Showing papers on "Output impedance published in 2006"

Wireless-Control Strategy for Parallel Operation of Distributed-Generation Inverters

Abstract: In this paper, a method for the parallel operation of inverters in an ac-distributed system is proposed. This paper explores the control of active and reactive power flow through the analysis of the output impedance of the inverters and its impact on the power sharing. As a result, adaptive virtual output impedance is proposed in order to achieve a proper reactive power sharing, regardless of the line-impedance unbalances. A soft-start operation is also included, avoiding the initial current peak, which results in a seamless hot-swap operation. Active power sharing is achieved by adjusting the frequency in load transient situations only, owing to which the proposed method obtains a constant steady-state frequency and amplitude. As opposed to the conventional droop method, the transient response can be modified by acting on the main control parameters. Linear and nonlinear loads can be properly shared due to the addition of a current harmonic loop in the control strategy. Experimental results are presented from a two-6-kVA parallel-connected inverter system, showing the feasibility of the proposed approach

Analysis and Optimization of Switched-Capacitor DC-DC Converters

Abstract: Analysis methods are developed that fully determine a switched-capacitor (SC) DC-DC converter's steady-state performance through evaluation of its output impedance. The simple formulation developed permits optimization of the capacitor sizes to meet a constraint such as a total capacitance or total energy storage limit, and also permits optimization of the switch sizes subject to constraints on total switch conductances or total switch volt-ampere (V-A) products. These optimizations then permit comparison among the switched-capacitor topologies, and comparisons of SC converters with conventional magnetic-based DC-DC converter circuits, in the context of various application settings. Significantly, the performance (based on conduction loss) of a ladder-type converter is found to be superior to that of a conventional boost converter for medium to high conversion ratios

A Series Elastic- and Bowden-Cable-Based Actuation System for Use as Torque Actuator in Exoskeleton-Type Robots

Abstract: Within the context of impedance controlled exoskeletons, common actuators have important drawbacks. Either the actuators are heavy, have a complex structure or are poor torque sources, due to gearing or heavy nonlinearity. Considering our application, an impedance controlled gait rehabilitation robot for treadmill-training, we designed an actuation system that might avoid these drawbacks. It combines a lightweight joint and a simple structure with adequate torque source quality. It consists of a servomotor, a flexible Bowden cable transmission, and a force feedback loop based on a series elastic element. A basic model was developed that is shown to describe the basic dynamics of the actuator well enough for design purpose. Further measurements show that performance is sufficient for use in a gait rehabilitation robot. The demanded force tracking bandwidths were met: 11 Hz bandwidth for the full force range (demanded 4 Hz) and 20 Hz bandwidth for smaller force range (demanded 12 Hz). The mechanical output impedance of the actuator could be reduced to hardly perceptible level. Maxima of about 0.7 Nm peaks for 4 Hz imposed motions appeared, corresponding to less than 2.5% of the maximal force output. These peaks were caused by the stick friction in the Bowden cables. Spring stiffness variation showed that both a too stiff and a too compliant spring can worsen performance. A stiff spring reduces the maximum allowable controller gain. The relatively low control gain then causes a larger effect of stick in the force output, resulting in a less smooth output in general. Low spring stiffness, on the other side, decreases the performance of the system, because saturation will occur sooner.

Current mode quadrature oscillator using current differencing transconductance amplifiers (CDTA)

Abstract: A CDTA-based quadrature oscillator circuit is proposed. The circuit employs two current-mode allpass sections in a loop, and provides high-frequency sinusoidal oscillations in quadrature at high impedance output terminals of the CDTAs. The circuit has no floating capacitors, which is advantageous from the integrated circuit manufacturing point of view. Moreover, the oscillation frequency of this configuration can be made adjustable by using voltage controlled elements (MOSFETs), since the resistors in the circuit are either grounded or virtually grounded.

Characterization and performance comparison of ripple-based control for voltage regulator modules

Abstract: Three recently developed control methods for voltage regulator modules, namely, V/sup 2/ control, enhanced V/sup 2/ control, and enhanced V/sup 2/ control without output voltage dynamic feedback, are analyzed and compared in this paper. All three methods utilize the output voltage switching ripple for pulse-width modulation (PWM), hence, are collectively referred to as ripple-based control. A general modeling method based on the Krylov-Bogoliubov-Mitropolsky ripple estimation technique is applied to develop averaged models for single-channel as well as multichannel buck converters employing each of the control methods. Unlike existing models that are limited to small-signal operation, the proposed models are valid for large-signal operation and are capable of predicting subharmonic instability without including any sample-and-hold block as used in previous models. The paper also shows that adding parallel, high-quality ceramic capacitors at the output, which are ignored in previous models, can lead to pulse skipping and ripple instability, and a solution based on proper selection of the ceramic capacitors and/or ramp compensation at the PWM is presented. The models are further applied to analyze and compare the performance of the three control methods in terms of ripple stability, effective load current feedforward gain, and output impedance.

Sliding-mode control for dc-dc converters with constant switching frequency

Abstract: A new approach implementing the sliding-mode controller is proposed for dc-dc converters. The equivalent control input is used as the system control input, which results in a duty cycle regulation control system. As designed, equivalent control input is maintained at a value between 0 and 1, similar to the desired duty cycle value. Thus, constant switching frequency can be achieved under changes of state conditions. Two sliding-mode controllers based on this method are designed for positive output elementary Luo converter. Traditional small-signal analysis is applied to study the close-loop system performance under proposed approach. Audio-susceptibility, control-to-output transfer functions and output impedance are derived on the basis of the small-signal model. It is shown that the proposed sliding-mode control approach retains the advantages of traditional sliding-mode control, as well as achieve constant switching frequency, which is decided by the input saw-tooth waveform. Results of the experiment are reported for both controllers and they verify the theoretical analysis.

Electrode surface treatment and electrochemical impedance spectroscopy study on carbon/carbon supercapacitors

Abstract: Power improvement in supercapacitors is mainly related to lowering the internal impedance The real part of the impedance at a given frequency is called ESR (equivalent series resistance) Several contributions are included in the ESR: the electrolyte resistance (including the separator), the active material resistance (with both ionic and electronic parts) and the active material/current collector interface resistance The first two contributions have been intensively described and studied by many authors The first part of this paper is focused on the use of surface treatments as a way to decrease the active material/current collector impedance Al current collector foils have been treated following a two-step procedure: electrochemical etching and sol-gel coating by a highly-covering, conducting carbonaceous material It aims to increase the Al foil/active material surface contact leading to lower resistance In a second part, carbon-carbon supercapacitor impedance is discussed in term of complex capacitance and complex power from electrochemical impedance spectroscopy data This representation permits extraction of a relaxation time constant that provides important information on supercapacitor behaviour The influence of carbon nanotubes addition on electrochemical performance of carbon/carbon supercapacitors has also been studied by electrochemical impedance spectroscopy

Low-power programmable gain CMOS distributed LNA

Abstract: A design methodology for low power MOS distributed amplifiers (DAs) is presented. The bias point of the MOS devices is optimized so that the DA can be used as a low-noise amplifier (LNA) in broadband applications. A prototype 9-mW LNA with programmable gain was implemented in a 0.18-/spl mu/m CMOS process. The LNA provides a flat gain, S/sub 21/, of 8 /spl plusmn/ 0.6dB from DC to 6.2 GHz, with an input impedance match, S/sub 11/, of -16 dB and an output impedance match, S/sub 22/, of -10 dB over the entire band. The 3-dB bandwidth of the distributed amplifier is 7GHz, the IIP3 is +3 dBm, and the noise figure ranges from 4.2 to 6.2 dB. The gain is programmable from -10 dB to +8 dB while gain flatness and matching are maintained.

Self-tuning radio frequency identification antenna system

Abstract: A self-tuning antenna that automatically adjusts its input impedance to compensate for externally induced impedance variations is provided. A variable impedance is adjusted by a control circuit to reconfigure the input impedance of than antenna to compensate for different environmental situations and different transponder mismatch situations. A negative-feedback signal is employed to determine or infer impedance mismatches and reconfigure the antenna input impedance (e.g., capacitance and/or resistance) until a desired equilibrium of the antenna input impedance is reached. A reference measurement (e.g., VSWR measurement) is automatically performed by an antenna tuning circuit that adjusts the antenna's impedance matching circuit to compensate for object interference. The antenna's impedance matching circuit includes a variable capacitor circuit having a plurality of individually controlled parallel plate capacitors that can be added or removed from the variable capacitor circuit, as necessary.

First-order allpass filter and sinusoidal oscillators using DDCCs

Abstract: A voltage-mode first-order allpass filter using one differential difference current conveyor (DDCC), one grounded capacitor and one floating resistor is presented. No passive component matching constraints are required. Because the output impedance of the proposed allpass filter is low, the output terminal can be directly connected to the next stage. Using the proposed first-order allpass filter as a basic building block, a new quadrature oscillator and even-phase sinusoidal oscillators can be obtained. The simulation results confirm the theoretical analysis.

Integrated load impedance sensing for tunable matching networks

Abstract: An impedance matching system may be used, for example, for impedance matching between a transmitter/receiver front-end and an antenna in a mobile communication device. In a tunable impedance matching system according to the invention a tunable impedance matching circuit (508) is used also as a measuring circuit for obtaining a value of load impedance. A real part and an imaginary part of a load impedance (503) is calculated based on voltages measured on nodes of the tunable impedance matching circuit and on known component values of the tunable impedance matching circuit. Values for adjustable electrical components (504, 505) of the tunable impedance matching circuit are determined based on the obtained load impedance value and on an impedance matching condition.

Current-mode variable-frequency control architecture for high-current low-voltage DC–DC converters [Letters]

Abstract: For controlling high-current low-voltage dc–dc converters, the control methods with variable switching frequency have the potential to achieve fast transient response and high efficiency. However, some issues in practical design limit the usefulness of the conventional variable-frequency control methods, such as the voltage-mode hysteretic control. This letter presents a novel implementation of current-mode variable-frequency control. The system architecture features a dual-loop feedback and a unique structure with symmetric signal paths for voltage and current signals. The symmetric structure provides practical advantages for integrated controller design to achieve accurate control on the droop resistance (or the load-line resistance). The system dynamics are analyzed with the small-signal model. Design guidelines are derived for simple compensation circuits to achieve constant output impedance. With variable switching frequency, the system achieves good dynamic response without requiring high switching frequency at steady-state. The system performance was verified by a two-channel interleaved controller chip implemented with CMOS technology.

Decentralized Control for Parallel Operation of Distributed Generation Inverters in Microgrids Using Resistive Output Impedance

Abstract: In this paper, a novel wireless load-sharing controller for islanding parallel inverters in an ac-distributed system is proposed. The paper explores the resistive output impedance of the parallel-connected inverters in an island microgrid. The control loops are devised and analyzed taking into account the special nature of a low voltage microgrid, in which the line impedance is mainly resistive and the distance between the inverters makes the control intercommunication between them difficult. In contrast with the conventional droop control method, the proposed controller uses resistive output impedance, and as a result a different control law is obtained. The controller is implemented by using a DSP board, which only uses local measurements of the unit, thus increasing the modularity, reliability, and flexibility of the distributed system. Experimental results are provided from two 6 kVA inverters connected in parallel, showing the features of the proposed wireless control.

High frequency cautery electric power source device

Abstract: A high frequency cautery electric power source (1), which is set in a processing device, applies high frequency electric power to processing electrodes when excision is started under electrically conductive liquid. When an output impedance detected at its application time is lower than a set value, a variable direct current power source circuit (HVPS) is set to a constant current control mode, so that high frequency electric power including an instantaneously high voltage value is intermittently applied to start discharge while output current is limited to the fixed. When the output impedance becomes or is higher than the set value, a constant voltage control mode is set, so that power with predetermined voltage is supplied and the cautery treatment is carried out by means of high frequency current suitable for subject living body.

A 90-nm CMOS Doherty power amplifier with minimum AM-PM distortion

Abstract: A linear Doherty amplifier is presented. The design reduces AM-PM distortion by optimizing the device-size ratio of the carrier and peak amplifiers to cancel each other's phase variation. Consequently, this design achieves both good linearity and high backed-off efficiency associated with the Doherty technique, making it suitable for systems with large peak-to-average power ratio (WLAN, WiMAX, etc.). The fully integrated design has on-chip quadrature hybrid coupler, impedance transformer, and output matching networks. The experimental 90-nm CMOS prototype operating at 3.65 GHz achieves 12.5% power-added efficiency (PAE) at 6 dB back-off, while exceeding IEEE 802.11a -25 dB error vector magnitude (EVM) linearity requirement (using 1.55-V supply). A 28.9 dBm maximum Psat is achieved with 39% PAE (using 1.85-V supply). The active die area is 1.2 mm/sup 2/.

Adaptive two-loop Voltage-mode control of DC-DC switching converters

Abstract: A new two-loop control scheme for voltage-mode control (VMC) of dc-dc switching converters is presented. The proposed method adds a high-gain robust loop with two controllers to the conventional VMC loop, achieving an analog "adaptive" loop in which the "equivalent voltage regulator" varies with the changing power stage parameters given as follows: 1) input voltage; 2) load; and 3) component tolerances. The loop significantly improves the disturbance rejection of the control system, i.e., closed-loop output impedance and audiosusceptibility while preserving the stability and the loop gain crossover frequency to a significant extent. Both the small-signal analysis and the experimental results carried out on a buck converter demonstrate the superiority of the proposed scheme with respect to the conventional single loop.

Method and device for measuring internal impedance of stationary battery

Abstract: Battery system is widely used in emergent power plant or communication network power plant and its effective management is important. When any one of batteries connected to each other in series is failed during operation of the battery system, since reliability of the system cannot be secured, a problem is arisen to stable operation of the communication network. In a method of separating inferior battery, the battery is operated in floating charge state without separation to generate square current containing charge current and easily generated to flow through the battery cell, voltage signal generated from terminal voltage of the battery by the measuring signal is processed such that only internal impedance voltage signal is separated from harmonics ripple voltage and noise voltage by a synchronized detection calculating algorithm to calculate the internal impedance or effective value thereof (resistance component). When the algorithm is applied after filtering only fundamental frequency and similar component by general filter, measuring precision can be improved and measuring time can be reduced.

High output impedance current-mode first-order allpass networks with four grounded components and two CCIIs

Abstract: Eight current-mode first-order allpass networks using second-generation current conveyors (CCII) are presented. Each of the proposed circuits employs two CCIIs, two grounded capacitors and two grounded resistors. The networks offer high output impedances. Experimental results are also included.

System and method for dynamic impedance tuning to minimize return loss

Abstract: A system for tuning an impedance at a node comprises a first component associated with a first impedance when the first component is operating and a second impedance when the first component is not operating. The system further comprises a second component coupled to the first component at a node. The second component is associated with a third impedance when the second component is operating and a fourth impedance when the second component is not operating. An impedance tuning circuit is coupled to the second component at the node and operable to tune an impedance at the node based at least in part upon a plurality of the first impedance, the second impedance, the third impedance, and the fourth impedance.

Semiconductor memory device with MOS transistors each having floating gate and control gate and method of controlling the same

Abstract: A semiconductor memory device includes memory cells, a memory cell array, a first voltage generating circuit, a reference voltage generating circuit, and a first voltage control circuit. Each of the memory cells includes a first MOS transistor comprising a floating gate and a control gate formed on the floating gate. The memory cell array includes the memory cells arranged in a matrix. The first voltage generating circuit generates a first positive voltage. The reference voltage generating circuit generates a first reference voltage. The first voltage control circuit sets the first positive voltage at a voltage value based on the first reference voltage and outputs a resulting second positive voltage. An output impedance of the first voltage control circuit varies depending on the number of bits into which data is simultaneously written. The second positive voltage is used to write and erase data into and from the memory cells.

Output buffer with switchable output impedance

Abstract: An output buffer with a switchable output impedance designed for driving a terminated signal line. The buffer includes a drive circuit, and a means for switching the output impedance of the drive circuit between a first, relatively low output impedance when the output buffer is operated in a ‘normal’ mode, and a second output impedance which is greater than the first output impedance when operated in a ‘standby’ mode. By increasing the drive circuit's output impedance while in ‘standby’ mode, power dissipation due to the termination resistor is reduced. When used in a memory system, additional power savings may be realized by arranging the buffer such that the increased impedance in ‘standby’ mode shifts the signal line voltage so as to avoid the voltage range over which a line receiver's power consumption is greatest.

Droop control method for the parallel operation of online uninterruptible power systems using resistive output impedance

Abstract: In this paper, a novel wireless load sharing controller for parallel connected online UPS inverters is proposed. As opposed to the conventional droop method, the proposed method achieves stable steady-state frequency and phase and an good dynamic response is obtained. A virtual output impedance is proposed in order to reduce its line impedance impact and to properly share nonlinear loads. Experimental results are presented from two 6-kVA UPS inverters controlled by DSP boards, showing the feasibility of the proposed approach.

Transmitting arrangement and method for impedance matching

Abstract: A transmitting arrangement includes a matching circuit, a reference circuit and a comparator. The output of the matching circuit can be coupled to an antenna and comprises an adjustable impedance. The reference circuit is connected to an input of the matching circuit and comprises a reference impedance. Inputs of the comparator are coupled to the matching circuit and the reference circuit and its output is coupled to the adjustable impedance via a control input of the matching circuit.

Battery management apparatus

Abstract: When impedance calculating conditions are satisfied after a system is started, the impedance Zn of a battery is calculated using the current of the battery I, a time variation in open circuit voltage DVOC thereof, a time variation in terminal voltage DVB thereof, a time variation in current DIB thereof, and a time variation in impedance DZ thereof (S6). The ratio Krz of the calculated impedance Zn to the initial impedance Zi is calculated (S7). The impedance ratio Krz is subjected to weighting and averaging, thus obtaining a weighted average Krc (S8). When the system is terminated, an impedance-correction-coefficient learned value Krl is updated using the weighted average Krc (S10). Thus, a change in impedance of the battery can be accurately grasped. Advantageously, parameters indicating the state of the battery, e.g., the remaining capacity thereof, reflect the change in impedance, resulting in accurate battery management.

Current Source for Multifrequency Broadband Electrical Bioimpedance Spectroscopy Systems. A Novel Approach

Abstract: New research and clinical applications of broadband electrical bioimpedance spectroscopy arise; increasing the upper limit frequency used in the measurement systems. The current source, an essential block of an electrical bioimpedance impedance analyzer, must have a large-enough output impedance at any frequency of operation to keep the output current constant regardless of the value of working load. In this paper a novel approach to increase the output impedance of a common voltage controlled current source is proposed. The circuit is analyzed, implemented and tested. The results, remarking the significant effect of the circuit parasitic capacitances, show a clear increment of the output impedance, but smaller than the originally expected.

Semiconductor integrated circuit controlling output impedance and slew rate

Abstract: The present invention provides a semiconductor integrated circuit that can perform impedance control and slew rate control independently of each other and simplify the structure of a control circuit. An output circuit comprising plural output MOSFETs connected in parallel is used, from among the plural output MOSFETs, the number of output MOSFETS to be turned on is selected by a first control means to control output impedance, and slew rate is controlled by a second control means controlling a drive signal of the output MOSFETs to be turned on.

Battery monitoring system

Abstract: A system for the monitoring of the state of a battery used in a vehicle and to which electrical elements comprising at least one electrical consumer and/or at least one electrical generator are connected comprises means for the detection of the battery voltage, means for the extraction of voltage frequency components from the detected battery voltage at different frequencies, means for the detection of the current flowing out of or into the battery, means for the extraction of current frequency components from the detected battery current at the same frequencies at which the voltage frequency components were extracted, means for the determination of internal impedances of the battery from the voltage frequency components and current frequency components extracted at a respective frequency, means for the storage of predetermined relationships between the internal impedance and the battery state for each of the respective frequencies and means for the determination of the battery state from the determined internal impedances and the predetermined relationships. In this connection, means are provided for the monitoring of the state of at least some of the electrical elements as well as means in order to select the time for a respective voltage and current detection in dependence on the detected state of the electrical elements and/or to fix the conditions for a respective voltage and current detection.

Low noise amplifier (LNA) gain switch circuit

Abstract: A circuit is formed to steer current in and out of an inductive load in a manner that enables an amplifier to provide a plurality of gain steps without modifying an LC time constant for the circuit and, therefore, without modifying the tuning or frequency of oscillation for the circuit. A first group of MOSFETs are coupled in parallel and define the circuit current flow. A second group of MOSFETs are coupled in parallel to each other and in series to an impedance device. A third group of MOSFETs coupled to steer current in and out of the impedance device to affect the output signal coupled to one end of the impedance device. The transistors in the second and third groups of MOSFETs are selectively activated to control the amount of current that goes through the impedance device.

Method and apparatus for reducing current consumption of mimo systems

Abstract: Apparatus and method for reducing the current consumption and increasing the efficiency of a MIMO system, consisting of one or more RF power amplifiers (PAs) and that is required to provide a desired total output power level. An individual output power level which is a portion of the total output power level is determined for each PA. The load, connected to the output stage of each PA, is dynamically or statically tuned to essentially match the output impedance of its output stage, such that its dynamic or static RF load line has a slope that corresponds to the impedance required to provide this portion. Whenever a smaller output power is desired in response to reduction in the input signal to MIMO system, a reduced portion is determined for each PA and the load is further tuned, such that the dynamic/static RF load line has a slope that causes each PA to essentially remain in saturation while providing the reduced portion.

Load-imposed instability and performance degradation in a regulated converter

Abstract: The stability and performance of a regulated converter is analysed based on its closed-loop output impedance. System theory is used to obtain a set of transfer functions that define the internal stability of an interconnected system consisting of source and load converters. The internal stability is described in terms of the ratio of the output impedance of the source converter and the input impedance of the load converter known as the minor-loop gain. Thus, the closed-loop output impedance of a source converter can be used to define safe operating areas that avoid instabilities in the load impedance. It is shown that the margins associated with the minor-loop gain (i.e. the gain and phase margins) do not generally match the margins of the output-voltage loop gain. The relationship is especially weak at frequencies close to and beyond the crossover frequency of the loop gain. This means that the margins given to the minor-loop gain should be gradually increased as the voltage-loop-gain crossover frequency is approached so as to avoid performance degradation (i.e. changes in margins and crossover frequency) in the supply converter. Experimental evidence is provided based on a buck converter under voltage- and peak-current-mode control.