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Controlled Rectifier DC Drives By Dr. Ungku Anisa Ungku Amirulddin Department of Electrical Power Engineering College of Engineering Dr. Ungku Anisa, July 20081EEEB443 - Control & Drives

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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 Dr. Ungku Anisa, July 2008EEEB443 - Control & Drives2

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Power Electronic Converters for DC Drives Speed Control Strategy: below base speed: V a control above base speed: flux control via V f 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 Dr. Ungku Anisa, July 2008EEEB443 - Control & Drives3

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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 Dr. Ungku Anisa, July 2008EEEB443 - Control & Drives4

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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 ) Dr. Ungku Anisa, July 20085EEEB443 - Control & Drives T Q1 Q2 Q3Q4

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Controlled Rectifier Fed – Single-phase DC Drives Two-quadrant drive For continuous current: Armature voltage where V m = peak voltage Armature current Field voltage Dr. Ungku Anisa, July 2008EEEB443 - Control & Drives6 90 o 180 o Single- phase supply +Va+Va iaia

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Controlled Rectifier Fed – Single-phase DC Drives Two-quadrant drive For Quadrant 1 operation: positive E a and V a positive a 90 I a positive Rectifier delivers power to motor, i.e. forward motoring. Dr. Ungku Anisa, July 2008EEEB443 - Control & Drives7 90 o 180 o Single- phase supply +Va+Va iaia +Ea+Ea Q1

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Controlled Rectifier Fed – Single-phase DC Drives Two-quadrant drive For Quadrant 4 operation: negative E a negative a > 90 V a negative I a positive (still in same direction) Rectifier takes power from motor, i.e. regenerative braking. Dr. Ungku Anisa, July 2008EEEB443 - Control & Drives8 90 o 180 o Single- phase supply Va+Va+ iaia Ea+Ea+ Q4

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Controlled Rectifier Fed – Single-phase DC Drives Four-quadrant drive Converter 1 for operation in 1 st and 4 th quadrant Converter 2 for operation in 2 nd and 3 rd quadrant Limited to applications up to 15 kW Dr. Ungku Anisa, July 20089EEEB443 - Control & Drives T Q1 Q2 Q3Q4 Converter 1Converter 2 Single- phase supply Single- phase supply +Va+Va iaia Two rectifiers connected in anti- parallel across motor armature

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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 (V m = peak supply voltage) Hence, firing angles of both converters must satisfy the following: Armature current Field voltage Dr. Ungku Anisa, July EEEB443 - Control & Drives +V1+V1 Converter 1Converter 2 V 2 +

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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 ) Dr. Ungku Anisa, July EEEB443 - Control & Drives T Q1 Q2 Q3Q4

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Controlled Rectifier Fed – Three-phase DC Drives For continuous current: Armature voltage where V L-L, m = peak line-to-line voltage Armature current Field voltage (assuming a three-phase supply is used for field excitation) Dr. Ungku Anisa, July 2008EEEB443 - Control & Drives12 90 o 180 o 3-phase supply +Va+Va iaia

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Three-phase Controlled Rectifier 2Q DC Drive – Example Dr. Ungku Anisa, July 2008EEEB443 - Control & Drives13

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Controlled Rectifier Fed – Three-phase DC Drives Four-quadrant drive Converter 1 for operation in 1 st and 4 th quadrant Converter 2 for operation in 2 nd and 3 rd quadrant Dr. Ungku Anisa, July EEEB443 - Control & Drives T Q1 Q2 Q3Q4 Converter 1Converter 2 3-phase supply 3-phase supply +Va+Va iaia Two rectifiers connected in anti- parallel across motor armature I a +ve, V a +ve or -ve I a -ve, V a +ve or -ve

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Controlled Rectifier Fed – Three-phase DC Drives Four-quadrant drive For continuous current: where V L-L, m = peak line-to-line voltage. Similar to single-phase drive: Dr. Ungku Anisa, July EEEB443 - Control & Drives T Q1 Q2 Q3Q4 Converter 1Converter 2 +Va+Va iaia Converter 1: I a +ve, V a +ve Converter 2: I a -ve, V a +ve Converter 1: I a +ve, V a -ve Converter 2: I a -ve, V a -ve

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Controlled Rectifier Fed – Three-phase DC Drives For continuous current: Armature current Field voltage Disadvantages: Circulating current Inductors L 1 and L 2 added to reduce circulating currents Slow response Dr. Ungku Anisa, July EEEB443 - Control & Drives +Va+Va Converter 1Converter 2 iaia L1L1 L2L2

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Three-phase Controlled Rectifier 4Q DC Drive – Example Dr. Ungku Anisa, July 2008EEEB443 - Control & Drives17

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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 1 st and 4 th quadrant R1 and R2 closed for operation in 2 nd and 3 rd quadrant Dr. Ungku Anisa, July EEEB443 - Control & Drives T Q1 Q2 Q3Q4 M1 M2 R1 R2 + V a - 3-phase supply iaia iaia

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Rectifier Fed DC Drives Problems 1. 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. 5 th and 7 th 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 Dr. Ungku Anisa, July 2008EEEB443 - Control & Drives19

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Rectifier Fed DC Drives Problems Dr. Ungku Anisa, July 2008EEEB443 - Control & Drives20 12-pulse converter – consists of two 6-pulse controlled rectifiers connected in parallel

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Rectifier Fed DC Drives Problems 2. 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) Dr. Ungku Anisa, July 2008EEEB443 - Control & Drives21

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Rectifier Fed DC Drives Problems 3. Effect on motor Ripple in motor current – harmonics present (most dominant is 6 th harmonic) causes torque ripple, heating and derating of motor solution: extra inductance added in series with L a Slow response Discontinuous current may occur if L a not large enough Motor is lightly loaded Effect of discontinuous current Rectifier output voltage increases motor speed increases (poor speed regulation under open-loop operation) Dr. Ungku Anisa, July 2008EEEB443 - Control & Drives22

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References Rashid, M.H, Power Electronics: Circuit, Devices and Applictions, 3 rd ed., Pearson, New-Jersey, Dubey, G.K., Fundamentals of Electric Drives, 2 nd ed., Alpha Science Int. Ltd., UK, Krishnan, R., Electric Motor Drives: Modeling, Analysis and Control, Prentice-Hall, New Jersey, Nik Idris, N. R., Short Course Notes on Electrical Drives, UNITEN/UTM, Ahmad Azli, N., Short Course Notes on Electrical Drives, UNITEN/UTM, Dr. Ungku Anisa, July EEEB443 - Control & Drives

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4/13/2015EEL 4242 by Dr. M.H. Rashid24 Three-Phase Full-Converter Figure 10.5 Reference: Rashid, M.H, Power Electronics: Circuit, Devices and Applictions, 3 rd ed., Pearson, New-Jersey, 2004

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4/13/2015EEL 4242 by Dr. M.H. Rashid25 Waveforms and Conduction Times Figure 10.5 Reference: Rashid, M.H, Power Electronics: Circuit, Devices and Applictions, 3 rd ed., Pearson, New-Jersey, 2004

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