Rectangular Current Waveforms Research Articles

Design and implementation of a versatile H-bridge power supply for experiments on the STOR-M Tokamak

An H-bridge power supply has been developed for different experiments on the STOR-M tokamak. Four insulated-gate bipolar transistors (IGBTs) are used to guide the current to the load from a capacitor bank discharge. The timing signal to the gates of the IGBTs is controlled by a field programmable gate array (FPGA). The power supply can be programmed to drive either a sinusoidal current waveform to an inductive load or a bipolar rectangular current waveform to a resistive load. The maximum frequency and current tested for the sinusoidal current waveform are 25 kHz and 2200 A, respectively. For bipolar current waveforms, the maximum current tested is 1500 A at 3 kHz. The sinusoidal current to a set of helical coils was used for the Resonant Magnetic Perturbation (RMP) experiments and the bipolar rectangular current waveform was used for both the electrode biasing experiments and the RMP experiments on the STOR-M tokamak.

Analysis of Linear Synchronous Motor Fed with Current Source Inverter at High Speeds and Low Speeds.(Dept.E)

A theoritical analysis of linear synchronous motor LSM fed by a current source inverter is presented. The analysis is carried out at the two ends of speed range using entirely two different models. The low speed model assumes a perfect rectangular current waveform which is established in the armature windings. So, the thrust is calculated from the product of specific electric loading and specific magnetic loading. The high speed model assumes that the commutating capacitors are permanently connected in parallel with the LSM and the resulting parallel commutation is fed by a quasi-square current waveform. The equivalent circuit which des-cribes the LSM during commutation is presented and the output power is calculated.

DESMEX: A novel system development for semi-airborne electromagnetic exploration

There is a clear demand to increase detection depths in the context of raw material exploration programs. Semi-airborne electromagnetic (semi-AEM) methods can address these demands by combining the advantages of powerful transmitters deployed on the ground with efficient helicopter-borne mapping of the magnetic field response in the air. The penetration depth can exceed those of classic airborne EM systems because low frequencies and large transmitter-receiver offsets can be realized in practice. A novel system has been developed that combines high-moment horizontal electric bipole transmitters on the ground with low-noise three-axis induction coil magnetometers, a three-axis fluxgate magnetometer, and a laser gyro inertial measurement unit integrated within a helicopter-towed airborne platform. The attitude data are used to correct the time series for motional noise and subsequently to rotate into an earth-fixed reference frame. In a second processing step, and as opposed to existing semi-AEM systems, we transform the data into the frequency domain and estimate the complex-valued transfer functions between the received magnetic field components and the synchronously recorded injection current by regression analysis. This approach is similar to the procedure used in controlled-source EM. For typical source bipole moments of 20–40 kAm and for rectangular current waveforms with a fundamental frequency of approximately 10 Hz, we can estimate reliable three-component (3C) transfer functions in the frequency range from 10 to 5000 Hz over a measurement area of [Formula: see text] for a single source installation. The system has the potential to be used for focused exploration of deep targets.

Reverse battery model for anodic arc discharges near atmospheric pressure

In this study, the macroscopic electrical parameters of anodic arc discharges performed with solid carbon and molybdenum anodes are described in terms of an equivalent circuit. The proposed 1D model shows that the plasma volume behaves as a dissipative medium combined with self-generated voltage from the plasma sheaths. This model is tested by fitting virtual circuits of resistors and batteries to the measured voltage–current (V–I) characteristics representative of atmospheric arc processes (300 and 500 Torr He), resulting in the identification of two phenomena relevant for arc technology. First, steady DC arc experiments show that a minimal arc voltage (V0 ≈ 20–30 V) or threshold voltage is necessary to keep the plasma arc on. Second, we prove that pulsed arc discharges excited with rectangular current waveforms (1–5 Hz) are never extinguished but remain ignited during the inactive time of the pulse as long as the aforementioned threshold voltage is maintained. In summary, an atmospheric anodic arc discharge with solid electrodes consumes electrical power as a voltage source opposed to the external voltage supply together with a resistor that accounts for the plasma impedance. This approach permits us to estimate basic plasma parameters from simple electrical diagnostics, as well as to predict how power consumption is distributed within an anodic arc and to understand dynamics of arc plasmas excited by periodic signals.

Multiple String LED Driver With Flexible and High-Performance PWM Dimming Control

The main objectives in driving multiple LED strings include achieving uniform current control and high performance PWM dimming for all strings. This work proposes a new multiple string LED driver to achieve not only current balance, but also flexible and wide range PWM dimming ratio for each string. A compact single-inductor multiple-output topology is adopted in the driver, accompanied by synchronous integrators and variable dimming frequency, to achieve both high efficiency and high performance dimming. By using the proposed variable dimming frequency scheme, high dimming frequency is applied to a string with high dimming ratio, which helps to maintain the deviation of LED string current in an acceptable range, while low dimming frequency is applied to a string with low dimming ratio, which helps to achieve rectangular LED current waveform. Meanwhile, the new time multiplexing control scheme automatically optimizes the LED string's bus voltages, thus minimizes each string's power loss. A three string LED driver prototype is constructed to validate the effectiveness of the peoposed control scheme, where the three strings can have different dimming ratios between 4% and 100%.

ANALYTICAL CALCULATIONS OF ELECTROMAGNETIC QUANTITIES FOR SLOTTED BRUSHLESS MACHINES WITH SURFACE-INSET MAGNETS

In this paper, two-dimensional (2-D) analytical magnetic field calculations are used to compute crucial quantities of Brushless permanent-magnet (PM) machines with surface-inset PMs. The analytical magnetic field distribution is based on the subdomain technique in which the slotting and tooth-tip effects have been considered. It includes both different magnetization patterns (e.g., radial, parallel and Halbach) and different spatial distribution of winding (e.g., concentrated and distributed with one or more layers). The saturation effect of the magnetic circuit is neglected. In this investigation, the phase and line induced back electromotive force (EMF) waveforms, electromagnetic/cogging/reluctance torques, self-/mutual-inductances and unbalanced magnetic forces (UMFs) have been analytically calculated. The analytical expressions can be used for Brushless machines having surface-inset PMs with any radius-independent magnetization pattern. In this study, two slotted Brushless PM machines with surface-inset PMs have been selected to evaluate the efficacy of the analytical expressions by comparing the results with those obtained by the finite-element method (FEM). One of the case studies is a 9-slots/8-poles Brushless DC (BLDC) machine with radially magnetized PMs, non-overlapping all teeth wound winding and six-step rectangular armature current waveforms. The other is a 15-slots/4-poles Brushless AC (BLAC) machine with Halbach magnetization PMs, double-layer overlapping winding and sinusoidal armature current waveforms.

Prediction of iron losses in doubly salient permanent magnet machine with rectangular current waveform

Iron losses in doubly salient permanent magnet (DSPM) machine are difficult to predict, as the flux waveforms are complex and dc bias existed. This paper measures iron losses at no load for different rotor speeds and these measured loss data are used to calibrate the iron loss model of the DSPM machine. Then the iron losses at rated load are predicted under three phase rectangular currents exerting on the armature windings. The result shows that small increment of iron losses is in the rotor at rated load which do benefit to the rotor thermal dissipation design.

Examination of the S–D curve for magnetic stimulation used in the treatment of urinary incontinence using an experimental eddy current waveform

Abstract Strength–Duration Curves (S–D Curves) for the intra-urethral sphincter muscle of the rat were measured using the rectangular waveform and the pseudo-eddy current waveform, which approximate the stimulation current waveform on magnetic stimulation. Finally, the pulse duration for minimum energy using magnetic stimulation is obtained from the measurement results of the S–D curve. The eddy current waveform differs from the rectangular current waveform commonly used in electrical applications. No basic study has examined the effects of magnetic stimulation on threshold values and other aspects of the eddy current waveforms. Magnetic stimulation has been reported to have good efficacy in the treatment of urinary incontinence. It is desirable that the eddy current density produced by a change in the strength of a magnetic field be greater than the excitability threshold of the muscles or nerves to be stimulated. However, effective magnetic stimulation requires the input of a large current into the stimulation coil. The requisite equipment is therefore large and costly, and so it is necessary to develop magnetic stimulators that can more efficiently stimulate tissues and that are more convenient to use than those that are currently available.

INVESTIGATION ON DEPTH OF HEAT AFFECTED ZONE OF DISCHARGE SPOT BY HIGH REPETITIVE RATE YAG LASER-INDUCED DISCHARGE TEXTURING

It is known that the press formability and the elongation of laser textured sheet are improved, and the service life of textured roll is longer than that of the un-textured roll due to hardening of the treated surface. One of the goals to develop high repetitive rate YAG laser-induced discharge texturing (LIDT) is to get deeper hardening zone. By observing and measuring cross-section of LIDT spots in different discharge conditions, it is found that the single-crater, which is formed by the discharge conditions of anode, which is covered by an oil film and with rectangular current waveform, has the most depth of heat affected zone (HAZ) comparing with other crater shapes when discharge energy is the same. The depth of HAZ is mainly depends on pulse duration when the discharge spot is single-crater. The results are analyzed.

Comparison of Torque-speed Characteristics of Interior-magnet Machines in Brushless AC and DC Modes for EV/HEV Applications

The torque-speed characteristics of an interior magnet brushless motor are compared with particular reference to the flux-weakening performance for EV/HEV applications, when it is operated in brushless AC (BLAC) mode, with 3-phase, sinusoidal current waveforms, and in brushless DC (BLDC) mode with both 2-phase, 120° conduction and 3-phase, 180° conduction rectangular current waveforms. It is shown that while 2-phase, 120° BLDC operation results in the highest torque capability for the same peak current and BLAC operation results in the highest specific torque per rms current when operating below the base-speed, 3-phase, 180° BLDC operation generally results in the best performance in the flux-weakening region.

Formation of the Layered Etch Films on AA1050 Aluminum Plates Etched in Nitric Acid Using Alternating Currents

The structure of the etch film on aluminum plates etched in nitric acid was systematically studied by varying the ratio of positive to negative charges provided by a rectangular current waveform. When etched using a symmetrical square current, the plates were dotted with the etch pits inside which a layered etch film formed via the stacking of dark-contrast vs. light-contrast layers. The former was presumably aluminum hydroxide, while the latter was the channels that were filled with the electrolyte during etching. The thickness of the aluminum hydroxide layer increased with increasing the charge passed during the cathodic half-cycle. Hydrogen discharge during the cathodic half-cycle led to the formation of the hydroxide layer. Hydrogen evolution at the interface formed microvoids and might induce defects in the hydroxide layer. Based on dissolution–passivation of the same pit, a possible mechanism was proposed to explain the formation of the layered etch film on aluminum etched in nitric acid using the alternating current with emphasis on the effects of hydrogen discharge.

A Five-Phase Brushless Dc-Machine Direct Drive System

The paper describes the design, analysis, simulation, modeling and control implementation of a high-torque, low-speed, multiphase, permanent magnet, brushless dc machine. The main focus is on issues regarding the high-level modeling, comprised of a transient model, in conjunction with corresponding experimental evaluation. The general assumption of ideal rectangular current waveforms for brushless-dc machines is not encountered in practice; the existing distortions can be modeled by incorporating mutual inductance and armature reaction in order to avoid erroneous control strategy development. Analyses are made to put together modeling efforts with the expected behavior so as to build a model of the expected behavior so realistic simulation results can be verified. Coherent and consistent results were observed by comparing simulation and experimentation. A digital signalprocessing(DSP) system control was developed to implement the strategies that corroborate the work.

Five-phase induction motor drives with DSP-based control system

This paper introduces two kinds of control schemes: vector control and direct torque control (DTC). These control schemes can be extensively applied to the operation of a five-phase induction motor using a fully digital implementation. Vector control of the five-phase induction motor not only achieves high drive performance, but also generates the desired nearly rectangular current waveforms and flux profile in the air-gap resulting in an improvement in air gap flux density and an increase of 10% in output torque. The DTC method has additional advantages when applied to multiphase, in this case a five-phase, induction motor. The five-phase inverter provides 32 space voltage vectors in comparison to 8 space voltage vectors provided by the three-phase inverter. Therefore, a more elaborate flux and torque control algorithm for the five-phase induction motor can be employed. Direct torque control of the five-phase induction motor reduces the amplitude of the ripples of both the stator flux and the torque, resulting in a more precise flux and torque control. A 32-b floating-point TMS320C32 digital signal processor (DSP) enables these two sophisticated control techniques to be conveniently implemented with high control precision. Experimental results show that an ideal control capability is obtained for both control methods when applied to the five-phase induction motor and further validates theoretical analysis.

Class-F power amplifiers with reduced conduction angles

This paper determines the characteristics of class-F power amplifiers (PAs) with class-C conduction angles (current flow for less than half of the RF cycle). Analyses are conducted for both clipped-sinusoidal (classical class-C) and rectangular current waveforms. It is not possible to define the voltage and current waveforms arbitrarily if the production or sinking of power at the harmonic frequencies is to be avoided. As a result, only a few cases are of practical interest. In these cases, the conduction angle is set to null a specific harmonic in the current. The nulled harmonic is then used to flatten the bottom of the voltage waveform, resulting in increased efficiency and increased power output.

Observations of a vacuum spark under different driver conditions of the applied voltage

Comparative observations of the Vacuum Spark discharge are presented under differing electrical drive conditions but identical geometrical conditions. A 1.5 Ω 120 nsec, coaxial line is used to provide maximum currents to 90 kA. The line may be operated in the usual switched mode to give a rectangular voltage and current wave form, or in the Hybrid mode, in which case the voltage builds slowly until breakdown occurs. In both modes of operation the value of dI/dt is about 1×1012 A/sec. A Nd:YAG is focused onto either electrode to initiate the discharge. With the laser focused onto the anode a low-density plasma accompanied by intense electron beams is formed. With the laser focused on the cathode a much higher plasma density is observed in the gap, with the formation of a dense tight pinch close to the cathode, in which hot spots form at peak current. The Hybrid mode is favored for its reproducible behavior.

A low-loss permanent-magnet brushless DC motor utilizing tape wound amorphous iron

An axial field permanent-magnet brushless DC motor that utilizes tape wound amorphous iron and an air gap winding is proposed. Simplified waveforms and performance equations for this type of machine are presented. The machine equations and waveforms are verified with a proof-of-concept machine. No-load iron losses are compared with manufacturer's data, and full-load iron losses are also presented. Output torque for rectangular and trapezoidal current waveforms are measured and compared. Machine designs from a computer program that demonstrate the possible benefits of this type of machine could be considerably more efficient than induction machines, and, additionally. cost competitive when a variable speed drive is already a system requirement.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Plateau potentials in alpha-motoneurones induced by intravenous injection of L-dopa and clonidine in the spinal cat.

1. Intracellular recordings were made from lumbar alpha-motoneurones in unanaesthetized decerebrate acute spinal cats. The response of motoneurones to direct current pulse injection or synaptic excitation was investigated following intravenous injection of L-beta-3,4-dihydroxyphenylalanine (L-DOPA, 20-120 mg/kg) alone, nialamide (10-50 mg/kg) and L-DOPA or clonidine (0.5-1 mg/kg). 2. The response properties of motoneurones were tested with rectangular and triangular current waveforms. Before L-DOPA treatment motoneuronal firing during a rectangular current pulse is characterized by an initial high firing frequency which rapidly decreases to a lower steady-state firing which is maintained only for the duration of the pulse. Following administration of L-DOPA an acceleration in firing frequency is apparent following the initial adaptation seen with rectangular current pulses. A transient after-depolarization or an after-discharge often followed the termination of the pulse. The frequency-current relation in response to a triangular current injection changed from a clockwise to a counter-clockwise hysteresis after L-DOPA treatment (i.e. after L-DOPA the firing frequency was higher for any given current during the descending phase than during the ascending phase of the triangular waveform). 3. Firing acceleration during and self-sustained firing after rectangular current pulses and counter-clockwise hysteresis of firing frequency with triangular current pulses are causally related to the presence of plateau potentials, which can be directly visualized after inactivation of the spikes. Plateau potentials in motoneurones could be generated by short-lasting intracellular depolarizing current pulses or brief excitatory synaptic inputs and terminated by short-lasting hyperpolarizing current pulses or brief inhibitory synaptic inputs. Plateau potentials were demonstrated in flexor and extensor motoneurones. 4. All bistable properties described in the preceding paragraphs following L-DOPA administration could also be seen after administration of the alpha-receptor agonist clonidine. 5. Slow rhythmic oscillations of the membrane potential (7.5-10 Hz) were seen superimposed on plateau potentials in a few cells after administration of L-DOPA and clonidine. The oscillations had an amplitude in the range 10-20 mV and represent the expression of an intrinsic property of the motoneurone. 6. It is demonstrated that plateau potentials in the motoneurones contribute to the late long-lasting reflexes observed in L-DOPA-treated spinal cats. 7. It is concluded that L-DOPA (and clonidine) change the response properties of the motoneurones in an analogous way to 5-hydroxy-DL-tryptophan (5-HTP).(ABSTRACT TRUNCATED AT 400 WORDS)

Programmable Current Regulator for High-Voltage Operation

A current regulator for the operation of gas discharges is described, capable of delivering peak currents up to 1 ampere and average currents of up to 0.5 ampere with voltage excursions to 9 kV. Completely floating two-terminal operation accomodates different load configurations. By means of externally supplied timing pulses the output current can be programmed to generate rectangular or trapezoidal current waveforms. For rectangular output pulses, switching speeds of 5 μs into low-impedance loads and slewing rates of 500 V/μs for high-impedance loads can be obtained. The output resistance is in excess of 107 ohms, shunted by 50-250 pF, depending on regulator configuration.

Instrumentation for the Measurement of the Electrical Double Layer Capacitance at Solid Electrodes

Two methods of measurement of double layer capacitance used by the authors are described. One method, involving the application of a rectangular current waveform, is convenient for obtaining qualitative information on the frequency dispersion of the double layer capacitance. The other, involving the application of a small sinusoidally varying potential of constant amplitude, is capable of an accurate and very rapid determination of capacitance over a wide potential range.

Information Cells on Intensity-Modulated CRT Screens

The distribution of current within the beam of a cathode-ray tube has a Gaussian variation. Consequently, if the wave form of a pulse of beam current is known, it is possible to determine the excitation of an intensity-modulated screen surface. In this report the nature of the excitation is discussed for an intensity-modulated sweep for both rectangular and triangular current waveforms. The results are extended to indicate what may be expected of an actual mapping radar set. The theoretical constants which arise in the development are evaluated from data obtained by the shrinking raster method of measuring spot size, which is termed line width in this paper for purposes of clarity. This permits determination of the size of an information cell on the screen as a function of pulse duration, sweep speed and line width. Then the number of information cells available on a tube may be determined. As a consequence, we find that there is no significant difference in the number of information cells available on the standard 5FP7, 7BP7, or 12DP7. Furthermore, the reduction of the over-all receiving-system frequency response by some radar displays may be estimated. In such a case the video bandwidth may be reduced.