Large Ripple Research Articles

Development of a new fault-tolerant induction motor control strategy using an enhanced equivalent circuit model

Variable speed induction motor drives operating with an open circuit phase fault generally have a high harmonic current content and impose a large torque ripple on the load. These effects result from the unbalanced nature of the faulted machine, and under these conditions, the effects of machine and converter non-linearities become more pronounced. It is important to include these non-linearities when modelling drive systems which may operate under fault conditions, and developing fault ride-through control algorithms. This paper proposes a modelling method for induction motor drives which includes machine saturation and space harmonics effects as well as inverter non-linearities, which does not require significant computation times. Results from an experimental test rig are presented to validate the model. The second part of the paper describes how the model was used to develop a new fault ride through control strategy for a voltage-fed vector controlled drive. Experimental results demonstrate the improved drive behaviour with an open-circuit winding fault when controlled with the new strategy.

The Improvement of DTC System Performance on Fuzzy Control

Abstract The large torque ripples exist in induction motors based on conventional direct torque control (DTC) system, especially at a low speed. For the problem of DTC, fuzzy control theory is applied to DTC system. Based on fuzzy control of induction motor direct torque control system model is constructed in this paper. Fuzzy controller in the system selects the voltage space vector. The control system is simulated on the platform of Matlab/simulink. The results of the simulation prove that the method of the fuzzy DTC controller can effectively improve the low-speed performance of the induction motor, reduce the torque ripple, and have a good dynamic response performance.

SPEED SENSORLESS CONTROL OF AN IPMSM DRIVE BASED ON ACTIVE FLUX CONCEPT

This paper investigates a novel direct torque control (DTC) for asensorless interior permanent magnet synchronous motor (PMSM) basedon a sliding mode technique (SMC). The speed and position of theinterior PMSM are estimated online based on active flux concept. Toovercome the large ripple content associated with the direct torque, atorque/flux sliding mode controller has been employed. Two integralsurface functions are used to construct the sliding mode controller(SMC). The command voltage is estimated from the torque and fluxerrors based on the two switching functions. The idea of total slidingmode is used to eliminate the problem of reaching phase stability. Thespace vector modulation (SVM) is combined with the sliding modecontroller to ensure minimum torque and flux ripples and provides highresolution voltage control. The proposed scheme has the advantages ofsimple implementation, and does not require an external signal injection.In addition, it combines the merits of the direct torque control, slidingmode controller, and space vector modulation beside the sensorlesscontrol.Simulation works are carried out to demonstrate the ability of theproposed scheme at different operating conditions. The results confirmthe high performance of the proposed scheme at standstill, low and highspeeds including load disturbances and parameters variation.

An Exploratory Study on Smart Campus Model

Smart Learning has been spreaded rapidly to the education and industry fields. Especially, Smart Learning of the university and Smart Campus are the focus of attention of the knowledge based age, because university education play a core role for lifetime education and has largest ripple effect. This article is exploring on the concept and realization conditions of 'Smart Campus'. We think, Smart Campus is an alternative solution for the continuous development of university education in the smart time. In this context, this paper will review the prior studies of Smart Learning, U-Learning and Smart Campus, and study the concept and realization conditions of 'Smart Campus'.

Forecasting PMLSM Direct Thrust Control Based on Neural Network by Considering Motors Dynamic Behavior and Speed Effects

The direct force thrust control (DTFC) is linear type of the direct torque control (DTC) method. The advantages of DTFC method are structure simplicity, low dependency to motor parameters and no requirement to coordination transformations. In this paper this method is modified in order to eliminate the defects that include the switching frequency and exciting large ripples of force and flux. In previous works, the structure simplicity of DTC, rare calculations to reduce the force ripples and fixing switching frequency are disaffirmed. With regards to keeping DTC advantages, a new method is presented in this paper to eliminate the defects by the aid of neural network. Also, the precise non-linear behavior of PMLSM motor in DTC has been considered by using space vector modulation. Finally, the simulation results concluded by the submitted intelligent DTC-SVM method are more satisfactory than other methods.

Periodic Nanostructure on 65Mn Produced by Femtosecond Laser Irradiation

The periodic microstructures on 65Mn plate were induced by the irradiation of the femtosecond laser with the laser wavelength of 800 nm and the pulse length of 130 fs. The parallel periodic ripples structures were observed at the laser fluence of 1 J/cm2 with different pulses number( N=5,50,400,800) which lied parallel to the laser electric polarization field vector. For 400 pulses, the nano-holes arrays were generated to interrupt the consistent ripples structures.For 800 pulses, initial nano-holes evolution to the grooves, which the direction were uncertainly. Further experiments have been made to induce large area consitent ripple structures by scanning, at the laser fluence of 1 J/cm2 with speed v=500μm/s. 2D arrays were induced by accurate processing control

A Dual-Mode Single-Inductor Dual-Output Switching Converter With Small Ripple

Single-inductor dual-output (SIDO) switching converters always suffer from large ripple and severe cross-regulation problem, when a large inductor current is switched between two outputs. This paper proposes a novel fly capacitor method for SIDO converters to reduce the output ripple and spike. An adaptive common-mode control is presented to suppress the cross-regulation problem. A duty-ratio-based current estimation method is proposed to detect the load current, and the converter can automatically switch between pulsewidth modulation and pulse-frequency modulation modes. The two outputs of the converter are specified for 1.2 V/400 mA and 1.8 V/200 mA with input voltage ranging from 2.7 to 5 V. The chip has been fabricated on a 0.25-? m CMOS mixed-signal process. The conversion efficiency is 82% at a total output power of 840 mW, while the output ripple is about 20 mV and spike is less than 40 mV. The maximum overshot voltage during load response is 50 mV.

Study of jet fluctuations in DC plasma torch using high speed camera

The power supplies used for the plasma torches are usually SCR controlled and have a large ripple factor. This is due to the fact that the currents in the torch are of the order of hundreds of amperes which prohibit effective filtering of the ripple. The voltage and current vary as per the ripple in the power supply and causes plasma jet to fluctuate. To record these fluctuations, the jet coming out from a D.C. plasma torch operating at atmospheric pressure was imaged using high speed camera at the rate of 3000 frame per second. Light emitted from a well defined zone in the plume was collected using an optical fibre and a Photo Multiplier Tube. Current, voltage and PMT signals were recorded simultaneously using a digital storage oscilloscope (DSO). The fast camera recorded the images for 25 ms and the starting pulse from the camera was used to trigger the DSO for recording voltage, current and optical signals. Each image of the plume recorded by the fast camera was correlated with the magnitude of the instantaneous voltage, current and optical signal. It was observed that the luminosity and length of the plume varies as per the product of instantaneous voltage and current i.e. electrical power fed to plasma torch. The experimental runs were taken with different gas flow rates and electrical powers. The images were analyzed using image processing software and constant intensity contours of images were determined. Further analysis of the images can provide a great deal of information about dynamics of the jet.

Origin of Parasitic Time-Periodic Torques and Forces in Electrical Machines

The origins of the time-periodic torques and forces acting on the rotor of an electrical machine are searched for. The main task of an electrical machine operated in a steady state is to produce a constant torque. In an ideal case, this would be the only magnetic force on the rotor. In practice, the electromagnetic torque usually has relatively large ripple and significant lateral forces may also occur. The examples discussed are from radial flux machines, especially, from cage induction motors. As the electromagnetic torque and forces can be calculated from the air-gap magnetic field, the air-gap flux density and its harmonics are under special examination. Understanding the magnetic interactions may provide means to actively control the air-gap flux density and eliminate the parasitic effects.

Multi-pulse train control technique for buck converter in discontinuous conduction mode

Multi-pulse train (MPT) control technique, a novel control technique for the control of switching DC-DC converters is proposed here. Unlike traditional pulse train (PT) control technique, which realises the output voltage regulation of switching DC-DC converters by a combination of two different control pulses, MPT control technique extends these two different pulses to multi-level pulses, and thus overcomes the drawback of relatively large output voltage ripple of PT control switching DC-DC converters. Buck converter operating in discontinuous conduction mode is taken as an example to illustrate the operation principle of MPT control technique. Comprehensive analysis on the control pulse combination within a MPT repetition cycle is performed and verified by simulation and experimental results. It also shows that MPT control buck converter has much lower output voltage ripple than PT control technique, and much better transient performance than traditional pulse-width modulation buck converter.

Design and Characterization of Differentially Enhanced Duty Ripple Control (DE-DRC) for Step-Down Converter

A new control method, differentially enhanced duty ripple control (DE-DRC), is proposed for step-down converters. The control method uses a differentially enhanced loop to amplify the output error with positive and negative differential difference amplifiers (DDAs), and a duty ripple loop to include the input voltage and the duty cycle information into the control scheme. The duty ripple loop generates a very large control ripple voltage, and the control ripple is compared with a negative control voltage to trigger an on-pulse generator to get the duty cycle. Because of the large duty ripple voltage with a big noise margin and the low pass filter effect of DDAs, the proposed DE-DRC can achieve good noise immunity. The easily configured positive and negative DDA gains can separately adjust the high and low frequency portion of the loop transfer function, and push the control bandwidth to high frequency to achieve fast transient response. Because of a unique first-order character of the inner duty ripple loop, this control can also completely eliminate the double pole peaking from the output impedance and achieve ideal closed loop output impedance in the control bandwidth, which is preferred for adaptive voltage position designs.

Bedform evolution around a submarine pipeline and its effects on wave-induced forces under regular waves

The paper presents an experimental investigation of seabed evolution behavior around a submarine pipeline and the hydrodynamic forces on the pipeline under regular waves. Unlike the previous flume tests that have largely used beds with median sands, this study focuses on fine sediments such as sandy silt and silt. The primary objective of the study was to investigate: (i) the scour process under different wave conditions and with different sediments and (ii) the influence of the bedform evolution on the hydrodynamic forces experienced by the pipeline. In terms of scour and ripple formation, four distinct regimes of the near-field bed evolution behavior are identified which are: (I) no scour, (II) scour without ripples, (III) scour with small ripples and (IV) scour with large ripples. The influence of bedform evolution on wave forces was found to vary significantly in different regimes. In regime I, the wave forces were quite stable; in regime II and III, the wave forces underwent a gradual reduction before reaching their equilibrium values at fairly early stages of the scour process; in regime IV, the wave forces were significantly affected by the migrating ripples and can be rather unsteady throughout the testing period.

자석 형상 최적화를 통한 축방향 이상 횡자속형 전동기의 토크 특성 향상에 관한 연구

Transverse flux machine(TFM) has been developed to drive a machine of large input power at low-speed. However, it has complicated structure and large torque ripple due to its inherent structure. In this paper the characteristics of torque of a rotatory two-phase TFM are analyzed by using the 3-dimensional finite element method and optimal design. This research shows that one of the effective design variables is the skew angle of permanent magnet. The skew angles of permanent magnet are optimized by using a genetic algorithm. It also shows that the proposed optimal skew magnet not only increases average torque but also decreases torque ripple of a rotatory two-phase TFM.

Magnetization Process of an HTS Motor and the Torque Ripple Suppression

This paper describes in detail the magnetization process of a synchronous motor, constructed with High Temperature Superconducting (HTS) elements on the rotor. The Pulse Field Magnetization (PFM) method is considered to magnetize the HTS rotor as a four-pole trapped flux magnet. A 2D model is built for the magnetization process. During the machine operation, intolerable torque ripples occur, which are mainly caused by the irregular field distribution from the magnetized HTS rotor. In order to suppress the large torque ripples, an iterative learning control method is used in addition to the traditional field-oriented control method.

Largest wind ripples on Earth?

Unique wind ripples attaining heights to 2.3 m, wavelengths to 43 m, and a crest maximum grain size of 19 mm occur on the Argentine Puna Plateau at ~4000 m altitude. These are the largest ripples reported on Earth, comparable only to Mars counterparts. They form in the presence of high proportions of low-density pumice clasts (0.91 g/cm 3 ), although crests are exclusively composed of varnished, normal-density clasts (2.43 g/cm 3 ). Mature ripple profiles are partly excavated on bedrock, so they form by a combination of deflation, winnowing of finer grains, minor wind drift of fine gravel, and lagging of clasts >4 cm. The large ripple size appears to be related to strong winds, dense saltation layers, and a long time for evolution. Ripple sizes are smaller on obstacles, as compared to flat terrain; there is a lack of correlation between clast size, wavelength, and the extreme ripple size (in spite of the thin atmosphere), all of which suggest that while small-scale gravel ripples may form according to a reptation model, their evolution into large-scale types may relate to aerodynamic instabilities originating at the saltation curtain–air interface.

Wave dunes とGiant ripplesの形成条件の違い ～粒径に依存する大型リップル形成の限界振動周期～

Wave dunes とGiant ripplesの形成条件の違い ～粒径に依存する大型リップル形成の限界振動周期～

Characterization of bedform morphology generated under combined flows and currents using wavelet analysis

The wavelet transform (WT) has been successfully implemented in many fields such as signal and image processing, communication theory, optics, numerical analysis, and fluid mechanics. However, the application of WT to describe bedform morphology in coastal areas, oceans, and rivers is rare. The present study demonstrates the capability of WT analysis to fully represent the space–frequency characteristics of signals describing bed topography generated in marine and river environments. In this study WT is used to examine the morphological characteristics of bedforms generated in two separate laboratory facilities: a wave tank and a meandering channel. In the wave tank a set of ripples superimposed upon large wave ripples were generated; while in the meandering channel, 2D and 3D migrating ripples and dunes were observed. The WT proved to be a useful tool in detecting the complex variability of the generated bedform structures. The size distribution of the bottom features such as ripples, large wave ripples and sandbars were first examined along a 2D bed profile. Later analysis studied the variability of features in the transverse direction by using the power Hovmöller. Experiments in the wave tank were conducted for a mobility number of ψ=(10, 28), and a Reynolds wave number of R ew =(17,500, 83,500) which correspond to waves alone (WA) and to combined flow (CF) scenarios, respectively. Experiments in the meandering channel were conducted under a morphological regime that produced mainly migrating sandbars.

Direct Torque Control of 5-phase 10/8 Switched Reluctance Motor by Using Fuzzy Method

A Switched Reluctance Motor (SRM) has several desirable features, including simple construction, high reliability and low cost. However, it suffers from large torque ripple and large noise. In addition, highly non-uniform torque output and magnetization characteristics lead to complication of the control system. Several studies have succeeded in torque ripple reduction for SRM using Direct Torque Control (DTC) technique. Compared to conventional methods including voltage control and current chopping mode control, DTC method has many advantages such as simple algorithm, less torque ripple and instantaneous response to the torque command. In this paper, DTC of a 5 phase 10/8 SR motor is proposed. Performance of the motor is studied through the computer simulation in Matlab/Simulink. The simulation results are compared to corresponding results of the same motor, controlled by hysteresis band method. The comparison results show that the proposed method results in a remarkable reduction in torque ripple for all levels of the motor torque without enforcing any drawbacks to the system performance, even in the transient conditions.

Design and Development of a Three-Stacked 12/8 Permanent-Magnet-Type Reluctance Generator

A permanent-magnet-type reluctance generator (PMRG) has a doubly salient pole structure. The permanent magnets are embedded in the stator yoke, and the concentrated windings are arranged individually around each stator pole. On the other hand, since the rotor has neither permanent magnets nor windings, the PMRG has a simple and robust structure, low cost, and high efficiency. Thus, it is suitable for wind-turbine generation and small-scale hydroelectric power generation. Although it has large torque ripple due to the salient pole structure, we have proposed a multi-stacked PMRG to reduce the torque ripple. This paper describes the design of a three-stacked 12/8 PMRG of 400 W by the finite element method (FEM). In addition, experimental results obtained with a trial generator are presented.

Aeolian Megaripples: Mathematical Model and Numerical Simulations

Aeolian sand ripples are a common feature on sandy deserts and beaches. Standard aeolian ripples have wavelengths of a few centimeters and amplitudes of a few millimeters. Sometimes, much larger ripples are observed. These are known by different names, such as ridges, granule ripples, gravel ripples, or megaripples. Aeolian megaripples are composed of a mixture of coarse and fine noncohesive material; a bimodal distribution of particle sizes is thought to be necessary for large, ripplelike bed forms to develop. Here, we discuss the extension of a recent model for the dynamics of aeolian megaripples. The model assumes that both the saltation and reptation fluxes are modulated by the emergent bed forms. We present a linear stability analysis of the full model as well as the results of numerical simulations. The modeled megaripples evolve through interactions between ripples of different sizes. The formation of megaripples is therefore another example of a self-organizing geomorphological system.