PhD Thesis - Cranfield University

Chapter 7
7.6 Battery Buck Mode - Charging mode (STATE 111)
V out
V batt
D T1 , f sw
C batt
L batt
i batt
T1
C DC
D2
R Load
V in
a) Current flow when T1 is ON b) Current flow when T1 is OFF
182
V out
V batt
C batt
Figure 7.4 Active converter section during battery buck mode
In the buck (charging) mode, the DC Bus voltage acts as the input voltage (V in) and the
battery voltage is the output voltage (V out) of the converter. Switch T1 operates in a
complementary manner with Diode D2. The duty cycle of T1 is represented by D T1 with a
fixed switching frequency, f sw
During the conduction period of T1, the voltage loop according to KVL is,
dibatt
V in −Vout
− Lbatt
= 0
(7-19)
dt
on
∆ibatt
V in −Vout
− Lbatt
f = 0
(7-20)
D
⇒ sw
T1
rearranging,
( V = L ⋅ ∆i
⋅ f
(7-21)
in −Vout ) DT1
batt
batt
sw
During the conduction period of Diode D2 ( when T1 is ‘off’), the KVL loop is,
dibatt
V out − Lbatt
= 0
(7-22)
dt
off
∆ibatt
V out − Lbatt
f = 0
(7-23)
1−
D )
⇒ sw
( T1
i batt
L batt
T1
C DC
D2
R Load
V in