Showing papers on "Negative impedance converter published in 2014"
TL;DR: In this paper, a small-signal impedance modeling of grid-connected three-phase converters for wind and solar system stability analysis is presented, where a converter is modeled by a positive-sequence and a negative-sequence impedance directly in the phase domain.
Abstract: This paper presents small-signal impedance modeling of grid-connected three-phase converters for wind and solar system stability analysis. In the proposed approach, a converter is modeled by a positive-sequence and a negative-sequence impedance directly in the phase domain. It is further demonstrated that the two sequence subsystems are decoupled under most conditions and can be studied independently from each other. The proposed models are verified by experimental measurements and their applications are demonstrated in a system testbed.
765 citations
TL;DR: A novel high step-up converter, which is suitable for renewable energy system, is proposed in this paper, and the configuration of the proposed converter not only reduces the current stress but also constrains the input current ripple, which decreases the conduction losses and lengthens the lifetime of the input source.
Abstract: A novel high step-up converter, which is suitable for renewable energy system, is proposed in this paper. Through a voltage multiplier module composed of switched capacitors and coupled inductors, a conventional interleaved boost converter obtains high step-up gain without operating at extreme duty ratio. The configuration of the proposed converter not only reduces the current stress but also constrains the input current ripple, which decreases the conduction losses and lengthens the lifetime of the input source. In addition, due to the lossless passive clamp performance, leakage energy is recycled to the output terminal. Hence, large voltage spikes across the main switches are alleviated, and the efficiency is improved. Even the low voltage stress makes the low-voltage-rated MOSFETs be adopted for reductions of conduction losses and cost. Finally, the prototype circuit with 40-V input voltage, 380-V output, and 1000-W output power is operated to verify its performance. The highest efficiency is 97.1%.
281 citations
TL;DR: The proposed active-network converter with switched-capacitor technique can achieve high voltage gain without extremely high duty ratio and the voltage stress of the active switches and output diodes is low.
Abstract: The voltage gain of traditional boost converter is limited due to the high current ripple, high voltage stress across active switch and diode, and low efficiency associated with large duty ratio operation. High voltage gain is required in applications, such as the renewable energy power systems with low input voltage. A high step-up voltage gain active-network converter with switched-capacitor technique is proposed in this paper. The proposed converter can achieve high voltage gain without extremely high duty ratio. In addition, the voltage stress of the active switches and output diodes is low. Therefore, low voltage components can be adopted to reduce the conduction loss and cost. The operating principle and steady-state analysis are discussed in detail. A prototype with 20-40-V input voltage, 200-V output voltage, and 200-W output power has been established in the laboratory. Experimental results are given to verify the analysis and advantages of the proposed converter.
219 citations
TL;DR: Experimental evidence of effective negative capacitance is presented here at room temperature in engineered devices, where it is stabilized by the presence of a paraelectric material, enabling low power operation and reduced self-heating.
Abstract: Effective negative capacitance has been postulated in ferroelectrics because there is a hysteresis in plots of polarization-electric field. Compelling experimental evidence of effective negative capacitance is presented here at room temperature in engineered devices, where it is stabilized by the presence of a paraelectric material. In future integrated circuits, the incorporation of such negative capacitance into MOSFET gate stacks would reduce the subthreshold slope, enabling low power operation and reduced self-heating.
218 citations
TL;DR: In this article, a new class of active elastic metamaterials with negative capacitance piezoelectric shunting is presented, which can be used for band gap control of both the longitudinal and bending waves.
Abstract: Elastic metamaterials have been extensively investigated due to their significant effects on controlling propagation of elastic waves. One of the most interesting properties is the generation of band gaps, in which subwavelength elastic waves cannot propagate through. In the study, a new class of active elastic metamaterials with negative capacitance piezoelectric shunting is presented. We first investigated dispersion curves and band gap control of an active mass-in-mass lattice system. The unit cell of the mass-in-mass lattice system consists of the inner masses connected by active linear springs to represent negative capacitance piezoelectric shunting. It was demonstrated that the band gaps can be actively controlled and tuned by varying effective stiffness constant of the linear spring through appropriately selecting the value of negative capacitance. The promising application was then demonstrated in the active elastic metamaterial plate integrated with the negative capacitance shunted piezoelectric patches for band gap control of both the longitudinal and bending waves. It can be found that the location and the extent of the induced band gap of the elastic metamaterial can be effectively tuned by using shunted piezoelectric patch with different values of negative capacitance, especially for extremely low-frequency cases.
190 citations
TL;DR: This paper presents a fast cost-effective technique for the measurement of battery impedance online in an application such as an electric or hybrid vehicle, and develops a measurement system for impedance that, for the first time, uses an excitation current generated by a motor controller.
Abstract: This paper presents a fast cost-effective technique for the measurement of battery impedance online in an application such as an electric or hybrid vehicle. Impedance measurements on lithium-ion batteries between 1 Hz and 2 kHz give information about the electrochemical reactions within a cell, which relates to the state of charge (SOC), internal temperature, and state of health (SOH). We concentrate on the development of a measurement system for impedance that, for the first time, uses an excitation current generated by a motor controller. Using simple electronics to amplify and filter the voltage and current, we demonstrate accurate impedance measurements obtained with both multisine and noise excitation signals, achieving RMS magnitude measurement uncertainties between 1.9% and 5.8%, in comparison to a high-accuracy laboratory impedance analyzer. Achieving this requires calibration of the measurement circuits, including measurement of the inductance of the current sense resistor. A statistical correlation approach is used to extract the impedance information from the measured voltage and current signals in the presence of noise, allowing a wide range of excitation signals to be used. Finally, we also discuss the implementation challenges of an SOC estimation system based on impedance.
179 citations
TL;DR: In this article, a novel A-source impedance network is proposed, which uses an autotransformer for realizing converters for any application that demand a very high dc voltage gain, and it utilizes a minimal turns ratio compared to other magnetically coupled impedance source networks to attain a high voltage gain.
Abstract: A novel A-source impedance network is proposed in this letter. The A-source impedance network uses an autotransformer for realizing converters for any application that demand a very high dc voltage gain. The network utilizes a minimal turns ratio compared to other magnetically coupled impedance source networks to attain a high voltage gain. In addition, the proposed converter draws a continuous current from the source, and hence it is suitable for many types of renewable energy sources. The derived network expressions and theoretical analysis are finally validated experimentally with an example single-switch 400-W dc–dc converter. For the closed-loop control design and stability assessment, a small signal model and its analysis of the proposed network are also presented in brief.
179 citations
TL;DR: Through the control of the power converter and duty-cycle perturbation, the ac impedance of the battery can be determined and the obtained impedance data are utilized for online state-of-charge estimation of lithium-ion batteries.
Abstract: This paper presents a simple online impedance measurement method for electrochemical batteries, including lithium-ion, lead-acid, and nickel–metal-hydride chemistries By using the proposed online impedance measurement method, there is no need to disconnect the battery from the system or to interrupt system operation, and there is no need to add ac signal injection circuits, costly response measurement, and analysis circuits/devices In practical battery-powered systems, a power converter is usually used to interface the battery with the load for voltage/current regulation purposes In this paper, through the control of the power converter and duty-cycle perturbation, the ac impedance of the battery can be determined The proposed method provides a low-cost and practical solution for the online measurement of the ac impedance of batteries Moreover, the proposed method can be either continuously or periodically performed without interrupting the normal operation of the battery system and the power converter In addition, this paper provides an example where the obtained impedance data are utilized for online state-of-charge estimation of lithium-ion batteries The proposed online impedance measurement method is validated by experiments conducted on a 26-Ah 18650-size lithium-ion battery interfaced to the load via a bidirectional dc–dc boost/buck converter
172 citations
TL;DR: In this paper, a new quadratic boost converter was proposed for high voltage and high voltage gain applications, which employed only one active switch and two LC (inductor-capacitor) filters.
Abstract: A new quadratic boost converter is presented in this study. Compared with the conventional quadratic boost converter, the proposed converter has the feature of lower buffer capacitor voltage stress. This advantage is very valuable for high voltage and high-voltage gain applications. The proposed converter also employed only one active switch and two LC (inductor-capacitor) filters. Detailed analysis for its continuous current mode operation and discontinuous current mode operation both are presented. In addition, modelling for the proposed converter is also developed in this study. A prototype circuit is built and the experimental results confirm the feasibility and performance of the high step-up converter.
155 citations
TL;DR: In this paper, a three-port converter with high-voltage gain for stand-alone renewable power system applications is proposed, which uses only three switches to achieve the power flow control.
Abstract: In this paper, a novel three-port converter (TPC) with high-voltage gain for stand-alone renewable power system applications is proposed. This converter uses only three switches to achieve the power flow control. Two input sources share only one inductor. Thus, the volume can be reduced. Besides, the conversion ratio of the converter is higher than other TPCs. Thus, the degree of freedom of duty cycle is large. The converter can have a higher voltage gain for both low-voltage ports with a lower turns ratio and a reasonable duty ratio. The voltage stress of switches is low; thus, conduction loss can be further improved by adopting low Rds(on) switches. Therefore, the converter can achieve a high conversion ratio and high efficiency at the same time. The operation principles, steady-state analysis, and control method of the converter are presented and discussed. A prototype of the proposed converter with a low input voltage 24 V for photovoltaic source, a battery port voltage 48 V, and an output voltage 400 V is implemented to verify the theoretical analysis. The power flow control of the converter is also built and tested with a digital signal processor.
135 citations
TL;DR: Room-temperature demonstration of negative capacitance in a ferroelectric-dielectric superlattice heterostructure is an important step toward lowering the subthreshold swing in a transistor below the intrinsic thermodynamic limit of 60 mV/decade and thereby improving energy efficiency.
Abstract: We demonstrate room-temperature negative capacitance in a ferroelectric–dielectric superlattice heterostructure. In epitaxially grown superlattice of ferroelectric BSTO (Ba0.8Sr0.2TiO3) and dielectric LAO (LaAlO3), capacitance was found to be larger compared to the constituent LAO (dielectric) capacitance. This enhancement of capacitance in a series combination of two capacitors indicates that the ferroelectric was stabilized in a state of negative capacitance. Negative capacitance was observed for superlattices grown on three different substrates (SrTiO3 (001), DyScO3 (110), and GdScO3 (110)) covering a large range of substrate strain. This demonstrates the robustness of the effect as well as potential for controlling the negative capacitance effect using epitaxial strain. Room-temperature demonstration of negative capacitance is an important step toward lowering the subthreshold swing in a transistor below the intrinsic thermodynamic limit of 60 mV/decade and thereby improving energy efficiency.
TL;DR: The proposed converter topology possesses the low switch voltage stress characteristic, which will allow one to choose lower voltage rating MOSFETs to reduce both switching and conduction losses, and the overall efficiency is consequently improved.
Abstract: In this paper, a novel transformerless interleaved high step-down conversion ratio dc-dc converter with low switch voltage stress is proposed. In the proposed converter, two input capacitors are series-charged by the input voltage and parallel-discharged by a new two-phase interleaved buck converter for providing a much higher step-down conversion ratio without adopting an extreme short duty cycle. Based on the capacitive voltage division, the main objectives of the new voltage-divider circuit in the converter are for both storing energy in the blocking capacitors for increasing the step-down conversion ratio and reducing voltage stresses of active switches. As a result, the proposed converter topology possesses the low switch voltage stress characteristic. This will allow one to choose lower voltage rating MOSFETs to reduce both switching and conduction losses, and the overall efficiency is consequently improved. Moreover, due to the charge balance of the blocking capacitor, the converter features automatic uniform current sharing characteristic of the interleaved phases without adding extra circuitry or complex control methods. The operation principles and relevant analysis of the proposed converter are presented in this paper. Finally, a 400-V input voltage, 25-V output voltage, and 400-W output power prototype circuit is implemented in the laboratory to verify the performance.
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TL;DR: Analysis of this 'inductance'-like behaviour from a capacitor presents an unprecedented insight into the intrinsic energy profile of the ferroelectric material and could pave the way for completely new applications.
Abstract: The Boltzmann distribution of electrons poses a fundamental barrier to lowering energy dissipation in conventional electronics, often termed as Boltzmann Tyranny. Negative capacitance in ferroelectric materials, which stems from the stored energy of phase transition, could provide a solution, but a direct measurement of negative capacitance has so far been elusive. Here we report the observation of negative capacitance in a thin, epitaxial ferroelectric film. When a voltage pulse is applied, the voltage across the ferroelectric capacitor is found to be decreasing with time-in exactly the opposite direction to which voltage for a regular capacitor should change. Analysis of this inductance-like behavior from a capacitor presents an unprecedented insight into the intrinsic energy profile of the ferroelectric material and could pave the way for completely new applications.
TL;DR: A bidirectional isolated full-bridge dc-dc converter with a conversion ratio around nine times, soft start-up, and soft-switching features for battery charging/discharging is proposed in this paper.
Abstract: A bidirectional isolated full-bridge dc-dc converter with a conversion ratio around nine times, soft start-up, and soft-switching features for battery charging/discharging is proposed in this paper. The converter is equipped with an active flyback and two passive capacitor-diode snubbers, which can reduce voltage and current spikes and reduce voltage and current stresses, while it can achieve near zero-voltage-switching and zero-current-switching soft-switching features. In this paper, the operational principle of the proposed converter is first described, and its analysis and design are then presented. A 1.5-kW prototype with a low-side voltage of 48 V and a high-side voltage of 360 V has been implemented, from which measured results have verified the discussed features.
TL;DR: In this paper, a non-isolated DC-DC converter with high-voltage gain and lowvoltage stress across the semiconductors is proposed, which consists of n stages of diode-capacitor-indicator (D-C-L) units at the input side and m units of voltage multiplier cells (VMCs) at the output side.
Abstract: A non-isolated DC–DC converter with high-voltage gain and low-voltage stress across the semiconductors is proposed in this study. The proposed converter consists of n stages of diode–capacitor–inductor (D–C–L) units at the input side and m units of voltage multiplier cells (VMCs) at the output side. Increasing of D–C–L units and VMCs, lead to high-voltage gain at low duty cycle. Lower values of duty cycle will result in increasing of converter controllability and increasing of operation region. Also by increasing of VMCs, the voltage stress across the main switch and other semiconductors is reduced severely. Decreasing of voltage stress across the main switch leads to use a switch with lower R DS-ON that reduces on state losses of the proposed converter. Besides, by decreasing of voltage stress across the diode rectifiers, diodes with less forward voltage drop can be adopted. The circuit performance will be compared with other solutions that were previously proposed for voltage step-up in the terms of voltage gain, main switch voltage stress and number of components. Finally, a 357 V–65.5 W laboratory prototype with 92% conversion efficiency is built in order to prove the satisfying operation of the proposed converter and carried mathematical analysis.
ETSI1
TL;DR: In this paper, an improved minimum time control approach for multiphase buck converter that is based on charge balance technique, aiming at fast output voltage transition is presented, which takes into account the phase delay and current ripple in each phase.
Abstract: The combination of minimum time control and multiphase converter is a favorable option for dc-dc converters in applications where output voltage variation is required, such as RF amplifiers and dynamic voltage scaling in microprocessors, due to their advantage of fast dynamic response. In this paper, an improved minimum time control approach for multiphase buck converter that is based on charge balance technique, aiming at fast output voltage transition is presented. Compared with the traditional method, the proposed control takes into account the phase delay and current ripple in each phase. Therefore, by investigating the behavior of multiphase converter during voltage transition, it resolves the problem of current unbalance after the transient, which can lead to long settling time of the output voltage. The restriction of this control is that the output voltage that the converter can provide is related to the number of the phases, because only the duty cycles at which the multiphase converter has total ripple cancellation are used in this approach. The model of the proposed control is introduced, and the design constraints of the buck converter's filter for this control are discussed. In order to prove the concept, a four-phase buck converter is implemented and the experimental results that validate the proposed control method are presented. The application of this control to RF envelope tracking is also presented in this paper.
16 Mar 2014
TL;DR: In this article, a new Voltage Source Converter (VSC) for Medium Voltage (MV) applications is presented which can operate over a wide range of voltages (2.4kV-7.2KV) without the need for connecting power semiconductor in series.
Abstract: In this paper, a new Voltage Source Converter (VSC) for Medium Voltage (MV) applications is presented which can operate over a wide range of voltages (2.4kV-7.2KV) without the need for connecting power semiconductor in series. The operation of the proposed converter is studied and analysed. In order to control the proposed converter, a Space Vector Modulation (SVM) strategy which benefits from the switching state redundancy has been used. This strategy helps to control the output voltage and stabilize voltages of the flying capacitors in the proposed converter. Performance of the converter under different operating conditions is investigated in the MATLAB/Simulink environment.
18 May 2014
TL;DR: In this article, the stability of paralleled voltage source converters in AC distributed power systems is analyzed based on Nyquist diagrams drawn for the terminal impedance of each converter, and the effect of the right halfplane zeros of terminal impedances in the derivation of impedance ratio for paralleled source-source converters is avoided.
Abstract: This paper analyses the stability of paralleled voltage source converters in AC distributed power systems. An impedance-based stability analysis method is presented based on the Nyquist criterion for multiloop system. Instead of deriving the impedance ratio as usual, the system stability is assessed based on a series of Nyquist diagrams drawn for the terminal impedance of each converter. Thus, the effect of the right half-plane zeros of terminal impedances in the derivation of impedance ratio for paralleled source-source converters is avoided. The interaction between the terminal impedance of converter and the passive network can also be predicted by the Nyquist diagrams. This method is applied to evaluate the current and voltage controller interactions of converters in both grid-connected and islanded operations. Simulations and experimental results verify the effectiveness of theoretical analysis.
TL;DR: In this article, a high step-up dc-dc converter with high voltage gain and reduced switch stress is proposed, which uses the coupled inductor to replace the boost inductor.
Abstract: In this study, a novel high step-up dc–dc converter with high voltage gain and reduced switch stress is proposed. Utilising the coupled inductor to replace the boost inductor for high step-up converter is widely used in the application of high voltage gain converter. It can not only achieve a high voltage gain but also use the core effectively by using the coupled inductor. The techniques of voltage lift, voltage multiplier and clamp mode are also used in the proposed topology. Furthermore, the proposed converter can avoid the extreme duty cycle that will cause a lot of conduction losses. The leakage inductance energy of the coupled inductor will cause a huge voltage on the components of circuit, so that it needs to choose the components with high voltage and current ratings; then the efficiency is reduced and the cost is increased. The converter proposed in this paper can not only recycle the leakage inductance energy to the output but also increase the efficiency. A 300 W prototype converter which is implemented with an input voltage of 26 V and an output voltage of 400 V will demonstrate the effectiveness of this proposed converter.
TL;DR: In this paper, a Zig-Zag transformer was proposed to construct an artificial neutral point and keep voltage balance between the positive pole and the negative pole in an ungrounded modular multilevel converter (MMC) transmission system.
Abstract: An unbalance voltage between a positive pole and negative pole will exist for a long time in an ungrounded modular multilevel converter (MMC) HVDC transmission system. A zig-zag transformer has been proposed to construct an artificial neutral point and keep voltage balance between the positive pole and the negative pole. An efficient grounding system consists of the zig-zag transformer and the neutral grounding resistor. In this paper, the different impedances, including positive-, negative-, zero-sequence impedance, and dc current impedance, have been analyzed, respectively. Then, the computer simulations have been performed to evaluate the characteristic of the zig-zag transformer under normal voltage, zero-sequence voltage and unbalanced dc voltage, respectively. The simulation results show that 1) the zig-zag transformer can effectively balance the unbalanced voltage in dc side of the MMC under different work conditions; 2) the zero-sequence impedance is low and zero-sequence current is convenient for the detection of a single-phase fault; 3) the power consumption of the neutral grounding resistor is of a light rating, and the cooling of the resistor is unnecessary. The method presented in this paper proves to be an efficient grounding method for the MMC-HVDC transmission system.
TL;DR: In this article, a -10pF negative capacitor over a bandwidth of 10-150 MHz has been implemented for frequency independent fast-wave (FW) propagation in a microstrip line that is periodically loaded with non-Foster circuits.
Abstract: Frequency independent fast-wave (FW) propagation with phase velocity greater than the speed of light can be ideally realized in a dielectric medium whose relative permittivity is positive, but less than 1. Conventionally, FW propagation is implemented by non-TEM waveguides or antiresonance-based metamaterials, which suffers from the narrow bandwidth due to the dispersion. In contrast, non-Foster circuits provide a brand new method for reducing the dispersion so as to broaden the bandwidth. This paper demonstrates broadband FW propagation in a microstrip line that is periodically loaded with non-Foster circuits. Discrete transistor-based non-Foster circuits functioning as negative capacitors are successfully designed with the novel modified negative impedance converter circuits. A -10-pF negative capacitor over a bandwidth of 10-150 MHz has been implemented. The fabricated circuits have been integrated into a microstrip line to form a FW waveguide. The retrieved phase velocity of the effective medium from the measured S-parameters characterizes a stable and causal FW medium with constant phase velocity of 1.2c from 60 to 120 MHz, and this has been further verified by Kramers-Kronig relations and the near-field measurements along the waveguide. In conclusion, a stable, causal, and broadband FW waveguide has been achieved by means of transistor-based non-Foster circuits. The implemented broadband FW propagation can potentially be applied in broadband leaky-wave antennas and cloaking techniques.
TL;DR: A novel voltage-boosting converter is presented, which combines one charge pump and one coupled inductor with the turns ratio, and the corresponding voltage gain is greater than that of the existing step-up converter combining KY and buck-boost converters.
Abstract: In this paper, a novel voltage-boosting converter is presented, which combines one charge pump and one coupled inductor with the turns ratio. The corresponding voltage gain is greater than that of the existing step-up converter combining KY and buck-boost converters. Since the proposed converter possesses an output inductor, the output current is nonpulsating. After some mathematical deductions, an experimental setup with 12-V input voltage, 72-V output voltage, and 60-W output power is used to verify the effectiveness of the proposed converter.
TL;DR: In this paper, a non-isolated DC-DC converter with highvoltage gain and low-voltage stress on switches is proposed, where n stages of diode-capacitor-inductor (D-C-L) units are used at the input that results in higher voltage gains.
Abstract: A non-isolated DC-DC converter with high-voltage gain and low-voltage stress on switches is proposed in this study. For absorption of energy n stages of diode-capacitor-inductor (D-C-L) units are used at the input that results in higher voltage gains. Actually, the proposed converter generalises the voltage lift circuit and combines it with a voltage multiplier cell. Therefore comparing to structures with one stage of D-C-L unit, it will be feasible to achieve supposed voltage gain at lower duty cycles. Lower values of duty cycle will result in increasing of converter controllability and increasing of operation region. The generalised analysis of the voltage and current stresses of the semiconductors and power components is carried out. The circuit performance will be compared with other solutions that were previously proposed for voltage step-up in the terms of voltage gain, switch and output diode voltage stress and number of components. The carried mathematical analysis and circuit performance are validated through both simulation and experimental results that match each other reasonably well.
TL;DR: Using a ferroelectric PbZrTiO3 gate stack, the range of the steep subthreshold swing in tunnel field effect transistors was extended by 3.5 orders of magnitude demonstrating an improvement in the swing (by approximately double the slope) as mentioned in this paper.
Abstract: Using a ferroelectric PbZrTiO3 gate stack, the range of the steep subthreshold swing in tunnel field-effect transistors was extended by 3.5 orders of magnitude demonstrating an improvement in the swing (by approximately double the slope). The drain conductance (gd) shows only 16% enhancement with large V DS (∼−1.5V) indicates internal voltage amplification with ferroelectric negative capacitance effect beneficial to small lateral drain-source bias voltages (−0.1 V). The concept of coupling the ferroelectric polarization is proposed. The power consumption is also discussed in low-power applications of steep subthreshold slope devices.
TL;DR: The proposed converter has zero voltage switching (ZVS) in all its switches with fewer conduction losses than other ZVS-PWM full-bridge converters, due to a novel auxiliary circuit scheme.
Abstract: A new soft-switching pulse-width-modulated (PWM) full-bridge converter is proposed in this paper. The proposed converter has zero voltage switching (ZVS) in all its switches with fewer conduction losses than other ZVS-PWM full-bridge converters, due to a novel auxiliary circuit scheme. In this paper, the operation of the new converter is explained and analyzed, a design procedure is presented and demonstrated with an example, and experimental results that confirm the feasibility of the converter are also presented.
TL;DR: It is shown that by cascading a NEMS with a ferroelectric capacitor, operating in the negative capacitance regime, the effective airgap can be reduced by almost an order of magnitude, without the need to reduce the airgap physically.
Abstract: Nanoelectromechnical system (NEMS) is seen as one of the most promising candidates for next generation extreme low power electronics that can operate as a versatile switch/memory/sensor/display element. One of the main challenges toward this goal lies in the fabrication difficulties of ultrascaled NEMS required for high density integrated circuits. It is generally understood that fabricating and operating a NEMS with an airgap below a few nanometer will be extremely challenging due to surface roughness, nonideal forces, tunneling, etc. Here, we show that by cascading a NEMS with a ferroelectric capacitor, operating in the negative capacitance regime, the effective airgap can be reduced by almost an order of magnitude, without the need to reduce the airgap physically. This would not only reduce the pull-in voltage to sub-1 V regime, but also would offer a set of characteristics which are difficult/impossible to achieve otherwise. For example, one can reduce/increase the classical travel range, flip the traditional stable-unstable regime of the electrode, get a negative pull-out voltage, and thus, center the hysteresis around zero volt. Moreover, one can also operate the combination as an effective ferroelectric memory with much reduced switching voltages. These characteristics promise dramatic saving in power for NEMS-based switching, memory, and other related applications.
TL;DR: In this paper, a single switch isolated step-up converter is presented, which is derived from the traditional flyback converter and charge pump concept, and the proposed converter possesses an output inductor, so the output current is non-pulsating.
Abstract: In this study, a single switch isolated step-up converter is presented, which is derived from the traditional flyback converter and charge pump concept. The proposed converter possesses an output inductor, so the output current is non-pulsating. Moreover, there are several advantages of the proposed converter over the traditional flyback converter, such as higher voltage conversion ratio with only additional four passive elements, and smaller voltage and current ripples, except the same switch voltage stress. In this study, some experimental results are provided to verify the effectiveness of the proposed converter.
27 Jul 2014
TL;DR: In this article, the authors discuss a selection of control aspects that are important for negative sequence current injection: negative sequence angle detection, converter current limitation, and voltage recovery after fault clearing.
Abstract: State-of-the-art distributed generation with a fully rated converter only injects positive sequence current into unbalanced faults. Recently, both publications and draft standards have suggested that the injection of negative sequence reactive current into unbalanced faults can have benefits for the power system. This paper discusses a selection of control aspects that are important for negative sequence current injection: negative sequence angle detection, converter current limitation, and voltage recovery after fault clearing. The impact of these control aspects, and negative sequence current injection in general, on the power system is also considered in the discussion.
TL;DR: In this article, a novel Z-source half-bridge converter is presented, in which less LC components are needed compared to the conventional one, which can solve not only the problems of the shoot-through and limited voltage but also the problem of imbalance at the midpoint voltage of input capacitors.
Abstract: Applying an LC network into a half-bridge converter, a novel Z-source half-bridge converter is presented, in which less LC components are needed compared to the conventional one. This Z-source half-bridge converter can solve not only the problems of the shoot-through and limited voltage but also the problem of imbalance at the midpoint voltage of input capacitors. Furthermore, it can generate a broader range of output voltage values and much more kinds of waveforms, such as the varied positive or negative output voltages and the varied time ratio between positive and negative voltages, which are particularly desirable for some special power supplies, like the electrochemical power supply. Finally, the proposed converter is implemented in a prototype, and the experimental results can verify the effectiveness of the proposed converter.
TL;DR: In this article, a hybrid dual full-bridge dc-dc converter for radio frequency (RF) power generator application is proposed to overcome the drawbacks of a conventional phase-shift fullbridge (PSFB) converter such as the large circulating current of the primary side and large output filter size.
Abstract: In this paper, a hybrid dual full-bridge dc-dc converter for radio frequency (RF) power generator application is proposed to overcome the drawbacks of a conventional phase-shift full-bridge (PSFB) converter such as the large circulating current of the primary side and large output filter size. The proposed converter adopts a dual full-bridge hybrid structure with a small series capacitor in the primary side and a full-bridge rectifier with two additional low-voltage-rated diodes in the secondary side. With this structure, the proposed converter has advantages of reduction of circulating current, zero-voltage switching (ZVS) operation of all primary switches, size reduction of the output inductor, and low conduction loss of the rectifier stage. Furthermore, the proposed converter can regulate the output voltage very wide by changing the operational mode according to the output voltage. These advantages result in the improvement of whole load efficiency. The operational principle and analysis of the proposed converter are presented and analyzed. A 3-kW 40-200-V output laboratory prototype is designed and built to verify the feasibility and the effectiveness of the proposed converter.