Patent GB-1002122-A (GB)
Title: Apparatus for controlling the polarity of electric current to a load
Inventor: PEARCE NOEL
IPC: H02M5/27
Filed: 1960-09-06
Abstract: 1,002,122. Phase-sensitive circuits. ENGLISH ELECTRIC CO. Ltd. Sept. 6, 1961 [Sept. 6, 1960] No. 30727/60. Heading H3A. [Also in Division H2] In a converter for supplying direct current of either polarity or low-frequency alternating current, one of two oppositely poled full-wave rectifiers, connected between the load and an A.C. supply, is selected in dependence upon whether the instantaneous values of the supply voltage and a reference voltage have the same or opposite polarity. In one arrangement (Fig. 1, not shown) two pairs of controlled rectifiers, each pair arranged as a bi-phase fullwave rectifier, are connected in opposite senses to the load. The reference voltage drives a circuit giving a pulse output at each polarity reversal, through a transformer with four secondaries, to each of the rectifiers. The one rectifier which has a forward anode to cathode applied voltage and the correct polarity triggering pulse is switched on. The other rectifier of the pair is switched in alternate half cycles. The reference voltage may be derived from the supply voltage through a Selsyn. In Fig. 2 the rotor winding 12 of a Selsyn 10 is fed from a single phase supply, and the stator winding 11 has induced in it a voltage whose magnitude and direction depend on the rotor position. Diodes D1, D2 and D3, D4 form fullwave bi-phase rectifiers, either of which may be switched on to the common load by controlled rectifiers CR1 and CR2. The control circuit for rectifiers CR1 and CR2 has a transformer T1 whose primary is connected to the supply and whose four secondaries 20, 21, 27, 28 are connected across diagonals of the phase-sensitive rectifiers 22, 23, 29, 30 through resistors R1, R2, R3, R4, and includes transformers T2, T2<SP>1</SP> whose primaries are connected across the stator 11, and whose secondaries are connected to the trigger and cathode of one of the controlled rectifiers through the phase-sensitive rectifiers as shown. Rectifier CR1 is controlled by windings 27 and 28 of transformer T1, phase-sensitive rectifiers 29 and 30, and transformer T2. When the reference and supply voltages are in phase, then for one half cycle the polarities are as shown in the Figure. Rectifier 29 conducts while rectifier 30 blocks, and consequently the trigger electrode of CR1 is made positive with respect to its cathode by the winding 31, and CR1 is switched on. For. alternative half cycles the same controlled rectifier is switched on by a voltage from winding 32 through rectifier 30. When the reference and supply voltages are out of phase, CR2 is similarly controlled. The conduction angle is always 180 degrees, but the output voltage depends on the Selsyn rotor position. When the Selsyn is rotated slowly at constant speed the output voltage waveform (Fig. 5, not shown) of this embodiment is a low-frequency sine wave with a ripple at twice supply frequency due to the full-wave rectification. The arrangement may be used to drive a permanent magnet synchronous motor for moving the control rods in a nuclear reactor. If the motor is polyphase one circuit is required for each phase, each being driven from a separate stator winding of the Selsyn.