Showing papers on "Output impedance published in 2005"

Output impedance design of parallel-connected UPS inverters with wireless load-sharing control

Abstract: This paper deals with the design of the output impedance of uninterruptible power system (UPS) inverters with parallel-connection capability. In order to avoid the need for any communication among modules, the power-sharing control loops are based on the P/Q droop method. Since in these systems the power-sharing accuracy is highly sensitive to the inverters output impedance, novel control loops to achieve both stable output impedance and proper power balance are proposed. In this sense, a novel wireless controller is designed by using three nested loops: 1) the inner loop is performed by using feedback linearization control techniques, providing a good quality output voltage waveform; 2) the intermediate loop enforces the output impedance of the inverter, achieving good harmonic power sharing while maintaining low output voltage total harmonic distortion; and 3) the outer loop calculates the output active and reactive powers and adjusts the output impedance value and the output voltage frequency during the load transients, obtaining excellent power sharing without deviations in either the frequency or the amplitude of the output voltage. Simulation and experimental results are reported from a parallel-connected UPS system sharing linear and nonlinear loads.

Decentralized control for parallel operation of distributed generation inverters 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 explorers the resistive output impedance of the parallel-connected inverters in an island microgrid

A 22.5 MHz current-mode KHN-biquad using differential voltage current conveyor and grounded passive elements

Abstract: In this paper, a current-mode (CM) Kerwin–Huelsman–Newcomb (KHN) biquad is proposed. The circuit employs three differential-voltage current conveyors (DVCCs) as active elements together with two capacitors and four resistors as passive elements, which all are grounded. The circuit simultaneously provides the three basic filter functions, namely bandpass (BP), highpass (HP) and lowpass (LP) functions. The notch and allpass (AP) functions can be obtained by connecting appropriate output currents directly without using additional active elements. The output signals are obtained at high output impedance ports, which is important for easy cascading in CM operation. SPICE simulation results are given to verify the theoretical analyses.

A compact large Voltage-compliance high output-impedance programmable current source for implantable microstimulators

Abstract: A new CMOS current source is described for biomedical implantable microstimulator applications, which utilizes MOS transistors in deep triode region as linearized voltage controlled resistors (VCR). The VCR current source achieves large voltage compliance, up to 97% of the supply voltage, while maintaining high output impedance in the 100 M/spl Omega/ range to keep the stimulus current constant within 1% of the desired value irrespective of the site and tissue impedances. This approach improves stimulation efficiency, extends power supply lifetime, and saves chip area especially when the stimulation current level is high in the milliampere range. A prototype 4-channel microstimulator chip is fabricated in the AMI 1.5-/spl mu/m, 2-metal, 2-poly, n-well standard CMOS process. With a 5-V supply, each stimulating site driver provides at least 4.25-V compliance and >10 M/spl Omega/ output impedance, while sinking up to 210 /spl mu/A, and occupies 0.05 mm/sup 2/ in chip area. A modular 32-site wireless neural stimulation microsystem, utilizing the VCR current source, is under development.

Small-signal and signal-flow-graph modeling of switched Z-source impedance network

Abstract: The Z-source inverter is a recently proposed converter topology that uses a unique X-shaped impedance network on its dc side for achieving both voltage-buck and boost capabilities. In the process of designing control schemes for the Z-source inverter, knowledge of the transfer function representing its unique dc impedance network is essential. Toward this end, this letter presents dynamic small-signal modeling of the Z-source impedance network using perturbed mathematical analysis and a signal-flow graph with parasitic components taken into consideration. In particular, the developed average control-to-output model reveals the presence of a right-hand-plane zero in the network transfer function, whose trajectories with variations in network parameters can be studied using classical root-locus analyses. Using the graphical signal-flow modeling approach, various disturbance-to-output transfer functions can also be derived with their parameter sensitivity similarly studied. Lastly, simulation and experimental results are presented for verifying the dynamic phenomena identified in this letter.

Impedance measurement for an implantable device

Abstract: A method and an apparatus for determining an impedance experienced by a lead associated with the implantable device. A substantially constant current signal is provided through a first terminal and a second terminal of the lead. A voltage across the first and second terminals is measured. An impedance across the first and second terminals is determined based upon the constant current signal and the measured voltage.

A method for real-time, wide-band identification of the source impedance in power systems

Abstract: In this paper, the principal problems of distribution system identification and accurate measurements of distribution system impedance frequency contour are discussed. Some new results of field identification are presented. The focus of this paper is on the effective method of signal processing adapted to real signals which appear in the power systems. The principal problem of accurate identification is in the system nonstationariness. Its influence on accuracy is discussed and illustrated with experimental results. The proposed method of impedance identification based on short 40-ms system observations is relatively insensitive to power system nonstationariness. The presented discussion confirms that, with the proper signal processing, 1-s-long system observations are quite sufficient to describe the system with an accuracy to satisfy practical demands.

Impedance controlled output driver

Abstract: An output driver has an output multiplexor and an output current driver. The output multiplexor receives a data signal and outputs a q-node signal. The output current driver receives the q-node signal and drives a bus based on the q-node signal. The output multiplexor processes the data signal in various ways to generate the q-node signal. The output current driver is responsive to current control bits to select a amount of output drive current. In addition, the output multiplexor is controlled such that the output impedance of the output current driver is maintained within a predetermined range.

High dynamic range time-varying integrated receiver for elimination of off-chip filters

Abstract: A quadrature mixer with an LO input is provided. The quadrature mixer receives a signal having a frequency FLO and a signal input having a frequency FSIG and has an output that comprises an output impedance that is high at frequencies of [FLO-FSIG] and [FLO + FSIG] and low at other. A mixer coupled to the output impedance interacts with the output impedance such that an impedance presented at the signal input is high for signals at FSIG if FSIG is a predetermined signal frequency, and low at other frequencies.

A 20 Gb/s VCSEL driver with pre-emphasis and regulated output impedance in 0.13 /spl mu/m CMOS

Abstract: Two 20 Gb/s optical transmitters are presented. They are a part of a 4/spl times/12 array intended for backplane data links. The drivers are fabricated in 0.13 /spl mu/m CMOS and include pre-emphasis and regulated output impedance. When coupled to 990 nm VCSELs, they provide optical modulation amplitude of 0 dBm and consume 70 mW and 120 mW.

Comparison of conventional and new flipped voltage structures with increased input/output signal swing and current sourcing/sinking capabilities

Abstract: A systematic comparison of flipped voltage followers circuits is presented. Two new versions of the flipped voltage follower are introduced. They are characterized by very low output impedance, high bandwidth speed, wide signal swing. All structures can be easily modified for class AB operation. Simulation results show that the newly introduced structures have optimal characteristics

AC Impedance Measurement Techniques

Abstract: Naval ship as well as aerospace power systems are incorporating a greater degree of power electronic switching sources and loads. Although these power electronics based components provide exceptional performance, they are prone to instability due to their high efficiency and constant power characteristics which lead to negative impedance. When designing these systems, integrators must consider the impedance versus frequency at a system interface (which designates source and load). Stability criterions have been developed in terms of source and load impedance for both DC and AC systems and it is often helpful to have techniques for impedance measurement. For DC systems, the measurement techniques have been well established. This paper suggests several methods for measuring AC impedance including utilization of power converters, induction machines and chopper circuits. Simulation results on an example AC system demonstrate the effectiveness of the proposed methods

Electrically tuned resonance circuit using piezo and magnetostrictive materials

Abstract: An impedance tuning system, especially for a cellular telephone system. The system can be used to match the impedance of an antenna element with that of an output stage of a transmitter driving the antenna element. The system includes a piezo capacitor in parallel with the magnetostrictive inductor to form an LC circuit. A voltage controller applies a voltage bias signal to the piezo capacitor and a current controller applies a current bias signal to the inductor. A primary controller monitors the frequency of the output signal from the transmitter and controls the voltage and current controllers as needed to alter the impedance of the system as needed to match the impedance of the antenna element with that of the output stage of the transmitter. In an alternative form an ultrasonic sensor is provided.

Continuously tunable impedance matching network using ferroelectric varactors

Abstract: A prototype of an electronically tunable impedance matching network in "T "-configuration at 1.95 GHz has been realized with discrete ferroelectric varactors of Barium-Strontium-Titanate Ba/sub 0.6/ Sr/sub 0.4/TiO/sub 3/ (BST). The tunable load impedance range has been analyzed in dependency of tuning voltage. For a 50 /spl Omega/ load and source impedance, the measured insertion loss is 1.15 dB. The high power handling capability of the varactors has been experimentally verified. A nonlinear varactor model was implemented to simulate the large-signal circuit behavior. Two-tone measurements on the network show an output IP/sub 3/ of 46.5 dBm at 26 dBm average input power and 52.8 dBm at 33 dBm average input power.

3-Mode Detection for Widening the Bandwidth of Resonant Gravitational Wave Detectors

Abstract: Along with peak sensitivity, an important parameter of a resonant gravitational wave detector is its bandwidth. In addition to the obvious advantage of making the detector more sensitive to short bursts, a wider bandwidth would allow, for instance, details of the signal emitted during a supernova gravitational collapse or the merger of compact binaries to be resolved [1]. Moreover, a wider bandwidth reduces the uncertainty in the burst arrival time [2] and consequently, with a detector network, permits a more precise source location and a higher efficiency of spurious events rejection [3]. The introduction of a mechanically resonant transducer, a standard practice in actual resonant detectors, has greatly improved the coupling between the bar and the amplifier, but the bandwidth is intrinsically limited [4], and in practice, according to the full width at half maximum (FWHM) definition applied to the two minima of the Shh strain noise spectra, values of a few Hz have been achieved [5]. The use of multimode resonant transducers should permit further improvements of the detector bandwidth [6]. This approach has been studied [7] in depth and a few 2-mode transducer prototypes have been realized [8] or are under development [9] to obtain 3mode operation of the resonant mass detectors. This Letter describes how a wider detection bandwidth can be obtained with an alternative 2-mode transduction system in which the resonant amplification is realized by means of a resonant mechanical mode plus a resonant electrical matching network. It also describes the key tests performed on the components of the transduction system in order to verify the achievement of the requirements set by analysis of the detector model. Figure 1 shows the electromechanical scheme of a cryogenic detector with a resonant capacitive transducer read by a SQUID amplifier. The matching transformer couples the output impedance of the transducer (a capacitance of a few nF) to the input impedance of the SQUID (a small

Compensation technique providing stability over broad range of output capacitor values

Abstract: A disclosed amplifier and buffer circuit, for example for a linear voltage regulator, comprises an input gain stage, an integrator and a unity-gain output stage. An output stage compensation scheme enables stable operation over a broad range of output capacitance. For low to moderate output capacitance, the design of the output stage effectively pushes the output pole to high frequencies while an internal pole provided by the integrator is dominant and rolls off the gain at lower frequencies. For high output capacitance, an input impedance of the buffer couples the internal pole and output pole, such that the output pole becomes dominant while the internal pole gets pushed to higher frequencies, maintaining stability. This input impedance connection may utilize the base-emitter resistance of a bipolar junction transistor connected to the internal node, or the connection may use an MOS transistor and a separate RC circuit.

Tight magnetic coupling in multiphase interleaved converters based on simple transformers

Abstract: Magnetic integration and magnetic coupling are very promising concepts to be applied in multiphase converters. Tight magnetic coupling allows energy transfer among phases. Ideally the magnetic component can act as a voltage source, with very low output impedance and with a perfect sharing of output current ripple. The main advantages provided by magnetic coupling are size and losses reduction and dynamic improvement. In this paper two winding transformer arrangements to be used in multiphase converters are presented, and validated with a new integrated transformer.

Power amplifier utilizing quadrature hybrid for power dividing, combining and impedance matching

Abstract: A power amplifier includes a quadrature hybrid and input impedance matching network. The power amplifier also includes at least one amplifier that includes an output electrode, and a quadrature hybrid and output impedance matching network. The quadrature hybrid and input impedance matching network exhibits a low pass frequency response.

A New Transadmittance Type First-Order Allpass Filter Employing Single Third Generation Current Conveyor

Abstract: A novel transadmittance (TA) mode first-order all-pass filter configuration is proposed. The proposed circuit uses a third generation current conveyor (CCIII), three resistors and a grounded capacitor. The output of the filter exhibits high output impedance so that the synthesized filter can be cascaded without additional buffers. The theoretical results are verified with PSPICE simulations using a CMOS realization of CCIII.

Skin condition estimating apparatus

Abstract: There is provided a skin condition estimating apparatus which allows a user to know a skin condition by more sensory characteristics. In impedance measuring means 101, a contact impedance and an internal impedance are measured. In biological equivalent model associated parameter estimating means 102, parameters associated with an equivalent model constituting a living tissue are estimated based on the measured internal impedance. In skin condition estimating means 103, a skin condition is estimated based on at least one of the measured contact impedance, the measured internal impedance, and the estimated parameters associated with an equivalent model constituting a living tissue.

Low-voltage high-performance voltage-mode and current-mode WTA circuits based on flipped voltage followers

Abstract: A new low-voltage CMOS winner-take-all (WTA) circuit is presented. The proposed circuit exhibits a linear increase of complexity with the number of inputs at the rate of only three transistors per input and it is based on a modified version of the common source scheme. In this case, each input follower is enhanced by local shunt feedback to increase its gain and to reduce its output impedance. Simulations demonstrate the potential of the circuit to operate at very high speed, with high precision and with a supply voltage close to a transistor's threshold voltage. Experimental verification of the circuit using a 0.5-/spl mu/m CMOS technology is also provided.

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. The 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, thanks to which the proposed method obtains 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 inverters system, showing the feasibility of the proposed approach.

Dynamic performance analysis of outer-loop current sharing control for paralleled DC-DC converters

Abstract: For paralleling DC/DC converters, this paper investigates the fundamental relationship between the outer-loop current sharing control and the voltage regulation control By using the concept of output impedance, the inherent function of the current sharing control is clarified and its influences on the voltage regulation of paralleling system are revealed Although there may exist tradeoffs between dynamic current sharing and voltage regulation, it is possible to have good performances on both aspects, as long as the closed-loop output impedances of individual modules are within a certain tolerance range After that, a design guideline for the current sharing compensator is proposed The analyses and designs are verified by the simulation and experimental results

Internal impedance detector, internal impedance detecting method, degradation degree detector, and degradation degree detecting method

Abstract: An internal impedance detecting apparatus for detecting the internal impedance of a secondary battery with high accuracy is provided. Processor 106 divides the variation of each voltage detected by voltage change detector 103 by the variation of the current detected by current change detector 105 for the same detecting time as that for the voltage variations to compute the internal impedances. Judging unit 107 checks the variations of the internal impedances computed by processor 106 and judges from the check result whether or not the internal impedances have reliability. Only when judging unit 107 judges that the internal impedances have reliability, generator 109 generates output internal impedance according to the internal impedances.

DC-DC Converters - Dynamic Model Design and Experimental Verification

Abstract: To obtain high performance control of a dc-dc converter, a good model of the converter is needed. The load usually affects the dynamics and one way to take this into consideration is to regard the load as a part of the converter. The load is often the most variable part of this system. If the load current and the output voltage are measured there are good possibilities to obtain a good model of the load on-line. Adaptive control can then be applied to improve the control. In peak current-mode control, the output voltage and the inductor current are measured and utilized for control. In the author's licentiate thesis, analytic models were derived for the case where the load current is also measured and utilized for control. The control-to-output transfer function, the output impedance, and the audio susceptibility were derived for the buck, boost, and buck-boost converters operated in continuous conduction mode in the case of resistive load. The use of load current can be seen as gain scheduling in the case where the load is a resistor. Gain scheduling can be considered a special case of adaptive control. The majority of the results in the licentiate thesis were validated by comparing the frequency responses predicted by the analytic models and switched large-signal simulation models. In this thesis, additional results are presented for the buck converter. Experimental results obtained by means of a network analyzer verify the derived control-to-output transfer function and the audio susceptibility but not the output impedance at low frequencies. In the experimental buck converter there are stray resistances in the inductor, transistor, and diode but these stray resistances were not considered in the licentiate thesis. A new transfer function for the output impedance is derived where these stray resistances are considered and it is in good agreement with the experimental result also at low frequencies. If the current to the output capacitor is measured in addition to the output voltage and the inductor current, the load current can be calculated as the difference between the inductor and capacitor currents in the case of the buck converter. Hence, the measurement of the load current can be replaced by measurement of the capacitor current. If this possibility is utilized and the capacitor current is measured by means of a current transformer, a low-frequency resonance is introduced in the frequency responses according to experimental results. The reason for this resonance is due to the high-pass-filter characteristics of the current transformer. A new analytic model is derived which predicts the resonance. (Less)

Implementation of a Transcutaneous Charger for Fully Implantable Middle Ear Hearing Device

Abstract: A transcutaneous charger for the fully implantable middle ear hearing device (F-IMEHD), which can monitor the charging level of battery, has been designed and implemented. In order to recharge the battery of F-IMEHD, the electromagnetic coupling between primary coil at outer body and secondary coil at inner body has been used. Considering the implant condition of the F-IMEHD, the primary coil and the secondary coil have been designed. Using the resonance of LC tank circuit at each coil, transmission efficiency was increased. Since the primary and the secondary coil are magnetically coupled, the current variation of the primary coil is related with the impedance of internal resonant circuit. Using the principle mentioned above, the implanted module could transmit outward the information about charging state of battery or coupling between two coils by the changing internal impedance. As in the demonstrated results of experiment, the implemented charger has supplied the sufficient operating voltage for the implanted battery within about 10 mm distance. And also, it has been confirmed that the implanted module can transmit information outward by control of internal impedance

DC/DC-less coupling of matched batteries to fuel cells

Abstract: A fuel cell system that employs a matched battery that matches the battery voltage to a fuel cell power bus voltage so as to eliminate the need for a DC/DC converter. The internal characteristics and parameters of the matched battery allow it to operate over the large load dependent voltage swing of the fuel cell, and prevent the battery state of charge from going below a damaging value. The battery type, number of battery cells and the battery internal impedance are selected to provide the desired matching. In one embodiment, the battery is a lithium ion battery. The system also includes a diode electrically coupled to the power bus line and a by-pass switch electrically coupled to the power bus line in parallel with the diode. The by-pass switch is selectively opened or closed to allow the fuel cell stack to recharge the battery and prevent the battery from being overcharged.

Wireless communication terminal and antenna switching control method

Abstract: A wireless communication terminal able to change a resonance frequency of a sub antenna, able to reduce interference to a main antenna, and able to suppress deterioration performance in a dual terminal compatible with a plurality of transmission systems, wherein, in a wireless communication unit, at the time of a CDMA2000 1xEVDO mode, a first receiver circuit, a second receiver circuit, and a transmitter circuit are in an operative state, and, in the second receiver circuit, an input impedance is held at the 50 ohm input impedance of a LNA by an impedance control unit, while at the time of a CDMA2000 1x mode, the first receiver circuit and the transmitter circuit are in the operative state, the second receiver circuit is in an inoperative state, and, in the second receiver circuit, the input impedance is controlled so as to be shifted from the 50 ohm input impedance of the LNA by the impedance control unit, and an antenna switching control method for the same.