Phase-matched frequency adaptive repetitive controller for a grid-supporting STATCOM

STATCOMs are widely used to provide voltage support in electrical distribution systems. However, if the grid voltage is distorted, the output current of a STATCOM may also be distorted unless a harmonic current controller is added to the control system. Repetitive controllers (RCs) provide an attractive solution for harmonic control in electronic power converters. These controllers are simple to design and implement but, unfortunately, their performance deteriorate with frequency deviations. This paper presents a solution called Phase-Matched filter to solve the frequency-adaptation problem of RCs. Compared to other filter methods already presented in the literature the proposed method provides additional degrees of freedom for the design. It will be shown the proposed filter improves the steady-state performance of RCs when the grid frequency varies. The proposed solution was applied to a STATCOM that provided voltage support in a weak grid. The main control system improvements were tested by simulation, and on a 15 kVA prototype.