Chapter 5 - DC to DC Converters (Choppers)

Ex 5.1 page 184

from __future__ import division
from math import sqrt
R=10    #  ohm
Vs=230    #  V
f=1*1000    #  Hz
Ton=0.4    #  ms
k=0.4     #  duty cycle

Vo=Vs*k    # V
Ioav=Vo/R    #  A
Vor=Vs*sqrt(k)    #  V
Po=Vor**2/R    #  W
print '\n Average load current = %.1f A'%( Ioav)
print '\n Power delivered = %.2f W'%(Po)

 Average load current = 9.2 A

 Power delivered = 2116.00 W

Ex 5.2 page 185

from __future__ import division
from math import sqrt

R=5    #  ohm
Vs=300    #  V
f=1*1000    #  Hz
Ton=20    #  ms
Toff=10    #  ms

k= Ton/(Ton+Toff)    #  duty ratio
f=1000/(Ton+Toff)    # Hz
Voav=Vs*k    #  V
Ioav=Voav/R    #  A
print '\n duty ratio = %.3f'%(k)
print '\n chopping frequency = %.2f Hz'%(f)
print '\n Average load voltage = %.2f V'%( Voav)
print '\n Average load current = %.2f A'%( Ioav)

 duty ratio = 0.667

 chopping frequency = 33.33 Hz

 Average load voltage = 200.00 V

 Average load current = 40.00 A

Ex 5.3 page 185

from __future__ import division
from math import sqrt

Vs=400    # V
alfa=0.25    #  duty cycle
delta_I=10    #  A
L=0.5    #  H
R=0    #  ohm

Vo=alfa*Vs    # V
#Vo+L*di/dt=Vs -- putting dt=Ton & di=delta_I
Ton=delta_I/((Vs-Vo)/L)*1000    #  ms
T=Ton/alfa    #  ms
f=1/T*1000    # Hz
print '\n chopping frequency = %d Hz'%(f)

 chopping frequency = 15 Hz

Ex 5.5 page 186

from __future__ import division
from math import sqrt

Vs=220    # V
Vo=660    #  V
Toff=100    #  us

#Vo=Vs/(1-alfa)
alfa=1-Vs/Vo    #  duty cycle
#alfa=Ton/(Ton+Toff)
Ton=alfa*Toff/(1-alfa)    #  us
T=Ton+Toff    # us
print 'Pulse width of output voltage, Ton = %d us & T = %d us'%(Ton,T)
#(ii) reduce pulse width by 50%
Ton=Ton/2    #  us
Toff=T-Ton    #  us
alfa=Ton/(Ton+Toff)    #  duty cycle
Vo=Vs/(1-alfa)    #  V
print '\nNew output voltage = %d V'%(Vo)

Pulse width of output voltage, Ton = 200 us & T = 300 us

New output voltage = 330 V