An integral constraint for single input two output feedback systems

Consider a linear feedback system for which the plant has a single input an d two outputs. Identify the direction of the plant at a fixed frequency by the range of the plant transfer function at that frequency. Suppose that th e direction of the plant varies significantly within the desired closed loo p bandwidth. We show that such plants are subject to inherent design limita tions. These limitations are described using an integral relation that must be satisfied by the output complementary sensitivity function. (C) 2001 El sevier Science Ltd. All rights reserved.