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Direct Torque Control of Induction Machine

Direct Torque Control of Induction Machine. Dr. Nik Rumzi Nik Idris Department of Energy Conversion, Faculty of Electrical Engineering, Universiti Teknologi Malaysia. Basic Principles of DTC. High performance induction motor drives. Field Oriented Control - FOC.

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Direct Torque Control of Induction Machine

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  1. Direct Torque Control of Induction Machine Dr. Nik Rumzi Nik Idris Department of Energy Conversion, Faculty of Electrical Engineering, Universiti Teknologi Malaysia

  2. Basic Principles of DTC • High performance induction motor drives • Field Oriented Control - FOC • Direct Torque Control - DTC

  3. Tref Sa + Voltage Source Inverter Voltage vector selector Sb _ IM T Sc ref + _   + Vdc - Stator flux and torque estimator Basic Principles of DTC • Stator flux and torque control within hysteresis bands • Voltage vector selected based on stator flux and torque demands

  4. Basic Principles of DTC How the voltage vectors control the flux? How the voltage vectors control the torque? These questions will be answered in the following slides

  5. Basic Principles of DTC • Space vector equations of IM :

  6. Basic Principles of DTC • Space vector equations of IM :

  7. Basic Principles of DTC Direct Flux Control • From stator voltage equation : • Neglecting drop across Rs :

  8. Basic Principles of DTC Direct Flux Control • Voltage vectors for 3-phase VSI

  9. 010 110 011 100 Dy 001 101 s Hysteresis Flux band y s Basic Principles of DTC Direct Flux Control

  10. Basic Principles of DTC Direct Flux Control q Sector IV Sector III 60o I d Sector II Sector V Sector I Sector VI

  11. vs,4 Sector II vs,3 vs,4 Sector I vs,3 vs,2 Hysteresis band vs,3 vs,4 vs,3 vs,5 vs,2 vs,16 vs,6 Basic Principles of DTC Direct Flux Control If the flux in kth sector k +1 vector increases  k + 2 vector reduces  • Voltage vector vs,2 and vs,3 in sector I • Voltage vector vs,3 and vs,4 in sector II

  12. ref + /2 ref Flux ref - /2 t Flux error status Flux error /2 ref 1 + Flux error 0 t - /2 _ 0 0 Flux Error Status 1 0 t   Basic Principles of DTC Direct Flux Control

  13. Basic Principles of DTC Direct Torque Control • IM torque equation

  14. Basic Principles of DTC Direct Torque Control • It can be shown that • Rotor flux follows the stator flux with a time constant r

  15. Basic Principles of DTC Direct Torque Control t = t1 t = t1 + t q q Applying voltage vectors rotating in the same direction s s Rotate continuously Rotate continuously sr sr d r r d q t = t1 + t Applying voltage vectors in opposite direction or zero voltage vectors Rotate continuously s sr r d

  16. Basic Principles of DTC Direct Torque Control • Three cases are considered : • Case 1 • Forward active voltage vectors • stator flux increases or decreases • Increases sr • Increases Torque

  17. Basic Principles of DTC Direct Torque Control Case 2 Zero voltage vectors • stator flux stops • Decreases sr • Decreases Torque

  18. Basic Principles of DTC Direct Torque Control Case 3 Reverse active voltage vectors • stator flux increases or decreases • Decreases sr rapidly • Decreases Torque rapidly

  19. 1 + Tref 0 -1 _ T T Basic Principles of DTC Direct Torque Control Torque reference Torque T/2 T/2 Torque error T Speed Torque error status 1 0 -1

  20. Basic Principles of DTC • By limiting the torque and flux within their hysteresis bands, de-coupling of torque and flux can be achieved

  21. Tref Sa + Voltage Source Inverter Voltage vector selector Sb _ IM T Sc ref + _   + Vdc - Stator flux and torque estimator Basic Principles of DTC • Stator flux and torque control within hysteresis bands • Voltage vector selected based on stator flux and torque demands

  22. Basic Principles of DTC Selection table for optimum switching pattern

  23. Stator Flux and Torque Estimation • Accurate estimation to ensure proper operation and stability • Various methods proposed • voltage model • current model • closed-loop observer

  24. Stator Flux and Torque Estimation • Stator flux- voltage model • Problems: • dc drift • stator resistance variation

  25. Stator Flux and Torque Estimation • Torque estimation • In d-q form

  26. Implementation of DTC • Basic I/O requirements: • Phase Current measurement • DC Link Voltage measurement • Speed measurement from Incremental Encoder for closed-loop speed control (optional) • Fast processor to reduce torque ripple

  27. Implementation of DTC

  28. Speed Current Torque d-flux Experimental Results • From oscilloscope • 55s sampling, 240V, ¼ HP IM Step speed reference

  29. Speed Current Torque Experimental Results • From oscilloscope • 55s sampling, 240V, ¼ HP IM Square wave speed reference

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