Distortion Compensation Research Articles

An Enhanced Power Sharing Scheme With Voltage Unbalance and Distortion Compensation in an Islanded AC Microgrid Using CSF‐MPC

ABSTRACTThis paper presents an enhanced power sharing scheme (EPSS) for parallelly connected distributed generators (DGs) in an islanded microgrid (MG) using a constant switching frequency‐model predictive control (CSF‐MPC). Unlike conventional droop control, wherein only accurate real power sharing among DGs is possible, the EPSS enables accurate sharing of reactive and harmonic powers even under mismatched line impedances. Additionally, the voltage unbalance and distortion at the point of common coupling (PCC) are mitigated. The EPSS is implemented using a reference voltage that consists of (1) the fundamental droop control; (2) the virtual impedance control; (3) the unbalance compensation control; and (4) the harmonic compensation control. The performance of the EPSS is tested on a MG consisting of two DGs of both similar and dissimilar capacities under a step changes in loads. The EPSS is implemented using CSF‐MPC, which offers superior performance compared with conventional proportional plus integral and proportional resonant controllers. The simulation and hardware‐in‐loop results confirm the effectiveness of the EPSS in addressing power sharing issues and mitigating both distortion and unbalance of PCC voltage.

Ultrasound-assisted aberration correction of transcranial photoacoustic imaging based on angular spectrum theory

To correct the refraction aberration induced by the skull in photoacoustic imaging, a method for phase distortion compensation is proposed based on the angular spectrum theory with the aid of ultrasonic signals. This method first updates the speed of sound distribution by iteratively performing aberration correction in the ultrasonic reconstruction. Then the speed of sound distribution obtained with ultrasound-assisted serves as prior knowledge to address phase distortion compensation by adjusting the phase shift factor of the wavefront in different media. Finally, the aberration-corrected ultrasonic-photoacoustic dual-modality image can be obtained. Numerical simulations and phantom experiments confirm the effectiveness of this method. Specifically, in simulations, the position error of the proposed method is reduced from −13.61% to 1.27% in depth compared to the method based on the reconstruction with constant speed. Moreover, a real ex-vivo rabbit skull experiment illustrates the potential biological application of the proposed method in transcranial photoacoustic imaging.

An improved digital predistortion scheme for nonlinear transmitters with limited bandwidth

In modern wireless communication systems, wide signal bandwidth is the most straightforward approach to accommodate high data rates. Wide signal bandwidth, on the other hand, introduces severe challenges to the power amplifier (PA) and digital predistortion (DPD) design in both performance and cost. Conventional DPD systems usually ignore the impact of the transmit low-pass filter (Tx LPF) bandwidth and assume the transmit bandwidth is sufficiently large. In wideband signal transmissions, the bandwidth of Tx LPF can become the system bottleneck, limiting DPDs compensation effects. Existing DPD studies mostly investigate the DPD with reduced feedback bandwidth. In this paper, we study the impact of Tx LPF bandwidth on the DPD performance. A full-band error minimization DPD based on direct learning structure is proposed. The DPD coefficients are estimated by minimizing the full-band error between the input signal and PA output signal in the frequency domain. Furthermore, we propose a weighted DPD with improved performance by introducing a weighting diagonal matrix to the error function. Compared to existing solutions, the weighted DPD achieves a good trade-off between the in-band distortion compensation and out-of-band spectral regrowth suppression. Simulations and experiments validate the effectiveness of the proposed DPD schemes.

Fast phase distortion identification and automatic distortion compensated reconstruction for digital holographic microscopy using deep learning

Digital holographic microscopy (DHM) is a quantitative phase measurement technique with full-field, contactless, and fast. The technique provides accurate micro-surface morphology of samples. These steps are essential for accurate phase reconstruction, such as holographic focusing, numerical diffraction, phase unwrapping and distortion compensation. Performing these processes manually is time-consuming and is not conducive to the general application of the technology. In order to improve the detection efficiency, this paper proposes a deep learning model that can achieve fast identification of DHM phase distortion and automatic phase distortion compensation reconstruction. The model can be preprocessed for holographic phase to accurately identify the type of phase distortion present in the phase. And adaptively adjust the network weight parameters for phase distortion compensation reconstruction. The experimental results show that the method proposed in this paper achieves fast and accurate identification of multiple phase distortions. The model has high accuracy and strong generalization ability. The reconstructed holographic phase map has PSNR of 35.2743dB and RMSE as low as 10-2 level in the face of complex mixed aberrations. The identification and reconstruction processes took 0.005s and 0.058s, both in milliseconds, respectively. The evaluation indexes SSIM, FSIM and NC can reach above 0.99. It is shown that the method in this paper is not only capable of reconstructing holograms, but also able to effectively retain the detailed features of the original image.

Refined speckle contrast estimation in OCT based on compensation of scattering-related distortions of speckle pattern parameters

Abstract Speckle contrast (SC) parameters in optical coherence tomography (OCT) scans are formed by the interplay of several factors—local level of optical wave backscattering by the material inhomogeneities, parameters of spatial distribution of the latter and the degree of cumulative optical wave attenuation during its fourth-and-back propagation. For the optical wavelengths used in OCT, this attenuation is usually dominated by the influence of scattering in the visualized turbid tissues rather than by absorption. For sufficiently high concentrations of scatterers (at least a few scatterers in the coherence volume) characterized by comparable scattering strengths and a fairly homogeneous distribution in space, the interference of locally scattered waves should be characterized by a Rayleigh distribution of speckle amplitudes, for which the local SC tends to 0.52. Equivalently, in terms of speckle intensities, the local SC tends to unity. Local spatial inhomogeneities or strongly uneven scattering strengths lead to the appearance of increased values of SC, which may serve as a diagnostic feature of some tissue components in OCT images. At the same time, in comparison to surface speckles formed by coherent-light scattering from rough surfaces, OCT-beam attenuation during its fourth-and-back propagation may introduce intensity inhomogeneities in OCT scans even for homogeneous tissue areas. This effect results in artefactual distortion of the visible SC in comparison with the above-mentioned expected value. Moreover, the presence of individual strong scatterers may additionally non-locally distort SC values due to the appearance of elongated shadows below such scatterers, which causes lateral inhomogeneities in OCT scans. Here, we propose a refined SC parameter, which is cleaned from distorting scattering-related effects in both axial and lateral directions. Depth-resolved estimation of the optical attenuation coefficient is used to restore attenuation-free OCT scans, for which the refined SC is estimated. The efficiency of the proposed approach is demonstrated using both digital OCT phantoms with highly controlled properties and experimental OCT data.

Impact of receiver bandwidth on the performance of nonlinear volterra equalizer in IM/DD systems

Nonlinear electrical equalization is an effective means to compensate for nonlinear waveform distortions in short-haul intensity-modulation (IM)/direct-detection (DD) optical transmission systems. Nonlinear distortions contain broader spectral components than the original signal. Thus, a wide receiver bandwidth and high sampling rate are beneficial to effective compensation of nonlinear distortions. However, this leads to poor signal-to-noise ratio at the receiver. In this paper, we investigate the impact of receiver bandwidth on the performance of 2nd-order nonlinear Volterra equalizer in IM/DD transmission systems. Through the computer simulation and the experimental verification performed with 4-ary pulse amplitude modulation signals, we show that an optimum receiver bandwidth for bit-error ratio performance increases with the amount of nonlinear distortions in IM/DD systems. We also show that the sampling rate should also be increased to avoid the aliasing of the nonlinear distortion components. The cost of the receiver increased by the wider receiver bandwidth and higher sampling rate could be offset in part by the non-integer fractionally sampled nonlinear Volterra equalizer.

Performance analysis of satellite-to-ground 16QAM coherent optical communication

Abstract Atmospheric turbulence and pointing errors are two major factors affecting satellite-to-ground coherent optical communication links. This study considers the effects of power scintillation and phase jitter caused by atmospheric turbulence, as well as active mode compensation for wavefront phase distortion. Additionally, residual pointing errors due to platform micro-vibrations are taken into account, and a statistical channel model is derived under the combined effects of atmospheric turbulence and residual pointing errors during tracking and acquisition. Based on this model, a closed-form approximate expression for the average bit error rate (BER) of 16QAM satellite-to-ground coherent optical communication is derived using the Meijer-G function. The results show that the derived BER expression matches well with numerical integration results, confirming its accuracy and applicability under various link conditions. Through numerical simulations, the effects of residual pointing error variance, turbulence strength, satellite zenith angle, and transceiver antenna aperture on the performance of 16QAM satellite-to-ground coherent optical communication are evaluated. The findings offer valuable theoretical insights for the design and optimization of future satellite-to-ground 16QAM coherent optical communication systems.

Auto Aligning, Error-Compensated Broadband Collimated Transmission Spectroscopy.

Broadband spectral measurements of the ballistic transmission of scattering samples are challenging. The presented work shows an approach that includes a broadband system and an automated adjustment unit for compensation of angular distortions caused by non-plane-parallel samples. The limits of the system in terms of optimal transmission and detected forward scattering influenced by the scattering phase function are investigated. We built and validated a setup that measures the collimated transmission signal in a spectral range from 300 nm to 2150 nm. The system was validated using polystyrene spheres and Mie calculations. The limits of the system in terms of optimal transmission and detected forward scattering were researched. The optimal working parameters of the system, analyzed by simulations using the Monte Carlo method, show that the transmission should be larger than 10% and less than 90% to allow for a reliable measurement with acceptable errors caused by noise and systematic errors of the system. The optimal transmission range is between 25% and 50%. We show that the phase function is important when considering the accuracy of the measurement. For strongly forward-scattering samples, errors of up to 80% can be observed, even for a very small numerical aperture of 6.6·10-4, as used in our experimental system. We also show that errors increase with optical thickness as the ballistic transmission decreases and the multiscattered fraction increases. In addition, errors caused by multiple reflections in the sample layer were analyzed and also classified as relevant for classical absorption spectroscopy.

Features of the defect structure of a lithium-gradient nonlinear optical single crystal LiNbO3 and their manifestation in the Raman spectra

LiNbO3 crystal with a lithium composition gradient of Li/Nb = 0.8 wt%/cm (Li0.97..1.01Nb1.03..0.99O3) were obtained. A monotonic change in the edge of the UV absorption edge is observed when scanning the surface of the gradient crystal along the growth direction. Raman spectra from different areas of studied crystal were analyzed in a wide frequency range, which includes the region of fundamental vibrations of the crystal lattice (100–900 cm−1) and the region of overtone processes (900–3000 cm−1). A compositionally homogeneous, congruent LiNbO3 crystal was used as a comparison sample. It was found that in the spectra obtained from different parts of the gradient crystal, there is a significant scatter in the frequency values of the lines corresponding to the fundamental vibrations of the crystal lattice, but at the same time, the number of lines corresponding to the fundamental vibrations of the lattice for the gradient and compositionally homogeneous LiNbO3 crystals is the same. Moreover, in the spectrum of a gradient crystal in the region of overtone processes of fundamental vibrations, significantly more lines (35 lines) are observed than in the spectrum of compositionally homogeneous crystals (15 lines). The data obtained show that the state of the defect structure of compositionally homogeneous crystals and gradient LiNbO3 crystal is significantly different. The discovered differences between the defective structure of a gradient crystal and the defective structure of a compositionally homogeneous crystal may be the reason for compensation (damping) of distortions during nonlinear optical conversion of laser radiation by a gradient crystal due to the uneven temperature distribution along the length of the crystal. In compositionally homogeneous crystals, such temperature distortions significantly limit the efficiency of nonlinear optical conversion.

Distortion prediction and geometry compensation using modified inherent strain method for additively manufactured Ti-6Al-4V

A laser powder bed fusion (LPBF) process enables the production of intricate geometries for specialized applications demanding high precision in various industries such as medical, aerospace, and automotive. However, substantial thermal gradients in the LPBF process often led to residual stress, resulting in noticeable distortion and potential part failure of fabricated parts. Therefore, the present work investigates distortion prediction and geometry compensation for additively manufactured Ti-6Al-4V components employing a modified inherent strain method. Unlike previous studies, both relaxed distortions from substrate removal and as-built distortion are considered, incorporating specimens with varying geometrical features such as height and thickness. The study aims to comprehensively evaluate the efficacy of the modified inherent strain approach in capturing distortion under different build scenarios and assess the effectiveness of geometrical compensation in minimizing as-built distortion. Overall, we found that numerical models effectively capture relaxed deflection for samples with varied geometrical features, showing reasonable agreement with experimental results. Additionally, the as-built distortion of samples with thicknesses of 5 mm and above is well-predicted, with an average deviation between numerical and experimental results of approximately 0.125 mm. Nonetheless, we noted the challenge in capturing out-of-plane distortion for thin wedges, suggesting avenues for future investigation. Furthermore, geometry compensation reduces maximum distortion from 0.68 to 0.28 mm and average distortion from 0.15 to 0.05 mm. Multiple iterations of compensation yield insignificant differences in distortion reduction, which suggests sufficient distortion alleviation from single compensation for geometries explored in the present work. Overall, the study provides valuable insights into distortion prediction and compensation strategies for additively manufactured Ti-6Al-4V components.

Neural networks for ID gap orbit distortion compensation in PETRA III

Undulators are used in storage rings to produce extremely brilliant synchrotron radiation. In the ideal case, a perfectly tuned undulator always has a first and second field integrals equal to zero. But, in practice, field integral changes during gap movements can never be avoided for real-life devices. As they significantly impact the circulating electron beam, there is the need to routinely compensate such effects. Deep Neural Networks can be used to predict the distortion in the closed orbit induced by the undulator gap variations on the circulating electron beam. In this contribution several state-of-the-art deep learning algorithms were trained on measurements from PETRA III. The different architecture performances are then compared to identify the best model for the gap-induced distortion compensation. It is found that realistic data, with several gaps moving simultaneously to arbitrary gaps must be used to train the neural networks. The deep feed-forward neural network was found to be more effective than the recurrent and convolutional neural networks.

Nonlinear integrated optical resonators for optical fibre data recovery

We apply in simulation a reservoir computer based on evanescently coupled GaAs microrings for real-time compensation of a nonlinear distortion of a 50 Gbaud 16-QAM signal with the launch power up to 14 dBm in a standard single-mode optical fibre. We clearly evidence the crucial role of fast nonlinear response in enabling all-optical signal recovery in real time. With our system we are able to recover from linear and nonlinear distortion caused by a 20 km fibre and 12 dBm launch power below the forward error correction limit.

Algorithm for Assessing the Characteristics of a Waveguide Slot Antenna Array when Changing Antenna Element Phasing

Introduction. When operating antennas in various radio-electronic systems, the influence of phase shifter (PS) failures on the characteristics of phased array antennas, waveguide-slot phased array antennas (WSPAA) in particular, should be taken into account. A review of publications shows a lack of research studies into failures of these elements.Aim. Research of WSPAA characteristics in the event of PS failures, when their phase takes a value equal to zero instead of the required value.Materials and methods. Statistical modeling methods were used to study the impact of PS failures on WSPAA characteristics. Calculations were carried out using a PC and the Mathcad 15 applied mathematics package.Results. An algorithm for statistical modeling of the impact of PS failures on WSPAA characteristics is proposed. A relationship that connects the radiation pattern with the statistical sample volume and the number of failed PSs is presented. Malfunctions of emitters from 5 to 35 out of 50 elements were investigated. Changes in the following characteristics were obtained: standard deviation - from 0.064 to 0.18; relative values: radiation pattern width - from 8 to 18 %; level of side lobes - from 13 to 59 %; radiation power - from 0.9 to 0.3.Conclusion. The results obtained can be generalized and used in radio-electronic systems with antenna arrays at the stage of their development. Future work will address the influence of PS failures with phases being established randomly and with random values, as well as PS failures in which power does not pass into the emitter. Another important area concerns compensation of distortions resulting from failures of antenna elements.

The Active Compensation Technique for Large Reflector Antennas Based on Quadratic Curve Fitting

Active reflectors are often used to compensate the surface distortion caused by environmental factors that degrade the electromagnetic performance of large high-frequency reflector antennas. This is crucial for maintaining high gain operation in antennas. A distortion compensation method for the active reflector of a large dual-reflector antenna is proposed. A relationship is established between the surface deformation and the optical path difference for the primary reflector by geometric optics. Subsequently, employing finite element analysis, a polynomial fitting approach is used to describe the impact of adjusting points on the reflector surface based on the coordinates of each node. By standardizing the positions of various panels on the reflector, the fitting ns can be applied to the reflector panels of similar shapes. Then, based on the distribution characteristics of the primary reflector panels, the adjustment equation for the actuators is derived by the influence matrix method. It can be used to determine the adjustment amount of actuators to reduce the rms of the optical path difference. And, the least squares method is employed to resolve the matrix equation. The example of a 110 m aperture dual-reflector antenna is carried out by finite element analysis and the proposed method. The results show that the optical path difference is reduced significantly at various elevation cases, which indicates that the proposed method is effective.

Comparative analysis of the effectiveness of passive and active filters of higher harmonics as part of the electrical complex of metal heat treatment

The presence of a nonlinear load connected to the power supply network causes a distortion of the sinusoidal shape of the current and voltage curves, resulting in higher harmonics. Higher harmonics lead to overloading and overheating of equipment, reduced reliability and reduced service life, and can have a negative impact on the quality of electricity. As part of the task of ensuring the reliability of power grids, an important task is to control the level of harmonic components and use special devices to minimize their impact. To combat higher harmonics in power grids, various devices have been developed and used, including line chokes, passive filters, and active filters. The choice of a particular device depends on the parameters of the power grid, the type and characteristics of the connected load, the level of harmonic components, and the requirements for the quality of electricity. Linear chokes are capable of reducing the level of harmonics in the power grid, but, having a number of disadvantages, require additional justification when deciding on their use. A passive filter has a circuit consisting of a choke, resistor, and capacitor, can have different configurations, and is tuned to the frequency of a specific harmonic to suppress its effects. Passive filters are more effective in combating higher harmonics generated by nonlinear noise, more economical and easier to maintain, but have a limited frequency range, fixed parameters and significant weight and dimensions, which limits their use. Active filters include active components to generate signals that are out of phase with harmonic components, thus compensating for higher harmonics. Active filters are more flexible, capable of correcting distorted and shaped signals, are much more efficient than chokes and passive filters, but are less cost-effective and more power-consuming. In the presented work, a passive six-link LC filter and a shunt active filter based on the principle of instantaneous compensation of active and reactive currents are investigated. In the active filter, harmonic distortion compensation is provided by a proportional-integral controller. In this paper, we have carried out simulation modeling of passive and active filters as part of an electrical complex for metal heat treatment and analyzed the results of harmonic distortion compensation

Data-driven distortion compensation for laser powder bed fusion process using Gaussian process regression and inherent strain method

The repeated melting and solidification cycles in the laser powder bed fusion (L-PBF) process lead to significant thermal gradients, resulting in notable distortion in the as-built part. Distortion compensation methods, which pre-deform the part design so the as-built shape aligns with the target, have been widely adopted to mitigate this issue. This research introduces a data-driven distortion compensation framework for the L-PBF process. It employs an experimentally-calibrated inherent strain method to generate a dataset and utilizes Gaussian process regression to create the compensated geometry. Experimental validation shows that the proposed method can reduce the maximum distortion by up to 82.5% for a lattice structure and 77.8% for a canonical part. Furthermore, the compensation results reveal that (1) the lumped layer thickness in finite element models has little impact on simulated distortion reduction but can notably affect the experimental reduction; (2) discrepancies between simulated and experimental compensation performance are largely attributed to the curvy surfaces with sharp transitions in trial and compensated shapes, a result of pre-deforming the design; (3) the number of trial geometries considerably affects the effectiveness of compensation, while the number of deformation states does not have a statistically significant impact.

The Optimization Research on RF Chip Signal Processing Based on Deep Learning Algorithms

With the rapid development of wireless communication technology, radio frequency (RF) chips, as the core components of communication systems, directly influence the overall system performance through their signal processing capabilities. Traditional signal processing methods often struggle to achieve optimal results in the face of complex and variable communication environments. In recent years, deep learning technology, due to its powerful feature learning and pattern recognition capabilities, has shown tremendous potential in various fields. This paper addresses the signal processing issues of RF chips and proposes an optimization method based on deep learning algorithms. Firstly, the status and challenges of RF chip signal processing are analyzed, followed by the design of a deep learning model suitable for RF signal processing. Through data pre-processing and feature extraction, the generalization ability of the model is enhanced. Experimental results demonstrate that the proposed method outperforms traditional methods in signal noise suppression, interference cancellation, and signal distortion compensation, significantly improving the signal processing performance of RF chips. This research provides new ideas and methods for the application of deep learning in the field of RF chip signal processing and holds significant theoretical and practical importance for the future development of wireless communication systems.

81‐4: Viewing Angle‐aware Color and Luminance Distortion Compensation for Automotive OLED Displays

Recently, Organic Light Emitting Diode (OLED) displays have been widely adopted in vehicles. However, OLED displays face a challenge in that color and luminance become distorted significantly depending on the viewing angle. This issue is particularly crucial for the Center Information Display (CID) installed to the right of the driver, which is always viewed at an angle. To address this problem, this paper proposes a software‐based method to compensate for the color and luminance distortions caused by viewing angles in vehicle OLED displays. This method involves analyzing the degree of distortion at different angles and applying corrections accordingly. We have validated the effectiveness of this approach through a series of experiments.

Synchronization and Equalization for Joint Close-In and Reciprocal Mixing Phase Noise Distortion Compensation in Packet-Based OFDM Systems

Synchronization and Equalization for Joint Close-In and Reciprocal Mixing Phase Noise Distortion Compensation in Packet-Based OFDM Systems

Self-phase modulation nonlinearity distortion compensation in wavelength division multiplexed optical systems

Self-phase modulation nonlinearity distortion compensation in wavelength division multiplexed optical systems