Robust Feedback Research Articles

Robust Feedback Instability Analysis in the ${\mathscr {L}}_{2}$-Gap

Robust Feedback Instability Analysis in the ${\mathscr {L}}_{2}$-Gap

Control Design and Implementation of Autonomous Robotic Lawnmower

This paper presents the trajectory tracking control design and implementation of feedback linearization (FL) and robust feedback linearization (RFL), applicable to a robotic lawnmower with four mecanum driving wheels. The RFL control design additionally includes a robust control law. These two nonlinear control laws are developed to enable the controlled robotic lawnmower to accurately follow any specified trajectory. The simulation outcomes illustrate that the suggested control law based on RFL displays superior trajectory tracking accuracy and resilience compared to the FL control method in the case of a robotic lawnmower operating under demanding conditions. These conditions encompass environmental disturbances and uncertainties in modeling. The RFL control method also exhibits lower energy consumption compared to the FL control method. Finally, using the RFL controller derived from this study, the error in trajectory tracking in computer simulations and the actual mowing performance have demonstrated outstanding results.

Optimal and simultaneous synthesis of fractional order QFT controllers and prefilters for non-minimum phase hydro power systems

Abstract Ideally, the operating frequency of the power units, working in parallel, must not deviate from its nominal value. However, due to the dynamic nature of the load, operating frequency varies throughout the day; thus, the control of governors in the prime movers is essential to balance out the demand, and prevent any frequency deviation. To address this, present study investigates the design of optimal and robust quantitative feedback theory based (QFT) controllers and pre-filters for single area load frequency control of hydro power systems. Hydropower system model considered in the present study features a right-hand side zero, thus exhibiting non-minimum phase; these characteristics make the control more challenging. Also, the work investigates the optimal design of the QFT controllers and prefilters simultaneously by automating the loop shaping procedure, which else follows a sequential manual process on Nichols charts. The proposed automation also empowers the control designer to predefine the controller structure. In the present work the design of fractional order QFT controllers and pre-filters is considered. The study also compares the proposed work with the methods proposed in the existing literature as well as the optimal controllers obtained using the time domain indices. The obtained results establishes that the developed fractional QFT controller offers good tracking, stability, and robustness to disturbances when compared to existing approaches. The proposed fractional order QFT controllers offer the elimination of the overshoot and the undershoot from the closed loop response of the system; outperforms the existing controllers in terms of disturbance rejection; offers 0% steady-state deviation, while providing improved phase margin (60.1°) for enhanced stability compared to existing controllers. Also, the proposed QFT-GA attains the ideal values for both the peak complementary sensitivity functions; thus, establishing excellent robustness. Also, the proposed controllers ensure adequate tolerance to frequency deviation in case of load change.

AVALIAÇÃO DE PROGRAMAS DE FORMAÇÃO DE PROFESSORES: CRITÉRIOS E IMPACTOS

Considering the incessant and turbulent social changes that permeate today's society, teacher training stands out as a vital path for updating and improving the professionals responsible for teaching and educating. Thus, the objective of teacher training is not limited to the discourses and epistemological bases that support teacher preparation but expands to foster a deep reflection on educational practice and equip professionals with the essential skills to align the profile of the citizen we educate with emerging social demands. Therefore, it becomes imperative to evaluate the results of training programs and actions aimed at teachers, to uncover the consequences of these initiatives and, thus, verify the real effectiveness of training programs aimed at teachers. In this scenario, the importance of evaluating training programs explodes in relevance, revealing itself as a crucial element in the incessant search for educational quality. This document aims to highlight, in a vibrant way, the urgent need to evaluate evaluation levels, identify the appropriate moments for each evaluation modality, and determine the instruments for collecting information. The analysis of the agents involved in this evaluation process will be addressed with intensity, highlighting how these aspects interconnect to create a robust and impactful feedback cycle, aiming to reveal the magnitude of the importance of continuous evaluation in improving teacher training and adapting to constantly changing social dynamics.

Implementation and effectiveness of the cashless banking system

This thesis analyses the implementation and effectiveness of the cashless banking system at Ecobank, focusing on various dimensions such as usability, stakeholder satisfaction, and customer perspectives. A mixed-methods approach was employed, incorporating quantitative and qualitative data from 25 participants to evaluate the system's performance. The analysis reveals that while the cashless banking system is generally well-received, particularly in ease of task completion and overall workflow improvements, there are notable challenges in usability, particularly with interface intuitiveness and performance during peak hours. Stakeholders and customers reported moderate satisfaction, with varying experiences regarding ease of use and reliability. The study concludes that although the cashless banking system has enhanced Ecobank’s service delivery and met broad expectations, further user experience, system performance, and continuous evaluation mechanisms are necessary to optimise its effectiveness and customer satisfaction. Recommendations include focusing on user-centred design, improving scalability for peak demand periods, and establishing robust feedback loops for ongoing system refinement.

Dynamic output feedback robust MPC hybrid fault-tolerant control for discrete uncertain systems: a switching control strategy

To guarantee the control performance of the discrete system under unmeasurable state and partial actuator failure, a robust dynamic output feedback predictive fault-tolerant control method derived from switching strategy is developed. A new iterative error switching model is established, which both ensures tracking performance and lays the foundation for the development of the next switching controller. Based on this model, output feedback switching fault-tolerant controller is developed. Compared with conventional fault-tolerant control methods, the designed controller can be used under the case of unmeasurable states, and it is more fault tolerant and less conservative. According to the Lyapunov stability theory, the robust stability analysis is carried out under normal and fault conditions, respectively. Then, depending on the findings of the stability analysis, sufficient conditions to guarantee the stability of the closed-loop normal and faulty system are derived. Finally, the suggested method's efficacy is confirmed using the injection moulding process as an example.

Influence of Community Participation on Sustainability of Non-Profit Organizations: The Case of Kenya Wildlife Conservancies Association (KWCA)

This paper examines the influence of community participation on the sustainability of non- profit organizations, with a particular focus on the Kenya Wildlife Conservancies Association (KWCA). Using stakeholder theory and participatory development theory as its theoretical framework, the study employed a descriptive research design and utilized stratified and purposive sampling. Data was collected from 100 respondents—including board members, staff, and stakeholders—via structured questionnaires and analyzed using SPSS with multiple regression. The findings demonstrated a significant positive correlation Y = 2.184 + 0.438X1 + Ԑ., between community participation and sustainability of non-profit organizations highlighting that community engagement fosters ownership, responsibility, and long-term support. The study revealed that community participation enhances resource mobilization, accountability, and transparency within non-profit organizations. Respondents emphasized the importance of community involvement in achieving these outcomes, aligning with prior research by Smith et al. (2020) and Mwangi and Njenga (2019), which also underscored the positive impact of community engagement on non-profit effectiveness and sustainability. By integrating community members into decision-making processes, non-profits can leverage local knowledge and skills, ensuring continued support and effective management. Based on these insights, several recommendations are proposed for KWCA and similar organizations. It is essential to prioritize and expand community involvement by developing more inclusive and interactive engagement programs. Establishing robust feedback mechanisms will facilitate community input and foster a sense of ownership. Additionally, investing in capacity-building initiatives to equip community members with the necessary skills and knowledge is crucial. These measures are expected to enhance community engagement, improve program effectiveness, and bolster the overall sustainability of KWCA’s initiatives.

Research on Longitudinal Control of Electric Vehicle Platoons Based on Robust UKF–MPC

In a V2V communication environment, the control of electric vehicle platoons faces issues such as random communication delays, packet loss, and external disturbances, which affect sustainable transportation systems. In order to solve these problems and promote the development of sustainable transportation, a longitudinal control algorithm for the platoon based on robust Unscented Kalman Filter (UKF) and Model Predictive Control (MPC) is designed. First, a longitudinal kinematic model of the vehicle platoon is constructed, and discrete state–space equations are established. The robust UKF algorithm is derived by enhancing the UKF algorithm with Huber-M estimation. This enhanced algorithm is then used to estimate the state information of the leading vehicle. Based on the vehicle state information obtained from the robust UKF estimation, feedback correction and compensation are added to the MPC algorithm to design the robust UKF–MPC longitudinal controller. Finally, the effectiveness of the proposed controller is verified through CarSim/Simulink joint simulation. The simulation results show that in the presence of communication delay and data loss, the robust UKF–MPC controller outperforms the MPC and UKF–MPC controllers in terms of MSE and IAE metrics for vehicle spacing error and acceleration tracking error and exhibits stronger robustness and stability.

Robust finite-time output feedback stabilisation for a class of uncertain planar systems with asymmetric output constraints

This paper considers the finite-time output feedback stabilisation (FTOFS) problem for a class of uncertain planar systems with asymmetric output constraints. The presence of unknown control coefficients, unknown measurement sensitivity and asymmetric output constraints makes the system under consideration essentially different from those in the existing related works. By constructing a new barrier Lyapunov function and applying homogeneous system theory, a simple proportional-derivative like finite-time output feedback controller is explicitly constructed, which only utilises the output information. A rigorous proof demonstrates that not only the closed-loop system is finite time stable, but also the requirement of asymmetric output constraint can be achieved. The novelty of the control approach lies in that it is capable to handle the FTOFS problem for uncertain planar systems with or without asymmetric output constraints in a unified manner, without changing the control structure. The efficiency of the proposed theoretical results are confirmed by simulation results.

Robust [formula omitted] output feedback control for polynomial discrete-time systems

This paper aims to design a robust output feedback controller with H∞ performance for polynomial discrete-time systems (PDTS). This is due to the lack of research available on PDTS’ output feedback control especially when uncertainty is considered in the system. To be specific, the norm-bounded uncertainties are considered instead of polytopic uncertainties and then a so-called ‘scaled’ system is established to relate the robust H∞ and the nonlinear H∞ output feedback control problem. The integrator approach is introduced to overcome the nonconvexity issue when the polynomial Lyapunov function is selected. The controller is obtained by solving the sufficient conditions which are formulated in Polynomial Matrix Inequalities (PMIs) which is then converted into Sum of Squares (SOS) form. Semidefinite Programming (SDP) is used to obtain the results. Finally, the efficacy of the method is shown through numerical examples.

MPC Optimization Algorithm and Strategy for HVAC System under Smart City Construction

As a giant in energy consumption, buildings urgently need to optimize control strategies for the main energy consuming equipment inside buildings. It is of great significance to design advanced control algorithms to improve the efficiency of the main energy consuming equipment in buildings, namely air conditioning, in the current energy shortage. The model predictive control algorithms and strategies were used in this study to control the HVAC system to improve the energy utilization of the city. Then linear matrix inequality with robust model predictive feedback controller was used to optimize and get the model predictive control optimization algorithm. The research results showed that, under the influence of different factors, the three regions controlled by the model predictive control optimization algorithm showed a little overshooting in the initial state. But it was quickly corrected after adjustment. Meanwhile, the average tracking error of temperature and humidity in each region was 0.139◦ C and 0.13g/kg dry air, respectively. The average predicted mean vote was 0.32. In actual office buildings, the proposed algorithm controlled the temperature within the reference value range of 0.1◦ C throughout the entire process. The total electricity consumption and electricity price costs were reduced by 12.11% and 22.54%, respectively. In summary, the proposed method has good performance for HVAC system application, which can effectively realize energy saving and emission reduction and improve human comfort. This method makes important contributions to promote the construction of smart cities and the development of green buildings.

Practical tracking control for a class of uncertain MIMO nonlinear systems with unmatched disturbances

This paper studies the output tracking control problem for a class of uncertain MIMO nonlinear systems. The motivation comes from how to deal with unknown coupling system dynamics between subsystems and achieve the desired tracking when the system has parameter uncertainties and external disturbances. The difficulty is to guarantee that tracking errors enter an arbitrarily prescribed neighbourhood within a finite time. Based on the construction of a time-varying dynamic gain associated with tracking errors and the effective manipulation of nonlinear parametrization, a novel robust feedback controller is built up to ensure the boundedness of all closed-loop signals and the convergence of tracking errors to a small neighborhood approaching the origin in a finite time. Finally, the feasibility of control strategy is verified by numerical and practical examples.

Current trends and perspectives of scoliosis research society travel fellows

Abstract Purpose This study aims to measure the impact of the Scoliosis Research Society’s travel fellowship on a spinal surgeon’s career. Methods A non-incentivized survey was sent to 78 previous SRS junior travel fellows from 1993 to 2021. The questionnaire assessed fellowship influence on academic and administrative positions, professional society memberships, and commercial relationships. The trend of these quantitative measures was created according to a compounded annual growth rate (CAGR) calculation of the reported values. The Scopus database was queried for all fellows’ publication counts and h-index before the fellowship, as well as 3 years, 5 years, and currently after the fellowship. A control cohort of matched surgeons who did not participate in travel fellowships was used to compare research productivity measures relative to travel fellows. Results This study had a 73% response rate. Over the periods of 3–5 years after the fellowship, and up to the present, the mean publication count increased by 31.0%, 31.6%, and 46.4%, respectively. Over the same interval, the mean h-index increased by 19.5%, 17.3%, and 11.3%, respectively. From the year of their respective fellowship to present day, the fellows observed a mean CAGR of + 3.2% in academic positions, + 6.7% in administrative positions, + 2.3% in society memberships, and + 4.7% in commercial relations. Previous fellows concurred the fellowship changed their clinical practice (42.1% Strongly Agree, 36.8% Agree), expanded their network (71.9% Strong Agree, 24.6% Agree), expanded their research (33.3% Strongly Agree, 54.4% Agree), and improved their surgical technique (33.3% Strongly Agree, 49.1% Agree). Conclusion Robust feedback from previous fellows suggests a traveling fellowship has a meaningful impact on a surgeon’s research productivity and career achievements.

Robust higher order sliding mode control of grid‐forming converters with LCL filter in weak grid scenarios for fast frequency support

AbstractThis paper presents a nonlinear higher‐order sliding mode control (HO‐SMC) designed for a droop control‐based grid‐forming converter. In weak grid scenarios, where the rate of change of frequency is notably high, achieving a rapid frequency response becomes imperative. The stable operation of a grid‐forming converter using droop control, coupled with classical vector control that employs cascaded voltage and current loops (multiloop) with PI controllers, faces limitations when higher droop coefficients are applied. This constraint on the application of classical vector control in weak grid conditions necessitates alternative solutions. Operating as a grid‐forming converter, the grid‐connected converter with an LCL filter represents a second‐order system. HO‐SMC mitigates the switching challenges associated with conventional SMC by integrating robust feedback linearized control. A graphical method is proposed for designing the switching gain using Lyapunov's direct method to counteract the impact of a matched disturbance. The study demonstrates that the implementation of HO‐SMC in the grid‐forming converter enhances fast frequency response by increasing the gain margin of the power frequency loop. Finally, it is illustrated that the proposed control method also improves the transient response of the converter.

Evaluating community-embedded elder care: A case study of supply and demand in Hangzhou, China.

With China's urbanization and demographic shifts significantly affecting elder care, this study examines the alignment of community-based elder care services in Hangzhou's Hemu Community. It addresses the gap in understanding how these services meet the needs of an aging population in a rapidly changing social context. A comprehensive mixed-methods approach was utilized, involving interviews with community residents, observations of elder care service operationsand thorough document analysis. The objective was to evaluate the adequacy, utilizationand satisfaction levels concerning these elder care services. The research identified that, although the services generally meet the community's needs, there are notable challenges in content specificity, quality assuranceand promotional efforts. These challenges lead to resistance among older adults. Additionally, issues with service visibility and the lack of robust feedback mechanisms were noted. This study highlights the critical need for a cooperative strategy involving government, community organizations, social entitiesand businesses in enhancing elder care services. It suggests that improvements in service visibility, content qualityand targeted promotion are crucial to address the evolving needs of the aging population and to reduce reluctance in service utilization.

Robust control design of uncertain nonlinear systems: a self-compensating and self-tuning approach

ABSTRACT The problem of robust stabilisation is considered for a class of uncertain nonlinear systems with linear control term. It is not required that the unforced nominal (nonlinear) system has to be stable and/or has to be known, which means that its Lyapunov function need not be known and/or found for designing a stabilising control scheme to compensate the effect of uncertainty on the systems like some traditional control design approaches. For such a class of uncertain nonlinear systems, a design approach, called a self-compensating and self-tuning one, is presented whereby some robust state feedback control schemes can be easily synthesised. The proposed design approach can result in a linear state feedback control scheme with a time-varying control gain for such a class of uncertain nonlinear systems, which implies the simplicity of the design approach and control results. In addition, the system uncertainty is also not required to have to satisfy the matching conditions.

Spreading anomaly semantic segmentation and 3D reconstruction of binder jet additive manufacturing powder bed images

Variability in the inherently dynamic nature of additive manufacturing introduces imperfections that hinder the commercialization of new materials. Binder jetting produces ceramic and metallic parts, but low green densities and spreading anomalies reduce the predictability and processability of resulting geometries. In situ feedback presents a method for robust evaluation of spreading anomalies, reducing the number of required builds to refine processing parameters in a multivariate space. In this study, we report layer-wise powder bed semantic segmentation for the first time with a visually light ceramic powder, alumina, or Al2O3, leveraging an image analysis software to rapidly segment optical images acquired during the additive manufacturing process. Using preexisting image analysis tools allowed for rapid analysis of 316 stainless steel and alumina powders with small data sets by providing an accessible framework for implementing neural networks. Models trained on five build layers for each material to classify base powder, parts, streaking, short spreading, and bumps from recoater friction with testing categorical accuracies greater than 90%. Lower model performance accompanied the more subtle spreading features present in the white alumina compared to the darker steel. Applications of models to new builds demonstrated repeatability with the resulting models, and trends in classified pixels reflected corrections made to processing parameters. Through the development of robust analysis techniques and feedback for new materials, parameters can be corrected as builds progress.

Mixed deterministic and stochastic disturbances in a discrete-time Nash game

This paper considers a discrete-time non-cooperative M-players linear affine quadratic game of pre-specified fixed duration, affected by stochastic noise and deterministic disturbances. The last one is seen as a pernicious fictitious player looking to maximise the expected cost functions of each player. Inspired in the discrete-time robust dynamic programming, sufficient conditions for the existence of a type of robust feedback NE are given in the solution of a set of discrete-time difference equations. A formal induction proof is provided for the closed form of the obtained robust set of strategies. Two illustrative simulation examples are included, one related to the problem of coordination of a two-echelon supply chain with uncertain seasonal demand. The goal of the agents is to reduce the expected cost of storage while satisfying a partially known demand. The second example is related to a game of government debt stabilisation. Comparing the simulation with the standard Nash strategy, the robust one achieves a better performance.

Exploring College Students’ Perceptions of Privacy and Security in Online Learning: A Comprehensive Questionnaire-Based Study

The rapid shift to online learning has intensified concerns about privacy and security among college students. This study aims to examine these perceptions and identify strategies to enhance user satisfaction and trust. The study’s novelty lies in exploring the impact of collaborative efforts between educational institutions and technology providers on improving online learning experiences. The research objectives are to examine how transparency influences trust in security, investigate the relationship between data control and perceived privacy, and identify strategies to improve user satisfaction and trust. A quantitative approach utilizing an analytic research design and a questionnaire method was employed, targeting 420 college students engaged in online learning. Data analysis was conducted using SPSS software. Findings supported six hypotheses: higher transparency in data handling leads to increased trust (H1, H4); more control over personal data correlates with greater perceived privacy and security (H2, H3, H5); and collaborative efforts enhance user satisfaction and trust (H6). Specifically, 71% of participants agreed that increased transparency would enhance trust, and participants emphasized the importance of data control for privacy protection and user empowerment. Collaborative strategies, such as robust feedback mechanisms and comprehensive support services, were identified as crucial for improving user satisfaction and trust. Regression analysis indicated significant relationships between transparency, data control, digital literacy, and user satisfaction. This study underscores the importance of transparency, data control, and collaboration in fostering a secure and trustworthy online learning environment, offering valuable insights for policymakers and educators.

Real-Time Milling Chatter Detection and Control with Axis Encoder Feedback and Spindle Speed Manipulation

This paper introduces a complete real-time algorithm, where the chatter is detected and eliminated by spindle speed manipulation via the chatter energy feedback calculated from the axis encoder measurement. The proposed method does not require profound knowledge of the machining dynamics; instead, the entire algorithm exploits the fact that milling vibrations consist of forced vibrations at spindle speed harmonics and chatter vibrations that are close to one of the natural modes, with sidebands which are spread at the multiples of spindle speed frequency above and below the chatter frequency. The developed algorithm is able to identify the amplitude, phase and frequency of all the harmonics constituting the periodic forced and chatter vibrations. The key challenge is to select dominant chatter frequencies for the calculation of a robust and accurate chatter energy ratio feedback; this is achieved by utilizing the frequency estimation variance of EKF as a novel chatter indicator. Based on the chatter energy ratio feedback, the controller overrides the spindle speed in order to suppress the chatter energy below a particular threshold value. The varying spindle speed challenge is handled by updating the state transition matrices of the Kalman filters and real-time calculation of the band-pass filter coefficients, based on the derived discrete time transfer functions. The developed algorithm is tested on a Deckel FP5cc CNC which is in-house retrofitted and has a PC-based controller for the real-time application of the proposed algorithm. It is shown that the real-time chatter frequency and amplitude estimates are compatible with off-line FFT analysis, and chatter can be successfully eliminated by energy feedback.