Keywords: First Order Sliding Mode, Chattering Analysis
Abstract: Frequency-domain methods are widely used in analysis and design of linear systems. This approach is possible due to the validity of the superposition principle. Sliding mode (SM) control systems are nonlinear and non-Lipschitz. Comprehensive analysis of SM systems by means of only frequency-domain methods seems impossible. The most commonly used frequency-domain approach in these systems is analysis of chattering, aimed at finding the amplitude and the frequency of chattering. This is a really strong application of the frequency domain approach in the domain of SM systems though, but nearly the only one. In the current plenary talk, a wider scope of frequency-domain analysis in SM systems is presented. The scope of the presented frequency-domain analysis stretches beyond finding the frequency and amplitude of chattering to the types of convergence and analysis of averaged on the period of chattering motions, which gives a more accurate picture of system performance than the model of ideal SM. Further, the concepts of phase deficit and dynamic harmonic balance are considered to give the necessary conditions of asymptotic and finite-time convergence. Orbital stability of the chattering oscillations is related with convergence of the sliding variable. Then, bias function and equivalent gain which allow one to find certain “effective” nonlinearities that describe propagation of averages through non-Lipschitz nonlinearities are considered. These and other concepts are considered with the use of the describing function (DF) method and the locus of a perturbed relay system (LPRS) method. New phenomena of chaotic chattering and existence of asymmetric oscillations in a fully symmetric system are explained through the LPRS method. The presented theory is illustrated by practical examples from power electronics, robotics and UAV control.

Keywords: Mobile Robots, Chattering Analysis, Electric Drives And Actuators
Abstract: Adaptation of control parameters in response to external effects or parametric changes is one of the basic capabilities required for high-performance unmanned aerial vehicle (UAV) applications. Adaptation can be done using forced excitations of the unknown UAV dynamics. In this work, we investigate the application of the modified relay feedback test (MRFT) to identify UAV dynamics in outdoor environments. In particular, we focus on UAVs using GPS for positioning and flying in the presence of external wind. The wind is introduced to the nonlinear UAV model and the resultant dynamics are analyzed. MRFT is also introduced to the position control loops to generate oscillations. The experimental results show that MRFT can be used to generate oscillations in outdoor environments. Some recommendations are given for the subsequent use of oscillations for identification and tuning.

Keywords: Mobile Robots, First Order Sliding Mode
Abstract: This paper explores the feasibility of using a propulsion-only control scheme for a high-altitude long-endurance UAV. This approach enables aircraft to operate even in the face of total control surface failures. A sliding mode scheme is used for the control law due to its invariance to matched uncertainty, and the reduced control authority is accommodated via a model-reference method. Similar performance compared to the fault-free case has been achieved in terms of following altitude and heading commands, in a numerical simulation using a 6-DOF nonlinear model.

Keywords: Multi-Agent Systems, Adaptive Sliding Mode, First Order Sliding Mode
Abstract: This paper introduces a formation control framework for a double integrator multi-agent system (MAS) utilizing adaptive sliding mode control (SMC) integrated with collision avoidance strategies. To prevent inter-agent collisions, a potential artificial function is employed, leveraging inter-agent positions and predefined safe and avoidance zones. A new sliding surface is defined to enhance tracking performance while incorporating collision avoidance functionalities. Additionally, a proportional reaching law-based control scheme is designed to expedite the convergence of sliding trajectories. The asymptotic stability of the tracking error system is demonstrated through Lyapunov analysis. A numerical calculation has been performed to evaluate the performance of SMC and adaptive SMC based on different indices. MATLAB simulation results are presented to illustrate the effectiveness of the proposed controller design.

Keywords: Multi-Agent Systems, Networked Control Systems, Higher Order Sliding Mode
Abstract: The super-twisting algorithm is widely used in the design of controllers, observers, and differentiators. This paper investigates its application to achieve consensus among a team of peer agents characterized by first-order perturbed dynamics. Agents communicate through a directed, weight-balanced communication topology. The key contributions include employing the super-twisting algorithm to solve the finite-time robust consensus problem and developing a method for constructing a family of strict Lyapunov functions to analyze its robust stability. The analysis is based on the Lyapunov approach, and the necessary conditions for the stability of the closed-loop system are derived. Simulations supporting the theoretical analysis are also provided.

Keywords: Networked Control Systems, First Order Sliding Mode, Application of Sliding Mode Control to other theoretical problems
Abstract: This paper proposes a decentralized sliding mode control approach to the voltage regulation problem in a DC microgrid consisting of distributed generation units interconnected with each other through resistive-inductive power lines and supplying unknown nonlinear loads. In particular, the portHamiltonian structure of the system suggests the design of a suitable sliding manifold such that the system on this manifold exhibits desired passivity properties. This approach simplifies the control design and relaxes some restrictive assumptions required by other controllers proposed in the literature, while offering satisfactory performance.

Keywords: Application of Sliding Mode Control to other theoretical problems, Higher Order Sliding Mode, Lyapunov Methods for Variable Structure Systems & Sliding Mode Control
Abstract: This paper presents a fast-terminal super-twisting control (FTSTC) technique to tackle the challenge of landing quadrotor UAVs on moving ships. A relative motion model for the quadrotor and ship is established, then convert it into a affine form to design the landing controller. By designing a nonlinear sliding surface, FTSTC guarantees the convergence of tracking errors to zero within a finite-time. The proposed control law reduces chattering and provides a faster convergence. Theoretical stability analysis using Lyapunov function ensures the finite-time stability of the closed-loop system. Finally, simulation results validate the effectiveness of the proposed method for landing quadrotor UAVs on moving ships.

Keywords: Networked Control Systems, Multi-Agent Systems, Lyapunov Methods for Variable Structure Systems & Sliding Mode Control
Abstract: In this paper, a sliding mode control (SMC) method is designed for the containment control of multi-unmanned surface vehicle (USV) systems under input and state quantization communication. Firstly, the ideal trajectory of follower USVs is calculated from the trajectory of leader USVs based on the properties of the Laplace matrix. Secondly, an SMC controller is designed for follower USVs to achieve decentralized containment control with input and state quantization. Then, we consider switching network topology. Furthermore, the stability analysis is given to guarantee that sliding variables and tracking errors can converge to specified ranges related to the quantization parameters. Finally, simulation results demonstrate the feasibility of the designed SMC approach.

Keywords: Networked Control Systems, First Order Sliding Mode, Application of Sliding Mode Control to other theoretical problems
Abstract: This paper proposes a networked control system to cope with stochastic time delays. The sensor signals are sampled periodically and sent by a computer network with stochastic communication delays of known distribution. The proposed control strategy is based on the sliding-mode control combined with a continuous-time state observer with sampled output signals. The stability properties of the closed-loop system are analyzed using an approach that takes advantage of the knowledge of the stochastic distribution, thus, may be much less conservative than usual robust approaches to deal with time-varying delays. An application example and simulation results illustrate chattering avoidance and the effectiveness of the proposed scheme.

Keywords: Adaptive Sliding Mode
Abstract: This paper aims to design and experimentally apply controllers to a floating wind turbine (FWT) in operating Regions II and III. To achieve this, adaptive sliding-mode controllers with only two tuning parameters are used, simplifying the design by eliminating the need for a detailed dynamical model. This is a significant advantage over conventional baseline controllers. These controllers are implemented for the first time on a realistic experimental setup in a test tank to assess their robustness. Experimental studies have shown that the adaptive slidingmode controllers deliver similar performance regarding generated power, rotor speed, and other parameters while requiring minimal control tuning effort.

Keywords: Power Electronics, Electric Drives And Actuators, Chattering Analysis
Abstract: This paper investigates the application of the modified relay feedback test (MRFT) to a DC-DC boost converter. Nonvanishing oscillations can be generated with MRFT in the control loop. Subsequently, a two-stage process, involving the test and the tuning parameters calculation, is employed for the tuning of the proportional-integral-derivative (PID) controller. The test stage generates self-sustained oscillations. The tuning stage calculates PID parameters based on the homogeneous tuning rules and the amplitude and frequency of the oscillations obtained from the test stage. The auto-tuning can be done online in a few milliseconds and does not require any prior knowledge of the plant. With properly designed tuning rules, the proposed auto-tuning method can guarantee specified gain margin. Performance of the proposed method is evaluated through simulations using Matlab/Simulink. Results show the effectiveness of the proposed method.

Keywords: Power Electronics, Higher Order Sliding Mode
Abstract: Replacing traditional power generation with distributed sources leads to a grid frequency that is more vulnerable to fluctuations. This can impact the efficiency and function of power converters, which are essential for integrating renewable energies into the electrical network. Instead of estimating and tracking the grid's frequency to counter these changes, this paper proposes a robust proportional-resonant (PR) controller that maintains reference tracking in the presence of a varying frequency. Unlike other approaches, the proposed controller does not require precise knowledge of the frequency. This is made possible by integrating into the PR controller a second-order bi-homogeneous differentiator, significantly improving the controller's tracking performance. The performance of the proposed approach is demonstrated through numerical simulations involving the operation of a grid-connected inverter during a frequency variation event.

Keywords: Multi-Agent Systems, Lyapunov Methods for Variable Structure Systems & Sliding Mode Control, First Order Sliding Mode
Abstract: This article deals with the fixed-time consensus (abbreviated as FXT) of perturbed first-order multi-agent systems (MASs) with directed communication topologies. For the leader-follower configuration, a fixed-time consensus problem is investigated with an unknown input to the leader. The controller is designed based on the integral sliding mode (ISM), where a nominal control and a discontinuous sliding mode control are combined. The performance of the system with nominal control guarantees the fixed-time convergence to the ISM surface. The discontinuous sliding mode control ensures this by eliminating the effect of disturbances. A numerical example is presented to verify the efficacy of the proposed design.

Keywords: Hydraulic/Pneumatic Systems, Higher Order Sliding Mode
Abstract: Despite the great potential of sliding mode controllers due to their inherent robustness properties, their utilization at the industrial level is still limited because of their complicated design and tuning. This study offers a Model-Free version of the well-established Super-Twisting algorithm for a class of electro-hydraulic systems, characterized by strong load forces. The design of a standard version of the controller is used as a starting point for its derivation, by matching the performance under certain hypotheses. The effectiveness of the solution is tested in simulation with an industrial case study, proving the effectiveness of the control action in a setup where realistic experimental conditions are utilized. The performance of the controller is evaluated under two tuning conditions, to assess the controller from both theoretical and practical perspectives, and its limits are explored.

Keywords: Electric Drives And Actuators, Higher Order Sliding Mode, Process Industry
Abstract: This paper focuses on developing and studying a phase shift control system for a two-rotor vibration mechatronic setup. The controller serves to maintain the desired revolving speed of the unbalanced rotors and the desired phase shift between them. The sliding mode motion is achieved using an integral relay controller in the phase loop, while PI controllers are employed in the velocity control loops. The numerical study, simulations, and experiments are performed using the IPME RAS Mechatronic Vibration Setup SV-2M. The velocity and phase shift control laws are studied, and the possibility of asymptotic sliding mode occurrence in the phase shift loop is examined through analytical and numerical analysis. The simulation and experimental results confirm the asymptotic emergence of sliding mode motion and demonstrate the dynamical properties of the closed-loop system.

Keywords: Fault Detection, Sliding Mode based Observation
Abstract: This paper proposes a fault-tolerant system for inertial measurement unit (IMU) sensors by identifying faults using a finite-time sliding mode observer (SMO). The finite-time SMO is designed based on a kinematic model suitable to diagnose IMU sensor faults. To overcome the fault quickly and accurately, we design the finite-time SMO that ensures fast convergence and can consider high-order derivatives of disturbance (fault). The identified faults are removed from sensor measurements to estimate healthy measurements. Fault simulations demonstrate that the observer quickly estimates the faults, enabling flight without degradation in attitude tracking performance.