Start-up system for a synchronous motor drive

Claim 2

In a load commutated inverter synchronous motor drive having an inverter including a plurality of thyristors controlled for conduction in a firing sequence related to a direction of motor rotation for providing under normal operation AC power to a synchronous motor having rotor windings and stator windings; the method of starting the motor from a rotor rest position with all the thyristors being initially in the OFF state; comprising the steps of: applying to the rotor windings a modulated field current to induce phase voltages into the respective said stator windings; deriving with said induced phase voltages a present combination of polarity signals; said present combination of polarity signals being correlated to a predetermined firing sequence of thyristors characterizing said rotor rest position; initiating said firing sequence of the thyristors in accordance with said predetermined firing sequence; thereby to cause motion of the rotor with a maximal torque in said direction; and applying a normal field current to said rotor winding for normal motor operation thereafter in said direction.

Claim 3

The motor drive of claim 1 with said modulated field current having a selected and constant rate and said induced phase voltages having respective constant magnitudes and corresponding polarities as said polarity signals; said polarity signals being correlated to corresponding rotor rest positions and corresponding firing sequences; said predetermined firing sequence being selected in accordance with the correlated present polarity signals; thereby to match the corresponding rest position of the motor.

Claim 4

The motor drive of claim 2 with said field current being applied successively with said constant rate for two opposite rate polarities.

Claim 5

In a load commutated inverter synchronous motor drive having an inverter including a plurality of thyristors controlled for conduction in a predetermined firing sequence for providing AC power to a synchronous motor having stator windings and rotor windings; a start-up system operative with said thyristors in the OFF state and with the rotor in a rest position; comprising: means for applying to said rotor a field current for inducing voltages in the stator; means responsive to said stator voltages for deriving a signal combination characteristic of said stator windings in relation to said rotor rest position; means for storing as a reference a series of ON-state thyristor combinations each representative of an individual in said predetermined firing sequence, each of said steps being correlated with a predetermined combination of said induced stator voltages in relation with the applied said field current; means for comparing said derived stator signal combination with said stored ON-state thyristor combinations for selecting a matching one of said ON-state combinations; and means for initially firing said thyristors in sequence from said matching combination; with said field current applying means generating a field current of constant rate; with said stator signal combination being a combination of polarity signs.

Claim 6

In a load commutated inverter synchronous motor drive having an inverter including a plurality of thyristors controlled for conduction in a predetermined firing sequence for providing AC power to a synchronous motor having stator windings and rotor windings; a start-up system operative with said thyristors in the OFF state and with the rotor in a rest position; comprising: means for applying to said rotor a field current for inducing voltages in the stator; means responsive to said stator voltages for deriving a signal combination characteristic of said stator windings in relation to said rotor rest position; means for storing as a reference a series of ON-state thyristor combinations each representative of an individual in said predetermined firing sequence, each of said steps being correlated with a predetermined combination of said induced stator voltages in relation with the applied said field current; means for comparing said derived stator signal combination with said stored ON-state thyristor combinations for selecting a matching one of said ON-state combinations; and means for initially firing said thyristors in sequence from said matching combination; with said field current applying means generating a field current of constant rate; with said stator signal combination being a combination of polarity signs.

Claim 7

The start-up system of claim 4 with each of said series of ON-state thyristors combinations being identified in relation to a combination of signs characterizing such signal combination.

Claim 8

The start-up system of claim 5 with said field current applying means generating a field current of successively opposite rates and of same amplitude.