Voltage Oscillations Research Articles

Hollow cathode discharge instability onset in electric thrusters

Hollow cathodes are an integral part of ion, and Hall thrusters are used for electric propulsion in deep space missions and in commercial communications satellites. Hollow cathodes are known to operate in a quiescent “spot mode” and in a noisy “plume mode” in which plasma instabilities generate erosive energetic ions. The onset of the plume mode in hollow cathodes has been defined historically as when the keeper voltage oscillation values exceed 5 Vpp (peak-to-peak). Using a LaB6 hollow cathode in a vacuum chamber setup that simulates operation in ion and Hall thrusters, a set of emissive and Langmuir probes have been used to investigate the plasma properties associated with plume mode onset as a function of discharge current and gas flow rate. We find that the plume mode onset occurs at even less than 2 Vpp of the keeper voltage for the 5–75 A hollow cathode investigated here and starts at higher gas flow rates than expected from the traditional 5 Vpp metric used by those in the field. Mode competition and coupling between three different instabilities observed in the near-cathode plume affect the overall plasma oscillation levels that are correlated to energetic ion production. We find that the plasma oscillation levels measured by in situ plasma diagnostics are more indicative of the presence of oscillations and the generation of energetic ions than indirect keeper voltage measurements.

Control Optimization Method for Ship Direct Current Microgrid Based on Impedance Reshaping

In response to the constant power negative impedance characteristics on the load side of a ship DC microgrid, leading to voltage oscillation issues in the DC bus, this paper proposes a control optimization method based on impedance reshaping using bus voltage feedback. First, a simplified small-signal diagram of a lithium battery energy storage system converter is analyzed. Combining active damping control technology, an impedance regulator is introduced, and its parameters are optimized to effectively reduce the output impedance magnitude on the power source side. Subsequently, a ship DC microgrid simulation model is constructed using MATLAB R2022a/Simulink for validation, and comparative analysis is conducted on the anti-interference ability of the DC bus voltage before and after impedance reshaping. Finally, a model is built on a semi-physical simulation platform to experimentally verify the proposed method. The research results indicate that the proposed control optimization method can effectively increase the system’s stability margin, suppress DC bus oscillations, and enhance the anti-interference ability of the ship DC microgrid’s bus voltage when facing significant power load variations.

Voltage oscillations during anodizing process of aluminum and their suppression

Voltage oscillations during anodizing process of aluminum and their suppression

Analytic Model of the Voltage Oscillation in a High-Power Converter With Silicon Carbide Devices

Analytic Model of the Voltage Oscillation in a High-Power Converter With Silicon Carbide Devices

Influence of magnetic field strength on plasma, microstructure, and mechanical properties of Cr thin films deposited by MPPMS and DOMS

Magnetic field strength plays a vital role in determining the discharge behavior in magnetron sputtering. It enables the customization of discharge plasma and thin film properties. This study aims to compare the discharge behavior and investigate the potential effects on Cr thin films deposited using modulated pulsed power magnetron sputtering (MPPMS) and deep oscillation magnetron sputtering (DOMS) at different magnetic field strengths. The magnetic field strength in the target center increased from 67 to 91 mT tuning by the target thickness from 8 to 3 mm, and the average electron temperature was higher in a DOMS discharge than that in a MPPMS discharge. For both MPPMS and DOMS deposited Cr thin films, the refractive index and mechanical properties have been promoted with the increase in magnetic field strength, and almost all Cr thin films showed a Cr(110) preferred orientation. The hardness and modulus increased from 11.3 and 275.6 to 13.8 to 285.1 GPa for MPPMS deposited thin films, while the hardness and modulus for DOMS Cr thin films were much higher, increasing from 11.2 and 283.6 to 17.3 to 297.2 GPa. The possible differences between MPPMS and DOMS were analyzed based on the plasma global model and empirical equations. The analysis revealed that the high discharge current of DOMS is primarily caused by the possibility of back-attraction ion difference between MPPMS and DOMS. The voltage oscillation in a DOMS discharge provides sufficient time for ionized ions to escape from cathode attraction. Regarding the difference in deposition rate, it should at least be the cooperative results of the target back-attraction effect and ion evacuation time difference in plasma.

Transient DC-link voltage oscillation stability assessment of VSC-HVDC systems using Lyapunov direct method

Lyapunov direct method is utilized in this paper to reveal the transient voltage oscillation stability mechanism for VSC-HVDC systems. Firstly, a reduced analytical nonlinear model for transient voltage oscillation stability assessment is proposed, which is a Liénard system. Based on the proposed model, a novel Lyapunov function is constructed and the conservative stability boundary is depicted, which reveals that the transient voltage oscillation can be well damped when the operating points are within the domain of asymptotic stability. In addition, it is found that there exists one limit cycle for VSC-HVDC systems. Once any system operation point exceeds the limit cycle, the divergent oscillations are triggered, and the aperiodic instability will eventually appear if the perturbations failed to be cleared in time. Finally, according to the limit cycle theory, one sufficient instability condition is derived and the transient voltage instability risk of the VSC-HVDC systems can be well evaluated.

A multi‐objective low‐voltage ride‐through control strategy for three‐phase grid‐interfaced solar power plant during symmetrical and asymmetrical faults†

SummaryThis paper presents a low‐voltage ride‐through capability (LVRT) solution for the photovoltaic (PV) grid‐connected inverters compliant with the Indian grid code. The LVRT strategy ensures the uninterrupted connection of solar energy to the grid, safeguarding against system shutdown in the event of various grid faults. During this time, the inverter supplies reactive power to the utility grid, effectively utilizing converter capacity and aiding the restoration of the voltage profile at the point of common coupling (PCC). The system used in this study involves a two‐stage grid‐interfaced solar PV setup with a boost converter that tracks the maximum power point (MPP) and an inverter that maintains the DC‐link voltage. A modified dynamic braking chopper control (MDBCC) has also been implemented to minimize the DC‐link voltage oscillations during asymmetrical faults while simultaneously injecting the sinusoidal current into the grid. To improve grid synchronization in the presence of unbalanced abnormalities, a modified dual second‐order generalized integrator phase‐locked loop (DSOGI‐PLL) has been employed to track the grid voltage angle precisely. Furthermore, a new control system has been developed in conjunction with the LVRT approach. The suggested system is simulated in MATLAB/Simulink to validate the efficacy of the LVRT control method during symmetrical and asymmetrical faults using a 100‐kW two‐stage grid‐interfaced solar PV facility. Finally, for experimental validation, a real‐time test bench (RTS) OPAL‐RT 4510 is used to implement the setup with its control, and the practical results are compared with the simulation outcomes.

Analysis of anode surface roughness influence on heaterless hollow cathode discharge

This research delves into the influence of cylindrical and planar anode surface roughness on heaterless hollow cathode discharge characteristics. Three surface roughness levels, Ra 1.6 μm, Ra 3.2 μm, and Ra 6.4 μm, along the cylindrical anode’s azimuthal direction and the planar anode’s radial direction, have been selected and modified by the machining process. A central finding is the correlation between the discharge voltage and anode surface roughness. As the roughness increases, cylindrical and planar anodes require less discharge voltage to sustain the primary discharge. This reduction is likely due to the enhanced surface area from the roughness, which aids in electron current collection. The discharge voltage oscillations appear inversely related to the surface roughness of planar anodes, which may be associated with changes in the neutral gas density gradient between the planar anode and the cathode. In contrast, cylindrical anodes show fewer effects from their surface roughness, likely due to the distinct neutral gas flow dynamics. These findings offer insights into standardizing hollow cathode testing and allow future research to explore these interactions more deeply.

A Hybrid Fuzzy Predictive DVR Model for Voltage Estimation Using Intelligent Learning

A self-constructing intelligence-based learning law is proposed for the prediction of power quality mitigation through a dynamic voltage restorer (DVR). To tackle voltage-based power quality concerns in the distribution network, a fuzzy neural-based hybridization control approach using an evolving Takagi–Sugeno–Kang (e-TSK) and radial basis function (RBFN) is developed. The estimated value of fundamental weight components is achieved by the eTSK predictive model. The evaluated weight values are used to update the parameters for the generation of the reference load voltage components. The RBFN is used to achieve the desired task of dc and ac link voltage regulation. The self-tuned control algorithm is developed based on an intelligence technique that avoids the trapping of local optima, and early convergence, and reduces the voltage oscillation to obtain an optimal solution. A meta-heuristic optimization approach of grey wolf optimization (GWO) and grey wolf-cuckoo search (GWOCS) is selected to optimize the parameters of eTKS and RBFN to find the best-fitted predictive model under the dynamic state. The hybridization of the model with GWO and GWOCS is implemented for improving the training and generalization capability. The performance of VSC-based DVR is validated using the d-SPACE Micro lab box under the various power quality scenario.

Experimental study on voltage instability of proton exchange membrane fuel cell: Types and boundaries

ABSTRACT This paper presents an experimental study on the voltage instability in proton exchange membrane fuel cells operating at high current densities, which is important for improving their reliability and durability. Based on experimental findings regarding transparent fuel cells, a method is proposed to identify different types of voltage instability via statistical results of linear changing rate and oscillation amplitude. The types and boundaries of voltage instability are elucidated while evaluating the impact of cathode relative humidity and flow rate on voltage instability. The findings reveal that (1) the voltage instability is greatly influenced by the cathode-side relative humidity and flow rate, (2) there are three typical types of voltage instability: voltage decline, voltage oscillation, and both, and (3) voltage decline occurs at low cathode humidity, while voltage oscillation becomes more severe at large cathode humidity and low flow rate; (4) Reduction of water content in the membrane leads to voltage decline, while an increase in water content in the catalyst layer, gas diffusion layer, and channels leads to voltage oscillation. A full-condition map diagram demonstrating voltage instability during high current density conditions is presented. The method for creating this map for voltage instability will be employed to enhance fuel cell performance.

Control Approach of Grid-Connected PV Inverter under Unbalanced Grid Conditions

In grid-connected photovoltaic (PV) systems, power quality and voltage control are necessary, particularly under unbalanced grid conditions. These conditions frequently lead to double-line frequency power oscillations, which worsen Direct Current (DC)-link voltage ripples and stress DC-link capacitors. The well-known dq frame vector control technique, which is effective under normal conditions, struggles with oscillatory component management in unbalanced grid conditions. To address this issue, this paper presents an advanced control approach designed for grid-connected PV inverters. The proposed approach is effective at reducing oscillations in the DC-link voltage at double the grid frequency, thereby enhancing system stability and component longevity. This method introduces a feedback control method designed to regulate oscillatory components that appeared within the dq frame and suppress the DC-link voltage oscillations under imbalance conditions, including single line-to-ground (SLG) faults. Additionally, the control scheme incorporates a maximum power point tracking (MPPT) controller to optimize PV efficiency. Comprehensive simulations demonstrate the effectiveness of this method in maintaining sinusoidal current injections and stabilizing DC-link voltage during unbalanced grid conditions. Simulation results show that the control scheme effectively stabilizes DC-link voltage, maintains balanced grid current, and ensures constant active power under various conditions, including SLG faults and solar irradiance changes.

An overview of the existing and future state of the art advancement of hybrid energy systems based on PV-solar and wind

Abstract Increasing solar and wind power use in existing power systems could create significant technical issues, especially for grids with poor connectivity or stand-alone systems needing more adequate storage capacity. This is due to the unpredictable and intermittent nature of solar and wind power. The intermittent nature of solar and wind resources can be reduced by integrating them optimally, making the entire system more reliable and cost-effective to operate. The advantages and disadvantages of hybrid wind and solar energy integration systems are discussed in this research. The impact of voltage and frequency oscillations and harmonics is amplified in weak grids, affecting both grid-connected and stand-alone systems. This may be fixed by ensuring that hybrid systems are well designed, equipped with cutting-edge quick reaction control capabilities, and optimized. This review offers an overview of existing advances in PV-solar and wind-based hybrid energy systems while exploring potential future developments. Further, this review also provides an overview of the primary studies published on optimum design considerations for compactness, topologies for power electronics, and control. As the global energy environment shifts toward sustainability and resilience, this review helps researchers, policymakers, and industry stakeholders understand, adapt, and enhance PV-solar-wind hybrid energy systems.

Control Optimization of the Offshore HVDC Grid based on Modular Multilevel Converter for Improving DC Voltage Stability

The aim of this paper is to reduce the voltage oscillation of the HVDC cable in an offshore point-to-point configuration based on the modular multilevel converter. An optimization methodology based on semidefinite programming is proposed, which improves the DC voltage stability under the worst-case initial perturbation scenario. This goal is achieved by implementing a centralized optimal linear feedback controller, which guarantees Lyapunov stability margins while considering constraints on control inputs and state variables. The scope of this work is twofold. First, to analyze small-signal eigenvalue stability of the modular multilevel converter-based HVDC grid to identify the source of the oscillations. Second, to use this analysis as a basis to design a centralized optimal linear feedback controller to improve stability margins. The linear feedback controller is first applied as an additional control layer to the standard control of the offshore point-to-point HVDC grid, and then it is implemented to substitute the droop control function of the grid. Finally, the applicability and validity of the results are verified by time-domain simulations.

Fuzzy Logic Based Maximum Power Point Tracking Using Boost Converter for Solar Photovoltaic System in Kuwait

Currently, the production of the rapid increasing electrical energy in Kuwait depends mainly on oil and its derivatives, which result in environmental pollution. Moreover, the export of oil production represents a key income for Kuwait and any saving in its consumption represents an essential concern to land’s economy. Therefore, the power utility and economy of Kuwait will benefit from substituting fossil fuels by clean and renewable energy resources such as solar energy. For efficient utilization of solar energy, the PV panel should track the maximum power point (MPP) under various weather conditions in Kuwait. Most of existing MPP tracking techniques depend mainly on perturb & observe (P&O) or incremental conductance (IC) algorithm using conventional PID controllers. On the other side, fuzzy logic controller (FLC) provides an adaptive nature, fast response, good performance and ability to handle non-linear characteristics. In this paper, the proposed (FLC) substitutes PID controller in P&O and IC (MPPT) under different weather conditions in Kuwait. The obtained results of the proposed (FLC) are compared with conventional PID controller. The performance of the implemented PV panel is validated and the results indicated that FLC has successfully tracked the MPP with minimum voltage oscillations.

Experimental Assessment of a Decentralized Control Strategy for a Back-to-Back Modular Multilevel Converter Operating in Low-Frequency AC Transmission

The Modular Multilevel Converter (MMC) has been widely used in high-power applications owing to its inherent advantages, including scalability, modularity, high-power density, and fault tolerance. MMCs have recently been used in Low-Frequency Alternating Current (LFAC) transmission, particularly in the integration of offshore wind power with onshore grids. However, LFAC applications produce significant voltage oscillations in floating capacitor voltages within the MMC. Early research efforts have successfully established and validated decoupled control strategies for LFAC-based MMC systems. However, validations are usually based on simulations or small-scale prototypes equipped with limited power cells. Consequently, this paper presents a decentralized voltage control strategy based on Nearest Level Control for an MMC-based LFAC system. Experimental results obtained with a 120-cell MMC prototype are presented to validate the effectiveness and operation of the MMC in LFAC applications.

Improved virtual space vector modulation for neutral point voltage oscillation and common-mode voltage reduction in neutral point clamped three-level inverter

Improved virtual space vector modulation for neutral point voltage oscillation and common-mode voltage reduction in neutral point clamped three-level inverter

Mitigation of Voltage and Frequency Oscillations of a Microgrid during Wind Gust by Using Fuzzy-Controlled Flywheel Energy Storage

Mitigation of Voltage and Frequency Oscillations of a Microgrid during Wind Gust by Using Fuzzy-Controlled Flywheel Energy Storage

Fuzzy Logic Based Adaptive P&O MPPT Control of a DC-DC Boost Converter Used in a Wind Energy Conversion System with a Permanent Magnet Synchronous Generator

In this paper, we present a Maximum Power Point Tracking (MPPT) algorithm employing Perturb and Observe (P&O) using Fuzzy Logic (FL) control to overcome limitations associated with the conventional P&O MPPT method in order to improve transient response and reduce steady-state terminal voltage oscillations. In particular, the FL approach was applied to define the perturbation amplitude for the P&O MPPT algorithm, according to the ratio between the incremental power and incremental voltage in the input of a DC-DC boost converter. The approach was a variable speed wind power conversion chain based on the permanent magnet synchronous machine. The MPPT control continuously adjusts the duty cycle of the DC-DC converter to maintain the wind turbine at the maximum power point. MATLAB-SIMULINK environment is used to simulate the entire system demonstrating the extraction of the maximum available power from the wind turbine under a varying wind speed.

Series Capacitance Gate Driver to Suppress Voltage Oscillation of SiC MOSFET

Series Capacitance Gate Driver to Suppress Voltage Oscillation of SiC MOSFET

Voltage Oscillations Stabilization in DC Microgrids: A Strategy Using Improved Model Predictive Control

Voltage Oscillations Stabilization in DC Microgrids: A Strategy Using Improved Model Predictive Control