Acceleration/Deceleration Is Not Smooth; Speed Varies During Operation - Mitsubishi Electric 800 Series Instruction Manual

Check first when you have a trouble
6.5.7

Acceleration/deceleration is not smooth

Check
points
Acceleration/deceleration time is too short.
Torque boost (Pr.0, Pr.46, Pr.112) setting is
improper under V/F control, so the stall
prevention function is activated.
Parameter
The base frequency does not match the motor
setting
characteristics.
Regeneration avoidance operation is
performed
Load
Parameter
Stall prevention (torque limit) function is
setting activated due to a heavy load.
Motor
6.5.8

Speed varies during operation

Under Advanced magnetic flux vector control, Real sensorless vector control, vector control, and encoder feedback control,
the output frequency varies between 0 and 2 Hz as the load fluctuates. This is a normal operation and not a fault.
Check
points
Load
Load varies during an operation.
Frequency setting signal is varying.
The frequency setting signal is affected by
EMI.
Malfunction is occurring due to the undesirable
Input
current generated when the transistor output
signal
unit is connected.
Multi-speed command signal is chattering.
Feedback signal from the encoder is affected
by EMI.
Fluctuation of power supply voltage is too
large.
Pr.80 Motor capacity and Pr.81 Number of
motor poles are not appropriate for the motor
capacity under Advanced magnetic flux vector
control, Real sensorless vector control, vector
control, or PM sensorless vector control.
Wiring length exceeds 30 m when Advanced
magnetic flux vector control, Real sensorless
vector control, vector control, or PM
sensorless vector control is selected.
Parameter
Under V/F control, wiring is too long and a
setting voltage drop occurs.
Hunting occurs by the generated vibration, for
example, when structural rigidity at load side is
insufficient.
652
PROTECTIVE FUNCTIONS
Possible cause
Possible cause
Countermeasure
Increase the acceleration/deceleration time.
Increase/decrease the Pr.0 Torque boost setting value by
0.5% increments so that stall prevention does not occur.
Under V/F control, set Pr.3 Base frequency, Pr.47 Second V/
F (base frequency), and Pr.113 Third V/F (base frequency).
Under vector control, set Pr.84 Rated motor frequency.
If the frequency becomes unstable during regeneration
avoidance operation, decrease the setting of Pr.886
Regeneration avoidance voltage gain.
Reduce the load weight.
Set Pr.22 Stall prevention operation level (torque limit level)
higher according to the load. (If Pr.22 is set too high, an
overcurrent trip (E.OC[]) is likely to occur.)
Check the capacities of the inverter and the motor.
Countermeasure
Select Advanced magnetic flux vector control, Real sensorless
vector control, vector control, or encoder feedback control.
Check the frequency setting signal.
Set filter to the analog input terminal using Pr.74 Input filter
time constant , Pr.822 Speed setting filter 1.
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.
Take countermeasures to suppress chattering.
Place the encoder cable far from the EMI source such as main
circuit and power supply voltage.
Earth (ground) the shield of the encoder cable to the enclosure
using a metal P-clip or U-clip.
Under V/F control, change the Pr.19 Base frequency voltage
setting (approximately by 3%).
Check the settings of Pr.80 and Pr.81.
Perform offline auto tuning.
In the low-speed range, set 0.5% in Pr.0 Torque boost.
Change the control method to Advanced magnetic flux vector
control or Real sensorless vector control.
Disable automatic control functions, such as the energy saving
operation, fast-response current limit operation, torque limit,
regeneration avoidance function, Advanced magnetic flux
vector control, Real sensorless vector control, vector control,
encoder feedback control, droop control, stall prevention, online
auto tuning, notch filter, and orientation control.
Under PID control, set smaller values to Pr.129 PID
proportional band and Pr.130 PID integral time.
Adjust so that the control gain decreases and the level of safety
increases.
Change Pr.72 PWM frequency selection setting.
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Refer to
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