1.
M
U
E
T
JAMSHORO
Department
of
Electrical
Engineering
AC Voltage
Controllers

2.
M
U
E
T
JAMSHORO
Department
of
Electrical
Engineering
 If a semiconductor switch is connected
between ac supply and load, the power flow
can be controlled by varying the rms value of
ac voltage applied to the load; and this type of
power circuit is known as ac voltage controller.

AC Voltage Controllers

3.
M
U
E
T
JAMSHORO
Department
of
Electrical
Engineering
AC Voltage Controllers
Single-phase
controllers
Bidirectional or
Full-wave control
Unidirectional or
Half-wave control
Bidirectional or
Full-wave control
Unidirectional or
Half-wave control
Three-phase
controllers

4.
M
U
E
T
JAMSHORO
Department
of
Electrical
Engineering
AC Voltage Controllers
•
• For power transfer in an AC converters, following types
of control methods are used:
• Phase angle control
• On-Off control (Extinction angle control) or Integral
cycle control or burst firing control
• PWM control
•
4

5.
M
U
E
T
JAMSHORO
Department
of
Electrical
Engineering
Principle of Phase Control
5

6.
Principle of On-Off Control (Integral cycle
control)

7.
M
U
E
T
JAMSHORO
Department
of
Electrical
Engineering
The basic principle of on-off control technique is explained
with reference to a single phase full wave ac voltage
controller circuit shown below. The thyristor switches T1and
T2 are turned on by applying appropriate gate trigger pulses
to connect the input ac supply to the load for ‘n’ number of
input cycles during the time interval Ton. The thyristor
switches T1 and T2 are turned off by blocking the gate
trigger pulses for ‘m’ number of input cycles during the time
interval Toff. The ac controller ON time Ton usually consists
of an integral number of input cycles.

8.
M
U
E
T
JAMSHORO
Department
of
Electrical
Engineering
(a) Power-circuit diagram (b) voltage and current waveforms
Single-phase unidirectional
ac voltage controller

9.
Single-phase Bidirectional full wave ac voltage
controller using two anti-parallel thyristors

10.
M
U
E
T
JAMSHORO
Department
of
Electrical
Engineering
Single phase Bi-directional full wave ac
voltage converter using TRIAC

11.
M
U
E
T
JAMSHORO
Department
of
Electrical
Engineering
Single phase full wave ac converter with common
cathode configuration

12.
M
U
E
T
JAMSHORO
Department
of
Electrical
Engineering
Single Phase Full Wave AC Voltage Converter
Using a Single Thyristor

13.
M
U
E
T
JAMSHORO
Department
of
Electrical
Engineering
Three-phase Full-Controlled AC Controller

14.
M
U
E
T
JAMSHORO
Department
of
Electrical
Engineering
APPLICATIONS OF AC-AC CONVERTERS
The most common applications of AC-AC converters are:
 Industrial heating and domestic heating
 On-load transformer connection changing
 Light controls
 Speed control of poly phase Induction Motors
 AC magnet controls
 Air-craft
 Household appliances
 Electronic ballasts.
14

15.
M
U
E
T
JAMSHORO
Department
of
Electrical
Engineering
THANKS