Torque controller for an AC motor drive and AC motor drive embodying the same

Claim 2

Apparatus for the determination of the torque of a rotating induction motor including p pairs of poles, having a rotor leakage inductance L 2 , a magnetizing inductance L M and a rotor resistance R 2 , comprising: first sensing means for deriving a first signal representative of the stator current I 1 ; second sensing means for deriving a second signal representative of the slip angular frequency ω 2 of the motor; first combining means responsive to said first signal for providing a third signal representative of I 1 2 ; and second combining means responsive to said second signal and to said third signal for deriving a signal representative of the instantaneous torque T in accordance with the formula: ##EQU5##

Claim 3

The apparatus of claim 1, with said first and second signals being converted into digital signals, respectively; with computer means being provided including said first and second combining means; said second combining means including a look-up table having stored data representing the function: ##EQU6## said computer means providing with said second digital signal an address signal representing (R 2 /ω 2 ) and addressing said look-up table in response thereto to provide a fourth signal representative of F; said computer means providing said third signal representative of I 1 2 in response to said first signal and combining said third signal with said fourth signal in accordance with the relation T=I 1 2 ×F to provide a fifth signal representative of the instantaneous torque T of the motor.

Claim 4

Apparatus for the determination of the torque of a rotating induction motor including p pairs of poles, having a rotor leakage inductance L 2 , a magnetizing inductance L M and a rotor resistance R 2 , comprising: first sensing means for deriving a first signal representative of the stator current I 1 ; second sensing means for deriving a second signal representative of the slip angular frequency ω 2 of the motor; with said first and second signals being converted into digital signals, respectively; with computer means being provided including a first look-up table having stored data representing the function: ##EQU7## said computer means providing with said second digital signal an address signal representing (R 2 /ω 2 ) and addressing said first look-up table in response thereto to provide a third signal representative of F; said computer means providing a fourth signal representative of I I 2 in response to said first signal and combining said third signal with said fourth signal in accordance with the relation T=I 1 2 ×F to provide a fifth signal representative of the instantaneous torque T of the motor; the apparatus being combined with a system for automatically correcting said fifth signal derived from the apparatus, the system comprising: means for storing in said computer means the value of R 2 under initial conditions of temperature and with the motor idle; means for measuring the temperature of the stator when the motor is running to derive a signal representaive of a temperature change upward from said initial conditions; means in said computer means for deriving with said temperature change representative signal a sixth signal indicative of a corresponding change in the rotor resistance R 2 ; said computer means applying said sixth signal as a corrective signal to said address signal (R 2 /ω 2 ).

Claim 5

Apparatus for the determination of the torque of a rotating induction motor including p pairs of poles, having a rotor leakage inductance L 2 , a magnetizing inductance L M and a rotor resistance R 2 , comprising: first sensing means for deriving a first signal representative of the stator current I 1 ; second sensing means for deriving a second signal representative of the slip angular frequency ω 2 of the motor; with said first and second signals being converted into digital signals, respectively; with computer means being provided including a first look-up table having stored data representing the function: ##EQU7## said computer means providing with said second digital signal an address signal representing (R 2 /ω 2 ) and addressing said first look-up table in response thereto to provide a third signal representative of F; said computer means providing a fourth signal representative of I I 2 in response to said first signal and combining said third signal with said fourth signal in accordance with the relation T=I 1 2 ×F to provide a fifth signal representative of the instantaneous torque T of the motor; the apparatus being combined with a system for automatically correcting said fifth signal derived from the apparatus, the system comprising: means for storing in said computer means the value of R 2 under initial conditions of temperature and with the motor idle; means for measuring the temperature of the stator when the motor is running to derive a signal representaive of a temperature change upward from said initial conditions; means in said computer means for deriving with said temperature change representative signal a sixth signal indicative of a corresponding change in the rotor resistance R 2 ; said computer means applying said sixth signal as a corrective signal to said address signal (R 2 /ω 2 ).

Claim 6

The system of claim 3, with said sixth signal being derived from said temperature change representative signal by calculating ΔR 1 /R 1 (c), where ΔR 1 is a change in the stator resistance R 1 (c) under said initial conditions of temperature, when the temperature change in the rotor is ΔTs.

Claim 7

The system of claim 4, with said sixth signal being scaled by a value representing R 2 (c) the rotor resistance for said initial conditions of temperature.

Claim 8

The system of claim 4, with said sixth signal being scaled by a value representing k[R 2 (c)] 2 /R 1 (c), where R 2 (c) and R 1 (c) are the rotor and stator resistances, respectively, for said initial conditions of temperature, and k is a coefficient of proportionality.

Claim 9

Apparatus for the determination of the torque of a rotating induction motor including p pairs of poles, having a rotor leakage inductance L 2 , a magnetizing inductance L M and a rotor resistance R 2 , comprising: first sensing means for deriving a first signal representative of the stator current I 1 ; second sensing means for deriving a second signal representative of the slip angular frequency ω 2 of the motor; with said first and second signals being converted into digital signals, respectively; with computer means being provided including a first look-up table having stored data representing the function: ##EQU8## said computer means providing with said second digital signal an address signal representing (R 2 /ω 2 ) and addressing said first look-up table in response thereto to provide a third signal representative of F; said computer means providing a fourth signal representative of I 1 2 in response to said first signal and combining said third signal with said fourth signal in accordance with the relation T=I 1 2 ×F to provide a fifth signal representative of the instantaneous torque T of the motor; the apparatus being combined with a system for automatically calibrating the apparatus whenever the motor is running at least at rated speed, the system comprising: means for sensing the power W d of the motor, the frequency ω 1 of the stator current to derive a power signal and a stator frequency signal, respectively; said computer means calculating the correct torque T c with the function: p×W.sub.d /ω.sub.1 =T.sub.c ; by combining said power signal and said stator frequency signal to derive a signal representative of the correct torque T c ; said computer means including a second look-up table based on the function: R.sub.2 /ω.sub.2 =f*(F) where f*(F) is the inverse function of said function F; said computer means addressing said second look-up table with a signal representative of said calculated value T c , thereby to derive a recalibrated value R 2 (a) based on said signal ω 2 and said value T c ; said apparatus deriving at speeds less than rated speed said recalibrated value R 2 (a) as an address combined with said ω 2 signal for addressing said first look-up table.

Claim 10

Apparatus for the determination of the torque of a rotating induction motor including p pairs of poles, having a rotor leakage inductance L 2 , a magnetizing inductance L M and a rotor resistance R 2 , comprising: first sensing means for deriving a first signal representative of the stator current I 1 ; second sensing means for deriving a second signal representative of the slip angular frequency ω 2 of the motor; with said first and second signals being converted into digital signals, respectively; with computer means being provided including a first look-up table having stored data representing the function: ##EQU8## said computer means providing with said second digital signal an address signal representing (R 2 /ω 2 ) and addressing said first look-up table in response thereto to provide a third signal representative of F; said computer means providing a fourth signal representative of I 1 2 in response to said first signal and combining said third signal with said fourth signal in accordance with the relation T=I 1 2 ×F to provide a fifth signal representative of the instantaneous torque T of the motor; the apparatus being combined with a system for automatically calibrating the apparatus whenever the motor is running at least at rated speed, the system comprising: means for sensing the power W d of the motor, the frequency ω 1 of the stator current to derive a power signal and a stator frequency signal, respectively; said computer means calculating the correct torque T c with the function: p×W.sub.d /ω.sub.1 =T.sub.c ; by combining said power signal and said stator frequency signal to derive a signal representative of the correct torque T c ; said computer means including a second look-up table based on the function: R.sub.2 /ω.sub.2 =f*(F) where f*(F) is the inverse function of said function F; said computer means addressing said second look-up table with a signal representative of said calculated value T c , thereby to derive a recalibrated value R 2 (a) based on said signal ω 2 and said value T c ; said apparatus deriving at speeds less than rated speed said recalibrated value R 2 (a) as an address combined with said ω 2 signal for addressing said first look-up table.

Claim 11

The system of claim 7 with said recalibrated value R 2 (a) being derived recurrently when the motor is running at least at rated speed, a new recalibrated value being combined with a preceding recalibrated value by an integrator to form said first look-up table address.

Claim 12

The apparatus of claim 1, with said motor being supplied from an inverter coupled to a DC voltage source, the inverter being controlled in relation to the frequency of the stator current for adjusting the speed of the motor; a torque controller being provided for adjusting the frequency of the stator in relation to said torque T representative signal and a torque reference signal.