Mitsubishi FB13PNT, Быстрый старт

Страница: 85 / 292

1-72 1-72
CHAPTER 1 CONTROLLER CHAPTER 1 CONTROLLER
9 9..3 3 IIn nv ve errtte err
The truc The truck battery k battery delivers DC delivers DC current, current, so the so the current current must be must be
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) (1) Cha Changi nging DC vo ng DC volta ltage cy ge cycli clical cally ly
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
the ratio, therefore, results in varying voltage. The ratio voltage. The ratio
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 possible to obtain cyclically
changing DC voltage shown in Fig. 3. changing DC voltage shown in Fig. 3.
(Fig. 3) (Fig. 3)
500967 500967
Switch Switch
V V B B V V L L
T1 T1 T2 T2 T1 T1 T2 T2
ON ON
ON ON
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 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
O O N N O O N N
O F O F F F O F O F F F
ON ON OFF OFF
Load Load
Average voltage VL Average voltage VL
VL VL = = x x VB VB
T1 + T2 T1 + T2
T1 T1
(2) (2) Conve Convertin rting DC g DC powe power int r into AC o AC powe powerr
Driving a three-phase AC Driving a three-phase AC motor using battery delivered 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.
(Fig. 4) (Fig. 4)
500968 500968
S1 S1
S S 3 3 S S 5 5
S2 S2 S S 4 4 S S 6 6
U U
V V
W W
Switching for U phase Switching for U phase
Switching for V phase Switching for V phase
Switching for W phase Switching for W phase
S1 ON S1 ON
S2 ON S2 ON
S3 ON S3 ON
S4 ON S4 ON
S5 ON S5 ON
S6 ON S6 ON