Proposed Compensation Strategy Research Articles

Gaze-contingent processing improves mobility, scene recognition and visual search in simulated head-steered prosthetic vision.


The enabling technology of visual prosthetics for the blind is making rapid progress. However, there are still uncertainties regarding the functional outcomes, which can depend on many design choices in the development. In visual prostheses with a head-mounted camera, a particularly challenging question is how to deal with the gaze-locked visual percept associated with spatial updating conflicts in the brain. The current study investigates a recently proposed compensation strategy based on gaze-contingent image processing with eye-tracking. Gaze-contingent processing is expected to reinforce natural-like visual scanning and reestablished spatial updating based on eye movements. The beneficial effects remain to be investigated for daily life activities in complex visual environments.

APPROACH:
The current study evaluates the benefits of gaze-contingent processing versus gaze-locked and gaze-ignored simulations in the context of mobility, scene recognition and visual search, using a virtual reality simulated prosthetic vision paradigm with sighted subjects.

MAIN RESULTS:
Compared to gaze-locked vision, gaze-contingent processing was consistently found to improve the speed in all experimental tasks, as well as the subjective quality of vision. Similar or further improvements were found in a control condition that ignores gaze-depended effects, a simulation that is unattainable in the clinical reality.

SIGNIFICANCE:
Our results suggest that gaze-locked vision and spatial updating conflicts can be debilitating for complex visually-guided activities of daily living such as mobility and orientation. Therefore, for prospective users of head-steered prostheses with an unimpaired oculomotor system, the inclusion of a compensatory eye-tracking system is strongly endorsed.

Multi-functional voltage and current based enhancement of power quality in grid-connected microgrids considering harmonics

The introduction of a renewable energy source (RES) based multi-functional grid-tied inverter (MFGTI) stands as a favorable remedy for addressing power quality concerns within distributed generation (DG) systems and microgrids. Nonetheless, the effectiveness of a traditional MFGTI will be restricted in addressing power quality issues based on voltage. The presented research proposes a novel structure for MFGTI to enhance power quality concerns associated with voltage, current, and harmonic distortions resulting from both grid and loads. Based on this strategy, the introduced MFGTI can be linked with the grid by bidirectional switches either in a parallel or series. This feature provides various operational conditions in response to diverse disruptions in the grid. To effectively adjust the voltage, current and voltage reduction are determined through mathematical analysis, considering both the grid conditions and the load requirements. Furthermore, this strategy offers different compensation strategies, control schemes, and transition modes in the MFGTI. The major disturbances such as unbalanced and balanced voltage swell/sag, harmonics, and interruption are compensated. The shunt compensation controller is based on a second order sequence filter (SOSF) to provide the load current active component. A damping PI regulator based series compensation controller is presented for the voltage swell/sag reduction. Moreover, a new three level hierarchical control is proposed in which a droop control for compensating the interruption and a decouple dual synchronous reference frame (DDSRF) for compensating the unbalanced voltage sag/swell are utilized. The simulations in the MATLAB/SIMULINK show that using the proposed compensation strategies, the proposed MFGTI can compensate effectively the different disturbances through changing the transition states by the proposed algorithm based bidirectional switches.

Compensation Method for Current Measurement Errors in the Synchronous Reference Frame of a Small-Sized Surface Vehicle Propulsion Motor

This paper proposes a new method for compensating current measurement errors in shipboard permanent magnet propulsion motors. The method utilizes cascade decoupling second-order generalized integrators (SOGIs) and adaptive linear neurons (ADALINEs) as the current harmonic extractor and the compensator, respectively. It can compensate for the dq-axes offset and scaling errors simultaneously, improving phase current distortion while reducing the ripples of motor speed and torque. Compared to the traditional motor model-based compensation strategies, the proposed method is robust against the changes in motor parameters with the online adaptive capability of the ADALINE algorithm. Furthermore, due to the good real-time performance of SOGIs and ADALINEs, the proposed compensation strategy can effectively operate in both the steady state and transient state of the motor. Finally, the effectiveness of the proposed method is verified through the physical and hardware-in-the-loop (HIL) experiments. After compensating for the current measurement errors of a 1 kW test motor with the propeller-characteristics load, the torque ripple and speed ripple are reduced by more than 65% and 80%, respectively. At the same time, the DC component and the second-order and third-order harmonics in the phase currents are also significantly reduced. Similar test results can be also obtained on the HIL platform with a 100 kW permanent magnet motor.

Hybrid physics-guided data-driven modeling for generalizable geometric accuracy prediction and improvement in two-photon lithography

Two-photon lithography (TPL) is an additive manufacturing technique to produce three-dimensional (3D) micro- and nano-scale structures. Geometric accuracy is of vital importance to ensure the quality and functionality of additively manufactured 3D structures. However, there exists limited research on modeling and improving the geometric accuracy of TPL. Moreover, there is a lack of understanding of the influence of TPL process parameters (e.g., scanning rate, laser power) and structure design on the resulting geometric accuracy. This paper presents a new hybrid physics-guided data-driven modeling framework for generalizable cross-design and cross-parameter geometric accuracy prediction and improvement. The proposed model decomposes TPL-produced geometric features into two levels: a global trend and a spatial trend. Guided by physical laws that govern voxel dimensions, we construct the global trend as a function of TPL process parameters. Our new findings reveal strong linear relationships among the parameters of the global trend model across structure design dimensions, which enable generalizable predictive modeling. Moreover, the spatial trend captures the spatially varying patterns in geometric features. A large-scale experimental design consisting of six hemisphere sizes and six parameter combinations is carried out to thoroughly test the effectiveness of the proposed method. Our modeling approach demonstrates high accuracy in predicting the geometric error of a target design with knowledge derived from other designs and parameters. The average prediction errors for radius and height are 5.23% and 4.66%, respectively. Furthermore, the proposed compensation strategy is shown to reduce the geometric errors from 22.19% to 3.21% for radius, and from 12.18% to 4.96% for height. Meanwhile, the within-sample variations are greatly reduced, indicating improved process consistency. To the best of our knowledge, this study is among the first to develop a generalizable method for cross-design and cross-parameter geometric accuracy modeling and improvement in TPL.

An Improved Acoustic Diffusion Equation Model for Long-Channel Underground Spaces.

The acoustic diffusion equation model has been widely applied in various scenarios, but a larger prediction error exists when applied to underground spaces, showing a significantly lower characteristic of the sound pressure level in the later stage compared to field tests since underground spaces have a more closed acoustic environment. Therefore, we analyze the characteristics of underground spaces differentiating from aboveground spaces when applying the model and propose an improved model from the perspective of energy balance. The energy neglected in the calculation of the acoustic diffusion equation model is compensated in long channel underground spaces named "acoustic escape compensation". A simulation and two field experiments are conducted to verify the effectiveness of the proposed compensation strategy in long-channel underground spaces. The mean square error is used to evaluate the differences between the classical model and the improved model, which shows a numerical improvement of 1.3 in the underground field test. The results show that the improved model is more suitable for describing underground spaces. The proposed strategy provides an effective extension of the acoustic diffusion equation model to solve the problem of sound field prediction and management in underground spaces.

Modelling and Compensation of SIC Imperfection in IRS-NOMA based 5G-System

This article considers the impairments in the application of successive interference cancellation (SIC) at the detection phase of non-orthogonal multiple access (NOMA) users. A practical approach is proposed to model the SIC impairment which takes into account the number of multiplexed users in NOMA’s power domain, in addition to the overall number of shared radio resources. In such case the imperfection of the SIC varies in accordance with the number of users. This strategy is closer to the situation in practice than the case where the SIC is modeled with fixed error factor as in the previous research articles that already considered the matter. A channel estimation approach is also proposed, which depends on the user’s channel gain variations to predict the change in its peers’ channel so as to compensate for the error resulting from SIC imperfection. The outcome of the proposed compensation strategy is promising as the simulation results reflect significant improvement in the achievable rate and energy efficiency.

Virtual Admittance Feedforward Compensation and Phase Correction for Average-Current-Mode-Controlled Totem-Pole PFC Converters

This paper explores a current distortion problem in totem-pole bridgeless power factor correction (PFC) converters with average current mode (ACM) control. With in-depth modeling for the current and voltage loops, it was found that the current distortion is caused by the limited current loop bandwidth and input filter capacitor. These factors lead to the presence of a susceptance component in the input admittance, which degrades the power factor (PF) and total harmonic distortion (THD) of the PFC converter. To solve this problem, this paper proposes virtual admittance feedforward compensation (VAFC) and phase correction methods to adjust the input admittance to pure conductance. The VAFC can generate virtual admittance that compensates for susceptance components in the input admittance, while phase correction can generate an equivalent current source that offsets the current in input capacitors. Furthermore, a phase lock loop (PLL) is introduced to realize the VAFC, which reduces the feedforward interference caused by input voltage sampling noise. Finally, an experimental prototype was built to verify the effectiveness of the proposed strategies. According to the test results, the proposed compensation strategy improves the PF by 1.23%, while reducing the THD by 2.52% and achieving a peak efficiency of 98.69%.

Differential Confocal Optical Probes with Optimized Detection Efficiency and Pearson Correlation Coefficient Strategy Based on the Peak-Clustering Algorithm.

Quantifying free-form surfaces using differential confocal microscopy can be challenging, as it requires balancing accuracy and efficiency. When the axial scanning mechanism involves sloshing and the measured surface has a finite slope, traditional linear fitting can introduce significant errors. This study introduces a compensation strategy based on Pearson's correlation coefficient to effectively reduce measurement errors. Additionally, a fast-matching algorithm based on peak clustering was proposed to meet real-time requirements for non-contact probes. To validate the effectiveness of the compensation strategy and matching algorithm, detailed simulations and physical experiments were conducted. The results showed that for a numerical aperture of 0.4 and a depth of slope < 12°, the measurement error was <10 nm, improving the speed of the traditional algorithm system by 83.37%. Furthermore, repeatability and anti-disturbance experiments demonstrated that the proposed compensation strategy is simple, efficient, and robust. Overall, the proposed method has significant potential for application in the realization of high-speed measurements of free-form surfaces.

Compensated fault impedance estimation for distance-based protection in active distribution networks

Electric distribution networks are experiencing fast changes mainly due to the integration of distributed energy resources. These changes originate the active distribution networks, where several distributed energy resources are integrated, usually using power converters. In these active networks, the conventional control, operation, and protection schemes used in power systems are unsuitable, and as a consequence, new approaches must be proposed and tested. This paper analyses the distance relay performance in active distribution networks; as the main contribution, a communication-less compensation strategy is proposed to deal with the effects of fault resistance and the distributed energy resources’ infeed and remote currents. The obtained results demonstrate the excellent performance of the proposed compensation strategy aimed at determining the true value of the estimated positive sequence impedance. This compensation can be easily integrated into the software of conventional distance relays to overcome fault resistance, infeed, and remote current effects.

A Compensation Strategy for Mitigating Intermittencies Within a PV Powered Microgrid Using a Hybrid Multilevel Energy Storage System

Solar PV intermittencies due to passing clouds with high ramp rates occurring for a short time produce a significant challenge to grid voltage and frequency regulations of a PV-rich microgrid. To compensate for these high ramp rates, battery and/or supercapacitors (SCs) are commonly employed using the control strategy based on a moving average (MA) or low pass filter (LPF). However, the traditional MA and LPF schemes suffer from memory and time lag effects, resulting in the need for increased storage size. To address these issues, this paper describes the design and implementation of a generic ramp-rate-based compensation strategy for smoothing the solar power output and meeting rapid load demands in grid-interactive microgrids using a hybrid multilevel storage system, consisting of high-capacity buffer storage such as battery system and hydrogen storage comprising a proton exchange membrane electrolyzer and a fuel cell, and short-term cache storage such as supercapacitors, integrated in the DC link of the power converter. This hybrid multilevel modular storage system is required to rapidly control fluctuations in solar PV outputs and load demands over a wide range of time scales and regulate the voltage at the point of common coupling (PCC). The proposed compensation strategy is modeled and validated through simulations using a measured 24-h solar irradiance profile applied to a 100-kW grid-interactive PV-dominated microgrid system.

The Full Load Voltage Compensation Strategy in Capacity Configuration of燯PQC Integrated PV-BESS

Unified power quality conditioner (UPQC) with energy storage is commonly based on conventional capacity configuration strategy with power angle control. It has problems such as phase jumping before and after compensation. DC-link cannot continuously emit active power externally. Therefore, this paper presents the compensation strategy of full load voltage magnitude and phase in capacity configuration of UPQC. The topology of UPQC is integrated a series active power filter (SAPF), a shunt active power filter (PAPF) and a photovoltaic-battery energy storage system (PV-BESS). The principle of full load voltage compensation is analyzed based on the PV-BESS-UPQC topology. The magnitude constant of load voltage is maintained by controlling the appropriate shunt compensation current. Then the UPQC capacity configuration is carried out using the full load voltage compensation strategy. The compensation capacity of UPQC series and shunt units are reduced. Finally, the simulation results show that the proposed compensation strategy reduces the capacity configuration by 5.11 kVA (36.4%) compared to the conventional compensation strategy. The proposed strategy can achieve full compensation of the load voltage, which can effectively reduce the capacity allocation and improve the economy of UPQC. It also has the PV-BESS units' ability of providing active power and can stabilize the DC-link voltage.

Sequential delay-free strategy for sliding mode position observer considering analog and digital implementations of PMSM drives

ABSTRACT This paper proposes a sequential delay-free strategy to avoid side effects of the delays arising from both analog and digital implementations of permanent magnet synchronous machine (PMSM) drives on the accuracy of sliding mode position observers used in the high-speed conditions. First, after establishing the sliding mode observer (SMO) used for position estimation, the principles of the analog delay, low-pass filter (LPF) delay and execution delay together with their impacts are presented at length, posing the necessity of investigating the delay-free techniques. Then, novel current-based, position-based and speed-prediction-based compensation strategies are developed to deal with the three kinds of delays, respectively. Because the proposed compensation strategies are achieved based on the direct signal compensation theories, they are simple to be understood and implemented in practice. Third, the implementation sequence of the sequential delay compensation-based SMO is illustrated clearly. Thanks to the proposed delay compensation approaches, not only the position estimation accuracy but also the current regulation process of the closed-loop control can be improved. Finally, experiment is conducted on a three-phase 8000 rpm PMSM to verify the effectiveness of the proposed delay compensation-based SMO algorithms.

Design and analysis of a load frequency control system based on improved artificial intelligence control algorithm

In actual industrial control, the performance of the control system may be undermined or destabilized by the various complex nonlinear control processes. To ensure the stability of the control system, this paper improves the generalized active disturbance rejection control (GADRC). Firstly, the dead zone of the governor was converted to obtain the total transfer function of the control system, and the system stability was analyzed, considering the applicability of GADRC to non-minimum phase processes. Then, an error compensation strategy was proposed to control the system performance. Simulation results show that the improved GADRC can fully utilize the known information of the plant model, and obtain proper gains of the controller and the observer. In addition, the load frequency control (LFC) system can work effectively, when the dead zone of the governor has nonlinear processes. Finally, the proposed error compensation strategy can ensure the control performance of the system.

Vibration Mechanism and Compensation Strategy of Magnetic Suspension Rotor System Under Unbalanced Magnetic Pull

The existing imbalance compensation strategies for magnetic suspension motors mainly focus on the mass unbalance force, ignoring the effects of the unbalanced magnet pull (UMP). This paper studied the vibration mechanism and compensation strategy of magnetic suspended permanent magnet synchronous motor (PMSM) under the influence of UMP. Firstly, an analytical model of the flux density was established based on equivalent magnetic circuit method, then the analytical expressions of UMP was deduced by Maxwell stress tensor method. Furthermore, an unbalanced compensation method based on hypothetical reference frame (HRF) transformation was proposed. The stability of the closed-loop system with compensation was analyzed based on the complex-coefficients theory. The proposed model and compensation strategy were verified by the simulations and experiments. The results indicate that the proposed compensation strategy can achieve effective suppression of the magnetic rotor vibration.

Digital Implementation of Single Current Sensor-Based IPMSM Drive With Sampling Error Delay Compensation

Single current sensor-based three-phase drives are gaining huge interest from industries for sensitivity mismatch issues and cost reduction. However, the current sampling error caused by multiple sampling points during current reconstruction from various single current sensor (SCS) topologies led to increase in speed fluctuation and torque ripple. In this paper, a computationally efficient and accurate model-based sampling error compensation scheme based on a new SCS with double branch current sampling technique is proposed for an interior permanent magnet synchronous motor (IPMSM) drive. In order to improve of current reconstruction precision, the compensation strategy includes rotor angle compensation of IPMSM and dead-time effect mitigation for reduction of non-ideal behavior of inverter, which does not require major computation. Also, dc-link voltage utilization is improved significantly without any external dc-link control. The efficacy of the proposed compensation strategy is verified by an experimental setup consisting of 1.5 kW IPMSM drive, which shows the effectiveness of proposed current reconstruction technique from SCS by reducing current sampling error with minimum computational burden.

Cascade tracking control of servo motor with robust adaptive fuzzy compensation

Servo motor drive systems with high-accuracy position tracking control suffer from some uncertainties from inherent mechanical friction and varying end-load. In this paper, a novel cascade controller with feedforward robust adaptive fuzzy compensation is proposed to overcome the negative impacts of the uncertainties. An adaptive fuzzy logic system is used to estimate the friction, which is applied for designing a feedforward compensator to improve the tracking performance. Based on Lyapunov stability theory, we show that closed-loop system can ensure the semi-global asymptotic tracking performance. Our proposed compensation strategy takes advantage of utilizing the cascade P/PI controller without changing the original control system structure, which is practical and valuable to industrial applications. Simulation results indicate some merits of the proposed controll scheme in terms of the system stability, adaptivity and robustness with respect to different uncertainties.

Motion-compensated 3D turbo spin-echo for more robust MR intracranial vessel wall imaging.

(1) To investigate the effect of internal localized movement on 3DMR intracranial vessel wall imaging and (2) to develop a novel motion-compensation approach combining volumetric navigator (vNav) and self-gating (SG) to simultaneously compensate for bulk and localized movements. A 3D variable-flip-angle turbo spin-echo (ie, SPACE) sequence was modified to incorporate vNav and SG modules. The SG signals from the center k-space line are acquired at the beginning of each TR to detect localized motion-affected TRs. The vNavs from low-resolution 3D EPI are acquired to identify bulk head motion. Fifteen healthy subjects and 3 stroke patients were recruited in this study. Overall image quality (0-poor to 4-excellent) and vessel wall sharpness were compared among the scenarios with and without bulk and/or localized motion and/or the proposed compensation strategies. Localized motion reduced wall sharpness, which was significantly mitigated by SG (ie, outer boundary of basilar artery: 0.68 ± 0.27 vs 0.86 ± 0.17; P = .037). When motion occurred, the overall image quality and vessel wall sharpness obtained with vNav-SG SPACE were significantly higher than those obtained with conventional SPACE (ie, basilarartery outer boundary sharpness: 0.73 ± 0.24 vs 0.94 ± 0.24; P = .033), yet comparable to those obtained in motion-free scans (ie, basilarartery outer boundary sharpness: 0.94 ± 0.24 vs 0.96 ± 0.31; P = .815). Localized movements can induce considerable artifacts in intracranial vessel wall imaging. The vNav-SG approach is capable of compensating for both bulk and localized motions.

Towards adaptive high-power lasers: Model-based control and disturbance compensation using moving horizon estimators

Thermally-induced disturbances limit the beam quality of high-power lasers and evoke set point-dependent disturbances. As a result, the beam parameters and the laser’s output power of conventional high-power lasers cannot be chosen independently. To overcome this issue, we suggest spherical intra-cavity mirrors as actuators to dynamically compensate the impact of thermal lensing within the framework of automatic control. While the optical system is represented stationary as a Gaussian cavity with multiple transverse modes, the disturbance and the actuator are dynamically modeled by distributed parameters systems. A reliable estimation and prediction of the disturbance is crucial to achieve a proper rejection. To this end, an optimization-based moving horizon state estimator is designed to cope with model uncertainties, noisy measurements and bifurcations causing parasitic solutions of the nonlinear output equation. To maintain real-time capability, the relevant transient effects are lumped to an efficient discrete-time design model. The proposed compensation strategy explicitly considers input constraints and involves a reference governor to ensure the feasibility of the control objective. The performance of the individual components of the controller are validated by means of simulations and experiments. Eventually, we prove the overall concept of controlled adaptive high-power lasers by means of a scalable experimental setup with output lasers powers exceeding 500W.

BER analysis of IQ imbalance compensation for GFDM systems

As one of the 5G waveform candidates, generalised frequency division multiplexing (GFDM) systems have been proposed to achieve lower out of band radiation and stronger robustness against synchronisation errors. However, theoretical BER performances of GFDM systems with in-phase/quadrature (IQ) imbalance, as well as compensation strategies, have not been widely investigated. In this Letter, the authors evaluate theoretical BER performances of GFDM systems with transmitter IQ imbalance (IQI) before and after a proposed compensation method. Basically, they give approximated BER expressions for different modulations through considering introduced IQI completely as useless interference, and then derive a more precise BER expression for QPSK modulation. Additionally, they put forward a compensation method to remove IQI interference in GFDM systems at the cost of enlarged noise. Furthermore, analytical BER expressions with IQI compensation are derived, and then the effectiveness of the proposed compensation strategy is proven by theoretical and simulation results.

Direct prediction compensation strategy of unified power quality conditioner based on FCS–MPC

The finite control set model predictive control (FCS–MPC) has drawn considerable attention in the integrated control of the unified power quality conditioner (UPQC) due to the characteristics of high dynamic response, internal decoupling and multiple constraints. In this study, a new direct prediction compensation strategy (DPCS) based on FCS–MPC is proposed, which eliminates the harmonic detection algorithm, simplifies the UPQC controller structure and reduces the steady-state errors. By compensating for the time delay of FCS–MPC, the UPQC can mitigate the power quality problems more accurately and timely. The FCS–MPC value function can be with various constraints, which makes the UPQC suitable for more situations. Compared with the indirect prediction compensation strategy, the designed DPCS has better time-delay compensation effects, which can reduce the harmonic components of the user-side under transient disturbances. The simulation results show that the proposed compensation strategy can achieve better dynamic and steady-state performance on power quality problems such as voltage sags, swells, interruptions and harmonics.