摘要:

Flux control in AC cage induction motor drives using third harmonic voltages and currents in star and delta connected machines, respectively, has been proposed and developed by a number of authors. To date, measured third harmonic components have enabled an accurate estimation of the airgap flux magnitude and a good estimate for its phase angle. This paper investigates the basis and the operating range of control techniques utilising these components, and describes steady state and dynamic characteristics for constant flux controllers based on observations of the triplen currents circulating in the delta winding of a machine. It is shown that the principal assumption inherent in the method, namely that there is a direct relationship between the airgap flux and the measured third harmonic component is not always valid so that the general applicability of the technique is restricted. Experimental results are presented for both steady state and transient conditions to determine the useful operating range that may be expected of drives under this strategy.

DOI:10.1049/ip-b.1992.0060

出版商:IEE    

年代:1992

数据来源: IET

摘要:

TORUS is a compact electrical machine particularly suitable for use as an engine-driven generator and which, when supplied via suitable switching circuits, can operate as a brushless DC motor to start the engine. The machine is of simple and cheap construction and gives high efficiency. The use of Neodymium-Iron-Boron permanent magnets gives good utilisation and small overall size and weight. Several 2.5 kW prototype machines have been built and tested, and have demonstrated all aspects of performance and capability of the TORUS configuration in the generating mode.

DOI:10.1049/ip-b.1992.0061

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Based on a conventional tap changer, a new diverter switch is described which features a single transition resistor and thyristor assisted suppression of arcing at the switch contacts. A simple arrangement of mechanical switch contacts ensures that the thyristor pairs used for arc suppression are only connected and triggered for a short interval of time prior to, during and after the operation of the switch contacts. A thyristor malfunction will not result in damage to the tap selector or transformer.

DOI:10.1049/ip-b.1992.0062

出版商:IEE    

年代:1992

数据来源: IET

摘要:

In this paper a passive waveshaping method for a three-phase diode rectifier is presented. It is shown that application of the proposed passive method yields a significantly higher input power factor, a lower input current distortion factor, a lower input RMS current and a lower total volt-ampére (VA) rating of the reactive components than the conventional three-phase diode rectifier. Relevant input and output current waveforms, component ratings, and power factor values are derived. Different modes of operation are investigated as a means of improving performance. Finally, predicted results are verified experimentally on a laboratory prototype unit.

DOI:10.1049/ip-b.1992.0063

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The paper investigates the dynamic representation of a group of induction motors by one or more equivalent motors for power system transient stability studies. Considering the fact that large induction motors constitute a large proportion of the total system load, and that the skin-effect has a very strong effect on the performance of these machines, this effect is therefore included in the model. To enable the skin effect (deep bar effect) to be included, the stator and the rotor windings leakage reactances are separated and the core losses are ignored; and the equivalent machine is represented by seven electrical parameters instead of the conventional five parameters. A clear procedure is described on how to obtain the unknown electrical and the mechanical parameters of the equivalent machine. An efficient grouping (homogeneity) criteria is proposed to obtain subgroups in the case of a diversified group of induction machines connected to the same bus and a power system subjected to disturbances of various types. The accuracy of the equivalent model is verified by simulating its response to different types of disturbances and comparing the results with the sum of the responses of the individual machines. Excellent agreement is obtained between the response of the model and the sum of the responses of the individual machines.

DOI:10.1049/ip-b.1992.0064

出版商:IEE    

年代:1992

数据来源: IET

摘要:

A comprehensive analytical study is presented of the current waveforms of a hybrid permanent-magnet synchronous/stepping motor exhibiting dynamic instability. It is shown that, in the stepping-motor mode the lower-modulation envelope of the total intake-current waveform is the source of a suitable stabilising signal. A low-cost stabilisation scheme is developed which utilises this signal to frequency-modulate the supply voltage. Stable operation to 10000 step/s, under conditions of significant torque loading, is demonstrated for a 200 step/revolution bifilar-wound stepping motor.

DOI:10.1049/ip-b.1992.0065

出版商:IEE    

年代:1992

数据来源: IET