Method of induction motor control and electric drive realizing this method

A method of induction motor control, wherein interrelated control is provided for the rotor speed, the torque of said induction motor, the amplitude of the rotor flux linkage, and steady-state, dynamic, electromagnetic, power and thermal processes in said induction motor by introducing vector phase-current control involving interrelated changes of the stator current phase and amplitude, the intensity and angular position of the magnetic field, which are defined by the phase and said amplitude of the rotor flux linkage as functions of the desired torque of said induction motor, and, to this end, comprises the steps of assigning a control input proportional to the desired amplitude of the rotor flux linkage;

• producing a first quadrature component of the desired stator current amplitude defined by the flux-producing component of said stator current amplitude as a function of said desired amplitude of the rotor flux linkage;
• assigning a second control input whose magnitude is proportional to said desired torque of said induction motor, as a function of the desired rotor speed and the actual magnitude of said rotor speed;
• producing a second quadrature component of said desired stator current amplitude, which defines the torque-producing component of said stator current amplitude, as a function of said magnitude of said desired torque of said induction motor;
• controlling, simultaneously with the step of producing the second quadrature component, the stator current synchronous frequency equal to the steady-state frequency of symmetrical instantaneous stator phase currents in steady-state conditions of said induction motor;
• generating the synchronization frequency defined by said stator current synchronous frequency equal to the sum of two components of said synchronization frequency;
• changing one component in proportion with said rotor speed;
• changing second component of said synchronization frequency as a function of the ratio of said desired torque of said induction motor to the square value of said desired amplitude of the rotor flux linkage;
• effecting phase-after-phase control of said symmetrical instantaneous stator phase currents in the phase windings of said stator of said induction motor, as a function of the difference between the desired and said measured instantaneous stator phase currents;
• producing said desired stator current amplitude equal to said instantaneous phase current amplitude and said stator current amplitude equal to the quadrature sum of said first and second quadrature components of said desired stator current amplitude;
• producing said phase of the desired and measured instantaneous phase currents by sweeping said synchronization frequency into a synchronization phase equal to said phase of said rotor flux linkage and the synchronous stator current phase and defined by the instantaneous phase of said instantaneous stator current phase in one of said stator phase windings, which is a reference phase winding of said stator, with the zero value of said desired torque of said induction motor;
• producing said current phase of said stator, which is defined by said instantaneous phase of the instantaneous stator phase current in said reference phase winding of said stator of said induction motor;
• changing said stator current phase relative to said synchronous stator current synchronous phase to a value of the stator current phase shift proportional to the inverse tangent function of the ratio of said torque-producing component of the stator current amplitude to said flux-producing component of the stator current amplitude;
• controlling the stator current amplitude as a function of the desired torque of said induction motor by increasing said desired amplitude of the rotor flux linkage in response to the increase in said torque of said induction motor;
• and analogously and symmetrically controlling said instantaneous phase currents in other said stator windings.