Part of Lecture series on EE321N, Power Electronics-I delivered by me during Fifth Semester of B.Tech. Electrical Engg., 2012 Z H College of Engg. & Technology, Aligarh Muslim University, Aligarh Please comment and feel free to ask anything related. Thanks!

1. EE-321 N
Lecture-15
Ramp Control Scheme

2. Introduction
• Similar to the cosine scheme, there is another
one called ramp comparator approach
• As the name suggests, this scheme involves
comparison of a ramp signal against a dc
control signal
• This scheme is suitable for Biphase Midpoint
converter and can be extended to three phase
converters also
9-Nov-12 EE-321N, Lec-15 2

3. A Biphase midpoint converter
9-Nov-12 EE-321N, Lec-15 3

4. Block Diagram & Waveforms
9-Nov-12 EE-321N, Lec-15 4

5. 9-Nov-12 EE-321N, Lec-15 5

6. 9-Nov-12 EE-321N, Lec-15 6
Vr
2
Comparator 1
Synchronized
I/P Supply
M/S 1 (For T1)

7. Operation
• The t/f secondary terminal provides
synchronized ac voltage which is converted to
square wave by using a ZCD
• The negative portion of the square wave is
suppressed by using a diode
• Square wave is used to generate synchronized
ramp signal
9-Nov-12 EE-321N, Lec-15 7

8. Operation...contd
• As soon as the control signal becomes equal
to the ramp signal, output from comparator is
obtained
• Comparator o/p is also a square wave whose
leading edge lags by an angle α, w. r. t. the
commencement of the ramp
• Comparator o/p wave is sufficient to trigger
the thyristor but pulse width is variable
9-Nov-12 EE-321N, Lec-15 8

9. Operation...contd
• But if a fixed duration pulse is required then a
monostable chip is used which provides a
small duration pulse signal or a pulse train.
• Again the relation between the firing angle
and the control voltage is linear given by
9-Nov-12 EE-321N, Lec-15 9
r
c c
r r
V V
k
V V

  

    