Bode Diagram Research Articles

Sensitization of AgInS2 nanoparticles enhances photoelectrochemical water splitting performance of CeO2 nanosheet arrays photoanode

In this study, we present a promising CeO2/AgInS2 heterostructure photoanode for photoelectrochemical (PEC) water decomposition. Mott-Schottky analysis is employed to confirm the formation of a type-II heterostructure between AgInS2 nanoparticles and CeO2 nanosheet arrays (NSAs) fabricated through electrochemical deposition and successive ionic layer adsorption and reaction. Electrochemical impedance spectroscopy, photoluminescence analysis, and Bode diagram spectroscopy confirm the effective charge carrier separation and significantly prolonged the charge lifetime of the CeO2/AgInS2 heterojunction photoanode. Consequently, the maximum photocurrent density of the constructed CeO2/AgInS2 photoanode relative to Ag/AgCl under zero bias test conditions is 69.8 times higher than the pure CeO2 NSAs. Additionally, the charge transfer mechanism is further verified by the calculated work function and differential charge density of CeO2/AgInS2 heterojunction. This study provides a valuable reference for the synthesis and preparation of heterojunction photoanode for efficient PEC water decomposition.

Impedance dynamics in tandem solar cells based on c-Si with upper layers of CsPbBr3 (CsPbI3) perovskite nanocrystals

The application of an additional nanoparticle layer is a common practice for enhancing the optical and electrical properties of third-generation solar cells. In this study, we present the results of impedance spectroscopy (IS) for modified solar cells using Nyquist and Bode diagrams. The structure investigated consists of a conventional double junction based on crystalline silicon (c-Si) coated with thin films of inorganic perovskite nanocrystals (NC) of lead halides CsPbI3 and CsPbBr3. The latter are characterized by a significant phonon disorder, which leads to unique electron-phonon interactions and dielectric responses. The IS results indicate that, under the same conditions, the measured Nyquist plots align well with the simulated ones. An equivalent circuit model is proposed, featuring ohmic resistance, recombination resistance, and geometric capacitance. These elements arise due to charge accumulation, charge transfer resistance, and/or additional interfacial electronic states. The study finds that the introduction of a CsPbI3 layer enhances the photoresponse under bias conditions, but this photoresponse leads to a decrease in DC conductivity. In contrast, the addition of a CsPbBr3 layer obstructs the photoresponse under bias while slightly improving the photoresponse in the absence of an applied voltage. The results obtained contribute to the improvement of tandem solar cell characteristics featuring top layers of perovskite nanocrystals.

Reliability analysis of a three-phase interleaved step-up DC-DC converter for electric vehicle

Increasing the amount of direct current (DC) loads in applications such as airplanes, spacecraft, electric vehicles (EV), and other similar applications DC-DC converters are commonly used. Hence, a three-phase interleaved step-up DC-DC converter (ISC) has been designed, and implemented, which is more appropriate for high-power applications. The modes of operation are explained in detail, and voltage gain calculations are performed. The state space matrix is derived from the voltage equation and the bode diagram is plotted using MATLAB code to investigate the stability study, which makes for a thorough frequency response analysis for the proposed converter. The military handbook (MIL-HDBK-217F) data have been used to perform the calculations to determine each and every component's reliability. The proposed ISC design is implemented into a hardware prototype that produces peak-to-peak output voltage of 139 V, rated voltage of 120 V and the testing outcomes are presented in great depth.

Validity of LiPON Conductivity Determined by Impedance Spectroscopy

A hypothesis that the generally accepted value of the LiPON conductivity should be attributed to the absorption and displacement currents is substantiated. The reason is a small contribution of the drift current due to field screening by the electric double layer. The basis for this assumption is the measurement of the LiPON absorption capacitance, according to which its dielectric constant is about 106. An alternative equivalent circuit containing a non-ideal absorption element is proposed and its impedance is calculated. It is shown that the Bode diagrams of the alternative circuit approximate the experimental curves well. Parameters and the magnitude of electric field screening are calculated based on a proposed model of a double electric layer. Considering the screening effect, the drift conductivity of LiPON is obtained, which is in good agreement with the data on lithium concentration and ion mobility.

Optical constants and thickness gradients for light intensities in glass substrate layers and for complex electric fields in indium tin oxide (ITO) transparent conductor thin film layer, using Bode and Nyquist wavelength-dependent diagrams

Abstract The optical constants of a thin film layer of transparent conductive indium tin oxide (ITO), deposited on a thick glass substrate (G), were obtained for an ITO-G sample using a multilayer matrix method by fitting the regular transmittance and specular reflectance measurements to the collimated equations of the four-flux model, once the optical constants of the glass substrate layer had previously been obtained from a G sample of a single glass substrate layer. The accuracy of the results was validated using a feedback system called the three-extinction matching requirement, that is, obtaining the same extinction coefficients from the optical constants and from the forward and backward collimated differential equations of the four-flux model. To calculate the extinction coefficients of the glass from optical constants, the compression of the wavelength of the incident light in the glass substrate and in the thin ITO film layer was demonstrated, with a thickness less than the wavelength of incident light. The thickness gradients of the forward and backward collimated light intensities, on the glass substrate of the ITOG sample, were compared with those obtained for the single-layer G sample. Then, the thickness gradients for the complex forward and backward electric fields of the ITO thin film layer were obtained and plotted using spectral magnitude and phase Bode plots and new Nyquist plots, i.e. imaginary versus real parts, dependent on wavelength.

A black‐box method for the stability analysis of multi‐inverter‐fed power systems using Bode diagrams

AbstractA multi‐inverter‐fed power system is susceptible to small‐signal instability owing to weak grid influence. This study proposes a black‐box method for small‐signal stability analysis of a multi‐inverter‐fed power system based on Bode diagrams. Not only did it consider the technical confidentiality on the engineering site, but it also took into account the presence of right‐half‐plane (RHP) pole in the aggregated impedance, achieving Nyquist circle acquisition through Bode diagrams. The stability analysis process is thus more accurate, intuitive, and convenient. First, black‐box impedance fitting for a single grid‐connected inverter and impedance aggregation for a multi‐inverter‐fed power system are discussed. Second, the principle of the proposed method is elaborated. Using the Bode diagram, the number of RHP poles of the aggregated impedance and actual number of circles for Nyquist curves are identified. Third, a multi‐inverter‐fed power system is constructed, and the effectiveness of the proposed method is verified using case analysis and hardware‐in‐the‐loop real‐time experiments based on RT‐LAB. Finally, the advantages of the proposed method are revealed by comparing it to the IF method.

A state feedback control with compensation for permanent magnet synchronous machine drives

Using the linear approach to design a controller is still prevalent. The state feedback control (SFC) is applied in this paper to improve the dynamic response of permanent magnet synchronous machine (PMSM) speed regulation systems. First, a third-order augmented system is constructed for the reason that a higher-order system has better disturbance rejection. It can be found through analysis and comparison that the order of the proposed speed controller is increased. The parameters of SFC are selected by utilizing the linear quadratic regulator (LQR), and the influence of matrix Q on dynamic performance is detailed through the Bode diagram. Additionally, considering parametric uncertainties and unmodeled dynamics, a disturbance observer (DOB) using the Luenberger observer is designed to further boost anti-disturbance performance. Finally, plenty of experimental results verify the effectiveness of the proposed methods.

In2S3 nanoparticles modify the porous Fe2V4O13 nanostructure photoanode to enhance charge separation efficiency and photoelectrochemical water splitting performance

In this study, we demonstrate for the first time a promising photoanode of Fe2V4O13/In2S3 (FVO/IS) nanoparticles (NPs) for photoelectrochemical (PEC) water splitting. Most importantly, this work presents the first application of X-ray photoelectron spectroscopy in tracking electron flow direction within FVO/IS to reveal the formation of heterojunction having the electron flow from IS to FVO. Mott-Schottky measurement confirms that the modification of IS NPs establishes the type II heterojunction between FVO and IS, favorable for the transport and separation of carriers. Spectral measurements of electrochemical impedance spectroscopy, photoluminescence and Bode diagram confirm the effective separation of carriers and the prolongation of the charge lifetime in the FVO/IS heterojunction photoanode. Moreover, the electrochemical measurements evidently demonstrate the substantial enhancement in the charge separation efficiency (ηseparation) and charge transfer efficiency (ηtransfer) of the photoanode, leading to significantly enhanced PEC water splitting capability. As a result, in contrast with the pure FVO NPs photoanode, the photocurrent density of the constructed FVO/IS NPs photoanode is increased by 27 times without bias. This study paves a new approach for boosting the PEC water splitting activity of FVO photoanodes by constructing heterostructures through modification with other semiconductors.

Spinel ferrites having conductive grains, resistive interfacial boundaries and relaxation mechanism for possible supercapacitor applications

Linear increase in crystallite size (16–24 nm) of MnxZn1−xFe2O4 nanostructures and mixed behavior of lattice constant (8.429–8.462 Å) is reported. The system exhibits considerable promise for microwave applications due to its elevated dielectric constants and minimal dispersion losses from 20 Hz to 20 MHz. With x = 0.75, sample is good for energy storage devices like supercapacitors due to large specific surface area (53 m2/g) and dielectric constant. These samples exhibit maximum relaxation times ranging from 1.97 × 10−7 s to 2.43 × 10−4 s, with corresponding relaxation energy values spanning from 159.22 meV to 341 meV for x = 0 and x = 1 samples. The Cole-Cole plots reveal that grains exhibit conductive behavior at lower frequencies, while grain boundaries contribute significantly to the resistive behavior. Additionally, we have introduced Bode diagrams and equivalent electronic circuit models for the first time, offering valuable insights into the electrical behavior of the nanomaterial samples.

Investigation of the microstructure, growth mechanism, and corrosion behavior of a new Zr–Ti conversion coating on 6016 aluminum alloy

A novel Zr–Ti conversion coating (ZrTiCC) was fabricated on 6016 aluminum alloy. The coating thickness was evaluated, and the corrosion resistance of the coating was investigated through CuSO4 drop experiments to determine the optimum process. Potentiodynamic polarization results revealed the corrosion current density of ZrTiCC (4.821 μA/cm2) was lower than that of bare specimen (12.263 μA/cm2), and the δE of ZrTiCC (0.752V) was significantly lower than bare specimen (0.087 V). Scanning electron microscope and energy dispersive spectrometer was used to characterize the morphology and composition changes of the coating during its growth. The coating was proved to have a double-layer structure, and cracks appeared when the coating thickness continued to increase, which reduced the corrosion resistance. The growth mechanism of the coating was explained in detail. X-ray photoelectron spectroscopy was used to determine the components of the coating, which comprised Al2O3 at the base, with TiO2, AlF3, and ZrF4 at the top and ZrO2 evenly distributed throughout. Bode diagram revealed the impedance modulus of the coating at low frequency was increased to 8.6 × 104 Ω/cm2 after five days immersion in 0.5 M NaCl. The coating's self-sealing behavior and active protection may relate to the formation of SiO2, as well as the dissolution and regeneration of the upper coating (AlF3 and ZrF4) on 6016 aluminum alloy.

A robust internal model control design for low-quality waste heat power generation systems

Recovering low-quality waste heat using industrial waste heat is challenging, and the reuse technology needs to erupt. Moreover, the gas source of low-quality waste heat is relatively volatile, which makes it challenging to keep the actual working condition of the plant stable. Therefore, it is inspiring to research the robustness of root-waste heat power generation processed measurement and control system to improve the stability of the plant operation. Hence, in this paper, we have applied uncertainty theory to analyze it and formulate the uncertainty model based on the Bode diagram. We also proposed a control method based on the uncertainty model, which combines robust control and internal model control to make the roots waste heat power generation system operate stably under the effect of external disturbances and changes of internal structure or parameters in actual operation. Experimental results show that the robust internal model control method has a speed deviation of no more than 7.9 r/min compared with the PID control method. The adjustment time to track the set value does not exceed 73.1 seconds within the allowed fluctuation range. The fluctuation variance is 30.95% of that of the PID controller. The dynamic performance is better, with strong anti-interference capability and significantly improved tracking performance. It ensures the stability of the roots-type waste heat utilization system, which is essential for future intelligent grid-connected power generation.

Small Disturbance Stability Analysis of Onshore Wind Power All-DC Power Generation System Based on Impedance Method

The Onshore Wind Power All-DC Generation System (OWDCG) is designed to integrate with renewable energy sources by modifying the grid structure. This adaptation supports the grid infrastructure and addresses the challenges of large-scale wind power AC collection and harmonic resonance during transmission. Crucially, small disturbance stability parameters are essential for ensuring the system’s stable operation. Unlike conventional power systems, the OWDCG exhibits strong coupling between subsystems, accentuating the small disturbance stability issue due to the dynamic nature of its converter control system. The impedance method facilitates the decomposition of such systems into subsystems, offering insights into the destabilization mechanism through the lens of negative impedance contribution. This approach is conducive to conducting small disturbance stabilization analyses. To tackle this issue, the initial step involves deriving the input and output equivalent impedance models of the subsystem, considering the topological structure, control features, and operational dynamics of the OWDCG. Subsequently, the impact of circuit and control parameters on the system’s impedance characteristics and small-disturbance stability is examined through Bode diagrams and Nyquist curves. This analysis identifies critical parameters for small-disturbance stability, guiding the stable operation and parameter optimization of the OWDCG. The analysis highlights that the main control strategies for stability are the Modular Multilevel Converter (MMC) DC voltage control and the inner-loop current control gain. Validation of the theoretical findings is achieved through simulation results using PSCAD/EMTDC.

Accurate Stability Analysis of Three-Phase Converter System Connected to Weak Grid under Coordinate System Transformation

This paper studies the simplified impedance criterion of the three-phase converter system in different coordinate systems. In addition, the influence of small signal stability of converter units under the weak grid is discussed in three-phase converter systems. Firstly, a small signal model of a three-phase grid-connected converter system is established based on the voltage and current double closed-loop control strategy in dq real coordinate system and the dynamic characteristics of SRF-PLL (Synchronous Reference Frame Phase-Locked Loop). Then, based on the coordinate transformation, the admittance models in the dq real coordinate system and the fb complex coordinate system are derived. Through the analysis of the admittance Bode diagram, the amplitude-frequency characteristics of the three-phase converter system have conjugate symmetry in the real coordinate system and diagonal conjugate symmetry in the complex coordinate system. Therefore, the three-phase symmetrical system can be stabilized only by drawing the Nyquist curve of the open-loop transfer function GHf or GHb. The three-phase asymmetric system can also be stabilized by drawing the Nyquist curve of the modified open-loop transfer function GHfM or GHbM . Finally, the simulation results show that the converter system loses stability when the transmission line impedance Lg = 0.6 pu. In this case, the three current decoupling terms will cause the system to lose stability, but the relative stability of the current reference value is the best, and the phase angle margin is −6.8°. Also, without considering the phase-locked loop dynamics, the system is in a steady state, otherwise, the system loses stability, and the system output current has a 39 Hz oscillation, which is consistent with the theoretical analysis results.

Design of Fault Diagnosis Method Based on Circuit Frequency Domain Characteristics Fault Dictionary Method

In recent years, with the rapid development of integrated circuits and the widespread application of smart chips, the internal structure of complex electronic systems have become increasingly complex, which greatly increases the difficulty of board-level circuit testing and fault diagnosis of complex electronic systems. At present, traditional manual testing methods are no longer able to meet the maintenance requirements of modern complex electronic system board-level circuit. Therefore, the development of intelligent and universal automatic testing systems has become an important issue in fault detection of complex electronic systems. Based on the testing requirements of the automatic test system(ATS), this paper designs the corresponding overall scheme, software scheme and hardware circuit, and studies the fault diagnosis and test of board-level circuit of complex electronic system, and proposes to apply the traditional Bode diagram to the engineering practice of ATS. Fault detection is realized by utilizing the frequency domain characteristics of the object under test.

Импеданс проточной измерительной электрохимической ячейки с системой планарных встречно-штыревых микроэлектродов

The article considers a flow-through electrochemical cell with planar interdigitated microelectrodes intended for impedance studies of liquids. To assess the influence of the cell height and geometric parameters of the interdigitated microelectrodes on the cell impedance, an analytical approach is proposed that uses several levels of modeling electrochemical processes in the cell. At first, an elementary two-dimensional subdomain is distinguished in the cell structure, for which the potential distribution is determined by solving the differential equation of electrical conductivity. Using the obtained potential distribution, the linear parameters of the elementary subdomain, its linear resistance and linear capacitance are determined, on the basis of which the resistance and capacitance of the interdigitated microelectrode system are found. The impedance of an electrochemical cell with interdigitated microelectrodes is determined using its equivalent electrical circuit, which includes the resistance and capacitance of the interdigitated microelectrode system, the capacitance of the double electric layer on the surface of each microelectrode, and the resistances of the interdigitated microelectrode leads. Using the expression for the impedance of the electrochemical cell, its Nyquist and Bode diagrams are determined for different values of the cell height and geometric parameters of the interdigitated microelectrode system. The presented approach can be used to analyze processes in a flow-through electrochemical cell with interdigitated microelectrodes, its design, and the development of methodological support for impedance studies of liquid substances with help of it.

A Single-Stage Isolated Battery Charger Using Nonbridged Positive Cuk Converter Configuration

This article presents a nonbridged isolated positive Cuk (NB-IPCuk) converter-based single-stage battery charging system (SSBCS). The architecture of the suggested charger ensures the intrinsic advantage of power quality improvement in discontinuous current conduction (DCC) mode at the supply mains. The suggested NB-IPCuk converter scheme has fewer components than other bridgeless/nonbridged Cuk converter schemes. This is because the NB-IPCuk converter is a partial integration of two Cuk converters. The usage of the Cuk converter garnishes the system with input and output inductances, which lessens supply current harmonic distortion and, thus supply terminal low pass filter requirement is eradicated. The advantages of the NB-IPCuk converter are the eradication of one inductor and multiple diodes (two back-feeding diodes), which are generally used in NB converter configurations. In place of two separate inductors, the NB-IPCuk converter uses a single secondary side output inductor. The usage of BL configuration of NB-IPCuk converter eradicates the bridge rectifier (BR) stage, and thus, the BR-associated losses also got eradicated. The NB-IPCuk converter also garnishes the system with electrical isolation which adds to the safety standards of the system. DCC mode operation of the NB-IPCuk converter is used in the present work. DCC mode requires lesser sensors in comparison to continuous current conduction mode. The abovementioned benefits of the NB-IPCuk converter make the SSBCS system cheaper, compact, and more efficient. The detailed stability analysis (Bode diagram and pole-zero map) and mathematics for the NB-IPCuk converter are also included in the paper. The prototype and MATLAB/Simulink model of NB-IPCuk converter-based SSBCS system with DCC mode control has been built, and results of both prototype and MATLAB/Simulink are deployed to verify SSBCS system’s performance during dynamic and steady-state conditions.

Linear switched system modelling and analysis for the servo system

AbstractAiming at resolving the parameter uncertainty of the servo system under multi‐working conditions, a flatness‐based switched linear system model is proposed. Firstly, a fifth‐order linear switched discrete‐time system with uncertain parameters is established. The flatness properties of switched system is described and a de Bruijn's graph‐based framework is introduced for graphical description of the switched system. In addition, non‐linear bode diagrams are obtained via sweeping signals with multiple amplitudes. The discrete equations of the electromechanical servo system are established by the bode plots. The unknown parameters of the subsystems in switched model are identified by the simulated annealing algorithm, and compared with the least squares method to verify the accuracy of the identified parameters. Finally, the simulation model and experimental platform are constructed to verify the effectiveness of the proposed method. The switched model is compared with the classical transfer function model and single subsystems. The results indicate that the resolution of parameter uncertainty in servo systems is effective. The accuracy of the established switched model is about 99.5%. The accuracy of the switched linear system model of the electromechanical servo system is verified and the proposed modelling method is validated.

Distributed damping reshaping control with constraints on dual stabilities for grid‐connected inverter in high penetration grid

SummaryThe penetration level is limited by the occurrence of harmonic resonance under weakening grid. Under conventional current control, the penetrations with different power scheduling are assessed by the impedance Bode diagrams. To further suppress the current harmonics and improve the penetration with minimum cost, this paper proposes a distributed damping reshaping method by introducing the grid current feedback loop into the modulated wave of the inverter. The additional feedback loop is obtained by moving forward the feedback point of real damping link in hardware loop. Its equivalent control block has actual physical meaning, which helps to design damping coefficient. Further, instead of relying on the experience of engineer to select the damping coefficient, considering the effect of different values of damping on the inverter's performance, a damping design principle with the dual constraints on GCI's self‐stability and the global stability of the system is proposed. In detail, the range of the possible values of damping can be obtained by setting the desired system phase margin and the desired GCI's pole‐zero locations. In this range, the damping parameter, which remains the maximum ability of harmonic suppression for penetration improvement, can be determined by setting the desired damping ratio of the poles near the imaginary axis. Finally, simulations and experimental results were conducted to verify the correctness of the theoretical analysis.

Fractional Order Weighted Mixed Sensitivity-Based Robust Controller Design and Application for a Nonlinear System

This paper focuses on fractional-order modeling and the design of a robust speed controller for a nonlinear system. An induction motor (IM), widely used in Electrical Vehicles (EVs), is preferred in this study as a well-known nonlinear system. The major challenge in designing a robust speed controller for IM is the insufficiency of the machine model due to inherent machine dynamics. Fractional calculus is employed to model the IM using the small-signal method, accounting for model uncertainties. In this context, experimental data is approximated using a fractional-order small-signal transfer function. Consequently, a mixed sensitivity problem is formulated with fractional-order weighting functions. The primary advantage of these weighting functions is their greater flexibility in solving the mixed sensitivity problem by involving more coefficients. Hereby, three robust speed controllers are designed using the PID toolkit of the Matlab program and solving the H∞ mixed sensitivity problem, respectively. The novelty and contribution of the proposed method lie in maintaining the closed-loop response within a secure margin determined by fractional weighting functions while addressing the controller design. After evaluating the robust speed controllers with Bode diagrams, it is proven that all the designed controllers meet the desired nominal performance and robustness criteria. Subsequently, real-time implementations of the designed controllers are performed using the dsPIC microcontroller unit. Experimental results confirm that the designed H∞-based fractional-order proportional-integral-derivative (FOPID) controller performs well in terms of tracking dynamics, exhibits robustness against load disturbances, and effectively suppresses sensor noise compared to the robust PID and fixed-structured H∞ controller.

High-energy storage capacity of cellulose nanofiber supercapacitors using bound water

The performance of electric double-layer capacitors and lithium-ion batteries deteriorates with increasing humidity. The desirable effect of bound water on the energy-storage properties of physically dry cellulose nanofiber (Na-ACF) supercapacitors with sodium (Na) carboxylate radicals was investigated using infrared and near-infrared spectroscopy, and nuclear magnetic resonance spectroscopy, alternating current impedance analyses, and first-principles calculations. The storage capacity decreased gradually upon heating to 423 K and reached zero upon exceeding 483 K, accompanied by increasing electrical resistance, forming a distorted semicircle in Nyquist diagram and drawing the phase angle to zero in Bode diagram. This is attributed to the water in the hydration gel bound to the Na+-ions that cross-link the cellulose chains, evaporating as the temperature increases, and finally becoming Na2O. The increased band-gap energy from the increase in bound water prevents leakage from the supercapacitor. In contrast to ordinary batteries, bound water is necessary for developing Na-ACF supercapacitors.