Yaskawa AC Drive P1000 Bypass Technical Manual - Manual (Page 86)

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.
For induction motors, the drive offers two types of Speed Search that can be selected by parameter b3-24 (Speed Estimation
and Current Detection). Both methods are explained below and followed by a description of all relevant parameters.
n Current Detection Speed Search (b3-24 = 0)
Current Detection Speed Search detects the motor speed by looking at motor current in IM motors. When Speed Search is
started it reduces the output frequency starting from either the maximum output frequency or the frequency reference while
increasing the output voltage using the time set in parameter L2-04 <1> . As long as the current is higher than the level set to
b3-02, the output frequency is lowered using the time constant set to b3-03. If the current falls below b3-02, the drive assumes
that the output frequency and motor speed are the same and accelerates or decelerates to the frequency reference.
<1> Details on this function can be found in the standard P1000 Technical Manual (SIEPYAIP1U01) at www.yaskawa.com.
Be aware that sudden acceleration may occur when using this method of Speed Search with relatively light loads.
Figure 5.7 illustrates Current Detection Speed Search operation after a momentary power loss (L2-01 must be set to 1 or 2):
AC power
supply
Output
frequency
Output
current
OFF ON
Output frequency before
momentary power loss
Selected
frequency
reference
Min. Baseblock Time (L2-03)
Decel time
set to b3-03
Waits for twice
as long as L2-04
Speed Search operation
current set to b3-02
b3-05
Figure 5.7 Current Detection Speed Search after Power Loss
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 set to
L2-03 before starting Speed Search. If L2-03 is lower than the time set to parameter b3-05, then b3-05 is used as the wait time.
Run command
Output
frequency
Output current
OFF ON
b3-02
Decel time set
set to b3-03 Waits for twice
as long as L2-04
Selected
frequency
reference
Minimum Baseblock Time (L2-03)
Max. output frequency
or the specified
frequency reference
Figure 5.8 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.
• 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.
5.2 b: Application
86 YASKAWA SIEP YAIP1B 01A YASKAWA AC Drive – P1000 Bypass Technical Manual