Control and modulation of a family of bidirectional AC-DC converters with active power compensation

In a single-phase grid-connected nanogrid system, a bidirectional AC-DC converter is usually required to transfer energy between the AC grid and a DC bus. However, a ripple power at twice the grid frequency may be injected from the AC grid into the DC bus if the ripple power is not properly compensated. In this paper, a family of bidirectional single-phase AC-DC three-phase-leg PWM converters for use in the nanogrid system is analyzed. The averaged DC power and the second-order AC power of the AC grid are actively decoupled. A proper AC voltage reference for AC power compensation is analyzed and selected for the charge storage capacitor for better efficiency. A generalized control structure is proposed for the family of converters. Applying modulation with extra zero-sequence voltage injection derived from the three-phase-leg PWM voltages, a significant reduction of the AC storage capacitance is achieved and the converter efficiency is also improved. Finally, the analysis is verified by simulations and experimental measurements.