# AC voltage regulator (AC to AC converter)

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## AC voltage regulator (AC to AC converter)

AC voltage regulator(controller)  is a device which is convert fixed Alternating voltage to variable Alternating voltage without changing frequency.

• There are Two types of ac voltage regulator.
1. Half wave AC controller
2. Full wave AC contoller

#### Half wave AC controller

•  fig shows voltage regulator using one thyristor in Anti-parallel with one diode.load is resistive, by changing the value of firing angle α of thyristor S we can controlled the load voltage. ##### Working:
• In positive half cycle of AC supply SCR S is turn ON at ωt=α. during this load voltage is positive now SCR will be turn OFF due to natural commutation at ωt=π. load current and source current are positive.
• In negative half cycle of AC supply Diode D1 will turn ON at ωt=π. During these cycle load voltage is negative. and load current and source current are negative.
• By controlling the firing angle α of the SCR we can control AC load voltage.

Average value of output voltage is given by,

= √2 Es/2π (cosα-1)

If α is varied from 0 to π, output voltage varies from Es to Es/ √2 and average value of output voltage varies from 0 to -√2 Es / π .

wave form is shown in fig….. #### Full wave AC controller

• Single phase full wave Ac controller consist two thyristors connected in anti-parallel.
• Load is resistive for low power application is used ,By controlling the firing angle α of the SCR we can control AC load voltage.
• Fig shows single phase full wave ac voltage controller with resistive load. ##### Working:
• During positive half cycle thyristor T1 is forward bias and during thyristor T2 is forward bias.
• During positive half cycle, T1 is trigger at firing angle α . T1 start conducting and source voltage is given to the load from ωt=α to π. At π Vs and Is fall to 0. after π T1 is reverse bias therefore it is turn OFF.
• During negative half cycle, T2 is trigger at (π+α) and T2 conducts from π+α to 2π.  After 2π T2 is reverse bias and it is commutated
• From 0 to α , T1 is forward bias there for VT1 = Vs
• After π, π to (π+α)  T1 is reverse  bias there for VT1 =Vs

average value of output voltage is given by,

Vs[1/π{π-α+(sin2α/2)}]½

If α is varied from 0 to π, The average output voltage is controlled from voltage Vs to 0.

wave form is shown in fig….. comment below…………………. ?

2. Michael Small
3. Swe Swe Moe