摘要:

A 7 kW voltage-sourced reversible rectifier (VSRR) which achieves bidirectional power flow between a single-phase AC supply and a DC busbar voltage is described. A current-forced control (CFC) strategy is used to switch two power transistors, enabling the device to operate with a unity power factor and a sinusoidal line current to produce a regulated DC busbar voltage. The advantages of the scheme are its simplicity, an extremely fast and well damped response and its adaptive nature to nonlinear effects such as transistor switching delays. Furthermore, the harmonic currents produced by multiple devices operating from the same point of supply do not add coherently because of their pseudorandom nature. The device operates with a DC busbar voltage which is greater than the peak-to-peak voltage of the utility supply so that it is especially suitable for use as a source of power in a variable-speed AC induction-motor drive.

DOI:10.1049/ip-b.1989.0028

出版商:IEE    

年代:1989

数据来源: IET

摘要:

Multiple prestriking transients are frequently produced in systems controlled by vacuum switching devices. The stresses that such transients produce in the windings of connected equipment cannot be accurately assessed until the characteristics of such transients have been evaluated. The paper describes solution methods for evaluating multiple prestriking transients in a source/cable/motor controlled with a vacuum switching device. A solution method based on the Fourier transform is developed. This method was chosen because of the wide range of frequencies which characterise multiple prestriking transients and the need to accurately represent parameters with frequency-dependent characteristics. The multiple prestriking condition is simulated by the reiterative use of voltage and current generators, and the piecewise Fourier transform is used to obtain the transforms of nonanalytic functions. A method is developed for modifying the usual piecewise Fourier transform expression so that it may be rapidly evaluated by fast Fourier transform techniques. A description is given of a series of studies made of a source/cable/motor system to determine which switch and system parameters are of significance in governing the number of prestrikes. It was found that the critical high-frequency current-interruption capability of the switch was the most significant factor in governing the number of prestrikes, but that a number of other parameters had an influence to a lesser extent.

DOI:10.1049/ip-b.1989.0029

出版商:IEE    

年代:1989

数据来源: IET

摘要:

The measurement of the capacitance and associated loss tangent over a range of voltages is a common method of assessing insulation condition. The work considers the use of such techniques for establishing aging trends and detecting abnormalities in high-voltage rotating plant stator insulation. Whereas the inherent accuracy of the technique, as determined by laboratory measurements, is good, measurements on site are shown to be subject to large variations. It is concluded that the variations below, discharge inception voltage are mainly due to environmental effects in the endwinding region, whereas discharge-related properties vary because of the time dependence of the discharge process. It is shown that, in some circumstances, environmental variability can be reduced by phase-to-phase comparisons.

DOI:10.1049/ip-b.1989.0030

出版商:IEE    

年代:1989

数据来源: IET

摘要:

The paper presents circuit configurations of a single-phase voltage-source AC-DC convertor for applications with a small output power, in which a regenerative capability is not required. In this circuits, MOSFETs are employed so that their integral reverse-conducting diodes are available for use. The supply current can be sinusoidally controlled with a near unity power factor by means of current reference hysteresis control The steady-state characteristics are investigated by experiments and state-space analysis. In addition, transient responses, with a PI controller using a microcomputer to keep the constant output voltage, are shown. These results confirm the usefulness of the presented circuit configurations.

DOI:10.1049/ip-b.1989.0031

出版商:IEE    

年代:1989

数据来源: IET

摘要:

The paper is concerned with the disturbance mechanisms which may exist between inverter-controlled asynchronous traction drives and low-frequency track circuits which commonly operate at industrial frequency. The paper presents a model for determining the input impedance of inverter-controlled equipment, such that the magnitude of a potentially disturbing interference current, due to substation-generated harmonics, may be calculated. The developed models are shown to be applicable to voltage-source inverters. Practical measurements using low-power inverter equipment are presented to support the proposed models.

DOI:10.1049/ip-b.1989.0032

出版商:IEE    

年代:1989

数据来源: IET