A High Frequency Link Multilevel DC Transformer for Medium and Low Voltage DC Power Distribution

Abstract

The invention discloses a high-frequency link multi-level DC transformer for medium and low voltage DC power distribution, which belongs to the field of electric power technology; it is composed of a low-voltage DC conversion stage, a high-frequency isolation conversion stage and a high-voltage DC conversion stage connected in sequence; the low-voltage DC conversion stage The high-frequency isolation conversion stage includes m identical high-frequency isolation transformers and a series inductor. The high-voltage DC conversion stage uses a modular multilevel converter; the low-voltage DC conversion stage uses The DC sides of the m full-bridge converters are connected in parallel to lead out the low-voltage DC terminals, the AC sides of the m full-bridge converters are respectively connected to the primary sides of the m high-frequency isolation transformers in the high-frequency isolation conversion stage, and the secondary sides of the high-frequency isolation transformers The sides are connected in series with series inductors in sequence, and connected to the AC terminal of the modular multilevel converter in the high voltage DC conversion stage, and the DC side of the modular multilevel converter leads to a high voltage DC terminal. The invention can and does increase power density, efficiency and reliability.

Description

technical field [0001] The invention belongs to the technical field of electric power and relates to a solid-state transformer, in particular to a high-frequency link multi-level DC transformer for medium and low voltage DC power distribution. Background technique [0002] In the DC grid, due to the maturity of the fully-controlled voltage source converter (VSC) technology, the flexible DC transmission technology has developed rapidly. Compared with the traditional DC transmission technology, flexible DC transmission does not need to use AC grid commutation, there is no problem of commutation failure, and it can supply power for passive systems; using pulse width modulation (PWM) technology, the harmonic content of voltage and current is relatively low. In addition, the fully-controlled VSC is flexible in control, can quickly and independently control active and reactive power, and the power flow can be adjusted in both positive and negative directions. Therefore, flexible ...

AI Technical Summary

Problems solved by technology

In this scheme, the dual-active full-bridge converter is connected in series at the high-voltage DC end to increase the voltage level, and connected in parallel at the low-voltage DC end to increase the current level, thus avoiding the direct series connection of switching devices, but the high-frequency isolation transformer of the dual-active full-bridge converter The voltage at both ends is a two-level high-frequency square wave. In the actual working process, when the DC voltage at both ends does not match the transformation ratio of the transformer, there will be a large circulating current, which will lead to a large current stress and low efficiency. its large-scale application

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