The Resonant Modular Multilevel DC-DC Converter Adopting Switched-Inductor Cells for High Step-Up Ratio

With the prosperous development of distributed renewable energy power generation, high-voltage direct-current (HVDC) system has evolved into large-scale practical applications from the initial stage, and high step-up conversion dc-dc converters have become a core technology to promote the development of HVDC system. This article proposes a new resonant modular multilevel dc-dc converter (MMDC) based on the conventional boost converter. The single-switch and diode of the conventional boost topology are replaced by submodules (SMs), which are clamped by floating capacitors, and the inductor is replaced by switched-inductor (SL) cells. The phase-shifted pulsewidth modulation (PS-PWM) is applied to regulate the state of SMs, i.e., inserted state or bypassed state, to ensure that there is a constant number of SMs supporting the output voltage at any time. The converter is operated in resonant mode with resonance between capacitors of SMs and the upper arm inductor. The step-up conversion ratio is dependent on the inductors charging ratio, the number of SMs, and SL cells. Hence, more regulation schemes are available. The proposed converter possesses the advantages of MMDC and has the inherent-balancing capability of SM capacitor voltages without additional complex balancing control. The structure of the converter, operating mode analysis, parameter design, and comparison with other MMDCs are presented, which have been verified by simulated and experimental results.