A Modular Single-Stage IIOS Voltage Balance Topology for Photovoltaics MVDC Integration

The modular input-independent output- series (IIOS) dc-dc converters are widely used in photovoltaic MVDC integration applications due to their single stage power conversion, low cost and high efficiency. However, the mismatched input PV power will result in unbalanced output voltage of submodule (SM) converter. The PV power mismatch will cause the SM output voltage to deviate from its rated value, which is not conducive to standardized multi-modular design and is prone to module damage. In this paper, a multiport modular dc-dc converter with low-loss resonant voltage balance bus (RVBB) has been proposed for MVDC integration of distributed PVs. An isolated full-bridge quadruple-voltage semi-active rectifier is used as the SM topology, which consists of a full-bridge (FB) circuit on PV side and a quadruple-voltage semi-active rectifier (QVSAR) circuit on grid side. The RVBB offers self-voltage balance, simple control, less uneven power transfer time and good dynamic characteristics. In addition, all switches can realize zero-voltage switching-on (ZVS-on) and all diodes can realize zero-current switching-off (ZCS-off), which is conducive to improve the system efficiency. Finally, the feasibility of the proposed topology is verified by both simulation and experimental results.