Scalar decoupled control for an induction machine

An induction machine drive for achieving fast transient response, comprising:

• a voltage fed inverter providing variable frequency a.c. power to the induction machine;
• torque sensing means coupled to said machine for generating a signal indicative of actual machine torque;
• first comparison means coupled to said torque sensing means for comparing a commanded torque signal to said signal indicative of actual machine torque to generate a commanded torque error;
• slip command generating means for generating a slip command from the commanded torque error;
• a first function generator coupled to said slip generating means and being responsive to commanded slip for providing a stator current magnitude command to maintain rotor flux constant during steady state condition at a predetermined value dependent on a predetermined relationship between slip and stator current, said stator current magnitude command providing a torque producing component;
• stator current measuring means coupled to said induction machine for generating a signal indicative of actual stator current;
• second comparison means coupled to said stator current measuring means and to said first function generator for comparing commanded stator current with actual stator current to generate a stator current error signal;
• stator voltage command signal generating means responsive to said stator current error signal for generating a first stator voltage command signal;
• signal generating means responsive to rotor speed of said machine for generating a signal indicative of actual rotor speed;
• first summation means coupling said slip command generating means and signal generating means to said inverter, said first summation means adding said slip command to said actual rotor speed to generate a stator frequency command for said inverter;
• a second function generator coupled to said summation means and being responsive to changes in commanded stator frequency for generating a decoupling signal to compensate said first stator voltage command to maintain rotor flux constant at said predetermined value during transient conditions due to changes in the commanded machine stator frequency;
• and
• second summation means coupling said second function generator and said stator voltage command signal generating means to said inverter, said second summation means adding the decoupling signal from said second function generator to said first stator voltage command signal for supplying a compensated stator voltage command signal to said inverter.