Patent GB-1428770-A (GB)
Title: Direct current power control arrangement
IPC: H02M3/137
Filed: 1973-03-01
Abstract: 1428770 Thyristor pulse generator circuits GENERAL ELECTRIC CO 1 March 1973 [3 March 1972] 9934/73 Heading H3T [Also in Division H2] A load 17 such as a D.C. motor is supplied with narrow-width pulses of power by the control circuit shown in Fig. 1, wherein a main thyristor 14 is fired by a gate circuit 28 to complete a circuit from a battery 10 through the load 17 and a capacitor 16, which turns off the thyristor 14 when it is fully charged. When a main switch 12 is closed, the capacitor 16 is charged through diode 22 and resistor 24, after which an auxiliary thyristor 20 is fired to reverse the charge on the capacitor, thus causing thyristor 20 to turn off and a capacitor 38 to be charged through a diode 34 and resistor 32. As a result of the last two actions, a transistor 30 is turned on to cause the thyristor 14 to turn on and supply a current pulse to the load until capacitor 16 is fully charged. Thereafter the firing of thyristor 20 causes the cycle to be repeated, the frequency of firing determining the power supplied to the load, since the pulse width is substantially constant at a narrow value determined by the RC time constant of the circuit comprising members 10, 14, 16, 17. The arrangement provides a low-level power of low ripple content and is used to drive the motor 40 in Fig. 2 at a low speed. High speeds are provided by firing a thyristor 48, which provides a high power, second mode of operation under the control of a pulse generator 60, a saturable transformer having primary and secondary windings 46, 58 and the components 14, 16, 20. In a typical high power cycle, the thyristors 20, 48 are fired sequentially by the generator 60 with the thyristor 20 fired a short time after thyristor 48. The charge on capacitor 16 drives the winding 58 into negative saturation, resulting in the capacitor charge being reversed, by which time the motor current will be driving the winding 46 into positive saturation to further increase the charge on capacitor 16. When saturation occurs, thyristor 20 is turned off by the capaitor 16 and causes a voltage reversal in the winding 58, in response to which the pulse generator 60 turns on the thyristor 14. The voltage on capacitor 16 now turns off the thyristor 48 and the motor current is diverted through members 14, 16, until the latter turns the former off. Thyristors 20, 48 are now fired again to commence another cycle. During interpulse periods a diode 90 carries the armature current minus the field current and a diode 92 carries the field current. A contactor 56 may be closed to shunt the thyristor 48 and apply maximum power to the motor. A circuit 86 provides plug braking of the motor, members 60, 86 comprising interconnected transistors, resistors, capacitors, diodes, amplifiers and a delay circuit, Fig. 3 (not shown). Plugbraking is effected by changing over contacts F1, F2 and R1, R2, the generated voltage so produced in the armature circulating through the shunting circuit of diode 90 and resistor 94. During plug-braking an inhibit circuit 62 is controlled by the circuit 86 to prevent firing of the thyristor 48, the generator 60 also being controlled by circuit 86 to prevent supply of low power to the motor through members 14, 16, 20, while the motor current exceeds a predetermined value. The inhibit circuit 62 is also described, Fig. 4 (not shown).