Optimization of Zero-Crossing Distortion for Unipolar BCM Grid-Tied Inverter

Inverter is the essential part of new energy distributed generation system. With the advantages of achieving zero-voltage switching (ZVS), high efficiency and power density, low cost, and fast dynamic response, inverter operating in boundary current mode (BCM) has caught researchers’ eyes recently, whereas when operating in a unipolar modulation strategy based on BCM, inverter suffers from zero-crossing distortion (ZCD) during zero-voltage crossing area due to inherent characteristics of the strategy. In this article, the reason of inductor current out of control near the zero-crossing point (ZCP) is analyzed from mathematical and physical aspects. Then, a hybrid modulation scheme of unipolar and discontinuous bipolar based on BCM is proposed in this article. The principle of operation, theoretical analysis, and simulation results is presented in this article. Compared with the traditional modulation strategies near the ZCP, the proposed hybrid modulation scheme suppresses ZCD, reduces the THD of the output current and the turn-off and conduction loss, and improves the efficiency at the same time. A 500-W BCM inverter prototype was built to verify the feasibility and effectiveness of the proposed hybrid BCM scheme.