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1-72
1-72
9 9 . . 3 3
I I n n v v e e r r t t e e r r
The truck battery
The truc
k battery delivers DC
converted into AC current to drive an AC motor. The device
converted into AC current to drive an AC motor. The device
that converts direct current into alternating current is
that converts direct current into alternating current is
generally called an "inverter." The processes involved in
generally called an "inverter." The processes involved in
creating AC current from DC current are described below.
creating AC current from DC current are described below.
(1) Cha
(1)
Changi
nging DC vo
ng DC volta
If the switch in a circuit like a one shown in Fig. 3 is
If the switch in a circuit like a one shown in Fig. 3 is
turned on for time T1 and then turned off for time T2
turned on for time T1 and then turned off for time T2
and this on-off operation is repeated many times, the
and this on-off operation is repeated many times, the
average of the voltage applied to the load is
average of the voltage applied to the load is
determined by the ratio between T1 and T2. Varying
determined by the ratio between T1 and T2. Varying
the ratio, therefore, results in varying voltage. The ratio
the ratio, therefore, results in varying
between T1 and T2 is called "duty ratio." By changing
between T1 and T2 is called "duty ratio." By changing
the duty ratio cyclically, it is
the duty ratio cyclically, it is possible to obtain cyclically
changing DC voltage shown in Fig. 3.
changing DC voltage shown in Fig. 3.
(2) Conve
(2)
Convertin
rting DC
g DC powe
Driving a three-phase AC
Driving a three-phase AC motor using battery delivered
power requires creating three phase outputs (U, V, W)
power requires creating three phase outputs (U, V, W)
of an identical waveform that differ in phase by 120°
of an identical waveform that differ in phase by 120°
using a circuit with six switches S1 to S6 that are
using a circuit with six switches S1 to S6 that are
arranged as shown in Fig. 4. The outputs thus created
arranged as shown in Fig. 4. The outputs thus created
forms a three-phase alternating current. Fig. 5 shows
forms a three-phase alternating current. Fig. 5 shows
on-off condition of each switch (arm) and output
on-off condition of each switch (arm) and output
voltage variation.
voltage variation.
Functioning as switches in the inverter of the AC motor
Functioning as switches in the inverter of the AC motor
trucks are MOS-FET transistors. The MOS-FET transistors
trucks are MOS-FET transistors. The MOS-FET transistors
can switch at very high speeds, thus creating smooth
can switch at very high speeds, thus creating smooth
waveforms of alternating current.
waveforms of alternating current.
delivers DC current,
current, so the
so the current
current must be
ltage cy
ge cycli clical
cally ly
voltage. The ratio
possible to obtain cyclically
power int
r into AC
o AC powe
power r
motor using battery delivered
Switching for U phase
Switching for U phase
Switching for V phase
Switching for V phase
Switching for W phase
Switching for W phase
must be
T1
T1
T2
T2
ON
ON
OFF
OFF
S
S
m
m
a
a
l
l
l
l
d
d
u
u
t
t
y
y
r
r
a
a
t
t
i
i
ON
ON
O
O
N
N
O
O
N
N
O F
O
FF
F
O F
O
FF
F
S1
S1
S2
S2
S1 ON
S1 ON
S2 ON
S2 ON
S5 ON
S5 ON
S6 ON
S6 ON
CHAPTER 1 CONTROLLER
CHAPTER 1 CONTROLLER
Switch
Switch
Load
Load
V
V
B
B
V
V
L
L
T1
T1
T2
T2
T1
T1
VL
VL
=
=
T1 + T2
T1 + T2
ON
ON
Average voltage VL
Average voltage VL
o
o
L
L
a
a
r
r
g
g
e
e
d
d
u
u
t
t
y
y
r
r
a
a
t
t
i
i
o
o
(Fig. 3)
(Fig. 3)
S
S
3
3
S
S
5
5
U
U
V
V
W
W
S
S
4
4
S
S
6
6
(Fig. 4)
(Fig. 4)
S3 ON
S3 ON
S4 ON
S4 ON
x
x
VB
VB
500967
500967
500968
500968
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