Showing papers on "Fundamental frequency published in 2019"

Harmonic Stability in Power Electronic-Based Power Systems: Concept, Modeling, and Analysis

Abstract: The large-scale integration of power electronic-based systems poses new challenges to the stability and power quality of modern power grids. The wide timescale and frequency-coupling dynamics of electronic power converters tend to bring in harmonic instability in the form of resonances or abnormal harmonics in a wide frequency range. This paper provides a systematic analysis of harmonic stability in the future power-electronic-based power systems. The basic concept and phenomena of harmonic stability are elaborated first. It is pointed out that the harmonic stability is a breed of small-signal stability problems, featuring the waveform distortions at the frequencies above and below the fundamental frequency of the system. The linearized models of converters and system analysis methods are then discussed. It reveals that the linearized models of ac–dc converters can be generalized to the harmonic transfer function, which is mathematically derived from linear time-periodic system theory. Lastly, future challenges on the system modeling and analysis of harmonic stability in large-scale power electronic based power grids are summarized.

Multi-Frequency Multi-Power One-to-Many Wireless Power Transfer System

Abstract: This paper proposes and implements a novel multi-frequency multi-power wireless power transfer (MFMP-WPT) system based on one single transmitter for simultaneously and compatibly energizing multi-standard receivers. Generally, implementing a multi-frequency WPT often requires a compromise in system complexity, control difficulty, switching frequency, or transmission efficiency. By using only a single transmitter with an artful inverter topology, the proposed MFMP-WPT system can effectively achieve multi-frequency multi-magnitude superposition and switching frequency reduction while maintaining the control fitness and convenience of square-wave generation with 50% duty cycle. Moreover, by switching at the fundamental frequency in a range of 80–130 kHz, the single transmitter becomes competent for one-to-many MFMP-WPT operation for diverse wireless power on-demands. Consequently, the fundamental and high-order harmonic wireless energies with multiple power levels can be, respectively, picked up by the multi-standard receivers, depending on their energy requirements. The experimental transmission and system efficiencies can reach 81.57% and 64.74% under MFMP-WPT, respectively. Theoretical analysis, computer simulation, and experimental results are provided to verify the feasibility of the proposed MFMP-WPT system.

Atomically Thin Nonlinear Transition Metal Dichalcogenide Holograms.

Abstract: Nonlinear holography enables optical beam generation and holographic image reconstruction at new frequencies other than the excitation fundamental frequency, providing pathways toward unprecedented...

An Improved CPS-PWM Scheme-Based Voltage Balancing Strategy for MMC With Fundamental Frequency Sorting Algorithm

Abstract: In this paper, a new voltage balancing strategy based on improved carrier-phase-shifted pulsewidth modulation (CPS-PWM) scheme and fundamental frequency sorting algorithm (FFSA) is proposed. FFSA is a salient method which sorts the capacitor voltages at fundamental frequency and utilizes the different charging ability of driving signals to converge the capacitor voltages. Unfortunately, under the CPS-PWM scheme with high carrier frequency, 250 Hz or higher, FFSA cannot bring the capacitor voltage to the nominal value once the unbalance occurs, because there is a little difference remaining in the driving signal's charging ability. To avoid this disadvantage, an improved CPS-PWM scheme is proposed. In this scheme, driving signals with proper phase angle differences are selected to be dealt with logic and/or processing according to the sorting result of FFSA. With the logic processing, new driving signals with obviously different charging abilities are synthesized, which are assigned to the corresponding unbalanced submodules to achieve the balance of capacitor voltages. And several regions for logic processing are set up, where the proper phase angle difference is selected for each region in order to both guarantee the convergence speed and avoid the voltage oscillations. With the proposed scheme, FFSA can be adopted under CPS-PWM with high carrier frequency. Moreover, the merits of FFSA are inherited, such as the reduced computational burden and the elimination of arm current detection. Performance and effectiveness of the proposed strategy are validated by both simulations and experimental results.

High-order harmonic mode-locked Yb-doped fiber laser based on a SnSe2 saturable absorber

Abstract: In this paper, tin diselenide (SnSe2) was successfully prepared with liquid phase exfoliation method and embedded into polyvinyl alcohol (PVA) as a saturable absorber (SA) for obtaining harmonic mode-locked Yb-doped fiber laser generations. Based on the fundamental frequency of 333 kHz, four kinds of high-order harmonic mode-locking (HML) with frequencies of 400, 460, 520 and 550 MHz were achieved, corresponding to 1200th, 1380th, 1560th and 1650th order harmonics, with maximum signal to noise ratios (SNRs: 40.55, 37.72, 36.42 and 34.18 dB) and maximum 3 dB spectrum widths (0.2043, 0.3448, 0.216 and 0.3033 nm) as well as minimum pulse widths (759.9, 567.7, 717.3 and 561.4 ps), respectively. This was the first demonstration focusing on the application of SnSe2 in high-order harmonic mode-locked Yb-doped fiber lasers and our results fully proved that SnSe2 had excellent performance in designing high frequency ultra-fast fiber lasers.

A SiGe-Based 240-GHz FMCW Radar System for High-Resolution Measurements

Abstract: In this paper, a fully integrated silicon-germanium (SiGe)-based compact high-resolution frequency-modulated continuous-wave (FMCW) radar sensor working in a frequency range from 198 to 250 GHz is presented. The wide modulation bandwidth of 52 GHz enables a range resolution better than 3 mm combined with a measurement accuracy in the micrometer regime. Together with a low power consumption of approximately 3.5 W, a high-focusing Teflon lens antenna, and a compact and robust housing, the presented radar system is capable of satisfying the needs of several novel measuring tasks. A compensated measurement accuracy of down to −0.5–0.4 $\mu \text{m}$ is achieved, which is demonstrated by distance measurements using a laser interferometer reference. Additionally, a calibration technique is shown enabling multi-target measurements reaching to the theoretical limit of the range resolution. As the fundamental feedthrough of common frequency doubler architectures cause false targets in the range profile, a dielectric fundamental frequency filter is presented as well, filtering the fundamental feedthrough signal and thus removing the false target, improving the unambiguousness of the presented radar sensor.

Static response and free vibration of MEMS arches assuming out-of-plane actuation pattern

Abstract: In this research work, the nonlinear structural behavior of a non-parallel plates micro-actuator design is investigated via a reduced-order modeling. The micro-actuator is considered to be made of an initially flexible curved doubly-clamped microbeam and two evenly arranged stationary rectangular shaped out-of-plane electrodes of different lengths. The subsequent actuating attractive electrostatic force is mainly formed by the unevenness of the electric fringing-fields (non-parallel) electrodes arrangement. Results of this numerical investigation show that by increasing the actuation voltage the shallow arch behavior tend to reach a softening like behavior, mainly due to its dominant flexibility effect. With a further increase in the actuation voltage, the micro-arch starts to stretch and thus develops a hardening like behavior. Furthermore, and for certain values of the design parameters (mainly the shape and the length of the stationary electrodes), the shallow arch presented a snap-through like bi-stability behavior. Indeed, when the voltage approaches a certain critical value, the micro-arch static profile alters from a symmetrical shape to an asymmetric one, thus showing a symmetry breaking like behavior that depends a lot on the shape and length of the stationary non-parallel actuating electrodes. It is also demonstrated that by varying few of the micro-actuator design parameters, the variation of the normalized fundamental frequency showed rises and declines for certain ranges of the applied bias voltage. This approves that with such electrostatically actuated micro-actuator design, and with a smart tuning of its geometrical design parameters, one can obtain softening as well as hardening like behaviors. Modes frequency variations curves showed also that for certain actuation DC loads, it is possible to achieve a one-to-one internal resonance state involving both the first symmetric and the first antisymmetric modes of the shallow micro-arch.

PWM Frequency Noise Cancellation in Two-Segment Three-Phase Motor Using Parallel Interleaved Inverters

Abstract: This paper proposed a novel method for two-segment three-phase motor to eliminate the harmonics nearby pulsewidth modulation (PWM) frequency. Due to PWM technique and switching losses considerations, ear-piercing high-frequency electromagnetic noise in drive system is common. By using magnetically coupled inductors (MCIs) and interleaved technique, the proposed novel method is able to remove the high-frequency harmonics located nearby the PWM frequency and other odd multiples in two-segment three-phase motor. With this method, the unpleasant acoustic noise could be removed when the PWM frequency is selected near 10 kHz. The size of MCIs mainly depends on the PWM frequency harmonic currents rather than the fundamental frequency currents. Thus, its size is very small compared with LC filter. Moreover, this method remains the control dynamics of two-segment three-phase motor without additional inductance for fundamental-frequency currents. The shift phase of two inverters PWM carriers is π, which is simple to implement. Finally, the effectiveness of the proposed method is verified by experimental results.

Control of electron dynamics, radical and metastable species generation in atmospheric pressure RF plasma jets by Voltage Waveform Tailoring

Abstract: Atmospheric pressure capacitively coupled radio frequency discharges operated in He/N2 mixtures and driven by tailored voltage waveforms are investigated experimentally using a COST microplasma reference jet and by means of kinetic simulations as a function of the reactive gas admixture and the number of consecutive harmonics used to drive the plasma. Pulse-type 'peaks'-waveforms, that consist of up to four consecutive harmonics of the fundamental frequency (f = 13.56 MHz), are used at a fixed peak-to-peak voltage of 400 V. Based on an excellent agreement between experimental and simulation results with respect to the DC self-bias and the spatio-temporal electron impact excitation dynamics, we demonstrate that Voltage Waveform Tailoring allows for the control of the dynamics of energetic electrons, the electron energy distribution function in distinct spatio-temporal regions of interest, and, thus, the generation of atomic nitrogen as well as helium metastables, which are highly relevant for a variety of technological and biomedical applications. By tuning the number of driving frequencies and the reactive gas admixture, the generation of these important species can be optimised. The behaviour of the DC self-bias, which is different compared to that in low pressure capacitive radio frequency plasmas, is understood based on an analytical model.

A New Pulse Active Width Modulation for Multilevel Converters

Abstract: This paper proposes a new pulse amplitude width modulation (PAWM) procedure for cascaded H-bridge multilevel inverters fed by dc voltage sources with unequal amplitudes. With proposed procedure, the generated output voltage is obtained modulating a sinusoidal reference signal at the desired fundamental frequency with equally spaced switching angles. It has been analytically demonstrated that, under these assumptions, all harmonics except those of order $n=2kl\pm 1$ , $k=1,2,\ldots$ are deleted from the output voltage waveform. After a detailed description of the method and a comparative analysis with others existing in the literature, its harmonics elimination capability has been experimentally verified with 5-, 7-, 9-, and 11-level cascaded H-bridge inverters, moreover, it has been mathematically demonstrated that it reduces total harmonic distortion below 5% with a 17-level inverter and it is capable of eliminating the first 49 harmonics considered by standards with a 27-level inverter.

Adaptive CDSC-Based Open-Loop Synchronization Technique for Dynamic Response Enhancement of Active Power Filters

Abstract: The shunt active power filters (SAPFs) are broadly utilized to improve the power quality (PQ) issues of electric power systems. A crucial issue in implementing these filters is the accurate estimation of the grid voltage phase/frequency. Indeed, the dynamic behavior and the performance of the SAPF strongly rely on this point. To deal with this challenge, a fast yet effective open-loop synchronization (OLS) technique based on Cascaded Delayed Signal Cancellation (CDSC) is presented in this paper. The proposed technique can reject the odd-order harmonics, the DC offset of the grid voltage, and its dynamic response during transients take an only half cycle of the fundamental frequency. To adapt the proposed OLS technique to the frequency changes, an efficient frequency estimator is also presented. The effectiveness of the proposed OLS technique is demonstrated using simulation and experimental results.

X-ray harmonic generation by orthogonally polarized two-color fields: Spectral shape and polarization

Abstract: Orthogonally polarized two-color fields, typically with a frequency ratio of 2:1, only rarely of 3:1, have been utilized for a variety of purposes. Driving high-order harmonic generation (HHG), the former yield linearly and the latter elliptically polarized harmonics. With emphasis on the 3:1 frequency ratio, we investigate the shape of the HHG spectrum for the fundamental frequency being in the midinfrared range (2200 nm). Depending on the relative phase between the two field components, a plethora of spectral shapes can be realized. For a suitable phase, the harmonic power can be concentrated within the highest 10% of the spectrum. The results are analyzed in terms of quantum orbits. For the 3:1 case, the scheme suggests an efficient table-top source of elliptically polarized soft x rays.

SPICE: Self-supervised Pitch Estimation

Abstract: We propose a model to estimate the fundamental frequency in monophonic audio, often referred to as pitch estimation. We acknowledge the fact that obtaining ground truth annotations at the required temporal and frequency resolution is a particularly daunting task. Therefore, we propose to adopt a self-supervised learning technique, which is able to estimate pitch without any form of supervision. The key observation is that pitch shift maps to a simple translation when the audio signal is analysed through the lens of the constant-Q transform (CQT). We design a self-supervised task by feeding two shifted slices of the CQT to the same convolutional encoder, and require that the difference in the outputs is proportional to the corresponding difference in pitch. In addition, we introduce a small model head on top of the encoder, which is able to determine the confidence of the pitch estimate, so as to distinguish between voiced and unvoiced audio. Our results show that the proposed method is able to estimate pitch at a level of accuracy comparable to fully supervised models, both on clean and noisy audio samples, although it does not require access to large labeled datasets.

Exploiting Third Harmonic of Differential Charge Pump for Wireless Power Transfer Antenna Alignment

Abstract: Wireless power transfer (WPT) always suffers from the antenna radiation direction and polarization misalignments between the base station and the WPT terminal. In this letter, the third harmonic of a differential charge pump is exploited for antenna alignment with only one pair of antennas. Due to the intrinsic nonlinearity of diodes, the third harmonic can be generated and reflected by the differential charge pump. A ring coupler is employed to distribute the received fundamental frequency power for rectification by the differential charge pump and couple the third-harmonic generation back to its input port. Such third-harmonic power is feedback by a dual-band antenna operating at the third-harmonic frequency. In consequence, the WPT antennas can be aligned by obtaining the maximum third-harmonic feedback at the base station. The whole system is theoretically analyzed and experimentally validated.

Harmonic RFID Communication Using Conventional UHF System

Abstract: In this paper, a harmonic radio frequency identification (hRFID) system is proposed to overcome the challenges that limits the capabilities of a conventional UHF radio frequency identification (RFID) system, such as self-jamming and multi-path interference without any extensive modifications to the existing infrastructure. The proposed system exploits the third harmonic generation from the existing RFID chips for communication. The system is realized by designing an additional RF interface layer between the conventional RFID interrogator and an RFID tag. The interface layer transmits the query signal at the fundamental frequency and receives the backscattered harmonic signal from an RFID tag. It down converts the backscattered third harmonic signal to the fundamental frequency, and feeds it back to the conventional UHF interrogator for extracting the information. A dual band antenna design is also shown for improving the radiation efficiency of hRFID tags using a conventional RFID ICs with improved signal to noise ratio (SNR) and increased read range. A path is shown for improving an hRFID system by performing a study that relates the read range, RFID IC’s sensitivity, and the noise level with efficiency. The proposed system can be easily adapted to any of the current RFID applications.

Generalized Class-E Power Amplifier With Shunt Capacitance and Shunt Filter

Abstract: This paper presents a generalized analysis of the Class-E power amplifier (PA) with a shunt capacitance and a shunt filter, leading to a revelation of a unique design flexibility that can be exploited either to extend the maximum operating frequency of the PA or to allow the use of larger active devices with higher power handling capability. The proposed PA fulfills zero voltage switching (ZVS) and zero voltage derivative switching (ZVDS) conditions, resulting in a theoretical dc-to-RF efficiency of 100%. Explicit design equations for the load-network parameters are derived, and the analytical results are confirmed by harmonic-balance simulations. Two PA prototypes were constructed with one designed at low frequency and the other at high frequency. The first PA, which employs a MOSFET and a lumped-element load-network, delivered a peak drain efficiency $(\!D\!E)$ of 93.3% and a peak output power of 37 dBm at 1 MHz. The second PA, which employs a GaN HEMT and a transmission-line (TL) load-network to provide the drain of the transistor with the required load impedances at the fundamental frequency as well as even and odd harmonic frequencies, delivered a peak $D\!E$ of 90.2% and a peak output power of 39.8 dBm at 1.37 GHz.

Energy Storage Requirement Optimization of Hybrid Modular Multilevel Converter With Circulating Current Injection

Abstract: This paper analyzes the characteristics of the submodule (SM) voltage fundamental frequency and second-order harmonic ripples with the consideration of negative voltage state of the full-bridge SM. The optimal operation point, which minimizes the fundamental frequency ripples, is derived. Both the design principle and analytical expressions for SM capacitance dimensioning are presented, and the comparison between energy storage requirements with and without negative voltage states in the arm reference voltages are also carried out under the same constraints on the transmission power, modulation index, and SM voltage fluctuations. However, the SM voltage fundamental frequency ripples increase significantly with reactive power increasing. Therefore, a circulating current injection (CCI) method is proposed in order to suppress the ripples caused by reactive power. Comparative simulations on a ±200 kV hybrid modular multilevel converter (MMC) and experimental results on a laboratory prototype verified the correctness of the presented design principle and the effectiveness of the proposed CCI method. It is shown that the energy storage requirements of the hybrid MMC with negative voltage in arm reference voltages can be reduced about 15%, and it achieves a significant reduction about 45% with the proposed CCI method.

Stator Harmonic Current Suppression for DFIG System Considering Integer Harmonics and Interharmonics

Abstract: This paper presents a stator harmonic current suppression method for a doubly fed induction generator (DFIG) under the distorted grid voltage with the consideration of integer harmonics and interharmonics. In the proposed control strategy, the stator current incomplete derivation controller instead of the resonant controller or a repetitive controller is employed to eliminate the negative impacts on the stator current caused by the distorted grid voltage. This approach can provide both the good dynamic response and the strong rejection ability against the integer harmonic voltages with the fixed frequency and the interharmonic voltages with the unfixed frequency. Based on the mathematic model of the DFIG, the stator current incomplete derivation feedback is designed in detail. Then, the robustness against the fundamental frequency variations and the DFIG parameter deviations is analyzed. Finally, the experimental results are presented to validate the effectiveness of the proposed control strategy.

Frequency-doubling effect in acoustic reflection by a nonlinear, architected rotating-square metasurface.

Abstract: Nonlinear acoustic metamaterials offer the potential to enhance wave control opportunities beyond those already demonstrated via dispersion engineering in linear metamaterials. Managing the nonlinearities of a dynamic elastic system, however, remains a challenge, and the need now exists for new strategies to model and design these wave nonlinearities. Inspired by recent research on soft architected rotating-square structures, we propose herein a design for a nonlinear elastic metasurface with the capability to achieve nonlinear acoustic wave reflection control. The designed metasurface is composed of a single layer of rotating squares connected to thin and highly deformable ligaments placed between a rigid plate and a wall. It is shown that during the process of reflection at normal incidence, most of the incoming fundamental wave energy can be converted into the second harmonic wave. A conversion coefficient of approximately 0.8 towards the second harmonic is derived with a reflection coefficient of <0.05 at the incoming fundamental frequency. The theoretical results obtained using the harmonic balance method for a monochromatic pump source are confirmed by time-domain simulations for wave packets. The reported design of a nonlinear acoustic metasurface can be extended to a large family of architected structures, thus opening new avenues for realistic metasurface designs that provide for nonlinear or amplitude-dependent wave tailoring.

Analytical Evaluation and Reduction of Torque Harmonics in Induction Motor Drives Operated at Low Pulse Numbers

Abstract: Induction motor drives operated with a low ratio of the switching frequency to the fundamental frequency (i.e., pulse number) are prone to have high magnitudes of low-order torque harmonics. This paper proposes a method to analytically evaluate the harmonic torque spectrum based on the pulsewidth-modulated voltage waveforms for low pulse number operation. The predicted torque harmonic spectra for different pulsewidth-modulated waveforms are validated through simulations and experiments. This paper also reports optimal switching angles to minimize the total rms value of torque harmonics of order 6, 12, 18 $,\dots,$ $6(N-1)$ , considering the number of switching angles per quarter ( $N$ ) to be 4 and 5. Compared to sine triangle pulsewidth modulation and selective harmonic elimination pulsewidth modulation with the same pulse number, the proposed optimal switching angles significantly reduce the total rms value of all harmonic torques of order lower than $6N$ . Extensive simulation and experimental results on a 3.7-kW induction motor drive are presented to demonstrate the superior performance of the proposed optimal pulsewidth modulation.