High-frequency link multi-level direct-current transformer used for middle- low-voltage direct current distribution

Abstract

The invention discloses a high-frequency link multi-level direct-current transformer used for middle- low-voltage direct current distribution, and belongs to the technical field of electricity. The transformer is formed by a low-voltage DC converter stage, a high-frequency isolation converter stage, and a high-voltage DC converter stage connected in series. The low-voltage DC converter stage comprises m same full-bridge converters. The high-frequency isolation converter stage comprises m same high-frequency isolation transformers and a serial inductor. The high-voltage DC converter stage uses a modularized multi-level converter. The DC sides of the m same full-bridge converters in the low-voltage DC converter stage lead out low-voltage DC ends in parallel. The AC sides of the m full-bridge converters are respectively connected with the primary sides of the m high-frequency isolation transformers in the high-frequency isolation converter stage. The secondary sides of the high-frequency isolation transformers are connected in series in sequence, and are connected in series with the serial inductor, and are connected with the AC ends of the modularized multi-level converter in the high-voltage DC converter stage. The DC sides of the modularized multi-level converter lead out high-voltage DC ends. The direct-current transformer can improve 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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