CYCLOCONVERTERS.ppt

cycloconverters

1. CYCLOCONVERTERS
MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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2. Cycloconverters
Cycloconvertersdirectly convert ac signals
of one frequency (usually line frequency) to ac
signals of variable frequency. These variable
frequency ac signals can then be used to
directly control the speed of ac motors.
Thyristor-based cycloconvertersare typically
used in low speed, high power (multi-MW)
applications for driving induction and wound
field synchronous motors
MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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3. Applications
•Cement mill drives
•Ship propulsion drives
•Rolling mill drives
•Scherbius drives
•Ore grinding mills
•Mine winders
MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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4. Types of Cycloconverters
MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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5. MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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6. Midpoint Cycloconverter
MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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7. Bridge type Cycloconverter
MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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8. MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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9. MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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10. Three phase cycloconverter
MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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11. Three-Phase to Single-Phase (3f-1f)
Cycloconverter
There are two kinds of three-phase to single-phase (3f-
1f) cyclo-converters
•3f-1f half-wave cyclo-converter
•3f-1f bridge cyclo-converter
MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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12. Three-Phase to Single-Phase (3f-1f)
Cycloconverter
•The 3f-1f cyclo converter applies rectified voltage to
the load. Both positive and negative converters can
generate voltages at either polarity, but the positive
converter can only supply positive current and the
negative converter can only supply negative current.
Thus, the cyclo converter can operate in four
quadrants: (+v, +i) and (-v, -i) rectification modes and
(+v, -i) and (-v, +i) inversion modes.
•The modulation of the output voltage and the
fundamental output voltage are Note that a is
sinusoidallymodulated over the cycle to generate
harmonically optimum output voltage
MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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13. 3f-1f half-wave cyclo-converter
MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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14. 3f-1f half-wave cyclo-converter
waveforms
MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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15. Three-Phase to Single-Phase (3f-1f)
Cycloconverter
•The load always requires the fundamental voltage
to be continuous. Therefore, during the current
polarity reversal, the average voltage supplied by
both of the converters should be equal.
•Otherwise , switching from one converter to the
other one would cause an undesirable voltage
jump.
•To prevent this problem, the converters are
forced to produce the same average voltage at all
times
MH1032/brsr/A.Y 2016-17/pe/AC TO AC
CONVERTERS

16. Three-Phase to Single-Phase (3f-1f)
Cyclo-converter
The output phase voltage v
0can be written as:
where V
0is the rms output voltage and 
0is
the output angular frequency. We can also
write:
where the modulation factor, m
fis given by:0 0 0
2 sinv V t 0 0 0 0 0
cos cos sin
d p d n f d
v V V m V t      00
2/
fd
m V V
MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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17. Three-Phase to Single-Phase (3f-1f)
Cyclo-converter
From these equations, we can write:
Thus for zero output voltage, m
f=0 and

P= 
N= /2. For max. phase voltage,
m
f=1 => 
P=0, 
N= .

Pand 
N values for m
f=0.5 and 1.1
0
cos [ sin ]
pf
mt

 NP
  
MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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18. Operating modes
The phase group of a cyclo-converter can be
operated in two modes:
1) Circulating current mode
2) Non-circulating current (blocking) mode
MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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19. Circulating current mode
•In the circulating current
mode, the current
continuously circulates
between the +veand -ve
converters. Although the
fundamental output
voltage waves of the
individual converters are
equal, the harmonics will
cause potential difference
which will result in short-
circuits without an IGR.
MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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20. Non-circulating current (blocking)
mode
In the blocking mode of
operation, no IGR is
used and only one
converter is conducting
at any time.
Zero current crossing
detection can be used
to select +veor -ve
converter conduction
MH1032/brsr/A.Y 2016-17/pe/AC TO AC
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