on number of components, conduction and switching losses. This analysis concludes that the proposed converter solution presents a reduction in costs and an expressive reduction in size and weight, in comparison to the modular multilevel converter. Thus, it should be a promising solution for high-power machine-drive applications that require compactness and lightness such as offshore wind turbines. In this paper, simulation results are presented explaining the behavior of the proposed converter, proving that it is capable of synthesizing a high-power-quality load voltage, with variable frequency, while exchanging power with the grid. Thus, this topology could be used to control the machine speed in a machine-drive application. Finally, experimental results are provided to validate the topology.

Theoretical study for adsorption and migration behavior of atoms/ions on sinusoidal corrugated graphene surface

The adsorption and migration behaviors of atoms/ions on the surface of infinite single-layer graphene are studied with the influence of surface corrugation taken into consideration. Based on Lennard-Jones (L-J) potential and Fourier expansion, the analytical expressions of the interaction potential and force between a single atom/ion and sinusoidal corrugated graphene are derived. The effects of lattice period, chirality, wavelength and amplitude of surface sinusoidal ripples on the mechanical behaviors of atom/ion adsorption and migration on graphene surface are analyzed. The interaction potential and force between the adsorbed atom/ion and graphene are found to be periodic when the lattice period of graphene and the wavelength of surface sinusoidal ripples meet a certain coupling relationship. Moreover, the periods of interaction potential and force, equilibrium position and diffusion barrier of the adsorbed atom/ion on the graphene surface can be regulated by changing the wavelength and amplitude of the sinusoidal ripples. Taking lithium-ion (Li1+) as an example, by changing the wavelength of the sinusoidal ripples, the equilibrium sites of a lithium-ion on the surface of graphene can be readjusted, and the magnitude and amount of the energy barriers that it gets over can be regulated when the lithium-ion moves along the surface of graphene. What is more, the amplitude of the sinusoidal ripples can significantly influence the tangential force exerted by the graphene on the moving lithium-ion. Finally, it is found that the migration of an adsorbed atom/ion on the surface of sinusoidal corrugated graphene is also dependent on the chirality of graphene. The magnitude and period of the energy barrier and tangential force are both different when a lithium-ion migrates on the graphene surface in its different chiral directions. This research may be helpful to lithium-ion batteries, monoatomic device design, and atoms/ions screening.

Gravity wave interaction with a submerged wavy porous plate

ABSTRACT A numerical model based on multi-domain boundary element method (BEM) is developed to study the gravity wave interaction with a horizontally submerged wavy porous plate. The boundary condition on the porous barrier is considered a quadratic pressure drop to incorporate the effect of wave height on the wave energy dissipation directly. The performance characteristics of the wavy porous plate are studied by analysing the hydrodynamic coefficients of the breakwater for different physical parameters. Numerical results demonstrate that wavy porous plate improves the energy dissipation and reduce wave transmission compared against the conventional flat plate. The increase in wave energy dissipation is governed by the ripple amplitude and the number of ripples. The proposed model is expected to act as an effective wave barrier in the attenuation of wave energy for the creation of a tranquillity zone in the marine environment for water depths ranging from intermediate to deep waters.

Analysis and Comparison of DC-DC Boost Converter and Interleaved DC-DC Boost Converter

The step-up converters are widespread use in many applications, including powered vehicles, photovoltaic systems, continuous power supplies, and fuel cell systems. The reliability, quality, maintainability, and reduction in size are the important requirements in the energy conversion process. Interleaving method is one of advisable solution for heavy-performance applications, its harmonious in circuit design by paralleling two or more identical converters. This paper investigates the comparison performance of a two-phase interleaved boost converter with the traditional boost converter. The investigation of validation performance was introduced through steady-state analysis and operation. The operation modes and mathematical analysis are presented. The interleaved boost converter improves low-voltage stress across the switches, low-input current ripple also improving the efficiency compared with a traditional boost converter. To validate the performance in terms of input and output ripple and values, the two converters were tested using MATLAB/SIMULINK. The results supported the mathematical analysis. The cancelation of ripple in input and output voltage is significantly detected. The ripple amplitude is reducing in IBC comparing with a traditional boost converter, and the ripple frequency is doubled. This tends to reduce output filter losses, and size.

Optimization of the interference parameters of an Orbit motor using genetic algorithm

In the present study, the leakage of fluid due to gap generation at the contact points is eliminated by introducing interference between the rotor and the stator of an Orbit motor. Interference is incorporated in the system by modifying the roller radius, the chordal thickness, and the pitch circle radius. In an Orbit motor of interference-fit type, the contact points and the rotor center deviate from their original positions as found in an Orbit motor of perfect-fit type. A corrective technique based on minimization of the potential energy of the system is used to obtain the rotor center of an interference-fit motor. The rotor profile is initially generated around the geometrically obtained center of a perfect-fit motor. It is then shifted in the direction of decreasing potential energy, until the rotor center corresponding to minimum energy is attained. The main drawback of introducing interference is the generation of an unbalanced torque which affects the output torque of the motor. Thus, optimization of interference parameters using genetic algorithm is carried out to determine a system for which no gap is generated at the contacts and simultaneously it is ensured that the unbalanced torque ripple amplitude is minimum.

SURFACE WAVE SCATTERING BY AN ELASTIC PLATE SUBMERGED IN WATER WITH UNEVEN BOTTOM

Wave interaction with a vertical elastic plate in presence of undulating bottom topography is considered, assuming linear theory and utilizing simple perturbation analysis. First order correction to the velocity potential corresponding to the problem of scattering by a vertical elastic plate submerged in a fluid with a uniform bottom is obtained by invoking the Green’s integral theorem in a suitable manner. With sinusoidal undulation at the bottom, the first-order transmission coefficient (T1) vanishes identically. Behaviour of the first order reflection coefficient (R1) depending on the plate length, ripple number, ripple amplitude and flexural rigidity of the plate is depicted graphically. Also, the resonant nature of the first order reflection is observed at a particular value of the ratio of surface wavelength to that of the bottom undulations. The net reflection coefficient due to the joint effect of the plate and the bottom undulation is also presented for different flexural rigidity of the plate. When the rigidity parameter is made sufficiently large, the results for R1 reduce to the known results for a surface piercing rigid plate in water with bottom undulation.

Differential propagation of ripples along the proximodistal and septotemporal axes of dorsal CA1 of rats.

The functional connectivity of the hippocampus with its primary cortical input, the entorhinal cortex, is organized topographically. In area CA1 of the hippocampus, this leads to different functional gradients along the proximodistal and septotemporal axes of spatial/sensory responsivity and spatial resolution respectively. CA1 ripples, a network phenomenon, allow us to test whether the hippocampal neural network shows corresponding gradients in functional connectivity along the two axes. We studied the occurrence and propagation of ripples across the entire proximodistal axis along with a comparable spatial range of the septotemporal axis of dorsal CA1. We observed that ripples could occur at any location, and their amplitudes were independent of the tetrode location along the proximodistal and septotemporal axes. When a ripple was detected on a particular tetrode ("reference tetrode"), however, the probability of cooccurrence of ripples and ripple amplitude observed on the other tetrodes decreased as a function of distance from the reference tetrode. This reduction was greater along the proximodistal axis than the septotemporal axis. Furthermore, we found that ripples propagate primarily along the proximodistal axis. Thus, over a spatial scale of ∼1.5 mm, the network is anisotropic along the two axes, complementing the topographically organized cortico-hippocampal connections.

Discontinuous Space Vector PWM Strategy for Three-Phase Three-Level Electric Vehicle Traction Inverter Fed Two-Phase Load

Discontinuous pulse width modulation (DPWM) strategies are usually adopted to reduce the switching loss and output current ripple of three-phase three-level traction inverters under three-phase load conditions. However, if there is a short circuit in any arbitrary phase or the inverter is used to feed a two-phase load, the output performance of conventional DPWM strategies will be deteriorated. Here, four improved DPWM (IDPWM) strategies for three-phase three-level neutral-point-clamped (NPC) traction inverter fed two-phase load are proposed. Unlike three-phase load conditions, the phase angle and the amplitude of each basic voltage vector in the space vector diagram are modified under two-phase load conditions. Consequently, sectors are re-divided and duty cycles of basic vectors during synthesis are recalculated. Clamping intervals of each phase for the four type discontinuous PWM (DPWM) strategies are rearranged according to the modified space vector diagram; then, the proposed DPWM strategies can be obtained. Compared with the conventional DPWM strategies, the output current waveform quality of the proposed strategy is significantly improved. Meanwhile, the amplitude of the neutral-point voltage ripple is also reduced.

High-voltage and high-current crowbar system based on pseudospark switches: from system design to verification

This paper presents a high-voltage and high-current crowbar system using pseudospark switches to produce a fast front edge and prolonged pulse current with low ripple amplitude. The crowbar system mainly consists of a main switch, a crowbar switch, an energy storage capacitor, and an inductive load. The basic parameters of the pseudospark switch crowbar system: the storage capacitance is 5 μF, the typical operation voltage is 30 kV, the peak discharge current is about 46.2 kA, the rise time is 4.3 μs, and the pulse duration time is approximately 109 μs, which is nearly 25 times of the rise time. In this paper, we report the timing setting for crowbar system. Experimental results show that crowbar timing should be set slightly after first current maximum, which has a great advantage of increasing the time scale without any reduction in the loss-free peak current. In addition, the pulse current characteristics are also studied. In the research, crowbar inductance Lc and crowbar resistance Rc have significant effects on the ripple amplitude and load current amplitude of pulse current. The experimental results also show that the crowbar current Ic can reach nearly twice of the coil load current Iload with low crowbar inductance Lc. The over-current capacity of the crowbar switch needs to be greater than that of the main switch. The experimental results in this paper can be used to optimize the inductive load current in high-voltage and high-current crowbar system.

Avanepneumatic motor modification to reduce torque ripples

AnnotationThe problem of determining and possible ways to reduce the amplitude of torque ripples in a vane pneumatic motor without a significant reduction of its energy efficiency is considered. This problem is important for improving the ergonomic performance of manual mechanized pneumatic tools and improving the accuracy of pneumatic servosystems. The results are presented for the traditional layout scheme of a vane pneumatic motor, as well as for the proposed modified design. The decision was made using a detailed mathematical model of a pneumatic motor. The prospects of the modified pneumatic motor to reduce the torque ripples at higher energy efficiency indicators are shown, compared with the original model with an increased number of vanes.

Terahertz generation by beating of two chirped pulse lasers in spatially periodic density plasma

The present paper reports on the combined influence of the chirp characteristics of pump pulses and spatially periodic density (density ripple) plasma, on terahertz (THz) radiation generation, by beating of two chirped pulses. The beating lasers exert a nonlinear ponderomotive force along the z-direction. A self-consistent field is generated due to the nonlinear oscillations of plasma electrons; as a result of these linear and nonlinear forces the plasma electrons attain an oscillatory velocity that couples with the density ripple to generate a stronger transient transverse current, driving THz radiation. The importance of chirp parameter, amplitude and periodicity of density structure are discussed for emitted THz radiation. Our numerical simulations disclose that the variation of the chirp frequency parameter and ripple amplitude have considerable roles in improving the nonlinear oscillating current. By optimizing the chirp parameter and amplitude of the density ripple, a notable change in the magnitude of the terahertz field amplitude is found. The present paper maybe useful for broadband THz pulses, for use in plasma diagnostics and time-domain spectroscopy.

High Voltage Gain Three Coupled Winding DC-DC Interleaved Boost Converter with Arduino Microcontroller for the PV Panel Control

In many applications, high-step converters are widely used, including powered vehicles, Photovoltaic (PV) systems, continuous power supplies, Gas lighting and fuel cell systems. The most important requirements in the energy conversion process are reliability, quality, maintenance and size reduction. This paper presents an Interleaved Boost Converter (IBC) to raise voltage gain with three coupled winding. This converter consists of three pairs of coupled inductors to collect energy in parallel and release energy to the series load, which provides a much higher output load voltage than the traditional DC-DC boost converter. To validate the performance, an investigation was introduced by means of steady state analysis and operation. The operation modes and mathematical analysis are presented. Arduino UNO microcontroller was used to implement Pulse Width Modulation (PWM) gate drive based on Maximum Power Point Tracking (MPPT). The DC-DC IBC with High Voltage Gain (HVG) produces low voltage stress across switches, low input and output current ripple, and also improves the efficiency. These features made this converter suitable for applications where a high voltage gain is demanded. This converter was tested using Matlab/Simulink to validate the performance in terms of input and output ripples. The results supported the mathematical analysis. The cancelation of the ripple in input and output voltages has significantly detected. The ripple amplitude is reducing in DC-DC HVG IBC comparing with traditional DC-DC boost converter, and the ripple frequency is doubled. This tends to reduce the output filter losses, and size. Also improves the efficiency of the converter.

Minimum Loss Operation and Optimal Design of High-Frequency Inductors for Defined Core and Litz Wire

This paper studies the loss-optimal design of a power inductor employed in a 2 kW, 400 V input DC–DC converter. The design of an inductor is subject to a large number of design parameters and the implications of the different design parameters on the losses are often not clearly traceable in a full optimization, e.g., different current ripple amplitudes can lead to designs with similar losses, as larger ripple amplitudes lead to increased AC core and winding losses but lower DC losses in the winding due to lower inductance values and/or numbers of turns. In an effort to achieve a comprehensible description of the implications of the key design parameters (switching frequency, $f_\text{s} $ , current ripple, r , number of turns, N ) on the losses, the remaining parameters, e.g., core (E55/28/21 N87) and type of conductor (litz wire), are considered to be given. In a first step, the investigation is based on a simplified analytical model, which is refined in a step-by-step manner, e.g., to consider core saturation. In a second step, the implications of further critical aspects on the losses, e.g., temperatures of core and coil, are examined using a comprehensive semi-numerical model. Surprisingly, the evaluation of the losses calculated in the $f_\text{s}$ – $r$ domain reveals that nearly minimum inductor losses are obtained for a current ripple that is inversely proportional to the frequency, i.e., for a constant inductance, within a wide frequency range, from 200 kHz to 1 MHz. Furthermore, the investigation reveals a decrease of the losses for increasing frequencies up to 375 kHz, e.g., from 4.32 W at 80 kHz ( r = 110 %) to 2.37 W at 375 kHz ( r = 18 %). The detailed analysis related to these results enables the compilation of a simple two-equation guide for the design of an inductor that achieves close to minimum losses. In a next step, interesting trade-offs are identified based on a study of the design space diversity, e.g., with respect to low cost and increased partial-load efficiency. The findings of this work are experimentally verified, i.e., the losses of three different inductors are measured with an accurate calorimetric method and at four different frequencies, ranging from 150 kHz to 700 kHz.

Analysis and Control of Current Ripples of Z-Source Inverters

Load current ripple is an important issue in the design and control of inverters since it influences the torque ripple and noise amplitude of a motor drive. The current ripple of Z-source inverter (ZSI) is analyzed in this paper. The expression of current ripple is derived and the current ripples of ZSI and voltage-source inverter (VSI) are compared. A variable DC-link voltage and switching frequency method was adopted to reduce conduction and switching losses without increasing the predicted peak current ripple. These theoretical findings were further verified by simulations and experiments.

Analysis of 6-Pulse and 12-Pulse in Conversion of the 115VAC/400Hz to 270 VDC for Application on Fighter

The development of aircraft secondary power technology is moving from mechanical power, pneumatic power and hydraulic power to electric power. The trend toward electric power is known as More Electric Aircraft (MEA). Modern military aircraft are designed using 270VDC for electric power system. Today, some military aircraft still use 115VAC/400Hz for their electrical power system. If this type of aircraft need provides 270VDC electrical power, then they require Multi-Pulse Transformer Rectifier Unit (TRU). The development of this type TRU has not been aimed to comply with aircraft military standards. This research investigates the variation of the number of pulses (p) and firing angle (α) to the amplitude ripple voltage, output voltage, and distortion factor in order to comply with the MIL-STD-704F standards. The multi-pulse transformer rectifier unit being analyzed consists of 6-Pulse and 12-Pulse. The research shows that the amplitude ripple voltage and distortion factor of the 6-Pulse TRU do not comply MIL-STD-704F. The amplitude ripple voltage and distortion factor of 12-Pulse comply MIL-STD-704F with firing angle (α) ≤4°.Keywords: Transformer Rectifier Unit, thyristor, ripple voltage, distortion factor, firing angle

Characterization and Modeling of Soft Magnetic Materials for Improved Estimation of PWM-Induced Iron Loss

This article investigates the iron loss properties of soft magnetic materials under conditions of high excitation frequency and varying premagnetized dc-bias fields (i.e., different magnetization states). Using measured iron loss data collected from the customized test equipment, a modified dynamic Jiles–Atherton model has been developed specifically for the purpose of achieving improved pulsewidth modulation (PWM)-induced iron loss estimation. The accuracy and scalability of the proposed prediction model for different conditions are evaluated including the flux ripple amplitude, excitation frequency, dc-bias field, and symmetry of the triangular waveform. Experimental results have confirmed that the proposed model can accurately predict the dynamic hysteresis loop and corresponding iron loss over a wide range of operating conditions. By introducing a companion iron loss model developed for fundamental and low-order harmonic fields, the total iron loss under inverter PWM voltage excitation is explored. The results show that model parameters derived from a limited number of tests can be used to predict the iron loss in a much broader operating range, which makes it a promising tool for PWM-induced iron loss estimation in new machine designs intended for demanding operating conditions.

A design of readout IC with capacitively-coupled chopper current-feedback instrumentation amplifier in a 0.18 μm CMOS process

This paper describes a readout IC (ROIC), which consists of a capacitively coupled instrumentation amplifier (CCIA) and a discrete-time delta–sigma modulator. An active high-pass filter is embedded in the ripple reduction loop to suppress the noise ripple amplitude due to chop modulation. To accommodate the input with large electrode offset, dc-servo loop (DSL) and a 6 bit capacitive DAC are employed to suppress large electrode offset, while a positive feedback loop to boost its input impedance. The complete CCIA is implemented in a standard 0.18 μm 1P6M CMOS process. It occupies an area of 0.56 mm2 (including DSL) and consumes 52 μA current from a 3.3 V supply voltage. Measurement results indicate that the input reference noise PSD is 53.8 nV√Hz.

Hydrogen on graphene with low amplitude ripples: First-principles calculations

Graphene and graphene-based materials are valuable to be used as hydrogen storage because of chemical inertness and high strength. Therefore a thorough study of hydrogen adsorption on graphene is of great interest. Although such studies have already been made for flat structures, rippled graphene was not properly addressed. In the present work, first-principles calculations of absorption of hydrogen atom on graphene with small amplitude zig-zag ripples were conducted. It was found that varying the ripple amplitude the binding energy for hydrogen atom attached inside the ripple can be lowered by about 25%, while for the hydrogen atom attached from outside the ripple the binding energy can be increased by 80%, compare to the adsorption on flat graphene.

Circuit Topology Analysis for LED Lighting and its Formulation Development

Light emitted diode (LED) is becoming more popular in the illumination field, and the design of LED lighting is generally made to provide illumination at lower power usage, helping save energy. A power electronic converter is needed to provide the power conversion for these LEDs to meet high efficiency, reduce components, and have low voltage ripple magnitude. The power supply for LED is revisited in this paper. The LEDs connected in series with diode, transistor, or inductor paths are examined. The formulation for each of the cases is described, including the classical converters of buck, boost, buck–boost, and Ćuk. The circuit reductions of the classic circuit, circuit without the capacitor, and without a freewheeling diode are studied. Using LED to replace freewheeling diodes is proposed for circuit component reduction. General equations for different connection paths have been developed. The efficiency and output ripple amplitude of the proposed power converters are investigated. Analytical study shows that the efficiency of proposed circuits can be high and voltage ripple magnitude of proposed circuits can be low. The results show that the proposed circuit topologies can be easily adapted to design LED lighting, which can meet the criteria of high efficiency, minimum components, and low-voltage ripple magnitude at the same time.

Input Current and Voltage Ripple Analysis in LDN Cells for H-Bridge Multilevel Inverters

This paper deals with the analysis of the input dc-link voltage ripple in multilevel inverter based on H-bridge and level doubling network (LDN). The LDN is basically a half-bridge fed by a floating capacitor, with voltage self-balancing capability, recalling the concept of a flying capacitor configuration. The amplitude of the LDN voltage ripple is analytically determined considering both the low-order and the switching harmonic components. In particular, peak-to-peak distributions of voltage ripples over the fundamental period are analytically determined, making possible the design of dc-link capacitor relying only on the dc-voltage ripple requirements. The case study makes reference to negligible switching ripple in the output current. It well represents either grid connection or passive load having almost sinusoidal currents. Numerical simulations carried out by MATLAB/Simulink and a complete set of experimental verifications are given to confirm the theoretical developments.