Large-signal Impedance Research Articles

Large-Signal Impedance Modeling and Stability Analysis of a Grid-Connected Inverter Considering the Influence of a Limiter in Different Control Links

The limiter in grid-connected inverter control may cause sustained oscillation in the system. The large-signal impedance model is provided since the traditional small-signal impedance model cannot accurately describe the characteristics of the limiter. In this paper, there are three established large-signal impedance models of grid-connected inverters that take into account the limiter in the phase-locked loop (PLL), the limiter in the current control loop and the limiter in the pulse width modulation (PWM). Based on the established models, the influences of these different limiters on the output impedance characteristics of the grid-connected inverter are discussed. Furthermore, the stability of the system considering the influence of different limiters is analyzed and the oscillation frequency and amplitude of the system are predicted. The simulation verifies the accuracy of the large-signal impedance model and the predicted oscillation frequency and amplitude.

Impedance-Based Prediction of Distortions Generated by Resonance in Grid-Connected Converters

Small-signal impedance-based analysis can effectively predict the frequency and damping of resonance modes in power electronic systems. However, it cannot predict the magnitude of resonance or explain resonance-generated distortions in the absence of an external disturbance at the resonance frequency. This paper presents an impedance-based theory for the prediction of the magnitude of resonance or resonance-generated distortions in grid-connected converters. It is discovered that the impedance response of a converter starts changing with the magnitude of resonance at its terminals. The changing converter impedance response may stabilize an unstable growing resonance mode beyond a certain magnitude, at which point the converter enters a limit cycle mode of sustained oscillations. The proposed theory uses large-signal impedance for the prediction of resonance-generated distortions; the large-signal impedance of an electrical equipment represents its impedance response for different magnitudes of perturbation injected at its terminals. Large-signal impedance-based prediction of resonance-generated distortions is demonstrated for a three-phase grid-connected voltage-source converter.

Large-Signal Impedance-Based Modeling and Mitigation of Resonance of Converter-Grid Systems

Large-signal impedance of grid-connected converters can be used to predict resonance-generated distortions in converter-grid systems. Note that the large-signal impedance of a network represents its impedance response for different magnitudes of perturbation injected at its terminals. This paper presents large-signal impedance-based modeling and mitigation of resonance of grid-connected voltage source converters. Challenges of large-signal modeling because of the inapplicability of the small-signal approximation are addressed by leveraging the dominating influence of hard nonlinearities (such as pulsewidth modulation saturation and limiters) over soft nonlinearities (such as Park's transformations and phase-locked loop (PLL)) in shaping the large-signal behavior of the converter. The paper develops large-signal gains of hard nonlinearities using different types of describing functions. The paper shows that the large-signal impedance of a voltage source converter (VSC) can be shaped to reduce resonance-generated distortions by inserting limiters in the control system of the VSC. Developed large-signal impedance models are validated using numerical simulations of a VSC with dq current control and PLL. Large-signal impedance measurements of a commercial 1 MW VSC-based inverter and a medium-voltage doubly-fed induction generator with approximate 4 MW rating are presented to experimentally demonstrate the influence of the injected perturbation magnitude on the impedance response.

An Optimized-Load-Impedance Calculation and Mining Method Based on <italic>I–V</italic> Curves: Using Broadband Class-E Power Amplifier as Example

Broadband power amplifier (PA) designs are usually based on optimized-load-impedance ( $Z_{\text{opt}}$ ) searching, which can be guided by PA theories or a load–pull method. After practical devices’ internal dc I–V curves and package parasitics are known, a direct impedance calculation method is realized in this paper to offer an alternate option. This method can offer relatively accurate $Z_{\text{opt}}$ solutions, which can satisfy both operation-mode and performance requirements for a practical device. Following this large-signal impedance calculation method, waveform regulations can be added to the design steps to realize a specific PA operation-mode through a robust and fast small-signal S-parameter simulator. A waveform-guided perturbation and selection process is introduced to expand the impedance space further. A broadband quasi-class-E PA example, across 1.4 to 2.4 GHz, is given to demonstrate this method. Its output matching network is designed accordingly to fit into the expanded impedance space, and its theoretical performances are verified by harmonic balance simulations and measurements. Finally, this PA is fabricated and measured to offer 39.0 to 40.9 dBm power, 11.6 to 14.0 dB gain, and 73% to 83% drain efficiency in its frequency band.

Si/SiC-based DD hetero-structure IMPATTs as MM-wave power-source: a generalized large-signal analysis

A full-scale, self-consistent, non-linear, large-signal model of double-drift hetero-structure IMPATT diode with general doping profile is derived. This newly developed model, for the first time, has been used to analyze the large-signal characteristics of hexagonal SiC-based double-drift IMPATT diode. Considering the fabrication feasibility, the authors have studied the large-signal characteristics of Si/SiC-based hetero-structure devices. Under small-voltage modulation (∼ 2%, i.e. small-signal conditions) results are in good agreement with calculations done using a linearised small-signal model. The large-signal values of the diode's negative conductance (5 × 106 S/m2), susceptance (10.4 × 107 S/m2), average breakdown voltage (207.6 V), and power generating efficiency (15%, RF power: 25.0 W at 94 GHz) are obtained as a function of oscillation amplitude (50% of DC breakdown voltage) for a fixed average current density. The large-signal calculations exhibit power and efficiency saturation for large-signal (> 50%) voltage modulation and thereafter decrease gradually with further increasing voltage-modulation. This generalized large-signal formulation is applicable for all types of IMPATT structures with distributed and narrow avalanche zones. The simulator is made more realistic by incorporating the space-charge effects, realistic field and temperature dependent material parameters in Si and SiC. The electric field snap-shots and the large-signal impedance and admittance of the diode with current excitation are expressed in closed loop form. This study will act as a guide for researchers to fabricate a high-power Si/SiC-based IMPATT for possible application in high-power MM-wave communication systems.

3 mm sub-harmonic mixer

A sub-harmonic mixer is presented with micro-strip at 3 mm wave length.The key device of the mixer is a pair of GaAs beam lead anti-parallel Schottky diode(type MS8251).According to the request of the local oscillator(LO),radio frequency(RF) and intermediate frequency(IF) networks of sub-harmonic mixer,the large signal impedance of anti-parallel diode pair,which is stimulated with the LO signal alone,is simulated by harmonic balance method firstly.The LO network is designed based on the result above.Then the small signal impedance of anti-parallel diode pair with LO stimulation is simulated and the RF network is designed.A 3 mm waveguide to micro-strip translation is also designed in the paper,and the sub-harmonic mixer is fabricated on the RF-Duroid 5880 with 0.127 mm thick and dielectric constant er of 2.22.According to the measurement result,the conversion loss which is lower than 15 dB is achieved with the RF ranged from 90 GHz to 95 GHz and the LO frequency of 46.3 GHz.

Model Parameterization of Nonlinear Devices Using Impedance Spectroscopy

In this paper, a new approach is used to identify the parameters of a large-signal lumped-element model for nonlinear devices based on small-signal impedance measurements at several operating points. Starting from the large-signal impedance of an equivalent circuit with nonlinear devices, the relationship between current and voltage is derived by the determining nonlinear system equation. This differential equation for a first-order model is then linearized via nonlinear series expansion using the perturbation approach. The linearized ac part (which is the fundamental frequency part) is then transformed into the frequency domain to find a representation of the complex small-signal impedance for a given operating point. Large-signal modeling based on small-signal measurements is successfully demonstrated for organic light-emitting diodes.

Multitone large-signal analysis of superconducting transition-edge sensors for astronomy

A simple transition-edge sensor (TES) is governed by two coupled, nonlinear equations, which when solved give the behavior of the device given the initial conditions. The two equations describe the full electrical and thermal characteristics of the device and the way in which the device interacts with the external electrical and thermal circuits. To date these coupled nonlinear equations have been solved analytically in the small-signal limit, by linearizing the equations about some operating point. The resulting coupled linear equations contain a wealth of interesting physics, and form the principal tool by which all detectors are currently designed and modeled. In this article we describe a numerical technique for solving the coupled nonlinear equations rigorously, without any assumptions about the magnitudes of the various signals and parameters that determine the behavior of a device. The technique is based on a harmonic balance algorithm that searches, in the frequency domain, for voltage, current, and temperature wave forms that are consistent with the solid-state physics of the device. Indeed, both the small and large signal limits can be simulated, and the full harmonic content of the system retrieved. In this article, we will outline the principal features of the algorithm, and show various results such as I−V curves, saturation when signal power is modulated, impedance response when the bias current is modulated and signal power kept constant, and pulsed signal power analysis that shows the dynamics of a device. Numerous extensions of this fundamental technique are now possible including multitone nonharmonic analysis, large-signal impedance calculation, modeling of complicated thermal circuits, noise models, and frequency-domain multiplexing. We believe that our algorithm will become the principle technique for analyzing the large-signal behavior of all TES detectors and on that basis we are developing computer aided design software.

Frequency-domain models for nonlinear microwave devices based on large-signal measurements

In this paper, we introduce nonlinear large-signal scattering ( ) parameters, a new type of frequency-domain mapping that relates incident and reflected signals. We present a general form of nonlinear large-signal -parameters and show that they reduce to classic -parameters in the absence of nonlinearities. Nonlinear large-signal impedance ( ) and admittance ( ) parameters are also introduced, and equations relating the different representations are derived. We illustrate how nonlinear large-signal -parameters can be used as a tool in the design process of a nonlinear circuit, specifically a single-diode 1 GHz frequency-doubler. For the case where a nonlinear model is not readily available, we developed a method of extracting nonlinear large-signal -parameters obtained with artificial neural network models trained with multiple measurements made by a nonlinear vector network analyzer equipped with two sources. Finally, nonlinear large-signal -parameters are compared to another form of nonlinear mapping, known as nonlinear scattering functions. The nonlinear large-signal -parameters are shown to be more general.

38-GHz-band high-power MMIC amplifier module for satellites on board use

The design and development results of 38-GHz high-power MMIC amplifier modules for use in the solid-state power amplifier (SSPA) to be carried aboard Engineering Test Satellite VI in 1993 are presented. This amplifier will be used in millimeter-wave intersatellite communication experiments. For the development of this amplifier, high-power, highly reliable FETs with 0.25- mu m-long gates were designed. The FET large-signal impedance was accurately measured using an improved load-pull method and MMIC transformers. The measurements were used to design two types of MMICs: one composed of two FET cells with 600- mu m-wide gates and the other of four FET cells with 400- mu m-wide gates. A two-stage amplifier package consisting of two of these MMICs that can be used at 38 GHz is also developed. A P/sub o/(1 dB) of 25 dBm and a gain of 11 dB are obtained. A 38-GHz test conducted during chip screening achieves a high production yield without circuits adjustment.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A generalized analytical model for the quantum well injection transit time diode

A generalized small-signal model of the quantum well injection transit time (QWITT) diode derived from the authors' previous large-signal model (see. ibid., vol.35, p.2315-2322, Dec. 1987), which includes not only the carrier space-charge effects but also the velocity transient effects and the carrier diffusion effects is presented. Simple closed forms for the device impedance have been obtained for efficient computation, where only one-dimensional integrations are required. It can be applied to any fashion of time dependence of the velocity transient and diffusivity transient, adopting a Gaussian form for the spatial profile of injected carriers. Using the formulas, the small-signal behavior and the design criteria for the QWITT diode are analyzed. Large-signal impedance of the device can also be estimated by the formulas. >

Analysis of an FET amplifier using power-dependent S-parameters

The paper describes a method to derive large-signal S-parameters as functions of the output power with application to calculating the large-signal power gain of an FET amplifier. The S-parameter S22 of a microwave power FET is used to describe the nonlinearity of its large-signal output impedance, based on which the output at a given load is determined from the measured data. The large-signal S-parameters of the FET can be expressed as a quadratic function of the output power, and are used to compute the gain compression effect of the FET amplifier. This is found to be in good agreement with experimental results.

Large-signal impedance measurements and power-efficiency consideration of n+pp+ GaAs IMPATT diodes

The experimental verification of the small and large-signal analyses for n+pp+ GaAs IMPATT diodes developed by the authors is presented. The measured results are found to be in good agreement with the theory which confirms its validity. The total power generated by the diode and its maximum efficiency are also determined. Es wird eine experimentelle Verifizierung der Klein- und Groß-Signalanalyse für n+pp+-GaAs-IMPATT-Dioden durchgeführt, die von den Autorenentwickelt wurde. Die Meßergebnisse befinden sich in guter Übereinstimmung mit der Theorie, was die Zuverlässigkeit bestätigt. Die Gesamtleistung, die durch die Diode geliefert wird, sowie ihr maximaler Wirkungsgrad werden ebenfalls bestimmt.

On the large-signal behavior of transferred-electron amplifiers with a cathode notch

Transferred-electron amplifiers (TEA) are finding applications where medium powers are required as driving stages. Most work has been done up to now under small-signal conditions. The present paper describes theoretical results of a large-signal analysis. From this analysis, it appears that different large-signal behaviors of TEA devices can be associated with their corresponding dc field distribution. We compare, by computer analysis, the evolution of the large signal impedance with the RF driving signal for different doping profiles (different stationary fields) and give design figures to increase the device added power.

Efficiency limitation by transverse instability in Si IMPATT diodes

Measurements of large-signal impedance, ac voltage and dc voltage V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> versus dc current I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> on Si p-n-n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> IMPATT diodes in pulse operation (80 ns) suggest that the efficiency of Si IMPATT diodes is limited by instability effects causing a splitup into regions with different current densities. The effect is explained by considering the I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> -V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> curves at constant ac voltage. These can be S-shaped owing to impact ionization in the drift region.

A current-excited large-signal analysis of IMPATT devices and its circuit implications

A large-signal analysis of a Read-type IMPATT diode is carried out with a sinusoidal current as the excitation. The results are compared with analyses that assume a sinusoidal voltage excitation. The large-signal impedance of the diode with current excitation is expressed in closed form. The circuit implications of choosing voltage or current as the excitation are discussed.

Nonlinear operating characteristics of impatt diodes

The nonlinear equations which describe the current and field in a Read-type IMPATT have been solved in closed form by assuming that the transit time of the carriers through the drift region is small compared with the period of the microwave oscillation. Using this solution the large-signal impedance of the diode is obtained. Impedance-plane plots for large-signal operation are presented. For small r-f voltages the results reduce to those obtained by Gilden and Hines. Larger voltages result in a decrease in the negative resistance of the diode and this leads to stable oscillator operation. A region of unstable operation similar to that found by Read is also predicted. The large-signal analysis predicts, a marked change in the current tuning of IMPATT diodes as compared to the small-signal case. Experiments have been performed on an IMPATT diode in a reentrant coaxial cavity. The experimental results on frequency tuning, impedance and other operating characteristics of the oscillator are in good agreement with the theoritical predictions. The experimental and theoretical results will be presented and compared.