Grid-Connected Induction Motor Using a Floating DC-Link Converter under Unbalanced Voltage Sag

This paper proposes a series compensator to mitigate balanced or unbalanced voltage sags of grid-connected induction motors. A conventional three-phase Voltage Source Inverter (VSI) is applied to regulate the motor voltage, which is connected in series with the grid and a three-phase machine with open-ended windings. The dc-link voltage is floating and there is no dc source or injection transformer. The proposed system is suitable for applications in which no frequency variation is required, like large pumps or fans. Even only the amplitude of motor voltage is manipulated the investigated converter has some interesting features, such as soft-start, motor performance improvement or reactive power generation. A 1.5 hp 4-pole induction motor has been used to verify the ride-through capability of the proposed compensator under unbalanced utility sags. The control system, operation boundaries, and components ratings are also discussed. Simulation and experimental results are presented to demonstrate the feasibility of the system.