High-performance flux-based two-degrees-of-freedom uninterruptible power supply

A three-phase flux-based two-degrees-of-freedom uninterruptible power supply with improved voltage regulation performance is presented. The proposed AC supply is controlled using an outer P+resonant voltage regulation loop to nullify voltage tracking errors and compensate for unbalanced voltages. Within this outer voltage loop is a flux-based two-degrees-of-freedom inner current regulation loop for the fast compensation of dynamic load changes and other external disturbances. This inner current regulator originates from the combined use of classical twodegrees- of-freedom control theory and a hysteretic flux modulation technique. By integrating the individual advantages of P+resonant compensators, two-degrees-of-freedom control and flux modulation, the proposed AC supply can achieve both precise steady-state tracking and a fast transient response. Theory and experimental results are presented to validate the performance of the proposed AC supply.