LMI versus non-linear techniques for the design of FACTS controller

Most countries in different parts of the world have already deregulated their power industry (or are in the process of doing so). Deregulation has often resulted in a significant increase in power transfers across transmission lines. For weak interconnection, this situation may lead to more constraints on power system oscillations. One of the most constraining type of oscillations is the inter-area oscillation where two groups of coherent machines oscillate against each-other. This paper explores the opportunity of damping inter-area oscillating modes: (1) in a stressed network using a supplementary control loop of FACTS devices; (2) where the proposed solution uses linear matrix inequalities design techniques; (3) where the obtained performances are compared with those obtained when using nonlinear techniques; and (4) where the proposed design methods are verified via small-signal analysis and dynamic simulations on a 4-machine 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 processed between economical players in power systems. This situation has added stress on interconnected systems. As a result, many systems have experienced very significant power transfers on tie-lines. Thus 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.