Low-frequency Voltage Research Articles

Simple Voltage Balancing Control of Four-Level Inverter

Multilevel inverters with improved voltage quality are widely used in applications such as motor control and electric vehicles. The four-level active neutral point clamped (4L-ANPC) inverter effectively meets the demands for high power density and low device voltage stress. However, balancing the capacitor voltage and reducing its low-frequency voltage fluctuation are critical challenges that need to be addressed. To address these challenges, this paper proposes a “variable reference + zero-sequence injection” method that requires only three reference voltage signals to determine the injected zero-sequence components. Particularly, the expression of the midpoint current, regarding the modulation index and phase current amplitude, is theoretically derived. This reveals the fundamental connection between the zero-sequence voltage signal and the midpoint current, providing a theoretical foundation for the zero-sequence injection method in four-level inverters. Subsequently, a simulation model and an experimental platform of the 4L-ANPC inverter were developed to compare and analyze the waveforms of the upper and lower capacitor voltages, phase currents, and line voltages under different modulation methods. Additionally, the upper and lower capacitor voltage waveforms were examined for various modulation indices. The results indicate that as the modulation index increases, the low-frequency voltage fluctuation in the upper and lower capacitor voltages also rises. At a modulation index of 0.95, the “variable reference + zero-sequence injection” method effectively suppresses the fluctuation in the upper and lower capacitor voltages to be no more than 1 V. These experimental findings validate the effectiveness of the proposed method.

Studies of dynamic spatio-temporal processes of electrons in a 50 kHz/5 MHz dual-frequency dielectric barrier discharge plasma at atmospheric pressure

Dual-frequency excitation of dielectric barrier discharge (DBD) plasma reactors, where the plasma is generated by a low-frequency (LF) source and modulated by a radio-frequency (RF) source, have been widely adopted in the low-pressure regime. However, the impacts of the RF voltage and LF voltage amplitudes on the plasma parameters, including the spatiotemporal distributions of ion and electron densities, electron dynamics, and gas temperatures, remain poorly understood in the atmospheric pressure regime. The present work addresses this issue by conducting joint experimental and simulation studies for an atmospheric-pressure 50 kHz/5 MHz dual-frequency driven DBD plasma reactor based on phase-resolved optical emission spectra and a drift–diffusion model. The results demonstrate that the dynamic spatiotemporal behaviors of electrons change dramatically as the voltage of the RF component increases from 50 V to 300 V with the voltage of the LF component fixed at 1 kV. Moreover, the RF component is further demonstrated to modulate other plasma characteristics, such as particle densities, gas temperature, and argon emissions. These results contribute toward the tailoring of the non-equilibrium and nonlinear plasma parameters obtained under atmospheric pressure conditions.

Air disinfection by nanosecond pulsed DBD plasma

Atmospheric pressure dielectric barrier discharge (DBD) plasma is an emerging and promising technique for air disinfection in public environments. Power supply is a crucial factor but it remains unclear about its impacts on the air disinfection performance of plasmas. In this work, a nanosecond (ns) pulsed power supply was applied to drive an in-duct grating-like DBD array to achieve fast single-pass air disinfection. The influence of pulse parameters and environmental factors on both the discharge characteristics and the single-pass bacterial inactivation efficiency were uncovered. At a close relative humidity (RH) level, the efficiency was dominated by the discharge power, namely, specific input energy could serve as the disinfection dose. A higher frequency, shorter pulse rising time, and suitable pulse width are preferred to obtain a higher Z value. The pulsed source was not notably superior to an alternating current source, or even worse at a low voltage frequency at the same discharge power. Airflow humidity was a predominant factor to improve the efficiency and a single-pass efficiency of ∼ 99% and a Z value of 2.2 L/J were achieved under an optimal RH of 50%–60%. This work provides fundamental knowledge of ns-pulsed DBD on discharge characteristics and air disinfection behaviors.

Design of Global RLC Interconnect Circuit with Analytical Delay Model

Background: With the advancement in technology nodes and scaling trends, the majority of the device performance depends upon the interconnections made between two or more devices. With these scaling trends, frequency plays a vital role. As the technology decreases, frequency tends to rise to giga-hertz. This increase in frequency gives rise to inductance parameters in the interconnect circuits. For long wires, the inductive impedance can become comparable to the resistive component due to which performance degradation can be observed along with overshoot and crosstalk issues that can no longer be ignored. Method: This article aims to examine the delay model and reconstruct an interconnect circuit that serves as a transmission line, ranging in length from 1 mm to 10 mm. Result: By keeping the frequency high, low voltage and rise/ fall time, performance parameters such as delay, power consumption, and overshoot are observed. Conclusion: The interconnect structure is compared with another state-of-the-art technique.

Dual-frequency sheath oscillations and consequences on the ion and electron transport in dielectric barrier discharges at atmospheric pressure

Current–voltage characteristics, space- and time-resolved optical emission spectroscopy, and 1D fluid modeling are used to examine the effect of dual-frequency sheath oscillations on the ion and electron transport in dielectric barrier discharges sustained by a combination of low frequency (LF, 50 kHz, 650 V) and radiofrequency (RF, 5.3 MHz, 195 V) voltages, exhibiting the α-to-γ mode transition. On one hand, when polarities of the LF and RF voltages are opposite, an electric field near the LF cathode (due to LF cathode sheath) drives the secondary electrons to the plasma bulk and an opposite electric field between the sheath edge and the LF anode attracts the electrons toward the LF cathode (to maintain quasi-neutrality in the plasma bulk). At the sheath edge, electrons become trapped and ions drift toward the cathode and the anode simultaneously according to their position in the gap. On the other hand, when the RF voltage has the same polarity as the LF voltage, the total applied voltage increases and this yields to enhanced production of electrons and ions in the sheath. To maintain quasi-neutrality in the bulk, the electric field along the gap exhibits the same polarity as the one in the sheath, allowing electrons created in the sheath to be evacuated toward the LF anode. The behavior of the LF cathode is, therefore, controlled by the LF sheath, and, thus, by the LF voltage amplitude, while the behavior in the bulk and at the anode alternates on the time scale of the RF voltage.

Effects of low-frequency voltage on nonlinear standing wave excitation, plasma uniformity, and ion dynamics in dual-frequency asymmetric capacitive discharges

It is known that in very-high-frequency (VHF) capacitively coupled plasmas, the higher harmonics generated by nonlinear sheath motion can enhance the standing wave effect (SWE), which can lead to center-peaked plasma density profiles. In this work, an improved nonlinear electromagnetic model incorporating a transmission line model, an electron momentum balance model, a bulk plasma model, a collisionless nonlinear numerical sheath model, and an ion Monte-Carlo collision (MCC) model is developed to study the effects of low-frequency (LF) voltage VL on the nonlinear standing wave excitation, plasma uniformity, and ion energy and angular distribution functions (IEDFs and IADFs) in dual-frequency (DF) asymmetric capacitive argon discharges at relatively low pressure of 3 Pa. The plasma diffusion in the radial direction and ion dynamics within the LF oscillating sheath are self-consistently considered. The LF voltage VL at 2 MHz varies from 0 to 700 V while the HF voltage VH at 60 MHz is fixed at 100 V. Simulation results indicate that without the addition of an LF source (i.e. VL= 0 V), there are a considerable number of high-order harmonics with short wavelengths, leading to significant SWE and central peak in the radial plasma density profile. Nevertheless, the high-order harmonic excitations tend to be weakened and merely occur around the phase of the full LF sheath collapse due to a shorter characteristic damping time of the surface waves as VL increases. This, combined with increased surface wavelengths of both the driving frequency and the higher harmonics at a higher VL , leads to suppressed standing waves and improved plasma uniformity. Meanwhile, the simulations show that both the low and the high energy peaks of IEDF move towards higher energies, and the energy peak separation width ΔE becomes wider with the increase of VL . The IEDF at the radial center of the powered electrode exhibits a broader ΔE than that at the edge. For the IADF, an increased VL results in more ions incident on the electrode with a smaller deflection angle. Because of a thinner sheath and a higher sheath voltage at the electrode center, the peak value of IADF at the electrode center is greater than that at the edge.

Design and simulation of a tunable comb-drive actuator with a wide frequency tuning range and low pull-in voltage

The presented paper describes the design, simulation, and analysis of a novel tunable comb-drive actuator that aims to increase the range of tuning resonance frequency while reducing the pull-in voltage. The conventional comb resonator has a limited resonant frequency tuning range, and hence, modifying the spring stiffness of the structure is crucial to obtaining a tunable comb resonator. The proposed design includes eight flexible beams on each side that support a set of comb finger parts. The actuator achieves the goal of shifting the resonance frequency both downwards and upwards by utilizing Serpentine nested-folded beams. A triangular comb with non-uniform varied finger lengths combined with variable gap fingers is designed to adjust the frequency downwards, while a comb with constant finger lengths combined with variable gap fingers is designed to adjust the frequency upwards. To simulate and design the structure, the IntelliSuite software is utilized. The results show that the actuator has a primary resonant frequency of 3052 Hz, which can be lowered to 335 Hz by applying a tuning voltage of 74 V to the downward tuning part. Similarly, the resonant frequency can be increased to 3159 Hz by applying a tuning voltage of 60 V to the upward tuning part. The resonator achieves a maximum frequency tuning range of 90%, and the simulation results are in good agreement with the theoretical predictions. However, it is worth noting that the size of this resonator is relatively small, approximately 1077 × 328 μm2. This innovative design offers potential applications in various fields, including micro-electromechanical systems (MEMS), micro-optics, and microsensors. Overall, the presented work demonstrates the feasibility of achieving a tunable comb resonator with a significantly improved resonant frequency tuning range and reduced pull-in voltage.

Microwave photonics doppler speed measurement based on sagnac loops and four-wave mixing effect in a highly nonlinear fiber

Photonic radars are increasingly being developed and offer a promising replacement for traditional RF radars. They feature higher precision, and smaller size compared to the current microwave radars. One important part of a moving target indicating (MTI) radar is the Doppler shift measurement used to measure the radial velocity of a moving target. Therefore, for any photonic radar operating at MTI mode, it is necessary to have a Doppler measurement subsystem. In this paper, a microwave photonic Doppler frequency measurement system is conceived and implemented for this purpose specifically. The operation is based on making a Doppler shift-dependent yet low-frequency voltage component. It is all-optical and hence has the potential to be integrated into many electronic warfare systems. This feature not only makes the system independent of any sophisticated electrical device but also makes the measurement time lower than that of the electrical counterparts. The specific design presented here provides a much better stability compared to the recent works. An error as low as 0.012 Hz at a 10 GHz radar frequency was obtained, and the system performance was demonstrated up to 40 GHz, at which a 4.75 Hz error was recorded.

Distinct neural signatures underlying information maintenance and manipulation in working memory.

Previous working memory research has demonstrated robust stimulus representations during memory maintenance in both voltage and alpha-band activity in electroencephalography. However, the exact functions of these 2 neural signatures have remained controversial. Here we systematically investigated their respective contributions to memory manipulation. Human participants either maintained a previously seen spatial location, or manipulated the location following a mental rotation cue over a delay. Using multivariate decoding, we observed robust location representations in low-frequency voltage and alpha-band oscillatory activity with distinct spatiotemporal dynamics: location representations were most evident in posterior channels in alpha-band activity, but were most prominent in the more anterior, central channels in voltage signals. Moreover, the temporal emergence of manipulated representation in central voltage preceded that in posterior alpha-band activity, suggesting that voltage might carry stimulus-specific source signals originated internally from anterior cortex, whereas alpha-band activity might reflect feedback signals in posterior cortex received from higher-order cortex. Lastly, while location representations in both signals were coded in a low-dimensional neural subspace, location representation in central voltage was higher-dimensional and underwent a representational transformation that exclusively predicted memory behavior. Together, these results highlight the crucial role of central voltage in working memory, and support functional distinctions between voltage and alpha-band activity.

Nonisolated Three-Phase Current DC-Link Buck–Boost EV Charger With Virtual Output Midpoint Grounding and Ground Current Control

Non-isolated three-phase AC/DC converter concepts facilitate more compact and more efficient realizations of future EV chargers. However, without the galvanic isolation and/or high common-mode (CM) impedance provided by an isolation transformer, non-isolated chargers must employ other means to suppress CM leakage currents to ground sufficiently and to prevent nuisance tripping of mandatory residual current devices (RCDs). Typically, the required EMI filters reduce high-frequency (HF) CM leakage currents to uncritical values. However, low-frequency CM voltages, e.g., generated by third-harmonic injection, may drive significant LF CM currents through the parasitic capacitances of the DC output (including the battery pack) to protective earth (PE). Therefore, considering a non-isolated three-phase buck-boost current DC-link PFC rectifier system that consists of a buck-type current-source rectifier (CSR) stage and a three-level boost-type DC/DC-stage, this paper first proposes a virtual grounding control (VGC) of the DC output voltage midpoint. VGC employs the DC/DC-stage to compensate the LF (third-harmonic) CM voltage inherently generated by the CSR-stage, and thus controls the LF CM voltage between the DC output midpoint and PE to zero. This enables further a direct connection of the DC output midpoint to PE, where an additionally proposed ground current control (GCC) ensures near-zero LF CM leakage current. The proposed concepts are verified with a 10kW hardware demonstrator (power density of 6.4 kW/dm3 or 107.5 W/in3, full-load peak efficiency of 98.5%) considering TT (Terra-Terra) and TN (Terra-Neutral) grounding systems. With a direct connection of the DC output midpoint to PE, GCC limits the LF CM leakage current to < 6mA RMS, i.e., significantly below typical RCD trip levels, and, using the human-body impedance model according to UL 2202, achieves a test voltage of 110mV that is clearly below the most stringent limit (250 mV) of the standard.

An 80–84.8 GHz PLL with auto-tracking Miller divider for FMCW applications

To generate high frequency signals for frequency modulated continuous wave (FMCW) application, components such as doubler, tripler or multiplier are usually utilized to process further signals from the low frequency voltage controlled oscillator (VCO). In this paper, a phase-locked loop (PLL) is intended to be the primary part used to generate frequency modulated continuous wave (FMCW) signals from 80 to 84.8 GHz by utilizing a fundamental frequency VCO. To divide those high frequency output signal and large output bandwidth, the auto-tracking Miller divider topology is proposed. This new topology can achieve 9 GHz locking range. In order to generate FMCW signals with a straight-line triangular chirp, the cascaded PLL is used. The integrated jitter from 1 kHz to 1 GHz is 887 fs for the cascaded PLL, while the single stage PLL used 1.264 ps. Moreover, when architecture with doubler or multiplier is used, the fundamental tone has an effect towards the next systems, while the cascaded PLL does not. It can be highlighted that this work achieves the best RMS-FMerror/BWchirp and RMS-FMerror/(BWchirp × fc × Tc) with value of 0.013% and 0.77e−12, respectively. The designed PLL for FMCW signal generator is implemented in 28 nm CMOS technology. By using a supply voltage of 1.2 V, the chip consumes power of 102 mW. Including all the chip pads, the implemented circuit occupies a silicon area of 1440 µm × 820 µm.

Awake brain mapping by direct cortical stimulation; technical note to get higher resection rate and low morbidity in low-grade glioma patients.

Direct cortical stimulation has been used for brain mapping and localization of eloquent areas in awake patients. This simplified technique is to provide the positive areas, which can be preserved if the tumor or lesions are involved eloquent areas. The main objective of this study is to determine whether direct cortical stimulation in awake brain mapping for low-grade glioma patients increases the rate of resection or not. The authors present a retrospective study between 2020 to 2022 that includes 35 cases in a single center, to get higher resection rate, and their consequences in awake craniotomy in low-grade glioma patients. Here, two neurosurgeons were involved and the minimum follow-up was 12 months. The authors achieved 80% removal of tumors. To get higher resection rate we emphasized negative mapping with prior anatomical analysis to understand functional realignment. Stimulation-related complications will be thoroughly discussed with a potential future direction to minimize the issues. The authors used PROMIS score to measure patients physical and mental health status and kernofsky score to measure performance status before and after successful surgery. The authors found three cases of transient deficit in repetitive stimulation. Repeated stimulation to identify the eloquent areas with low voltage frequency is a good option. Numbness in the face related to stimulation may continue for 6 weeks. Functional realignment in shifted brain and edema can be seen while doing cortical and subcortical stimulation. Most of the stimulation from low to high for language mapping may vary from patient to patient. For safe removal of low-grade glioma a steep learning curve is needed to find out the negative areas, though the authors emphasize positive mapping of areas to secure the maximum eloquence.

Experimental and numerical study on atmospheric‐pressure air dielectric barrier discharge via 50 Hz/5000 Hz dual‐frequency excitation

AbstractA dual‐frequency (DF) dielectric barrier discharge, excited by the superposition of a 50 Hz low frequency (LF) and a 5000 Hz intermediate frequency (IF), is proposed to enhance discharge. The effect of the LF voltage component on the breakdown behaviour of the DF discharge during different periods has been studied both experimentally and numerically. The number of high‐current pulses rises as the LF voltage increases. The statistical analysis shows that the number of the current pulse amplitude above 80 mA in the DF discharge reaches nearly 6 times that in the IF discharge. Additionally, the total discharge energy in the DF discharge is significantly higher than that in the IF discharge. The simulation reproduces the temporal variation of the breakdown behaviours in the DF discharge. The simulated results reveal that the maximal electric field strength of the breakdown process is greater in the DF discharge compared to the IF discharge during a half‐period of DF. Finally, the comparison between the IF and DF discharges exhibits that the LF voltage regulates the accumulation of residual charged species on the dielectric surface after the breakdown by modulating the residual voltage between the air gap.

An experimental and computational study on the ignition process of a pulse modulated dual-RF capacitively coupled plasma operated at various low-frequency voltage amplitudes

The ignition process of a pulse modulated capacitively coupled argon discharge driven simultaneously by two radio frequency voltages [12.5 MHz (high frequency) and 2.5 MHz (low frequency, LF)] is investigated by multifold experimental diagnostics and particle in cell / Monte Carlo collision simulations. In particular, (i) the effects of the LF voltage amplitude measured at the end of the pulse-on period, VL,end , on the spatiotemporal distribution of the electron impact excitation rate determined by phase resolved optical emission spectroscopy, and (ii) the electrical parameters acquired by analyzing the measured waveforms of the plasma current and voltage, are studied. Computed electrical parameters and spatio-temporal excitation maps show a good qualitative agreement with the experimental results. Especially, various breakdown mechanisms are found at different VL,end . At low values of VL,end , the ‘RF-avalanche’ mode (volume process) dominates the electron multiplication process. By increasing VL,end , the ionization caused by the volume electrons is suppressed and the electron loss at the electrodes is enhanced, leading to a delayed ignition. At higher values of VL,end , the avalanche ionization is significantly enhanced by ion-induced secondary electron emission at the electrodes, so that the ignition is significantly advanced.

Skin Care Experience of a Case of Multiple Organ Failure Caused by High-Voltage Electrical Injury

Background: High-voltage electrical burns are caused by the direct transmission of electric current through the body and the conversion of electric energy into heat energy, which directly heats the tissues and leads to organ function damage. Especially after high-voltage electric burns (more than 1000W), it can not only cause coagulation necrosis of the skin and even carbonization, but also cause serious deep tissue damage .The degree of tissue damage depends on the type of current, the magnitude of current, the frequency, the voltage, the resistance of the tissue, the skin humidity, the duration, the contact area, and other factors. Low voltage and low frequency electric shock mainly affect the heart and respiration, which can lead to insignificant soft tissue damage. High voltage electric shock mainly causes serious soft tissue damage, which can be accompanied by changes in the circulatory system and respiratory system.[1] Subject and Method: We collected the data of a case of multiple organ failure caused by high-voltage electricity that was successfully treated in July 2023.In the course of this patient's successful treatment, The main nursing measures were analyzed: The intake and output volume were actively controlled. Albumin supplementation, Debridement and dressing change were performed daily, Covered with nano-silver ion dressing, Try to ensure a sterile environment during operation, Maintain ambient temperature and humidity. Results: Twenty days later,the skin damage caused by electric burns was reduced from 30% to 1%. Conclusion: These are very important links: The intake and output volume were actively controlled, The balance of intake and output was maintained for 24 hours, and lactic acid was less than 2mmol/L. Albumin supplementation Controlled above 30g/L, Debridement and dressing change were performed daily, Covered with nano-silver ion dressing, Try to ensure a sterile environment during operation, Maintain ambient temperature 28~30℃ and humidity 40%~50%.

A Coordinated Voltage-Frequency Support Method for VSC-MTDC Integrated Offshore Wind Farms System

Voltage and frequency stability is one of the major concerns with the continuously increasing penetration of offshore wind farms (OWFs) integrated into onshore grid via VSC-MTDC system, and it is a challenge to coordinate its low voltage ride-through (LVRT) and frequency regulation (FR) control when a local fault or large disturbance occurs in onshore grid. To address this challenge, a coordinated voltage-frequency support (CVFS) method for the VSC-MTDC integrated OWFs system is proposed in three parts: 1) an adaptive maximum power point tracking (MPPT) strategy is developed for wind turbines (WTs) to satisfy the power demands for LVRT and FR; 2) an active and reactive power quantification strategy, which firstly considers the static load characteristics of nodes nearest the grid side VSC (GSVSC) stations, is proposed for GSVSC stations to support LVRT and FR respectively; 3) an adaptive power allocation strategy, which considers the capacity constraint and the coordination factor with deviation and rate of change of voltage and frequency of different GSVSC stations, is conducted to achieve differential power distribution between LVRT and FR. Extensive test results have validated the effectiveness and performance of the proposed CVFS method.

Low-Frequency Voltage Ripple Suppression for MMCs With Split-Capacitor Submodules

Low-Frequency Voltage Ripple Suppression for MMCs With Split-Capacitor Submodules

Particle-in-cell simulations of high frequency capacitively coupled plasmas including spatially localised inductive-like heating

High frequency (HF) capacitively coupled plasmas (CCPs) are ubiquitous, having several industrial applications, especially in the semiconductor industry. Inductive heating effects within these plasmas play an important role and therefore understanding them is key to improve industrial applications. For this purpose kinetic research, using particle-in-cell (PIC) codes, offers significant opportunity to study, and improve, industrial plasma processes that operate at the atomic level. However, PIC codes commonly used for CCPs are electrostatic and thus cannot be used to simulate electromagnetically induced currents. Therefore we have developed EPOCH-LTP, a 1D PIC code with a current heating model, that enables the simulation of inductive heating effects in HF CCPs. First simulation results, from an HF CCP (60 MHz) operated at 1 mTorr of argon, show that inductive currents couple most of their power to the electrons at the interface between the bulk plasma and the sheath. Furthermore, the simulation of a dual-frequency CCP, where a HF inductive current and a low-frequency (LF) voltage waveform at 400 kHz are applied, have shown a synergy between the HF and LF waveforms that increase the inductive heating rate.

Frequency-Variant Electronic Capacitor to Simultaneously Reduce Low-Frequency DC-Link Voltage Ripple and Improve Current THD of Grid-Connected Power Converters

Electronic Capacitor (EC) is a circuit typically aimed to replace (in part or entirely) the bulk DC-link capacitor of a grid-interfacing power converter in plug-and-play manner. EC is realized by a bidirectional DC-DC converter terminated with small auxiliary capacitor. The converter is controlled such that its DC-link side terminals mimic the behavior of a capacitor with much higher constant capacitance. In this paper, a modification of the classical EC control structure is proposed, imposing the DC-link side terminals to emulate a frequency-variant capacitor rather than a constant one. The proposed algorithm allows achieving simultaneous reduction of both DC link voltage ripple and grid-side current total harmonic distortion (THD) compared to ones attained by classical solutions, thus improving the trade-off between DC link voltage dynamics and AC-side current quality inevitably present in any grid-connected power converter. The proposed methodology is well-supported by experiments.

Low-frequency operation control method for medium-voltage high-capacity FC-MMC type frequency converter

The application of modular multilevel converters (MMCs) to large drive systems is subject to severe low-frequency operation restrictions. The fluctuation of capacitor voltage and the high amplitude of common mode voltage in sub-modules is a thorny problem. In this paper, a novel fly-across capacitor modular multilevel converter topology is adopted to eliminate low-frequency voltage ripples by using the fly-across capacitor as a power transfer channel between the upper and lower bridge arms of the MMC. A novel finite compensation method is proposed—instead of the traditional full compensation method—that introduces a real-time variable limiting factor to change the amplitude of the mixed injected high-frequency differential-mode voltage and high-frequency differential-mode current and reduce the amplitude of the common-mode voltage on the AC side while lowering the current stress of the power devices. Finally, a complete system simulation model is constructed, and the topology with the proposed control strategy are verified to have good output characteristics under different operating conditions; good results are achieved in suppressing the sub-module fluctuation and common-mode voltage.