Current control of a three-phase inverter grid connected through an LCL filter

This paper presents a current controller for a transformerless three-phase two-level inverter grid connected by means of an LCL output filter. The proposed controller indirectly controls the grid-side current by controlling the inverter-side current. In this fairly simple controller, the damping injection is done by a simple proportional action of the measured inverter-side current, where the main issue is the design of the inverter-side current reference. It is shown that the inverter-side current has to be as distorted as necessary to guarantee a grid-side current of a pure balanced sinusoidal shape. The proposed controller considers positive and negative sequences of signals, and includes a harmonic compensation mechanism. Therefore, it is aimed to properly perform under unbalance and harmonic distortion. Simulations are presented to assess the performance of the proposed scheme.