Time-delay Filter Research Articles

An Improved Current Signal Extraction-Based High-Frequency Pulsating Square-Wave Voltage Injection Method for Interior Permanent-Magnet Synchronous Motor Position-Sensorless Control

The high-frequency (HF) voltage injection method is widely applied in achieving position-sensorless control for interior permanent-magnet synchronous motors (IPMSMs). This method necessitates precise and rapid extraction of the current signal for accurate position estimation and field-oriented control (FOC). In the traditional methods, the position error signal and fundamental current are extracted from the current signal using band-pass filters (BPFs) and low-pass filters (LPFs), or a method based on time-delay filters. However, the traditional extraction method falls short in ensuring simultaneous dynamic performance and accuracy, particularly when the switching frequency is limited or when encountering harmonic and noise interference. In this article, a novel HF pulsating square-wave voltage injection method based on an improved current signal-extraction strategy is proposed to improve the extraction accuracy while maintaining good dynamic performance. The newly devised current signal-extraction method is crafted upon a notch filter (NF). Through harnessing NF’s effective separation characteristics of specific frequency signals, the current signal is meticulously processed. This process yields the extraction of the position error signal and fundamental-current component, crucial for accurate position estimation and motor FOC. Simulation and hardware-in-the-loop (HIL) testing are conducted to validate the effectiveness of the proposed approach.

A Deep Time Delay Filter for Cooperative Adaptive Cruise Control

Cooperative adaptive cruise control (CACC) is a smart transportation solution to alleviate traffic congestion and enhance road safety. The performance of CACC systems can be remarkably affected by communication time delays, and traditional control methods often compromise control performance by adjusting control gains to maintain system stability. In this paper, we present a study on the stability of a CACC system in the presence of time delays and highlight the trade-off between control performance and tuning controller gains to address increasing delays. We propose a novel approach incorporating a neural network module called the deep time delay filter (DTDF) to overcome this limitation. The DTDF leverages the assumption that time delays primarily originate from the communication layer of the CACC network, which can be subject to adversarial delays of varying magnitudes. By considering time-delayed versions of the car states and predicting the present (un-delayed) states, the DTDF compensates for the effects of communication delays. The proposed approach combines classical control techniques with machine learning, offering a hybrid control system that excels in explainability and robustness to unknown parameters. We conduct comprehensive experiments using various deep-learning architectures to train and evaluate the DTDF models. Our experiments utilize a robot platform consisting of MATLAB, Simulink, the Optitrack motion capture system, and the Qbot2e robots. Through these experiments, we demonstrate that when appropriately trained, our system can effectively mitigate the adverse effects of constant time delays and outperforms a traditional CACC baseline in control performance. This experimental comparison, to the best of the author’s knowledge, is the first of its kind in the context of a hybrid machine learning CACC system. We thoroughly explore initial conditions and range policy parameters to evaluate our system under various experimental scenarios. By providing detailed insights and experimental results, we aim to contribute to the advancement of CACC research and highlight the potential of hybrid machine learning approaches in improving the performance and reliability of CACC systems.

UDE-Based Current Controller With Enhanced Grid Frequency Fluctuation Adaptability for LCL-Type Grid-Tied Inverters

The uncertainty and disturbance estimator (UDE) with a time delay filter has been widely used for inverter systems due to its satisfactory harmonic rejection performance. However, the control performance may be affected when the grid frequency fluctuates. In this article, a modified UDE (FUDE) is proposed to improve the grid frequency fluctuation adaptability of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$LCL$</tex-math></inline-formula> grid-tied inverter systems, which contains a compound filter consisting of time delay, zero-phase low-pass, and high-pass filters. Compared with the traditional time delay UDE, it can offer a wider notch bandwidth at the selected frequencies. A dual-loop controller is built in the separate-structure-type UDE-based controller, containing an outer loop PR controller and an inner loop FUDE. The sufficient conditions for the system stability are obtained by the small-gain theorem. The comparison experiments of the dual-loop controller with the proposed FUDE and the conventional time delay zero-phase low-pass UDE are performed on a 2-kW experimental platform, and the results demonstrate the effectiveness of the proposed FUDE.

Minimum time control of a gantry crane system with rate constraints

This paper focuses on the development of minimum time control profiles for point-to-point motion of a gantry crane system in the presence of uncertainties in modal parameters. Assuming that the velocity of the trolley of the crane can be commanded and is subject to limits, an optimal control problem is posed to determine the bang-off-bang control profile to transition the system from a point of rest to the terminal states with no residual vibrations. Both undamped and underdamped systems are considered and the variation of the structure of the optimal control profiles as a function of the final displacement is studied. As the magnitude of the rigid body displacement is increased, the collapse and birthing of switches in the optimal control profile are observed and explained. Robustness to uncertainties in modal parameters is accounted for by forcing the state sensitivities at the terminal time to zero. The observation that the time-optimal control profile merges with the robust time-optimal control is noted for specific terminal displacements and the migration of zeros of the time-delay filter parameterizing the optimal control profile are used to explain this counter intuitive result. As a comparison to the proposed controller, an acceleration constrained time-optimal control is analyzed which as expected demands a larger maneuver time. A two degree of freedom gantry crane system is used to experimentally validate the observations of the numerical studies and the tradeoff of increase in maneuver time to the reduction of residual vibrations is experimentally illustrated.

A deep reinforcement learning-based optimization method for vibration suppression of articulated robots

To solve the vibration problem of articulated robots, a deep reinforcement learning-based optimization method for input shaping (RLIS) is proposed. The optimization method applies the arbitrary time-delay filter as the model and includes two main stages: determining the RLIS initial parameter ranges; and constructing and improving the RLIS optimization strategy. In the first stage, a post-adaptive method based on the recursive least squares algorithm is used to determine the RLIS initial parameter ranges. In the second stage, the input shaping optimization problem is modelled as a Markov decision process, and the RLIS optimization strategy is constructed using a deep reinforcement learning algorithm. Subsequently, a selection mechanism based on state value and a fuzzy reward system is proposed to increase the learning efficiency and simplify the design process. Finally, several groups of experiments are designed to demonstrate the effectiveness and stableness of the proposed method in residual vibration suppression.

Uncertainty and disturbance estimator with improved steady‐state performance for grid‐connected power converters

The study suggests a method aimed to improve the performance of practical grid-connected converters connected to distorted mains, utilising total uncertainty and disturbance estimator (TUDE) based control structures with time-delay filter. Such a TUDE filter enhances disturbance rejection performance by possessing near-unity magnitude and near-zero phase at integer multiples of the base frequency, imposing repetitive-control-alike behaviour. However, it is well-known that in repetitive control, disturbance rejection at mid-frequencies, were non-periodic disturbances and noise may exist, is deteriorated. This study presents an enhancement, allowing to retain good disturbance rejection at mid-frequencies within the low-frequency portion of control bandwidth (relevant in practical systems) while trading-off the performance in the high-frequency control bandwidth part. The proposed methodology is verified by application to output current control of LCL-filter based inverter feeding distorted AC mains. The validity and performance of the proposed methodology are well-supported by simulations and experiments.

Research on Grab Swing Control Method Based on Time Delay Filter

Grab swing during crane acceleration and deceleration will have an impact on work efficiency and safety. In this regard, the swing amplitude of the grab during the operation must be controlled within a certain range. According to the mechanical analysis of bridge crane’s grab, the mathematical model between crane’s horizontal movement and grab swing is established. A time delay filter technique is applied to shape the acceleration control signal, thus effectively control the swing angle of the grab. Simulation results show that the control method with time delay filter could eliminate the swing of the grab even without measuring the swing angle, and is feasible for engineering applications.

Optimal True Time Delay Filter With Application to FPGA Firmware‐Based Phased Array Radar Signal Processing

AbstractThe European Incoherent Scatter‐3D phased array radar system will be largely based on field‐programmable gate array (FPGA) firmware electronics that carry out the signal processing by using different digital filters. In this paper we have presented a method of designing an optimal true time delay finite impulse response filter with applications to an FPGA firmware‐based multichannel signal processing system. The method provides an optimal true time delay finite impulse response filter with the desired responses at both band pass and stopband. This is possible by finding a mathematical minimization solution for the total power of all filter coefficients longer than a prespecified half‐length. The analysis is based on freely choosing the responses in the transition band until user‐specified desired responses are achieved. We have investigated the performance of these optimal digital filters in terms of the required digital signal processing (DSP) resources in GMACs (giga multiply accumulates per second) by considering both all‐in‐one stage filtering and cascaded solutions for ion and plasma line incoherent scatter radar measurements. We have shown that the cascaded solution provides more efficient utilization of DSP resources and hence represents the optimal choice for processing the proposed European Incoherent Scatter‐3D phased array radar signals. An example is demonstrated in which 906.88 GMACs are required to process 208 ion line beams with 2×4‐bit resolution in all‐in‐one stage processing, as compared to the 79.16 GMACs needed for a similar task in a cascaded solution.

Broadband Frost Adaptive Array Antenna with a Farrow Delay Filter

In a broadband adaptive array antenna with a space-time filter, a delay filter is required before digital beamforming when the Frost algorithm is used to obtain the weight vector. In this paper, we propose a Farrow structure instead of a direct form FIR structure to implement the time delay filter since it can satisfy the demand for real-time update and is very suited for the FPGA platform. Furthermore, a new off-line algorithm to calculate the Farrow filter coefficient is presented if the filter coefficient is symmetric. Finally, simulations are presented to illustrate that the design methodology for the Farrow filter is correct. The simulations also prove that the Frost broadband adaptive antenna effectively mitigates the interferences with a Farrow filter.

Band gap synthesis in elastic monatomic lattices via input shaping

This work describes control-theoretic methods for inducing a band gap-like behavior in elastic monatomic lattices. The dynamics of the system under consideration are derived in detail. Open-loop pre-filtering techniques, in the form of Posicast and user-selected time delay filters, are then utilized to eliminate specific frequency contents from the response of the multi-degree of freedom spring-mass chain. The input shaping approach is used to synthesize one or more band gaps in a homogenous lattice that can be designed to resemble Bragg-scattering in phononic crystals, as well as local resonance effects in acoustic metamaterials. The presence of the synthesized band gaps in the lattice’s dispersion behavior is validated using a spatiotemporal Fourier transform of the system’s impulse response as well as the frequency response of the end-to-end transfer function. Finally, an analysis of the control effort required to cancel the targeted system poles is carried out.

Periodic Signal Tracking for Lightly Damped Systems

The focus of this paper is on the development of time-delay filters to accomplish tracking of periodic signals with zero phase errors. The class of problems addressed include systems whose dynamics are characterized by lightly damped modes. A general approach for the zero-phase tracking of periodic inputs is presented followed by an illustration of single harmonic tracking of underdamped second-order systems with relative degree two. A general formulation of the approach is then posed for higher-order systems and systems including zeros. The paper concludes with the illustration of enforcing constraints to desensitize the time-delay filter to uncertainties in the location of the poles of the system and forcing frequencies. A numerical practical design case based on a medical X-ray system is used to illustrate the potential of the proposed technique.

Study on flow characteristics and flow ripple reduction schemes of spool valves distributed radial piston pump

This paper studies the flow characteristics and flow ripple reduction techniques of a spool valves distributed radial piston pump. The mathematical models of the pump are established, and simulations based on the mathematics are performed in AMESim environment. The results indicate that the spool valves distributed radial piston pump has fewer flow fluctuations than the pump distributed by check valves, due to the rigid motion of its distribution component—the spool valves. Then, in order to reduce the flow ripple of the spool valves distributed radial piston pump, three techniques, namely, time delay, relief chamfer and transition compression filter volume, are proposed and their working principles are illustrated. Particularly, the design method of time delay is elaborated and its effectiveness is evaluated. The simulation results suggest that with the usage of the time delay method, the fluctuation range of the spool valves distributed radial piston pump is expected to be reduced by 21.7%.

Application of a Time-Delay Pre-Filter Design for Periodic Signal Tracking of Lightly-Damped Multivariable Systems

The aim of this work is the illustration of time-delay filter applications for three current industrial high-performance motion control problems. The main focus is on time-delay filters that enable zero phase tracking of periodic signals, however this is not a restriction for the introduced approaches. The first problem introduced in this paper is the point-of-interest or inferential control problem where the feedback variable typically is not the same as the performance variable. The second illustration is an application of time-delay filter design on a multivariable robotic system. The third challenge illustrates how a robust time-delay filter design allows for practical implementations on medical X-ray systems.

Active flutter suppression of a multiple-actuated-wing wind tunnel model

In this study, a multi-input/multi-output (MIMO) time-delay feedback controller is designed to actively suppress the flutter instability of a multiple-actuated-wing (MAW) wind tunnel model in the low subsonic flow regime. The unsteady aerodynamic forces of the MAW model are computed based on the doublet-lattice method (DLM). As the first attempt, the conventional linear quadratic-Gaussian (LQG) controller is designed to actively suppress the flutter of the MAW model. However, because of the time delay in the control loop, the wind tunnel tests illustrate that the LQG-controlled MAW model has no guaranteed stability margins. To compensate the time delay, hence, a time-delay filter, approximated via the first-order Pade approximation, is added to the LQG controller. Based on the time-delay feedback controller, a new digital control system is constructed by using a fixed-point and embedded digital signal processor (DSP) of high performance. Then, a number of wind tunnel tests are implemented based on the digital control system. The experimental results show that the present time-delay feedback controller can expand the flutter boundary of the MAW model and suppress the flutter instability of the open-loop aeroelastic system effectively.

Design and characterization of arrayed waveguide gratings using ultra-low loss Si3N4 waveguides

Planar waveguides with ultra-low propagation loss are necessary for integrating optoelectronic systems that require long optical time delay or narrowband optical filters. In this paper, we review an ultra-low loss planar waveguide platform that uses thin ( 8 μm) SiO2 cladding layers. In particular, we discuss the performance of arrayed waveguide gratings (AWGs) fabricated with the platform. We propose the use of a practical design method that takes the statistical nature of worst-case crosstalk into account. We also demonstrate the measurement of amplitude and phase error distributions in an AWG using an optical backscatter reflectometer. We show that the waveguides have phase errors small enough to achieve AWG crosstalk below −30 dB, while crosstalk below −40 dB should also be possible with optimization of the component design.

Time-Optimal Output Transition for Minimum-Phase Systems

The time-optimal output transition control problem for stable or marginally stable systems with minimum-phase zeros is discussed in this paper. A double integrator system with a real left-half plane zero is used to illustrate the development of the time-optimal output transition controller. It is shown that an exponentially decaying postactuation control profile is necessary to maintain the output at the desired final location. It is shown that the resulting solution to the output transition time-optimal control profile can be generated by a time-delay filter whose zeros and poles cancels the poles and zeros of the system to be controlled. The design of the time-optimal output transition problem is generalized and illustrated on the benchmark floating oscillator problem.

Noise Cancellation in Knee Joint Vibration Signals Using a Time-Delay Neural Filter and Signal Power Error Minimization Method

Removal of random noise is an essential signal preprocessing procedure before the diagnostic analysis of knee joint vibration signals. This article presents a novel noise cancellation method for the knee joint vibration signal processing using a time-delay neural filter. The filter contains a single neuron that convolves the reference input with synaptic weights. The synaptic weights of the filter can be adaptively optimized by a novel instantaneous signal power error minimization method. The results of knee joint vibration signal filtering experiments showed that the time-delay neural filter outperformed the wavelet matching pursuit decomposition method, with less execution time consumption and a higher signal-to-noise ratio.

Transient analysis with fast Wilson-Daubechies time-frequency transform

The time-frequency transforms are important tools for identification of transient events in the output of the gravitational-wave detectors. Produced by the terrestrial and possibly by astrophysical sources, the transient events can be identified as patterns on the time-frequency plane with the excess power above stationary detector noise. In this paper we consider a particular case of the Wilson-Daubechies time-frequency transform for use in the gravitational-wave burst analysis. The presented Wilson-Daubechies basis shares some properties with the Gabor frames, but circumvents the Balian-Low theorem. It also shares similarity with the Meyer wavelet, which is actively used in the gravitational-wave burst analysis. The main advantages of the Wilson-Daubechies transform are the low computational cost, spectral leakage control, flexible structure of the frequency sub-bands, and the existence of the analytic time-delay filters, which are important for localization of the gravitational-wave sources in the sky. These properties of the Wilson-Daubechies transform may prove useful not only in the transient analysis, but also in other areas of the gravitational wave data analysis and detector characterization.

Vibration Control of a Flexible Manipulator Driven by a Pneumatic Rodless Cylinder

A pneumatic rodless cylinder driven flexible manipulator control system is proposed for positioning and vibration suppression of the manipulator, using pulse code modulation (PCM) method. Firstly, the system model of the pneumatic flexible manipulator is derived. Theoretical analysis of the composite positioning and vibration suppression control algorithm is performed. Secondly, because the hysteretic problem of control effect is caused by the following factors, such as long stroke of the cylinder, compressibility of air, nonlinearity of pneumatic driving and time delay of valves'; switch, thus, the limit cycle oscillation of high-frequency modes vibration can be easily excited, and the observation and control spillover will be caused. Also, the stability of the control system will be affected. In order to solve this problem, compensation of time delay and low-pass filter methods are introduced into the control algorithm. Finally, experiments on positioning and vibration suppression of the pneumatic flexible manipulator are conducted. The experimental results demonstrate that the composite control method can suppress the low-frequency mode vibration of the flexible manipulator effectively and achieve the purpose of positioning simultaneously.

Implementation of frequency-shaped tip reference in conjunction with learning controller for improved tip-tracking control

In the flexible manipulator control, tip-tracking control of flexible manipulator results in non-colocated control problem, which has a non-minimum phase dynamic characteristic. The level of tip-tracking performance in the non-colocated control system depends on the characteristics of the tip reference trajectory to be followed, as well as on the characteristics of the flexible manipulator system itself. In a previous research the use of a tip reference trajectory, filtered by a properly designed time-delay command shaping filter, has been proposed and a multirate repetitive learning control (MRLC) has been used as the tip-tracking controller. The practical implementation of this approach, however, requires estimation of the tip position, which is not easy to obtain. In this paper, a practical implementation of the approach is considered and the tip position is estimated with a fourth-order Kalman filter. The experimental results show that, with the use of Kalman filter, the proposed scheme results in a drastic reduction in residual tip vibrations and the required actuation effort.