Beijer Electronics AN-BEI-P2-050 - Manual (Page 6)

APPLICATION NOTE AN-BEI-P2-050 Date: 15/02/12
AN-BEI-P2-050 Open Loop Permanent Magnet Motor Control 6
Optimisation for Permanent magnet motors:
Once the basic set-up procedure is complete for the Beijer Frequency Inverter P2 with PM motor the following
parameters can be adjusted to improve or optimise performance.
Changing Speed Controller Ramp Rates
Acceleration Ramp Rate:
Parameter P1-03 sets acceleration ramp rate. If adjusting speed controller gains (P4-03 & P4-04) always set
required ramps rates prior to tuning these values. Ensure ramp rate setting and acceleration / deceleration cycle
does not result in the drive operating excessively in the over-current (>100%) region such that nuisance tripping
might occur.
Deceleration Ramp Rate:
Parameter P1-04 sets deceleration ramp rate. If adjusting speed controller gains (P4-03 & P4-04) always set
required ramps rates prior to tuning these values. Ensure deceleration ramp rate setting does not result in
excessively braking energy being returned to the drive such that an over-voltage nuisance trip occurs.
Changing Beijer Frequency Inverter P2 Output Switching Frequency
Parameter P2-24 sets the drive effective output switching frequency. If adjusting speed controller gains (P4-03 &
P4-04) always set required switching frequency prior to tuning these values.
Higher values result in smoother motor operation but are less efficient and may require some de-rating of the
drive. Set for optimised performance, or optimised efficiency or combination thereof.
Note: For smooth operation and consistent performance the minimum recommended switching frequency for
PM motor control is 16 kHz.
Entering Motor / Load Inertia Ratio
Parameter P7-10 allows the inertia ratio between the motor and connected load to be entered into the Beijer
Frequency Inverter P2. This value can normally be left at the default value (10); however it is used by the Beijer
Frequency Inverter P2 control algorithm as a feed forward term in order to provide optimum torque / current to
accelerate the load. Hence accurate setting of the inertia ratio will produce better system response and dynamics.
If value is unknown then leave value set to default (10).
The value entered into P7-10 is given as;
P7-10 = (J
Tot
/ J
Mot
) . 10
Where; J
Tot
is Total Inertia (including motor, load, and any coupling)
J
Mot
is Motor Inertia
Motor inertia will be given by the motor manufacturer as part of their standard motor data.
Total inertia must either be known from the system design or measured.
Tuning Speed Controller Responses
Changes to the speed controller tuning parameters should be made very gradually with close observation of the
resulting effect on system response.
P4-03: Speed Controller proportional Gain
The proportional gain is used to change the output to the motor as a proportional of the error in the speed loop
controller (difference between commanded and actual speed). The proportional response of the drive is adjusted
by multiplying the error by a constant called the proportional gain that is set in parameter P4-03. Increasing the
value in parameter 4.03 decreases drive response times / improves system dynamics.
If proportional gain is set too low the system response will be poor (slow) however if set too high the system could
oscillate and could grow unstable.
P4-04: Speed Controller integral time constant
The integral gain is an ‘accumulated’ gain based on both the magnitude of the error in the speed controller and the
time the error has existed, essentially working to eliminate prolonged and steady state error in the system.