摘要:

The paper is concerned with the stability of closed-loop control systems incorporating controlled rectifiers. A suitable small-signal model for a convertor is developed which takes into account the discrete behaviour of the controlled rectifier. This model permits the use of standard sampled-data control-system theory in the stability analysis of the system. Contrary to usual practice, the a.c. system reactance is not neglected in the modelling. It is shown that the commutation angle is an important factor in the determination of stability boundaries. Finally, again-correction factor is employed to allow for the effect of the ripple under finite-commutation-angle conditions. Discrete Laplace transformation (z transformation) is used throughout the analysis together with root-locus techniques. Stability boundaries derived from the new model and other existing models are compared, and it is shown that experimental results are in good agreement with the theory developed in this paper.

DOI:10.1049/piee.1972.0255

出版商:IEE    

年代:1972

数据来源: IET

摘要:

The behaviour of the arc in the throat of an air-blast circuit breaker around a current zero is analysed by applying a simplified energy-balance equation to a constant-pressure model having a flexible radial temperature distribution and a variable conducting radius, as determined by a boundary-loss empirical formula derived from the steady v/i characteristic. Such a model, in a single-frequency-fault circuit, is examined on a computer, and clear/fail conditions are determined. Results may be simply displayed by a single curve using co-ordinates of suitably normalised combinations of arc and circuit parameters and initial conditions, if linear gas properties between σ, S and ∫ ρ dh are assumed. Alternatively, arcs with nonlinear gas properties may readily be examined in specific cases. The radial S distributions show considerable deviations from steady-state profiles; there are marked variations of instantaneous arc time constants, and the total loss varies widely. This model is therefore able to more faithfully follow real life than could simpler models used previously, and gives encouraging agreement with real test results of, say, voltage and current against time and (dG/dt)/G against power.

DOI:10.1049/piee.1972.0257

出版商:IEE    

年代:1972

数据来源: IET

摘要:

A general theory of the torque/slip and current/slip characteristics of solid-rotor induction machines is developed in terms of dimensionless coefficients, and its validity is demonstrated by measurements on machines in the range 6–1500 W. Generalised characteristics are presented in the form of curves of the dimensionless coefficients. The analysis is based on an expression for equivalent rotor impedance which is inversely proportional to the product of airgap flux and slip and which has a constant phase angle. Various methods of calculating eddy-current losses in solid rotors give impedances of this form, and the use of some of these in the generalised analysis is assessed.

DOI:10.1049/piee.1972.0258

出版商:IEE    

年代:1972

数据来源: IET

摘要:

The paper describes a digital simulation of a 3-phase model of a synchronous generator, directly in phase quantities. It is shown how, on the assumption that saturation arises principally from the resultant direct-axis current, the corresponding nonlinearities may be included in the equations of the model. The equations are developed in a form suitable for the study of both symmetrical and asymmetrical operating conditions of an isolated machine, and a digital-computer program using predictor-corrector techniques is described for their solution. Predictions of the transient conditions following a variety of switching operations are shown to compare closely with experimentally obtained results on a 15 kV A machine.

DOI:10.1049/piee.1972.0259

出版商:IEE    

年代:1972

数据来源: IET

摘要:

The paper is a review of the aims and experiences of the London Electricity Board, over the 23 years since its formation in 1948, in standardising all the major items of plant and equipment used in the supply of electricity to the inner areas of Greater London. During this period, a growth in demand of some 2400 MW has been met by replacement and reinforcement of existing systems using a very limited variety of standard designs and sizes. The review describes the development of the standard designs, which range from substation plant installed at points of bulk supply from the Central Electricity Generating Board to terminal equipment installed on the premises of domestic consumers. It covers switchgear, transformers, underground-link disconnection boxes and fusible cutouts for use at voltages ranging from 66 kV to 240 V.

DOI:10.1049/piee.1972.0260

出版商:IEE    

年代:1972

数据来源: IET

摘要:

The performance of a cylindrical-rotor generator, without damper windings, connected to an uncontrolled bridge-rectifier load, is considered. Assuming constant field-flux linkages, equations are derived which enable the performance of generators to be predicted. The commutation angle, the displacement angle and the field-current perturbation are the quantities which characterise generators with rectifier loads. Modification of the equations for a controlled bridge is discussed. The equations are supported by some practical tests on a laboratory machine.

DOI:10.1049/piee.1972.0263

出版商:IEE    

年代:1972

数据来源: IET

摘要:

The basic theory of solid-state slip-power-recovery systems is now well established. One of the disadvantages of such systems has been the lack of a suitable method of regenerative braking: this is frequently an important requirement for many applications. The paper describes two methods of incoporating regenerative braking in slip-power-recovery systems. One method requires a separate source of direct current and is called the ‘separately excited’ regenerative brake; the second method employs direct current from the d.c. link in the system and is called the self-excited system. Both systems are shown to be practicable and capable of operation down to speeds of at least 0.05 p.u.

DOI:10.1049/piee.1972.0264

出版商:IEE    

年代:1972

数据来源: IET

摘要:

A method of d.c.-power reversal with point-on-wave control and adjustable speed characteristics is proposed, and its implementation by integrated-circuit logic is described. The stresses imposed on the d.c. cable and convertor plant are calculated by dynamic-simulation techniques on a digital computer and a selection of results is used to demonstrate the feasibility of fast power-reversal control.

DOI:10.1049/piee.1972.0265

出版商:IEE    

年代:1972

数据来源: IET

摘要:

Suitable models for the analysis of internal oscillations in multibridge h.v. d.c. convertors are described. These oscillations may be due to blocking and deblocking operations, normal commutations between convertor valves and abnormal commutations resulting from the development of convertor faults. A digital-computer program is developed and used to investigate the most severe voltage and current oscillations expected at the convertor main valves and bypass valves.

DOI:10.1049/piee.1972.0266

出版商:IEE    

年代:1972

数据来源: IET

摘要:

An algorithm, based on the fixed-point contraction-mapping principle of functional analysis, for calculating the optimal controls for time-varying linear multivariable systems is considered. By an appropriate transformation of the operators involved, it is shown that the convergence rate may be maximised and that the resulting optimal algorithm will always converge. Comparison of the optimal algorithm with the steepest-descent and conjugate-gradient schemes shows the optimal algorithms to have significantly superior convergence rates, as well as requiring appreciably smaller computer storage.

DOI:10.1049/piee.1972.0270

出版商:IEE    

年代:1972

数据来源: IET