Showing papers on "Equivalent circuit published in 2015"

Design and Operation of a Hybrid Modular Multilevel Converter

Abstract: This paper presents a hybrid modular multilevel converter (MMC), which combines full-bridge submodules (FBSM) and half-bridge submodules (HBSM). Compared with the FBSM-based MMC, the proposed topology has the same dc fault blocking capability but uses fewer power devices hence has lower power losses. To increase power transmission capability of the proposed hybrid MMC, negative voltage states of the FBSMs are adopted to extend the output voltage range. The optimal ratio of FBSMs and HBSMs, and the number of FBSMs generating a negative voltage state are calculated to ensure successful dc fault blocking and capacitor voltage balancing. Equivalent circuits of each arm consisting of two individual voltage sources are proposed and two-stage selecting and sorting algorithms for ensuring capacitor voltage balancing are developed. Comparative studies for different circuit configurations show excellent performance balance for the proposed hybrid MMC, when considering dc fault blocking capability, power losses, and device utilization. Experimental results during normal operation and dc fault conditions demonstrate feasibility and validity the proposed hybrid MMC.

Design and Modeling of Spoof Surface Plasmon Modes-Based Microwave Slow-Wave Transmission Line

Abstract: This paper presents a theoretical model and validates experimentally the microwave slow-wave transmission line (SW-TL) based on spoof surface plasmon (SSP) modes Equivalent circuit models are first presented for characterizing the SSP structures and developed to serve as an insightful guideline to design the SW-TL at a given cutoff frequency and Bloch impedance A mode converter connecting a conventional microstrip transmission line to the SW-TL is necessarily proposed to ensure that the quasi-TEM modes of the microstrip line are gradually transformed to the operating TM modes of the SW-TL The presented schematic of SW-TL paves a promising avenue for the unprecedented interconnector footprint miniaturization of integrated circuits, and the enhanced electromagnetic compatibility, for example, in multilayered monolithic microwave integrated circuits

Topological properties of linear circuit lattices.

Abstract: Motivated by the topologically insulating circuit of capacitors and inductors proposed and tested by Jia et al. [arXiv:1309.0878], we present a related circuit with fewer elements per site. The normal mode frequency matrix of our circuit is unitarily equivalent to the hopping matrix of a quantum spin Hall insulator, and we identify perturbations that do not backscatter the circuit's edge modes. The idea behind these models is generalized, providing a platform to simulate tunable and locally accessible lattices with arbitrary complex spin-dependent hopping of any range. A simulation of a non-Abelian Aharonov-Bohm effect using such linear circuit designs is discussed.

Adaptive Nonlinear Model-Based Fault Diagnosis of Li-Ion Batteries

Abstract: In this paper, an adaptive fault diagnosis technique is used in Li-ion batteries. The diagnosis process consists of multiple nonlinear models representing signature faults, such as overcharge and overdischarge, causing significant model parameter variation. The impedance spectroscopy of a Li-ion $(\hbox{LiFePO}_{4})$ cell is used, along with the equivalent circuit methodology, to construct nonlinear battery signature-fault models. Extended Kalman filters are utilized to estimate the terminal voltage of each model and to generate residual signals. The residual signals are used in the multiple-model adaptive estimation technique to generate probabilities that determine the signature faults. It can be seen that, by using this method, signature faults can be detected accurately, thus providing an effective way of diagnosing Li-ion battery failure.

Square Loop and Slot Frequency Selective Surfaces Study for Equivalent Circuit Model Optimization

Abstract: This paper presents a parametric study of square loop and square slot frequency selective surfaces (FSSs) aimed at their equivalent circuit (EC) model optimization. Consideration was given to their physical attributes, i.e., the unit cell dimensions and spacing, substrate thickness and dielectric properties, for several frequencies and plane wave incident angles. Correlation analysis and evaluation of the influence of physical related input parameters on the FSS performance are presented. Subsequent optimization factor for the square loop classical EC model is analyzed, and a novel EC model formulation for the square slot FSS is proposed. The performance of the proposed EC model was assessed against results obtained from appropriate electromagnetic (EM) simulations, based on a root-mean-square error (RMSE) criteria. Results demonstrate the validity of the optimized EC model, in which good estimations of the frequency response of FSS structures were obtained. Significant reduction of the resonant frequency offsets, in the order of 650 (from 910 to 260) and 460 (770 to 310) MHz, was obtained for square loops and square slots, respectively. The models were further validated against measurements performed on two physical FSS prototypes inside an anechoic chamber at 2.4 GHz. Relatively good agreement was obtained between measurements of real FSS prototypes and results obtained with the EC model. Finally, this work is sought to provide the necessary refinement of elementary models for further studies with more complex and novel FSS structures.

Zero-Sequence Current Suppression Strategy of Open-Winding PMSG System With Common DC Bus Based on Zero Vector Redistribution

Abstract: The open-winding configuration with a common dc bus provides a zero-sequence current loop which allows the zero-sequence current flowing. With the application in permanent magnet synchronous generator (PMSG) systems, the existing zero-sequence current is inevitably caused by the common mode voltage generated by pulsewidth modulation (PWM) techniques and the third back EMF by the inherent flux harmonic component. With the mathematical modeling analysis, the zero-sequence equivalent circuit based on the PMSG system is proposed. Meanwhile, a zero-sequence current suppression controller is designed. In this paper, a zero vector redistribution PWM technique is proposed. With this technique, the dwell times of zero vectors (000) and (111) for both converters are determined. Meanwhile, it gives the zero-sequence component overmodulation analysis. Both the control method and improved PWM technique are implemented in a 1-kW open-winding PMSG experimental setup, and the experimental results are discussed.

Characteristic Investigation and Control of a Modular Multilevel Converter-Based HVDC System Under Single-Line-to-Ground Fault Conditions

Abstract: This paper presents the analysis and control of a multilevel modular converter (MMC)-based HVDC transmission system under three possible single-line-to-ground fault conditions, with special focus on the investigation of their different fault characteristics. Considering positive-, negative-, and zero-sequence components in both arm voltages and currents, the generalized instantaneous power of a phase unit is derived theoretically according to the equivalent circuit model of the MMC under unbalanced conditions. Based on this model, a novel double-line frequency dc-voltage ripple suppression control is proposed. This controller, together with the negative- and zero-sequence current control, could enhance the overall fault-tolerant capability of the HVDC system without additional cost. To further improve the fault-tolerant capability, the operation performance of the HVDC system with and without single-phase switching is discussed and compared in detail. Simulation results from a three-phase MMC-HVDC system generated with MATLAB/Simulink are provided to support the theoretical analysis and proposed control schemes.

Adaptive Nonlinear Model-Based Fault Diagnosis of Li-ion Batteries

Abstract: In this paper, an adaptive fault diagnosis technique is used in Li-ion batteries. The diagnosis process consists of multiple nonlinear models representing signature faults, such as overcharge and overdischarge, causing significant model parameter variation. The impedance spectroscopy of a Li-ion $(\hbox{LiFePO}_{4})$ cell is used, along with the equivalent circuit methodology, to construct nonlinear battery signature-fault models. Extended Kalman filters are utilized to estimate the terminal voltage of each model and to generate residual signals. The residual signals are used in the multiple-model adaptive estimation technique to generate probabilities that determine the signature faults. It can be seen that, by using this method, signature faults can be detected accurately, thus providing an effective way of diagnosing Li-ion battery failure.

An Equivalent Circuit Model of FSS-Based Metamaterial Absorber Using Coupled Line Theory

Abstract: An equivalent circuit model of an ultra-thin metamaterial absorber comprising a square-ring-shaped frequency selective surface (FSS) is presented. The model can be considered as series $RLC$ resonators connected in parallel with coupling capacitance and short-circuited transmission line. The even- and odd-mode couplings have been incorporated to accurately determine the lumped parameters as well as the absorption frequency of the absorber structure. The effects of substrate thickness and dielectric permittivity variation on the lumped parameters and full width at half-maximum (FWHM) bandwidth are investigated based on the proposed model. The absorber has been fabricated, and close matching among the calculated, simulated, and measured results has been observed.

An equivalent circuit grid model for no-insulation HTS pancake coils

Abstract: An equivalent circuit grid (ECG) model is proposed to analyse the time-varying characteristics of no-insulation (NI) ReBCO pancake coils. In the model, each turn of the coil is subdivided into fine elements in the azimuthal direction, and each element is equivalent to a circuit parameter. Then, the coil is equivalent to a circuit grid. A math model based on Kirchhoff's law is proposed to solve the circuit grid model. The distribution of the electrical current inside the NI coil is analysed for the charging and discharging process. A finite element method (FEM) model is coupled to calculate the magnetic field induced by the coil. To validate the model, a double pancake (DP) coil is fabricated by coated conductor ReBCO tapes. Charging and discharging tests are performed on the coil at 77 K. The results from simulations and experiments exhibit a good agreement. Then, this model is used for more studies on the current distribution inside the NI coil in the charging and discharging process. The charging and discharging delay of NI coil is analysed and explained by the model. The model can also be applied to partial insulated (PI) coils and magnets consisting of NI coils.

High-Efficient Wideband Slot Transmitarray Antenna

Abstract: A novel high-efficient, wideband, and single-linear-polarized slot-based transmitarray antenna is presented. The unit cell comprises three thin metallic layers with air gap in between, without use of any dielectric substrate. Each metallic layer has a square wide slot within which there are a number of parallel stubs. The wide slot has a high-pass response with notch at zero frequency. Addition of the stubs creates an extra controllable notch within the wide slot high-pass response. Due to the large spacing between the two notches, a passband with low-slope phase shift response is created which leads to a wideband transmitarray. The linear polarization behavior of the antenna along with a suitable feed horn and with no dielectric loss present has resulted in higher antenna efficiency. The design of a three metallic layer unit cell is also carried out through a simple circuit-based analysis approach. The transmitarray is fabricated and results are compared with those of simulation. The proposed transmitarray has a measured $- 1\;\text{dB}$ -gain bandwidth of 15.5%, peak efficiency of 55%, and a cross-polarization level of better than $-29\;\text{dB}$ . The structure is simulated via HFSS software and ADS package is used for equivalent circuit (EC) simulation.

Design and Synthesis of Multilayer Frequency Selective Surface Based on Antenna-Filter-Antenna Using Minkowski Fractal Structures

Abstract: A multilayer frequency selective surface (FSS) with subwavelength fractal elements based on the antenna-filter- antenna (AFA) concept is proposed in this paper. The upper fractal patches are inductive and non-resonant, and the fractal slots on the ground provide a capacitance. The thin substrate is equivalent to a transformer and some resonant modes are produced. Multiple transmission poles are obtained by cascading multilayer two-dimensional periodic structure array of the fractal patches and slots on the ground. The cell periods along $x$ and $y$ directions are the same and the total height is 8 mm, and the fractional bandwidth reaches 30% at normal incidence. To analyze and understand the operating mechanism of the FSS, the equivalent circuit model (ECM) is proposed to analyze the transmission and reflection characteristics. The results of the synthesis from ECM agree well with the results of full-wave simulation. The multilayer AFA-FSS has been manufactured and measured to verify the effectiveness and correctness of the design and synthesis. The simulated results are in good agreement with the tested ones.

Equivalent Circuit Representation and Analysis of Galloping-Based Wind Energy Harvesting

Abstract: Small-scale wind energy can be harvested for wireless sensing applications by exploiting the galloping phenomenon of a bluff body attached to a piezoelectric cantilever. Certain predictive model is required to understand the behavior of such a galloping-based piezoelectric energy harvester (GPEH). Conventional analytical and numerical models have simplified the interface circuit as a pure resistor. In practice, the energy generated by the harvester should be rectified before delivery to a real application. In such a case, the formulation of analytical or numerical model becomes cumbersome considering the complex coupling between the structure, fluid, piezoelectric transducer, and practical interface circuit. This paper proposes an equivalent circuit representation approach to predict the performance of GPEHs, capable of incorporating various interface circuits. The mechanical parameters and piezoelectric coupling in the system are represented by standard electronic components and the aerodynamic force by a user-defined component (nonstandard). The entire system is modeled in a circuit simulator for system-level simulation and evaluation. The proposed approach is verified by theoretical solution and experiment. Subsequent parametric study is performed to investigate the influence of standard ac and dc interfaces on the GPEH's behavior, with a focus on the threshold of galloping, power output, and induced electrical damping.

Organic electrochemical transistors for cell-based impedance sensing

Abstract: Electrical impedance sensing of biological systems, especially cultured epithelial cell layers, is now a common technique to monitor cell motion, morphology, and cell layer/tissue integrity for high throughput toxicology screening. Existing methods to measure electrical impedance most often rely on a two electrode configuration, where low frequency signals are challenging to obtain for small devices and for tissues with high resistance, due to low current. Organic electrochemical transistors (OECTs) are conducting polymer-based devices, which have been shown to efficiently transduce and amplify low-level ionic fluxes in biological systems into electronic output signals. In this work, we combine OECT-based drain current measurements with simultaneous measurement of more traditional impedance sensing using the gate current to produce complex impedance traces, which show low error at both low and high frequencies. We apply this technique in vitro to a model epithelial tissue layer and show that the data can be fit to an equivalent circuit model yielding trans-epithelial resistance and cell layer capacitance values in agreement with literature. Importantly, the combined measurement allows for low biases across the cell layer, while still maintaining good broadband signal.

Modeling of Permanent-Magnet Synchronous Machine Including Torque Ripple Effects

Abstract: A model of permanent-magnet synchronous machine (PMSM), including the electromagnetically originated torque ripple, is presented in this paper. This unique representation of such equivalent circuit is highly critical to understand the torque ripple content and to develop an appropriate mitigation scheme for low torque ripple applications requiring four quadrant operations. This research proposes a method to quantify the various sources of torque ripple and modifies the existing dq-model to enhance the modeling capabilities for both surface-mount and interior PMSMs. Finite-element (FE) analysis is used for modeling various PMSMs to verify the lumped circuit model proposed in this research. The theoretical results obtained from analytical and FE analysis are validated using experimental test.

Design of broadband and tunable terahertz absorbers based on graphene metasurface: equivalent circuit model approach

Abstract: This study presents an effective method to model, analyse and design graphene metasurface-based terahertz (THz) absorbers using equivalent circuit model approach. Broadband and tunable absorbers consisting of graphene metasurface and metal-backed dielectric layer have been designed based on the formulas derived from this approach and verified by full-wave electromagnetic simulation. By properly constructing the graphene metasurface, broadband absorption over 70% fraction bandwidth has been achieved, showing that graphene can provide a wideband absorption in the low THz spectrum. Furthermore, tunability of the graphene metasurface has also been investigated. It is demonstrated that the absorption peak frequencies can be tuned while maintaining the peak absorption unchanged, which is highly desirable for THz sensing applications.

Experiment and simulation validated analytical equivalent circuit model for piezoelectric micromachined ultrasonic transducers

Abstract: An analytical Mason equivalent circuit is derived for a circular, clamped plate piezoelectric micromachined ultrasonic transducer (pMUT) design in 31 mode, considering an arbitrary electrode configuration at any axisymmetric vibration mode. The explicit definition of lumped parameters based entirely on geometry, material properties, and defined constants enables straightforward and wide-ranging model implementation for future pMUT design and optimization. Beyond pMUTs, the acoustic impedance model is developed for universal application to any clamped, circular plate system, and operating regimes including relevant simplifications are identified via the wave number-radius product ka. For the single-electrode fundamental vibration mode case, sol-gel Pb(Zr0.52)Ti0.48O3 (PZT) pMUT cells are microfabricated with varying electrode size to confirm the derived circuit model with electrical impedance measurements. For the first time, experimental and finite element simulation results are successfully applied to validate extensive electrical, mechanical, and acoustic analytical modeling of a pMUT cell for wide-ranging applications including medical ultrasound, nondestructive testing, and range finding.

State-of-Charge Estimation for Lithium-Ion Batteries Using a Kalman Filter Based on Local Linearization

Abstract: State of charge (SOC) estimation is of great significance for the safe operation of lithium-ion battery (LIB) packs. Improving the accuracy of SOC estimation results and reducing the algorithm complexity are important for the state estimation. In this paper, a zeroaxial straight line, whose slope changes along with SOC, is used to map the predictive SOC to the predictive open circuit voltage (OCV), and thus only one parameter is used to linearize the SOC-OCV curve near the present working point. An equivalent circuit model is used to simulate the dynamic behavior of a LIB, updating the linearization parameter in the measurement equation according to the present value of the state variables, and then a standard Kalman filter is used to estimate the SOC based on the local linearization. This estimation method makes the output equation of the nonlinear battery model contain only one parameter related to its dynamic variables. This is beneficial to simplify the algorithm structure and to reduce the computation cost. The linearization method do not essentially lose the main information of the dynamic model, and its effectiveness is verified experimentally. Fully and a partially charged battery experiments indicate that the estimation error of SOC is better than 0.5%.

Optical Peaking Enhancement in High-Speed Ring Modulators

Abstract: Ring resonator modulators (RRM) combine extreme compactness, low power consumption and wavelength division multiplexing functionality, making them a frontrunner for addressing the scalability requirements of short distance optical links. To extend data rates beyond the classically assumed bandwidth capability, we derive and experimentally verify closed form equations of the electro-optic response and asymmetric side band generation resulting from inherent transient time dynamics and leverage these to significantly improve device performance. An equivalent circuit description with a commonly used peaking amplifier model allows straightforward assessment of the effect on existing communication system architectures. A small signal analytical expression of peaking in the electro-optic response of RRMs is derived and used to extend the electro-optic bandwidth of the device above 40 GHz as well as to open eye diagrams penalized by intersymbol interference at 32, 40 and 44 Gbps. Predicted peaking and asymmetric side band generation are in excellent agreement with experiments.