Vector control unit for an induction motor

Claim 2

A vector control unit for an induction motor connected with an inverter, the motor being not only electrically driven but also working in a regenerative condition, comprising: detection means for detecting that said induction motor is being operated at a low speed and for detecting that the sign of a velocity command and the sign of a slip angular velocity command differ from each other; control means for performing control such that the slip angular velocity is not included in the magnetic flux angular velocity command when said induction motor is being operated at a low speed and the sign of the velocity command and the sign of the slip angular velocity command differ from each other.

Claim 3

The vector control unit according to claim 1, wherein, said detection means comprises a multiplier for calculating the product of a velocity command ωr* and a torque current command Iτ*, an absolute value circuit for outputting the absolute value of a magnetic flux angular velocity command ωψ*, a first comparator for comparing the product of the velocity command ωr* and the torque current command Iτ* with zero, a second comparator for comparing the absolute value of the magnetic flux angular velocity command ωψ* with a reference value, a gate circuit which inputs outputs of the first and second comparators and outputs a signal of a predetermined logical level when the product of the velocity command ωr* and the torque current command Iτ* is less than zero and the absolute value of the magnetic flux angular velocity command ωψ* is smaller than the reference value; said control means is a switch provided in the former stage of an adder which adds the slip angular velocity command ωs* to a presumed velocity ωr to output the magnetic flux angular velocity command ωψ*, and said switch outputs said slip angular velocity command ωs* to said adder when said predetermined logic level signal is not outputted from said gate circuit and outputs zero to said adder instead of said slip angular velocity command ωs* when said predetermined logic level signal is outputted.

Claim 4

The vector control unit for an induction motor connected with an inverter, the motor being not only electrically driven but also working in a regenerative operation, comprising: detection means for detecting that said induction motor is being operated at a low speed and for detecting that the sign of a velocity command and the sign of a slip angular velocity command differ from each other; control means for subtracting the slip angular velocity command from an ordered velocity command to output the result of subtraction as a new velocity command when said induction motor is being operated at a low speed and the sign of the velocity command and the sign of the slip angular velocity command differ from each other.

Claim 5

The vector control unit for an induction motor connected with an inverter, the motor being not only electrically driven but also working in a regenerative operation, comprising: detection means for detecting that said induction motor is being operated at a low speed and for detecting that the sign of a velocity command and the sign of a slip angular velocity command differ from each other; control means for subtracting the slip angular velocity command from an ordered velocity command to output the result of subtraction as a new velocity command when said induction motor is being operated at a low speed and the sign of the velocity command and the sign of the slip angular velocity command differ from each other.

Claim 6

The vector control unit according to claim 3, wherein, said detection means comprises a multiplier for obtaining the product of a velocity command ωr* and a torque current command Iτ*, an absolute value circuit for outputting the absolute value of a magnetic flux angular velocity command ωψ*, a first comparator for comparing the product of the velocity command ωr* and the torque current command Iτ* with zero, a second comparator for comparing the absolute value of the magnetic flux angular velocity command ωψ* with a reference value, a gate circuit which inputs outputs of the first and second comparators and outputs a signal of a predetermined logical level when the product of the angular command ωr* and the torque current command Iτ* is less than zero and the absolute value of the magnetic flux angular velocity command ωψ* is smaller than the reference value; said control means is a switch provided in the former stage of a subtracter which subtracts a slip angular velocity command ωs* from a presumed velocity command ωr and outputs zero to said subtracter instead of said slip angular velocity command ωs* when said predetermined logic level signal is not outputted from said gate circuit and inputs said slip angular velocity command ωs* to said subtracter when said predetermined logic level signal is outputted from said gate circuit.