A novel method for voltage support control under unbalanced grid faults and grid harmonic voltage disturbances

As an important ancillary service for smart grid, voltage support has the capability to improve the grid condition when grid voltage unbalanced fault occurs. Several solutions, taking into account not only the root mean square voltage, but also the shape of the voltage fault, have been proposed. In particular, the control scheme proposed in this study introduces two contributions: a novel reference generator for voltage support and a new current tracking controller. Taking into account of the shape of the grid voltage, this reference generator has the capacity to increase the positive sequence fundamental voltage magnitude and decrease the negative sequence fundamental voltage magnitude, which improves the grid condition when unbalanced fault and voltage sags occur. Compared with other works, phase locked loop is eliminated in this generator which simplifies the structure of the controller. On the basis of output regulation theory, a simple-structure current tracking controller is proposed, which has a zero steady error under arbitrary order (or their combination) grid voltage harmonic disturbance. Simulations and experiments have verified the proposed control scheme.