Closed-loop Control Strategy Research Articles

Bio-Z-Based Feedback-Controlled External Diaphragm Pacing System

In this brief, a bio-impedance (Bio-Z) based closed-loop control scheme is proposed for a wearable external diaphragm pacing (EDP) system. EDP delivers functional electrical stimulation to strengthen the muscle within the respiration system. Bio-Z sensor continuously and non-invasively measures the thoracic change to provide a linear relation of the respiratory rate and volume. The estimated slope of the Bio-Z variation generates and updates the needed stimulating parameters in real-time. The proposed EDP system yields a Bio-Z based feedback-controlled diaphragmatic stimulation, alongside with an improved degree of accuracy and robustness regarding to the open-loop controlled commercially available EDP devices.

Development and evaluation of a closed-loop z-axis control strategy for wire-and-arc-additive manufacturing using the process signal

Wire-and-arc-additive manufacturing (WAAM) is an additive manufacturing technology with a high deposition rate. WAAM usually employs a layer wise build-up strategy. This makes it necessary to know the height of each deposited layer to determine the height the z-axis has to travel after each layer. Current bead geometry models (BGM) lead to variations, which can gradually accumulate over the layers. The present study focuses on the development of a closed-loop control system capable of keeping the contact tube working distance (CTWD) constant during short-circuit gas metal arc welding (GMAW) based WAAM. The algorithm calculates the CTWD based on the resistance during the short circuit. The closed-loop strategy is compared to an open-loop control strategy, which moves along a predefined height step after each layer. Using the proposed control strategy, WAAM becomes a fully automated process without the need for preliminary experiments to determine the height step. Only a short calibration slope is necessary for a complete closed-loop additive build-up. To study the influence of the control strategy on the workpiece the energy input, mechanical strength, microhardness, porosity, and microstructure were analyzed. It is shown that the CTWD of the open-loop deposited component increases slowly. Due to the novel control approach, this is prevented by the closed-loop control, while the mechanical strength and microhardness remain.

A Soft-Start-Based Method for Active Suppression of Magnetizing Inrush Current in Transformers

The occurrence of high-amplitude magnetizing inrush current during the energization of a transformer without load poses significant challenges to the stable operation of both the transformer and the power grid, potentially leading to malfunctions in relay protection devices. This paper analyzes the underlying mechanisms of transformer inrush current and presents a novel approach utilizing a soft-start-based method for effectively suppressing inrush currents. The proposed method employs an inrush current suppressor comprising anti-parallel thyristors and filters to mitigate the adverse effects caused by the inrush current. A comparative study is conducted to evaluate the filtering efficacy of three types of filters incorporated in the inrush current suppressor: an LCLC damping filter, a high-order single trap filter and a high-order double trap filter. Through careful analysis and optimization, the high-order double trap filter with parallel RC damping damper is selected as the optimal configuration. To ensure effective suppression, it is necessary to incorporate a filter at the termination point of the anti-parallel thyristor. Additionally, a closed-loop control strategy is implemented to ensure a smooth start and actively suppress the magnetizing inrush current. To validate the effectiveness of the proposed method, comprehensive simulations are performed using Matlab/Simulink. The results demonstrate the successful suppression of inrush current and the maintenance of stable operation for the transformer. This inrush suppression method does not require considering the influence of residual magnetism and the grounding mode of the transformer’s neutral point. It is also suitable for various transformer structures and wiring methods, which makes it highly applicable.

A Torque Control Strategy for a Robotic Dolphin Platform Based on Angle of Attack Feedback.

Biological fish can always sense the state of water flow and regulate the angle of attack in time, so as to maintain the highest movement efficiency during periodic flapping. The biological adjustment of the caudal fin's angle of attack (AoA) depends on the contraction/relaxation of the tail muscles, accompanying the variation in tail stiffness. During an interaction with external fluid, it helps to maintain the optimal angle of attack during movement, to improve the propulsion performance. Inspired by this, this paper proposes a tail joint motion control scheme based on AoA feedback for the high-speed swimming of bionic dolphins. Firstly, the kinematic characteristics of the designed robot dolphin are analyzed, and the hardware basis is clarified. Second, aiming at the deficiency of the tail motor, which cannot effectively cooperate with the waist joint motor during high-frequency movement, a compensation model for the friction force and latex skin-restoring force is designed, and a joint angle control algorithm based on fuzzy inference is proposed to realize the tracking of the desired joint angle for the tail joint in torque mode. In addition, a tail joint closed-loop control scheme based on angle of attack feedback is proposed to improve the motion performance. Finally, experiments verify the effectiveness of the proposed motion control scheme.

Research on stability control strategy of adjustable pressure wall-climbing robot based on adsorption identification

In order to solve the problem that it is difficult to accurately model the complex fluid domain in the negative pressure chamber of the robot in the process of wall climbing, and thus cannot quickly and steadily adsorb, a double closed-loop control strategy based on parameter identification and particle swarm optimization is proposed in this paper to improve the speed and stability of the adsorption response of the robot in the process of wall climbing. Firstly, a vacuum negative pressure wall climbing robot with a spring pressure regulating structure is developed, and the critical conditions of the robot’s instability are solved by mechanical analysis. Then, the rigid-flexible coupling model of the whole machine was established based on mass, spring and Maxwell viscoelastic elements. The model parameters of the adsorption system were identified by vacuum adsorption test. Compared with the experimental data, the accuracy of the model was more than 80%. On this basis, PID controller is used to adjust the adsorption response speed of the robot, a double closed-loop stable adsorption control strategy is designed, and the control parameters of the adsorption system are adjusted by using the dynamic weight standard particle swarm optimization algorithm. Finally, simulation and prototype tests show that, the proposed control strategy can shorten the static and dynamic response time of the adsorption system by about 3.5 s and 1.4 s, the flow response time by about 1.15s, the maneuvering performance of the whole system is improved by about 26%, and the parameter overshoot and steady-state error are lower, which provides a theoretical reference for the stability control and engineering application of the wall-climbing robot.

Real-Time Estimation of Jet-Surface Interaction Noise

Motivated by the growing concerns for the noise emissions generated by the interaction between the engine jet and the airframe surfaces consequent to the progressive increase of the engine by-pass ratio in commercial aircraft architectures, we study the estimation of the far-field noise radiated by a jet in an installed configuration based on sensor readings in the near field of the jet. We carry out an experimental investigation of the jet-surface interaction phenomena in a simplified set-up where a flat plate is installed parallel to the nozzle axis of a subsonic jet. Real-time estimation is performed using empirical linear transfer functions identified between near-field sensors and far-field observers. The transfer function and the accuracy of the noise estimation performed are characterised as a function of jet flow conditions, type and streamwise position of near-field sensors and radial distance between the jet and the edge. This analysis can guide the positioning of near-field sensors for the implementation of closed-loop control strategies for the jet-surface interaction noise.

A Flexible and Fully Autonomous Breast Ultrasound Scanning System

The quality of breast ultrasound imaging is greatly affected by the contact force of the probe, which largely requires experienced sonographers to complete the clinical examination. We propose a flexible and fully autonomous ultrasound scanning system for breast ultrasound imaging. It consists of an ultrasound machine, a dual robotic arms system, a multi-structured light system, a human&#x2013;computer interaction system, and a flexible ultrasound probe clamping device (FUPCD). First, the dynamics model of the FUPCD was analyzed, and a closed-loop force control strategy was established. We then implemented an automatic scanning system. The hysteresis characteristics of the FUPCD and transient response of the force controller were experimentally verified. The system could keep the steady-state error less than <inline-formula> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula> 5<inline-formula> <tex-math notation="LaTeX">$\%$</tex-math> </inline-formula> within 0.5 s. Second, the performance of the control system to maintain constant contact force at different scanning speeds (<inline-formula> <tex-math notation="LaTeX">$&lt;$</tex-math> </inline-formula>20 mm/s) was evaluated. In a series of comparative studies, the fluctuation range of the target contact force applied by the flexible automatic scanning was 10<inline-formula> <tex-math notation="LaTeX">$\%$</tex-math> </inline-formula>. The force control capability of the system was 30.84 times higher than that of traditional manual scanning, 18.48 times higher than that of flexible automatic scanning (FC off), and 24.3 times higher than that of rigid automatic scanning (FC on). Furthermore, the effectiveness of the FUPCD arc design and flexibility was verified. In addition, the change trend of the average grayscale level (GSL) of the ultrasound image was basically the same as the contact force, demonstrating that the stability and repeatability of the ultrasound image can be improved by controlling the stability of the contact force. In conclusion, the proposed system can simplify the workflow of breast ultrasound examination and improve the diagnostic capabilities of the ultrasound imaging system. <i>Note to Practitioners</i>&#x2014;The motivation of this study is to solve the problem of poor image reproducibility in breast ultrasound scanning, but the proposed system can also be applied to ultrasound scanning of other parts of the body. The position, direction, and contact force of the ultrasound probe affects the image quality and repeatability of the ultrasound, thereby affecting the diagnostic ability. Therefore, we propose and develop a flexible and fully autonomous breast ultrasound scanning system. We aimed to improve the autonomy and stability of the scanning process by designing end-to-end automated scanning strategies, flexible clamping devices, and closed-loop force control strategies. Among them, the fully automatic three-dimensional perception and trajectory planning can provide global fitting capabilities to different forms of breast surfaces and control the probe to maintain the best contact posture. At the same time, the fully automatic workflow reduces additional interference and reduces the complexity of the workflow. The flexible ultrasound probe clamping device improves the passive applicability to flexible tissues and reduces the resistance in the scanning process. The closed-loop force control strategy can adjust the contact force in real time. Experiments verified that the repeatability could be evaluated by contact force. A series of human&#x2013;machine comparison experiments verified the advancement and effectiveness of the system. In future research, we will further solve the problem of abnormalities and repeatability of ultrasound images acquired during the scanning process by combining the multi-modal feedback of images and forces.

Perspectives on adaptive dynamical systems.

Adaptivity is a dynamical feature that is omnipresent in nature, socio-economics, and technology. For example, adaptive couplings appear in various real-world systems, such as the power grid, social, and neural networks, and they form the backbone of closed-loop control strategies and machine learning algorithms. In this article, we provide an interdisciplinary perspective on adaptive systems. We reflect on the notion and terminology of adaptivity in different disciplines and discuss which role adaptivity plays for various fields. We highlight common open challenges and give perspectives on future research directions, looking to inspire interdisciplinary approaches.

Computed torque control and force analysis for mechanical leg with variable rotation axis powered by servo pneumatic muscle

It is difficult for a humanoid leg driven by two groups of antagonistic pneumatic muscles (PMs) to achieve a flexible humanoid gait, and its inherent strong coupling nonlinear characteristics make it hard to achieve good tracking performance in a large range of motion. Therefore, a four-bar linkage bionic knee joint structure with a variable axis and a double closed-loop servo position control strategy based on computed torque control are designed to improve anthropomorphic characteristics and the dynamic performance of the bionic mechanical leg powered by servo pneumatic muscle (SPM). Firstly, the relationship between the joint torque, the initial jump angle and the bounce height of the mechanical leg is established, and then we design a double-joint PM bionic mechanical leg containing a four-bar linkage mechanism of the knee joint. Secondly, a cascade position control strategy is developed, which consists of the outer position loop and the inner contraction force loop, and the mapping relationship is designed between joint torque and antagonistic PM contraction force. Finally, we further project bounce action timing of mechanical leg to realize the periodic jumping movement of the mechanical leg, and simulation and physical experiments of the real-style machine platform have been provided to demonstrate the effectiveness of the designed SPM controller.

A Low-Noise Interface ASIC for MEMS Disk Resonator Gyroscope.

This paper proposes a low-noise interface application-specific integrated circuit (ASIC) for a microelectromechanical systems (MEMS) disk resonator gyroscope (DRG) which operates in force-to-rebalance (FTR) mode. The ASIC employs an analog closed-loop control scheme which incorporates a self-excited drive loop, a rate loop and a quadrature loop. A ΣΔ modulator and a digital filter are also contained in the design to digitize the analog output besides the control loops. The clocks for the modulator and digital circuits are both generated by the self-clocking circuit, which avoids the requirement of additional quartz crystal. A system-level noise model is established to determine the contribution of each noise source in order to reduce the noise at the output. A noise optimization solution suitable for chip integration is proposed based on system-level analysis, which can effectively avoid the effects of the 1/f noise of the PI amplifier and the white noise of the feedback element. A performance of 0.0075°/√h angle random walk (ARW) and 0.038°/h bias instability (BI) is achieved using the proposed noise optimization method. The ASIC is fabricated in a 0.35 μm process with a die area of 4.4 mm × 4.5 mm and power consumption of 50 mW.

Experimental mitigation of large-amplitude transverse gusts via closed-loop pitch control

In this work, we experimentally demonstrate the utility of unsteady potential flow models in developing closed-loop control strategies for mitigating the lift transients on a wing experiencing large-amplitude transverse gusts. The developed closed-loop controller mitigates lift for gusts of various strengths and directions and for wings with pre- and post-stall angles of attack. Time-resolved force and flow field measurements are used to discover the salient flow physics during these encounters and illustrate how closed-loop actuation mitigates their lift transients.

Reinforcement Learning for Multiple Daily Injection (MDI) Therapy in Type 1 Diabetes (T1D)

In this study, we propose a closed-loop insulin administration framework for multiple daily injection (MDI) treatment using a reinforcement learning (RL) agent for insulin bolus therapy. The RL agent, based on the soft actor–critic (SAC) algorithm, dynamically adjusts insulin dosages based on real-time glucose readings, meal intakes, and previous actions. We evaluated the proposed strategy on ten in silico patients with type 1 diabetes undergoing MDI therapy, considering three meal scenarios. The results show that, compared to an open-loop conventional therapy, our proposed closed-loop control strategy significantly reduces glucose variability and increases the percentage of time the glucose levels remained within the target range. In particular, the weekly mean glucose level reduced from 145.34 ± 57.26 mg/dL to 115.18 ± 7.93 mg/dL, 143.62 ± 55.72 mg/dL to 115.28 ± 8.11 mg/dL, and 171.63 ± 49.30 mg/dL to 143.94 ± 23.81 mg/dL for Scenarios A, B and C, respectively. Furthermore, the percent time in range (70–180 mg/dL) significantly improved from 63.77 ± 27.90% to 91.72 ± 9.27% (p = 0.01) in Scenario A, 64.82 ± 28.06% to 92.29 ± 9.15% (p = 0.01) in Scenario B, and 58.45 ± 27.53% to 81.45 ± 26.40% (p = 0.05) in Scenario C. The model also demonstrated robustness against meal disturbances and insulin sensitivity disturbances, achieving mean glucose levels within the target range and maintaining a low risk of hypoglycemia, which were statistically significant for Scenarios B and C. The proposed model outperformed open-loop conventional therapy in all scenarios, highlighting the potential of RL-based closed-loop insulin administration models in improving diabetes management.

Closed-Loop Control Strategy for Simulated Smoke Concentration in Aircraft Cargo Compartment Mock-Up

Closed-Loop Control Strategy for Simulated Smoke Concentration in Aircraft Cargo Compartment Mock-Up

H5-CFDAB: A Current-Fed Dual-Active-Bridge Converter for Application in Modular DC Solid-State Transformer

Isolated DC-DC converters in DC Solid-State Transformers (DCSSTs) must conform to stringent requirements such as high voltage conversion ratio, high efficiency, and reliable operation with grid fault handling capabilities. This paper proposes a novel current-fed Dual-Active-Bridge (CFDAB) converter, named H5-CFDAB, for modular DCSST application. Compared to the existing topologies, the proposed converter provides a single-stage power conversion with reduced component count and semiconductor Volt-Ampere (VA) rating. The proposed modulation scheme makes the pulse widths of the transformer winding voltages independent of the duty ratio. This allows further optimization of the high-frequency-link (HFL) characteristics like minimized HFL conduction losses and full range Zero-Voltage-Switching (ZVS) at turn ON for the switches, further increasing the converter efficiency. Several modules of the proposed H5-CFDAB converter connected in Input-Series-Output-Parallel (ISOP) configuration makes the system suitable for Medium-Voltage (MV) high-power applications. The operation of the proposed converter is analyzed in detail, including the HFL characteristics and derivation of the ZVS conditions for the switches. In addition, a closed-loop control scheme is proposed for achieving tight regulation of the converter outputs during transients. A 1.2 kW laboratory prototype is built to verify the effectiveness of the proposed converter, along with the control scheme.

A System-Level Harmonic Control Method Based on Multibus Voltage Detected APF Without Exact Phase Synchronization

The decentralized distribution of nonlinear harmonic loads drives the trend of harmonic control from local compensation to system-level mitigation. Based on the active power filter (APF) with multi-bus harmonic detections, comprehensive control of harmonic distortions in multiple buses achieves, which is so-called system-level harmonic mitigation. However, existing system-level harmonic mitigation methods require high-speed data exchange for real-time phase synchronization among multiple buses, which reduces the feasibility of the methods. To reduce the burden of communication, a system-level harmonic mitigation method without inter-bus phase synchronization is proposed in this paper. Firstly, the phase synchronization problem is analyzed, and control system of multi-bus detected APF is proposed, in which the reference phase of each detector could be set locally. Then, a new online system-level harmonic mitigation model is introduced and solved to obtain the optimal APF current reference. Subsequently, the closed-loop control strategy of multi-bus detected APF is raised and four control stages are designed to cope with different situations. Finally, an eight-bus network with dynamic harmonic loads is designed in simulation and experiment. According to the results, multi-bus harmonic voltage distortions in the network could meet the standard. The proposed method contributes to achieving good harmonic compensation performance without multi-bus phase-synchronization.

Novel closed-loop dual control algorithm for solar trackers of parabolic trough collector systems

Parabolic trough systems require accurate, reliable, and robust solar trackers to achieve their maximum thermal efficiency. This paper presents a dual closed-loop control strategy for single-axis solar trackers of parabolic trough systems. This strategy consists of the use of a dual control feedback through the integration of a typical photodiode-based solar sensors, to perform the coarse control, and a proposed shadow-based visual device that performs the fine position adjustment. A comparative analysis between a simple closed-loop control, typically used in parabolic trough systems, and the proposed control algorithm was conducted. Experimental tests were carried out for several days under different weather conditions. The experimental results showed that the mean solar tracking error obtained with the simple control was 0.97°, while the error of the proposed dual control was 0.21°; i.e., the error decreased by 78%, demonstrating greater stability and robustness of solar tracking. The proposed strategy proved to be a technically and economically feasible option to increase accuracy, reliability, and robustness in single-axis solar tracking systems of parabolic trough systems.

Study on Active Disturbance Rejection Control of Permanent Magnet Synchronous Motor Based on Variable Structure Extended State Observer

Linear extended state observer (linear extended state observer, LESO) is the core component of linear active disturbance rejection control (linear active disturbance rejection control, LADRC), and its performance is critical to the control effect. The linear ADRC is applied to the speed loop of the permanent magnet synchronous motor control system with a double closed-loop control strategy. By adding a scale factor to the linear extended state observer, the utilization efficiency of the observed signal and the observation speed is improved. On this basis, a hybrid switching strategy is adopted to achieve a smooth transition between the traditional ESO and the improved ESO, avoiding the motor speed imbalance and motor chattering caused by direct switching. Finally, the improved ADRC strategy and the traditional ADRC strategy are compared and analyzed through simulation, which verifies the effectiveness and superiority of the improved strategy.

Data-Driven Modelling of Soil Moisture Dynamics for Smart Irrigation Scheduling

In the face of increasing water scarcity and uncertainties of climate change, improving crop water use efficiency and productivity, while minimizing negative environmental impacts, is becoming crucial to meet the surging global food demand. Smart irrigation has a potential of improving water use efficiency in precision agriculture especially when efficient irrigation control strategies are adopted. Conventionally, irrigation systems rely on heuristic methods to schedule irrigation which either leads to over-irrigation or under-irrigation. This influences the crop physiological characteristics as well as the water use efficiency. To tackle this menace, model-based irrigation management has been overemphasized. A closed-loop irrigation control strategy relies on a mathematical model of the system for irrigation scheduling decisions. In this study, a data-driven approach was used to learn soil moisture dynamics from a drip irrigated tomato in an open field agricultural system. A total number of 9674 data samples were collected using an ATMOS41 weather station, TERROS 12 soil moisture sensor and a YFS-201 flow sensor for crop evapotranspiration and precipitation, soil moisture and irrigation volumes respectively. Data driven modelling was then performed using the system identification toolbox in a MATLAB environment. The model formulation was a multi-input single-output (MISO) system with reference evapotranspiration, irrigation and rainfall as inputs and soil moisture as the output. Different model structures including transfer functions, state space models, polynomial models and ARX models were evaluated. Model performance was evaluated using the mean square error (MSE), final prediction error (FPE) and estimated fit of the model approaches. Simulation results indicate that the soil moisture dynamics model provides a satisfactory approximation of the process dynamics with a state space model giving an estimated fit of 97.04 %, MSE and FPE of 1.74×10−7 and 1.75×10−7 respectively. This model will be used to design a model predictive controller for smart irrigation scheduling in open field environmental conditions.

Study of Fractional Order PI DC-DC Converter Based on Dual Closed-loop Control

In this paper, the dual closed-loop control strategy with fractional-order PI is applied to the field of the DC-DC converter, which effectively improves the dynamic performance and static performance of the output voltage of the power electronic DC chopper converter. The open-loop transfer function of the Boost converter is obtained by modeling and analyzing the operating principle and small-signal model of the Boost converter, and the fractional-order PI parameters of the double closed-loop control are obtained by combining the frequency-domain analysis design method of control theory. The Simulink simulation model is built, and the fractional-order PI control model is compared and analyzed with the single-voltage loop control and the integer-order PI control model. The results show that the fractional-order PI-controlled Boost converter has a faster response and stronger anti-interference capability, which effectively improves the dynamic performance and static performance index of the DC-DC converter and provides a theoretical basis for the research of dual closed-loop control strategy of the DC-DC converter.

Experimental Investigation into Closed-Loop Control for HTPB-Based Hybrid Rocket Motors

Space exploration greatly facilitates the development of advanced propulsion systems. Extensive research has shown that hybrid rocket motors have bright prospects for use in variable-thrust propulsion systems. However, the variable-thrust precision control of a hybrid rocket motor with a high-mass fraction of aluminum has not been adequately explored. In this paper, we propose a closed-loop control system for a high-performance laboratory-scale hybrid rocket motor, and verify its performance through tests on a hybrid rocket motor containing 98% hydrogen peroxide and hydroxyl-terminated polybutadiene with 58% of an aluminum additive. The results show that, first, the average value of thrust in the stable sections in the three stages were 400.7 N, 599.1 N, and 400.1 N when the target values were 400 N, 600 N, and 400 N, respectively. Second, the average thrust was stable, and the control error of the average value was better than 0.5%. Third, the real-time error in thrust was controlled to within ± 20 N with a steady-state error smaller than 5%. These results indicate that the proposed closed-loop control strategy for hybrid rocket motors with a high-mass fraction of aluminum can maintain a constant thrust and smooth transitions in case of variable thrust.