Course Teacher:
Dr. Md. Shamsul Arifin
Assistant Professor
Dept. of EEE, CUET
Introduction
➢ The output voltage of thyristor rectifiers is varied by
controlling the delay or firing angle of a thyristors.
➢ These phase-controlled rectifiers are simple and less
expensive.
➢ The efficiency of these rectifiers is, in general, above 95%.
➢ Because these rectifiers convert form AC to DC, hence, the
controlled rectifiers are also called AC-DC converters.
➢ They are used extensively in industrial applications,
especially in variable-speed drives, ranging from fractional
horsepower to megawatt power level.
➢ The phase-controlled converters can be classified into two
types, depending on the input supply:(1) single-phase
converters and (2) three-phase converters. Each type can
be subdivided into (a) semi converter, (b) full converter,
and (c) dual converter.
Dr. Md. Shamsul Arifin, EEE,CUET
3
Principle of Phase Controlled Converter
Operation
 When the thyristor 𝐓𝟏 is fired at 𝛚𝐭 =
𝛂, 𝐓𝟏 conducts and the input voltage
appear across the load. When the input
voltage starts to be negative at 𝛚𝐭 = 𝛑,
𝐓𝟏 is reverse biased.
Dr. Md. Shamsul Arifin, EEE,CUET
4
Single Phase Full Converters
 During
the positive halfcycle, thyristors 𝐓𝟏 and
𝐓𝟐 are forward biased: and
when these thyristors are
fired simultaneously at 𝛚𝐭 =
𝛂, the load is connected to
the input supply through 𝐓𝟏
and 𝐓𝟐 .
 Due to the inductive load,
thyristors 𝐓𝟏 and 𝐓𝟐 continue
to conduct beyond 𝛚𝐭 = 𝛑,
event thought the input
voltage is already negative.
Dr. Md. Shamsul Arifin, EEE,CUET
5
Single Phase Full Converters
 The DC output voltage
 The rms output voltage
Dr. Md. Shamsul Arifin, EEE,CUET
6
Single Phase Dual Converters
 If
two of these full
converters are connected
back to back, both the
output voltage and load
current can be reversed.
This system provides a
four quadrant operation
and called a dual
converter.
 Dual
converter
are
normally used in highpower variable speed
drives.
Dr. Md. Shamsul Arifin, EEE,CUET
7
Single Phase Dual Converters
 The average output voltage
of converter1 and converter
2 are
𝟐𝐕𝐦
𝐜𝐨𝐬 𝛂𝟏
𝛑
𝟐𝐕
𝐕𝐝𝐜𝟐 = 𝐦 𝐜𝐨𝐬 𝛂𝟐
𝛑
𝐕𝐝𝐜𝟏 =
 As 𝐕𝐝𝐜𝟏 =- 𝐕𝐝𝐜𝟐
𝐜𝐨𝐬 𝛂𝟏 = − 𝐜𝐨𝐬 𝛂𝟐
= 𝐜𝐨𝐬 (𝛑 − 𝛂𝟏 )
 So, 𝛂𝟐 = 𝛑 − 𝛂𝟏
Dr. Md. Shamsul Arifin, EEE,CUET
8
❑ Three-phase
converters
provide higher average
output voltage and in
addition the frequency of
the ripples on the output
voltage
is
higher
compared with that of
single-phase converters.
❑ As a result, the filtering
requirements
for
smoothing out the load
current and load voltage
are simpler.
❑ For these reasons threephase converters are used
extensively in high-power
variable-speed drives.
Principle of Three Phase
Half Wave Converters
Dr. Md. Shamsul Arifin, EEE,CUET
9
Principle of Three Phase Half Wave Converters
❑ For average output voltage for a
continuous load current is
𝟓𝛑
𝟔 +𝛂
𝟑
𝐕𝐝𝐜 =
න
𝐕 𝐬𝐢𝐧 𝛚𝐭 𝐝𝛚𝐭
𝟐𝛑 π+α 𝐦
6
𝟑 𝟑
=
𝐕𝐦 𝐜𝐨𝐬𝛂
𝟐𝛑
Dr. Md. Shamsul Arifin, EEE,CUET
10
Principle of Three Phase
Full Wave Converters
Dr. Md. Shamsul Arifin, EEE,CUET
11
Three Phase Dual Converters
Dr. Md. Shamsul Arifin, EEE,CUET
12
Single Phase Semi
Converters
Dr. Md. Shamsul Arifin, EEE,CUET
13
Three Phase Semi
Converters
Dr. Md. Shamsul Arifin, EEE,CUET
14
Chapter Ends
Thank You
Dr. Md. Shamsul Arifin, EEE,CUET
15