Design and control of a synchronous reluctance machine drive

This thesis investigates the design, performance and control of a synchronous reluctance machine (Synchrel) drive. The Synchrel machine is proposed for variable speed drives because of its advantages over other machines. The rotor has no cage winding, brushes or slip rings. The torque ripple levels are lower in the Synchrel machine than the switched reluctance machine as it operates from a standard sine wave supply. An axially laminated rotor was designed based on finite element analysis, with the aim of producing the same output power as obtained from an induction motor (M) with a similar stator. Using vector control, the developed torque is controlled by regulating the stator current vector. Two vector control schemes are used, maximum torque per ampere and constant current in the direct axis. The output torque characteristics of the machine have been confirmed by finite element analysis. Slotine's approach of sliding mode control is used for position control of the vector controlled synchronous reluctance machine. A comparison is undertaken between the performance of a fixed gain controller with two sliding mode controllers, for both the regulator and servo cases. Invariant performance is obtained using Slotine's sliding mode control approach, unlike with a fixed gain controller. Robustness to parameter variation is an important feature of this technique. This robustness can be achieved through the control law design, assuming parameter variation bounds are known. These improvements are demonstrated for variations in load inertia. Inductance ripple affects machine performance, for example decreasing output torque and increasing core losses. A state space model for the machine that incorporates this inductance effect, yields drive simulation results that agree with experimental results

Design of a Torque Current Generator for Strapdown Gyroscopes

The design, analysis, and experimental evaluation of an optimum performance torque current generator for use with strapdown gyroscopes, is presented. Among the criteria used to evaluate the design were the following: (1) steady-state accuracy; (2) margins of stability against self-oscillation; (3) temperature variations; (4) aging; (5) static errors drift errors, and transient errors, (6) classical frequency and time domain characteristics; and (7) the equivalent noise at the input of the comparater operational amplifier. The DC feedback loop of the torque current generator was approximated as a second-order system. Stability calculations for gain margins are discussed. Circuit diagrams are shown and block diagrams showing the implementation of the torque current generator are discussed

Advances in Sensors and Sensing for Technical Condition Assessment and NDT

The adequate assessment of key apparatus conditions is a hot topic in all branches of industry. Various online and offline diagnostic methods are widely applied to provide early detections of any abnormality in exploitation. Furthermore, different sensors may also be applied to capture selected physical quantities that may be used to indicate the type of potential fault. The essential steps of the signal analysis regarding the technical condition assessment process may be listed as: signal measurement (using relevant sensors), processing, modelling, and classification. In the Special Issue entitled “Advances in Sensors and Sensing for Technical Condition Assessment and NDT”, we present the latest research in various areas of technology

Aerometry instrumentation study Final report

Techniques and instruments for meteorological measurements in Mars and Venus atmosphere

Measurements, Models, Systems and Design

531 s.

Vibrating transducers for fluid measurements

When a body vibrates in a fluid, some of the fluid is carried with it and the mass loading lowers its resonant frequency. Similarly, when compression of the fluid occurs, there is an added stiffness which by design can be made to predominate. In addition, there is an energy dissipation arising from viscous losses and acoustic radiation. The starting point of this research was a tuning fork with flat rectangular tines, designed to trap a narrow laminar of gas which is forced to pump in and out as the tines vibrate. The increase in kinetic energy, contributed by this high velocity' gas, gives the device a relatively large sensi ti vi ty as a gas density transducer. The change in frequency between vacuum and atmospheric pressure is typically a few percent, during which period the mechanical "Q" remains high enough to keep the fork sharply resonant. A high stability oscillator incorporating the transducer as the frequency controlling element was built. Small piezoelectric Cp2t) elements were used to drive the transducer and pick up the vibrations. A typical stability, equivalent to a pressure change of 0. 05 mBar was achieved. The supporting equipment re qui red for the work centred around a vacuum system with facilities for introducing a range of gases at precise rates. Computer control enabled the transducer's temperature, frequency, and "Q" factor to be measured and stored as the gas pressure was increased from vacuum. Extensive experiments were carried out on a range of tuning fork transducers, including a circular one in which a pair of disks clamped at the center acted as the tines and gave a simple radial gas displacement. Common to all these transducers is, the linearity of 1/f 2 with gas density for pressures above about 50 mBar; a departure from. linearity below this pressure; and below 10 mBar an overriding stiffness effect, where from vacuum to a few mBar the frequency paradoxically increases. The resultant calibration to this non-linear response, while exhibiting high stablility, is unattractive for general use. It has however applications over limited ranges as for example, those of a barometer or altimeter. Insight gained from experience with the double disk resonator, led to a new geometry which has resulted in an extremely viable transducer, without calibration anomalies, and capable of operating in a pressure or dehsity mode. Here, the gas is confined in two cylindrical cavities above and below a thin circular diaphragm, clamped at the periphery and again made to vibrate using p2t elements. In the fundamental mode, the alternating change in cavity volume due to compression and rarefaction of the gas, adds stiffness to the diaphragm. In the next mode, there is no net volume change, but the gas is pumped across the cavities adding inertial loading. No anomalies were experienced in the empirical calibrations obtained for each mode- the fundamental being linear with pressure Cf 2 proportional to Pl, and the first overtone linear with density (1/f 2 proportional to pl. A simple theory, which is sufficiently accurate for general design purposes, has been developed. Future work, which is of a straightforward development nature, is proposed. The high degree of stability achieved for these vibrating structures was later realised in a different geometry. In this, a long rod was excited into a torsional mode so as to produce two nodes a quarter wavelength from. either end. By securing the rod at these points and immersing the lower length in a liquid, a sensitive, robust, viscometer was produced. Driving the rod with a burst of oscillations, shears the liquid in contact with it. By removing this drive and measuring the rate of vibrational decay under the action of viscous dissipatiop, an indication of the viscosity can be obtained. The features of a pure shearing force, and the real-time, on-line nature of the device, makes it attractive for the characterisation of both thick and thin liquids and automatic process control

First International Symposium on Strain Gauge Balances

The first International Symposium on Strain Gauge Balances was sponsored and held at NASA Langley Research Center during October 22-25, 1996. The symposium provided an open international forum for presentation, discussion, and exchange of technical information among wind tunnel test technique specialists and strain gauge balance designers. The Symposium also served to initiate organized professional activities among the participating and relevant international technical communities. Over 130 delegates from 15 countries were in attendance. The program opened with a panel discussion, followed by technical paper sessions, and guided tours of the National Transonic Facility (NTF) wind tunnel, a local commercial balance fabrication facility, and the LaRC balance calibration laboratory. The opening panel discussion addressed "Future Trends in Balance Development and Applications." Forty-six technical papers were presented in 11 technical sessions covering the following areas: calibration, automatic calibration, data reduction, facility reports, design, accuracy and uncertainty analysis, strain gauges, instrumentation, balance design, thermal effects, finite element analysis, applications, and special balances. At the conclusion of the Symposium, a steering committee representing most of the nations and several U.S. organizations attending the Symposium was established to initiate planning for a second international balance symposium, to be held in 1999 in the UK