PROJECT TITLE :

PWM Control Scheme for Buck/Boost Modular Multilevel DC/DC Converter with Reduced Sub module Capacitance - 2017

ABSTRACT:

High-voltage direct current (HVdc) grid that incorporates multiple dc transmission lines will have in depth application since it has higher operating flexibility and enhances the facility trade. DC/DC converters are important parts in the HVdc grid. The buck/boost modular multilevel dc/dc converter (MMDCC), that uses 0.5-bridge submodules to cut back the voltage stresses across the power switches, could be a good alternative for the nonisolated applications in the HVdc grid. This paper proposes a pulse width modulation (PWM) management theme for the buck/boost MMDCC, that uses a lot of smaller submodule capacitors than those in the prevailing part-shifted (PS) management scheme, therefore reducing the converter volume and weight considerably. The operating principle of the proposed PWM control scheme is elaborated, along with the submodule capacitor voltage balancing strategy and therefore the closed-loop control flowchart. Besides, the capacitance requirement of the buck/boost MMDCC in the PWM management scheme is calculated and compared to that in the PS management theme, showing a dramatic reduction. The reason for the capacitance requirement difference of the two schemes is additionally explained. Simulation and experimental results validate the effectiveness of the proposed PWM management scheme and its ability to scale back the submodule capacitance.