High Frequency Current Oscillations Research Articles

A nonlinear time–frequency control based FOC for permanent magnet synchronous motors

PI control based field oriented control (FOC) scheme is the predominant method for the control of permanent magnet synchronous motors (PMSMs) in applications requiring high performance. A novel nonlinear time–frequency control based FOC design for the fast, accurate, and robust control of PMSMs is presented. Featuring a single nonlinear time–frequency controller and a PI controller as the 2 primary components in the control configuration, the new scheme is evaluated against a classic PI control based FOC design for performances in response to rapid speed-switching and abrupt external torque variation. The scheme displays significantly smaller steady-state tracking errors undergoing speed shifting and no high frequency current oscillations or electromagnetic torque ripple in the motor, as does the PI based scheme. The tracking errors corresponding to changes in torque are free of distortion and oscillation that would otherwise indicate instability and inaccuracy. Precision positioning control is also realized through incorporating a P controller into the controller configuration. When the motor reference position is briskly flipped between 360° and 1°, the novel controller design is shown to perform well with a rotor position error that is less than 0.13°.

High-frequency current oscillations in charge-density-wave 1T-TaS2 devices: Revisiting the “narrow band noise” concept

We report on the current oscillations in quasi-2D 1T-TaS2 charge-density-wave two-dimensional devices. The MHz-frequency range of the oscillations and the linear dependence of the frequency of the oscillations on the current closely resemble the narrow band noise, which was often observed in the classical bulk quasi-1D trichalcogenide charge-density-wave materials. In bulk quasi-1D materials, the narrow band noise was interpreted as direct evidence of charge-density-wave sliding. Despite the similarities, we argue that the nature of the MHz oscillations in 1T-TaS2 is different from the narrow band noise. Analysis of the biasing conditions and current indicates that the observed oscillations are related to the current instabilities due to the voltage-induced transition from the nearly commensurate to incommensurate charge-density-wave phase.

The effects of high frequency current ripple on electric vehicle battery performance

The power electronic subsystems within electric vehicle (EV) powertrains are required to manage both the energy flows within the vehicle and the delivery of torque by the electrical machine. Such systems are known to generate undesired electrical noise on the high voltage bus. High frequency current oscillations, or ripple, if unhindered will enter the vehicle’s battery system. Real-world measurements of the current on the high voltage bus of a series hybrid electric vehicle (HEV) show that significant current perturbations ranging from 10Hz to in excess of 10kHz are present. Little is reported within the academic literature about the potential impact on battery system performance and the rate of degradation associated with exposing the battery to coupled direct current (DC) and alternating currents (AC). This paper documents an experimental investigation that studies the long-term impact of current ripple on battery performance degradation. Initial results highlight that both capacity fade and impedance rise progressively increase as the frequency of the superimposed AC current increases. A further conclusion is that the spread of degradation for cells cycled with a coupled AC–DC signal is considerably more than for cells exercised with a traditional DC waveform. The underlying causality for this degradation is not yet understood. However, this has important implications for the battery management system (BMS). Increased variations in cell capacity and impedance will cause differential current flows and heat generation within the battery pack that if not properly managed will further reduce battery life and degrade the operation of the vehicle.

Damped current oscillations in a horizontal ungrounded loop and their correlation with ground water infiltration

An ungrounded horizontal loop used for the exci� tation of induction transitients in the earth is one of the main elements used in the system for pulse induc� tive electrical prospecting. When the current is switched off in the loop, an eddy electric field appears in the space surrounding the loop, which induces eddy currents in the earth. After this, the secondary mag� netic field excited by these currents is measured. It is usually assumed in the theory that the current and correspondingly the primary field are switched off on instantaneously. However, a real loop is inertial, and after it is switched off from a battery or generator, high frequency current oscillations appear in the loop

High- and low-frequency noise in Cs and in liquid metal ion sources

Fundamental Physics space missions set rigid thrust noise limits for liquid metal ion thrusters used as actuators on drag-free platforms aboard the spacecraft. We have measured current-, voltage- and thrust noise of Cs and In LMIS, foreseen as prime candidates in these missions. In the high-frequency range, quasiperiodic oscillations around ∼10 5 Hz can be observed for both types of emitters with frequency depending on emission current. In the low-frequency range (1–10 −3 Hz), which is particularly important for drag-free control, different types of noise events are observed, which in some instances show definite signs of deterministic chaos (period doubling, self-similarity). High-frequency current oscillations are generally ascribed to electro-hydrodynamic oscillations of the TAYLOR cone and the jet at its apex, with concomitant emission of charged nanodroplets. Comparison of theory and experiment shows unsatisfactory agreement in predicted vs. measured current oscillation frequencies and large disagreement in droplet emission frequencies. No theory is presently available for describing low-frequency noise events. In terms of a linearized Mair theory it is, however, shown that these noise events can be efficiently described by spontaneous variations in electrical emitter impedance. In spite of this impedance noise, the mission requirements for thrust noise (<0.1 μN/Hz 1/2) can be met by a thrust-stabilized In emitter.

Pulsating electrospray modes at the liquid-liquid interface

Unforced liquid-liquid electrosprays have been demonstrated for water/heptane and ethylene glycol/heptane couples which exhibit stable high frequency current oscillations in the kilohertz range. Using in-line flow sensor measurements, the controlled ejection of subpicoliter volumes into an immiscible liquid phase was shown possible.

Diagnostics of the plasma series resonance effect in radio-frequency discharges

The intention of the paper is to give an example on how different plasma diagnostics can be combined in a synergistic way in order to investigate new physics. The link between the individual diagnostics has to be provided by theoretical concepts that predict certain relations between the different plasma parameters. The example chosen here is the effect of self-excited plasma series resonances in asymmetric capacitively coupled RF discharges. These resonance oscillations lead to high frequency current oscillations and are caused by a series resonance between the capacitive sheath and the effective inductance of the bulk which results from electron inertia. The non-linearity of the sheath is essential for the self-excitation of these oscillations. Laser spectroscopic electric field measurements, phase and space resolved optical emission spectroscopy, current, voltage, and Langmuir probe measurements are combined. The synergistic effect of these diagnostics in combination with a simple analytical model for the modification of the electron energy distribution function by electron beams yields information on cause and effect of electron heating and a better understanding of these fundamental phenomena.

Optically Driven Domain Instability and High-Frequency Current Oscillations in Photoexcited GaAs under Nonuniform Electron Heating

Fast domain instabilities induced by light-interference pattern in dc-biased semi-insulating GaAs are investigated. Current oscillations in GHz-frequency range are observed due to nonuniform electron heating and domains formation in light-induced grating. Characteristic features of the oscillations under various experimental conditions are presented. Numerical calculations based on the hot-electron hydrodynamic model are used to explain the observed nonlinear features under various external bias and periods of the grating.

High-frequency current oscillations in doped GaAs/AlAs superlattices by travelling dipole domains

We report on current oscillations at different oscillation frequencies (2–46 GHz) in GaAs/AlAs superlattices with different miniband widths (16–55 meV) and on the application in microwave oscillators.

High-frequency current oscillations in GaAs/AlGaAs single quantum wells

High-frequency current oscillations have been observed in highly doped single quantum well structures of GaAs/AlGaAs. Several samples of the same structure, but aligned along different crystallographic directions, have been studied. The field, temperature and time dependences of these oscillations have been investigated. Various mechanisms associated with current oscillations are discussed including NDR, trapping and dual streaming, but as yet no single mechanism fully describes the observations. In some samples, the period doubling was observed, which has been related by others with routes to chaos.

High-frequency current oscillations in solid dielectrics

Experimental evidence is provided that common industrial organic insulators (phenol-impregnated pressboard, bakelite) may exhibit negative differential resistance. Insulators have been subjected to high non-uniform electric fields with maximum values which varied between 0.2 MV cm-1 and 1.2 MV cm-1 and, according to experimental data, the time-averaged I-V characteristics showed a distinct N-type NDR region, followed by an S-type NDR region, for electric fields near the pre-breakdown region. Various impulse voltages have been applied to solid dielectrics and periodic current pulses were received by the anode electrode. The aging region, at about 0.8 MV cm-1, was associated with successive current pulse formation with typical values of the order of 2 A and frequencies of the order of 1 MHz. During the breakdown (which occurred for applied electric fields of the order of 1.2 MV cm-1) only two or three current pulses of 20-40 A were observed. An attempt has been made to interpret and correlate the above results with similar phenomena which occur in semiconductors with a negative differential resistance.

High-frequency current oscillations in submicron bipolar structures

The current oscillations with frequency of the order of plasma frequency in the submicron GaAs bipolar diodes are obtained by Monte Carlo simulation. It is shown that current oscillations are the result of carrier bunching, which occurs due to either the two-stream instability or optical-phonon emission.

Relaxation oscillations induced in semi-insulating CdS with helium neon laser irradiation

Abstract Non-sinusoidal high frequency current oscillations have been observed in photo-sensitive CdS under He-Ne laser irradiation. It is suggested that these are due to the emptying and filling of the traps in the high field region.

Negative differential conductivity and current oscillations in lightly doped N-type silicon

High field current—voltage characteristics of N-type silicon have been calculated by the Monte Carlo method for the <111> and <100> directions at different temperatures. The <100> curve exhibits a region of negative differential conductivity for temperatures below about 50°K. Coherent high frequency current oscillations have been found experimentally for <100> samples at and below about 50°K.

On some properties of CdSnP 2 in strong electric field

High frequency current oscillations in a new ternary semiconducting compound have been predicted theoretically and observed experimentally.

High frequency current oscillations in photoconductive cadmium sulphide illuminated by a multiple-band pattern

Current oscillations at frequencies up to 11 MHz have been observed in photoconductivite CdS under high field conditions with the specimen illuminated in a series of light and dark bands. The frequency is very closely correlated with the periodic width of the band pattern.

High-frequency current oscillations in vapour-deposited CdS thin films

High-frequency small-amplitude current modulation has been observed in a vapour-deposited CdS thin film subjected to high electric stress in the ruby substrate plane. The possibility that this modulation may be attributed to travelling-charge domains formed by acoustoelectric interaction in the acoustic waveguide system is discussed.