Acceleration/Deceleration Is Not Smooth; Speed Varies During Operation - Mitsubishi 700 Series Instruction Manual

Check first when you have a trouble
4.6.7

Acceleration/deceleration is not smooth

Check
points
Acceleration/deceleration time is too short.
Torque boost (Pr. 0, Pr. 46) setting is improper under V/F
control, so the stall prevention function is activated.
The base frequency does not match the motor
characteristics.
Parameter
Setting
Stall prevention function is activated due to a heavy
load.
Regeneration avoidance operation is performed
4.6.8

Speed varies during operation

When the slip compensation is selected, the output frequency varies between 0 and 2Hz as with load fluctuates. This is a
normal operation and not a fault.
Check
points
Input
Multi-speed command signal is chattering.
signal
Load
Load varies during an operation.
Frequency setting signal is varying.
The frequency setting signal is affected by EMI.
Input
signal
Malfunction is occurring due to the undesirable current
generated when the transistor output unit is connected.
Pr. 80 Motor capacity setting is improper for the
capacities of the inverter and the motor for General-
purpose magnetic flux vector control.
Fluctuation of power supply voltage is too large.
Parameter
Setting
Hunting occurs by the generated vibration, for example,
when structural rigidity at load side is insufficient.
Wiring length exceeds 30m when General-purpose
magnetic flux vector control is performed.
Others
Wiring length is too long for V/F control, and a voltage
drop occurs.
114
Possible Cause
Possible Cause
Countermeasures
Increase acceleration/deceleration time.
Increase/decrease Pr. 0 Torque boost setting value by
0.5% increments to the setting.
For V/F control, set Pr. 3 Base frequency and Pr. 47 Second
V/F (base frequency).
For General-purpose magnetic flux vector control, set Pr.
84 Rated motor frequency.
Reduce the load weight.
Set Pr. 22 Stall prevention operation level higher according
to the load. (Setting Pr. 22 too large may result in
frequent overcurrent trip (E.OC ).)
Check the capacities of the inverter and the motor.
If the frequency becomes unstable during regeneration
avoidance operation, decrease the setting of Pr. 886
Regeneration avoidance voltage gain.
Countermeasures
Take countermeasures to suppress chattering.
Select General-purpose magnetic flux vector control.
Check the frequency setting signal.
Set filter to the analog input terminal using Pr. 74 Input
filter time constant.
Take countermeasures against EMI, such as using
shielded wires for input signal lines.
Use terminal PC (terminal SD when source logic) as a
common terminal to prevent a malfunction caused by
undesirable current.
Check the Pr. 80 Motor capacity setting.
Change the Pr. 19 Base frequency voltage setting (about
3%) under V/F control.
Disable automatic control functions, such as energy
saving operation, fast-response current limit function,
regeneration avoidance function, General-purpose
magnetic flux vector control, and stall prevention.
Adjust so that the control gain decreases and the level of
safety increases.
Change Pr. 72 PWM frequency selection setting.
Perform offline auto tuning.
Adjust Pr. 0 Torque boost by increasing with 0.5%
increments for low-speed operation.
Change to General-purpose magnetic flux vector
control.
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