Control Strategy of Unidirectional Modular Multilevel DC-DC Converter

doi:10.3969/j.issn.1000－7229.2018.09.006

Abstract

Abstract: DC power grid is the research hotspot to solve the stability problem related to grid-connected renewable energy. DC-DC converters play the key role to connect DC grid at different voltage level. Modular multilevel DC-DC converters adopt modular topology which is suitable for high-voltage and high-power applications. The unidirectional modular multilevel DC-DC converter is suitable for voltage conversion with a certain direction of power transmission. It has low cost and simple control method. But research on this topology is still relatively less. Corresponding control strategy is still mainly following the nearest level modulation（NLM）of MMC, and there is no practical demonstration project in China. So it is necessary to study the topology more deeply and put forward the control strategy which is suitable for the topology, and provide some reference values for practical demonstration projects. A new control strategy for unidirectional modular multilevel DC-DC converter is presented in this paper. The control strategy adopts current tracking instead of traditional voltage tracking, and calculates the numbers of the inserted sub-modules at the beginning of each cycle. By controlling the switch, the output current will follow the reference current. Finally, a simulation model of unidirectional modular multilevel DC-DC converter is built. The simulation results show that the control strategy can realize the voltage transformation well and current fluctuation at the input side is small. It is an effective control strategy.

Key words: DC power grid, unidirectional modular multilevel DC-DC converter, current tracking, new energy power generation, pnotovoltaic power-generation

CLC Number:

TM 46

WANG Jian，WANG Yi，FU Chao. Control Strategy of Unidirectional Modular Multilevel DC-DC Converter[J]. Electric Power Construction, 2018, 39(9): 47-53.

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