OPERATING MODES ON GRID CONNECTED INDUCTION MOTOR BY DC – LINK CONVERTER

Abstract

This article proposes a series compensator with un balanced voltage sag ride-through capability 
applied to grid connected induction motors. A conventional three-phase voltage source inverter 
(VSI) is intended to regulate the motor voltages. The VSI is connected in series with the grid 
and a three-phase machine with open-ended windings. The proposed system is suitable for 
applications in which no frequency variation is required, like large pumps or fans. The VSI DC 
link voltage operates as a floating capacitor through the energy minimized compensation 
(EMC) technique, in which there is no dc source or 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 and experimental results are presented to demonstrate the 
feasibility of the system