Frequency Ripple Research Articles

A New Modeling and Control Scheme for Cascaded Split-Source Converter Cells

Cascaded split-source inverter (CSSI) is a new single-stage modular multilevel topology. Each cell of this converter converts dc to ac power in the buck or boost operation mode without any additional power switch. This article develops a design method based on a detailed model for CSSI. This model shows that energy storage elements experience double-fundamental frequency ripples besides high-frequency ones. It accurately calculates voltage gains and capacitor voltage and inductor current ripples. On the other hand, common carrier-based multilevel modulations have been modified in terms of both reference and carrier signals to control the inverter under symmetric and asymmetric conditions. With proposed simple modulations, the cell inductor is charged with the constant duty cycle. Also, the reverse recovery of diodes occurs in the minimum level of input current once per switching cycle and output power is distributed equally between cells. These characteristics reduce power losses, the input inductance of each cell, and the complexity of the system model. By phase-shifted pulsewidth modulation (PWM), the output voltage harmonics of three-cell CSSI are centralized around multiples of the triple switching frequency. In this method, high-frequency ripples on the network impedance are one-third of those in level-shifted PWM. Also, CSSI has been compared with cascaded multilevel inverters with voltage boosting ability and other SSI-based multilevel topologies. Validity of operation principles, mathematical relations, and modulation schemes are verified through simulation and experimental results.

A Soft-Switched Power-Factor-Corrected Single-Phase Bidirectional AC–DC Wireless Power Transfer Converter With an Integrated Power Stage

Bidirectional ac–dc wireless power transfer (WPT) converters are widely used in grid-connected electric vehicle systems for grid-to-vehicle and vehicle-to-grid applications. They usually apply a two-stage topology with a bidirectional ac–dc power factor correction converter and a bidirectional dc–dc WPT converter. Such a two-stage topology cannot achieve high efficiency and low cost. Recently, single-stage matrix bidirectional ac–dc WPT converters have been proposed. However, the matrix-converter-based topologies do not utilize remarkably lower count of power switches and generate large double-line frequency ripple in the dc-side voltage or current. This article proposes a new single-phase bidirectional ac–dc WPT topology with an integrated power stage to overcome the drawbacks of the matrix-converter-based topologies and retain the advantages of single-stage topologies. Description of the proposed topology with the modulation and control methods, theoretical analysis, and reference design procedure are presented in detail. Finally, a scaled-down laboratory prototype with 500-W output power is implemented with experimental results presented to validate the principle, analysis, and design.

Key technology research on magnetorheological finishing based on suppression of surface mid-spatial frequency ripple errors

A high-energy laser system imposes demanding requirements on the total frequency range of its optical components, mainly the mid-spatial frequency (MSF) error. This error will seriously reduce the optical performance of this system. In order to suppress the MSF ripple error of optical components after magnetorheological finishing (MRF), the influence of the rotation angle of MRF removal functions on the surface MSF ripple error was explored by computer simulation at first. Subsequently, the suppression effect of magnetorheological ribbon fluctuation on surface MSF ripple errors was simulated. Finally, the fused silica components were scanned uniformly under the conditions of different rotation angles and the same MRF ribbon fluctuation. The simulation analysis and experimental results demonstrated that the same removal function had multiple preferred angles under different line feed spacing values. When the preferred angle is reached for the removal function, the surface MSF ripple error of the machined component can be significantly reduced. However, the MSF ripple error cannot be eliminated by simply rotating the preferred angle during MRF. Nevertheless, this part of the MSF ripple error can be swamped by the additional material removal caused by the magnetorheological ribbon fluctuation, which can significantly improve the surface quality of the component. Therefore, the MSF ripple error on the component surface can be eliminated by controlling the rotation angle of the removal function and the fluctuation of the magnetorheological ribbon. This method can significantly improve the root mean square (RMS) of surface MSF ranges and reduce the surface MSF error of high-power laser components.

Ripple density resolution dependence on ripple width.

The goal of the study was to investigate how variations in ripple width influence the ripple density resolution. The influence of the ripple width was investigated with two experimental paradigms: (i) discrimination between a rippled test signal and a rippled reference signal with opposite ripple phases and (ii) discrimination between a rippled test signal and a flat reference signal. The ripple density resolution depended on the ripple width: the narrower the width, the higher the resolution. For distinguishing between two rippled signals, the resolution varied from 15.1 ripples/oct at a ripple width of 9% of the ripple frequency spacing to 8.1 ripples/oct at 64%. For distinguishing between a rippled test signal and a non-rippled reference signal, the resolution varied from 85 ripples/oct at a ripple width of 9% to 9.3 ripples/oct at a ripple width of 64%. For distinguishing between two rippled signals, the result can be explained by the increased ripple depth in the excitation pattern due to the widening of the inter-ripple gaps. For distinguishing between a rippled test signal and a non-rippled reference signal, the result can be explained by the increased ratio between the autocorrelated and uncorrelated components of the input signal.

Lithium-ion battery modeling under high-frequency ripple current for co-simulation of high-power DC-DC converters

Studying the output response of lithium-ion batteries under high-frequency ripple current is important for the co-simulation and optimal design of high-power DC-DC converters using IGBTs. However, this influence has not been sufficiently investigated. In this paper, seven equivalent circuit models which include integer and fractional order models are used to simulate the high frequency characteristics of lithium-ion batteries. Thirteen experiments are designed and implemented on three test platforms, including a self-designed DC-DC platform for triangular wave. These experiments consist of average currents of different amplitudes, ripple currents of different types, amplitudes and frequencies. Unlike previous research, the current excitation and voltage response of high frequency ripple are obtained by separating the short and long time scale signals. The equivalent circuit model components are selected based on the frequency domain characteristics of the impedance spectrum. The HMPSO method is employed to implement the parameter identification and simulation analysis of the high frequency model under time domain data. By contrast, the first-order RL model is selected as the preferred choice through modeling and co-simulation. The complexity of the model and co-simulation time is reduced while maintaining voltage accuracy. For the case presented in this paper, the co-simulation time of R(RL) can be reduced by 11.3 % and 30.2 % compared to the RL and R(RL)(RL) models.

An Improved Cascade Buck Converter for High Step-Down DC-DC Applications

This article focuses on the efficiency improvement of the cascade buck converter (CBC). By changing the position of the second stage inductor, the output current is shared between both the first and second stage inductors and as a result, the total volume of the magnetic components and their conduction losses are decreased. Besides, by proper design of the inductors, the frequency of the output current ripple will increase to twice the conventional CBC with lower p-p amplitude, which results in a further decrease in the size of passive components. The proposed improved CBC is analyzed, and its operating principles are presented. The theoretical analysis is verified by the experimental results of a 400-V input and 24 V–120 W output prototype converter.

A Single-Stage Bidirectional AC–DC Converter Feasible for Onboard Battery Chargers

This article proposes a novel topology of a single-stage single-phase bidirectional ac–dc converter with high-frequency isolation feasible for onboard chargers. Its structure uses the interleaving concept associated with an autotransformer that is responsible for sharing the current stresses and increasing the current ripple frequency, as well as obtaining a five-level voltage waveform. A theoretical study of the structure, the operation principle, and a detailed loss analysis are performed. The mathematical analysis and control strategy are validated through simulations and a 1-kW small-scale experimental prototype. The topology is also redesigned to 6.6 kW and a comparison with a traditional two-stage solution usually employed in onboard chargers is presented, thus demonstrating that the proposed structure is competitive with other similar counterparts. Despite the proposed converter presents higher capacitive losses, when operating at 200 kHz, it has reduced volume of magnetics, resulting in an efficiency of 95.71%. If the proposed converter is designed for the operation at 80 kHz, a similar magnetic volume results when compared with the two-stage solution, but with a higher efficiency of 96.36% and avoiding the volume of resonant capacitors.

Advanced age has dissociable effects on hippocampal CA1 ripples and CA3 high frequency events in male rats

Sharp wave/ripples/high frequency events (HFEs) are transient bursts of depolarization in hippocampal subregions CA3 and CA1 that occur during rest and pauses in behavior. Previous studies have reported that CA1 ripples in aged rats have lower frequency than those detected in young animals. While CA1 ripples are thought to be driven by CA3, HFEs in CA3 have not been examined in aged animals. The current study obtained simultaneous recordings from CA1 and CA3 in young and aged rats to examine sharp wave/ripples/HFEs in relation to age. While CA1 ripple frequency was reduced with age, there were no age differences in the frequency of CA3 HFEs, although power and length were lower in old animals. While there was a proportion of CA1 ripples that co-occurred with a CA3 HFE, none of the age-related differences in CA1 ripples could be explained by alterations in CA3 HFE characteristics. These findings suggest that age differences in CA1 are not due to altered CA3 activity, but instead reflect distinct mechanisms of ripple generation with age.

Linear active disturbance rejection control for a dual unified power quality conditioner

In this paper, a linear active disturbance rejection control (LADRC) method is presented for a dual unified power quality conditioner (iUPQC). Compared with the traditional PI controller that requires double closed-loop control and decoupling design, the presented LADRC control method with Quasi-resonant (QR) feedforward has the benefits to simplify controller structure, and improve system steady-state, dynamic and anti-interference performance under the conditions with system uncertainty and external disturbances. By considering the unfavorable factors as control disturbances, the LADRC control method is able to obtain ideal performance through utilizing linear error state feedback (LESF) and dynamic disturbances compensation. In addition, in order to reduce DC link voltage fluctuation and eliminate double frequency ripple, a super capacitor is connected to DC link through a bidirectional DC/DC converter. By controlling the PWM signal of converter, the DC link capacitor can be charged or discharged to keep its voltage stable. Finally, the feasibility and effectiveness of this method are verified by MATLAB/SIMULINK simulation on a three-phase power distribution system.

Brain temperature affects quantitative features of hippocampal sharp wave ripples.

Biochemical mechanisms are temperature dependent. Brain temperature shows wide variations across brain states, and such changes may explain quantitative changes in network oscillations. Here, we report on the relationship between various hippocampal sharp wave ripple features to brain temperature. Ripple frequency, occurrence rate, and duration correlated with temperature dynamics. By focal manipulation of the brain temperature in the hippocampal CA1 region, we show that ripple frequency can be increased and decreased by local heating and cooling, respectively. Changes of other parameters, such as the rate of sharp wave-ripple complex (SPW-R) and ripple duration were not consistently affected. Our findings suggest that brain temperature in the CA1 region plays a leading role in affecting ripple frequency, whereas other parameters of SPW-Rs may be determined by mechanisms upstream from the CA1 region. These findings illustrate that physiological variations of brain temperature exert important effects on hippocampal circuit operations.NEW & NOTEWORTHY During physiological conditions, brain temperature fluctuates approximately 3°C between sleep and active waking. Here, we show that features of hippocampal ripples, including the rate of occurrence, peak frequency, and duration are correlated with brain temperature variations. Focal bidirectional manipulation of temperature in the hippocampal CA1 region in awake rodents show that ripple frequency can be altered in the direction expected from the correlational observations, implying that temperature plays a significant role.

Understanding and reducing mid-spatial frequency ripples during hemispherical sub-aperture tool glass polishing

During sub-aperture tool polishing of glass optics, mid-spatial surface ripples are generated because of material removal non-uniformities during tool linear translation (resulting in feed ripples) and tool pathway step overlaps (resulting in pitch ripples). A variety of tool influence function (TIF) spots, trenches, and patches were created to understand and minimize such ripples on fused silica workpieces after polishing with cerium oxide slurry using a rotating hemispherical pad-foam tool. The feed ripple amplitude can be decreased by reducing the non-uniformities in the pad texture and/or by minimizing a derived feed ripple metric (rf=Vmax0.5Vf/Rt) via adjustments in processing parameters. Pitch ripples can be minimized by reducing relative step distance to spot radius ratio (xs/at) and by achieving a flat bottom trench shape cross section or by reducing the material removal per pass. Using the combined methods, an overall ripple error of ∼1.2nm rms has been achieved.

Effects of ripple width on ripple density resolution

Effects of ripple width in rippled-spectrum signals on ripple density resolution was investigated. Two measurement paradigms were tested: (i) ripple density resolution for discrimination between two rippled signals and (ii) discrimination between a rippled test signal and non-rippled reference signal. The ripple widths varied from 9% to 64% of the ripple frequency spacing. For both paradigms, the ripple density resolution increased with deceasing the ripple width. For discrimination between two rippled signals, the resolution was 8.1 ripples/oct for a ripple width of 64% and increased to 15.1 ripples/oct at the ripple width of 9%. For discrimination between a rippled test and non-rippled reference signal, the resolution was 9.3 ripples/oct at a ripple width of 64% and increased to 85 ripples/oct at a ripple width of 9%. Discrimination between two rippled signals is hypothesized to depend on ripple depth in the excitation pattern; the depth increases with narrowing the ripple width. Discrimination between a rippled test and non-rippled reference signal is hypothesized to depend on temporal processing; the effect of the ripple width appears due to increasing the ratio of the autocorrelated to uncorrelated components of the input signal with narrowing the ripples.

99%—Efficient, interleaved bidirectional DC‐DC converter with new interleaved PWM method of parallel‐connected Mosfets

AbstractA new high efficiency interleaved pulse‐width modulation (HE‐IPWM) method using parallel‐connected Mosfets is presented. The IPWM is evaluated using a bidirectional DC‐DC converter for charging and discharging a battery. The results show an excellent DC voltage gain without an extremely large duty cycle. Compared with conventional pulse‐width modulation (CPWM), the IPWM reduces by half the ripple of the battery current. The current ripple of IPWM is four times higher of the switching frequency, while CPWM is two times higher. The proposed interleaved strategy also double the inductor current ripple frequency, whereas in general, is equal to the switching frequency. As a result, the use of the IPWM reduces the weight and size of inductor design. Furthermore, IPWM provides the best battery current ripple at the duty cycle close to 25%. The operating stage, mathematical analyses, and design guidelines of the two proposed modulations are explained in detail. The IPWM experimental results of a 250‐W prototype confirmed the circuit performance. The maximum efficiency of 98.9% is obtained at 250 W for boost mode and 99% for buck mode.

Research on Cascaded Single Phase PFC Based on Predictive PI Control

In order to improve the charging speed and reduce the occupied volume of an electric vehicle charger, a single-phase boost power factor corrector (PFC) system with cascade CHB (cascaded H-bridge) topology was adopted. Due to the periodic fluctuation of single-phase AC input, there is a large double power frequency ripple component in the output voltage of an AC-DC converter. When capacitor voltage is used as output for feedback control, the control system has the characteristics of a non-minimum phase system. In light of these factors that affect the dynamic stability of the system, a control method is proposed to improve the dynamic characteristics of the system without affecting its steady-state performance. The predictive PI control strategy was adopted to predict the error input signal of the lag process to attenuate the jitter in the control system and improve the dynamic performance and anti-interference of the system. Finally, the feasibility of the scheme was verified by experiments.

Torque ripple minimization in direct torque control at low-speed operation using alternate switching technique

Direct torque control (DTC) of induction motor is prominent to offer instant torque and flux control with a simple control structure. However, this scheme suffers from two major drawbacks namely high torque ripple and variable switching frequency of the inverter, especially during low-speed operation. During the low-speed condition, the positive torque slope is very steep and torque overshoot occurs frequently resulting in the torque ripple become of great significance. This paper proposes a new and effective technique to reduce the torque ripple by integrating the alternate switching technique to the inverter switching status to limit the torque slope surge. By varying the frequency and duty cycle of the alternate switching, the rate of surge can be controlled resulting in the chances of overshoots, and selection of reverse voltage vector can be avoided. The feasibility of the proposed technique has been validated using MATLAB/Simulink software and through experimental results. The results show the proposed alternate switching technique minimizes over 40% reduction in the torque ripple while maintaining the simple structure of DTC.

Third-Harmonic Current Injection for Wear-Out Reduction in Single-Phase PV Inverters

The expansion of grid-connected photovoltaic (PV) systems over the years has been followed by concerns about the PV inverter reliability. It is well known that single-phase grid-connected PV inverter has a double-line frequency ripple in the dc-link voltage, which increases the wear-out failure probability of the dc-link capacitor and affects the overall inverter reliability. This work uses a third-harmonic current injection to attenuate the double-line frequency ripple in the dc-link capacitor voltage and to improve the PV system reliability. An analytical model capable to describe the effects of the third-harmonic current injection method in the dc-link capacitor is derived. The proposed strategy is validated by simulation and experimental results. The lifetime evaluation is developed considering a 3 kVA PV inverter and one-year mission profiles. The PV inverter failure probability considering an operation period equal to 20 years decreased in 27.17% for the adopted case study. Moreover, this strategy provides a straightforward retrofit of the current inverter technology, requiring no hardwarechanges.

Performance enhancement of direct torque control induction motor drive using space vector modulation strategy

Purpose. The main objective of this work is to demonstrate the advantages brought by the use of space vector modulation technique in the direct torque control of the induction motor. To achieve this purpose, two different direct torque control approaches (with space vector modulation) are proposed and studied from a comparative aspect with each other and with the conventional direct torque control. The novelty of this work consists in the employment of an Integral-Proportional (IP) speed controller in the two proposed direct torque control approaches and a more in-depth evaluation for their performance mainly the switching frequency of inverter semiconductor components and motor torque ripples. Methods. Two different direct torque control approaches that use the space vector modulation strategy and/or fuzzy-logic control, are described in detail and simulated with IP speed controller. The simulation experiments are carried out using Matlab/Simulink software and/or fuzzy-logic tools. Results. Practical value. Comparison results show that the two proposed direct torque control structures (with space vector modulation) exhibit a large reduction in torque ripples and can also avoid random variation problem of switching frequency (over a wide range of speed or torque control). On the other hand, the use of IP speed regulator ensured good dynamic performance for the drive system as well as considerably minimized peak overshoot in the speed response. Practically all of these benefits are achieved while retaining the simplicity and the best dynamic characteristics of the classical direct torque control, especially with the modified direct torque control approach in which the design or implementation requires minimal computational effort.

A machine learning approach to characterize sequential movement-related states in premotor and motor cortices.

Nonhuman primate (NHP) movement kinematics have been decoded from spikes and local field potentials (LFPs) recorded during motor tasks. However, the potential of LFPs to provide network-like characterizations of neural dynamics during planning and execution of sequential movements requires further exploration. Is the aggregate nature of LFPs suitable to construct informative brain state descriptors of movement preparation and execution? To investigate this, we developed a framework to process LFPs based on machine-learning classifiers and analyzed LFP from a primate, implanted with several microelectrode arrays covering the premotor cortex in both hemispheres and the primary motor cortex on one side. The monkey performed a reach-to-grasp task, consisting of five consecutive states, starting from rest until a rewarding target (food) was attained. We use this five-state task to characterize neural activity within eight frequency bands, using spectral amplitude and pairwise correlations across electrodes as features. Our results show that we could best distinguish all five movement-related states using the highest frequency band (200-500 Hz), yielding an 87% accuracy with spectral amplitude, and 60% with pairwise electrode correlation. Further analyses characterized each movement-related state, showing differential neuronal population activity at above-γ frequencies during the various stages of movement. Furthermore, the topological distribution for the high-frequency LFPs allowed for a highly significant set of pairwise correlations, strongly suggesting a concerted distribution of movement planning and execution function is distributed across premotor and primary motor cortices in a specific fashion, and is most significant in the low ripple (100-150 Hz), high ripple (150-200 Hz), and multiunit frequency bands. In summary, our results show that the concerted use of novel machine-learning techniques with coarse grained queue broad signals such as LFPs may be successfully used to track and decode fine movement aspects involving preparation, reach, grasp, and reward retrieval across several brain regions.NEW & NOTEWORTHY Local field potentials (LFPs), despite lower spatial resolution compared to single-neuron recordings, can be used with machine learning classifiers to decode sequential movements involving motor preparation, execution, and reward retrieval. Our results revealed heterogeneity of neural activity on small spatial scales, further evidencing the utility of micro-electrode array recordings for complex movement decoding. With further advancement, high-dimensional LFPs may become the gold standard for brain-computer interfaces such as neural prostheses in the near future.

THE RESULTS OF RESEARCH PNEUMATIC ELECTROMAGNETIC PULSATOR COMBINED WITH COLLECTOR

This article demonstrates the results of experimental research one of the pulsators. Its main difference from others is a pneumatic electromagnetic pulsator in combination with a collector. Therefore, this article describes in detail the process of studying the pulsator. The planned experiment was carried out on by Factorial experiments with multiple factors. The influence of factors (the ripple frequency n, the milk ejection q and the ratio between strokes t/T) on the vacuum pressure in the inter wall chamber of teat cups was studied. The regression equation of the dependence response criterion on factors is modeled. This dependence is demonstrated graphically. Also there is a contour graph which is for more detailed information.

The Impact of an Overlaid Ripple Current on Battery Aging: The Development of the SiCWell Dataset

Fast-switching semiconductors induce ripple currents on the high-voltage DC bus in the electric vehicle (EV). This paper describes the methods used in the project SiCWell and a new approach to investigate the influence of these overlaid ripples on the battery in EVs. The ripple current generated by the main inverter is demonstrated with a measurement obtained from an electric vehicle. A simulation model is presented which is based on an artificial reference DC bus, according to ISO 21498-2, and uses driving cycles in order to obtain current profiles relevant for battery cycling. A prototype of a battery cycling tester capable of high frequency and precise ripple current generation was developed and is used to cycle cells with superimposed ripple currents within an aging study. To investigate the impact of the frequency and the amplitude of the currents on the battery’s lifetime, these ripple parameters are varied between different test series. Cell parameters such as impedance and capacity are regularly characterized and the aging of the cells is compared to standard DC cycled reference cells. The aging study includes a total of 60 automotive-sized pouch cells. The evaluation of ripple currents and their impact on the battery can improve the state-of-health diagnosis and remaining-useful life prognosis. For the development and validation of such methods, the cycled cells are monitored with a measurement system that regularly measures current and voltage with a sampling rate of 2 MHz. The resulting dataset is suitable for the design of future ripple current aging studies as well as for the development and validation of aging models and methods for battery diagnosis.