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**EEEB443 Control & Drives Controlled Rectifier DC Drives By**

Dr. Ungku Anisa Ungku Amirulddin Department of Electrical Power Engineering College of Engineering Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives Dr. Ungku Anisa, July 2008

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**Outline Power Electronics Converters for DC Drives**

Controlled Rectifier Fed DC Drives Single Phase Two-quadrant Four-quadrant Three Phase References Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives

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**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 Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives

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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 2008 EEEB443 - Control & Drives

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**Controlled Rectifier Fed – Single-phase DC Drives**

Q1 Q2 Q3 Q4 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 2008 EEEB443 - Control & Drives

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**Controlled Rectifier Fed – Single-phase DC Drives**

supply + Va ia Two-quadrant drive For continuous current: Armature voltage where Vm = peak voltage Armature current Field voltage 90o 180o Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives

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**Controlled Rectifier Fed – Single-phase DC Drives**

supply + Va ia + 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. 90o 180o Q1 Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives

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**Controlled Rectifier Fed – Single-phase DC Drives**

supply Va + ia 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. 90o 180o Q4 Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives

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**Controlled Rectifier Fed – Single-phase DC Drives**

Q1 Q2 Q3 Q4 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 Single-phase supply + Va ia Two rectifiers connected in anti-parallel across motor armature Converter 1 Converter 2 Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives

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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 (Vm = peak supply voltage) Hence, firing angles of both converters must satisfy the following: Armature current Field voltage + V1 Converter 1 Converter 2 V2 Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives

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**Controlled Rectifier Fed – Three-phase DC Drives**

Q1 Q2 Q3 Q4 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 2008 EEEB443 - Control & Drives

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**Controlled Rectifier Fed – Three-phase DC Drives**

supply + Va ia 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) 90o 180o Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives

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**Three-phase Controlled Rectifier 2Q DC Drive – Example**

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

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**Controlled Rectifier Fed – Three-phase DC Drives**

Q1 Q2 Q3 Q4 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 3-phase supply + Va ia Two rectifiers connected in anti-parallel across motor armature Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives

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**Controlled Rectifier Fed – Three-phase DC Drives**

Four-quadrant drive For continuous current: where VL-L, m = peak line-to-line voltage. Similar to single-phase drive: + Va ia Converter 1 Converter 2 Converter 2: Ia -ve, Va +ve Converter 1: Ia +ve, Va +ve T Q1 Q2 Q3 Q4 Converter 2: Ia -ve, Va -ve Converter 1: Ia +ve, Va -ve Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives

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**Controlled Rectifier Fed – Three-phase DC Drives**

For continuous current: Armature current Field voltage Disadvantages: Circulating current Inductors L1 and L2 added to reduce circulating currents Slow response + Va Converter 1 Converter 2 ia L1 L2 Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives

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**Three-phase Controlled Rectifier 4Q DC Drive – Example**

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

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**Controlled Rectifier Fed – Three-phase DC Drives**

Q1 Q2 Q3 Q4 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 M1 M2 R1 R2 + Va - 3-phase supply ia ia Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives

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**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 Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives

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**Rectifier Fed DC Drives Problems**

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

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**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) Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives

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**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 La 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 2008 EEEB443 - Control & Drives

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

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**Three-Phase Full-Converter**

Figure 10.5 Reference: Rashid, M.H, Power Electronics: Circuit, Devices and Applictions, 3rd ed., Pearson, New-Jersey, 2004 4/10/2017 EEL 4242 by Dr. M.H. Rashid

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**Waveforms and Conduction Times**

Figure 10.5 Reference: Rashid, M.H, Power Electronics: Circuit, Devices and Applictions, 3rd ed., Pearson, New-Jersey, 2004 4/10/2017 EEL 4242 by Dr. M.H. Rashid

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