A Multiport Modular DC–DC Converter With Low-Loss Series LC Power Balancing Unit for MVDC Interface of Distributed Photovoltaics

An input-independent and output-series modular dc-dc converter with multiple input ports and high voltage conversion ratio can apply well to medium-voltage dc interface of distributed photovoltaics (PV). However, PV power mismatch will result in output voltage imbalance of the submodules (SMs), which is contrary to the standardized multimodule design. In this article, a multiport modular dc-dc converter with low-loss series LC power balancing unit (PBU) is proposed to address this problem. An isolated dc-dc converter is employed as the SM, which consists of full-bridge (FB) circuit on the PV side and half-bridge (HB) circuit on the grid side. Independent maximum power point tracking can be realized by controlling the phase shift between the FB and the HB, while voltage balancing (or power balancing) of SMs can be achieved by regulating the phase shift between adjacent HBs. Only one inductor and one capacitor are used in the PBU and all the switches of SM turn on with zero-voltage switching, which contributes to the low-cost and low-loss characteristic of the converter. Simulations and experiments are carried out to verify the validity of the theory.