Digital firing control for a converter

An apparatus for controlling the firing angle of triggerable switches in a converter, comprising:

• a source of a first signal representing a desired change in the firing angle;
• a clock means for generating a train of pulses;
• a source of a second signal representing said desired change in the firing angle pulse the angle between firing command signals when said first signal is zero wherein said source of a second signal includes a first counting means responsive to said clock pulse train for generating said second signal in digital form;
• and
• means responsive to said first and second signals for generating said firing command signals for turning on said triggerable switches in a predetermined sequence.

An apparatus for controlling the firing angle of a triggerable switch converter, comprising:

• a power source for supplying alternating current power to said converter;
• clock means responsive to the alternating current wave form of said power source for generating a train of pulses, each of said pulses representing a predetermined angular increment of a cycle of said wave form;
• a source of a first signal representing a desired change in the firing angle;
• a first counting means responsive to said first signal and said pulses for generating said first signal in digital form;
• a second counting means responsive to said pulses for generating a second signal in digital form representing said desired change in the firing angle pulse the angle between firing command signals when said first signal is zero;
• and
• means responsive to said first and second signals in digital form for generating said firing command signals for turning on said triggerable switches in a predetermined sequence.

A direct current transformer for generating a relatively noise free output signal, comprising:

• a source of a signal representing current flow in a load;
• a first transformer;
• first switching means connected between said signal source and the primary of said first transformer;
• second switching means connected to the secondary of said first transformer;
• clock means for generating a train of clock pulses;
• and
• means responsive to said clock pulses for switching said first and second switching means for generating said relatively noise free output signal at the output of said second switching means.

An apparatus for determining when at least one phase of a multi-phase alternating current power source is not connected to a load comprising:

• rectifying means connected to said power source at said load for generating a half wave rectified output signal;
• a source of a signal having a polarity opposite the polarity of said output signal;
• and
• means responsive to said output signal and said signal of opposite polarity for generating a power line missing signal when at least one of the phases of said power source is not connected to said load wherein said means for generating said power line missing signal includes an amplifier having an input connected to said rectifying means and said source of an opposite polarity signal and an output, a first capacitor and a first diode connected in series between said amplifier output and ground and a second diode connected in series with said first diode between said input and ground whereby said amplifier generates said power line missing signal at said output.

An apparatus for determining when at least one phase of a multi-phase alternating current power source is incorrectly connected to a load, comprising:

• means for generating an alternating current wave form having a predetermined phase relationship with one of the phases of said power source;
• means responsive to said one phase for generating at least one unipolar signal coinciding with the negative portion of said alternating current wave form when the phases of said power source are correctly connected to said load wherein said means for generating at least one unipolar signal includes means responsive to said one phase and a first pulse train of a first predetermined frequency for generating a control signal, means responsive to said control signal for generating a second pulse train of a second predetermined frequency, first frequency dividing means responsive to said second pulse train for generating said first pulse train, and second frequency dividing means responsive to said second pulse train for generating said unipolar signal;
• and
• means responsive to said alternating current wave form and said one unipolar signal for generating an incorrect phasing signal when at least one of said phases of said power source is incorrectly connected to said load.

An apparatus for determining when at least one phase of a three phase alternating current power source is incorrectly connected to a load, comprising:

• means for generating an alternating current wave form having a predetermined phase relationship with one of the phases of said power source wherein said means for generating said alternating current wave form includes a first transformer having a primary connected to a first phase of said power source, a second transformer having a primary connected to a second phase of said power source, a first impedance element connected between the junction of one end of the secondary of said first transformer and one end of the secondary of said second transformer and ground, a second impedance element connected between the other end of the secondary of said first transformer and ground and a third impedance element connected between the other end of the secondary of said second transformer and ground whereby said alternating current wave form is developed across said third impedance element;
• means responsive to said one phase for generating at least one unipolar signal coinciding with the negative portion of said alternating current wave form when the phases of said power source are correctly connected to said load;
• and
• means responsive to said alternating current wave form and said one unipolar signal for generating an incorrect phasing signal when at least one of said phases of said power source is incorrectly connected to said load.

The combination, comprising:

• a power source for supplying electric power having a cyclic wave form;
• a load;
• at least one triggerable switch connected between said power source and said load;
• timing means responsive to said cyclic wave form for generating timing signals representing a predetermined angular increment of a cycle of said wave form;
• means responsive to said timing signals for generating a first signal in digital form representing a desired change in a standard timed interval;
• means responsive to said timing signals for generating a second signal representing said desired change in said standard timed interval plus the duration of said standard timed interval between said firing command signals generated when said first signal is zero;
• and
• means responsive to said first and second signals for generating firing command signals at timed intervals for turning on said triggerable switch on a time basis referenced form the previously generated firing command signal.

A method of controlling the firing angle of a triggerable switch, comprising the steps of:

• applying electric power having a cyclic wave form to an input of said triggerable switch;
• generating timing signals representing a predetermined angular increment of a cycle of said wave form;
• generating a first signal representing a desired change in a standard timed interval in response to said timing signals;
• generating a second signal in digital form, representing said desired change in said standard timed interval plus the duration of said standard timed interval between said firing command signals generated when said first signal is zero, in response to said timing signals;
• and
• generating firing command signals at timed intervals in response to said first and second signals for turning on said triggerable switch on a time basis referenced from the previously generated firing command signal.