Analysis, control and design of a long-lifetime AC-DC bus converter within a nanogrid

In an AC-DC hybrid bus nanogrid, a bidirectional converter is commonly used to transfer energy between the single-phase AC system and the DC system with stable operation and long lifetime. Therefore, the single-phase AC-DC converter should be designed to avoid using the short lifetime electrolytic capacitor. In this paper, a bidirectional single-phase AC-DC PWM converter using an additional line-level AC storage capacitor as the AC-DC power balancing device is proposed. A condition for zero ripple DC bus voltage is established such that a small DC bus capacitor can be used. Both the AC-DC power balancing and DC bus filtering capacitors can be designed small without using electrolytic capacitor in order to extend the converter lifetime. A control strategy that minimizes the size of capacitance is proposed, analyzed and verified. Finally, the analysis is verified by numerical simulations and experimental measurements.