Jeff K. Pieper

Adaptive Control of a Variable-Speed Variable-Pitch Wind Turbine Using Radial-Basis Function Neural Network

In order to be economically competitive, various control systems are used in large scale wind turbines. These systems enable the wind turbine to work efficiently and produce the maximum power output at varying wind speed. In this paper, an adaptive control based on radial-basis-function neural network (NN) is proposed for different operation modes of variable-speed variable-pitch wind turbines including torque control at speeds lower than rated wind speeds, pitch control at higher wind speeds and smooth transition between these two modes The adaptive NN control approximates the nonlinear dynamics of the wind turbine based on input/output measurements and ensures smooth tracking of the optimal tip-speed-ratio at different wind speeds. The robust NN weight updating rules are obtained using Lyapunov stability analysis. The proposed control algorithm is first tested with a simplified mathematical model of a wind turbine, and then the validity of results is verified by simulation studies on a 5 MW wind turbine simulator.

Robust Gain Scheduled Control of a Hydrokinetic Turbine

A vertical-axis hydrokinetic turbine speed control system is developed that guarantees stability and performance properties for the entire range of operation including tracking of the maximum power point below rated speeds and power regulation above rated speed. Secondary objectives include explicitly incorporating a tuning method to adjust the tradeoff between reference tracking and load transients and an advanced control methodology to attract industry acceptance. To facilitate this, an H∞ linear parameter varying (LPV) controller was developed based on a physical model and iterative simulation-based testing. This paper outlines development of the turbine mathematical model, control objectives, control strategy, controller design as well as the results of simulation and field testing on a 5 kW hydrokinetic turbine. Results are compared to a fixed point PI controller tuned for reference tracking only.

Air/fuel ratio control using sliding mode methods

To meet demands for high performance and low fuel consumption and emissions, control of air/fuel ratio in spark ignition (SI) engines has received significant attention. Here, a nonlinear, fuel injected SI engine model is developed which includes intake manifold, fuel wall-wetting and crankshaft dynamics as well as load effects and process delays inherent in four-stroke engines. A sliding mode controller is designed and implemented for a linearized model using state estimates.

Model-following control of a helicopter in hover

Tracking with model-following behavior for a Bell 205 helicopter is investigated using linear-quadratic optimal control. The objective of the design is to produce the desired performance in simulation for a nominal plant model of the Bell 205 in hovering flight. Two fundamentally different types of model-following control designs, explicit and implicit, are studied and discussed in this paper. The two designs result in controllers of different structures. The primary objective of the paper is to compare the merits of the resulting closed-loop systems.

Gain-Scheduled

The fast-growing technology of large scale wind turbines demands control systems capable of enhancing both the efficiency of capturing wind power, and the useful life of the turbines themselves. l1-Optimal control is an approach to deal with persistent exogenous disturbances which have bounded magnitude (l∞-norm) such as realistic wind disturbances and turbulence profiles. In this brief, we develop an efficient method to compute the l1-norm of a system. As the control synthesis problem is nonconvex, we use the proposed method to design the optimal output feedback controllers for a linear model of a wind turbine at different operating points using genetic algorithm optimization. The locally optimized controllers are interpolated using a gain-scheduled technique with guaranteed stability. The controller is tested with comprehensive simulation studies on a 5 MW wind turbine using fatigue, aerodynamics, structures, and turbulence (FAST) software. The proposed controller is compared with a well-tuned proportional-integral (PI) controller. The results show improved power quality, and decrease in the fluctuations of generator torque and rotor speed.

\ell _{1}

This paper presents an adaptive haptic control for a one degree-of-freedom master-slave teleoperated device. The aim is to reduce excessive collision forces that occur when there are significant time delays in master-slave communication. The control design also allows the operator to move the slave in free space and in a soft medium. Previous approaches to haptic teleoperation typically design for either movement in a medium or constrained contact with a solid surface; then, it is up to the operator to avoid collisions or precisely anticipate collisions. The proposed control runs on the slave side inner loop, with no time delay, and tracks commanded forces from the outer loop. A Lyapunov-stable backstepping-with-tuning-functions design provides a way to ensure smooth forces are applied that guarantee stability in the presence of unmodeled environmental stiffness and viscosity. Experiments using a Phantom hand controller interacting with simulated environment show that collision forces are substantially reduced compared to two other control methods. In collision-free operation, the performance is comparable to other methods.

-Optimal Control of Variable-Speed-Variable-Pitch Wind Turbines

Presented is the design and analysis of robust full authority e ight controllers to improve the handling qualities of a e y-by-wire Bell 205 helicopter. The emphasis is to meet stringent U.S. Army handling qualities specie cations against the constraint of robust stability. The designer goal is to reproduce specie cations constituting an ideal target model in the actual Bell 205, which does not naturally exhibit good handling qualities. A solution to robust e ight controllers is a mixed-norm control design methodology that incorporates both optimal nominal modelfollowingperformanceandrobuststabilityobjectives.Mixed-norm optimizationaddressesanoutstandingproblem inhelicoptere ightcontrol, which hasbeen theunrealisticmapping ofmultipledesign objectivesinto a single norm. Errordynamicsbetweentheresponseofthemodelandtheactualhelicopterareexplicitlydee nedfromexperimental data to reducetheperformancevsrobustnesstradeoff. Themixed-norm control problem addresses genuinesystem requirements without compromise. Analysis and simulation results show an effective robust controller designed for the Bell 205.

Adaptive Haptic Control for Telerobotics Transitioning Between Free, Soft, and Hard Environments

Presented are results of a study of the application of linear quadratic optimal model-following control applied to a Bell 205 helicopter in hover. The primary objective of good in-flight stability robustness and performance was accomplished via singular value analysis using perturbed systems. Nominal aircraft models were compared with experimental data and discrepancies quantified in a robustness criterion. Current military handling quality requirements were specified as a target model to be followed. The linear quadratic optimal control and command feedforward was found suitable for these requirements. Design analyses enabled consideration of the tuning process, where effects of variations in selected tuning parameters demonstrated their sensitivity to the design.

Mixed Norm Control of a Helicopter

This paper explores the effectiveness of a state feedback mixed H/sub 2//H/sub /spl infin// optimal control design applied to the 1990 ACC benchmark problem. This simple mechanical system captures many of the challenging robust control issues of more complex aerospace applications. A robust controller is derived that achieves H/sub /spl infin// robust stability with optimal nominal H/sub 2/ performance for a system with real parameter variations. Detailed analysis, including /spl mu/ analysis of the robust stability characteristics for the closed-loop system is also presented. Results indicate that a controller may be synthesized to meet the design objectives, but is conservative in terms of robustness.

Linear quadratic optimal model-following control of a helicopter in hover

This paper gives precise conditions for the existence of a state feedback sliding-mode controller to achieve a complex, closed-loop eigenstructure. This structure can be advantageous in providing maximum flexibility in specifying closed-loop dynamics. It is found that the controller is inherently dynamic in general, and recovers standard sliding-mode control results when all real elements are chosen for the switching surface matrix. A control design algorithm is presented, and robustness of the resulting closed-loop system is demonstrated. An illustrative example is provided.