GB1206212A - Improvements in or relating to d.c. converters and inverters - Google Patents

Abstract

1,206,212. Automatic voltage control. SIEMENS A.G. April 26, 1968 [April 28, 1967], No.19812/68. Heading G3R. [Also in Division H2] In a D.C./A.C./D.C. converting system wherein transistors T s1, T s2 Fig.1 are controlled to conduct alternately current from a D.C. source whereby to apply a rectangular A. C. waveform to a transformer T r1, the symmetry of voltage half cycles is maintained by a control circuit, including saturable reactors, which also provides automatic regulation of the transformers' rectified voltage to a load R L . Commutation. The control circuit includes square loop saturable reactors D r1, D r2 in which main energizing windings I are connect to secondary windings c, d, of a transformer T r2, so that when one core is being magnetized the other is being demagnetized. When, for example, D r1 is being magnetized the transistor T s1, which it controls through a thyristor T h1, is turned ON. When its core is saturated the current in R5 rises steeply, diode G r1 conducts, and the gate electrode of T h1 becomes more positive than its cathode. T h1 then fires and blocks transistor T s1 . In a similar manner D rz controls the conduction periods of T s2. Controlling Symmetry. If components are mismatched e.g. the saturable reactors D r1, D r2, then the magnetizing time of D r1 for example, is longer therefore the pulse width is somewhat longer so that capacitor C 1 will discharge to a greater extent than C 2. There will thus be a difference in potential between the centre of a potential divider comprising C 1, C 2 (actual mean value) and the centre tap of R 4 (reference value), which potential difference provides the symmetry control. Current will be caused thereby to flow from the tap point of R 4 via R 3 and reactor windings III. Reactor D r1 will therefore be more rapidly magnetized and D r2 more slowly, i.e. the pulse widths are made to approach the condition of exact symmetry. Voltage Regulation. A transistor T s3 in a regulator R is made more conductive or less conductive according to the value of output voltage to the load R L. This causes increase or decrease in current in the reactors control windings II, thus adjusting the magnetizing time of the reactors and hence the conduction period of the switching transistors T s1, T s2 which determines the output voltage magnitude. Push-pull switching circuits are illustrated in Figs. 5, 6 (not shown) and a full bridge switching circuit in Fig.4 (not shown).