Small-signal Behavior Research Articles

Predictive Trajectory Control with Online MTPA Calculation and Minimization of the Inner Torque Ripple for Permanent-Magnet Synchronous Machines

This paper presents an extended predictive trajectory control scheme combined with an inner torque ripple minimization considering the current-, flux-linkage-, and voltage-planes of permanent magnet synchronous machines. The extension of a fundamental machine model with flux-linkage harmonics allows the calculation of the inner torque ripple and enables its minimization. For this, the control is divided in two cases: (1) The dynamic operation or large signal behavior which uses the maximal torque gradient for the trajectory strategy during each control period for fastest dynamic operation, and (2) The stationary operation or small signal behavior, utilizing a real time capable polynomial approximation of the rotor position dependent torque hyperbolas (iso-torque curves) of permanent magnet synchronous machines for the ideal torque to current reference values. Since dynamic and steady-state operation is covered, torque to current look-up tables, such as maximum torque per ampere (MTPA)/maximum torque per volt/voltage (MTPV) look-up tables, are not required anymore. The introduced, new control approach is implemented in Matlab/Simulink based on finite element analysis and measured data. Furthermore, test-bench implementations based on measurement data are presented to show the real-time capability and precision.

Modeling and controller optimization for current-fed isolated bidirectional DC–DC converters

Current-fed isolated bidirectional DC–DC converters (CF-IBDCs) play an important role in battery energy storage systems. However, the closed-loop dynamics is rather slow with conventional proportional–integral controllers because a precise mathematic model remains absent for optimization. In this paper, a simple precise mathematical model is presented to describe the large and small-signal behaviors of the CF-IBDC. The full-order continuous model can accurately capture the dynamic behaviors and cover all operation conditions. The small-signal model is derived, and the DC filter inductors and clamp capacitors are found to be the natural causes of instability. Based on this finding, special controllers are proposed to optimize the dynamic response of the full closed-loop control system. The dynamic response time of the CF-IBDC is greatly reduced with the proposed controller. The correctness of the presented model and the dynamic response of the optimized closed-loop control system are verified by simulations.

Equivalent Circuit Modeling of LLC Resonant Converter

LLC resonant converter is widely used in industry. However, up to now, no simple and accurate small-signal equivalent circuit model is available. This article proposes an equivalent circuit model of LLC resonant converter. The simple equivalent circuit model is derived based on modification and simplification of extended describing function method, which has already been successful deriving equivalent circuit model in series resonant converter [15] . The model can well predict the small-signal behaviors observed in pulse-frequency-modulated LLC resonant converter, whenever switching frequency is below, close to, or above the resonant frequency. For the first time, analytical expressions for control to output voltage, input to output voltage, input impedance, and output impedance are provided to aid closed-loop feedback design. SIMPLIS simulation and experimental results are presented to prove the accuracy of the model.

Modeling of high-side active clamp forward converter with resistive parasitics

Purpose The purpose of this paper is to derive the small-signal/canonical model derivation of the high-side active clamp forward converter (ACFC) with diode rectification for ideal and with resistive parasitics. It also covers the analysis of ACFC small-signal model with resistive parasitics using computer-aided modeling software Personal Computer Simulation Program with Integrated Circuit Emphasis (PSPICE) 16.6. The effects of variation of system parameters on the ACFC’s state transfer functions and operations have been highlighted in this paper. Design/methodology/approach The large-signal model and small-signal model of the ACFC with diode rectification has been derived using AC small-signal modeling approach. Findings The operating point of the converter changes with the consideration of resistive parasitics compared with the ideal case. The response obtained from the hardware matches with the time domain response of the averaged model and switch model developed in PSPICE. Research limitations/implications This paper limits the study of ACFC small-signal behavior by using computer-aided design software PSPICE. The dead time of the converter is not considered because it is negligible when compared with the on and off time. The leakage inductance which plays a role in zero voltage switching of the ACFC switches is neglected in the analysis as it is very small compared to the magnetizing inductance. The switching losses are not considered in the modeling. Practical implications The mathematical computation of deriving the system transfer functions from canonical model is complex and time consuming. Originality/value The modeling with resistive parasitics improves the effectiveness of the equivalent model. Also, the analysis with computer-aided modeling software PSPICE gives reliable results in less time.

Reduced‐order small signal modelling of high‐order high step‐up converters with clamp circuit and voltage multiplier cell

Generally, the modelling of high step-up converters with a large number of passive components consisting of inductors, coupled-inductors (CL) and capacitors is very complex. Recently, to further increase the voltage gain in high step-up converters in a simple and low-cost manner, voltage multiplier (VM) circuits have been increasingly used. Also, to reduce the switch voltage spike, clamp circuits are applied. This leads to an increase in the order of systems and operational modes as well. Thus, for simpler modelling and reducing the state variables, the use of reduced-order techniques are required. A general structure for small signal modelling of such converters including passive clamp, CL and VM circuits is presented. For this purpose, an example of these types of converters is selected. At first, a full-order model of this high-order converter is derived using the state-space averaging method. Then, two reduced-order models of the converter are derived and then compared with the full-order model. Also, the small signal and low frequency behaviour is evaluated. In addition, the impact of the parameter variations on the frequency response and stability margin is investigated. Finally, experimental results based on laboratory prototype are presented to verify the validity of the theoretical analysis.

Small-Signal Modeling of LLC Converters Using Homopolarity Cycle

The widespread use of the LLC converter in dc–dc applications has increased the importance of small-signal modeling to control the converter below- to above-resonant frequency. The analysis of LLC converters is complicated, since they process the electrical energy through a high-frequency resonant tank that causes excessive nonlinearity. As a result of this complexity, small-signal modeling of the LLC converter is traditionally performed using empirical methods, iterative simulation approaches, or theory limited to the vicinity of the resonant frequency. Often, such approaches may lead to limited insight (just empirical trends) or low accuracy below and above resonance. This article proposes a new average small-signal modeling technique for the LLC converter, and it is performed in the time domain. The proposed technique is based on the analysis of the homopolarity cycle and accurately predicts not only the small-signal dynamic behavior of the LLC converter at resonance, but also below and above resonance. By using the homopolarity cycle, the theoretical analysis of the LLC converter is significantly simplified to a level that the small-signal dynamic behavior of the LLC converter is expressed by two second-order circuit models. Experimental and simulation results of a 650-W LLC converter are provided to verify the theoretical analyses and accuracy of the circuit models. The results have shown that the proposed small-signal circuit models can accurately predict the small-signal dynamic behaviors of the LLC converter from below- to above-resonant operations.

RF analysis and noise characterization of junctionless nanowire FETs by a Boltzmann transport equation solver

The junctionless nanowire field-effect transistor (JN-FET) stands out among the most promising architectures for future MOSFETs. While a fair amount of the published literature has focused on the static performance of JN-FETs, detailed numerical investigation of their RF small-signal and noise behavior on the device level still lacks. This paper reports the ac and noise characteristics of JN-FETs with different gate lengths and shows that due to the improved electrostatic control and better immunity to short-channel effects, several key quantities such as the drain/gate excess noise factors and correlation coefficient demonstrate classical long-channel behavior for channel lengths as small as 16 nm. The results are obtained using an in-house simulation tool, which provides the deterministic and self-consistent solution of the multi-subband Poisson, Schrodinger, and Boltzmann equations.

Fixed Switching Frequency Digital Sliding-Mode Control of DC-DC Power Supplies Loaded by Constant Power Loads with Inrush Current Limitation Capability

This paper proposes a digital sliding-mode controller for a DC-DC boost converter under constant power-loading conditions. The controller has been designed in two steps: the first step is to reach the sliding-mode regime while ensuring inrush current limiting; and the second one is to move the system to the desired operating point. By imposing sliding-mode regime, the equivalent control and the discrete-time large-signal dynamic model of this system are derived. The analysis shows that unlike with a resistive load, the boost converter under a fixed-frequency digital sliding-mode current control with external voltage loop open and loaded by a constant power load, is unstable. Furthermore, as with a resistive load, the system presents a right-half plane zero in the control-to-output transfer function. After that, an outer controller is designed in the z-domain for system stabilization and output voltage regulation. The results show that the system exhibits good performance in startup in terms of inrush current limiting and in transient response due to load and input voltage disturbances. Numerical simulations from a detailed switched model are in good agreement with the theoretical predictions. An experimental prototype is implemented to verify the mathematical analysis and the numerical simulation, which results in a perfect agreement in small-signal and steady-state behavior but also in a small discrepancy in the current limitation due a small propagation delay. Some efficient solutions have been proposed to mitigate the inrush current in the experimental results.

Small-Signal Modeling and Stability Analysis of Hybrid AC/DC Microgrids

The deployment of hybrid ac/dc microgrids is a promising alternative for using local distributed energy resources to serve both ac and dc loads. Hybrid ac/dc microgrids, like other types of microgrids, are subjected to dynamic instability when operated in island mode. This paper analyzes the small-signal stability of islanded hybrid ac/dc microgrids and proposes a droop-based control mechanism to coordinate the operation of ac and dc sections. A general approach is presented which uses a linearized state-space model of microgrids for establishing adequate stability margins in hybrid ac/dc microgrid operations. The proposed case studies are conducted to investigate the small-signal behavior of a hybrid ac/dc microgrid based on time-domain simulations and frequency-domain analyses.

Linearity Distortion Assessment and Small-Signal Behavior of Nano-Scaled SOI MOSFET for Terahertz Applications

Fully-Depleted Silicon-on-Insulator (FD SOI) MOS technology has already been reported as a strong contender in nanoscale CMOS designs. This work presents the linearity-distortion assessment, small-signal and radio-frequency noise-behavior of dual-metal-insulated-gate (DMIG) source-engineered (SE) FD SOI MOSFET for terahertz (THz) applications. Here, linearity-distortion performance has been monitored on the basis of numerical calculations of transconductance and its higher-order derivatives along with the voltage-intercept points, and various parameters of intermodulation-distortion. This analysis also practices the guidelines of device design with least linearity-distortion in radio-frequency integrated-circuits based communication systems at 50 nm technology node. Further, the small-signal and RF noise-behavior have been examined on the basis of high-frequency scattering-parameters for the analysis of input/output reflection-coefficients (S11/S22), reverse/forward transmission-coefficients (S12/S21), Stern's-stability-factor (K), minimum noise-figure, noise-conductance and cross-correlation factor (<VN-in.VN-out*>). The analysed results affirm the ultimate reduction in reflection-coefficients and a significant increase in transmission-coefficients in case of DMIG FD SOI MOSFET at THz range as compared to existing MOS structures. Also, the analysis reveals the considerable reduction in various radio-frequency noise FOMs and thus represents the device efficacy in low-noise-amplifiers. All these studies have been carried out by performing numerical simulations over TCAD-ATLAS simulator from Silvaco along with quantum-mechanical-effect (QME) and Bohm-quantum-potential (BQP) models.

In2O5Sn based transparent gate recessed channel MOSFET: RF small-signal model for microwave applications

This paper discusses the small signal RF model of Transparent Gate Recessed Channel (TGRC) MOSFET using a 3D TCAD device simulator. Small signal model is studied in terms of microwave parameters such as S (scattering) parameters, Z (impedance) parameters, Y (admittance) parameters, and h (hybrid) parameters with an aim to analyze the behavior of TGRC MOSFET at microwave frequency. All the results of TGRC-MOSFET have been compared with Conventional Recessed Channel (CRC) MOSFET having aluminum as gate metal electrode. Modeled results have also been compared with simulation results and found good agreement with the 3D-simulation results. Moreover, it is perceived from the results that 99.4% enhancement in the input impedance of TGRC-MOSFET and input admittance is improved by 32.9% in the proposed device (TGRC-MOSFET) in comparison to CRC-MOSFET. It has also been observed that the transit (cut-off) frequency (fT) and maximum oscillator frequency (fMAX) enhances significantly by 42.85% and 123% respectively in TGRC MOSFET owing to the remarkable reduction in intrinsic capacitances. Results reveal that the proposed device design improves the small signal behavior thus, may provide detailed insight to RF engineers for microwave applications and testing of RF ports.

Small Signal Dynamics of DFIG-Based Wind Turbines During Riding Through Symmetrical Faults in Weak AC Grid

Instability issues of the grid-connected doubly fed induction generator (DFIG) based wind turbines (WTs) during low-voltage ride-through (LVRT) have got little attention yet. In this paper, the small-signal behavior of DFIG WTs attached to weak ac grid with high impedances during the period of LVRT is investigated, with special attention paid to the rotor-side converter. First, based on the studied LVRT strategy, the influence of the high-impedance grid is summarized as the interaction between phase-looked loop (PLL) and rotor current controller (RCC). As modal analysis result indicates that the underdamped poles are dominated by PLL, complex torque coefficient method, which is conventionally applied in power system to study the interaction between mechanical and electrical subsystems of synchronous generator, is generalized to analyze how the PLL-RCC interaction influence the phase motion of PLL. Then, the concerned small-signal stability of the PLL-synchronized DFIG system can be discerned by the developed complex phase coefficients. Impacts of PLL's and RCC's parameters are highlighted, as well as the system's operating conditions during LVRT. Finally, the analytical result is validated by experiments.

On g m-boosted follower-amplifier and its novel circuit transformation based mid-band derivations

This brief paper investigates the small-signal mid-band behavior of g m-boosted follower-amplifiers which has not been explored previously and whose analysis is not available in text-books or any other source. Both g m-boosted source follower and g m-boosted emitter follower are considered in the mid-band analysis. A novel circuit/source transformation based “pictorial” technique with progressively simplified circuit diagrams is employed for this mid-band analysis which generally eliminates the need for solving nodal or mesh equations. Final expression is often achieved by inspection of the simplified circuit without the need for circuit analysis. The paper also discusses g m-boosted BiCMOS follower amplifier using substrate PNP device in a pure CMOS process. The analysis demonstrates that the unity gain accuracy of follower-amplifier can be considerably enhanced using the g m-boosting technique without sacrificing bandwidth.

Electrothermal feedback in kinetic inductance detectors

In kinetic inductance detectors (KIDs) and other similar applications of superconducting microresonators, both the large and small-signal behaviour of the device may be affected by electrothermal feedback. Microwave power applied to read out the device is absorbed by and heats the superconductor quasiparticles, changing the superconductor conductivity and hence the readout power absorbed in a positive or negative feedback loop. In this work, we explore numerically the implications of an extensible theoretical model of a generic superconducting microresonator device for a typical KID, incorporating recent work on the power flow between superconductor quasiparticles and phonons. This model calculates the large-signal (changes in operating point) and small-signal behaviour of a device, allowing us to determine the effect of electrothermal feedback on device responsivity and noise characteristics under various operating conditions. We also investigate how thermally isolating the device from the bath, for example by designing the device on a membrane only connected to the bulk substrate by thin legs, affects device performance. We find that at a typical device operating point, positive electrothermal feedback reduces the effective thermal conductance from the superconductor quasiparticles to the bath, and so increases responsivity to signal (pair-breaking) power, increases noise from temperature fluctuations, and decreases the noise equivalent power (NEP). Similarly, increasing the thermal isolation of the device while keeping the quasiparticle temperature constant decreases the NEP, but also decreases the device response bandwidth.

Output Impedance Improvement Using Coupled Inductors

When using a single DC/DC converter with multiple outputs and having a buck topology, which has one filter inductor per output, the designer can choose to couple these outputs together. This paper demonstrates additional benefits of coupling output inductors together. Apart from saving mass and volume, and due to an improved small signal behaviour it also reduces the output impedance of the regulated output. The paper will analyse a seven output push-pull converter used as a space power converter module and verify the theoretical results with experimental measurements.

Dynamic Magnetomechanical Behavior of Tb&lt;italic&gt;x&lt;/italic&gt;Dy1–&lt;italic&gt;x&lt;/italic&gt;Fe&lt;italic&gt;y&lt;/italic&gt;Alloy Under Small-Signal AC Drive Fields Superposed With Various Bias Fields

The small-signal vibration model of Tb x Dy1– x Fe y plate was developed by mechanical-electrical analogy method. Based on the model, we demonstrated the reasonableness of measuring the small-signal magnetomechanical behaviors by a laser Doppler vibrometer. The strain coefficient of the Tb x Dy1– x Fe y plates was measured as a function of frequency and bias field ( $H_{\mathrm{ dc}})$ , and Young’s modulus, mechanical quality factor ( $Q_{m})$ , relative permeability, and magnetomechanical coupling coefficient were investigated as a function of $H_{\mathrm{ dc}}$ . Many novel characteristics were observed under the drive of a small-signal field (7.96 A/m). The change tendency of the strain coefficient at resonance differs from that at low frequency, and the resonant strain coefficients are significantly high (>85 nm/A) in a wide range of bias field from 4.78 to 55.72 kA/m. Both the negative- $\Delta E$ and positive- $\Delta E$ effects are observed, and the negative- $\Delta E$ effect in the low field range is also remarkable. In particular, $Q_{m}$ sharply decreases from the initial value of 104 to a minimum value of 11.4 and, then, increases slowly, and the ratio of the maximum variation of $Q_{m}$ over $H_{\mathrm{ dc}}$ to the minimum value of $Q_{m}$ exceeds $\sim 812.3$ %. This is an important systematic investigation on the small-signal dynamic magnetomechanical behavior of Tb x Dy1– x Fe y , and the results are highly beneficial to the designing of magnetostrictive devices.

Influence of gate metal engineering on small-signal and noise behaviour of silicon nanowire MOSFET for low-noise amplifiers

In this paper, we have investigated the small-signal behaviour and RF noise performance of gate electrode workfunction engineered (GEWE) silicon nanowire (SiNW) MOSFET, and the results so obtained are simultaneously compared with SiNW and conventional MOSFET at THz frequency range. This work examines reflection and transmission coefficients, noise conductance, minimum noise figure and cross-correlation factor. Results reveal significant reduction in input/output reflection coefficient and an increase in forward/reverse transmission coefficient owing to improved transconductance in GEWE-SiNW in comparison with conventional counterparts. It is also observed that minimum noise figure and noise conductance of GEWE-SiNW is reduced by 17.4 and 31.2 %, respectively, in comparison with SiNW, thus fortifying its potential application for low-noise amplifiers (LNAs) at radio frequencies. Moreover, the efficacy of gate metal workfunction engineering is also studied and the results validate that tuning of workfunction difference results further improvement in device small-signal behaviour and noise performance.

TFT Small Signal Model and Analysis

We present an accurate small signal model for thin-film transistors (TFTs) taking into account non-idealities, such as contact resistance, parasitic capacitance, and threshold voltage shift. The model gives high accuracy in S-parameters, and the predicted cutoff frequency yields 1% discrepancy compared with measurement results. In contrast, the conventional CMOS small signal model adapted for TFTs yields 12.5% error. The TFT’s cutoff frequency is also evaluated under bias stress to examine the effect of device instability on small signal behavior.

Small-signal Modeling and Analysis of KY Buck–Boost Converter

The KY buck–boost converter, constructed by combining the KY converter and the traditional synchronously rectified buck converter, is a good topology for bucking or boosting the input voltage to the desired output voltage with the same polarity since it has several good features, including always operating in continuous conduction mode operations and non-pulsating output current. This article investigates the small-signal modeling and analysis of a KY buck–boost converter. After deriving the mathematical model of the KY buck–boost converter, its averaged model and small-signal model are established by using the averaging method and the geometrical technique; then the corresponding transfer functions are derived, analyzed, and confirmed by circuit experiments. The results show that the derived small-signal model here is an effective and accurate model to describe the small-signal dynamical behaviors of the KY buck–boost converter.

InGaZnO TFT behavioral model for IC design

This paper presents a behavioral model for amorphous indium---gallium---zinc oxide thin-film transistor using artificial neural network (ANN) based equivalent circuit (EC) approach to predict static and dynamic behavior of the device. In addition, TFT parasitic capacitances (CGS and CGD) characterization through measurements is also reported. In the proposed model, an EC is derived from the device structure, in terms of electrical lumped elements. Each electrical element in the EC is modeled with an ANN. Then these ANNs are connected together as per the EC and implemented in Verilog-A. The proposed model performance is validated by comparing the circuit simulation results with the measured response of a simple common-source amplifier, which has shown 12.2 dB gain, 50 μW power consumption and 85 kHz 3-dB frequency with a power supply of 6 V. The same circuit is tested as an inverter and its response is also presented up to 50 kHz, from both simulations and measurements. These results show that the model is capable of capturing both small and large signal behavior of the device to good accuracy, even including the harmonic distortion of the signal (that emphasizes the nonlinear behavior of the parasitic capacitance), making the model suitable for IC design.