Civil Engineering Reference
In-Depth Information
FIGURE 11-9
Battery discharge converter circuit for pv systems (DC to DC boost converter).
I
=+
I
∆
I
(11-8)
1
2
peak
o
L
where the load current I
= V
/R
o
out
load
= average value of the inductor current.
The algebraic manipulation of the above equations leads to the following:
VVD
out
=⋅
(11-9)
in
It is seen from Equation 11-9 that the output voltage is controlled by
varying the duty ratio D. This is done in a feedback control loop with the
required battery charge current as the reference. The duty ratio is controlled
by modulating the pulse width of T
. Such a converter is, therefore, also
known as the Pulse Width Modulated (PWM) converter.
on
11.5.2
Battery Discharge Converter
The battery discharge converter circuit is shown in
Figure 11-9
.
It steps up
the sagging battery voltage during discharge to the required output voltage.
When the transistor switch is on, the inductor is connected to the DC source.
When the switch is off, the inductor current is forced to flow through the
diode and the load. The output voltage of the boost converter is derived
again from the volt-second balance in the inductor. With duty ratio D of the
switch, the output voltage is given by the following:
V
V
=
in
(11-10)
out
1
−
D
For all values of D < 1, the output voltage is always greater than the input
voltage. Therefore, the boost converter can only step up the voltage. On the
