Current Loop Gain Scheduling

Current Loop Gain Scheduling is an advanced feature which allows the current loop gain to be adjusted for motors with varying inductance. A 256-element lookup table is used to select a gain adjustment scale factor based on current.

This feature is needed when the motor inductance is saturated during normal operation. As the current loop gain is calculated using the motor inductance, if the inductance changes, the current loop is at risk of becoming unstable.

If a motor is being used under high loads, the inductance is probably saturated if one or more of the following occurs:

  • Audible chirping

  • Chirping gets louder with higher commanded current.

  • Instability occurs under high current loads (at or near motor peak current MOTOR.IPEAK AXIS#.MOTOR.IPEAK )

To fix this problem, Gain Scheduling is used to change the current loop gain as a function of the current.

Using the Gain Scheduling View in WorkBench

The entries of the scaling table (0 - 100%) are calculated automatically within the drive based on the motor inductance saturation - AXIS#.MOTOR.LISAT .

Element

Sub-Element

Description

Axis IPeak

 

Displays the drive peak rated current in Arms. AXIS#.IPEAK

Proportional Gain

 

Displays the proportional gain of the PI-loop that controls the q-component of the current. AXIS#.IL.KP

Motor Inductance Saturation

 

Displays the quadrature axis inductance (Lqll) saturation characteristic as a function of quadrature current (Iq).AXIS#.MOTOR.LISAT

Table

AXIS#.IL.CMD

Current command for this index (

AXIS#.IPEAK/157 * AXIS#.ILKPLOOKUP@<Index>

)

Table Index

The index of the entry in the table (referred to as <Index>)

Value

Scaling value for this index

ResultingAXIS#.IL.KP

Calculated resulting current loop proportional gain for that index, respectively for that current.

Graph

 

The graph represents the resulting current loop proportional gain (AXIS#.IL.KP ) in function of the current command (AXIS#.IL.CMD ).

Import

 

There is no Import functionality available in AKD2G, as the table is calculated automatically by the drive.

Export

 

Export the table as a CSV file for external use.

Using the Terminal View for Gains Scheduling

The values are accessible through the Terminal usingAXIS#.IL.KPLOOKUP (read/only access).

Rules for Populating Gain Scheduling Table

The gain scheduling table is populated according to the following rules:

  1. When the drive powers up:
    a. If AXIS#.MOTOR.AUTOSET=1 and Motor Memory Version >= 0.3 (FB#.PRINTMOTORDATA), the entries are calculated based on the value of AXIS#.MOTOR.LISAT loaded from the motor memory.
    b. Otherwise, the entries are calculated based one AXIS#.MOTOR.LISAT as set in the drive.
  2. When DRV.RSTVAR is commanded:
    a. Rule 1a is applied.
    b. Otherwise, rule 1b is applied.
  3. When AXIS#.MOTOR.AUTOSET is set to 1, rules 1a to 1b are applied in order.