Susy Thomas

Model Predictive Control (MPC) is a viable control scheme for constrained nonlinear MIMO systems but the high computational complexity and numerical sensitivity issues associated with long prediction horizons hamper the real-time implementation of this control technique. To alleviate the computational burden and problems associated with numerical ill-conditioning, an Exponentially Weighted Laguerre Function based Model Predictive Controller (EWLMPC) is proposed in this paper. EWLMPC deploys orthonormal Laguerre functions to parametrize the control input trajectory which helps in alleviating the real-time computational load. The inclusion of exponential data weight facilitates the use of large prediction horizons without jeopardizing the numerical stability of the algorithm. The effectiveness of the controller is established through experimental studies on a benchmark MIMO system, the Twin Rotor Multi-Input Multi-Output System (TRMS).

This paper addresses the suitability of sliding mode control as a control strategy for free flight autopilot system. When used for practical applications, chattering which is an inherent limitation of SMC has to be mitigated adequately. Reaching law approaches for SMC design are being investigated in-order to identify an appropriate strategy that can ensure chattering-free operation for autopilot system. It is found that conventional reaching law-based SMC methodology leads to shortened sliding mode phase, slow system response and/or unbounded control action. Hence, each of the conventional reaching law methods are investigated not only for their efficacy in providing chattering free operation but also for sufficient sliding mode motion, fast response and bounded control action. Since it is observed that the conventional reaching laws fail in achieving these attributes concurrently, the authors propose an improved reaching law, viz., power rate exponential reaching law that can satisfy all the aforesaid desired attributes.

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.

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.

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.

Today’s rapid growth in air transportation demand leads to the problem of congestion in air traffic routes. In recent years, free flight concept is widely discussed as the solution to this problem. Free flight is a decentralized method of air traffic management, in which each aircraft has the freedom to self optimize its own route. Conflict detection and its subsequent resolution are the major challenges in the realization of this concept. Today’s modern navigation and surveillance equipment can ensure accurate conflict predictions. Once a conflict is detected, it should be avoided through suitable conflict avoidance maneuvers. An autopilot capable of initiating these conflict free maneuvers should be a necessary part of any aircraft in free flight to ensure conflict avoided flight. Controller design based on Sliding Mode Control (SMC) strategy is presented in this paper for the purpose of free flight autopilot implementation. Since SMC has the inherent property of robustness in sliding mode, it can ensure a highly efficient autopilot design. Conventional and reaching law approaches of SMC design are considered here for controller design. Conventional SMC technique usually exhibits an unacceptable phenomenon, viz., chattering. Reaching law approaches for SMC design are being investigated here so as to identify an appropriate strategy that can ensure near chattering free operation. Considering typical free flight conflict avoidance modes of operation, the performance of all the considered SMC strategies are compared through simulation studies. The comparison is based on their ability to reduce chattering and the effectiveness in ensuring quick conflict resolution maneuvers, so that an efficient controller for free flight autopilot system can be recommended.

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.