Mitsubishi Electric FR-A700 Technical Manual page 248

(2) Operation
Speed control adjusts the difference between the
speed command and speed feedback (actual speed
under vector control, estimated speed under Real
sensorless vector control) is 0, i.e. to match the
speed command and actual speed or estimated
speed.
The speed loop gain parameter that adjusts speed
control operation status is provided for the
Although stable operation is possible with the initial
value, refer to the following to make parameter
adjustment when vibration, noise or any other
unfavorable condition occurs due to large load inertia
or gear backlash, for example, or when you want to
exhibit the best performance that matches the
machine.
The following figure indicates operation under speed
control.
Speed
Start signal
RUN signal
• Turning ON the start signal increases the speed
up to the preset speed according to the
acceleration time.
• Turning OFF the start signal decreases the
speed according to the deceleration time. When
the speed has decreased down to the DC brake
operation speed, operation changes to DC
injection brake operation.
A700
[Pr.8]
[Pr.7]
[Pr.13]
(3) Concept of speed control gains
Speed control gain with motor alone is stated below.
Refer to page 286 for how to adjust the speed control
gain.
1) Speed control P (proportional) gain
During vector control, [Pr. 820 = 60%]
equivalent to 120rad/s. During Real sensorless
vector control, [Pr. 820 = 60%] is equivalent to
.
60rad/s.
For the 75K or more, response level becomes
half.
Increasing the proportional gain increases the
response level. However, a too high gain will
produce vibration and/or unusual noise.
[Pr.10]
2) Speed control integral time
[Pr. 821 = 0.333s] is equivalent to 3rad/s.
Decreasing the integral time shortens the return
time at a speed change. However, a too short
time will generate an overshoot. (Refer to the
drawing below.)
Load
fluctuation
Speed
3) Speed gain when the load inertia is attached
When there is load inertia, the actual speed gain
decreases as indicated below.
Actual speed gain =
282
PARAMETER
Proportional gain
200rad/s
120rad/s
60% 100%
(initial value)
Response under vector control (55K
or less)
Since increasing the proportional gain enhances the
response level and decreases the speed fluctuation.
Decreasing the integral time shortens the return time taken.
Speed gain when with a
motor alone
J : Inertia of motor
M
J : Motor shaft-equivalent load inertia
L
is
[Pr. 820]
Setting
J
M
J J
M + L