Lead/Lag Filter

Referenced Keywords
Parameter Description Drive Keyword

PL.KP

Position Loop Proportional Gain

AXIS#.PL.KP

VL.ARTYPE#

Anti-Resonace Filter Type

AXIS#.VL.ARTYPE1 to AXIS#.VL.ARTYPE4

VL.ARZF#

Filter Zero Cutoff Frequency

AXIS#.VL.ARZF1 TO AXIS#.VL.ARZF4

VL.ARZQ#

Filter Zero Q Value

AXIS#.VL.ARZQ1 TO AXIS#.VL.ARZQ4

VL.ARPF#

Filter Pole Frequency

AXIS#.VL.ARPF1 TO AXIS#.VL.ARPF4

VL.ARPQ#

Filter Pole Q Value

AXIS#.VL.ARPQ1 TO AXIS#.VL.ARPQ4

VL.KI

Velocity Loop Integral Gain

AXIS#.VL.KI

VL.KP

Velocity Loop Proportional Gain

AXIS#.VL.KP

A lead lag filter is a filter that has 0 dB gain at low frequencies and a user specified gain at high frequencies. The transition frequency where the gain is applied is also user specified.

Review: The Controller [C] trace shows the frequency response of VL.KP, VL.KI, PL.KP, AR Filters 1 & 2

Note: Here VL.KP is set to 1.0 so that the gain of the system is at 0dB

 

A Lead Lag filter is a very powerful and flexible filter. It has two parameters:

  • Center frequency

  • High frequency gain

A Lead Lag is a means of either reducing or increasing high frequency gain. The user specifies the gain change, and a center frequency.

The filter increases/decreases at 40db/decade (second order filter)

Shown to the side is a 1000Hz -15dB Lead Lag

When should a Lead Lag filter be used?

  • Anywhere a Low pass would normally be used

  • Any time a phase “bump” is needed to increase stability at a specific frequency

When comparing the phase loss from a Lead Lag compared with the Low pass, the Lead Lag will always win, with less phase loss! This translates to high stability, and higher system performance.

Note that the peak of the phase dip is at the Center frequency, allowing the user to specify where the phase dip.

Unlike a Lowpass, a Lead Lag filter can also be used to raise high frequency gain. Often this use is not to raise the gain of the system, but to boost the phase. (Positive Gain = Positive Phase).

There are very few tuning parameters that can boost your phase (add stability), most decrease phase.

A Lead Lag filter can be used to precisely place additional phase where it is needed most.

Need more Phase, just add more gain.

Adjusting Lead/Lag in the Velocity Loop

To specify a Lead Lag filter, you must specify the Center Frequency and high frequency Gain (dB). To do this, see the following example by clicking on the Velocity Loop:

  1. Open the Velocity Loop pane.

  2. Open the AR Filter tab and select the AR filter that will function as Lead Lag.

  3. Select 3 - Lead Lag as the Filter Type.

  4. Set the desired Center Frequency and Gain.

Adjusting Lead/Lag Using the Manual Tuning Simulator

Within the Velocity Loop section of the Simulation pane, the filter type and values can be entered for AR filters 1-4.

Once the filter type is set to Lead Lag, the Bode Plot Drag+Drop tool may be used to visually adjust the values.

After setting the values within the Simulation pane or using the Drag+Drop sliders, the settings must be written to drive to take effect.