Showing papers on "Negative impedance converter published in 2011"

Ferroelectric negative capacitance MOSFET: Capacitance tuning & antiferroelectric operation

Abstract: A design methodology of ferroelectric (FE) negative capacitance FETs (NCFETs) based on the concept of capacitance matching is presented. A new mode of NCFET operation, called the “antiferroelectric mode” is proposed, which, besides achieving sub-60mV/dec subthreshold swing, can significantly boost the on-current in exchange for a nominal hysteresis. Design considerations for different device parameters (FE thickness, EOT, source/drain overlap & gate length) are explored. It is suggested that relative improvement in device performance due to FE negative capacitance becomes more significant in very short channel length devices because of the increased drain-to-channel coupling.

Experimental evidence of ferroelectric negative capacitance in nanoscale heterostructures

Abstract: We report a proof-of-concept demonstration of negative capacitance effect in a nanoscale ferroelectric-dielectric heterostructure. In a bilayer of ferroelectric Pb(Zr0.2Ti0.8)O3 and dielectric SrTiO3, the composite capacitance was observed to be larger than the constituent SrTiO3 capacitance, indicating an effective negative capacitance of the constituent Pb(Zr0.2Ti0.8)O3 layer. Temperature is shown to be an effective tuning parameter for the ferroelectric negative capacitance and the degree of capacitance enhancement in the heterostructure. Landau’s mean field theory based calculations show qualitative agreement with observed effects. This work underpins the possibility that by replacing gate oxides by ferroelectrics in nanoscale transistors, the sub threshold slope can be lowered below the classical limit (60 mV/decade).

A New Topology of Cascaded Multilevel Converters With Reduced Number of Components for High-Voltage Applications

Abstract: In this paper, a new topology of a cascaded multilevel converter is proposed. The proposed topology is based on a cascaded connection of single-phase submultilevel converter units and full-bridge converters. Compared to the conventional multilevel converter, the number of dc voltage sources, switches, installation area, and converter cost is significantly reduced as the number of voltage steps increases. In order to calculate the magnitudes of the required dc voltage sources, three methods are proposed. Then, the structure of the proposed topology is optimized in order to utilize a minimum number of switches and dc voltage sources, and produce a high number of output voltage steps. The operation and performance of the proposed multilevel converter is verified by simulation results and compared with experimental results of a single-phase 49-level converter, too.

An Isolated DC/DC Converter Using High-Frequency Unregulated $LLC$ Resonant Converter for Fuel Cell Applications

Abstract: This paper suggests an isolated dc/dc converter using an unregulated LLC converter for fuel cell applications. The LLC converter operates as an isolated voltage amplifier with a constant voltage gain, and a nonisolated converter installed in the input stage regulates the output voltage under a wide variation of fuel cell stack voltage. By separating the functions, the unregulated LLC converter can be operated at an optimal switching condition, and the high-frequency operation of 300 kHz can be accomplished without introducing an excessive switching loss. The prototype converter with a 1-kW design (Vin = 24 ~ 48 V/Vo = 400 V) shows an efficiency of above 90.2% under a 24-V input and full load conditions.

Novel High Step-Up DC–DC Converter With Coupled-Inductor and Voltage-Doubler Circuits

Abstract: In this paper, a novel high step-up dc-dc converter with coupled-inductor and voltage-doubler circuits is proposed. The converter achieves high step-up voltage gain with appropriate duty ratio and low voltage stress on the power switches. Also, the energy stored in the leakage inductor of the coupled inductor can be recycled to the output. The operating principles and the steady-state analyses of the proposed converter are discussed in detail. Finally, a prototype circuit of the proposed converter is implemented in the laboratory to verify the performance of the proposed converter.

Novel High Step-Up DC–DC Converter With Coupled-Inductor and Switched-Capacitor Techniques for a Sustainable Energy System

Abstract: In this paper, a novel high step-up dc-dc converter is proposed for a sustainable energy system. The proposed converter uses coupled-inductor and switched-capacitor techniques. The capacitors are charged in parallel and discharged in series by the coupled inductor to achieve high step-up voltage gain with an appropriate duty ratio. Besides, the voltage stress on the main switch is reduced with a passive clamp circuit; low on-state resistance Rds(on) of the main switch can be adopted to reduce the conduction loss. In addition, the reverse-recovery problem of the diode is alleviated by a coupled inductor. Thus, the efficiency can be further improved. The operating principle and steady-state analyses of voltage gain are discussed in detail. Finally, a prototype circuit with 24-V input voltage, 400-V output voltage, and 200-W output power is implemented in the laboratory to verify the performance of the proposed converter.

Hybrid Flying-Capacitor-Based Active-Neutral-Point-Clamped Five-Level Converter Operated With SHE-PWM

Abstract: A five-level flying-capacitor (FC)-based active-neutral-point-clamped (ANPC) converter is an arrangement of a three-level ANPC converter and a two-level cell. In this paper, a control strategy is proposed to regulate the voltage across the FCs at their respective reference voltage levels by swapping the switching patterns of the switches based on the polarity of the output current, the polarity of the FC voltage, and the polarity of the fundamental line-to-neutral voltage under selective harmonic elimination pulsewidth modulation. The voltage across the FCs and the dc-link capacitors are simultaneously controlled at their reference voltage levels. The proposed control strategy is applied using power system computer aided design/electromagnetic transients including dc on a static synchronous compensator operating under a power-factor-correction mode to verify its performance. Experimental results are also presented for low and high number of angles per quarter period using a low-power laboratory prototype.

Nonisolated High Step-Up Stacked Converter Based on Boost-Integrated Isolated Converter

Abstract: To obtain a high step-up gain with high efficiency in nonisolated applications, a high step-up technique based on isolated-type converters is introduced in this paper. By stacking the secondary side of an isolated converter in addition to its primary side, a high step-up conversion ratio and a distributed voltage stress can be achieved. Moreover, a careful choice of an isolated converter can provide zero-voltage switching, continuous input current, and reduced reverse recovery on diodes. Based on a conventional voltage-doubler-rectifier boost-integrated half-bridge converter, the derived converter satisfies all these features, which make it suitable for high step-up applications. The operational principle and characteristics of the proposed converter are presented, and verified experimentally with a 135-W, 24-V input, 250-V output prototype converter for a LED driver.

Analysis, design and experimental results of a floating-output interleaved-input boost-derived DC-DC high-gain transformer-less converter

Abstract: In transformer-less energy systems sourced from low and unregulated voltage generated by a fuel cell or photovoltaic source, the voltage gain of the power electronic conditioning stage is required to be as high as possible. Although component parasitic elements limit the practically realisable voltage gain of any converter topology, this becomes a critical issue in the case of the basic step-up converter. In this study, a high-gain interleaved boost-derived converter topology is discussed. The proposed converter topology offers modularity, lower ripple for both input current and output voltage, and lower voltage and current ratings of the various circuit elements when compared to the basic boost converter. Analysis, design and key converter waveforms operating in the continuous conduction mode are provided along with design guidelines. Experimental results taken from a 1 kW laboratory prototype operating at 60 kHz are presented to confirm the validity of the analysis and design considerations.

The origin of anomalous peak and negative capacitance in the forward bias capacitance-voltage characteristics of Au/PVA/n-Si structures

Abstract: The frequency dependence of capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of the Au/polyvinyl alcohol (Ni, Zn-doped)/n-Si Schottky barrier diodes (SBDs) was investigated in the frequency range of 3 kHz-3 MHz at room temperature by considering series resistance (Rs) and interface states (Nss) effects. The C-V and G/ω-V characteristics confirm that the Rs and Nss are important parameters that strongly influence the electrical parameters of SBDs. The C-V plots show an intersection point (∼2.9 V) at low frequencies (f ≤ 30 kHz) and then take negative values, which is known as negative capacitance (NC) behavior. The negativity of the C increases with the decreasing frequency in the forward bias voltage region, and this decrement in the NC corresponds to the increment in the conductance. Also, the forward bias C-V plots show an anomalous peak in the voltage range of 1.55–1.9 V depending on the frequency such that the anomalous peaks shift toward positive voltage values with the incre...

Current sensing apparatus and method for a capacitance- sensing device

Abstract: A capacitance-sensing device including a current-to-voltage converter and an analog-to-digital converter is described. A sense element is coupled to an input of the current-to-voltage converter. The current-to-voltage converter is configured to convert current changes in the coupled sense element to an output voltage and to maintain a constant voltage at the input. The analog-to-digital converter is configured to convert the output voltage generated by the current-to-voltage converter to a digital value.

Control of a Doubly Fed Induction Generator via an Indirect Matrix Converter With Changing DC Voltage

Abstract: This paper presents a control strategy for a doubly fed induction generator (DFIG) using an indirect matrix converter, which consists of an input side matrix converter and an output side voltage source converter (VSC). The capability of the input converter to generate different “virtual dc link” voltage levels is exploited. The commutation of the VSI with reduced voltage is illustrated for operating points where the output voltage demand is low without any deterioration of the current control performance. The proposed method leads to a reduction in the commutation losses in the output converter and reduced common-mode voltage. For the input converter, soft switching commutation is obtained by synchronizing the input and output converter pulsewidth-modulation patterns. This modulation strategy is particularly applicable in DFIG applications because the required rotor voltage decreases when the DFIG speed is close to the synchronous speed. The complete control strategy is experimentally validated using a 2-kW rig.

Series Voltage Compensation for DFIG Wind Turbine Low-Voltage Ride-Through Solution

Abstract: This paper introduces a new solution for doubly fed induction generators to stay connected to the grid during voltage sags. The main idea is to increase the stator voltage to a level that creates the required flux to keep the rotor side converter current below its transient rating. To accomplish this goal, a series compensator is added to inject voltage in series to the stator side line. The series converter monitors the grid voltage and provides compensation accordingly to accomplish this aim. Since the turbine and converter stay connected, the synchronization of operation remains established during and after the fault and normal operation can be resumed immediately after the fault is cleared. To keep the current at its minimum, a control strategy has been developed to keep the injected voltage and line voltage in phase during and after the fault.

Examination of the Possibility of Negative Capacitance Using Ferroelectric Materials in Solid State Electronic Devices

Abstract: We show here, using fundamental energy storage relationships for capacitors, that there are severe constraints upon what can be realized utilizing ferroelectric materials as FET dielectrics. A basic equation governing all small signal behavior is derived, a negative capacitance quality factor is defined based upon it, and thousands of carefully measured devices are evaluated. We show that no instance of negative capacitance occurs within our huge database. Furthermore, we demonstrate that highly nonlinear biasing behavior in a series stack could be misinterpreted as giving a negative capacitance.

Application of a Negative Capacitance Circuit in Synchronized Switch Damping Techniques for Vibration Suppression

Abstract: In the synchronized switching damping (SSD) techniques, the voltage on the piezoelectric element is switched synchronously with the vibration to be controlled using an inductive shunt circuit (SSDI). The inherent capacitance and the inductance in the shunt circuit comprise an electrically resonant circuit. In this study a negative capacitance is used in the shunt circuit instead of an inductance in the traditional SSD technique. The voltage on the piezoelectric element can be effectively inverted though the equivalent circuit is capacitive and no resonance occurs. In order to investigate the principle of the new SSD method based on a negative capacitance (SSDNC), the variation of the voltage on the piezoelectric element and the current in the circuit is analyzed. Furthermore, the damping effect using the SSDNC is deduced, and the energy balance and stability of the new system are investigated analytically. The method is applied to the single mode control and two-mode control of a composite beam, and its control performance was confirmed by the experimental results. For the first mode in single mode control, the SSDNC is much more effective than SSDI. In other cases, the SSDNC is also more effective than the SSDI, although not significantly.

A Bidirectional Multilevel Boost–Buck DC–DC Converter

Abstract: A novel noninverting boost-buck dc-dc converter topology is presented, applicable when both sides of the converter need to have the same grounding. It is based on the back-to-back connection of two n-level active-clamped or diode-clamped converter legs, and allows bidirectional power flow. A simplified topology is proposed for unidirectional power flow applications. Two new pulse width modulation strategies with different advantages are proposed to operate the converter guaranteeing dc-link capacitor voltage balance in every switching cycle for all possible operating conditions and using small capacitance values. The semiconductor device losses are compared through analysis, simulation, and experiments to the losses in a conventional two-level boost-buck converter. The analysis yields a higher efficiency for the multilevel converter, especially as the number of levels increases. Experimental results are presented to validate the good converter performance in four- and five-level converter prototypes.

A variable series resistance mechanism to explain the negative capacitance observed in impedance spectroscopy measurements of nanostructured solar cells.

Abstract: A simple model for conductivity modulation in a recombination diode is discussed to explain the observation of negative capacitance at forward bias observed in many optoelectronic devices. We formulate the basic recombination-modulation model in terms of an equivalent circuit for small ac perturbation and discuss the application of the results in measurements of impedance spectroscopy of dye-sensitized solar cells, organic solar cells and related systems.

Band gap control of phononic beam with negative capacitance piezoelectric shunt

Abstract: Periodic arrays of negative capacitance shunted piezoelectric patches are employed to control the band gaps of phononic beams. The location and the extent of induced band gap depend on the mismatch in impedance generated by each patch. The total impedance mismatch is determined by the added mass and stiffness of each patch as well as the shunting electrical impedance. Therefore, the band gap of the shunted phononic beam can be actively tuned by appropriately selecting the value of negative capacitance. The control of the band gap of phononic beam with negative capacitive shunt is demonstrated numerically by employing transfer matrix method. The result reveals that using negative capacitive shunt to tune the band gap is effective.

Control method for single-phase grid-connected lcl inverter

Abstract: A method of controlling the grid-side current of a single-phase grid-connected converter having an LCL filter connected between the output of the converter and the grid includes measuring a grid voltage and at least one signal in a group of signals consisting of a grid-side current, a converter-side current and a capacitor voltage, estimating the fundamental component of the grid voltage, forming a grid-side current reference, a converter-side current reference and a capacitor voltage reference for the grid-side current of the LCL filter, forming estimates for the non-measured signals in the group of signals, forming a grid-side current difference term, a converter-side current difference term and a capacitor voltage difference term, and controlling the output voltage of the converter based on the grid voltage, a formed injection term and a formed estimate of the harmonic distortion term to produce a grid side current corresponding to the current reference.

Voltage generator circuit, digital-to-analog converter, ramp generator circuit, analog-to-digital converter, image sensor system, and method for generating voltage

Abstract: A resistor-ladder voltage generator circuit is provided, which controls so that k switches among consecutive (k+1) switches out of a plurality of switches connected to the resistor ladder circuit are simultaneously set to an ON state, and which temporally switches the value of k. This allows voltage waveforms having different slopes to be arbitrarily obtained, ranging from a voltage waveform having a small slope to a voltage waveform having a large slope, thereby improving the resolution of a generated voltage waveform without increasing the numbers of resistors and switches, while A/D conversion time is not increased even if the number of bits is increased. In addition, by using this voltage generator circuit as a ramp generator circuit, and by dynamically switching the slope of the ramp wave, acceleration of an image sensor is achieved.

Zero voltage switching in flyback converters with variable input voltages

Abstract: The disclosed embodiments provide a system that operates a flyback converter. During operation, the system senses an input voltage for the flyback converter. Next, the system uses the input voltage to determine a negative peak current that enables zero voltage switching for a primary switch in the flyback converter. Finally, the system uses the negative peak current to perform the zero voltage switching for the primary switch based on the input voltage, wherein the negative peak current reduces a power loss of the flyback converter.

Step-up converter combining KY and buck-boost converters

Abstract: A step-up converter is presented, which combines the KY converter and the traditional buck-boost converter. By doing so, the limitations on voltage conversion ratio of the KY converter, up to two, can be improved. Aside from this, such a converter possesses a non-pulsating output current, thereby not only decreasing current stress on the output capacitor but also reducing output voltage ripple.

Circuit topology for pulsed power energy harvesting

Abstract: An energy harvesting circuit harvests energy from a voltage source and charges a storage element with the harvested energy. The energy harvesting circuit includes an energy source, a storage capacitor to store energy output from the energy source, a power converter circuit, an energy storage element, and an enabling circuit. The enabling circuit turns the boost converter circuit on and off according to a monitored capacitance voltage of the storage capacitor. When the boost converter circuit is turned off, the storage capacitor accumulates energy output from the energy source until a reference voltage is reached, whereupon the boost converter circuit is turned on, enabling current flow from the storage capacitor to the storage element. When the storage capacitor discharges to a minimum voltage level, the boost converter circuit is turned off. The enabling circuit and a reference voltage supply are powered by the energy source.

Family of zero-voltage transition pulse width modulation converters with low auxiliary switch voltage stress

Abstract: A new family of zero-voltage transition (ZVT) pulse width modulation (PWM) converters is introduced. In this converter family there is no additional voltage stress on the main switch in comparison to the hard switching counterpart. Also, the voltage and current rating of the auxiliary switch is low. The proposed zero-voltage transition PWM buck converter is analysed and design considerations are discussed. A prototype converter is implemented and the experimental results are presented.

Low-voltage high-performance current mirrors: Application to linear voltage-to-current converter

Abstract: Current mirror is one of the basic building blocks of analog VLSI systems. For high-performance analog circuit applications, the accuracy and bandwidth are the most important parameters to determine the performance of the current mirror. This paper presents an efficient implementation of a CMOS current mirror suitable for low-voltage applications. This circuit combines a shunt input feedback, a regulated cascade output and a differential amplifier to achieve low input resistance, high accuracy and high output resistance. A comparison of several architectures of this scheme based on different architectures of the amplifier is presented. The comparison includes: input impedance, output impedance, accuracy, frequency response and settling time response. These circuits are validated with simulation in 0.18µm CMOS TSMC of MOSIS. In this paper, a linear voltage to current converter, based on the adapted current mirror, is proposed. Its static and dynamic behaviour is presented and validated with the same technology. Copyright © 2009 John Wiley & Sons, Ltd.

Thermal control of solid state light sources by variable series impedance

Abstract: A thermal protection circuit, and system and method including same, is provided. The circuit includes a variable impedance circuit configured to be coupled to a constant current source and a plurality of solid state light sources. The constant current source provides a current to the plurality of solid state light sources and provides an output voltage to establish a supply voltage for the circuit. The circuit also includes a temperature sensor configured to sense a temperature of the plurality of solid state light sources. The circuit also includes a control circuit configured to receive the supply voltage and to drive the variable impedance circuit based on the sensed temperature, to adjust the current to the plurality of solid state light sources when the supply voltage is a least a minimum supply voltage of the control circuit.

Controlling a bidirectional dc-to-dc converter

Abstract: A system and method for regulating power flow and limiting inductor current in a bidirectional direct current (DC)-to-DC converter is provided In one aspect, a feedback circuit is provided to control power flow and/or limit inductor current based on the input/output voltage and/or current conditions in the bidirectional DC-DC converter During a boost mode of operation, the duty cycle of a low-side switch within the bidirectional DC-DC converter is reduced, based on an analysis of the high-side voltage and positive inductor current Further, during a buck mode of operation, the duty cycle of the low-side switch is increased, based on an analysis of the low-side voltage and negative inductor current Moreover, the duty cycle of the low-side switch is adjusted, such that, the high-side voltage, low-side voltage and inductor current (in both directions) do not exceed preset threshold and the bidirectional DC-DC converter returns to a steady state