Mitsubishi Electric FR-A720-0.4K Instruction Manual page 88

Phenomenon
4 Motor speed is unstable.
Motor or machine hunts
5 (vibration/noise is
produced).
Acceleration/deceleration
6 time does not match the
setting.
Machine operation is
7
unstable
Speed fluctuates at low
8
speed.
Cause
(1) The speed command varies.
(2) Insufficient torque.
(3) The speed control gains do not
match the machine. (mechanical
resonance)
(1) The speed control gain is high.
(2) The torque control gain is high.
(3) The motor wiring is wrong.
(1) Insufficient torque.
(2) Large load inertia.
(1) The speed control gains do not
match the machine.
(2) Slow response because of
improper acceleration/
deceleration time of the inverter.
(1) Adverse effect of high carrier
frequency.
(2) Low speed control gain.
Countermeasures
(1) -1 Check that a correct speed command comes from
the command device. (Take measures against
noises.)
(1) -2 Decrease Pr. 72 PWM frequency selection.
(1) -3 Increase Pr. 822 Speed setting filter 1. (Refer to
Chapter 4 of the Instruction Manual (Applied) )
(2) Increase the torque limit value.
(Refer to torque limit of speed control on Chapter 4 of
the Instruction Manual (Applied) )
(3) -1 Perform easy gain tuning. (Refer to page 76)
(3) -2 Adjust Pr. 820, Pr. 821. (Refer to page 78)
(3) -3 Perform speed feed forward/model adaptive speed
control.
(1) -1 Perform easy gain tuning. (Refer to page 76)
(1) -2 Decrease Pr. 820 and increase Pr. 821.
(1) -3 Perform speed feed forward control and model
adaptive speed control.
(2) Decrease the Pr. 824 value. (Refer to Chapter 4 of
the Instruction Manual (Applied) )
(3) Check the wiring
(1) -1 Increase the torque limit value.
(Refer to torque limit of speed control on Chapter 4
of the Instruction Manual (Applied) )
(1) -2 Perform speed feed forward control.
(2) Set the acceleration/deceleration time that meets the
load.
(1) -1 Perform easy gain tuning. (Refer to page 76)
(1) -2 Adjust Pr. 820, Pr. 821. (Refer to page 78)
(1) -3 Perform speed feed forward control and model
adaptive speed control.
(2) Change the acceleration/deceleration time to an
optimum value.
(1) Decrease Pr. 72 PWM frequency selection.
(2) Increase Pr. 820 Speed control P gain 1.
Before operation
81
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