Accurate Compensation Research Articles

Boundary Integral Equation Method for Compensating Magnetostatic Fields of Thin Shells

In traditional design of degaussing systems, the layout of degaussing coils is usually predefined. In order to calculate the electric currents in coils, the inverse problem of minimizing the magnetic field in a set of points outside the demagnetized object is solved. The article proposes a direct approach which allows estimating the coil currents together with the coil geometry based on computing surface distributions of compensating currents. For a thin ferromagnetic shell, these currents can be represented by a single boundary layer placed on the inner or outer side of the shell. The surface density of the current layer is expressed via a stream function and computed using a boundary-integral equation derived from zero tangential trace of the vector magnetic potential on the exterior side of the shell. Unlike other integral equations with respect to boundary layer densities, new equation contains rotation operator, which maps the div-conforming edge element space to the curl-conforming one. This involves alternative representations of the surface magnetization of the shell. As a result, the field compensation error depends on the layer position (inside or outside the shell), mesh size, and approximation of the surface magnetization. The accuracy of compensation and spatial characteristics of compensation currents are investigated using test models of spherical and cubic shells, and a ship computer model.

New Adaptive Dynamic Output Feedback Control of Double-Pendulum Ship-Mounted Cranes With Accurate Gravitational Compensation and Constrained Inputs

Output feedback control without using velocities is an effective way of dealing with problems caused by unmeasurable velocities and noise magnification by numerical difference, which are practical issues associated with crane control. This article proposes a new adaptive dynamic output feedback control approach for double-pendulum ship-mounted cranes in the presence of unknown parameters (e.g., cargo masses). The problems caused by the unknown masses are addressed through a new adaptive gravitational compensation law. Also, the input constraints are tackled by introducing bounded functions. Specifically, to handle the complicated disturbances caused by ship motions, new state variables are constructed to transform the dynamic model. Then, Lyapunov-based stability analysis is proceeded to design the controller and the adaptive law. To the best of authors’ knowledge, this is the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"/> first <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"/> control method proposed for double-pendulum ship-mounted crane systems <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"/> without <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"/> using velocity signals, which can simultaneously eliminate steady errors, suppress unexpected cargo swing, achieve accurate gravitational compensation, and satisfy input constraints. The closed-loop system’s state variables asymptotically converge to the equilibrium point, which is rigorously proven. A series of experiments are implemented on a hardware testbed, which further illustrate the satisfactory performance of the proposed method.

An Accurate VSI Nonlinearity Modeling and Compensation Method Accounting for DC-Link Voltage Variation Based on LUT

The nonlinearity of the voltage source inverter (VSI) leads to the error between output voltage and reference voltage, and causes the phase current harmonics. It is necessary to compensate its influence in the fields such as parameter identification, sensorless control, and servo drives. In this article, an industrial solution for VSI nonlinear compensation method based on lookup table (LUT) is introduced. The characteristics of semiconductor devices, equivalent dead-time and influence of parasitic capacitance effects are calculated quantitatively though injecting increase and decrease current during self-commissioning process. The critical current value for parasitic capacitor and the variation of equivalent dead time are verified through different distorted voltage curves. Considering dc-link voltage variation is irresistible for industrial products, 3-D linear interpolation is adopted to compensate the variation of VSI nonlinearity under different voltage conditions. Proposed LUT method does not require VSI datasheet and complicated calculation formula during implementation. Experiments are carried out on a commercial permanent magnet synchronous motor drive system to verify the proposed LUT method.

Bidirectional Optical Carrier Frequency Commonality Method for Optical Fiber Delay Measurement

The transmission delay in an accurate time-transfer system using an optical fiber is calculated by accurately measuring the roundtrip delay of the fiber. The delays in the forward and backward paths of the transmission line must be identical to achieve a highly accurate transmission delay compensation. The effect of chromatic dispersion, which occurs when the optical wavelengths of the forward and backward signals are different, and the effect of backscattering, which occurs in the fiber, are crucial and must be considered for higher accuracy. In this study, we present a fiber transmission delay measurement method that uses optical signals of the same wavelength for the forward and backward paths to overcome these problems. Signal separation can be achieved between the forward and backward signals and between the transmission and backscattered signals by shifting the modulation frequency of a sub-carrier of the optical signal at the remote station. The experimental results demonstrate that a highly accurate time-transfer of more than 1 ns can be expected over a 250 km fiber transmission.

Research on Nonlinear Compensation of the MEMS Gyroscope under Tiny Angular Velocity.

The Micro-Electro-Mechanical System (MEMS) gyroscope has been widely used in various fields, but the output of the MEMS gyroscope has strong nonlinearity, especially in the range of tiny angular velocity. This paper proposes an adaptive Fourier series compensation method (AFCM) based on the steepest descent method and Fourier series residual correction. The proposed method improves the Fourier series fitting method according to the output characteristics of the MEMS gyroscope under tiny angular velocity. Then, the optimal weights are solved by the steepest descent method, and finally the fitting residuals are corrected by Fourier series to further improve the compensation accuracy. In order to verify the effectiveness of the proposed method, the angle velocity component of the earth’s rotation is used as the input of the MEMS gyroscope to obtain the output of the MEMS gyroscope under tiny angular velocities. Experimental characterization resulted in an input angular velocity between −0.0036°/s and 0.0036°/s, compared with the original data, the polynomial compensation method, and the Fourier series compensation method, and the output nonlinearity of the MEMS gyroscope was reduced from 1150.87 ppm, 641.13 ppm, and 250.55 ppm to 68.89 ppm after AFCM compensation, respectively, which verifies the effectiveness and superiority of the proposed method.

Synchronization for mini‐UAV‐based high‐resolution BiSAR systems: Lost direct signal estimation based on Hampel filtering

In mini-unmanned aerial vehicle-based high-resolution bistatic synthetic aperture radar systems, the rotation of the unmanned aerial vehicle platforms will cause direct signal loss, resulting in the reduction of synchronization error compensation accuracy. Here, a synchronization algorithm is proposed to estimate the lost direct signal. First, bistatic time and phase synchronization signal models are established. Then, Hampel filtering is used to estimate the time delay of the lost direct signal, and the time and phase synchronization errors are estimated based on third-order polynomial fitting. A high-resolution synthetic aperture radar image is used to demonstrate the validity of the proposed algorithm in mini-unmanned aerial vehicle-based high-resolution bistatic synthetic aperture radar systems.

An adaptive tracking control method for offshore cranes with unknown gravity parameters

The offshore crane system is a typical underactuated system which is installed on the ship and carried out the payload transportation in the offshore environment. The payload transportation for offshore cranes is extremely sensitive to the influence of the ship motion. High couplings also exist between the offshore crane state variables. These factors may lead to large payload swing, and the offshore crane control problem is very difficult. In addition, since some physical parameters of the offshore crane system are difficult to be measured, there usually exist parameter uncertainties, which may lead to positioning errors. In order to tackle the above problems, a new adaptive tracking control method for offshore crane system is proposed, which brings satisfactory tracking performance of the reference trajectories and realizes the control objectives of the payload accurate and fast transportation, the payload swing elimination, and the accurate gravity compensation. Unlike the traditional adaptive control method, an elaborately designed adaptive estimation update law is proposed, which is used to ensure the accurate online estimation for gravity-related parameters. By using Lyapunov stability theory, it is proved that the proposed adaptive tracking controller is effective. Simulations are included to further show the performance of the proposed method.

A novel switching method in PV‐fed quasi‐ZSI‐DVR for voltage quality enhancement of photovoltaic integrated networks

AbstractIn this work, a novel switching method for the photovoltaic‐fed (PV‐fed) dynamic voltage restorer (DVR) system based on a quasi‐Z‐source inverter (quasi‐ZSI) is proposed. This proposed switching control strategy is implemented in such a way that a wider voltage boost gain and lower voltage stress across the switches and capacitors are achieved. The major drawback with the traditional switching method is that always three switches will be in conduction. However, in the proposed switching method, only two switches are triggered simultaneously to achieve the required output. It also obviates the need for zero states. The proposed switching method for the PV‐fed quasi‐ZSI‐DVR provides an accurate compensation for various voltage disturbances, such as sags, swells, and interruptions, thereby eliminating the voltage harmonics at the point of common coupling. The integration of PV and battery is suggested for the quasi‐ZSI‐DVR to tackle the pertinent issue regarding sporadically transferring energy in the PV arrays and also recharging of batteries. Simulation and experimental results validate the suitability of the proposed PV‐fed quasi‐ZSI‐DVR configuration with the proposed switching control method. It is inferred that the proposed system provides the lowest voltage harmonics and additional benefits like smaller capacitors, higher voltage gain, and lower voltage stress rates.

SLES: Scheduling-Based Low Energy Synchronization for Industrial Internet of Things

The growth in the Industrial Internet of Things (IIoT) drives the development of large-scale wireless sensor networks (WSN), such as smart cities. Time synchronization is essential and primary for enabling collaborative operations among sensor nodes. Generally, all sensor nodes in the network synchronize through exchanging messages, increasing energy consumption. This study introduces scheduling-based low-energy synchronization (SLES) for IIoT. SLES aims to reduce the number of transmitted messages, which in turn reduces the overall energy consumption. In addition, SLES establishes a schedule of distinct synchronization messaging times for each reference node to alleviate the collision problem among the sensor nodes. SLES is constructed and evaluated using real WSNs with different configurations. The experimental results showed that SLES achieves significantly less message traffic than the previous algorithms: FADS – fast scheduling and accurate drift compensation for time synchronization, EERS – energy-efficient reference node selection, and R-sync – robust time synchronization. In this study, we used a simulation to evaluate the performance of SLES in large-scale networks. For the 4-way grid network, the experiential results show that SLES reduced the number of transmitted messages by approximately 22% compared to EERS and FADS. Moreover, SLES outperformed the R-sync algorithm by a factor of 2.5.

An Online Combined Compensation Method of Geomagnetic Measurement Error

The online error compensation of the three-axis magnetic sensor is the key to a high accuracy geomagnetic assisted navigation. Traditionally, the least squares or its improved methods are used for error compensation, which are offline and need to assume that measurement errors are Gaussian. In this paper, the geomagnetic measurement error is modeled based on the error source analysis, and then the compensation parameters are converted through the ellipsoid hypothesis. To eliminate the negative effect of abnormal values, iterative least squares is designed to calculate static compensation parameters and corresponding residuals, then different weights are assigned to each geomagnetic measurement data through robust estimation. Also, to avoid data saturation phenomenon and finally complete online error compensation, a forgetting factor is introduced into the iterative least squares, and the dynamic coefficients are constructed by weights of measurement data to derive the online updated compensation parameters. Simulation and experiment results both show that the online combined compensation method possesses higher adaptability, which can eliminate the influence of abnormal data effectively. And its accuracy and stability of error compensation are better than other state-of-the-art methods.

A high-efficiency feedforward compensation method for capacitor-less LDO

This paper proposes a new structure of compensation for LDO. A feedforward path is added to this system and the gain of this feedforward stage is well-controlled by using the proposed structure so that it can accurately change the position of the zero generated by this system for accurate frequency compensation. The structure substantially improves stability at low power consumption, so that this structure implements a high-efficiency compensation method. This LDO is under SMIC 0.18μm CMOS process with a total area of 0.031 mm2. When the load current is 20 mA, the line regulation can be as low as 0.33 mV/V. The phase margin of proposed LDO can reach around 90 deg and the recovery time is less than 2μs. It is worth mentioning that the total quiescent current consumption of proposed LDO is only 6.58 μA and the current efficiency is above 99.94%.

Depth-resolved dispersion compensation method for optical coherence tomography imaging based on rectangular window function optimization

In the optical coherence tomography system, the mismatch in dispersion between the two interference arms will reduce the axial resolution of the system. Therefore, dispersion compensation is required. However, the current depth-resolved dispersion compensation method uses a fixed window function to extract signals at different depths, which has phase calculation error and reduces the accuracy of dispersion compensation. In this paper, we optimized the rectangular window function for the signal interception. According to the functional relationship between the phase and the wave number in the presence of dispersion, the second-order fit to the obtained phase is performed and the standard error of the fit result is used as the criterion. The optimized rectangular window is used to intercept the signal and perform FFT, thereby effectively reducing the phase error caused by the window function. And we accurately extracted the dispersion coefficients of samples to improve the accuracy of dispersion compensation.

Spatial phase shifting algorithm in digital holographic microscopy with aberration: More than the speed concern

Accurate aberration phase compensation is significant for high spatial phase sensitivity in digital holographic microscopy (DHM). The model widely used in state-of-the-art methods regards the aberration phase as an additional and independent phase term and we just need to subtract it out. However, owing to the instable phase carrier induced by this additional phase term, the phase demodulation procedure will suffer from a non-additive phase distortion which cannot be directly subtracted out by digital post-processing. Consequently, it is necessary to remove this aberration phase and suppress the non-additive distortion at the same time. In this work, we propose a modified spatial phase shifting (MSPS) algorithm by making the phase demodulation procedure be adaptable to the interferogram with instable spatial carrier. Using such MSPS algorithm, the aberration phase can be automatically estimated before 2D unwrapping and the non-additive phase distortion can be effectively suppressed at the same time.

A Frequency Adaptive Repetitive Control for Active Power Filter With 380V/75A SiC-Inverter

Active power filters (APFs) with repetitive control (RC) could compensate for the harmonics. However, there are some problems in IGBT-380V-APFs with RC, such as the adaptability of grid frequency varying because of the noninteger value of RC parameters. SiC- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> s that could reach high switching frequency provide a new way to increase the compensation accuracy and the frequency adaptability for 380V/APFs. In this article, a novel frequency adaptive fast repetitive control (FAFRC) for APF with SiC- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> inverter to achieve optimal performance in variable frequency girds through changing RC order <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> was proposed. Taking the advantage of the high switching and sampling frequency of SiC-APF, the control method proposed could compensate for the harmonics more accurately with an integer RC order <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> . The control method with 50 kHz switching and the sampling frequency is described, designed, and verified experimentally in a two-level 380V/75A APF prototype made up of SiC- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> s, which volume is 37L that 66% of IGBT-APFs. The results obtained that 380V/75A-SiC-APFs with the control method proposed have a high compensation accuracy (THD<5%) with the grid frequency variations.

Real-Time Iterative Compensation Framework for Precision Mechatronic Motion Control Systems

With regard to precision/ultra-precision motion systems, it is important to achieve excellent tracking performance for various trajectory tracking tasks even under uncertain external disturbances. In this paper, to overcome the limitation of robustness to trajectory variations and external disturbances in offline feedforward compensation strategies such as iterative learning control (ILC), a novel real-time iterative compensation (RIC) control framework is proposed for precision motion systems without changing the inner closed-loop controller. Specifically, the RIC method can be divided into two parts, i.e., accurate model prediction and real-time iterative compensation. An accurate prediction model considering lumped disturbances is firstly established to predict tracking errors at future sampling times. In light of predicted errors, a feedforward compensation term is developed to modify the following reference trajectory by real-time iterative calculation. Both the prediction and compensation processes are finished in a real-time motion control sampling period. The stability and convergence of the entire control system after real-time iterative compensation is analyzed for different conditions. Various simulation results consistently demonstrate that the proposed RIC framework possesses satisfactory dynamic regulation capability, which contributes to high tracking accuracy comparable to ILC or even better and strong robustness.

Fractional-Order Multiperiodic Odd-Harmonic Repetitive Control of Programmable AC Power Sources

In this article, a generic plug-in fractional-order multiperiodic odd harmonic repetitive control (FOMP-OHRC) scheme is proposed to provide a simple high-performance control solution to the programmable ac power sources. The proposed FOMP-OHRC scheme evolves from the plug-in multiperiodic OHRC scheme, which can take both advantages of the multiperiodic OHRC controller and the feedback controller—the feedback controller provides fast response and good robustness, and the plug-in multiperiodic OHRC controller offers accurate compensation of the multiperiodic signals. The stability criteria and the control gain tuning rules have been developed to facilitate the analysis and synthesis of the plug-in multiperiodic OHRC scheme. More critically, in order to exactly compensate the multiperiodic signals with unavoidable fractional periods in practice, the multiperiodic OHRC controller is transformed into the FOMP-OHRC controller by substituting the fractional period elements with the Lagrange-polynomial-based interpolation filters. Experimental results indicated the programmable ac power source with the proposed FOMP-OHRC can generate required multiperiodic voltages with high accuracy, fast transient response, and good robustness.

Numerical studying of broadband tunable dispersion compensation based on photonic crystal fiber

We propose a broadband tunable negative dispersion photonic crystal fiber (BT-ND-PCF) for dispersion compensation over the S + C + L wavelength bands. BT-ND-PCF is a dual-core structure in which air holes are arranged with a hexagonal lattice and temperature-sensitive liquid is infiltrated into the air holes of the fourth layer. The performance of BT-ND-PCF is numerically analyzed by the finite element method with an anisotropic perfect matching layer. The results show that BT-ND-PCF has a broadband negative dispersion coefficient of −1533.2 to −2836.4 ps / km / nm over the S + C + L wavelength bands, a dispersion coefficient of −2268.9 ps / km / nm at 1550 nm, and a kappa value of 287.9 nm at 1550 nm, which matches with Corning single-mode fiber 28 (SMF). The residual dispersion (RD) after compensating for the dispersion of 1 km SMF is in the range of −0.22 to +0.16 ps / nm. In addition, the dispersion coefficient is changed by 0.679 ps/km/nm per 1°C by controlling the temperature, which is conducive to the accurate compensation of RD. Due to its unique optical properties, BT-ND-PCF can be used in broadband dispersion compensation for dense wavelength division multiplexing optical fiber communication systems.

Application of an Improved Calibration Flight Scheme in Aeromagnetic Interference Compensation

AbstractIn aeromagnetic measurement, accurate compensation for the interference magnetic field generated by the aircraft platform due to the aircraft maneuvering in the Earth's magnetic field is an important prerequisite for the accurate identification of the magnetic anomaly signal of the detection target. The flaws of the traditional calibration flight scheme in aeromagnetic interference compensation are firstly analyzed, and then an improved scheme is proposed, featuring smaller calibration flight areas, more simplified maneuvers, shorter flight route and less influence from the magnetometer's direction and extreme weather. The improved scheme can enhance the robustness of the aeromagnetic interference compensation matrix and improve the compensation efficiency, and thus both the solved magnetic compensation coefficients and compensation effects are significantly improved. The experimental results of the aeromagnetic interference compensation in an area of Inner Mongolia of China show that the average accuracy of the repeated survey lines, which are compensated by the improved scheme, can be increased by 5 and 3 nT, respectively, compared with the uncompensated results and the results compensated by the traditional scheme. Therefore, the effectiveness and superiority of the improved calibration flight scheme is fully proved.

A new stylus orientation planning strategy for sculpture surface inspection based on touch position graph

On-machine inspection (OMI) is an important technology for precise machining. Accuracy and efficiency improvement is a challenge for sculpture surface inspection. Before the inspection, if the practical touch position on the stylus tip is calibrated accurately, more accurate compensation of the pre-travel error could be applied in the inspection results. Meanwhile, time consumption on the calibration process could be reduced if the number of preset to-be-calibrated positions in the calibration is as small as possible. Thus, for precise compensation, the practical touch position on the stylus tip needs to be assigned during the inspection. In further, to reduce the calibration time, the quantity of practical touch position on the stylus tip requires to be least. A new stylus orientation planning strategy that controls the practical touch positions on the stylus tip is investigated in this paper. In terms of the strategy, a touch position graph (TPG) is proposed for the five-axis machine tool to discover the relationships between the practical touch positions, the angle combinations of rotary axis and the stylus orientations. The practical touch positions on the stylus tip and the rotation direction change of the machine tool’s rotary axes can be reduced as much as possible by optimizing the stylus orientations. In further, the pre-travel error on each to-be-inspected point can be compensated by accurate calibration results and the introduction of the rotation axes error can be decreased to prove the inspection accuracy improvement. At last, an experiment is applied on the impeller to verify the proposed OMI planning strategy.

Ductile machining of optical micro-structures on single crystal germanium by elliptical vibration assisted sculpturing.

Microstructure surfaces are widely and deeply applied in optical fields to decrease the volume of an optical system and realize sophisticated optical requirements. This paper studies the machining of optical micro-structures with micro-scale height on single crystal germanium by elliptical vibration assisted sculpturing (EVAS) method in which two vibration amplitudes keep constant. Due to the superimposition of low-frequency sculpture path and high-frequency elliptical locus, the investigations are focused on cutting plane to describe motion trajectory of the tool tip of cutting tool for desired complex motion path and to calculate the sculpture path of elliptical vibration cutting device to make corresponding path of tool tip be the envelope of target profile. A comparative experiment is firstly conducted to verify that elliptical locus would deteriorate machining accuracy without accurate compensation for the ellipse. Following that, 2D and 3D sinusoidal surfaces and a picture, whose structural heights are all not less than 2.0µm, are experimentally machined on single crystal germanium. Satisfying experimental results demonstrate the feasibility of EVAS method for fabricating optical micro-structures on germanium.