Srikant Sukumar

• PhD
• Professor (Associate) at Indian Institute of Technology Bombay

Although adaptive control schemes for spacecraft attitude tracking are abundant in controls literature, very few are designed to guarantee consistent performance for a spacecraft with both rigid and non-rigid (time-varying) inertia components. Because inertia matrix changes are a common occurrence due to phenomena like fuel depletion or mass displa...

We develop a new technique for stabilizing multi-input linear systems with unstable drift and time-varying, singular gains on the control. The results presented here assume the control gain to be sufficiently smooth and satisfy a persistence of excitation condition. A novel persistence filter construction is proposed that enables a non-trivial gene...

This article deals with the consensus problem involving agents with time-varying singularities in the dynamics or communication in undirected graph networks. Existing results provide control laws which guarantee asymptotic consensus. These results are based on the analysis of a system switching between piecewise constant and time-invariant dynamics...

We propose new results on input-to-state stability (ISS) subject to time delays in the input for compact, invariant sets that contain the origin. First, using non-linear small-gain theory, we prove a Razumikhin-type theorem that ensures ISSfor sets in the context of functional differential equations with delayed disturbances. Next we demonstrate th...

A novel framework, namely synchronization of network coupled outputs has been introduced in this article. Synchronization of coupled outputs have applications in coverage control, formation control and several other cooperative tasks. Unlike output synchronization, coupled outputs have not been studied in the cooperative systems community. We formu...

State and input constraints are ubiquitous in all engineering systems. In this article, we derive adaptive controllers for uncertain linear systems under pre-specified state and input constraints. Several modifications of the model reference adaptive control (MRAC) framework have been proposed to address input constraints in uncertain linear system...

We propose an adaptive algorithm for identifying the unknown parameter in a linear exponentially stable single-input single-output infinite-dimensional system. We assume that the transfer function of the infinite-dimensional system can be expressed as a ratio of two infinite series in s (the Laplace variable). We also assume that certain identifiab...

We study a formation control problem of nonholonomic vehicles which consists in making a group of them gather around a given rendezvous set-point and acquire a common orientation. This task may be regarded as part of a more complex maneuver, e.g., requiring the robots to advance in a scouting mission on a path composed of straight lines and occasio...

A novel distributed control law for consensus of networked double integrator systems with biased measurements is developed in this article. The agents measure relative positions over a time-varying, undirected graph with an unknown and constant sensor bias corrupting the measurements. An adaptive control law is derived using Lyapunov methods to est...

The problem of rigid body pose estimation is treated in discrete-time via discrete Lagrange–d’Alembert principle and discrete Lyapunov methods. The position and attitude of the rigid body are to be estimated simultaneously with the help of vision and inertial sensors. For the discrete-time estimation of pose, the continuous-time rigid body kinemati...

The study demonstrates the preservation of set-input-to-state stability under a small input time delay for compact, invariant sets that contain the origin. A Razumikhin type theorem that ensures input-to-state stability (ISS) for sets in functional differential equations (FDEs) with disturbances is proved using the nonlinear small-gain theory. Thes...

The problem of rigid body pose estimation is treated in discrete-time via discrete Lagrange-d'Alembert principle and discrete Lyapunov methods. The position and attitude of the rigid body are to be estimated simultaneously with the help of vision and inertial sensors. For the discrete-time estimation of pose, the continuous-time rigid body kinemati...

A novel distributed control law for consensus of networked double integrator systems with biased measurements is developed in this article. The agents measure relative positions over a time-varying, undirected graph with an unknown and constant sensor bias corrupting the measurements. An adaptive control law is derived using Lyapunov methods to est...

We study dynamic consensus for general networked (homogeneous) linear autonomous systems, that is, it is only assumed that they are stabilizable. Dynamic consensus pertains to a general form of consensus in which, as a result of the systems’ interactions, they exhibit a rich collective dynamic behavior. This generalizes the classical consensus para...

The rigid body attitude estimation problem is treated using the discrete-time Lagrange-d'Alembert principle. Three different possibilities are considered for the multi-rate relation between angular velocity measurements and direction vector measurements for attitude: 1) integer relation between sampling rates, 2) time-varying sampling rates, 3) non...

We study stability of multivariable control-affine nonlinear systems under sparsification of feedback controllers. Given a stabilizing feedback, sparsification in our context refers to the scheduling of the individual control inputs one at a time in rapid periodic sweeps over the set of control inputs, which corresponds to round-robin scheduling. W...

This article treats optimal sparse control problems with multiple constraints defined at intermediate points of the time domain. For such problems with intermediate constraints, we first establish a new Pontryagin maximum principle that provides first order necessary conditions for optimality in such problems. Then we announce and employ a new nume...

In this paper, we consider the problem of constructing constrained smoothing splines, which are of great importance in data science. The novelty of this work is to formulate the problem as an optimal control problem, and we mathematically analyze the optimal smoothing spline with intermediate constraints using first-order optimality condition from...

In this article, we consider the problem of estimating a scalar field using a network of mobile sensors which can measure the value of the field at their instantaneous location. The scalar field to be estimated is assumed to be represented by positive definite radial basis kernels and we use techniques from adaptive control and Lyapunov analysis to...

This article treats optimal sparse control problems with multiple constraints defined at intermediate points of the time domain. For such problems with intermediate constraints, we first establish a new Pontryagin maximum principle that provides first order necessary conditions for optimality in such problems. Then we announce and employ a new nume...

The rigid body attitude estimation problem under multi-rate measurements is treated using the discrete-time Lagrange-d'Alembert principle. Angular velocity measurements are assumed to be sampled at a higher rate compared to the direction vector measurements for attitude. The attitude determination problem from two or more vector measurements in the...

A geometric estimator is proposed for the rigid body attitude under multi-rate measurements using discrete-time Lyapunov stability analysis in this work. The angular velocity measurements are assumed to be sampled at a higher rate compared to the attitude. The attitude determination problem from two or more vector measurements in the body-fixed fra...

We study a constrained optimal control problem for an ensemble of control systems in a centralized setting. Each system evolves on a matrix Lie group, and must satisfy given state and control action constraints pointwise in time. In addition, the controller must be shared between the plants in the sense that at any time instant the control signal m...

The Global Navigation Satellite Systems (GNSS) like GPS suffer from accuracy degradation and are almost unavailable in indoor environments. Indoor positioning systems (IPS) based on WiFi signals have been gaining popularity. However, owing to the strong spatial and temporal variations of wireless communication channels in the indoor environment, th...

This work deals with the synchronization of coupled outputs in multi-agent systems using a distributed control where each agent is a Euler Lagrange system. We use ideas similar to that of output synchronization and discuss a potential technique for synchronization of coupled function of states/coupled measurements with distributed implementation. T...

In this paper, we consider the problem of estimating a scalar field using mobile sensor networks equipped with sensors which can measure the value of the field at their instantaneous location. The scalar field to be estimated is assumed to be represented by positive definite radial basis kernels and we use techniques from adaptive control and Lyapu...

This paper is concerned with the deployment of multiple mobile robots in order to autonomously cover a region Q. The region to be covered is described using a density function which may not be apriori known. In this paper, we pose the coverage problem as an optimization problem over some space of functions on Q. In particular, we look at L 2 -dista...

In this paper, we consider the problem of estimating a scalar field using a network of mobile sensors which can measure the value of the field at their instantaneous location. The scalar field to be estimated is assumed to be represented by positive definite radial basis kernels and we use techniques from adaptive control and Lyapunov analysis to p...

We study the qualitative behavior of multivariable control-affine nonlinear systems under sparsification of feedback controllers. Sparsification in our context refers to the scheduling of the individual control inputs one at a time in rapid periodic sweeps over the set of control inputs, which we call the round robin scheduling. We prove that if a...

This article treats two problems of sparse and optimal multiplexing a finite ensemble of linear control systems. Given an ensemble of linear control systems, multiplexing of the controllers consists of an algorithm that selects, at each time t, only one from the ensemble of linear systems is actively controlled whereas the other systems evolve in o...

This paper addresses the problem of distributed coordination control of spacecraft formation. It is assumed that the agents measure relative positions of each other with a non-zero, unknown constant sensor bias. The translational dynamics of the spacecraft is expressed in Euler-Lagrangian form.We propose a novel distributed, model independent contr...

In this paper, we present a novel quaternion-based event-triggered control strategy for trajectory tracking with a quadrotor that is suitable for implementation on digital platforms with hardware constraints. The proposed control ensures asymptotic convergence to the desired position trajectory and finite time convergence to a desired attitude traj...

A state constrained control design problem is addressed in this article via Lyapunov techniques. We show that for systems in a special linear strict feedback form, it is possible to impose constraints on states unmatched with the control using a backstepping technique while achieving the stabilization objective. Initially, in this article, we forma...

The notion of feedback integrators permits Euclidean integration schemes for dynamical systems evolving on manifolds. Here, a constructive Lyapunov function for the attitude dynamics embedded in an ambient Euclidean space has been proposed. We then combine the notion of feedback integrators with the proposed Lyapunov function to obtain a feedback l...

We study a constrained optimal control problem for an ensemble of control systems. Each sub-system (or plant) evolves on a matrix Lie group, and must satisfy given state and control action constraints pointwise in time. In addition, certain multiplexing requirement is imposed: the controller must be shared between the plants in the sense that at an...

This paper addresses the problem of distributed coordination control of spacecraft formation. It is assumed that the agents measure relative positions of each other with a non-zero, unknown constant sensor bias. The translational dynamics of the spacecraft is expressed in Euler-Lagrangian form. We propose a novel distributed, model independent cont...

This article treats three problems of sparse and optimal multiplexing a finite ensemble of linear control systems. Given an ensemble of linear control systems, multiplexing of the controllers consists of an algorithm that selects, at each time \(t\), only one from the ensemble of linear systems is actively controlled whereas the other systems evolv...

The problem of scheduling a shared control channel between several systems controlled from a remote location is studied in this work. Control scheduling and design is addressed via an approach based on optimally sparse control design. Specifically, for a linear control system we propose a sparse Mayer problem with a special action set to codify con...

This paper proposes a general framework for distributed coverage control of mobile robotic sensors. We pose the multiagent coverage problem as an optimization problem over the space of density functions. We show that the popular locational optimization framework for coverage can be viewed as a special case of optimizing the Kullback-Leibler diverge...

In this paper we investigate sufficient conditions for consensus of double integrators interconnected under constant directed graphs, under the condition that there exists a rooted spanning tree. We assume that only relative position as well as absolute own velocity measurements are available that is, each agent disposes of its own velocity only as...

This article studies the problem of asymptotic consensus of linear systems for a class of switching graphs. We significantly relax several reciprocity and connectivity assumptions prevalent in the consensus literature and employ switched-systems techniques to prove consensus under weak assumptions. The current analysis relies solely on the certain...

This work deals with decentralized control of multiple nonholonomic mobile sensors for optimal coverage of a given area for sensing purposes. We assume a density function over the region to be covered, which can be viewed as a probability density of the phenomena to be sensed. The density function is unknown but assumed to be linearly parameterized...

We present consensus analysis of systems with single integrator dynamics interacting via time-varying graphs under the event-triggered control paradigm. Event-triggered control sparsifies the control applied, thus reducing the control effort expended. Initially, we consider a multi-agent system with persistently exciting interactions and study the...

We present consensus analysis of systems with single integrator dynamics interacting via time-varying graphs under the event-triggered control paradigm. Event-triggered control sparsifies the control applied, thus reducing the control effort expended. Initially, we consider a multi-agent system with persistently exciting interactions and study the...

We study the problem of achieving position consensus in a multi-agent rigid-body system operating under measurement bias. It is assumed that the agents measure relative positions of each other with a constant sensor bias. A Lyapunov function based approach is utilized to develop a novel adaptive controller to estimate measurement bias and attempt t...

In this paper, we use the Kirchhoff equations to model of the dynamics of underwater rigid-bodies under some assumptions on the surrounding fluid. The Kirchhoff tensor, which totally characterizes the interaction of the rigid-body with the fluid is assumed to be unknown. We then propose a control law with an estimate of the Kirchhoff tensor and a c...

This paper considers adaptive relative attitude tracking control of two spacecraft formulated in SO(3) using line-of-sight measurements. The objective is to control the attitudes of individual spacecraft with unknown moment of inertia so as to track a specified time-varying relative attitude trajectory. We propose an estimation scheme for the momen...

This paper proposes an algorithm for decentralized adaptive control for coverage of a given convex region using multiple agents with double integrator dynamics. The result is then extended to nonholonomic mobile robots. The density function which describes the event of interest to be sensed by the agents is assumed to be unknown and an adaptation l...

The aim of the current article is to establish myriad convergence rate estimates to consensus for time-varying graphs with persistent interaction. Several novel analysis methodologies for consensus protocols employing the notions of persistence of excitation and Lyapunov functions are provided. The estimates are compared with each other and existin...

This paper deals with attitude and position tracking of rigid bodies immersed in a fluid (generally water) and proposes a control law to achieve the same. Underwater dynamics of rigid bodies are modelled using the 'Kirchhoff Tensor', assuming the fluid to be irrotational, inviscid and incompressible. Specifically we consider the case of asymmetrica...

We consider coupled attitude and position control of two spacecraft where absolute attitudes are not available. The objective is to attain a formation requiring a desired distance between two spacecraft and alignment of attitudes along the inertial line-of-sight (LOS) direction between the center of masses of the spacecraft. A relative attitude and...

This paper considers the problem of formation control of three spacecraft consisting of one leader and two followers. The leader spacecraft controls its attitude and position to track a desired attitude and position trajectory in the Earth Centered Inertial (ECI) frame. Each follower spacecraft tracks a desired relative attitude and relative positi...

This article treats two problems dealing with control of linear systems in the presence of a jammer that can sporadically turn off the control signal. The first problem treats the standard reachability problem, and the second treats the standard linear quadratic regulator problem under the above class of jamming signals. We provide necessary and su...

This paper proposes and analyzes a novel multi-agent opinion dynamics model in which agents have access to actions which are quantized version of the opinions of their neighbors. The model produces different behaviors observed in social networks such as disensus, clustering, oscillations, opinion propagation, even when the communication network is...

This paper proposes and analyzes a novel multi-agent opinion dynamics model in which agents have access to actions which are quantized version of the opinions of their neighbors. The model produces different behaviors observed in social networks such as disensus, clustering, oscillations, opinion propagation, even when the communication network is...

This paper deals with the consensus problem of agents communicating via time-varying communication links in undirected graph networks. The highlight of the current work is to provide practically computable rates of convergence to consensus that hold for a large class of time-varying edge weights. A novel analysis technique based on classical notion...

In this paper an attempt is made to compare four steering laws used for Single Gimbal Control Moment Gyros (SG CMGs). The performance of a rigid spacecraft to execute multi-target acquisition and tracking with four SG CMGs in pyramid configuration is studied and steering law performance evaluated. The first steering law under consideration is the c...

This article proposes a technique to compute convergence rate to consensus for multi-agent systems with double integrator agent dynamics interacting via time-varying, undi-rected and persistent communication graphs. Existing results provide control laws guaranteeing asymptotic convergence to consensus but no practically computable estimate of the c...

The article deals with the problem of imposing attitude constraints during trajectory tracking for a spacecraft. A Lyapunov function based approach is utilised to develop a novel nonlinear backstepping controller for implementation of the imposed attitude constraints, while guaranteeing reference attitude tracking. The result combines a static opti...

This article presents a comparative study of convergence rate estimates for degenerate gradient flows in the context of multi-agent systems. A novel analysis methodology was introduced in (Roy Chowdhury and Srikant, 2014) based on the classical notions of persistence of excitation (PE) and uniform complete observability (UCO) to study the exponenti...

This work studies formation control of two spacecraft formation where communication architecture has a serial network structure. The leader controls its absolute position and absolute attitude with respect to an inertial frame, and the follower controls its relative position and attitude with respect to leader. Both absolute attitude and relative a...

This paper considers the problem of attitude synchronization and formation keeping of two spacecrafts, with a leader. Attitudes of spacecrafts are not measured directly, instead control torques are determined from the line-of-sight (LOS) vectors between two spacecrafts, and another set of LOS vectors from a common leader. We provide distributed pos...

Motion planning of an autonomous robot in an unknown environment is a challenging task. The prerequisite of any motion planning task is collision avoidance. This paper aims on designing a steering control-law for constructing Generalized Voronoi Diagram (GVD) of an unknown environment. The GVD is a roadmap which offers a maximum clearance path and...

This paper considers the problem of controlling relative attitude between two spacecrafts, so as to follow a smoothly time varying desired relative attitude trajectory. The spacecrafts are modelled as rigid bodies and attitudes are represented in non-linear state space of SO(3). The attitude control law proposed does not need relative attitude meas...

Although adaptive control schemes for spacecraft attitude tracking are abundant in controls literature, very few are designed to guarantee consistent performance for a spacecraft with both rigid and nonrigid (time-varying) inertia components. Because inertia matrix changes are a common occurrence due to phenomena like fuel depletion or mass displac...

This paper proposes a new methodology for design of a stabilizing control law for multi-input linear systems with time-varying, singular gains on the control. The results presented here rely on a non-triviality assumption on the gain signal namely “persistence of excitation”. The control design is based on a novel persistence filter construction in...

We investigate state observer and feedback control design for systems with state-and time-dependent control or measurement gains. In this framework, we look at reversible transducers that are continually switched between the actuation and sensing modes at some prespecified schedule. Design and analysis of stable state-observers and feedback control...

The attitude stabilization problem of a microsatellite employing a variable-amplitude cold-gas thruster is considered to ensure zero torque commands during thruster rise and fall times. A new time-varying controller for spacecraft attitude and angular velocity stabilization is developed assuming a possible singular-control scaling. The control desi...

Unstart detection techniques based on high-frequency pressure measurements made in a hypersonic inlet isolator model are investigated. In this study, data that were acquired in a previous study of backpressure-induced unstart were examined. The data were acquired in a simplified-geometry inlet isolator model that consisted of a 6 deg compression ra...

This paper describes an experimental investigation using an array of high-frequency pressure transducers located in the isolator/combustor region of a direct-connect hydrocarbon-fueled, scramjet combustor. Isolator/combustor entrance conditions were fixed and representative of a Mach-5.5 flight condition. Mean, standard deviation, and spectral cont...

Thrusters are important candidates for attitude control actuators in micro-satellites due to low complexity and high power to weight ratios. Conventional control schemes are not applicable to thrusters due to their inability to account for non-trivial rise and fall times. The attitude control of a micro-satellite is considered with low-cost, cold-g...

The paper addresses the generic problem of devising stabilizing control laws for systems with time-varying control gains and unstable drift terms. Specifically, a large class of single-input, linear, control affine systems are considered wherein the control gains (coefficients) can become singular at certain instants in time or stay singular for la...

The generic problem of devising stabilizing control laws for systems with time-varying control gains is considered. This class of systems do not in general permit controller design through the standard feedback linearization techniques. The control gains can become singular at certain instants in time or stay singular for large time intervals, thus...