Patent GB-1529878-A (GB)
Title: Dc electronic control systems
IPC: G05F/
Filed: 1975-12-18
Abstract: 1529878 Commutating converters ATELIERS DE CONSTRUCTIONS ELECTRIQUES DE CHARLEROI 18 Dec 1975 [27 Dec 1974] 51935/75 Heading H2F A D.C. electronic control system comprises a first circuit having at least one controlled electrode semi-conductor switch in anti-parallel with a respective diode, and having a first end connectible to one terminal of a D.C. supply and a second end connectible to a load-supply conductor; a second circuit having at least one controlled electrode semi-conductor switch in anti-parallel with a respective diode, and having a second end connectible to the load-supply conductor; an oscillating circuit connected in series with the second circuit between the one terminal of the D.C. supply and the first end of the second circuit; and at least one control signal generator for supplying firing signals to the semi-conductor switches alternately, the polarities of the switch and diode in the second circuit being oppositely arranged with respect to those of the first circuit, whereby oscillatory currents may be permitted to flow in a closed loop defined by the two circuits and the oscillating circuit. Figure 1 shows the application of the invention to control a D.C. motor 1 energized from a battery 2 or, if the motor is used for traction, from a D.C. supply applied through a pantograph and filter circuit, Fig. 2 (not shown). Two series-connected combinations, each comprising a thyristor 6 in antiparallel with a diode 7, are connected in series with the motor and in parallel with the series circuit consisting of a capacitor 11, inductance 10 and two seriesconnected combinations, each comprising a thyristor 8 in antiparallel with a diode 9. Signals from generators 13, 14 make the pairs of thyristors 6, 8 alternately conductive at a constant frequency to supply the motor with a desired voltage. In a typical cycle of operations, Figs. 3 to 6 (not shown), for successive firing of the thyristors 6, 8, the following sequence occurs:- (1) Thyristors 6 are fired at time to to produce a current I through the motor, the capacitor 11 having an initial voltage U poled in the conducting direction of thyristors 8. (2) At time t 1  the thyristors 8 are fired and an oscillatory current i flows firstly through members 6, 8, 10, 11 to reverse the capacitor voltage at a time t 2  and secondly through members 7, 9, 10, 11 to turn off the thyristors 6 when the oscillatory current i equals the motor current I at a time t 3 , thyristors 6 and 8 being reverse-biased by the forward voltages across the diodes 7, 9. (3) After time t 3  the oscillatory current i peaks, then falls to equal the motor current I at time t 4 , remains constant at this value until time t 5  at which the diode 5 becomes forward-biased to pass a current of (I-i), and finally falls to zero during time t 5  to t 6 . During the period t 2  to t 6  the capacitor 11 charges to its original polarity and reaches a final voltage of U+e, a value which is maintained during subsequent cycles of operation. The voltage E across the motor reduces at time t 4  to the difference between the source voltage U and capacitor voltage u, and then falls to zero during the period t 4 -t 5 . If it is desired to maintain a voltage U across the capacitor 11 during operation, members 15, 16 are added to the circuit. The voltage U is reached aperiodically after time t 5 , Fig. 5 (not shown), by suitable choice of the values of members 10, 11, 15.