Droop Control - Mitsubishi Electric FR-A800 Series Instruction Manual

 Selection of encoder feedback control (Pr.367)
• When a value other than "9999" is set in Pr.367 Speed feedback range, encoder feedback control is enabled. Set a target
value (frequency at which stable speed operation is performed) and specify the range around the value. Normally, use the
frequency converted from the slip amount (r/min) at the rated motor speed (rated load). If the setting is too large, response
becomes slow.
Speed feedback range
Set value
(Set command)
• Example: when the rated speed of a motor (4 poles) is 1740 r/min at 60 Hz
Slip Nsp = Synchronous speed - Rated speed
= 1800 - 1740
= 60 (r/min)
Frequency equivalent to slip (fsp) = Nsp × Number of poles/120
 Feedback gain (Pr.368)
• Set Pr.368 Feedback gain when the rotation is unstable or response is slow.
• Response of the feedback will become slow when the acceleration/deceleration time is long. In such case, increase the
setting value of Pr.368.
Pr.368 setting
Pr.368 > 1
1 > Pr.368
 Overspeed detection (Pr.285)
• To prevent malfunction when the correct pulse signal cannot be detected from the encoder, when
[detection frequency] - [output frequency] ≥ Pr.285
during encoder feedback control, a protective function (E.MB1) will be activated to shut off the inverter output.
• Overspeed detection is not performed when Pr.285 = "9999".
NOTE
• Couple the encoder on the same axis as the motor axis without any mechanical clatter, with speed ratio of 1:1.
• Encoder feedback control is not performed during the acceleration and deceleration to prevent unstable operation such as
hunting.
• Encoder feedback control is performed after the output frequency has reached [set frequency] ± [speed feedback range] once.
• When following status occurs during encoder feedback control operation, the inverter output is not shut off, the output
frequency becomes the value obtained by [set frequency] ± [speed feedback range], and tracking of the motor speed is not
performed.
When the pulse signal from the encoder is lost due to a break, etc.
When correct pulse signal cannot be detected due to induction noise, etc.
When the motor is forcefully accelerated (regenerative rotation) or decelerated (motor lock) due to large external force
• Use the Inverter running (RUN) signal when releasing the brake from the motor with a brake. (The brake may not be released
when the Output frequency detection (FU) signal is used.)
• Do not turn OFF the external power supply for the encoder during encoder feedback control. Normal encoder feedback control
will not be possible.
Parameters referred to
Pr.81 Number of motor

5.16.16 Droop control

Magnetic flux Sensorless Magnetic flux Magnetic flux Sensorless Sensorless Vector
This is a function to give droop characteristics to the speed by balancing the load in proportion with the load torque during the
Advanced magnetic flux vector control, Real sensorless vector control, Vector control, and PM sensorless vector control.
738
5. PARAMETERS
5.16 (G) Control parameters
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Driven load
Regenerative load
= 60 × 4/120
= 2 (Hz)
Response will become faster but it may cause overcurrent or unstable operation.
Response will become slower but the operation will become more stable.
polespage 221, page 532
Vector Vector PM PM PM
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