Large Ripple Research Articles

An Advanced Modulation Technique Featuring Neutral Point Voltage Ripple Suppression of Three-Level Converters in High-Speed Drives

This paper introduces an advanced space vector modulation technique for three-level neutral-point-clamped (3L-NPC) converters. The studied 3L-NPC converters within aircraft electric starter generator (ESG) systems normally operate at high modulation index, low pulse ratio and full power factor range for most of the operation time. Conventional modulation techniques exhibit large neutral point voltage ripple and possible voltage imbalance under such conditions. The increase of neutral point voltage ripple implies significant increase in converter capacitor size and decrease in capacitor reliability. The modulation technique introduced in this paper achieves improved neutral point voltage balancing within each switching period through enhanced applications of small vectors and restriction on medium vectors. The advanced implementation of small vectors is achieved using a sharing factor aided by a robust incremental current prediction procedure. With the predicted machine currents, the proposed method enables the optimum application of small vectors to balance the neutral point voltages. Simulation results based on a PLECS/Simulink model and experimental results obtained from a 45kVA, 32krpm aircraft electric starter generator prototype platform validate the reduction of the neutral point voltage ripple.

Modular multilevel converter with thyristor DC-link switch for full-torque variable-speed drives

The modular multilevel converter (MMC) is a promising topology for medium-voltage drive applications due to its high-quality output waveforms, low device switching frequency and voltage rating. However, the large cell capacitor voltage ripple is a severe challenge faced by MMC at low motor speeds. Recently, a hybrid MMC (HMMC) topology is proven to be a competitive solution because of its lower cell capacitor voltage ripple and no common-mode voltage (CMV) problem compared with other methods. However, the dc-link switch with IGBT limits HMMC to be applied for high-voltage applications. This paper uses the thyristor instead of IGBT as the dc-link switch. To ensure the thyristor can be softly turned on and safely turned off, a new control scheme is proposed. When using this proposed scheme, HMMC can also tolerate the failure of thyristor's turning-off without shutting down the system, improving the reliability effectively. The cell capacitor voltage ripple analysis is presented considering the effects of the thyristor switching process. In addition, a decoupled energy balancing control is utilized to suppress the fluctuation of dc current. Experimental results obtained from a 380 V/7.5 kW downscaled prototype validate the effectiveness of starting up a motor from the standby mode to rated speed with full-torque.

Capacitor Lifetime Extension in a Hybrid Active Neutral-Point-Clamped Inverter With Reduction of DC-Link Ripple Current and Common-Mode Voltage

This paper proposes a reduction method for DC-link ripple current and common-mode voltage (CMV) in a hybrid active neutral-point-clamped (ANPC) inverter. A Si and SiC hybrid ANPC inverter has been developed recently to overcome the extremely high cost of a full-SiC ANPC inverter. A hybrid ANPC requires much fewer SiC MOSFETs than a full-SiC ANPC inverter while providing a comparable power density. Voltage source inverters such as hybrid ANPC inverters utilize electrolytic capacitors, which have a large capacitance per volume, as a DC link. However, an electrolytic capacitor is one of the most vulnerable components in a power electronic converter due to its small allowable ripple current. A large ripple current flowing into the electrolytic capacitor generates a heat loss, which shortens the lifetime of the capacitor. Furthermore, the common-mode voltage (CMV) causes an undesirable leakage current and electromagnetic interference. The CMV depends on the pulse-width modulation of the voltage source inverters. The proposed method enhances the reliability of the hybrid ANPC inverter by reducing the DC-link ripple current and CMV simultaneously. The effectiveness and validity of the proposed method are verified through simulations and experimental results.

Interleaved Modulation Scheme With Optimized Phase Shifting for Double-Switch Buck-Boost Converter

Owing to low voltage stresses, wide range of input voltage and the same polarity of output voltage and input voltage, double-switch buck-boost converter (DSBBC) is a popular choice to achieve dc/dc conversion in photovoltaic generations (PV), power factor correction (PFC), portable devices and so on. Combined control (CC) makes DSBBC operate efficiently, but large ripples of output voltage are unavoidable during mode transition. With two equal duties, interleaved modulation (IM) makes the inductor ripple current decrease remarkably compared with synchronous modulation (SM) while inductor average current is still high. By introducing duty offset, inductor average current declines and efficiency is enhanced obviously under interleaved modulation with duty cycle offset (IMDO). However, with 180-degree phase-shifted angle, the ripple current is not low enough in some cases. Thus, to make further improvement on ripple current, an interleaved modulation scheme with optimized phase shifting (IMOPS) is proposed for DSBBC in this paper. Current features, optimal phase-shifted angle (OPSA) and operating region under IMOPS are described meticulously. Besides, theoretical and quantitative comparisons of different modulation schemes are presented, including inductor average current, inductor ripple current and ratio of direct power transfer (DPT). Based on a 150W prototype, the feasibility and effectiveness of IMOPS are demonstrated by experimental results.

Rapid gravity flow transformation revealed in a single climbing ripple

Abstract Sediment gravity flows demonstrate a wide range of rheological behaviors, and past work has shown how transformations between flow types generate spatiotemporal changes in the resultant sedimentary successions. We used the geometrical characteristics of a single climbing ripple to demonstrate how such flows can transform from a turbulent to a quasi-laminar plug flow, with the transitional clay flow sequence being manifested by abnormally large heterolithic sand-clay current ripples with small backflow ripples, and then abundant clay deposition associated with smaller ripples. Analysis of ripple size, angle of climb, grain size, internal erosional surfaces, and soft-sediment deformation suggests that transformation in the rheological character of the sediment gravity flow was rapid, occurring over a period of tens of minutes, and thus probably over a spatial scale of hundreds of meters to several kilometers. Our study indicates how the character of flow transformation can be elucidated from the details of a small-scale sedimentary structure.

Performance Evaluation of CKF Based Sensorless Vector Controlled PM Synchronous Motor Drive

Sensor-less vector control of Surface Mount Permanent Magnet Synchronous Motor (SPMSM) throughout the entire speed regime is a challenging problem in PMSM drive. This paper addresses this control problem and presents the design and simulation study of sensor-less vector control of SPMSM using Cubature Kalman filter (CKF) based rotor position and speed estimator. The use of CKF for speed and position estimation of PMSM is reported in recently literature. However, the results are not substantial. Position and speed estimation errors are quite large, also the estimated speed and position contain considerably large ripple. In the present work the performance of CKF observer in terms of position and speed estimation accuracy is significantly improved. The dynamic performance of the drive throughout the entire speed zone under variable load torque is also improved.

New adaptive hysteresis band width control for direct torque control of induction machine drives

This paper presents a new adaptive hysteresis band control approach used in direct torque control (DTC) of the induction motor (IM) drives with the switching tables for the generation of PWM signals. Constant Hysteresis Direct torque control (CHB-DTC) method used the torque and stator flux errors to generate the stator voltage reference and frequency vectors for controlling the three-phase induction motor. The CHB-DTC gives better torque transient performance but it has large steady state ripples. To reduce torque and stator current ripples in CHB-DTC controlled induction motor drives a new adaptive hysteresis band control (AHB) approach is proposed, where the hysteresis band is adapted in real time with the stator flux and torque errors variation, instead of fixed bandwidth. Both classical CHB-DTC method and the proposed adaptive hysteresis band DTC (AHB-DTC) fed three induction motor have been simulated using Matlab/Simulink. The simulation results at different operating conditions over a wide speed range demonstrate the validity, effectiveness, and feasibility of the proposed scheme. The measurements showed that torque ripples were significantly decrease with the new AHB-DTC technique and better speed response in step up or down compared to the CHB-DTC.

Artificial neural network-based current control of field oriented controlled induction motor drive

A hysteresis current controller (HCC) is commonly used in high-performance AC motor drives to control the current directly. Recently, the predictive current controller (PCC) is also used as an alternative to the classical current controller for speed and torque regulation of induction motor (IM) drives. However, PCC has drawbacks of large flux and torque ripples, large total harmonic distortions (THDs) in current and voltage and dependency on parameters. This paper proposes current control with artificial neural network (ANN) for a field-oriented controlled induction motor (FOCIM) drive. The ANN has input current error between the reference and the measured stator currents. The output function of neuron is a hyperbolic tan (or tan-sigmoid) function to apply error Levenberg–Marquardt (L–M) back propagation as learning rule because of its fast convergence. The proposed method is based on a new approach in which hysteresis band is replaced by ANN comparator to improve the performance of the FOCIM drive. It minimizes torque ripples, flux ripples, voltage and current THDs over the existing HCC and PCC methods. The superiority of the proposed method compared to existing methods is established by simulation and experimental results.

The sedimentary architecture of hyperpycnites produced by transient turbulent flows in a shallow lacustrine environment

Hyperpycnal flows are river-derived extrabasinal turbidity currents transporting both sand and clay to lacustrine, coastal, shelf and deepwater sedimentary environments. Experimental research in the past twenty years has shown that the presence of clay in sediment-laden flows promotes a transitional behavior between fully turbulent flow and a quasi-laminar plug flow regime. However, to date, most work concerning the fluid dynamic interpretation of lacustrine hyperpycnal flows has been founded on concepts based on fully turbulent flows, and relatively little is known about the influence of clay on the rheological and turbulence characteristics of these flows. With the help of 3D seismic volume and wire-line logging data, the present study undertakes a description and interpretation of subsurface mixed sandstone–mudstone bedforms observed in cores from the Upper Cretaceous Heidimiao Sandstone, Nenjiang Formation, Songliao Basin, NE China. Six lithofacies and five lithofacies associations are recognized from the cores and interpreted as formed under both turbulent and transitional flows. Typical bedforms of transitional flows include large current ripples and low-amplitude bedwaves. The delta-fed shallow lacustrine hyperpycnal flow deposits are characterized by proximal sinuous channels (extending for c. 20 km) and lobe deposits (extending for >20 km), showing a fan-like geometry associated with distributary channel extension in the down-dip direction. Basal erosion in the proximal channels is produced by the initial turbulent and turbulence-enhanced transitional flows, with channel infill dominated by upper transitional plug flows or quasi-laminar plug flows. The lobe deposits possess a fan-like geometry with large aspect ratio, and were formed from turbulence-enhanced and lower transitional plug flows. The downdip transformation of sediment-laden flows in the lacustrine basin varies from an initial turbulent flow, via quasi laminar plug flows to upper and lower transitional plug flows, to turbulence enhanced transitional flows. These transitional flows are interpreted to have experienced gradual dilution and deceleration and eventually transformed to turbulent flows in their distal regions. A new model for delta-fed shallow lacustrine hyperpycnal flow deposits is presented incorporating decelerated transitional flows and flow transformations. This new model can aid understanding of the depositional processes of lacustrine transitional flows and the facies distribution of hyperpynal flows in both modern and ancient sediments.

Design and Finite Element Analysis of a Novel Permanent Magnet Assisted Reluctance Synchronous Motor

In this paper, a permanent magnet assisted synchronous reluctance machine (PMASRM) with optimized permanent magnet width and asymmetric rotor structure is proposed. A typical PMASRM is selected as the reference motor (Pre-optimized PMASRM). In order to reduce the large torque ripple of conventional PMASRM, an optimization method to design the permanent magnet width is investigated and the Optimized Magnet-width PMASRM is proposed. On this basis, an asymmetric flux barriers structure is proposed to further reduce the torque ripple. Some electromagnetic characteristics including air-gap flux density, no-load back EMF and motor efficiency are examined by Finite Element Analysis (FEA). The simulation results show that the proposed PMASRM can not only decrease the harmonic component of no-load back EMF obviously, but also reduce the torque ripple in steady-state operation, which proves the rationality of the motor structure.

Simultaneous Tuning of Rotor Shape and Phase Current of Switched Reluctance Motors for Eliminating Input Current and Torque Ripples With Reduced Copper Loss

Switched reluctance motor (SRM) is recently emerging as a cost-effective but mechanically and thermally robust motor for vehicle propulsion. However, the conventional driving method of the SRM causes a large input current and torque ripples, both of which are scarcely acceptable for vehicle application. Recently, a promising driving method has been proposed that tunes the phase current to eliminate the input current and torque ripples simultaneously, although this method suffers from large copper loss when applied to the normal SRMs. To solve this problem, this article proposes simultaneous tuning of the rotor shape in combination with the recently proposed driving method, which includes only tuning of the phase current. Tuning of the rotor shape is targeted at minimizing the copper loss. Meanwhile, the stator structure is the same as the normal SRM design. The proposed approach was revealed to reduce the effective value of the phase current by 18% in simulation and by 23% in experiment compared with the recently proposed driving method, without increasing the input current and torque ripples. This result suggests the effectiveness of tuning both the rotor shape and the phase current for applying SRMs to vehicle propulsion.

Capacitor Voltage Ripple Estimation and Optimal Sizing of Modular Multi-Level Converters for Variable-Speed Drives

This work deals with the sizing of submodule capacitors for modular multilevel converters (MMCs) used for variable speed drives for medium voltage and high voltage electric machines. Variable speed drives are required to run over a wide frequency range from zero to a few hundred Hz or even over 1 kHz. Under low frequency operation (<30 Hz), a large current ripple flowing through the MMC submodule capacitors will cause significant capacitor voltage fluctuation. This article proposes an optimal submodule capacitor selection method based on the common-mode voltage injection. The proposed sizing model includes two functions: 1) accurately estimating the capacitor voltage ripple based on the drive system parameters; and 2) identifying the minimum capacitance of the submodule capacitors based on the allowed maximum capacitor voltage fluctuations. Simulation and experimental results show that the error between the actual and estimated values of the voltage fluctuation is within 3% using the proposed model.

EMI Noise Reduction of DC-DC Switching Converters with Automatic Output Ripple Cancellation

This paper proposes new EMI reduction technologies and automatic output voltage ripple cancellation method for the PWM buck converter with voltage-mode or current-mode and the ripple-controlled converters. Genenrally, modfying the clock frequeny is effective to reduce the EMI noise, but it may increase the output ripple substantially. We have developed techniques to cancel the increased ripple by modifying the slope of the saw-tooth signal or current of the ripple injection circuit. The EMI spectrum of the operating frequency is reduced by more than 15dB and the modified large ripple is canceled to the stable level.

Improved Stator/Rotor-Pole Number Combinations for Torque Ripple Reduction in Doubly Salient PM Machines

Doubly salient permanent magnet (DSPM) machines suffer from a large torque ripple due to unbalanced three phases, nonsinusoidal-phase back electromotive force, large cogging torque, etc. To suppress the torque ripple, this article proposes a new type of stator/rotor-pole number combinations. The number of stator poles is 18, while the number of rotor poles differs from the conventional counterpart (i.e., 12) by one. The DSPM machines with different stator/rotor-pole number combinations are globally optimized under the fixed copper loss and machine envelope. It shows that compared with the 18/12 stator/rotor-pole DSPM machine, the torque ripples of 18/11 and 18/13 stator/rotor-pole DSPM machines are reduced significantly, while their torque densities remain almost the same. An 18/13 stator/rotor-pole DSPM machine is built and tested so as to experimentally verify such improvement.

A Broad Continuum of Aeolian Impact Ripple Morphologies on Mars is Enabled by Low Wind Dynamic Pressures

AbstractAeolian ripples are common in sandy environments on Earth and Mars. On Earth, ripples in sorted dune sands typically are &lt;1 cm high and are erased in high winds. On Mars in similar sands, ripple wavelengths commonly exceed 2 m, with much smaller ripples superimposed. Large Martian ripple sizes and juxtaposition of multiple wavelengths have raised questions about origins and the applicability of terrestrial aeolian physics to different planetary environments. Here, two hypotheses are evaluated for large Martian ripples: (1) fluid/wind drag, analogous to ripples formed under water on Earth, as proposed previously for Martian large ripples; and (2) saltation impact splash, the mechanism creating aeolian ripples of much smaller size on Earth. This study evaluates these hypotheses with numerical experiments and Mars rover observations, and concludes that large Martian ripples develop through the saltation impact splash mechanism. The low‐density Martian atmosphere enables aeolian impact ripples to grow much higher into the boundary layer before reaching maximum heights constrained by wind dynamic pressure effects at crests. In this concept, boundary layer conditions influence mature ripple heights more directly than wavelengths. On Mars, low wind dynamic pressures, combined with the impact splash mechanism, also help to explain other distinctively Martian aeolian bedforms, including large longitudinal ripples observed by rovers and orbiters, and transverse aeolian ridges (TARs) distributed widely across the Martian surface. Compared with Earth, low wind dynamic pressures on Mars permit a wider range of ripple sizes, relative ages, morphologies, and orientations in close proximity, as displayed in rover observations.

Double Vector Model Predictive Control to Reduce Common-Mode Voltage Without Weighting Factors for Three-Level Inverters

The conventional model predictive control (MPC) suffers from high common-mode voltage (CMV) magnitude and large current ripples. In this article, the reduced CMV MPC strategy with double vector (RCMV-MPCDV) is proposed for three-level inverters, which adopts double vector to reduce the CMV and current ripples simultaneously in per-sampling period. First, based on geometric relationship of median, a novel cost function that evaluates median line distance is proposed to reduce the computational complexity, rather than evaluating the closest distance. Second, in order to reduce the computational burden, the double vector preselection algorithm is presented with fewer evaluation times. Third, the candidate vectors are reclassified and regrouped from partial basic vectors, which restricts CMV magnitude within one-sixth of dc-link voltage. In addition, to select more satisfactory double vectors for RCMV-MPCDV scheme, two improved methods are proposed to compensate the losing candidate vectors. The simulation and experimental results with steady-state performance and dynamic response validate the effectiveness of the proposed method.

표면부착형 영구자석 동기전동기의 토크 리플 저감을 위한 가변 샘플링 기반 모델예측제어

This paper proposes a model predictive control with variable sampling time for reducing torque ripple in SPMSM drive system. Although the MPC has a fast dynamic response, a large torque ripple is generated by a long and fixed sampling period. Even if the torque ripple is reduced by using a short sampling period, it causes another problem that comes from increased switching losses. In this paper, the proposed method has a smaller switching losses compared to the conventional method while reducing torque ripple. The validity of the proposed method is verified with simulation and experiment results.

Evaluation of Three Improved Space-Vector-Modulation Strategies for the High-Speed Permanent Magnet Motor Fed by a SiC/Si Hybrid Inverter

The large current ripple caused by the limited switching frequency significantly degrades the control performance of the high-speed permanent magnet motor drive system. To mitigate the current ripple, the switching frequency of the inverter should be high enough. The purpose of this article is to reduce the current ripple of the HSPMSM drive system. First, a Silicon-Carbide/Silicon(SiC/Si) hybrid inverter is designed. The designed hybrid inverter consists of two SiC-MOSFETs and six Si-IGBTs, and the circuit modals of the SiC/Si hybrid inverter are analyzed. Second, based on the SiC/Si hybrid inverter, three improved space-vector-modulation (SVM) strategies are proposed. The core principle of the proposed SVM strategies is that most of the switching actions are transferred from the Si-IGBTs to the SiC-MOSFETs. The benefit from the low switching loss of the SiC device is that the total power loss can be significantly reduced. Besides, the SiC-MOSFETs can create the zero-voltage-switch condition for the Si-IGBTs, and then the switching loss of the Si-IGBTs can be almost eliminated. Finally, to verify the effectiveness of the proposed methods, sufficient simulations and experiments are implemented. The stator current ripple, total-harmonic-distortion, and the conversion efficiency of the inverter in the full power range are compared under the same condition based on the full-Si-IGBT inverter, the full-SiC-MOSFET inverter, and the SiC/Si hybrid inverter. The evaluated results sufficiently verify the superiority of the proposed SiC/Si hybrid inverter and the improved SVM strategies.

Four-Level Hysteresis-Based DTC for Torque Capability Improvement of IPMSM Fed by Three-Level NPC Inverter

Direct torque control (DTC) is considered one of the simplest and fastest control strategies used in motor drives. However, it produces large torque and flux ripples. Replacing the conventional two-level hysteresis torque controller (HTC) with a four-level HTC for a three-level neutral-point clamped (NPC) inverter can reduce the torque and flux ripples in interior permanent magnet synchronous motor (IPMSM) drives. However, the torque will not be controlled properly within the upper HTC bands when driving the IPMSM in the medium and high-speed regions. This problem causes the stator current to drop, resulting in poor torque control. To resolve this problem, a simple algorithm based on a torque error average calculation is proposed. Firstly, the proposed algorithm reads the information of the calculated torque and the corresponding torque reference to calculate the torque error. Secondly, the average value of torque error is calculated instantaneously as the reference torque changes. Finally, the average value of the torque error is used to indicate the operation of the proposed algorithm without the need for motor speed information. By using the proposed algorithm, the torque can be controlled well in all speed regions, and thus, a better stator current waveform can be obtained. Simulation and experimental results validate the effectiveness of the proposed method.

Predictive Torque Control Based on Discrete Space Vector Modulation of PMSM without Flux Error-Sign and Voltage-Vector Lookup Table

The conventional finite set–predictive torque control of permanent magnet synchronous motors (PMSMs) suffers from large flux and torque ripples, as well as high current harmonic distortions. Introducing the discrete space vector modulation (DSVM) into the predictive torque control (PTC-DSVM) can improve its steady-state performance; however, the control complexity is further increased owing to the large voltage–vector lookup table that increases the burden of memory. A simplified PTC-DSVM with 73 synthesized voltage vectors (VVs) is proposed herein, for further improving the steady-state performance of the PMSM drives with a significantly lower complexity and without requiring a VV lookup table. The proposed scheme for reducing the computation burden is designed to select an optimal zone of space vector diagram (SVD) in the utilized DSVM based on the torque demand. Hence, only 10 out of 73 admissible VVs will be initiated online upon the optimal SVD zone selection. Additionally, with the proposed algorithm, no flux error is required to control the flux demand. The proposed PTC-DSVM exhibits high performance features, such as low complexity with less memory utilization, reduced torque and flux ripples, and less redundant VVs in the prediction process. The simulation and experimental results for the 11 kW PMSM drive are presented to prove the effectiveness of the proposed control strategy.