5.2 b: Application
116
YASKAWA ELECTRIC
SIEP C710606 44B YASKAWA AC Drive T1000V Technical Manual
Current Injection
This method is used when there is no detectable back EMF, e.g. 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 outputs the detected frequency and increases
the voltage using the time constant set in parameter L2-04. If the resulting current is higher than the level in b3-02 the
output frequency is reduced. When the current becomes lower than b3-02 the motor speed is assumed to be found and the
drive starts to accelerate or decelerate to the frequency reference.
Figure 5.12
Figure 5.12 Speed Search at Start
<1> The wait time for Speed Search (b3-05) determines the lower limit.
Note:
If the Run command is quickly switched off and then back on again when the drive is set to “Coast to stop” as the stopping
method, Speed Search will operate as shown in
.
Notes on Using Speed Estimation Type Speed Search
• Auto-Tuning needs to be first performed if you plan to use Speed Estimation. Perform Auto-Tuning again if the there is
a change in the cable length between the drive and motor.
• Use Current Detection to search for speeds beyond 130 Hz or if the application is running multiple motors from the
same drive, or if the motor is considerably smaller than the capacity of the drive.
• Speed Estimation may have trouble finding the actual speed if the motor cable very long. Current Detection should be
used in such situations.
• Use Current Detection instead of Speed Estimation when operating motors smaller than 1.5 kW. Speed Estimation can
end up stopping smaller motors as it might not be able to detect the speed or rotation direction of such small motors.
• Use Short circuit Braking instead of Speed Estimation when using Open Loop Vector Control for PM motors along
with a fairly long motor cable.
• Use Short circuit Braking instead of Speed Estimation if attempting to find the speed of a motor coasting faster than
120 Hz in Open Loop Vector Control for PM motors.
■
Current Detection Type Speed Search (b3-24 = 0)
Current Detection Speed Search can be applied to any motor. Be aware that sudden acceleration may occur when using
Current Detection with relatively light loads.
This method detects the motor speed by reducing the output frequency and measuring the current. The frequency
reduction starts from the maximum output frequency or from the set frequency reference. As long as the output
frequency is higher than the rotor speed, the slip will cause a high current. The closer the output frequency comes to the
rotor speed, the lower the current draw will be. When the output current drops below the level as set in b3-02, the output
frequency stops decreasing and normal operation resumes.
Run command
Output
frequency
Output
current
OFF
ON
b3-02
Starts at the speed
speed that was detected
Waits twice as long as L2-04
Frequency reference
set to the drive
Decelerates at the Speed
Search decel time set to b3-03
1.0 s
Min. Baseblock Time (L2-03)
<1>
