Method and system for controlling induction motors

Claim 1

A method of controlling an induction motor comprising the steps of sequentially adding digital quantities corresponding to a slip frequency of said induction motor at a predetermined time interval, adding the sum of said sequentially added digital quantities to a digital quantity proportional to an angle of rotation of said motor to obtain a sum value, computing a primary current vector of said induction motor from said sum value and a current component which influences only the torque of said motor, and controlling the primary current of said induction motor based upon said primary current vector.

Claim 2

A method of controlling an induction motor comprising the steps of sequentially adding digital quantities corresponding to a slip frequency of said induction motor at a predetermined time interval, adding the sum of said sequentially added digital quantities to a digital quantity proportional to an angle of rotation of said motor to obtain a sum value, computing a primary current vector of said induction motor from said sum value and a current component which influences only the torque of said motor, and controlling the primary current of said induction motor based upon said primary current vector.

Claim 7

A method of controlling an induction motor comprising the steps of sequentially adding, at a first time interval inversely proportional to the secondary resistance of said motor, digital quantities corresponding to a slip frequency of said motor, computed from a torque instruction and a flux instruction thereof to obtain a first sum value, adding said first sum value to a digital quantity proportional to an angle of rotation of said motor by sampling said digital quantity at said time interval to obtain a second sum value, sample computing a primary current vector of said induction motor, at a second time interval proportional to said first time interval, from said second sum value, a current component computed from said second sum value, said torque instruction and said flux instruction and influences only the torque of said motor and a current component which influences the flux of said motor, and controlling the primary current of said induction motor based on said primary current vector.

Claim 8

A method of controlling an induction motor comprising the steps of sequentially adding, at a first time interval inversely proportional to the secondary resistance of said motor, digital quantities corresponding to a slip frequency of said motor, computed from a torque instruction and a flux instruction thereof to obtain a first sum value, adding said first sum value to a digital quantity proportional to an angle of rotation of said motor by sampling said digital quantity at said time interval to obtain a second sum value, sample computing a primary current vector of said induction motor, at a second time interval proportional to said first time interval, from said second sum value, a current component computed from said second sum value, said torque instruction and said flux instruction and influences only the torque of said motor and a current component which influences the flux of said motor, and controlling the primary current of said induction motor based on said primary current vector.

Claim 9

A system of controlling an induction motor comprising frequency converting apparatus including a rectifier and an inverter for supplying variable frequency alternating current to said motor; means responsive to a predetermined torque instruction T and a predetermined flux instruction Φ o to produce a slip frequency signal Δθ s ; means responsive to said slip frequency signal to produce a slip angle signal θ s ; means responsive to the rotation of said motor for producing a rotational angle signal θ r ; a first adder for adding together said slip angle signal θ s and said rotational angle signal θ r ; selection a switch means for selecting predetermined one θ.sub.α of a plurality of rotational angles of said motor; a second adder for adding together the outputs of said first adder and said first transfer switch means; means responsive to said torque instruction and said flux instruction for producing a current signal i 1q which influences the torque of said motor; means responsive to said flux instruction and a flux change of said motor during a sampling period for producing a current signal i 1d which influences the magnetic flux of said motor; a function circuit for producing a trigonometric function of the output of said second adder; a multiplier for multiplying the output of said function circuit with either one of said current signals i 1q and i 1d ; means responsive to the output of said multiplier for controlling said frequency converting apparatus; and a sequence controller for sequentially operating various means and elements described above.

Claim 10

A system of controlling an induction motor comprising frequency converting apparatus including a rectifier and an inverter for supplying variable frequency alternating current to said motor; means responsive to a predetermined torque instruction T and a predetermined flux instruction Φ o to produce a slip frequency signal Δθ s ; means responsive to said slip frequency signal to produce a slip angle signal θ s ; means responsive to the rotation of said motor for producing a rotational angle signal θ r ; a first adder for adding together said slip angle signal θ s and said rotational angle signal θ r ; selection a switch means for selecting predetermined one θ.sub.α of a plurality of rotational angles of said motor; a second adder for adding together the outputs of said first adder and said first transfer switch means; means responsive to said torque instruction and said flux instruction for producing a current signal i 1q which influences the torque of said motor; means responsive to said flux instruction and a flux change of said motor during a sampling period for producing a current signal i 1d which influences the magnetic flux of said motor; a function circuit for producing a trigonometric function of the output of said second adder; a multiplier for multiplying the output of said function circuit with either one of said current signals i 1q and i 1d ; means responsive to the output of said multiplier for controlling said frequency converting apparatus; and a sequence controller for sequentially operating various means and elements described above.