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EEEB443 Control & Drives

EEEB443 Control & Drives. Controlled Rectifier 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 Two-quadrant

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EEEB443 Control & Drives

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  1. EEEB443 Control & Drives Controlled Rectifier DC Drives By Dr. UngkuAnisaUngkuAmirulddin Department of Electrical Power Engineering College of Engineering EEEB443 - Control & Drives

  2. Outline • Power Electronics Converters for DC Drives • Controlled Rectifier Fed DC Drives • Single Phase • Two-quadrant • Four-quadrant • Three Phase • Two-quadrant • Four-quadrant • References EEEB443 - Control & Drives

  3. Power Electronic Converters for DC Drives • Speed Control Strategy: • below base speed: Va control • above base speed: flux control via Vf control • Power electronics converters are used to obtain variable voltage • Highly efficient • Ideally lossless • Type of converter used is depending on voltage source : • AC voltage source  Controlled Rectifiers • Fixed DC voltage source  DC-DC converters EEEB443 - Control & 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 EEEB443 - Control & Drives

  5. Q1 Q2 Q3 Q4 T Controlled Rectifier Fed – Single-phase DC Drives • Two-quadrant drive • Limited to applications up to 15 kW • Regeneration (Q4) only be achieved with loads that can drive the motor in reverse (-ve) EEEB443 - Control & Drives

  6. 90o 180o ia + Va  Single-phase supply Controlled Rectifier Fed – Single-phase DC Drives • Two-quadrant drive For continuous current: • Armature voltage where Vm = peak voltage • Armature current • Field voltage EEEB443 - Control & Drives

  7. 90o 180o ia + Va  Single-phase supply Controlled Rectifier Fed – Single-phase DC Drives + Ea  • Two-quadrant drive For Quadrant 1 operation: •  positive  Ea and Va positive • a  90 • Ia positive • Rectifier delivers power to motor, i.e. forward motoring.  Q1 EEEB443 - Control & Drives

  8. 90o 180o ia  Va + Single-phase supply Controlled Rectifier Fed – Single-phase DC Drives  Ea + • Two-quadrant drive For Quadrant 4 operation: •  negative  Ea negative • a > 90  Va negative • Ia positive (still in same direction) • Rectifier takes power from motor, i.e. regenerative braking.  Q4 EEEB443 - Control & Drives

  9. + 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 Two rectifiers connected in anti-parallel across motor armature Converter 1 Converter 2 EEEB443 - Control & Drives

  10. + V1  Controlled Rectifier Fed – Single-phase DC Drives • Four-quadrant drive For continuous current: • Both converters are operated to produce the same dc voltage across the terminal, i.e.: where and (Vm = peak supply voltage) • Hence, firing angles of both converters must satisfy the following: • Armature current • Field voltage  V2 + Converter 1 Converter 2 EEEB443 - Control & Drives

  11. Q1 Q2 Q3 Q4 T Controlled Rectifier Fed – Three-phase DC Drives • Two-quadrant drive • Limited to applications up to 1500 kW • Regeneration (Q4) only be achieved with loads that can drive the motor in reverse (-ve) EEEB443 - Control & Drives

  12. 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) EEEB443 - Control & Drives

  13. Three-phase Controlled Rectifier 2Q DC Drive – Example EEEB443 - Control & Drives

  14. + 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 +ve, Va +ve or -ve Ia -ve, Va +ve or -ve Converter 1 Converter 2 ia Two rectifiers connected in anti-parallel across motor armature EEEB443 - Control & Drives

  15. + Va   Q1 Q2 T Q3 Q4 Controlled Rectifier Fed – Three-phase DC Drives • Four-quadrant driveFor continuous current: where VL-L, m = peak line-to-line voltage. • Similar to single-phase drive: Converter 1 Converter 2 Converter 2: Ia -ve, Va +ve Converter 1: Ia +ve, Va +ve ia Converter 2: Ia -ve, Va -ve Converter 1: Ia +ve, Va -ve EEEB443 - Control & Drives

  16. + Va  Controlled Rectifier Fed – Three-phase DC Drives • For continuous current: • Armature current • Field voltage • Disadvantages: • Circulating current • Inductors L1 and L2added to reduce circulating currents • Slow response L1 ia L2 Converter 1 Converter 2 EEEB443 - Control & Drives

  17. Three-phase Controlled Rectifier 4Q DC Drive – Example EEEB443 - Control & Drives

  18. 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 ia ia EEEB443 - Control & Drives

  19. Rectifier Fed DC Drives Problems • Distortion of Supply • Controlled rectifier introduces harmonics to supply currents and voltages which cause: • heating and torque pulsations in motor • resonance in power system network – interaction between rectifier RL with capacitor banks in system • Solution - eliminate most dominant harmonics by: • install LC filters at input of converters – tuned to absorb most dominant harmonics (i.e. 5th and 7th harmonics) • Use 12-pulse converter – consists of two 6-pulse controlled rectifiers connected in parallel • Selective switching of supply input using self-commutating devices (eg. GTOs, IGBTs) in the converter EEEB443 - Control & Drives

  20. Rectifier Fed DC Drives Problems 12-pulse converter – consists of two 6-pulse controlled rectifiers connected in parallel EEEB443 - Control & Drives

  21. Rectifier Fed DC Drives Problems • Low supply power factor • Power factor related to firing angle  of rectifier • Low power factor especially during low speed operations • Solution: • Employ pulse-width modulated (PWM) rectifiers using GTOs, IGBTs • High power factor • Low harmonic supply currents • Low efficiency - high switching losses (disadvantage) EEEB443 - Control & Drives

  22. Rectifier Fed DC Drives Problems • Effect on motor • Ripple in motor current – harmonics present (most dominant is 6th harmonic) • causes torque ripple, heating and derating of motor • solution: extra inductance added in series with La • Slow response • Discontinuous current may occur if • Lanot large enough • Motor is lightly loaded • Effect of discontinuous current • Rectifier output voltage increases  motor speed increases (poor speed regulation under open-loop operation) EEEB443 - Control & Drives

  23. 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. EEEB443 - Control & Drives

  24. Three-Phase Full-Converter Figure 10.5 Reference: Rashid, M.H, Power Electronics: Circuit, Devices and Applictions, 3rd ed., Pearson, New-Jersey, 2004 EEL 4242 by Dr. M.H. Rashid

  25. Waveforms and Conduction Times Figure 10.5 Reference: Rashid, M.H, Power Electronics: Circuit, Devices and Applictions, 3rd ed., Pearson, New-Jersey, 2004 EEL 4242 by Dr. M.H. Rashid

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