Three-phase Bridge Converter Research Articles

Complete Analysis of the Operating Modes of the Resistance--Inductance-Fed Bridge Rectifier

Equations describing the ac-dc terminal relationships of the resistance-inductance-fed three-phase full-wave bridge converter from no load to short circuit are provided. Modal boundaries are plotted in the µ-α plane showing the limits within which these equations are valid. Results show the resistance to have a significant effect on the terminal characteristics. Modal boundaries are shown to be nonlinear functions of the commutation resistance-direct current product.

Equivalence in Harmonics Between Cycloconverters and Bridge Converters

The similarity between a six-pulse three-phase cycloconverter operating in the circulating current-free mode and a six-pulse three-phase bridge converter is discussed analytically with regard to the rms value and the harmonics of the respective output voltages. A method is presented for calculating the rms voltage of a family of sideband frequencies which are generated in the output voltage of the cycloconverter. The results obtained from the analysis help to predict the amplitudes of subharmonics and beat frequencies with the cycloconverter and are essential for the design of the output filters. Analytical results are verified by comparison with those of experiment and digital computer simulation.

A Study of Asymmetrical Gating for Phase-Controlled Converters

The low power factor of phase-controlled converters when the output voltage is less than the maximum is of-concern in high-power equipment. In a converter consisting of two commutating groups in cascade, the usually low power factor can be improved by firing or gating the thyristors in the two groups asymmetrically. One of the groups is fully advanced (or retarded) to minimize its reactive power, while the other group is controlled to give the desired dc Output. The technique is not recommended for single three-phase bridge converters because of third-hannonic output ripple, second-harmonic line current distortion, and danger of commutation failure. These objections are overcome by combining pairs of three-phase bridges. When regeneration is not required, half of the thyristors can be replaced by diodes, reducing the cost. The method should offer substantial improvement in the power factor of cycloconverter ac motor drives as well as dc motor drives.

A System for Recording Thyristor and Rectifier Current Waveforms

To faithfully reproduce waveforms of both high-forward current and high-speed reverse recovery current in a high-power three-phase bridge converter is a difficult task. Ordinary dc shunts, or fuses which are sometimes used as shunts, are too inductive to satisfactorily reproduce the reverse recovery current. Noninductive shunts are available but suffer from several serious disadvantages which are explained in the paper. A system is described which overcomes all of these difficulties. It uses specially designed miniature through-type CTs that have good frequency response from dc through several hundred kHz. Saturation by the dc component is avoided by a core resetting scheme. A circuit is also described which relieves the CT of its burden thereby permitting reproduction of short-circuit currents without CT saturation.