US 4,399,395 A · Line-to-line voltage reconstruction for synchronizing thyristor power converter

Abstract

The effect of commutation notches 35 appearing in the nominally sinusoidal alternating current (AC) line-to-line voltage, for example, v.sub.ab used to synchronize the firing of thyristors in three phase, phase-locked power converters 12 and 14 is essentially eliminated by reconstructing the corrupted line-to-line voltage by summing the integral of the corrupted line-to-line voltage .PSI..sub.ab with a signal proportional to the product of the delta load current, for example, i.sub.ab and the commutation inductance L.sub.c. The composite waveform .PSI..sub.ab +i.sub.ab .times.L.sub.c) resulting from the summation has well defined zero crossings 41 from which synchronizing pulses are generated for synchronizing the phase-locked thyristor firing circuit 18 implemented by either software or hardware techniques. Additionally, the reconstructed waveform is used to control commutation, particularly in the control of a load side converter i.e. inverter 14 which is utilized in an AC motor drive system.

Claims30

Dependent claims

A method of generating a control signal for controlling a synchronization and commutation of thyristor firing circuitry included in a phase-locked electrical power converter coupled to a polyphase AC power line, comprising the steps of:

(a) deriving at least one voltage signal representing the line-to-line voltage on said AC power line;
(b) deriving at least one delta current signal indicative of the current in a phase of said AC power line;
(c) generating a pseudo flux signal waveform from said voltage signal;
(d) providing an electrical analog of the commutation inductance of said power converter and generating a product signal corresponding to the product of said delta current signal and said analog of the commutation inductance;
(e) combining said pseudo flux signal waveform with said product signal to provide a composite signal therefrom;
(f) thereafter generating said control signal from said composite signal;
and
(g) applying said control signal to said thyristor firing circuitry of said power converter.

5 more elements

Apparatus for generating a signal adapted to synchronize the firing of thyristors in a phase-locked power converter having a commutation inductance associated therewith and coupled to a polyphase AC power line comprising in combination:

(a) means providing at least one signal representing the line-to-line voltage on said power line;
(b) means for sensing the phase currents of said power line and providing at least one signal corresponding to the difference of two of said phase currents to provide a delta current signal;
(c) means for integrating said at least one signal representing the line-to-line voltage on said power line to provide a flux wave signal;
(d) means for scaling said delta current signal by a predetermined factor to provide a signal corresponding to the delta current signal multiplied by said commutation inductance;
(e) means for combining said flux wave signal with said scaled delta current signal to provide a composite signal substantially devoid of commutation notches while having substantially abrupt zero crossings;
(f) a phase lock loop for controlling the firing of said thyristors in said power converter;
and
(g) means for applying said composite signal to said phase-lock loop.

5 more elements

Dependencies are inferred from the claim text.

Line-to-line voltage reconstruction for synchronizing thyristor power converter

Life of this patent

Line-to-line voltage reconstruction for synchronizing thyristor power converter

Life of this patent

Abstract

Claims30