Phase Compensation Research Articles

Improved current control strategies for LCL grid-connected inverters for weak grids

Abstract With the continuous progress of new energy technology, the application of LCL-type grid-connected inverters is becoming more and more widespread. However, these inverters have harmonic and stability problems during the grid-connection process. Especially when the grid impedance is large, their quality and safety are easily affected. Therefore, in this study, an improved current control strategy is proposed to solve the above problems. In this study, the first important task is to establish an accurate mathematical model, which takes into account the special characteristics of weak grids and the dynamic behavior of LCL filters. On this basis, the shortcomings of the traditional control strategy are analyzed and targeted improvement measures are proposed, including a control method based on phase compensation and a fuzzy control filter design. The current control strategy reduces the external disturbance and improves the system stability by controlling the current according to the magnitude of the disturbance effect after the disturbance is generated and before the controlled variable changes.

Subarray Implementation via Phase Compensation in Circularly Polarized Arrays

Subarray Implementation via Phase Compensation in Circularly Polarized Arrays

Echo-Influenced Source Localization Algorithm Using Frequency Masking and Phase Compensation

Echo-Influenced Source Localization Algorithm Using Frequency Masking and Phase Compensation

A Nonlinear Phase Compensation Method for FMCW Radar Based on VNCMD

A Nonlinear Phase Compensation Method for FMCW Radar Based on VNCMD

Velocity Estimation of Passive Target Based on Sparse Bayesian Learning Cross-Spectrum.

To solve the poor performance or even failure of the cross-spectrum (CS) method in hydroacoustic weak-target passive velocimetry, a sparse Bayesian learning cross-spectrum method (SBL-CS), combining phase compensation with sparse Bayesian learning (SBL) is proposed in this paper. Firstly, the cross-correlation sound intensity is taken as the observation quantity and compensates for each frequency point of the cross-spectrum, which enables the alignment of cross-spectrum results at different frequencies. Then, the inter-correlation sound intensity of all frequencies is fused in the iterative estimation of the target velocity, verifying the proposed method's ability to suppress the background noise when performing multi-frequency processing. The simulation results show that the proposed method is still effective in estimating the target velocity when the CS method fails and that the performance of the proposed method is better than the CS method with a decrease in SNR. As verified using the SWellEx-96 sea trial dataset, the RMSE of the proposed method for surface vessel speed measurement is 0.3545 m/s, which is 46.1% less than the traditional CS method, proving the feasibility and effectiveness of the proposed SBL-CS method for the estimation of the radial speed of a passive target.

A high efficiency wideband co‐polarised metalens antenna

AbstractThe traditional co‐polarised metasurface achieves 360° phase coverage only at the resonant frequency but not full phase coverage across a wide bandwidth. This paper proposes a multilayer structure metasurface, which composes of five layers of metal patch and four layers of medium, forming the Fabry–Perry resonator, using the principle of the cancellation of two polarisation conversion, which can achieve a wideband efficient co‐polarisation transmission. Based on the metasurface transmission phase principle, 360° phase coverage has been achieved by changing the geometric parameters of the intermediate metal patches. Through phase compensation arrangement, a metalens is designed using the proposed metasurface unit cell. At the same time, horn antenna is used as a feed to feed the metalens, which can significantly improve the gain of the antenna within a wideband. Simulated and measured results show that the proposed metalens antenna operates at 22–26 GHz, and the maximum measured gain of the metalens antenna reaches 24.16 dBi at 25 GHz, which is 10.85 dB higher than the horn antenna without metasurface compensation, showing good focusing performance. The proposed multilayer metasurface breaks the narrow band limit of the traditional stacked metasurface in principle, opening a way in the broadband metasurface design.

High-frequency average phase compensation method for gamma nonlinearity based on optimal-frequency strategy

The accuracy of fringe projection phase-shifting profilometry (PSP) is affected by gamma nonlinearity greatly, and the average phase compensation method is an effective technique to reduce the nonlinear error. However, double fringe patterns are commonly required, especially combined with the multi-frequency phase unwrapping method (MFPU), using 6 × 3 images in three-frequency method, which limits the measurement eiciency. To reduce the number of required images, this paper presents an efficient average phase compensation method using 6f h + 3f l + 3f u algorithm based on an optimal-frequency strategy. Six high-frequency standard and π/3 shifted 3-step phase-shifting fringe patterns are used together to generate high-accuracy wrapped phase. Three unit-frequency and three low-frequency fringe patterns are used to obtain coarse a unit-frequency wrapped phase and a coarse low-frequency wrapped phase, respectively. To ensure the robust phase unwrapping for high-frequency phase, the mathematical model of the optimal frequency is derived and determined by phase error amplitude calculation. Simulation and experimental results verified that only applying average phase compensation under the guidance of optimal-frequency selection strategy could achieve robust phase unwrapping and high-accurate measurement by reducing the nonlinear error substantially.

Suppression of synchronous current of active magnetic bearings considering radial displacement inconsistency

Suppressing rotor synchronous current is vital for achieving precise control in active magnetic bearing (AMB) rotor systems. The displacement amplitude inconsistency in orthogonal channels presents new challenges for synchronous current suppression. This paper proposes an improved complex least mean square (CLMS) algorithm with error compensation to effectively mitigate rotor unbalanced vibration. Firstly, a dynamic model of the AMB-rotor system with an unbalanced mass is established, and the displacement amplitude inconsistency within the orthogonal channels of the radial magnetic bearings is analyzed. Subsequently, the rotor displacement signal from the orthogonal channels is converted into a complex plane signal. By calculating the negative sequence weight component, the displacement signal is reconstructed, and an error compensation channel based on the CLMS is introduced to enable real-time tracking and compensation of displacement amplitude inconsistencies in the orthogonal channels. Moreover, system stability across the full speed range is ensured through the application of the phase compensation angle method. Finally, experimental validation on a magnetic levitation molecular pump prototype confirms the effectiveness of the proposed algorithm.

Achromatic Full Stokes Polarimetry Metasurface for Full-Color Polarization Imaging in the Visible Range.

Metasurfaces provide an ultrathin platform for compact, real-time polarimetry. However, their applications in polychromatic scenes are restricted by narrow operating bandwidths that causes spectral information loss. Here, we demonstrate full-color polarization imaging using an achromatic polarimeter consisting of four polarization-dependent metalenses. Leveraging an intelligent design scheme, we achieve effective arbitrary phase compensation and multiobjective matching with a limited database. This system provides broadband achromaticity across wavelengths from 450 to 650 nm, resulting in a relative bandwidth of approximately 0.364 for full Stokes imaging. Experimental reconstruction errors for wavelengths of 450, 550, and 650 nm are 7.5%, 5.9%, and 3.8%, respectively. Performance is evaluated based on both achromatic bandwidth and crosstalk, with our design achieving three times the performance of the current state-of-the-art. The full-color, full-polarization imaging capability of the device is further validated with a customized object. The proposed scheme advances polarization imaging for practical applications.

Gain improvement of conformal circularly polarized Fabry-Perot resonator antenna based on metasurface

Conformal antenna can keep consistent with the shape of the carrier perfectly, which greatly saves the space of the carrier, so it is widely used in military, aerospace and other fields. In this paper, a cylindrical conformal circular polarization Fabry-Perot resonator antenna is designed, and the adverse effect of conformal on antenna gain is overcome by transmission phase compensation. Firstly, a linear to circular polarization conversion metasurface with adjustable transmission phase is designed. The main reason for choosing the metasurface here is to take advantage of its excellent electromagnetic control ability. The metal structures of the metasurface are printed on the ultra-thin dielectric plates, and then attached to the support structure machined by 3D printing, so as to achieve the conformal design of the metasurface. Secondly, the proposed metasurface is used as the superstructure and is combined with a conformal feed to form a cylindrical conformal circularly polarized Fabry Perot resonator antenna. The conformal feed is a patch antenna which is conformal designed in the same way as the metasurface. The conformal feeder is placed under the conformal metasurface to ensure that the electromagnetic wave radiated by the feeder can enter the resonant cavity composed of the feeder and the metasurface. The curvature of the cylindrical conformal of feed and metasurface is the same, which can ensure the high unity of the different positions in the resonator. Next, by adjusting the transmission phase of the unit on the metaurface, the phase compensation of the transmitted electromagnetic wave is realized, so that the electromagnetic wave radiated by the conformal antenna still presents the characteristic of plane wave. Finally, the conformal Fabry-Perot resonator antenna obtains the same high-gain radiation characteristics as the planar resonator antenna. The designed antenna achieves a maximum gain of 13.1dBic at 10 GHz. The size of the antenna is 2.9λ × 2.9λ, so the aperture efficiency is about 19.9 %. The antenna proposed in this paper overcomes the influence of conformal design on the gain of the antenna, so that it can be conformal on the surface of a cylindrical object and obtain better gain characteristics.

An in-phase filter-based flux observation strategy for sensorless control of PMSMs

Due to the complexity of determining the initial rotor flux and detecting errors, conventional rotor flux observation methods are easily affected by direct current (DC) components and harmonics. To address this issue, this paper proposes an in-phase filter (IPF)-based rotor flux observation strategy for sensorless control of permanent magnet synchronous machines (PMSMs). The core components of the IPF consist of a double second-order generalized integrator (DSOGI) and a phase angle compensation transfer function (PACTF). The DSOGI provides a accurate electrical angular frequency, while the PACTF implements a phase correction to the vq′ signals. By employing IPF structure, accurate observations for rotor flux, electronic speed, and rotor position are achieved, which can be effectively used in the sensorless control of PMSMs, eliminating the need for magnitude and phase compensations. Finally, the proposed observation strategy is applied to an experimental bench of a PMSM, and its effectiveness is illustrated by experimental results. From experimental results, it can be concluded that the IPF is significantly better than the LPF, and 5% more accurate than the observer based on cascade second-order generalized integral(CSOGI) overall.

A Rapid Circuit Phase Error Identification and Compensation Method for MEMS QMG Achieving 99.7% Reduction in ZRO Drift

A Rapid Circuit Phase Error Identification and Compensation Method for MEMS QMG Achieving 99.7% Reduction in ZRO Drift

A High-Selectivity Circularly Polarized Filtering Antenna Based on Wavefront Phase Compensation

A High-Selectivity Circularly Polarized Filtering Antenna Based on Wavefront Phase Compensation

A wideband transmitarray antenna based on polarization conversion metasurface with 2‐bit phase compensation

AbstractA wideband transmitarray antenna (TA) incorporating a polarization conversion metasurface (PCM) is proposed. Four PCM elements with annular metallic polarizers are utilized to provide 2‐bit phase compensation without altering the geometric parameters of the elements, resulting in a wideband TA with a bandwidth comparable to that of the individual elements. A prototype of the proposed TA is designed, fabricated, and measured. The measured 1‐ and 3‐dB gain bandwidths of the proposed TA are found to be 10–13.6 GHz (30%) and 9.2–15 GHz (48.3%), respectively, while the effective 1‐dB transmission band of the individual elements is 7.8–14.6 GHz. The similarity between the bandwidth of the proposed TA and that of elements used in our design demonstrates less wastage of element bandwidth by the proposed approach. A measured peak gain of 27.2 dBi and a peak aperture efficiency (AE) of 48.7% highlight the promising potential of the proposed TA for long‐distance communication, point‐to‐point communication, and other applications.

Magnetic and thermodynamic properties of mixed spin-3/2 and spin-3 Ising ferrimagnets on a 2D triangular lattice: Monte Carlo study

Monte Carlo methods in the presence and absence of an external magnetic field were used to investigate the thermodynamic and magnetic properties of the mixed spins (3/2, 3) Ising ferrimagnets in a 2D triangular lattice consisting of sublattices A, B, and C. Two types of mixing were considered: S→=(SA,SB,SC)=(3/2,3,3) (Model I) and S→=(SA,SB,SC)=(3/2,3,3/2) (Model II). In contrast to bipartite lattices, the antiferromagnetic coupling between spin-3/2 and spin-3 in the triangular lattice leads to geometric frustrations that impact magnetic properties. Determination of ground state phase diagrams, combined with verification of whether or not there was magnetic hysteresis when crossing each transition line, revealed first- and second-order phase transition lines, as well as multicritical points. The temperature investigation in the absence of an external magnetic field revealed rich magnetic properties such as 1st- and 2nd-order phase transitions, N- and L-type compensation points, tricritical points, and critical endpoints, as well as M-, P-, Q-, R- and S-type total magnetization behaviours. The effect of the crystal field on finite-temperature phase diagrams and compensation behaviour was also carried out. As a result, the critical temperatures of Model II become constant when the crystal field is sufficiently strong. In contrast, several critical values of the crystal field for which the critical temperature is zero were identified for Model I. In the presence of a magnetic field, hysteresis behaviour and associated magnetic properties such as coercivity and magnetic remanence were investigated. The effect of crystal field and temperature was explored. Hysteresis of one to four loops were found at low temperatures when the crystal field varied. Finally, as the temperature rises, the hysteresis loops' area decreases to zero at high temperatures.

Motion coprime array-based DOA estimation considering phase disturbance of sensor array

To address the phase disturbance issue faced by sensor arrays in practical applications, a cascaded deep convolutional neural network structure is proposed to achieve direction-of-arrival (DOA) estimation for motion coprime arrays. Firstly, the synthesized covariance matrix obtained after motion is inputted into the first-level network for estimating the phase disturbance matrix. Then, we analyze the impact of phase perturbation on the synthesized covariance matrix and utilize the estimated disturbance phase to obtain an undisturbed synthesized covariance matrix. Finally, after phase compensation, the synthesized covariance matrix performs DOA estimation through the second-level network. Furthermore, to acquire three times the virtual unique lags of the coprime array, the synthesis condition about moving distance and unique lags is derived. The proposed method is shown to be effective and superior through the experiment results.

Design of HTS linear phase bandpass filter based on the inline topology

Abstract Inline topology filters have the advantages of a simple structure and fewer coupling coefficients. Based on the inline topology, this paper constructs a phase compensation topology of the filter, which can independently and controllably introduce two types of transmission zeros (TZs), and is convenient to realize the Chebyshev-like function response and compensate group delay. The finite frequency transmission zero is directly introduced through the source and load (S/L), and the real zero point is introduced and adjusted through the cross-coupling unit of the main path in this inline phase compensation topology. The two types of TZs can be introduced and regulated independently, so the side-band suppression and group delay compensation can be freely adjusted. A High-temperature superconducting (HTS) filter with inline is designed and processed with a typical structure based on application requirements. The filter introduces two pairs of symmetrical real TZs to improve sideband rejection and a pair of real TZs to control group delays to realize the linear phase. In addition, it has a small size and straightforward construction, and the results of the full-wave analysis method and the theoretical analysis approach match well with the measured results of the frequency response characteristics.

Detection and Anti-Detection with Microwave-Infrared Compatible Camouflage Using Asymmetric Composite Metasurface.

Detection and anti-detection with multispectral camouflage are of pivotal importance, while suffer from significant challenges due to the inherent contradiction between detection and anti-detection and conflict microwave and infrared (IR) stealth mechanisms. Here, a strategy is proposed to asymmetrically control transmitted microwave wavefront under radar-IR bi-stealth scheme using composite metasurface. It is engineered composed of infrared stealth layer (IRSL), microwave absorbing layer (MAL), and asymmetric microwave transmissive structure (AMTS) with polarization conversion from top to bottom. Therein, IR emissivity, microwave reflectivity, and transmissivity are simultaneously modulated by elaborately designing the filling ratio of ITO square patches on IRSL, which ensures both efficient microwave transmission and IR camouflage. Furthermore, full-polarized backward microwave stealth is achieved on MAL by transmitting and absorbing microwaves under x- and y- polarization, respectively, while forward wavefront is controlled by precise curvature phase compensation on AMTS according to ray-tracing technology. For verification, a proof-of-concept metadevice is numerically and experimentally characterized. Both results coincide well, demonstrating spiral detective wavefront manipulation under y-polarized forward wave excitation while effective reduction of radar cross section within 8-18GHz and low IR emissivity (<0.3) for backward detection. This strategy provides a new paradigm for integration of detection and anti-detection with multispectral camouflage.

Model-based wavefront measurement and compensation in atmospheric turbulence.

The model-based method can measure phase aberration without special wavefront detectors. However, the influence of non-uniform beam intensity distribution was not considered, leading to non-negligible system errors. Moreover, no experiments were employed to verify its capability and practicability in atmospheric turbulence. This paper proposes the aberrated pupil method, which can enhance the accuracy of phase recovery by introducing an aberrated pupil function into the traditional model-based method. The effectiveness of the model-based phase measurement and compensation method was experimentally investigated and verified in the application of free-space optical communication. Compared with the traditional model-based method, the aberrated pupil method can reduce the coupling power loss caused by turbulence from 2.59 to 0.87 dB, resulting in a reduction of 1.72 dB. With coherent communication experiments, the model-based phase recovery method significantly improved the communication power budget by about 13.5 dB. The proposed method can measure and compensate for the phase aberration to significantly improve the communication quality of free-space optical communication.

Design of a Near-Field Synthetic Aperture Radar Imaging System Based on Improved RMA

Traditional near-field synthetic aperture radar (SAR) imaging algorithms reveal target features by exploiting signal amplitude and phase information. However, electromagnetic wave propagation is constrained by short distance. Therefore, the spherical wave approximation needs to be considered. In addition, it is also limited by equipment ambient noise, azimuth-distance coupling, wave scattering, and transmission power. Both the amplitude and phase of the signal suffer from the interference of multiple clutter, so they cannot be effectively utilized. To address these issues, this paper introduces a covering penetration detection system based on an improved Range Migration Algorithm (IMRMA) imaging method. Firstly, the proposed method minimizes interferences from the front end of the system using an optimized window to balance denoising and information preservation. Next, interval non-uniform interpolation, instead of Stolt interpolation decoupling, is employed to reduce the computational overhead significantly. To minimize the effects due to wave scattering and propagation loss, distance information is enhanced using amplitude and phase compensation. This reduces scattering effects and enhances image quality. An experimental system is constructed based on a vector network analyzer (VNA) to image the target. The proposed method takes about half the time of traditional RMA. The PSNR in the chunky bowl experiment is higher than 14 dB, which is higher than all the compared methods in the paper. The test results show that the designed system and the reported method can effectively achieve high-resolution images by strengthening the target intensity and suppressing the environmental artifacts.