DOI:10.1049/piee.1967.0015

出版商:IEE    

年代:1967

数据来源: IET

摘要:

The paper describes a 3-phase thyristor convertor with good input/output-voltage linearity and compensation for mains fluctuations. A form of electronic protection is used which safeguards the controller from faults, yet allows a margin of overcurrent capability. The firing circuit of the controller consists of tristable transistor circuits which appear to be especially suited to driving a 3-phase system of thyristors. Details of performance are given.

DOI:10.1049/piee.1967.0016

出版商:IEE    

年代:1967

数据来源: IET

摘要:

Temperature distributions in a 400kV through joint and associated cable, as used in directly buried transmission circuits, are obtained for natural cooling and various forms of artificial cooling. The joint, rather than the cable, is seen to limit the current rating for all forms of cooling. With the higher ratings resulting from artificial cooling, the joint limitation becomes more severe. In all the cases considered, including the use of water jackets around the glass-fibre box surrounding the joint, the conductor temperature at the centre of the joint is above 85°C when the rating is decided by the cable alone. A thermal resistivity of the soil of 120degCcm/W, and a maximum coolant-temperature rise of 20degC are assumed. Investigation into joint power factors in the. range 0.004–0.008 shows a large temperature dependence with natural cooling, but small dependence with artificial cooling.

DOI:10.1049/piee.1967.0017

出版商:IEE    

年代:1967

数据来源: IET

DOI:10.1049/piee.1967.0019

出版商:IEE    

年代:1967

数据来源: IET

摘要:

It is shown that the calculation of the performance of a class of suboptimal linear control systems is similar to the calculation of the performance of an equivalent optimal system. The performances of both optimal and suboptimal linear systems have terms for cost owing to uncertainty about the initial state of the plant, a nonzero mean of the initial state, error in the estimate of the state, and error in control owing to additive noise at the input. A suboptimal system, in addition to having greater costs than the optimal system for each of these terms, has a cost term which vanishes if either optimal control or optimal estimation is used.

DOI:10.1049/piee.1967.0020

出版商:IEE    

年代:1967

数据来源: IET

摘要:

A method of transient analysis which applies to autonomous and nonautonomous nonlinear systems of any order or configuration is presented. After noting that the transients which occur in such systems may be represented by an exponentially damped sinewave with time-varying damping and frequency, it is shown, by assuming the damping and frequency to be piecewise constant, that the nonlinearity in the system may be adequately characterised by an equivalent gain for transient phenomena. The equation governing the damping and frequency is then derived and shown to be nonlinear. An approximate solution of this equation is obtained, and a method is then developed for calculating the error in the approximation. Application of the theory to a bang-bang position-control system and a position-control system with resetter backlash illustrates the technique for systems with single-valued and phase-shifting nonlinearities. It is shown that the accuracy of prediction is similar to that obtained when the describing-function technique is used to predict limit cycles. Finally the results from this method are compared with those based on the describing-function characterisation, and it is found that appreciable improvement in the accuracy of prediction is obtained.

DOI:10.1049/piee.1967.0021

出版商:IEE    

年代:1967

数据来源: IET

摘要:

In a simplified analysis of thyristor amplifiers in closed-loop control systems, the amplifier is represented at all frequencies by its d.c. gain, and the effect of the output ripple voltage is neglected. This approach is inadequate for wide-bandwidth systems, and fails to predict the occurrence of ripple instability. A more accurate analysis is made in the paper, taking into account the sampling action of the amplifier in the presence of alternating component voltages in the loop. Ripple instability is characterised by the generation of continuous oscillations at a subharmonic of the balanced-amplifier ripple frequency, and manifests itself in the amplifier as a periodic variation in the firing pattern. The behaviour of anm-phase amplifier in an otherwise linear system of any order is investigated, and an exact analysis is given for subharmortic oscillations of order ½. At the ½-order, and other, subharmonic frequencies, describing functions are derived, and the amplifier response is seen to differ markedly from the simple assumption of constant gain at all frequencies. The describing-function technique is extended to evaluate phase margins which must be satisfied at the various subharmonic frequencies to prevent ripple instability, thus allowing a straightforward design technique based on conventional frequency-response methods. The results of the analysis are compared with experimental results from regulated power-supply systems, and good agreement is reached.

DOI:10.1049/piee.1967.0022

出版商:IEE    

年代:1967

数据来源: IET

摘要:

Whiteley's demodulating compensating network for use in a.c. servomechanisms is analysed in a phase-lag mode of operation. The transfer function is derived, and the notch frequency is shown to be related to the reference carrier frequency. The criterion that (ωsT)2≫ 1 must be satisfied is discussed.

DOI:10.1049/piee.1967.0023

出版商:IEE    

年代:1967

数据来源: IET

摘要:

Contrast-transfer characteristics based on a simplified model of a retinal receptive field using a very limited number of receptors are described. The model is linear for given luminance levels. Of the many possible methods of switching these models, the one chosen uniformly changes the weighting coefficients associated with all receptors and is expressed as a change in static-transfer coefficient. Contrast-transfer characteristics are given as a function of optical-signal size (or spatial frequency) for various binary patterns. These characteristics may be used to select a compromise condition between the static- and contrast-transfer requirements of a pattern preprocessor, which in turn is a compromise between detectability and processing fidelity of signals.

DOI:10.1049/piee.1967.0024

出版商:IEE    

年代:1967

数据来源: IET

摘要:

A method is described for automatically focusing a high-power optical microscope using an extremum controller. The principle used is that of maximising the amplitudes of certain high-frequency components of a signal derived by scanning the object. The optimum bandpass filter required in selecting these frequency components is derived on the basis of expected power spectra, and the reasons for deviating, somewhat from this optimum are explained on the basis of the statistical variations in harmonic amplitudes of practical objects. A practicable system employing a peak-holding controller is described, in which the average hunting excursion about focus is less than the normally accepted depth of focus of the optical system.

DOI:10.1049/piee.1967.0025

出版商:IEE    

年代:1967

数据来源: IET