摘要:

The paper deals with variable-speed drives using an induction machine with wound rotor, controlled by variation of an external rotor resistor by a parallel electronic chopper. After tracing the historical development of this type of controlled drive, the power-flow relationships are investigated to arrive at the fundamental characteristics of this type of system. Considerations leading to the selection of a variable-slip system with rotor control rather than stator control are covered, leading to a discussion of the structure for a simple variable-speed drive using a force-commutated rotor chopper. The system is modelled by idealising the power switches and analysing their behaviour as function of slip, and the switched induction machine is modelled by a torque directly proportional to chopper input current. A second-order total system model is arrived at by taking only a speed-loop time constant and a mechanical time constant into account. Particular attention is given to establishing design relationships for this kind of drive. Component ratings, rotor resistor value and commutation requirements are related to operational requirements such as maximum slip, minimum torque, rated current and minimum expected current. No detail of power-chopper design is given. Some practical characteristics of typical variable-speed drives in the 11 kW to 22 kW range arc presented to illustrate the validity of the approach taken in analysis and design. These results indicate that the simple analysis presented is adequate for understanding and predicting the steady-state behaviour of the system. The second-order model gives sufficient accuracy in predicting dynamic behaviour to be useful for the design of systems in the response range normally applicable to this type of drive in practice. When designing systems for fast dynamic response, the modelling will have to be improved.

DOI:10.1049/ij-epa.1979.0025

出版商:IEE    

年代:1979

数据来源: IET

摘要:

This paper proposes a novel method for decreasing the undesirable torque-vibration of a 2-phase servomotor in an unbalanced-drive condition. The cancellation is achieved by superposing odd harmonic signals on the voltage applied to the control winding. A testrun indicated that the vibration on the shaft could be reduced to ⅛ by cancelling the second and the fourth harmonic components.

DOI:10.1049/ij-epa.1979.0026

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The paper describes the constraints on the selection of the pulse-width-modulated sinewaves produced by a 3-phase inverter. An example of a 7.5 kW induction-motor drive is used to demonstrate how waveforms can be selected to ensure an almost constant flux density throughout the required frequency range, together with a minimum motor loss. A comparison is made between experimental and theoretical results for the performance of the motor, and also between the performances when fed with sinusoidal and with pulse-width-modulated waveforms.

DOI:10.1049/ij-epa.1979.0027

出版商:IEE    

年代:1979

数据来源: IET

摘要:

Capacitive-coupled amplifier-type voltage transformers are described that are used to measure voltages in metal-clad h.v. switchgear. The stack capacitor of an active voltage divider forms a part of the switchgear itself. Tests and long-term experience in substations show the accuracy and long-term stability to be better than 0.2%. Tests on the dynamic performance are discussed.

DOI:10.1049/ij-epa.1979.0028

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The technique of ‘shorting-coil’ switching proposed in this paper provides a novel method of static power conversion. It overcomes the restrictions imposed by the voltage/current ratings of the available power, semiconductor devices and conventional convertor circuit configurations. This is achieved by modulating flux waves in multilimb magnetic circuits via auxiliary windings called shorting coils.

DOI:10.1049/ij-epa.1979.0029

出版商:IEE    

年代:1979

数据来源: IET