Self-balancing non-isolated modular multilevel DC-DC converter

Abstract

The invention provides a self-balancing non-isolated modular multilevel DC-DC converter, which comprises a power main circuit and a power balance circuit which are connected to each other, wherein thepower balance circuit comprises a plurality of air core inductors and a diode; the air core inductors are sequentially connected with the diode in series; the power main circuit is formed by sequentially connecting an input filter inductor, an output buffer inductor and a plurality of submodules through a series chain in series; and when the submodules are in a removal state, a bus capacitor of one submodule and the bus capacitor of the adjacent submodule carry out energy transfer through the power balance circuit. AC running through a bridge arm of the converter is avoided, the switching loss is reduced and the DC side filter inductance is reduced.

Description

technical field [0001] The invention relates to new energy DC convergence and transmission technology, in particular to a self-balancing non-isolated modular multilevel DC-DC (direct current-direct current) converter. Background technique [0002] With the increasingly prominent energy crisis and environmental protection issues, the development and utilization of clean and renewable energy is becoming more and more important. Offshore wind power has huge potential. It is of great significance to study the efficient and reliable collection and transmission of large-scale offshore wind power. With its advantages of low loss and no need for reactive power compensation equipment, HVDC transmission has been widely used in large-scale new energy long-distance transmission. Extending the concept of DC to the internal network of wind farms, adopting the medium-voltage DC aggregation scheme, replacing the bulky AC power frequency transformer with a DC-DC converter with higher power...

AI Technical Summary

Problems solved by technology

At present, the commonly used non-isolated modular multilevel DC-DC converter adopts conventional half-bridge sub-modules in series to construct the upper and lower bridge arm structure. In order to realize the power balance between the sub-modules and the upper and lower bridge arms, it is necessary to inject circulating current between the bridge arms. Causes a large AC circuit to flow through the capacitors and switches of the sub-modules, increasing switch stress and switching losses

At the same time, the AC flows through the DC side to form a large ripple, which requires the installation of inductance and a huge filter inductor, which reduces the power density of the converter

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