Proposed Compensation Method Research Articles

Improvement of the Geometric Accuracy for Microstructures by Projection Stereolithography Additive Manufacturing

Projection stereolithography creates 3D structures by projecting patterns onto the surface of a photosensitive material layer by layer. Benefiting from high efficiency and resolution, projection stereolithography 3D printing has been widely used to fabricate microstructures. To improve the geometric accuracy of projection stereolithography 3D printing for microstructures, a compensation method based on structure optimization is proposed according to mathematical analysis and simulation tests. The performance of the proposed compensation method is verified both by the simulation and the 3D printing experiments. The results indicate that the proposed compensation method is able to significantly improve the shape accuracy and reduce the error of the feature size. The proposed compensation method is also proved to improve the dimension accuracy by 21.7%, 16.5% and 19.6% for the circular, square and triangular bosses respectively. While the improvements on the dimension accuracy by 16%, 17.6% and 13.8% for the circular, square and triangular holes are achieved with the proposed compensation method. This work is expected to provide a method to improve the geometric accuracy for 3D printing microstructures by projection stereolithography.

P‐39: The IR Drop Compensation Method of AMOLED Display for Dynamic Power Control

In this paper, a new compensation method to solve IR‐drop on AMOLED panel for using dynamic power setup. This paper discusses the dynamic power setup bring the different loading effect and representing the varied level of IR drop on AMOLED panel. If only compensate the IR drop in a fixed current driving condition, the IR drop of the other condition could be worse. In order to improve this problem, the proposed method reduces IR drop phenomenon due to the different power setup by using adjustable compensation ratio for different combination of power setup. Additionally, instead of by full band full tuning, the proposed compensation method is support scaling factors fine tuning for different combination of power & EM setting.

Research on dead-time compensation of common DC bus OW-PMSM based on 120°decoupling modulation

To suppress the switching dead-band in the Open-End Winding Permanent Magnet Synchronous Machine with Common DC bus (OW-PMSM-CDCB) drive system, the dual-inverter switch dead-band generates zero-sequence voltage and current during 120°decoupling modulation. The generation mechanism of dead-band voltage is analyzed with the help of Matlab/Simulink and a method to compensate for the zero-sequence voltage resulting from the dead-band of dual-inverter switches is discussed in this study. With the help of current polarity detection, the zero-sequence voltage resulting from the dead-band of the switch is offset by solving the dead-band voltage compensation amount, and an OW-PMSM-CDCB drive system experimental platform is built for experimental verification. Simulation and experimental show that the proposed compensation method can effectively suppress the zero-sequence current of OW-PMSM-CDCB.

Common-Mode Voltage Reduction and Neutral-Point Voltage Control Using Space Vector Modulation for Coupled Ten-Switch Three-Phase Three-Level Inverter

Space vector pulsewidth modulation (SVPWM) provides enhanced performance for the coupled ten-switch three-phase three-level inverter (TP-TLI). However, it suffers from high common-mode voltage (CMV) and unbalanced neutral-point voltage (NPV). To solve this problem, a CMVR_SVPWM with CMV reduction and NPV control (NPVC) is proposed in this article. By using suitable vectors with lower CMVs and sequences, the amplitude of CMV is suppressed to 50% of the previous strategies for ten-switch TP-TLI. A newly control degree is explored to regular the NPV through the two pairs of newly virtualized vectors in each sector. The dwell time of each selected vector is indirectly calculated to cooperate the NPVC with the CMVR_SVPWM. By enhancing the dwell time of the desired small vector, the NPV can be balanced while maintaining the almost same output quality. The dead-time effect is analyzed, and the resulting CMV spikes is eliminated by increasing the dwell time of the vector which is less than twice the compensation time. It preferentially attempts to eliminated the CMV spikes based on volt-second balance. This minimizes the effect of the proposed compensation method on output quality. A 3-kVA experimental prototype is built up to verify the feasibility and performance of the proposed CMVR_SVPWM.

Matching Measurement Strategy and Form Error Compensation for Freeform Surface Machining Based on STS Turning

The freeform surface quality is limited by the measurement, and form error cannot be convergent via compensation machining. This paper proposed a surface matching measurement strategy based on the least squares principle and iterative precision adjustment to precisely obtain surface form error after manufacturing by single point diamond turning. Through the coordinate transformation of translation and rotation, the measured surface was aligned with theoretical surface at the same coordinate system. The corresponding simulation was carried out to verify the performance of the proposed method, and the simulation results indicated that this method can achieve accurate alignment in a sub-nanometer range. Finally, with XY polynomial freeform surface as the ideal surface, compensation experiments were undertaken. The form error of freeform converged continuously after compensation machining for three times, during which the form accuracy of PV and RMS were down to 335 nm and 34 nm respectively from 1.4 um and 173 nm. The results showed that capability of the proposed compensation method was verified and the form accuracy could be improved effectively.

Improved MIMO Modeling and Enhanced Transient Performance of Phase-Locked Loop During Grid Fault

A phase-locked loop (PLL) is commonly used in grid-connected power converter for synchronization. A single input single output (SISO) linear model of PLL with the phase angle of the point of common coupling (PCC) voltage as input and the estimated phase angle as the output is generally used in the PLL analysis and design. However, an undesirable coupling between the magnitude and phase of the input voltage is present when a filtering stage is incorporated before the control loop, which a SISO model cannot capture, and could result in a significant disturbance in the PLL estimated phase during grid faults. This paper proposes a generalized multi-input multi-output (MIMO) linear model that captures the complete PLL dynamics during symmetrical faults for a PLL equipped with any prefilter. Furthermore, a compensation method that decouples the magnitude dynamics of the input voltage from the phase dynamics is proposed in this paper. The proposed compensation improves the PLL's phase tracking performance by ensuring that the prefiltered PLL acts only on the PCC voltage phase changes. A vital application of the proposed compensation method for PLL is during a grid fault case, wherein the converters are expected to contribute to the fault current, which requires an accurate measurement of the PCC voltage phase. The compensation method's effectiveness is demonstrated using power hardware in the loop simulation of a hardware voltage source converter interfaced to a distribution system simulated in real-time.

Residual field suppression for magnetocardiography measurement inside a thin magnetically shielded room using bi-planar coil

For a magnetocardiography (MCG) system inside a magnetically shielded room (MSR), the residual field should be further suppressed to obtain high-quality MCG signals. In this paper, a compensation system has been developed based on the bi-planar coil and the proportional-integral-derivative (PID) controller. The bi-planar coil, derived from the target-field theory and the Tikhonov regularization method, is utilized to generate magnetic field with high uniformity in the pre-defined target region. And the PID controller is introduced to provide dynamic compensation current for the coil, according to the residual field change monitored by a reference SQUID magnetometer. The measurement results show that the noise suppression ratio (NSR) can reach above 20 dB in the low-frequency range from 0.1 Hz to 50 Hz. The DC component and the fluctuation of the residual field in time-domain can be respectively suppressed to 0 pT and 4 pT, indicating that this proposed compensation method is useful for the MCG measurement.

Improved Accuracy of Power Electronic-Based Motor Emulation With Compensation for Signal Transmission Delay

The power electronic based motor emulator (ME) has shown the prospect of replacing the mechanical back-to-back dynamometers with a power converter to validate the performance of the inverter under test (IUT). In real application of the ME to test the IUT, the controller of the IUT is independent from the ME, so that there’re time delays caused by the input voltage sampling of ME, ME calculation and the position signal transmission. Such a delay will cause cross coupling between dq axis which severely influence the emulation accuracy, especially under higher emulated motor speed. A compensation method is proposed to eliminate the cross coupling. A prototype is designed and simulation and experiment results are provided and compared to that of the normal motor emulator to verify the compensation effect. The experimental results have shown that the proposed compensation method can improve the emulation accuracy and a wider speed range of the motor can be emulated accurately.

Implementation of High Precision Error Amplification Scheme for AC-DC Converter

these days, demand for small volume and low cost of the home automation device is getting higher and higher. Converter with single-stage scheme has advantages of simple structure, low cost, and small theoretical volume, but it often suffers bad output accuracy in low output voltage applications. This paper proposes a constant voltage compensation circuit for AC/DC converters to improve the output accuracy which can also be used in a BUCK AC/DC converter with low output voltage. To verify the feasibility of the proposed compensation method, a BUCK controller based on the proposed circuit is implemented in Episil 0.5μm/40V-HVCMOS process and occupies a die size of 0.99×0.8 mm2. By the help of the proposed circuit, the output accuracy of the prototype with single-stage structure, which has advantages of small volume and low cost, can reach as high as those converters with multi-stage structure. Test results show that the load regulation of the prototype is about 1.3% with 3.3V output and less than 0.9% with 5V and 12V outputs.

A Compensation Component Injection Method Based on a Hybrid Modulation for Minimizing the Neutral-Point Voltage Oscillations in a Five-Level Flying Capacitor Rectifier

Neutral-point (NP) voltage oscillating is an inherent problem for multilevel converters with split dc-link capacitors. In this article, a compensation component injection method based on a hybrid modulation for minimizing the NP voltage oscillations in a five-level flying capacitor rectifier is proposed. In specific, the equivalent modulation waves are first obtained by adopting an existing simplified space-vector modulation method. And a hybrid modulation which gives both the same optimal harmonic performance as phase-disposition pulse width modulation (PWM) and the same superiority of flying capacitor voltage regulation as phase-shifted PWM is adopted. Meanwhile, the solved optimal compensation component in each subsector is injected to make the average NP current equal to zero for minimizing the NP voltage oscillations. Simulations and experiments were conducted to verify the performance of the proposed compensation method based on the hybrid modulation.

DOA Estimation of Linear Dipole Array With Known Mutual Coupling Based on ESPRIT and MUSIC

AbstractIn this paper, multiple signal classification and estimation of signal parameters via rotational invariance technique (ESPRIT) algorithms are proposed to estimate the direction of arrival (DOA) of multiple incident signals under known mutual coupling among elements of the antenna array. These algorithms use the same subspace based techniques to achieve the separation of the eigenvectors into two subspaces: the signal space and the noise space. However, ESPRIT only uses the signal space. The performance of subspace based DOA estimation algorithm is evaluated using uniform linear arrays of dipole elements. The simulation results show the exact number of samples and elements, signal‐to‐noise ratio and spacing between the antennas elements used are the most important parameters in the algorithms, to sustain the accuracy of the DOA of the incident signals. The problem of calculating mutual coupling coefficient of the array elements is formed into a matrix has been considered. It is shown from the simulation results that the performance of the DOA estimation techniques considering the mutual coupling effect can be improved by the proposed compensation method. The different results obtained are in good agreement with those of the literature.

Adaptive feed-forward friction compensation through developing an asymmetrical dynamic friction model

This article presents an adaptive feed-forward method to compensate for the dynamic friction in the machine tool systems so that the tracking errors of the machine axes can be reduced. To achieve this aim, a dynamic friction model is firstly established by constructing a continuous and differentiable two-segmented arc tangent curve to characterize the asymmetrical and nonlinear static friction phenomenon in relation to the positive and negative velocity ranges of the machine axes. Subsequently, a new feed-forward method is proposed to compensate for the friction by constructing an adaptive controller with three advantages, i.e. no need of velocity and acceleration measurement, large adaptive rate and high steady-state accuracy. During the model establishment, a discontinuous projection mapping in the learning process is constructed. Especially, the stability of the adaptive controller is strictly proved by theoretical derivation. Besides, a new two-step adaptive method is formulated to analytically calculate the unobservable parameter z. Finally, both simulations and experiments confirm that the proposed compensation method can reach to lower tracking errors, especially in the velocity reversal area, by comparing with the existing approaches.

Mobile Robotic Platform for Contactless Vital Sign Monitoring

The COVID-19 pandemic has accelerated methods to facilitate contactless evaluation of patients in hospital settings. By minimizing in-person contact with individuals who may have COVID-19, healthcare workers can prevent disease transmission and conserve personal protective equipment. Obtaining vital signs is a ubiquitous task that is commonly done in person by healthcare workers. To eliminate the need for in-person contact for vital sign measurement in the hospital setting, we developed Dr. Spot, a mobile quadruped robotic system. The system includes IR and RGB cameras for vital sign monitoring and a tablet computer for face-to-face medical interviewing. Dr. Spot is teleoperated by trained clinical staff to simultaneously measure the skin temperature, respiratory rate, and heart rate while maintaining social distancing from patients and without removing their mask. To enable accurate, contactless measurements on a mobile system without a static black body as reference, we propose novel methods for skin temperature compensation and respiratory rate measurement at various distances between the subject and the cameras, up to 5 m. Without compensation, the skin temperature MAE is 1.3°C. Using the proposed compensation method, the skin temperature MAE is reduced to 0.3°C. The respiratory rate method can provide continuous monitoring with a MAE of 1.6 BPM in 30 s or rapid screening with a MAE of 2.1 BPM in 10 s. For the heart rate estimation, our system is able to achieve a MAE less than 8 BPM in 10 s measured in arbitrary indoor light conditions at any distance below 2 m.

A Compensation Method for Relative Movement Between a Sensor Array and the Abdomen for Magnetic Localization of Capsule Endoscopes

Magnetic localization is an excellent candidate for localization of capsule endoscopes. A small magnet is embedded into the capsule, and its magnetic field is measured at a sensor array around the patient’s abdomen. However, relative movement between the abdomen and the array causes high localization errors. In this study, an innovative movement compensation method is proposed. A rigid array comprising 12 sensors was used to localize a permanent magnet. Furthermore, two orthogonal reference coils fed with a low-frequency signal were assumed to be fixed at the abdomen. The coils were alternately switched on and off, and thus, all three magnetic objects were separately localized since their magnetic fields can be distinguished in the time and frequency domains. A reference coordinate system was set up with the coils, in which the magnet was localized. The proposed compensation method was evaluated for relative rotations and displacements between the sensors and the three magnetic objects. Moreover, the compensation method was evaluated for two reference magnets and compared with the coil-based approach. The mean position error was reduced by approximately a factor of 10 from 41.5 ± 15.5 to 3.8 ± 1.1 mm, respectively, and the orientation error did not exceed 3° for the coil-based compensation method. In contrast, with two reference magnets, the mean position and orientation errors were higher than 30 mm and 20°, respectively. Consequently, it was shown that the coil-based method is the next step toward a wearable magnetic localization system to compensate for relative movement.

Компенсация нестабильности гетеродинов спутников-ретрансляторов для местоопределения наземных источников радиоизлучения

Unintentional and intentional interference of terrestrial radio sources operating via geostationary relay satellites to legal users of satellite communication systems requires accurate determination of their location. Methods of terrestrial radio sources location are based on the calculation of an cross-аambiguity function by additive mixtures of signals and noise received from relay satellites. In the presence of frequency-phase instability of relay satellites heterodynes the retransmitted signals have phase distortions, which lead to a decrease in the signal-to-noise ratio (SNR) when calculating the cross- ambiguity function. The paper is aimed to study the effect of phase distortions caused by the instability of relay satellites heterodynes on SNR at the correlator output and to develop methods for their compensation based on statistical radio engineering and digital signal processing. The study of the proposed compensation methods was carried out by statistical simulation modeling. The SNR dependences at the correlator output on the duration of correlated signals for the model with a domi-nant frequency noise and frequency random walk have been obtained and a method for compensat-ing phase distortions caused by the instability of the relay satellites heterodynes has been developed. The energy gain has been estimated by applying the proposed compensation method. It has been shown that the developed method of compensation of relay satellites heterodynes instability allows achieving a significant gain in the SNR at the correlator output and contributes to increasing the probability of radio source signal detection from auxiliary relay satellites.

An Effective Reactive Power Compensation Method and a Modern Metaheuristic Algorithm for Loss Reduction in Distribution Power Networks

In this paper, a new method of reactive power compensation is proposed for reducing power loss of distribution power networks. The new method is the combination of local compensation at each load and distribution line compensation. In the method, local capacitors at each load are determined to increase power factor of load to an expected value first and then a number of capacitors are placed in distribution lines with two factors, location and capacity by using the three applied methods. Particle swarm optimization (PSO), parasitism predation algorithm (PPA), and tunicate swarm algorithm (TSA) are applied for the proposed method on four distribution systems with 15, 33, 69, and 85 buses. The comparisons of results with previous methods indicate that the three applied methods can reach higher loss reduction for all study cases. TSA can reach loss reduction more effectively than others by 19.4%, 0.5%, 7.9%, and 10.76% for the four distribution systems, respectively. The most important emphasis is that PSO, which was considered to be of low effectiveness in previous studies, can reach much better loss than approximately all previous methods thank to the proposed compensation method. PSO also reached better loss reduction than others by 18.97%, 0.4%, 7.73%, and 10.21%, respectively. Consequently, it is recommended that the proposed compensation method is useful for distribution systems in minimizing total power loss and TSA can be selected a new and powerful method for the problem.

Adaptive Doppler compensation method for coherent LIDAR based on optical phase-locked loop

Coherent LIDAR is a potential and effective technology to detect and identify space debris. However, for the high-speed space debris, the large Doppler frequency shift (DFS) generated by high-speed relative motion challenges the bandwidth of the photoelectric detection system and increases the difficulty of datasampling and processing. In this paper, we propose an effective method to compensate this large DFS adaptively by using an optical phase-locked loop (OPLL), and thus the relative velocity between the target and LIDAR platform can be obtained. A laboratory experiment for moving targets with our OPLL method has been conducted, and it revealed that our method worked well to compensate for 64 MHz frequency difference, thus the relative velocity is about 26 m/s based on the compensated DFS. And the beat frequency is always locked to the reference frequency, while the DFS generated by variable speed motion is compensated adaptively. The proposed compensation method could improve the performance of coherent LIDAR significantly, especially when detecting high-speed target.

Current balance method of dual windings parallel coils based on distributed capacitor compensation in high‐power WPT systems

Dual windings parallel (DWP) coils are often used in high-power wireless charging applications to reduce current stress and internal resistance. Due to the inconsistent self-inductance and strong coupling of the two windings, the advantages of the DWP coils cannot be fully utilized. In particular, the current stresses of the two windings are different, which will cause one of the stress to exceed the limit, and the temperature rise is too high. The reason for the current imbalance in the two windings is analysed in this work, and a distributed capacitor compensation method is proposed to balance the current stress in the two windings. Finally, a WPT system with the DWP transmitting coil was built as an example to demonstrate the effectiveness of the proposed method. The experimental results show that the current ratio in two windings decreased from 1.70 to 1.05 after using the proposed compensation method.

Homography-based robust pose compensation and fusion imaging for augmented reality based endoscopic navigation system

BackgroundAugmented reality (AR) based fusion imaging in endoscopic surgeries rely on the quality of image-to-patient registration and camera calibration, and these two offline steps are usually performed independently to get the target transformation separately. The optimal solution can be obtained under independent conditions but may not be globally optimal. All residual errors will be accumulated and eventually lead to inaccurate AR fusion. MethodsAfter a careful analysis of the principle of AR imaging, a robust online calibration framework was proposed for an endoscopic camera to enable accurate AR fusion. A 2D checkerboard-based homography estimation algorithm was proposed to estimate the local pose of the endoscopic camera, and the least square method was used to calculate the compensation matrix in combination with the optical tracking system. ResultsIn comparison with conventional methods, the proposed compensation method improved the performance of AR fusion, which reduced physical error by up to 82%, reduced pixel error by up to 83%, and improved target coverage by up to 6%. Experimental results of simulating mechanical noise revealed that the proposed compensation method effectively corrected the fusion errors caused by the rotation of the endoscopic tube without recalibrating the camera. Furthermore, the simulation results revealed the robustness of the proposed compensation method to noises. ConclusionsOverall, the experiment results proved the effectiveness of the proposed compensation method and online calibration framework, and revealed a considerable potential in clinical practice.

A comparison of automatic and manual compensation methods for the calculation of tube currents during off-centered patient positioning with a noise-based automatic exposure control system in computed tomography.

Automatic exposure control (AEC) is used to optimize the X-ray tube output during computed tomography (CT) scans. However, calculation of the tube current by AEC can be affected when a patient is not aligned with the rotational center of the X-ray tube. An automatic couch height-positioning compensation mechanism provides a corrective function when the patient is off-center. In this study, we aimed to (a) evaluate the performance characteristics of the positioning compensation mechanism and (b) confirm whether our proposed compensation method can be properly applied to a noise-based AEC system even if the CT device is not equipped with a positioning compensation mechanism. An elliptical phantom was scanned at various table heights on systems without/with the positioning compensation mechanism. Expressions describing the offset from the gantry's isocenter and adjusted standard deviation settings were derived and used in our proposed compensation method. A phantom was scanned at various table heights with our proposed compensation method, and volume CT dose index (CTDIvol) and image noise levels were obtained. An anthropomorphic chest phantom was also scanned using the proposed compensation method to verify its accuracy. When the positioning compensation mechanism was used, it yielded a constant CTDIvol and image noise levels at various table heights tested. A comparison between our proposed method and the positioning compensation mechanism for both the elliptical and chest phantoms yielded similar CTDIvol. Therefore, both automatic and manual positioning compensation methods are useful for avoiding AEC miscalculations in off-centered patient positioning cases.