Linde T20 AP, Service Training

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Section 6
Page 7
Service Training
Moreover, by varying the time during which each MOSFET is on, it is possible to control the average voltage applied
to each motor winding at any moment. In this manner, an almost sinusoidal voltage is applied to each winding when
the motor is running.
The frequency at which the six MOSFETS are activated and deactivated ON and OFF is much faster than that of the
AC supply seen by the motor. Typically, the traction motor will see an AC frequency of 180 Hz at the maximum speed,
while the MOSFETS will be switched at ON and OFF status at 8 KHz.
MOTOR RUNNING AT SEMI-SPEED (A SINGLE PHASE SHOWED FOR REASONS OF CLARITY)
MOTOR RUNNING AT FULL-SPEED (A SINGLE PHASE SHOWED FOR REASONS OF CLARITY)
180 Hz seen by the motor
90 Hz seen by the
motor
12 V
0 V
17 V EFF
0 V
First active pair of
MOSFETS
17 V EFF
24 V
24 V
8.5 V EFF
8.5 V EFF
12 V
Second active pair
of MOSFETS
First active pair
of MOSFETS
Second active
pair of MOSFETS
0% 0% 50%
0% 100% 0%
Percentage of time
during which the
MOSFETS are on
Percentage of time during which the
MOSFETS are on
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