Frequency Spectrum Of Voltage Research Articles

Research on Single Transistor Open Fault Diagnosis of Photovoltaic Grid-Connected Inverter

Power semiconductor device and its control circuit of photovoltaic grid-connected inverter is the weakest part in the photovoltaic generation system. Fault feature extraction is the key to the inverter fault diagnosis. Output voltage of inverter is the most sensitive characteristic quantity which can reflect its working status directly. The single transistor open fault diagnosis of photovoltaic grid-connected inverter can be achieved by extracting the output voltage frequency spectrum with the help of windowed STFT. The simulation results demonstrate the effectiveness of the method.

Precessional magnetization induced spin current from CoFeB into Ta

The spin dynamics at the interface between the CoFeB and Ta layer has been studied using spin pumping and spin wave characterizations. The spin pumping driven by the ferromagnetic resonance in the CoFeB layer injects a spin current into Ta layer which results in an electromotive force across the Ta layer due to the inverse spin Hall effect. Upon changing the polarity of the bias magnetic field, the polarity of the output voltage inverts and the output voltage increases linearly in respect to the microwave signal power which are consistent with the spin pumping characteristics. The effect of the in-plane magnetization angle on the output voltage has been studied. Furthermore, it is found that the frequency spectrum of the spin Hall voltage is modified by the annealing temperature and the full width at half maximum of the spin pumping increases by more than 40% with the increase of the annealing temperature from 200 °C to 300 °C. The spin Hall angle at the Ta-CoFeB interface is determined to be 0.014, and the damping constant of the CoFeB increases from 0.006 in pure CoFeB to 0.015 in Ta/CoFeB film.

New mixture of hybrid stacked multicell with half‐cascaded converter to increase voltage levels

This study presents a new topology of hybrid stacked multicell (SM) converter which generates high number of output voltage levels with fewer number of power electronic switches. The proposed topology is composed of three parts including traditional SM converter, half-cascaded converter and H-bridge converter. In other words, this converter is the mixture of H-bridge converter and SM converter series with half-cascaded converter. Number of output voltage levels and the rootmean- square value in proposed converter is four times than that of traditional flying capacitor multicell and SM converters. Moreover, it improves output voltage frequency spectrum and decreases the number and rating of components, stored energy and rating of flying capacitors which are available in the proposed converter. For switching this converter, phase-shifted pulse-width modulation method has been used. Therefore the self-balancing trait of the flying capacitor converter is preserved in presented converter. The suggested topology is simulated using MATLAB/SIMULINK software, and simulation results are presented to indicate the well-performance of the novel converter. In addition, the experimental results of proposed topology prototype have been presented to validate its practicability.

Flying Capacitors Reduction in an Improved Double Flying Capacitor Multicell Converter Controlled by a Modified Modulation Method

This paper proposes an improved configuration of double flying capacitor multicell (DFCM) converter. The main advantages of the proposed converter, compared to the conventional DFCM converter, are the doubling of the number of output voltage levels and improvement of the output voltage frequency spectrum. This progress is achieved by adding only two low-power switches and one dc voltage source, whose voltage rating is a small fraction of the main dc-link voltage rating, to the conventional configuration of the DFCM converter. However, the number and voltage rating of high-frequency switches and capacitors and the number of high-frequency switchings during a full cycle are kept constant. The doubling of the number of output voltage levels in the proposed converter makes it possible to decrease the number of cells, the number of flying capacitors, as well as their voltage rating and the amount of stored energy in flying capacitors. Moreover, a modulation method based on phase-shifted carrier pulsewidth modulation is proposed to control the new converter. Simulation and measured experimental results are presented to illustrate the performance of the proposed configuration and its control strategy.

Online Computation of Hysteresis Boundary for Constant Switching Frequency Current-Error Space-Vector-Based Hysteresis Controller for VSI-Fed IM Drives

This paper proposes a current-error space-vector-based hysteresis controller with online computation of boundary for two-level inverter-fed induction motor (IM) drives. The proposed hysteresis controller has got all advantages of conventional current-error space-vector-based hysteresis controllers like quick transient response, simplicity, adjacent voltage vector switching, etc. Major advantage of the proposed controller-based voltage-source-inverters-fed drive is that phase voltage frequency spectrum produced is exactly similar to that of a constant switching frequency space-vector pulsewidth modulated (SVPWM) inverter. In this proposed hysteresis controller, stator voltages along α- and β-axes are estimated during zero and active voltage vector periods using current errors along α- and β-axes and steady-state model of IM. Online computation of hysteresis boundary is carried out using estimated stator voltages in the proposed hysteresis controller. The proposed scheme is simple and capable of taking inverter upto six-step-mode operation, if demanded by drive system. The proposed hysteresis-controller-based inverter-fed drive scheme is experimentally verified. The steady state and transient performance of the proposed scheme is extensively tested. The experimental results are giving constant frequency spectrum for phase voltage similar to that of constant frequency SVPWM inverter-fed drive.

New mixed stacked multicell converter with interesting advantages

Multilevel converters are very interesting alternatives for medium and high-power applications. This study presents a new configuration of multicell converters. The main advantages of the proposed converter, in comparison with conventional flying capacitor multicell (FCM) and stacked multicell (SM) converters, are doubling the number of output voltage levels and the root mean square (RMS), improving the output voltage frequency spectrum and lowering the number and rating of components and decreasing the converter losses. Furthermore, the stored energy and rating of flying capacitors will be decreased to half in this topology in comparison with FCM and SM converters. These improvements are achieved by adding only four low-frequency switches to the conventional SM converters configuration. In this topology, the number of high-frequency switches is decreased while the voltage ratings of them during a full cycle are kept constant. Also, a modified phase shifted pulse-width-modulation-based control method has been applied to the proposed topology, which can decrease the harmonic distortions and THD. The circuit is simulated using PSCAD/EMTDC software and simulation results are presented to validate the effectiveness and advantages of the proposed configuration. In addition, the experimental results of proposed configuration prototype have been presented to examine its practicability.

Research on Stator Winding Inter Turn Short-Circuit Faults of Aeronautical Fault-Tolerant Machine Based on Maxwell 2D

Stator winding inter turn short-circuit fault is one of the most common internal faults of fault-tolerant machine, which can disconnect the fault phases and keep operating correctly in the event of a failure. Stator winding short-circuit fault model is established through analysis. Based on finite element method, the high-power density fault-tolerant machine internal magnetic field simulation and analysis is implemented using Maxwell2D and induced voltage frequency spectrum is analyzed by FFT method. The characteristics of stator winding short-circuit faults are summarized, which lay a solid foundation for fault-tolerant machine earlier faults prediction and winding switching.

Double Flying Capacitor Multicell Converter Based on Modified Phase-Shifted Pulsewidth Modulation

Multilevel converters are very interesting alternatives for medium and high-power applications. The main reason is the increase in the number of output voltage levels and its apparent frequency. This paper presents a new configuration of flying capacitor multicell (FCM) converter. The main advantages of the proposed converter, in comparison with FCM and stacked multicell converters, are doubling the rms and the number of output voltage levels, improving the output voltage frequency spectrum, and canceling the midpoint of dc source. This progress is achieved by adding only two low-frequency switches to the conventional configuration of FCM converter while the number of high-frequency switches and capacitors, voltage ratings of capacitors and switches, and the number of high-frequency switchings during a full cycle are kept constant. This converter is controlled by a modified phase-shifted pulsewidth modulation, therefore, the self-balancing property of the flying capacitor converter is maintained in the proposed converter. The circuit is simulated using power systems computer-aided design/electromagnetic transients in DC systems (EMTDC) software and simulation results are presented to validate the effectiveness and advantages of the proposed configuration as well as its control strategy. Additionally, measurements taken from an experimental setup are presented in order to study the practical configuration.

Acoustic Scattering and Active Control From a Near-Surface Underwater Piezoelastic Spherical Shell Transducer

In this paper, the 3-D interaction of a time-harmonic plane-progressive incident sound wave with a bilaminate hollow sphere, composed of an outer layer of steel perfectly bonded to an inner layer of radially polarized piezoceramic material (PZT4), and submerged near a free/rigid flat boundary, is considered. The translational addition theorem for spherical wave functions along with the classical transfer matrix approach within the context of state-space formulation is employed to obtain an analytical solution for the acoustic scattering problem. When the transducer is operating in the receive mode, the frequency spectrum of voltage induced within the piezoelectric sensor layer along with the associated backscattering form functions are calculated and discussed for selected distance parameters, angles of incidence, and interface impedance conditions. Also, when the transducer is operating in the active transmission mode, the effects of latter parameters on the control voltages required for partial or complete cancellation of the reflected pressure field are investigated.

Research on critical technology of micro/nano bioparticles manipulation platform based on light-induced dielectrophoresis

On the basis of the research on the status and problems of micro/nano bio-particles manipulation using dielectrophoresis, the theoretical basis and the model simulation of micro/nano bio-particles manipulation using light-induced dielectrophoresis were discussed. The space distribution of electric field and dielectrophoresis forces in different heights were also obtained. On this basis, the core component of the micro manipulation system, that is, photoconductive layer of the chip, was completed in the material selection, fabricating process and performance analysis testing. Then the voltage drop of the suspension and the effective voltage frequency spectrum were obtained. Finally, by combining the machine vision detection with real-time tracking system, the micro/nano bio-particles manipulation platform based on the light-induced dielectrophoreisis was established, and then the manipulations for micro/nano bio-particles, such as quick collection, transport, separation, were implemented. This provided a basis for rapid, accurate, and low-cost detection of serious diseases based on the micro-fluidic biochip and early diagnosis.

Effects of helical anisotropy on nonlinear voltage response in amorphous wires

The nonlinear voltage response in soft magnetic amorphous wires exciting by an alternating current is studied. The frequency spectrum of the voltage in the pick-up coil wound around the wire with a helical anisotropy is found in the framework of a model based on quasi-static Stoner−Wohlfarth magnetization reversal. The effect of a deviation of the anisotropy axis from the azimuthal direction on the field dependences of amplitudes of voltage harmonics is analyzed. It is shown that the field sensitivity of even harmonics increases with the anisotropy axis deviation angle. The current amplitude range to obtain a maximal field sensitivity of the second harmonic is found. The influence of the skin effect on the frequency spectrum of the pick-up coil voltage is discussed. The results obtained may be of importance for the development of sensors of a weak magnetic field.

Design and Implementation of a Novel Vector-controlled Drive by Direct Injection of Random Signal

The distribution of harmonics of an inverter output voltage in a PWM inverter can be improved by using a Random Pulse Width Modulation (RPWM) scheme. RPWM dose not affect the fundamental frequency component of voltage, however it can significantly reduce the acoustic noise and mechanical vibrations of an inverter-fed ac motor drive. Up to now, RPWM has been studied in many researches and various RPWM techniques have been introduced, but none of them have actually shown the effects of the behavior of the random signal on the frequency spectrum of the inverter output voltage and performance of the motor drive. In this paper, three different methods of random signals are employed. These different methods and the Probability Density Function (PDF) of the random signal generator will be studied and the performance of the drive is examined. Also a new method in utilizing random signal is proposed. In this method, the random signal is injected to reference value of the quadrature-axis current. It should be noted that the RPWM technique can not be utilized in hysterisis drives. Here, the random signal with different PDF is injected directly to quadrature axis current. The injection of random signal will directly affect the output responses. In this research, comparison between RSPWM technique and direct injection of random signal has been carried out. Different criteria such as total harmonic distortion (THD), torque ripple and frequency spectrum, efficiency and mechanical vibration have been analyzed. The indirect field oriented vector control drive is simulated by using Matlab-Simulink first, and the effects of various methods of employing random signal are compared and the best alternative is introduced. For the validation of the simulation results an experimental set-up is built. The experimental results confirm the simulation outputs. The simulation and experimental result show superiority of Direct Injection of Random Signal (DIRS) method in comparison with randomized Sinusoidal pulse width modulation (RSPWM) technique. Also it is realized that the DIRS method is very simple for implementation and does not need any extra hardware.

Attenuation of Electromagnetic Interference in a Shunt Active Power Filter

Shunt active power filters (APF) are commonly used for the reduction of current harmonics and improvement of the power factor in power systems with nonlinear loads, such as diode rectifiers. A pulsewidth modulation (PWM) power converter constitutes the main component of the APF. The low-order harmonics of the line current are attenuated, but the switch-mode operation of the converter results in electromagnetic interference (EMI) spreading to the grid. Specifically, clusters of harmonics appear in the frequency spectra of voltages and currents of the converter at multiples of the switching frequency. In this paper, transferring the discrete spectral power of those harmonics to the continuous spectral power density is proposed as means for mitigation of the EMI. It is accomplished by randomization of the switching periods using a novel random PWM method (RPWM II). In contrast to the existing random PWM methods, in RPWM II the sampling frequency of the digital modulator is constant and equal to the average switching frequency. Computer simulations and experimental investigation of an APF designed for shipboard power systems are described, and the results are presented. They demonstrate significant reduction of the EMI, a feat achieved at practically no expense.

Accurate and Computationally Efficient Implementation of the IEEE 1459-2000 Standard in Three-Phase Three-Wire Power Systems

The definitions for the measurement of electrical power quantities under sinusoidal, nonsinusoidal, balanced, or unbalanced conditions are established in IEEE Standard 1459-2000. Measured magnitudes, such as apparent powers or effective quantities, are evaluated considering the frequency spectrum of voltage and current signals (fundamental, nonfundamental, and combined magnitudes). Previous papers implement these definitions in the frequency domain (DFT) and in the time domain (Clarke-Park Transformations). In the time domain, low-pass filters (LPFs) must be applied to obtain the fundamental magnitudes but, in this case, the quality of the measurements depends on the LPFs orders and their cutoff frequencies. This paper proposes a time-domain implementation of the standard definitions without LPFs and employs a recursive averaging algorithm which improves the measurements precision and reduces the computational burden. Simulation and experimental tests showing the proposed method performance are included

The frequency spectrum of a voltage measured in an amorphous wire magnetized in alternating magnetic field

We have studied the process of magnetization reversal in amorphous microwires under the action of a longitudinal (axial) high-frequency magnetic field. The amplitudes of harmonics in the frequency spectrum of the response voltage between the wire ends were measured as functions of the high-frequency field amplitude and a dc axial magnetic field strength. For relatively large amplitudes of the high-frequency field, the first several harmonics in the frequency spectrum of the response voltage are highly sensitive with respect to the dc magnetic field. The experimental results are interpreted within the framework of a simple electrodynamic model.

The influence of moving domain walls on the appearance of the second harmonic in the magnetoimpedance spectrum of a cobalt-based amorphous microwire

We have studied the influence of moving domain walls (DWs) on the magnetoimpedance of a cobalt-based amorphous microwire. A model describing the DW motion in the electric field of an alternating current in the absence of a skin effect is proposed. When the current amplitude exceeds a certain threshold value, the DW motion leads to the appearance of a second harmonic component in the frequency spectrum of the sample response voltage. The second harmonic amplitude has been studied as a function of the external longitudinal magnetic field, the current frequency, and the angle of deviation of the microwire anisotropy axis from the circular direction. The sensitivity of the second harmonic to the external magnetic field can be significantly higher than that of the first harmonic.

Rapid Calculation of the Periodic Steady State for Electronically Switched, Time Varying Power System Loads

The periodic steady state of power distribution system loads is studied for electronically switched, time varying cases. Many loads of this type appear on contemporary power systems as energy saving and controllable demands. Several alternative methods of calculating the periodic steady state are discussed and a new method is proposed based on the frequency modulation property of the discrete Fourier transform. The new method is termed the gain-shift formula (GSF) because the format of the technique entails adding frequency shifted terms which represent the parameter to be calculated. An example of a triac-switched load on the distribution system is given. The main advantages of the GSF are: rapid calculation of the periodic steady state; and efficient calculation of the frequency spectrum of voltages and currents in the periodic steady state.

Rapid calculation of the periodic steady state for electronically switched, time varying power system loads

The periodic steady state of power distribution system loads is studied for electronically switched, time varying cases. Many loads of this type appear on contemporary power systems as energy saving and controllable demands. Several alternative methods of calculating the periodic steady state are discussed and a new method is proposed based on the frequency modulation property of the discrete Fourier transform. The new method is termed the gain-shift formula (GSF) because the format of the technique entails adding frequency shifted terms which represent the parameter to be calculated. An example of a triac-switched load on the distribution system is given. The main advantages of the GSF are: rapid calculation of the periodic steady state; and efficient calculation of the frequency spectrum of voltages and currents in the periodic steady state.

A single-phase delta-modulated inverter for UPS applications

The performance characteristics of the rectangular wave delta modulation (RWDM) scheme for uninterruptible power supply (UPS) applications is investigated. Normalized characteristic curves that show the effect of various modulator parameters on the frequency spectrum of the inverter output voltage are obtained using discrete Fourier transform (DFT) and harmonic analysis techniques. The performance of a single-phase half-bridge inverter with an LC filter is discussed, and experimental results are provided to validate the predicted and simulated results. It is shown that the harmonic content of the inverter output waveform can be controlled through the control of the modulator parameters.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of DC Excitation on Instrument Transformers

Experimental results are presented and evaluated showing the effects of DC excitation on a current transformer and a potential transformer. Parameters measured are phase angle, current and voltage ratios, and frequency spectra of important voltages and currents.