Function Of Modulation Index Research Articles

An Examination of Polarization Mode Transitions in Pulsar Radio Emission

A statistical model is used to determine how stochastic fluctuations in the intensities of orthogonal polarization modes contribute to the modulation and depolarization of pulsar radio emission. General expressions for the distributions of the Stokes parameters, linear polarization, polarization position angle, and fractional polarization are derived when the mode intensities follow the same or different probability distributions. The transition between modes is examined. When the mode intensities follow the same distribution, the fractional linear polarization and modulation index are symmetric about the transition. The symmetry is disrupted when the mode intensities follow different distributions. The fractional linear polarization is minimum and the mode frequency of occurrence changes rapidly at transitions where the mode intensity distributions are the same and the modulation index is small. A lower limit on the fractional linear polarization that can be attained via the simultaneous occurrence of the modes as a function of modulation index is quantified.

An improved selective harmonics elimination technique for PV assisted single phase grid-tied PWM inverter

Purpose The purpose of this study is to present a new methodology of selective harmonics elimination (SHE) technique suitable for single-phase photovoltaic (PV) tied pulse width modulated (PWM) inverter. Design/methodology/approach In the proposed SHE, switching angles for inverter control are determined offline through numerical techniques and stored in a microcontroller memory as a function of modulation index (md). The methodology uses the solution that leads to a lower change of switching angles from the previous modulation index (md) for storing in the processor memory for multiple solutions. This leads to a smaller number of sections when a piecewise mixed model is considered for storing the entire switching angle curve for the online inverter control. The proposed idea is simulated and experimentally validated on a laboratory prototype of PV (500 W) grid-tied PWM inverter. The control environment is then realized in NI c-RIO 9082. Findings This proposed technique is suitable for limiting voltage total harmonics distortion (THD) in single-phase PV tied grid connected voltage source inverter (VSI). Moreover, it is found that filter (L-C) size requirement is less. Originality/value The proposed SHE with piecewise mixed model technique effectively reduces voltage THD with less filter size (L-C) in a single-phase PV-tied system.

Evaluation of DC‐link voltage ripple in five‐phase PWM voltage source inverters

This paper presents the analysis of the DC-link voltage switching ripple in five-phase PWM voltage source inverters with balanced load. The analysis is particularly important for the design and selection of a DC-link capacitor making it possible to meet desired electrical performance of the inverter system. Simple and practical equation for designing the DC-link capacitor is proposed relating the value of capacitance to the maximum value (peak-to-peak) of the DC-link voltage ripple. The amplitude of the DC-link voltage switching ripple is analytically derived as a function of modulation index, and the amplitude of the output current and phase angle. In order to show peak-to-peak voltage ripple distribution, different diagrams are introduced. Reference is made to continuous symmetric centred PWM modulation (i.e., space vector modulation SVM). In order to verify proposed developments, simulations have been carried out by Matlab/Simulink considering full range of modulation index and output phase angle.

Controlling the light shift of the CPT resonance by modulation technique

Motivated by recent developments in atomic frequency standards employing the effect of coherent population trapping (CPT), we propose a theoretical framework for the frequency modulation spectroscopy of the CPT resonances. Under realistic assumptions we provide simple yet non-trivial analytical formulae for the major spectroscopic signals such as the CPT resonance line and the in-phase/quadrature responses. We discuss the influence of the light shift and, in particular, derive a simple expression for the displacement of the resonance as a function of modulation index. The performance of the model is checked against numerical simulations, the agreement is good to perfect. The obtained results can be used in more general models accounting for light absorption in the thick optical medium.

Analytical evaluation of DC capacitor RMS current and voltage ripple in neutral-point clamped inverters

The sizing of the DC-link capacitor in a three-level inverter is based on the RMS current flowing through it. This paper analyses the DC-link capacitor RMS current in a neutral-point clamped (NPC) inverter and expresses the same as a function of modulation index, line-side current amplitude and power factor. Analytical closed-form expressions are derived for the capacitor RMS current for single-phase half-bridge, single-phase full-bridge and three-phase three-leg topologies of a three-level inverter. The worst-case capacitor current stress is determined for each topology based on the analytical expressions. Further, analytical expressions are derived for the RMS values of low-frequency and high-frequency capacitor currents. These expressions are then used to estimate voltage ripple across the DC capacitor for sinusoidally modulated three-phase NPC inverter. The analytical expressions for the RMS current and voltage ripple are validated experimentally over a wide range of operating points.

Optimisation‐based improved switching technique for static VAr compensator considering minimum source harmonic injection

A selective harmonic elimination and minimisation-based improved switching technique is proposed for static VAr compensator (SVC) considering minimum source harmonic injection without external filter. Fixed capacitor–insulated gate bipolar transistor controlled reactor (IGBTCR) is used for the proposed SVC model. The switching function of IGBTCR is optimised for minimum reactor voltage total harmonic distortion (THD) which leads to less harmonic injection to line resulting minimisation of source current THD. The best possible optimised switching angles are computed offline using gravitational search algorithm with varying modulation indices to obtain minimum reactor voltage THD. Piecewise mixed model approximation technique is used to store these switching angles as a function of modulation index in the processor memory for online application. The proposed switching significantly improves source current THD compared to conventional switching. Proper simulations as well as experimental results are presented to confirm the proposed scheme.

Tunable diode laser spectroscopy of benzene near 1684 nm with a low-temperature VCSEL

We describe the application of a long-wavelength vertical-cavity surface-emitting laser (VCSEL) with extended tuning range to the detection of benzene vapor at atmospheric pressure. A benzene absorption feature centered at 1684.24 nm was accessed by reducing the heat sink temperature of a VCSEL designed for room-temperature operation to −55°C. This allowed us to increase the injection current and thus to extend a single-scan tuning interval up to 46.4 cm−1 or 13.2 nm around a central wavelength of 1687.4 nm. Five absorption lines of methane in the 5903–5950 cm−1 range could be acquired within single laser scans at a repetition rate of 500 Hz. A benzene absorption feature between 5926 and 5948 cm−1 was recorded for concentration measurements at atmospheric pressure using a single-pass 1.2 m absorption cell. A 50 ppmv mixture of CH4 in N2 was introduced into the cell along with benzene vapor to calibrate benzene concentration measurements. Benzene mixing ratios down to ∼90 ppmv were measured using a direct absorption technique. The minimum detectable absorbance and detection limit of benzene were estimated to be ∼10−4 and 30 ppmv, respectively. Using the wavelength modulation technique, we measured a second harmonic sensor response to benzene vapor absorption in air at atmospheric pressure as a function of modulation index. We conclude that a low-temperature monolithic VCSEL operating near 1684 nm can be employed in compact benzene sensors with a detection limit in the sub-ppm range.

Errors in Determining the Center of a Resonance Line Using Sinusoidal Frequency (Phase) Modulation

The errors in determining the center of a resonance line, which are due to residual imperfections in practical high-precision electronic systems using sinusoidal Frequency or phase modulation, are reviewed. In particular, the effects of residual amplitude modula- tion, baseline distortion, and harmonic distortion in the modulation process and the demodulator are qualitatively analyzed for a Loren- tzian line in the limit of small modulation index. This permits one to calculate analytically the frequency offsets as a function of modulation index, the transfer function of the fundamental, and various harmon- ics of the modulation frequency. Using this model one can easily for- mulate accurate tests for experimentally measuring the Frequency er- rors in practical servosystems, even if the original assumptions about small modulation index and a pure Lorentzian line are not exactly ful- filled.

Rectangular-Wave Modulation and Pulse-Length Modulation

Rectangular-wave modulated pulse lengths are expressed as a function of modulation index. The theoretical expressions are experimentally verified. A pulse-length modulation (PLM) system is obtained...