Synchro-phasor based three phase state estimation using modal components

Abstract

Power systems may not always operate under fully balanced conditions due to unbalanced loads. Such cases will necessitate full three-phase monitoring of the system state. Thus, positive sequence network model and associated state estimation formulation will not be valid for such operating conditions. It is clearly possible to use a simple extension of the least squares (WLS) estimator to formulate a full three-phase state estimation problem. However, this may require significant changes to existing state estimator software and will greatly increase the computational burden compared to the positive sequence counterpart. This paper proposes a simple alternative that uses modal transformation and synchronized measurements provided by phasor measurement units (PMU). Both state estimation and subsequent bad data processing will be accomplished using the proposed modal component based approach. Details of the method along with examples will be given to illustrate its effectiveness.