Noise covariances estimation for systems with bias states

This paper presents a new approach to noise covariances estimation for a linear, time-invariant, stochastic system with constant but unknown bias states. The system is supposed to satisfy controllable/observable conditions without bias states. Based on a restructured data representation, the covariance of a new variable that consists of measurement vectors is expressed as a linear combination of unknown parameters. Noise covariances are then estimated by employing a recursive least-squares algorithm. The proposed method requires no a priori estimates of noise covariances, provides consistent estimates, and can also be applied when the relationship between bias states and other states is unknown. The method has been applied to strapdown inertial navigation system initial alignment. Simulation results indicate a satisfactory performance of the proposed method     

Stability Analysis of a Buck Regulator Employing Input Filter Compensation

The interaction between the input filter and the regulator often causes serious degradation of performance. The reduction in loop gain due to input filter interaction can result in system instability. An exact stability analysis of the buck regulator system is presented. The input filter parameter values are varied and system instability is predicted for the case without feedforward. The eigenvalues of the system can be brought back into the unit circle and the system thus stabilized with the addition of the feedforward loop. Measurements made for the cases with and without feedforward confirm the analytical prediction.     

Design of Switching Regulator with Combined FM and On-Off Control

The design and implementation of a switching regulator incorporating a high-frequency series-resonant converter and a combined FM and on-off feedback control is presented. The combined FM and on-off control results in a better conversion efficiency and a wider range of operational input voltage and output current. A 22.5 V, 50 W experimental regulator has been built to demonstrate the practicality of the circuit and its high efficiency, typically 92 to 96 percent, depending on the input and loading conditions.     

Optimal Design Strategy of Switching Converters Employing Current in jected Control

This paper analyzes a buck/boost regulator employing current-injected control (CIC). It reveals the complex interactions between the dc loop and the current-injected loop and underlines the fundamental principle that governs the loop gain determination. Three commonly used compensation techniques are compared. The integral and lead/lag compensation are shown to be most desirable for performance optimization and stability.     

A multioutput LLC-type parallel resonant converter

When an LLC-type parallel resonant converter (LLC-PRC) operates above resonant frequency, the switching transistors can be turned off at zero voltage. Further study reveals that the LLC-PRC possesses the advantage of lower converter voltage gain as compared with the conventional PRC. Based on the analytic results derived, a complete set of design curves from which a systematic design procedure is developed is obtained. Experimental results from a 150-W, 150-kHz, multioutput LLC-type PRC power supply are presented     

Gender differences in organ density in a rat simulated microgravity model

Research investigating the physiological effects of microgravity on the human body has demonstrated a shift of body fluids in actual spaceflight and in simulated Earth-based microgravity models in both males and females, possibly causing many deleterious physiological effects. Twenty-five anatomically normal female (NF) and 20 ovariectomized (OE) Fischer 344 rats were randomly selected to be in an experimental (1 h of 45 degrees head-down tilt, 45HDT) or control (1 h of prone position) group. At the end of the hour experimental period, the density of the brain, lungs, heart, liver, and left and right kidneys were measured using spiral computed tomography (SCT) while the rats remained in their experimental positions. A sub-group of OE rats (N=6) was administered estrogen replacement therapy on a daily basis (5 micrograms/kg body weight, s.c.) for 4 days and then underwent 1 h of 45HDT and SCT analysis at one day, 2 days, and 5 days to determine if estrogen replacement therapy would alter organ densities. Our data demonstrate that 1 h of 45HDT produced significant increases (p<0.05) in the organ densities of the brain, liver, left kidney, and lung of the OE female group compared to their prone controls. However, only the brain density was significantly increased in the NF group. Estrogen replacement therapy caused a significant decrease in brain organ density at the 5 day time point compared to the 24 h time point. We conclude that estrogen plays a role in fluid distribution in a rat 45HDT model.     

An Adaptive-Control Switching Buck Regulator-Implementation, Analysis, and Design

Describing-function techniques and averaging methods have been employed to characterize a multiloop switching buck regulator by three functionsl blocks: power stage, analog signal processor, and pulse modulator. The model is employed. to explore possible forms of pole-zero cancellation and the adaptive nature of the control to filter parameter changes. Analysis-based design guide lines are provided including a suggested additional RC-compensation loop to optimize regulator performances such as stability, audiosusceptibility, output impedance, and load transient response.     

Autonomous Upgrading of Inertial Navigation Systems

The performance of substandard inertial platform gyros can be improved through the sampled supervision of their operation by a higher grade gyroscope mounted directly on the platform. The relative drift rates of the susbstandard platform gyros are estimated on a cyclical basis. This paper describes techniques for estimating the drift rates. It deals with the method of applying these estimated values in the form of platform correction signals.     

Long-term changes in indices of geomagnetic activity at the auroral station Sodankylä

Here we compare the traditional analog measure of geomagnetic activity, Ak, with the more recent digital indices of IHV and Ah based on hourly mean data, and their derivatives at the auroral station Sodankylä. By this selection of indices we study the effects of (i) analog vs. digital technique, and (ii) full local-time vs. local night-time coverage on quantifying local geomagnetic activity. We find that all other indices are stronger than Ak during the low-activity cycles 15–16 suggesting an excess of very low scalings in Ak at this time. The full-day indices consistently depict stronger correlation with the interplanetary magnetic field strength, while the night-time indices have higher correlation with solar wind speed. The Ak index correlates better with the digital indices of full-day coverage than with any night-time index. However, Ak depicts somewhat higher activity levels than the digital full-day indices in the declining phase of the solar cycle, indicating that, due to their different sampling rates, the latter indices are less sensitive to high-frequency variations driven by the Alfvén waves in high-speed streams. On the other hand, the night-time indices have an even stronger response to solar wind speed than Ak. The results strongly indicate that at auroral latitudes, geomagnetic indices with different local time coverage reflect different current systems, which, by an appropriate choice of indices, allows studying the century-scale dynamics of these currents separately.