PPT on speed control of induction motor using Triac

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1 Speed Control of Induction motor Using TRIAC Presented by:- Yagnadattu prasanth satya Vijay kumar , Balaram .

CONTENTS: 

CONTENTS Thyristor(SCR) Triac Triacs (Triode AC Switch) Triacs (Triode AC Switch) – triggering 3-Phase AC-AC Voltage Regulator Induction Motor Speed Control Advantages & Disadvantages Conclusion 2

Thyristor(SCR):-: 

Thyristor(SCR):- SCR(Silicon Controlled Rectifier) was praposed by william shockly in 1950, and it is championed by Moll and others at bell labs was developed in 1956. A thyristor is a solid-state semiconductor device with four layers and 3 junctions of alternating N and P-type material. They act as bistable switches, conducting when their gate receives a current pulse, and continue to conduct while they are forward biased 3

TRIAC: 

TRIAC Thyristor (SCR) connection is called anti-parallel/inverse parallel, This connectivity is equivalent to using a single triac , . A triac is a thyristor that can conduct in both directions. . Triac – T4xx series 600-800V, 4A 4

TRIAC (Triode AC Switch): 

TRIAC (Triode AC Switch) Triacs are equivalent to two back to back thyristors in the one device. Only for smaller currents to 10-20A max, then use thyristors.

TRIAC (Triode AC Switch) – triggering: 

TRIAC (Triode AC Switch) – triggering Triacs can be triggered with either polarity of gate current, for either conduction direction 1,2,3,4 also known as 1+, 1-, 3-, 3+. Avoid quadrant 4 (3+), since much less sensitive.

Triacs (Triode AC Switch) – triggering: 

Triacs (Triode AC Switch) – triggering Light dimmers trigger with gate polarity = mains polarity, i.e. quadrants 1, 3 (1+, 3-)

AC–AC conversion: 

AC–AC conversion AC-AC converters are used in induction motor control Also used in dimmer light switches 8

Observations: : 

Observations: The thyristors cannot conduct simultaneously When either thyristor is on V o = V s and V sw = 0 When both thyristors are off V o = 0 and V sw = V s The average source and load current is zero if both thyristors conduct for an equal time The average current in each thyristor is not zero since they conduct in one direction RMS current in each thyristor is 1/√2 the RMS load current 9

Cond...: 

Cond... Normalised RMS output voltage vs. delay angle, α 10

Cond..: 

Cond.. The non-sinusoidal output voltage and current leads to a lot of harmonic distortion Assuming sinusoidal input we only have odd harmonics 11

3-Phase AC-AC Voltage Regulator: 

3-Phase AC-AC Voltage Regulator The thyristors are switched on in sequence 1-2-3-4-5-6 at 60 o intervals. Gate signals are maintained throughout the possible conduction angle. Triple n Harmonics are eliminated. Delta connection requires breaking load which is often not possible. 12

Cond..: 

Cond.. 13 At any instant three , two or zero thyristors are conducting Instantaneous line voltages are: Line-to-neutral (three on) Half-line-to-line (two on) Zero (none on)

Cond..: 

Cond.. Which thyristors are conducting depends on the delay angle, α 0 < α < 60 o : two or three thyristors conduct 60 o < α < 90 o : only two thyristors conduct 90 o < α < 150 o : only two thyristors conduct α > 150 o : no thyristors conduct 14 -> The range of output voltage for the three phase AC--AC converter is between full source voltage and zero -> Harmonics present in output are 5 th , 7 th , 11 th , 13 th , and so on

Induction Motor Speed Control: 

Induction Motor Speed Control Squirrel-cage induction motor speed can be controlled by varying voltage or frequency The torque produced by an induction motor is proportional to the square of the applied voltage Operating speed corresponds to the intersection of the torque-speed curves and the load 15

Slide 16: 

Device Description: A gate-controlled silicon AC switch in a plastic package. Design Notes: Application: The gate on /off control of the Triac is referenced to the voltage across the resistor. It therefore controls the AC current of the starting winding of the motor. Solution Description: Triac selection depends on the line voltage, nominal load current, maximum surge load current and the specific trigger circuit employed. Typical Triac Part number as Q6006DH3. Companion Solutions: Min /Max Alternistor current rating from 6 to 10A , Voltage rating from 200Volts in a 800 volts. PTC thermistor could also be used for AC Start winding. One drawback of the PTC is that it take time for PTC to cool down. This means the motor should not be started right after it being stopped. Regulatory Issues: N/A Unique Features: N/A Application Warnings N//A Control Triac Control Triac for Start winding AC Induction Motor Control Using a Triac Triac OVP Control Triac for Start winding

Slide 17: 

Design Notes: Application: Control Triacs are used as on/off control for heating element. With appropriate control program, Triac also allows very accurate control of duty cycle and average heating power by controlling on/off status of each AC half-cycle. Solution Description: Triac selection depends on the line voltage, nominal load current, maximum surge load current and the specific trigger circuit employed. For high-current application like heater, Alternister type Triac such as Q6040K7 would be typical selection. Companion Solutions: n/a Regulatory Issues: n/a Unique Features: n/a Application Warnings: n/a Control Triac for Heating Element Heating Element Heating Element Control P Control Triac Triac OVP

Cond..: 

Cond.. Torque-speed curves for an induction motor 18

Proceduce:-: 

Proceduce :- Capacitors are placed in parallel with inductive loads for power factor improvement If load has constant reactive (VAR) requirement, a fixed capacitor can be selected to set PF to unity If load has varying VAR requirement a fixed capacitor will result in changing PF 19

Cond..: 

Cond.. Static VAR control – AC voltage controller maintains unity PF for varying VAR requirement Fixed capacitor supplies a fixed amount (generally more than required) of reactive power to the load Inductor absorbs a varying amount of reactive power dependent on the delay angles used to fire the SCRs 20

Cond..: 

Cond.. Net reactive power supplied by Capacitor-Inductor combination is controlled to match that absorbed by the load As the VAR requirement changes the delay angle is adjusted to maintain unity power factor 21

Advantages:-: 

Advantages:- Adjusts to changing VAR requirement very quickly, continuously adjustable (rather than at discrete levels as for capacitor banks) Filters needed to remove harmonic component introduced by the switched inductor 22

Disadvantages:-: 

Disadvantages:- Energy efficiency is poor using the AC-AC controllers we have looked at especially at low speeds (use PWM control) The large slip at low speeds results in large rotor losses Typical applications is where the load is small, such as single-phase fractional horse power motors or where the time of low-speed operation is short 23

Conclusion:-: 

Conclusion:- 24 ->When Compared to other machines it is the Quickly adjusting the VAR, ->So This Control method is useful for the small load requirements Conclusion

Slide 25: 

25 Any Quiries ……?

Slide 26: 

26 Thanking you