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In this circuit, both switches act together, i.e. both are closed or open. When the switches are open, the
inductor current builds. At a suitable point, the switches are opened. The inductor then supplies current to
the load through a path incorporating both diodes, D1 and D2.
Numerical probelms
1.
In a dc chopper, the average load current is 30 Amps, chopping frequency is 250 Hz.
Supply
voltage is 110 volts. Calculate the ON and OFF periods of the chopper if the load resistance is 2
ohms.
Solution:
2.
A step up chopper has input voltage of 220 V and output voltage of 660 V. If the non-conducting
time of thyristor chopper is 100 micro sec compute the pulse width of output voltage. In case the
pulse width is halved for constant frequency operation , find the new output voltage
3.
A chopper operating from 220V dc supply with for a duty cycle of 0.5
and chopping frequency of
1KHz drives an R L load with R = 1Ω , L=1mH and E = 105V. Find whether the current is
continuous and also
find the values of I
max
and I
min.
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UNIT
–
V
INVERTERS
Introduction to Inverters
The word ‘inverter’ in the context of power
-electronics denotes a class of power conversion (or
power
conditioning) circuits that operates from a dc voltage source or a dc current source and converts it into ac
voltage or current. The inverter does reverse of what ac-to-dc converter does (refer to ac to dc converters).
Even though input to an inverter circuit is a dc source, it is not uncommon to have this dc derived from an
ac source such as utility ac supply. Thus, for example, the primary source of input power may be
utility ac
voltage supply that is converted to dc by an ac to dc converter and then ‘inverted’ back to ac using an
inverter. Here, the final ac output may be of a different frequency and magnitude than the input ac of the
utility supply
A single phase Half Bridge DC-AC inverter is shown in Figure below
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