Power quality improvement using an advanced control of a four-leg multilevel converter

In this paper, the transient operation of a Three-Level Neutral Point Clamped (3LNPC) four-leg inverter equipped with an innovative control strategy able to improve the power quality in renewable energy based weak grids is investigated. The 3LNPC four-leg inverter is controlled to manage a Hybrid Energy Storage System in order to satisfy the energy/power demand in a weak grid and simultaneously to balance the AC voltage during unbalanced 3-phase loads. The proposed control strategy uses a special designed offset for the DC power/energy division and the decomposition of the supply three-phase voltage and current into symmetrical components using phasor representation for voltage balance. Real time simulations and experimental tests have been performed using a RT-LAB simulator, a 3LNPC converter prototype and an experimental MicroGrid in order to prove the effectiveness of the proposed system in a weak grid context.