Vector control system for induction motors

Claim 2

A vector control method for a three-phase ac induction motor comprising the steps of: applying an exciting current command value and a torque current command value in a rotating magnetic field coordinate system; detecting an actual exciting current value and torque current value; detecting a deviation between said exciting current command value and said detected exciting current value and a deviation between said torque current command value and said detected actual torque current value; producing three phase ac voltage command values in a stator coordinate system tending to reduce said deviations to zero; and determining voltages and a frequency for driving said induction motor in accordance with said three phase ac voltage command values; said actual exciting current value and torque current value detecting step further comprising, integrating a value of each of selected two phase ac inputs of three phase ac inputs of said induction motor and then sampling the integrated values at a predetermined period; subjecting each of said sampled values of the integrated two phase ac inputs to a definite integration at said predetermined period; and transforming said definite integrated values respectively to an actual exciting current value and torque current value in a rotating magnetic field coordinate system.

Claim 3

A method according to claim 1, wherein said predetermined period is selected to be the same with or an integral multiple of a period of harmonics contained in said three phase ac inputs.

Claim 4

A method according to claim 2, where said integer is preferably selected between 1 and 5.

Claim 5

A method according to claim 3, wherein said sampling and definite integration steps comprise converting the magnitude of each of said two phase ac inputs to a number of pulses indicative thereof, counting each said number of pulses for said predetermined period, holding each said count value every said predetermined period, and calculating a difference between a value held at an nth period and a value held at a (n+1)th period, thereby calculating each said definite integrated value.

Claim 6

A method according to claim 4, wherein said transforming step transforms each said definite integrated value in said stator coordinate system to a value in said rotating field coordinate system in accordance with coordinate reference signals, and wherein said coordinate reference signals are produced in accordance with a value of a primary angular frequency of said induction motor.

Claim 7

A method according to claim 5, wherein said coordinate reference signals are produced on the basis of a signal delayed from said primary angular frequency signal by a phase angular value concerning to a product of said primary angular frequency of said induction motor and said predetermined period.

Claim 8

A method according to claim 5 or 6, wherein said transforming step further comprises correcting an amplitude value of each said coordinate transformed value in accordance with a value concerning to a magnitude of said predetermined period.

Claim 9

A method according to claim 5 or 6, wherein said transforming step further comprises correcting an amplitude value of each said coordinate transformed value in accordance with values concerning to a magnitude of said predetermined period and the value of said primary angular frequency.

Claim 10

A vector control method for a three-phase ac induction motor driven by a pulse width modulation-type power converter comprising the steps of: applying an exciting current command value and a torque current command value in a rotating magnetic field coordinate system; detecting an actual exciting current value and torque value; detecting a deviation between said exciting current command value and said detected actual exciting value and a deviation between said torque current command value and said detected actual torque value; producing three phase ac voltage command values in a stator coordinate system tending to reduce said deviations to zero and using the same as control signals for said PWM-type power converter; and causing said power converter to determine voltages for driving said induction motor and a frequency in accordance with said three phase ac voltage command values; said actual exciting current value and torque current value detecting step further comprising, integrating a value of each of two phase ac inputs of three phase ac inputs of said induction motor and then sampling the integrated values at a predetermined period; subjecting each of said sampled values of the integrated two phase ac values to definite integration at said predetermined period; and transforming said definite integrated values to an actual exciting current value and torque current value in said rotating magnetic field coordinate system.

Claim 11

A vector control method for a three-phase ac induction motor driven by a pulse width modulation-type power converter comprising the steps of: applying an exciting current command value and a torque current command value in a rotating magnetic field coordinate system; detecting an actual exciting current value and torque value; detecting a deviation between said exciting current command value and said detected actual exciting value and a deviation between said torque current command value and said detected actual torque value; producing three phase ac voltage command values in a stator coordinate system tending to reduce said deviations to zero and using the same as control signals for said PWM-type power converter; and causing said power converter to determine voltages for driving said induction motor and a frequency in accordance with said three phase ac voltage command values; said actual exciting current value and torque current value detecting step further comprising, integrating a value of each of two phase ac inputs of three phase ac inputs of said induction motor and then sampling the integrated values at a predetermined period; subjecting each of said sampled values of the integrated two phase ac values to definite integration at said predetermined period; and transforming said definite integrated values to an actual exciting current value and torque current value in said rotating magnetic field coordinate system.

Claim 12

A method according to claim 9, wherein said predetermined period is selected to be integral multiple of a period of a carrier wave of said PWM-type power converter.

Claim 13

A method according to claim 10, wherein said sampling and definite integration step comprises converting a magnitude of each of said two phase ac inputs to a number of pulses indicative thereof, counting each said number of pulses for said predetermined period, holding each said count value at said predetermined period, and calculating a difference between a value held at an nth period and a value held at a (n+1)th period, thereby calculating each said definite integrated value.

Claim 14

A method according to claim 11, wherein said transforming step transforms each said integrated value in said stator coordinate system to a value in said rotating magnetic field coordinate system in accordance with coordinate reference signals, and wherein said coordinate reference signals are produced in accordance with a value of a primary angular frequency of said induction motor.

Claim 15

A method according to claim 12, wherein said coordinate reference signals are produced on the basis of a signal delayed from said primary angular frequency signal by an angular phase value concerning to a product of said primary angular frequency of said induction motor and said predetermined period.

Claim 16

A method according to claim 12 or 13, wherein said transforming step further comprises correcting an amplitude value of each said coordinate transformed value in accordance with a value concerning to a magnitude of said predetermined period.

Claim 17

A method according to claim 12 or 13, wherein said transforming step further comprising correcting an amplitude value of each said coordinate transformed value in accordance with values concerning to a magnitude of said predetermined period and the value of said primary angular frequency.

Claim 18

A vector control method for a three-phase ac induction motor comprising the steps of: applying an exciting current command value and a torque current command value in a rotating magnetic field coordinate system; detecting an actual exciting current value and torque current value; detecting a deviation between said exciting current command value and said detected actual exciting current value and a deviation between said torque current command value and said detected actual torque current value; producing three phase ac voltage command values in a stator coordinate system tending to reduce said deviations to zero; and determining voltages and a frequency for driving said induction motor in accordance with said three phase ac voltage command values; said actual exciting current value and torque current detecting step further comprising, transforming three phase ac inputs of said induction motor to orthogonal two phase ac currents in said stator coordinate system, integrating the orthogonal two phase ac currents, sampling the integrated value of each of said two phase ac currents at a predetermined period, detecting a difference between an integrated value of an nth sampled value and an integrating value of a (n+1)th sampled value (n represents a positive integer) of each said ac current value, and transforming said difference values to an actual exciting current value and torque current value, respectively, in said rotating magnetic field coordinate system.

Claim 19

A vector control method for a three-phase ac induction motor comprising the steps of: applying an exciting current command value and a torque current command value in a rotating magnetic field coordinate system; detecting an actual exciting current value and torque current value; detecting a deviation between said exciting current command value and said detected actual exciting current value and a deviation between said torque current command value and said detected actual torque current value; producing three phase ac voltage command values in a stator coordinate system tending to reduce said deviations to zero; and determining voltages and a frequency for driving said induction motor in accordance with said three phase ac voltage command values; said actual exciting current value and torque current detecting step further comprising, transforming three phase ac inputs of said induction motor to orthogonal two phase ac currents in said stator coordinate system, integrating the orthogonal two phase ac currents, sampling the integrated value of each of said two phase ac currents at a predetermined period, detecting a difference between an integrated value of an nth sampled value and an integrating value of a (n+1)th sampled value (n represents a positive integer) of each said ac current value, and transforming said difference values to an actual exciting current value and torque current value, respectively, in said rotating magnetic field coordinate system.

Claim 20

A method according to claim 16, wherein said predetermined period is selected to be the same or integral multiple of a period of harmonic components contained in said three phase ac inputs.

Claim 21

A method according to claim 17, wherein said integer is preferably selected to be between 1 and 5.

Claim 22

A method according to claim 19, wherein said integrating, sampling and detecting of difference steps include converting a magnitude of each of said two phase ac inputs to a number of pulses indicative thereof, counting each said number of pulses for said predetermined period, holding each said count value at said predetermined period, and calculating a difference between a value held at an nth period and a value held at a (n+1)th period, thereby calculating each said difference value.

Claim 23

A method according to claim 19, wherein said transforming step transforms each said definite integrated value in said stator coordinate system to a value in said rotating magnetic field coordinate system in accordance with coordinate reference signals, and wherein said coordinate reference signals are produced in accordance with a value of a primary angular frequency of said induction motor.

Claim 24

A method according to claim 20, wherein said coordinate reference signals are produced on the basis of a signal delayed from said primary angular frequency signal by an angular phase value concerning to a product of said primary angular frequency of said induction motor and said predetermined period.

Claim 25

A method according to claim 20 or 21, wherein said transforming step further comprising correcting an amplitude value of each said coordinate transformed value in accordance with a value concerning to a magnitude of said predetermined period.

Claim 26

A method according to claim 20 or 21, wherein said transforming step further comprising correcting an amplitude value of each said coordinate transformed value in accordance with values concerning to a magnitude of said predetermined period and the value of said primary angular frequency.

Claim 27

A vector control method for a three-phase ac induction motor comprising the steps of: applying an exciting current command value and a torque current command value in a rotating magnetic field coordinate system; detecting an actual exciting current value and torque current value; detecting a deviation between said exciting current command value and said detected exciting current value and a difference between said torque current command value and said detected actual torque current value; producing three phase ac voltage command values in a stator coordinate system tending to reduce said deviations to zero; and determining voltages and a frequency for driving said induction motor in accordance with said three phase ac voltage command values; said step for detecting said actual exciting current value and torque current value further comprising, integrating a value of each of two phase ac inputs of three phase ac inputs to said induction motor and then sampling the integrated values at a predetermined period; transforming said integrated value to orthogonal two phase ac values in said stator coordinate system; detecting a difference between integrated values of nth and (n+1)th sampled values of each of said transformed orthogonal two phase ac values (n is a positive integer); and transforming said difference values to an actual exciting current value and torque current value, respectively, in said rotating magnetic field coordinate system.

Claim 28

A vector control method for a three-phase ac induction motor comprising the steps of: applying an exciting current command value and a torque current command value in a rotating magnetic field coordinate system; detecting an actual exciting current value and torque current value; detecting a deviation between said exciting current command value and said detected exciting current value and a difference between said torque current command value and said detected actual torque current value; producing three phase ac voltage command values in a stator coordinate system tending to reduce said deviations to zero; and determining voltages and a frequency for driving said induction motor in accordance with said three phase ac voltage command values; said step for detecting said actual exciting current value and torque current value further comprising, integrating a value of each of two phase ac inputs of three phase ac inputs to said induction motor and then sampling the integrated values at a predetermined period; transforming said integrated value to orthogonal two phase ac values in said stator coordinate system; detecting a difference between integrated values of nth and (n+1)th sampled values of each of said transformed orthogonal two phase ac values (n is a positive integer); and transforming said difference values to an actual exciting current value and torque current value, respectively, in said rotating magnetic field coordinate system.

Claim 29

A method according to claim 24, wherein said predetermined period is selected to be the same or integral multiple of a period of harmonic components contained in said three phase ac inputs.

Claim 30

A method according to claim 25, wherein said integer is preferably selected to be between 1 and 5.

Claim 31

A method according to claim 26, wherein said sampling and integrating step comprises converting a magnitude of each of said two phases ac inputs to a number of pulses indicative thereof, counting each said number of pulses for said predetermined period, and holding each said count value every said predetermined period, and wherein said difference detecting step comprises calculating a difference between a value held at an nth period and a value held at a (n+1)th period for each of said transformed orthogonal two phase ac values.

Claim 32

A method according to claim 27, wherein said transforming step transforms each said integrated value in said stator coordinate system to a value in said rotating magnetic field coordinate system in accordance with coordinate reference signals, and wherein said coordinate reference signals are produced in accordance with a value of a primary angular frequency of said induction motor.

Claim 33

A method according to claim 28, wherein said coordinate reference signals are produced on the basis of a signal delayed from said primary angular frequency signal by an angular phase value concerning to a product of said primary angular frequency of said induction motor and said predetermined period.

Claim 34

A method according to claim 28 or 29, wherein said transforming step further comprises correcting an amplitude value of each said coordinate transformed value in accordance with a value concerning to a magnitude of said predetermined period.

Claim 35

A method according to claim 28 or 29, wherein said transforming step further comprises correcting an amplitude value of each said coordinate transformed value in accordance with values concerning to a magnitude of said predetermined period and the value of said primary angular frequency.

Claim 36

A vector control system for a three-phase ac induction motor comprising: a power converter for generating three phase ac currents; an induction motor for receiving said three phase ac currents; means for detecting a value of each phase current of said three phase ac currents; means for receiving an exciting current command value and a torque current command value in a rotating magnetic field coordinate system for said induction motor; means for detecting an actual exciting current value and torque current value; means for detecting a deviation between said exciting current command value and said detected exciting current value and a deviation between said torque current command value and said detected torque current value; means for producing voltage commands in said rotating magnetic field coordinate system tending to reduce said deviations to zero; first coordinate transformation means for transforming said voltage commands to three phase ac voltage commands in a stator coordinate system; means responsive to said three phase ac command values to control said power converter; said actual exciting current value and torque current value detecting means including, means for integrating a value of each of two phase ac currents of said detected three phase ac currents and sampling said integrated value at a predetermined period; means for subjecting each of said sampled value of the integrated two phase ac currents to definite integration at said predetermined period; and second coordinate transformation means for transforming said definite integrated values to an actual exciting current value and torque current value, respectively, in said rotating magnetic field coordinate system.

Claim 37

A vector control system for a three-phase ac induction motor comprising: a power converter for generating three phase ac currents; an induction motor for receiving said three phase ac currents; means for detecting a value of each phase current of said three phase ac currents; means for receiving an exciting current command value and a torque current command value in a rotating magnetic field coordinate system for said induction motor; means for detecting an actual exciting current value and torque current value; means for detecting a deviation between said exciting current command value and said detected exciting current value and a deviation between said torque current command value and said detected torque current value; means for producing voltage commands in said rotating magnetic field coordinate system tending to reduce said deviations to zero; first coordinate transformation means for transforming said voltage commands to three phase ac voltage commands in a stator coordinate system; means responsive to said three phase ac command values to control said power converter; said actual exciting current value and torque current value detecting means including, means for integrating a value of each of two phase ac currents of said detected three phase ac currents and sampling said integrated value at a predetermined period; means for subjecting each of said sampled value of the integrated two phase ac currents to definite integration at said predetermined period; and second coordinate transformation means for transforming said definite integrated values to an actual exciting current value and torque current value, respectively, in said rotating magnetic field coordinate system.

Claim 38

A system according to claim 32, wherein said predetermined period is selected to be the same or integral multiple of a period of harmonic components contained in said three phase ac inputs.

Claim 39

A system according to claim 33, wherein said integer is preferably selected to be between 1 and 5.

Claim 40

A system according to claim 34, wherein said sampling means and definite integration means comprise voltage-frequency converting means for converting a magnitude of each of said two phase ac values to a number of pulses indicative thereof, means for counting each said number of pulses for said predetermined period, latch means for holding each said count value every said predetermined period, and differential computation means for calculating a difference between a value held at an nth period and a value held at a (n+1)th period to calculate each said definite integrated value.

Claim 41

A system according to claim 35, wherein said second coordinate transformation means comprises reference signal generating means for producing coordinate reference signals in accordance with a value of a primary angular frequency of said induction motor, thereby transforming each said definite integrated value in said stator coordinate system to a value in said rotating magnetic field coordinate system in accordance with said coordinate reference signals.

Claim 42

A system according to claim 36, wherein said reference signal generating means produces said coordinate reference signals in accordance with a signal delayed from said primary angular frequency signal by an angular phase value concerning to a product of said primary angular frequency of said induction motor and said predetermined period.

Claim 43

A system according to claim 36 or 37, wherein said second coordinate transformation means further comprises phase correcting means for correcting an amplitude value of each said coordinate transformed value in accordance with a value concerning to a magnitude of said predetermined period.

Claim 44

A system according to claim 36 or 37, wherein said second coordinate transformation means further comprises gain compensating means for correcting an amplitude value of each said coordinate transformed value in accordance with values concerning to a magnitude of said predetermined period and the value of said primary angular frequency.

Claim 45

A vector control system for a three phase ac induction motor comprising: a pulse width modulation-type power converter for generating three phase ac currents; an induction motor for receiving said three phase ac currents; means for detecting a value of each of said three phase ac currents; means for receiving an exciting current command value and a torque current command value in a rotating magnetic field coordinate system for said induction motor; means for detecting an actual exciting current value and torque current value; means for detecting a deviation between said exciting current command value and said detected exciting current value and a deviation between said torque current command value and said detected torque current value; means for producing voltage commands in said rotating magnetic field coordinate system tending to reduce said deviations to zero; first coordinate transformation means for transforming said voltage commands to three phase ac voltage commands in said stator coordinate system; and means responsive to said three phase ac voltage command values to control said power converter; said actual exciting current value and torque current value detecting means including, means for integrating a value of each of two phase ac currents of said detected phase currents and sampling the integrated value at a predetermined period; means for subjecting each of said sampled value of the integrated two phase ac currents to definite integration at said predetermined period; second coordinate transformation means for transforming said definite integrated values to an actual exciting current value and torque current value, respectively, in said rotating magnetic field coordinate system.

Claim 46

A vector control system for a three phase ac induction motor comprising: a pulse width modulation-type power converter for generating three phase ac currents; an induction motor for receiving said three phase ac currents; means for detecting a value of each of said three phase ac currents; means for receiving an exciting current command value and a torque current command value in a rotating magnetic field coordinate system for said induction motor; means for detecting an actual exciting current value and torque current value; means for detecting a deviation between said exciting current command value and said detected exciting current value and a deviation between said torque current command value and said detected torque current value; means for producing voltage commands in said rotating magnetic field coordinate system tending to reduce said deviations to zero; first coordinate transformation means for transforming said voltage commands to three phase ac voltage commands in said stator coordinate system; and means responsive to said three phase ac voltage command values to control said power converter; said actual exciting current value and torque current value detecting means including, means for integrating a value of each of two phase ac currents of said detected phase currents and sampling the integrated value at a predetermined period; means for subjecting each of said sampled value of the integrated two phase ac currents to definite integration at said predetermined period; second coordinate transformation means for transforming said definite integrated values to an actual exciting current value and torque current value, respectively, in said rotating magnetic field coordinate system.

Claim 47

A system according to claim 40, wherein said predetermined period is selected to be integral multiple of a period of a carrier wave of said pulse width modulation-type power converter.

Claim 48

A system according to claim 42, wherein said sampling means and definite integration means comprise voltage-frequency converting means for converting a value of each of said two phase ac currents to a number of pulses proportional to the magnitude thereof, counting means for counting each said number of pulses for said predetermined period, latch means for holding each said count value every said predetermined period, and differential computation means for calculating a difference between a value held at an nth period and a value held at a (n+1)th period thereby calculating each said definite integrated value.

Claim 49

A system according to claim 42, wherein said second coordinate transformation means comprises reference signal generating means for producing coordinate reference signals in accordance with a value of a primary angular frequency of said induction motor whereby each said definite integrated value in said stator coordinate system is transformed to a value in said rotating magnetic field coordinate system in accordance with said coordinate reference signals.

Claim 50

A system according to claim 43, wherein said reference signal generating means produces said coordinate reference signals on the basis of a signal delayed from said primary angular frequency signal by an angular phase value concerning to a product of said primary angular frequency of said induction motor and said predetermined period.

Claim 51

A system according to claim 43 or 44, wherein said second coordinate transformation means further comprises phase correcting means for correcting an amplitude value of each said coordinate transformed value in accordance with a value concerning to a magnitude of said predetermined period.

Claim 52

A system according to claim 43 or 44, wherein said second coordinate transformation means further comprises gain compensating means for correcting an amplitude value of each said coordinate transformed value in accordance with values concerning to a magnitude of said predetermined period and the value of said primary angular frequency.

Claim 53

A vector control system for a three-phase ac induction motor comprising: a power converter for generating three phase ac currents; an induction motor for receiving said three phase ac currents; means for detecting a value of each of said three phase ac currents; means for receiving an exciting current command value and a torque current command value in a rotating magnetic field coordinate system for said induction motor; means for detecting an actual exciting current value and torque current value; means for detecting a deviation between said exciting current command value and said detected exciting current and a deviation between said torque current command value and said detected torque current value; means for producing voltage commands in said rotating magnetic field coordinate system tending to reduce said deviations to reduce; first coordinate transformation means for transforming said three phase voltage commands to three phase ac voltage commands in a stator coordinate system; and means responsive to said three phase ac voltage command values to control said power converter; said actual exciting current value and torque current value detecting means comprising, 3phase-2 phase converting means for converting said detected three phase currents to orthogonal two phase ac currents in said stator coordinate system; means for integrating a value of each of said orthogonal two phase ac currents and sampling the integrated value at a predetermined period; means for detecting a difference between an integrated value of an nth sampled value and an integrated value of a (n+1)th sampled value (n is a positive integer); and second coordinate transformation means for transforming said differential values to an actual exciting current value and torque current value, respectively, in said rotating magnetic field coordinate system.

Claim 54

A vector control system for a three-phase ac induction motor comprising: a power converter for generating three phase ac currents; an induction motor for receiving said three phase ac currents; means for detecting a value of each of said three phase ac currents; means for receiving an exciting current command value and a torque current command value in a rotating magnetic field coordinate system for said induction motor; means for detecting an actual exciting current value and torque current value; means for detecting a deviation between said exciting current command value and said detected exciting current and a deviation between said torque current command value and said detected torque current value; means for producing voltage commands in said rotating magnetic field coordinate system tending to reduce said deviations to reduce; first coordinate transformation means for transforming said three phase voltage commands to three phase ac voltage commands in a stator coordinate system; and means responsive to said three phase ac voltage command values to control said power converter; said actual exciting current value and torque current value detecting means comprising, 3phase-2 phase converting means for converting said detected three phase currents to orthogonal two phase ac currents in said stator coordinate system; means for integrating a value of each of said orthogonal two phase ac currents and sampling the integrated value at a predetermined period; means for detecting a difference between an integrated value of an nth sampled value and an integrated value of a (n+1)th sampled value (n is a positive integer); and second coordinate transformation means for transforming said differential values to an actual exciting current value and torque current value, respectively, in said rotating magnetic field coordinate system.

Claim 55

A system according to claim 47, wherein said predetermined period is selected to be the same or integral multiple of a period of harmonic components contained in said three phase ac currents.

Claim 56

A system according to claim 48, wherein said integer is preferably selected to be between 1 and 5.

Claim 57

A system according to claim 49, wherein said sampling means and integrating means comprise voltage frequency converting means for converting a value of each of said two phase ac currents to a number of pulses proportional to the magnitude thereof, counter means for counting each said number of pulses for said predetermined period, and latch means for holding each said count value every said predetermined period, and said differential detecting means comprises differential computation means for calculating a difference between a value held at an nth period and a value held at a (n+1)th period thereby calculating each said differential value.

Claim 58

A system according to claim 50, wherein said second coordinate transformation means comprises reference signal generating means for producing coordinate reference signals in accordance with a value of a primary angular frequency of said induction motor whereby each said definite integrated value in said stator coordinate system is transformed to a value in said rotating magnetic field coordinate system in accordance with said coordinate reference signals.

Claim 59

A system according to claim 51, wherein said reference signal generating means produces said coordinate reference signals on the basis of a signal delayed from said primary angular frequency signal by an angular phase value concerning to a product of said primary angular frequency of said induction motor and said predetermined period.

Claim 60

A system according to claim 51 or 52, wherein said second coordinate transformation means further comprises phase correcting means for correcting an amplitude value of each said coordinate transformed value in accordance with a value concerning to a magnitude of said predetermined period.

Claim 61

A system according to claim 51 or 52, wherein said second coordinate transformation means further comprises gain compensating means for correcting an amplitude of each said coordinate transformed value in accordance with values concerning to a magnitude of said predetermined period and the value of said primary angular frequency.

Claim 62

A vector control system for a three-phase ac induction motor comprising: a power converter for generating three phase ac currents; an induction motor for receiving said three phase ac currents; means for detecting a value of each of said three phase ac currents; means for receiving an exciting current command value and a torque current command value in a rotating magnetic field coordinate system for said induction motor; means for detecting an actual exciting current value and torque current value; means for detecting a deviation between said exciting current command value and said detected exciting current value and a deviation between said torque current command value and said detected torque current value; means for producing voltage commands in said rotating magnetic field coordinate system tending to reduce said deviations to zero; first coordinate transformation means for transforming said voltage commands to three phase ac voltage commands in said stator coordinate system; and means responsive to said three phase ac voltage command values to control said power converter; said actual exciting current value and torque current value detecting means including; means for integrating a value of each of two phase ac currents of said detected three phase ac currents and sampling the integrated value at a predetermined period; phase converting means for converting said integrated values to orthogonal two phase ac values in said stator coordinate system; means for detecting a difference between an integrated value of an nth sampled value and an integrated value of a (n+1)th sampled value of each of said converted orthogonal two phase ac values (n is a positive integer); and second coordinate transformation means for transforming said differential values to an actual exciting current value and torque current value, respectively, in said rotating magnetic field coordinate system.

Claim 63

A vector control system for a three-phase ac induction motor comprising: a power converter for generating three phase ac currents; an induction motor for receiving said three phase ac currents; means for detecting a value of each of said three phase ac currents; means for receiving an exciting current command value and a torque current command value in a rotating magnetic field coordinate system for said induction motor; means for detecting an actual exciting current value and torque current value; means for detecting a deviation between said exciting current command value and said detected exciting current value and a deviation between said torque current command value and said detected torque current value; means for producing voltage commands in said rotating magnetic field coordinate system tending to reduce said deviations to zero; first coordinate transformation means for transforming said voltage commands to three phase ac voltage commands in said stator coordinate system; and means responsive to said three phase ac voltage command values to control said power converter; said actual exciting current value and torque current value detecting means including; means for integrating a value of each of two phase ac currents of said detected three phase ac currents and sampling the integrated value at a predetermined period; phase converting means for converting said integrated values to orthogonal two phase ac values in said stator coordinate system; means for detecting a difference between an integrated value of an nth sampled value and an integrated value of a (n+1)th sampled value of each of said converted orthogonal two phase ac values (n is a positive integer); and second coordinate transformation means for transforming said differential values to an actual exciting current value and torque current value, respectively, in said rotating magnetic field coordinate system.

Claim 64

A system according to claim 55, wherein said predetermined period is selected to be the same or integral multiple of a period of harmonic components contained in said three phase ac currents.

Claim 65

A system according to claim 56, wherein said integer is preferably selected to be between 1 and 5.

Claim 66

A system according to claim 57, wherein said sampling means and integrating means comprise voltage-frequency converting means for converting a value of each of said two phase ac currents to a number of pulses porportional to the magnitude thereof, counter means for counting each said number of pulses for said predetermined period, and latch means for holding each said count value every said predetermined period, and wherein said differential detecting means comprises differential computation means for calculating a difference between a value held at an nth period and a value held at a (n+1)th period thereby calculating each said differential value.

Claim 67

A system according to claim 58, wherein said second coordinate transformation means comprises reference signal generating means for producing coordinate reference signals in accordance with a value of a primary angular frequency of said induction motor whereby each said definite integrated value in said stator coordinate system is transformed to a value in said rotating magnetic field coordinate system in accordance with said coordinate reference signals.

Claim 68

A system according to claim 59, wherein said reference signal generating means produces said coordinate reference signals on the basis of a signal delayed from said primary angular frequency signal by an angular phase value concerning to a product of said primary angular frequency of said induction motor and said predetermined period.

Claim 69

A system according to claim 59 or 60, wherein said second coordinate transformation means further comprises phase correcting means for correcting an amplitude value of each said coordinate transformed value in accordance with a value concerning to a magnitude of said predetermined period.

Claim 70

A system according to claim 59 or 60, wherein said second coordinate transformation means further comprises gain compensating means for correcting an amplitude value of each said coordinate transformed value in accordance with values concerning to a magnitude of said predetermined period and the value of said primary angular frequency.