| 摘要 |
992,828. Inverting. M. ETTER. July 31, 1963 [Aug. 13, 1962], No. 30315/63. Heading H2F. A converting arrangement comprising series thyristors 5, 6, shunted by reverse diodes 3, 4, and disposed across a D.C. supply, includes an arrangement to extinguish the conducting thyristors. As shown in Fig. 1 a 3-phase supply for a motor M is derived from a D.C. supply at ab through a polyphase bridge arrangement, the frequency of the firing pulses and the duration of the conducting periods of the thyristors being variable to vary the frequency and amplitude of the output. In order to extinguish all the conducting thyristors these are all fired simultaneously causing a capacitor 16 in a resonant circuit 16, 17 to become reversely charged. When this capacitor discharges again it causes a reverse current through the thyristors to extinguish these. In order that the short circuit occurring when all the thyristors fire may not cause excessive current, the primary winding 9 of a transformer 10 is included in the D.C. line; the secondary winding 11 of the transformer is in series with a diode 12 which prevents secondary current on rising forward line current so that the winding 9 behaves as an inductor. After the thyristors are blocked current in the motor continues through the diodes 3 and 4 flowing in the reverse sense through the supply ab; thus the current in the winding 9 is reversed tending to cause an overvoltage, but this is prevented by the presence of the secondary winding 11, secondary current flowing back to the supply through the diode 12. A further protective circuit comprises a capacitor 18, diode 15, inductance 13 and resistance 14. The resonant circuit 13, 18 has a period twice that of the circuit 16, 17 so that the capacitor 18 is discharged when the thyristors are extinguished. This arrangement limits the voltage arising across the series thyristors. In a further arrangement (Fig. 3) by which A.C. may be supplied to a resistive load 19 or by which current may be supplied in either direction to a reversible D.C. motor, the centre tap of a D.C. supply is earthed as is one end of the load 19 whose other end is connected to the junction of thyristors 5, 6. A capacitor 22 is charged through a diode 35. To extinguish a conducting thyristor a further thyristor 24 is fired allowing the capacitor 22 to discharge through an inductor 23 with which it forms a resonant circuit. The inverse voltage produced extinguishes the thyristor and the thyristor 24 is extinguished by its own resonant circuit 25, 26. Inductors 27, 28 shunted by resistors 29, 30 are provided to prevent rapid current rise, and diodes 31, 32 are provided for reverse supply to the load. A modification of the connections of thyristors 5, 6, and diodes 3, 4, which includes additional diodes is disclosed (Fig. 4, not shown). |
