Closed-loop Filter Research Articles

Initial validation of a closed loop filter and controller approach for active stabilization of thermomechanical distortions

Increasing technological progress in space technology is accompanied by an increased demand for accuracy. The alignment of optical instruments or antennas on the satellite platform requires structural stability that can no longer be achieved with traditional, passive methods, such as the use of materials with high stiffness or low coefficient of thermal expansion. Within the Infrared Astronomy Satellite Swarm Interferometry (IRASSI) project, an approach to actively stabilizing structures against low-frequency periodic heat induced deformations has been developed and simulated. In this study, the basic functionality of that thermomechanical FEM model is demonstrated by means of the thermal transfer functions between the changes in the applied heat and the resulting temperature changes, as well as a closed loop filter and controller approach consisting of a Linear Quadratic Regulator (LQR) and a Kalman filter. For this purpose, an experimental setup consisting of an aluminum plate with 14 temperature sensors, four heating elements for controlling the structure and one heating element for simulating the perturbation is used. The evaluation of the thermal transfer functions in the model compared to the experimental setup shows a deviation of the phase shift of less than 0.6% and an amplitude shift of less than 3.5% on average. A Kalman filter processes the temperature measurement in order to obtain an optimal estimate for the LQR controller, which then calculates the necessary change in the heating power of the four control heating elements to minimize the displacements at the desired two positions in x- and y-direction. The verification is performed by a camera system as an external validation tool, which is able to resolve micron-scale displacements by measuring the spatial displacement of a speckle pattern applied to the structure using sub-pixel accurate image correlation algorithms. While the range of values of the amplitudes of the displacements is 8.93 μ in the uncontrolled case, an improvement of more than 4.6dB could be achieved by applying the filter and controller system. Thus, it is demonstrated that this method has the potential to further improve already highly stable structures or to make lighter and cheaper materials with poorer passive stability values usable through active structural stabilization.

Experimental demonstration of a method to actively stabilize satellite structures against random perturbations of thermal boundary conditions using a closed-loop filter and controller approach

Modern space travel requires increasingly stable support structures for optical instruments or antennas, which can hardly be realized with the traditional approaches. Therefore, an approach for active structural stabilization of thermal-induced distortions was developed, simulated, and patented within the framework of the Infrared Astronomy Satellite Swarm Interferometry (IRASSI) project. Based on this approach, the thermomechanical transfer functions between the change in heat flux and the change in displacement of the finite-element (FE) model of a structure have already been validated in their basic functionality. In an experimental setup, the FE model was extended to include a closed-loop filter and controller approach consisting of a Kalman filter processing the temperature measurements in conjunction with a Linear Quadratic Regulator (LQR). It was shown that this setup can compensate for predefined sinusoidally oscillating disturbance heat flows, with an improvement of 4 dB compared to the uncontrolled case. In this paper, an experimental setup revised with respect to the positioning of the sensors and control heating elements, in conjunction with an extension of the filter and controller approach, will demonstrate that the system can respond to reproducible, random fluctuations in the disturbance heat flux, as well as stepped changes, and that performance has improved due to the revision.

Adaptive Kalman Filter Enhanced With Spectrum Analysis for Wide-Bandwidth Angular Velocity Estimation Fusion

The optoelectronic inertial stabilization platform is widely used in the fields of astronomical observation, monitoring and search, quantum communication and other fields, which all need strong vibration suppression and tracking capability. To realize high-precision angular measurement throughout the wide bandwidth for inertial stabilization platform, the fusion algorithm is studied to fuse the signals of magnetohydrodynamic (MHD) and microelectromechanical (MEMS) gyroscope. The basic adaptive Kalman filter experiences signal-to-noise ratio and fusion-frequency jitter problems because of the measurement transfer matrix deviation, making it unsuitable for quick dynamic systems. This paper proposes an adaptive Kalman filter enhanced with spectrum analysis by connecting the measurement covariance with the signal frequencies. This method divides the trace of the modified measurement covariance into three parts according to frequency domain characteristics. Based on the frequency analysis, the filter output mainly depended on the MEMS gyroscope at low frequencies, fusion results of the two gyroscopes in the intermediate frequency-domain, and the MHD gyroscope at high frequencies. This theory is verified in the swept frequency experiment and comparative experiments, including multi-harmonic sinusoidal and step response tests compared with combing filter and closed-loop filter. The tests results show that the fusion signal is identical with the actual signal throughout the measurement bandwidth, and the fusion signal-to-noise ratio is improved. The frequency characteristics and noise level of the fusion algorithm satisfy the requirements of optoelectronic inertial stabilization vibration measurement.

Open-Loop Switched-Capacitor Integrator for Low Voltage Applications

An architecture of a switched-capacitor integrator that includes a charge buffer operating in an open-loop is hereby proposed. As for the switched-capacitor filters, the gain of the proposed integrator, which is given by the input/output capacitor ratio, ensures desensitization to process, voltage, and temperature variations. The proposed circuit is suitable for low voltage supplies. It enables a significant power saving compared to a traditional switched-capacitor integrator. This was demonstrated through an analytical comparison between the proposed integrator and a traditional switched-capacitor integrator. The mathematical results were supported and verified by simulations performed on a circuit prototype designed in 16 nm finFET technology with 0.95 V supply. The proposed switched-capacitor integrator consumes 76 µW, resulting in more than twice the efficiency for the traditional closed-loop switched-capacitor filter as an input voltage equal to 31.25 mV at 7 ns clock period is considered. The comparison of architectures was led among the proposed integrator and the state-of-the-art technology in terms of the figure of merit.

10-GHz Fully Differential Sallen–Key Lowpass Biquad Filters in 55nm SiGe BiCMOS Technology

Multi-GHz lowpass filters are key components for many RF applications and are required for the implementation of integrated high-speed analog-to-digital and digital-to-analog converters and optical communication systems. In the last two decades, integrated filters in the Multi-GHz range have been implemented using III-V or SiGe technologies. In all cases in which the size of passive components is a concern, inductorless designs are preferred. Furthermore, due to the recent development of high-speed and high-resolution data converters, highly linear multi-GHz filters are required more and more. Classical open loop topologies are not able to achieve high linearity, and closed loop filters are preferred in all applications where linearity is a key requirement. In this work, we present a fully differential BiCMOS implementation of the classical Sallen Key filter, which is able to operate up to about 10 GHz by exploiting both the bipolar and MOS transistors of a commercial 55-nm BiCMOS technology. The layout of the biquad filter has been implemented, and the results of post-layout simulations are reported. The biquad stage exhibits excellent SFDR (64 dB) and dynamic range (about 50 dB) due to the closed loop operation, and good power efficiency (0.94 pW/Hz/pole) with respect to comparable active inductorless lowpass filters reported in the literature. Moreover, unlike other filters, it exploits the different active devices offered by commercial SiGe BiCMOS technologies. Parametric and Monte Carlo simulations are also included to assess the robustness of the proposed biquad filter against PVT and mismatch variations.

ПЛИВ ФАЗОВОЇ НЕСТАБІЛЬНОСТІ ГЕНЕРАТОРІВ НА ПАРАМЕТРИ РОБОТИ СИСТЕМИ СИНХРОНІЗАЦІЇ НЕСУЧОЇ ЧАСТОТИ НА ФОНІАДИТИВНОГО ГАУСІВСЬКОГО ШУМУ ТА ДОППЛЕРІВСЬКОГО ЗМІЩЕННЯ ЧАСТОТИ

The article deals with the systems of phase synchronization of radio engineering devices of communication technology. The purpose of the article is theoretical research in the direction of development, analysis and improvement of known and synthesis of new phase synchronization circuits, characterized by high noise immunity, accuracy and speed with simplicity of design. The problem is solved to investigate the possibilities of closed and combined synchronization systems for operation under conditions of phase instability of generators in a communication channel against the background of external additive Gaussian noise and Doppler frequency shift. The following results were obtained. The analysis of closed-type synchronization systems during operation under the conditions of phase instability of generators is carried out and its inconsistency is shown in order to minimize the phase error variance and increase the dynamics during carrier frequency monitoring. The process of synthesis of open communication in the combined synchronization system is refined and analytical dependences are offered, which allow to refine the technique of synthesis of open communication for the combined synchronization system with regard to the phase instability of the generators against the background of the influence of the adducts. Conclusions. Increasing the noise bandwidth of the proportional-integrating filter of the closed-loop phase-in-phase synchronization system to the parameters of the ideal filter impairs the dynamics of the specified system. For the combined synchronization system, in the conditions of phase instability of the generators, an increase in the noise bandwidth of the input signal can be achieved by applying a closed-loop proportional-integrating filter and by making appropriate selection of parameters of the transfer function of the link of the open channel. In the conditions of phase instability of the generators in the combined system of synchronization by selecting the parameters of the proportional-integrating filter, it is possible to provide the necessary dynamics of the system and to achieve the optimal value of the dispersion of the phase error in it. Taking into account Doppler noise under conditions of phase instability of generators for a closed-type synchronization system and a combined synchronization system requires a reduction of the optimal value of the noise bandwidth.

Optimization of Part Consolidation for Minimum Production Costs and Time Using Additive Manufacturing

AbstractThis research presents a method of optimizing the consolidation of parts in an assembly using metal additive manufacturing (MAM). The method generates candidates for consolidation, filters them for feasibility and structural redundancy, finds the optimal build layout of the parts, and optimizes which parts to consolidate using a genetic algorithm. Results are presented for both minimal production time and minimal production costs, respectively. The production time and cost models consider each step of the manufacturing process, including MAM build, post-processing steps such as support structure removal, and assembly. It accounts for costs affected by part consolidation, including machine costs, material, scrap, energy consumption, and labor requirements. We find that developing a closed-loop filter that excludes consolidation candidates that are structurally redundant with others dramatically reduces the number of candidates, thereby significantly reducing convergence time. Results show that when increasing the number of parts that are consolidated, the production cost and time at first decrease due to reduced assembly steps, and then increase due to additional support structures needed to uphold the larger, consolidated parts. We present a rationale and evidence justifying that this is an important tradeoff of part consolidation that generalizes to many types of assemblies. Subsystems that are smaller, or can be oriented with very little support structures or have low material costs or fast deposition rates can have an optimum at full consolidation; for other subsystems, the optimum is less than 100%. The presented method offers a promising pathway to minimize production time and cost by consolidating parts using MAM. In our test-bed results for an aircraft fairing produced with powder-bed electron beam melting, the solution for minimizing production cost (time) is to consolidate 17 components into four (two) discrete parts, which leads to a 20% (25%) reduction in unit production cost (time).

Cost-Effective Islanded Electrical System With Decentralized Interleaving PWM for Converter Harmonic Reduction

For a conventional islanded microgrid, each distributed generation (DG) unit usually equips with an LC filter and a closed-loop filter capacitor voltage control is applied to ensure an accurate tracking of DG voltage. In this article, a cost reduction microgrid and DG units configuration is developed via the following two steps. First, an L -type filter is adopted by each DG unit and a centralized shunt capacitor is placed at point of common coupling (PCC). Then, the inherent synchronization feature of droop control is further exploited as an inherent synchronizer to identify the carrier angle relationships between parallel inverters, but without any communications between them. With the carrier information obtained, a decentralized interleaving pulsewidth modulation (PWM) among parallel inverter can be easily achieved via a slow proportional integral (PI) regulation of each DG unit relative carrier. Accordingly, the high-frequency switching harmonics of PCC voltage are suppressed even with simplified and size reduced DG output chokes. Second, a virtual impedance control is applied to DG units to cancel the voltage drops on the DG feeder in a direct PWM manner. Accordingly, mitigating the low-order harmonic PCC voltages is obtained without using any closed-loop voltage tracking at DG unit local processor. Comparative experimental results have been provided to validate the correctness of the proposed method.

Convergent Properties of Riccati Equation with Application to Stability Analysis of State Estimation

Since the recursive nature of Kalman filtering always results in a growing size of the optimization problem, state estimation is usually realized by use of finite‐memory, receding horizon, sliding window, or “frozen” techniques, which causes difficulties on stability analysis. This paper proposes a novel method on selection of an initial covariance matrix and a horizon for the Kalman filter to make sure that a sequence of the closed‐loop Kalman filters are stable as time‐invariant filters at subsequent time instant. Convergent properties of Riccati Difference Equation (RDE) are first exploited. Based on these properties, sufficient conditions for stability of a sequence of Kalman filters are obtained. Compared with the existent literature, the convergent properties and the stability conditions are less conservative since they provide analytic results and are applicable to more common cases where the RDEs are not monotonic.

Fast reactive current detection method for single‐phase grid‐connected inverters

This study presents a fast reactive current detection (RCD) method based on closed-loop resonant filter for single-phase grid-connected inverters. The developed closed-loop resonant filter-based RCD (CLRF-RCD) technique with shorter time delay can enhance the dynamic performance of reactive current detection, which is beneficial for achieving faster reactive current compensation and/or reactive power regulation in single-phase grid-connected power systems. The optimal design of CLRF-RCD is presented in detail, together with the comparison of CLRF-RCD with the conventional second-order generalised integrator-based RCD. Finally, the simulation and experimental results validate the feasibility of the developed CLRF-RCD algorithm.

Closed-loop magnetic separation of nanoparticles on a packed bed of spheres

In this work, we consider magnetic separation of iron oxide nanoparticles when a nanoparticle suspension (diluted ferrofluid) passes through a closed-loop filter composed of a packed bed of micro-beads magnetized by an externally applied magnetic field. We show that the capture of nanoparticles of a size as small as 60 nm is easily achieved at low-to-moderate magnetic fields (16–32 kA/m) thanks to relatively strong magnetic interactions between them. The key parameter governing the capture process is the Mason number—the ratio of hydrodynamic-to-magnetic forces exerted to nanoparticles. The filter efficiency, Λ, defined through the ratio of the inlet-to-outlet concentration shows a power-law dependency on Mason number, Λ∝Ma−0.83, in the range of 102<Ma<104. The proposed theoretical model allows a correct prediction of the Mason number dependency of the filter efficiency. The obtained results could be of potential interest for water purification systems based on chemical adsorption of micro-pollutants on magnetic nanoparticles, followed by magnetic separation of the nanoparticles.

Closed-loop EKF-based Pulsar Navigation for Mars Explorer with Doppler Effects

To eliminate the impact of the Doppler effects caused by the motion of the Mars explorer, a novel X-ray pulsar navigation method based on a closed-loop filter is proposed. In the pulsar signal observation period, the Doppler velocity predicted by the orbit dynamic model and the prior information is utilised to compensate the X-ray photon time-of-arrival (TOA). However, because of the error in prior information, there is a bias caused by the Doppler compensation in the pulse time-of-arrival. The pulse TOA bias and the Mars explorer's state estimation error are correlated, which results in the decline of the Kalman filter performance. To deal with this problem, we build the TOA measurement model with respect to the state estimation error, and utilise the closed-loop extended Kalman filter (EKF) as the navigation filter, where the predicted state error is adopted as the state estimation. The simulation results demonstrate the feasibility, real-timeliness and effectiveness of the proposed navigation method. The navigation method based on the closed-loop EKF using the measurement model with the Doppler effects is more accurate than the traditional one.

A Novel Closed-Loop Time-Delayed Filter for Unstable System

Aiming to improve the stability dynamic performance of the oscillating system, an internal closed-loop time-delayed filter with negative pulse is designed. To make the unstable system into stable, a reasonable time delay is introduced within the feedback control system, based on optimization theory to design the delay filter parameters. Matlab/SIMULINK simulation software is used on system performance analysis. Simulation results show that the designed internal closed-loop time-delayed filter can effectively improve the system stability, but also inhibit the high-frequency noise, with a strong anti-interference ability.

A 4th-Order Active-<tex>$G_m$</tex>-RC Reconfigurable (UMTS/WLAN) Filter

A fourth-order low-pass continuous-time filter for a UMTS/WLAN receiver of a reconfigurable terminal is presented. The filter uses the cascade of two Active-Gm-RC biquad cells. A single opamp is used for each biquad and its unity-gain-bandwidth is comparable to the filter cut-off frequency. Thus, the opamp power consumption is strongly reduced w.r.t. other closed-loop filter configurations. The cut-off frequency deviation due to the technological spread, aging and temperature variation is adjusted by an on-chip tuning circuit. The device in a 0.13 mum CMOS technology occupies a 0.9 mm2 area and it consumes 3.4 mW and 11 4.2 mW for the UMTS and WLAN, respectively. The full chip has been designed using an automatic design tool, which is validated by the agreement between the experimental results and the expected performance

Control of nonlinear processes using functional expansion models

Functional expansion (FEx) models are a subclass of the general block-oriented model structure for nonlinear process systems. Controller design in this context uses the internal model control (IMC) paradigm, and one can show that the resulting controllers are easily implementable. The primary advantage arises from the fact that inverting the nonlinear dynamic operator is avoided by taking advantage of the partitioned model inverse due to the special structure of FEx models. The robust stability and performance of the closed-loop system can be analyzed by expressing the FEx model as a linear uncertain system and using the structured singular value framework. We present a case study of a polymerization reactor and, for this SISO system, analyze nominal and robust stability and performance conditions as a function of the closed-loop filter constants for a given range of the input variable.

Monotonicity and stabilizability- properties of solutions of the Riccati difference equation: Propositions, lemmas, theorems, fallacious conjectures and counterexamples

The problem considered is that of selecting an initial covariance matrix for the Kalman filter to ensure that the closed-loop filter at every subsequent time instant is exponentially asymptotically stable as a time-invariant filter. Sufficient conditions are derived based on monotonicity properties of the solution of the Riccati difference equation. The results have application in observer design, and the cases of filtering for nonstabilizable systems and systems with singular system matrices are included.

Closed-loop control performance sensitivity to parameter variations

A very efficient technique for computing the closed loop performance sensitivities to parameter variations of a dynamic system with a reduced order controller has been developed. The eigensystem of the closed loop system is computed once. With this information, the closed loop filter and state rms responses, and the first and second derivatives of these rms values with respect to given parameters are computed. Detailed numerical examples using the JPL flexible beam and a 55 meter offset fed, wrap-rib antenna are included.

Minimum-Variance Design of Constant-Gain Filters Subject to Stability Constraints

A computer-oriented systematic approach to constant-gain filter design for time-invariant linear systems is developed. The trace of the error covariance matrix is minimized subject to constraints on the closed-loop filter eigenvalues. For continuous system representations, the eigenvalues are restricted to a region in the s plane defined by damping ratio and decrement factor inequalities, while discrete representations involve a decrement factor inequality in the z plane. Properties of inner determinants and Lyapunov equations are employed to allow a unified approach to both continuousand discrete-time system representations. The approach is applied to three examples which illustrate filter settling time considerations, transient/steady-state gain tradeoffs, and combined control-estimation possibilities.

Optimum Reset of Ship's Inertial Navigation System

Optimum linear filter and control theory is applied to the practical problem of supplementing an inertial navigation system with discrete reference information. The information takes the form of position obtained from Loran C or Decca, for example, and occasional azimuth fixes obtained from star sightings. In particular, optimum use of this information is discussed for the Ship's Inertial Navigation System (SINS) installations intended for missile carrying submarines and warships. A model representative of the SINS dynamics is formulated appropriate for application of optimum filter and control theory. Interpretation of the optimum control dictated in part by the augmented SINS model is discussed. Simulation studies that show the relative transient behavior and the stabilizing effect of the closed-loop filter and control processes are also presented.