Linear Compensation Research Articles

Adaptive saturated control for spacecraft rendezvous and docking under motion constraints

This paper investigates the problem of position tracking and attitude synchronization for spacecraft rendezvous and docking with a tumbling target, in which kinematic couplings, unknown disturbances, motion constrains, and input saturation are considered. A novel artificial potential function (APF) is developed to encode both three-dimensional pose information and two-dimensional image information regarding path constraint and field of view constraint, respectively. By integrating the APF into the sliding mode technique, an adaptive control strategy is proposed to realize the arrival of the chaser at the docking port without any risk of collision or loss of target features. In addition, a linear anti-windup compensator is introduced to compensate for the input saturation effect. Uniformly ultimately bounded of the closed-loop system is guaranteed through Lyapunov analysis. A specific simulation scenario of docking with the defunct satellite Envisat is created to demonstrate the effectiveness and robustness of the proposed control strategy.

New Method Based on Model-Free Adaptive Control Theory and Kalman Filter for Multi-Product Unsteady Flow State Estimation

Abstract In this paper, a new methodology is proposed to realize real-time unsteady flow estimation for a multi-product pipeline system. Integrating transient flow model, adaptive control theory, and adaptive filter, this method is developed to solve the contradiction between the efficiency and accuracy in traditional model-based methods. In terms of improving computational efficiency, the linear flow model based on frequency response and difference transforming is established to replace the traditional nonlinear flow model for transient flow state estimation. To reduce the deviation between actual observations and linear model estimates, we first introduce a model-free adaptive control method as linear compensation of the reduced order unsteady flow state model. To overcome the interference of observation noise, the Kalman filter method is applied to the modified state space model to obtain the one-step-ahead transient flow estimation. The proposed method is applied to the transient flow state estimation of a multi-product pipeline system and compared with the model-based method and two data-driven methods. The proposed method can reduce the deviation of transient flow estimation between the reduced order linear model and the traditional nonlinear model to less than 0.5% under unforeseen conditions and shows strong robustness to noise interference and parameter drift.

Optimal Compensation Under Inventory Delegation and Supply/Demand Mismatch

Problem definition: We study how a firm should design its compensation plan to include both the sales performance and the operational performance (i.e., the supply/demand mismatch), for its sales division, who not only exerts unobservable demand-enhancement efforts but also makes the inventory ordering decision based on her private information about the local sales territory. Methodology/results: We build on the classical agency model by incorporating the supply/demand mismatch and inventory ordering delegation. We derive the closed-form expression for the firm's optimal compensation scheme in the most general contract space and show that it takes a simple form, coupling the classical linear compensation scheme with a compensation component contingent on some operational metric. Managerial implications: First, the firm should include a compensation component that is tied to operational metrics such as the sales division's leftover inventory and the unfulfilled demand. Second, the optimal compensation scheme needs to be adapted to the distinct operational features such as demand being censored or not, lost sales or backorder. Third, the optimal compensation scheme possesses the property of piece-wise linearity in demand (or sales) with a drop in the commission rate after demand exceeds the available inventory. This is in contrast not only with the classical linear compensation scheme, but also with the quota-based compensation scheme featuring a progressively increased commission rate when the demand exceeds a prespecified quota.

Energy absorption of human red blood cells and conductivity of the cytoplasm influenced by temperature

The energy absorbed into tissues is known as the specific energy absorption (SAR) which is dependent on conductivity of the tissue. We calculated cytoplasmic conductivity of human red blood cell (HRBC) using the intracellular ionic concentrations and the Debye-Hückel-Onsager relation. The overall concentration is determined by cell volume and cell water content. The calculated HRBC conductivity at 25 o C was σc,25 = 0.5566 ± 0.0146 S m−1, ±SE). It is exponentially related to temperature: Q10 ≈ 1.866. At 37 o C, the calculated SAR value is 1.6 W kg−1 using a linear temperature compensation of conductivity. However, if using a biologically realistic non-linear temperature compensated conductivity, the SAR is ≈ 2.62 ± 0.05 W kg−1. The relationship between SAR and temperature increase is not straightforward. Since there is a wide variance in cellular ionic and water perfusion rates more tissue-specific SAR limits which consider temperature-related factors would be valuable.

Modeling of optical fiber dispersion on QAM protocol in affordable RF-over-fiber channels

We investigate the effect of optical chromatic dispersion on ordinary double-sided modulation (DSM) quadrature amplitude modulation (QAM-M) protocol in RF-over-fiber (RFOF) channels. QAM-M protocol is common in RFOF communications channels. An analytical expression was derived for the channel’s response, the standard deviation of the QAM’s clusters, and for the estimations of the channel’s bit error rate (BER). The main findings are as follows: (A) unlike single-sided modulation (SSM) QAM or coherent QAM, ordinary DS QAM is governed by three length scales, and therefore it is much more susceptible to dispersion; (B) the QAM’s clusters cannot be bounded, even for weak dispersion, and therefore, zero-error detection is unattainable without dispersion compensation; and (C) a linear dispersion compensation filter was derived to mitigate the dispersion effects post-detection. These results suggest that it is not essential to operate the channel in a SSM QAM mode. A simpler and affordable option may be to operate the channel in an ordinary DSM QAM method and to apply a dispersion compensating filter in the electrical or even in the digital domain. This method is a low-cost solution to improve substantially the RFOF channels performances.

Dynamic Compensation of Ultra-Low-Range Pressure Sensors

A technique has been developed to compensate pressure readings from arrays of highly sensitive membrane-type pressure sensors for deflections caused by acceleration normal to the plane of the membrane using a single inertial measurement unit. By normalizing the fourth-order unsteady Kirchoff-Love equation, it can be shown that inertial body pseudoforces and applied surface pressure elicit a similar and additive response from the sensors. Inertial effects arising from linear and angular acceleration as well as angular velocity may therefore be converted to ‘pseudopressures’ and eliminated by means of a simple linear compensation process which can be calibrated using only gravity. To demonstrate, signals from a conventional six-axis inertial measurement unit (including three orthogonal components each of angular velocity and linear acceleration) are used to provide an approximation of the acceleration of the sensing dies within a seven-channel distributed array of ultra-low pressure sensors. Applying the proposed correction reduces the maximum full-scale uncertainty of the measurements by as much as 50%.

Linear Superposition Compensation Strategy to Optimize Transient Response for Critical Conduction Mode Boost Converter

For boost converter operating in the Critical Conduction Mode (CRM), linear compensation strategy is widely used to improve the control performance. However, conventional linear compensation is designed for limited input, since transfer functions for different input are often incompatible. In this paper, transient responses with respect to input/reference voltage and load variations are optimized simultaneously by a linear superposition compensation strategy. The objective closed-loop transfer functions for each kind of variations are investigated, which contribute to the overall compensation loop design. According to linear superposition principle, the compensation results are summed as reference current, based on which the switching on/off time is modulated. Although the summed results are convergence, separate compensation loop that includes integral terms can lead to divergence in calculation process. To eliminate the potential divergence, the overall compensation loop is re-designed so as to suit digital implementation. Experimental results show that the linear superposition compensation strategy achieves great transient performance to different kind of variations.

THERMALLY GUIDED DEHYDRATION OF BINUCLEAR [Ni2(en)2(H2O)6(pyr)]·4H2O COMPLEX: A FURTHER INSIGHT

Thermally prompted dehydration of binuclear [Ni2(en)2(H2O)6(pyr)]·4H2O complex occurs within a 326 K to 410 K temperature region, presenting an asymmetrical DSC peak. The process is endothermal and results in the loss of 10 molecules of water accounting for 26.8% of the total mass of the sample. Values of the apparent activation energy of 71 kJ/mol and 93 kJ/mol were determined by using Kissinger's and the isoconversional KAS approach, respectively. The probable reaction mechanism was determined by Dollimore's analysis. Deconvolution of the experimental DSC peak on different heating rates shows that the mechanism of dehydration changes with the change in the heating regime. Using the linear compensation effect, values of invariant activation energy of 61 kJ/mol as well as of Arrhenius pre-exponential factor of 6·107 min-1 were determined.

Nonlinear compensation algorithm for multidimensional temporal data: A missing value imputation for the power grid applications

In smart grid, the missing values do influence the real-time grid monitoring and bring biases of conclusions from the grid data mining. From the analysis on the data from smart grid, every variable shows global variation and local variation. Based on these characters, a novel statistical and machine learning-based imputation method is proposed, taking advantage of the global trend capturing by one-dimension interpolation of the variable of interest and the local variation capturing by linear compensation of multidimensional variables. By using KCPA, the multidimensional nonlinear variables are mapped into a feature space, and obtained new variables linearly couple with the variable of interest. Then these new variables together with the multidimensional linear variables are used for that linear compensation. The comparative experiment indicates that the proposed method outperforms the commonly used methods by reducing the RMSE by 29.19% and MAE by 44.73% on average, and having the best R2 closest to 1. A test on public dataset shows that the proposed method still has a good performance. At last, the sensitivity analysis on missing rate shows that the imputation error of the proposed methods remains steady for all the variables with the increase of missing rates from 5% to 10%.

A Linear Compensation Method for Improving the Accuracy of an Absolute Multipolar Magnetic Encoder

This paper proposes a linear compensator algorithm to improve the performance of an absolute multipolar magnetic encoder (AMPME). An AMPME is an absolute magnetic rotary encoder that uses a multipolar magnet (MPM) to increase the resolution. The resolution can be dramatically increased in proportion to the number of poles in the MPM. However, various hardware problems that occur during the encoder manufacturing process degrade the AMPME performance. Also, harmonic components occur in the raw data due to various problems, such as the resistance error of the analog circuit, magnetic field overlap between the magnets, position error between the sensor and magnet, and pole-pitch difference. In particular, during the magnetization process of the MPM, the pole-pitch difference becomes a problem when the sizes of each pole are not uniform. This problem causes harmonic components that reduce the absolute position accuracy. To solve these problems, this paper proposes a linear compensation method. The proposed linear compensator consists of two parts. The first part is the enhanced ratiometric linearization for phase calculation and calibration. The second is the phase compensator for removing the phase difference via the pole-pitch difference of the MPM. The linear compensator improves various parameters by precomputing the offset, amplitude, and phase corrections. After compensating for sinusoidal signals, the linear compensator applies appropriate parameters at the appropriate times. This method is faster, easier to set up, and more accurate than the conventional method. Furthermore, this method is experimentally verified against the existing harmonic rejection method. Experimental results are provided to verify the effectiveness of the proposed method.

Modeling and filtering for a stochastic uncertain system in a complex scenario

This paper presents a new approach to filter signals for discrete-time physical problems with stochastic uncertain in the presence of random data transmission delays, out-of-order packets and correlated noise. To deal with the packet disorder, the system model synthesizing the transmission delays and out-of-order packets from the plant to the filter is established by utilizing signal reconstruction schemes based on the zero-order-holder and logic zero-order-holder. A robust finite horizon Kalman filter is proposed by augmenting the state-space model and minimizing the error covariance. To further improve the filtering performance, a linear estimation-based delay compensation strategy is proposed by employing the reorganized time-stamped measurements. Moreover, for solving the missing measurement problem whilst reducing the computational costs, an artificial delay compensation approach is established using an one-step prediction approach. Simulation results show the effectiveness of the proposed method.

Improved Odd-Harmonic Repetitive Control Scheme for Cuk-derived Inverter

This paper proposes an improved odd-harmonic repetitive control (IORC) scheme for a uk-derived inverter. The IORC is composed of a modified odd-harmonic repetitive controller (RC) combined with a proportional-integral (PI) controller plus a feedforward controller to achieve a zero steady-state error in the uk-derived inverter. The IORC features larger gains at odd-harmonic frequencies by modification of the conventional odd-harmonic RC. And, it also adopts a linear phase-lead compensator to compensate for the phase lag of the uk-derived inverter. Hence, the IORC can effectively eliminate the odd-harmonic components in the output current of the grid-connected uk-derived inverter. In addition, it requires less memory space and provides faster transient response compared to conventional RC schemes. However, the distinctive structure of the IORC makes it difficult to guarantee the stability of the overall control system. Thus, in this paper, a new stability analysis method for the IORC system are given, and then a practical design guideline is also provided to obtain the optimal control parameters. Experimental results are presented to validate the proposed controller in the 300-W uk-derived inverter prototype.

Linear Adaptive Fault Tolerant Control against Aircraft Actuator Failures for Wing Rock Suppression

In this paper we consider the problem of the suppression of wing rock phenomenon in presence of actuator faults. The main aim of this work is the application of a linear adaptive actuator failure compensation control scheme for wing rock motion of a slender delta wing. First, the analytical nonlinear model that characterizes the phenomenon of wing rock is given, and its behavior for different angles of attack is presented. Then, an adaptive actuator failure compensation redundant control design is proposed, and applied for a rolling motion regulation in the presence of actuator faults. Finally, numerical simulations are conducted to show the effectiveness of the control scheme for wing rock suppression for different actuator failures scenarios.

Compensation and Staffing to Trade Off Speed and Quality in Large Service Systems

Most common queueing models used for service system design assume the servers work at fixed (possibly heterogeneous) rates. However, real-life service systems are staffed by people, and people may change their service speed in response to their compensation incentives. The delicacy is that the resulting employee service rate affects the staffing, but also the staffing affects the resulting employee service rate. Our objective in this paper is to find a joint staffing and compensation policy that induces optimal service system performance.We do this under the assumption that there is a trade-off between service speed and quality, and employees are paid based on both. The employees each selfishly choose their own service speed in order to maximize their own expected utility, which can have both a monetary and a non-monetary component. We characterize the symmetric equilibrium service speed in large systems under a simple linear staffing and compensation policy. We show that there is a limiting first best policy within that class. The important insight is that in the large system limit the problem decouples into one where the system manager first jointly determines the staffing and service speed, and second uses the compensation to achieve that desired service speed. We further show the conditions under which a critically loaded, efficiency-driven, quality-driven, or mixed regime — in which there is simultaneous customer abandonment and server idling — emerges under a first-best policy.

Subzero temperature dependence of electrical conductivity for permafrost geophysics

Temperature dependence of the electrical conductivity of natural waters due to viscosity-based reduction in ionic mobility is well-established for unfrozen conditions. For cold regions, a model for the temperature dependence of electrolyte conductivity at subzero temperatures is required for geophysical studies of permafrost terrain, for which salinity and tension forces may result in freezing-point depression. Extension of the linear temperature model for unfrozen conditions has been applied to geophysical studies of permafrost, but has not been experimentally validated. The temperature dependence of electrical conductivity is measured at subzero temperatures, but above the depressed freezing point for NaCl solutions at a range of concentrations from seawater to brine. Measurements show near-linear dependence of electrical conductivity on temperature down to the lowest experimental temperature of ˗9 °C with no distinct change in behavior observed for subzero temperatures. Given the observed temperature dependence, the linear temperature-conductivity compensation equation is extended to ˗9 °C with a temperature compensation coefficient of 0.019 °C˗1 for a reference temperature of 20 °C with subzero prediction errors of 1–6%. This equation can be used to compensate for temperature dependence of electrical conductivity with reasonable accuracy for geophysical experiments in permafrost terrain. Subzero accuracy is improved by adopting a quadratic temperature compensation equation that accounts for an observed increase in nonlinear behavior at lower temperatures distant from the reference.

Adaptive robust precision motion control of single PAM actuated servo systems with non-local memory hysteresis force compensation

An adaptive robust controller with non-local memory hysteresis force compensation is investigated for the precision tracking control of pneumatic artificial muscle (PAM). The proposed controller presents a two-layer cascade structure, and each layer has an adaptive law part and a robust control law part. A modified operator based Prandtl–Ishlinskii (PI) model is employed in the development of the robust control algorithm with the hysteresis feedback linearization compensation. Moreover, in the robust control law part, the problem of unbounded uncertain nonlinearities introduced by the hysteresis force term is addressed by applying an on-line monitoring method. In the adaptive law part, model parameters including weights of the modified operator are updated online by the recursive least squares estimation (RLSE) method, and then the effect of the hysteresis non-local memory characteristic is further attenuated. The tracking error is guaranteed to converge to a small residual set. Comparative experimental results demonstrate the significance of the non-local memory hysteresis force compensation, then, a desired precision can be guaranteed.

Simulation of an Exoskeleton with a Hybrid Linear Gravity Compensator

Purpose of research. Development of a mathematical model of an exoskeleton equipped with a hybrid linear gravity compensator (HLGC), dynamic analysis on the example of a typical exoskeleton application scenario (in the process of lifting a load), obtaining time patterns of changes in system parameters, including electric drive torques allowing assessment of power plan power consumption and energy efficiency. The article deals with the challenging issue of improving the efficiency of the exoskeletal suit by means of HLGC. The use of a hybrid approach makes it possible to increase the efficiency of assisting the exoskeletal suit when performing various technological operations, for example, when lifting a load, when tilting and holding. Methods. When developing a mathematical model, an original approach was used to form the motion trajectory of the exoskeleton sectors during operation, based on the use of seventh-order polynomials. The paper uses a mathematical model represented by a system of second-order differential equations that connects the moments acting on the operator and the exoskeleton, the angular accelerations of the operator's back and the exoskeleton. Results. During numerical simulation, time diagrams of changes in system parameters, angles of rotation of exoskeleton hinges, moments that occur in a hybrid LGC, as well as graphs of current consumption of engines when performing lift and tilt with a load are obtained. Conclusion. In the course of the research, a kinematic model of an exoskeleton suit equipped with a GLGC was developed, second-order differential equations describing the dynamic behavior of the electromechanical system were written, and numerical simulation was performed to estimate the forces and energy consumption in the exoskeleton hinges and the drive of the hybrid linear gravity compensator.

Dynamic Force Loading Strategy for Effective Force Testing Considering Natural Velocity Feedback Compensation and Nonlinearity

The effective force testing is a promising seismic testing method for evaluating the structural dynamic response to earthquakes for conciseness and efficiency. However, two challenging loading issues are associated with this method, i.e. the natural velocity feedback (NVF) and nonlinearities related to the interaction between the loading system and specimen, thereby hindering its development and extensive applications. To address these issues, this study proposes a dynamic force loading strategy using a hybrid algorithm with linear compensation for NVF and model reference adaptive control via the minimal control synthesis (MCS) method. Online identification of linear compensation gain in preliminary tests is conceived based on the gradient descent method. A series of numerical simulations on a nonlinear loading system model with linear/trilinear single/two degree(s)-of-freedom specimens are conducted using five loading strategies, including linear and nonlinear compensations and MCS method. Comparative studies show that the proposed method and nonlinear compensation strategy outperform the other three methods, and sometimes the proposed method performs best. In summary, the proposed method is promising because of its accuracy and robustness as well as its ease of implementation and cost-effectiveness.

Thermal Stability of a Eutectic Mixture of Bis(2,2‐dinitropropyl) Acetal and Formal: Part C. Kinetic Compensation Effect

AbstractThe aging behavior of a eutectic mixture of bis(2,2‐dinitropropyl) acetal and formal [called NP here] has been studied in various atmospheres [dry (air or nitrogen) versus wet] at temperatures 70 °C and below. The properties of aged samples were analyzed using Fourier transform infrared (FTIR) spectroscopy, Karl Fischer (KF) titration, liquid chromatography/mass spectrometry (LC/MS), and thermogravimetric analysis (TGA) over a period of three years. The results indicate that at aging temperatures up to 55 °C, the initial rates of water production from nitrous acid (HONO) formation and decomposition into the water, NO, and NO2 follows a 1st order rate law and the rate constants follow an Arrhenius law as a function of temperature. The activation energies and pre‐factors for water and volatiles production yield a single linear kinetic compensation plot, suggesting a common degradation pathway between NP and the various combinations of its constituents. Within a narrow temperature range, around 55 °C, a trace amount of water in NP stabilizes its properties by preventing HONO elimination. When the aging temperature is substantially higher than 55 °C, the nature of the degradation mechanism changes. It is suspected that the degradation products of NOx, water, and HNO3 serve as catalysts to auto‐catalyze (kinetics beyond the 1st order) and further degrade NP. The effect of headspace volume on this auto‐catalytic process will be discussed.

Compensation of nonlinear distortion in coherent optical OFDM systems using a MIMO deep neural network-based equalizer.

A novel nonlinear equalizer based on a multiple-input multiple-output (MIMO) deep neural network (DNN) is proposed and experimentally demonstrated for compensation of inter-subcarrier nonlinearities in a 40 Gb/s coherent optical orthogonal frequency division multiplexing system. Experimental results reveal that MIMO-DNN can extend the power margin by 4 dB at 2000 km of standard single-mode fiber transmission when compared to linear compensation or conventional single-input single-output DNN. It is also found that MIMO-DNN outperforms digital back propagation by increasing up to 1 dB the effectiveQ-factor and reducing by a factor of three the computational cost.