Minimum copper loss control of a single-phase grid-connected wound rotor machine over full speed range

This paper proposes control algorithms for the minimum copper loss (MCL) operation of a single-phase grid-tied wound rotor machine. The wound rotor machine, which has a single-phase winding in the stator and three-phase windings in the rotor, has been proposed as an attractive alternative of the conventional ac machines in single-phase grid system. In the proposed system, the stator winding is directly fed by the single-phase grid while the rotor windings are connected to an isolated three-phase inverter for the variable speed operation. Characteristics of the system were analyzed based on the machine model, and the condition of the minimum copper loss (MCL) operation was derived in the entire speed range. For tracking of the MCL operating point, the proposed method adjusts the ratio between rotor current variables while power factor of the grid, speed, and dc link voltage are simultaneously controlled. The feasibility and MCL tracking performance of the proposed control system were verified by experiments under various operating conditions.