Design of damping controllers using linear matrix inequalities techniques and distant signals to reduce control interactions

In large interconnected networks, the number and the complexity of controllers are still increasing in order to enhance the performance of power systems. But the proximity between controllers leads to interactions between each other, also called "control interactions". These interactions are very often detrimental to the overall system performance : they are "adverse interactions". Design and co-ordination of damping controllers, while trying to mitigate control interactions, are relevant topics of modern power engineering research. The linear matrix inequalities design techniques, added to distant signals used as inputs of controllers, allows adverse interactions to be reduced. Indeed, distant signals, coming from synchronized phasor measurements units, permit a global knowledge of the system in real time to be achieved. The designed controllers are those of FACTS (flexible AC transmission systems) devices and PSS (power system stabilizers). Furthermore, these techniques take into account the damping of critical oscillatory modes, and more particularly inter-area modes. The proposed design methods are verified via small-signal analysis and dynamic simulations on a 4-machines test power system.

I. Introduction

Electrical networks are operated closer and closer to their stability limit. This is due to several economic, ecological and technical constraints. In addition, the open access has resulted in a significant increase in the number of transactions between economical players in power systems. This situation has added stress on interconnected systems. As a result, these systems have experienced very significant power transfers on tie-lines. On the other hand, these power transfers reveal power oscillations, named “inter-area oscillations”. These oscillations restrict the power production as well as the power transfers in the network.