Control of grid-interfacing inverters with integrated voltage unbalance correction

This paper presents the control of a grid-interfacing inverter with integrated voltage unbalance correction. It is proposed to add an additional function to the inverter to decrease the negative-sequence voltage at the point of connection with the utility grid. Based on a symmetric sequence voltage decomposition and using an improved multi-variable filter, the grid-interfacing inverter intentionally absorbs a small amount of negative-sequence current from the grid, thereby helping to correct the negative-sequence voltage. Although the amplitude reduction contributed by each individual inverter system is small compared to the total negative-sequence component, grid-interfacing inverter modules can collectively achieve substantial results in the grid. The integrated function and proposed control has been verified in simulations and by experiments on a laboratory prototype.