Method and apparatus for controlling AC motors
First Claim
1. An AC motor control method comprising the steps of:
- (a) a step of obtaining slip frequency, phase difference and primary current amplitude using a speed command and an actual speed;
(b) a step of determining angular frequency in accordance with the actual speed of the AC motor;
(c) a step of producing a three-phase current command having a frequency by using the slip frequency, phase difference and primary current amplitude obtained in step (a), as well as said angular frequency; and
(d) a step of driving the AC motor by said three-phase current command, wherein step (a) includesi computing a torque command from a deviation between said speed command signal and actual speed, where a torque-slip frequency relation and a slip frequency-primary current vector relation which take the secondary leakage reactance of said AC motor into account are predetermined;
ii finding said slip frequency using the torque command obtained in step (i) and the torque-slip frequency relation; and
theniii finding said primary current amplitude and phase difference using said slip frequency and slip frequency-primary current vector relation.
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Accused Products
Abstract
An AC motor control method and apparatus therefor, for controlling an AC motor 11 by holding the excitation current I0 of the AC motor 11 constant and varying primary current I1 in accordance with a speed deviation Δn. Stored previously in a memory device 18 are a torque T-slip frequency ωs characteristic, a slip frequency ωs -primary current vector I1 characteristic, and a slip frequency ωs and phase φ1 characteristic which take secondary leakage reactance into account. Slip frequency ωs, primary current vector I1 and phase φ1 are read out of the memory device in accordance with the torque command T obtained from the speed deviation Δn, whereby three-phase current commands iu, iv, iw are produced. Accordingly, torque irregularity is suppressed and an excellent response obtained.
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Citations
8 Claims
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1. An AC motor control method comprising the steps of:
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(a) a step of obtaining slip frequency, phase difference and primary current amplitude using a speed command and an actual speed; (b) a step of determining angular frequency in accordance with the actual speed of the AC motor; (c) a step of producing a three-phase current command having a frequency by using the slip frequency, phase difference and primary current amplitude obtained in step (a), as well as said angular frequency; and (d) a step of driving the AC motor by said three-phase current command, wherein step (a) includes i computing a torque command from a deviation between said speed command signal and actual speed, where a torque-slip frequency relation and a slip frequency-primary current vector relation which take the secondary leakage reactance of said AC motor into account are predetermined; ii finding said slip frequency using the torque command obtained in step (i) and the torque-slip frequency relation; and
theniii finding said primary current amplitude and phase difference using said slip frequency and slip frequency-primary current vector relation. - View Dependent Claims (2, 3, 4, 5)
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6. An AC motor control apparatus including:
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a speed sensor for sensing the actual speed of the AC motor; angular frequency detection means for providing an angular frequency signal in accordance with the actual speed of the AC motor; torque command generating means for generating a torque command on the basis of a speed deviation between a speed command and an actual speed from said speed sensor; memory means for storing a torque-slip frequency characteristic, a slip frequency-amplitude characteristic and a slip frequency-phase characteristic which take secondary leakage reactance into account, for providing a slip frequency in accordance with said torque command and said torque-slip frequency characteristic, for providing a primary current amplitude in accordance with said slip frequency and said slip frequency-amplitude characteristic, and for providing a phase signal in accordance with said slip frequency and said slip frequency-phase charcteristic; an arithmetic circuit for computing a three-phase current command from said slip frequency, said primary current amplitude, said phase signal, and from said angular frequency signal; and a drive circuit for driving the AC motor by means of the three-phase current command from said arithmetic circuit. - View Dependent Claims (7)
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8. A method for controlling an AC motor in accordance with a slip frequency, a phase difference, a primary current amplitude, a commanded speed and an actual speed, said method comprising the steps of:
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(a) computing a torque command in accordance with the difference between said commanded speed and said actual speed; (b) computing the slip frequency in accordance with the torque command, and the following relation ##EQU11## wherein T corresponds to said torque command, and ##EQU12## where r2 is the secondary resistance, 1m is the excitation inductance, 12 is the secondary leakage inductance, ws is the slip frequency and Io is the excitation current; (c) computing the primary current amplitude using said slip frequency and the following equation ##EQU13## wherein k3 122, k4 =1/r22 ·
212 (12 1m) r22 1m2),and ##EQU14## (d) computing a phase difference using said slip frequency and the following relation ##EQU15## (e) determining an angular frequency in accordance with the actual speed of AC motor; (f) generating a three-phase primary current command using the slip frequency, the phase difference, the primary current amplitude and the angular frequency; and (g) driving the AC motor in accordance with said three-phase primary current command.
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Specification