Frequency domain design methodology for uncertain cascaded multiple-loop systems with plant modification

Since the internal signal level increases after using a plant modification loop, Horowitz and Wang (1979, 1988) proposed a quantitative synthesis feedback design method using the bandwidth propagation effect to take care of the internal signal level. The bandwidth increase phenomenon makes it difficult to maintain internal signal level reasonably. Moreover, the noise components are most important in the high-frequency range. It is desirable to decrease loop transmission functions as fast as possible in the high-frequency range to achieve minimum sensor noise sources. In the paper, a frequency domain design methodology for uncertain cascaded multiple-loop systems with plant modification is developed. The plant uncertainties are transferred to the values of equivalent external disturbances at the plant output. Thus, the design problem will become an equivalent external disturbance rejection problem. At the same time the bandwidth propagation effect can be eliminated and loop transmission functions decrease as quickly as possible