Third harmonic distortion calculation of a self-oscillating power amplifier

It is difficult to analyze the harmonic distortion of a self-oscillating power amplifier (SOPA),because the SOPA is a hard nonlinear system without an external clock.The single or multiple sinusoidal inputs describing function (DF) method is commonly used to linearize a nonlinear element,but this method considers only the components at the same frequencies as the input signals (i.e.,fundamental components) at the nonlinear element's output.In this paper,besides the fundamental components,the third harmonic components are also calculated at the output of a comparator with three sinusoidal inputs,to create a linearized model of the comparator,and thus of the SOPA.The third harmonic distortion of the SOPA is calculated.The models of the zeroth and the first order SOPA are verified by behavioral simulation using MATLAB.

Rotor Position Estimation for Single-and Dual-Three-Phase Permanent Magnet Synchronous Machines Based on Third Harmonic Back-EMF under Imbalanced Situation

In this paper,an improved rotor position estimation strategy based on third harmonic back-EMF for single-and dual-three-phase permanent magnet synchronous machines(PMSMs)under imbalanced situation is proposed.Due to the imbalanced machine impedance,back-EMF or sensing resistor network,the measured triplen harmonic back-EMF will contain certain fundamental component distortion which may severely deteriorate the performance of rotor position estimation.With the aid of the fundamental component compensator,this distortion can be significantly compensated,and the rotor position estimation error can be minimized considerably.The proposed strategy has been implemented on a dSPACE platform with a prototype of dual-three-phase PMSM with serious imbalanced parameters,and operate at single-and dual-three-phase conditions.The experimental results prove that the proposed strategy can significantly improve the steady-state and dynamic performance of rotor position estimation under imbalanced situation.

Enhanced wide-angle third-harmonic generation in flat-band-engineered quasi-BIC metagratings

Nonlinear metasurfaces and photonic crystals provide a significant way to generate and manipulate nonlinear signals owing to the resonance-and symmetry-based light-matter interactions supported by the artificial structures.However,the nonlinear conversion efficiency is generally limited by the angular dispersion of optical resonances especially in nonparaxial photonics.Here,we propose a metagrating realizing a quasi-bound-state in the continuum in a flat band to dramatically improve the third harmonic generation(THG)efficiency.A superior operating angular range is achieved based on the interlayer and intralayer couplings,which are introduced by breaking the mirror symmetry of the metagrating.We demonstrate the relation of angular dispersion between the nonlinear and linear responses at different incident angles.We also elucidate the mechanism of these offaxis flat-band-based nonlinear conversions through different mode decomposition.Our scheme provides a robust and analytical way for nonparaxial nonlinear generation and paves the way for further applications such as wide-angle nonlinear information transmission and enhanced nonlinear generation under tight focusing.

Generation of femtosecond laser pulses at 263 nm by K_3B_6O_(10)Cl crystal

The third harmonic generation(THG) of a linear cavity Ti:sapphire regenerative amplifier by use of a K_3B_6O_(10)Cl(KBOC) crystal is studied for the first time. Output power up to 5.9 mW is obtained at a central wavelength of 263 nm,corresponding to a conversion efficiency of 4.5% to the second harmonic power. Our results show a tremendous potential for nonlinear frequency conversion into the deep ultraviolet range with the new crystal and the output laser power can be further improved.

Design optimization of 3.9GHz fundamental power coupler for the SHINE project

The third harmonic superconducting cryomodule is being designed for the Shanghai High repetition rate XFEL and Extreme light facility(SHINE)project,which is under construction.In contrast to the European X-ray Free Electron Laser(E-XFEL)project,the 3.9 GHz cryomodules in the SHINE project will operate in the continuous wave regime with higher radio frequency average power for both cavities and couplers.We propose a 3.9 GHz fundamental power coupler with an adjustable antenna length,for satisfying the SHINE project requirements.Here,we describe the 3.9 GHz fundamental power coupler's design considerations and power requirements for various operating modes of the SHINE Linac.We also present the results of the radio frequency simulation and optimization,including the studies on multipacting and thermal analysis of the proposed 3.9 GHz coupler.

A method of improving SFDRs of 1-bit signals for a monobit receiver

This paper proposes a method to improve the spu-rious-free dynamic ranges(SFDRs)of 1-bit sampled signals greatly,which is very beneficial to multi-tone signals detection.Firstly,the relationship between the fundamental component and the third harmonic component of 1-bit sampled signals is analyzed for determining four contiguous special frequency bands,which do not contain any third harmonics inside and co-ver 77.8%of the whole Nyquist sampling frequency band.Then,we present a special 4-channel monobit receiver model,where appropriate filter banks are used to obtain four desired pass bands before 1-bit quantization and each channel can sample and process sampled data independently to achieve a good in-stantaneous dynamic range without sacrificing the real-time per-formance or computing resources.The simulation results show that the proposed method effectively eliminates the effect of the most harmonics on SFDRs and the mean SFDR is increased to to 20 dB.Besides,the multi-signals simulation results indicate that the maximum amplitude separation(dynamic range)of two signals in each channel is 12 dB while the proposed monobit re-ceiver can deal with up to eight simultaneous arrival signals.In general,the designing method proposed in this paper has a po-tential engineering value.

Zero-sequence Current Suppressing Strategy for Dual Three-phase Permanent Magnet Synchronous Machines Connected with Single Neutral Point

Dual three-phase permanent-magnet synchronous machines(DTP-PMSM)connected with a single neutral point provide a loop for zero-sequence current(ZSC).This paper proposes a novel space vector pulse width modulation(SVPWM)strategy to suppress the ZSC.Five vectors are selected as basic voltage vectors in one switching period.The fundamental and harmonic planes and the zero-sequence plane are taken into consideration to synthesis the reference voltage vector.To suppress the ZSC,a non-zero zero-sequence voltage(ZSV)is generated to compensate the third harmonic back-EMF.Rather than triangular carrier modulation,the sawtooth carrier modulation strategy is used to generate asymmetric PWM signals.The modulation range is investigated to explore the variation of modulation range caused by considering the zero-sequence plane.With the proposed method,the ZSC can be considerably reduced.The simulated and experimental results are presented to validate the effectiveness of the proposed modulation strategy.

Vibration Reduction and Torque Improvement of Integral-slot SPM Machines Using PM Harmonic Injection

This study aimed to improve the vibration and torque of an integral-slot surface-mounted permanent magnet(SPM)machine by optimizing the shape of the harmonically injected permanent magnet(PM).First,the effect of the third harmonic injected into the sinusoidal PM shape on the electromagnetic performance of a 36-slot/12-pole SPM machine was investigated,including the torque performance and vibration response.It was found that the Sin+3rd harmonic-shaped PM had a contrary effect on the torque and vibration performance of the integral-slot machine,which improved the torque capability but worsened the vibration performance.Second,the response surface model and Barebones multi-objective particle swarm optimization algorithm based on a trade-off between the average torque and vibration were implemented to determine the optimal harmonic injection.Subsequently,the performances of the optimal Sin+3rd-shaped and eccentric PM machines were compared,showing the excellent torque and vibration performance of the adopted method.Finally,a prototype was manufactured and tested to verify the results of the theoretical analysis.

High-energy,high-repetition-rate ultraviolet pulses from an efficiency-enhanced,frequency-tripled laser

In this study,a high-energy,temporally shaped picosecond ultraviolet(UV)laser running at 100 Hz is demonstrated,with its pulses boosted to 120 mJ by cascaded regenerative and double-pass amplifiers,resulting in a gain of more than 10^(8).With precise manipulation and optimization,the amplified laser pulses were flat-top in the temporal and spatial domains to maintain high filling factors,which significantly improved the conversion efficiency of the subsequent third harmonic generation(THG).Finally,91 mJ,470 ps pulses were obtained at 355 nm,corresponding to a conversion efficiency as high as 76%,which,as far as we are aware of,is the highest THG efficiency for a high-repetition-rate picosecond laser.In addition,the energy stability of the UV laser is better than 1.07%(root mean square),which makes this laser an attractive source for a variety of fields including laser conditioning and micro-fabrication.

Structure and principles of self-assembly of giant“sea urchin”type sulfonatophenyl porphine aggregates

Principles of molecular self-assembly into giant hierarchical structures of hundreds of micrometers in size are studied in aggregates of meso-tetra(4-sulfonatophenyl)porphine(TPPS_(4)).The aggregates form a central tubular core,which is covered with radially protruding filamentous non-branching aggregates.The filaments cluster and orient at varying angles from the core surface and some filaments form bundles.Due to shape resemblance,the structures are termed giant sea urchin(GSU)aggregates.Spectrally resolved fluorescence microscopy reveals J-and H-bands of TPPS_(4)aggregates in both the central core and the filaments.The fluorescence of the core is quenched while filaments exhibit strong fluorescence.Upon drying,the filament fluorescence gets quenched while the core is less affected,showing stronger relative fluorescence.Fluorescencedetected linear dichroism(FDLD)microscopy reveals that absorption dipoles corresponding to J-bands are oriented along the filament axis.The comparison of FDLD with scanning electron microscopy(SEM)reveals the structure of central core comprised of multilayer ribbons,which wind around the core axis forming a tube.Polarimetric second-harmonic generation(SHG)and thirdharmonic generation microscopy exhibits strong signal from the filaments with nonlinear dipoles oriented close to the filament axis,while central core displays very low SHG due to close to centrosymmetric organization.Large chiral nonlinear susceptibility points to helical arrangement of the filaments.The investigation shows that TPPS_(4)molecules form distinct aggregate types,including chiral nanotubes and nanogranular aggregates that associate into the hierarchical GSU structure,prototypical to complex biological structures.The chiral TPPS_(4)aggregates can serve as harmonophores for nonlinear microscopy.