Implication of multiple dipolarization event near 9 RE for the physics of substorms

In 2001, 2002 and 2003, the Polar spacecraft probed the near equatorial plasma sheet at 9 R_E near local midnight. Using the magnetic field observations, the signatures at substorm onsets are studied. Close to the flux pile-up region, the Polar spacecraft readily detects the dipolarization front, especially for pseudo onsets. An event with two distinct onsets has been examined. The signatures are found to be consistent with the multiple-onset model suggested by Russell [Russell, C.T. How northward turnings of the IMF can lead to substorm expansion onsets. Geophys. Res. Lett. 27, 3257–3259, 2000] which is a modified Near-Earth Neutral Line (NENL) model. Another similar event is also examined showing the effects of different Interplanetary Magnetic Field (IMF) conditions upon substorms. Moreover, ground effects can be very weak compared to in situ observations, especially for pseudo onsets, because these signatures appear to be localized and not global.     

An output feedback controller for a synchronous generator

A novel approach using eigenstructure assignment is developed for the design of excitation controllers for synchronous generators. The computation procedure for the method is easy to apply, and an exact solution can be obtained without iteration. Controllers designed by the proposed approach can be easily implemented by means of proportional-integral (PI) controllers. Practical considerations in reaching an optimum selection of closed-loop eigenvalues are addressed. Time-domain simulation results are presented to verify the effectiveness of the design method     

Self-Tuning Excitation Control for Synchronous Machine

A novel scheme for the control of synchronous generator excitation system is described. The proposed controller, which makes use of self-tuning proportional-integral (PI) control, is very effective for improving the dynamic performance of the synchronous machine over a wide range of operating conditions when the machine is subjected to major disturbances or small random load changes. A fixed-gain PI excitation controller is also included for comparison.     

Dust in and Around the Heliosphere and Astrospheres

Space Science Reviews - The ESA Swarm mission, launched on 22 November 2013, consists of three spacecraft each equipped with a Micro Advanced Stellar Compass ( $\mu $ ASC) from the Technical...     

Coordinated Frequency and Voltage Control of Synchronous Generators

Three different types of controllers, i.e., the conventional controller, the linear optimal controller (LOC), and the variablestructure controller (VSC) are proposed for the coordinatedfrequency and voltage control of synchronous generators. Theinteraction between the frequency and voltage control loops is takeninto account by incorporating both the speed-governing system andthe excitation system into the mathematical model of thesynchronous generator. Results obtained from computer simulationindicate that the variable structure controller can yield the bestdynamic responses following a step load change.     

Excitation control of a synchronous generator using a lookup table

A scheme involving the use of a lookup table is developed for the excitation control of a synchronous generator. The proposed control scheme, generator speed deviation, and acceleration deviation are taken as the input signals. These input signals are sampled and converted to linguistic terms before they are fed into the controller. The controller generates the desired output (control) signal by using a set of production rules (if-then rules) that are based on previous experience to relate the input signals to the output. The output signal is converted from linguistic terms to a numerical value before it is sent to the excitation system of the synchronous machine. To demonstrate the effectiveness of the proposed control scheme, digital simulations of a synchronous generator subject to a three-phase fault under different operating conditions were performed. It was found that the controller can improve the dynamic performance of a synchronous generator over a wide range of operating conditions. Since the controller does not require model identification, it is computationally efficient and is suitable for online excitation control, using a microcomputer     

Self-organizing fuzzy learning CLOS guidance law design

A new self-organizing fuzzy logic control (SOFLC) design method is proposed. The proposed method is applied to the command line-of-sight (CLOS) guidance law design. The SOFLC contains two sets of fuzzy inference logic. One is the fuzzy logic controller and the other is the rule modifier. The new learning method of the rule modifier is developed based on a fuzzy learning algorithm. The modification value of each rule is based on the fuzzy firing weight, so that learning of the rule bases is reasonable. Finally, two engagement scenarios are examined, and a comparison between a fuzzy logic control (FLC), an optimal learning FLC, and the proposed SOFLC CLOS guidance laws is made. Simulation results show that the proposed SOFLC guidance law can achieve better guidance performance than the other guidance laws.     

Unified Voltage and Pitch Angle Controller for Wind-Driven Induction Generator System

A unified voltage and pitch angle controller (UVPC) for a wind-driven induction generator system is presented to reach effective voltage control and to stabilize generator speed and system frequency. The proposed UVPC comprises a linear optimal controller (LOC), a supplementary voltage regulator (SVR), and a supplementary pitch angle controller (SPC). An ac voltage regulator and a dc voltage regulator are designed in the SVR to generate the desired voltage magnitude and phase angle for the voltage-sourced inverter (VSI). On the other hand, the SPC is designed based on fuzzy logic inference rules in order to generate the desired pitch angle command for the variable blade pitch such that the mechanical power can be controlled in a very efficient manner. When the system is operated in the islanding condition, an approach based on the concept of relative rotating speed has been developed for the measurement of system frequency deviation. Simulation and experimental results reveal that both bus voltage and mechanical power can be effectively controlled by the proposed UVPC for the wind energy conversion system (WECS) either connected with or disconnected from the power grid when there is sufficient wind energy.     

Thermocapillary-driven convection in supported and floating-zone crystallization

Marangoni flow was induced in a thin disk of molten tin with an atomically clean surface by heating it from below in an ultra high vacuum apparatus. The radial distribution of temperature was measured and no temperature oscillations were observed. Strong mechanical disturbances introduced at a Marangoni number of about 4300 died out quickly with time indicating that the system was stable. Mathematical models indicate that strong flows in a two cell structure exist under the conditions studied, and that the velocity profile in the cell near the surface is of the bouindary layer type which varies rapidly with depth.     

Damping of Generator Oscillations Using Static VAR Compensators

The design of a novel static VAR compensator for the damping of electromechanical oscillation in a synchronous generator is presented. The proposed compensator, which is made up of a fixed capacitor and a thyristor-controlled inductor, is installed at the generator terminal to provide the required damping without deteriorating the voltage profile under disturbance conditions. In order to have better dynamic performance, a supplementary proportional-integral-derivative (PID) controller of which the parameters are determined by eigenvalue assignment is incorporated in the static VAR compensators. The dynamic responses of the synchronous machine subjected to a three-phase fault are given to demonstrate the effectiveness of the static VAR compensators. A comparison study of the proposed controller and a PID excitation controller is made with respect to damping enhancement and terminal voltage deviation.