power electronics lec 6 - triac gto
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Power Electronics MUHAMMAD NAVEED IQBAL G.C UNIVERSITY LAHORE
Week Lecture Class Task
Week 1
Introduction to power electronics
Solid-state devices used in power electronics
Week 2
The Power Diode
Thyristors
Week 3
GTO Thyristors
Power Bipolar Transistors, Assignment 1 [OUT]
Week 4
The Power MOSFET
Insulated Gate Bipolar Transistor, DIAC, TRIAC
Week 5
Quiz 1 Assignment 1 [IN]
Diode Rectifiers
Week 6
Single-Phase Controlled Rectifiers
Three-Phase Controlled Rectifiers
Week 7
Twelve-pulse and Twenty-four pulse rectifiers;
DC to DC conversation, buck converter
Week 8
boost converter, buck-boost converters
Isolated converters, forward converters
Week Lecture Class Task
Week 1
Introduction to power electronics
Solid-state devices used in power electronics
Week 2
The Power Diode
Thyristors
Week 3
Thyristors turn On and Off characteristics
Thyristors types, Assignment 1 [OUT]
Week 4
TRIAC, GTO Assignment 1 [OUT]
The Power MOSFET Insulated Gate Bipolar Transistor,
Week 5
Power Bipolar Transistors, Diode Rectifiers
Quiz 1 Assignment 1 [IN]
Week 6
Single-Phase Controlled Rectifiers
Three-Phase Controlled Rectifiers
Week 7
Twelve-pulse and Twenty-four pulse rectifiers;
DC to DC conversation, buck converter
Week 8
boost converter, buck-boost converters
Isolated converters, forward converters
Week Lecture Class Task
Week 9 Flyback converters
Quiz 2 [Mid Term]
Week 10 Single-Phase Voltage Source Inverters, 3-Phase Voltage Source Inverters
pulse-width-modulated (PWM) inverters
Week 11 Resonant Switch
Quasi-Resonant Converters
Week 12 Zero voltage switch Assignment 2 [out]
Three-phase inverters
Week 13 Single-Phase AC -AC Voltage Controller, 3-Phase AC-AC Voltage Controllers
Quiz 3 Assignment 2 [IN]
Week 14 Cyclo-converters
DC=DC Conversion, Positive Ouput Luo-Converters
Week 15 Negative Ouput Luo-Converters
Double Output Luo-Converters
Week 16 Revision
Revision
TRIAC
• Developed by GE in 1964
• Two Thyristors connected in anti-parallel
• Bi-directional device can conduct current in either direction
• Structure is quite complicated
• Can be triggered when 𝑀𝑇2 is +ive with respect to 𝑀𝑇1 and positive gate 𝐼𝐺 is applied w.r.t. M𝑇1
• Can be triggered when 𝑀𝑇2 is -ive with respect to M𝑇1 and –ive gate 𝐼𝐺 is applied w.r.t. 𝑀𝑇1
Limitations
• For Thyristors, 𝑑𝑉
𝑑𝑡 during OFF state is shown
• Device may go in conduction mode due to 𝑑𝑉
𝑑𝑡 during off state
• When i= 0, V across it is very different from zero
• Has less time than Thyristors to recover its blocking power
•𝑑𝑉
𝑑𝑡 rating is lower
SCR Limitations
• SCR is nearly an ideal switch
• Require a sharp pulse to turn On
• Block +ive as well as –ive V
• High V and high I devices are available
• Rugged
• Inability to turn-off by application of a control signal at the gate
• Inclusion of turn-off, capability in Thyristors requires device modification with some compromise in operational capability
Gate turn-off Thyristors (GTO)
• Lower power rating GTO developed by GE in 1961
• 1981 2.5 kV and 1kA device manufactured by hitacht, toshiba
• Can be turned on by +ive 𝐼𝐺
• Can be turned off by –ive 𝐼𝐺
• Four layer structure
• Thickness of 𝑃2 < that is SCR
• 𝑁2 layer is remover by itching in place where gate contacts are situated
• These cells are surrounded by gate, they are brought together by a cathode plate
• GTO can be seen as a large number of GTO in parallel
• At large intervals n region penetrates P1 layer to make contact with n region
• Used to speed up the turn-off process
• No reverse blocking capability (only J2 can block –ive V, very low)
• GTO without anode short can block –ive V
Interdigitation
• High level of gate interdigitation results in
• Even a remote part of cathode region is very near to a gate edge
• Fast turn On speed
• Like SCR only the area of cathode adjacent to the gate electrode is turned on initially and then spreads
• Turn on area is large
• High di/dt
ON-state characteristics
• They are similar to SCR
• Gate signal can be removed if 𝐼𝐴 > 𝐼𝐿𝐴𝑇𝐶𝐻𝐼𝑁𝐺
• Recommended that +ive 𝐼𝐺 is not removed
• 𝐼𝐻𝑂𝐿𝐷𝐼𝑁𝐺 𝐺𝑇𝑂 𝑖𝑠 > 𝐼𝐻𝑂𝐿𝐷𝐼𝑁𝐺 of SCR
• Under transient condition if 𝐼𝐴 ↓ below 𝐼𝐻𝑂𝐿𝐷𝐼𝑁𝐺 some regions may be turned off
• Anode I now↑ at high rate
• Could be destructive
ON-state characteristics
• During turn ON,𝑑𝑖𝐺
𝑑𝑡 peak value of 𝐼𝐴 should be large enough to
ensure that all cathode islands begin to conduct & there is a sharing of anode I
• Otherwise, hot spots may result
• 𝐼𝐺𝑀 = 10𝐼𝐺𝑇
OFF-state characteristics
• When Thyristors (or GTO) is ON, both T1 and T2 are in saturation
• By ↓ 𝐼𝐵2, T2 can be brought out of saturation
• The total saturation current 𝑖𝑠 𝑖𝐴 =𝛼2𝐼𝐺+𝐼𝐶𝐵𝑂
1− 𝛼1+𝛼2
• 𝐼𝐶𝐵𝑂 = 𝐼𝐶𝐵𝑂1 + 𝐼𝐶𝐵𝑂2
• When GTO is in on state, 𝐼𝐺 is very small
OFF-state characteristics
• 𝐼𝐴 𝑜𝑛 =𝐼𝐶𝐵𝑂
1− 𝛼1+𝛼2 is the current required to turn off
• If 𝐼𝐴 = 0, there is a large gate current such that 𝐼𝐺 =−𝐼𝐶𝐵𝑂
𝛼2
•𝐼𝐴 𝑜𝑛
𝐼𝐺=
𝛼2
𝛼1+𝛼2 −1
• 𝛼2 should be high as possible for transistor N1 P2 N2
• i.e should have a high gain
• 𝑃2 layer should be very thin and 𝑁2 highly doped
OFF-state characteristics
• Gate is reversed biased w.r.t cathode
• Holes are extracted from P2
• V drop is developed in P-base region
• Eventually reverse biased the gate-cathode region and cut off injection of electrons
• As holes extraction continue P2 is further depleted
• Conduction area decreases
OFF-state characteristics
• Anode I flows through the area far away from gate
• May be high current density
• May lead to localized heating
• Should be controlled
• Device may fail
• Eventually device turn off
OFF-state characteristics
• Turn off of GTO is greatly influenced by turn off circuit
• Turn of gain is very low 6-15
• Anode current is 100 A than Ig be around 10A
OFF-state characteristics
• When gate current starts flowing out anode current remains constant for some time called storage time
• Snubber circuits must be used
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