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Rectifier fed Separately Excited DC Drives

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- CONVERTER FED DC MOTOR DRIVE Dr.P.Subha Karuvelam Professor (CAS)/EEE GCE, Tirunelveli
- Content • Steady state analysis of the single and three phase converter fed separately excited DC motor drive for continuous conduction • Time ratio and current limit control • 4 quadrant operation of converter / chopper fed drive • Applications
- Single Phase fully controlled rectifier fed DCM
- Single Phase fully controlled rectifier fed DCM
- Single Phase fully controlled rectifier fed DCM 1. When T1 & T3 conducts, when T2& T4 conducts, 2. When biasing of thyristor depends on when biasing of thyristor depends on 3.
- Single Phase fully controlled rectifier fed DCM is obtained by is obtained by speed reversal (IV quadrant) is obtained by Field current reversal (II quadrant) Armature current reversal (II quadrant)
- Single Phase fully controlled rectifier fed DCM 4. Rate of change of armature current
- Single Phase fully controlled rectifier fed DCM 1. Duty Interval Any one pair of Thyristor is ON when T1 & T3 conducts, when T2 & T4 conducts, 2. Zero Current Interval
- Single Phase fully controlled rectifier fed DCM Motoring Mode Mode – I, II, III & IV Regeneration Mode Mode – V, VI & VII Continuous Current Mode Mode I & V Dis-continuous Current Mode Mode II,III,IV,VI & VII
- Mode I – Motoring Mode
- Mode I – Motoring Mode For interval T1& T3 conducts • When Energy supplied by = Energy consumed by • When Energy consumed by = Energy supplied by • When is negative Energy consumed by = Energy supplied by
- Mode I – Motoring Mode • Duty Interval when T1 & T3 conducts when T2 & T4 conducts
- Mode I – Transient Analysis In interval T1 & T3 conducts The Current is due to AC source is Back EMF is Transient component is
- Mode I – Transient Analysis • Where • In steady state
- Mode I – Steady State Analysis • Motor Torque is • Ave. Terminal voltage = Ave VD in + Ave VD in + Back EMF Average Terminal Voltage
- Mode I – Steady State Analysis • Average voltage drop in Ra Average voltage drop across La
- Mode V – Regeneration Mode Motoring Regeneration
- Mode V – Regeneration Mode is obtained by is obtained by speed reversal (IV quadrant) is obtained by Field current reversal (II quadrant) Armature current reversal (II quadrant)
- Mode V – Regeneration Mode
- Speed – Torque Characteristics • For firing angle • For firing angle
- Speed – Torque Characteristics
- Three Phase full converter fed DCM
- Three Phase fully converter fed DCM • Line voltage VAB is taken as reference • Motoring mode – I & II • Regeneration Mode – III &IV • Continuous Current mode – I & III • Dis-continuous Current mode – II & IV
- Three Phase Voltage
- Phase voltage and Line voltage
- Conduction Interval For = 0 Thyristor Conduction Period T1 60 - 180 T2 120 - 240 T3 180 - 300 T4 240 - 360 T5 300 - 60 T6 0 - 120 For = 30 Thyristor Conduction Period T1 90 - 210 T2 150 - 270 T3 210 - 330 T4 270 - 30 T5 330 - 90 T6 30 - 150
- Conduction Interval For = 60 Thyristor Conduction Period T1 120 - 240 T2 180 - 300 T3 240 - 360 T4 300 - 60 T5 0 - 120 T6 60 - 180 For = 90 Thyristor Conduction Period T1 150 - 270 T2 210 - 330 T3 270 - 30 T4 330 - 90 T5 30 - 150 T6 90 - 210
- Conduction Interval For = 120 Thyristor Conduction Period T1 180 - 300 T2 240 - 360 T3 300 - 60 T4 0 - 120 T5 60 - 180 T6 120 - 240 For = 180 Thyristor Conduction Period T1 240 - 360 T2 300 - 60 T3 0 - 120 T4 60 - 180 T5 120 - 240 T6 180 - 300
- Mode I – Motoring mode
- Mode I – Motoring mode • For Duty interval
- Mode I – Motoring mode
- Mode III – Regeneration Mode
- Mode III – Regeneration Mode is obtained by is obtained by speed reversal (IV quadrant) is obtained by Field current reversal (II quadrant) Armature current reversal (II quadrant)
- Speed – Torque Characteristics When No load operation is obtained When No load operation is obtained
- Speed – Torque Characteristics
- 4 quadrant operation of DCM
- 4 quadrant operation of converter fed drive Armature Current Reversal Single Phase full wave rectifier with Reversing switch RS Dual Converter Field Current Reversal Single Phase full wave rectifier with Reversing switch RS Dual Converter
- Armature Current Reversal Single Phase full wave rectifier with RS
- Single Phase full wave rectifier with RS Positive Armature Current – I & IV quadrant Negative Armature Current – II & III quadrant • Procedure for speed reversal Firing angle increased to highest value Armature current reduces Zero armature current is sensed Dead time of 2 – 10ms Armature is reversed by RS Firing angle is reduced hence armature current increases
- Single Phase full wave rectifier with RS Drawbacks Slow response Contactor reversal time is 50-100ms Need a accurate zero current sensor Frequent maintenance due moving contact Advantage Low cost
- Dual Converter Non-simultaneous control Simultaneous control
- Non-simultaneous control • Only one rectifier operates at a time (I & IV ) • Procedure for speed reversal Firing angle 1 increased to highest value Armature current reduces Zero armature current is sensed Dead time of 2 – 10ms Firing pulses are withdrawn from rectifier1 Firing pulses are given to rectifier 2 Armature current increases
- Non-simultaneous control • EMF matching method 2 is set to make Armature current increases Restricted to rated value in current limiter Maximum (negative) torque developed by motor Fast response
- Simultaneous control • Two converters are controlled simultaneously • One converter – Rectifier • Other converter – Inverter • Instantaneous voltages are not equal
- Simultaneous control • In quadrant I, Converter 1 in rectification with Converter 2 in inversion with • Procedure for speed reversal 1 is increased and 2 is decreased Armature current shifts to rectifier 2 Zero speed is reached when 2 is reduced below 90 & 1 in increased above 90
- Simultaneous control
- Simultaneous control • Advantages Control is simple Continuous current conduction Good Speed regulation • Disadvantages Presence of inductor increases cost, size, weight Poor transient response Low PF and Efficiency
- Field Current Reversal Reversible Switch Dual Converter
- Field Current Reversal Positive Field Current – I & IV quadrant Negative Field Current – II & III quadrant Field current is very small, rectifier rating also small Larger field time constant, larger field current reversal time

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