Outline
    Introduction
    Analogy to DC Drive
    Principles of Field Orientation Control
    Rotor Flux Orientation Control
       
         Indirect Rotor Flux Orientation (IRFO)
       
         Direct Rotor Flux Orientation (DRFO)
    Stator Flux Orientation Control
       
         Direct Stator Flux Orientation (DSFO)
    References
                                                         2
                           Introduction
     
        Induction Motor (IM) drives are replacing DC drives 
       because:
        
           Induction motor is simpler, smaller in size, less maintenance
        
           Less cost
        
           Capability of faster torque response
        
           Capability of faster speed response (due to lower inertia)
     
        DC motor is superior to IM with respect to ease of control
        
           High performance with simple control 
        
           Due to decoupling component of torque and flux
                                                                         3
                               Introduction
                             Induction Motor Drive
               Scalar Control                   Vector Control or Field Orientation 
                                                              Control
  •
   Control of current/voltage/frequency      •
                                               control of magnitude and phase of 
  magnitude based on steady-state            currents and voltages based on dynamic 
  equivalent circuit model                   model
      • ignores transient conditions             • Capable of observing steady state 
                                                   & transient motor behaviour
      • for low performance drives               • for high performance drives
  •
   Simple implementation                     •
                                              Complex implementation
  •
   Inherent coupling of torque and flux      •
                                              Decoupling of torque and flux
      • Both are functions of voltage and        • similar to the DC drive
        frequency                            •
                                              Suitable for all applications previously 
  •
   Leads to sluggish response                covered by DC drives
  •
   Easily prone to instability
                                                                                 4
                     Analogy to DC Drive
   •  In the DC motor: T  = k  I
                           e      f  a                       
   •    controlled by controlling I                           f
        f                            f
   •  I  same direction as field 
       f                          f
   •  I same direction as field 
       a                          a
   •  I and  always perpendicular 
       a      f
      and decoupled
   •  Hence, T  = k  I
                e       f  a          
                   = k’ I I sin 90    a
                        f  a 
                 = k’(I x I )
                        f   a
   •  Keeping  constant, T  
                 f            e
      controlled by controlling I
                                  a
   •  I , I  ,   and   are space vectors
       a  f  a       f
                                                                           5
                  Analogy to DC Motor
                                   •  In the Induction Motor:
           s                              T  = k x 
                   a                        e       r     s
                                  r
        c’                     b’  •    produced by stator currents
                                        s 
                                   •  r produced by induced rotor 
                                      currents
                                   •  Both   and  rotates at 
                                              s       r
                                      synchronous speed  
        b                                                 s
                               c   •  Angle between   and  
                                                        s       r
                                      varies with load, and motor 
                                      speed 
                                              r
                                   •  Torque and flux are coupled.
                                                                    6