Deadband Region Research Articles

The dead band in the performance of cross-flow turbines: Effects of Reynolds number and blade pitch

The performance of a three straight bladed Cross-Flow or Vertical Axis Turbine based on symmetrical profiles, with a chord-to-diameter ratio of 0.16 has been studied in detail. The research is focused on the effects of Reynolds number and blade pitch angle, not only in the performance itself, but in the appearance or not of a dead band region in which aerodynamic loading cannot overcome resistive loads. Experiments were carefully designed in order to cover the transitional region were this dead band is incipient, for Reynolds numbers in the range from 3 to 5·105.Results show how the performance is highly dependent on pitch angle at all Reynolds numbers investigated. Efficiencies over 25% are reached at tip speed ratios (blade to free stream velocity ratio) slightly larger than 2, for pitch angles in the range 4–8°. The appearance of the dead band is conditioned by the combination of Reynolds number and pitch angle.

Coordinated Voltage Control Scheme for SEIG-Based Wind Park Utilizing Substation STATCOM and ULTC Transformer

This paper presents a coordinated voltage control scheme for improving the network voltage profile and for minimizing the steady-state loading of the STATCOM to effectively support the system during contingencies. The paper addresses implementation issues associated with primary voltage control and optimal tracking secondary voltage control for wind parks based on self-excited induction generators which comprise STATCOM and under-load tap changer (ULTC) substation transformers. The voltage controllers for the STATCOM and ULTC transformer are coordinated and ensure the voltage support. In steady-state operation, the voltage is controlled by only stepping the tap changer when the voltage is outside the deadband region of the ULTC to minimize the number of taps changes. Thus, the STATCOM will be unloaded and ready to react with higher reactive power margin during contingencies. In the paper, the effects of the short circuit ratio of the interconnection and the inherent communication delay between the wind park and the remote bus on the performance of the controllers and the maximum critical clearing time of fault are considered. Simulation results are presented to demonstrate the performance of the controllers in steady-state and in response to system contingency situations.

East–west stationkeeping of satellite orbits with resonant tesseral harmonics

Satellite orbits that are eccentric and inclined with near-repeating ground tracks can exhibit complex dynamical motions. This class of orbit is typically in resonance with multiple Earth tesseral harmonics. Depending on the selected resonance (i.e. orbits with a 24 h period, 12 h period, etc.), inclination, and eccentricity, the interaction between tesserals produces a variety of motions ranging between responses that are periodic, quasiperiodic, and chaotic. Furthermore, the type of motion encountered by a satellite can have a significant impact on the east-west stationkeeping process. Indeed, the classical stationkeeping algorithm is shown to be potentially non-convergent in regions of the phase space that possess higher order periodic, quasiperiodic, and/or chaotic motions. Poincaré sections provide insight into the location of these regions, and suggest improvements to the classical control technique. Combining this information with an asymptotic analysis, an alternative method is developed and demonstrated to remain stable in the complex regions of the phase space. The proposed method retains the ‘grazing’ strategy of the classical algorithm; however, the algorithm adapts to the dynamical environment to ensure stability of the process. Preliminary results demonstrate that the algorithm remains stable in chaotic regions of the phase space and accomplishes the primary objective of maintaining motion in a prescribed deadband region.

Influence of pinned joints on damping and dynamic behavior of a truss

This paper discusses measured damping characteristics of a three-bay truss that uses pinned joints. A clevis/tang joint design was used. Pinned joints normally have a small amount of clearance between the pins and the clevis/tang fittings. The small gap can cause very significant changes in the dynamics and damping of a truss structure, particularly when the joint can traverse the deadband region. If the gravity induced loads prevent a joint from entering the deadband region, one might expect damping to be effected. Test results demonstrate that structures using pinned joints can have damping that is dependent on gravity. Damping rates can change by a factor of up to five due to variation of gravity induced loads. This variation could be very significant when characterizing space structures in a 1-g environment. The data also suggest that impact, as the joint gaps open and close, transfers vibration energy from low-frequency global modes to high-frequency local modes, increasing the rate of energy dissipation through material damping.

Displacement and Velocity Feedback Control of a Beam with a Deadband Region

ABSTRACT The problem of controlling the dynamic response of a beam by means of displacement and velocity feedback is solved. The objective of the control is to prevent the maximum deflection and/or velocity of a beam from exceeding given upper and lower bounds. The control is The theory is illustrated by two numerical examples that involve displacement and velocity feedback control. An assessment is made of the effectiveness of the proposed control by defining a performance measure. It is observed that the dynamic response of the beam can be kept within specified bounds by applying a large enough control force, which also depends on the extent of the deadband region. A measure of force spent in the control process is defined and plotted against the dynamic response, which is observed to decrease rapidly as the bounds approach the values set by the uncontrolled beam.