Thyristor control system

A control circuit for gating portions of an AC waveform from an AC source to a load, comprising:

• a thyristor coupled between the AC source and the load and triggerable to pass portions of the AC waveform to the load;
• a clock for generating clock pulses;
• a first counter means for counting the clock pulses to vary the count in proportion to the number of clock pulses coupled to the first counter means;
• a detector coupled to the AC source for generating a reference signal when the AC waveform has a predetermined phase angle, and gate means coupled between the clock and the first counter means for passing clock pulses to the first counter means upon receipt of the reference signal to thereby effectively synchronize the count of the first counter means with the predetermined phase angle;
• a second counter means connectable to the clock for counting the clock pulses to vary an angle count in proportion to the number of received clock pulses, means for gating the second counter means to the clock for a time period representing a desired phase angle which is to be passed by the thyristor to the load, and means effective after termination of the time period for transferring the angle count of the second counter means to the first named counter means to set the first counter means to the angle count representing the desired phase angle;
• and
• trigger means coupled to the first counter means for triggering the thyristor in response to the occurrence of a predetermined count.

A control circuit for gating portions of AC waveforms to a load from a three-phase AC source with three power lines each having thereon an AC waveform phase shifted by a fixed phase angle with respect to the AC waveforms on the remaining power lines, comprising:

• at least three thyristors each coupled between a different one of the power lines and the load and triggerable to pass portions of the AC waveforms to the load;
• a clock for generating clock pulses;
• counter means for counting the clock pulses to vary the count in proportion to the number of clock pulses coupled to the counter means;
• synchronizing means coupled to the AC source for effectively synchronizing the count of the counter means with a predetermined phase angle of the AC waveform;
• a first trigger control responsive to the occurrence of a predetermined count for triggering one of the thyristors;
• and
• a second trigger control including a counter coupled to the clock in response to triggering of the one thyristor for counting to a fixed phase angle representing number which triggers the second thyristor.

A control circuit for gating portions of an AC waveform from an AC source to a load which produces an output variable in relation to the amount of the AC waveform gated thereto, comprising:

• a thyristor coupled between the AC source and the load and triggerable to pass portions of the AC waveform to the load;
• memory means for storing a number which represents the phase angle of the AC waveform which is to be gated to the load;
• trigger means responsive to the memory means for triggering the thyristor when the AC waveform has a phase angle corresponding to the number stored in the memory means;
• feedback means responsive to the variable output for producing a corresponding feedback signal;
• and
• correction means responsive to the feedback signal for changing the number stored in the memory means to to maintain a fixed output from the load.

A control circuit for gating portions of an AC waveform from an AC source to a load which produces an output variable in relation to the amount of the AC waveform gated thereto, comprising:

• a thyristor coupled between the AC source and the load and triggerable to pass portions of the AC waveform to the load;
• a clock for generating clock pulses;
• a memory counter responsive to the clock pulses for changing a number which represents the phase angle of the AC waveform which is to be gated to the load in proportion to the number of received clock pulses, a clock input coupled through a gate to the clock for changing the number when the gate is actuated, an up control input for causing the memory counter to increment the number in response to clock pulses at the clock input, a down control input for causing the memory counter to decrement the number in response to control pulses at the clock input;
• trigger means responsive to the memory counter for triggering the thyristor when the AC waveform has a phase angle corresponding to the number stored in the memory means;
• feedback means responsive to the variable output for producing a corresponding feedback signal;
• reference means for producing a reference signal representing a fixed output desired from the load;
• and
• correction means including the gate for coupling the clock to the memory counter in order to change the number stored in the memory means to thereby maintain a fixed output from the load and a comparator coupled to the feedback means and the reference means for comparing the feedback signal with the reference signal to activate the up control input or the down control input of the memory counter when the signals do not match.

A control circuit for gating portions of an AC waveform from an AC source to a load which produces an output variable in relation to the amount of the AC waveform gated thereto, comprising:

• a thyristor coupled between the AC source and the load and triggerable to pass portions of the AC waveform to the load;
• memory means for storing a number which represents the phase angle of the AC waveform which is to be gated to the load;
• a clock for generating clock pulses;
• trigger means responsive to the memory means for triggering the thyristor when the AC waveform has a phase angle corresponding to the number stored in the memory means including a counter for counting the clock pulses, means to preset the number stored in the memory means in the counter, means coupled to the counter for triggering the thyristor in response to reaching a predetermined count, and synchronizing means coupled to the AC source and responsive to the occurrence of a predetermined phase angle of the AC waveform for enabling the counter to count towards the predetermined count;
• feedback means responsive to the variable output for producing a corresponding feedback signal;
• and
• correction means responsive to the feedback signal for changing the number stored in the memory means to maintain a fixed output from the load.

A control circuit for gating to a motor portions of phase shifted AC waveforms on three lines of a three-phase AC source, comprising:

• at least three thyristors each coupled between a different one of the three lines and the motor, each being triggerable to pass portions of the corresponding phase shifted AC waveform to the motor;
• a clock for generating clock pulses;
• counter means for counting the clock pulses to vary its count in proportion to the number of received clock pulses;
• means for loading the counter means with an initial count which represents a preselected phase angle of the AC waveform which is to be initially gated to the motor;
• gate means coupled between the clock and counter means and responsive to a predetermined phase relationship of one of the AC waveforms for passing clock pulses to the counter means;
• first trigger means coupled to the counter means for triggering one of the thyristors when the counter means reaches a predetermined count;
• and
• second trigger means responsive after triggering of the one thyristor for triggering the second and third thyristors at phase angles which correspond to the phase angle passed by the one thyristor.