bode plots

g9u5dd43 snipped-for-privacy@yahoo.com wrote:


Whoever "they" are, they have the luxury of working on easier systems than I have. While some of the nonlinearities I have dealt with can be linearized away, friction, backlash, and actuator saturation cannot be ignored or linearized if you want to come close to an optimum trajectory from point A to point B -- and using a low-order nonlinear state-space representation as shown by the OP is often the clearest way to represent the system.

--

Tim Wescott
Wescott Design Services
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On Fri, 16 Apr 2004 08:48:22 -0700, Tim Wescott

Granted you can represent a nonlinear systems using a "state-space" representation and use this representation for simulation. But what "control design tool" do you use that can directly uses this representation for the purpose of design?
I'm trying to think of a nonlinear control design approach that contrasts a linear state space design techniques like H_infinity that uses a linear representation of the plant for the purposes of generating a linear controller.
For things like backlash, and actuator saturation, I would typically do the linear control design for the linear dynamic part of the plant and then wrap this system with logic to handle the specific nonlinearity.....actuactor limit tracking to prevent integrated windup for example.
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Hello,
g9u5dd43 snipped-for-privacy@yahoo.com wrote:
[]

Think of model predictive control where you take the model (whatever you can afford building), create your optimality functional (where you can penalize excessive actuator movements), impose some certain constrains, create two "horizons" -- one for control and one for model predictions, and run an optimization algorithm to minimize said functional subject to all imposed constrains. It should be noted that tuning and all that of this algorithm is more difficult than the one of PID and the optimizer at the core should be appropriate for the task. However, it is an example of a nonlinear control technique. There are linear versions of MPC, as well. And MPC may work better with PIDs as the baseline control.
Andrey
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On Thu, 15 Apr 2004 08:57:50 -0700, Tim Wescott

I've found the UK publication: Control Engineering Practice to be a good combination of theory and practice. The ASME's Journal of Dynamic Systems, Measurement, and Control is another reference with a a good combination of theory and practice.
IEEE Transactions on Control Systems Technology went the way of IEEE's Automatic Controls,...no fun to read.
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