Showing papers on "Ripple published in 2009"

Controlled ripple texturing of suspended graphene and ultrathin graphite membranes

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

Ripple-Based Control of Switching Regulators—An Overview

Abstract: Switching regulators with ripple-based control (ie, ?ripple regulators?) are conceptually simple, have fast transient responses to both line and load perturbations, and some versions operate with a switching frequency that is proportional to the load current under the discontinuous conduction mode These characteristics make the ripple regulators well-suited, especially for power management applications in computers and portable electronic devices Ripple regulators also have some drawbacks, including (in some versions) a poorly defined switching frequency, noise-induced jitter, inadequate dc regulation, and a tendency for fast-scale instability This paper presents an overview of the various ripple-based control techniques, discusses their merits and limitations, and introduces techniques for reducing the noise sensitivity and the sensitivity to capacitor parameters, improving the frequency stability and the dc regulation, and avoiding fast-scale instability

A Near-State PWM Method With Reduced Switching Losses and Reduced Common-Mode Voltage for Three-Phase Voltage Source Inverters

Abstract: The near-state pulsewidth modulation (NSPWM) method, which reduces the common-mode voltage/current, is proposed for three-phase pulsewidth modulation (PWM) inverter drives. The method is described, its optimal voltage vectors are found, and the sequence that these vectors are applied is determined. Its voltage linearity and DC bus and AC output PWM current ripple characteristics are studied. Its output line-to-line voltage pattern is carefully studied with regard to switching transients that may cause overvoltages at the motor terminals, particularly for long-cable applications. The NSPWM method is thoroughly investigated, and its performance is compared to conventional PWM methods. Theory, simulations, and experiments show that NSPWM exhibits superior common-mode performance and satisfactory input/output PWM ripple performance characteristics. It is also illustrated that even though the method has bipolar line-to-line output voltage pulses, due to the sufficient zero-voltage time intervals for the switching transients to settle, these pulses do not cause additional overvoltages at the motor terminals compared to the conventional methods. The method is feasible for motor drives, particularly for operation in the high modulation index range, where its overall performance exceeds the performances of the state-of-the-art PWM methods.

High-Efficiency Fuel Cell Power Conditioning System With Input Current Ripple Reduction

Abstract: A high-efficiency fuel cell power conditioning system with input current ripple reduction is proposed. The proposed system consists of a high-efficiency high-step-up current-fed resonant push-pull converter and a full-bridge inverter. The converter conserves inherent advantages of a conventional current-fed push-pull converter such as low input-current stress and high voltage conversion ratio. Also, a voltage-doubler rectifier is employed in order to remove the reverse-recovery problem of the output rectifying diodes and provide much higher voltage conversion ratio. The current ripple reduction control without an external component is suggested. Therefore, the proposed system operates in a wide input-voltage range with a high efficiency. By using a current-ripple reduction control, the input current ripple is furthermore reduced. A 1.5-kW prototype is implemented with input-voltage range from 30 to 70 V. Experimental results show that minimum efficiency at full load is about 92.5% and that ripple current is less than 2% of the rated input current.

Cost-Effective Hundred-Year Life for Single-Phase Inverters and Rectifiers in Solar and LED Lighting Applications Based on Minimum Capacitance Requirements and a Ripple Power Port

Abstract: Energy storage requirements for converters with a dc port and a single-phase grid-connected port are evaluated, based on the unavoidable double-frequency power requirement. The minimum energy storage requirement is linked to a minimum capacitance requirement for converters that use capacitance energy storage. It is shown how to employ a ripple power port to manage energy storage and decouple capacitor ripple from power ripple. A ripple power port allows a designer to make a choice of capacitor voltage independent of system voltages. This in turn allows film capacitors of modest size to be used for energy storage in these applications. A combination of ac link converter and ripple power port leads to a dramatic increase in reliability: it is shown that converters with nominal ratings up to 200 W can be designed with expected mean-time-between-failure ratings on the order of 1.4 million hours - sufficient for hundred-year operation in long-life applications such as photovoltaic converters and LED lamps. This large increase in life is achieved with minimal extra cost.

Optimal Variable Switching Frequency Scheme for Reducing Switching Loss in Single-Phase Inverters Based on Time-Domain Ripple Analysis

Abstract: The choice of switching frequency for pulsewidth modulation single-phase inverters, such as those used in grid-connected photovoltaic application, is usually a tradeoff between reducing the total harmonic distortion (THD) and reducing the switching loss. This paper discusses an approach to minimize the switching loss while meeting a given THD requirement using variable switching frequency schemes (switching schemes with the switching frequency varying within a fundamental period). An optimal switching scheme is proposed based on time-domain current ripple analysis and the calculus of variations. The analysis shows that, to meet the same THD requirement, the optimal scheme has a significant saving on switching loss, compared to the fixed switching frequency scheme and the hysteresis control scheme, in addition to other benefits such as reduced peak switching loss and a spread spectrum of the current harmonics. The optimal scheme has been implemented in a prototype and the experimental results have verified the theoretical analysis. Also, a straightforward design method for designing filter inductors for single-phase converters is provided based on the time-domain current ripple analysis.

Cost-Effective Hundred-Year LifeforSingle-Phase Inverters andRectifiers inSolar andLEDLighting Applications Based on MinimumCapacitance Requirements andaRipple PowerPort

Abstract: Energystorage requirements forconverters withadc portandasingle-phase grid-connected portareevaluated, based ontheunavoidable double-frequency powerrequirement. The minimumenergystorage requirement islinked toaminimum capacitance requirement forconverters thatusecapacitance energy storage. Itisshownhowtoemployaripple powerportto manageenergystorage anddecouple capacitor ripple from powerripple. A ripple powerportallows adesigner tomakea choice ofcapacitor voltage independent ofsystem voltages. This inturnallows filmcapacitors ofmodestsize tobeusedforenergy storage inthese applications. A combination ofaclinkconverter andripple powerportleads toadramatic increase inreliability: itisshownthatconverters withnominal ratings upto200W can bedesigned withexpected mean-time-between-failure ratings on theorderof1.4million hours- sufficient forhundred-year operation inlong-life applications suchasphotovoltaic converters andLED lamps.Thislargeincrease inlife isachieved with minimal extra cost.

A General Analytical Method for Calculating Inverter DC-Link Current Harmonics

Abstract: Accurate identification of a DC-link ripple current is an important part of switched power-converter design, since the spectral content of this current impacts on DC bus-capacitor lifetime, the stability of the converter control, and the electromagnetic-interference (EMI) performance of the system. Conventionally, the RMS magnitude of the ripple current is used to evaluate this impact, but this approach does not readily differentiate between pulsewidth-modulation (PWM) strategies, and can be challenging to evaluate for more complex converter topologies. This paper presents a new generalized approach that analytically determines the harmonic spectrum of the DC-link and DC-bus capacitor currents for any voltage-source switched converter topology. The principle of the strategy is that the product of a phase-leg-switching function and its load current in the time domain, which defines the switched current flowing through the phase leg, can be evaluated in the frequency domain by convolving the spectra of these two time-varying functions. Since PWM has a discrete line-frequency spectrum, this convolution evaluates as an infinite summation in the frequency domain, which reduces to a simple frequency shift of the PWM spectrum when the load current is assumed to be a fundamental single-frequency sinusoid. Hence, the switched currents flowing through the phase legs of an inverter can be evaluated as a summation of harmonics for any PWM strategy or inverter topology and can then be readily combined using superposition to determine the DC-link and DC bus-capacitor currents. The analytical approach has been verified against experimental results for an extensive range of two-level and multilevel converter topologies and PWM strategies.

Switching power supply device

Abstract: A switching power supply device for a ripple control system that can obtain the ripple component with the necessary amplitude without using discrete elements. On capacitor Ci of CR integrator 11 , a voltage is generated corresponding to the integration value of the voltage applied to inductor Lo. The ripple voltage generated on capacitor Ci has a waveform similar to that of the ripple current flowing through inductor Lo. The voltage of capacitor Ci is converted into current Iq by voltage/current converter 12 , and the current is injected in resistor R 3 arranged on the transmission path of output feedback voltage VFB in comparator 2 . Resistor R 3 generates ripple voltage (Iqxr 3 ) corresponding to the ripple current flowing through inductor Lo. The synthetic voltage of the ripple voltage and output feedback voltage VFB is compared to reference voltage Vref.

Ripple Current Reduction of a Fuel Cell for a Single-Phase Isolated Converter using a DC Active Filter with a Center Tap

Abstract: This paper proposes a ripple reduction method in current without using any additional switching devices. The current ripple that has double frequency component of the power supply is generated in the DC part when a single-phase PWM inverter is used for a grid connection. The current ripple causes short lifetime for electrolytic capacitors, batteries and fuel cells. The proposed circuit realizes a DC active filter function without increasing the number of the switching device because the energy buffer capacitor is connected to the center tap of the isolation transformer. In addition, the buffer capacitor voltage is controlled by the common mode voltage of the inverter. This paper describes the features of the proposed circuit, control strategy and experimental results. As a result, about 1/5 times of the ripple can be reduced.

Novel Two-Phase Interleaved LLC Series-Resonant Converter Using a Phase of the Resonant Capacitor

Abstract: An LLC series-resonant converter has many unique characteristics and improvements over pulsewidth-modulation topologies. However, many output capacitors are needed in parallel to satisfy an output voltage ripple and a rated ripple current of the capacitors. This paper deals with a novel two-phase interleaved LLC resonant converter using a phase of the resonant capacitor. The proposed converter satisfies low output-voltage ripple requirement and meets the rated ripple of output capacitor's current with few output capacitors. The operation and features are considered in detail, and a prototype with a 12-V-100-A output is investigated.

Analysis of Output Current Ripple rms in Multiphase Drives Using Space Vector Approach

Abstract: Multiphase variable-speed drives, supplied from two-level voltage source inverters (VSIs), are nowadays considered for various industrial applications. Although numerous pulsewidth modulation (PWM) schemes for multiphase VSIs, aimed at sinusoidal output voltage generation, have been developed, no detailed analysis of the impact of these modulation schemes on the output current ripple has ever been reported. This paper presents a comprehensive analytical analysis and comparison of the output current ripple caused by the application of three different continuous PWM schemes, using a five-phase VSI as an example. Main properties of sinusoidal PWM, fifth harmonic injection PWM, and space vector PWM are elaborated and analyzed using the harmonic flux concept. Space vector theory is applied in the analysis. As a result, harmonic distortion factors are obtained for each PWM scheme. Theoretical considerations are verified by simulations and experimental investigation using a custom-designed five-phase VSI-fed induction motor drive.

A Control Strategy for Four-Switch Three-Phase Brushless DC Motor Using Single Current Sensor

Abstract: A control strategy based on single current sensor is proposed for a four-switch three-phase brushless DC (BLDC) motor system to lower cost and improve performance. The system's whole working process is divided into two groups. In modes 2, 3, 5, and 6, where phase c works, phase-c current is sensed to control phases a and b, and phase-c current is consequently regulated. In modes 1 and 4, the combination of four suboperating modes for controlling phase-c current is proposed based on detailed analysis on the different rules that these operating modes have on phase-c current. Phase-c current is maintained at nearly zero level first, and phase- a and phase-b currents are regulated by speed circle. To improve control performance, a single-neuron adaptive proportional-integral (PI) algorithm is adopted to realize the speed regulator. Simulation and experimental systems are set up to verify the proposed strategy. According to simulation and experimental results, the proposed strategy shows good self-adapted track ability with low current ripple and strong robustness to the given speed reference model. Also, the structure of the drive is simplified.

A single-phase current source solar inverter with reduced-size DC link

Abstract: This paper presents a new current source converter topology that is primarily intended for single-phase photovoltaic (PV) applications. In comparison against the existing PV inverter technology, the salient features of the proposed topology are: a) the low frequency (double of line frequency) ripple that is common to single-phase inverter has been eliminated; b) the absence of low frequency ripple enables significantly reduced-size passive components to achieve necessary stiffness; and c) improved maximum-power-point-tracking performance is readily achieved due to the tightened current ripple even with reduced-size passive components. This paper presents the proposed topology and its working principle backed up with numerical verifications.

Study of Energy Storage Capacitor Reduction for Single Phase PWM Rectifier

Abstract: It is well known that there exist second-order harmonic current and corresponding ripple voltage on dc bus for single phase PWM rectifiers. The low frequency harmonic current is normally filtered using a bulk capacitor in the bus which results in low power density. This paper studies the energy storage capacitor reduction methods for single phase rectifiers. The minimum ripple energy storage requirement is derived independent of a specific topology. Based on the minimum ripple energy requirement, the feasibility of the active capacitor's reduction schemes is verified. Then, we propose a bidirectional buck-boost converter as our ripple energy storage circuit that can effectively reduce the energy storage capacitance. Simulation and experimental results are provided for verification purposes.

Current sharing in three-phase LLC interleaved resonant converter

Abstract: In this paper, a novel approach for multi-phase interleaved LLC resonant converter is presented. The proposed solution, based on the use of three LLC modules with star connection of transformer primary windings, allows a drastic reduction of the output current ripple and consequently of the output filter capacitor size. Differently from other multi-phase solutions, that are greatly susceptible to resonant components' tolerance causing current imbalance, the proposed topology exhibits an inherent current sharing capability. Moreover, a closed-loop phase-shift control is introduced to additionally compensate for current mismatch and completely balance the current supplied by each module. The benefit of such solution on the reduction of output current ripple and the phase-shift control interaction and effect on load-step variations are also investigated. Measurements on a prototype are added to simulations as validation of the assertions and proposals.

Optimal Use of Zero Vectors for Minimizing the Output Current Distortion in Matrix Converters

Abstract: This paper is focused on the current quality of matrix converter controlled by space vector modulation (SVM) feeding inductive loads. The analysis carried out in this paper leads to the determination of the optimal use of zero vectors, i.e., the switching pattern leading to the minimum rms value of the load current ripple. The optimization of the switching pattern is based on the graphical analysis of the loci described by the ripple of the current vector in the alpha- beta reference frame. As a result, a set of analytical relationships that allow the online calculation of the duty cycles of the zero vectors is presented. Finally, simulation and experimental results confirm that the current ripple of the proposed modulation strategy is lower than that of traditional SVM strategies and, in some cases, with a reduced number of commutations.

Design and research on parameter of LCL filter in three-phase grid-connected inverter

Abstract: Since LCL filter has smaller inductance value comparing to L type filter with the same performance in harmonic suppression. it is gradually used in high-power and low-frequency current-source-controlled grid-connected converters. However design of LCL filter's parameter not only relates switch frequency ripple attenuation, but also impacts on performance of grid-connected current controller. This paper firstly introduced a harmonic model of LCL filter in grid-connected operation, then researched the variable relationship among LCL filter's parameter and resonance frequency and high-frequency ripple attenuation. Based on above analysis a reasonable design method was brought out in order to achieve optimal effect under the precondition of saving inductance magnetic core of LCL filter, at the same time guaranteeing the resonance frequency of LCL filter was not too small lest restrict current controller resign. Finally this design method was verified by the experimental results.

Chattering reduction using multiphase sliding mode control

Abstract: For the system with sliding mode controllers operated by on/off switches, ‘chattering’ appears in the output of the system when its switching frequency is restricted. In power systems, the switching frequency is commonly limited to prevent power losses, and chattering or ‘ripple’ appears especially in the system current. Common methods to decrease such ripple are based on ‘harmonic cancellation’ using the multiple number of phase channels having the desired phase shift that brings cancellation in the sum of outputs from the individual channels. In this article, a design principle of sliding mode control for a multiphase controller is proposed. The methodology is originated from the concept of multidimensional sliding mode and provides desired phase shifts between phases with the help of adaptive width for the hysteresis loops in switching elements. The chattering suppression effect is demonstrated by simulations for the DC–DC converter systems in various situations.

Predictive Direct Control Applied to AC Drives and Active Power Filter

Abstract: This paper presents different applications of a method called direct control. The previously developed approach has been redefined into a generalized form. The method relies on the prediction of either current or flux in discrete-time intervals and, consequently, selects the inverter voltage vector that produces the fastest possible transient. Depending on the task, two possible variants have been developed, offering a compromise between ripple in the controlled variable and switching frequency. A special effort has been made to overcome problems due to various delays (processing time, acquisition, gate driver delay, etc.) in the prediction routine, thus achieving maximum performance. The approach has been upgraded for application in AC drives, which allows additional torque control. The functional versatility of the approach has been demonstrated on different applications of power electronics (active power filter, induction machine, surface-mounted permanent-magnet synchronous machine). All applications have been tested on different laboratory models and have confirmed the validity of the approach.

Three-Mode Dual-Frequency Two-Edge Modulation Scheme for Four-Switch Buck–Boost Converter

Abstract: Four-switch buck-boost (FSBB) converter features low-voltage stress across the power switches and positive output voltage. They have two active power switches and two synchronous rectifiers, so two freedoms, i.e., the duty cycles of the two active switches, are available to regulate the output voltage. This paper proposes a two-edge modulation (TEM), in which the two active switches are trailing-edge and leading-edge modulated, respectively. Thus, the inductor current ripple can be reduced. Furthermore, a 3-mode TEM is derived to reduce the root-mean-square value of the inductor current to reduce the conduction loss. The line range is divided into three regions, and FSBB operates at boost, buck-boost, and buck modes in the lower, medium, and higher input voltage regions, respectively. At buck and boost modes, only two switches are high-frequency switched, so that the total switching loss is reduced. In the buck-boost mode, the inductor current ripple is very low compared with other two modes. Hence, the switching frequency is lowered to reduce the switching loss. The 3-mode TEM can achieve high efficiency over the line range, which is verified by a 48-V (36-75 V) input, 48-V @ 6.25-A output prototype. The measured efficiency is higher than 96.5% over the line range and the efficiency at the nominal input voltage is 97.8%.

A 82% efficiency 0.5% ripple 16-phase fully integrated capacitive voltage doubler

Abstract: A fully integrated voltage doubler is presented. Using a 16-phase switching strategy, the output voltage ripple is reduced to less then 0.5% of the output voltage. To the author's knowledge, the peak efficiency and nominal efficiency of this voltage doubler, respectively 82% and 79%, exceed the efficiency of any known fully integrated converter, inductive as well as capacitive. The converter is fabricated in a 130nm CMOS process.

High-efficiency module-integrated photovoltaic power conditioning system

Abstract: A module-integrated, photovoltaic (PV) power conditioning system with a high-efficiency, high step-up DC-DC converter is proposed. The step-up DC-DC converter employs an active-clamp circuit for soft switching of the power semiconductor switches. Also, a dual series-resonant rectifier is employed in order to remove the reverse-recovery problem of the output-rectifying diodes and to provide a much higher voltage conversion ratio. The PV current is estimated without using a DC current sensor, and the PV current ripple reduction technique is suggested to reduce the current ripple without an external component. A 1 kW prototype for the PV voltage range of 30-60 V is implemented, and all algorithms and controllers are implemented on a single-chip microcontroller. Experimental results show that the power efficiency is 92.5-94% and the ripple current is 3.5% of the rated input current.

Optimal Periodic Trajectories for Band-Limited Systems

Abstract: The speed of an electromechanical scanner is limited by its first resonance frequency. To maximize scan speed, input signals are required that contain negligible frequency components near, or above the first resonance frequency. Such signals are usually obtained by low-pass filtering the desired scan trajectory. However, this introduces curvature and ripple into linear (constant velocity) scan regions. In this work, input signals are designed with guaranteed linear regions and minimal harmonic components above a chosen frequency. The proposed scanning trajectories are proven by simulation and experiment to induce less vibration than existing techniques.

Digitally assisted quasi-V2 hysteretic buck converter with fixed frequency and without using large-ESR capacitor

Abstract: The rapid advancement of processor technology has posed stringent challenges on power supply design. For high efficiency, switching converters are used. Frequent load switching requires the converters to have fast load transient response with recovery times in the order of µs, and therefore the switching frequency in the MHz range [1]. The transient overshoot and undershoot voltages must be within 10% of the output voltage, and such specifications are difficult to meet for a processor core voltage of 0.8V. For fast load transient, inductor current should be fed forward to the PWM generator, which needs a high performance integrated current sensor. In the output feedforward (or V2) converter, inductor current is sensed by the equivalent series resistor (ESR) of the output capacitor instead. The generic implementation of a V2 buck converter is shown in Fig. 26.3.1 [2,3]. The output voltage, V o , is fed back to the error-correction path (ECP) for precision output voltage control, and V o is also directly fed to the PWM generator through the feedforward path (FFP). It is shown that the output voltage ripple, ΔV o , is dominated by ΔI l ×R ESR , and any change in V o requires the PWM generator to adjust the inductor current immediately, thus speeding up the response. However, to make sure that the V2 converter operates properly without pulse skipping, a large ESR is needed. To eliminate a large ESR, a derivative-output-voltage (DOV) technique is suggested in [3] to extract the inductor current ripple through differentiating V o . However, V o is a noisy node and is affected by frequent load changes, and therefore obtaining accurate current information is challenging.

A CMOS–MEMS RF-Tunable Bandpass Filter Based on Two High- $Q$ 22-MHz Polysilicon Clamped-Clamped Beam Resonators

Abstract: This letter presents the design, fabrication, and demonstration of a CMOS-MEMS filter based on two high-Q submicrometer-scale clamped-clamped beam resonators with resonance frequency around 22 MHz The MEMS resonators are fabricated with a 035-mum CMOS process and monolithically integrated with an on-chip differential amplifier The CMOS-MEMS resonator shows high-quality factors of 227 in air conditions and 4400 in a vacuum for a bias voltage of 5 V In air conditions, the CMOS-MEMS parallel filter presents a programmable bandwidth from 100 to 200 kHz with a <1-dB ripple In a vacuum, the filter presents a stop-band attenuation of 37 dB and a shape factor as low as 25 for a CMOS-compatible bias voltage of 5 V, demonstrating competitive performance compared with the state of the art of not fully integrated MEMS filters

Phase-Locked Loops using State Variable Feedback for Single-Phase Converter Systems

Abstract: A crucial component of a grid-connected converter system is the Phase-Locked Loop (PLL) that synchronizes the control to the grid voltage. Accurate, fast responding PLLs are required to provide phase angle and frequency measurements of the grid voltage for control and protection purposes. This paper proposes novel feedback mechanisms using the estimated frequency and phase in single-phase PLLs (in the stationary and rotating reference frames) which enhances performance. The estimated frequency ripple is eliminated without using low-pass filters (LPFs), and feedback terms are shown to improve the synchronization speed, by as much as 80% in some cases. Mathematical analyses, simulation, and hardware results are presented to verify the methods.

Comparison of active and passive damping methods for application in high power active power filter with LCL-filter

Abstract: LCL-type filter possessing sufficient attenuation ratio for switching ripple with small LC parameters is appropriate to be used as output filter to get high slew rate of compensation current. However, LCL-filter, as a three order resonant circuit itself, is difficult to be stable. This paper compares active and passive methods for LCL filter resonance damping; assesses their suitability for the high power active power filter application and presents their benefits and drawbacks. The results presented show that both methods compensate harmonics effectively and attenuate switching ripple sufficiently. However, there are still some differences both in the filtering performance and the power losses in the high power application. The active methods require more sensors and increase algorithm complexity, while additional damping resistors are needed in the passive methods and result in large losses. Simulation validates the feasibility of the method proposed by this paper.

Method and system for balancing receive-side supply load

Abstract: Described are digital communication systems that transmit and receive parallel sets of data symbols. Differences between successive sets of symbols induce changes in the current used to express the symbol sets, and thus introduce supply ripple. A receiver adds compensation current to reduce supply ripple. The compensation current is calculated based upon prior data samples rather than the current symbols, and consequently increases the maximum instantaneous current fluctuations between adjacent symbol sets as compared with circuits that do not include the compensation. The frequency response of the power-distribution network filters out the increased data dependence of the local supply current, however, and consequently reduces the fluctuations of total supply current. Some embodiments provide compensation currents for both transmitted and received symbols.