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

In this project, a series compensator for grid-connected induction motors with unbalanced voltage sag ride-through capability is proposed. A traditional three-phase voltage source inverter (VSI) is designed to regulate motor voltages. The VSI is linked to the grid and a three-phase machine in series with unrestricted windings the proposed system is appropriate for applications requiring no frequency variation, such as large fans or pumps Through the energy minimized compensation (EMC) technique, the VSI dc-link voltage acts as a floating capacitor. Which lacks a dc source and an injection transformer. 

The motor load condition determines the minimum grid voltage positive component (sag severity) to keep EMC operation. Meanwhile, a voltage unbalance may increase the dc-link voltage requirements. A 1.5-hp four-pole induction motor has been used to verify the ride-through capability of the proposed compensator under grid voltage disturbances. 

A total harmonic distortion (THD) analysis of grid currents demonstrates that the proposed system provides low THD even if no passive filter is used. The operating principle, converter output voltage analysis, pulse width modulation technique, control strategy, and components ratings are discussed as well. Simulation results are presented to demonstrate the feasibility of the system

Keywords: Floating capacitor, induction motor, series compensator, unbalanced voltage sag.