Patent GB-1047681-A (GB)
Title: Improvements relating to inverter frequency changer circuits
Inventor: PELLY BRIAN RAYMOND
IPC: H03K3/282
Filed: 1963-03-26
Abstract: 1,047,681. Automatic voltage control. WESTINGHOUSE BRAKE & SIGNAL CO. Ltd. Nov. 29, 1963 [March 26,1963], No. 11882/63. Heading G3R. [Also in Divisions H2 and H3] In an inverter circuit a capacitor C1 is discharged by the operation of switching means (as shown a thyristor CR2) through an inductor L1 into a tuned circuit C2 L2, causing this to oscillate, the tuned circuit comprising or being in parallel with a load, and the capacitor C1 being charged from a D.C. source through a further thyristor CR1. As shown Fig. 1 the D.C. source includes an input filter C3, L4, and the circuit values are such that the frequency of the circuit L2 C2 is high compared with the frequency of switching CR2. In operation C1 is charged resonantly through L3 when CR1 is fired and after half a cycle the current through CR1 falls to zero. CR1 stops conducting since the voltage on C1 is greater than the supply voltage. CR2 is then fired and discharges C1 through L1 into the tuned circuit. The current through CR2 is also oscillatory and after a period of time depending on the circuit values this current ends to zero and the thyristor is shut off. The circuit values are chosen such that the tuned circuit-to which a pulse of energy has been givencompletes several oscillations before CR2 is again fired. In a modified arrangement (Fig. 3 not shown) four capacitors C1 are provided each with its own charging and discharging thyristor. These are fired sequentially, the firing pulse frequency being eight times that of the circuit L2 C2. The voltage output of the arrangements of Figs. 1 and 3 is dependent on the triggering frequency and on the load and automatic regulation by feedback to control the triggering frequency is envisaged. Similarly protection against excess current may be effected by a feedback arrangement to reduce the triggering frequency. In a modification (Fig. 5 not shown) a push-pull arrangment is disclosed in which the LC circuit L2 C2 is the secondary circuit of a transformer whose primary winding is centre tapped, the halves being fed by circuits as in Fig. 1. In a further arrangement (Fig. 6 not shown) the tuned circuit connected between the centre tap of a D.C. supply and the common junction of a pair of circuits such as Fig. 1, one to supply negative pulses and the other to supply positive pulses. Another arrangement (Fig. 7 not shown) discloses a circuit which is essentially a "series inverter" as contrasted with the "parallel inverter" of Fig. 5. Thyristor CR1 is fired to charge C1 resonantly so that this thyristor is eventually shut off. CR2 is then fired discharging into the load circuit and becoming shut off, the LC circuit providing higher frequency oscillations. CR11 and CR21 are similarly rendered conductive and the cycle is then repeated. It is contemplated that CR1 and CR21 could be rendered conductive simultaneously as could CR2 and CR22 but this method is not discussed. The use of additional bursts of energy by duplication of elements as in Fig. 3 is contemplated for the embodiments of Figs. 5, 6 and 7. In a further modification Fig. 9 not shown the components L1, L11, CR2, CR21, of Fig. 7 are replaced by a saturable reactor, a triggering circuit for this circuit being disclosed in Fig. 11 (not shown). A circuit for charging a low polyphase current to a higher single phase current is also disclosed, Fig. 12 (not shown).