YASKAWA A1000 Technical Manual page 161

Figure 5.20
AC power
Note: After power is restored, the drive waits until the time set to b3-05 has passed before performing Speed Search. Thereby the Speed
Search may start not at the end of L2-03 but even later.
When Speed Search is applied automatically with the Run command, the drive waits for the minimum baseblock time
L2-03 before Speed Search is started. If L2-03 is smaller than the time set in parameter b3-05, then b3-05 is used as the
wait time.
Figure 5.21
Run command
Max. output frequency
or the specified
frequency reference
Output
frequency
Output current
Figure 5.21 Current Detection Speed Search at Start or Speed Search Command by Digital Input
Notes on Using Current Detection Type Speed Search
• Shorten the Speed Search deceleration time set to b3-03 if an oL1 fault occurs while performing Current Detection
Speed Search.
• Current Detection Speed Search is not available when using Open Loop Vector Control for PM motors.
• Increase the minimum baseblock time set to L2-03 if an overcurrent or overvoltage fault occurs when performing
Speed Search after power is restored following a momentary power loss.

Speed Estimation Type Speed Search (b3-24 = 1)
This method can be used for a single induction motor connected to a drive. It should not be used if the motor is one or
more frame sizes smaller than the drive, at motor speeds above 200 Hz, or when using a single drive to operate more than
one motor.
Speed Estimation is executed in two steps as described below.
Step 1: Back EMF Voltage Estimation
This method is used by Speed Search after short baseblock (e.g., a power loss where the drive's CPU kept running and
the Run command was kept active). Here, the drive estimates the motor speed by analyzing the back EMF voltage. It
outputs the estimated frequency and increases the voltage using the time constant set in parameter L2-04. After that, the
motor is accelerated or decelerated to the frequency reference starting from the detected speed. If there is not enough
residual voltage in the motor windings to perform the calculations described above, then the drive will automatically
proceed to step 2.
YASKAWA ELECTRIC SIEP C710616 27G YASKAWA AC Drive A1000 Technical Manual
Output frequency before
momentary power loss
supply
ON OFF
Output
frequency
Output
current
Min. Baseblock Time (L2-03)
Figure 5.20 Current Detection Speed Search after Power Loss
Decel time set
set to b3-03
OFF ON
Minimum Baseblock Time (L2-03)
Decel time
Waits for twice
set to b3-03
as long as L2-04
Speed Search operation
current set to b3-02
b3-05
Waits for twice
as long as L2-04
Selected
frequency
reference
5.2 b: Application
Selected
frequency
reference
b3-02
(Speed search operation current)
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