Non linear Controller in Power Electronics

[sac1991]

I want to discuss about what a non linear controller offers as compare to what we are now using linear control strategy, compensator design all these. Do we really need non linear control in the are of power electronics. There are hundreds of paper on non linear control of power electronics system but my question is that what will be the most visible improvement on the converter performance if we will use these control technique in hardware. In theory everything works fine.

 

[FvM]

I presume you are not discussing obvious non-linear aspects of controllers like limited manipulated value (e.g. modulator duty cycle) or simple non-linear functions like current limiting.

"all real control systems are nonlinear", quoted from https://en.wikipedia.org/wiki/Nonlinear_control

In some cases, you want to compensate an inherent non-linearity of the control process, e.g. the gain variation involved with transition between DCM and CCM of a switch mode converter. Compensating the gain variation in the controller will improve control dynamic.

 

[sac1991]

No I am talking about non linear control techniques such as sliding mode control, passivity based control, H infinity control. Where we don't have to design controller based on small signal model.

 

[dick_freebird]

The main benefit that I imagine is, ability to break the
classical linkage between small signal stability and high
load-step slew capability. With an all-linear loop there
is a pretty fixed relation. But a loop that is (say) high
gain low bandwidth near null, but lower gain / higher
BW as you slide away from setpoint, can perform much
better in applications where the load current is highly
and abruptly variable. I know older generations of the
Vicor converters did this, "linear style" but with a split
loop - one "DC" amp and one "transient" amp. Of course
a digital control core offers arbitrary transfer function
capability (provided it can keep up). And you'd need some
way of proving (formally, in many critical-application
markets) that the design is indeed stable. That is one
reason why the traditional designs persist, they are so
well understood and documented. There are plenty of
academic schemes which are touted as great (for
something) but will never amount to anything because
they are not OK for everything (list of must-XYZ for
acceptance).

 

[sac1991]

Yes that's what I see. As if we can do all things we need with linear control. That's why linear control is still alive and blooming in this era also. I just want to find a real life problem in power electronics where non linear control scheme will out-perform linear control.