Load-Adaptive Zero-Phase-Shift Direct Repetitive Control for Stand-Alone Four-Leg VSI

This paper dealswith a dedicated load-adaptive phase compensation algorithm to be used in repetitive control (RC) based stand-alone four-leg voltage source inverter (VSI). The plant model is achieved; its inherent modifications according to the operating point are highlighted and used to properly adapt the RC structure. Modification of the RC parameters is described to obtain the desired phase compensation capabilities achieving a zero-phase-shift condition at each harmonic. This allows us to increase the gain of the repetitive controller at high-order harmonics, thus yielding a better VSI output voltage with strongly reduced total harmonic distortion and faster dynamic response. As a consequence, the VSI output voltages are almost independent from the loads to be fed, and the four-leg VSI with the proposed zero-phase-shift direct RC is an ideal candidate to supply sensitive loads in microgrid, in particular for stand-alone applications.