GB1030233A - Control circuit for electrical converters - Google Patents

Abstract

1,030,233. Phase changing. ALLMANNA SVENSKA ELEKTRISKA A.B. March 14, 1963 [March 17, 1962], No. 10084/63. Heading H2F. A phase-shifting circuit for controlling electrical converters comprises a bridge of two inductive or resistive arms, such as the two halves of the secondary winding 3 of a transformer 1, a reactive arm 4 and an arm including a current limiting member. In the arrangement of Fig. 2 the current limiting member comprises a bridge of diodes 7 and a transistor 8 whose base current Is determines the maximum current I circulating in the phase shifting bridge. In another embodiment (Fig. 5, not shown) the diode bridge and transistor is replaced by two transistors connected in series in opposite senses but controlled together. The transistor 8 (Fig. 2) may be protected against over-voltages (Fig. 6, not shown). Fig. 3 shows the voltages e 1 , e 2 at the ends of the secondary winding 3, and the current I in the phase shifting bridge which rises at a rate determined by the inductance 4 to a maximum value determined by the transistor. While the current I is rising the voltage across the transistor is small, so that the output voltage Es follows e 2 . When the transistor saturates the voltage across the inductance becomes zero, as the current is then constant, and Es then follows e 1 , so that there is a steep wave front in the output voltage. The height of this wave front depends on the value of I (Fig. 4, not shown). The circuit may control a converter valve directly or through a bi-stable circuit, and a polyphase converter may be controlled by a number of circuits according to the invention, each circuit sharing a common current limiting transistor (Fig. 7, not shown).