YASKAWA FSDrive-MV1000 Parameter Manual page 104

2.2 b: Application
Speed Estimate Speed Search
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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 120 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 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> Once 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 not enough residual voltage remaining in the motor. This might occur after
after longer power losses, when Speed Search is applied with the Run command (b3-01 = 1), or if an External search
command is used. It injects the 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 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.
Figure 2.13
Run command
Output
frequency
Output
current
Min. Baseblock Time (L2-03)
The wait time for Speed Search (b3-05) determines the lower limit.
104
AC power
supply
ON
Output
frequency
Output
current
Min. Baseblock Time
(L2-03)
Figure 2.12 Speed Search after Baseblock
Decelerates at the Speed
Search decel time set to b3-03
ON
OFF
Starts at the speed
speed that was detected
1.0 s
<1>
Figure 2.13 Speed Search at Start
OFF
Starts at the speed
that was detected
Several ten miliseconds
b3 -05 <1>
Waits twice as long as L2-04
YASKAWA ELECTRIC EZZ010930 FSDrive-MV1000 Parameter Guide
Selected
frequency
reference
Frequency reference
set to the drive
b3-02