YASKAWA FSDrive-MV1000 Parameter Manual page 110

2.2 b: Application
u b3: Speed Search
The Speed Search function allows the drive to detect the speed of a rotating motor shaft that is driven by external forces
and start the motor operation directly from the detected speed without first stopping the machine.
Example: When a momentary loss of power occurs, the drive output shuts off and the motor coasts. When power returns,
the drive can find the speed of the coasting motor and restart it directly.
Speed Estimate Type Speed Search
n
This method can be used for a single induction motor connected to a drive. Do not use this method if the motor is one or
more frame sizes smaller than the drive 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. Here, the drive estimates the motor speed and rotation
direction by analyzing the Back EMF voltage. It outputs the estimated rotation direction, frequency, and voltage, and
then recovers the voltage using the deceleration rate set in L2-04 to correspond to the V/f pattern selected. After that, the
motor is accelerated or decelerated in accordance with the output frequency reference selected. If there is not enough
residual voltage in the motor, then the drive will automatically proceed to step 2.
Figure 2.12
<1> After AC power is restored, the drive will wait for at least the time set to b3-05. If the power interruption is longer than the
minimum baseblock time set to L2-03, the drive will wait until the time set to b3-05 has passed after power is restored before
starting Speed Search.
Step 2: Current Injection
Current Injection is performed when there is insufficient residual voltage in the motor after extended power losses, when
Speed Search is applied with the Run command (b3-01 = 1), or when an External search command is used.
This feature the amount of DC current set in b3-06 to the motor and detects the speed by measuring the current feedback.
The drive recovers the voltage according to the Momentary Power Loss Ride-Thru Voltage Recovery Ramp Time set in
L2-04 using the estimated output frequency. As long as the drive output current is higher than the level set in b3-02, the
output frequency is lowered using the deceleration time set in b3-03. If the current falls below b3-02, the drive assumes
that the output frequency and motor speed are synchronized and accelerates or decelerates to the frequency reference.
Note: Be aware that sudden acceleration may occur when using this method of Speed Search with relatively light loads.
110
AC power
supply
ON
Output
frequency
Output
current
Min. Baseblock Time
(L2-03)
Figure 2.12 Speed Search after Baseblock
OFF
Starts at the speed
that was detected
Several ten ms
b3 -05 <1>
YASKAWA ELECTRIC TOEP C710687 03B FSDrive-MV1000 Parameter Guide
Selected
frequency
reference