GB1287116A - Inverters - Google Patents

Abstract

1287116 Static DC/AC converters THOMSON CSF 12 Nov 1969 [14 Nov 1968] 55477/69 Heading H2F In a D.C./A.C. converter as shown Fig. 7, having a D.C. supply 7 and comprising a three arm tank circuit including primary winding 1, primary winding 2 and a capacitor 3 respectively controlled rectifiers 5, 6 (e.g. thyristors or thyratrons) conduct alternately to supply positive and negative half cycles of sinusoidal current to a load 4. Controlled rectifiers 10, 11 in series with secondaries 9, 8 respectively are rendered conductive selectively to control the load current by returning energy to the source 7. When rectifier 6 conducts a half sine wave of current is applied to the load 4 via primary 1 and capacitor 3. When rectifier 5 conducts rectifier 6 is blocked and the capacitor 3 discharges through primary 2 providing the next half sine wave. Control of load current. If during the conduction period (0 to t 4 ) of the rectifier 6, the rectifier 10 is turned on, then the energy stored in primary 1 is no longer passed to the capacitor 3 and the load, but is returned to the source via the secondary 9. Thus the load current is cut-off when rectifier 10 is turned on. Fig. 8(a) shows the secondary voltage cosine curve during the period 0-t 4 when rectifier 6 is conductive. As long as the secondary voltage is lower than the source voltage E 0 , i.e. until time t 2 , the rectifier 10 cannot conduct. As shown it is turned on at time t 2 and the srcondary voltage drops to the level E 0 and as a result load current as shown in full line Fig. 8(b) drops to zero. Figs. 9(a), 9(b) show the secondary voltage and load current conditions respectively when the rectifier 10 is turned on at time t 3 , i.e. preceding the turn on of main rectifier 5 by a smaller angle # compared with Fig. 8. Thus the load current is proportional to the angle # and the inverter power output can be controlled by varying the magnitude of #. The effect of the turning on of rectifier 11 is similar in the alternate half cycles. In an inverter, Fig. 11 (not shown), several groups of circuit elements as shown Fig. 7, are combined, each group being connected to a respective primary of a transformer the single secondary of which is connected to the load 4, and the groups may be controlled to operate simultaneously or successively. In the latter case the output may be a frequency modulated wave train.