Induction motor control system

Claim 1

A control system for controlling an induction motor, comprising an induction motor speed control network which includes a digital data processing loop for controlling rotation of the induction motor by means of an AC voltage based on a speed command in the form of an analog voltage, and for feeding the actual value of the rotational speed of the induction motor back to the input side of the induction motor speed control network in order to make the rotational speed of the induction motor follow up the commanded speed, said speed control network including a frequency-to-voltage converter for delivering the actual speed value of the induction motor, an adder-subtractor for combining the speed command and the actual speed value, and a proportional integrating circuit coupled to the output side of the adder-subtractor, said frequency-to-voltage converter, said adder-subtractor and said proportional integrating circuit constituting analog circuitry.

Claim 6

A system for controlling an induction motor which comprises: a memory having the following data stored therein in advance, a torque-current amplitude characteristic, a torque-phase characteristic, a rotational speed-slip characteristic and a rotational angle-sinusoidal value characteristic; means for deriving a difference voltage between a voltage indicative of a speed command and a voltage indicative of the actual induction motor speed; voltage-to-frequency conversion means for converting the difference voltage into a digital pulse train P ; means for reading, at fixed periods and as torque information, N e -number of pulses of the pulse train P , and for reading, at fixed periods and as induction motor speed information, N v - number of pulses of a pulse train the frequency whereof is proportional to the induction motor speed; means for deriving a numerical value corresponding to the N v -number of pulses on the basis of the rotational speed-slip characteristic stored in said memory; a first counter into which said numerical value is set, and which receives the pulse train P e as an input, for dividing said pulse train P e by said numerical value to produce a pulse train P s indicative of induction motor slip; means for mixing the pulse train P s with said pulse train the frequency whereof is proportional to the induction motor speed; a second counter for counting the pulses in the mixed pulse trains to produce rotational angle information θ; means for generating three-phase AC signals i u , i v , i w by executing a predetermined operation to control slip frequency, on the basis of said N e -number of pulses, said rotational angle 0, said torque-current amplitude characteristic, said torque-phase characteristic, and said rotational angle-sinusoidal value characteristic; and means for driving the induction motor on the basis of the three-phase sinusoidal AC signals i , i v , i w .

Claim 7

A system for controlling an induction motor which comprises: a memory having the following data stored therein in advance, a torque-current amplitude characteristic, a torque-phase characteristic, a rotational speed-slip characteristic and a rotational angle-sinusoidal value characteristic; means for deriving a difference voltage between a voltage indicative of a speed command and a voltage indicative of the actual induction motor speed; voltage-to-frequency conversion means for converting the difference voltage into a digital pulse train P ; means for reading, at fixed periods and as torque information, N e -number of pulses of the pulse train P , and for reading, at fixed periods and as induction motor speed information, N v - number of pulses of a pulse train the frequency whereof is proportional to the induction motor speed; means for deriving a numerical value corresponding to the N v -number of pulses on the basis of the rotational speed-slip characteristic stored in said memory; a first counter into which said numerical value is set, and which receives the pulse train P e as an input, for dividing said pulse train P e by said numerical value to produce a pulse train P s indicative of induction motor slip; means for mixing the pulse train P s with said pulse train the frequency whereof is proportional to the induction motor speed; a second counter for counting the pulses in the mixed pulse trains to produce rotational angle information θ; means for generating three-phase AC signals i u , i v , i w by executing a predetermined operation to control slip frequency, on the basis of said N e -number of pulses, said rotational angle 0, said torque-current amplitude characteristic, said torque-phase characteristic, and said rotational angle-sinusoidal value characteristic; and means for driving the induction motor on the basis of the three-phase sinusoidal AC signals i , i v , i w .