Low-frequency Voltage Research Articles

A 12 mV Input, 90.8% Peak Efficiency CRM Boost Converter With a Sub-Threshold Startup Voltage for TEG Energy Harvesting

This paper proposed a high efficiency boost converter targeting thermoelectric generator energy harvesting. The proposed converter adopts the critical conduction mode rather than the discontinuous mode to reduce the conduction loss, which can improve the peak efficiency at high input power. To reduce the minimum input voltage, an adaptive on-resistance switch, which can automatically change the high side and low side on-resistance according to the input voltage, is used. To maximize the output power, a maximum power point tracking circuit is designed to track the internal source resistance. Radio frequency (RF) kick-up and low voltage startup are used to improve the cold start voltage. The proposed converter is implemented in a 0.18- $\mu \text{m}$ standard CMOS process, which occupies a chip area of about 0.48 mm2. Measurement results show that the peak efficiency of the converter can be up to 90.8% and 60% at 180 and 20 mV of the open-circuit voltage, respectively. Owing to the cold startup circuit, the proposed converter can start successfully with 260-mV open-circuit voltage or −16-dBm RF input. Moreover, the open-circuit voltage can be further lowered to 12 mV with 1.5- $\mu \text{W}$ output power after startup.

A Multimode Space Vector Overmodulation Strategy for Ultrasparse Matrix Converter With Improved Fundamental Voltage Transfer Ratio

In order to increase fundamental voltage transfer ratio for ultrasparse matrix converter, a novel multimode space vector overmodulation strategy is proposed. First, the relationship among voltage transfer ratio (VTR), the output voltage harmonic distortion rate under three inverter modulation methods and the input current harmonic distortion rate under two rectifier modulation methods is analyzed. After that, according to minimum principle of output voltage and input current harmonics, the three overmodulation modes are divided: the output voltage minimum-phase-error, input current minimum-magnitude-error (MME), and output voltage MME overmodulation strategies are realized in overmodulation mode I, II, and III, respectively. The proposed multimode overmodulation strategy not only extends the maximum VTR to 1.05, but also reduces the output low-frequency harmonic voltage components of the overmodulation mode I and mode II. In addition, the harmonic components of output voltage and input current in overmodulation mode are analyzed by double Fourier integral transform method. Finally, the effectiveness of the proposed multimode overmodulation strategy and the correctness of harmonic analysis method are verified by experiments.

Feature Extraction and Comprehension of Partial Discharge Characteristics in Transformer Oil from Rated AC Frequency to Very Low Frequency

The reactive current can be reduced effectively by decreasing the frequency of the voltage in partial discharge (PD) test, especially for equipment with large capacitance. Thus, the cost and volume of the test power supply can be economized. To figure out the difference of PD characteristics in transformer oil between rated alternating-current (AC) frequency (50 Hz) and low frequency, tests are conducted from rated AC frequency to very low frequency (0.1 Hz) based on impulse current method. The results show that with the decrease of frequency, the inception voltage increases. The maximum and mean magnitude of discharge and pulse repetition rate first increase slightly, then decrease obviously. The main features of the variation of phase resolved PD (PRPD) patterns, discharge statistical patterns (phase distribution of maximum and mean discharge magnitude, pulse repetition rate qmax–φ, qmean–φ, n–φ; and number distribution of discharge magnitude n–q), and their characteristic parameters (skewness Sk+, Sk−; kurtosis Ku+, Ku−; asymmetry Asy; and correlation coefficient Cc) are depicted in detail, which should be paid attention to when using low frequency voltage. The inner mechanism for these variations is discussed from the aspects of the influence on electric field distribution and discharge process of frequency. Additionally, the variation trend of PD characteristics with the decrease of frequency can provide more information about insulation defect, which can be the supplement for discharge mode recognition.

An Approach to Suppress Low Frequency Oscillation in the Traction Network of High-Speed Railway Using Passivity-Based Control

The traction blockade in depots of multiple electric multiple units (EMUs) is generally considered to be caused by the voltage low frequency oscillation (LFO) of the high-speed railway traction network. As a possible solution, a strategy using single-phase EMUs rectifiers with passivity-based control (PBC) is proposed in this paper. First, the mathematical model of the four-quadrant pulse width modulation rectifier is constructed based on the port controlled Hamiltonian with dissipation. Next, with the insertion of damping, the new energy function can be minimized at the equilibrium point of the system, which enables the derivation of the rectifier control law based on the interconnection and damping assignments PBC. Comparison of simulation results with those of the traditional proportional integral (PI) scheme, autodisturbance rejection control and multivariable control verifies that the proposed PBC controller has better dynamic and static performance. Among all strategies considered, the resulting line current has the least total harmonic distortion, and the dc-link voltage of single-phase EMUs rectifier has the least oscillation and the shortest adjustment time, when using the PBC. Meanwhile, the simulations of multi-EMUs accessed a traction network show that the proposed method significantly suppresses the voltage LFO of the traction network. Finally, the LFO signal modal analysis is performed using the fast Fourier transform and the estimating signal parameters via the rotational invariance techniques. It indicates that PBC can suppress the symmetrical frequency components and effectively reduce the third, fifth, and other harmonic components compared with the PI control in EMUs.

Research on ON-LINE Insulation Monitoring Instrument of IT Power System in the Down Hole Mine

Base on The characteristics of IT power distribution system in metal mine downhole, on the basis of the analysis and comparison of existing insulation monitoring methods, with the low-frequency power injection method, the online insulation monitoring instrument of the IT power distribution system is designed in the metal mine down hole. By injecting the low-frequency power in the IT power distribution system, urge Low frequency signal source and insulation resistance and ground make up of circuit, Real-time detect voltage and current in the circuit. Sampling signals filtered By means of hardware and software filter, extracting low-frequency voltage and current in the circuit, implement ON-LINE insulation monitoring of IT power distribution system. Proved by experiment, the instrument is highly accurate and can complete the insulation performance monitoring of the whole IT power system.

Effects of secondary electron emission on plasma density and electron excitation dynamics in dual-frequency asymmetric capacitively coupled argon plasmas

Effects of secondary electron emission (SEE) on the plasma density and electron excitation dynamics in dual-frequency (2 MHz and 14 MHz) capacitively coupled Ar plasmas are investigated. The plasma density np is measured with a hairpin probe, and the spatio-temporal distribution of electron excitation rate (ground state into Ar 2p1 state) is determined by phase resolved optical emission spectroscopy. It is generally found that as the low-frequency (LF) voltage ϕL increases, np first decreases at low ϕL, due to compressed the plasma bulk length by the LF source, and then increases slightly with ϕL, suggesting that the plasma is dominated by the α mode. When ϕL exceeds some critical value, np increases dramatically with ϕL, due to significantly enhanced ionization by secondary electrons, indicating a α–γ mode transition. An excitation pattern caused by SEE at the edge of the completely expanded LF sheath is observed at relatively high ϕL. Under various conditions, including the high-frequency voltage ϕH, the pressure p, the electrode gap L, and the electrode material, different dependences of np on ϕL are also discussed. It is found that the discharge turns into the γ mode at a lower ϕL when ϕH is higher. As p increases, the density peak moves axially towards the powered electrode, due to reduced sheath thickness, while its distance to the powered electrode is almost independent of other external conditions (ϕH, L, electrode material, etc). A higher p or higher L is favorable for the enhancement of np in γ mode, because secondary electrons can contribute more to the ionization. Due to the higher SEE coefficient of the aluminum electrode, a more significant increase in np in the γ mode can be seen than that with a stainless steel or copper electrode. Meanwhile, the spatio-temporal distributions of the electron excitation rate under the same conditions are analyzed to further understand the SEE effects.

Void discharge behaviours as a function of cavity size and voltage waveform under very low‐frequency excitation

Measurement of partial discharge (PD) is a vital method to assess the health of the electrical insulation in high-voltage power equipment. As diagnostic testing at very low frequency (VLF) is increasingly being used, it is important to investigate PD behaviours under such a low-frequency voltage excitation. This study presents the PD characteristics at VLF excitation under different applied voltage waveforms, including sinusoidal and trapezoid-based waves. Also, the effects of cavity size on PD behaviours at VLF are investigated. Experiments were performed to measure PDs in a cylindrical void bounded by solid insulation. The results show that discharge activities at VLF, in general, exhibit lower magnitude and repetition rate when compared with power frequency. Also revealed is the strong dependency of discharge parameters on the rate of voltage rise. Physical mechanisms to explain discharge behaviours are given.

Experimental investigation of standing wave effect in dual-frequency capacitively coupled argon discharges: role of a low-frequency source

It is well known that the plasma non-uniformity caused by the standing wave effect has brought about great challenges for plasma material processing. To improve the plasma uniformity, a low-frequency (LF) power source is introduced into a 100 MHz very-high-frequency (VHF) capacitively coupled argon plasma reactor. The effect of the LF parameters (LF voltage amplitude ϕL and LF source fL) on the radial profile of plasma density has been investigated by utilizing a hairpin probe. The result at a low pressure (1 Pa) is compared to the one obtained by a 2D fluid-analytical capacitively coupled plasma model, showing good agreement in the plasma density radial profile. The experimental results show that the plasma density profile exhibits different dependences on ϕL and fL at different gas pressures/electrode driven types (i.e., the two rf sources are applied on one electrode (case I) and separate electrodes (case II)). At low pressures (e.g., 8 Pa), the pronounced standing wave effect revealed in a VHF discharge can be suppressed at a relatively high ϕL or a low fL in case I, because the HF sheath heating is largely weakened due to strong modulation by the LF source. By contrast, ϕL and fL play insignificant roles in suppressing the standing wave effect in case II. At high pressures (e.g., 20 Pa), the opposite is true. The plasma density radial profile is more sensitive to ϕL and fL in case II than in case I. In case II, the standing wave effect is surprisingly enhanced with increasing ϕL at higher pressures; however, the center-high density profile caused by the standing wave effect can be compensated by increasing fL due to the enhanced electrostatic edge effect dominated by the LF source. In contrast, the density radial profile shows a much weaker dependence on ϕL and fL in case I at higher pressures. To understand the different roles of ϕL and fL, the electron excitation dynamics in each case are analyzed based on the measured spatio-temporal distributions of the electron-impact excitation rate by phase resolved optical emission spectroscopy.

Characterization and comprehension of corona partial discharge in air under power frequency to very low frequency voltage

For the partial discharge test of electrical equipment with large capacitance, the use of low-frequency voltage instead of power frequency voltage can effectively reduce the capacity requirements of test power supply. However, the validity of PD test under low frequency voltage needs to be evaluated. In order to investigate the influence of voltage frequency on corona discharge in the air, the discharge test of the tip-plate electrode under the frequency from 50 to 0.1 Hz is carried out based on the impulse current method. The results show that some of the main features of corona under low frequency do not change. The magnitude of discharge in a positive half cycle is obviously larger than that in a negative cycle. The magnitude of discharge and interval in positive cycle are random, while that in negative cycle are regular. With the decrease of frequency, the inception voltage increases. The variation trend of maximum and average magnitude and repetition rate of the discharge in positive and negative half cycle with the variation of voltage frequency and magnitude is demonstrated, with discussion and interpretation from the aspects of space charge transportation, effective discharge time and transition of discharge modes. There is an obvious difference in the phase resolved pattern of partial discharge and characteristic parameters of discharge patterns between power and low frequency. The experimental results can be the reference for mode identification of partial discharge under low frequency tests. The trend of the measured parameters with the variation of frequency provides more information about the insulation defect than traditional measurements under a single frequency (usually 50 Hz). Also it helps to understand the mechanism of corona discharge with an explanation of the characteristics under different frequencies.

A novel MR-compatible sensor to assess active medical device safety: stimulation monitoring, rectified radio frequency pulses, and gradient-induced voltage measurements

To evaluate the function of an active implantable medical device (AIMD) during magnetic resonance imaging (MRI) scans. The induced voltages caused by the switching of magnetic field gradients and rectified radiofrequency (RF) pulse were measured, along with the AIMD stimulations. An MRI-compatible voltage probe with a bandwidth of 0-40kHz was designed. Measurements were carried out both on the bench with an overvoltage protection circuit commonly used for AIMD and with a pacemaker during MRI scans on a 1.5T (64MHz) MR scanner. The sensor exhibits a measurement range of ± 15V with an amplitude resolution of 7mV and a temporal resolution of 10µs. Rectification was measured on the bench with the overvoltage protection circuit. Linear proportionality was confirmed between the induced voltage and the magnetic field gradient slew rate. The pacemaker pacing was recorded successfully during MRI scans. The characteristics of this low-frequency voltage probe allow its use with extreme RF transmission power and magnetic field gradient positioning for MR safety test of AIMD during MRI scans.

Development of a dielectrophoresis-assisted surface plasmon resonance fluorescence biosensor for detection of bacteria

To detect biological substances such as bacteria speedily and accurately, a dielectrophoresis-assisted surface plasmon resonance (SPR) fluorescence biosensor is being developed. Using Escherichia coli as a target organism, an appropriate voltage frequency to collect E. coli cells on indium tin oxide quadrupole electrodes by dielectrophoresis is analyzed. Then, E. coli is stained with 4′,6-diamidino-2-phenylindole (DAPI). To clearly detect fluorescence signals from DAPI-stained E. coli cells, the sensor is optimized so that we can excite SPR on Al electrodes by illuminating 405 nm photons. As a result, the number of fluorescence signals is increased on the electrodes by the application of a low-frequency voltage. This indicates that E. coli cells with a lower permittivity than the surrounding water are collected by negative dielectrophoresis onto the electrodes where the electric field strength is lowest.

Flash Sintering of Oxide Ceramics under Microwave Heating

We report on the results of the analysis of the effect of flash sintering, which is observed upon heating compacted powder materials by high-intensity microwave radiation. Ceramic samples of Y2O3, MgAl2O4, and Yb: (LaO)2O3 were sintered to a density exceeding 98–99% of the theoretical value during 0.5–5 min without isothermal hold. The specific microwave power absorbed volumetrically in the samples was 20–400 W/cm3. Based on the analysis of the experimental data (microwave radiation power and heating and cooling rates) and of the microstructure of the obtained materials, we propose a mechanism of flash sintering based on the evolution of the thermal instability and softening (melting) of the grain boundaries. The proposed mechanism also explains the flash sintering effect observed when a dc or a low-frequency ac voltage is applied to the samples. The microwave heating makes it possible to implement flash sintering without using electrodes for supplying energy to the articles being sintered.

Flexible Third Harmonic Voltage Control of Low Capacitance Cascaded H-Bridge STATCOM

The recently presented low-capacitance cascaded H-bridge (LC-CHB) STATCOM presents a compact and cost-effective STATCOM solution, which varies the averaged dc voltage according to the compensated reactive power during operation to intentionally enlarge the low-frequency dc voltage ripple and meanwhile keep the dc voltage within the allowed range. This letter further optimizes the operational performance of LC-CHB STATCOM by using a flexible third harmonic control method, which could reduce the voltage stress on semiconductors during operation and the switching losses in consequence. Experimental prototype verified the performance of the proposed control strategy.

Impact of the Graded-Gap Layer on the Admittance of MIS Structures Based on MBE-Grown n-Hg1 – xCd x Te (x = 0.22–0.23) with the Al2O3 Insulator

The impact of the presence of the near-surface graded-gap layers with an increased content of CdTe on the admittance of MIS structures based on MBE-grown n-Hg1–xCdxTe (x = 0.22–0.23) with the Al2O3 insulating coating has been experimentally studied. It has been shown that the structures with a gradedgap layer are characterized by a deeper and wider capacitance dip in the low-frequency capacitance–voltage (CV) characteristic and by higher values of the differential resistance of the space-charge region than the structures without such a layer. It has been found that the main features of the hysteresis of capacitance dependences typical of the graded-gap structures with SiO2/Si3N4 are also characteristic of the MIS structures with the Al2O3 insulator. The factors that cause an increase in the CV characteristic hysteresis upon formation of the graded-gap layer in structures with SiO2/Si3N4 or Al2O3 are still debatable, although it may be assumed that oxygen plays a certain role in formation of this hysteresis.

A novel distance protection scheme for HVDC lines based on R-L model

HVDC transmission system is becoming increasingly desirable for its obvious technical and environmental advantages. A novel single-end distance protection scheme for HVDC lines is proposed in this paper. It is based on the linear distribution of low frequency voltage signals between the relay point and setting point. An internal fault can be detected if the low-pass filtered measure voltage is opposite in sign with the compensating voltage at the setting point, which can be calculated with the R-L differential-equation algorithm. To find a tradeoff between operating speed and accuracy, the protection is divided into K zones, each of which has different protection scopes and cut-off frequencies. A two-terminal HVDC system and a multi-infeed HVDC system are respectively built in EMTDC. Comprehensive simulation results have indicated that the proposed protection scheme has satisfactory operation performance and will be not influenced by system topologies or parameters. Besides, it is not sensitive to noises or voltage levels. Compared with many other single-end protections for HVDC lines, this novel distance protection has clear setting principles, lower sampling frequency, smaller calculation amount and faster operating speed.

Synthesis of Pt nanoparticles as catalysts of oxygen reduction with microbubble-assisted low-voltage and low-frequency solution plasma processing

In the preparation of metallic nanoparticles by conventional solution plasma (SP) techniques, unstable plasma emission becomes an issue when the voltage and frequency of the waves applied between two electrodes placed in solution are lowered to avoid the boiling of the solution. In this study, we confirm that, in the presence of microbubbles, plasma is generated stably at low voltage (440 V) and low frequency (50–100 Hz) and small-size (≤10 nm) Pt nanoparticles (PtNPs) are synthesized in succession using a flow cell. The smallest PtNPs, ∼3.3 nm in diameter, are obtained using half-wave rectification, a tungsten wire anode, and a platinum wire cathode. The PtNPs are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and thermogravimeter-differential thermal analysis. The oxygen reduction reaction (ORR) is investigated in 0.1 M HClO4 solution on carbon-supported PtNPs using a rotating ring-disk electrode. The catalytic activities per initial electrochemical active surface area of the carbon-supported PtNPs synthesized employing the low-voltage, low-frequency (LVLF)–SP technique is higher than that of the commercially available 20 wt% Pt on Vulcan XC-72R. These results indicate that the LVLF-SP technique is a promising approach to producing carbon-supported PtNPs that catalyze ORR with low energy consumption.

Atmospheric-pressure diffuse dielectric barrier discharges in Ar/O2 gas mixture using 200 kHz/13.56 MHz dual frequency excitation

Atmospheric-pressure diffuse dielectric barrier discharges (DBDs) were obtained in Ar/O2 gas mixture using dual-frequency (DF) excitation at 200 kHz low frequency (LF) and 13.56 MHz radio frequency (RF). The excitation dynamics and the plasma generation mechanism were studied by means of electrical characterization and phase resolved optical emission spectroscopy (PROES). The DF excitation results in a time-varying electric field which is determined by the total LF and RF gas voltage and the spatial ion distribution which only responds to the LF component. By tuning the amplitude ratio of the superimposed LF and RF signals, the effect of each frequency component on the DF discharge mechanism was analysed. The LF excitation results in a transient plasma with the formation of an electrode sheath and therefore a pronounced excitation near the substrate. The RF oscillation allows the electron trapping in the gas gap and helps to improve the plasma uniformity by contributing to the pre-ionization and by controlling the discharge development. The possibility of temporally modifying the electric field and thus the plasma generation mechanism in the DF discharge exhibits potential applications in plasma-assisted surface processing and plasma-assisted gas phase chemical conversion.

Design of capacitive voltage divider for measuring ultrafast voltages

The aim of this paper is to consider and analyze design of capacitive voltage divider for measuring ultrafast voltage occurrence. Measuring pulse voltages by means of a capacitive divider in nanosecond range is affected by problems related to the construction of the divider and materials used. However, an appropriate constructive solution could minimize the budget of measuring uncertainty of the measurement pertaining to parasitic inductivity and capacitance. Consequently, the right selection of dielectric materials could offset the effects of high-voltage and low-voltage frequency characteristics of the capacitor. Four types of capacitive dividers have been constructed for the purpose of this paper. The high-voltage capacitor of each divider is a gas capacitor (intended to avoid both electrostatic and electrodynamic influence on measurement uncertainty). Ultrafast pulse response is measured by dividers constructed in this way, and compared with the corresponding response obtained from numerical simulations.

DC ANALYSIS OF p-n-p-n TUNNELING FIELD-EFFECT TRANSISTOR BASED ON In0.35Ga0.65As

Using calibrated simulations, we report the In0.35Ga0.65As based tunnel field-effect transistor (TFET) with thin ?-doped n+ pocket at the source-channel interface to improve the parameters such as on current (Ion), off-current (Ioff) and subthreshold swing (SS). The simulations results of proposed device is compared with analytical model that is shown with high precision of DC parameters by examining the effects of III-V semiconductor materials. Furthermore, the influence of pocket doping, pocket width, doping level, effective oxide thickness (EOT), temperature and mole fraction of III-V semiconductor material on device performance have been investigated. The results show that proposed device has a higher ON current (1×10-5 A/µm) and a steeper subthreshold swing (35 mV/decade) as compared with the conventional TFET. It shows a lot of promise for future scale CMOS technology for low voltage and high frequency application

Low‐power 2.4 GHz ZigBee transceiver with inductor‐less radio‐frequency front‐end for Internet of things applications

A fully integrated low-power 2.4 GHz ZigBee transceiver with inductor-less radio-frequency front-end in 180 nm complementary metal–oxide–semiconductor is presented. The proposed double push–pull low noise amplifier collaborates with a current-mode down-converter to provide wideband low-noise amplification, as well as the out-of-band blocker resilience. To save power, a sliding frequency synthesiser (FS) with a low-frequency running voltage controlled oscillator is employed to provide the local oscillation for both the receiver and transmitter. Measurement results show that the RX reaches −102 dBm sensitivity and dissipates 11 mA power. The FS achieves −91 dBc/Hz in-band phase noise with only 6.5 mA DC power. The TX features +7.6 dBm maximum output channel power, 4% error vector magnitude at the cost of 19.5 mA power.