Figure 3.35: H 2 optimal controller frequency response.
Figure 3.36: Compensated open-looped transfer function frequency response.
Self-induced NRRO imposes fundamental limitations on the viability of very
high-TPI drives while RRO components can be compensated for using sim-
ple methods such as look-up table. Hence, while calculating the feedback
controllers above, only the NRRO component in the output disturbance is
Moreover it should be noted that the H 2 -optimal control attempts to min-
imize the TMR without considering any other specificationssuchaslowfre-
quency gain for counter-reacting the bias force, which typically needs an in-
tegral action. Also, the resultant controller might be of very high bandwidth
which the actuator may not necessarily be compatible to the actuator. How-
ever, the resulting controller provides a good reference of the tracking accuracy
that is achievable for more practical control designs.
In general, higher order models can represent the disturbance more ac-
curately. However, considering higher order models for different disturbance
sources ends up with a controller, which is very high order and requires more