The alignment angle approach to inherent design limitations

Inherent design limitations involves a study of system properties and characteristics that is used to assess the potential difficulty of a feedback control design. Such knowledge is useful in the early stage of engineering design cycle, in order to configure the plant and sensor/actuator locations. This paper suggests an approach on design limitations by observing the alignment between plant and disturbance subspaces. We illustrate via an active noise control example that plant-disturbance misalignment causes undesirable closed-loop behaviors such as poor stability margins or amplification at the measurement output. We also show that some choice of sensor/actuator placement, called the "symmetric configuration," is prone to plant-disturbance misalignment.