power electronics(i)
TRANSCRIPT
Suggested Books
1. M.H Rashid “ Power Electronics Circuits Devices & Applications 3rd Edition
2. NED Mohan “ Power Electronics Applications and design”
3. Cyril Lander “Power Electronics”
4. B.K Bose “ Modern Power Electronics and AC derives”
5. Dr. M.R Abro “Power Electronics And Applications”
IEEE Journals
• There are 4 IEEE journals related to Power Electronics.
1. IEEE journal on Power Electronics
2. IEEE Journal on Industrial application.
3. IEEE Journal On Industrial Electronics
4. IEEE Journal on Power Delivery
Quotes from IEEE Papers
“We now live in a truly global society. In the highly automated industrial front with economic competitiveness of nation, in future two technologies will dominate:
Computers and Power Electronics – the former providing intelligence as to “what to do” and the latter “ the means to do it”
Quotes from IEEE Papers
• “Modern Computers, Communication and Electronic Systems get their life blood from power electronics”
• “Solid State Electronics brought 1st electronic revolution , where as solid state power electronics brought in the second electronics revolution”
Energy Scenario Globally
87% percentage energy comes from burning fossil fuels (coal, oil, natural gas)
6 % comes from Nuclear power plants.Remaining from renewable energies.According to one IEEE Journal PaperNatural Uranium fuel lasts for approximately 50
years.Oil for approximately 100 years.Natural gas approximately 150 years.Coal for approximately 200 years.
Energy Scenario Globally
• This period can be expanded by
1. Use electrical energy efficiently.
2. Improve Conversion Efficiency.
3. Explore Renewable Energies.
If input is 100 KW of fuel energy, output is 15-20 KW of useful work.
Every KW of loss saved in the process drive. 6 KW of energy is saved on the front end.
Energy Scenario Globally
• The power stations burn the fossil fuels tomake our electricity and in that process a lotof greenhouse gas is made, including carbondioxide and methane. This is why they arecalled dirty sources of energy.
• Coal, oil and gas are non-renewable sources ofenergy because we can only use what isavailable and once they have been used up,that's it!
Energy Scenario Globally
• The energy of the sun, wind, waves andwater, amongst these sources of energyproduce only very small amounts ofgreenhouse gas once operating, if any at all -now that's clean!
• They are also renewable which means theycan be used over and over again.
Energy Scenario Globally
• Renewable is a term applied to natural resourcesand refers to those resources that can berenewed or replenished in a short period of time.
• Renewable energy is also called “clean” or“green” energy because it does not pollute the airor harm the environment.
• As the demand for energy increases renewableenergy will play an important role in supplyingthe worlds clean energy needs.
Types of EnergyNon renewable energy
cannot be generated
again and again, limited
sources
Petroleum
Natural Gas
Coal
Nuclear
Renewable energy can be generated continuously practically without decay of source. e.g.,
Solar
Wind
Hydropower
Biomass
Ocean energy
Geothermal
Power Consumption
• Bulk of the power is used by motors globally. Major loads are induction motor driving either a fan , pump or compressor.
• Lighting consumes other good percentage of power.
• If you save this power, significant over all benefit can be achieved.
Control Speed of Fan• Compare both fan regulators.
• Power electronic Fan control uses Power semiconductor devices which enables smooth control of power. It has very less heat dissipation, high conversion efficiency, small size, reliable.
Your Assignment
Find out different applications of powerelectronics. You have to just list differentapplications. Detailed analysis will be done inthe subject.
Power Electronics Definition & Goal
• “Power electronics is the technology associated with efficient conversion and control of electronic power by power semiconductor devices.”
Goal of Power Electronics:-
• “To contribute the flow of energy from electric source to electric load.
Power Electronics Definition & Goal
Interfacing is done by P.E Equipment. Depending upon nature of source and load this power electronic equipment will change.
SourceP.E
EquipmentLoad
Why Power Electronics is successful
Highly Efficient
Highly Reliable.
Size, Weight and cost should be low.
If it will be highly efficient, surely heat losses will be minimum so cooling requirement comes down. So temp: is low so we can package various elements closely. So size comes down.
History of Power Electronics• BRIEF HISTORY OF POWER ELECTRONICS
• The first Power Electronic Device developed was the Mercury ArcRectifier during the year 1900. Then the other Power devices like metaltank rectifier, grid controlled vacuum tube rectifier, ignitron,
• phanotron, thyratron and magnetic amplifier, were developed & usedgradually for power control applications until 1950.
• The first SCR (silicon controlled rectifier) or Thyristor was invented anddeveloped by Bell Lab’s in 1956 which was the first PNPN triggeringtransistor.
• The second electronic revolution began in the year 1958 with thedevelopment of the commercial grade Thyristor by the General ElectricCompany (GE). Thus the new era of power electronics was born. Afterthat many different types of power semiconductor devices & powerconversion techniques have been introduced.The power electronicsrevolution is giving us the ability to convert, shape and control largeamounts of power.
Power Semiconductor Devices
• Advances in Power Electronics is primarily due to the advances in semiconductor devices.
• Power semiconductor devices are heart and soul of modern Power electronics Equipment.
• They are used as Switches.
Properties of Ideal Switch
When the switch is off Is=0, there should not be any current flowing through the switch when it is open and it should be able to withstand any voltage across it. In other words this switch should be able to withstand any voltage from minus infinity to plus infinity.
When it is on what should happen……………….? the voltage across it should be zero and it should be capable of passing any current through it.
Properties of Ideal Switch
Power dissipation that happens in switch when it is on or off is zero because when it is off current through it is zero and when it is on voltage through it is zero so Pd=0.
When the switch is conducting or blocking. The conduction loss and blocking loss should be zero.
Switch should be turned on and off instantaneously. Turn on and turn off losses should be zero Ton=0 and Toff=0 ( switching losses should be zero).
Non ideal Switch
• Can you have this ideal characteristics in practice………………………………………………????
• Difference should be low between ideal and non ideal switch.
• So in non ideal switch off state( S is open) current is non zero. A small current flows. And when it is off it can not block any voltage. There is some limit. Example MCB used at home have some rating. So a semiconductor has some rating above which it fails.
Non ideal Switch
• Also when switch is on, voltage across it is non zero. There is also maximum current carrying capability.
• So off state current is non zero, losses will happen when is off/blocking. When the switch is on voltage across it is non zero, there will conduction losses.
• So both blocking and conduction losses are finite. • Transition from on state to off state is not going
to be instantaneous. There are finite losses during switching. Switching losses happen.
Non ideal Switch• Every devices has maximum power dissipation limit.
All the devices are thermally unstable. • As the power losses increases, junction temperature
will increase and if it increases certain value it will fail, what we called thermal limit.
• So each device has safe operating area(SOA). The operating point should lie in SOA. (see the figure). So each device is thermally unstable because power dissipation is finite during conduction period, switching and blocking.
• You need to calculate or know heat sink requirement/cooling requirement. Power supply used in computer has cooling fan.
Various types of switches in Power electronics.
1. Uncontrolled Switch:-
Because on and off is determined by state of the circuit in which device is connected.
Diode is uncontrolled switch.
Various types of switches in Power electronics.
2. Semi controlled Switch:-It is because switch may be turned to one of its state using controlled terminal and other state is reachable through circuit only.It is three terminal device. SCR is an example. You can turn on the device by supplying positive gate current when the device is FB. (see figure)Having turn on the device you can not turn it off using gate. Hence the name semicontrolled.
Various types of switches in Power electronics.
• 3. Fully controlled Switch:
Both on and off should be possible using controlled terminal.
Example is BJT.
I can turn it on by supplying positive base current and off if base current=0.
Diode• 2 terminal device. Anode and Cathode.
• VAK should be positive. It is FB and diode conducts.
• Low power silicon VAK= 0.7
• For a power diode approxmately VAK=1.5
• VI Characterstics ( You are familiar)
• PIV ( You are familiar)
Diode
• During on state there is going to be finite voltage drop across diode (Vf) and Ia is current flowing through diode. So on state loss or conduction loss= Vf * Ia.
• If it is above a certain limit, you will mount on heat sink. So for diode you will mount it on heat sink. Small signal diodes does not need heat sink.
• In power electronics off state circuit , the way the diode turns off is important.
Power Diode• Power semiconductor diode
is the “power level” counterpart of the “low powersignal diodes”.
• The symbol of the Powerdiode is same as signal leveldiode. However, theconstruction and packagingis different.
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Power Diode• Power dides are required to carry up to several KA of current
under forward bias condition and block up to several KV underreverse biased condition.
• Large blocking voltage requires wide depletion layer.
• This requirement will be satisfied in a lightly doped p-njunction diode of sufficient width to accommodate therequired depletion layer.
• Such a construction, however, will result in a device with highresistively in the forward direction. There fore almost 1.5 V.
• If forward resistance (and hence power loss) is reduced byincreasing the doping level, reverse break down voltage willreduce.
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Reverse Recovery Time of a diode
Reverse Recovery Time of a diode
• Reverse Recovery time is time required for the diode to change from FB to RB.
• Forward Recovery time is time required to change from RB to FB.
• Generally reverse recovery dominates over forward recovery time because less minority carrier move.
Switching Characteristics of Power Diodes
• Power Diodes take finite time to make transition from reverse bias to forward bias condition (switch ON) and vice versa (switch OFF).
• Behavior of the diode current and voltage during these switching periods are important due to the following reasons.
– Severe over voltage / over current may be caused by a diode switchingat different points in the circuit using the diode.
– Voltage and current exist simultaneously during switching operation ofa diode. Therefore, every switching of the diode is associated withsome energy loss. At high switching frequency this may contributesignificantly to the overall power loss in the diode.
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Turn Off Characteristics
• The reverse recoverycharacteristics shown istypical of a particular typeof diodes called “normalrecovery” or “softrecovery” diode.
• The total recovery time (trr)in this case is a few tens ofmicroseconds.
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Turn Off Characteristics
• This is acceptable for line frequency rectifiers (these diodesare also called rectifier grade diodes).
• High frequency circuits (e.g PWM inverters) demand fasterdiode recovery, other wise this reverse recovery currentcan cause damage.
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Types of Diodes
• Depending on the application requirement varioustypes of diodes are available.
– Schottky Diode
– Fast Recovery Diode
– Line Frequency Diode/general-purpose diode
Types of Diodes Schottky Diode
Lets see an important video on Schottky diode
https://www.youtube.com/watch?v=bXEyCf1P0UU
Used for high frequency and fast switching applications.
Formed by joining n-type with metal such as gold, silver, platinum. So a metal to
semiconductor junction.
It operates with only majority carrier and there is no reverse current in it.
Since it operates with no minority carriers therefore applicable in high frequency
switching applications.
These diodes are used where a low forward voltage drop (typically 0.3 v) is needed.
These diodes are limited in their blocking voltage capabilities to 50v- 100v. It can not
block much reverse voltage. This is disadvantage.
Types of Diodes
Fast Recovery Diode
These diodes are designed to be used in high frequency
circuits in combination with controllable switches where a
small reverse recovery time is needed.
They are used in dc-dc or dc-ac where speed of recovery is
critical important.
At power levels of several hundred volts and several hundred
amperes such diodes have trr rating of less than few
microseconds.
Types of Diodes
Line Frequency Diode
The on state of these diodes is designed to be as low as
possible.
As a consequence they have large trr, which are
acceptable for line frequency applications.
Comparison between different types of Diodes
25rrt s 0.1 s to 5 srrt a few nano secrrt
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Characteristics Gernal purpose diode
Fast recovery diode Schottky diode
Working Voltage Up to 6000V &
3500A
Up to 6000V and
1100A
Up to 100V and
300A
Reverse recovery time
High Low Extremely low
Turn off time high low Extremely low
Trr
Switching
frequency
– Low
(Max 1KHz)
– High
(Max 20KHz)
– Very high.
(Max 30KHz)
Vf
25rrt s 0.1 s to 5 srrt a few nano secrrt
0.7 to 1.2VFV 0.8 to 1.5VFV 0.4 to 0.6VFV
Silicon Carbide Diodes
• Ulta low power loss
• Ulta fast switching behaviour
• Highly reliable ( no temperature influence on the switching behaviour).
• Then why it not so common as compared to silicon diode?????????????????????????????
• One of the most important type of power semiconductordevice.
• Compared to transistors, thyristors have lower on-stateconduction losses and higher power handling capability.
• However, they have worse switching performances thantransistors.
• Name ‘thyristor’, is derived by a combination of the capitalletters from THYRatron and transISTOR.
• It is semi controlled switch.
Introduction
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• Thyristors are four-layer pnpn powersemiconductor devices.
• These devices switch between conducting andnonconducting states in response to a controlsignal.
• Thyristors are used in timing circuits, AC motorspeed control and switching circuits.
Introduction
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Thyristors • Bell Laboratories were the first to fabricate a silicon-
based thyristor.
• Its first prototype was introduced by GE (USA) in 1957.
• Later on many other devices having characteristicssimilar to of a thyristor were developed.
• These semiconductor devices are SCR, SCS, Triac, Diac,PUT, GTO, e.t.c.
• This whole family of semiconductor devices is giventhe name thyristors.
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Why not germanium controlled rectifier
• The device is made of silicon because leakage current is very small in silicon as compared to germanium. since device is used as switch, it will carry leakage current in off condition which should be as small as possible.
• It got its name because it is silicon device and is used as rectifier and that rectification can be controlled.
Thyristor/ SCR
• SCR is a three terminal, four layers solid statesemiconductor device, each layer consistingof alternately N-type or P-type material, i.e;P-N-P-N,
• It can handle high currents and high voltages,with better switching speed and improvedbreakdown voltage .
A K
G
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Thyristor/ SCR• Thyristor can handle high currents and high voltages.
• Typical rating are 1.5kA & 10kV which responds to 15MWpower handling capacity.
• This power can be controlled by a gate current of about 1Aonly.
• Thyristor acts as a bistable switch.– It conducts when gate receives a current pulse, and
continue to conduct as long as forward biased (till devicevoltage is not reversed).
– They stay ON once they are triggered, and will go OFF onlyif anode current is too low or when triggered off.
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Thyristor/ SCR Operation• Refer VK mehta book.• When the anode voltage is made
positive with respect to the cathode,junctions J1 and J3 are forward biasedand junction J2 is reverse biased.
• The thyristor is said to be inthe forward blocking or off-statecondition.
• A small leakage current flows fromanode to cathode and is called the off-state current.
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Thyristor/ SCR Operation
• If the anode voltage VAK is increased to asufficiently large value, the reverse biasedjunction J2 would breakdown.
• This is known as avalanche breakdown and thecorresponding voltage is called the forwardbreakdown voltage VBO.
• Since the other two junctions J1 and J3 arealready forward biased, there will be freemovement of carriers across all three junctions.
• This results in a large forward current and thedevice is now said to be in a conducting or on-state.
• The voltage drop across the device in the on-state is due to the ohmic drop in the four layersand is very small (in the region of 1 V).
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Thyristor/ SCR
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Thyristor Operating modes
Thyristors have three modes :
• Forward blocking mode:Only leakage current flows,so thyristor is notconducting.
• Forward conducting mode:large forward current flowsthrough the thyristor.
• Reverse blocking mode:When cathode voltage isincreased to reversebreakdown voltage ,Avalanche breakdownoccurs and large currentflows.
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Important terms
Latching Current IL
• This is the minimum anode current required to maintain the thyristor inthe on-state immediately after a thyristor has been turned on and thegate signal has been removed.
• If a gate current greater than the threshold gate current is applied untilthe anode current is greater than the latching current IL then thethyristor will be turned on or triggered.
Holding Current IH
• This is the minimum anode current required to maintain the thyristor inthe off-state.
• To turn off a thyristor, the forward anode current must be reducedbelow its holding current for a sufficient time for mobile charge carriersto vacate the junction.
• Generally the value of holding current is 1/1000 of the rated anodecurrent.
• http://aueeestudents.blogspot.com/2015/01/what-is-difference-between-holding.html
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Important characteristics
Reverse Current IR
• When the cathode voltage is positive with respect to theanode, the junction J2 is forward biased butjunctions J1 and J3 are reverse biased. The thyristor is saidto be in the reverse blocking state and a reverse leakagecurrent known as reverse current IR will flow through thedevice.
Forward Breakover Voltage VBO
• If the forward voltage VAK is increased beyond VBO , thethyristor can be turned on. But such a turn-on could bedestructive. In practice the forward voltage is maintainedbelow VBO and the thyristor is turned on by applying apositive gate signal between gate and cathode.
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• We will derive expression for anode current
Mathematical analysis of two transistor model
Mathematical analysis of two transistor model• relationship between IC and IB is
Mathematical analysis of two transistor model
Mathematical analysis of two transistor model
Mathematical analysis of two transistor model
• Do you expect a thyristor to turn ON if a positive gate pulse is applied under reverse bias condition (i. e cathode positive with respect to anode)?
• Answer: The two transistor analogy of thyristorshown in Fig 4.2 (c) indicates that when a reverse voltage is applied across the device the roles of the emitters and collectors of the constituent transistors will reverse. With a positive gate pulse applied it may appear that the device should turn ON as in the forward direction. However, the constituent transistors have very low current gain in the reverse direction. Therefore no reasonable value of the gate current will satisfy the turn ON condition (i.e.∝1 + ∝2 = 1). Hence the device will not turn ON.
Thyristor turn-ON methods
• Thyristor turning ON is also known as Triggering.
• With anode is positive with respect to cathode, a thyristorcan be turned ON by any one of the following techniques :
– Forward voltage triggering
– Gate triggering
– dv/dt triggering
– Temperature triggering
– Light triggering
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1. Forward Voltage Triggering
• When breakover voltage (VBO) across a thyristor is exceededthan the rated maximum voltage of the device, thyristor turnsON.
• At the breakover voltage the value of the thyristor anode currentis called the latching current (IL) .
• Breakover voltage triggering is not normally used as a triggeringmethod, and most circuit designs attempt to avoid its occurrence.
• When a thyristor is triggered by exceeding VBO, the fall time of theforward voltage is quite low (about 1/20th of the time takenwhen the thyristor is gate-triggered).
• This method is not preferred because during turn on ofthyristor, it is associated with large voltage and large currentwhich results in huge power loss and device may bedamaged.
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2. Gate Triggering• Turning ON of thyristors by gate triggering is simple and
efficient method of firing the forward biased SCRs.
• Whenever thyristor’s turn-ON is required, a positive gatevoltage b/w gate and cathode is applied.
• The pulse remains for some time untill the anode currenthas increased to a certain value known as latchingcurrent or pick up current.
• Forward voltage at which device switches to on-statedepends upon the magnitude of gate current.– Higher the gate current, lower is the forward
breakover voltage .85
Gate Triggering• Turning ON of thyristors by gate triggering is simple and
efficient method of firing the forward biased SCRs.
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Thyristor Gate Control Methods
• An easy method to switch ON a SCR into conduction is to applya proper positive signal to the gate.
• This signal should be applied when the thyristor is forwardbiased and should be removed after the device has beenswitched ON.
• Thyristor turn ON time should be in range of 1-4 microseconds, while turn-OFF time must be between 8-50 microseconds.
• Thyristor gate signal can be of three varieties.– D.C Gate signal– A.C Gate Signal– Pulse
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Thyristor Gate Control Methods
D.C Gate signal: Application of a d.c gate signal causes the flowof gate current which triggers the SCR.
– Disadvantage is that the gate signal has to be continuouslyapplied, resulting in power loss.
– Gate control circuit is also not isolated from the mainpower circuit.
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Thyristor Gate Control MethodsA.C Gate Signal: In this method a phase - shifted a.c voltage derived from
the mains supplies the gate signal.
– Instant of firing can be controlled by phase angle control of the gatesignal.
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Thyristor Gate Control MethodsPulse: Here the SCR is triggered by the application of a positive pulse of
correct magnitude.
– For Thyristors it is important to switched ON at proper instants in acertain sequence.
– This can be done by train of the high frequency pulses at properinstants through a logic circuit.
– A pulse transformer is used for circuit isolation.
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3. Temperature Triggering
• If the temperature of the thyristor is high, it results inincrease the leakage current ICBO1 and ICBO2 andleakage current is strong function of temperature. Theyapproximately double for every 10 °C rise intemperature. If they increase collector current as well asα1 & α2 raise and in case (α1 + α2) approach one, anodecurrent increases and device goes into conductionmode.
• This type turn on is not preferred as it may result inthermal turn away and hence it is avoided.
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4. Light Triggering
• In this method light particles (photons) are made tostrike the reverse biased junction, which causes anincrease in the number of electron hole pairs andtriggering of the thyristor.
• For light-triggered SCRs, a slot (niche) is made in theinner p-layer.
• When it is irradiated, free charge carriers aregenerated just like when gate signal is applied b/wgate and cathode.
• Pulse light of appropriate wavelength is guided byoptical fibers for irradiation.
• If the intensity of this light thrown on the recessexceeds a certain value, forward-biased SCR is turnedon. Such a thyristor is known as light-activated SCR(LASCR).
• Light-triggered thyristors is mostly used in high-voltage direct current (HVDC) transmission systems.
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5. dv/dt triggering
• With forward voltage across anode & cathode of a thyristor, twoouter junctions (A & C) are forward biased but the inner junction(J2) is reverse biased.
• The reversed biased junction J2 behaves like a capacitor because ofthe space-charge present there.
• As p-n junction has capacitance, so larger the junction area thelarger the capacitance.
• If a voltage ramp is applied across the anode-to-cathode, a currentwill flow in the device to charge the device capacitance accordingto the relation:
• If the charging current becomes large enough, density of movingcurrent carriers in the device induces switch-on.
• This method of triggering is not desirable because high chargingcurrent (Ic) may damage the thyristor.
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Thyristor Switching characteristics • Also called thyristor dynamic characteristics or on-off
characteristics of scr. • The switching characteristics are important particularly
at high-frequency, to define the device velocity in changing from conduction state to blocking state and vice versa.
• Losses occurring in the device during switching from ON state to OFF state and OFF state to ON state is known as Switching Losses.
• The device’s switching characteristics tells us about the switching losses, which is very important parameter to decide the selection of device.
• At high frequency, the switching losses are more.
• (a) Rate of rise of anode voltage dv/dt: It isthe slope of the line showing anode voltageVAK between time t0 and t1. Rapid rising ofthe voltage produces a transient currentacross junction J2. This causes falsetriggering. Typical value of dv/dt rating is100-300 volts per microseconds.
Dynamic Characteristics of Thyristor
• (b) Rate of rise of Anode current di/dt:When gate pulse is applied the conductionof anode current starts near the gateconnection and spreads from there acrossthe whole area or the junction. If di/dt islarge, than a local hot spot will be formeddue to the high current density and mayresult in failure of device. Typical value ofdi/dt rating is 100-500 amps per μs.
Dynamic Characteristics of Thyristor
• Rate of rise of re-applied voltage dv/dt: It isshown as slope of the line between time t8 and t9.Turn-off time increases with the increase of re-applied dv/dt. Re-applied dv/dt is more crucialthan initial applied dv/dt. This is because thecurrent carriers at the junction take finite time torecombine naturally and cause the blocking state.
Dynamic Characteristics of Thyristor
Turn ON Time of SCR
• A forward biased thyristor can be turned on by applying a positive voltage between gate and cathode terminal. But it takes some transition time to go from forward blocking mode to forward conduction mode. This transition time is called turn on time of SCR and it can be subdivided into three small intervals as delay time (td) rise time(tr), spread time(ts).
• Rise time inversely proportional to magnitude of gate current and its build up rate. Thus tr can be reduced if high and step pulses are applied to gate.
Turn off mechanism
Thyristor protection and cooling system of thyristor.
Lecture 6
ENGR. JAHANGEER BADAR SOOMRO
• COOLING SYSTEM OF THYRISTOR
Gate Protection of Thyristor
TYPES OF THYRISTOR
Lecture 7
ENGR. JAHANGEER BADAR SOOMRO
Your assignment
• Compare and contrast between SCR and TRIAC.
• What are disadvantages and limitation of TRIAC.
• Different application where QUDRAC(diac-triac) together are used (Hint vk mehta book)
• Last date is 1 october.
GATE TURN OFF THYRISTORS(GTO)
Turn on and Turn off time of SCR
• GTO can be brought into conduction very rapidly because it can tolerate higher di/dt values due to gate cathode interdigitation. Or in simple words at the instant of turn on more area gate cathode is available so therefore you can have high di/dt.
• GTO suffers more power losses when we turn it off because a large negative pulse it applied at gate to turn it off. During turn off, the forward voltage of the device must be limited until the current tails off. If the voltage rises too fast (reapplied-dv/dt is too fast) not all of the device will turn off and GTO will fail and destroy. So during turn off snubber circuit should be used in GTO.
Advantages over SCR
• Fully controlled.
• Elimination of commutating components in forced commutation, resulting in reduction in cost, weight, and volume.
• Reduction in acoustic and electro-magnetic noise due to the elimination of commutation chokes.
• Faster turn-off permitting high switching frequencies and
• Improved efficiency of converters.
• High over current capabilities( High di/dt)
Disadvantages as compared to SCR
• Magnitude of latching, holding currents is more. The latching current of the GTO is several times more as compared to conventional thyristors of the same rating.
• On state voltage drop and the associated loss is more.• Due to multicathode structure of GTO, triggering gate
current is higher than that required for normal SCR.• Gate drive circuit losses are more. Its reverse voltage
blocking capability is less than the forward voltage blocking capability.
• Turn off losses are significant.• It requires a minimum gate current to sustain on-state
current.