How Can I Implement Dynamic Max/Min Control in Simulink for a 2 D.O.F System?

[19dan87]

I am modelling the vibration of a 2 D.O.F system with damping in Simulink.

I want to set up control such that if the control value is between two values (max and min) then it sets the control value to the specified input but if it is outside the max and min interval then the control value is set to the max or min as appropriate.

eg.

Fd> Fmax , then set to Fmax
Fd< Fmin , then set to Fmin

If not set to Fd.

Fmax and Fmin will vary slightly throughout the simulation so can not use a max/min since they vary with time during the simulation.

Any ideas how it will be best to do this. Basically going to be three inputs into the block from the system which need to be evaluated and then the appropriate input set as the output.

I have tried IF blocks but they won't work properly for the simulation.

Thanks

Dan

 

[viscousflow]

What you are describing is a saturation block. Basically, you can set your upper and lower limits of the saturation to Fmax and Fmin respectively, with Fd as your single input.

I do not see why you would want 3 inputs unless you have Fmax and Fmin as simulink block constants. Which in that case you can simply hard code it into the upper and lower limits of the saturation block directly and throw away your Fmax and Fmin constant blocks.

 

[19dan87]

Hi Viscousflow thanks for the reply. The saturation block was what I was describing but unfortunately I didn't think through the problem I was modelling properly and a simple saturation block will not work.

I am modelling Semi active damping with skyhook control. (MR damper with 2 DOF)

I want the control force to be; Fsky=Csky*x1
Ales the control force falls outside the Fmax and Fmin limits then I want to set the control force to Fmax or Fmin.

Fmax= sgn(Fy) + C(x1-x2) , sgn(Fy) is simply the offset force
Fmin= C(x1-x2)

The force-velocity diagram in the link below will help visualize the problem I am describing.
http://postimage.org/image/9rqiokn8/

Now 2 problems arise when using the saturation block alone.

(x1-x2) can be negative meaning I would have to swap the upper and lower limits around for the case when the relative velocity is negative.

Also If Fmax and Fmin are negative but the control force Fsky (Fd on the diagram) is positive and still between the +Fmax and +Fmin then I want the control force to be set to Fsky.

Any ideas how it would be best to model this problem in Simulink. Any suggestions would be very helpful. Thanks.

 

[viscousflow]

Well in that case, investigate the dynamic saturation block. You can place your equations into the upper and lower limit blocks to have moving limits.