Showing papers on "Fundamental frequency published in 2015"

Analysis and Calculation of DC-Link Current and Voltage Ripples for Three-Phase Inverter With Unbalanced Load

Abstract: In this paper, an analysis and calculation of the dc-link current and voltage ripples are presented for a three-phase inverter with unbalanced load. A comparison of the dc-link average and root-mean-square (rms) currents between considering and ignoring high frequency harmonics of the output current is drawn. It is shown that high frequency harmonic currents have little effect on the dc-link current, and therefore, they can be ignored. Based on the symmetrical components method, the dc-link average and harmonic rms currents are derived, and the dc-link voltage ripple is compared between the balanced and unbalanced loads. It can be found that the dc-link current and voltage ripples consist of not only high frequency harmonics but also the double fundamental frequency harmonic, and the voltage ripple is independent of the positive-sequence component and determined by the negative-sequence component, under the unbalanced load. Experimental results are shown to verify the accuracy of the theoretical analysis.

Second-harmonic generation from metal nanoparticles: resonance enhancement versus particle geometry.

Abstract: We demonstrate that optical second-harmonic generation (SHG) from arrays of noncentrosymmetric gold nanoparticles depends essentially on particle geometry. We prepare nanoparticles with different geometrical shapes (L and T) but similar wavelengths for the polarization-dependent plasmon resonances. In contrast to recent interpretations emphasizing resonances at the fundamental frequency, the T shape leads to stronger SHG when only one, instead of both, polarization component of the fundamental field is resonant. This is explained by the character of plasmon oscillations supported by the two shapes. Our numerical simulations for both linear and second-order responses display unprecedented agreement with measurements.

Current Harmonics Compensation Based on Multiresonant Control in Synchronous Frames for Symmetrical $n$ -Phase Machines

Abstract: Low-order odd current harmonics arise in practical multiphase drives due to machine and converter nonlinear behavior (e.g., deadtime and flux saturation). If the windings are distributed, some harmonics cause torque ripple, whereas others produce losses. The latter is aggravated by the small impedance in the no-torque subspaces. Current harmonics can be compensated without steady-state error by proportional–integral controllers in multiple synchronous frames (SFs); however, a heavy computational load is required. In three-phase systems, the computational burden of this multiple SF (MSF) scheme is often avoided by implementing instead resonant controllers (RCs) tuned at the harmonics that are multiples of six in an SF rotating with the fundamental frequency. A similar structure has been proposed for nonlinearities compensation in asymmetrical six-phase machines. This paper extends this multiple RC (MRC) strategy to symmetrical machines of any phase number. The optimum frequencies for the RCs and for the SF in each plane, so that the number of RCs is minimized, are established. Then, the computational load of the resulting generic MRC scheme is assessed and compared with that of the MSF structure. The conditions in which the former is particularly preferable over the latter are identified. Experimental results are provided.

Seismic active earth pressure on walls using a new pseudo-dynamic approach.

Abstract: Seismic active soil thrust, soil pressure distribution and overturning moment are obtained in closed form using a new pseudo-dynamic approach based on standing shear and primary waves propagating on a visco-elastic backfill overlying rigid bedrock subjected to both harmonic horizontal and vertical acceleration. Seismic waves respect the zero stress boundary condition at the soil surface, backfill is modeled as a Kelvin–Voigt medium and a planar failure surface is assumed in the analysis. Effects of a wide range of parameters such as amplitude of base accelerations, soil shear resistance angle, soil wall friction angle, damping ratio are discussed. Results of the parametric study indicate that amplitude of the horizontal base acceleration and soil shear resistance angle are the factors most influencing active pressure distribution whereas the presence of the vertical acceleration always results in a quite small increase in seismic active thrust. Damping ratio is important mainly close to the fundamental frequency of shear wave where seismic active thrust is maximum. Unlike the original pseudo-dynamic approach the effect of a different frequency for S-wave and P-wave is considered in the analysis. Seismic active thrust is found to increase when the frequency of P-wave is greater than that of S-wave. The results obtained by the proposed approach are found to be in agreement with previous studies, provided that the seismic input is adapted to include amplification effects.

Multifrequency focusing and wide angular scanning of terajets.

Abstract: In the past, it has been demonstrated that it is possible to produce terajets with high resolution at its focus using 3D dielectric cuboids under plane-wave illumination. Here, a systematic study of the harmonic and angular response of terajets using cuboids is performed. Mutifrequency focusing is demonstrated at the fundamental frequency and two higher frequency harmonics showing an intensity enhancement of ∼10, ∼18, and ∼14 for each case. This capability to use 3D dielectric cuboids to produce terajets at the fundamental frequency and first harmonic is experimentally evaluated at sub-THz frequencies, with good agreement with numerical results. Moreover, a robust angular response is demonstrated numerically and experimentally showing that the intensity at the focal position is maintained in a wide angular range (from 0° to 45°), demonstrating the capability to work as a wide scanning terajet-focusing lens. The results here presented may be scaled at different frequency bands such as optical frequencies and may be used in microscopy techniques and sensors.

A new pattern of instability observed in an annular combustor: The slanted mode

Abstract: In annular combustion chambers of aero-engines and gas turbines, acoustic coupling may arise from azimuthal modes which are less well damped than axial modes. Also, since the circumference is the largest length in the combustor, the azimuthal modes have the lowest resonance frequencies and are most prone to instability. Such a coupling raises many scientific issues which are considered in a small number of fundamental experiments. The present investigation focuses on this problem and provides experimental data on a special type of combustion instability in which the thermo-acoustic resonant coupling involves a combination of modes. This produces an unusual pattern of flame responses in which the distribution of heat release rate is slanted. Data are provided in the form of free radical light intensity patterns (interpreted as heat release rate distributions) and microphone signals detected in the plenum and chamber. It is shown that the slanted pattern is the signature of a combination of two modes with coinciding frequencies, the first being a standing azimuthal mode while the second is an axial mode. Measurements of the flame describing function on a single matrix burner at the fundamental frequency are used to explain the observed phase shift and amplitude in the flame responses of the different injectors in the annular combustor.

On Design and Evaluation of Harmonic Transponders

Abstract: Performance and characterization of harmonic transponders is investigated both theoretically and experimentally. The harmonic response of a transponder based on a Schottky diode is analytically derived in the case when the excitation power is low. Theoretical calculations prove that at high frequencies, capacitive nonlinearity contributes more to frequency multiplication than resistive nonlinearity. This means that the feasibility of a particular diode for harmonic transponder applications largely depends on its varactor properties. Figures-of-merit (FOM) are derived both for the mixing diode and the transponder antenna. The validity of the proposed theoretical model is investigated experimentally using a harmonic transponder operating at 1 GHz fundamental frequency.

A Primer on the Physical Principles of Tissue Harmonic Imaging

Abstract: Tissue harmonic imaging (THI) is a routinely used component of diagnostic ultrasonography (US). In this method, higher-frequency harmonic waves produced by nonlinear fundamental US wave propagation are used to generate images that contain fewer artifacts than those seen on conventional fundamental wave US tissue imaging. Harmonic frequencies are integer multiples of the fundamental frequency. The majority of current clinical US systems use second harmonic echoes for THI image formation. Image processing techniques (ie, bandwidth receive filtering, pulse inversion, side-by-side phase cancellation, and pulse-coded harmonics) are used to eliminate the fundamental frequency echoes, and the remaining harmonic frequency data are used to generate the diagnostic image. Advantages of THI include improved signal-to-noise ratio and reduced artifacts produced by side lobes, grating lobes, and reverberation. THI has been accepted in US practice, and variations of the technology are available on most US systems typically used for diagnostic imaging in radiologic practice. Differential THI is a further improvement that combines the advantages of THI, including superior tissue definition and reduced speckle artifact, with the greater penetration of lower frequency US, which permits high-quality harmonic imaging at greater depth than could previously be performed with conventional THI.

Fundamental Switching Frequency Optimal Pulsewidth Modulation of Medium-Voltage Cascaded Seven-Level Inverter

Abstract: Multilevel converters (MLCs) emerged as standard solutions for medium voltage (MV) high-power industrial ac drives. MV drives require low device switching frequency operation due to the higher switching losses of semiconductor devices. However, low device switching frequency operation leads to an increase in the harmonic distortion of machine stator currents. Therefore, there is a need to implement low switching frequency modulation technique for MLCs, which does not compromise on the harmonic distortion of machine currents. The goal of this paper is to propose a new optimal pulsewidth modulation technique for a cascaded seven level (7L) inverter such that the maximum device switching frequency is limited to the rated fundamental frequency (50/60 Hz) and all power semiconductor devices operate at identical switching frequency. Optimal switching patterns were determined offline assuming steady-state conditions. Later, switching angles for each semiconductor device are determined and stored in an FPGA controller. A low-power prototype of the 7L cascade inverter has been developed to demonstrate the proposed modulation technique. The experimental results demonstrated that the proposed optimal modulation technique maintains the quality of machine stator currents while the device switching frequency is limited to the rated fundamental frequency.

Cat Swarm Optimization as Applied to Time-Modulated Concentric Circular Antenna Array: Analysis and Comparison with Other Stochastic Optimization Methods

Abstract: In this communication, a 9-ring time-modulated concentric circular antenna array (TMCCAA) with isotropic elements has been studied based on an evolutionary optimization algorithm called cat swarm optimization (CSO) for the reduction of side lobe level (SLL) and improvement in the Directivity, simultaneously. The comparative case studies as Case-1 and Case-2 are made with three control parameters like interelement spacing in rings, interring radii, and the switching “ on ” times of rings with the help of same algorithm. Experimental results show a considerable SLL reduction with respect to the uniformly excited case. The numerical results show Case-2 outperforms Case-1 with respect to SLL and Directivity. Apart from this, the powers radiated at the center/fundamental frequency and the first two sideband frequencies, and dynamic efficiency have been computed. It has been observed that as the sideband frequency increases, both the powers radiated by harmonic frequencies and sideband levels (SBLs) decrease.

Application of memetic algorithm for selective harmonic elimination in multi-level inverters

Abstract: Multi-level inverter (MLI) is a promising technology, able to generate high-quality power with lower switching frequency. Therefore it leads to high conversion efficiency and low switching losses. Selective harmonic elimination is a fundamental frequency switching strategy that theoretically provides desirable output waveform for MLIs by elimination of low order harmonics. Unfortunately, complexity, non-linearity and solvability features attached to this method have limited its industrial application. In this study, a particle swarm optimisation (PSO)-based memetic algorithm (MA) guided by mesh adaptive direct search is introduced as a suitable choice for the harmonic optimisation problem. This algorithm is precise and applicable to any MLI. The results show that MA converges to the exact solution for feasible modulation index. When the problem has no exact solution, the algorithm finds a relatively proper solution to regulate the fundamental component of the voltage. Furthermore, the comparison between MA and other methods shows that the probability of convergence of MA is higher than others. For 48% of the analysed data MA reaches to a fitness value lower than 10 -30 whereas this probability is 5% for PSO and almost zero for genetic algorithm and bee algorithm. The proposed method has been implemented on a cascade seven-level inverter.

Dynamic Phasor Modeling of Type 3 DFIG Wind Generators (Including SSCI Phenomenon) for Short-Circuit Calculations

Abstract: Short-circuit modeling of wind generators is crucial to determine protective relay and control settings, equipment ratings, and to provide data for protection coordination. The short-circuit contribution of a Type 3 wind farm connected to a series-compensated line is affected by subsynchronous interactions, making it essential to model such behavior. Fundamental frequency models are unable to represent the majority of critical wind generator fault characteristics. The complete electromagnetic transient (EMT) models, though accurate, demand high levels of computation and modeling expertise. This paper proposes a novel modeling technique for a Type 3 wind farm based on the generalized averaging theory, where system variables are represented using time-varying Fourier coefficients known as dynamic phasors. The novelty and advantage of the proposed modeling technique is that it does not just include 60-Hz frequencies but also other dominant frequencies, such as 36 Hz, that are present due to the SSCI in the system. Methods currently used by the industry mostly rely on fundamental frequency-based analysis. Only the appropriate dynamic phasors are selected for the required fault behavior to be represented, improving computational efficiency. Once the SSCI behavior (waveforms showing resonant frequency at the point of common coupling) of a series-compensated Type 3 wind farm from real-time field data is available, the developed model could be used to simulate the scenario without necessarily having to know the exact control blocks of the wind generator controls. A 450-MW Type 3 wind farm, consisting of 150 units, was modeled using the proposed approach. The method is shown to be accurate for representing faults at the point of interconnection of the wind farm to the grid for balanced and unbalanced faults as well as for nonfundamental frequency components present in fault currents during subsynchronous interactions.

Hybrid Synchronous/Stationary Reference-Frame-Filtering-Based PLL

Abstract: Designing an effective phase-locked loop (PLL) for three-phase applications is the objective of this paper. The designed PLL structure is able to provide an accurate estimation of the grid voltage frequency and the phase, even in the presence of all harmonic components of both positive and negative sequences and the dc offset in its input. In addition to offering a high disturbance rejection capability, the suggested PLL structure has a fast transient response and provides a settling time of around two cycles of the fundamental frequency. The effectiveness of the suggested PLL structure is confirmed using numerical results.

Resonant–Repetitive Combined Control for Stand-Alone Power Supply Units

Abstract: This paper investigates a combined resonant–repetitive (RR) control structure for a three-phase four-leg dc/ac converter power supply. The RR control configuration is composed by a resonant controller tuned at the system fundamental frequency working in conjunction with a plug-in-type repetitive controller. The resonant part of the control scheme is used to assure prompt tracking of the inverter output voltage and to achieve as fast as possible system response to load variations; to this purpose, it is tuned at the fundamental frequency. At the same time, the resonant controller is able to stabilize the system without the necessity of any further additional controller; the repetitive part of the scheme is implemented for the fine regulation at the system harmonic frequencies. The proposed control configuration is used to regulate the power supply output voltage, providing very good tracking of the output voltage reference even in the presence of a nonlinear load. Experimental validation from a 40-kVA converter prototype is presented to validate the operation of the proposed converter and control.

Optimal Low-Switching Frequency Pulsewidth Modulation of Medium Voltage Seven-Level Cascade-5/3H Inverter

Abstract: Low-switching frequency modulation of multilevel inverters for medium-voltage high-power industrial ac drives is essential to reduce switching losses and, thus, improve the overall energy efficiency of the system. However, minimizing the switching frequency increases the total harmonic distortion (THD) of machine currents. Synchronous optimal pulsewidth modulation (SOP) is an emerging technique for controlling multilevel inverters at low-switching frequency without compromising on the THD of machine currents. The goal of our experiment was to implement SOP technique for controlling seven-level cascade inverter for an induction motor drive at an average device switching frequency limited to rated fundamental frequency. First, optimal seven-level waveforms were obtained by ofline optimization assuming steady-state operating conditions. Then, the switching angles for each semiconductor device were obtained that ensure equal distribution of switching losses as well as minimal unbalance in dc-link capacitor voltages. The proposed SOP technique is validated by experimental results obtained from the seven-level cascade inverter feeding a 1.5-kW induction motor.

Control of ion energy distributions using phase shifting in multi-frequency capacitively coupled plasmas

Abstract: Control of ion energy distributions (IEDs) onto the surface of wafers is an ongoing challenge in microelectronics fabrication The use of capacitively coupled plasmas (CCPs) using multiple radio frequency (rf) power sources provides many opportunities to customize IEDs In dual-frequency CCPs using a fundamental frequency and its second harmonic, varying the relative voltages, powers, and phases between the fundamental and second harmonic biases have demonstrated potential as control mechanisms for the shape of the IEDs In this paper, we report on computational and experimental investigations of IED control in dual-frequency and triple-frequency CCPs where the phase between the fundamental and second harmonic frequency voltage waveform is used as a control variable The operating conditions were 5–40 mTorr (067–533 Pa) in Ar and Ar/CF4/O2 gas mixtures By changing the phase between the applied rf frequency and its second harmonic, the Electrical Asymmetric Effects was significant and not only shifted the dc self-bias but also affected plasma uniformity When changing phases of higher harmonics, the energies and widths of the IEDs could be controlled With the addition of a 3rd high-frequency source, the plasma density increased and uniformity improved Computed results for IEDs were compared with experimental results using an ion energy analyzer in systems using rf phase locked power supplies

The Use of a Modified Prony Method to Track the Broken Rotor Bar Characteristic Frequencies and Amplitudes in Three-Phase Induction Motors

Abstract: The knowledge of the broken rotor bar characteristic frequencies and amplitudes has a great importance for all related diagnostic methods. The monitoring of motor faults requires a high resolution spectrum to separate different frequency components. The discrete Fourier transform (DFT) has been widely used to achieve these requirements. However, DFT can give meaningful information only for stationary harmonics which cannot be guaranteed in real cases. In addition, a long data sequence is necessary for DFT to get high frequency resolution. Nevertheless, the signals are time varying, and the steady-state conditions can be lost for a long time acquisition. As a solution for these problems, this paper proposes an efficient time-domain technique based on a modified Prony method for the estimation of the frequencies/amplitudes of broken rotor bar faults. Using this technique, the stator current is divided into short overlapped time windows, and each one is analyzed by the least squares Prony method. The proposed technique provides a linear time–frequency/amplitude representation with high frequency resolution and adjustable time resolution. It is shown that this technique allows tracking the frequencies and amplitudes of the sidebands around the fundamental frequency component with a very high accuracy. The efficiency of the proposed method is verified by simulation and experimental tests.

Analysis of SiC based power electronic inverters for high speed machines

Abstract: Silicon carbide (SiC) based power switching devices have been extensively studied by researchers and engineers in recent years because of their superior physical properties compared to silicon However, the benefits of using SiC devices have yet to be fully explored, especially for high-speed or high-fundamental frequency motor drive applications Hence, this paper contributes to the understanding of the benefits of SiC inverters as applied to high-speed or high-fundamental frequency drives This research investigates the high switching frequency capabilities of SiC inverter to improve the performance of high-speed machines or high fundamental frequency operation and achieve lower weight and volume of the both motor and inverter

Third Harmonic Exploitation in Passive UHF RFID

Abstract: This paper unfolds the recent concept of using harmonic signals generated by the nonlinear behavior of traditional passive UHF RF identification (RFID) chips. The harmonics generation of passive RFID chips is analyzed to highlight the influences of the matching network and the tag antenna. The proposed study relies on a theoretical model that explains the role in the harmonic production of different elements constituting the tag. The model also shows how to achieve a second communication channel exploiting the third harmonic frequency in addition to the fundamental frequency channel. Specifications and methodology are explained in a harmonic communication scenario. The regulations, harmonic RFID reader considerations, harmonic tag guidelines design, and metrics for its evaluation are discussed. In compliance with the standard regulations EPC Class-1 Gen2 RFID, a design example is presented. The performance of the solution is illustrated from simulation and measurements. The prototype example operates simultaneously at fundamental and third harmonic frequencies with a read range greater than 4.5 m.

Analytical Formulas for Phase Voltage RMS Squared and THD in PWM Multiphase Systems

Abstract: The analysis and assessment of the pulsewidth modulation (PWM) techniques is commonly based on the comparison of the total harmonic distortion (THD) results. THD is usually calculated by application of the Fourier transformation and by taking a limited number of harmonics into the consideration. In this paper, derivation of analytical formulas for the phase voltage THD is presented. The considered system is a symmetrical multiphase starconnected load, supplied from a multilevel pulsewidth-modulated voltage-source inverter (VSI, three-phase case is also covered). The solution is based on the Parseval’s theorem, which links frequency spectrum and time domain through the average power (i.e., rootmean- square (rms) squared value) of the signal. The assumption throughout the derivations is that the ratio of the switching to fundamental frequency is high. Derivations are based on the integration of the power of the PWM signal in a single switching period over the fundamental period of the signal. Only ideal sinusoidal reference voltages are analyzed, and no injection of any type is considered. Formulas for phase voltage THD for any number of phases are derived for two- and three-level cases, for themost commonly used carrier-based methods. Comparison of the analytically obtained curves with simulation and experimental results shows a high level of agreement and validates the analysis and derivations.

Single-Phase Grid Voltage Frequency Estimation Using Teager Energy Operator-Based Technique

Abstract: This paper reports the performance of a technique for the estimation of single-phase grid voltage fundamental frequency under distorted grid conditions. The technique combines a Teager energy operator (TEO) with a frequency adaptive bandpass filter (BPF). The TEO is based on three consecutive samples and is used to estimate the fundamental frequency. The BPF relies on a recursive discrete Fourier transform (RDFT) and an inverse RDFT, and is used to extract the normalized amplitude of the grid voltage fundamental component. The technique is computationally efficient and can also reject the negative effects caused by dc offset and harmonics. It requires less computational effort, can provide faster estimation, and is also less affected by harmonics as compared with a technique relying on the RDFT-based decomposition of the single-phase system into orthogonal components. The performance of the technique is verified using both simulation and experimental results.

Triangular Microwave Waveforms Generation Based on an Optoelectronic Oscillator

Abstract: We demonstrate a novel scheme to generate full-duty-cycle triangular microwave waveforms using an optoelectronic oscillator (OEO). The OEO produces high-quality local oscillator signal. Thus, an external microwave source, which is usually involved in orthodox approaches obviates the need. A polarization modulator is involved in both the OEO loop and a microwave photonic filter (MPF) structure. To generate a triangular waveform, the undesired electrical harmonics are suppressed by the MPF. The proposed method is theoretically analyzed and experimentally verified. Triangular waveforms at fundamental tone of 4.6 GHz and frequency doubling tone of 9.2 GHz are generated, which fit well with the stimulated ones. The root mean square errors between the generated and the simulated triangular waveforms are 6.6e-5 and 1.61e-3 for triangular pulses at 4.6 and 9.2 GHz, respectively.

Optimal Low Switching Frequency Pulsewidth Modulation of Nine-Level Cascade Inverter

Abstract: Synchronous optimal pulsewidth modulation (SOP) permits low switching frequency modulation of multilevel inverter for medium-voltage high-power industrial ac drives without compromising on total harmonic distortion (THD). An aim of our experiment was to operate a nine-level cascade inverter of an induction motor drive at an average device switching frequency limited to rated fundamental frequency by using SOP technique. To reduce the number of separate dc sources, a three-level diode clamped converter was used as a cell in the nine-level cascade inverter. Using SOP technique, optimal nine-level waveforms were obtained by ofline optimization assuming steady-state operation of the induction machine. The switching angles for each semiconductor switch are then obtained from optimal nine-level waveforms based on the criteria to minimize the switching frequency as well as unbalance in dc-link capacitor voltages. Experimental results obtained from the 1.5-kW induction motor drive show THD 5% for stator currents. The results indicate that SOP technique reduces the switching frequency of operation without compromising on THD.