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EEEB2833 Electrical Machines & Drives

EEEB2833 Electrical Machines & Drives. DC Drives By Dr. Ungku Anisa Ungku Amirulddin Department of Electrical Power Engineering College of Engineering. Outline. Power Electronics Converters for DC Drives Controlled Rectifier Fed DC Drives Single Phase Three Phase

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EEEB2833 Electrical Machines & Drives

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  1. EEEB2833 Electrical Machines & Drives DC Drives By Dr. UngkuAnisaUngkuAmirulddin Department of Electrical Power Engineering College of Engineering EEEB283 - Electrical Machines & Drives

  2. Outline • Power Electronics Converters for DC Drives • Controlled Rectifier Fed DC Drives • Single Phase • Three Phase • DC – DC Converter Fed Drives • Step Down Class A Chopper • Step Up Class B Chopper • Two-quadrant Control • Four-quadrant Control • Closed-loop Control (Brief overview) • References EEEB283 - Electrical Machines & Drives

  3. Power Electronic Converters for DC Drives • To obtain variable voltage • Efficient • Ideally lossless • Depending on voltage source: • AC voltage source  Controlled Rectifiers • Fixed DC voltage source  DC-DC converters (switch mode converters) EEEB283 - Electrical Machines & Drives

  4. Controlled Rectifier Fed DC Drives • To obtain variable DC voltage from fixed AC source • DC current flows in only 1 direction • Example of a drive system EEEB283 - Electrical Machines & Drives

  5. Controlled Rectifier Fed DC Drives • Contains low frequency AC ripple • To reduce ripple: extra inductance added in series with La • Slow response • Discontinuous current may occur if • Lanot large enough • Motor is lightly loaded • Half-wave rectifier is used • Effect of discontinuous current • Rectifier output voltage increases  motor speed increases (poor speed regulation under open-loop operation) EEEB283 - Electrical Machines & Drives

  6. Q1 Q2 Q3 Q4 T Controlled Rectifier Fed – Single-phase DC Drives • Two-quadrant drive • Limited to applications up to 15 kW • During regeneration, Ea can be reversed by reversing field excitation EEEB283 - Electrical Machines & Drives

  7. 90o 180o ia + Va  Single-phase supply Controlled Rectifier Fed – Single-phase DC Drives • For continuous current: • Armature voltage where Vm = peak voltage • Armature current • Field voltage EEEB283 - Electrical Machines & Drives

  8. + Va   Single-phase supply Single-phase supply Q1 Q2 Q3 Q4 T Controlled Rectifier Fed – Single-phase DC Drives • Four-quadrant drive • Converter 1 for operation in 1st and 4th quadrant • Converter 2 for operation in 2nd and 3rd quadrant • Limited to applications up to 15 kW ia Converter 1 Converter 2 EEEB283 - Electrical Machines & Drives

  9. + Va  Controlled Rectifier Fed – Single-phase DC Drives • For continuous current: • Armature voltage: • If Converter 1 operates • If Converter 2 operates where Vm = peak voltage • Armature current • Field voltage ia Converter 1 Converter 2 EEEB283 - Electrical Machines & Drives

  10. Q1 Q2 Q3 Q4 T Controlled Rectifier Fed – Three-phase DC Drives • Two-quadrant drive • Limited to applications up to 1500 kW • During regeneration, Ea can be reversed by reversing field excitation EEEB283 - Electrical Machines & Drives

  11. ia + Va  3-phase supply  90o 180o Controlled Rectifier Fed – Three-phase DC Drives • For continuous current: • Armature voltage where VL-L, m = peak line-to-line voltage • Armature current • Field voltage (assuming a three-phase supply is used for field excitation) EEEB283 - Electrical Machines & Drives

  12. + Va   3-phase supply 3-phase supply Q1 Q2 Q3 Q4 T Controlled Rectifier Fed – Three-phase DC Drives • Four-quadrant drive • Converter 1 for operation in 1st and 4th quadrant • Converter 2 for operation in 2nd and 3rd quadrant ia Converter 1 Converter 2 EEEB283 - Electrical Machines & Drives

  13. + Va  Controlled Rectifier Fed – Three-phase DC Drives • Disadvantage: • Circulating current • Slow response • For continuous current: • Armature voltage: • If Converter 1 operates • If Converter 2 operates where VL-L, m = peak line-to-line voltage • Armature current • Field voltage ia Converter 1 Converter 2 EEEB283 - Electrical Machines & Drives

  14. R1 M1  3-phase supply Q1 Q2 + Va - Q3 Q4 T M2 R2 Controlled Rectifier Fed – Three-phase DC Drives • Four-quadrant drive • One controlled rectifier with 2 pairs of contactors • M1 and M2 closed for operation in 1st and 4th quadrant • R1 and R2 closed for operation in 2nd and 3rd quadrant EEEB283 - Electrical Machines & Drives

  15. DC – DC Converter Fed Drives • To obtain variable DC voltage from fixed DC source • Self-commutated devices preferred (MOSFETs, IGBTs, GTOs) over thyristors • Commutated by lower power control signal • Commutation circuit not needed • Can be switched at higher frequency for same rating • Improved motor performance (less ripple, no discontinuous currents, increased control bandwidth) • Suitable for high performance applications • Regenerative braking possible up to very low speeds even when fed from fixed DC voltage source EEEB283 - Electrical Machines & Drives

  16. Q1 Q2 Q3 Q4 T DC – DC Converter Fed Drives- Step Down Class A Chopper Motoring EEEB283 - Electrical Machines & Drives

  17. DC – DC Converter Fed Drives- Step Down Class A Chopper Motoring S is ON (0  t  ton) Duty Interval - ia EEEB283 - Electrical Machines & Drives

  18. DC – DC Converter Fed Drives- Step Down Class A Chopper Motoring S if OFF (ton t  T) Freewheeling Interval - ia EEEB283 - Electrical Machines & Drives

  19. DC – DC Converter Fed- Step Down Class A Chopper Motoring • Duty cycle • Under steady-state conditions • Motor side: • Chopper side: • Hence, Duty Interval - ia Freewheeling Interval - ia averageVa averageIa kT EEEB283 - Electrical Machines & Drives

  20. Q1 Q2 Q3 Q4 T DC – DC Converter Fed Drives- Step Up Class B Chopper Regenerative Braking • Possible for speed above rated speed and down to nearly zero speed • Application: • Battery operated vehicles • Regenerated power stored in battery EEEB283 - Electrical Machines & Drives

  21. DC – DC Converter Fed Drives- Step Up Class B Chopper Regenerative Braking S is ON (0  t  ton) • Va = 0 • ia increases due to E • Mechanical energy converted to electrical (i.e. generator) • Energy stored in La Energy Storage Interval - ia EEEB283 - Electrical Machines & Drives

  22. DC – DC Converter Fed Drives- Step Up Class B Chopper Regenerative Braking S if OFF (ton t  T) • ia flows through diode D and source V • Energy stored in La & energy supplied by machine are fed to the source Duty Interval - ia EEEB283 - Electrical Machines & Drives

  23. DC – DC Converter Fed Drives- Step Up Class B Chopper Regenerative Braking • Duty cycle • Under steady-state conditions • Generator side: • Chopper side: • Hence, Energy Storage Interval - ia Duty Interval - ia averageVa averageIa  T EEEB283 - Electrical Machines & Drives

  24. T1 D1 Q1 Q2 Q3 Q4 T + Va - T2 D2 DC – DC Converter Fed Drives- Two-quadrant Control • Forward motoring Q1 - T1 and D2 • Forward braking Q2 – T2 and D1 + V - No Speed Reversal D2 EEEB283 - Electrical Machines & Drives

  25. Q1 Q2 Q3 Q4 T Va Eb DC – DC Converter Fed Drives- Two-quadrant Control • AverageVa positive • AverageVa made larger than back emfEb • Ia positive • D2 conducting: Va = 0 • Forward motoring Q1 • T1 conducting: Va = V T1 D1 + V  ia + Va - D2 T2 T1 D1 + V  ia + Va - D2 T2 EEEB283 - Electrical Machines & Drives

  26. Q1 Q2 Q3 Q4 T Eb Va DC – DC Converter Fed Drives- Two-quadrant Control • AverageVa positive • AverageVa made smallerthan back emfEb • Ia negative • Forward braking Q2 • D1 conducting: Va = V • T2 conducting: Va = 0 T1 D1 + V  ia + Va - D2 T1 T2 D1 + Vdc  ia + Va - D2 T2 EEEB283 - Electrical Machines & Drives

  27. D1 D3 T1 T3 Q1 Q2 + Va- Q3 Q4 T T4 T2 D2 D4 DC – DC Converter Fed Drives- Four-quadrant Control • Operation in all quadrants • Speed can be reversed EEEB283 - Electrical Machines & Drives

  28. D1 D3 T1 T3 Q1 Q2 + Va- Q3 Q4 T T4 T2 D2 D4 DC – DC Converter Fed Drives- Four-quadrant Control T3 and T4 off • Forward Motoring Q1 • T1 and T2 on • Va = V • Ia increases • Reverse Braking Q4 (Regeneration) • T1 off but T2 still on • Va = 0 • Ia decays thru T2 and D4 • T1 and T2 off • Va = -V • Ia decays thru D3 and D4 • Energy returned to supply + V - EEEB283 - Electrical Machines & Drives

  29. D1 D3 T1 T3 Q1 Q2 + Va- Q3 Q4 T T4 T2 D2 D4 DC – DC Converter Fed Drives- Four-quadrant Control T1 and T2 off • Reverse Motoring Q3 • T3 and T4 on • Va = -V • Ia increases in reverse direction • Forward Braking Q2 (Regeneration) • T3 off but T4 still on • Va = 0 • Ia decays thru T4 and D2 • T3 and T4 off • Va = V • Ia decays thru D1 and D2 • Energy returned to supply + V - EEEB283 - Electrical Machines & Drives

  30. Closed-loop Control • Feedback loops may be provided to satisfy one or more of the following: • Protection • Enhancement of speed response • Improve steady-state accuracy • Variables to be controlled in drives: • Torque – achieved by controlling current • Speed • Position • Controllers are designed based on a linear averaged model EEEB283 - Electrical Machines & Drives

  31. + Va – + vc iref  controlled rectifier current controller firing circuit - Closed-loop Control • Variables to be controlled in drives: • Torque – achieved by controlling current • Commonly employed current sensor: • Current shunt – no electrical isolation, cheap • Hall effect sensor – provides electrical isolation • Speed is governed by torque: e.g. With phase-controlled rectifier EEEB283 - Electrical Machines & Drives

  32. Closed-loop Control • Variables to be controlled in drives: • Speed – with or without current loop • Commonly employed speed/position sensor: • Tachogenerator – analog based • Digital encoder – digital based, converts speed to pulses • Torque is governed by speed demand: • Without current loop: no limit on current – can be too high • With current loop: current can be limited EEEB283 - Electrical Machines & Drives

  33. Power Electronic Converters + va  + vc Speed controller * Tacho -  Closed-loop Control • Variables to be controlled in drives: • Speed control without current loop: • Simple implementation • Current can be too high  may damage converter EEEB283 - Electrical Machines & Drives

  34. Power Electronic Converters + va  * ia* vc + + Speed controller Current controller - - ia  Tacho Closed-loop Control • Variables to be controlled in drives: • Speed control with current loop: • Two controllers required: speed and current • Current limited by limiting ia* EEEB283 - Electrical Machines & Drives

  35. References • Rashid, M.H, Power Electronics: Circuit, Devices and Applictions, 3rd ed., Pearson, New-Jersey, 2004. • Dubey, G.K., Fundamentals of Electric Drives, 2nd ed., Alpha Science Int. Ltd., UK, 2001. • Krishnan, R., Electric Motor Drives: Modeling, Analysis and Control, Prentice-Hall, New Jersey, 2001. • Nik Idris, N. R., Short Course Notes on Electrical Drives, UNITEN/UTM, 2008. • Ahmad Azli, N., Short Course Notes on Electrical Drives, UNITEN/UTM, 2008. EEEB283 - Electrical Machines & Drives

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