A Non-isolated Bidirectional Modular DC-DC Converter with Unipolarand Bipolar Structure for dc Networks Interconnection

In this paper, a novel bidirectional modular dc-dc converter (BMC) with unipolar and bipolar structure for dc networks interconnection is proposed. Compared with traditional dc grid-connecting converters, the proposed converter can realizes high voltage gain with a transformerless structure and reduce the voltage stress across switches. Then, to solve the unbalanced current problem among power units in the BMC, a submodular structure is introduced. The control system was optimized for grid-connection applications by introducing the phase-interval operation between submodules to reduce the current and voltage ripple in both sides. Besides, the control system can provide various control strategies, including output voltage control, voltage gain control and power control to maintain the voltage level or keep a constant voltage gain of the networks and performing precise power control. Finally, simulations of both sub-modular unipolar BMC and bipolar BMC were implemented, and a 1-kW experimental 3-level unipolar prototype was developed.