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Psge 71 oe 92 rank constraint for DbAcan 2e interpreted as the condition that all measurement s have some noise contri] ution. This prevents the optimiz ation from creating very large o2 server gains y would tend to its optimal value. In the Ro2 ust Control Tool2 Ox, and in the u 1 naly sis and Synthesis Tool2 ox in M. H. B,(6.32) must 2e satisfied in order to compute the( su2- opUn H) Hence, when setting up a design pro2 lem,(6.32)must 2e taken into consideration. In short this amounts to making sure that for each control input of u(a), there is at least one of the transfer functions to the error signals of f'(a) having equally many poles and zeros, this corresponds to having a feed-through term(a ' term). Similarly, for each of the measurement signals of y(a) there has to 2 e at least one of the transfer functions from the distur ances of d(a) having equally many poles and zeros. Often, in the process of making 2 oth rank constraint s satisfied, the designer would 2 e lead to intro ducing additional(fictitious) In the sequel, the structure of the H)compensator will 2e compared to the well-known L structure. To that end, Figure 6.4 illustrates the structure of the LQG compensator, Figure 6.5 similarly illustrates the H)compensator d BA Bb CA DAb Bb OH Figure 6.4: LQG compensator structure as a 2 X 2 block problem. N(a is given by the upper bor and the log compensator as the lower box ! 8 . - $ ' #$)(& # & #$)(& ! ! 8 # = = & ' 8 2 ! ! # & ! :;< 3 $* :;< 3 $+ % % 3 $*" )5 ! # )5 #