Loop Delay Research Articles

SOA-based reservoir computing using upsampling.

We introduce a new, to the best of our knowledge, approach to reservoir computing based on upsampling and modulation, utilizing a semiconductor optical amplifier (SOA) and photodetector as nonlinear elements without conventionally used delay loop. We demonstrated the 400-step prediction capability of the proposed scheme for the Mackey-Glass (MG) time series test.

Zynq FPGA for hardware co-simulation of Takagi-Sugeno neuro-fuzzy for MPPT algorithm incorporating sensorless wind speed estimation in grid-connected wind system

This paper presents a hardware implementation on the Field Programmable Gate Array (FPGA) Zed-Board of a Maximum Power Point Tracking (MPPT) incorporating pitch angle control system and sensorless wind speed estimation using the Takagi-Sugeno (TS) Adaptive Neuro-Fuzzy Inference System (ANFIS). The described approach is applied specifically to a grid-connected Permanent Magnet Synchronous Generator-based Variable Speed Wind Turbine (VSWT). Firstly, the paper proposes an estimator-based TS-ANFIS model for real-time wind speed estimation, addressing challenges with conventional anemometers, such as precision, and susceptibility to adverse weather conditions. The estimated wind speed guides the calculation of an optimized mechanical speed for MPPT control. Secondly, an MPPT-based TS-ANFIS controller is introduced to achieve the maximum power point, integrating pitch angle control to prevent turbine failures in high wind speeds. Finally, the paper emphasizes the hardware implementation on the FPGA Zed-Board, leveraging its parallel processing capabilities to enhance control system quality by reducing sampling periods and loop delays. Validation includes simulations in Matlab/Simulink using the Xilinx system generator and hardware co-simulation on the FPGA Zed-Board. A comparative analysis highlights the contributions and advancements of the proposed models and controllers compared to recent schemes in the field. Indeed, the proposed MPPT-based TS-ANFIS approach effectively maximizes the power extracted from the VSWT, achieving an estimated average efficiency of 99.84 %. In contrast, PID methods show average efficiencies of 92.63 %. Additionally, compared to other published works, the proposed MPPT-based TS-ANFIS method demonstrates a rapid response time of 0.001 s and lower static error at 0.02 %. Furthermore, the proposed WSE-based TS-ANFIS model exhibits superior performance and effectiveness, yielding a root mean squared error (RMSE) of 0.0085381, a determination coefficient (R2) value of 0.99985, and a Pearson correlation coefficient (r) value of 0.99996. Moreover, the proposed hardware implementation of these approaches maintains lower power usage, operating at a high frequency of 80.38 MHz and achieving a high throughput of 2572.16 Mbps.

A high-static-low-dynamic-stiffness delayed resonator vibration absorber

Delayed resonator (DR), which enables complete vibration suppression through loop delay tuning, has been extensively investigated as a linear active dynamic vibration absorber since its invention. Besides, the nonlinear high-static-low-dynamic stiffness (HSLDS) has been widely used in vibration isolators for broadband (yet incomplete) vibration reduction. This work combines the benefits of DR and the nonlinear HSLDS characteristics, thus creating a nonlinear DR (NDR). Three unexplored topics are considered: (1). To address the nonlinear dynamics that are made complicated by the introduction of delay and the nonlinearity coupled between the NDR and the primary structure; (2). To tune the control parameters to seek possible complete vibration suppression in the nonlinear case, and accordingly, to determine the operable frequency band; (3). To evaluate how the HSLDS characteristics can enhance the performance of the linear DR (LDR) and how to design an NDR to maximize its benefits. Without loss of generality, a classic nonlinear HSLDS structure with three springs and two links is considered, and mathematical tools and computational algorithms are introduced or proposed to efficiently address theoretical analysis. Using the parameters of an experimental setup, we show that a properly tuned NDR suppresses the vibrations on the primary structure to a sufficiently low level. Besides, the HSLDS characteristics extend the operable frequency band compared with the LDR, while strong nonlinearity limits such extension. The proposed analysis procedures for delay-coupled nonlinear dynamics, alongside the control parameter tuning, determination of operable frequency bands, and structural design rules, establish a basic theoretical framework for the NDR design.

Microwave local oscillator signal generation with low near-carrier phase noise based on cascaded optoelectronic oscillators

A new scheme to generate microwave local oscillator (LO) signals with low near-carrier phase noise is proposed based on cascaded optoelectronic oscillators (OEOs). In the proposed scheme, an active mode-locking OEO is utilized to generate a microwave comb with low near-carrier phase noise. Through injecting the generated microwave comb into another OEO with a well-designed loop delay, microwave LO signals with low near-carrier phase noise can be generated. The feasibility of the scheme is numerically and experimentally demonstrated. In the experiment, a microwave LO signal at 10.0005 GHz is generated with a spurious suppression ratio of 25 dB and a near-carrier phase noise of −91 dBc/Hz@100 Hz. Compared with the microwave LO signal directly generated by using the OEO without injection, the near-carrier phase noise is reduced by 23 dB. The proposed scheme can thus be used to enhance the sensitivity of the pulse Doppler radar system for detecting small targets with low altitude and slow speed.

Rapid Prototyping and Hardware-In-the-Loop Verification of Enhanced Sliding Mode Control of an Asynchronous Machine Using a Xilinx System Generator and an FPGA-Zynq Board

This article describes rapid prototyping using the Xilinx system generator (XSG) of a direct field oriented control (DFOC) strategy based on improved super twisting sliding mode controllers (ISTSMCs) of an asynchronous machine to succeed a hardware implementation on a field programmable gate array (FPGA) board. The main goal is to enhance regulation loops governing rotor speed, rotor flux, and stator current components within the classical DFOC structure. These ISTSMCs replace integral proportional controllers, resulting in improved system dynamics, faster speed and torque responses, and heightened robustness against load and rotor resistance variations, surpassing other control methods. Additionally, the article aims to implement this DFOC-ISTSMC method on an FPGA board to reduce control system sampling time and loop delays, leveraging the FPGA’s parallel processing capabilities. The hardware architecture is designed using XSG in the MATLAB/Simulink environment, enabling effective simulation, testing, discrete algorithm creation, and VHDL code generation for FPGA implementation via the hardware-in-the-loop (HIL) process. Assessment involves digital simulation studies and HIL processes using XSG with a Xilinx FPGA Zynq 7000 under MATLAB/Simulink, demonstrating improved system performance, reduced time delays, and efficient FPGA utilization. This approach validates the effectiveness of the proposed DFOC-ISTSMC algorithm in enhancing control strategy for asynchronous machines.

System dynamics approach for assessing the performance of safety management systems in petrochemical plants

Accidents in process industries, such as chemical, petrochemical, and refinery sectors, often stem from intricate causes. Consequently, safety management systems (SMS) have emerged as crucial mechanisms for accident prevention. In process industries, this is an interrelated and sociotechnical system consisting of numerous interacting components. However, current safety management approaches appear to be limited by linear thinking in terms of enhancing safety performance. Adopting systems thinking that considers the feedback loop and time delay is necessary to improve the efficiency and effectiveness of system performance. This study proposes a model that can predict the performance of SMS in petrochemical plants to manage risks using system dynamics (SD). Methods are proposed to build causal relationships in SMS and to develop a simulation model grounded in SD, facilitating performance evaluation within process industries. The proposed model is applied to an organization as a case study, and scenario-based simulations are performed. The case study results indicate that senior management interests are more influential to safety performance. The model is expected to be able to forecast the performance level of SMS and help decision-makers identify better policies and obtain insights to improve safety.

Precise cortical contributions to sensorimotor feedback control during reactive balance.

The role of the cortex in shaping automatic whole-body motor behaviors such as walking and balance is poorly understood. Gait and balance are typically mediated through subcortical circuits, with the cortex becoming engaged as needed on an individual basis by task difficulty and complexity. However, we lack a mechanistic understanding of how increased cortical contribution to whole-body movements shapes motor output. Here we use reactive balance recovery as a paradigm to identify relationships between hierarchical control mechanisms and their engagement across balance tasks of increasing difficulty in young adults. We hypothesize that parallel sensorimotor feedback loops engaging subcortical and cortical circuits contribute to balance-correcting muscle activity, and that the involvement of cortical circuits increases with balance challenge. We decomposed balance-correcting muscle activity based on hypothesized subcortically- and cortically-mediated feedback components driven by similar sensory information, but with different loop delays. The initial balance-correcting muscle activity was engaged at all levels of balance difficulty. Its onset latency was consistent with subcortical sensorimotor loops observed in the lower limb. An even later, presumed, cortically-mediated burst of muscle activity became additionally engaged as balance task difficulty increased, at latencies consistent with longer transcortical sensorimotor loops. We further demonstrate that evoked cortical activity in central midline areas measured using electroencephalography (EEG) can be explained by a similar sensory transformation as muscle activity but at a delay consistent with its role in a transcortical loop driving later cortical contributions to balance-correcting muscle activity. These results demonstrate that a neuromechanical model of muscle activity can be used to infer cortical contributions to muscle activity without recording brain activity. Our model may provide a useful framework for evaluating changes in cortical contributions to balance that are associated with falls in older adults and in neurological disorders such as Parkinson's disease.

A Single Op-Amp Resonator-Based Continuous-Time Sigma–Delta Modulator With Time-Division Switching for Excess Loop Delay Compensation

A Single Op-Amp Resonator-Based Continuous-Time Sigma–Delta Modulator With Time-Division Switching for Excess Loop Delay Compensation

Efficient Resource Scheduling in Fog: A Multi-Objective Optimization Approach

Fog computing is a novel idea that extends cloud computing by offering services like processing, storage, analysis, and networking on fog devices closer to IoT devices. Numerous fog devices are required to process the ever-growing amount of data generated by IoT applications. The heterogeneous tasks from various IoT applications compete for a limited number of resources of these devices. The process of assigning this set of tasks to different available fog nodes according to QoS requirements for processing is resource scheduling. Resource scheduling aims to optimize resource utilization and performance metrics however, the dynamic nature of the Fog environment, resource-constrained, and heterogeneity in fog devices make resource scheduling a complex issue. This research presents the design and implementation of a multi-objective optimization-based resource scheduling algorithm using Modified Particle Swarm Optimization (MPSO) that addresses the application module placement and task allocation issues. This two-step MPSO-based resource scheduling model finds the optimal fog node to place each application module and assigns appropriate tasks to the most optimal fog nodes for execution. The proposed model unlocks the full potential of fog resources along with maximization of overall system performance in terms of optimization of cost, latency, energy consumption, and network usage. The simulation results indicate that using MPSO energy consumption is reduced by 53.94% and 43.58% as compared to First Come First Serve (FCFS) and Particle Swarm Optimization (PSO), respectively. The loop delay, network usage and cost using MPSO are reduced by 40.3%, 67.69% and 90.01% respectively, as compared to PSO algorithm.

Small-Signal Stability of Hybrid Inverters with Grid-Following and Grid-Forming Controls

In the modern power grid, characterized by the increased penetration of power electronics and extensive utilization of renewable energy, inverter-based power plants play a pivotal role as the principal interface of renewable energy sources (RESs) and the grid. Considering the stability characteristics of grid-following (GFL) inverters when the grid is relatively weak, the application of grid-forming (GFM) controls becomes imperative in enhancing the stability of the entire power plant. Thus, there is an urgent need for suitable and effective models to study the interaction and stability of the paralleled inverters employing GFL and GFM controls. Thus, the small-signal modeling with full-order state-space model and eigenvalues analysis are presented in this paper. First, the small-signal state-space model of the individual GFL and GFM inverters is obtained, considering the control loop, interaction, reference frame, transmissions, and time delays. Then, the models of the individual inverter are extended to the hybrid inverters to study the effects of the GFM inverters on the small-signal stability of the entire system. And the impacts of the inertia and damping are analyzed by the eigenvalues of the state-transition matrix. A case comprising three parallel GFL inverters and two GFL inverters with one GFM inverter, respectively, are studied to examine the effectiveness and accuracy of the model. Finally, the stability margin obtained from the eigenvalue analysis of the entire system is verified by time-domain simulations.

Beam steering using delays generated from an optical OAM mode shifting recirculating loop

This paper investigates the performance of generated delays from an orbital angular momentum mode shifting recirculating delay loop (OAM-SL) in simulation using Kirchhoff-Fresnel diffraction (KFD) and the delays applicability for RF signal beam steering applications. OAM-SL is a novel structure that has been recently reported to produce multiple delayed signal replicas on independent OAM carriers using a single compact system. The objective of this research is to explore the impact of several limiting factors on the quality of OAM-SL delays for beam steering applications, such as where there is (i) displacement of the OAM mode shifter, (ii) displacement of the center of the OAM mode demultiplexer at the loop output, and (iii) the limited resolution. The methodology includes: (i) simulating the beam propagation using KFD, (ii) producing the output as a coherent summation of the recirculating beams, and (iii) characterizing the SCR by dividing the power of the recirculating beam (ρ) on its OAM mode by the power accumulated from the other recirculating beams. Our findings show that delays generated from a system with lin=−30, lshift=+1, and a resolution of 1024 pixels can steer a 100 MHz signal at a steering angle of 11.5° in a four antenna system with 0.1° error if loop alignment is perfect. Also, for steering the 100 MHz signal in an eight antenna system, we analyze the system assuming the system loss can be compensated, and a similar result of 0.1° error is obtained. Additionally, we report the beam steering performance at 23.6° and 36.8°.

Delayed resonator for complete vibration suppression of primary structures with nonlinear stiffness

Delayed resonator (DR) is an active vibration absorber and is known for its complete vibration suppression capability by manipulating the feedback loop delay. This work aims to extend the DR concept from the widely considered linear applications to suppress vibrations on primary structures with nonlinear stiffness, based on the motivation that absolute linearity does not exist and nonlinearity is inherent in many structures to be protected. The nonlinearity stems from the commonly seen nonlinear symmetrical restoring forces. Threefold objectives are pursued: (1). To generalize the tuning mechanism of the DR and the dynamical analysis of the system to the nonlinear case. (2). To evaluate the effect of such nonlinearity on system dynamics and vibration suppression. (3). To enhance control performance by properly constructing nonlinearity and, accordingly, to establish the design criteria. Without loss of generality, a widely considered three-spring-two-link model is borrowed as an example for constructing the stiffness nonlinearity. Then, an exclusive resultant-based calculation procedure is introduced to efficiently handle the delay-coupled nonlinear dynamics. Besides, the feedback tuning for complete vibration suppression and the related stability issues are tackled, showing that the nonlinearity can significantly extend the operable frequency band while posing no extra demands on the control law. Based on the parameters of an actual experimental setup, numerous comparisons between linear and nonlinear cases are performed to demonstrate how the DR settles a nonlinear primary structure and, furthermore, how such nonlinearity can affect control performance and how it can be utilized to enhance vibration suppression.

Delayed resonator with multiple distributed delays – Considering and optimizing the inherent loop delay

We generalize the distributed delayed resonator (DDR) concept by incorporating the previously unutilized but inevitable feedback loop delay, thus creating a so-called multiple-delay distributed delayed resonator (MD-DDR) for complete vibration suppression. The necessary parameter tuning and control stability analysis become more involved but remain analytically solvable. Particularly, we take the operability of control parameters imposed by hardware as an explicit condition for parameter tuning and show that the loop delay (even if it is small) can lead to incomplete vibration suppression and, counter-intuitively, even no suppression if the excitation frequency exceeds a threshold value. On the other hand, such negative effects are neutralized by correcting control parameters. The loop delay is then intentionally augmented to seek enhanced performance, yielding a considerably extended operable frequency band for the desired complete vibration suppression. Furthermore, it is optimized to expedite response speed by achieving the leftmost placement of the dominant (i.e., the rightmost) characteristic root. Instead of applying a brute-force sweeping procedure as in the previous works, we analyze the dominant root locus and seek if the jump phenomenon occurs to conduct exact optimization at a low computational cost. Finally, extensive comparisons using actual experimental parameters are performed to explore various effects of the loop delay on vibration suppression and the benefits of the proposed MD-DDR in handling such issues over the conventional DDR that treats a single delay. This study fully exploits the strength of the distributed delayed control logic, moving the DDR concept closer to real applications and aiming to establish a broader design and analysis framework for the delayed resonator from a multiple-delay perspective.

Time-delayed control of a nonlinear self-excited structure driven by simultaneous primary and 1:1 internal resonance: analytical and numerical investigation

<p>Main objective of this research to eliminate the resonant vibrations and stabilize the unstable motion of a self-excited structure through the implementation of an innovative active control strategy. The control strategy coupling the self-excited structure with a second-order filter, which feedback gain $ \lambda $ and control gain $ \beta $, as well as a first-order filter, which feedback gain $ \delta $ and control gain $ \gamma $. The coupling of the second-order filter to establish an energy bridge between the structure and the filter to pump out the structure's vibration energy to the filter. In contrast, the primary purpose of coupling the first-order filter to stabilize the closed loop by adjusting the damping of the system using the control keys $ \delta $ and $ \gamma $. Accordingly, the mathematical model of the proposed control system formulated, incorporating the closed-loop time delay $ \tau $. An analytical solution for the system model obtained, and a nonlinear algebraic system for the steady-state dynamics of the controlled structure extracted. The system's bifurcation characteristics analyzed in the form of stability charts and response curves. Additionally, the system's full response simulated numerically. Findings the high performance of the introduced controller in eliminating the structure's resonant vibrations and stabilizing non-resonant unstable motion. In addition, analytical and numerical investigations revealed that the frequency band within which the second-order filter can absorb the structure's resonant oscillation relies on the algebraic product of $ \beta $ and $ \lambda $. Furthermore, it was found that the equivalent damping of the system depends on the algebraic product of $ \gamma $ and $ \delta $, which can be employed to stabilize the negatively damped self-excited systems. Finally, it reported that although the loop delay can potentially degrade vibration control performance, the time-delay stability margin is nonlinearly proportional to the product of $ \gamma $ and $ \delta $. This finding that increasing the value of $ \gamma \times \delta $ can compensate for the adverse effects of loop delay on both system stability and vibration suppression efficiency.</p>

Fractional loop delays in adaptive optics modeling and control.

This paper revisits the problem of optimal (minimum variance) control for adaptive optics (AO) systems when measurement and command applications are asynchronous, resulting in a non-integer servo loop delay. When not properly accounted for, such fractional delays may severely degrade the AO performance, especially in the presence of high-frequency vibrations. We present evidence of this performance degradation thanks to in-lab experimental measurements on the Gran Telescopio Canarias Adaptive Optics (GTCAO) system controlled with standard suboptimal linear quadratic Gaussian (LQG) controllers. A constructive, easy to implement LQG control design is then proposed and validated in a simulation for vibrations affecting the tip-tilt modes. Our methodology is very interesting because it allows a performance assessment for any linear controller in terms of variance, rejection transfer functions, power spectral densities, and stability margins. We also show how the continuous-time disturbance model can be derived from standard discrete-time disturbance data-based modeling.

Interference fading suppression for distributed acoustic sensor using frequency-shifted delay loop

In order to suppress the interference fading of phase-sensitive optical time domain reflectometer (Φ-OTDR), a multi-frequency detection method based on frequency-shifted delay loop (FSDL) is proposed. A probe pulse train with up to five consistent frequency components are generated by periodic frequency-shifted, amplification, delay and filtering processing in FSDL. The piecewise aggregate approximation (PAA) is introduced to compress the amount of operational data. Wavelet energy spectrum analysis and support vector machine (SVM) are used to extract features and realize the fading classification. With the help of fading label making and restoration, the multi-frequency signals are intelligently aggregated using rotated-vector-sum (RVS). Experimental results show that PAA has applicability in data compression of beat signals. After 5-layer wavelet energy spectrum analysis, the fading binary classification accuracy can reach 96.77 %, and the fading signals identified after segmentation can be restored to the original data. The fading probability based on SVM output labels can be reduced to 1.89 %. The SVM-based classification output labels aggregation shows that the vibration positioning signal-to-noise ratio (SNR) can be increased to 13.52 dB, the phase demodulation curve is smoother, and the demodulation SNR can be up to 17.63 dB. Finally, the R-Square of 0.997 for the amplitude of demodulated vibration signal in repeatability experiment verifies the validity of this effective scheme for fading recognition and suppression.

Dynamical analysis and design theory for active bistable vibration isolators considering delay effect

Bistable vibration isolators (BVIs), which can undergo intra- and inter-well motions, have recently gained much attention as different motions can lead to different low-frequency isolation properties. To fully exploit the strength of BVIs, feedback actuation is injected into a classic three-spring-two-link bistable structure, and the classic PD control is applied to tune system's stiffness and damping. Moreover, the effect of the inevitable loop delay on BVI performance is considered. Operable regions of control parameters to maintain bistable characteristics and robustness regions where active BVIs are operable regardless of delay perturbations are determined. Besides, bistable dynamics, complicated by the transcendentality caused by delay, are investigated. By taking the BVI as phase zero, the number of variables to be solved is reduced, and an efficient frequency-sweeping-based calculation procedure is proposed. The BVI is evaluated by force and displacement transmissibility, showing that both intra- and inter-well motions benefit vibration isolation. For the former, the BVI yields broadband vibration isolation similar to conventional high-static-low-dynamics-stiffness vibration isolators. For the latter, an isolation valley can occur, resulting in exclusive ultra-low-frequency vibration isolation. Furthermore, properly tuning feedback actuation enhances the vibration isolation performance in both cases, and the often-overlooked loop delay can play a very positive role. Finally, the mechanism of isolation valley is qualitatively elucidated. The presented theories, including control stability analysis, delay-coupled nonlinear dynamical analysis, and beneficial parameter tuning, establish a basic design framework for active BVIs.

Analysis and Synthesis of Cooperative Adaptive Cruise Control Against the Hetero-Integration Poly-Net Loop Delays

Cooperative Adaptive Cruise Control (CACC) is a promising technology for improving the capacity and energy efficiency of the ground transportation system. In this paper, a novel CACC control scheme is proposed to deal with the adverse impacts of both inter- and intra-vehicle network delays. First, a hetero-integration poly-net (PN) loop delay analysis method is presented to clarify the system delays in CACC considering both inter- and intra-vehicle network influences. A mathematic equation is put forward to calculate the upper bound of the PN loop delays. Then a collaborative software-defined network scheme is presented to deal with the PN loop delays, which consists of the application/strategy, network-control and network-data planes. In the network-control plane, a fraction-type basic period scheduling method is adopted. In the application/strategy plane, a delay-tolerant model predictive controller is designed for decision-making while a combination of an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H_∞</i> controller and a linear quadratic regulator is adopted for acceleration tracking control against local intra-vehicle network delays. Finally, the proposed scheme is verified under a variety of scenarios based on comprehensive Hardware-in-the-Loop tests.

An All-Digital Optical Phase-Locked Loop Suitable for Satellite Downlinks

The optical signal propagation used in satellite uplinks and downlinks is influenced by absorption, scattering, and changes in the atmospheric refractive index or turbulence, causing optical signal attenuation. A free space optics (FSO) communications system using coherent communication can improve the link sensitivity and reach higher distances. This article proposes a new architecture for the phase detector in an all-digital optical phase-locked loop (OPLL) for coherent optical detection. Firstly, the performance of the proposed phase detector is evaluated under Gaussian noise, where the best operation point is found for the OPLL working with two sample rates: 625 MSa/s and 10 GSa/s. The system analyses also take a non-negligible delay into account. Then, it will be evaluated and compared with an OPLL using an analog phase detector in the presence of atmospheric turbulence. Finally, in three different atmospheric turbulence conditions, the effect of wind speed on communication quality is investigated through the obtained bit error rate (BER) from the recovered data for a bit rate of 20 Gbps. The results show that the proposed digital phase detector can track a signal under longer feedback loop delays and fading signals.

High-speed polarization tracking using thin film lithium niobate integrated dynamic polarization controller.

Dynamic polarization controllers (DPCs) are essential devices in various optical applications. We develop a thin film lithium niobate (TFLN) integrated DPC driven by the real-time implemented Jacobian control algorithm for fast polarization tracking. Experimental results demonstrate a high polarization tracking speed of 100 krad/s when targeting a specific linear state of polarization, with a low control loop delay of 420 ns, half-wave control voltages of 2.75 V, and a fast polarization restoring time of 1.6 us. Compared to previously reported integrated DPCs, the TFLN-based DPC achieves significantly higher tracking speed and lower loop delay. The results highlight the effectiveness of the Jacobian method and the outstanding performance of TFLN-based DPCs. The study opens up possibilities for further advancements in DPC solutions using TFLN technology.