Mitsubishi Electric FR-A700 Instruction Manual page 274

Speed control by real sensorless vector control, vector control
When using a multi-pole motor (8 poles or more)
Specially when using a multi-pole motor with more than 8 poles under vector control (with
encoder, real sensorless), adjust speed control P gain (Pr. 820) and torque control P gain (Pr.
824) according to the motor referring to the following methods.
● For speed control P gain Pr. 820, increasing the setting value improves the response level,
but a too large gain will produce vibration and/or unusual noise.
● For torque control P gain Pr. 824, note that a too low value will produce current ripples,
causing the motor to generate sound synchronizing the cycle of current ripples.
No.
1
2
3
4
5
6
Tab. 6-15: Adjustment method
6 - 94
Phenomenon/Condition
The motor rotation is unstable in
the low speed range.
Speed trackability is poor
Speed variation at the load fluctu-
ation is large
Torque becomes insufficient or
torque ripple occurs at starting or
in the low speed range under real
sensorless vector control.
Unusual motor and machine vibra-
tion, noise or overcurrent occurs.
Overcurrent or overspeed (E.OS)
occurs at a start under real sen-
sorless vector control.
Adjustment Method
Set a higher value in Pr. 820 "Speed control P gain 1" according to the
motor inertia.
Since the self inertia of a multi-pole motor tends to become large,
make adjustment to improve the unstable phenomenon, then make
fine adjustment in consideration of the response level using that setting
as reference. In addition, when performing vector control with encoder,
gain adjustment according to the inertia can be easily done using easy
gain tuning (Pr. 819 = 1).
Set a higher value in Pr. 820 "Speed control P gain 1".
Increase the value 10% by 10% until just before vibration or unusual
noise is produced, and set about 0.8 to 0.9 of that value.
If you cannot make proper adjustment, increase the value of Pr. 821
"Speed control integral time 1" double by double and make adjustment
of Pr. 820 again.
Set the speed control gain a little higher. (same as No. 1)
If the problem still persists after gain adjustment, increase Pr. 13
"Starting frequency" or set the acceleration time shorter if the inverter
is starting to avoid continuous operation in the ultra low speed range.
Set a lower value in Pr. 824 "Torque control P gain 1".
Decrease the value 10% by 10% until just before the phenomenon is
improved, 6 and set about 0.8 to 0.9 of that value.
Parameter