Voltage Oscillations Research Articles

Bifurcation Behavior Analysis and Stability Region Discrimination for Series-Parallel Architecture Electric Energy Router

Electric energy routers (EERs) can effectively deal with the energy management issues caused by the access of multi-sources and multi-loads. Different from the energy transmission form in the existing series architecture EER (SA-EER) for low-voltage distribution networks, a new series-parallel architecture EER (SPA-EER) has the advantages of high-power transmission capability and reactive power flexible operation. However, if controller parameters change beyond their critical stability boundaries, SPA-EER will produce slow- and fast-scale bifurcation behaviors, which are manifested as low- and high-frequency oscillations of port voltages or port currents in varying degrees. To avoid the system instability caused by controller parameter changes, how to discriminate the stability regions of controller parameters for SPA-EER is a key research content in this paper. To this end, the stroboscopic mapping discrete model of SPA-EER system is first established, and system bifurcation behaviors are analyzed based on bifurcation theory. Furthermore, the critical stability boundaries of controller parameters are discriminated by using Jacobian matrix, root locus and bifurcation diagram. After that, a time delay feedback control (TDFC) is employed to suppress system bifurcation behaviors. Finally, the correctness of bifurcation analysis and the effectiveness of TDFC are verified by a hardware-in-the-loop (HIL) experimental platform.

Analysis and Suppression of Rectifier Diode Voltage Oscillation Mechanism in IPOS High-Power PSFB Converters

Parasitic oscillations in the rectifier diode voltage of phase-shifted-full-bridge (PSFB) converters limit their application in high-voltage and high-power situations. The conventional analysis method for parasitic oscillation in rectifier diode voltage in PSFB converters treats the filter inductor as a constant current source and fails to consider the impact of changes in filter inductor current on the rectifier diode’s parasitic oscillation. Consequently, this approach does not apply when analyzing the rectifier diode voltage’s parasitic oscillations in high-power PSFB converters employing an input-parallel output-series (IPOS) configuration with interleaved drive. This research paper introduces an innovative equivalent circuit model for analyzing the parasitic oscillations of rectifier diode voltage in IPOS high-power PSFB converters. The model takes into account the mutual influence of rectifier diode voltage oscillations between submodules under interleaved control, considering the influence of changes in filter inductor current on rectifier diode parasitic oscillation. Based on the circuit model, we explain the mechanism of multiple oscillations of the rectifier diode voltage and the reason for the high peak of the first oscillation. Consequently, the interplay of rectifier diode voltage oscillations in IPOS high-power k-module PSFB converters under interleaved control is analyzed. To mitigate the adverse effects of rectifier diode voltage parasitic oscillation, a buffering strategy involving the connection of a resistor capacitor diode (RCD) circuit in parallel after the rectifier bridge is adopted, considering the structure of the IPOS high-power PSFB converter. The study provides a detailed analysis of the circuit’s operation mechanism upon incorporating the RCD buffer circuit and establishes the relationship between buffer capacitance, resistance, and spike voltage. Furthermore, a design method for buffer capacitors and discharge resistors in buffer circuits is presented. Finally, a 100 kW prototype is tested to verify the rectifier diode voltage oscillation mechanism of the IPOS high-power PSFB converter and the rationality of the buffer capacitor and discharge resistor design method under the interleaved drive approach.

Artificial Spiking Neuron with Bursting Dynamics for Noise-Resistant Neuromorphic Coding

Emulating complex neuronal functionalities in human brains using emerging biomimetic electronics is critical for next-generation brain-like chips and artificial general intelligence. Burst firing, featured with the repeated firing of discrete groups of spikes, is high-order neuronal dynamics for reliable signal transmission, coding, and processing. Here, we report a memristor (Pt/Co3O4–x/ITO) that can natively produce periodic voltage oscillation groups under current stimulation, capturing the burst-firing features of actual biological neurons. This behavior stems from the dynamic formation/rupture of conductive filaments regulated by the VO concentration at the grain boundaries. The burst frequency can be tuned by adjusting the driving current intensity and used to implement burst frequency coding. The bursting neuron-based artificial neural system achieves a recognition accuracy of 86% for the Fashion-MNIST tasks, under the disturbance of random noise spikes. This work provides a promising platform to realize complex neuronal dynamics and to construct robust brain-inspired neuromorphic systems.

Analysis of Dynamic Voltage and Frequency Oscillations in Low-Inertia Power Systems

Analysis of Dynamic Voltage and Frequency Oscillations in Low-Inertia Power Systems

A Phase-Shifting DC-Link Voltage Control Strategy for Parallel Inverters to Suppress Interharmonics in PV Systems

The large-scale installation of PV systems leads to interharmonic problems, which greatly affect the power quality of power system. It has been revealed that the DC-link voltage oscillation caused by the perturbation maximum power point tracking (MPPT) algorithm is one of the main causes of interharmonics. To address this issue, a phase-shifting DC-link voltage control strategy for parallel inverters to suppress interharmonics in PV systems is proposed. In this method, the relationship between interharmonic characteristics and reference DC-link voltage is the basis for suppressing interharmonics. The proposed system contains two parallel inverters whose reference DC-link voltages are antiphase. Therefore, the interharmonic current can be eliminated with each other. Simulations and experiments have been constructed to verify the effectiveness of the proposed interharmonic suppression strategy.

Concurrent recordings of slow DC-potentials and epileptiform discharges: Novel EEG amplifier and signal processing techniques

Ionic currents within the brain generate voltage oscillations. These bioelectrical activities include ultra-low frequency electroencephalograms (DC-EEG, frequency less than 0.1 Hz) and conventional clinical electroencephalograms (AC-EEG, 0.5–70 Hz). Although AC-EEG is commonly used for diagnosing epilepsy, recent studies indicate that DC-EEG is an essential frequency component of EEG and can provide valuable information for analyzing epileptiform discharges. During conventional EEG recordings, DC-EEG is censored by applying high-pass filtering to i) obliterate slow-wave artifacts, ii) eliminate the bioelectrodes' half-cell potential asymmetrical changes in ultralow-low frequency, and iii) prevent instrument saturation. Spreading depression (SD), which is the most prolonged fluctuation in DC-EEG, may be associated with epileptiform discharges. However, recording of SD signals from the scalp's surface can be challenging due to the filtering effect and non-neuronal slow shift potentials. In this study, we describe a novel technique to extend the frequency bandwidth of surface EEG to record SD signals. The method includes novel instrumentation, appropriate bioelectrodes, and efficient signal-processing techniques. To evaluate the accuracy of our approach, we performed a simultaneous surface recording of DC- and AC-EEG from epileptic patients during long-term video EEG monitoring, which provide a promising tool for diagnosis of epilepsy. Data Availability StatementThe data presented in this study are available on request.

Development of a lanthanum hexaboride hollow cathode for a magnetic octupole thruster

Electric propulsion has undergone significant advancements, leading to increased usage in satellite constellation management and orbital transfer vehicles. This study describes the design and development of a lanthanum hexaboride (LaB6) hollow cathode for the Magnetic Octupole Plasma Thruster (MOPT), a novel electric propulsion concept for future space missions. Its operational characteristics are also provided. To gain insights into the coupling behavior between the cathode plume and the octupole magnetic field, the hollow cathode was operated with and without an octupole magnet over a range of discharge currents and flow rates. The results indicate that the discharge voltage was anti-correlated with the discharge current and flow rate. Notably, the octupole magnetic field observed reduced discharge voltage oscillations in both high- and low-discharge-current regimes. Nonetheless, the existence of the magnetic field was associated with the amplification of ionization-like instabilities in the high-flow-rate regime. Finally, the paper also delves into the plasma behavior under the influence of the octupole magnetic field, signifying an advancement in developing LaB6 hollow cathodes for their potential use in space-based MOPT applications.

Ultrafast (400 Hz) network oscillations induced in mouse barrel cortex by optogenetic activation of thalamocortical axons.

Oscillations of extracellular voltage, reflecting synchronous, rhythmic activity in large populations of neurons, are a ubiquitous feature in the mammalian brain, and are thought to subserve important, if not fully understood roles in normal and abnormal brain function. Oscillations at different frequency bands are hallmarks of specific brain and behavioral states. At the higher end of the spectrum, 150-200 Hz ripples occur in the hippocampus during slow-wave sleep, and ultrafast (400-600 Hz) oscillations arise in the somatosensory cortices of humans and several other mammalian species in response to peripheral nerve stimulation or punctate sensory stimuli. Here we report that brief optogenetic activation of thalamocortical axons, in brain slices from mouse somatosensory (barrel) cortex, elicited in the thalamorecipient layer local field potential (LFP) oscillations which we dubbed "ripplets". Ripplets originated in the postsynaptic cortical network and consisted of a precisely repeating sequence of 2‑5 negative transients, closely resembling hippocampal ripples but, at ~400 Hz, over twice as fast. Fast-spiking (FS) inhibitory interneurons fired highly synchronous 400 Hz spike bursts entrained to the LFP oscillation, while regular-spiking (RS), excitatory neurons typically fired only 1-2 spikes per ripplet, in antiphase to FS spikes, and received synchronous sequences of alternating excitatory and inhibitory inputs. We suggest that ripplets are an intrinsically generated cortical response to a strong, synchronous thalamocortical volley, and could provide increased bandwidth for encoding and transmitting sensory information. Importantly, optogenetically induced ripplets are a uniquely accessible model system for studying synaptic mechanisms of fast and ultrafast cortical and hippocampal oscillations.

DC Link Voltage Enhancement in DC Microgrid Using PV Based High Gain Converter with Cascaded Fuzzy Logic Controller

Renewable-based sources can be interconnected through power electronic converters and connected with local loads and energy storage devices to form a microgrid. Nowadays, DC microgrids are gaining more popularity due to their higher efficiency and reliability as compared to AC microgrid systems. The DC Microgrid has power electronics converters between the DC loads and renewable-based energy sources. The power converters controlled with an efficient control algorithm for maintaining stable DC bus voltage in DC microgrids under various operating modes is a challenging task for researchers. With an aim to address the above-mentioned issues, this study focuses on the DC link voltage enhancement of a DC Microgrid system consisting of PV, DFIG-based wind energy conversion system (WECS), and battery Energy Storage System (ESS). To elevate PV output voltage and minimize the oscillations in DC link voltage, a high-gain Luo converter with Cascaded Fuzzy Logic Controller (CFLC) is proposed. Droop control with virtual inertia and damping control is proposed for DFIG-based WECS to provide inertia support. Artificial Neural Network (ANN) based droop control is utilised to regulate the ESS’s State of Charge (SOC). The effectiveness of the proposed converter and its control algorithms for maintaining stable DC bus link voltage has been analysed using MATLAB/Simulink and experimentally validated using a prototype model and FPGA Spartan 6E controllers.

Applying a Multiple-Input Single-Output Interleaved High Step-Up Converter with a Current-Sharing Device Having Different Input Currents to Harvest Energy from Multiple Heat Sources

In this paper, a thermoelectric conversion system for multiple heat sources is proposed. For design convenience, the overall system employs only a single-stage converter. Such a converter uses coupling inductors and switched capacitors to increase the voltage gain. In order to reduce the high-frequency voltage oscillation of the turn-off of the main switches created from leakage inductors, two active clamp circuits with zero voltage switching (ZVS) turn-on are employed. By doing so, although the current-sharing device with interleave control is embedded in the proposed converter, the input currents can be unequal. Therefore, the inputs of the converter can operate under individual maximum power points and transfer the energy from different thermoelectric generators (TGs) to a single load. Furthermore, the main switches have low voltage stress during the turn-off period. As for the maximum power point tracking (MPPT) method, it utilizes a three-point-weighting method to improve the tracking stability. In addition, the number of inputs of this converter can be extended. The MPPT simulation is presented to verify the feasibility as well as several experimental waveforms to demonstrate the effectiveness. The field programmable gate array (FPGA) is used as a digital control kernel to control the thermoelectric conversion system.

A Front-End CMOS Interface Circuit With High Voltage Charge Pump and Oscillator for Capacitive Micromachined Ultrasonic Transducers

Label-free biosensors, combined with miniaturized micro-electromechanical sensory platforms, offer an attractive solution for real-time and facile monitoring of biomolecules due to their high sensitivity and selectivity without the need for specifically labeling. Resonators have been acknowledged as an efficient technology for measuring biomolecular binding events including those involving nucleic acid and antibody. Among these, capacitive micromachined ultrasonic transducers (CMUTs) have emerged as a promising candidate for biosensing. However, their usage is often limited by the requirement for high voltage supply and continuous frequency tracking, which can result in significant parasitic effects and measurement errors. In this paper, we present a novel front-end interface circuit for a CMUTs-based biosensor. The circuit, fabricated using TSMC 0.18-μX;Jm Bipolar-CMOS-DMOS (BCD) technology, incorporates an on-chip high voltage charge pump and feedback frequency monitoring. The CMUTs array features 20×20 circular cells, fabricated using a low-temperature direct bonding technology, with an experimental parallel-resonant frequency of 1.724 MHz and a high quality factor of up to 40.9. To fit the measured electrical characteristics, a five-element equivalent lumped element model is proposed. The high voltage charge pump provides an output voltage of 20 V, while the feedback oscillator has a ms-level start-up time and a total power dissipation of 3.8 mW. The proposed front-end interface is designed to function as a stand-alone chip for CMUTs-based resonant biodetection.

Wide zero‐voltage switching range full‐bridge converter based on adjustable parallel current

AbstractAiming at the problems of narrow ZVS range, large duty cycle loss, and severe voltage oscillation of phase‐shift‐controlled full‐bridge converters, this paper proposes a converter that realizes ZVS by adjusting the parallel current. No additional series inductor is required, avoiding large duty cycle loss and weakening voltage oscillations on the secondary side. The converter with small duty cycle loss can use a transformer with a larger turns ratio, which can reduce the voltage stress of the secondary diodes and the filter inductor current ripple. The parallel current required to realize ZVS is analyzed theoretically considering the influence of leakage inductor energy on ZVS. A comparative experiment between the proposed converter and the conventional full‐bridge converter is carried out to verify the performance of the proposed converter.

Active hybrid energy storage management in a wind-dominated standalone system with robust fractional-order controller optimized by Gases Brownian Motion Optimization Algorithm

Accessibility to sustainable and reliable electrical energy for remote area power supply (RAPS) systems under high penetration levels of wind energy requires adopting appropriate technologies and controllers. In recent years, energy storage has gained significant attention for smoothing inherent voltage and power fluctuations of standalone systems. This paper presents a filtration-based fractional-order PI (FOPI) controller optimized by Gases Brownian Motion Optimization (GBMO) algorithm to manage an active battery-supercapacitor hybrid energy storage system (HESS) in a wind-dominated RAPS system. The GBMO algorithm has a high accuracy and convergence rate among optimization algorithms introduced in recent years. Moreover, a fuzzy logic controller (FLC) guarantees the wind turbine generator's maximum power point tracking (MPPT) at any wind condition while mitigating its fluctuating torque. The proposed RAPS system uses the advantages of the FOPI controller, the GBMO optimization algorithm, the FLC-based MPPT algorithm, and a high-pass filter to manage precise coordination between different components of the RAPS system. The high-pass filter decouples high and low-frequency voltage oscillations to modify the HESS performance and relieve battery stress, thereby extending its lifespan. The proposed controller's performance and robustness are verified in comparison with an optimal PI controller based on GBMO under turbulent wind speed and load step changes in a detailed model of the system. The results demonstrate the superiority of the optimal FOPI controller over the optimal PI controller.

A variable frequency injection method for modular multilevel converters in variable speed drives

Modular multilevel converter (MMC) is a novel circuit that has appeared in the last few decades, and has been extensively applied to medium/high voltage scenarios, especially in motor drive owing to its scalability and easy to supply a higher number of output voltage levels. As theoretical analysis shows, the sub-module (SM) capacitor voltage magnitude is positively related to the converter output current amplitude and conversely connected to the fundamental frequency. Therefore, the prime challenge of applying MMC to variable speed drives is that there is a huge voltage oscillation in SM capacitor voltage during low-speed working. An innovative high-frequency voltage injection modality to diminish the fluctuation of the capacitor voltage in variable speed drives is proposed in this paper, in which the frequency of the injected component can be changed with the operating frequency of the converter and the low frequency component of power can be converted into high frequency component. The discussed measure not only significantly reduces the voltage float in capacitor, but also avoids the overmodulation of arm voltage modulation waveform caused by high frequency of injection component when converter works in low frequency. With the improved method, the performance of motor at low frequency is enhanced. Finally, the feasibility and effectiveness of the proposed improved high-frequency voltage injection method are verified by simulation and experiment.

Dynamic Performance Improvement of a Single-Phase VSI with Digital Implementation of an On-Line Optimal Trajectory Control Algorithm

A single-phase voltage source inverter (VSI) still suffers from a long settling time and significant voltage overshoot/undershoot under the abrupt step-change of load current. This article analyzes the comprehensive large-signal dynamic process and limitation of the linear controller during step change in load current. The combination of linear and nonlinear control is presented which is a realistic, simple, and low-cost technique for enhancing the dynamic response of the single-phase VSI. A nonlinear controller based on the simplified capacitor charge balance algorithm is employed to drive the inductor current and capacitor voltage to attain the target value by precisely following the projected optimal trajectory during the transient process in a brief period. A linear PI controller is utilized during the steady-state operations such as input voltage variations, temperature drifts, and component ageing. The complete mathematical derivation as well as a design method is presented to guide the practical hardware implementation for the given main circuit parameters and identified load step change. Even though accurate time instants can be obtained using off-line numerical calculations, reasonable simplifications are provided for real-time practical engineering applications in DSP. Finally, simulation and experimental verifications prove that the single-phase VSI achieves a substantial settling time decrease and reduced voltage oscillations.

Theory of multidimensional quantum capacitance and its application to spin and charge discrimination in quantum dot arrays

Quantum states of a few-particle system capacitively coupled to a metal gate can be discriminated by measuring the quantum capacitance, which can be identified with the second derivative of the system energy with respect to the gate voltage. This approach is here generalized to the multivoltage case, through the introduction of the quantum capacitance matrix. The matrix formalism allows us to determine the dependence of the quantum capacitance on the direction of the voltage oscillations in the parameter space and to identify the optimal combination of gate voltages. As a representative example, this approach is applied to the case of a quantum dot array, described in terms of a Hubbard model. Here, we first identify the potentially relevant regions in the multidimensional voltage space with the boundaries between charge stability regions, determined within a semiclassical approach. Then, we quantitatively characterize such boundaries by means of the quantum capacitance matrix. Altogether, this provides a procedure for optimizing the discrimination between states with different particle numbers and/or total spins.

A Highly Integrated Multichip SiC MOSFET Power Module With Optimized Electrical and Thermal Performances

This paper proposes a highly integrated multichip silicon carbide (SiC) MOSFET power module packaging with optimized electrical and thermal performances. The structure of the module is to stack the two power switches up and down with the cooling system and the decoupling circuit integrated inside the module. The structural characteristics of the module realize the co-optimization of the switching performance, thermal management, and electromagnetic interference (EMI) issue of the multichip SiC module, which effectively solve the contradiction in the optimization of the electrical and thermal performance. In addition, by optimizing the process flow and designing a variety of soldering fixtures, the feasibility of the process and the engineering margin is increased. Experiments and simulations show that the proposed SiC power module has good electrical and thermal performance. The loop parasitic inductance is reduced to 2.02 nH and the common-mode (CM) current is eliminated. The drain–source voltage overshoot during the turn-off transient is reduced by 76.5%, and the voltage oscillation is significantly improved due to the integration of the decoupling circuit. At the same time, the integrated liquid-cooling heatsink greatly improves the cooling efficiency of the module on the premise of ensuring the insulation performance of the module.

Analytical predictions of periodic oscillations in a piezoelectric energy harvester under combined aeroelastic and harmonic excitation.

This work studies a piezoelectric energy harvester subjected to both fluid flow and harmonic excitation. A lumped parameter model that incorporates fluid-structure interaction is presented to analyze the effects of both fluid flow and harmonic excitation on the proposed harvester. The method of implicit mapping is employed to calculate the periodic displacement, voltage, and velocity oscillations. Stabilities and bifurcations of periodic oscillations are determined based on the eigenvalues of the resultant matrix of mapping structures. The displacement and voltage nodes of the proposed energy harvester varying with excitation amplitude and frequency are investigated. The maximum eigenvalue magnitudes are illustrated. Utilizing the periodic nodes of the displacement and voltage, the harmonic amplitudes and phases are calculated using the fast Fourier transform. The harmonic amplitudes of both displacement and voltage varying with excitation frequency are depicted. For the stable periodic responses, the implicit maps and numerical simulations are presented to demonstrate the effectiveness of the energy harvesting system. The theoretical analysis presented in this study can be useful for the design and optimization of the proposed energy harvester.

Active voltage damping method with negative DC link current feedback in electric and hybrid electric transmissions

Electric and hybrid electric transmissions in traction drive have a limited capacity power source. Since the traction drive operates in the torque source mode, the DC link voltage becomes unstable and goes into oscillatory mode. This leads to the software protection reaction which prevents the traction inverter overvoltage breakdown. The transition boundary to the oscillatory mode is determined by the power and the value of the capacitance installed in the electric transmission DC link. To increase reliability of the traction inverters, large-capacity electrolytic capacitors are replaced with small-capacity film capacitors which makes the system more prone to oscillations. To solve this problem, active damping methods are used allowing changing the engine dynamic characteristics by means of the control system. The software methods with power and torque proportional control are most widely used. Proportional power control is the simplest method in which the traction drive simulates an RL load. The torque proportional control method adjusts the torque reference according to the change in the DC link voltage. This paper proposes a new negative DC link feedback method. In this case, the torque is adjusted dynamically depending on the current consumed by the traction inverter from the electric transmission common DC link. Mathematical modeling methods were used to compare the known and proposed methods of DC link voltage active damping. Mathematical models have been developed in the MATLAB Simulink environment which makes it possible to investigate the damping capacity at various values of the power consumed by the traction inverter. It is shown that the proposed method with negative DC link current feedback demonstrated tuning simplicity. In comparison with proportional power and torque control methods, the proposed option is robust when setting parameters, provides a large damping coefficient over the entire range of traction drive power, and has a short duration of the transient process. The proposed method can be used to suppress DC link voltage oscillations on any type of hybrid electric and all-electric vehicles traction inverters and ensures stable and reliable equipment operation.

Voltage Control of a Quasi Z-Source Converter Under Constant Power Load Condition Using Reinforcement Learning

The goal of this paper is to design an adaptive optimal controller for voltage control of DC–DC Z-Source (ZS) converters under a challenging load situation called Constant Power Load (CPL) without a need for any knowledge about their dynamics. These converters have been developed to remedy the drawbacks of the conventional converters and several works have been recently carried out to increase the voltage gain and decrease the voltage stress in these converters. Meanwhile, from a control point of view, voltage control of a very high voltage gain ZS DC–DC converter is unquestionably more sophisticated than the traditional converters (like Boost). Firstly, due to the non-minimum phase functionality, ZS converters present an additional challenge to controller design processes compared with traditional converters. Secondly, their output voltage sensitivity is high, and small oscillations in the control signals can lead to large oscillations in the output voltage. On the other hand, CPLs can further threaten the performance of the converter’s voltage controller due to incremental negative resistance. To alleviate these problems Reinforcement Learning (RL), one of the promising optimal and adaptive model-free control algorithms, can be used. Contrary to traditional controllers which manipulate PWM’s duty cycle, here the proposed controller directly controls the power switches inside the converter. Due to the fact that the action space is discrete and finite, this gives rise to significant simplifications in the architecture of the RL-based controller and better convergence in the training phase. Voltage control of various ZS converter topologies can be carried out by the proposed algorithm. In this paper, for instance, it is experimentally applied to a quasi ZS converter under CPL condition, and its performance compared to other classical controllers such as single-loop PI controller, dual-loop PI controller, and finite state model predictive controller is reported which confirms the better performance of the proposed algorithm in terms of voltage stability and transient tracking error.