Interactions and multivariable design of multiple control functions of a unified power flow controller

Abstract

One of the most important features of a unified power flow controller (UPFC) is its multiple control function. These control functions have been suggested to be implemented by multiple controllers. However, study examples presented in the paper demonstrate the existence of the dynamic interactions among different UPFC controllers, i.e. power flow controller, AC voltage controller and DC voltage controller. Due to the interactions, it is demonstrated in the paper that there are cases where separately designed and individually implemented stable UPFC controllers may result in poor control performance and even the closed-loop system instability when they are in joint operation. Hence, it is suggested in this paper that the multiple functional UPFC is treated as a multi-input and multi-output (MIMO) control system such that a single multivariable controller can be designed for the UPFC to perform the multiple control functions, which takes full account of the control interactions in the MIMO UPFC system.