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@inproceedings{bib_Modu_2025, AUTHOR = {Yadav, Rishabh Dev and Swati, Dantu and Pan, Wei and Sun, Shihao and Roy, Spandan and Baldi, Simone }, TITLE = {Modular Adaptive Aerial Manipulation under Unknown Dynamic Coupling Forces}, BOOKTITLE = {IEEE/ASME Transactions on Mechatronics}. YEAR = {2025}}

Successful aerial manipulation largely depends on how effectively a controller can tackle the coupling dynamic forces between the aerial vehicle and the manipulator. However, this control problem has remained largely unsolved as the existing control approaches either require precise knowledge of the aerial vehicle/manipulator inertial couplings, or neglect the statedependent uncertainties especially arising during the interaction phase. This work proposes an adaptive control solution to overcome this long standing control challenge without any a priori knowledge of the coupling dynamic terms. Additionally, in contrast to the existing adaptive control solutions, the proposed control framework is modular, that is, it allows independent tuning of the adaptive gains for the vehicle position sub-dynamics, the vehicle attitude sub-dynamics, and the manipulator subdynamics. Stability of the closed loop under the proposed scheme is derived analytically, and real-time experiments validate the effectiveness of the proposed scheme over the state-of-the-art approaches.

@inproceedings{bib_RE-C_2025, AUTHOR = {Suraj, Bonagiri V Sai Gopala and Roy, Spandan and Krishna, K Madhava }, TITLE = {RE-CONFIGURABLE UNMANNED AERIAL VEHICLE}, BOOKTITLE = {United States Patent}. YEAR = {2025}}

An embodiment herein provides a re-configurable unmanned aerial vehicle that re-configures its shape based on the shape, size, weight of a payload, and efficiently performs payload delivery in real-time. The re-configurable unmanned aerial vehicle includes one or more rotor units placed at corners and is connected by one or more scissor units. The re-configurable unmanned aerial vehicle approaches the payload in a first location, and analyses the position and dimension of the payload with a camera, that enables the one or more scissor units to adjust its length by at least one elongation or compression following size and shape of the payload and fit the payload within the re- configurable unmanned aerial vehicle. The re-configurable unmanned aerial vehicle takes off carrying the payload from the first location and lands at a second location.

@inproceedings{bib_An_I_2025, AUTHOR = {Yadav, Rishabh Dev and Jones, Brycen and GUPTA, SAKSHAM and Sharma, Amitabh and Sun, Jiefeng and Zhao, Jianguo and Roy, Spandan }, TITLE = {An Integrated Approach to Aerial Grasping: Combining a Bistable Gripper with Adaptive Control}, BOOKTITLE = {IEEE/ASME Transactions on Mechatronics}. YEAR = {2025}}

Grasping using an aerial robot can have many applications ranging from infrastructure inspection and maintenance to precise agriculture. However, aerial grasping is a challenging problem since the robot has to maintain an accurate position and orientation relative to the grasping object, while negotiating various forms of uncertainties (e.g., contact force from the object). To address such challenges, in this paper, we integrate a novel passive gripper design and advanced adaptive control methods to enable robust aerial grasping. The gripper is enabled by a pre-stressed band with two stable states (a flat shape and a curled shape). In this case, it can automatically initiate the grasping process upon contact with an object. The gripper also features a cable-driven system by a single DC motor to open the gripper without using cumbersome pneumatics. Since the gripper is passively triggered and initially has a straight shape, it can function without precisely aligning the gripper with the object (within an 80 mm tolerance). Our adaptive control scheme eliminates the need for any a priori knowledge (nominal or upper bounds) of uncertainties. The closed-loop stability of the system is analyzed via Lyapunov-based method. Combining the gripper and the adaptive control, we conduct comparative realtime experimental results to demonstrate the effectiveness of the proposed integrated system for grasping. Our integrated approach can pave the way to enhance aerial grasping for different applications.

@inproceedings{bib_Impe_2025, AUTHOR = {Sharma, Amitabh and Munish, Gupta Saksham and Singh, Shivansh Pratap and Yadav, Rishabh Dev and Song, Hongyu and Pan, Wei and Roy, Spandan and Baldi, Simone }, TITLE = {Impedance and Stability Targeted Adaptation for Aerial Manipulator with Unknown Coupling Dynamics}, BOOKTITLE = {Internationcal Conference on Control, Automation and Systems}. YEAR = {2025}}

Stable aerial manipulation during dynamic tasks such as object catching, perching, or contact with rigid surfaces necessarily requires compliant behavior, which is often achieved via impedance control. Successful manipulation depends on how effectively the impedance control can tackle the unavoidable coupling forces between the aerial vehicle and the manipulator. However, the existing impedance controllers for aerial manipulator either ignore these coupling forces (in partitioned system compliance methods) or require their precise knowledge (in complete system compliance methods). Unfortunately, such forces are very difficult to model, if at all possible. To solve this long-standing control challenge, we introduce an impedance controller for aerial manipulator which does not rely on a priori knowledge of the system dynamics and of the coupling forces. The impedance control design can address unknown coupling forces, along with system parametric uncertainties, via suitably designed adaptive laws. The closed-loop system stability is proved analytically and experimental results with a payload-catching scenario demonstrate significant improvements in overall stability and tracking over the state-of-the-art impedance controllers using either partitioned or complete system compliance.

@inproceedings{bib_Cont_2024, AUTHOR = {Roy, Spandan }, TITLE = {Control Adaptation in Quadrotors under Actuator Faults and Unknown State-dependent Dynamics}, BOOKTITLE = {Internatinal Conference on Automation Science and Engineering}. YEAR = {2024}}

@inproceedings{bib_An_a_2024, AUTHOR = {Roy, Spandan }, TITLE = {An annular event-triggered artificial time-delayed control-based guidance approach}, BOOKTITLE = {International Journal of Control}. YEAR = {2024}}

This work proposes a resource efficient robust control scheme for missile-target engagement scenarios subjected to external disturbances. The robustness is achieved by using an annular event-triggered artificial time-delayed control (ET-TDC) methodology with input saturation. The ET-TDC philosophy uses the TDC strategy through a dynamic predefined triggering mechanism which overcomes the requirement to update the control periodically for every sampling instant, unlike conventional TDC and other robust control schemes. Thus the proposed methodology can tackle uncertainties with minimal a-priori knowledge while significantly reducing the over-utilisation of system resources. In addition, the adopted event-triggered mechanism facilitates further conservation of energy which might be crucial for mid-to-long range engagement scenarios. The closed-loop stability is derived analytically and the simulation results illustrate the efficacy of the proposed guidance framework in comparison with other state-of-art robust control methodologies.

@inproceedings{bib_Adap_2024, AUTHOR = {Dantu, Swati and Yadav, Rishabh Dev and Anantha, and Roy, Spandan and Baldi, Simone }, TITLE = {Adaptive Tracking and Anti-Swing Control of Quadrotors Carrying Suspended Payload Under State-Dependent Uncertainty}, BOOKTITLE = {IEEE/ASME Transactions on Mechatronics}. YEAR = {2024}}

Transportation of a suspended payload using quadrotor demands a controller to simultaneously track the desired path and stabilize the planar payload swing angles. Such a control objective is made challenging by the need to orchestrate the coupling between fully actuated dynamics (quadrotor attitude) and underactuated dynamics (quadrotor position and planar payload swings). State-of-the-art controllers cannot orchestrate such coupled dynamics in the presence of unmodeled and state-dependent terms, such as aerodynamic drags and rotor downwash. This article solves this control challenge by adaptively estimating the state-dependent uncertainty. Closed-loop stability for the coupled underactuated and fully actuated dynamics is established analytically. Extensive real-time experiments confirm significant improvements over the state-of-the-art under various scenarios, such as path tracking with suspended payload and anti-swing control against externally induced payload swings.

@inproceedings{bib_Dist_2024, AUTHOR = {Tao, Tian and Roy, Spandan and Schutter, Bart De and Baldi, Simone }, TITLE = {Distributed Adaptive Synchronization in Euler–Lagrange Networks With Uncertain Interconnections}, BOOKTITLE = {IEEE Transactions on Automatic Control}. YEAR = {2024}}

In this article, we propose a new practical synchronization protocol for multiple Euler–Lagrange systems without structural linear-in-the-parameters (LIP) knowledge of the uncertainty and where the agents can be interconnected before control design by unknown state-dependent interconnection terms. This setting is meant to overcome two standard a priori assumptions in the literature concerning uncertainty with LIP structure and absence of interaction among agents before designing the synchronization protocol. To overcome these assumptions, we propose an adaptive distributed control mechanism having the purpose of estimating the coefficients of the resulting state-dependent uncertainty structure.

@inproceedings{bib_Adap_2024, AUTHOR = {Tao, Tian and Roy, Spandan and Schutter, Bart De and Baldi, Simone }, TITLE = {Adaptive synchronization of uncertain underactuated Euler-Lagrange agents}, BOOKTITLE = {IEEE Transactions on Automatic Control}. YEAR = {2024}}

This article proposes a framework for adaptive synchronization of uncertain underactuated Euler–Lagrange (EL) agents. The designed distributed controller can handle both state-dependent uncertain system dynamics terms and state-dependent uncertain interconnection terms among neighboring agents. No structural knowledge of such terms is required other than the standard properties of EL systems (positive definite mass matrix, bounded gravity, velocity-dependent friction bound, etc.). The study of stability relies on a suitable analysis of the nonactuated and the actuated synchronization errors, resulting in stable error dynamics perturbed by parametrized state-dependent uncertainty. This uncertainty is tackled via appropriate adaptation laws, giving stability in the uniform ultimate boundedness sense, in line with available literature on state-dependent uncertain system dynamics and/or state-dependent uncertain interconnections. An example with a network of boom cranes is used to validate the proposed approach.

@inproceedings{bib_Adap_2024, AUTHOR = {Munish, Gupta Saksham and Sharma, Amitabh and Mulgundkar, Aditya Srinivas and Yadav, Rishabh Dev and Roy, Spandan }, TITLE = {Adaptive Control of Quadrotor under Actuator Loss and Unknown State-dependent Dynamics}, BOOKTITLE = {International Conference on Automation Science and Engineering}. YEAR = {2024}}

This paper examines the enhancement of quadrotor efficiency through adaptive control to address the critical need for Fault-Tolerant Control (FTC) in quadrotors amidst operational uncertainties and component inefficiency. State-of-the-art adaptive FTC strategies often assume the uncertainties to be bounded by a constant a priori; however, imprecise knowledge of inertial system parameters lead to state-dependent uncertainties which do not follow such assumption. Remain unattended, statedependent uncertainties can lead to instability, especially under actuator faults. The proposed adaptive FTC offers actuator fault mitigation while tackling unknown (statedependent) uncertainties via suitably designed adaptive laws. Additionally, real-time fault detection and control allocation are used simultaneously to avoid conservative control application. The closed-loop system stability is studied analytically and the effectiveness of the proposed solution is verified on a realistic simulator in comparison to the state of the art.

@inproceedings{bib_Adap_2023, AUTHOR = {S., Viswa Narayanan and Satpute, Sumeet and Roy, Spandan and Nikalokopoulos, George }, TITLE = {Adaptive Control of Euler-Lagrange Systems under Time-varying State Constraints without a Priori Bounded Uncertainty}, BOOKTITLE = {IFAC-PapersOnLine}. YEAR = {2023}}

In this article, a novel adaptive controller is designed for Euler-Lagrangian systems under predefined time-varying state constraints. The proposed controller could achieve this objective without a priori knowledge of system parameters and, crucially, of state-dependent uncertainties. The closed-loop stability is verified using the Lyapunov method, while the overall efficacy of the proposed scheme is verified using a simulated robotic arm compared to the state of the art.

@inproceedings{bib_Adap_2023, AUTHOR = {Swati, Dantu and Yadav, Rishabh Dev and Rachakonda, Ananth and Roy, Spandan and Baldi, Simone }, TITLE = {Adaptive Anti-swing Control for Clasping Operations in Quadrotors with Cable-suspended Payload}, BOOKTITLE = {Conference on Decision and Control}. YEAR = {2023}}

Crucial phases in aerial transportation and de- livery of suspended payloads are the clasping and unclasping of the payload to the cable. During these phases, along with the uncertainties in the quadrotor and in the environment, the inevitable payload swings induced by the human interaction or by other external interaction will create additional state- dependent uncertainties; such uncertainties pose a significant challenge in terms of control. If they continue unabated, these uncertainties can cause safety hazard for the quadrotor, the payload and, most importantly, for the human operating the clasping/unclasping tasks. As the state-of-the-art adaptive controllers cannot tackle such uncertainties or considers them as bounded terms, this paper presents an adaptive anti-swing controller where all uncertainties are taken in a state-dependent form. This choice is made to better capture uncertain clasping and unclasping operations of the suspended payload. The closed-loop stability is studied analytically and the real-time experiments confirm significant performance improvements for the proposed scheme over the state of the art.

@inproceedings{bib_Adap_2023, AUTHOR = {Sankaranarayanan, Viswa Narayanan and Satpute, Sumeet and Roy, Spandan and Nikolakopoulos, George }, TITLE = {Adaptive Control of Euler-Lagrange Systems under Time-varying State Constraints without a Priori Bounded Uncertainty}, BOOKTITLE = {Technical Report}. YEAR = {2023}}

In this article, a novel adaptive controller is designed for Euler-Lagrangian systems under predefined time-varying state constraints. The proposed controller could achieve this objective without a priori knowledge of system parameters and, crucially, of state-dependent uncertainties. The closed-loop stability is verified using the Lyapunov method, while the overall efficacy of the proposed scheme is verified using a simulated robotic arm compared to the state of the art.

@inproceedings{bib_An_A_2023, AUTHOR = {Banerjee, Arunava and Sarkar, Rajasree and Mukherjee, Joyjit and Roy, Spandan }, TITLE = {An Annular Event Triggered Artificial Time-Delayed Control Based Guidance Approach}, BOOKTITLE = {International Journal of Control}. YEAR = {2023}}

This work proposes a resource efficient robust control scheme for missile-target engagement scenarios subjected to external disturbances. The robustness is achieved by using an annular event-triggered artificial time-delayed control (ET-TDC) methodology with input saturation. The ET-TDC philosophy uses the TDC strategy through a dynamic predefined triggering mechanism which overcomes the requirement to update the control periodically for every sampling instant, unlike conventional TDC and other robust control schemes. Thus, the proposed methodology, can tackle uncertainties with minimal a priori knowledge while significantly reducing the over-utilization of system resources. In addition, the adopted event triggered mechanism facilitates further conservation of energy which might be crucial for mid-to-long range engagement scenarios. The closed-loop stability is derived analytically and the simulation

@inproceedings{bib_Intr_2023, AUTHOR = {Rayguru, Madan Mohan and Roy, Spandan and Yi, Lim and Mohan, Rajesh Elara and Baldi, Simone }, TITLE = {Introducing Switched Adaptive Control for Self-Reconfigurable Mobile Cleaning Robots}, BOOKTITLE = {IEEE Transactions on Automation Science and Engineering}. YEAR = {2023}}

Reconfigurable robots provide an attractive option for cleaning tasks, thanks to their better area coverage and adaptability to changing environment. However, the ability to change morphology creates drastic changes in the reconfigurable robot dynamics, and existing control design techniques do not take this into account. Neglecting configuration changes can lead to performance degradation and, in the worst scenarios, instability. This paper proposes to embed the changes arising from reconfiguration in the control design, via a switched uncertain Euler-Lagrangian model. Accordingly, a novel switched adaptive design is proposed for trajectory tracking. Closed-loop stability is assured using the multiple Lyapunov function framework, and the design is implemented and validated on a self-reconfigurable pavement cleaning mobile robot (PANTHERA). Note to Practitioners —Self-reconfigurable mobile cleaning robots, which can change their configurations as per the application requirements, are now predominantly used for cleaning and maintenance operations because of their better area coverage, less manpower requirement and consistent performance. However, the state-of-the-art control strategies for conventional robots cannot always ensure stability and performance under the simultaneous effects of configuration changes and uncertainties. The switched Euler-Lagrange model formulated in this work can capture the configuration changes of the robot and the proposed switched adaptive controller can tackle uncertainties of each configurations of the robot. The simulation and experimental results clearly show the potential issues of the state-of-the-art methods and the remarkable benefits of the proposed approach.

@inproceedings{bib_Dist_2023, AUTHOR = {Tao, Tian and Roy, Spandan and Schutte, Bart De and Baldi, Simone }, TITLE = {Distributed Adaptive Synchronization in Euler Lagrange Networks with Uncertain Interconnections}, BOOKTITLE = {IEEE Transactions on Automatic Control}. YEAR = {2023}}

In this work we propose a new practical synchronization protocol for multiple Euler Lagrange (EL) systems without structural linear-in-the-parameters (LIP) knowledge of the uncertainty and where the agents can be interconnected before control design by unknown state-dependent interconnection terms. This setting is meant to overcome two standard a priori assumptions in the literature concerning uncertainty with LIP structure and absence of interaction among agents before designing the synchronization protocol. To overcome these assumptions, we propose an adaptive distributed control mechanism having the purpose of estimating the coefficients of the resulting state-dependent uncertainty structure.

@inproceedings{bib_Adap_2023, AUTHOR = {Sankaranarayanan, Viswa Narayanan and Banerjee, Avijit and Satpute, Sumeet and Roy, Spandan and Nikolakopoulos, George }, TITLE = {Adaptive control for a payload carrying spacecraft with state constraints}, BOOKTITLE = {Control Engineering Practice}. YEAR = {2023}}

In this article, a novel adaptive trajectory tracking controller is designed for a payload-carrying spacecraft under full state constraints. The proposed controller can tackle state-dependent uncertainties without a priori knowledge of their structures and upper bounds. The controller ensures time-varying constraints on all states and their time derivatives. The closed-loop stability of the proposed scheme is verified analytically via the Lyapunov method, and real-life experiments using a robotic testbed validated the effectiveness of the proposed adaptive controller over the state-of-the-art.

@inproceedings{bib_Arti_2023, AUTHOR = {Roy, Spandan and Baldi, Simone and Sankaranarayanan, Viswa N. and Li, Peng }, TITLE = {Artificial-Delay Adaptive Control for Under-actuated Euler-Lagrange Robotics}, BOOKTITLE = {IEEE/ASME Transactions on Mechatronics}. YEAR = {2023}}

Artificial-delay control is a method in which state and input measurements collected at an immediate past time instant (i.e., artificially delayed) are used to compensate the uncertain dynamics affecting the system at the current time. This article formulates an artificial-delay control method with adaptive gains in the presence of nonlinear (Euler–Lagrange) underactuation. The appeal of studying Euler–Lagrange dynamics is to capture many robotics applications of practical interest, as demonstrated via stability and robustness analysis and via robotic ship and robotic aerial vehicle test cases.

@inproceedings{bib_An_A_2022, AUTHOR = {Roy, Spandan and Baldi, Simone and Ioannou, Petros A. }, TITLE = {An Adaptive Control Framework for Underactuated Switched Euler–Lagrange Systems}, BOOKTITLE = {IEEE Transactions on Automatic Control}. YEAR = {2022}}

The control of underactuated Euler–Lagrange systems with uncertain and switched parameters is an important problem whose solution has many applications. The problem is challenging as standard adaptive control techniques do not extend to this class of systems due to structural constraints that lead to parameterization difficulties. This note proposes an adaptive switched control framework that handles the uncertainty and switched dynamics without imposing structural constraints. A case study inspired by autonomous vessel operations is used to show the effectiveness of the proposed approach

@inproceedings{bib_Adap_2022, AUTHOR = {Swati, Dantu and Yadav, Rishabh Dev and Roy, Spandan and Lee, Jinoh and Baldi, Simone }, TITLE = {Adaptive Artificial Time Delay Control for Quadrotors under State-dependent Unknown Dynamics}, BOOKTITLE = {International Conference on Robotics and Biomimetics}. YEAR = {2022}}

Quadrotors are becoming more and more essen- tial for applications such as payload delivery, inspection and search-and-rescue. Such operations pose considerable control challenges, especially when various (a priori unbounded) state- dependent unknown dynamics arises from payload variations, aerodynamic effects and from reaction forces while operating close to the ground or in a confined space. However, existing adaptive control strategies for quadrotors cannot handle un- known state-dependent uncertainties. We address such unsolved control challenge in this work via a novel adaptive method for artificial time delay control, where unknown dynamics is robustly compensated by using input and state measurements collected at immediate past time instant (i.e., artificially delayed). Closed-loop stability is established via Lyapunov theory. The effectiveness of this controller is validated using experimental results

@inproceedings{bib_Intr_2022, AUTHOR = {Suraj, Bonagiri V Sai Gopala and S, Viswa Narayanan and Yadav, Rishabh Dev and Roy, Spandan }, TITLE = {Introducing Scissor Mechanism based Novel Reconfigurable Quadrotor: Design, Modelling and Control}, BOOKTITLE = {International Conference on Robotics and Biomimetics}. YEAR = {2022}}

Quadrotors are increasingly used nowadays as a mode of aerial transport during relief operations, payload delivery etc. However, in addition to higher inertia, large size payload may interfere with prop wash (displaced mass of air by the propeller), leading to unstable behaviour. On the other hand, using different quadrotors according to payload size is not feasible either economically or operationally. Therefore, in this work, we have developed a unique scissor-mechanism based reconfigurable quadrotor which can adapt to various sizes of payloads. A robust controller is also proposed to negotiate the parametric variations stemming from the reconfigurations in the system. The effectiveness of the proposed mechanism is studied extensively via comparative experiments.

@inproceedings{bib_Adap_2022, AUTHOR = {Tao, Tian and Roy, Spandan and Baldi, Simone }, TITLE = {Adaptive single-stage control for uncertain nonholonomic Euler-Lagrange systems}, BOOKTITLE = {Conference on Decision and Control}. YEAR = {2022}}

This work introduces a new single-stage adaptive controller for Euler-Lagrange systems with nonholonomic con- straints. The proposed mechanism provides a simpler design philosophy compared to double-stage mechanisms (that ad- dress kinematics and dynamics in two steps), while achieving analogous stability properties, i.e. stability of both original and internal states. Meanwhile, we do not require direct access to the internal states as required in state-of-the-art single-stage mechanisms. The proposed approach is studied via Lyapunov analysis, validated numerically on wheeled mobile robot dy- namics and compared to a standard double-stage approach

@inproceedings{bib_Adap_2022, AUTHOR = {Wang, Ximan and Roy, Spandan and Farì, Stefano and Baldi, Simone }, TITLE = {Adaptive Vector Field Guidance Without a Priori Knowledge of Course Dynamics and Wind}, BOOKTITLE = {IEEE/ASME Transactions on Mechatronics}. YEAR = {2022}}

The high maneuverability of fixed-wing un- manned aerial vehicles (UAVs) exposes these systems to several dynamical and parametric uncertainties, severely affecting the fidelity of modeling and causing limited guid- ance autonomy. This article shows enhanced autonomy via adaptation mechanisms embedded in the guidance law: a vector-field method is proposed that does not require a priori knowledge of the UAV course time constant, cou- pling effects, and wind amplitude/direction. Stability and performance are assessed using the Lyapunov theory. The method is tested on software-in-the loop and hardware-in- the-loop UAV platforms, showing that the proposed guid- ance law outperforms state-of-the-art guidance controllers and standard vector-field approaches in the presence of significant uncertainty. Index Terms—Adaptive guidance, adaptive sliding-mode control, fixed-wing unmanned aerial vehicles (UAV), un- known dynamics, vector field (VF).

@inproceedings{bib_Spec_2022, AUTHOR = {Baldi, Simone and Baldi, Simone and Roy, Spandan and Yuan, Shuai and Roy, Sayan Basu and Li, Le }, TITLE = {Special Issue on “Recent Advances in Robust Adaptive Control”}, BOOKTITLE = {International Journal of Adaptive Control and Signal Processing}. YEAR = {2022}}

As compared to conventional adaptive control, robust adaptive control aims to provide robustness against unmodeled dynamics, coupling effects, and other endogenous and exogenous disturbances. Robust adaptive control has been an active research area over more than three decades, and has flourished in many application domains. Despite the advances, some bottlenecks still need to be circumvented for further progressing in the field. This special issue collects recent advances in robust adaptive control from theoretical and application perspectives. Theoretical aspects in robust adaptive control addressed in this special issue are:• Relaxing the persistence of excitation (PE) condition, standard in adaptive control and estimation: Katuyar, Roy, and Bhasin propose a novel condition, called finite persistence excitation (f-PE), milder than PE in terms of excitation requirement and online verifiability.

@inproceedings{bib_Robu_2022, AUTHOR = {Ganguly, Sourish and Sankaranarayanan, Viswa N and Suraj, Bonagiri V Sai Gopala and Yadav, Rishabh Dev and Roy, Spandan }, TITLE = {Robust Manoeuvring of Quadrotor under Full State Constraints}, BOOKTITLE = {IFAC-PapersOnLine}. YEAR = {2022}}

Quadrotors have become extremely popular in various application scenarios which include disaster response, maintenance etc. A crucial challenge in terms of control design surfaces when a quadrotor has to operate under space constraints (e.g. pipeline inspection from inside, payload delivery at a precise location) under parametric perturbations and environmental disturbances (e.g. wind, gust). To deal with such scenarios, a suitable controller should simultaneously ensure tracking accuracy within predefined bounds to avoid constraint violation and tackle uncertainties. However, the state-of-the-art designs are either inapplicable for quadrotor system which is under-actuated in nature, or are unable to tackle system parametric uncertainties while being under full state (i.e. position, attitude angle, linear velocity and angular velocity) constraints. To address such issues in literature, a robust controller is introduced in …

@inproceedings{bib_Robu_2022, AUTHOR = {Swayampakula, Rahul K and Sankaranarayanan, Viswa N and Yadav, Rishabh D and Ganguly, Sourish and Roy, Spandan }, TITLE = {Robustifying Payload Carrying Operations for Quadrotors Under Time-Varying State Constraints and Uncertainty}, BOOKTITLE = {IEEE Robotics and Automation Letters}. YEAR = {2022}}

Quadrotors find a vast potential use in delivery and disaster relief operations. Control becomes critical in such sce- narios, especially when quadrotors have to manoeuvre through constrained spaces or deliver payloads at precise locations in the presence of external disturbances and parametric uncertainties stemming from uncertain payloads. Therefore, the controller has to guarantee a predefined tracking accuracy not to violate the state constraints. On the other hand, conventional fixed-valued state constraints are not suitable in many scenarios such as (i) initial offset being well beyond the expected accuracy, (ii) system dynam- ics experiencing significant transients due to the dropping of the payload. However, to the best of the authors’ knowledge, state- of-the-art controllers do not provide any solution for an underac- tuated system like a quadrotor when the system needs to honour time-varying constraints under uncertainties. This work proposes a controller for quadrotors which is robust against external distur- bances and parametric variations and guarantees a time-varying predefined position, velocity, attitude, and attitude-rate accuracy. The closed-loop system stability is established analytically, and the effectiveness of the proposed controller is validated experimentally compared to the state-of-the-art under a precision payload delivery scenario.

@inproceedings{bib_An_U_2022, AUTHOR = {Baldi, Simone and Roy, Spandan and Yang, Kang and Liu, Di }, TITLE = {An Underactuated Control System Design for Adaptive Autopilot of Fixed-Wing Drones}, BOOKTITLE = {IEEE/ASME Transactions on Mechatronics}. YEAR = {2022}}

Effective design of autopilots for fixed-wing unmanned aerial vehicles (UAVs) is still a great challenge, due to unmodeled effects and uncertainties that these vehi- cles exhibit during flight. Unmodeled effects and uncertain- ties comprise longitudinal/lateral cross-couplings, as well as poor knowledge of equilibrium points (trimming points) of the UAV dynamics. The main contribution of this article is a new adaptive autopilot design, based on uncertain Euler–Lagrange dynamics of the UAV and where the control can explicitly take into account under-actuation in the dy- namics, reduced structural knowledge of cross-couplings and trimming points. This system uncertainty is handled via appropriately designed adaptive laws: stability of the con- trolled UAV is analyzed. Hardware-in-the-loop tests, com- parisons with an Ardupilot autopilot and with a robustified autopilot validate the effectiveness of the control design, even in the presence of strong saturation of the UAV actua- tors.

@inproceedings{bib_Effi_2021, AUTHOR = {Ganguly, Sourish and Sankaranarayanan, Viswa N. and Suraj, Bonagiri V Sai Gopala and Yadav, Rishabh Dev and Roy, Spandan }, TITLE = {Efficient Manoeuvring of Quadrotor under Constrained Space and Predefined Accuracy}, BOOKTITLE = {International Conference on Intelligent Robots and Systems}. YEAR = {2021}}

In recent times, quadrotors have become immensely applicable in scenarios such as relief operations, infrastructure maintenance, search-and-rescue missions etc. A key control design challenge arises in these applications when the quadrotor has to manoeuvre through constrained spaces such as narrow windows, pipelines in the presence of external disturbances and parametric uncertainties: such conditions necessitate the controller to guarantee predefined tracking accuracy so as to not violate the constraints and simultaneously tackle uncertainties. However, state-of-the-art controllers dealing with constrained system motion are not applicable either for an underactuated system like quadrotor or for an uncertain system dynamics. This work proposes a robust controller that enables the quadrotor to follow a trajectory with predefined tracking accuracy in constrained space as well as to tackle uncertainties stemming from imprecise system modelling and external disturbances. The closed-loop system stability is analysed via the Barrier Lyapunov approach and the effectiveness of the proposed controller is validated via simulation with state of the art.

@inproceedings{bib_Arti_2021, AUTHOR = {Roy, Spandan and Baldi, Simone and Li, Peng and Sankaranarayanan, Viswa Narayanan }, TITLE = {Artificial-Delay Adaptive Control for Underactuated Euler–Lagrange Robotics}, BOOKTITLE = {IEEE/ASME Transactions on Mechatronics}. YEAR = {2021}}

Artificial-delay control is a method in which state and input measurements collected at an immediate past time instant (i.e., artificially delayed) are used to compensate the uncertain dynamics affecting the system at the current time. This article formulates an artificial-delay control method with adaptive gains in the presence of nonlinear (Euler–Lagrange) underactuation. The appeal of studying Euler–Lagrange dynamics is to capture many robotics applications of practical interest, as demonstrated via stability and robustness analysis and via robotic ship and robotic aerial vehicle test cases.

@inproceedings{bib_Mane_2021, AUTHOR = {Mukherjee, Joyjit and Roy, Spandan and Kar, Indra Narayan and , }, TITLE = {Maneuvering control of planar snake robot: An adaptive robust approach with artificial time delay}, BOOKTITLE = {Robust and Nonlinear control}. YEAR = {2021}}

This article proposes an adaptive-robust maneuvering control framework for a planar snake robot under the influence of parameter uncertainties. The entire control objective of maneuvering control can be viewed as the simultaneous establishments of two goals: one to maintain a time-varying body shape of the snake robot for consistent motion (called the outer layer) and the other dealing with the velocity and head-angle tracking of the same (called the inner layer). Unknown variations in the ground friction coefficients have been considered to be the primary source of time-varying uncertainties which affects the control performance in both the layers. Accordingly, an artificial time delay-based adaptive-robust control (ARC) framework, dual adaptive-robust time-delayed control (ARTDC), is proposed. The term dual signifies simultaneous application of ARTDC for the outer as well as the inner layer. ARTDC comprises of two segments: an artificial time delay-based time-delayed estimation (TDE) part and an ARC part. While TDE approximates the completely unknown friction forces, the ARC tackles the approximation error arising from the TDE. More importantly, compared with the existing ARC methodologies, the proposed ARTDC neither presumes the overall uncertainty to be upper bounded by a constant nor requires any prior knowledge of the bound of uncertainty to implement the controller. A Lyapunov function-based method has been adopted for analyzing the stability of the closed-loop system. Simulation studies affirm the improved performance of the ARTDC in contrast to the classical artificial delay-based methodology.

@inproceedings{bib_A_Sw_2021, AUTHOR = {Ye, Jun and Roy, Spandan and Godjevac, Milinko and Baldi, Simone }, TITLE = {A Switching Control Perspective on the Offshore Construction Scenario of Heavy-Lift Vessels}, BOOKTITLE = {IEEE Transactions on Control Systems Technology}. YEAR = {2021}}

Position control for heavy-lift construction vessels is crucial for safe operation during offshore construction. During the various phases of a typical offshore construction assignment, considerable changes in the dynamics of the crane-vessel system occur. Operational hazard was reported if such interchanging dynamics are not properly handled. However, to date and the best of our knowledge, no systematic control solution is reported considering multiphase offshore construction scenarios. This article proposes a switched dynamical framework to model the interchanging phases and to formulate a comprehensive position control solution for heavy-lift vessels. Stability and robustness against modeling imperfections and environmental disturbances are analytically assessed. The effectiveness of the solution is verified on a realistic heavy-lift vessel simulation platform; it is shown that the proposed switched framework sensibly improves accuracy and reduces hazard compared with a nonswitched solution designed for only one phase of the construction scenario. Index Terms— Dynamic positioning (DP) system, heavy-lift construction vessel, observer-based control, switched systems.

@inproceedings{bib_Wide_2021, AUTHOR = {Patel, Abhilash and Roy, Spandan and Baldi, Simone }, TITLE = {Wide-Area Damping Control Resilience Towards Cyber-Attacks: A Dynamic Loop Approach}, BOOKTITLE = {IEEE Transactions on Smart Grid}. YEAR = {2021}}

By increasingly relying on network-based operation for control, monitoring, and protection functionalities, modern wide-area power systems have also become vulnerable to cyber- attacks aiming to damage system performance and/or stability. Resilience in state-of-the-art methods mostly relies on known characteristics of the attacks and static control loops (i.e., with fixed input/output channels). This work proposes a ‘dynamic loop’ wide-area damping strategy, where input/output channel pairs are changed dynamically. We study ‘reactive’ dynamic switching in case of detectable attack and ‘pro-active’ dynamical switching, in case of undetectable (stealth) attacks. Stability of the dynamic loop is presented via Lyapunov theory, under para- metric perturbations, average dwell time switching and external perturbations. Using two- and five-area IEEE benchmarks, it is shown that the proposed strategy provides effective damping and robustness under various detectable (e.g., false data injection, denial-of-service) and stealth (replay, bias injection) attacks. Index Terms—Cyber-attack, dynamic loop, resilience, switched controller, wide-area damping control.

@inproceedings{bib_Adap_2021, AUTHOR = {Tao, Tian and Roy, Spandan and Baldi3, Simone }, TITLE = {Adaptive Synchronization of Uncertain Complex Networks under State-dependent a priori Interconnections}, BOOKTITLE = {Conference on Decision and Control}. YEAR = {2021}}

We address a distributed adaptive synchronization problem for complex networks composed of nonlinear nodes under state-dependent a priori interconnections, i.e. interconnection terms acting before control design. The interconnection terms are uncertain and the heterogeneous dynamics of the network nodes further contain state-dependent uncertainty and uncertain input matrix gain. Adaptive distributed control laws are proposed to tackle such an unsolved design. The proposed controller is verified in simulation via a multi-area load frequency control for power systems.

@inproceedings{bib_Mode_2021, AUTHOR = {Rayguru, Madan Mohan and Elara, M. R. and Hayat, A. A. and Ramalingam, B. and Roy, Spandan }, TITLE = {Modeling and Control of PANTHERA Self-Reconfigurable Pavement Sweeping Robot under Actuator Constraints}, BOOKTITLE = {International Conference on Intelligent Robots and Systems}. YEAR = {2021}}

The focus of this paper is (i) to derive a suitable dynamic model for a self-reconfigurable pavement sweeping robot PANTHERA and (ii) to design a robust controller for the same to tackle uncertainties stemming from the reconfiguration process, external disturbances and from actuator saturation. To meet the first objective, an Euler-Lagrangian dynamic model is proposed to incorporate the effects of configuration changes on the system dynamics. Based on this model, the second objective is met via designing a singular perturbation based robust controller which can tackle the aforementioned uncertainties without violating the actuation limits. To circumvent the vulnerability toward actuator saturation, the proposed controller is built on contraction theory, which, compared to a conventional Lyapunov theory based design, allows to improve closed-loop tracking performance without reducing the singular perturbation parameter. Experimental results on the PANTHERA reconfigurable robot validate the effectiveness of the proposed controller over the state of the art.

@inproceedings{bib_Robu_2021, AUTHOR = {Ye, Jun and Roy, Spandan and Godjevac, Milinko and Reppa, Vasso and Baldi, Simone }, TITLE = {Robustifying Dynamic Positioning of Crane Vessels for Heavy Lifting Operation}, BOOKTITLE = {IEEE/CAA Journal of Automatica Sinica}. YEAR = {2021}}

Construction crane vessels make use of dynamic positioning (DP) systems during the installation and removal of offshore structures to maintain the vessel’s position. Studies have reported cases of instability of DP systems during offshore operation caused by uncertainties, such as mooring forces. DP “robustification” for heavy lift operations, i.e., handling such uncertainties systematically and with stability guarantees, is a long-standing challenge in DP design. A new DP method, composed by an observer and a controller, is proposed to address this challenge, with stability guarantees in the presence of uncertainties. We test the proposed method on an integrated cranevessel simulation environment, where the integration of several subsystems (winch dynamics, crane forces, thruster dynamics, fuel injection system etc.) allow a realistic validation under a wide set of uncertainties.

@inproceedings{bib_An_O_2021, AUTHOR = {Mohan, Rajesh Elara and Rayguru, Madan Mohan and Parween, Rizuwana and , Lim Yi and Le, Anh Vu and Roy, Spandan }, TITLE = {An Output Feedback Based Robust Saturated Controller Design for Pavement Sweeping Self-Reconfigurable Robot}, BOOKTITLE = {IEEE/ASME Transactions on Mechatronics}. YEAR = {2021}}

—Mobile robots play a crucial role in cleaning, maintenance, and surveillance applications. This article advocates for the use of a novel robust output feedback based path following controller, for a class of selfreconfigurable mobile robot under actuator saturation. The reconfigurability property of such platforms is captured via an uncertain Euler–Lagrange dynamics. The proposed control framework estimates the unmeasurable states and the uncertain dynamics terms through two extended high gain observers, whereas the actuator limits are honored via a fast dynamic compensator. The closed-loop stability is analyzed via contraction theory, which, compared to the conventional Lyapunov based approaches, avoids the requirement of arbitrarily large controller and observer gains. Such a feature is of particular interest in view of actuator saturation. The experimental results with PANTHERA self-reconfigurable robot validate the effectiveness of the proposed technique over the state of the art.

@inproceedings{bib_Adap_2021, AUTHOR = {Bhaskar, Amisha and Dantu, Swati and Roy, Spandan and Baldi, Simone }, TITLE = {Adaptive Artificial Time Delay Control for Bipedal Walking with Robustification to State-dependent Constraint Forces}, BOOKTITLE = {International Conference on Advanced Robotics}. YEAR = {2021}}

Long standing challenges in adaptive bipedal walking control (i.e. control taking care of unknown robot parameters) were to unify the control design instead of designing multiple controllers for different walking phases as well as to bypass computing constraint forces, since it often leads to complex designs. A few attempts to design a single controller for all walking phases ignored or oversimplified the constraint forces. However, these forces are state-dependent and may lead to conservative performance or instability if not countered properly. This work proposes an innovative adaptive control method, based on artificial time delay control, which covers the entire bipedal walking phase and provides robustness against state-dependent unmodelled dynamics such as constraint forces and external impulsive forces arising during walking. Studies using a high fidelity simulator under various forms of disturbances show the effectiveness of the proposed design over the state of the art.

@inproceedings{bib_Adap_2021, AUTHOR = {Yadav, Rishabh Dev and N.Sankaranarayanan, Viswa and Roy, Spandan }, TITLE = {Adaptive Sliding Mode Control for Autonomous Vehicle Platoon under Unknown Friction Forces}, BOOKTITLE = {International Conference on Advanced Robotics}. YEAR = {2021}}

A crucial challenge in maintaining formation in an autonomous vehicle platoon rests on designing a suitable control scheme that can tackle external disturbances and uncertain system parameters, especially the friction forces between wheel and ground, which vary with change in road surface, wear in tires and speed of the vehicle. State-of-the-art adaptive controller negotiating such uncertainties can typically handle a priori bounded (or non state-dependent) uncertainties. However, besides the difficulty in accurate modelling and identification of frictional forces, in general, these forces are state-dependent and cannot be a priori bounded (e.g., viscous friction). This paper proposes an adaptive sliding mode controller for nonholonomic wheeled mobile robot based vehicle platoon which can handle unknown complex behaviour of frictional forces without a priori knowledge of its parameters and structures. The effectiveness of the proposed controller is verified in Gazebo simulation in comparison with the state of the art.

@inproceedings{bib_Effi_2021, AUTHOR = {Ganguly, Sourish and S, Viswa Narayanan and Suraj, Bonagiri V Sai Gopala and Yadav, Rishabh Dev and Roy, Spandan }, TITLE = {Efficient Manoeuvring of Quadrotor under Constrained Space and Predefined Accuracy}, BOOKTITLE = {International Conference on Intelligent Robots and Systems}. YEAR = {2021}}

In recent times, quadrotors have become immensely applicable in scenarios such as relief operations, infrastructure maintenance, search-and-rescue missions etc. A key control design challenge arises in these applications when the quadrotor has to manoeuvre through constrained spaces such as narrow windows, pipelines in the presence of external disturbances and parametric uncertainties: such conditions necessitate the controller to guarantee predefined tracking accuracy so as to not violate the constraints and simultaneously tackle uncertainties. However, state-of-the-art controllers dealing with constrained system motion are not applicable either for an underactuated system like quadrotor or for an uncertain system dynamics. This work proposes a robust controller that enables the quadrotor to follow a trajectory with predefined tracking accuracy in constrained space as well as to tackle uncertainties stemming from imprecise system modelling and external disturbances. The closed-loop system stability is analysed via the Barrier Lyapunov approach and the effectiveness of the proposed controller is validated via simulation with state of the art.

@inproceedings{bib_Robu_2021, AUTHOR = {Shukla, Harsh and Roy, Spandan and Gupta, Satyam }, TITLE = {Robust Adaptive Control of Steer-by-Wire Systems under Unknown State-dependent Uncertainties}, BOOKTITLE = {International Journal of Adaptive Control and Signal Processing}. YEAR = {2021}}

Over the past two decades, a growing thrust area of research has been electrification of different mechanical and hydraulic systems in ground vehicles, which offers less environmental concerns due to the removal of hydraulic fluids and continual engine parasitic losses. The electrical equivalents for traditional mechanical linkages and hydraulic power assist systems include ‘brakeby-wire’, ‘steer-by-wire’ and ‘throttle-by-wire’ system. These equivalents, collectively known as ‘X-by-Wire’ technologies, form the fundamental structure for the Semi and Fully Autonomous Driving Systems 1 . As compared to a traditional steering system, a Steer-by-Wire (SBW) system removes the mechanical shaft that connects the steering column and steering pinion: therefore, in absence of any physical connection, the steering input is transmitted via a by-wire electronic communication module 2 (cf. Fig. 1). In order to have the SBW equipped vehicle have the similar features to that of a conventional steering system, it is important to devise a tracking control mechanism for the steering actuator such that the steering commands from hand-wheel are followed as precisely as possible. Initial attempts were made to solve such control problem employing conventional PID controller 3,4; however, in presence of inevitable modelling imprecision and parametric uncertainties, advanced control strategies are eventually

@inproceedings{bib_On_v_2020, AUTHOR = {Roy, Spandan and Kosmatopoulos, Elias B. and Baldi, Simone }, TITLE = {On vanishing gains in robust adaptation of switched systems: A new leakage-based result for a class of Euler–Lagrange dynamics}, BOOKTITLE = {Systems & Control Letters}. YEAR = {2020}}

In the presence of unmodelled dynamics and uncertainties with no a priori constant bounds, conventional robust adaptation strategies for switched systems cannot allow the control gains of inactive subsystems to remain constant during inactive intervals: vanishing gains are typically required in order to prove bounded stability. As a consequence, these strategies, known in literature as leakage-based adaptive methods, might introduce poor transients at each switching instant. Leakage-based adaptive control becomes even more problematic in the switched nonlinear case, where non-conservative state-dependent upper bounds for uncertainties and unmodelled dynamics are required. This work shows that, for a class of switched Euler–Lagrange systems, such difficulties can be mitigated: a novel leakage-based stable mechanism is introduced which allows the gains of inactive subsystems to remain constant. At the same time, unmodelled dynamics and uncertainties with no a priori bounds can be handled by a quadratic state-dependent upper bound structure that reduces conservativeness as compared to state-of-the-art structures. The proposed design is validated analytically and its performance is studied in simulation with a pick-and-place robotic manipulator example.

@inproceedings{bib_Robu_2020, AUTHOR = {TianTao, and Roy, Spandan and Yuan, Shuai and Baldi, Simone }, TITLE = {Robust Adaptation in Dynamically Switching Load Frequency Control}, BOOKTITLE = {Science Direct}. YEAR = {2020}}

he presence of switching/evolving topologies of the power system. In today’s smart grids, switching topologies often arise from reconfiguration and resilience against faults or from switching among different control ar

@inproceedings{bib_The__2020, AUTHOR = {Wang, Ximan and Roy, Spandan and Far`, Stefano and Baldi, Simone }, TITLE = {The problem of reliable design of vector-field path following in the presence of uncertain course dynamics}, BOOKTITLE = {Science Direct}. YEAR = {2020}}

Reliable guidance of fixed-wing Unmanned Aerial Vehicles (UAVs) is challenging, as their high maneuverability exposes them to several dynamical changes and parametric uncertainties. Reliability of state-of-the-art guidance methods is often at stake, as these methods heavily rely on precise UAV course dynamics, assumed in a decoupled first-order form with known time constant. To improve reliability of guidance for fixed-wing UAVs, this work proposes a novel vector field law that can handle uncertain course time constant and state-dependent uncertainty in the course dynamics arising from coupling. Stability is studied in the Lyapunov framework, while reliability of the proposed method is tested on a software-in-the loop UAV simulator. The simulations show that, in the presence of such uncertainty, the proposed method outperforms the standard vector field approaches.

@inproceedings{bib_Aeri_2020, AUTHOR = {S, Viswa Narayanan and Roy, Spandan and Baldi, Simone }, TITLE = {Aerial Transportation of Unknown Payloads: Adaptive Path Tracking for Quadrotors}, BOOKTITLE = {International Conference on Intelligent Robots and Systems}. YEAR = {2020}}

With the advent of intelligent transport, quadrotors are becoming an attractive aerial transport solution during emergency evacuations, construction works etc. During such operations, dynamic variations in (possibly unknown) payload and unknown external disturbances cause considerable control challenges for path tracking algorithms. In fact, the statedependent nature of the resulting uncertainties makes stateof-the-art adaptive control solutions ineffective against such uncertainties that can be completely unknown and possibly unbounded a priori. This paper, to the best of the knowledge of the authors, proposes the first adaptive control solution for quadrotors, which does not require any a priori knowledge of the parameters of quadrotor dynamics as well as of external disturbances. The stability of the closed-loop system is studied analytically via Lyapunov theory and the effectiveness of the proposed solution is verified on a realistic simulator.

@inproceedings{bib_Adap_2020, AUTHOR = {Roy, Spandan and Shukla, Harsh }, TITLE = {Adaptive-Robust Controller for a Class of Systems with Time Varying Input Delay and State-Dependent Uncertainty}, BOOKTITLE = {Control Strategy for Time-Delay Systems: Part I: Concepts and Theories}. YEAR = {2020}}

In this endeavour, a new adaptive-robust control framework is devised for tracking control problem of a class of uncertain systems having state-dependent uncertainty and under the influence of time-varying input delay. In comparison to the existing adaptive-robust control (ARC) strategies, the proposed ARC framework removes the conservative assumption of a priori bounded uncertainty. In addition, the Razumikhin theorem based stability analysis allows the proposed scheme to deal with arbitrary variation in input delay. The effectiveness of the proposed ARC is verified via simulations and via experimentations using a wheeled mobile robot demonstrating improved tracking accuracy compared to the state of the art. Keywords: Adaptive-robust control, Input delay, Razumikhin theorem, State-dependent uncertainty, Wheeled mobile robot

@inproceedings{bib_Towa_2020, AUTHOR = {Baldi, Simone and Roy, Spandan and Yang, Kang }, TITLE = {Towards adaptive autopilots for fixed-wing unmanned aerial vehicles}, BOOKTITLE = {Conference on Decision and Control}. YEAR = {2020}}

Control of fixed-wing Unmanned Aerial Vehicles (UAVs) is typically organized according to two layers: the low-level control or autopilot, and the high-level control or guidance. The disadvantage of this modular design is that an intelligent guidance layer may become ineffective if the autopilot layer cannot deal with uncertainty. In fact, the required knowledge derived from linearization of equations of motion (trimming points) makes most autopilots sensitive to uncertainty. In this work, we study an autopilot framework where the knowledge of the UAV dynamics and of trimming points is not required. The proposed design, tested with complex UAV dynamics, can emulate the behavior of a carefully tuned off-the-shelf autopilot, without using its a priori knowledge.

@inproceedings{bib_Stab_2020, AUTHOR = {Tao, Tian and Roy, Spandan and Baldi, Simone }, TITLE = {Stable Adaptation in Multi-Area Load Frequency Control under Dynamically-Changing Topologies}, BOOKTITLE = {IEEE Transactions on Power Systems}. YEAR = {2020}}

Multi-area load frequency control (LFC) selects and controls a few generators in each area of the power system in an effort to dampen inter-area frequency oscillations. To effectively dampen such oscillations, it is required to enhance and lower the control activity dynamically during operation, so as to adapt to changing circumstances. Changing circumstances should cover not only parametric uncertainties and unmodelled dynamics (e.g. aggregated area dynamics and bus dynamics), but also the increasing structural flexibility of modern power systems (e.g. protection mechanisms against faults and cyber-attacks, or topology reconfiguration mechanisms for demand response). As formal stability guarantees around such an attractive adaptive multi-area LFC concept are still lacking, this work proposes framework in which adaptation and switching are combined in a provably stable way to handle parametric uncertainty, unmodelled dynamics, and dynamical interconnections of the power system. Stability is studied in the Lyapunov theory sense using the standard structure-preserving modelling approach, and the resulting adaptive multi-area LFC design is validated using an IEEE 39-bus benchmark.

@inproceedings{bib_Intr_2020, AUTHOR = {Sankaranarayana, Viswa Narayanan and Roy, Spandan }, TITLE = {Introducing switched adaptive control for quadrotors for vertical operations}, BOOKTITLE = {Optimal Control Applications and Methods}. YEAR = {2020}}

With the advent of intelligent transport, quadrotors are becoming an attractive solu-tion while lifting or dropping of payloads during emergency evacuations, construc-tion works etc. During such operations, dynamic variations in (possibly unknown)payload cause considerable changes in the system dynamics. However, a systematic control solution to tackle such interchanging dynamical behaviour is still missing.This paper proposes a switched dynamical framework to capture the interchanging dynamics of a quadrotor during vertical operations and a robust adaptive control solution to tackle such dynamics when it is unknown. The stability of the closed-loop system is studied analytically and the effectiveness of the proposed solution is verified via simulations

@inproceedings{bib_On_v_2020, AUTHOR = {Roy, Spandan and Kosmatopoulos, Elias B. and Baldi, Simone }, TITLE = {On vanishing gains in robust adaptation of switched systems: A new leakage-based result for a class of Euler–Lagrange dynamics}, BOOKTITLE = {IEEE Control Systems Letters}. YEAR = {2020}}

In the presence of unmodelled dynamics and uncertainties with no a priori constant bounds, conventional robust adaptation strategies for switched systems cannot allow the control gains of inactive subsystems to remain constant during inactive intervals: vanishing gains are typically required in order to prove bounded stability. As a consequence, these strategies, known in literature as leakage-based adaptive methods, might introduce poor transients at each switching instant. Leakage-based adaptive control becomes even more problematic in the switched nonlinear case, where non-conservative state-dependent upper bounds for uncertainties and unmodelled dynamics are required. This work shows that, for a class of switched Euler–Lagrange systems, such difficulties can be mitigated: a novel leakage-based stable mechanism is introduced which allows the gains of inactive subsystems to remain constant. At the same time, unmodelled dynamics and uncertainties with no a priori bounds can be handled by a quadratic state-dependent upper bound structure that reduces conservativeness as compared to state-of-the-art structures. The proposed design is validated analytically and its performance is studied in simulation with a pick-and-place robotic manipulator example.

@inproceedings{bib_On_a_2020, AUTHOR = {Roy, Spandan and Baldi, Simone and Fridman, Leonid }, TITLE = {On adaptive sliding mode control without a priori bounded uncertainty}, BOOKTITLE = {Automatica}. YEAR = {2020}}

Adaptive Sliding Mode Control (ASMC) aims to adapt the switching gain in such a way to cope with possibly unknown uncertainty. In state-of-the-art ASMC methods, a priori boundedness of the uncertainty is crucial to ensure boundedness for the switching gain and uniformly ultimately boundedness. A priori bounded uncertainty might impose a priori bounds on the system state before obtaining closed-loop stability. A design removing this assumption is still missing in literature. A positive answer to this quest is given by this note where a novel ASMC methodology is proposed which does not require a priori bounded uncertainty. An illustrative example is presented to highlight the main features of the approach, after which a general class of Euler–Lagrange systems is taken as a case study to show the applicability of the proposed design.

@inproceedings{bib_A_Ne_2020, AUTHOR = {Roy, Spandan and Lee, Jinoh and Baldi, Simone }, TITLE = {A New Adaptive-Robust Design for Time Delay Control Under State-Dependent Stability Condition}, BOOKTITLE = {IEEE Transactions on Control Systems Technology}. YEAR = {2020}}

This brief proposes a new adaptive-robust formulation for time-delay control (TDC) under a less-restrictive stability condition. TDC relies on estimating the unknown system dynamics via the artificial introduction of a time delay, often referred to as time-delay estimation (TDE). In conventional TDC, the estimation error, called TDE error, is taken to be upper bounded by a constant under the assumption of small time delay and, most importantly, of a priori bounded states. We highlight the issues of such a conventional methodology via an unstable the upper bound of the TDE error is formulated, which has an explicit dependence on system states and is valid for any chosen time delay. This insight leads to a new TDC design, namely, time-delayed adaptive-robust control (TDARC). The effectiveness of TDARC is substantiated via a multiple-degrees-of-freedom robot.

@inproceedings{bib_Towa_2020, AUTHOR = {Roy, Spandan and Baldi, Simone }, TITLE = {Towards structure-independent stabilization for uncertain underactuated Euler–Lagrange systems}, BOOKTITLE = {Automatica}. YEAR = {2020}}

Available control methods for underactuated Euler–Lagrange (EL) systems rely on structure-specific constraints that may be appropriate for some systems, but restrictive for others. A generalized (structure-independent) control framework is to a large extent missing, especially in the presence of uncertainty. This paper introduces an adaptive-robust control framework for a quite general class of uncertain underactuated EL systems. Compared to existing literature, the important attributes of the proposed solution are: (i) avoiding structure-specific restrictions, namely, symmetry condition property of the mass matrix, and a priori bounds on non-actuated states or state derivatives; (ii) considering Coriolis, centripetal, friction and gravity terms to be unknown, while only requiring the knowledge of maximum perturbation around a nominal value of the mass matrix; (iii) handling state-dependent uncertainties irrespective of their linear or nonlinear in parameters structure. These features significantly widen the range of underactuated EL systems the proposed solution can handle in comparison to the available methods. Stability is studied analytically and the performance is verified in simulation using offshore boom crane dynamics.

@inproceedings{bib_The__2020, AUTHOR = {Tao, Tian and Roy, Spandan and Baldi, Simone }, TITLE = {The issue of transients in leakage-based model reference adaptive control of switched linear systems}, BOOKTITLE = {Nonlinear Analysis: Hybrid Systems}. YEAR = {2020}}

The literature has proven that attaining good transient behavior in leakage-based robust adaptive control of uncertain switched systems is intrinsically challenging. In fact, because the gains of the inactive subsystems must exponentially vanish during inactive times as an effect of leakage action, new learning transients will repeatedly arise at each switching instant. In this paper, a new leakage-based mechanism is designed for robust adaptive control of uncertain switched systems: in contrast to the available designs, the key innovation of the proposed one is that the adaptive gains of the inactive subsystems can be kept constant to their switched-off values, thus preventing vanishing gains. Bounded stability of the closed-loop switched system is guaranteed thanks to the introduction of an auxiliary gain playing the role of leakage. A benchmark example commonly adopted in adaptive switched literature shows that the proposed strategy can consistently improve the transient behavior under various families of switching signals.

@inproceedings{bib_Obse_2019, AUTHOR = {Ye, Jun and Roy, Spandan and Godjevac, Milinko and Baldi, Simone }, TITLE = {Observer-based robust control for dynamic positioning of large-scale heavy lift vessels}, BOOKTITLE = {IFAC-PapersOnLine}. YEAR = {2019}}

With the growing demand of large-scale heavy lift vessels in the deep-sea offshore construction works, high performance of Dynamic positioning (DP) systems is becoming ever crucial. However, current DP systems on board of heavy lift vessels do not consider model uncertainty (typically arising from mooring forces). In this paper, an observer-based robust controller is designed that can tackle model uncertainty in hydrodynamic damping and mooring forces, environmental disturbances as well as can filter out the high-frequency vessel movement. Closed-loop system stability is analytically established in terms of uniformly ultimately boundedness. In addition, several key performance indicators are provided for tuning the performance of the controller. The effectiveness of the proposed control framework is studied in simulation with a crane-vessel system.

@inproceedings{bib_A_ne_2019, AUTHOR = {Roy, Spandan and Lee, Jinoh and , Simone Baldi }, TITLE = {A new continuous-time stability perspective of time-delay control: Introducing a state-dependent upper bound structure}, BOOKTITLE = {IEEE Control Systems Letters}. YEAR = {2019}}

In the literature of any time-delay control (TDC)-based methods, the boundedness of the error due to time-delay estimation (TDE) is crucial to prove the stability. However, the TDE error has been studied by discretizing the closed-loop system while neglecting the effect of discretization error; consequently, the TDE error is considered to be upper bounded by a constant. This letter proves that such constant upper bound is restrictive in nature due to the explicit involvement of system states in the TDE error. Thereby, without discretizing the closed-loop system, a new structure of the upper bound of TDE error is directly formulated in the continuous-time domain which has an explicit dependency on the system states. Via this formulation, this letter solves the long-standing problem for TDC of having consistent stability analysis and control design in continuous time. Based on the newly proposed structure of TDE error, an enhanced robust control law is formulated. The effectiveness of the proposed method is experimentally substantiated as compared to the conventional TDC using a multiple-degrees-of-freedom robot.

@inproceedings{bib_A_si_2019, AUTHOR = {Roy, Spandan and Baldi, Simone }, TITLE = {A simultaneous adaptation law for a class of nonlinearly parametrized switched systems}, BOOKTITLE = {IEEE Control Systems Letters}. YEAR = {2019}}

This letter proposes a new adaptive control method for a class of nonlinearly parametrized switched systems that includes Monod kinetics and Euler-Lagrange systems with nonlinear in parameters form as special cases. As compared to the adaptive switched frameworks proposed in literature, the proposed adaptation framework has the distinguishing feature of updating the gains of the active and inactive subsystems simultaneously: by doing this it avoids high gains for the active subsystems or vanishing gains for the inactive ones. The design is studied analytically and its performance is validated in simulation with a robotic manipulator example.

@inproceedings{bib_New__2019, AUTHOR = {Sharma, Nalin Kumar and Roy, Spandan and Janardhanan, S. }, TITLE = {New design methodology for adaptive switching gain based discrete-time sliding mode control}, BOOKTITLE = {International Journal of Control}. YEAR = {2019}}

The adaptive sliding mode control technique relaxes the assumption of known bound of the disturbance in discrete-time systems. However, the existing technique of gain adaptation in discrete-time sliding mode control has issues of gain overestimation and underestimation. Therefore, this paper proposes a technique to adapt the switching gain such that the adaptive gain can tackle the uncertainty without any knowledge of the bound of uncertainty while overcoming the over- and under-estimation problems of switching gain.

@inproceedings{bib_Addr_2019, AUTHOR = {, Stefano Farí and Wang, Ximan and Roy, Spandan and , Simone Baldi }, TITLE = {Addressing Unmodeled Path-Following Dynamics via Adaptive Vector Field: A UAV Test Case}, BOOKTITLE = {IEEE Transactions on Aerospace and Electronic Systems}. YEAR = {2019}}

The actual performance of model-based path-following methods for unmanned aerial vehicles (UAVs) shows considerable dependence on the wind knowledge and on the fidelity of the dynamic model used for design. This study analyzes and demonstrates the performance of an adaptive vector field (VF) control law which can compensate for the lack of knowledge of the wind vector and for the presence of unmodeled course angle dynamics. Extensive simulation experiments, calibrated on a commercial fixed-wing UAV and proven to be realistic, show that the new VF method can better cope with uncertainties than its standard version. In fact, while the standard VF approach works perfectly for ideal first-order course angle dynamics (and perfect knowledge of the wind vector), its performance degrades in the presence of unknown wind or unmodeled course angle dynamics. On the other hand, the estimation mechanism of the proposed adaptive VF effectively compensates for wind uncertainty and unmodeled dynamics, sensibly reducing the path-following error as compared to the standard VF.

@inproceedings{bib_Over_2019, AUTHOR = {Roy, Spandan and Roy, Sayan Basu and Lee, Jinoh and , Simone Baldi }, TITLE = {Overcoming the underestimation and overestimation problems in adaptive sliding mode control}, BOOKTITLE = {IEEE/ASME Transactions on Mechatronics}. YEAR = {2019}}

Underestimation and overestimation problems are commonly observed in conventional adaptive sliding mode control (ASMC). These problems refer to the fact that the adaptive controller gain unnecessarily increases when the states are approaching the sliding surface (overestimation) or improperly decreases when the states are getting far from it (underestimation). In this paper, we propose a novel ASMC strategy that overcomes such issues. In contrast to the state of the art, the proposed strategy is effective even when an a priori constant bound on the uncertainty cannot be imposed. Comparative results using a two-link manipulator demonstrate improved performance as compared to the conventional ASMC. Experimental results on a biped robot confirm the effectiveness and robustness of the proposed method under various practical uncertainties.

@inproceedings{bib_Time_2019, AUTHOR = {Rayguru, Madan Mohan and Roy, Spandan and Kar, Indra Narayan }, TITLE = {Time-Scale Redesign-Based Saturated Controller Synthesis for a Class of MIMO Nonlinear Systems}, BOOKTITLE = {IEEE Transactions on Systems, Man, and Cybernetics Part-B}. YEAR = {2019}}

A consideration of actuator saturation is an important aspect to study the effectiveness of a designed controller in practice. However, the conventional Lyapunov theory-based design is not always suitable to analyze the quantitative behavior of closed-loop system. This article presents a time-scale redesign-based saturated tracking controller for a class of feedback linearizable multi-input-multi-output (MIMO) nonlinear systems. The proposed controller is built upon the frameworks of contraction and partial contraction theories which ensures that bounded tracking performance as well as quantify the steady-state error bounds in terms of the various control design parameters. Notably, in contrast to the existing Lyapunov-method-based designs, the proposed approach allows to tune the controller performance without arbitrary reduction of singular perturbation parameters. Therefore, the vulnerability of the controller toward actuator saturation and noise, due to the ill-effects of high-gains stemming from the conventional high-gain controllers, are reduced. The extensive experimental results using a wheeled mobile robot are provided to demonstrate the effectiveness of the proposed controller.

@inproceedings{bib_On_r_2019, AUTHOR = {Roy, Spandan and Baldi, Simone }, TITLE = {On reduced-complexity robust adaptive control of switched Euler–Lagrange systems}, BOOKTITLE = {Nonlinear Analysis: Hybrid Systems}. YEAR = {2019}}

State-of-the-art adaptive or robust adaptive techniques for several classes of uncertain switched systems demand structural knowledge of the system dynamics in order to appropriately select the regressor terms in the adaptive law. As a result, the number of unknown parameters to be adapted increases with system complexity, which can lead to very complex adaptive laws. In this work we propose, for the relevant class of Euler-Lagrange systems subject to time-dependent slow switching, a switched robust adaptive control framework with reduced complexity: the number of unknown parameter to be adapted is independent on the system complexity, whereas the regressor terms in the adaptive laws do not require any structural knowledge of the system dynamics. Stability analysis is provided to illustrate the benefit of the proposed design, and the performance of the controller is verified using a switched system stemming from the combination of mooring and free-hanging operations in dynamic positioning of offshore ships

@inproceedings{bib_The__2019, AUTHOR = {Roy, Spandan and Baldi, Simone }, TITLE = {The role of uncertainty in adaptive control of switched Euler-Lagrange systems}, BOOKTITLE = {Conference on Decision and Control}. YEAR = {2019}}

This work presents a Lyapunov-based approach to adaptive control of uncertain Euler-Lagrange (EL) systems in a slow switching scenario. Fundamental trade-offs arising from considering uncertain dynamics with unknown uncertainty bounds are presented and discussed. Contrary to the nonswitched scenario, the use of acceleration feedback seems to be unavoidable in the switched scenario: this is due to the fact that an acceleration feedback and an appropriate Lyapunov function must be adopted to make the switching law independent from the unknown uncertainty bounds. In the absence of such feedback or using different Lyapunov functions, a stabilizing switching law would exist but could not be determined as it would depend on an unknown uncertainty bound.

@inproceedings{bib_Adap_2018, AUTHOR = {Sharma, Nalin Kumar and Roy, Spandan and Janardhanan, S. and Kar, Indra Narayan }, TITLE = {Adaptive discrete-time higher order sliding mode}, BOOKTITLE = {IEEE Transactions on Circuits and Systems}. YEAR = {2018}}

The concept of discrete-time higher order sliding mode (DHOSM) has received increased attention. However, because of the dearth of knowledge on bound of the external disturbance in the system, an adaptive control law is desirable. This brief presents a technique to design a DHOSM control with adaptive switching gains where the bound on the disturbance is considered to be unknown.

@inproceedings{bib_Anal_2018, AUTHOR = {Roy, Spandan and Patel, Abhilash and Kar, Indra Narayan }, TITLE = {Analysis and Design of a Wide-Area Damping Controller for Inter-Area Oscillation With Artificially Induced Time Delay}, BOOKTITLE = {IEEE Transactions on Smart Grid}. YEAR = {2018}}

One of the major issues in an interconnected power system is the low damping of inter-area oscillations. A proportional-derivative (PD) compensator is a popular control method which is extensively being used as an active damping control in various domains such as robotics, smart structure, etc. However, existence of noise in wide-area signal makes an ideal PD compensator unrealisable in power systems. In this endeavour, a new methodology christened as time-delayed control is proposed where artificial delay is used to provide derivative action which acts as a damping component of wide-area controller. The delay margin is computed for the closed loop system using Razumikhin approach. It is observed that the proposed controller is able to damp the oscillations adequately with reduced sensitivity to the noise in the signals. Further, the proposed controller is able to provide robustness against uncertainties arising from the system dynamics and inherent delay in communication channel.

@inproceedings{bib_A_ne_2018, AUTHOR = {Roy, Spandan and Roy, Sayan Basu and Kar, Indra Narayan }, TITLE = {A new design methodology of adaptive sliding mode control for a class of nonlinear systems with state dependent uncertainty bound}, BOOKTITLE = {International Workshop on Variable Structure Systems}. YEAR = {2018}}

In this paper, a new Adaptive Sliding Mode Control (ASMC) framework is proposed for the tracking control of a class of uncertain nonlinear systems where system states are present explicitly in the upper bound of the overall (or lumped) system uncertainty. Conventional ASMC strategies presume that either the overall (or lumped) uncertainty of the system or its time derivative is norm bounded by a constant. However, such assumption restricts the evaluation of the states a priori for the class of systems that has been considered in this paper. The proposed ASMC law does not presume such constant upper bound on the system uncertainties and, rather, exploits the unique structure of the uncertainty bound to design the control law. Moreover, the adaptive law of the proposed ASMC alleviates the overestimation-underestimation problems of switching gain which is commonly observed in the existing ASMC laws. Simulation results using a two-link manipulator demonstrate improved control performance of the proposed controller in comparison to the conventional ASMC.