Patent GB-1229699-A (GB)
IPC: H02M1/06
Filed: 1969-09-24
Abstract: 1,229,699. Static inverters. COMPAGNIE GENERALE D'ELECTRONIQUE INDUSTRIELLE LEPAUTE. 24 Sept., 1969 [2 Oct., 1968; 12 Dec., 1968], No. 46945/69. Heading H2F. In a series inverter comprising two controlled rectifiers 8, 11 (Fig. 1) in series across the D.C. source 1, 2, and each having its own quenching circuit including a series resonance circuit and auxiliary controlled rectifier, the maximum charge in the resonance circuit capacitor is limited to the voltage of the source to avoid damage to the main rectifiers. Quenching operation.- Considering the quenching circuit of main rectifier 11. Commutation capacitor C31 is previously charged from the D.C. source through R32, L7, CR8 and fuse 9. With main rectifier 11 conducting a gate pulse (from the same firing pulse source, not shown, as for the main rectifiers) is applied to auxiliary rectifier 33 which conducts and discharges C31 through CR33, L35, rectifier 11 and fuse 12 to the source terminal 2 in a damped oscillation. The oscillation period is determined by the values of L35 and C31. After three-quarters of the oscillation period the oscillatory current reaches a maximum in the opposite direction to that at the beginning of the discharge and to the conducting direction of CR11. This current passes through a diode 14 and together with current drawn from the load via L10 blocks CR11 turning it OFF, and from thence current passes through L35 and diode 34 (blocking CR33 and turning it OFF also) back to C31. Since CR33 is now OFF the oscillation terminates. The oscillatory current is not quite zero when interrupted because of the characteristics of diode 34. This results in h.f. oscillations in L35 with its distributed capacity. These oscillations are damped by a circuit including elements 51 to 57. A similar quenching circuit turns OFF main rectifier 8. After CR11 is quenched current from the load passing through inductor 10 and L35 in the same direction as the oscillator current resulting in a complementary charge in C31. The voltage in C31 will thus tend to exceed the source voltage E but this is limited by a diode 36 in parallel with R22 and which restores surplus energy to the source. In addition a circuit including a diode 71 in series with a resistor 72 shunted across inductor 10 absorbs energy stored therein to prevent accidental reenergization of the main rectifiers and also to limit the direct voltage applied to the main rectifier 11 to the value of source voltage E. Diode 61 and R62 perform the same function with L7 and rectifier 8. Diodes 17, 18 return energy from inductive loads, fed from output terminals 3, 4, to the source. In another embodiment of the inverter (Fig. 2, not shown) saturable inductors (107) (110) are arranged in series with L7, L10 and rectifiers 8, 11 across the D.C. source. These inductors have small reactance with normal current and a high impedance when the current is close to zero, and limit the rate of change of current through CR8 and CR11 to protect them on triggering. Each auxiliary CR is connected in parallel with the respective series resonance circuit and across the respective main rectifier through a diode. In this case the oscillatory current does not pass through the main rectifiers so that their rating can be reduced compared with the Fig. 1 embodiment.