Susy Thomas

Reaching law based sliding mode control for discrete MIMO systems

This paper analyzes the effectiveness of the reaching law approach for sliding mode control of discrete time systems. The method is extended for sliding mode control for multi-input multi-output (MIMO) systems. Modified reaching law for reducing the chattering is proposed. The performance of the proposed controller is analyzed by carrying out simulation studies on MIMO systems. The performance of the controller is also compared with that of the equivalent control.

Sliding mode controller design for MIMO nonlinear systems: A novel power rate reaching law approach for improved performance

Abstract This paper proposes a novel approach to the design of reaching law based on Sliding Mode Controller (SMC) for multi input multi output (MIMO) non-linear systems so as to overcome the drawbacks associated with conventional reaching law based SMC design strategies. The modification is proposed with an aim to completely eliminate chattering, to ensure control inputs within admissible limits and to guarantee fast response when SMC is used. Modification to conventional power rate reaching law is the point of interest here in order to ensure complete elimination of chattering. Two different modifications to power rate reaching law are presented which incorporate control constraints during controller design so that admissible control input limits are not exceeded. The first modified method ensures limited control effort as well as complete chattering free response, but does not improve the reaching characteristics. So a second adaptive modification to power rate reaching law is also presented here. This method ensures fast reaching to the sliding surface along with properties of complete elimination of chattering and bounded control inputs. However, as in power rate reaching law these modified methods retain the limitation of not possessing robustness properties. The method is applied to a three degree of freedom robotic arm which is typically a non-linear MIMO system. The ability of the presented method to satisfy attributes, viz., chattering free operation, bounded control inputs and fast response is compared with the performance of various reaching law methods available in the literature. The performance of the proposed method is validated through simulation studies on the robotic arm example.

Cyclic Pursuit of mobile robots: A linear approach

Cyclic Pursuit is a distributed control law wherein competitive or non-cooperative local interactions among agents are used to achieve cooperative global behaviors. Due to their inherent nonlinear dynamics, unicycle models are widely used in designing cyclic pursuit control laws for mobile robots. This paper introduces a simplified technique for design of linear, distributed control laws for achieving cyclic pursuit among a group of differential drive mobile robots. The control laws discussed in this paper can be used to design simple yet fully functional cyclic pursuit algorithms. The efficacy of these linear control laws for mobile robots featuring nonlinear dynamics was verified through V-REP simulations.

Improved LTVMPC design for steering control of autonomous vehicle

An improved linear time varying model predictive control for steering control of autonomous vehicle running on slippery road is presented. Control strategy is designed such that the vehicle will follow the predefined trajectory with highest possible entry speed. In linear time varying model predictive control, nonlinear vehicle model is successively linearized at each sampling instant. This linear time varying model is used to design MPC which will predict the future horizon. By incorporating predicted input horizon in each successive linearization the effectiveness of controller has been improved. The tracking performance using steering with front wheel and braking at four wheels are presented to illustrate the effectiveness of the proposed method.

Improved sliding mode controller performance through power rate exponential reaching law

Chattering alleviation is an area of great interest as far as the practicality of sliding mode controllers (SMC) are concerned. Reaching law based SMC design is a well-known chattering alleviation method available in the literature. Among the different conventional reaching law strategies that are available in the literature, power rate reaching law (PRRL) is found to be effective in terms of chattering alleviation and fast reaching. The main disadvantage of PRRL is that it bypasses the major portion of sliding mode motion in order to reduce chattering and to ensure fast reaching. It is well known that the most important advantage of SMC is that it guarantees robustness in the sliding mode phase. Since PRRL reduces the duration of sliding mode phase, the robustness property of SMC is compromised. This limitation of PRRL is being overcome here through an exponential modification so that the attributes of chattering alleviation, fast reaching and robustness in sliding mode phase are guaranteed simultaneously. We propose to call this modified PRRL as Power Rate Exponential Reaching Law (PRERL). The efficacy of the proposed method is validated through simulation studies on a three joint robotic arm set point regulation problem.

MIMO model predictive controller design for a twin rotor aerodynamic system

Model Predictive Control (MPC) is a viable control strategy for Multi-Input Multi-Output (MIMO) systems owing to its capability of handling multivariable interactions and constraints on input, output as well as state. MPC design for MIMO systems generally resort to decoupling the system and adopting the Single-Input Single-Output (SISO) design approach. In this paper, the SISO MPC design approach is extended to a MIMO system without compromising on the system dynamics by decoupling it. The effectiveness of the designed controller is validated in simulation using a benchmark MIMO system, the Twin Rotor Multi-Input Multi-Output System (TRMS). The control objective is to stabilize the system in a coupled condition and make its beam to track a specified reference trajectory accurately or reach desired positions in two degrees-of-freedom (2 DOF). Simulation results in presence of external disturbances and parameter variations are presented to corroborate the robustness and effectiveness of the control strategy.

H∞ based integral sliding mode controller design for stabilization of cart pendulum system

H∞ based sliding mode control has several advantage viz. fast response, robustness to parameter variation and disturbance rejection ability. Inverted pendulum qualifies as a benchmark system to test the suitability of controller design for under-actuated, nonlinear unstable system. In this context, H∞ based integral sliding mode controller is designed for inverted pendulum for stabilizing the system. The H∞ state feedback gains are obtained by formulating the Riccati equation. These gains stabilize not only the closed loop transfer function, which maps the performance output to the disturbance input but also the system around its unstable equilibrium point. However this will not account for parameter variation and disturbance effect. Hence, a robust integral sliding surface is constructed such that during sliding motion the closed loop system will lead to disturbance rejection. Next, the switching control law is synthesized to maintain the states on the sliding surface from the initial time. The effectiveness of the controller design is verified by considering various uncertainties.

Intelligent Switching Surface for Variable Structure Adaptive Model Following Control

This paper presents the application of genetic algorithms (GAs) to the design of an intelligent switching surface for variable structure adaptive model following controller for higher order systems with unmodelled dynamics/parameter variations. The conventional approach for the design of switching surface by pole placement method often lead to large value of control signals. A method for obtaining an intelligent switching surface in a computationally efficient manner is proposed in this paper. The proposed method make use of GAs to evolve a switching surface which ensures minimum disruption of the poles when variations/uncertainties act on the system. If minimum disruption of the poles is not ensured, higher control signal will be required to maintain sliding mode motion. The proposed methodology is applied to a practical system namely a flexible one-link manipulator and the results obtained are compared to the results obtained by applying the conventional design. The comparison reveals the efficacy of the proposed method