Voltage Mode Research Articles

Terminal Voltage and Common Mode Voltage Analysis for Various PV Inverter Topologies

The switching function method is critical for understanding the effect of different switching mechanisms or Pulse Width Modulation (PWM) designs on both terminal voltage and common mode voltage. The switching patterns of numerous five-level inverter topologies are determined using modified PWM in this study. The switching function technique is used in this study to investigate the terminal voltage of the PV array and the common mode voltage of the inverter. Notably, as compared to normal PWM approaches, five-level common mode voltage source inverters (CMLIs) need less carrier waves. The study gives thorough insights into the overall architecture of the examined converter, as well as terminal and common mode voltage expressions. When compared to normal PWM, any five-level CMLI requires less carrier waves. This document also details the converter’s overall structure, terminal and common mode voltage expressions, and switching patterns.

Water flooding diagnosis of proton exchange membrane fuel cell based on current density scanning

It is necessary to diagnose the flooding state of PEMFC in real time to ensure its long-term safe and efficient operation. However, the existing water flooding diagnosis methods still have many limitations, especially for the real-time monitoring of water flooding. Herein, a water flooding diagnosis method based on current density scanning is proposed, which can quantify the flooding severity and determine the flooding location by measuring the dynamic change of current density distribution. In this work, the current density distribution of a 50 cm2 single fuel cell is measured in situ using a current scan shunt (CSS) module with 256 current collecting segments, and the feasibility of this diagnosis method is verified by electrochemical impedance spectroscopy (EIS). The characteristics of serious flooding are explored under different load modes, and the results show that the voltage will decrease rapidly in a short time and there is a risk of electrode reversal under constant current mode; However, owing to the negative feedback effect, the severity of flooding under constant voltage mode eventually reaches a dynamic equilibrium. This work provides an effective evaluation method for water flooding diagnosis of PEMFC.

Single‐differential difference current conveyor‐based first‐order VM/TAM universal filter and its applications

AbstractA new first‐order universal filter structure is presented in this article using a single differential difference current conveyor (DDCC). The proposed circuit can provide three first‐order filter functions namely, high‐pass filter (HPF), low‐pass filter (LPF), and all‐pass filter (APF) in voltage mode (VM) and transadmittance mode (TAM) both. A voltage amplifier with a gain of 2 is required for the realization of the APF functions in both the modes while for LPF and HPF, no condition is required. The pole frequency and gain of the proposed circuit can be controlled separately. The effect of the parasitic impedances of the DDCC has been modeled in the nonideal equivalent circuit from which nonideal parameters have been evaluated and compared with their ideal ones. Application examples of the proposed circuits configured as amplitude equalizer (in both modes) and in the realization of a simple wideband band‐pass filter are also discussed. The functionality of the proposed circuit as well as its mentioned application circuits is verified using complementry metal oxide semiconductor DDCC to support the theoretical propositions. Some experimentally observed frequency responses and transient responses of the various VM filters have also been corroborated using DDCC implemented using AD844 ICs.

Tunable broadband metamaterial absorber with voltage and temperature modulation

It is well known that VO2 has temperature-controllable phase transition properties, and that graphene surface conductivity's can be changed by applying a gate voltage to control the Fermi energy level. On the basis of temperature and voltage controllability, we numerically simulate a broad-band mid-infrared absorber. The metamaterial absorber (MA) operates in the mid-infrared band of 7∼30 μm, and when VO2 is in the metallic state, the absorption bandwidth can reach 9 μm and the average absorption can reach 98%. The absorption bandwidth is temperature-adjustable. By maintaining graphene's Fermi energy level (EF) at 0.4 EF. When VO2 transitions between insulating and metallic states, MA can achieve mid-infrared narrowband-broadband interconversion. When VO2 is in the insulating state, tuning the EF of graphene, MA can achieve single-peak and double-peak absorption in mid-infrared wavelength, respectively. When VO2 is in the metallic state, the EF can be used to dynamically modulate the absorption bandwidth. The MA reveals its thermal switching properties. This research is expected to have promising future applications in the fields of multiparameter tunable optical devices, temperature sensing, infrared detection, etc.

A Symmetric Parity–Time Coupled Optoelectronic Oscillator Using a Polarization–Dependent Spatial Structure

We propose and experimentally investigate a symmetric parity-time (PT) coupled optoelectronic oscillator (COEO) based on a polarization-dependent spatial structure. In such a COEO system, the gain/loss and coupling coefficients of two orthogonal polarization optical waves can be controlled by adjusting the polarization controller (PC) and the bias voltage of a Mach-Zehnder modulator (MZM). The single-mode selection of a microwave signal can be implemented by the PT symmetry breaking of a special mode. The performance of the proposed COEO is experimentally examined, and a 10.0 GHz microwave signal with a phase noise of −109.1 dBc/Hz @ 10 kHz and a side mode suppression ratio of 51.4 dB is generated. Moreover, an optical frequency comb with a comb tooth spacing of 10.0 GHz and a bandwidth of 100 GHz within a 10 dB amplitude variation can be simultaneously generated.

Multifunctional Al-doped ZnO thin films for vertically aligned liquid crystal devices

The integration of ITO-free transparent conductive layers remains a big challenge for development of next generation technologies. Here, we demonstrate the feasibility of transparent and conductive Aluminum-doped Zinc Oxide (AZO) thin films to operate simultaneously as electrode and alignment layer in Liquid Crystal (LC) device configuration. Controlling the growth process of AZO thin films by Atomic Layer Deposition (ALD) technique results of predominantly (100) crystallographic oriented AZO with very high transparency and excellent conductivity. The exceptionally low surface free energy of (100) oriented AZO, along with the topological modification following the mechanical rubbing treatment were used to elucidate the mechanism of LC molecules alignment on the surface of AZO film. The uniform vertical orientation of the nematic LC director was confirmed by polarized optical microscopy and pretilt angle measurements. The competitive electro-optical performance in terms of phase modulation, threshold and saturation voltages and contrast ratio of the assembled LC device reveals the great potential of AZO thin films as transparent electrode and alignment layer for future LC display applications with versatile functionality.

High-accuracy control of variable blank holding force driven by electromagnetics based on pulse width modulation with grading voltage and mode matching

Using variable blank holding force, which is conventionally achieved by hydraulic or mechanical drive, can effectively reduce defects in the forming process. To overcome the obstacles of low response and high complexity of conventional drives, this paper proposes a holding system for variable blank holding force driven by the electro-permanent magnet. Focusing on the variable electromagnetic force, a control method based on grading voltage pulse width modulation and mode matching is addressed. The model of the transient electromagnetic force is first established, the relationship between electromagnetic force and current is obtained, and the migration law of the working point of the magnet with the change of current is analyzed. Then, the grading voltage pulse width modulation control, which regulates current by the pulse width and its amplitude, is developed for continuously increasing or decreasing force control. When force variations occur, mode matching is introduced to identify the working point and allocate matching parameters for better control. To validate the feasibility of the control method, the co-simulation based on Simulink-Simplorer-Maxwell and the experiment bench are built. Results of electromagnetic force show that the step response time is 0.13 s and the mean relative error is less than 1% for a given variable blanking force. The control method can reduce the thickness variations of sheet metal by 14–20% compared to the existing electro-permanent magnet blank holder. This work assists in realizing the loading of variable blank holding force driven by electromagnetics to improve the forming quality of parts.

A new approach to the synthesis of anodic titania photonic crystals with desired position and high reflectance of photonic band gaps

Anodic titanium oxide photonic crystals (ATO PhCs) are promising for optical sensing and photocatalysis due to their photonic band gaps (PBGs). The ability to control the spectral position and width of the PBG are essential for application of ATO PhCs. Anodizing charge density has recently been reported to be a main factor affecting the porosity and hence the effective refractive index (neff) and PBG position of ATO PhCs. In this paper, we propose a method for accurate determining the dependence of neff of ATO PhCs on the etching charge density varying in a wide range. The method is based on an analysis of the spectral positions of PBGs in photonic heterostructures. The obtained dependence was used for the synthesis of the ATO PhCs with desired PBG positions in a wide wavelength range (400–1500 nm) by the periodic voltage modulation on optical path length. The deviation of the experimental PBG position from the specified one does not exceed 10 %. The prepared PhCs possess ∼100 % reflectance in the PBG region.

Experimental study on robust non‐fragile control of DC‐DC buck converter

AbstractThe presence of uncertainty in the converter model and controller parameters affects the system's stability and dynamic performance. This paper presents a comparative analysis of robust non‐fragile control based on (i) the Kharitonov method and (ii) the linear matrix inequality (LMI) technique so that the controller can cope with the effect of both uncertainties. The first approach based on Kharitonov theorem determines the robust performance region with guaranteed gain margin and phase margin under parametric uncertainty. The second approach (LMI technique) is based on devising a control law that can quadratically stabilize the closed‐loop system subject to uncertainties and satisfy the H∞ norm bound constraint on disturbance attenuation. Based on these two approaches, a robust non‐fragile PI controller is designed for voltage mode control of dc‐dc buck converter. The effectiveness of the control approaches is evaluated based on (i) robustness against large plant parameter perturbations and load disturbance and (ii) fragility against controller parameter perturbations. The performance of the designed controllers (using the Kharitonov method and the LMI technique) has been thoroughly evaluated and validated through simulation and experimental results.

Mode Predictive Direct Power Control Scheme with Fixed Operation Frequency for a Vienna Rectifier Based on Voltage‐Sensorless

Model predictive direct power control (MPDPC) is a suitable method for the highly nonlinear system of a three‐level Vienna rectifier. However, the traditional MPDPC suffers from irregular switching states, which can decrease current tracking accuracy and generate high current ripple and electromagnetic noise. Additionally, the use of sensors can increase system hardware costs and complexity. To enhance operational reliability and reduce the fault impact of AC voltage sensors, a double closed‐loop control strategy based on voltage‐sensorless MPDPC in the inner loop and sliding mode control (SMC) in the outer loop is proposed. First, the virtual flux model of the three‐phase Vienna rectifier is established in the two‐phase static coordinate system, and the second‐order low‐pass filter is used to improve the voltage observer to estimate the grid‐voltage. Meanwhile, an improved grid voltage observer based on the second‐order low‐pass filter is designed to improve the observation effect. Second, to solve the variable switching operation, current fluctuation and wide harmonic spectrum caused by the traditional MPDPC effectively, a double closed‐loop control strategy with constant switching frequency based on voltage‐sensorless MPDPC in the inner loop and SMC control in the outer loop is proposed. Based on the principle of SVPWM modulation, the modulation voltage of SVPWM is calculated directly, in order to verify the correctness of the theoretical analysis, extensive simulation and matching experimental is presented to verify the correctness of the theoretical analysis. © 2023 The Authors. IEEJ Transactions on Electrical and Electronic Engineering published by Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Switched Capacitor Based Cascaded Half-Bridge Multilevel Inverter with Voltage Boosting Feature

Abstract: In many applications, cascading multilevel inverter (CMI) topologies are common. However, the biggest disadvantage of CMI is the need for many separate switches and DC sources. As a result, the CMI topology becomes more expensive, more complex, and larger, and its performance suffers. In the proposed SC-CHMI, only one DC source is used and the other DC sources are replaced by switched capacitor cells. Thanks to the self-balancing function, the capacitor charging process occurs naturally without the need for any auxiliary equipment. In the proposed SC-CHMI, the inrush current of the capacitor is attenuated using a load inductor or a front-end boost converter. To improve the performance of multi-level inverters, several types of techniques can be tested with existing multi-level inverters. Due to the modulation algorithm, modulation frequency, voltage drop on the switches and bus voltage modulation, the output voltage of the inverter has overall harmonic distortion, leading to overheating of the device and shortening the life of the device bag. In the proposed SC-CHMI, a level-shifted pulse width modulation technique is proposed to improve the output voltage quality and reduce the total harmonic distortion. This new control scheme is applicable to nine-level, eleven-level and fifteen-level SC-CHMI. The proposed topology can be used as a general-purpose inverter in renewable energy systems, due to its voltage gain characteristics, minimal number of switches, and single DC source. The effectiveness of the proposed inverter topology is confirmed by simulation results.

Graphene/silicon heterojunction for reconfigurable phase-relevant activation function in coherent optical neural networks

Optical neural networks (ONNs) herald a new era in information and communication technologies and have implemented various intelligent applications. In an ONN, the activation function (AF) is a crucial component determining the network performances and on-chip AF devices are still in development. Here, we first demonstrate on-chip reconfigurable AF devices with phase activation fulfilled by dual-functional graphene/silicon (Gra/Si) heterojunctions. With optical modulation and detection in one device, time delays are shorter, energy consumption is lower, reconfigurability is higher and the device footprint is smaller than other on-chip AF strategies. The experimental modulation voltage (power) of our Gra/Si heterojunction achieves as low as 1 V (0.5 mW), superior to many pure silicon counterparts. In the photodetection aspect, a high responsivity of over 200 mA/W is realized. Special nonlinear functions generated are fed into a complex-valued ONN to challenge handwritten letters and image recognition tasks, showing improved accuracy and potential of high-efficient, all-component-integration on-chip ONN. Our results offer new insights for on-chip ONN devices and pave the way to high-performance integrated optoelectronic computing circuits.

Polarization and Spectrum Multi‐Dimensional Sensitive Perovskite Photodetectors

AbstractWithout optical and mechanical components, resolving information from composite light is challenging even from two dimensions. 3D (intensity, spectrum, and polarization state) reconstruction is extremely rare and only explored in the infrared region. Herein, the first polarization‐ and spectrum‐sensitive photodetector in the visible region is constructed, which relies on orientations of perovskite nanowire arrays and in situ voltage modulation. This detector can realize real‐time detection of spectral information and Stokes vector simultaneously. Such a design successfully obtains the information from three dimensions, and the multi‐dimensional imaging capability has also been demonstrated. This work provides a valid instance of multi‐dimensional photodetection and shows a development direction of extracting target features from miscellaneous information.

Improved field emission properties of reduced graphene oxide decorated with indium nanoparticles

Low work function metals decoration of graphene is a effective method for the improvement of electron field emission properties. Indium, a relatively lower work function metal, is used to decorate reduced graphene oxide (RGO) films for the first time by simple and efficient solution process combined with magnetron sputtering method and the field emission properties are investigated. At continue voltage mode, the indium decorated RGO films display lower turn-on and threshold field as well as better emission stability than those of pristine RGO films. Moreover, the field emission performance of indium decorated RGO films is affected by the spacing between the cathode and anode. At pulse voltage mode, the indium decorated RGO films show approximately 10 times higher maximum emission current density compared to that at continue voltage mode. The calculation results by density functional theory indicate that the indium decoration of RGO significantly increases the density of states (DOS) near Fermi level and reduces the work function.

Multi‐Functional Platform for In‐Memory Computing And Sensing Based on 2D Ferroelectric Semiconductor α‐In2Se3

Abstract2D layered semiconductors with excellent light−matter interaction and atomic‐scale thickness have been envisioned as promising candidates for more than Moore and beyond Moore technologies. Here, for the first time, a multi‐functional platform is reported that is fabricated entirely from wrinkle‐free 2D ferroelectric semiconductor α‐In2Se3 integrated with a photodetector, reconfigurable logic switching, and visual perception processing functions. The intensity‐ and wavelength‐dependent resistance is used to demodulate broadband optical information into electrical signals and perform reconfigurable logic switching. Moreover, the platform offers dynamically modulated photosensitive visual sensing in different working modes at the pixel level. Using photo‐assisted piezoresponse force microscopy, the optical‐engineered ferroelectric polarization switch behavior is explored. The platform has excellent sensitivity to both optical and electrical stimuli and can respond to lights in the visible to short‐wavelength infrared region in volatile/non‐volatile manner under gate voltage modulation, with a response of 98 mA W−1 (to 1800 nm light), a current on/off ratio of over 106, and a high field‐effect mobility of 137.55 cm2 V−1 s−1. With its simple structure, unique photoelectric interaction, and controllable operating mechanism, the platform has the potential to simplify the complexity of neuromorphic computing circuitry systems, paving the way for high‐performance hybrid technologies suitable for artificial intelligence applications.

Tunable Environment-Enhanced Mid-Infrared Absorber Based on Voltage Modulation

Tunable Environment-Enhanced Mid-Infrared Absorber Based on Voltage Modulation

Optimized Voltage Equalization Algorithm for Modular Multilevel Converters

The switching frequency of modular multilevel converters increases with the number of bridge arm submodules. Therefore, an improved voltage equalization technology based on fast sorting algorithm is proposed, which introduces the maximum voltage deviation between sub-modules and reduces the unnecessary switching operations caused by small changes in the capacitor voltage of factor modules. With the help of Matlab/Simulink, a modular multilevel converter with optimized control was simulated to verify the downscaling effect of the voltage-sharing optimization method.

An Asymmetrical Active-Neutral-Point-Clamped Five-Level H-bridge Inverter for Open-Winding Motor Applications With Its Modulation Strategy

Asymmetrical active-neutral-point-clamped five-level H-bridge (ANPC5L-HB) inverter has reduced switch count and fewer high-frequency switches compared with other existing five-level H-bridge topologies. However, multiphase ANPC5L-HB inverter for open-winding motor applications is rarely researched. In this paper, a three-phase ANPC5L-HB inverter for open-winding motor applications is proposed. The modulation and neutral point (NP) voltage balance strategies for the inverter are also proposed. By using the proposed modulation strategy, transitions between different switching states are constrained to avoid unexpected intermediate states. Meanwhile, zero voltage switching (ZVS) of low-frequency switches could be achieved. For the NP voltage balance problem, optimal switching states are selected by using the MPC approach, and a better NP control performance is realized compared with the classical method. The effectiveness and high efficiency of the inverter are validated by a 25kW experimental prototype. And a peak efficiency of 98.685% is confirmed under 10kHz switching frequency. The good performances of the proposed strategies have been fully verified.

Grid-Forming Services From Hydrogen Electrolyzers

Hydrogen electrloyzers are power-to-gas storage devices that can facilitate large-scale integration of intermittent renewable sources into the future power systems. Due to their fast response and capability to operate in different loading conditions, they can be used as responsive loads providing support to AC grid during transients. This paper suggests taking one step further and using hydrogen electrolyzers to provide grid-forming services to the grid. As a result, the electrolyzer's role is elevated from supporting the grid (responsive load) to actively participating in forming voltage and frequency of the grid. The grid-forming capability of electrolyzer is linked to its hydrogen production constraints, which can potentially pose limitations on the grid-forming services. Besides the grid-forming mode, two additional operating modes, i.e., DC voltage mode and constant power mode, are proposed to ensure a safe operation of the electrolyzer in case of adversary interaction between grid-forming operation and hydrogen production constraints. This paper also studies the impacts of grid-forming services on the electrolyzer's physical features such as hydrogen stack temperature and efficiency. Comprehensive simulations are conducted on a low-inertia test network whose topology is inspired by a portion of the transmission grid in South Australia to confirm the effectiveness of the proposed concept under various operational conditions of the electrolyzer and upstream AC grid. Moreover, the practical feasibility of the proposed control system is experimentally validated by conducting hardware-in-the-loop tests.

A Study on the Comparison of VNCa and VMI+ Image Quality and Optimized Method according to kV Modulation of DECT: A Porcine Ankle Ligament Model

This study conducted a quantitative and qualitative assessment of the effectiveness of Single-Energy and Dual-Energy Virtual non-calcium imaging, as well as Virtual Monoenergetic Imaging at 55, 65, and 75 keV, for diagnosing ligament conditions with regard to tube voltage modulation. A porcine hindlimb ankle ligament model was utilized for this evaluation. The two widest regions within the ligament model were designated as regions of interest, and measurements of Hounsfield Units, Signal-to-Noise Ratios, and Contrast-to-Noise Ratios were obtained. Quantitative evaluation was then conducted based on the average values. Furthermore, qualitative assessments of ligament diagnosis were carried out by five musculoskeletal radiologists and five radiological technologists, each with over five years of experience in Computed Tomography laboratory work. Following both quantitative and qualitative evaluations, it was observed that the Dual-Energy Virtual non-calcium image obtained at 70/Sn150 kVp and the Virtual Monoenergetic Imaging Plus 65 keV image exhibited superior image quality compared to the Single-Energy CT image. These differences were statistically significant (p<0.05). Moreover, the highest image quality was noted at 65 keV within the Virtual Monoenergetic Imaging Plus energy range. The Dual-Energy Virtual non-calcium image was found to be more suitable for imaging ligaments than the Virtual Monoenergetic Imaging Plus 65 keV image.(p<0.05) Notably, lower tube voltages were associated with improved image quality across all images. Consequently, it was determined that 70/Sn150 kVp Dual-Energy Virtual non-calcium images are more optimized than Single-Energy CT and Virtual Monoenergetic Imaging Plus 65 keV images for diagnosing ligament diseases in patients who present challenges for Magnetic Resonance Imaging and in emergency cases. Additionally, employing Virtual non-calcium Color Coding images for accurately describing ligament thickness or length may enhance the diagnostic value of the images.