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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
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