GB1479449A - Digital control of electric supplies - Google Patents

Abstract

1479449 Automatic control CLARKE CHAPMAN Ltd 12 Feb 1975 [22 Dec 1973] 59718/73 Heading G3R An electric supply is controlled by deriving timing signals from a polyphase input, producing pulses at a rate determined by differences between actual and demanded voltage or current values, the pulses driving counters during periods defined by the timing signals, and using the outputs of the counters to control rectifiers by way of logic elements. As shown in Fig. 1, a three-phase supply is connected to input terminals 10, 12, 14. Each phase line contains a filter circuit 30 shifting the phase by 90 degrees, and a zero detection circuit 32, connected through NOR gates NO1-NO9 to reset terminals of six binary counters CO1-CO6. The counters are driven through NOR gates NO13- NO18 by pulses from a voltage controlled oscillator circuit 80, the frequency of which is determined by the relative magnitudes of a feedback voltage and a reference voltage on terminals 18, 16 respectively. The counter outputs are connected through NAND gates NA1-NA6 and amplifiers 50-60 to terminals 66 which supply gate signals to an array of SCR's, thereby regulating the quantity represented by the feedback at terminal 18. In one application, Fig. 3 (not shown), the supply is used to provide welding current over a series transistor current regulator circuit. An array of SCR's is connected in the input to the regulator circuit and controlled by a circuit as shown in Fig. 1 responsive to the voltage across the series regulator. Another arrangement, Fig. 4 (not shown), uses the circuit of Fig. 1 to control the speed and armature current of an A.C. or D.C. motor. The motor speed is measured by a tachogenerator producing a voltage or current representing the speed.