Static vs Dynamic tuning of VFD motor 1

[rockman7892]

What is the difference between a static tune and a dynamic or rotational tune on a motor controlled by a vfd? I have seen several VFD's which present both of these options but am not sure of the difference between the two?

My understanding is that by doing these tunes the drive estimates/calculates all of the motor equivelent circuit paramaters for use in the control alagorithim weather is sensorless vector, FOC, etc...

Does the drive calculate these parametes differently depending on what type of tune is performed?

 

[DickDV]

In sensorless vector systems, the drive must build something of a motor model in its own memory. This is typically done at initial commissioning. In the brands I work with, this is called a Motor ID Run or similar terminology. I suspect that there are other brands that might call this a Static Tune altho I don't see where anything is being "tuned".

Once the motor model has been established in sensorless vector or in all closed loop flux vector systems, once the load has been connected to the motor, the speed loop needs to be tuned for speed accuracy and step-change response. I could see this being called a Dynamic Tune.

As is clear, I'm guessing here because the OP didn't specify the brand involved.

 

[rockman7892]

The specific brand that I am referring to is an AB Powerflex700. I looked in the manual and heres what I found. The VFD has (3) different tuning tests that it runs with each one as described.

The first test is called a static tune and is a non-rotational tune used to calculate the IR voltage drop in the motor (I'm assuming the stator) as well as the leakage inductane IX voltage drop. How does the drive go about calculting these results. Does it send an output and measure results? How are these two particular paramaters then used for contorl modes in the drive?

The second test is called a Rotate Tune, to determine the best possible possible automatic setting for the Flux Current Reference. It mentions to run this test with the motor uncoupled if using a SVLC control mode. How does the motor calculate this flux reference? Since the motor has no load, does it assume that the rotor circuit in opened and therefore all current in the motor in the motor is flux current (minus losses) similar to a no-load motor test used to calculate Xm? How is this value then used in the drive control?

The final test is called an Intertia Tune and is used to calculate the total inertia? I'm assuming this is calculating the total inertia of both the motor and load, however for SVLC mode it states to perform this test with the motor uncoupled? How would this then calculate load inertia? How does the drive perform this calculation and how is it used in the cotrol scheme of the drive?

There was also another parameter/test that involved slip compensation. How is this slip compensation typically used in a drive?

 

[DickDV]

Usually, slip compensation is used in open loop V/Hz drives to compensate partially for the speed error caused by the motor slip. Trying to get rid of more than about half the slip will usually result in instability.

 

[cswilson]

The first test is simply to determine the basic electrical properties of the motor. Voltages are applied to the phases and the resulting currents are monitored. From the measured current patterns, circuit properties such as resistances and inductances are measured. Typically, there is a lot of "secret sauce" in what patterns are applied and what calculations are done from the measurements. No motion is required here.

The second test is used to determine the various relationships involving the flux field, torque, slip, velocity, etc. This requires motion. In theory, this could be done with or without the load attached, because these properties are "load independent". In practice, you always want to do these without a load, both for safety reasons, and to have better confidence that the test will create the full range of conditions (e.g. high velocities) needed.

The third test is used to tune the velocity loop so it is stable and responsive. For this, it must know the total inertia being controlled (and possibly things like coupling stiffness as well), because this is a critical part of the loop dynamics.

Note: The above is based on my general knowledge of what this type of control requires -- I don't have specific knowledge of the AB internals.

Curt Wilson
Delta Tau Data Systems