Controlled Three-Phase LCL- Filter PWM Rectifier with BESS-oriented Applications Under Unbalanced Grid Conditions

The present paper aims to analyze the Battery Energy Storage System (BESS), which is connected to the grid in the distribution network, exclusively when it is operating as a battery charger under unbalanced grid voltage. The hypothesis establishes that it is possible to ride through an unbalanced voltage condition (typically caused by unsymmetrical loads, unsymmetrical transformer windings and transmission impedance) by using a nonlinear controller based on input-output linearization using only the current loops for each phase and generating the current references based on the balanced power. The methodology is based on the use of the mathematical model fora three-phase LCL-filter PWM rectifier (because the analysis is Just for the battery charge mode of the BESS), delta connected and 100 kW. To test the closed-loop system, simulations including the battery model have been performed by using PSCAD/ENITDC.