Hammad Ahmad

An Experimental Test Setup for Advanced Estimation and Control of an AirborneWind Energy System

This chapter gives a detailed description of a test setup developed at KU Leuven for the launch and recovery of unpropelled tethered airplanes. The airplanes are launched by bringing them up to flying speed while attached by a tether to the end of a rotating arm. In the development of the setup, particular care was taken to allow experimental validation of advanced estimation and control techniques such as moving horizon estimation and model predictive control. A detailed overview of the hardware, sensors and software used on this setup is given in this chapter. The applied estimation and control techniques are outlined in this chapter as well, and an analysis of the closed loop performance is given.

Control allocation with actuator dynamics for aircraft flight controls

This paper addresses the control allocation to several aircraft flight controls to produce required body axis angular accelerations. Control law is designed to produce the virtual control effort signals, which are then distributed by solving a sequential least squares problem using active set method to the flight control surfaces to generate this effort. Two cases are described: in the first case the control law and allocation for the healthy aircraft is implemented, and in the second case, jamming of one control surface is introduced at time zero. In this case, it was shown how the controller and allocation compensate for this failure without changing the control law. To implement this system it was assumed that there is a good fault identification system onboard. Normally aircraft are over-actuated and in the case of a control failure this over actuation is more pronounced due to coupling of aircraft dynamics. Instead of using one-to-one mapping between control allocator and control surfaces, actuator dynamics was included in the system. The discrepancy in the optimal signal from control allocation due to this additional dynamics was compensated using the scheme mentioned in this paper. Each gain corresponding to the actuator is tuned using genetic algorithms (GA). The controller and allocation design are implemented on a nonlinear B747 model with actuator dynamics. Nomenclature aor δ = right outboard aileron (deg) air δ = right inboard aileron (deg) aol δ = left outboard aileron (deg) ail δ = left inboard aileron (deg) eor δ = right outboard elevator (deg) eir δ = right inboard elevator (deg) eol δ = left outboard elevator (deg) eil δ = left inboard elevator (deg) ih δ = stabilizer (deg) ur δ = upper rudder (deg) dr δ = down rudder (deg) p = roll rate about body x-axis (rad/s) q = pitch rate about body y-axis (rad/s) r = yaw rate about body z-axis (rad/s) T V = true airspeed (m/s)

Non-Reversing Generators in a Novel Design for Pumping Mode AirborneWind Energy Farm

The design of a pumping mode airborne wind energy (AWE) farm is presented in this chapter. This design centres on the use synchronous generators on a local frequency wild bus, with full scale power converter located at the point of grid connection. The design is well suited to a remotely located or offshore farm. The focus of the chapter is on the modelling of a ground based electromechanical system which provides a continuous electrical power output from multiple AWE devices whose individual operation delivers periodic mechanical power. The generators are not reversed during operation as the system presented separates the power and recovery tasks of the winch. Furthermore the use of permanent magnet synchronous generators (PMSG) enables the direct interconnection of multiple devices to a local bus. The AWE farm design philosophy is detailed and encouraging simulation results are discussed.

Design of control law and control allocation for B747-200 using a linear quadratic regulator and the active set method

Abstract This study applies the control allocation (CA) to several aircraft flight controls to produce the required body axis angular accelerations. The control law was designed using the linear quadratic regulator technique to produce the virtual control effort signals. This control law is effectively a multi-input multi-output proportional-integral controller. The virtual control efforts that are produced by the controller are then distributed by solving a multi-branch CA problem using the active set method. The solution of this CA problem is then distributed to the control surfaces. The solution is computed at a sampling frequency of 1 kHz. The designed control law and CA were then implemented in a non-linear B747-200 simulation model. The tracking performance in terms of the attitudes of the aircraft is presented.

Airborne wind energy: Simulation of directly interconnected synchronous generators for a novel wind energy technology

This paper presents the design and simulation of a simple wind farm consisting of three identical airborne wind energy systems. The novel concept of airborne wind energy (AWE) is briefly introduced. The focus of the paper is on the modelling of an operational method that provides a continuous power supply from a cluster of AWE systems whose individual operation delivers a non-continuous, periodic supply. The devices are directly interconnected on a local bus with an operation schedule to provide a continuous power output. A synchronisation routine is described, which enables an offline machine to join the bus. This setup is simulated under typical operating scenarios with results presented and discussed within.

Novel Multi-Sonar Controller and Other Advanced Features Developed and Tested on Latis, a Smart, Remotely Operated Vehicle

This paper describes in detail a novel multi-sonar controller developed at the University of Limerick and tested on the new smart, remotely operated vehicle (ROV) Latis at sea in March 2009. The multi-sonar controller allows the simultaneous operation of similar-frequency imaging and mapping sonar by interrogating the sonar returns of the multi-beam sonar in real time and adaptively triggering the pings of each sonar in a terrain-adaptive manner to avoid cross-talk and interference in sonar returns. The technique has benefits in hydrographic mapping and in payload sonar management on unmanned underwater vehicles. Detailed results on the testing of the sonar controller system are reported. The paper also describes the smart ROV Latis, designed and built at the University of Limerick, on which the sonar systems have been tested. With its advanced control systems and high-bandwidth networking capabilities, the ROV Latis is an ideal platform for experimentation of new techniques such as the multi-sonar controller, which can be ported to other ROVs and autonomous underwater vehicle platforms once proven.

Compensation of jammed control surface of large transport aircraft by control reconfiguration

This paper addresses the control allocation to several aircraft flight controls to produce required body axis angular accelerations. Two methods of control law design are used to produce the virtual control effort signals, which are then distributed by solving sequential least squares problem using active set method to the flight control surfaces to generate this effort. Two cases are described: in the first case the control law and allocation for the healthy aircraft is implemented, and in the second case, jamming of one control surface is introduced at time zero. In this case it was shown that how controller and allocation compensate for this failure without changing the control law. To implement this system it was assumed that there is a good fault identification system onboard. Normally aircraft are over-actuated and in the case of a control failure this over actuation is more pronounced due to coupling of aircraft dynamics. The problem of control allocation presented here is a convex problem so there is always a unique solution.

Development and Testing of a Control System for the Automatic Flight of Tethered Parafoils

This paper presents the design and testing of a control system for the robotic flight of tethered kites. The use of tethered kites as a prime mover in airborne wind energy is undergoing active research in several quarters. There also exist several additional applications for the remote or autonomous control of tethered kites, such as aerial sensor and communications platforms. The system presented is a distributed control system consisting of three primary components: an instrumented tethered kite, a kite control pod, and a ground control and power takeoff station. A detailed description of these constituent parts is provided, with design considerations and constraints outlined. Flight tests of the system have been carried out, and a range of results and system performance data from these are presented and discussed.

Application of Evolutionary Computing in Control Allocation

This issue of interaction of control allocation and actuator dynamics and has been dealt with by very few researchers. What was not considered in most control allocation algorithms is the fact that the control surfaces are manipulated by either hydraulics or electric actuators, and constitute a dynamic system which cannot produce infinite accelerations. In other words, if a control was initially at rest, and later commanded to move at its maximum rate in some direction for a specified amount of time, it would gradually build up speed until it reached the commanded rate. The final position of the control would therefore not be the same as that calculated using the commanded rate and the time during which it was instructed to move (Bolling 1997). In this chapter, a method, which post-processes the output of a control allocation algorithm, is developed to compensate for actuator dynamics. The method developed is solved for a diagonal matrix of gain corresponding to individual actuators. This matrix is then multiplied with the commanded change in control effector settings as computed by the control allocator and actuators dynamics interactions. The basic premise of this method is to post process the output of the control allocation algorithm to overdrive the actuators so that at the end of a sampling interval the actual actuator positions are equivalent to the desired actuator positions (Oppenheimer and Doman 2004). The overdriving of the actuators is done by multiplying the change in commanded signal with the identified gain matrix which is called the compensator. This identification is done by using a soft computing technique (i.e. genetic algorithms). The simulation setup including control allocator block, compensator and actuator rig makes a non-linear set up. During the identification of the compensator using this setup by soft computing technique such as genetic algorithms, the likelihood of the solution being a global minimum is high as compared to other optimisation techniques. This is why genetic algorithms have been used in this analysis rather than other techniques such as linear programming. The main contribution is to design a compensator using an evolutionary computing technique (i.e. genetic algorithms) to compensate the interaction between control allocation and actuator dynamics. It should be mentioned that in this method the model of the actuator does not need to be known. The simulation setup consists of excitation signals, the control allocation block, the compensator and the actuators rig. When designing control allocation typically the actuator dynamics are ignored because the bandwidth of the actuators is larger than the frequencies of the rigid body modes of the aircraft. Fig. 1 shows a control allocator with actuator dynamics neglected. If there is a case

Integration and Testing of Multi-Purpose Platform Technologies System and High Resolution Multi-Beam Sonar on ROV Holland I

Abstract This paper describes the integration and testing of multi-purpose platform technologies system (MPPT-Ring), high resolution multi-beam sonar and state-of-the-art navigation system with the Ireland national work class ROV Holland I. In addition, the paper presents results of high resolution sea bed mapping along with the results of MPPT-Ring augmented reality support tools in offshore applications.