YASKAWA GA800 Technical Reference page 735

Speed Estimation Speed Search uses these two steps to estimate the motor speed:
1. Residual Voltage Search
When there is a short baseblock time, the drive searches for residual voltage. The drive uses the residual voltage
in the motor to estimate the motor speed and direction of rotation. The drive outputs the estimated motor speed as
frequency, then uses the deceleration rate set in L2-04 to increase the voltage. When the output voltage aligns
with the V/f pattern, the drive accelerates or decelerates the motor to the frequency reference. If the drive cannot
estimate the motor speed because of low residual voltage, it will automatically do Current Injection.
Note:
After you return power, the drive waits for the time set in b3-05. If power loss is longer than the time set in L2-03, the drive will start Speed
Search when the time set in b3-05 is expired after the power recovery.
2. Current Injection
If there is not sufficient residual voltage in the motor, the drive does Current Injection. The drive injects the
quantity of DC current set in b3-06 [Speed Estimation Current Level 1] into the motor windings to estimate the
motor speed and direction of rotation. The drive outputs the estimated motor speed as frequency, then uses the
deceleration rate set in L2-04 to increase the voltage. When the output voltage aligns with the V/f pattern, the
drive accelerates or decelerates the motor to the frequency reference.
Note:
Set the lower limit of the delay time to b3-05 for when Speed Search starts.
■
Speed Search and Operation Conditions
These conditions apply to Speed Search operation. When A1-02 = 0, 1, 2 [Control Method Selection = V/f Control, V/
f Control with Encoder, Open Loop Vector], set b3-24 [Speed Search Method Selection] before you do Speed Search.
• Do Speed Search with each Run Command
The drive ignores a Speed Search command from the external terminals.
• Use an MFDI to do an External Speed Search Command
To use an MFDI to do Speed Search, input the Run command at the same time that terminal Sx set for Speed Search
activates, or after Speed Search activates.
YASKAWA SIEPC71061737D GA800 Drive Technical Reference
Figure 12.30 Speed Search after Baseblock
Figure 12.31 Speed Search Selection at Start
12.3 b: Application
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