Balanced grid currents in three-level voltage-source inverters connected to the utility under distorted condition using symmetrical components and linear quadratic regulator

This paper proposes a control approach to achieve balanced grid currents in three-level voltage-source inverters connected to the utility under dip or unbalanced condition. Fast sequence separation method for symmetrical components is used concurrently with linear quadratic regulator in the current controller, in order to take advantage of the multivariable structure of the system. The harmonic content of the grid voltages can affect the type of sequence separation method to be used. Controller parameters are tuned by simulation. Experimental results have been obtained with a distorted grid, with significant harmonic content, under dip or unbalance condition, verifying the validity of the proposed control approach.