Aman Behal

Voltage regulation with STATCOMs: modeling, control and results

This paper presents system modeling and control design for fast load voltage regulation using static compensators (STATCOMs). The modeling strategy gives a clear representation of load voltage magnitude and STATCOM reactive current on an instantaneous basis. The particular coordinate transformation employed here also facilitates extraction of linearized system dynamics in conjunction with circuit simulators. It is rigorously shown that the control problem of load voltage regulation using reactive current is nonminimum phase. Linear and nonlinear controllers for the regulation problem are designed and compared via simulation results. Internal dynamics of the STATCOM are modeled using the same strategy. Lyapunov based adaptive controllers are designed for controlling the STATCOM reactive current while maintaining its dc bus voltage. Simulation results of the controlled STATCOM integrated with the load bus voltage controller are presented to show efficacy of the modeling and control design.

Multi-Input/Multi-Output Adaptive Output Feedback Control Design for Aeroelastic Vibration Suppression

Via the use of leading- and trailing-edge control surface actuation, an adaptive output feedback controller is designed for suppressing aeroelastic vibrations on a nonlinear wing section. Although a single flap under adaptive control can suppress vibrations, the response rate is limited by the system zero dynamics. Under the restriction that only pitching and plunging variables are available for measurement but their rates are not, the proposed algorithm addresses the problem of designing a singularity-free adaptive output feedback controller when the control inputs are coupled via an input gain matrix for which the parameters are uncertain. The stability result achieved is global asymptotic tracking. Simulation results demonstrate the efficacy of the multi-input/multi-output control toward suppressing flutter and limit-cycle oscillations, as well as reducing the vibrational level in the subcritical flight-speed range. Pertinent conclusions are outlined.

Adaptive homography-based visual servo tracking for a fixed camera configuration with a camera-in-hand extension

In this brief, a homography-based adaptive visual servo controller is developed to enable a robot end-effector to track a desired Euclidean trajectory as determined by a sequence of images for both the camera-in-hand and fixed-camera configurations. To achieve the objectives, a Lyapunov-based adaptive control strategy is employed to actively compensate for the lack of unknown depth measurements and the lack of an object model. The error systems are constructed as a hybrid of pixel information and reconstructed Euclidean variables obtained by comparing the images and decomposing a homographic relationship. Simulation results are provided to demonstrate the performance of the developed controller for the fixed camera configuration.

Nonlinear Adaptive Control of an Aeroelastic Two-Dimensional Lifting Surface

Adaptive control of a nonlinear two-dimensional wing-flap system operating in an incompressible flowfield is studied. An output feedback control law is implemented, and its performance toward suppressing flutter and limit cycle oscillations, as well as reducing the vibrational level in the subcritical flight speed range, is demonstrated. The control law proposed here is applicable to minimum phase systems, and conditions for stability of the zero dynamics are provided. The control objective is to design a control strategy to drive the pitch angle to a setpoint while adaptively compensating for uncertainties in all of the aeroelastic model parameters. It is shown that all of the states of the closed-loop system are asymptotically stable. Furthermore, an extension is presented to include flap actuator dynamics. Simulations have been presented to validate the efficacy of the proposed strategy. Pertinent conclusions have been outlined.

Sensorless rotor velocity tracking control for induction motors

We present a sensorless control algorithm that achieves semi-global exponential rotor velocity tracking for the full-order nonlinear dynamic model of an induction motor actuating a mechanical subsystem. The proposed controller utilizes stator current measurements, but is termed sensorless due to the fact that no mechanical sensors are required and that stator current measurements can be obtained in an inexpensive/simplistic manner. The control strategy utilizes a novel rotor velocity observer which facilitates the potential for improved rotor velocity tracking transient performance. In addition, the observed integrator backstepping technique is utilized to ensure that the observer-based controller remains bounded. Experimental results are included to verify the effectiveness of the controller.

Adaptive set–point control of robotic manipulators with amplitude–limited control inputs

This paper addresses the link position setpoint control problem of n–link robotic manipulators with amplitude-limited control inputs. We design a global-asymptotic exact model knowledge controller and a semi-global asymptotic controller which adapts for parametric uncertainty. Explicit bounds for these controllers can be determined; hence, the required input torque can be calculated a priori so that actuator saturation can be avoided. We also illustrate how the proposed control algorithm in this paper can be slightly modified to produce a proportional-integral-derivative (PID) controller which contains a saturated integral term. Experimental results are provided to illustrate the improved performance of the proposed control strategy over a standard adaptive controller that has been artificially limited to account for torque saturation.

Homography-Based Visual Servo Control With Imperfect Camera Calibration

In this technical note, a robust adaptive uncalibrated visual servo controller is proposed to asymptotically regulate a robot end-effector to a desired pose. A homography-based visual servo control approach is used to address the six degrees-of-freedom regulation problem. A high-gain robust controller is developed to asymptotically stabilize the rotation error, and an adaptive controller is developed to stabilize the translation error while compensating for the unknown depth information and intrinsic camera calibration parameters. A Lyapunov-based analysis is used to examine the stability of the developed controller.

Model-Free Control Design for Multi-Input Multi-Output Aeroelastic System Subject to External Disturbance

In this paper, a class of aeroelastic systems with an unmodeled nonlinearity and external disturbance is considered. By using leading- and trailing-edge control surface actuations, a full-state feedforward/feedback controller is designed to suppress the aeroelastic vibrations of a nonlinear wing section subject to external disturbance. The fullstate feedback control yields a uniformly ultimately bounded result for two-axis vibration suppression. With the restriction that only pitching and plunging displacements are measurable while their rates are not, a high-gain observer is used to modify the full-state feedback control design to an output feedback design. Simulation results demonstrate the efficacy of the multi-input multi-output control toward suppressing aeroelastic vibration and limit cycle oscillations occurring in pre and postflutter velocity regimes when the system is subjected to a variety of external disturbance signals. Comparisons are drawn with a previously designed adaptive multi-input multi-output controller.

Tracking and regulation control of an underactuated surface vessel with nonintegrable dynamics

A continuous, time-varying tracking controller is designed that globally exponentially forces the position/orientation tracking error of an underactuated surface vessel to a neighborhood about zero that can be made arbitrarily small (i.e., global uniformly ultimately bounded, GUUB). The result is facilitated by fusing a filtered tracking error transformation with the dynamic oscillator design presented in Dixon et al. (1999). We also illustrate that the proposed tracking controller yields a GUUB result for the regulation problem. In addition, an extension is provided that illustrates that the proposed unified tracking/regulation controller can be applied to a twin rotor helicopter model.

How Autonomy Impacts Performance and Satisfaction: Results From a Study With Spinal Cord Injured Subjects Using an Assistive Robot

We report a small dual cohort pilot study with traumatic spinal cord injured (SCI) subjects designed to investigate the utility of a wheelchair-mounted robotic arm for these subjects. The UCF-MANUS, a vision-based 6DOF assistive robotic arm, has been designed to aid individuals with upper limb extremities to complete tasks of daily living that they would otherwise be unable to complete themselves. Pick-and-place IADL tasks were designed and ten (10) users post-SCI were selected under IRB guidelines to be trained and tested with the system for 1 to 2 h weekly over a period of three weeks. During this time, they controlled the robot either through a manual or an autonomous (supervised) mode of operation. Baseline characteristics (pre-study), quantitative performance metrics (during study), and psychometrics (post-study) were obtained and statistically analyzed to test a set of hypotheses related to performance and satisfaction with the two control modes. At the end of the study, both the autonomous and the manual mode had comparable task completion times while user effort required for operating the robot in autonomous mode was significantly less than that for the manual mode. However, the autonomous mode failed to commensurately raise the users level of satisfaction. Over the three-week study, the manual mode users showed a pronounced learning effect in terms of reducing mean task completion time and number of commands while the auto mode users showed improvement in terms of reduction of variability. Based on qualitative feedback and quantitative results, possible directions for system design are presented to concurrently achieve better performance and satisfaction outcomes.