Field Current Estimation for Brushless Wound-Field Synchronous Machine Equipped With Synchronous Exciter

Owing to the high reliability and low maintenance requirement, brushless synchronous generators (BLSG) are used in many applications from small power generating sets to large-capacity turbo-generators. In BLSG, direct measurement of the field current and its voltage is normally not possible. Consequently, accurate estimation of these quantities is essential for condition monitoring, state and parameter estimation, control and protection purposes. In this paper, a new method based on extended Kalman filter with unknown input (EKF-UI) is proposed for estimation of field current. This method which considers the field voltage as an unknown input is used for field current estimation in BLSG equipped with synchronous excitation system. The proposed method is validated by several case studies, including open loop and closed loop control systems and rotating rectifier faults. The experimental and simulation results show that, using the proposed method, the field current can be accurately estimated in both steady states and transients.