Non-sinusoidal Pulse Research Articles

PWM Common Mode Reference Generation for Maximizing the Linear Modulation Region of CHB Converters in Islanded Microgrids

Microgrid-interactive converters are increasingly expected to provide auxiliary services, particularly during islanded microgrid operation. Unbalanced, non-sinusoidal pulse width modulation (PWM) references may be required when converters provide auxiliary services, such as negative-sequence compensation. Since PWM references cannot exceed dc-bus voltage defined limits without causing overmodulation, the maximum positive-sequence voltage producible by microgrid-interactive converters may be diminished unless reference waveforms are adjusted. In this paper, a technique for maximizing the linear modulation region by injecting a common mode component into PWM references is proposed for microgrid-interactive cascaded H-bridge (CHB) converters. The technique presented can be implemented in real-time without lookup tables, is controller independent, is compatible with any carrier-based PWM method, enabling its use for symmetric and asymmetric CHB, and enables continued operation after internal fault events when utilized with fault tolerant PWM schemes. Experimental data verify the common mode injection technique.

Theoretical harmonic analysis of cascaded H‐bridge inverter under hybrid pulse width multilevel modulation

This study investigates the analytical approach for determining the spectral components of a hybrid pulse width modulation (HPWM) strategy for cascaded H-bridge (CHB) multilevel inverters. By decomposing the HPWM voltage into a staircase waveform and a non-sinusoidal pulse width modulation waveform and applying the one-dimensional Fourier series as well as double Fourier series methods, the closed-form solution for arbitrary level HPWM voltage is derived. Based on the derived solution, analysis of HPWM output with a changed modulation index is also performed, with good stability and control dynamic demonstrated. The spectral analytical expression is verified extensively by comparison of theoretical calculation results with those of the simulation and laboratory experiment, which coincide with each other very well. Furthermore, a brief switch function rotation balancing method for HPWM-based CHB inverter is utilised, and is also validated by experimental results.

Barkhausen criterion for pulse oscillators

This work presents the study of the conditions for forming periodic oscillations of non-sinusoidal pulse waveforms in oscillatory systems consisting of a linear frequency-dependent circuit and an active nonlinear element. Based on Barkhausen stability criterion, an application under the frequencies of all harmonics of output oscillations is discussed.

SDSS J184037.78+642312.3: THE FIRST PULSATING EXTREMELY LOW MASS WHITE DWARF

We report the discovery of the first pulsating extremely low mass (ELM) white dwarf (WD), SDSS J184037.78+642312.3 (hereafter J1840). This DA (hydrogen-atmosphere) WD is by far the coolest and the lowest-mass pulsating WD, with Teff = 9100 \pm 170 K and log g = 6.22 \pm 0.06, which corresponds to a mass ~ 0.17 Msun. This low-mass pulsating WD greatly extends the DAV (or ZZ Ceti) instability strip, effectively bridging the log g gap between WDs and main sequence stars. We detect high-amplitude variability in J1840 on timescales exceeding 4000 s, with a non-sinusoidal pulse shape. Our observations also suggest that the variability is multi-periodic. The star is in a 4.6 hr binary with another compact object, most likely another WD. Future, more extensive time-series photometry of this ELM WD offers the first opportunity to probe the interior of a low-mass, presumably He-core WD using the tools of asteroseismology.

Photometry of the intermediate polar 1RXS J062518.2+733433: Characteristics of its periodic brightness variations

We present the results of our photometry of the recently discovered intermediate polar 1RXS J062518.2+733433. The observations were made using the 70 cm telescope of the Astronomical Observatory of the Ural State University with a multichannel photometer, and were carried out during 13 nights in March–May 2004. Our analysis reveals brightness variations with periods of 19.788 ± 0.003 min, corresponding to the rotational period of the white dwarf, 21.273 ± 0.003 min, corresponding to the orbital sideband, and 283.3 ± 0.5 min, which is the orbital period. The variations with the white dwarf’s rotational period show a stable amplitude and a quasi-sinusoidal pulse shape persistent over a long time. In contrast, the orbital-sideband variations have an unstable amplitude and a significantly nonsinusoidal pulse shape that varies with time. Variations of the amplitude and pulse shape of the orbital-sideband variations can be related to structural changes of the accretion disk surrounding the white dwarf.

Spatiotemporal behavior of ultrashort pulses in the far field

By using the complex analytic signal representation and far-field approximation, a solution of the wave equation in free space is found, which enables us to study the spatiotemporal behavior of ultrashort pulses in the far field. The consistency of our result with the previous work is interpreted. Some interesting phenomena of ultrashort pulses propagating in free space, such as the pulse broadening, spectrum narrowing and redshifting, etc., are illustrated with nonsinusoidal Poisson-type pulses.

Detection of optical oscillations of the intermediate polar V709 Cassiopeae (RX J0028.8+5917)

We report detection of low-amplitude optical oscillations at periods of 312.77 s and 317.94 s of the intermediate polar V709 Cas. Within the accuracy of measurement these periods agree with the X-ray period reported by Motch et al. ([CITE]) and refined by Norton et al. ([CITE]) and its synodic counterpart if we specify an orbital period of 5.4 h, which is one of the two possible orbital periods reported by Motch et al. ([CITE]). The oscillation at a period of 317.94 s has the strong first harmonic which is evidence for the nonsinusoidal pulse profile of this oscillation. The data folded at a period of 317.94 s reveal a double-peaked pulse profile of this oscillation, which is highly variable from night to night. A weak periodic signal corresponding to the first harmonic of the oscillation at a period of 312.77 s is also detected in the lightcurves of V709 Cas.

Large-current radiator with avalanche transistor switch

The development and experimental investigation of a large-current radiator (LCR) with a pulse generator using avalanche transistors is reported. The LCR is intend for radiating nonsinusoidal pulse electromagnetic waves with a duration of 2 ns. The radiated field strengths in both the near and the far field are measured. The LCR described produces magnetic field strengths of about 4.2 mA/m at a distance of 5 m for radiator current amplitudes of about 0.7 A with rise time of 1 ns. The width of the antenna pattern, measured by the drop of the field strength to one half of its peak value is 120/spl deg/.

The pulsating DAV white dwarf BPM 31594 (VY Hor): evidence for non-linear mode coupling by direct resonance

300 hr of high-speed photometry of the pulsating DAV white dwarf BPM 31594 obtained during 1975-89 is presented. The light curve shows non-sinusoidal pulses with a peak-to-peak range of 30 per cent but with obvious modulation in amplitude and pulse shape. The mean amplitude spectrum shows that the dominant contributor to these oscillations is the principal frequency f=1.62 mHz. Most of the remaining significant power occurs, with variable amplitude, either at frequencies nf or at (1.54±n)f, where n is an integer. Other frequencies near f and at 1.48f, 2.48f and 3.48f are occasionally seen, as well as evidence for low-amplitude peaks (∼0.1 per cent) unrelated to nf or (1.54±n)f

Circular array and nonsinusoidal waves

A theory of circular array antennas based on nonsinusoidal (rectangular) pulses, is developed. Different antenna patterns such as peak amplitude, peak power, energy, and slope pattern are derived and plotted. The antenna patterns yield the resolution angle for the circular array as a function of array radius and frequency bandwidth. The effect of additive Gaussian noise on the angular resolution capability of the circular array is analyzed. The analysis is based on calculating slope patterns by using linear regression algorithm for different signal-to-noise power ratios.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Steady-State Analysis of the Series Resistance-Inductance Circuit Controlled by Asymmetrical Triggering of Thyristors

The load waveforms produced by asymmetrical triggering of an inverse parallel connected pair of thyristors are of two categories. If each of the two firing angles α,β are greater than load phase angle ϕ, the load curtent consists of asymmetrical discontinuous nonsinusoidal pulses. For the case when firing angle ϕ is less than ϕ and satisfies the relationship β ⪕ 𝒳 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</sub> . - π (where 𝒳 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</sub> is the extinction angle corresponding to the other firing angle α), complete half-sinusoids of load voltage appear. Both modes of triggering result in load waveforms with even harmonic content, which are not present with symmetrical triggering.