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SIMOVERT P 6SE21 Series Inverters
Once steps (1) to (3) have been performed, P04 can be changed to match the requirements of the application.
Note
Speed control only operates in one direction of rotation – negative values of the actual speed feedback signal on
terminal X11.12 are not permitted.
6.2.2 Speed Control Operation
Stop the inverter and adjust the slip limit (P35) to 10.0 (unless the application requires the slip to be limited to a lower
value). Set the required frequency to a value in the middle of the operating range (i.e. approximately half way between
the minimum and maximum frequencies required in operation). Set the inverter to run and increase the setting of P32
gradually until the motor speed starts to oscillate. Reduce the value of P32 until a stable speed is obtained.
6.2.3 Speed Control Optimisation
If it is not possible to achieve stable operation with P32 set to a value of greater than 10, there must be excessive noise
on the feedback signal. It may be possible to filter out this noise by increasing the setting of the sampling rate parameter
(P36). If this fails then the feedback signal should be shielded and, in extreme cases, smoothed using suitable
capacitors.
Check the performance of the speed regulation. If the speed regulation is satisfactory when the load on the motor
changes then no further adjustments are required. However, the integral term and differential term parameters (P33
and P34 respectively) allow further adjustments to be made to the control loop to compensate for delay and/or lead
terms in the motor and its associated speed sensor. This can provide better speed regulation in certain systems.
Reducing the value of the proportional gain term will normally give more stable operation but with slightly degraded
speed–holding performance.
The slip limit parameter (P35) can be used to limit the maximum permissible deviation between the instantaneous
value of actual frequency and the output frequency.
6.2.4 Slip Limit (P35)
The slip limit parameter (P35) allows the difference between the actual frequency (from the tachometer) and the
inverter output frequency to be limited to a maximum level. This may be used to prevent motor stalling under overload
conditions.
6.2.5 Sample Rate (P36)
This parameter allows the rate at which the actual frequency value used by the speed regulator is updated to be
changed in 30 ms increments. When P36 is set to 001, the value is updated every 30 ms; when it is set to 002 it is
updated every 60 ms, etc.
Longer sample rates may be required in applications where electrical noise is present on the analogue feedback signal
or where the value of the analogue signal only responds slowly to changes in inverter/motor frequency.
Siemens plc 1995
English
Operating Instructions
G85139–A1615–U156–A
02.95
33
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