Wound Rotor Machine Fed by a Single-Phase Grid and Controlled by an Isolated Inverter

This paper proposes a novel energy conversion system for variable speed drives. It consists of a wound rotor machine and an inverter without any rectifier and input filter. In the proposed system, the stator of the machine is directly connected to a single-phase grid and the rotor is connected to three-phase inverter isolated with any external power source. The inverter can not only be connected through slip rings but also integrated on the rotor due to the structure. In this paper, based on the positive and negative sequence model, the rotor, stator powers, and the torque capability in the rotor energy balance and unity grid power factor are analyzed. From these analyses, the vector control methods of the torque, speed, the dc-link voltage of the isolated inverter, and the grid power factor are proposed. Since the power supplied from the single-phase grid is pulsating and the machine is directly connected to the grid, the controlled torque and power inevitably pulsates at twice the grid frequency. Nevertheless, the machine can start, accelerate, and decelerate in the wide range. The experimental results present the performance and the feasibility of the proposed system.