Showing papers by "Mark J. Balas published in 2005"

Adaptive Torque Control of Variable Speed Wind Turbines for Increased Region 2 Energy Capture

Abstract: We have previously shown that region 2 energy capture can be increased by using adaptive torque gain control on variable speed turbines. This adaptive torque control works by compensating for unknown and time-varying aerodynamic parameters such as the maximum power coefficient Cpmax and its corresponding optimal tip speed ratio λ*. This paper extends our earlier research in two ways in order to make the adaptive control technique more appealing to the commercial wind turbine industry. These two extensions are the use of the nacelle anemometer and the extension to a second-order discrete filter in the gain adaptation law. We believe that these two extensions will allow the adaptive controller to achieve its increased energy capture at lower cost and less sensitivity to noise than was possible with our original adaptive control strategy.

The Influence of Internal Damping on the Rotordynamic Stability of a Flywheel Rotor With Flexible Hub

Abstract: An investigation about the influence of internal damping on the rotordynamic stability of high-speed flywheel energy storage systems made from carbon fiber epoxy is presented. The research effort consists of simulation studies coupled with experimental testing and evaluation. Damping values obtained from composite beam samples and a composite rotor hub design are shown. The effect of vibration frequency on damping is examined and discussed. These parameters are then used in a series of simulation studies that examine the effects of internal damping on rotordynamic behavior. An experimental model has been developed to verify the conclusions made from the simulations. The experimental testing consisted of creating a prototype rig, characterizing the system parameters, applying these parameters to determine the expected critical speed and experimentally determine the actual critical speed. These results are presented and their implications for flexible hub flywheel designs discussed.Copyright © 2005 by ASME

Modification of Adaptive Disturbance Rejection Control for an Active Magnetic Bearing

Abstract: Recent work in Adaptive Disturbance Rejection Control has shown this method to be effective to reject forces due to imbalance, runout and base motion disturbances on magnetically supported flywheels over a large span of frequencies. The method, however, requires certain properties (such as almost -strict positive realness) that active magnetic bea rings do not possess, limiting the applicability of the method. In this work, the adaptive disturbance rejection control law is modified (with relaxed assumptions) and a design methodology is presented to allow for a much wider range of frequencies to be r ejected. The ideas used here include using a reduced order model, appropriate state estimator design, and modifying the original adaptive gains. Computer simulation and experimental results are given to validate the ideas presented.

Some Conditions for Strict Positive Realness of Second Order and Almost Second Order Systems

Abstract: This technical note describes two theorems that provide necessary conditions for a linear time invariant system to be Strictly Positive Real, (SPR). The first theorem applies to a single mode, structural system with positive damping. In the first case considered, the system is under output feedback control. It is shown that the inclusion of the output feedback loop extends the range of damping and modal frequency that a single mode single input, single output system can have and still be SPR. Further more, it is shown that an output feedback gain can always be found for a single mode SISO, minimum phase, controllable/observable system such that the closed-loop system is SPR. The second theorem provides necessary conditions for satisfaction of the SPR definition for a multi-mode, MIMO system with any input or output matrices. In the second case a particular type of feedback is not considered. However, the theorem provides a useful system test for SPR based on the modal frequency and damping of each mode of the structural system.

Precision Tracking Control Against Dynamic Targets for High-Energy Laser Systems

Abstract: Precision control of a fast-steering mirror is coupled with an open-loop acquisition system to perform tracking control against a dynamic target. The integration of a high-bandwidth tracking control system with a much lowerbandwidth acquisition system is accomplished by offloading signals from the former to the latter. This technique precludes saturation of the inner loop when large-amplitude, unexpected changes occur in the target trajectory. Particular attention is given to the sensitivities of inner-loop transient response and steady-state error responses to design conditions and sample rate. Control design solutions are presented and demonstrated via experiments and simulations.