Control system for firing scr{3 s in power conversion apparatus

Claim 2

In a digital control system for controlling the flow of power from an AC source to a load comprising in combination controllable rectifiers poled in opposite directions, connected between the AC source and the load, a digital error generator, phase detection logic means operatively connected to the AC source, an output of said phase detection logic means occuring at the earliest point in each half cycle of the AC wave at which one of said controllable rectifiers is permitted to conduct, and a clock generator, an improved firing circuit including: a. a counter operatively connected to said clock generator and to said phase detection logic means, to cause a predetermined digital number to be preset into said counter upon the occurrence of an output signal from said phase detection logic means, said counter contents thereafter being counted by said clock generator; and b. comparison means operative connected to said counter and to said digital error generator, said comparison means being operative to generate an output when a predetermined relation between the contents of said digital error generator and the contents of said counter changes, said output resulting in the generation of a firing pulse for a selected one of said controllable rectifiers.

Claim 3

A digital firing circuit as recited in claim 1 wherein said counter is a reversible counter which counts in one direction when an AC source voltage is positive in polarity and in the other direction when said AC source voltage is negative in polarity.

Claim 4

The digital firing circuit as recited in claim 1 wherein said counter is a reversible counter adapted to count down when the AC source voltage is positive in polarity and to count up when the AC source voltage is negative in polarity, and where said predetermined digital number is positive when the AC source voltage is positive and negative when the AC source voltage is negative.

Claim 5

The digital firing circuit as recited in claim 2 wherein said change in predetermined relation sensed by said comparison means is a change in the sign of the difference between the contents of said digital error generator and the contents of said counter.

Claim 6

The digital firing circuit as recited in claim 4 wherein said comparison means produces a firing pulse for said positively poled controlled rectifier when the contents of said digital error generator exceed the contents of said reversible counter, and produces a firing pulse for said negatively poled controlled rectifier when the contents of said reversible counter are greater than or equal to the contents of said digital error generator.

Claim 7

The digital firing circuit as recited in claim 1 wherein the combination includes a dynamoelectric machine as a load.

Claim 8

A digital firing circuit as recited in claim 1 wherein said phase detection logic means operates to initiate possible conduction during at last 120* of each half cycle of the AC input and continuing through the first 60* of the following half cycle.

Claim 11

The method set forth in claim 8 wherein the signal of step (b) presets a predetermined digital number of given polarity into the counter and thereafter controls the direction of counting thereof.

Claim 12

The method as set forth in claim 8 wherein step (b) comprises generating a signal at 120* advance during each half cycle.

Claim 13

In a digital firing circuit operative to fire either polarity of oppositely poled controllable rectifiers connected between an AC source and a load in response to a digital error signal, the improvement comprising: a. A digital counter arranged to count at a predetermined rate; b. phase detection logic means for sensing the earliest point in each half cycle of the AC wave at which a firing pulse can be generated, the output of said phase detection logic means being operatively connected in said digital firing circuit to define a control interval in which a predetermined digital number is preset into said digital counter, said digital counter thereafter counting in a predetermined direction from said preset number; and c. a digital comparator hAving operatively connected thereto the digital error signal and the contents of said digital counter, said digital comparator being operative to produce an output signal whenever the sign of the difference between the digital error signal and the contents of said digital counter changes, said output being relayed to fire one of the controllable rectifiers.

Claim 14

In a digital firing circuit operative to fire either polarity of oppositely poled controllable rectifiers connected between an AC source and a load in response to a digital error signal, the improvement comprising: a. A digital counter arranged to count at a predetermined rate; b. phase detection logic means for sensing the earliest point in each half cycle of the AC wave at which a firing pulse can be generated, the output of said phase detection logic means being operatively connected in said digital firing circuit to define a control interval in which a predetermined digital number is preset into said digital counter, said digital counter thereafter counting in a predetermined direction from said preset number; and c. a digital comparator hAving operatively connected thereto the digital error signal and the contents of said digital counter, said digital comparator being operative to produce an output signal whenever the sign of the difference between the digital error signal and the contents of said digital counter changes, said output being relayed to fire one of the controllable rectifiers.

Claim 15

The improved digital firing circuit as recited in claim 11 wherein said digital counter comprises a reversible counter which counts in one direction when an AC source voltage which is positive in polarity and which counts in the other direction when an AC source voltage is negative in polarity.

Claim 16

The improved digital firing circuit as recited in claim 12 wherein said reversible counter is preset by the signal from said phase detection logic means to a positive digital number when an AC source voltage is positive in polarity, the reversible counter thereafter counting down from the positive preset number, and wherein the signal from said phase detection logic means presets a negative digital number into said reversible counter when said AC source voltage is negative in polarity, the reversible counter thereafter counting up from the negative preset number.

Claim 17

The digital firing circuit recited in claim 11 wherein said phase detection logic means operates to define a control interval starting 120* advanced for each polarity of the AC input.

Claim 18

The improved digital firing circuit recited in claim 11 wherein the combination includes a dynamoelectric machine as a load.

Claim 19

A closed loop, speed-regulated, reversing motor control system comprising drive motor means; oppositively poled controllable rectifier means in each line of miltiphase AC source for coupling electrical energy therefrom to said drive motor; the improvement comprising digital circuit means for synchronizing the generation of firing pulses for said controllable rectifier means with the corresponding phase and polarity of the AC source; the firing pulses controlling the passage of electrical energy through said controllable rectifiers to said motor in accordance with an error signal derived from a comparison of digital command signals with digital feedback signals; the command signal representing desired motor performance and the feedback signal indicating actual motor performance, said digital circuit means comprising, in combination: a. a pulse generator driven by said motor at a speed representative of said motor speed and having an output of at least one pulse per revolution; b. a digital command generator for providing the command signal; c. a digital error generator, means for electrically coupling said pulse generator, wherein a comparison of the output of said pulse generator with the command signal results in an error signal; d. phase detection logic means coupled to the AC source to sense the polarity of each phase of the source voltage and having an output which presets a predetermined digital number into digitally operated firing circuits at the earliest point in each half cycle of the source voltage at which firing pulses may be generated for controlled rectifiers of corresponding phases; e. a digitally operated firing circuit per phase of the input power operatively connected to said phase detection means and to said digital error generator, each of said firing circuits comprising a digital comparator and a reversible digital counter arranged to count in a predetermined direction from the predetermined digital number preset thereinto by said phase detection logic means, said firing circuit providing firing pulses to appropriately poled corresponding controllable rectifiers when said digital comparator detects a change in sign of the difference existing between the contents of said digital counter and the digital error signal; and f. a clock generator operatively connected to said digital counters in said firing circuits, said clock generator operating at a fixed frequenCy to count the contents of said digital counter from the predetermined digital number.

Claim 20

A closed loop, speed-regulated, reversing motor control system comprising drive motor means; oppositively poled controllable rectifier means in each line of miltiphase AC source for coupling electrical energy therefrom to said drive motor; the improvement comprising digital circuit means for synchronizing the generation of firing pulses for said controllable rectifier means with the corresponding phase and polarity of the AC source; the firing pulses controlling the passage of electrical energy through said controllable rectifiers to said motor in accordance with an error signal derived from a comparison of digital command signals with digital feedback signals; the command signal representing desired motor performance and the feedback signal indicating actual motor performance, said digital circuit means comprising, in combination: a. a pulse generator driven by said motor at a speed representative of said motor speed and having an output of at least one pulse per revolution; b. a digital command generator for providing the command signal; c. a digital error generator, means for electrically coupling said pulse generator, wherein a comparison of the output of said pulse generator with the command signal results in an error signal; d. phase detection logic means coupled to the AC source to sense the polarity of each phase of the source voltage and having an output which presets a predetermined digital number into digitally operated firing circuits at the earliest point in each half cycle of the source voltage at which firing pulses may be generated for controlled rectifiers of corresponding phases; e. a digitally operated firing circuit per phase of the input power operatively connected to said phase detection means and to said digital error generator, each of said firing circuits comprising a digital comparator and a reversible digital counter arranged to count in a predetermined direction from the predetermined digital number preset thereinto by said phase detection logic means, said firing circuit providing firing pulses to appropriately poled corresponding controllable rectifiers when said digital comparator detects a change in sign of the difference existing between the contents of said digital counter and the digital error signal; and f. a clock generator operatively connected to said digital counters in said firing circuits, said clock generator operating at a fixed frequenCy to count the contents of said digital counter from the predetermined digital number.