Suppression of Low-frequency Voltage Ripple in Cascaded H-bridge Multilevel Converters-based Large-scale PV Systems

Cascaded H-bridge (CHB) multilevel converters are promising candidates for large-scale grid-connected PV systems thanks to its modularity, scalability and distributed maximum power point tracking (DMPPT). However, CHB converters inherently have low-frequency power ripple in dc links, thus require large dc-link electrolytic capacitors to mitigate the resulting voltage ripple, which will lead in reduction of system reliability. In order to solve the above issues, this paper adopts the system topology architecture composed of CHB multilevel converter and quadruple active bridges (QAB) dc-dc converters, combining with the intercross control structure. This scheme not only can improve the system reliability by decreasing the dc-link capacitance, but also can prevent the low-frequency ripple propagating to the PV ports. Simulation results clearly verify the effectiveness and feasibility of the topology and control strategy.