Unified Circuit Model Research Articles

Calculation of Earth Surface Potential and Neutral Current Caused by HVDC Considering Three-Dimensional Complex Soil Structure

In ground return mode of high-voltage direct current (HVDC) transmission, direct current is injected into the soil through a ground electrode, causing ground potential rise in different areas and direct current at the neutral point of transformers. Earth surface potential (ESP) and neutral current are closely related to the 3-D structure of soil, but few studies treat the soil three dimensionally when calculating these two parameters. In this article, a 3-D resistor network (RN) is developed to construct the soil model, and a soil–grid unified circuit model is proposed to simplify the calculation of neutral current. The RN method is verified by calculating ESP of a horizontal multilayer soil model and contrasting the result with that of CDEGS software. The feasibility and accuracy of the soil–grid unified circuit model is demonstrated through comparing neutral currents of two substations with the results calculated by finite-element method (FEM). The influence of resistivity changes in a water-bearing fault on ESP and neutral current is specifically analyzed using RN method and FEM to prove the necessity of considering the 3-D complex soil structure. The results of this article contribute to the simulation of DC distribution of wide-area HVDC transmission in complex soil structures.

A Physics Based Unified Circuit Model for Single Photon and Analog Detector

Photodetectors having an internal carrier multiplication mechanism such as avalanche detectors and recently discovered detectors with cycling excitation process (CEP) have attracted tremendous interests for their high sensitivity and flexibility of being operable in analog, sub-Geiger and Geiger mode. Detection of single or few photons in Geiger mode or sub-Geiger mode is particularly interesting as LiDAR systems are finding a wide range of applications in autonomous driving, augmented and virtual reality, robotics, imaging, sensing, and communications. In this paper, we present a universal detector equivalent circuit model, applicable to all modes of operation, for photodetectors with carrier multiplication gain. The bias-dependent gain, bandwidth, as well as gain buildup dynamics are rooted in device physics and translated into an equivalent circuit model that can be readily incorporated into integrated circuit design. The model simulates the characteristics of devices biased below and above breakdown voltage, making seamless transitions between analog, sub-Geiger, and Geiger mode with the same set of parameters directly obtained from the material properties. As a result, circuit designers can choose detectors using different gain medium (e.g., Si, InP, InAlAs) to simulate device effects on system performance. The circuit model is implemented in Orcad PSpice circuit simulator. Its wide applicability is demonstrated by simulating the device in linear, sub-Geiger and Geiger mode with external amplifiers and quenching circuits, as well as the gain-bandwidth product of detectors with a Si and InAlAs gain medium.

A Topology Synthetization Method for Single-Phase, Full-Bridge, Transformerless Inverter with Leakage Current Suppression Part I

Single-phase full-bridge transformerless topologies, such as the H5, H6, or the highly efficient and reliable inverter concept (HERIC) topologies, are commonly used for leakage current suppression for photovoltaic (PV) applications. The main derivation methodology of full-bridge topologies has been used based on both a DC-based decoupling model and an AC-based decoupling model. However, this methodology is not suited to the search for all possible topologies, and cannot verify whether they are inclusive. Part I of this paper will propose a new topology derivation methodology based on unipolar sinusoidal pulse width modulation (USPWM) to search all possible full-bridge topologies for leakage current suppression. First of all, a unified circuit model is proposed, instead of the DC- and AC-based models. Secondly, a mathematic method called the MN principle is then proposed to search for all possible topologies, and a derivation procedure is provided. It was verified that all existing topologies could be found using the proposed method; furthermore, seven new topologies were derived. The proposed topology derivation methodology is extended to search topologies under Double-Frequency USPWM (DFUSPWM). Twenty topologies under USPWM and four topologies under DFUSPWM have been derived.

Dynamic Wireless Charging for Inspection Robots Based on Decentralized Energy Pickup Structure

To deal with the problems of charging for inspection robots in substations such as frequent charging, complex mechanical interface, and insufficient battery capacity, a dynamic wireless charging system is proposed. The structure design of energy pickup device and the indispensable positioning strategy is presented in this paper. First, the dynamic wireless charging systems based on centralized energy pickup and decentralized energy pickup (DEP) are investigated and the unified circuit model is built for two kinds of systems simultaneously. Based on the comparison of working performances, the DEP structure is selected as the pickup device in this paper. Then, the positioning scheme is realized based on imitative relaying coil structure including the DEP device and the additional sensor coil. A switching control strategy of the segmented transmitting coils is proposed further to implement the dynamic wireless charging for inspection robots. The theoretical analyses are validated by the relevant experiments.

Circuit Models for Ferroelectrics—Part II: Analysis of FE-Nonvolatile Latches

We present a detailed analysis of hybrid ferroelectric (FE)-CMOS nonvolatile latches, based on simulations with the unified physical circuit model from Part-I and experimental verification with circuit measurements. Hybrid FE-CMOS latches are categorized into three classes by the circuit topology of the readout operation. The effect of the physical model parameters is studied in all regions of operation by a variational analysis. Design intuition for the signal timing and sensing margin is provided and the strategies for the design optimization are discussed. Signal degradation due to imprint and fatigue in each latch topology is also compared.

A Generalized 2-D Multiport Model for Planar Circuits With Slots in Ground Plane

A new approach for multiport network modeling (MNM) of multilayer planar circuits coupled through slots in ground plane is introduced. Generalized network formulation for aperture problems is combined with Okoshi's model for planar circuits to obtain a unified circuit model for two irregularly shaped planar circuits coupled through a slot of arbitrary shape in their common ground plane. The methodology, which can be generalized to structures having more than two layers, is described by applying the method to a two-layer structure. Results for several sample structures will also be presented

A unified circuit model for static and dynamic analyses of semiconductor optical amplifiers and laser diodes

Semiconductor optical amplifiers (SOAs) and laser diodes (LDs) are important components for optical systems. The structure and principle of SOAs and LDs are similar. In this paper, we have proposed a unified equivalent circuit model, which includes time delay circuit and different boundary conditions, for the simulations of traveling wave (TW) SOAs, Fabry–Perot (FP) SOAs and LDs. The effect of amplified spontaneous emission on FP-SOAs is also taken into account. Using this circuit model, our simulation results are in good agreement with published results for SOAs. This model has also been applied to analyze the static and dynamic behavior in LDs. A good agreement between our simulated results and the theoretical calculations is observed for LDs.

Identification of a new function model for the AC-impedance of thermally evaporated undoped selenium films using the Eigen-coordinates method

The experimental AC-impedance data of undoped amorphous and polycrystalline selenium films were taken at T=300K in the frequency range 100 Hz–10 kHz in the dark and under band-gap illumination. The data were analyzed using the Eigen-coordinates method in conjunction with a ‘separation’ procedure without prior use of equivalent circuits. A unified circuit model with generalized impedances was recognized to parameterize well the observed AC-impedance behavior. The features of this electrical model were linked to the fractality of the heterogeneous structural regions in these selenium specimens via one or two recap elements, each represented by a complex impedance of fractional power-law frequency behavior. These recap elements reflect the electric properties of scale-invariant circuits of self-affine normal (ideal) resistor–capacitor (RC) cells of the Cauer/Forster type.

Unified equivalent-circuit model of planar discontinuities suitable for field theory-based CAD and optimization of M(H)MIC's

Unified dynamic equivalent-circuit model for characterizing planar unbounded discontinuities is reported for use in the field-theory-based computer-aided design and optimization of high-frequency integrated circuits and structures such as monolithic and hybrid microwave integrated circuits (M(H)MIC's). The proposal of the circuit model is stemmed from a new scheme called the short-open calibration (SOC) technique. This SOC technique is directly accommodated in a full-wave method-of-moments (MoM) algorithm. The developed MoM algorithm is applied to the modeling of unbounded planar discontinuities that can be segmented into two distinct sections: static model of feed lines and dynamic model of circuit discontinuity. In this paper, the MoM, is formulated in such a way that the port voltages and currents are explicitly represented through relevant network matrices. The SOC technique is used to remove or separate unwanted parasitics brought by the approximation of the impressed voltage source and also the problem of resulting consistency between the two-dimensional and three-dimensional simulations. Results for a class of planar circuit discontinuities are very well compared with measurements and also available publications. Generalized end-to-end coupling structure having offset and unequal input/output lines (to name a specific example) is studied to indicate the parametric and dispersion effects on its equivalent capacitance and radiation conductance. Advantageous features of the proposed unified circuit model suggests its practical usefulness and high accuracy in the design and optimization of a wide range of M(H)MIC's and planar antennas.

A unified circuit model for bipolar transistors including quasi-saturation effects

This paper describes a compact model for bipolar transistors which includes quasi-saturation effects. The assumptions used in the formulation of this model are clearly stated and justified, and a step by step derivation of the model equations is presented. These equations model both de and charge storage effects. Parameter extraction techniques are qualitatively described and the compact model is evaluated using detailed physical simulations of a high voltage bipolar transistor. In addition, simulations employing this model are compared with measurements and are found to be in excellent agreement.