Vector Control of Single-Phase Voltage-Source Converters Based on Fictive-Axis Emulation

This paper presents an alternative way for the current regulation of single-phase voltage-source dc-ac converters in direct-quadrature (dq) synchronous reference frames. In a dq reference frame, ac (time varying) quantities appear as dc (time invariant) ones, allowing the controller to be designed the same as dc-dc converters, presenting infinite control gain at the steady-state operating point to achieve zero steady-state error. The common approach is to create a set of imaginary quantities orthogonal to those of the real single-phase system so as to obtain dc quantities by means of a stationary-frame to rotating-frame transformation. The orthogonal imaginary quantities in common approaches are obtained by phase shifting the real components by a quarter of the fundamental period. The introduction of such delay in the system deteriorates the dynamic response, which becomes slower and oscillatory. In the proposed approach of this paper, the orthogonal quantities are generated by an imaginary system called fictive axis, which runs concurrently with the real one. The proposed approach, which is referred to as fictive-axis emulation, effectively improves the poor dynamics of the conventional approaches while not adding excessive complexity to the controller structure.