On the sensitivities of network variables for FACTS device damping control

Feedback control of FACTS (flexible AC transmission system) devices typically relies on network variables because generator signals are not usually available locally. Based on the multi-modal decomposition approach, a crucial factor in selecting a feedback variable is the impact of the variable on the inner-loop gain, which consists of mostly the sensitivity of the network variable with respect to the change in the control input variable. Recent investigations have shown that flow variables are more suitable for shunt control devices and nodal variables are more suitable for series control devices. In this paper, the authors use a simple system to demonstrate this concept. In addition, the impact of the interarea modes on the inner-loop gain is studied with a system with two interarea modes.