Showing papers on "Negative impedance converter published in 2009"

Three-Port Series-Resonant DC–DC Converter to Interface Renewable Energy Sources With Bidirectional Load and Energy Storage Ports

Abstract: In this paper, a three-port converter with three active full bridges, two series-resonant tanks, and a three-winding transformer is proposed. It uses a single power conversion stage with high-frequency link to control power flow between batteries, load, and a renewable source such as fuel cell. The converter has capabilities of bidirectional power flow in the battery and the load port. Use of series-resonance aids in high switching frequency operation with realizable component values when compared to existing three-port converter with only inductors. The converter has high efficiency due to soft-switching operation in all three bridges. Steady-state analysis of the converter is presented to determine the power flow equations, tank currents, and soft-switching region. Dynamic analysis is performed to design a closed-loop controller that will regulate the load-side port voltage and source-side port current. Design procedure for the three-port converter is explained and experimental results of a laboratory prototype are presented.

An Analytical Investigation of DC/DC Power Electronic Converters With Constant Power Loads in Vehicular Power Systems

Abstract: Stability of multi-converter power systems, which exist in advanced more electric vehicles, is of great importance. The stability issue is investigated in this paper, and design considerations and limitations of the methods that stabilize the open-loop converters are presented. By stabilizing the open-loop converter, it is shown that the feedback loop design is usually translated into a conventional feedback design task. The behavior of the unstable converter is also discussed, and a method for decreasing the amplitude of the output voltage oscillations is proposed. The model of a tightly regulated practical converter is presented. This model is used to decide how much damping should be added to make the feeder converter stable. Furthermore, because we have this information about the load converter, the feeder converter can be redesigned so that it does not see the load converter as a constant power load.

Two Types of KY Buck–Boost Converters

Abstract: A novel voltage-bucking/boosting converter, named as KY buck-boost converter (i.e., 2D converter), is presented herein. Unlike the traditional buck-boost converter, this converter possesses fast transient responses, similar to the behavior of the buck converter with synchronous rectification. In addition, it possesses the non-pulsating output current, thereby not only decreasing the current stress on the output capacitor but also reducing the output voltage ripple. Furthermore, it has the positive output voltage, different from the negative output voltage of the traditional buck-boost converter. Above all, there are two types of KY buck-boost converters presented herein. In this paper, the basic operating principles of the proposed converters are first illustrated in detail, and second, some experimental results are offered to verify the effectiveness of the proposed topologies.

A Single-Inductor Step-Up DC-DC Switching Converter With Bipolar Outputs for Active Matrix OLED Mobile Display Panels

Abstract: A single-inductor step-up DC-DC switching converter with bipolar outputs is implemented for active-matrix OLED mobile display panels. The positive output voltage is regulated by a boost operation with a modified comparator control (MCC), and the negative output voltage is regulated by a charge-pump operation with a proportional-integral (PI) control. The proposed adaptive current-sensing technique successfully supports the implementation of the proposed converter topology and enables the converter to work in both discontinuous-conduction mode (DCM) and continuous-conduction mode (CCM). In addition, with the MCC method, the converter can guarantee a positive output voltage that has both a fast transient response of the comparator control and a small output voltage ripple of the PWM control. A 4.1 mm2 converter IC fabricated in a 0.5 mum power BiCMOS process operates at a switching frequency of 1 MHz with a maximum efficiency of 82.3% at an output power of 330 mW.

Analysis and Design of a Modular Three-Phase AC-to-DC Converter Using CUK Rectifier Module With Nearly Unity Power Factor and Fast Dynamic Response

Abstract: In this paper, the analysis and design of a modular three-phase AC-to-DC converter using single-phase isolated Cuk rectifier modules is discussed based on power balance control technique. This paper analyzes the operation of a modular converter as continuous-conduction-mode power factor correction (CCM-PFC). Design equations, as well as an average small-signal model of the proposed system to aid the control loop design are derived. It is used to obtain the inductor current compensator, thus the output impedance and audio susceptibility become zero, and therefore, the output voltage of the converter presented in this paper is independent of the variations of the dc load current and the utility voltage. The control strategy consists of a single output voltage loop and three-inductor current calculator. The main objective of the proposed system is to reduce the number of stages and improve dynamic response of DC bus voltage for distributed power system. The proposed scheme offers simple control strategy, flexibility in three-phase delta or star-connected, simpler design, fast transient response, good inductor current sharing, and power factor closed to unity. Both simulation and experimental results are presented. They are in agreement with the theoretical analysis and experimental work.

Negative capacitance in light-emitting devices

Abstract: The negative capacitance behavior in light-emitting diodes and laser diodes has been observed and characterized by using ac admittance–voltage method. Experimental results proved that the strong negative capacitance behavior is always accompanied by remarkable light emission. We confirmed that the negative capacitance is an effect of the junction instead of other behavior or measurement error. We presented a numerical calculation by solving one dimension continuity equation based on a simple diode model. The results show that the negative capacitance behavior in light-emitting diodes has great relation to injected carriers recombination in the active region of luminescence.

Renewable Energy Systems Instability Involving Grid-Parallel Inverters

Abstract: This paper presents a study of renewable energy system stability based on impedance models of the sources and the grid. The focus is grid-parallel inverters controlled in the current injection mode. System stability analysis based on source output impedance and load input impedance is generalized to current-source systems. Output impedance modeling of current-controlled PWM inverters for grid interface of renewable sources is presented to provide the necessary impedance models for system stability analysis. The effects of current control loop design and output filter configurations on the inverter output impedance are considered. A practical method to measure grid impedance using a frequency analyzer is presented, and the associated difficulties due to the presence of harmonics in the grid voltage are discussed. An example system involving a single-phase grid-connected inverter is presented to demonstrate the application of the proposed system analysis method.

Three-Level AC–DC–AC Z-Source Converter Using Reduced Passive Component Count

Abstract: This paper presents a three-level AC-DC-AC Z-source converter with output voltage buck-boost capability. The converter is implemented by connecting a low-cost front-end diode rectifier to a neutral-point-clamped inverter through a single X-shaped LC impedance network. The inverter is controlled to switch with a three-level output voltage, where the middle neutral potential is uniquely tapped from the star-point of a wye-connected capacitive filter placed before the front-end diode rectifier for input current filtering. Through careful control, the resulting converter can produce the correct volt-second average at its output, while simultaneously achieving inductive voltage boosting by shooting through either an appropriately selected inverter phase-leg or two phase-legs being commanded simultaneously. More interestingly, these performance features are achieved with no increase in the number of semiconductor commutations, and hence, no increase in switching losses. The proposed converter therefore offers a low-cost alternative to applications that need to ride through frequent input voltage sags. For confirming the converter performance, experimental testing using a constructed laboratory prototype is performed with its captured results presented in a later section of the paper.

An Improved AC–DC Single-Stage Full-Bridge Converter With Reduced DC Bus Voltage

Abstract: A new ac-dc single-stage voltage-fed pulsewidth-modulation (PWM) full-bridge converter is proposed in this paper. The converter can simultaneously perform input power factor correction and dc-dc conversion using conventional phase-shift PWM and can maintain a primary-side dc bus voltage of less than 450 V even at a high input line voltage of 265 Vrms. This is a combination of features that few, if any, other converters of the same type have. The proposed converter has these features due to the novel implementation of an asymmetrical auxiliary transformer winding that is placed in series with the input inductor and acts as a boost switch. In this paper, the operation of the proposed converter is explained in detail, its outstanding features are discussed, and a detailed design procedure is given and demonstrated with an example. Experimental results that confirm the feasibility of the converter and its ability to meet IEC1000-3-2 Class D standards for electrical equipment are also presented in this paper.

Single-Stage Single-Switch Switched-Capacitor Buck/Buck-Boost-Type Converter

Abstract: A new dc-dc converter featuring a steep step-down of the input voltage is presented. It answers a typical need for on-board aeronautics modern power architectures: power supplies with a large conversion ratio able to deliver an output voltage of 1-1.2 V. The proposed structure is derived from a switched-capacitor circuit integrated with a buck converter; they share the same active switch. The proposed solution removes the electromagnetic interference (EMI) emission due to the large di/dt in the input current of the switched-capacitor power supplies. Compared with a quadratic buck converter, it presents a similar complexity, a smaller reduction in the line voltage at full load (but less conduction losses due to smaller input inductor current and capacitor voltage), lower voltage stresses on the transistor and diodes, lower current stresses in the diodes, and smaller size inductors. A similar structure using a buck-boost converter as the second stage is also presented. The experimental results confirm the theoretical developments.

Converter with active fault current limitation

Abstract: A voltage source converter (20) for high voltage DC power transmission that is connectable, in use, between a DC network (22) and another electrical network (24) to interconnect the DC network (22) and the other electrical network (24). The voltage source converter (20) comprises a converter unit (26) to convert power flowing between the DC network (22) and the other electrical network (24) and at least one fault unit (28). The or each fault unit (28) includes at least one fault module (30) having a voltage source (36) that is operable, in the event of a short circuit in a DC network (22) connected to the voltage source converter (20), to produce a voltage that acts to reduce current flowing through the voltage source converter (20) and the short circuit.

Step-up dc/dc voltage converter with improved transient current capability

Abstract: A DC/DC voltage converter includes an inductive switching voltage regulator and a capacitive charge pump connected in series between the input and output terminals of the converter. The charge pump has a second input terminal connected to the input terminal of the converter. This reduces the series resistance in the current path by which charge is transferred from the capacitor in the charge pump to the output capacitor and thereby improves the ability of the converter to respond to rapid changes in current required by the load.

General mechanism for negative capacitance phenomena

Abstract: Received 4 June 2009; revised manuscript received 25 August 2009; published 20 October 2009 The existence of a negative static dielectric constant has drawn a great deal of theoretical controversy. Experimentally, one has never been observed. However, low-frequency negative capacitance has been widely reported in fields including physics, chemistry, biology, geology, and electronics. This wide variety of systems possesses an extremely diverse set of physical processes that, surprisingly, share similar characteristics. We present a general mechanism that unites the various instances of negative capacitance under a common framework. The mechanism demonstrates that the negative capacitance arises from dc/ac signal mixing across a nonlinear conductor. Verification of the model is performed in physically distinct samples: an electrorheological fluid, a fuel cell, and a solar cell. Furthermore, we argue that the negative capacitance, under appropriate conditions, can be associated with a negative-differential dielectric constant, possibly even in the static limit.

Dc bus voltage harmonics reduction

Abstract: In one aspect, in general, the invention features a control system configured for use with a three-phase PWM converter. The control system receives an input signal from a three-phase power supply and provides an output signal at a DC link. A voltage-separating module generates on the basis of the input signal a positive sequence voltage component and a negative sequence voltage component in a rotating reference frame. A reference current computation module uses at least the positive sequence voltage component and the negative sequence voltage component to compute a first reference current and a second reference current. A current regulating module uses at least the first reference current and the second reference current to generate a command signal. The command signal is provided to a driving circuit of the three-phase PWM converter for generating a regulated DC bus voltage at the DC link.

A novel integrated three-phase, switched multi-winding power electronic transformer converter for wind power generation system

Abstract: In this paper, a novel wind power generation system is proposed which uses an intermediate high frequency (few kHz) ac link for power conversion. The high frequency ac link is achieved by using a reduced switch-count three-phase power electronic transformer (PET). There are two primary windings and one secondary winding in each phase of the PET. The primary windings are coupled in exact phase opposition. A 3×3 matrix converter is used to convert the high frequency secondary voltage to the desired low frequency voltage to be applied at the generator terminals. Two modulation modes as a part of the PWM of the matrix converter are described. In the first mode of operation, the common-mode voltage is eliminated at the generator terminals however, the output voltage transfer ratio of the matrix converter is limited to 0.75. The other modulation mode has higher output voltage transfer ratio equal to 0.866 with finite high-frequency common-mode voltage at the generator terminals. A method for smooth transition between the two modes of operation is described.

Eddy-Current Displacement Transducer With Extended Linear Range and Automatic Tuning

Abstract: Design details and measurement results of the eddy-current displacement transducer with extended linear range and automatic tuning are presented. The transducer is based on a resonant impedance inversion method of transfer curve linearization where the displacement probe circuit is kept in resonance by the resonance control loop. The transducer exhibits an extended linear range due to the compensation of displacement probe losses by a negative impedance converter (NIC) at the transducer input. Particular attention is paid to the NIC design and its temperature compensation. The new voltage-controlled NIC circuit is introduced, which can easily be realized with a standard commercial integrated circuit (LM 1496). Details of the transducer's reference generator and the NIC control voltage generator are also presented. The transducer's linear range extends from 0.25 to 3.75 mm (approximately 44% of the 8-mm probe diameter) while maintaining nonlinearity within plusmn2% F.S. This result is, at least, a 75% improvement to the best commercially available eddy-current displacement transducers (a linear range of 80 mil ~2 mm for an 8-mm probe). Further linearization can be achieved by postlinearization of the detected signal.

A novel control strategy of power converter used to direct driven permanent magnet wind power generation system

Abstract: This paper presents a novel control strategy of power converter used to direct-drive permanent magnet wind power system. The system consists of permanent magnet synchronous generator (PMSG), the generator side converter and the grid side converter. The voltage space vector PWM in field-oriented control is adopted in the control of the generator side converter. Both outer speed loop and inner current loop is implemented by a novel antiwindup PI controller. By means of the field-oriented control, the highest efficiency of wind turbine can be reached. The wind turbine is controlled to work at optimal tip speed ratio and to capture maximum wind energy. The control principle of grid-side converter was designed on the basis of the grid-side voltage oriented vector control. The outer voltage loop which is adopted fuzzy logic control method is used to keep DC-link voltage constant. And unit power factor gird connected inverter is realized, and current of grid-side is controlled to sine value by the control of inner current loop. Simulation and experiment results show that the controllers can regulate the voltage and frequency, extract maximum power under varying wind, and the novel control strategy has very good dynamic and steady-state performances.

Control of Venturini Method Based Matrix Converter in Input Voltage Variations

Abstract: Matrix converter is a single-stage converter which directly connects a three-phase voltage source to a three-phase load without dc-link components Therefore, any harmonic distortion and imbalance in input voltage directly reflect to the output of the converter Recently, many researchers have made an effort to cope with this problem In this paper, under distorted input voltage conditions, behaviors of the MC controlled with Venturini method are analyzed and a PI controller based compensation method to prevent negative effects of input voltage is proposed Since the proposed method is based on closed loop control of the output currents, it not only reduces the output harmonic contents but also ensures a stable control of the load currents Some results are presented to prove the effectiveness of the proposed compensation technique

A self-adaptive switched-capacitor voltage converter with dynamic input load control for energy harvesting

Abstract: This paper presents an implementation of a fully-integrated switched capacitor voltage converter with self-adjusting source loading. A charge control unit ensures improved load matching to the power source, which can be an RFID antenna or vibration energy harvesting generator. In conjunction with an adaptive stacking scheme voltage-up conversion is also realized leading to capacitor storage voltages which are higher than the generator voltage amplitudes. This and the improved load matching result in a higher generator output power. In addition, due to the switched capacitor charge pump no diode for rectification is necessary. The converter design is completely implemented and fully-integrated in a standard 0.35 µm twin-well CMOS process. Generator powers of up to 780 µW can be treated, and maximum conversion efficiency is close to 48%. Input voltage amplitudes are possible between 0.5 V – 2.5 V , while the supply voltage range is 0.9 V – 3.6 V.

Simplified maximum power point control utilizing the pv array voltage at the maximum power point

Abstract: A converter system adapted to be connected between a photovoltaic power source and a load comprises a converter circuit, a control circuit, and a PWM generator circuit. The converter circuit is operatively connected to transfer energy from the photovoltaic power source to the load. The control circuit generates a raw control signal based on at least a voltage generated by the photovoltaic power source. The PWM generator circuit is operatively connected to the converter circuit and generates a PWM switch signal based on the raw control signal. The converter circuit transfers energy from the photovoltaic power source to the load based on the PWM switch signal.

Perturb voltage as a decreasing non-linear function of converter power

Abstract: Methods, apparatus and media for controlling a switching circuit controlling an amount of power drawn from an energy converter, to optimize the amount of power drawn from the energy converter. An output voltage and an output current of the energy converter are measured to produce signals representing converter output voltage and current. Converter power is calculated from the product of the converter output voltage and current. A perturb voltage is calculated as a decreasing nonlinear function of the converter power. A new reference voltage signal representing a desired converter output voltage is produced in response to a previous reference voltage signal and the perturb voltage. The reference voltage signal is used by the switching circuit to adjust the power drawn from the converter to achieve the desired converter output voltage.

Novel interleaved ZVS converter with ripple current cancellation

Abstract: This paper presents a zero voltage switching (ZVS) converter with interleaved pulse-width modulation scheme. An active clamp circuit is adopted in the proposed converter to recycle the energy stored in the leakage inductor of the transformer and reduce the voltage stress of the main power switch in the converter. The ZVS feature of switches can be achieved due to the resonance during the transition interval of two power switches. Two full-wave rectifiers with ripple current cancellation are connected in parallel at the output side to reduce the current stress of the secondary winding of transformers. Instead of the conventional interleaved forward converter, power switches in the proposed converter can perform the functions of both forward converter and active clamp at the same time. Therefore, the circuit components in the power circuit are less than that of in the conventional interleaved forward converter. The operation principle and system analysis of the proposed converter are provided. Some experimental results for a 240 W (12 V-20 A) prototype are provided to demonstrate the effectiveness of the proposed converter. Copyright © 2008 John Wiley & Sons, Ltd.

Power supply apparatus and semiconductor integrated circuit device

Abstract: The present invention is directed to largely improve the efficiency at the time of light load of a power supply apparatus using a power factor correction (PFC) controller. A PFC controller is provided with a voltage-current converter. The voltage-current converter converts voltage of a signal output from an error amplifier for detecting voltage level of output voltage to an arbitrary current value and outputs the current value as a correction current. The voltage-current converter outputs a correction current of a large current value when the error amplifier detects that the load is light, and the PFC controller performs control to decrease the output voltage.

PFC converter having two-level output voltage without voltage undershooting

Abstract: A switching controller for a PFC converter is provided. The switching controller comprises a switching-control circuit, a current-command circuit, a programmable feedback circuit, a modulator, an over-voltage detection circuit, and a light-load detection circuit. The switching controller is capable of regulating a bulk voltage of the PFC converter at different levels in response to load conditions of the PFC converter. A turbo current eliminates a first voltage undershooting of the bulk voltage at the transient that the bulk voltage decreases to arrive at a second level from a first level. A voltage-loop error signal is maximized to eliminate a second voltage undershooting of the bulk voltage at the transient that the bulk voltage starts to increase toward the first level from the second level.

Apparatus for lighting LEDs

Abstract: An apparatus for lighting LEDs includes an LED group load having the LEDs, a converter to generate a voltage applied to the LED group load, a current controller to control a current of the LED group load, a voltage controller to control an output voltage provided by the converter, a time division circuit to intermittently pass a current through the LED group load, and a selector. The selector, during a period in which the time division circuit passes a current through the LED group load, selects the current controller to control a current of the LED group load and thereby control an output voltage provided by the converter, and during a period in which the time division circuit passes no current through the LED group load, selects the voltage controller to control an output voltage provided by the converter.

Evaluating Voltage Notch Problems Arising from AC/DC Converter Operation

Abstract: This paper analyzes the voltage notches in ac/dc converters and the problems that they create. Voltage notch disturbs the voltage's waveform and excites the natural frequencies of the system. In some systems, these excisions create considerable high-frequency oscillations in the voltages of the converter and the adjacent buses; this can damage capacitor banks, create parallel resonance, and generate radio disturbances. This paper analyzes the effect of snubber circuits on the voltage oscillations that arise from commutation. It also presents the theoretical foundation and analytical derivation that are used to calculate notch depth and the frequency of oscillations. To achieve accurate and applicable results, various loads of the converter, the dc current ripple, and the characteristic impedance of the system are considered. Several experimental results are shown in order to illustrate the effects of changes in the system and converter parameters on the voltage waveform of the converter. Computer simulations and experimental results indicate the accuracy of the theoretical relations. The proposed equations make it possible to effectively study the harmonic and power quality in networks that include high-power converters.

Self-adjusting switched-capacitor converter with multiple target voltages and target voltage ratios

Abstract: A method for constructing a direct-current to direct current (DC-DC) converter from an input voltage to an output voltage. The DC-DC converter has multiple capacitors and multiple switches connectible the capacitors. A target voltage ratio is obtained based on the input voltage and the output voltage. The target voltage is expressed as a radix number. The radix number is spawned into a code of the target voltage ratio. The code is translated into a switched-capacitor converter (SCC) configuration including the switches and the capacitors. The code may be an extended binary representation code or a Generic Fractional Numbers code. The switched-capacitor converter (SCC) configuration is preferably modified to obtain charge balance.

A DC-DC buck converter chip with integrated PWM/PFM hybrid-mode control circuit

Abstract: This paper proposes a DC-DC buck power converter chip with a novel integrated PWM/PFM hybrid-mode control The DC-DC converter chip with synchronous rectifier not only uses current-mode feedback control but also possesses constant-frequency-mode control and hybrid-mode control functions at the same time Furthermore, the operational modes of the converter can be selected by an external voltage signal In the part of constant-frequency-mode control, as the inductor current is below zero, the synchronous rectifier switch of the converter will be automatically turned off in order to reduce the loss of the reverse inductor current About the hybrid-mode control, the operational modes of the converter can be judged by the proposed PWM/PFM hybrid-mode control circuit When the converter is operated in CCM, the constant-frequency-mode control is applied and when the inductor current is in DCM, the converter is operated under the variable-frequency-mode control At this moment, the switching frequency of the converter is designed to decrease proportionally with the load to reduce the high switching loss at light load The synchronous rectifier switch will also be turned off in order to reduce the reverse conduction loss All the above functions are integrated in one chip Simulation and experimental results verify that the converter chip works functionally The power converter chip with PWM/PFM hybrid-mode control proposed here is very suitable for the portable electronic products with the requirements of low voltage, low power, high efficiency, and wide load range

Dc-dc converter and method for minimizing battery peak pulse loading

Abstract: The invention relates to an electronic device, comprising a DC-DC converter for converting a primary supply voltage into an output voltage at an output node to be coupled to a super capacitor and a control stage for operating the regulated DC-DC converter in a forward direction in a boost mode providing a boost voltage level at the output node and for operating the regulated DC-DC converter in a reverse direction in a buck mode providing a buck voltage level at an auxiliary node arranged between a primary voltage supply providing the primary supply voltage and the output node, wherein the control stage is adapted to control the DC-DC converter when operating in reverse direction to provide a current to the auxiliary node using the super capacitor as a power source.