a ,
b or
c and entering the neutral point
n is assumed to be positive.
• All the three resistances are equal,
.
In this mode of operation each switch conducts for 180°. Hence, at any instant of time
three switches remain
on . When
S 1
is
on , the terminal
a gets connected to the positive terminal of input DC
source. Similarly, when
S 4
is
on , terminal
a gets connected to the negative terminal of input DC source.
There are six possible modes of operation in a cycle and each mode is of 60° duration and the explanation
of each mode is as follows:
Figure: 5.16 Circuit diagram of three phase bridge inverter with star connected load Mode 1 : In this mode the switches
S 5
,
S 6
and
S 1
are turned
on for time interval
. As a result
of this the terminals
a and
c are connected to the positive terminal of the input DC source and the
terminal
b is connected to the negative terminal of the DC source. The current flow
through
R a ,
R b and
R c is shown in Figure
and the equivalent circuit is shown in Figure
. The equivalent
resistance of the circuit shown in
Figure is
158 |
P a g e
(1)
The current
i delivered by the DC input source is
(2)
The currents
i a and
i b are
(3)
Keeping the current convention in mind, the current
i b is
(4)
Having determined the currents through each branch, the voltage across each branch is
