Patent GB-991862-A (GB)
Title: An inverter for producing an alternating current in a load from a direct current power supply
IPC: H02M7/515
Filed: 1962-02-01
Abstract: 991,862. Inverting. GENERAL ELECTRIC CO. Feb. 1, 1962 [Feb. 23, 1961], No. 3869/62. Heading H2F. [Also in Division H3] An inverter circuit utilizing semi-conductor controlled rectifiers for conversion, also includes at least one further pair of semi-conductor controlled rectifiers and a series circuit of inductance and capacitance to effect commutation. As shown in Fig. 1, current is supplied to a load 17 in alternate directions through S.C.R.'s 11 and 12 from a centre-tapped D.C. source 16. With current flowing in rectifier 11, a capacitor 18 is charged as shown, this capacitor together with an inductor 19 and a controlled rectifier 18 completing a series circuit through a diode 21 which is disposed across, but reversely poled to, the rectifier 11. For commutation, the rectifier 13 is gated on causing the capacitor to discharge through the series circuit and provide a reverse voltage across rectifier 11 to cut this off. Subsequently the rectifier 13 cuts off, and a firing pulse then gates rectifier 12 into conduction for alternate current flow. A corresponding commutation procedure is effected bythe components 18, 19, 14 and 22 for this rectifier. Voltage curves for points 23, 24 and 25 (output voltage) are indicated in Fig. 13 (a). Developments of this arrangement include a single-phase bridge circuit (Fig. 2, not shown), which is in essence a duplication of Fig. 1, a single-phase bridge in which only one L.C. circuit is used, additional controlled rectifiers being provided (Fig. 4, not shown), a threephase bridge (Fig. 5, not shown), and a " biphase " inverter (Fig. 3, not shown). In Fig. 6, the single-phase bridge (11, 12, 11<SP>1</SP>, 12<SP>1</SP>) includes cushioning and transient-limiting networks such as R.C. circuits 81, 82 across the commutating rectifiers 13, 14, 13<SP>1</SP>, 14<SP>1</SP>, circuits 83, 84, 85 across the main rectifiers and saturable transformers 89, 89<SP>1</SP>. A circuit for producing signals to control the rectifiers of Fig. 6 is disclosed in Fig. 14 which shows a unijunction transistor oscillator 101 and two transistor circuits 102, 103 which supply, through various saturable reactors, the required time-delayed phases. One base of the transistor 104 is connected to the centre tap of a saturable transformer winding 105 whose ends are connected to a negative terminal through pairs of reversely poled diodes. Signals at the junctions of these diodes from lines 142, 143 selectively connect the ends of winding 105 to the negative terminal. Inductively coupled with the winding 105 is a winding 111 which is energized in alternate directions and is in the base circuit of the transistor inverter 102 whose output across a transformer winding 114 feeds, through a current limiting circuit 119, a saturable transformer 124. This transformer feeds gating circuits in the main inverter. The winding 114 is also coupled with windings 127, 128, to produce further gating signals. The inverter 102 also supplies triggering potentials to the inverter 103 through a magnetic amplifier 135 in series with a wave-shaping circuit across the winding 114. This shaping circuit including a saturable reactor 138 which is inductively coupled to the signal winding 1111. The inverter 103 is similar to 102 and supplies further gating pulses. An output from the inverter 103 is supplied to lines 142, 143 to synchronize the pulses of the unijunction oscillator. A basically different form of the invention is disclosed in Fig. 7, which discloses two back-toback commutating controlled rectifiers 201, 202 in series with the capacitance and inductance 203, 204. As shown, current from a centretapped D.C. source is supplied to a load in alternate directions through main rectifiers 205, 206, and for commutation the appropriate rectifier 201 or 202 is fired to complete a series circuit through a diode 207 or 208 to shut off the conducting main rectifier. In developments a pair of capacitors are used (Fig. 8, not shown), single-phase bridges are disclosed (Figs. 9 and 10, not shown), a biphase circuit is disclosed (Fig. 11, not shown) and a polyphase bridge is disclosed (Fig. 12, not shown).