Patent GB-1055030-A (GB)
Title: Improvements in d.c. power converter circuits
IPC: H02M1/06
Filed: 1964-11-16
Abstract: 1,055,030. Control systems for consumption apparatus; inverting; control of D.C. motors. GENERAL ELECTRIC CO. Nov. 16, 1964 [Dec.27, 1963], No. 46645/64. Headings H2F, H2H and H2J. [Also in Division H3] D.C. or A.C. power in a load is con trolled by switching an SCR (of equivalent-see below) on and off at predetermined times and smoothing the resulting pulses, the switching of of the SCR being performed by a series resonant circuit of a capacitor, ar auxiliary SCR and a parallel corn bination of a linear and a saturable inductor, such that the saturated inductor resonates with the capacitor at the desired commutating frequency and the other inductor resonates with the capacitor at a lower frequency The SCR's may be replaced by another 2- or 3-electrode device which cannot be turned off at its gate electrode, e.g. a triac or power diac. In Fig. I an SCR 11 is gated (by means not shown) to switch D.C. power through a load 12, and a capacitor 19 is charged to the potential of the D.C. source, the firing of the SCR 11 blocking the diode 22 and thus holding the charge on the capacitor. An inductor 15 smooths out the pulses to provide a steady value of load current. To turn off the SCR, a gating pulse is applied to an auxiliary SCR 21, and the series resonant circuit 19, 17 executes a half-cycle to reverse the polarity of the charge on the capacitor, the diode 20 preventing any further change. The capacitor charging current has driven the inductor 18 to saturation, but now some of the current through the SCR 21 flows through 18 in the reverse direction, making it unsaturated. When the polarity of the capacitor voltage reverses, however, current flows through the inductor 18 in the original direction, driving it to saturation again and raising the potential of the point 25 above that of the supply. Both SCR'S are then turned off and the capacitor charge leaks away through the load. The reverse potential across the SCR's is limited by a diode 26. To ensure recharging of the capacitor 19 with low load currents, an auxiliary charging circuit is provided by inductor 27 and diode 28; this inductor releases its stored energy during the commutation period. Efficiency is increased due to the fact that the energy in the commutation period is partly discharged through the load and partly returned to the supply through diode 26. The auxiliary SCR 21 and diode 22 can be replaced by a bi-directionally conducting four- or five-layer device (" triac " -Fig. 2, not shown). In another embodiment (Fig. 3) the SCR 11 and diode 26 are replaced by a bi-directionally conducting five-layer diode 81 (" power diac "). Since this device has no gate electrode it is turned on by triggering a transistor 88 which when cut off allows capacitor 82 to charge up. At a certain potential, avalanche diode 84 conducts and applies the potentials on capacitors 82 and 87 in series to drive point 25 negative and fire the diode 81. A similar circuit comprising transistor 91 (of opposite conductivity type to 88), capacitors 82<SP>1</SP> and 87<SP>1</SP>, and avalanche diode 84<SP>1</SP> fires the diode 81 in the opposite direction; this circuit is triggered by the reversal of potential across capacitor 19, and causes the diode 81 to act in the same way as diode 26 in Fig. 1, the load being short-circuited by diode 16. In another version (Fig. 4, not shown) the SCR 11 and diode 26 are replaced by a " triac ", whose gating electrode is shorted by a transistor 57 triggered from the commutating capacitor 19 to prevent gating while the potential on the capacitor is being reversed. Inverters.-The invention can also be applied to a bridge-type power inverter (Fig. 5, not shown) using four circuits 17-22 with four SCR's 11 and four diodes 26; these may be replaced by " diacs " or " triacs " as described above.