Showing papers on "Output impedance published in 2009"

Control and Resonance Damping of Voltage-Source and Current-Source Converters With $LC$ Filters

Abstract: In this paper, the closed-loop control of both voltage-source converter (VSC) and current-source converter (CSC) systems with LC filters is investigated, with a focus being put on the damping of LC resonance. First, both single-loop and multiloop control schemes for a voltage-source inverter (VSI) with output LC filter are analyzed, where the design and tuning procedure can also be applied to a current-source inverter (CSI) with output CL filter. It is shown that both VSI and CSI systems are subject to LC resonance, even with multiloop control, while the CSI system is also subject to LC resonant frequency variations. On the other hand, the LC resonant frequencies in both current-source rectifier (CSR) and voltage-source rectifier (VSR) systems with input LC filter circuits are relatively fixed due to the small variation range of source impedance. To further dampen the LC resonance in these converter systems, active damping techniques such as virtual harmonic damper and control-signal-shaping methods are investigated, and their implementation into the converter systems is discussed in detail. Experimental results from both a VSC system and a CSC system are obtained.

Small-Signal Impedance Measurement of Power-Electronics-Based AC Power Systems Using Line-to-Line Current Injection

Abstract: Naval ships as well as aerospace power systems are incorporating a greater degree of power electronic switching sources and loads. Although these components provide exceptional performance, they are prone to instability due to their high efficiency and constant power characteristics that can exhibit negative impedance nature at certain frequencies. When designing these systems, integrators must consider the impedance versus frequency at an interface (which designates source and load). Stability criteria have been developed in terms of source and load impedances 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 introduces a new method of impedance measurement for three-phase ac systems. By injecting an unbalanced line-to-line current between two lines of the ac system, all impedance information in the traditional synchronous reference frame d-q model can be determined. For medium-voltage systems, the proposed technique is simpler and less costly than having an injection circuit for each phase. Since the current injection is between only two phase lines, the proposed measurement device can be used for both ac and dc interfaces. Simulation and laboratory measurements demonstrate the effectiveness of this new technique.

Multilayer Substrate Integrated Waveguide Four-Way Out-of-Phase Power Divider

Abstract: In this paper, a multilayer substrate integrated waveguide (SIW) four-way out-of-phase power divider is investigated. In a previous research (Eom , 2009), the four-way power division was studied by a 3-D mode coupling method, which was achieved by a vertical Y-junction as well as a lateral Y-junction of half mode substrate integrated waveguides (HMSIW) using a multilayer substrate. In this research, resistive coupling slots, for obtaining good isolation between four output ports and impedance matching at all the ports, are realized on the lateral HMSIW Y-junctions and the vertical HMSIW Y-junctions using isolation resistors. From the measurement results, excellent performances of insertion loss, isolation, impedance matching, and amplitude balancing were simultaneously achieved for the X-band range. It is expected that the proposed design of a multilayer substrate integrated waveguide (ML-SIW) power divider will play an important role in the future integration of compact multiway SIW circuits and systems.

ARC generation in a fluid medium

Abstract: An electrosurgical generator is disclosed. The generator includes a radio frequency output stage configured to generate a frequency waveform to an active electrode of an electrosurgical instrument when the active electrode is disposed in a fluid medium. The generator also includes a sensor circuit configured to measure tissue impedance and a controller configured to increase power of the radio frequency waveform to a predetermined electrical arcing level in response to the tissue impedance being within an open circuit impedance range and tissue contact impedance range. The controller is further configured to lower the power of the radio frequency waveform to a lower level when the tissue impedance is outside the open circuit impedance range and the tissue contact impedance range.

A Current Distortion Compensation Scheme for Four-Switch Inverters

Abstract: The four-switch inverter, having a lower number of insulated gate bipolar transistors(IGBTs), has been studied for the possibility of reducing the inverter cost. But it has a limited performance in the low-frequency region, because the balance among the phase currents collapses due to the fluctuation of the center tap voltage of the DC-link capacitors. This problem could be solved if the DC-link capacitance is infinitely large, but it is a costly solution. In this paper, this problem is looked at from the perspective of source impedance and the voltage variation caused by the current flow through the capacitors. The source impedance of the center tap is large compared with other normal IGBT arms. This causes an asymmetry among the three voltage sources, resulting in phase current distortion and unbalance. Second, the capacitor voltage change caused by current flow is another source of current distortion and unbalance. The voltage errors are derived, and based on them, a compensation method is proposed. Effectiveness of the proposed method is demonstrated by the simulation and experimental results.

Fault-Location Algorithms Without Utilizing Line Parameters Based on the Distributed Parameter Line Model

Abstract: This paper presents novel power system transmission-line fault-location algorithms without requiring transmission-line parameters. The voltages and currents from both ends of a line are taken as inputs and no synchronization is required. Both prefault and fault data may be utilized. The proposed methods are based on a distributed parameter line model and, hence, fully consider the impacts of shunt capacitance of the line. Positive-sequence line parameters may also be estimated as a byproduct. No assumption on the source impedance and fault resistance is made. Evaluation studies based on Electromagnetic Transients Program (EMTP) simulation data demonstrate that the new methods are able to achieve quite accurate estimates.

Non-contact power transmission apparatus and power transmission method using a non-contact power transmission apparatus

Abstract: Disclosed is a non-contact power transmission apparatus provided with an AC power source and a resonant system. The resonant system has a primary coil that is connected with the AC power source, a primary-side resonance coil, a secondary-side resonance coil, a secondary coil and a load that is connected with the secondary coil. In addition, the non-contact power transmission apparatus is provided with a state detection unit and a variable-impedance circuit. The state detection unit detects the state of the resonant system. The variable-impedance circuit is constructed so as to adjust its own impedance in accordance with the state of the resonant system detected by the state detection unit, in such a way that the input impedance and the output impedance at the resonant frequency of the resonant system are matching.

Input Impedance Modeling and Analysis of Line-Commutated Rectifiers

Abstract: This paper presents the modeling and analysis of small-signal input impedance for line-commutated rectifiers. The recently developed impedance mapping method, which has been applied to single-phase rectifiers with sinusoidal line inputs, is generalized to single-phase rectifiers with distorted lines as well as three-phase rectifiers. The modeling method assumes known impedance of the circuit on the dc side of the rectifier bridge (including its output filter and the load), and determines the corresponding ac input impedance by using a current and voltage mapping function that describes the operation of the rectifier bridge in the frequency domain. In this approach, closed-form analytical expressions are derived for the ac input impedance as functions of the dc circuit impedance. The resulting models are intended for stability analysis and design of large ac power systems involving significant number of rectification loads, such as more-electric aircraft power systems and microgrids. Detailed derivation of the models is presented in this paper. Numerical simulation and experimental measurement results are also presented to validate the developed models.

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.

Analysis of Parallel Operation of Uninterruptible Power Supplies Loaded through Long Wiring Cables

Abstract: This paper discusses and analyses the parallel operation of Uninterruptible Power Supplies (UPS) units when loaded through long wiring cables having non-negligible inductance and resistance. This scenario is often encountered in practice, as the UPS power supplies are often located far from the load they are actually powering. The analysis demonstrates how long cable connections between the power supply system and the load deeply modify the behavior of the single UPS unit. More precisely, it is shown how the cable inductance interacts with the UPS closed-loop output impedance modifying the control loop gain, ultimately generating resonance phenomena which deteriorate or even compromise system stability and performances if suitable provisions are not taken at the design stage. Simulation and experimental results carried out on two paralleled three-phase, 40kVA UPS units based on voltage-source inverters topologies confirm the validity of the theoretical discussion and the practical relevance of the phenomenon.

Current-mode multiphase sinusoidal oscillator using CDTA-based allpass sections

Abstract: In this work, a current tunable current-mode multiphase sinusoidal oscillator (MSO) employing current differencing transconductance amplifier (CDTA)-based first-order allpass sections is presented. The proposed MSO circuit, which uses only two CDTAs and one virtually grounded capacitor for each phase, can generate arbitrary 2n-phase current-output signals (n=2,3,4,…) equally spaced in phase, all at high output impedance terminals. The oscillation condition and the oscillation frequency can be controlled electronically and independently by adjusting the bias current of the CDTA. The oscillator has low-sensitivity performance. Simulation results are also given to verify the functionality of the proposed oscillator.

Electrosurgical Generator Having Boost Mode Control Based on Impedance

Abstract: A method of controlling output power of an electrosurgical generator apparatus that controls a variable output signal to a pair of electrodes includes setting the output power of the generator apparatus to a selected power output level. An impedance is measured across the electrodes when the electrodes are applied to an area of tissue. The output power of the generator apparatus is changed to a boost power output level greater than the selected power output level. The boost power output level corresponds to a calculation based at least in part on the measured impedance. The method further includes applying the output signal to the electrodes at the boost power output level for a first time duration and changing the power output to the selected power output level after the first time duration. An electrosurgical generator apparatus operating in accordance with the method is also described.

A mixed-mode KHN-biquad using DVCC and grounded passive elements suitable for direct cascading

Abstract: In this paper a mixed-mode (input and output signals can be current or voltage) Kerwin–Huelsman–Newcomb (KHN) biquad with low-high input impedance and high-low output impedance depending on the type of the corresponding signal (current-voltage) is presented. The circuit is constructed using three differential voltage current conveyors (DVCCs), two grounded capacitors and three grounded resistors. The circuit simultaneously provides bandpass (BP), highpass (HP) and lowpass (LP) responses when the output is current and notch, BP and LP responses when the output is voltage. The notch and allpass responses can be obtained by connecting appropriate output currents directly without using additional active elements. Because of the low input and high output impedance of the circuit for current signals and the high input and low output impedance for voltage signals, it can be used in cascade for realizing higher-order filters. SPICE simulation results are given to verify the theoretical analysis. Copyright © 2008 John Wiley & Sons, Ltd.

Single FDCCII-based mixed-mode biquad filter with eight outputs

Abstract: The transconductance and the transresistance modes might act as the bridge transferring from voltage-mode to current-mode and vice versa, respectively. A novel mixed-mode (including voltage, current, transconductance, and transresistance modes) biquad filter with one input and seven outputs or two inputs and eight outputs is presented. The proposed filter structure only uses a single fully differential current conveyor (FDCCII), three resistors and two grounded capacitors, which are the least components necessary for realizing voltage, current, transresistance modes all five standard filter functions and transconductance-mode band-pass, high-pass filter functions from eight output terminals. Moreover, the new mixed-mode biquad filter still enjoys (i) the employment of two grounded capacitors (attractive for absorbing shunt parasitic capacitance and ideal for IC implementation), (ii) orthogonal control of ω 0 and Q (easy for tunability), and (iii) high output impedance of three current outputs (good for cascadability). H-Spice simulation results verify the theoretical analysis.

Power amplifier with switched output matching for multi-mode operation

Abstract: Exemplary embodiments are directed to a transmitter with a power amplifier and a switched output matching circuit implementing a plurality of output paths for a plurality of operating modes is described. The power amplifier receives an input RF signal and provides an amplified RF signal. An output matching network performs impedance transformation from low impedance at the power amplifier output to higher impedance at the matching network output. The plurality of output paths are coupled to the output matching network. Each output path provides a different target output impedance for the power amplifier and routes the amplified RF signal from the power amplifier to an antenna when that output path is selected. Each output path may include a matching network coupled in series with a switch. The matching network provides the target output impedance for the power amplifier when the output path is selected. The switch couples or decouples the output path to/from the power amplifier.

Comparison of a new integrated current source with the modified Howland circuit for EIT applications

Abstract: Multi-frequency electrical impedance tomography (MF-EIT) systems require current sources that are accurate over a wide frequency range (1 MHz) and with large load impedance variations. The most commonly employed current source design in EIT systems is the modified Howland circuit (MHC). The MHC requires tight matching of resistors to achieve high output impedance and may suffer from instability over a wide frequency range in an integrated solution. In this paper, we introduce a new integrated current source design in CMOS technology and compare its performance with the MHC. The new integrated design has advantages over the MHC in terms of power consumption and area. The output current and the output impedance of both circuits were determined through simulations and measurements over the frequency range of 10 kHz to 1 MHz. For frequencies up to 1 MHz, the measured maximum variation of the output current for the integrated current source is 0.8% whereas for the MHC the corresponding value is 1.5%. Although the integrated current source has an output impedance greater than 1 MΩ up to 1 MHz in simulations, in practice, the impedance is greater than 160 kΩ up to 1 MHz due to the presence of stray capacitance.

Design and characterization of a high-power ultrasound driver with ultralow-output impedance

Abstract: We describe a pocket-sized ultrasound driver with an ultralow-output impedance amplifier circuit (less than 0.05 ohms) that can transfer more than 99% of the voltage from a power supply to the ultrasound transducer with minimal reflections. The device produces high-power acoustical energy waves while operating at lower voltages than conventional ultrasound driving systems because energy losses owing to mismatched impedance are minimized. The peak performance of the driver is measured experimentally with a PZT-4, 1.54 MHz, piezoelectric ceramic, and modeled using an adjusted Mason model over a range of transducer resonant frequencies. The ultrasound driver can deliver a 100 V(pp) (peak to peak) square-wave signal across 0-8 MHz ultrasound transducers in 5 ms bursts through continuous wave operation, producing acoustic powers exceeding 130 W. Effects of frequency, output impedance of the driver, and input impedance of the transducer on the maximum acoustic output power of piezoelectric transducers are examined. The small size, high power, and efficiency of the ultrasound driver make this technology useful for research, medical, and industrial ultrasonic applications.

Piezoelectric Energy Harvesting Improvement with Complex Conjugate Impedance Matching

Abstract: One way to enhance the efficiency of energy harvesting systems is complex conjugate impedance matching of its electrical impedance. In Piezoelectric energy Harvesting systems the match is done to i...

A Novel First-Order Current-Mode All-Pass Filter Using CDTA

Abstract: This paper presents a new realization of a firstorder current-mode (CM) all-pass filter (APF) using the recently proposed modern active building block (ABB), namely the current differencing transconductance amplifier (CDTA). The CM APF is made using minimum number of components, namely a single CDTA and one grounded capacitor. The circuit does not use any external resistors and offers the advantages of current-tunable pole frequency, low input impedance and high output impedance. Non-ideal analysis and sensitivity analysis are provided and PSPICE simulation results are included to verify the workability of the circuit.

High frequency grid impedance analysis by current injection

Abstract: The impedance of the electrical grid is frequency and time depending. Therefore it is very useful to know its value in the frequency range between grid fundamental frequency and frequencies in the kHz-range. The proposed grid impedance analysis contributes to optimize energy feed especially from decentralized converter equipped renewable sources. This paper presents an advanced impedance measurement system with a high frequency range for the energized electrical low voltage grid. A sinusoidal current of predetermined frequency is injected into the grid. The grid impedance at that frequency is calculated from the measured magnitude and phase of the injected current and resulting voltage. The measurements are executed at nearby frequencies to produce nearly continuous impedance versus frequency characteristic. The basic concept and a prototype of test equipment are presented.

Bi-directional wireless acoustic telemetry methods and systems for communicating data along a pipe

Abstract: A bi-directional acoustic telemetry system is presented for communicating data and/or control signals between a first modem and a second modem along tubing. The system includes a communication channel defined by the tubing, a transducer of the first modem, and a transducer of the second modem. The transducer of each modem are configured to transmit and receive data and/or control signals, and are further configured to electrically communicate with a power amplifier characterized by an output impedance Zs and a signal conditioning amplifier characterized by an input impedance Zr. The system also includes a reciprocal response along the communication channel between the output impedance Zs and the input impedance Zr.

SoC Li-ion battery monitoring with impedance spectroscopy

Abstract: The state of charge (SoC) of Li-ion coin batteries is investigated as a function of impedance variation. Batteries are submitted to highly stressed conditions to simulate the operation of active loads and impedance is measured in real time both for charge and discharge. In particular, modulus and phase dependence as a function of SoC is studied with impedance spectroscopy in the range 40 Hz to 20 kHz. Phase is found to be the most sensitive parameter. It decreases with battery discharge and increases with battery charge. Impedance is simply modelled with a 3 parameters circuit, two resistors and a constant phase element (CPE). Selected frequencies are then proposed to estimate the SoC of the battery.

A 28.1dBm class-D outphasing power amplifier in 45nm LP digital CMOS

Abstract: A 2.25GHz outphasing power amplifier is implemented in a 45nm LP digital CMOS process. The PA is designed in class-D mode for low output impedance and good linearity. The PA delivers 28.1dBm peak CW power with 19.7% system efficiency (includes all drivers). Average OFDM power is 21.4/20.3dBm with efficiency 8.0/6.5% when transmitting WiFi/WiMAX signals respectively.

An integrated Shunt-LDO regulator for serial powered systems

Abstract: In this paper, a new type of regulator is proposed for integration in ASICs used in serially powered systems. In the serial powering scheme, modules are placed in series and fed by a constant current source to reduce the IR drop on the cables which increases powering efficiency. At the module level the needed supply voltages are generated redundantly out of the current supply by several parallel operating ASICs with integrated regulation circuitry. A Shunt-LDO regulator has been developed to allow robust and redundant regulator operation and the generation of different supply voltages by parallel placed devices. The Shunt-LDO regulator scheme combines the capability of Low Drop-Out regulators to generate a constant supply voltage with the feature of shunt regulators to assure a constant current flow through the device. The Shunt-LDO regulator has been developed for application in the framework of next generation hybrid pixel detectors used in high energy physics experiments. This circuit has been prototyped in a 130nm CMOS technology, capable of generating voltages in a range of 1.2-1.5V with a minimum drop out voltage of 200mV. The maximum shunt current is 500mA with a load regulation factor corresponding to an output impedance of 30mΩ.

Directional coupler including impedance matching and impedance transforming attenuator

Abstract: The present invention provides a compact weakly coupled directional coupler combined with an integrated impedance transformation and matching circuit where the impedance transformation and matching circuit facilitates the fabrication of a highly miniaturized directional coupler with optimum electrical performance where the physical dimensions of the coupled transmission lines fall inside the constraints of the fabrication process.

Novel SQUID Current Sensors With High Linearity at High Frequencies

Abstract: We have developed novel SQUID current sensors consisting of a sensitive 16-SQUID input stage followed by an output stage of 40, 160, or 640 low-inductance SQUIDs. A highly gradiometric design of the individual SQUIDs with ap 5 mum maximum linewidth makes the devices insensitive to external magnetic noise and allows cool-down and operation in the Earth magnetic field. Output current feedback (OCF) is used to increase the linear signal range. When driving a terminated 50 Omega coaxial cable, the sensor with 160 output SQUIDs exhibits a signal range of one flux quantum Phi0 at a power dissipation of about 100 nW. At 10 MHz and 4.2 K, a total flux noise level of 0.34 muPhi0/radic(Hz) is achieved corresponding to a dynamic range of plusmn 1.5 times 106 radic(Hz). At higher frequencies, interaction of preamplifier voltage noise with the output cable impedance increases the sensor noise (a general problem in high-speed SQUID systems). The small-signal bandwidth is >200 MHz. A very high slew rate of > 50 Phi0/mus is achieved allowing one to use the full signal range at frequencies up to 16 MHz with a total harmonic distortion below ap1%.

Design-Oriented Analysis of Modern Active Droop-Controlled Power Supplies

Abstract: Active droop control of voltage regulators and point of loads is a preferred way of implementing adaptive voltage positioning to save motherboard space. This paper develops an improved model and design methodology for this control. The conventional model is explained and need for an improved model is described. Based on this improved model, a generalized design procedure, applicable irrespective of the modulation scheme, is developed. Experimental verifications on a five-phase/120-A prototype are presented to validate the design procedure. Results show that the loop performance and output impedance predictions of the model are accurate.

Load-line adaptation

Abstract: According to the general concept disclosed herein, a circuit for adaptive matching of a load impedance to a predetermined load-line impedance of a load-line connected to a power amplifier output includes a fixed matching network between the power transistor and an adaptive matching network, whereby the fixed matching network acts as an impedance inverter which results in a relatively low insertion loss at high power. Results indicate that the impedance-inverting network can be used over more than a factor of 10 in impedance variation. Further, the usage of the fixed matching network, close to the power transistor, allows for the implementation of transmission zeros and/or for a well defined load impedance at a predetermined harmonic frequency, independent of the (variable) load impedance at the fundamental frequency.

High output-impedance current-mode third-order quadrature oscillator based on CCCCTAs

Abstract: This article presents a 3rd order current-mode quadrature oscillator using current controlled current conveyor transconductance amplifiers (CCCCTAs) as active elements. The proposed circuit is realized from a non-inverting lossless integrator and an inverting second-order lowpass filter. The oscillation condition and oscillation frequency can be electronically/orthogonally controlled via input bias currents. The circuit description is very simple, consisting of merely 2 CCCCTAs and 2 grounded capacitors. Without any external resistors and using only grounded elements, the proposed circuit is then suitable for IC architecture. Due to high-output impedances, the proposed circuit is enable easy cascading in current-mode. The PSPICE simulation results are depicted, and the given results agree well with the theoretical anticipation. The power consumption is approximately 2.43mW at ±3V supply voltages.