AC Regulators

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AC Regulators

Anoop MathewHead of the Dept;Electronics and Communication Engg.Vedavyasa Institute of Tech.


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AC Regulatorsp Alternatively called as AC voltage controllers

p RMS value of the output is varied by using a semiconductor switch.

p No need of extra commutation circuitry-Natural commutation

p Fixed AC to Variable AC

p Output frequency = input frequency

p Implemented by AC switch

p AC switch – Bidirectional switch


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Applications

p Lighting control

p Industrial heating

p Resistance welding

p On-load transformer tap change

p Speed control of IM


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Methods of voltage control

Integral cycle control Phase control

• ON-OFF Control.• Connect the source to load

for a few complete cycles and disconnect it for a few.

• Suitable for systems with large time constant.

• Control by changing the

firing angle.

• Suitable for systems with

small time constant.


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Types of Gating Signals


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Single phase half wave voltage regulator


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Single Phase AC regulators


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Single Phase AC regulators – Alternate forms


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Waveforms - Single Phase AC regulators with R load


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Class Work.......

? Find RMS and DC value of the output current and voltage


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Waveforms - Single Phase AC regulators with RL load


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Class Work.......

? Find RMS and DC value of the output current and voltage


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γ versus α curves for AC regulator with RL load


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Sequence Controlp To improve system p.f and reduction of

harmonics in the source and load current.

p Two or more stages of voltage controllers are

used in parallel.

p Parallel voltage regulators are triggered in proper

sequence to get desired output.

p Sequence controlled AC regulators are also called

as synchronous tap changers or transformer tap

changers.


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Two Stage Sequence control – Power Circuit


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Two Stage Sequence control of AC Regulator

p Two parallel stages are employed.

p Turn-ratio from each primary to secondary is unity

p Range of output voltage control is from Zero to Vs (Vs is the peak value of input voltage) using the switch pair T3 & T4.

firing angle, α=0 for output Vs &

α=180 for output zero.


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Two-stage AC regulator

p Using the switch pair T1 & T2.

firing angle, α=0 for output 2Vs &

α=180 for output Vs.


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Waveforms - Two-stage AC regulator with R-load


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Waveform Analysis (R-Load)

p Both current and voltage are identical.p For positive half-cycle firing angle for T3 &

T4 are always zero.p At this range firing angle for T1 & T2 vary

to get output voltage in the range Vs to 2 Vs.

p As T1 fires, output voltage=e1+e2p In the negative half-cycle, T2 fires at

some firing angle.


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Class Work.......

? Find RMS and DC value of the output

current and voltage


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Waveforms - Two-stage AC regulator with RL-load


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Waveform Analysis (RL-Load)p Switching pattern is same as R-load.p At ώt=π, Vo = zero but current non-zero

due to the load inductance.p T1 continues conducting to an elapsed

angle say, βp At β, T1 turns OFFp At ώt=π, T4 fired but from the point π+β to π+α, Vo=Vs

p T2 and T3 won’t conduct simultaneously-No short circuit threat.


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Multi-stage sequence Control – Power circuit


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Multi-stage sequence Controlp As stage increasesà improved p.f and lower

harmonics.

p Transformer has ‘n’ secondary windings.

p Secondary rating is ‘es/n’

p Voltage at node-P w.r.to ‘K’ is ‘es’

p Voltage control from (n-3)es/n to (n-2)es/n can be achieved by controlling the firing angle of switch pair-4.

p Output harmonic content is proportional to the magnitude of voltage variation.


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References

[1] A. Maamoun, “A review on semiconductor voltage controllers”, IEEE Trans. 2003.

[2] Ned Mohan et al, “Power Electronics”, Weily publications 2005

[3] M.D. Singh & K.B Khanjandani, “Power Electronics”, TMH 2006

[4] Cyril W. Lander “ Power Electronics”, McGraw Hill International Editions 2007

[5] Rashid M.H “ Power Electronics”, printice Hall Int. 2001

[6] Krein “Elements of Power Electronics”, Oxford Press 2005


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Thank you

Questions ??????

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AC Regulators

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