Vector control method and system for an induction motor

Claim 1

An induction motor decoupled vector control system, which comprises: (a) speed sensing means (4) for detecting a rotor angular frequency w r of an induction motor; (b) proportional integrating means (5) for generating a primary reference current i 1 β * corresponding to a secondary reference driving current on the basis of a difference between a reference rotor angular frequency w r * and a detected rotor angular frequency w r in order to obtain a reference torque; (c) supply voltage angular frequency calculating means (6) for calculating a primary supply voltage angular frequency w 0 on the basis of the primary reference current i 1 β *, a primary reference current i 1 α * corresponding to a secondary magnetic flux, a detected rotor angular frequency w r , and a ratio τ 2 of a secondary inductance L 2 to a secondary resistance r 2 ; (d) SIN/COS signal generating means (8) for generating a sine wave signal with an angular frequency w 0 and a cosine wave signal with an angular frequency w 0 , independently; (e) first calculating means (3D) for calculating fixed d-q coordinate primary voltages e 1d and e 1q on the basis of the primary reference currents i 1 α * and i 1 β * and the sine and cosine wave signals in accordance with following expressions: e.sub.1d =(r.sub.1 +L.sub.1 S) cos w.sub.0 t·i.sub.1α *-(r.sub.1 +L.sub.σ S) sin w.sub.0 t·i.sub.1β * e.sub.1q =(r.sub.1 +L.sub.1 S) sin w.sub.0 t·i.sub.1α *+(r.sub.1 +L.sub.σ S) cos w.sub.0 t·i.sub.1β * where r 1 denotes a primary resistance; L 1 denotes a primary inductance; L.sub.σ denotes an equivalent leakage inductance (L 1 L 2 -M 2 )/L 2 M: mutual inductance; S denotes a Laplace operator; (f) second calculating means (7D) for calculating three-phase primary reference voltages e a *, e b *, e c * on the basis of the calculated 2-phase primary reference voltages e 1d , e 1q in accordance with the following expressions: ##EQU12## (g) triangular signal generating means (9) for generating a triangular wave signal in synchronization with said SIN/COS wave signals said triangular signal generating means including: (1) an absolute value detecting unit (11) for generating a signal the voltage level of which is proportional to the magnitude of supply voltage angular frequency w 0 irrespective of the plus or minus sign thereof; (2) a voltage-frequency converter (12) for converting the output of said absolute value detection unit into a signal with a frequency proportional to the output voltage level of said absolute value detection unit; (3) a plurality of series-connected dividers (13, 14, 15) for dividing the frequency of the signal outputted from said voltage-frequency converter; (4) a switching signal generator (17) for outputting a plurality of switching signals according to the magnitude of supply voltage angular frequency w 0 ; (5) a switching unit (16) selectively connected to said series-connected dividers for selectively outputting the signal outputted from said voltage-frequency converter in such a way that less-times divided converter signals are outputted when the supply voltage frequency is low and many-times divided converter signals are outputted when the supply voltage frequency is high; (6) a second up-down counter (18) for counting the converter signals up or down repeatedly in response to carry signals generated therefrom; (7) a third digital-analog converter (20) for converting the counted digital value into analog values corresponding thereto; and (8) a pulse generator (37) for outputting a pulse signal with a predetermined frequency to said switching unit (16) when the supply voltage angular frequency is substantially zero or when the motor stops in order to apply an initial secondary magnetic flux; and (h) PWM inverter means (2C) for generating three PWM (pulse width modulated) control signals in response to the calculated three-phase primary voltages e a *, e b *, e c * and the generated triangular wave signals, in order to drive a 3-phase induction motor.

Claim 3

A method of vector-controlling an induction motor, which comprises the following steps of: (a) detecting a rotor angular frequency w r of an induction motor; (b) determining a primary reference current i 1 β * corresponding to a secondary reference driving current on the basis of a difference between a reference rotor angular frequency w r * and a detected rotor angular frequency w r in order to generate a reference torque; (c) calculating a primary supply voltage angular frequency w 0 on the basis of the determined primary reference current i 1 β *, a constant primary reference current i 1 α * corresponding to a secondary magnetic flux, a detected rotor angular frequency w r and a ratio τ 2 of a secondary inductance L 2 to a secondary resistance r 2 ; (d) generating a sine wave signal with an angular frequency w 0 and a cosine wave signal with an angular frequency w 0 , independently; (e) calculating fixed d-q coordinate primary voltages e 1d and e 1q on the basis of the primary reference currents i 1 α * and i 1 β * and the sine and cosine wave signals in accordance with following expressions: e.sub.1d =(r.sub.1 +L.sub.1 S) cos w.sub.0 t·i.sub.1α *-(r.sub.1 +L.sub.σ S) sin w.sub.0 t·i.sub.1β * e.sub.1q =(r.sub.1 +L.sub.1 S) sin w.sub.0 t·i.sub.1α *+(r.sub.1 +L.sub.σ S) cos w.sub.0 t·i.sub.1β * where r 1 denotes a primary resistance; L 1 denotes a primary inductance; L.sub.σ denotes an equivalent total leakage inductance (L 1 L 2 -M 2 )/L 2 M: mutual inductance; S denotes a Laplace operator; (f) calculating primary reference three-phase voltages e a *, e b *, e c * on the basis of the calculated primary reference 2-phase primary voltages e 1d , e 1q in accordance with the following expressions: ##EQU13## (g) generating a triangular wave signal with an angular frequency w 0 in synchronization with said SIN/COS wave signals, and further a triangular wave signal with a predetermined frequency when the motor stops in order to apply an initial secondary magnetic flux; and (h) generating three PWM (pulse width modulated) control signals in response to the calculated three-phase primary voltages e a *, e b *, e c * and the generated triangular wave signals, in order to drive a 3-phase induction motor.

Claim 4

A method of vector-controlling an induction motor, which comprises the following steps of: (a) detecting a rotor angular frequency w r of an induction motor; (b) determining a primary reference current i 1 β * corresponding to a secondary reference driving current on the basis of a difference between a reference rotor angular frequency w r * and a detected rotor angular frequency w r in order to generate a reference torque; (c) calculating a primary supply voltage angular frequency w 0 on the basis of the determined primary reference current i 1 β *, a constant primary reference current i 1 α * corresponding to a secondary magnetic flux, a detected rotor angular frequency w r and a ratio τ 2 of a secondary inductance L 2 to a secondary resistance r 2 ; (d) generating a sine wave signal with an angular frequency w 0 and a cosine wave signal with an angular frequency w 0 , independently; (e) calculating fixed d-q coordinate primary voltages e 1d and e 1q on the basis of the primary reference currents i 1 α * and i 1 β * and the sine and cosine wave signals in accordance with following expressions: e.sub.1d =(r.sub.1 +L.sub.1 S) cos w.sub.0 t·i.sub.1α *-(r.sub.1 +L.sub.σ S) sin w.sub.0 t·i.sub.1β * e.sub.1q =(r.sub.1 +L.sub.1 S) sin w.sub.0 t·i.sub.1α *+(r.sub.1 +L.sub.σ S) cos w.sub.0 t·i.sub.1β * where r 1 denotes a primary resistance; L 1 denotes a primary inductance; L.sub.σ denotes an equivalent total leakage inductance (L 1 L 2 -M 2 )/L 2 M: mutual inductance; S denotes a Laplace operator; (f) calculating primary reference three-phase voltages e a *, e b *, e c * on the basis of the calculated primary reference 2-phase primary voltages e 1d , e 1q in accordance with the following expressions: ##EQU13## (g) generating a triangular wave signal with an angular frequency w 0 in synchronization with said SIN/COS wave signals, and further a triangular wave signal with a predetermined frequency when the motor stops in order to apply an initial secondary magnetic flux; and (h) generating three PWM (pulse width modulated) control signals in response to the calculated three-phase primary voltages e a *, e b *, e c * and the generated triangular wave signals, in order to drive a 3-phase induction motor.